There is a disseration by german archaelogist Stefan Mäder ("Stähle, Steine und Schlangen", Berlin, 2001) , who brought 3 european blades from the early middle ages to Japan and there these blades were polished by japanese sword polishers and also shown to japanese sword smiths. He could prove that (here in quite short summary) the techniques (refining/folding, partly clay quenching and to a certain extend even polishing) were pretty much the same in both areas, one blade even had a clear hamon line. I would strongly recommend to read his work, every detail is thoroughly described and underpinned. I think it is really admirable that he brought these two cultures together in this context and didn't limit himself to the usual comparing of blades. Sadly, since the document is in german, I guess his work isn't that well known worldwide.
It's not only differential hardening that gives you the difference in edge vs back. You can also use differential temper. I even guess that method was used on some of the curved blades you've shown. The Japanese use it too, using a heated copper block. Semi modern knife makers use a torch to draw back the spine to a lower hardness (edge in water, heat to the spine).
@@edgarburlyman738 It's got to be old, since iron axes were one of the first iron tools, and differential hardening/tempering is still commonly used today on those. The blacksmith dips only the edge in water, while the back is still glowing. Then he takes the whole thing out and observes how the residual heat from the back tempers the edge. When he's happy with the result, he dips the whole thing in the bucket to arrest the process.
There is medieval European art of blade smiths using red-hot iron rods to differentially temper arming swords and other double edged blades. Not sure on the era but I think it was 14th-15th century.
@@toddellner5283 I think you and bakters are talking about differential hardening, which isn't what I meant. I have heard it called tempering before so there might be some confusion there. I mean having an actual spring temper in the body of the blade, while also having the edge as hard as possible. What Brenda said might be it though.
Most one edge slashing/chopping blades are quenched in water because the softer back will absorb the shock when slashing/chopping. Malaysian way is to dip the edge first and slowly the whole blade into the water. Need some skill on timing, to hear and feel if something is wrong. Slashing/chopping one edge blades don't need to be springy/flexible because obviously it do slash and chop, the cutting point is so small, the momentum/vibration effect small area and spread to the back of the blade. Double edged straight weapons need to be springy/flexible because it is mainly to be used for stabbing, if not springy/flexible it will break, the stabbing point carry momentum/vibration to the whole blade behind the stabbing point. Double edged straight blades cannot be quenched by water because they are usually thinner than one edged weapon, the quick cooling from water might make the blade disfigured and break. Keris for example is a stabbing weapon, quenched in oil, usually coconut oil. My late uncle was a part time blacksmith, I used to sit by and watch he make weapons/tools.
That's very interesting. I thought it was the other way round, basing on the observation that the Estoc is very stiff (and in fact, some of them even have diamond shaped cross section), as you don't want energy in the thrust to deform the blade, and instead be transferred into the target. Then again, the Estoc is a highly specialised weapon, and perhaps would be wrong to conflate it with other more "generic" cut-and-thrust swords.
@@Pallyrulez That weapon need to be stiff to absorb the momentum and spread it evenly to the back and still maintain it's shape. The reason why most spear head are short is because of this. Even small blade spear head are usually wide with diamond or "eye" shape, not a thin blade. If you want a long spear head you can't make it in thin blade shape, because it will break on impact.
That's also how the American Bladesmith Society's basic course teaches it. Sometimes it's oil (or Goddard's Goop made out of oil, paraffin wax, and old hydraulic fluid), but the same idea is used.
One thing to remember when discussing weapon designs, most ancient cultures don't design their weapon based on scientific reason, they're more into belief in magic and such thing. While maybe certain way of designing the weapon is for doing certain job/purpose, it is not always true. For example, the Keris, most of Keris are wavy shape, or serrated, scientifically it is better for hacking and slashing because the contact point is smaller, so the energy focused on the point. But, Malay people designed it NOT to slash and chop, it's for stabbing. The wavy part will give irreparable damage to the flesh when stab, twist and pull out. There is a belief where certain amount of the wave give certain amount of magic, curses and suitable to fight against enemy who use certain type of magic and curses. For example, 7 wave (we call it Luk) will demand 7 souls when the Keris coming out from it's sheathe. After kill one, it wants 6 more, and the 6 souls might be innocents. That is the reason why only certain people have 7 Luk Keris. There are many other mystical beliefs in weapon making in South East Asia. So we can't view at them with wholly logical and scientific thinking, must also consider mystical belief behind them
Some schools of Japanese swordsmithing have the whole blade covered in clay and change the thickness of clay at the edge/s. This allows for more detail to be drawn onto the hardened edge. Soft back has its own problem of getting pieces cut off when the swordsman has to impact with the back edge. Lots of schools teach sliding the back on the fingers and scabbard at sheathing. The large chip formed on the back can cut the fingers as well. Some Japanese swords have what they called full hardening with large areas of the back hardened.
While differential hardening was occasionally used, it's quite likely that differential *tempering* was used more often. It's simply easier to harden the whole blade, but then heat up only the back, while even using some cooling procedure on the edge, in order to prevent it from softening. (Dipping the edge in mud or sticking some vegetables on it.) Also, I would not assume that the use of clay covering during hardening is exclusive to Japan. It's a very logical solution to a very common problem. Especially a thin edge is vulnerable to decarbonization. Covering the blade with clay prevents it and it also prevents the scale from being formed. It really seems to me that Japan, with its reverence for tradition, simply preserved plenty of historical techniques, while the rest of the world quickly forgot them, as newer and better solutions became available. For example, in order to replicate many historical blades from historical materials, it's necessary to use folding and reforging approach extremely similar to that of Japan. No reason to assume that other parallels are less likely.
If you know of any decent sized arrowhead collections, it would be pretty simple to get some Tsubosan HRC testing files and test the front and back for hardness difference.
I'm a CNC machinist and not a blacksmith, but can someone explain the use of files to test for hardness to me? I'm used to several concepts for testing material hardness in manufacturing settings, but none of them use files. How does it work?
@@danorris5235 With modern files, they have the hardness listed. You start with a "soft" file, and run it along a corner - if the tested metal is harder than the file it will "skitter", while if the file is harder it will "bite". (It's like rockwell testing, but using files of differing hardness instead of the listed items) It's a home smith's "quick and dirty" way to see if the quench & temper took properly.
I am working on a dagger and it has an auto hamon. I quenched in parks 50 with no clay but because of the thickness of the base it had enough mass to slow the quench. So it can be unintentional to have a hamon without aiming for one.
PBS did a fantastic episode on NOVA called 'Secrets of the Samurai Sword'; I highly recommend watching it. It followed the forging of a Japanese blade in the traditional manner by one of the few remaining great Japanese swordsmiths. That craftsman used layering of different 'tough' and 'hard' metals in the folding of the steel during the forging process. It took several weeks before the 'clenching in water' was attempted which instantly transformed the straight blade to the signature Katana curved blade.
