I’ve learned how to use a katana in ninjutsu style and this have really helped me. Thank you for making this series. Now I finally can buy an original katana without wondering how it was made.
Being a mechanical engineer a lot of this wasn't new to me, but it made me happy to see someone explain it so well. One issue I had was in the claim that the harder edge will assist in cutting through bone. Bone is softer than any steel, the the things that determine how well it will cut are edge profile and sharpness. The real benefit of the martensitic edge is that it will stay sharper much longer.
So odd why they had to harden it that much though. I mean high carbon steel will have more edge retention like what this guy said compared to mild steel but it's easier to sharpen mild steel than high carbon steel and unless the wielder really sucks or they make thin-bladed, mild steel swords, then the edge should be fine for hours or even days of battle. So really what's the point of the Japanese for doing that?
The short answer is they didn't have the technology/knowledge to temper, so this got a blade that could be used with the slight bonus that it had an edge that would last slightly longer in normal use.
Differential hardening didn't allow for tempering and the lack of advanced smelting techniques didn't allow for mono-steel forging. As such, making a really high-hardness edge is the only thing they could have done without advancements in their smelting process.
actually tempering did exist to a point, it wasnt as accurate but they could do it. some katana appear to have been further tempered after quenching while others seem to have been used as is. the differential heat treating process appears to be a left over trait from older period swords before further refinements in the forging processes. earlier chokuto swords often actually appear to have been clayed, however many are never polished like katana or tachi so this fact is hidden in many cases. it would appear they preferred the trade off for a more durable sword with a sharper edge, by this i mean a katana can bend many times and be straightened before it becomes an issue, however with swords that arent clayed a bend is much more damaging. also there are some katana that from my understanding were not differentially heat treated though this appears to have only been done by specific schools and seems to have been meant for cheaper more disposable blades meant for wars. also the katana can comein many different stack ups for the billet, first off there are different grades of tamahagane another sword grade steel called orishigane as well as the ones mentioned in the video, as well as the presence of european imported steels in swords made by certain schools and smiths. the thing to keep in mind that katanas depending on quality were made with varrying amounts of different quality steels as well as receiving different amounts of attention from different skill levels of smith.
Slight correction, steel doesn't GLOW blue when it gets hot, it just turns blue because it's oxidizing. If it's GLOWING blue that means you've just made solar plasma, in which case you should probably stop, because when stars start turning into iron it means they're about to go supernova.
That's because the gravitational force of the star isn't enough to fuse iron atoms together. The star collapses and creates enough force to explode. I'm not sure iron solar plasma would actually explode, but correct me if I'm wrong (still ridiculously dangerous though, so still run).
A comment from an M.Sc. in chemistry: Well done! Although you have not studied chemistry or materials science you have explained the 'different irons' , the 'host-guest-chemistry' and the other processes involved very well. Body centered cubic (bcc) and face centered cubic (fcc) were explained and used correctly. You did even mention a tetragonal cell ..... Well done! About quenching and tempering..... those two processes are easy to explain! In general if we chemists 'quench' something we want to stop a reaction or a process instantly or at least very quickly! Like using an emergency-break to stop a train from moving. In a kitchen you blench the beans in boiling water and then you 'quench' them in cold water with ice. It will stop the cooking-process immediately and they retain their color. The result: They will not get too soft aka overkooked if they stayed warm for too long or cooled down too slowly. Tempering means to heat something up again but NOT to its melting temperature! You MUST stay below. As you mentioned you can influence the properties of that material enormously. A very good example is glass! When a drinking glas is produced from molten glas, you will get raw-glasses first. You could snap your finger against it and it will break into pieces after cooling down. BUT: If you heat them up once more below the melting temperature (tempering) and then cool them down slowly the glass will not shatter to pieces when you clink the glasses with your friends! Btw: The German word for pig iron retranslated back into English is: raw-iron. ;-)
The katana was forged all the way into the 20th century. The last recorded instance of battlefield-ready katana being made and then used was during WWII. They were mono-steel, or binary steel of martensite and pearlite. I do not know if they attempted to temper it, but I just want to make this known. Many of the Katana's legends of cutting through rifles and machine guns may have come from US soldiers fighting against a banzai charge, running out of bullets, and having to defend against an officer's sword with the barrel of their rifle/machine gun. The resulting cut would damage the barrel enough that it needs to be replaced. No soldier in their right mind would use a cut barrel. The pressure would make it explode. Anyways, the stories would get passed on as "You see this sword? Cut a machine gun in half. I'll let you buy it off me for thirty bucks, 3 packs of cigarettes, and that Japanese dress for my wife." In short, the point I am trying to make is that "the katana" as a sword type cannot be summarized into a singular era of production. Like with all swords, its production had undergone much development as industrialization improved. It has an unusually long (and modern) service history for a singular blade design. This is an excellent series of videos, and you shouldn't change a thing. However, perhaps you may want to go do research on the different varieties of 'katana' throughout history. This would make for a lovely video or series of videos. It would be less about comparing European and Japanese things, but more about the blades themselves. There are a great deal of sword designs in Europe that have undergone a similar history. The basic geometry is respected, but the forging techniques were refined to improve them. Just a thought.
By the last recorded instance of forging, I mean with the purpose of reaching the battlefield. The ones made in the traditional aspect today are usually set-pieces for display and parade or use in sport and martial art without ever meaning to draw blood.
+Belle La Victorie Those were no Katanas, they were Guntos. Tashi, Katana and Gunto look similar, but they are not the same. Guntos are more like Katana-shaped Sabres
+Belle La Victorie So were the european swords, cavalry used mainly sabers(because you can't aim guns while on a horseback properly) and the last cavalry charge with drawn sabers was performed in 1942. ;)
he was comparing traditional katana to the traditional spring sword which were around the time period around the 16 century of course swords in general in the process of making the sword have changed. He compares both swords because of their differences in making the sword, durability and usefulness in battle which is important.
As someone looking to get into the Katana thing for the first time, I've found these videos to be invaluable. I was able to follow the science, you did a great job explaining it. Thank you for taking the time. Onto video #5.
Here's my interpretation, as a blacksmith. If I had very little access to iron ore, I would try to make every bit of it count. The Katana uses as little high-carbon steel as it possibly can to produce a useable sword. And the cool thing is, that sword design would work even without hardening. Yes, hardening makes it BETTER, but if you imagine how the technology may have evolved, you would start with unhardened high carbon steel on an iron core. Then later you discover hardening and all the swords that you through-harden will break so then you only harden the edge. Well, due to the fact that you have a soft core, you have no real reason to develop tempering technology which you WOULD need to develop for mono-steel swords. To put it more succinctly, I think the use of an iron core and an overly hard edge is due to being frugal. Why spend all of your high carbon steel on one sword when you could make 3. Viking era axes show this same sensibility with high carbon welded cutting bits.
I agree. The Katana process makes a very economical sword that is almost as good as a western sword for most purposes. The Japanese islands are relatively resource poor, so they developed a quite ingenious technique for creating high quality swords with poor materials.
rapturedmourning the amount of iron is the same but the amount of high-quality steel is much less when you only need to make the edge from high carbon steel and the rest is mild steel or iron. Compare that to a European blade where the entire thing needs to be made out of high purity steel or it will snap in half at any weak point when it is supposed to flex and spring.
A good discussion but you completely missed the most important aspects of the katana design. If you notice in the background video of the katana being quenched, it starts off as a straight piece of metal and the quenching actually causes the curve. The reason for the curve is that the different molecular structures mentioned have different densities. In the process of quenching, the martinsitic low density structure is frozen in while the spine of the sword first contracts (causing the curve) then wants to expand into its ferite form. With the cutting edge frozen in place the expansion of the spine is held in check. This arrangement puts the cutting edge of the katana under compression, actually making the cutting edge much harder than just plain old martinsite. The net result, the objective of having a cutting edge under compression is that the katana can be polished to razor blade sharpness. It is a similar surface compression technique that makes the Gorilla Glass cover for iPhones so much tougher than regular glass. So, one final thing that distinguishes the Katana from most other swords is that a well polished katana (they cost about $100 US per inch to have polished by a pro) will be much much sharper than any other sword. Polishing a katana with a grinder actually eats away the surface compression layer and destroys much of what makes a katana a katana. There is a book about the Japanese defeat at Midway called "Shattered Sword." The title reference the fat that a well made and traditionally polished katana will not bend, it shatters when the surface compression layer is breached.
Good job sir. This is literally the only youtube video I've found that accurately portrays the methods and science behind differential quenching and tempered mono steel. Your attention to detail was immaculate, and believe me, it was refreshing to hear someone who wasn't either a fanboy or a basher really look at the facts. The only thing that I might point out would be differential tempering. I don't claim to be some kind of master or anything, especially not about swords, but I have had some training in blacksmithing and a bit in the knife making sector of bladesmithing. It is possible to impart different levels of hardness on a mono steel blade by controlling the amount of heat used on different areas of the blade (i.e. the edge as apposed to the flat.) during tempering. If you relax the crystal structure more on the flat so that the heat only seeps towards the edges you can have a spring steel center, and hardened edges. I will say that this might be less practical if you're using a somewhat impure steel, but if the steel was smelted properly you have a sword that is still flexible (because it has the spring steel instead of iron or untempered steel towards the middle of the flat) but has slightly harder edges than it otherwise would. Again, I'm not an expert, but I know this technique is used in knifemaking as well as the making of some set tools used on cold metal, (it would be pointless on tools used on hot metal as the heat from the stock you're working would just loosen the structure right up every time you used the tool) and I don't see any reason why it wouldn't work on a sword blade. I'm just throwing that out there, but I don't know how historical this method is, and due to the thorough nature of your video I'm guessing that if it was used during that era you would have mentioned it. It might just be a more modern thing. Either way consider me a subscriber. I look forward to seeing more of your videos. Cheers mate. :)
Metatron Just don't forget Icarus! :) Seriously good job! I only discovered your channel about a week ago, but went through quite a few of your videos since then (and with 3 kids that's saying something). Very good, thanks for your effort.
Shad's saying "the sword won't snap in half" is quite correct, in a historical, or at least a mythical, point of view. According to the Japanese legend about the sword, a smith by the name "Amakuni Yasutsuna", living in Japan around 700 AD., used the structure of different carbon contents and differential hardening process, in order to prevent the sword from snapping in half. Especially, the wavy pattern of the Hamon (the tempered line) is intended to stop a crack from going throughout the entire length of the cutting edge, or exactly to localise a crack within a wave. Additionally, the Katana (or during Amakuni's time, the Tachi) was better to be razor sharp, so the hardness of spring steel would not do the work, so they needed hardness of 60 Rockwell, because the Tachi was designed to fight the Ainu, native people who were clad in leather armor (I am sorry for bringing this issue up, but it is history), so the razor-sharp edge worked better than a cutting edge, who hardness was around 45-50 Rockwell, whereas, against human flesh, 45-50 Rockwell and 60 Rockwell work almost the same.
Just an idea but: Maybe they wanted to have harder edge because they used the word more for cutting non-steal armor. The harder edge gave better cutting performance on such targets and the weapons didn't have as much fear of getting bent and broken because they didn't hit steel armor or other hard targets quite as much.
Ive studied this entire subject about as far as possible. Im subscribing because of this video. You fekkin NAILED it. But in an incredibly inclusive and well presented way. I liked you before. Now i deeply respect you.
29:11 I think the reason Japan used the Katana & it’s hard steel is much more simple than that, and it relates to something Shad himself mentioned earlier: Japan had a low iron/steel content. That means that iron/steel armour was going to be not only rare, but incredibly expensive and wasteful, because for what it takes to make full plate, you can arm many more people with swords. This led to Japanese soldiers wearing wooden armour (samurais, etc…), which would be tough to cut through with spring steel. So this is why they opted for the differentially hardened Katana & it’s superior cutting ability because it didn’t have to just go through bone, it had to go through wood, flesh and then bone, and a spring steel sword might not have been able to achieve that reliably. If you aren’t going to face an army wearing steel plate armour, it makes no sense to take a spring steel sword, but it makes absolute sense to take a katana which can cleave through wooden armour.
Been watching this series from beginning in one sitting. Incredibly insightful and interesting. Presentation is also top notch, entertaining and easy to follow.
I have a BA in Mechanical Engineering and this video finally helped me understand why hardened steel is actually hard! Thanks Shad, better teacher than my uni material science course
Fantastic series of videos you've got here. I learned more about katanas than I ever would've expected to! Your videos raised a "what if" thought in my head that leaves me with a question. (Anyone who sees this who might know is welcome to answer.) Let's say that in a setting where magic can assist in forging a sword, they take a different approach to differential hardening. Instead of the soft metal on the inside, let's say they use spring steel, while the outside is still the hardened metal we know. What would this do for the katana's build and effectiveness? My expectation is that the sword will be durable as you expect from spring steel, but that the outside will chip under stress. The trade off I expect is that it keeps the cutting power that hardened steel offers. If I'm right about this, it might be a good way to make katanas special in a magical setting. That is, assuming people involved care that much about the inner workings of the blade!
I love metallurgy, so I'm glad that you took the time and effort to delve into the nitty-gritty details, with all the terminology one could hope for. Thanks a lot for this video and the series! I think that a good reason, or at least one seen as valid, for keeping this technique rather than using spring steel is that the katana became a symbol of status, where perhaps a little practicality was sacrificed for prestige. Also, if we're talking about praticality of the weapon, we must not forget that Japanese warfare was not carried out with swords alone. Bows and polearms have huge roles in any army, both for infantry and cavalry, so a katana is more of a sidearm, I guess. At least, that is how I see it. In short, I think that the misconceptions are essentially debunked, so we can all appreciate the asthetics of the katana. One video left in the playlist to see what else you have to say.
Two more comments... In metallurgy there is a concept called a Time-Temperature-Transformation (or TTT) diagram. The combination of the wedge cross-section and the clay placed on the spine before heat treating enables different regions of the sword to pass through different regions of the TTT diagram for iron producing both different iron structures in the sword and the edge surface compression I discussed in my previous comment. The katana metallurgy is very complex which is the reason why metallurgist go ga-ga over samurai swords. A monolithic piece of iron, no matter what the design or quality of the steel, does not have the same appeal. Regarding the polish, a friend of mine showed his katana to an English gentlemen who slapped his own side with the sword in a gesture that I take is common with English military officers. He required stitches from hip to ankle to close the wound. A properly polished katana will be every bit as sharp as a modern razor blade.
Very nice video, however a small correction: The springsteel was in use before, for example the lombards at the battle of Veerneuil in 1424 used tempered steel armor, and that is as you will agree, well before the 16th century. I did'nt recognise it as such before you went into detail with the color however, thats when I went "huh... now thats something I heard about before!" and I went back and checked and yup: As usual, our forefathers knew a bit more about this than most gave them credit for.