A brief summery of heat treatment as a toolmaker with over 30 years work experience I often cringe at lots of novices u tube videos this one is well done but if you are trying to replicate anything that was achieved by the old armorers just remember that they knew how to get the best result out of the materials that they had at the time. But if you are using modern steels read the manufactures spec sheet and understand that modern metallurgy is a very exact science and trying to use old techniques on modern steel may well lead to cracking and other problems there are lots of different steels and if the specks say air oil or water hardening that what is required . Good luck
I've made a few blades and polishing in japanese style. The edge is hardened and forms martensite, the back is in the pearlite state which is considered unhardened steel. The transition between those can show as a line when polished and etched with ferric chloride which is effective at showing grain structure transitions and is also used on cross sections of welds to study penetration and heat affected zone. It's the polishing technique that makes it look white and you have to carefully follow the hamon line when doing the final polishing with the hazuya stones on the edge, jizuya are used for the back. This is because of the different crystal structures in the steel. The different hardness makes the polishing stones cut differently, the jizuya stone I think is higher grit than the hazuya and therefor gives a more mirror like finish and the hasuya is a bit cloudy. The kissaki(tip) is polished the hazuya only which therefor can make the hamon shades look inverted to the rest of the blade where the softer perlite structure appears whiter than the harder martensite edge. An other interesting thing with the water quenche is that much of the curve in the blade comes from it. When the edge rapidly cools it shrinks a little bit and the blade bends forward but as the back cools more slowly it shrinks more than the edge and the blade ends up with a backwards curve. This does not happen in oil though, in oil it stays curved forward and the hamon line does not follow the clay line like it does in water, it seems to follow the blades thickness instead. I think this has to do with the water and oils boiling temps and heat transfer properties. I'm just guessing here but I think water might draw more heat out of the exposed steel but the lower boiling temp and agitation creates an air pocket around the clay and cools that part slower than the oil. Oil has a softer cooling on the exposed edge with it's higher boiling temperature but at the same time also cools the clay area faster compared to water. Japanese swords where also often laminated with a soft iron core to prevent them from snapping in half, the edge could crack but the core and back would bend and stay bent which could be a benefit but also a drawback as they wasn't very springy and bent easily and required more skill to use.
I differentially harden using tempering rather than quenching. In drawing a temper, you quench and then reduce the hardness by partial reheating - you grind the steel (or part of it) clean and the color of the oxide that forms on the steel during reheating indicates the heat. To do this, I water-quench and then partially reheat the blade using glowing-hot iron bars to heat some parts of a blade more than others. High-carbon steel that has been fully quenched even in oil must be tempered or it will be very brittle, surely this was done on European swords. Salt water is another option for quenching, with a hardness between fresh water and oil. Sometimes blood was used, more for magical superstition than it's actual value, but I'd guess it would be another shade between salt water and oil.
One nitpick about water vs oil hardening. It has much to do with the alloy and how fast it NEEDS to cool in order to harden properly. Water quench steels will often not get hard at all in oil, while oil quench steels are almost guaranteed to crack when quenched in water. Also some steels can be done with either, though for most it's not an optional choice. And, some are even air hardening. Ask Todd for more details.
I would love to get a antique kukri that I own tested for edge hardness. I did a restoration on it, and decided to re-sharpen the blade. It is one of the hardest most difficult to sharpen steels I have ever experienced, and I have hand sharpened allot of modern knives and swords.
3:39 This is a kind of generalization that led to misconceptions. To correct Matt here, the edge of a Japanese blade Would be more prone to chipping if it weren’t for niku/appleseeding. Niku on Japanese blades is very overlooked as it is the the type of blade shape the would have been taken into battle. It basically keeps more material on the edge so it wouldn’t chip as easily. Many antiques nowadays have lost the niku due to centuries of regrinding, resharpening, and polishing. Just something to keep in mind. Edit: the reason why niku is very underrepresented in modern times is because modern Chinese reproductions make katanas for people who want to do simple backyard cutting with soft targets (water bottles and tatami) so it would make sense for your product to have an edge to cut soft targets better.
One might add that the edge is polished sharp, not ground. This is important as for a chip to develop, there needs to be a micro chip to start the process. The smoother the edge, and almost total lack of grief lines, the less it is prone to chipping or cracking. This philosophy carries forward to Rockstead Knives today, that are hardened up to 67 Rockwell.
I also believe to have heard somewhere that the niku was sometimes segmented (kind of like a row of teeth) to keep cracks from spreading along its length.
Many just enjoy competition and winning in that particular competition. Japanese swords of apple seed grinding like Ichimonji school of Yoshindo still exist. And he enjoyed another fame of helmet cutting with such fatter edge. Certain tatami cutter use flat grinded blade for thinness and marvelous cutting ability with tatami. So, horses for causes. It is showmanship for many. In my experience, the fatter shape cannot reduce chipping significantly. A sword/katana could fight a few warrior(like 7) before getting too blunt or chipped to kill more or cutting into more flesh. Killing enemies is an expensive business. So, the film 7 samurai expressed the need of using many swords in war.
Matt is correct that steels that are more hardened will be more brittle. You are correct that the comparison between Japanese and European blades is an over generalization.
Thanks for the breakdown, it's a good recap, but also there was a lot of new information for me to think about! Suggestions: Korean weapons, or the sosun pattah sword (it looks like a recurve sabre, which is really intriguing to me!
Does the fact that the edges in euro swords would cool faster, thanks to them being both thinner and at the....edges of the sword cause them to be a bit harder than the spine and internal meat just by virtue of physics of cooling ?
Yes, definitely. If the edge is thin when quenched it will cool much faster than a thicker spine or centre. 0.5mm thick vs 6mm thick can be the difference between 64HRC and 40 HRC, depending on steel alloy and quench medium.
@@louisvictor3473 not always no, depends on if bevels have been forged or ground in by then, many now grind them in after hardening to stop potential cracking and warping
Differential hardening can also be done by use of insertion or lamination, where differing carbon content steels are forge welded together, and the different carbon contents result in different as-quenched hardness, the whole tool then being uniformly tempered. This was common practice in American, UK, and Nordic scythe blades, where a laminate of high carbon steel comprising the edge and medium carbon spring steel comprising the back were clade in plain iron. This method had the extra benefit of taking advantage of the way that rigidity scales cubically with changes in thickness, which is why a high-hardness safety razor blade can flex so much without breaking when an only slightly thicker straight razor edge can chip from an accidental impact with a faucet. By having the high-hardness edge supported by iron you achieve both high hardness and excellent edge retention alongside excellent ductility/toughness, and the spring steel at the back of the blades helped them hold their proper shape instead of taking a set (which they still could do if used poorly--they're tools of finesse.)
Quick point of discussion. The kukri being differentially hardened, the back and belly being softer. do you think the “notch” at the base of the blade acts like a hinge, or a place for the shock from a strike to go into the softer steel instead of the hard brittle edge? I think this may be the the elusive purpose for the notch. Would like to hear from others.