Ever since I went through welding school and got into metalworking I've gained a pretty decent understanding of metallurgy. Looking at the subject through the window of sword making is very interesting, and everything you've said seems to agree with what I was taught and have observed as a welder. At Lincoln Electric's school we had excellent teachers, and I remember them teaching us about how carbon gets distributed during different stages of heating and quenching, and how to avoid causing cracks in large structures from improper pre-heat and all that.
Cool vid, lots of info. I think one of the big things that many people misunderstand about fighting with a sword and I know this more specifically in the area of Eastern martial arts, is that the style of fighting and defending an attack are not what you typically see in cinema depictions. I'm talking about the signature sword on sword 'clash'... In most of the Eastern combat techniques you don't block an incoming sword the way it's shown in movies, rather you parry or redirect the incoming attack OR simply reposition yourself to avoid the strike as you counter attack. So in the context of fighting in the samurai style, the katana was more than adequate and with the hardened edge you could maintain your edge much longer and retain your cutting effectiveness through different media, skin, bone, clothing, leather etc. So when you look at various sword 'torture tests' of katana blades where they are smashing on the side of the blade and it bends or breaks, of course it would with enough force, it's just simple physics. The katana was made for a style of fighting, it wasn't made to be a sort of a 'shield' that could absorb astronomical amounts of force rather it could parry and be angled to allow the opponent's attack to be redirected off the centerline and give the defender the ability to counter... I'm going to emphasize the point you made about spring steel swords. A spring steel sword that might be resilient to bending and staying bent is going to vibrate much more as you see in slow motion videos, that in itself dissipates and lessens the amount of potential energy that the weapon can impart through its target. The katana which is much less 'springy' is then going to impart more force into the cut AND with the slight curve of the blade will focus more of the force into a smaller area which further increases the cutting ability. The katana isn't a magical blade by any means, nothing is magic but form follows function... The katana was not developed to fight movie-style battles, not nearly as efficient nor effective ;)
As someone who is going to University for mechanical engineering I think I can add a little detail. Both hardness and ductility help determine how much force can be applied to on object. The harder something is, the more force can be applied to it before significant deformation or damage happens, while ductility allows it to deform to a certain regard before permanent deformation or damage occurs. Tempering allows for a stronger force to be applied, and depending on how you temper you can drastically affect the final hardness and ductility. In theory an ultra hard ceramic could out-cut any steel blade as the hardness could be immense, however even the minimal deformation that is practically guarantee a structural failure. So technically a katana should be able to chip and damage a mono sword with less force. However when a clash of damaging force occurs the katana would fail to a larger degree than the mono sword. Given everything I've said is correct (could have some details wrong so please correct me if you notice anything) They both outperform in different aspects, however the mono can take more force than the katana.
Agree with everything except the hardness/edge retention thing. I'm pretty sure what they meant by the sword will retain its edge longer was in relation to standard use. There are two ways that edges get dull: either by abrasion/chipping or folding. A soft steel edge will be more likely to both abrade (due to softer materials being able to cut it) and fold (due to its ductility). A sword with a Rockwell hardness in the high 50s will retain an edge much better than a sword in the 40s. A harder steel will be more likely to catastrophically fail, but in unarmored combat (which from what I understand was the scenario in which swords were most expected to perform in), that shouldn't really be a problem.
Sooooo, the katana cuts harder things than the spring steel sword and is less likely to snap when it encounters resistant it can't overcome. But it bends, which is just as bad as the sword is ruined. Spring steel swords are somewhat less hard. They still do what the katana does, just not as neatly. However it survives contact with too hard things a lot more than the katana does. It is indeed the superior technique. But it makes sense, considering it is older as well, by a couple of hundred years. Why the japanese didn't adapt later, is unknown. Either they liked how the katanas looked, didn't know any better, or something else entirely. I have zero data or research to back it up. I just think this, but maybe they simply didn't see the need. They already had a sword that can cut bones, and no technique would give them a sword that cuts armor. They were also on an island and didn't have to worry about non-japanese beating them in an arms race. Once the isolation ended, they can just conquer everyone with toyota, instant ramen, anime and final fantasy VII anyway.
Hi, Shad! I loved all of the videos in this playlist. I only noticed one mistake about the cutting. You did a circular cut, but when we train in the dojo, we do not do an circular cut. We try to use the cutting side as much as we can when we do the move. So it would be a kind of an oval shape, so we can maximaze the cutting superfice. I could do a video to show you, if you want. And you can do another comparisson in your summulator.
Some thoughts on hardness ... Is RC-60 a number you've actually encountered in a sword edge? This surprises me. A cutting edge that hard is very brittle and will chip easily, especially in situations where it comes into contact with hard materials (armor, bones, other swords, etc.). As a cook who uses Japanese knives, I'd consider bone-cutting to be a situation where you would specifically want a softer knife. My knives that are in the RC-60 to RC-62 range don't ever go near bones. Nor do they get used on tough, woody herbs, or anything that might grab the edge. These are situations where I reach for a softer, fatter, usually European knife. There are really just two advantages to a harder edge, all being equal-they will take a sharper edge, and they will hold onto that edge longer during normal use (which excludes use that will deeply chip or break the thing). Which is all to say, I don't think a very hard sword edge would be an advantage if you were really trying to smash through bones (and we are absolutely talking about smashing through them ... a sharp edge does not cut bone). The hard edge is an advantage if you plan to be slicing soft flesh and clothing all day long, are going to be careful about banging it into anything hard, and don't want to stop and re-sharpen.
I choose differential hardening over mono steel because of two reasons. 1. The beautiful hamon line makes the sword look like an art. 2. It holds a very sharp edge for a longer time. I had a chat with a swordsmith via email and he told me that the edge is so hard that niku (convex shape of the edge) is unnecessary, and it can hold a razor sharp edge for a long time.
Shad, This comment might be a bit late, and possibly somebody mentioned this already (didn't see a comment about it in the short time i looked), but as a sword enthousiast, engineer and (hobby) sword/blade smith I can add that the higher hardness that can be accomplished with differential hardening can have a (possibly) significant bonus. A higher hardness means that the blade can be made sharper than a blade with a lower hardness could be, and it will retain this sharpness longer (that's why razors are [generally] made of high carbon (and alloy) steel). And of course, sharper blade means easier cutting, and since in japan armors were for a long time made of cloth and/or leather and less of metal (correct me if i'm wrong here), easier cutting can be a significant adventage, therefor a good (possible) reason they kept using this method instead of monohardening. That having said, I myself prefer european swords, but like you said yourself, the thruth is important, and both katana's and european swords are good in what they're designed for. Love your video's shad, keep 'em coming
Good video, mate. Nice to see that somebody else researched the steel phases and how steel is made. I have to admit I kinda overlooked your katana videos, strange... But I am here now! But I have to say you overlooked some things (and I hope that I now will not overlook something). Ferrite, to be precise alpha-ferrite is the pure iron with a body-centred cubic crystal structure, it's the basis of steel and gives it the magnetic properties. Pearlite is not a crystal structure for itself (maybe I misunderstood you here and you actually said that, feel free to correct me) it is a structure composed of two crystal structes alpha-ferrite and cementite. And cementite is actually a chemical connection between iron and carbon (Fe3C). With increasing amount of carbon your increase the amount of pearlite in the iron (alpha-ferrite) and therefore increasing the hardness. Austenite has actually two meanings in steel, first it's a iron phase (defined by it's face-centred cubic structure) but also it can be a solid solution when carbon is an alloying element. This last point is what you described when the carbon is dissolved (but not connected) in the iron and then when you form martensite in which the carbon is forced to stay solved in the new formed crytal, through the speed, which leads to a distortion and strenghten the structure further. If you cool austenite slowly down than the carbon inside would dissolve in surounding areas and have a reaction with the iron forming cemenite, at a lower temperature the steel is back in its alpha-ferrite phase. There is by the way a phase between martensite and pearlite called Bainite, but we can disregard that here for now. When you form martensite in steel, there will be everytime a certain amount of austenite left which can lead to big problems. This austenite is very instable and can became martensite (inside of the martensite(!)) through cooling or stress and there is allready stress there through the higher volume of the martensite pushing against ech other and so hindering some of the austenite forming proper martensite during the quenching. But this an be solved also through heating then the left austenite will become ferite and cementite again (tempering). In steel are always different amounts of phases, in depends on the carbon content and the heat treating how high the amounts are and therefore affecting the steel properties. I hope this added some additional information, understanding and that I wrote it understandable. By the way, the video in which they tested katana vs longsword, is by the way a German show called "Welt der Wunder" literally World of Wonders, states that the tamahagane is well tamahagane. Therefore traditional made steel from Japan, they produce it once a year and is made out of iron sand. The same stuff they used in medieval Japan. So it us realy tradtional, the pureness is like back than (of course iron sand can be differently pure depending on the source) and iron sand is not iron ore by the way, just saying it gets often confused.
+Strategiusz I'm honored you like mate! As to your awesome question, my guess, and it is a guess, is that the hard edge wouldn't flex properly with the rest of the sword, which would mean when the sword does flex the edges would chip along the stress points of the bend. I think this means that the only practical option is to try and make the sword as stiff as possible to prevent all flex and bending, thus to maintain the edge, which is exactly what a traditional katana does.
I am Shad Thanks! So the "softness" of the core is only a relative term and the blade is stiffer than European swords made of "harder" spring steel for some reason (crosssection or lamination)?
+Strategiusz Oh the core is still soft, but the katana is thick and if it has an upper/back fuller it would make a structure similar to a steel T bar which makes a fairly stiff sword. Because European swords are MUCH thinner, especially towards the tip and their spring steel has so much give, even though it is a type of hardened steel, they will vibrate much more than a katana, which causes European swords like the longsword to be less forgiving in the cut. I'll be diving into all of this in part 5 ^_^
Interesting series filled with a lot of information. I've not finished it yet, (one more episode!), but I wanted to offer some thoughts: In a prior episode you mentioned 'inclusions/contaminants' (including carbon). As in the example of carbon, not all inclusions are bad. In fact, many steels, including tool steels - the hardest, are alloys which include other elements. These other elements affect the morphology of the steel and thus the physical attributes. The addition Mn, Cr, Si and other compounds can affect the form of steel upon cooling. Perhaps some of these inclusions helped create the martensite (in addition to the quenching) at the hardened edge? Sometimes you mix comparisons, although it may not be intentional. E.g. comparing spring steel to a katana. One is a form of steel alloy, the other is a finished product which uses steel. There is absolutely no doubt the steel of today is superior to steel from centuries past. But a sword is a sum of its parts and craftsmanship. You can make crap swords when starting with modern steel (seen quite a few of these). As far as why did the Japanese smiths construct swords the way they did? I have to assume because it met the needs for the type of warfare they developed in their civilization. We severely underestimate the capabilities of ancient man - whether examining the color of steel to better understand how hard it may be, to building pyramids, aqueducts, etc. I doubt it was for purely aesthetic reasons ;) From what I have seen in comparing HEMA and Japanese martial arts - there are probably more similarities than people expect. After all, the body moves only in certain ways, and creating a steel extension of that body will create similar strikes, guards, and counters. Thanks again for the great series. People will always debate the merit of one thing vs another (scotch vs bourbon, ST vs SW, vanilla vs chocolate). Oh one last thing - the entry for steel in wiki has an excellent phase diagram for steel morphology.
any germans here who recognized the welt der wunder logo in that clip that's played at the end? :D good job, shad. i wish had found those videos way earlier...
+SchmoopyHD Then I'll most certainly try to make more in the future! Part 5 is still coming out but after this series I might make a few simpler videos before I tackle something else to this level of detail, they take a LOT of work ^_^
Great vid Shad. You could've brought up the concept of plastic vs. elastic deformation, maybe it would've helped on the explanation about why bending or not
you did a good job explaining the metal structure. I took a Metallurgy course in college so i know about the structures of different metals and alloys. I have to say you did just as good a job of explaining it as my teacher would have
something people tend to overlook when comparing sword types, is that knights and samurai would probably have never used the blade to party. that's something we see a LOT of in movies and games, where one constant comes in with a chop or swipe and the other combatant uses his own blade to block, or Parry, the attack. bit the way swords were designed in the middle ages, both east and west, would have made this type of strategy very dangerous, as the blades would have chipped, bent and snapped, depending on the steel quality and method of forging and tempering and so on. more often than not, the flat surface of plate armor and flesh was the target, since the thin, sharpened edge of another sword would cause serious deformities to your own blade. parrying was usually the realm of weapons with a shaft they would not easily break, such as the bec-de-corbin and other polearms or shafted weapons. later in history, parrying daggers became common to accomplish this exact tactic. so comparing the chopping capabilities of different swords against each other is very impractical and won't give you very good information on what the blade is capable of withstanding.
I mean, most martial arts using a Katana don't block by simply putting the sword directly in front of you. In fact, most blocking in all sword based martial arts doesn't work like that at all. When you block an enemy attack, you let his blade slide of yours, using the same motion of the block (parry) to drive your blade forward in an attack.
***** I did say "most blocking techniques" didn't I? I know there are a few techniques for blocking something straight on, but the situations where you can do such are extremely limited. Limited compared to slide blocking, at least.
+firstoftheoutcast I'm sorry to inform you, but IMO you never practiced any swordplay. Correct me if I'm wrong. In my experience with longsword you don't really get to choose how you block, there's no time for that. And a simple straight block is much easier than any other technique. The more significant reason why blocking with the Katana works, is because the edge isn't straight. Now I'm not familiar with Kenjutsu or anything, so I can't comment on the preferred technique. I've heard that they often block with the other side, and I can see that working for some attacks but not all, so I'd wager the curvature makes the opponent's blade slide off more easily, which would also explain why they preferred this shape.
+Sagrotan A heavy swing would ideally be "brushed off" rather than blocked, yes, however properly performed, that brushing motion can actually impart even more stress and force on the edge and the general structure of the blade.
phileas007 And if you're trained for that scenario you can react accordingly. For example by quickly attacking after slightly altering the enemy blade's course. While what you've said is certainly true, depending on the enemy, "normal" blocks can cause more impairment as well. The effectiveness of a technique comes down to the skill of the user, so what form of blocking is best depends mostly on which the weapon's wielder has more experience with. So whether you "brush off", "catch" or "stop" an enemy's attack won't matter if you're equally inexperienced with all forms: each will bring almost the same amount of stress on the blade.
+firstoftheoutcast Very true, almost everything in fencing depends on the skill level. The stress on the material is roughly proportional to the forces at work. A static block is indeed one of the worst conditions, the reason it is less stressful is because the point of impact is (ideally) much closer to the grip than the active "brushing" whereby you strike the other blade with the farther half of yours. So the bending moment is greater and therefore the stress on the material.
Since I am running off at the mouth, one more set of comments.... As I note and as is shown in the background video, the katana is made from a straight piece of metal. To get the curve without warping, all aspects of the sword must be precise (wedge cross-section, thickness and density of the clay on the spine, carbon levels, temperature of the water it is quenched in). Such swords come from swordmasters specifically trained to make katanas and involve about 9 man-months of effort. As such, an authentic katana is $50-100K and as I mentioned each sword gets a $5k polish when it is done. There are plenty of videos of folk "putting katanas to the test" on RUclips and destroying the swords. I suspect these swords are forged with the curve there already, sharpened on a grinding wheel and have little to none of the actual metallurgy that makes a katana a katana. Again, the curve is not a style element, it is a consequence of the heat treating and the curve imparts compressive forces to the cutting edge of the sword. A reasonable analogy is a bow. Other than a mechanical or compound bow, a bow that is the same shape strung and unstrung will not work very well as a bow due to the absence of stored compression. Molding a bow with a curve is not the same thing as stringing a bow and causing the same amount of curve. Forging a sword with the same curvature as a katana is not a katana.
There is no benefit what so ever from the curve. None. The blade isn't going to be mysteriously sharper just because there's more compression. All kinds of swords can have the "razor blade" sharpness on them, after all they're all made out of steel. The "Grosse Messer" seems to cut same way as the katana while providing better protection for the hands, being better at thrusting and more durable due to spring steel.
You can differential harden mono spring steel. First you harden eges in cold water (swift cut in cold water), then submerge all blade in hot oil (or cold air). In that case you will get mono spring steel differently harden.
+Almus Quotch I have and the interesting thing is that, from what I can gather, for all other swords except the katana it doesn't really matter how they are made, spring, hardened etc. as long as they have the right shape and design, they will be called that type of sword. Generally a longsword is a longsword regardless if is is made of spring steel or hardened. Only the katana has this expectation and standard in regard to its internal properties. I could certainly look at other swordsmithing techniques in general, like pattern welding and such.
Boy I'm glad we got that strait. So, if a bunch of Knights would have met up with a bunch of Samurai the Knights would have had to sharpen their swords after that battle.
Thanks for the video. I personally believe the Japanese used differential hardening because of the test you showed, the bend and not snap in two test. As a consumer, unaware of all the science behind sword smithing, if I saw two blades clash, one of which snapped clean in two, the other of which snapped the edge and bent beyond future use, but not into two pieces, I would assume the one that remained one piece was a superior blade. And henceforth, I would only buy blades made in that style. A style which would simply become the standard over time. Also, I was really waiting for this video not exclusively for its content, but I wanted to see how you'd be holding the swords in your thumbnail, since part 3 was so epic.
+icspps It is critical to point out two things in the debate over historical 'katana'. Firstly during the period when the best blades were being produced, the late 13th and early 14th centuries they were in some ways functionally superior to many but by no means all European blades, this is where the confusion originally arose. There has been an unfortunate tendency for people to take 13th century technology Japanese blades and compare them directly to 16th century technology Indo-European blades without looking at those found in Europe during the 13th century at all. Secondly it must not be forgotten that Japanese swordsmiths did not just make blades for katana, they also made wakasahi, tanto, naginata and yari blade amongst others too and these due to their proportions and the manner in which they are used are far less susceptible to the disadvantages inherent in the Japanese blade smithing process. The katana in contrast with its longer, narrower, shallower proportions was more susceptible to bending in use when cutting.
i liked the science aspects right up to the end where you underestimated what the rockwell numbers mean. as armor is hardened and you mentioned getting through armor, which you also say in your other videos is pretty much impossible. A strike on armor wont cut it, but will blunted a sword like no tomorrow if it is softer than the armor. So in a battle where there are strikes on armor the harder sword makes more sense as it will still stay sharper (albeit with some chips), but the spring steel is better if there is wresting type moves as bending is more likely. so just comes down to the different swords requiring very different techniques to use. each one fits the types of fights they were used in and the types of defenses their opponents were wearing.
Differential hardening for the katana was made necessary by the higher level of inclusions in the forged steel. Harder steel is naturally more brittle (even modern steel) than a softer steel. The harder the steel, the more significant the impact of inclusions on the strength of the steel. If you compare two pieces of steel, with the exact same Rockwell Hardness, the piece with more impurities/inclusions is much more likely to fracture under stress. Due to the relatively higher level of inclusions in the steel; if the entire blade were hardened to the level of the edge, it would be highly likely the blade would fracture during use. By the spine being a softer steel, it lessens the impact of the inclusions since the steel is more likely to bend than break. It should be noted that this approach, of using different hardness of steel combined to create a sword is not a distinct idea from the pattern welding used during the early middle ages (i.e. migration period swords). We need to consider the timeline to realize that the Japanese were still using more primitive methods of smelting at the same time that Europeans had developed more modern smelting techniques allowing them to make more pure mono steels.
This may be years too late, but I think the answer for why is that the lack of iron quantity meant that shields and plate armor were not developed. So the super hard edge could survive in an environment where the risk of it impacting another hardened steel was low and it provided a cutting edge that could overwhelm armor made out of a few iron pieces, leather and cloth.
Just a quick correction, during the tempering process the steel does not "glow" blue. The bluing effect is a chemical reaction between the surface of the steel and the air, and depends on the temperature. The color is permanent, but will come off during polishing.
Great video, but you didn't hit all of the angles...I began learning the way of the sword with blades that were mono steel (5160, 9260, 1060) and mono tempered (through hardened). These swords have different characteristics - 9260 is one tough cookie, can be bent up to 90 degrees. That is due to the silicone added to the steel. It also takes dents in the side of the blade. 5160 is a bit different, one of my favorite spring steel alloys. It won't bend to 90 degrees, will snap around 45-60 degrees. It scratches very easily, which is irritating. It holds an edge, it seems to me, longer and sharper than 9260. 1060 is the hardest when mono tempered. It is scratch resistant. I do not know how much bend it can take before snapping. It is my current favorite in the mono temper mono steel. The angle you missed - mono steel that is differentially hardened. Yeah...such as T10 that has been clayed. That is where I finally went, after a series of discoveries regarding steel and cutting. The edge I can put on a diff hardened mono steel is considerably sharper than any of my mono steel blades will take. It is insane how sharp a diff hardened edge can be. That being said, the material is the same throughout - mono steel. The characteristics of this combination are unique, and quite frankly unknown to me at this point. I don't know how tough this blade is, or how much bend it can take.
thank you Shad , you just solved a mystery from KCD , i had often wondered why Blacksmith Mikesh double quenched his swords, the second one was actually tempering , bloody good one!
Something to point out..... You can deferentially harden spring steel. I don't know if they did this with swords but you do with scythes. From time to time you will "peen" the edge on a scythe anvil with a hammer. This work hardens the edge which you then sharpen. Since they did do this with scythes I would be surprised if they didn't do it with swords if they wanted to. They might not have wanted to though because as you say hard edge = brittle edge and smacking a sword on someones armour and chipping the edge might be something they want to avoid.
Samurai were essentially a headhunter cult from a historical perspective. Samurai often got paid by presenting heads that they collected on the battlefield, heads belonging to someone of a higher rank, or other samurai of renown would yield better payment. They even had officials to judge the quality of heads collected. This could be a possible reason as to why they decided to go with differential hardening over spring steel because decapitation was so much a part of their culture. Japan was also pretty isolated being an island so it's a wonder that their methods were so advanced. We aren't even 100% sure when the Japanese came up with the idea of differential hardening but we do know Masamune created the Susho method sometime in the late 1200's or the early 1300's. The Susho tradition distributes hagane, kawagane, and shigane in seven different locations within the construction of the sword. The method of construction you show is the Kobuse, (hagane outer with kawagane core) and Shihozume (hagane edge, shigane sides, kawagane core). Kobuse method is often what you find in Japanese swords made for officers during WWII, while swords from the Shihozume tradition are much older antiques, and are rarely found with origins later than the 16th century. There are quite a few counterfeits of Nagasone Kotetsu swords that use the Shihozume tradition which date to the late 17th century. Funny enough many of the counterfeits of Nagasone Kotetsu were superior to the real one. Minimoto Kiyomaro is a prime example making high quality swords faked as a Nagasone Kotetsu. Incidentally enough I bought a sword believed to be an actual Nagasone Kotetsu about 12 years ago only to find out it was a high quality forgery 5 years after that but still dates back to the early 1620's. Often Kotetsu himself couldn't tell the difference between his own work and that of a forgery without looking at the mei (signature) and sometimes not even then.
I have heard it said (possibly in one of your other videos or from another swordTuber) that spring steel can be harder to cut with because it vibrates, and this interferes slightly with edge alignment.
Ah yes, the memories from my metallurgy studies ... I heard what you said and immediately felt like home. Good times. :D Also: LOL just noticed the "World of Wonders" logo on the vid about the cutting test against the sword. ^^
I definitely see why the durability of spring steel can be an advantage, but I think I personally prefer a stiff sword for the greater control, particularly at the tip. Of course, this means that the sword must be used more like a fillet knife, or a surgeon's scalpel, rather than a meat cleaver (i.e. for slashing rather than chopping). Rule # 3 of my swordfighting style is "Protect your blade", which means that any kind of impact should be avoided, and the edge of the blade in particular should never even come in contact with anything hard (including bone, which can cause it to chip or to get stuck and potentially bend).
My 5 cents: If you study kendo or kenjutsu you could see you are hitting a bone a lot. A LOT. Actually the #1 strike is men (hitting the head trying to split the skull), #2 kote (chopping off the wrist), #3 do (hitting the belly with possibility of chopping the ribs) and #4 is tsuki (stab to the throat with high probability of hitting the spine bones). So it does have some sense to have great bone chopping ability. The back of the katana made from weaker steel or iron has some sense if you consider you would actually try to cover yourself from strikes of your enemy by the back of the katana. Massive mune made from weaker material will help to absorb the hits. Weaker steel protects not only the whole sword from shattering but could also serve as some sort of shield. Its kinda hard to use the back properly but training helps. Spring steel has some disadvantages as well, at least from my point of view. It has very unpleasant tendency to vibrate after hits. Vibrations do increase with the length of the blade. After a few strikes it is actually hard to fight or even hold the vibrating sword. One handed sabres are really unpleasant with this effect but long swords are pretty bad too. Triangle-ish cross section of the katana suppresses this vibration effect even if it is made from mono steel.
Awesome video! I really enjoyed it! I actually did this research years ago, back when I was 15 and saving up to buy a "real" katana, I had a stainless one. I was definitely a fanboy. I didn't go quite into the depth which you have, but I came to the same conclusion. I was happy to see you reconfirmed it for me. :) I have had this question though this entire time, and I never managed to find the answer. What exactly is L6 steel and how does it compare to the other ones?
*Please do a sword ( & other weapons ) techniques ( skills / moves ) series .* *I work with metals .* *Tool steel is indeed hard but also brittle .* *I have broke many files and other tools by by them striking other metal .* *Tool steel is really brittle and should not strike it at any point .*
As to why the Japanese kept differential hardening as opposed to tempering. I think culturally, once the Japanese get an idea in their heads that there's a "perfect" way to do something, they will do it that way from now until the end of time. I think also that they valued the extreme sharpness that a differentially hardened edge gave them. It's worth noting, and it's a point that many people miss, is that swords are not the go to weapons for battle. These really are side arms that a person carries around in battle as a backup to their primary weapons, or everyday for personal protection (or in the case of the Samurai as a symbol of their status). If you're carrying a sword for protection, it's unlikely you'll suddenly be faced by someone wearing armor strong enough to defeat the edge of your sword. So having such a hard (and therefore brittle) edge isn't a huge consideration in the grand scheme of things. That being said, anyone who thinks that the Katana is sharper and cuts more easily, therefore it's superior, needs to learn that best is the enemy of good. Making the katana a "perfect" cutter weakens the blade in other ways and ignores the fact that there isn't much that the katana can do that a mono-steel blade (I.e. A longsword) can't. Both cut up tatami mats equally well, they can both cut off limbs and heads. The only real advantage that the katana has, as near as I can tell, is that it does it a little more easily and thus requires a little less skill or practice.
I'd like to add what you _almost_ said, but stopped just short of: because of the presence of hocho-tetsu in katana, there would be no point in tempering it. You would lose the martensite edge but gain no springy qualities. There are, however, two traditional styles of lamination which do not use shigane (hocho-tetsu). The first is maru, which is no lamination at all; the entire blade is hard (hagane). The other is wariha tetsu, which features a hard edge (hagane) and a body of medium hardness (kawagane). All other styles of lamination use shigane, but it goes to show... they had the knowledge but not the will, it seems. It may well have been for traditionalist reasons, as you say, because you'll find many interesting variations that surely have nothing to do with practicality (eg. one broad fuller on one side of the blade; three narrow fullers on the other - or swords with asymmetrical cross sections). Oh, and just a side note on that video featuring Stephan Roth: the sword which is broken by the longsword is... also a longsword. But these are stresses of which neither katana nor longsword would expect to experience anyway, so while a longsword made of spring steel will be stronger than a traditionally made katana, a traditionally made katana will be strong enough. Just like the katana will be sharper, but the longsword sharp enough.
+Gilmaris I agree with everything! All your comments are very insightful my friend, thank you for sharing them. I hope I conveyed the same thought in my video, that a katana will still be more than strong enough for standard use, but you most certainly said it much clearer than me ^_^
I am Shad Hey, thanks! I enjoy this video series immensely, and I feel that teachers in schools everywhere should be presenting it in Katana class. For too long we have lived under the yoke of fan-boys and bashers!
Hello Shad, I have a suggestion as to why the Japanese continued using water to harden their steel, and that is quality of oil available. In Europe you have large amounts of plant oils available in different grades so you can create the oil you need to harden the steel correctly. In Japan, I'm not sure they had the correct material. And if the steel is hardened in water, it would very difficult to temper the blade evenly without warping it. The temperature range between tempering and annealing the steel is narrow if the steel is that hard. So a swordsmith trying to make a katana out of mono steel the first couple of times would either anneal the edge and blunt the sword or leave it brittle and snap it. After which he goes sod it and makes the next one as he was trained.
really cool series.. and full of true facts.. and yeah i agree on what you say in the end.. the katana is a piece of art.. no matter what steel and forging and smelting techs are superior.. the katana is to me still the most beautiful sword of them all.. but what impresses me the most is that those traditional japanese sword smiths managed to create such a perfect blade in terms of metallurgy just by trial and error without any real knowledge about carbon conent of steel, imperfections and the microstructure of steel through different heats and hardening processes.. with modern tools like powerful microscopes we can look at a 500 year old katana and say yeah.. we see what you did there.. but in the end one should keep in mind that they didn't have this techs to analyze anything at all.. there is a reason why we still use different types of steel for a different kind of purpose still in our modern age.. sometimes you need something that is hard and brittle over something soft and flexible.. and i guess most of that also happened in the past.. and that's also why swords were forged different everywhere in the world.. they all tried to make them as good as they could for their use of it in the end.. so in this case the enemys they fought and the armor they wore at this time.. also: yes there would be ways to improve the katana from the smelting to the forging but there is a simple reason they never did.. ranged weapons like guns came to japan and that made the sword useless at some point.. so what would be the point of improving a weapon that's useless anyway in the end? at this point it was made to keep the tradition alive and that's why it's still forged the way it was hundrets of years ago..