Matt, don’t forget to mention quenching in salt water! Salt water quenching is best for medium carbon steel. Too low of carbon will have no effect. To high carbon will cause warping cracking or breaking. From what I understand medieval steel tools like a draw knife or axe bit for example may have been medium steel quenched in salt water.
It might be worth noting the choice of what to quench with, depends a lot on how easily hardenable the steel is. As the carbon content goes down, you need a faster quench. So with modern high carbon steels, hardening in water can go right past sanely hard into warped, cracked, glassy junk. Doubly so in tool steels. Some tool steels are even considered "air quenched". AKA you heat them up, and "quench" by letting them cool in the "not furnace". The other thing of note is that you get differential hardness (not necessarily hardening) by having different steel/metal at different places. This is another technique common throughout the world, but again, one used by Japanese blades a lot. Katanas are typically 3 types of steel, the core soft steel, the edge hard steel, and a shell of something in between. Then forge welded together and differentially quenched. But, again, different steels isn't unique. You can achieve different mmetal properties in different ways, the most common today, is actually case hardening. You pack the item in graphite or some other fine carbon, heat it, and the outside absorbs some of the carbon into the metal crystal structure, but only around the surface. European swords mostly stopped using a lot of these techniques, not because they were lazy or stupid of course. Once you have hardenable spring steel, you can just make the whole thing out of that. The ultimate hardness of the edge might go down a bit, but the trade off in every other blade property is well worth it. Depending on use case of course. Context context context. I'll just be over here with my collection of tungsten carbide edged knives if anyone wants to claim katanas are absolutely the best of the best.
Hardenability has more to do with alloying elements like manganese, chromium, and molybdenum. A modern steel like Hitachi White #2 has very high carbon at 1% but also needs a very fast quench because it only has 0.25% manganese.
Thanks for bringing this topic up. I have also seen fine temperlines along good wootz shamshirs (not all) exactly as you described. Any idea how a curved blade can be differentially tempered like that without clay? Have been looking for it in Persian sources, so far nothing found..
This is a figure from a book by Kamil Haydakov titled: "Shamshirs: Old sabers and the secrets of ancient sword making" published in Moscow, 2013. It shows the variation of heat treatment patterns on shamshir blades. Some may suggest usage of clay, but I am not sure. drive.google.com/file/d/1b1PeZjdmB1zSqS0G2pIQq79puWxdfRWF/view?usp=sharing
All swords are differentially hardened to some extent, but you would need to take a cross-section of the blade to measure it. The surface that's exposed to the oil or water will get harder than the core of the blade as it's cooled quicker. The thinner edge especially will cool much quicker. It's not going to be nearly double the Rockwell hardness as in Japanese swords, but I would expect to see a 15 or 20% difference throughout the cross-section (unless the blade is very thin).
Saw a video years ago of some natives using some very very large kukri shaped weapons to chop heads off of cattle at the neck. Never could find any more information on those blades, I was wondering if you had any knowledge of this. One swing and that was all they needed, it was a clip from a nat geo documentary I believe
I have seen talloires hardened with a water-soaked sheepskin the process is to draw the hot blade Edge through the sheepskin quenching it I do not know how common the practice is however that would make it work and it uses the least amount of water which makes sense because we're talkin about desert people water is a precious commodity use as little as possible polluting it
I think part of why Japan emphasizes and is known for the hamon is that there was a time where swords were banned, so, craftsmen needed to show that they were making works of art, and not just weapons. So, the hamon became an artistic feature, so that they could maintain their craft.
In the talks I have seen by the owners of antique Japanese swords, the claim is made that the quenching water was always at uniquely cold. Is that an issue?
The blade that you're holding in the opening is very short. Are you able to share its dimensions and maybe some more details about it? I have a strong interest in 'short katana' or kodachi, as they're the preferred sword of my martial style, but finding them is hard.
What do you make of the interaction of the differential hardening and the low[er] carbon back and high carbon jacket/edge? It seems to me that the clay and quench style stems from the construction method, and likewise, the swordplay from the characteristics of the blade.
I was going to point this out as well. Different carbon steels have different hardenability. It might be possible that clay was needed for Japanese style swords with different carbon steel pieces wielded together where as monosteel blades had no need for clay.
You can read Doctor Larrin Thomas's article about quenching that just came out in knife steel nerds. Modern makers use engineered quench oil that often quench nearly as fast as water. The difference is just the quench speed at certain times doesn't strain the blade as bad. Most antiques would have used very simple steels. Alloy let's a steel harden slower. Without alloy it is common to get what we in modern times call an auto hamon where the hamon forms because of the thickness of the blade does not allow for the thicker part to harden. When they happen they can be some of the most dramatic. What I have come across from sword makers they say it is likely that European swords were not fully through hardened since it is extremely difficult to even get 1/4" to through harden with very simple steels. If there were trace alloys if things like Manganese or Chromium then it would have been easier. The clay of a hamon is just painted on and that little bit is all that is needed to slow things down. If it is out in to thick the heat will creep back out to the edge and make it very shallow or have unhardened spots. Don't ask me how I found out. This heat creep is what is called and auto temper. Speaking of tempering.... Hardening in water can give you max hardness and it is needed for full conversion with ultra simple steel( carbon and iron is as simple as steel gets). So long as they understood tempering that is the way hardness should be brought down. To control it by under quenching has a lot of negative side affects. As far as I know the main reason European swords were more springy was that they had a lower carbon content. That is the best way to gain better toughness since high carbon steel will not be as tough as a medium carbon steel even if they are at the same hardness. The biggest advantages we have now is our ability for precision heat input. We can get more out of the carbon and alloy by holding it at just the right temperature to let everything desolve into solution without growing the grain more than necessary. The condition the steel is in makes a big difference as well. There is a reason that some of this stuff had myth and legend around it. Things like seeing shadows running through the steel show phase transition where the steel gets cooler as the phase changes even though it is still heating. The trained human eye is only good at telling temperature for about 200 degrees because of how our eyes adjust to light. Finding a spot to start paying attention and then things like a dark moonless night help get closer. 25 degrees can make a big difference in how a blade performs. With the limited tech ritual was how you made the best possible blade. Blades are still one of the highest performance uses if steel. A common blacksmith never built fine blades like in the movies. If you ever wanted to do a steel theory video I think there is a good chance that you could get Larrin Thomas on your show. He does other podcast and RUclips videos and is the best expert in blade steel out there right now. I posted your Seax video and he was one if the first to respond. If not I would crowd source info on the forums from sword makers. I know most of them well enough to sift and could put together a list of info for you or better yet give you an interduction and I bet they would help you out. A lot of those guys have done some serious research and have made real wootze and pattern welded stuff and would love it if someone was putting good info out there. You would have the best researched thing out there on any well followed format. You are great at making it understandable and you have the historical "Context" to put the whole package together. You can reply back to this or find me as StormW on Blade Forums in the makers area. I can tell you a fair bit of modern theory and how stuff works but I'm not a true expert although I know more than most. I am still open to make you something out if modern steel as payment for all the hours of enjoyment I have received. Interest in what you talk about has even shaped what I did for a living and my hobbies of bow and knife making.
10:18 To make things clear, China was the one to bring the folding and differential hardening to Japan. It went from China to Korea and then to Japan. China and Korea were very tight with each other and this will be important later. In around the 9th century, japan caught word of China and Korea making stronger blades. They the imported many smiths from both lands to teach their smiths how to do it. In the following centuries, japan would improve on the technique and would end up making better swords in this style. Fast forward to the Imjin war (1590s), Japan is beating Korea on the land but not at sea. The Koreans beat the Japanese through naval technology but then imported Japanese smiths to teach them how to make better swords. They realized Japanese swords were of better quality and they had not improved the folding method because China didn’t either. It turns out, the Koreans were only folding 2-3 time opposed to the Japanese who innovated and were folding over 10 times. I speculate that the method of folding from the 9th century only did a few folds but since then, the Japanese figured out more folds mean less impurities. Hence why Korea and China then had to learn the Japanese style of forging all those centuries after China introduced Japan to it.
Differential hardening was actually indigenously developed in Japan, it was the folding of steel that was imported. Differential hardening would inevitably curve the blade, and during the time period in which the Japanese were importing sword technology from China, all Japanese and Korean swords were universally straight, while the Chinese blades of the time that were curved were made as such during forging, not quenching. Much later, after the Japanese developed differential hardening, the Koreans imported that technology through trade, and long before the Imjin wars, at that.
Some Japanese school do not understand purity of steel. On the whole Art sword appreciation enjoys areas of great difference in concentration and composition to make interesting pattern in/on the sword body. From museum antique it can be seen that the earliest example of Chinese and Japanese swords have many folds. Modern Pilipino blades still have very few folds. People fold steel to obtain interesting visual pattern often. Some (cheap?) Chinese swords have added hard edge and no metal folding. Some European antique and modern Western blades have beautiful geometric pattern. Japanese sword polishing has improved greatly. Some fine patterns the smiths of old induced into their blades could not be seen at their time. It is an enjoyment to see quality steel pattern. I have blades that look like cold ice and blades that look oily(muji hada). Some Japanese did not care about sword body patterns. The use of Western imported steel frequently produce swords that do not show steel pattern. They are known or coded as mirror pattern. Some of these can show a hada or grain pattern with great modern Japanese polishing. With modern abortion culture, lots of people enjoy throwing their babies out together with their bath water. Therefore perhaps we have a flying baby culture or 2.
@@alexsitaras6508 They did, and they laminated their axes as well. A harder, but more brittle, higher-carbon steel core sandwiched between two tougher lower-carbon steel laminates, with the central layer being larger and protruding out from the laminates out in front. It is this core that was hardened and sharpened to form the edge, while the lower-carbon steel laminates protected the brittle core from torsion and impacts.
@@avd-wd9581 I don't know where I heard that, so I'm not sure - that's why I was asking in the first place. The only serious info I could find is this study: A METALLURGICAL STUDY OF SOME VIKING SWORDS core.ac.uk/download/pdf/268620377.pdf From what I've read, some swords were fully made of steel, others of iron with added steel edges, and some may have been hardened. In some cases it states that the edges have been hardened - but often there is no sample analysis from the interior of the blade. I'm also not competent enough to properly interpret on my own the results of the metalurgical analysis. For an example, look at pages 10 and 11 of the PDF (130 and 131 of the study).
@@XCodes Yeah, it wasn't pure iron, it had impurities, including carbon. Perhaps the term "iron alloy" should be used instead of steel, the same way "copper alloy" is now often used instead of bronze.
There's art of European medieval art of differential tempering of double edged blades by placing red hot bars down the centre of the blade. Tempering lessens the hardness slightly and allows a more durable/springy steel to recrystalise.
From what i know, traditional tamahagane katanas have steels with less carbon at the spine and sides ? Not sure if that could be tempered to a spring temper ? Thats why they had to be so thick there, to make up for that.
@@vedymin1 AIUI blades made of different steels were a relatively late development in Japan, with edges, backs and sides of the blade forge-welded of different steels specifically to obtain different hardness and "toughness" in different parts of the blade. (Whether using different steels began in Japan or wherever is AFAIK unknown.) Allegedly toward the end of traditional sword making in Japan they had advanced to coating blades thickly with clay at the back and less on the edge to allow the edge to cool quicker than the rest but not "instantly" as it would with no clay. That took some of the hardness from the edge but also made it less brittle. There are so many conflicting sources, and so much "lore" touted as fact that it's difficult to know for sure, but the physics does make sense. What I find fascinating is that traditional sword makers everywhere for centuries discovered all of this though trial and error, refining their techniques without needing to know any of the modern details of alloy content and the thermodynamics of crystal formation in iron alloys, doing things like identifying critical stages in quenching by eye. How was tempering developed? Who first took a forged and quenched blade and thought "if I heat this back up not quite to redness and let it cool by itself it will be stronger", or was it accidental i. e. storing quenched blades near enough the forge to temper them and discovering later that they were stronger?
This could be a modern thing, but i have seen swords quenched in narrow trough, allowing the smith to lower the hot blade lengthways into the water/oil edge-first, where they hold it for a while so that only the edge is in the liquid, before they finally plunge the entire thing into the now somewhat warmer water/oil to quench the rest too.
Here in some parts of the Philippines, it is called SUGBO or SUGBU method. I am not sure if it's a modern way but I think it is most likely a traditional method.
Blacksmiths in Europe have differentially hardened and tempered tools for a terribly long time. It's one of the first things an apprentice learns when making punches, chisels, and other tools. It only makes sense that the same technique would be applied to specialized cutlery.
Similar to the Nepalese method of partial blade quenching is the SUGBO method. In some parts of the Philippines it's called (sugbo) method and I think it is due to Chinese, Indian, and Middle eastern influences; dipping the edge on the quenching tub first and letting the whole blade cool a little before dipping the whole blade. I think as far as China is concerned they started with a similar process to the sugbo(classical period like han dynasty) and then developed the clay insulating method during (medieval period like sui and t'ang dynasty) which latter got to Japan, after that China returned to the sugbo method in the period that they were influenced by steppe sword designs ( like song, yuen, ming, and qing dynasty) and after a while some copied Japanese sword designs and clay quenching again (during ming dynasty I think). I think china had spring steel, differentially hardened(sugbo), and Differentially hardened(clay) blades pretty much all at the same time, the only difference is the predominance of one or two types/methods at a given time and for certain types of blades. An example is during the T'ang dynasty, they had spring steel and differentially hardened(clay) swords predominantly and at the same time had swords and other tools using (sugbo)like methods on a lesser extent/amount. Korea probably followed Chinese trends but adopted less steppe influence in their sword/sabre designs(maintaining older Chinese designs while changing it a little bit and with some Japanese design influence). The (sugbo method) was less controlled, less artistic than the clay method and produced more utilitarian looking but just as good blades, something the Chinese needed when arming a large imperial army with munitions grade weapons.