+Dunkelelf3 Hmmm... coulda sworn i said almost the exact same thing some years back. Did you lift that post from me? :) Anyway, in relation to your last point, sure, i could see guns having some influence on the decline of the katana. But consider too, that when it came down to it, Japan chose their traditions over technology & eventually banned the further importation of guns, & clung to the katana! Why would they do this? The katana was not even the "primary" weapon of the samurai in battle. It was a side arm. But it seems that it's metaphysical symbolism elevated it far above it's practical function, & perhaps this had something to do with why the traditions surrounding it's manufacture remained intact long after their practical relevance had passed. It had become a spiritualized, religious pursuit by that point. Just a thought. I really don't know :)
***** yeah it think that's also a point.. the katana really is a symbol in japan and also i think they try to honor their ancestors by keeping the tradition and everything around it alive..i think it's a good thing.. humanity has lost so much knowledge by just forgetting what was well known in the past.. for example are we so proud of our modern medicine and drugs like antibiotics but we forgot about so many herbs and plants that could be used instead really well in many cases.. i don't think that it's a good thing.. yes ofc progress is good but it shouldn't be the reason that we forget about anything else we learned in the past..
I think partially the reason why they used differential hardening is because the way it is used and the target they are used against. In feudal Japan, iron is scarce, and to arm as many men as possible, it is more efficient to make weapons than to make armours. Hence, most of the combatants in battle go without armour. Therefore, the katana is primarily used for cutting through human flesh, and bones, and a harder edge is more preferable. On the other hand, a European sword has historically been put against full plates, the ability to retain its shape is important as full punch collisions against armour and other weapons often occur in battle. The fighting styles of the two weapons are also a reflection of the use mentioned above. Samurais emphasise on the striking speeds and evasion because their weapons are not designed for parrying. European swords are often straight, facilitating its tip to penetrate armour.
According to Mr. Roth, (the forge is called seelenschmiede) the smith doing the destructive tests on the two swords, the steel used for the European one was phosphorous steel of a composition you'd get when using bog iron as basis for a late medieval smelting process.
Great explanation on the metallurgy of hardening here, thx. But, you can't blame Marten. The poor guy now plays the guitar with Meshuggah ;) The structure is named after German metallurgist Adolf Martens (1850-1914). :)
Where did you get all of the information on the molecular and crystal structures. I'm writing a paper on heat treatment and I'm having a hard time finding information on the structures.
29:14 A speculated historical reason, besides aesthetics (you're not really wrong about that, it was given almost undue levels of importance in the "higher" society, which were the people who used katanas in the first place) is infact... the usage of the weapon. As you know far better than me, the medieval European warfare scenario quickly escalated into a one-upmanship between weapons and armour, which is why, swords were not expected to deliver fatal slashes, so much so as to survive the punishment of clashing against armour. So the need was for a weapon that would not break, rather than one that could slice a tomato. Contrast that with warfare in Japan, where duels did not permit armour, the capitals did not permit armour unless a state of war had been declared, and rebellions of the downtrodden never managed to get their hands on chainmail (which is hands down, one of the most useful things to be wearing to protect oneself against a slashing weapon). Thus, a sword that could slice deeply, and deliver fatal wounds on targets with minimal armour, was the requirement. And in cases of actual warfare, even for the samurai, most of the combat was from horseback using glaives, spears, or archery, hence, once again, not directly clashing swords against armour. So essentially, their form of warfare never developed in a fashion where they might need anything other than a slashing sword, compared to the European swords which were meant to slash, hack, stab, bash and pummel using the pommel (see what I did there ;)
Well, one obvious reason why they might have stuck with the differential hardening instead of going with spring steel is edge retention. When you're slashing flesh or melons or whatever, having the harder edge would've allowed a sharper edge and better edge retention. If you were striking full plate armor or steel shields, you would have quickly understood the limitations of differential hardening. The fact steel was so rare in japan is a great indication of why this never occurred to them.
I think maybe two reasons the Japanese stuck with their methods may have been: 1. They really did love cutting, so anything which decreased cutting at all might be seen as less desirable. This seems historically borne out. And on a related note, the katana seems to have been more about samurai dueling and honour than about warfare. Remember that katanas are sidearms; the primary weapons in war would be spears and bows. And, as long as everyone is using a similar weapon for dueling, that's fine! (Think of how a European rapier would have an advantage over a smallsword, but as long as both duelists have smallswords, that's irrelevant). 2. This is more speculative, but when you don't have modern chemistry and metallurgy, you're going to tend to stick with what you know works, even if something better is out there, because you don't KNOW there's a better option. Unless you happen to have someone stumble upon a better option. And you're less likely to have someone stumble on it or know someone has stumbled on it in an isolated place like Japan, with limited contact with other cultures and smiths.
One question, if you can bend a katana with your bare hands/feet, can you bent again it to repair it? System D like? (then go to the blacksmith because it's not optimal.) I'm not a pro europe or japanese swords but aren't they cheating in their mega stress test with the two european swords ? When he break through the sword 1 with the sword 2 : -The sword 1 is keep against the table : it can't bend (even a slightest in the edge alignment) and can't react properly to the attack. It mean it must absorb all the shock by itself, but can't and break. -The man doesn't hold the sword 2 in a straight way, you can see he's tilting it to his left : Then the sword 2 freely bent in the plate side, absorb the shock easier, and the crack following a weird path instead of going upright through the blade. Then a got a paradox : why does the sword 1 break that way with a strike weakened by the tilt of the sword 2 ? Would the sword 1 break if he didn't tilt s2? Yes. Would the Sword 2? Yes i think. I think they pre-cut the Sword 1 and tilt the sword 2, that way the sword 2 stay clear.
there are modern smiths who make differentially hardened catanas with spring body and martensitic edge :) Howard Clark with his L6 swords are one of them. some production firms like hanwei also make those.
Japan was very isolated being an island nation and they didn't really have to battle and fight other people with different technology. In Europe new weapons were made to combat the different defenses of people around you and in turn technology geared into stronger defense and a chain began to get ahead. but in Japan where it was only one culture and one group of people with limited resources they didn't have to change new technology, they perfected a weapon to fit their needs. I'm sure if there was more interaction with other armies maybe they would have changed techniques, combat style, or weapons all together (the Romans had to change many times do to conquest and interaction with new tech). necessity brings around invention and it wasn't necessary for the Japanese to change. considering all of that and the challenge the sword crafters had to overcome to even achieve useful steel to make a weapon, the katana will always be my favorite sword and one of the better swords in history. I'm not saying it's the best or that it will outshine all other swords, which it clearly wont, I'm just saying with what they had to work with they made an amazing weapon to combat what they had to. That and it looks badass
Actually the Japanese did interact with other nations and went to war with other nations and were even conscripted as mercenaries by other nations.Secondly I agree the katana is awesome
That is somewhat true, the Japanese didn't have extensive military interactions with the continent during the period where katanas were most used, however, they were not a single unified group for much of that period, they spent quite a long time in varying degrees of civil war (or, depending on how pragmatically you view the position of the emperor, you might argue that Japan as a unified country ceased to exist for a period).
In 5:00 you seem to be confusing differential heating with, bimetallism (2 types of metal in the same blade, in katanas spine is low carbon steel aka soft, and edge high carbon steal aka hard). You can deferentially heat-treat a mono-steal (one type of metal) blade perfectly fine (it all has to do with the application of a layer of clay on the blade prior heat-treatment).
A bend blade sounds much easier to repair in case it can't be simply replaced, compared to a snapped one. So maybe that's one reason why they chose this method.
I actually appreciate the katana only because of its aesthetics. I like most other types of swords more for cutting practise but the katana just looks absolutely beautiful (in my opinion).
A reference can be made to the 'Tang Dao', from which the katana derived. It has a straight blade and a smaller edge (a third of the depth of the blade), supposed to the katana (over half of the depth of the body). The Japanese blade is adapted to killing mostly unarmoured opponents, therefore they only needed the katana just stronger than the human body that it doesn't bend in combat.
Wouldn't the differential hardening be better suited for a sword like a katana? If I recall correctly the majority of the cutting done is done with the last few inches of the blade which on a mono steel sword would have been outside the point of percussion and thereby reduce the effectiveness of the cut. As such a katana needs to be differentially hardened to make it more suitable for its intended use right?
To be honest, I watched all 4 parts now and am about to start the 5th, I understood all of it and I was glad to be learning something. This episode however went over my head, I couldn't follow it all that well, unarguably due to my own stupidity but I feel like I have to re-watch it 4 more times to understand it completely.
The magnet hardening temperature is a myth too. All steels lose their magnetic properties at around 744 C, yet only 0.6-0.7% C content steels can be quenched at that temperature. Most steels require 100-200 degrees more than that otherwise you get a partial quench and inconsistent results.
really great series Shad :) I have a question, european swords of the medieval era, 13th 14th 15th early 16th century were or were not spring steel? and which is better, ulfberht steel or spring steel? was the steel quality of the ulfberht better than of the spring steel european swords of medieval era? I am kinda at a loss there, ulfberht steel was liquified, but was the spring steel on the medieval era also liquified?, and why was ulfberht steel patternwelded when it was already liquified? no need for patterwelding then, right?
+John Pepper GREAT questions mate. So according to my understanding, spring steel swords were rare before the 15th century. Could there have been cases of spring steel before? yes I do believe there were but that they weren't widespread. I've never read that any ulfbehrt was spring steel, though I suspect they could have been made into spring steel if the smiths new the techniques. Spring steel will be more durable than the ulfbehrt steel (which I suspect would be pearlite with traces of martensite) when under high stresses but what we need to remember is that the ulfbehrt sword was still very serviceable and of high quality. Pearlite still makes great swords, they're just not as durable as springs when under extreme stress. From my study I believe that the great feature of a true Ulfbehrt is the purity of the steel, but purity doesn't grantee a great blade, it has to be quenched right. The quality and purity of medieval era steel could vary quite a lot but the best of the best would be very pure stuff, definitely equivalent to Ulfbehrt steel. And yes, I don't believe there is any reason to pattern weld steel that is already in a pure state, except for beauty. Indeed any type of extensive forging to decently pure steel would be FAR more detrimental to it than anything else, as parts of the scale (iron oxide) will be mixed into it and it will also lose carbon.
+I am Shad thanks for the answer, I mixed the quality of steel with the process of tempering (for making spring steel) I watched a documentary about the Ulfberht, (secrets of the viking sword) and frankly it confused me more than clarify things, you know, but you sir you made it clear, thank you for the series :) just one more question, about the damascus steel, if this steel was made by melting the metal to liquid state, why the patters? aesthetics again?
One thing that I was hoping you would discuss/consider is the argument that the differentially hardened quench allows for shock absorption (and compared with spring steel). Another thing that would have been good to talk about is the question of differential tempering (whether it's possible, been done, effectiveness, etc.) Perhaps you could update the description, or even make a miniature addendum video if these topics warrant such? +Shadiversity
The Katana is ideally designed for its purpose, that is slicing through the human body. Other swords are better designed for other purposes, like stabbing into a body and getting back out (the springiness would seem to me to be ideally suited for this). I tend to think that weapons were designed for use cases(duh), and European swords were made in the context of trying to poke through or into the seams of plate armor. Katanas were great for lopping off limbs at the seams of armor, or against an unarmored foe, hitting at the shoulder and going diagonal across the chest. (this is also why the curve is in the blade because it makes it easier to hit someone at the shoulder at a higher velocity with minimum recoil through the blade)
I know this video is relatively old now, but as a material science engineer who just saw this I would like to point out that what really dictated the names of pearlite etc. is actually how the cementite precipitates looked… Otherwise so far this seems like a great video (10 minutes in)
Please turn the top sword on the wall blade side up, all the photos of genuine swords you’ll see that’s how they’re presented 🤓 On a serious note, have you seen why they use a concave Polish for katana, I sharpen my kitchen knives with a concave Polish for the reason. I also used to practise tamashigiri with a live katana, the curve shows the difference between a slice and the chop of a straight edge. I’ve had access to historical katana, you’ll see the back of the blade can have blade marks in it suggesting it’s used for blocking, yes some of the blades I’ve seen have small chips in them. The Hamon is not part of most katana, the clay actually is not insulation, it provides a greater surface area for cooling as a study a few years showed.
While I will admit I didn't really learn anything new in this I did enjoy it and am finding the series on a whole very informative. And to a person who doesn't know as much about the forging process I'm sure this video was very helpful. Great job Shad keep it up. I can't help but wonder if your name is actually Martin....
This man deserves more than this... Christ this is something i have wanted to know for SO LONG
Yea! This is a question that has been bugging me forever.
I’ve learned how to use a katana in ninjutsu style and this have really helped me. Thank you for making this series. Now I finally can buy an original katana without wondering how it was made.
same... i've always been kinda in between the katana fanboy and the katana basher. however i still VERY much prefer the longsword
Study metallurgy, we cover this in the second semester xD
Being a mechanical engineer a lot of this wasn't new to me, but it made me happy to see someone explain it so well.
One issue I had was in the claim that the harder edge will assist in cutting through bone. Bone is softer than any steel, the the things that determine how well it will cut are edge profile and sharpness. The real benefit of the martensitic edge is that it will stay sharper much longer.
This is very true.
So odd why they had to harden it that much though. I mean high carbon steel will have more edge retention like what this guy said compared to mild steel but it's easier to sharpen mild steel than high carbon steel and unless the wielder really sucks or they make thin-bladed, mild steel swords, then the edge should be fine for hours or even days of battle. So really what's the point of the Japanese for doing that?
The short answer is they didn't have the technology/knowledge to temper, so this got a blade that could be used with the slight bonus that it had an edge that would last slightly longer in normal use.
Differential hardening didn't allow for tempering and the lack of advanced smelting techniques didn't allow for mono-steel forging. As such, making a really high-hardness edge is the only thing they could have done without advancements in their smelting process.
actually tempering did exist to a point, it wasnt as accurate but they could do it. some katana appear to have been further tempered after quenching while others seem to have been used as is. the differential heat treating process appears to be a left over trait from older period swords before further refinements in the forging processes. earlier chokuto swords often actually appear to have been clayed, however many are never polished like katana or tachi so this fact is hidden in many cases. it would appear they preferred the trade off for a more durable sword with a sharper edge, by this i mean a katana can bend many times and be straightened before it becomes an issue, however with swords that arent clayed a bend is much more damaging. also there are some katana that from my understanding were not differentially heat treated though this appears to have only been done by specific schools and seems to have been meant for cheaper more disposable blades meant for wars. also the katana can comein many different stack ups for the billet, first off there are different grades of tamahagane another sword grade steel called orishigane as well as the ones mentioned in the video, as well as the presence of european imported steels in swords made by certain schools and smiths. the thing to keep in mind that katanas depending on quality were made with varrying amounts of different quality steels as well as receiving different amounts of attention from different skill levels of smith.
Slight correction, steel doesn't GLOW blue when it gets hot, it just turns blue because it's oxidizing.
If it's GLOWING blue that means you've just made solar plasma, in which case you should probably stop, because when stars start turning into iron it means they're about to go supernova.
That's because the gravitational force of the star isn't enough to fuse iron atoms together. The star collapses and creates enough force to explode. I'm not sure iron solar plasma would actually explode, but correct me if I'm wrong (still ridiculously dangerous though, so still run).
I know this is an old comment but...
I just love the casual idea of:
“Just outrun a supernova”
It also glows blue when the presense of orcs is about
A comment from an M.Sc. in chemistry: Well done! Although you have not studied chemistry or materials science you have explained the 'different irons' , the 'host-guest-chemistry' and the other processes involved very well. Body centered cubic (bcc) and face centered cubic (fcc) were explained and used correctly. You did even mention a tetragonal cell ..... Well done!
About quenching and tempering..... those two processes are easy to explain! In general if we chemists 'quench' something we want to stop a reaction or a process instantly or at least very quickly! Like using an emergency-break to stop a train from moving. In a kitchen you blench the beans in boiling water and then you 'quench' them in cold water with ice. It will stop the cooking-process immediately and they retain their color. The result: They will not get too soft aka overkooked if they stayed warm for too long or cooled down too slowly.
Tempering means to heat something up again but NOT to its melting temperature! You MUST stay below. As you mentioned you can influence the properties of that material enormously.
A very good example is glass! When a drinking glas is produced from molten glas, you will get raw-glasses first. You could snap your finger against it and it will break into pieces after cooling down. BUT: If you heat them up once more below the melting temperature (tempering) and then cool them down slowly the glass will not shatter to pieces when you clink the glasses with your friends!
Btw: The German word for pig iron retranslated back into English is: raw-iron. ;-)
The katana was forged all the way into the 20th century. The last recorded instance of battlefield-ready katana being made and then used was during WWII. They were mono-steel, or binary steel of martensite and pearlite. I do not know if they attempted to temper it, but I just want to make this known.
Many of the Katana's legends of cutting through rifles and machine guns may have come from US soldiers fighting against a banzai charge, running out of bullets, and having to defend against an officer's sword with the barrel of their rifle/machine gun. The resulting cut would damage the barrel enough that it needs to be replaced. No soldier in their right mind would use a cut barrel. The pressure would make it explode.
Anyways, the stories would get passed on as "You see this sword? Cut a machine gun in half. I'll let you buy it off me for thirty bucks, 3 packs of cigarettes, and that Japanese dress for my wife."
In short, the point I am trying to make is that "the katana" as a sword type cannot be summarized into a singular era of production. Like with all swords, its production had undergone much development as industrialization improved. It has an unusually long (and modern) service history for a singular blade design.
This is an excellent series of videos, and you shouldn't change a thing. However, perhaps you may want to go do research on the different varieties of 'katana' throughout history. This would make for a lovely video or series of videos. It would be less about comparing European and Japanese things, but more about the blades themselves.
There are a great deal of sword designs in Europe that have undergone a similar history. The basic geometry is respected, but the forging techniques were refined to improve them.
Just a thought.
By the last recorded instance of forging, I mean with the purpose of reaching the battlefield. The ones made in the traditional aspect today are usually set-pieces for display and parade or use in sport and martial art without ever meaning to draw blood.
+Belle La Victorie Those were no Katanas, they were Guntos.
Tashi, Katana and Gunto look similar, but they are not the same.
Guntos are more like Katana-shaped Sabres
+Belle La Victorie So were the european swords, cavalry used mainly sabers(because you can't aim guns while on a horseback properly) and the last cavalry charge with drawn sabers was performed in 1942. ;)
he was comparing traditional katana to the traditional spring sword which were around the time period around the 16 century of course swords in general in the process of making the sword have changed. He compares both swords because of their differences in making the sword, durability and usefulness in battle which is important.
well the last time a Claymore and a Longbow was used was Mad Jack Churchill... also WWII...
As someone looking to get into the Katana thing for the first time, I've found these videos to be invaluable. I was able to follow the science, you did a great job explaining it. Thank you for taking the time. Onto video #5.
Can I just say that you explain chemistry better than my teacher does
same
Here's my interpretation, as a blacksmith. If I had very little access to iron ore, I would try to make every bit of it count. The Katana uses as little high-carbon steel as it possibly can to produce a useable sword. And the cool thing is, that sword design would work even without hardening. Yes, hardening makes it BETTER, but if you imagine how the technology may have evolved, you would start with unhardened high carbon steel on an iron core. Then later you discover hardening and all the swords that you through-harden will break so then you only harden the edge. Well, due to the fact that you have a soft core, you have no real reason to develop tempering technology which you WOULD need to develop for mono-steel swords.
To put it more succinctly, I think the use of an iron core and an overly hard edge is due to being frugal. Why spend all of your high carbon steel on one sword when you could make 3. Viking era axes show this same sensibility with high carbon welded cutting bits.
I agree. The Katana process makes a very economical sword that is almost as good as a western sword for most purposes. The Japanese islands are relatively resource poor, so they developed a quite ingenious technique for creating high quality swords with poor materials.
How does whether they quench some or all of it change how much iron ore is required to form the blade?
rapturedmourning the amount of iron is the same but the amount of high-quality steel is much less when you only need to make the edge from high carbon steel and the rest is mild steel or iron. Compare that to a European blade where the entire thing needs to be made out of high purity steel or it will snap in half at any weak point when it is supposed to flex and spring.
So basically, it was designed with making the most of what was available in mind.
A good discussion but you completely missed the most important aspects of the katana design. If you notice in the background video of the katana being quenched, it starts off as a straight piece of metal and the quenching actually causes the curve. The reason for the curve is that the different molecular structures mentioned have different densities. In the process of quenching, the martinsitic low density structure is frozen in while the spine of the sword first contracts (causing the curve) then wants to expand into its ferite form. With the cutting edge frozen in place the expansion of the spine is held in check. This arrangement puts the cutting edge of the katana under compression, actually making the cutting edge much harder than just plain old martinsite.
The net result, the objective of having a cutting edge under compression is that the katana can be polished to razor blade sharpness. It is a similar surface compression technique that makes the Gorilla Glass cover for iPhones so much tougher than regular glass. So, one final thing that distinguishes the Katana from most other swords is that a well polished katana (they cost about $100 US per inch to have polished by a pro) will be much much sharper than any other sword. Polishing a katana with a grinder actually eats away the surface compression layer and destroys much of what makes a katana a katana.
There is a book about the Japanese defeat at Midway called "Shattered Sword." The title reference the fat that a well made and traditionally polished katana will not bend, it shatters when the surface compression layer is breached.
nice explain
Fantasy nonsense. Katana fanboy cope.
Good job sir. This is literally the only youtube video I've found that accurately portrays the methods and science behind differential quenching and tempered mono steel. Your attention to detail was immaculate, and believe me, it was refreshing to hear someone who wasn't either a fanboy or a basher really look at the facts.
The only thing that I might point out would be differential tempering. I don't claim to be some kind of master or anything, especially not about swords, but I have had some training in blacksmithing and a bit in the knife making sector of bladesmithing. It is possible to impart different levels of hardness on a mono steel blade by controlling the amount of heat used on different areas of the blade (i.e. the edge as apposed to the flat.) during tempering. If you relax the crystal structure more on the flat so that the heat only seeps towards the edges you can have a spring steel center, and hardened edges. I will say that this might be less practical if you're using a somewhat impure steel, but if the steel was smelted properly you have a sword that is still flexible (because it has the spring steel instead of iron or untempered steel towards the middle of the flat) but has slightly harder edges than it otherwise would. Again, I'm not an expert, but I know this technique is used in knifemaking as well as the making of some set tools used on cold metal, (it would be pointless on tools used on hot metal as the heat from the stock you're working would just loosen the structure right up every time you used the tool) and I don't see any reason why it wouldn't work on a sword blade.
I'm just throwing that out there, but I don't know how historical this method is, and due to the thorough nature of your video I'm guessing that if it was used during that era you would have mentioned it. It might just be a more modern thing. Either way consider me a subscriber. I look forward to seeing more of your videos. Cheers mate. :)
Graz on 1k subs pal :D
ps: that intro deserves 5k subs xD
+Metatron I am truly honored you think so my friend!
+Metatron But have you sped your wings?
Marek Dohojda I have spread my wings two years and two months ago ;)
Metatron Just don't forget Icarus! :)
Seriously good job! I only discovered your channel about a week ago, but went through quite a few of your videos since then (and with 3 kids that's saying something).
Very good, thanks for your effort.
Marek Dohojda Thank you very much for watching my content I really appreciate :D
ps: Icarus only had two wings, Metatron has 72 ;)
Shad's saying "the sword won't snap in half" is quite correct, in a historical, or at least a mythical, point of view. According to the Japanese legend about the sword, a smith by the name "Amakuni Yasutsuna", living in Japan around 700 AD., used the structure of different carbon contents and differential hardening process, in order to prevent the sword from snapping in half. Especially, the wavy pattern of the Hamon (the tempered line) is intended to stop a crack from going throughout the entire length of the cutting edge, or exactly to localise a crack within a wave. Additionally, the Katana (or during Amakuni's time, the Tachi) was better to be razor sharp, so the hardness of spring steel would not do the work, so they needed hardness of 60 Rockwell, because the Tachi was designed to fight the Ainu, native people who were clad in leather armor (I am sorry for bringing this issue up, but it is history), so the razor-sharp edge worked better than a cutting edge, who hardness was around 45-50 Rockwell, whereas, against human flesh, 45-50 Rockwell and 60 Rockwell work almost the same.
Just an idea but: Maybe they wanted to have harder edge because they used the word more for cutting non-steal armor. The harder edge gave better cutting performance on such targets and the weapons didn't have as much fear of getting bent and broken because they didn't hit steel armor or other hard targets quite as much.
Ive studied this entire subject about as far as possible.
Im subscribing because of this video.
You fekkin NAILED it. But in an incredibly inclusive and well presented way.
I liked you before. Now i deeply respect you.
29:11 I think the reason Japan used the Katana & it’s hard steel is much more simple than that, and it relates to something Shad himself mentioned earlier:
Japan had a low iron/steel content. That means that iron/steel armour was going to be not only rare, but incredibly expensive and wasteful, because for what it takes to make full plate, you can arm many more people with swords.
This led to Japanese soldiers wearing wooden armour (samurais, etc…), which would be tough to cut through with spring steel.
So this is why they opted for the differentially hardened Katana & it’s superior cutting ability because it didn’t have to just go through bone, it had to go through wood, flesh and then bone, and a spring steel sword might not have been able to achieve that reliably.
If you aren’t going to face an army wearing steel plate armour, it makes no sense to take a spring steel sword, but it makes absolute sense to take a katana which can cleave through wooden armour.
Been watching this series from beginning in one sitting. Incredibly insightful and interesting. Presentation is also top notch, entertaining and easy to follow.
I have a BA in Mechanical Engineering and this video finally helped me understand why hardened steel is actually hard! Thanks Shad, better teacher than my uni material science course
Fantastic series of videos you've got here. I learned more about katanas than I ever would've expected to!
Your videos raised a "what if" thought in my head that leaves me with a question. (Anyone who sees this who might know is welcome to answer.) Let's say that in a setting where magic can assist in forging a sword, they take a different approach to differential hardening. Instead of the soft metal on the inside, let's say they use spring steel, while the outside is still the hardened metal we know. What would this do for the katana's build and effectiveness? My expectation is that the sword will be durable as you expect from spring steel, but that the outside will chip under stress. The trade off I expect is that it keeps the cutting power that hardened steel offers.
If I'm right about this, it might be a good way to make katanas special in a magical setting. That is, assuming people involved care that much about the inner workings of the blade!
i love ur humor ur easily my favorite RUclipsr right now complete balance in what ur passionate about ^-^
I love metallurgy, so I'm glad that you took the time and effort to delve into the nitty-gritty details, with all the terminology one could hope for. Thanks a lot for this video and the series!
I think that a good reason, or at least one seen as valid, for keeping this technique rather than using spring steel is that the katana became a symbol of status, where perhaps a little practicality was sacrificed for prestige. Also, if we're talking about praticality of the weapon, we must not forget that Japanese warfare was not carried out with swords alone. Bows and polearms have huge roles in any army, both for infantry and cavalry, so a katana is more of a sidearm, I guess. At least, that is how I see it.
In short, I think that the misconceptions are essentially debunked, so we can all appreciate the asthetics of the katana. One video left in the playlist to see what else you have to say.
Two more comments... In metallurgy there is a concept called a Time-Temperature-Transformation (or TTT) diagram. The combination of the wedge cross-section and the clay placed on the spine before heat treating enables different regions of the sword to pass through different regions of the TTT diagram for iron producing both different iron structures in the sword and the edge surface compression I discussed in my previous comment. The katana metallurgy is very complex which is the reason why metallurgist go ga-ga over samurai swords. A monolithic piece of iron, no matter what the design or quality of the steel, does not have the same appeal.
Regarding the polish, a friend of mine showed his katana to an English gentlemen who slapped his own side with the sword in a gesture that I take is common with English military officers. He required stitches from hip to ankle to close the wound. A properly polished katana will be every bit as sharp as a modern razor blade.
Very nice video, however a small correction: The springsteel was in use before, for example the lombards at the battle of Veerneuil in 1424 used tempered steel armor, and that is as you will agree, well before the 16th century.
I did'nt recognise it as such before you went into detail with the color however, thats when I went "huh... now thats something I heard about before!" and I went back and checked and yup: As usual, our forefathers knew a bit more about this than most gave them credit for.
Ever since I went through welding school and got into metalworking I've gained a pretty decent understanding of metallurgy. Looking at the subject through the window of sword making is very interesting, and everything you've said seems to agree with what I was taught and have observed as a welder. At Lincoln Electric's school we had excellent teachers, and I remember them teaching us about how carbon gets distributed during different stages of heating and quenching, and how to avoid causing cracks in large structures from improper pre-heat and all that.