Does anyone know of any good books on this matter? I see the edge quenching is abundant in Southeast Asia. I’m interested in doing it on a small knife. As far as I understand, After the edge is quenched in the water, the residual heat in the blade tempers it. And I see them consistently putting the edge back into the water lest it tempers it too much. Thanks in advance.
Differential Hardening with Clay(Chinese:覆土燒刃) is originated in China, not unique in Japan. Many Chinese swords also have differential hardening, the oldest ones can be traced back to Han dynasty. You can also ask LK Chen if you like.
Clay tempering did not begin until about the mid-Kamakura period with only at the end of the period did it start to resemble what people recognized today, recommend to look up" 唐刀不算日本刀祖先 但中国古刀不逊任何日本刀".
Japan has a quite unique way to do differential hardening. They utilise clays to control the exact pattern on the blade. I wonder if similar techniques had been practiced elsewhere or not.
I think the Chinese taught the Japanese clay differential hardening method, but the Chinese preferred the "suguha" type(straight pattern and not wavy) of "hamon" on their blades, probably partly due to the way Chinese T'ang era sabers's bevels were designed making the hamon less visible to begin with, so making fancy patterns was useless; while the Japanese treat the suguha pattern as very old and traditional.
Edit required; Japanese blades are fully coated in a clay mix prior to heating and quenching,thinner along the edge where the swordsmith also adds adds clay in fine lines to create activities like 'ashi'. The hardened edge section of the blade is the 'yakiba'. The 'hamon' is the outline of the 'yakiba'. Your description is not accurate or well researched.
With historical weapons and lower quality steel, yes, maybe. It could make for a hard cutting edge and tough spine, which is more important with low quality steel. It would allow the sword to bend, and stay bent, rather than snap. The other approach is to fully harden the blade to a lower hardness so it is not as hard but very elastic. With modern steels there is no real advantage to differential hardening and is mostly done for aesthetic reasons.
What is the difference between mono steel blades, and poly steel ( and/or steel and soft Iron blades(( ie. The Indonesia Kriss ect.)) And water quenching?
It's a bit self-explanatory. Mono-steel is a blade of one alloy of steel. Laminated steel has different alloys forge welded together, most commonly a high carbon steel for the cutting edge and lower carbon steel or wrought iron for the spine or cheeks of the blade. This is typically done for lower cost or in some tools ease of sharpening. In some blades like a katana the different alloys may be used to impart toughness.
If I understand your description of Nepalese kukri hardening, it should actually be less severe than the Japanese process, not more. The kukri's spine isn't being quenched at all, and there's a transition from hard (at the edge) to less hard (just past the edge) to not especially hardened, with more time built in. The Japanese process stresses the entire blade at once, and has a single, defined boundary between the edge hardening and the rest.
The kukri method does tend to warp the blades though. Thinner wider blades more and thicker narrower (sirupati type) less. Also the tip and edge of the blade near the handle is left softer.
More often than not axes are not so much differentially hardened as they are made of two different materials usually a high carbon and a low carbon steel so that when quenched the high-carbon steel turnstep spring steel and the low carbon steel remains Steel or soft Steel in this case both steals our quench hardened it's just the high-carbon steel takes on a spring steel qualities will the low carbon steel does not have enough carbon to harden as hard I've never seen high carbon and super high carbon because well the super high-carbon would simply shatter I do believe it is be called because high carbon steel is considered spring steel super high carbon steel is either considered glass or Pig
Steel metallurgist (and hobby bladesmith/blacksmith) here. Matt - Please take a class or two about metallurgy. I think it will help you a lot. Generally speaking with blades, when we talk about hardening we are looking for a change in phase, specifically looking to form martensite. This is a very hard and brittle phase, and when tempered becomes less brittle at the expense of some of it's hardness. When we talk about softer spines we are not (typically) talking about martensite with more of a temper, but in fact a phase that is not martensite. Typically this softer phase we want to be pearlite, but bainite is also a good one to have. Both pearlite and bainite can also be tempered, but being much softer (lower stress) than martensite, it is not as critical. Quenching in water vs oil does not change the hardness of the martensite (at least in an appreciable way). What it changes is the amount of martensite formed. If one were to look up the TTT (or CCT) diagram for a given alloy you will see that you have a set amount of time to cool from the critical temperature (different for every alloy; "non-magnetic" is not good enough as critical is often above the Curie Temperature) to the martensite start temperature, or at least past the curve of the TTT diagram. Things like 1095 have less than 1 second to get down to below the curve in the TTT, but alloys with more Mn and Cr (among other elements) can take several seconds, or even minutes to pass the curve and still form 100% martensite. This is what can lead to great differential hardening. An alloy matched with a quench media and blade geometry that allows the edge material to "beat the nose of the curve" but not the spine. This can even happen without adding any clay or quenching just the edge, if the spine is thick enough to retain heat long enough to miss the nose of the curve you can get an "auto-hamon". Obviously the subject can get a lot more in depth, but there is a little more information for anyone wanting to read this.
The Curie point thing makes me wonder; we know all of this due to modern science, but did ancient smiths ever use lodestones (natural magnets) to test their steels while working them?
I suspect they did not, because it isn't actually reliably helpful. Recalescence and decalescence, on the other hand, show you exactly what you need to know, even if you don't know (as they wouldn't) that you were actually seeing the steel pass through the critical temperature.
@@markfergerson2145 They probably did not. A good smith can use the glowing color to determine the proper temperature. I had some training in smithing. The instructor could see from 10 yards away when the steel was not hot enough for the quench. Modern performance tool steels often are less forgiving. Keeping proper temperatures and cooling curves is crucial. Typically they are not hand forged or heat treated in a simple forge.
Is it possible to reduce the brittleness that results from a water quench through the tempering? By for instance tempering at a slightly higher temperature?
Sort of - the tempering almost completely overrides the quench, so you don't need to adjust. Japanese swords were not tempered. Highly skilled American blacksmiths and cutlers making the tools for the Industrial Revolution typically used water quenches for most things except for small/thin items. I'd imagine the Europeans did the same. The thickness of the steel affects the quench just like the quench medium does. If you're going to temper it, the quench medium is only really important to stop warping or breaking (which small items like springs are prone to in a water quench, and long thin items like a European sword can warp a bit if you aren't careful and lucky.