Cool vid, lots of info. I think one of the big things that many people misunderstand about fighting with a sword and I know this more specifically in the area of Eastern martial arts, is that the style of fighting and defending an attack are not what you typically see in cinema depictions. I'm talking about the signature sword on sword 'clash'... In most of the Eastern combat techniques you don't block an incoming sword the way it's shown in movies, rather you parry or redirect the incoming attack OR simply reposition yourself to avoid the strike as you counter attack. So in the context of fighting in the samurai style, the katana was more than adequate and with the hardened edge you could maintain your edge much longer and retain your cutting effectiveness through different media, skin, bone, clothing, leather etc. So when you look at various sword 'torture tests' of katana blades where they are smashing on the side of the blade and it bends or breaks, of course it would with enough force, it's just simple physics. The katana was made for a style of fighting, it wasn't made to be a sort of a 'shield' that could absorb astronomical amounts of force rather it could parry and be angled to allow the opponent's attack to be redirected off the centerline and give the defender the ability to counter... I'm going to emphasize the point you made about spring steel swords. A spring steel sword that might be resilient to bending and staying bent is going to vibrate much more as you see in slow motion videos, that in itself dissipates and lessens the amount of potential energy that the weapon can impart through its target. The katana which is much less 'springy' is then going to impart more force into the cut AND with the slight curve of the blade will focus more of the force into a smaller area which further increases the cutting ability. The katana isn't a magical blade by any means, nothing is magic but form follows function... The katana was not developed to fight movie-style battles, not nearly as efficient nor effective ;)
This video did a very good job of explaning some fairly complex metallurgy, in a reasonably simple way, that a lot of people can understand. Good job.
As someone who is going to University for mechanical engineering I think I can add a little detail.
Both hardness and ductility help determine how much force can be applied to on object. The harder something is, the more force can be applied to it before significant deformation or damage happens, while ductility allows it to deform to a certain regard before permanent deformation or damage occurs.
Tempering allows for a stronger force to be applied, and depending on how you temper you can drastically affect the final hardness and ductility.
In theory an ultra hard ceramic could out-cut any steel blade as the hardness could be immense, however even the minimal deformation that is practically guarantee a structural failure.
So technically a katana should be able to chip and damage a mono sword with less force. However when a clash of damaging force occurs the katana would fail to a larger degree than the mono sword.
Given everything I've said is correct (could have some details wrong so please correct me if you notice anything) They both outperform in different aspects, however the mono can take more force than the katana.
Shadiversity!!!
You literally helping understand my current manufacturing subject. Which is steel things like that.
Agree with everything except the hardness/edge retention thing. I'm pretty sure what they meant by the sword will retain its edge longer was in relation to standard use. There are two ways that edges get dull: either by abrasion/chipping or folding. A soft steel edge will be more likely to both abrade (due to softer materials being able to cut it) and fold (due to its ductility). A sword with a Rockwell hardness in the high 50s will retain an edge much better than a sword in the 40s. A harder steel will be more likely to catastrophically fail, but in unarmored combat (which from what I understand was the scenario in which swords were most expected to perform in), that shouldn't really be a problem.
Sooooo, the katana cuts harder things than the spring steel sword and is less likely to snap when it encounters resistant it can't overcome. But it bends, which is just as bad as the sword is ruined. Spring steel swords are somewhat less hard. They still do what the katana does, just not as neatly. However it survives contact with too hard things a lot more than the katana does. It is indeed the superior technique. But it makes sense, considering it is older as well, by a couple of hundred years.
Why the japanese didn't adapt later, is unknown. Either they liked how the katanas looked, didn't know any better, or something else entirely. I have zero data or research to back it up. I just think this, but maybe they simply didn't see the need. They already had a sword that can cut bones, and no technique would give them a sword that cuts armor. They were also on an island and didn't have to worry about non-japanese beating them in an arms race. Once the isolation ended, they can just conquer everyone with toyota, instant ramen, anime and final fantasy VII anyway.
Hi, Shad! I loved all of the videos in this playlist. I only noticed one mistake about the cutting. You did a circular cut, but when we train in the dojo, we do not do an circular cut. We try to use the cutting side as much as we can when we do the move. So it would be a kind of an oval shape, so we can maximaze the cutting superfice. I could do a video to show you, if you want. And you can do another comparisson in your summulator.
Some thoughts on hardness ... Is RC-60 a number you've actually encountered in a sword edge? This surprises me. A cutting edge that hard is very brittle and will chip easily, especially in situations where it comes into contact with hard materials (armor, bones, other swords, etc.). As a cook who uses Japanese knives, I'd consider bone-cutting to be a situation where you would specifically want a softer knife. My knives that are in the RC-60 to RC-62 range don't ever go near bones. Nor do they get used on tough, woody herbs, or anything that might grab the edge. These are situations where I reach for a softer, fatter, usually European knife. There are really just two advantages to a harder edge, all being equal-they will take a sharper edge, and they will hold onto that edge longer during normal use (which excludes use that will deeply chip or break the thing).
Which is all to say, I don't think a very hard sword edge would be an advantage if you were really trying to smash through bones (and we are absolutely talking about smashing through them ... a sharp edge does not cut bone). The hard edge is an advantage if you plan to be slicing soft flesh and clothing all day long, are going to be careful about banging it into anything hard, and don't want to stop and re-sharpen.
I choose differential hardening over mono steel because of two reasons.
1. The beautiful hamon line makes the sword look like an art.
2. It holds a very sharp edge for a longer time. I had a chat with a swordsmith via email and he told me that the edge is so hard that niku (convex shape of the edge) is unnecessary, and it can hold a razor sharp edge for a long time.
Shad, This comment might be a bit late, and possibly somebody mentioned this already (didn't see a comment about it in the short time i looked), but as a sword enthousiast, engineer and (hobby) sword/blade smith I can add that the higher hardness that can be accomplished with differential hardening can have a (possibly) significant bonus. A higher hardness means that the blade can be made sharper than a blade with a lower hardness could be, and it will retain this sharpness longer (that's why razors are [generally] made of high carbon (and alloy) steel). And of course, sharper blade means easier cutting, and since in japan armors were for a long time made of cloth and/or leather and less of metal (correct me if i'm wrong here), easier cutting can be a significant adventage, therefor a good (possible) reason they kept using this method instead of monohardening. That having said, I myself prefer european swords, but like you said yourself, the thruth is important, and both katana's and european swords are good in what they're designed for. Love your video's shad, keep 'em coming
Good video, mate. Nice to see that somebody else researched the steel phases and how steel is made.
I have to admit I kinda overlooked your katana videos, strange... But I am here now!
But I have to say you overlooked some things (and I hope that I now will not overlook something).
Ferrite, to be precise alpha-ferrite is the pure iron with a body-centred cubic crystal structure, it's the basis of steel and gives it the magnetic properties.
Pearlite is not a crystal structure for itself (maybe I misunderstood you here and you actually said that, feel free to correct me)
it is a structure composed of two crystal structes alpha-ferrite and cementite. And cementite is actually a chemical connection between iron and carbon (Fe3C). With increasing amount of carbon your increase the amount of pearlite in the iron (alpha-ferrite) and therefore increasing the hardness.
Austenite has actually two meanings in steel, first it's a iron phase (defined by it's face-centred cubic structure) but also it can be a solid solution when carbon is an alloying element. This last point is what you described when the carbon is dissolved (but not connected) in the iron and then when you form martensite in which the carbon is forced to stay solved in the new formed crytal, through the speed, which leads to a distortion and strenghten the structure further.
If you cool austenite slowly down than the carbon inside would dissolve in surounding areas and have a reaction with the iron forming cemenite, at a lower temperature the steel is back in its alpha-ferrite phase.
There is by the way a phase between martensite and pearlite called Bainite, but we can disregard that here for now.
When you form martensite in steel, there will be everytime a certain amount of austenite left which can lead to big problems. This austenite is very instable and can became martensite (inside of the martensite(!)) through cooling or stress and there is allready stress there through the higher volume of the martensite pushing against ech other and so hindering some of the austenite forming proper martensite during the quenching. But this an be solved also through heating then the left austenite will become ferite and cementite again (tempering).
In steel are always different amounts of phases, in depends on the carbon content and the heat treating how high the amounts are and therefore affecting the steel properties.
I hope this added some additional information, understanding and that I wrote it understandable.
By the way, the video in which they tested katana vs longsword, is by the way a German show called "Welt der Wunder" literally World of Wonders, states that the tamahagane is well tamahagane. Therefore traditional made steel from Japan, they produce it once a year and is made out of iron sand. The same stuff they used in medieval Japan. So it us realy tradtional, the pureness is like back than (of course iron sand can be differently pure depending on the source) and iron sand is not iron ore by the way, just saying it gets often confused.
GREAT! But I have a question. What if a sword would have a hard edge and a spring core? Why the katana has to (or doesn't?) have the soft back?
+Strategiusz I'm honored you like mate! As to your awesome question, my guess, and it is a guess, is that the hard edge wouldn't flex properly with the rest of the sword, which would mean when the sword does flex the edges would chip along the stress points of the bend. I think this means that the only practical option is to try and make the sword as stiff as possible to prevent all flex and bending, thus to maintain the edge, which is exactly what a traditional katana does.
I am Shad
Thanks! So the "softness" of the core is only a relative term and the blade is stiffer than European swords made of "harder" spring steel for some reason (crosssection or lamination)?
+Strategiusz Oh the core is still soft, but the katana is thick and if it has an upper/back fuller it would make a structure similar to a steel T bar which makes a fairly stiff sword. Because European swords are MUCH thinner, especially towards the tip and their spring steel has so much give, even though it is a type of hardened steel, they will vibrate much more than a katana, which causes European swords like the longsword to be less forgiving in the cut. I'll be diving into all of this in part 5 ^_^
Interesting series filled with a lot of information. I've not finished it yet, (one more episode!), but I wanted to offer some thoughts:
In a prior episode you mentioned 'inclusions/contaminants' (including carbon). As in the example of carbon, not all inclusions are bad. In fact, many steels, including tool steels - the hardest, are alloys which include other elements. These other elements affect the morphology of the steel and thus the physical attributes. The addition Mn, Cr, Si and other compounds can affect the form of steel upon cooling. Perhaps some of these inclusions helped create the martensite (in addition to the quenching) at the hardened edge?
Sometimes you mix comparisons, although it may not be intentional. E.g. comparing spring steel to a katana. One is a form of steel alloy, the other is a finished product which uses steel. There is absolutely no doubt the steel of today is superior to steel from centuries past. But a sword is a sum of its parts and craftsmanship. You can make crap swords when starting with modern steel (seen quite a few of these).
As far as why did the Japanese smiths construct swords the way they did? I have to assume because it met the needs for the type of warfare they developed in their civilization. We severely underestimate the capabilities of ancient man - whether examining the color of steel to better understand how hard it may be, to building pyramids, aqueducts, etc. I doubt it was for purely aesthetic reasons ;)
From what I have seen in comparing HEMA and Japanese martial arts - there are probably more similarities than people expect. After all, the body moves only in certain ways, and creating a steel extension of that body will create similar strikes, guards, and counters.
Thanks again for the great series. People will always debate the merit of one thing vs another (scotch vs bourbon, ST vs SW, vanilla vs chocolate).
Oh one last thing - the entry for steel in wiki has an excellent phase diagram for steel morphology.
any germans here who recognized the welt der wunder logo in that clip that's played at the end? :D
good job, shad. i wish had found those videos way earlier...
Amazing work my man! This is the stuff that needs to be on PBS!
Great series! I really enjoy your full length in depth videos. I hope to see more in the future.
+SchmoopyHD Then I'll most certainly try to make more in the future! Part 5 is still coming out but after this series I might make a few simpler videos before I tackle something else to this level of detail, they take a LOT of work ^_^
+zaco21 I feel it would be as easy as melting down iron, the difficulty I see is in managing the carbon content.
thank you for the hard work involved in this playlist it's really great
Great vid Shad. You could've brought up the concept of plastic vs. elastic deformation, maybe it would've helped on the explanation about why bending or not
you did a good job explaining the metal structure. I took a Metallurgy course in college so i know about the structures of different metals and alloys. I have to say you did just as good a job of explaining it as my teacher would have
something people tend to overlook when comparing sword types, is that knights and samurai would probably have never used the blade to party. that's something we see a LOT of in movies and games, where one constant comes in with a chop or swipe and the other combatant uses his own blade to block, or Parry, the attack. bit the way swords were designed in the middle ages, both east and west, would have made this type of strategy very dangerous, as the blades would have chipped, bent and snapped, depending on the steel quality and method of forging and tempering and so on. more often than not, the flat surface of plate armor and flesh was the target, since the thin, sharpened edge of another sword would cause serious deformities to your own blade. parrying was usually the realm of weapons with a shaft they would not easily break, such as the bec-de-corbin and other polearms or shafted weapons. later in history, parrying daggers became common to accomplish this exact tactic. so comparing the chopping capabilities of different swords against each other is very impractical and won't give you very good information on what the blade is capable of withstanding.
I mean, most martial arts using a Katana don't block by simply putting the sword directly in front of you. In fact, most blocking in all sword based martial arts doesn't work like that at all. When you block an enemy attack, you let his blade slide of yours, using the same motion of the block (parry) to drive your blade forward in an attack.
***** I did say "most blocking techniques" didn't I? I know there are a few techniques for blocking something straight on, but the situations where you can do such are extremely limited. Limited compared to slide blocking, at least.
+firstoftheoutcast
I'm sorry to inform you, but IMO you never practiced any swordplay.
Correct me if I'm wrong.
In my experience with longsword you don't really get to choose how you block, there's no time for that. And a simple straight block is much easier than any other technique.
The more significant reason why blocking with the Katana works, is because the edge isn't straight. Now I'm not familiar with Kenjutsu or anything, so I can't comment on the preferred technique. I've heard that they often block with the other side, and I can see that working for some attacks but not all, so I'd wager the curvature makes the opponent's blade slide off more easily, which would also explain why they preferred this shape.
+Sagrotan
A heavy swing would ideally be "brushed off" rather than blocked, yes, however properly performed, that brushing motion can actually impart even more stress and force on the edge and the general structure of the blade.
phileas007 And if you're trained for that scenario you can react accordingly. For example by quickly attacking after slightly altering the enemy blade's course.
While what you've said is certainly true, depending on the enemy, "normal" blocks can cause more impairment as well.
The effectiveness of a technique comes down to the skill of the user, so what form of blocking is best depends mostly on which the weapon's wielder has more experience with.
So whether you "brush off", "catch" or "stop" an enemy's attack won't matter if you're equally inexperienced with all forms: each will bring almost the same amount of stress on the blade.
+firstoftheoutcast
Very true, almost everything in fencing depends on the skill level.
The stress on the material is roughly proportional to the forces at work. A static block is indeed one of the worst conditions, the reason it is less stressful is because the point of impact is (ideally) much closer to the grip than the active "brushing" whereby you strike the other blade with the farther half of yours. So the bending moment is greater and therefore the stress on the material.
Since I am running off at the mouth, one more set of comments.... As I note and as is shown in the background video, the katana is made from a straight piece of metal. To get the curve without warping, all aspects of the sword must be precise (wedge cross-section, thickness and density of the clay on the spine, carbon levels, temperature of the water it is quenched in). Such swords come from swordmasters specifically trained to make katanas and involve about 9 man-months of effort. As such, an authentic katana is $50-100K and as I mentioned each sword gets a $5k polish when it is done.
There are plenty of videos of folk "putting katanas to the test" on RUclips and destroying the swords. I suspect these swords are forged with the curve there already, sharpened on a grinding wheel and have little to none of the actual metallurgy that makes a katana a katana. Again, the curve is not a style element, it is a consequence of the heat treating and the curve imparts compressive forces to the cutting edge of the sword. A reasonable analogy is a bow. Other than a mechanical or compound bow, a bow that is the same shape strung and unstrung will not work very well as a bow due to the absence of stored compression. Molding a bow with a curve is not the same thing as stringing a bow and causing the same amount of curve. Forging a sword with the same curvature as a katana is not a katana.
Norman Hairston good argument friend!
There is no benefit what so ever from the curve. None. The blade isn't going to be mysteriously sharper just because there's more compression. All kinds of swords can have the "razor blade" sharpness on them, after all they're all made out of steel. The "Grosse Messer" seems to cut same way as the katana while providing better protection for the hands, being better at thrusting and more durable due to spring steel.
You can differential harden mono spring steel. First you harden eges in cold water (swift cut in cold water), then submerge all blade in hot oil (or cold air).
In that case you will get mono spring steel differently harden.
Great series of videos, have you considered doing videos looking at the material science of other historical blades?
+Almus Quotch I have and the interesting thing is that, from what I can gather, for all other swords except the katana it doesn't really matter how they are made, spring, hardened etc. as long as they have the right shape and design, they will be called that type of sword. Generally a longsword is a longsword regardless if is is made of spring steel or hardened. Only the katana has this expectation and standard in regard to its internal properties. I could certainly look at other swordsmithing techniques in general, like pattern welding and such.
This series of videos has been fascinating.
Boy I'm glad we got that strait. So, if a bunch of Knights would have met up with a bunch of Samurai the Knights would have had to sharpen their swords after that battle.
Thanks for the video.
I personally believe the Japanese used differential hardening because of the test you showed, the bend and not snap in two test. As a consumer, unaware of all the science behind sword smithing, if I saw two blades clash, one of which snapped clean in two, the other of which snapped the edge and bent beyond future use, but not into two pieces, I would assume the one that remained one piece was a superior blade. And henceforth, I would only buy blades made in that style. A style which would simply become the standard over time.
Also, I was really waiting for this video not exclusively for its content, but I wanted to see how you'd be holding the swords in your thumbnail, since part 3 was so epic.
+icspps I have had so much fun with the thunbnails of these videos ^_^ I hope you like the knew one.
I am Shad I do like the new one. I wonder how the next one will be.
+icspps It is critical to point out two things in the debate over historical 'katana'.
Firstly during the period when the best blades were being produced, the late 13th and early 14th centuries they were in some ways functionally superior to many but by no means all European blades, this is where the confusion originally arose.
There has been an unfortunate tendency for people to take 13th century technology Japanese blades and compare them directly to 16th century technology Indo-European blades without looking at those found in Europe during the 13th century at all.
Secondly it must not be forgotten that Japanese swordsmiths did not just make blades for katana, they also made wakasahi, tanto, naginata and yari blade amongst others too and these due to their proportions and the manner in which they are used are far less susceptible to the disadvantages inherent in the Japanese blade smithing process.
The katana in contrast with its longer, narrower, shallower proportions was more susceptible to bending in use when cutting.
i liked the science aspects right up to the end where you underestimated what the rockwell numbers mean. as armor is hardened and you mentioned getting through armor, which you also say in your other videos is pretty much impossible. A strike on armor wont cut it, but will blunted a sword like no tomorrow if it is softer than the armor. So in a battle where there are strikes on armor the harder sword makes more sense as it will still stay sharper (albeit with some chips), but the spring steel is better if there is wresting type moves as bending is more likely. so just comes down to the different swords requiring very different techniques to use. each one fits the types of fights they were used in and the types of defenses their opponents were wearing.
Differential hardening for the katana was made necessary by the higher level of inclusions in the forged steel. Harder steel is naturally more brittle (even modern steel) than a softer steel. The harder the steel, the more significant the impact of inclusions on the strength of the steel. If you compare two pieces of steel, with the exact same Rockwell Hardness, the piece with more impurities/inclusions is much more likely to fracture under stress. Due to the relatively higher level of inclusions in the steel; if the entire blade were hardened to the level of the edge, it would be highly likely the blade would fracture during use. By the spine being a softer steel, it lessens the impact of the inclusions since the steel is more likely to bend than break. It should be noted that this approach, of using different hardness of steel combined to create a sword is not a distinct idea from the pattern welding used during the early middle ages (i.e. migration period swords). We need to consider the timeline to realize that the Japanese were still using more primitive methods of smelting at the same time that Europeans had developed more modern smelting techniques allowing them to make more pure mono steels.
This may be years too late, but I think the answer for why is that the lack of iron quantity meant that shields and plate armor were not developed. So the super hard edge could survive in an environment where the risk of it impacting another hardened steel was low and it provided a cutting edge that could overwhelm armor made out of a few iron pieces, leather and cloth.
Just a quick correction, during the tempering process the steel does not "glow" blue. The bluing effect is a chemical reaction between the surface of the steel and the air, and depends on the temperature. The color is permanent, but will come off during polishing.
Great video, but you didn't hit all of the angles...I began learning the way of the sword with blades that were mono steel (5160, 9260, 1060) and mono tempered (through hardened). These swords have different characteristics - 9260 is one tough cookie, can be bent up to 90 degrees. That is due to the silicone added to the steel. It also takes dents in the side of the blade. 5160 is a bit different, one of my favorite spring steel alloys. It won't bend to 90 degrees, will snap around 45-60 degrees. It scratches very easily, which is irritating. It holds an edge, it seems to me, longer and sharper than 9260. 1060 is the hardest when mono tempered. It is scratch resistant. I do not know how much bend it can take before snapping. It is my current favorite in the mono temper mono steel. The angle you missed - mono steel that is differentially hardened. Yeah...such as T10 that has been clayed. That is where I finally went, after a series of discoveries regarding steel and cutting. The edge I can put on a diff hardened mono steel is considerably sharper than any of my mono steel blades will take. It is insane how sharp a diff hardened edge can be. That being said, the material is the same throughout - mono steel. The characteristics of this combination are unique, and quite frankly unknown to me at this point. I don't know how tough this blade is, or how much bend it can take.
thank you Shad , you just solved a mystery from KCD , i had often wondered why Blacksmith Mikesh double quenched his swords, the second one was actually tempering , bloody good one!
Something to point out..... You can deferentially harden spring steel.
I don't know if they did this with swords but you do with scythes. From time to time you will "peen" the edge on a scythe anvil with a hammer. This work hardens the edge which you then sharpen.
Since they did do this with scythes I would be surprised if they didn't do it with swords if they wanted to. They might not have wanted to though because as you say hard edge = brittle edge and smacking a sword on someones armour and chipping the edge might be something they want to avoid.
Samurai were essentially a headhunter cult from a historical perspective. Samurai often got paid by presenting heads that they collected on the battlefield, heads belonging to someone of a higher rank, or other samurai of renown would yield better payment. They even had officials to judge the quality of heads collected. This could be a possible reason as to why they decided to go with differential hardening over spring steel because decapitation was so much a part of their culture. Japan was also pretty isolated being an island so it's a wonder that their methods were so advanced. We aren't even 100% sure when the Japanese came up with the idea of differential hardening but we do know Masamune created the Susho method sometime in the late 1200's or the early 1300's. The Susho tradition distributes hagane, kawagane, and shigane in seven different locations within the construction of the sword. The method of construction you show is the Kobuse, (hagane outer with kawagane core) and Shihozume (hagane edge, shigane sides, kawagane core). Kobuse method is often what you find in Japanese swords made for officers during WWII, while swords from the Shihozume tradition are much older antiques, and are rarely found with origins later than the 16th century. There are quite a few counterfeits of Nagasone Kotetsu swords that use the Shihozume tradition which date to the late 17th century. Funny enough many of the counterfeits of Nagasone Kotetsu were superior to the real one. Minimoto Kiyomaro is a prime example making high quality swords faked as a Nagasone Kotetsu. Incidentally enough I bought a sword believed to be an actual Nagasone Kotetsu about 12 years ago only to find out it was a high quality forgery 5 years after that but still dates back to the early 1620's. Often Kotetsu himself couldn't tell the difference between his own work and that of a forgery without looking at the mei (signature) and sometimes not even then.
I have heard it said (possibly in one of your other videos or from another swordTuber) that spring steel can be harder to cut with because it vibrates, and this interferes slightly with edge alignment.
Ah yes, the memories from my metallurgy studies ... I heard what you said and immediately felt like home. Good times. :D
Also: LOL just noticed the "World of Wonders" logo on the vid about the cutting test against the sword. ^^
These are wonderful videos, thanks! Would you consider making a video on the "mythical" Damascus steel?
I definitely see why the durability of spring steel can be an advantage, but I think I personally prefer a stiff sword for the greater control, particularly at the tip. Of course, this means that the sword must be used more like a fillet knife, or a surgeon's scalpel, rather than a meat cleaver (i.e. for slashing rather than chopping). Rule # 3 of my swordfighting style is "Protect your blade", which means that any kind of impact should be avoided, and the edge of the blade in particular should never even come in contact with anything hard (including bone, which can cause it to chip or to get stuck and potentially bend).
Very well done! :) Will you or have you already done a video how medieval swords( like a longsword or zweihänder etc.) were made?
While a bit too repetitive I like the amount of reaserch you did and the easy way you described it
My 5 cents: If you study kendo or kenjutsu you could see you are hitting a bone a lot. A LOT. Actually the #1 strike is men (hitting the head trying to split the skull), #2 kote (chopping off the wrist), #3 do (hitting the belly with possibility of chopping the ribs) and #4 is tsuki (stab to the throat with high probability of hitting the spine bones). So it does have some sense to have great bone chopping ability.
The back of the katana made from weaker steel or iron has some sense if you consider you would actually try to cover yourself from strikes of your enemy by the back of the katana. Massive mune made from weaker material will help to absorb the hits. Weaker steel protects not only the whole sword from shattering but could also serve as some sort of shield. Its kinda hard to use the back properly but training helps.
Spring steel has some disadvantages as well, at least from my point of view. It has very unpleasant tendency to vibrate after hits. Vibrations do increase with the length of the blade. After a few strikes it is actually hard to fight or even hold the vibrating sword. One handed sabres are really unpleasant with this effect but long swords are pretty bad too. Triangle-ish cross section of the katana suppresses this vibration effect even if it is made from mono steel.
Awesome video! I really enjoyed it! I actually did this research years ago, back when I was 15 and saving up to buy a "real" katana, I had a stainless one. I was definitely a fanboy. I didn't go quite into the depth which you have, but I came to the same conclusion. I was happy to see you reconfirmed it for me. :) I have had this question though this entire time, and I never managed to find the answer. What exactly is L6 steel and how does it compare to the other ones?
*Please do a sword ( & other weapons ) techniques ( skills / moves ) series .*
*I work with metals .*
*Tool steel is indeed hard but also brittle .*
*I have broke many files and other tools by by them striking other metal .*
*Tool steel is really brittle and should not strike it at any point .*
This deserves way more views than it has. Series was certainly enlightening for me
+Rane Drane And that makes it all worth while. My channel is still in it early days but with viewers like you I'm confident things will grow ^_^
As to why the Japanese kept differential hardening as opposed to tempering. I think culturally, once the Japanese get an idea in their heads that there's a "perfect" way to do something, they will do it that way from now until the end of time. I think also that they valued the extreme sharpness that a differentially hardened edge gave them. It's worth noting, and it's a point that many people miss, is that swords are not the go to weapons for battle. These really are side arms that a person carries around in battle as a backup to their primary weapons, or everyday for personal protection (or in the case of the Samurai as a symbol of their status). If you're carrying a sword for protection, it's unlikely you'll suddenly be faced by someone wearing armor strong enough to defeat the edge of your sword. So having such a hard (and therefore brittle) edge isn't a huge consideration in the grand scheme of things.
That being said, anyone who thinks that the Katana is sharper and cuts more easily, therefore it's superior, needs to learn that best is the enemy of good. Making the katana a "perfect" cutter weakens the blade in other ways and ignores the fact that there isn't much that the katana can do that a mono-steel blade (I.e. A longsword) can't. Both cut up tatami mats equally well, they can both cut off limbs and heads. The only real advantage that the katana has, as near as I can tell, is that it does it a little more easily and thus requires a little less skill or practice.
I'd like to add what you _almost_ said, but stopped just short of: because of the presence of hocho-tetsu in katana, there would be no point in tempering it. You would lose the martensite edge but gain no springy qualities. There are, however, two traditional styles of lamination which do not use shigane (hocho-tetsu). The first is maru, which is no lamination at all; the entire blade is hard (hagane). The other is wariha tetsu, which features a hard edge (hagane) and a body of medium hardness (kawagane). All other styles of lamination use shigane, but it goes to show... they had the knowledge but not the will, it seems. It may well have been for traditionalist reasons, as you say, because you'll find many interesting variations that surely have nothing to do with practicality (eg. one broad fuller on one side of the blade; three narrow fullers on the other - or swords with asymmetrical cross sections).
Oh, and just a side note on that video featuring Stephan Roth: the sword which is broken by the longsword is... also a longsword. But these are stresses of which neither katana nor longsword would expect to experience anyway, so while a longsword made of spring steel will be stronger than a traditionally made katana, a traditionally made katana will be strong enough. Just like the katana will be sharper, but the longsword sharp enough.
+Gilmaris I agree with everything! All your comments are very insightful my friend, thank you for sharing them. I hope I conveyed the same thought in my video, that a katana will still be more than strong enough for standard use, but you most certainly said it much clearer than me ^_^
I am Shad Hey, thanks! I enjoy this video series immensely, and I feel that teachers in schools everywhere should be presenting it in Katana class. For too long we have lived under the yoke of fan-boys and bashers!