Water quenching doesn't increase brittleness. Water quenching has inherent risks of cracking a blade, especially with modern steel alloys. If the blade survives the quench it doesn't need to be tempered differently because it was water quenched. Japanese swords were tempered immediately after quenching, by reheating to a lower temperature over the forge. I see some modern bladesmiths do this and flick water on the blade to see when it gets hot enough that water droplets skip off with the leidenfrost effect, around 200°C.
@@gustavchambert7072 Yes and no. All else being equal, 67 HRC as quenched W2 steel is just as hard and brittle whether it was quenched in oil or water. Water doesn't increase brittleness, it increases the hardening response, which may or may not be an issue, but is more likely to be an issue than using a slower quench medium. Though with the slower quench medium, you may have an issue with inadequate cooling rate, depending on the steel alloy.
@@FuckYouYouFuck Mmmf, right and wrong both. The thing is if you water-quench the same steel vs. oil quench, you will get both more hardness (HRC) and more brittleness in the water than the oil. If you specify HRC 67, you are specifying the result, not the means to produce it. You can't quench the same piece in oil and water and get the same Rockwell Hardness with both quenching liquids and the same steel thickness and composition.
Quenching is part of heat treatment. Clay the blade, heat to 800°C, quench in water, reheat the blade to ~200°C to temper it. With a modern steel and process you would heat the blade to 200°C and hold it at that temperature for 2 hours, then cool it off, then repeat the process of heating it to 200°C for 2 hours. Quenching from 800°C makes the blade very hard, say 65 on the Rockwell C hardness scale, but also very brittle. Tempering relaxes the steel reducing its hardness and making it tough and elastic, say 60 HRC.
So, historically, is there any evidence for differential tempering? It's used in modern blades to produce a harder edge and softer body, I think my sword was treated that way. The maker through hardens the blade, and then during the tempering process heats part of the blade to a higher temperature that the edge, so that part becomes slightly softer. Is that a modern thing?
@@quintoblanco8746 I got the idea it was modern from the descriptions I've read of the process. The blade his heated in a precise way in one area, say the spine, with a gas torch until the steel begins to change color to blue. As the blue color from the heating moves through the blade, the smith watches until it reaches a certain point, maybe just before it touches the edge, and then removes the blade from the heat and allows it to cool. The result is a blade which is differentialy hard, softer at the part of the blade which was more exposed to the heat, and harder towards the edge. I'm curious, do you know of any pre modern cultures who did this? It seems like it would be difficult without modern equipment like a blowtorch.
@@johnhanley9946 What you are describing is a specific type of differential hardening that is sometimes used in the making of chisels. The more common method is differential tempering by the methods described in the video. The results are essentially the same. Obviously people did not always have gas torches, but I have seen traditional tool makers position the blade in a way where it's possible that the blunt part of the machete acts like a heatsink (dissipates heat to the air) and the edge gets hotter than the back of the blade because it's thinner and closer to the fire. Whether or not that actually does something meaningful, I don't know. The resulting tools weren't very hard. To my mind the water pouring method is more precise.
@@scholagladiatoria Residual heat in the core can be used for that. After the quench the forging scales are removed to watch the color of the oxide layer. The color turns from yellowish to gray. When the edge has the proper color, the blade is cooled completely. It´s not easy. Timing is crucial. I have seen it done.
Quenching causes a change in the crystal structure of the steel. Depending on the content of the steel and the desired product you need to have a certain cooling curve (if you you want to go into more detail "the iron - carbon phase or equilibrium diagram" is the place to look). Cooling too slowly will leave the steel softer. Cooling too fast will cause stress for the material and potentially cause cracks. In "Forged in Fire" the usually use steels that need to be quenched in oil and they make thick blades which are are more critical because the outer layers contract and the core still is hot and expanded. Fun facts: Some modern tool steels even quench in air. Cooling them after anealling need to be really slow (e. g. in hot sand). Steels that are not magnetic at room temperature cannot be hardened by quenching.
On the contrary, Kanbun era swords are almost straight and quite tapered, hence the attribution of this one. Greater sori was found before and after the Kanbun period, though the sori was located in different regions of the blade before than after, in general. To confuse matters, in the late Edo, many swords were made to look like older blades, and could come in any of the earlier styles.
Most of your heat treating information is wrong... Selection of quench media is solely a product of your alloying elements and phase diagram. Oil hardening a water quenching steel will result in an incomplete hardening or no hardening. Harder materials are usually oil or air quenched because of their alloy content. Tool steels and high speed steels are typically air quenched or vacuum gas quenched. If you tried to water or oil harden them they would crack. D2 is a good example of a material that is air hardened, which will substantially outperform any carbon steel in terms of hardness and cannot be water quenched. Similarly, high speed steels, which substantially outperform anything you're likely to be familiar with, are gas quenched and maintain hardnesses above 60 Rc (up to 68+) whilst maintaining toughnesses higher than annealed carbon steels etc. Similarly the quench has pretty well nothing to do with the toughness of the blade, this is primarily associated with the following tempers. For the most part differential hardness used as a bit of a crutch for poor performing steels (poor quality etc).
Very good information! Except on D2. Plenty of carbon steels can get as hard or harder than D2. It seems to top out at around 64HRC as quenched with liquid nitrogen cryo. Most 1% carbon low alloy steels can get to 66 or 67HRC as quenched. None of the simple carbon steels will have wear resistance/edge retention as good as D2 though.
@@FuckYouYouFuck I can't see the point in considering pre tempering hardness, because, especially with carbon steels, you can't use them without tempering because they're about as fragile as glass. Pre tempering all of these things shouldn't be miles off each other in terms of hardness because we're talking about precipitated carbides. The point of high alloy materials is retained hardness, not pre temper hardness... That being said, you can get high alloy materials which will demonstrate substantially higher hardnesses post temper than carbon steels will demonstrate pre temper... ie; in the order of 70Rc but I've never seen a knife made out of them... Not much point I guess, something like an M4HSS blade is nearly pointlessly high performance already and D2 is perfectly adequate for pretty much anything IMO.
@@drew79s Post-tempering hardness or potential hardness is proportional. Working hardness for D2 is typically 58-61 HRC, I'm not afraid to leave it at 62 HRC with liquid nitrogen cryo. Most production knives in carbon steels are fairly soft, 57-61 HRC, very rarely 62 HRC. Well made carbon steel knives can be harder, a high-end kitchen knife in Hitachi White or Blue, 26C3, 52100, or W2 might be 63-65 HRC. They're not especially tough and not intended for chopping through bone, but they will stand up to routine use. The carbon steel outdoors knives I used to make I would aim for a working hardness of 62 HRC. They can be hammered through nails or thrown tip first into concrete. They're not sharp afterwards but they're not broken. The main point of high alloy steels is carbides. Carbides are extremely hard relative to the steel matrix that is holding them. CPM M4 tempered back to 58 HRC is full of 84-89 HRC tungsten and vanadium carbides that give it great wear resistance/edge holding. No point going that soft though, CPM M4 is better left as ~64 HRC, excellent toughness and even better edge holding. There's only a handful of custom makers world wide using super hard exotic steels like CPM Rex 121, Maxamet, Hap 40, S390, etc. and they're more commonly 66-68 HRC, very rarely as high as 70 HRC. Very few makers know how to use it and far fewer are willing to grind it.