Hello Shad, I have a suggestion as to why the Japanese continued using water to harden their steel, and that is quality of oil available. In Europe you have large amounts of plant oils available in different grades so you can create the oil you need to harden the steel correctly. In Japan, I'm not sure they had the correct material. And if the steel is hardened in water, it would very difficult to temper the blade evenly without warping it. The temperature range between tempering and annealing the steel is narrow if the steel is that hard. So a swordsmith trying to make a katana out of mono steel the first couple of times would either anneal the edge and blunt the sword or leave it brittle and snap it. After which he goes sod it and makes the next one as he was trained.
really cool series.. and full of true facts.. and yeah i agree on what you say in the end.. the katana is a piece of art.. no matter what steel and forging and smelting techs are superior.. the katana is to me still the most beautiful sword of them all.. but what impresses me the most is that those traditional japanese sword smiths managed to create such a perfect blade in terms of metallurgy just by trial and error without any real knowledge about carbon conent of steel, imperfections and the microstructure of steel through different heats and hardening processes.. with modern tools like powerful microscopes we can look at a 500 year old katana and say yeah.. we see what you did there.. but in the end one should keep in mind that they didn't have this techs to analyze anything at all..
there is a reason why we still use different types of steel for a different kind of purpose still in our modern age.. sometimes you need something that is hard and brittle over something soft and flexible..
and i guess most of that also happened in the past.. and that's also why swords were forged different everywhere in the world.. they all tried to make them as good as they could for their use of it in the end.. so in this case the enemys they fought and the armor they wore at this time..
also: yes there would be ways to improve the katana from the smelting to the forging but there is a simple reason they never did.. ranged weapons like guns came to japan and that made the sword useless at some point.. so what would be the point of improving a weapon that's useless anyway in the end? at this point it was made to keep the tradition alive and that's why it's still forged the way it was hundrets of years ago..
+Dunkelelf3 Hmmm... coulda sworn i said almost the exact same thing some years back. Did you lift that post from me? :) Anyway, in relation to your last point, sure, i could see guns having some influence on the decline of the katana. But consider too, that when it came down to it, Japan chose their traditions over technology & eventually banned the further importation of guns, & clung to the katana! Why would they do this? The katana was not even the "primary" weapon of the samurai in battle. It was a side arm. But it seems that it's metaphysical symbolism elevated it far above it's practical function, & perhaps this had something to do with why the traditions surrounding it's manufacture remained intact long after their practical relevance had passed. It had become a spiritualized, religious pursuit by that point. Just a thought. I really don't know :)
***** yeah it think that's also a point.. the katana really is a symbol in japan and also i think they try to honor their ancestors by keeping the tradition and everything around it alive..i think it's a good thing.. humanity has lost so much knowledge by just forgetting what was well known in the past.. for example are we so proud of our modern medicine and drugs like antibiotics but we forgot about so many herbs and plants that could be used instead really well in many cases.. i don't think that it's a good thing.. yes ofc progress is good but it shouldn't be the reason that we forget about anything else we learned in the past..
I think partially the reason why they used differential hardening is because the way it is used and the target they are used against. In feudal Japan, iron is scarce, and to arm as many men as possible, it is more efficient to make weapons than to make armours. Hence, most of the combatants in battle go without armour. Therefore, the katana is primarily used for cutting through human flesh, and bones, and a harder edge is more preferable.
On the other hand, a European sword has historically been put against full plates, the ability to retain its shape is important as full punch collisions against armour and other weapons often occur in battle.
The fighting styles of the two weapons are also a reflection of the use mentioned above. Samurais emphasise on the striking speeds and evasion because their weapons are not designed for parrying. European swords are often straight, facilitating its tip to penetrate armour.
According to Mr. Roth, (the forge is called seelenschmiede) the smith doing the destructive tests on the two swords,
the steel used for the European one was phosphorous steel of a composition you'd get when using bog iron as basis for a late medieval smelting process.
Great explanation on the metallurgy of hardening here, thx. But, you can't blame Marten. The poor guy now plays the guitar with Meshuggah ;)
The structure is named after German metallurgist Adolf Martens (1850-1914). :)
Amazing Job! Thank you so much for the time and effort you put into this for us.
Where did you get all of the information on the molecular and crystal structures. I'm writing a paper on heat treatment and I'm having a hard time finding information on the structures.
29:14 A speculated historical reason, besides aesthetics (you're not really wrong about that, it was given almost undue levels of importance in the "higher" society, which were the people who used katanas in the first place) is infact... the usage of the weapon. As you know far better than me, the medieval European warfare scenario quickly escalated into a one-upmanship between weapons and armour, which is why, swords were not expected to deliver fatal slashes, so much so as to survive the punishment of clashing against armour. So the need was for a weapon that would not break, rather than one that could slice a tomato. Contrast that with warfare in Japan, where duels did not permit armour, the capitals did not permit armour unless a state of war had been declared, and rebellions of the downtrodden never managed to get their hands on chainmail (which is hands down, one of the most useful things to be wearing to protect oneself against a slashing weapon). Thus, a sword that could slice deeply, and deliver fatal wounds on targets with minimal armour, was the requirement. And in cases of actual warfare, even for the samurai, most of the combat was from horseback using glaives, spears, or archery, hence, once again, not directly clashing swords against armour. So essentially, their form of warfare never developed in a fashion where they might need anything other than a slashing sword, compared to the European swords which were meant to slash, hack, stab, bash and pummel using the pommel (see what I did there ;)
Well, one obvious reason why they might have stuck with the differential hardening instead of going with spring steel is edge retention. When you're slashing flesh or melons or whatever, having the harder edge would've allowed a sharper edge and better edge retention. If you were striking full plate armor or steel shields, you would have quickly understood the limitations of differential hardening. The fact steel was so rare in japan is a great indication of why this never occurred to them.
I think maybe two reasons the Japanese stuck with their methods may have been:
1. They really did love cutting, so anything which decreased cutting at all might be seen as less desirable. This seems historically borne out. And on a related note, the katana seems to have been more about samurai dueling and honour than about warfare. Remember that katanas are sidearms; the primary weapons in war would be spears and bows. And, as long as everyone is using a similar weapon for dueling, that's fine! (Think of how a European rapier would have an advantage over a smallsword, but as long as both duelists have smallswords, that's irrelevant).
2. This is more speculative, but when you don't have modern chemistry and metallurgy, you're going to tend to stick with what you know works, even if something better is out there, because you don't KNOW there's a better option. Unless you happen to have someone stumble upon a better option. And you're less likely to have someone stumble on it or know someone has stumbled on it in an isolated place like Japan, with limited contact with other cultures and smiths.
One question, if you can bend a katana with your bare hands/feet, can you bent again it to repair it? System D like? (then go to the blacksmith because it's not optimal.)
I'm not a pro europe or japanese swords but aren't they cheating in their mega stress test with the two european swords ?
When he break through the sword 1 with the sword 2 :
-The sword 1 is keep against the table :
it can't bend (even a slightest in the edge alignment) and can't react properly to the attack. It mean it must absorb all the shock by itself, but can't and break.
-The man doesn't hold the sword 2 in a straight way, you can see he's tilting it to his left :
Then the sword 2 freely bent in the plate side, absorb the shock easier, and the crack following a weird path instead of going upright through the blade.
Then a got a paradox : why does the sword 1 break that way with a strike weakened by the tilt of the sword 2 ?
Would the sword 1 break if he didn't tilt s2? Yes.
Would the Sword 2? Yes i think.
I think they pre-cut the Sword 1 and tilt the sword 2, that way the sword 2 stay clear.
there are modern smiths who make differentially hardened catanas with spring body and martensitic edge :) Howard Clark with his L6 swords are one of them. some production firms like hanwei also make those.
Japan was very isolated being an island nation and they didn't really have to battle and fight other people with different technology. In Europe new weapons were made to combat the different defenses of people around you and in turn technology geared into stronger defense and a chain began to get ahead. but in Japan where it was only one culture and one group of people with limited resources they didn't have to change new technology, they perfected a weapon to fit their needs. I'm sure if there was more interaction with other armies maybe they would have changed techniques, combat style, or weapons all together (the Romans had to change many times do to conquest and interaction with new tech). necessity brings around invention and it wasn't necessary for the Japanese to change. considering all of that and the challenge the sword crafters had to overcome to even achieve useful steel to make a weapon, the katana will always be my favorite sword and one of the better swords in history. I'm not saying it's the best or that it will outshine all other swords, which it clearly wont, I'm just saying with what they had to work with they made an amazing weapon to combat what they had to. That and it looks badass
Actually the Japanese did interact with other nations and went to war with other nations and were even conscripted as mercenaries by other nations.Secondly I agree the katana is awesome
That is somewhat true, the Japanese didn't have extensive military interactions with the continent during the period where katanas were most used, however, they were not a single unified group for much of that period, they spent quite a long time in varying degrees of civil war (or, depending on how pragmatically you view the position of the emperor, you might argue that Japan as a unified country ceased to exist for a period).
In 5:00 you seem to be confusing differential heating with, bimetallism (2 types of metal in the same blade, in katanas spine is low carbon steel aka soft, and edge high carbon steal aka hard). You can deferentially heat-treat a mono-steal (one type of metal) blade perfectly fine (it all has to do with the application of a layer of clay on the blade prior heat-treatment).
A bend blade sounds much easier to repair in case it can't be simply replaced, compared to a snapped one.
So maybe that's one reason why they chose this method.
cheers Shad..brilliant and amazing..also thanks for all the work you put in to let us be educated...
I actually appreciate the katana only because of its aesthetics. I like most other types of swords more for cutting practise but the katana just looks absolutely beautiful (in my opinion).
So I am interested in buying a spring steel katana with a hamon line, does the spring steel actually have any benefit in this instance?
Shad: The door was locked before they could get out.
Me: That sounds like the setup for a horror movie.
A reference can be made to the 'Tang Dao', from which the katana derived. It has a straight blade and a smaller edge (a third of the depth of the blade), supposed to the katana (over half of the depth of the body). The Japanese blade is adapted to killing mostly unarmoured opponents, therefore they only needed the katana just stronger than the human body that it doesn't bend in combat.
Wouldn't the differential hardening be better suited for a sword like a katana? If I recall correctly the majority of the cutting done is done with the last few inches of the blade which on a mono steel sword would have been outside the point of percussion and thereby reduce the effectiveness of the cut. As such a katana needs to be differentially hardened to make it more suitable for its intended use right?
To be honest, I watched all 4 parts now and am about to start the 5th, I understood all of it and I was glad to be learning something. This episode however went over my head, I couldn't follow it all that well, unarguably due to my own stupidity but I feel like I have to re-watch it 4 more times to understand it completely.
The magnet hardening temperature is a myth too. All steels lose their magnetic properties at around 744 C, yet only 0.6-0.7% C content steels can be quenched at that temperature. Most steels require 100-200 degrees more than that otherwise you get a partial quench and inconsistent results.
really great series Shad :) I have a question, european swords of the medieval era, 13th 14th 15th early 16th century were or were not spring steel? and which is better, ulfberht steel or spring steel? was the steel quality of the ulfberht better than of the spring steel european swords of medieval era? I am kinda at a loss there, ulfberht steel was liquified, but was the spring steel on the medieval era also liquified?, and why was ulfberht steel patternwelded when it was already liquified? no need for patterwelding then, right?
+John Pepper GREAT questions mate.
So according to my understanding, spring steel swords were rare before the 15th century. Could there have been cases of spring steel before? yes I do believe there were but that they weren't widespread. I've never read that any ulfbehrt was spring steel, though I suspect they could have been made into spring steel if the smiths new the techniques. Spring steel will be more durable than the ulfbehrt steel (which I suspect would be pearlite with traces of martensite) when under high stresses but what we need to remember is that the ulfbehrt sword was still very serviceable and of high quality. Pearlite still makes great swords, they're just not as durable as springs when under extreme stress. From my study I believe that the great feature of a true Ulfbehrt is the purity of the steel, but purity doesn't grantee a great blade, it has to be quenched right. The quality and purity of medieval era steel could vary quite a lot but the best of the best would be very pure stuff, definitely equivalent to Ulfbehrt steel. And yes, I don't believe there is any reason to pattern weld steel that is already in a pure state, except for beauty. Indeed any type of extensive forging to decently pure steel would be FAR more detrimental to it than anything else, as parts of the scale (iron oxide) will be mixed into it and it will also lose carbon.
+I am Shad thanks for the answer, I mixed the quality of steel with the process of tempering (for making spring steel) I watched a documentary about the Ulfberht, (secrets of the viking sword) and frankly it confused me more than clarify things, you know, but you sir you made it clear, thank you for the series :) just one more question, about the damascus steel, if this steel was made by melting the metal to liquid state, why the patters? aesthetics again?
Thanks for that series as a katana fanboy this was very informative
One thing that I was hoping you would discuss/consider is the argument that the differentially hardened quench allows for shock absorption (and compared with spring steel). Another thing that would have been good to talk about is the question of differential tempering (whether it's possible, been done, effectiveness, etc.)
Perhaps you could update the description, or even make a miniature addendum video if these topics warrant such?
+Shadiversity
The Katana is ideally designed for its purpose, that is slicing through the human body. Other swords are better designed for other purposes, like stabbing into a body and getting back out (the springiness would seem to me to be ideally suited for this).
I tend to think that weapons were designed for use cases(duh), and European swords were made in the context of trying to poke through or into the seams of plate armor.
Katanas were great for lopping off limbs at the seams of armor, or against an unarmored foe, hitting at the shoulder and going diagonal across the chest. (this is also why the curve is in the blade because it makes it easier to hit someone at the shoulder at a higher velocity with minimum recoil through the blade)
I know this video is relatively old now, but as a material science engineer who just saw this I would like to point out that what really dictated the names of pearlite etc. is actually how the cementite precipitates looked… Otherwise so far this seems like a great video (10 minutes in)
Please turn the top sword on the wall blade side up, all the photos of genuine swords you’ll see that’s how they’re presented 🤓
On a serious note, have you seen why they use a concave Polish for katana, I sharpen my kitchen knives with a concave Polish for the reason.
I also used to practise tamashigiri with a live katana, the curve shows the difference between a slice and the chop of a straight edge.
I’ve had access to historical katana, you’ll see the back of the blade can have blade marks in it suggesting it’s used for blocking, yes some of the blades I’ve seen have small chips in them.
The Hamon is not part of most katana, the clay actually is not insulation, it provides a greater surface area for cooling as a study a few years showed.
While I will admit I didn't really learn anything new in this I did enjoy it and am finding the series on a whole very informative. And to a person who doesn't know as much about the forging process I'm sure this video was very helpful. Great job Shad keep it up.
I can't help but wonder if your name is actually Martin....
+DaManJoeWho *Glances around in paranoia. "They're on to me."
Thanks mate!