@@MtRevDr Too expensive to risk. Hand crafted, and probably pride pieces to be displayed to guests. We're not talking nobility here. In Asia crafts people were, in some places still are, considered just a step above merchants,who are just a step from those who handle dead bodies. Not exactly rich people.
@@MizanQistina You have to remember that traditional smiths did not start with degrees in metallurgy and thermodynamics; they experimented with whatever was available, remembered what worked and passed it down to their apprentices who repeated the cycle often with materials their teachers dd not have. Yes, they often used alchemical "reasoning" to do their testing; "Horses are strong and urine has a strong smell, so maybe using horse urine will lend that strength to the steel". Sounds silly to us maybe, but there's also the fact that hot steel will absorb nitrogen from materials like leather or urine producing a slightly harder, tougher, rust-resistant "case hardened" nitrided surface. This was apparently discovered using similar alchemical "reasoning".
@@markfergerson2145 Proper chemistry had to start somewhere, after all. The only difference between science and screwing around is writing down the results.
@@eagle162 Very true. High expectations are the fastest route to disappointment. Damn, now that that sunk in, I really should take my own advice and not be so invested or so critical.
@@eagle162 Proof? Sources? As I understand it the "Japanese development" was wavy or irregular hamon shapes, not the use of clay differential hardening. Chinese swords were using clay to produce straight hamon long before the Japanese, as early as the Han Dynasty (206 BCE-220 CE)
People need to understand that geniuses are a myth. Ideas come from your surroundings and if something makes sense multiple people will come up with it.
China copied somebody else's good ideas? Where and when have I heard about that before? oh yeah always from everywhere joking aside if someone is doing something better than you it's best to learn from them to improve
There is a disseration by german archaelogist Stefan Mäder ("Stähle, Steine und Schlangen", Berlin, 2001) , who brought 3 european blades from the early middle ages to Japan and there these blades were polished by japanese sword polishers and also shown to japanese sword smiths. He could prove that (here in quite short summary) the techniques (refining/folding, partly clay quenching and to a certain extend even polishing) were pretty much the same in both areas, one blade even had a clear hamon line. I would strongly recommend to read his work, every detail is thoroughly described and underpinned. I think it is really admirable that he brought these two cultures together in this context and didn't limit himself to the usual comparing of blades. Sadly, since the document is in german, I guess his work isn't that well known worldwide.
I have long thought that the most unique part of Japanese bladesmithing was not the steel or laminating or clay hardening, but the polishing.
"Context Squad" showing up as soon as they can :P
Depending on circumstances :v
It's not only differential hardening that gives you the difference in edge vs back. You can also use differential temper. I even guess that method was used on some of the curved blades you've shown. The Japanese use it too, using a heated copper block. Semi modern knife makers use a torch to draw back the spine to a lower hardness (edge in water, heat to the spine).
Differential tempering seems really advanced. I wonder who were the first to do it.
@@edgarburlyman738 It's got to be old, since iron axes were one of the first iron tools, and differential hardening/tempering is still commonly used today on those. The blacksmith dips only the edge in water, while the back is still glowing. Then he takes the whole thing out and observes how the residual heat from the back tempers the edge. When he's happy with the result, he dips the whole thing in the bucket to arrest the process.
@@edgarburlyman738 It's in the oldest blacksmithing manuals that I have seen, and I'm sure it's much older than that.
There is medieval European art of blade smiths using red-hot iron rods to differentially temper arming swords and other double edged blades. Not sure on the era but I think it was 14th-15th century.
@@toddellner5283 I think you and bakters are talking about differential hardening, which isn't what I meant. I have heard it called tempering before so there might be some confusion there. I mean having an actual spring temper in the body of the blade, while also having the edge as hard as possible. What Brenda said might be it though.
You learn something new every day ;-)
Thanks Matt, useful and interesting as always!
Most one edge slashing/chopping blades are quenched in water because the softer back will absorb the shock when slashing/chopping. Malaysian way is to dip the edge first and slowly the whole blade into the water. Need some skill on timing, to hear and feel if something is wrong. Slashing/chopping one edge blades don't need to be springy/flexible because obviously it do slash and chop, the cutting point is so small, the momentum/vibration effect small area and spread to the back of the blade.
Double edged straight weapons need to be springy/flexible because it is mainly to be used for stabbing, if not springy/flexible it will break, the stabbing point carry momentum/vibration to the whole blade behind the stabbing point. Double edged straight blades cannot be quenched by water because they are usually thinner than one edged weapon, the quick cooling from water might make the blade disfigured and break. Keris for example is a stabbing weapon, quenched in oil, usually coconut oil.
My late uncle was a part time blacksmith, I used to sit by and watch he make weapons/tools.
That's very interesting. I thought it was the other way round, basing on the observation that the Estoc is very stiff (and in fact, some of them even have diamond shaped cross section), as you don't want energy in the thrust to deform the blade, and instead be transferred into the target. Then again, the Estoc is a highly specialised weapon, and perhaps would be wrong to conflate it with other more "generic" cut-and-thrust swords.
@@Pallyrulez That weapon need to be stiff to absorb the momentum and spread it evenly to the back and still maintain it's shape.
The reason why most spear head are short is because of this. Even small blade spear head are usually wide with diamond or "eye" shape, not a thin blade. If you want a long spear head you can't make it in thin blade shape, because it will break on impact.
That's also how the American Bladesmith Society's basic course teaches it. Sometimes it's oil (or Goddard's Goop made out of oil, paraffin wax, and old hydraulic fluid), but the same idea is used.
One thing to remember when discussing weapon designs, most ancient cultures don't design their weapon based on scientific reason, they're more into belief in magic and such thing. While maybe certain way of designing the weapon is for doing certain job/purpose, it is not always true.
For example, the Keris, most of Keris are wavy shape, or serrated, scientifically it is better for hacking and slashing because the contact point is smaller, so the energy focused on the point. But, Malay people designed it NOT to slash and chop, it's for stabbing. The wavy part will give irreparable damage to the flesh when stab, twist and pull out.
There is a belief where certain amount of the wave give certain amount of magic, curses and suitable to fight against enemy who use certain type of magic and curses. For example, 7 wave (we call it Luk) will demand 7 souls when the Keris coming out from it's sheathe. After kill one, it wants 6 more, and the 6 souls might be innocents. That is the reason why only certain people have 7 Luk Keris.
There are many other mystical beliefs in weapon making in South East Asia. So we can't view at them with wholly logical and scientific thinking, must also consider mystical belief behind them
Some schools of Japanese swordsmithing have the whole blade covered in clay and change the thickness of clay at the edge/s. This allows for more detail to be drawn onto the hardened edge. Soft back has its own problem of getting pieces cut off when the swordsman has to impact with the back edge. Lots of schools teach sliding the back on the fingers and scabbard at sheathing. The large chip formed on the back can cut the fingers as well. Some Japanese swords have what they called full hardening with large areas of the back hardened.
While differential hardening was occasionally used, it's quite likely that differential *tempering* was used more often. It's simply easier to harden the whole blade, but then heat up only the back, while even using some cooling procedure on the edge, in order to prevent it from softening. (Dipping the edge in mud or sticking some vegetables on it.)
Also, I would not assume that the use of clay covering during hardening is exclusive to Japan. It's a very logical solution to a very common problem. Especially a thin edge is vulnerable to decarbonization. Covering the blade with clay prevents it and it also prevents the scale from being formed.
It really seems to me that Japan, with its reverence for tradition, simply preserved plenty of historical techniques, while the rest of the world quickly forgot them, as newer and better solutions became available. For example, in order to replicate many historical blades from historical materials, it's necessary to use folding and reforging approach extremely similar to that of Japan. No reason to assume that other parallels are less likely.
If you know of any decent sized arrowhead collections, it would be pretty simple to get some Tsubosan HRC testing files and test the front and back for hardness difference.
I'm a CNC machinist and not a blacksmith, but can someone explain the use of files to test for hardness to me?
I'm used to several concepts for testing material hardness in manufacturing settings, but none of them use files.
How does it work?
@@danorris5235 With modern files, they have the hardness listed. You start with a "soft" file, and run it along a corner - if the tested metal is harder than the file it will "skitter", while if the file is harder it will "bite". (It's like rockwell testing, but using files of differing hardness instead of the listed items)
It's a home smith's "quick and dirty" way to see if the quench & temper took properly.
@@muninrob Thanks. This concept makes total sense to me after an explanation.
Thanks for taking the time.
I am working on a dagger and it has an auto hamon. I quenched in parks 50 with no clay but because of the thickness of the base it had enough mass to slow the quench. So it can be unintentional to have a hamon without aiming for one.
PBS did a fantastic episode on NOVA called 'Secrets of the Samurai Sword'; I highly recommend watching it. It followed the forging of a Japanese blade in the traditional manner by one of the few remaining great Japanese swordsmiths. That craftsman used layering of different 'tough' and 'hard' metals in the folding of the steel during the forging process. It took several weeks before the 'clenching in water' was attempted which instantly transformed the straight blade to the signature Katana curved blade.
Agree completely
Man I'm glad to see that tulwar and parang Definitely some of my favorites in your collection.
A brief summery of heat treatment as a toolmaker with over 30 years work experience I often cringe at lots of novices u tube videos this one is well done but if you are trying to replicate anything that was achieved by the old armorers just remember that they knew how to get the best result out of the materials that they had at the time. But if you are using modern steels read the manufactures spec sheet and understand that modern metallurgy is a very exact science and trying to use old techniques on modern steel may well lead to cracking and other problems there are lots of different steels and if the specks say air oil or water hardening that what is required . Good luck
I've made a few blades and polishing in japanese style. The edge is hardened and forms martensite, the back is in the pearlite state which is considered unhardened steel. The transition between those can show as a line when polished and etched with ferric chloride which is effective at showing grain structure transitions and is also used on cross sections of welds to study penetration and heat affected zone. It's the polishing technique that makes it look white and you have to carefully follow the hamon line when doing the final polishing with the hazuya stones on the edge, jizuya are used for the back. This is because of the different crystal structures in the steel. The different hardness makes the polishing stones cut differently, the jizuya stone I think is higher grit than the hazuya and therefor gives a more mirror like finish and the hasuya is a bit cloudy. The kissaki(tip) is polished the hazuya only which therefor can make the hamon shades look inverted to the rest of the blade where the softer perlite structure appears whiter than the harder martensite edge.
An other interesting thing with the water quenche is that much of the curve in the blade comes from it. When the edge rapidly cools it shrinks a little bit and the blade bends forward but as the back cools more slowly it shrinks more than the edge and the blade ends up with a backwards curve. This does not happen in oil though, in oil it stays curved forward and the hamon line does not follow the clay line like it does in water, it seems to follow the blades thickness instead. I think this has to do with the water and oils boiling temps and heat transfer properties. I'm just guessing here but I think water might draw more heat out of the exposed steel but the lower boiling temp and agitation creates an air pocket around the clay and cools that part slower than the oil. Oil has a softer cooling on the exposed edge with it's higher boiling temperature but at the same time also cools the clay area faster compared to water.
Japanese swords where also often laminated with a soft iron core to prevent them from snapping in half, the edge could crack but the core and back would bend and stay bent which could be a benefit but also a drawback as they wasn't very springy and bent easily and required more skill to use.
I differentially harden using tempering rather than quenching. In drawing a temper, you quench and then reduce the hardness by partial reheating - you grind the steel (or part of it) clean and the color of the oxide that forms on the steel during reheating indicates the heat. To do this, I water-quench and then partially reheat the blade using glowing-hot iron bars to heat some parts of a blade more than others.
High-carbon steel that has been fully quenched even in oil must be tempered or it will be very brittle, surely this was done on European swords. Salt water is another option for quenching, with a hardness between fresh water and oil. Sometimes blood was used, more for magical superstition than it's actual value, but I'd guess it would be another shade between salt water and oil.
One nitpick about water vs oil hardening. It has much to do with the alloy and how fast it NEEDS to cool in order to harden properly. Water quench steels will often not get hard at all in oil, while oil quench steels are almost guaranteed to crack when quenched in water. Also some steels can be done with either, though for most it's not an optional choice. And, some are even air hardening. Ask Todd for more details.
Great video. Well said.
I would love to get a antique kukri that I own tested for edge hardness. I did a restoration on it, and decided to re-sharpen the blade. It is one of the hardest most difficult to sharpen steels I have ever experienced, and I have hand sharpened allot of modern knives and swords.
The only video, that was worth to look what's going on at youtube today...
Love your videos Matt. Even if I have to stay up late to view them early...
3:39
This is a kind of generalization that led to misconceptions. To correct Matt here, the edge of a Japanese blade Would be more prone to chipping if it weren’t for niku/appleseeding. Niku on Japanese blades is very overlooked as it is the the type of blade shape the would have been taken into battle. It basically keeps more material on the edge so it wouldn’t chip as easily. Many antiques nowadays have lost the niku due to centuries of regrinding, resharpening, and polishing. Just something to keep in mind.
Edit: the reason why niku is very underrepresented in modern times is because modern Chinese reproductions make katanas for people who want to do simple backyard cutting with soft targets (water bottles and tatami) so it would make sense for your product to have an edge to cut soft targets better.
And it is said that removing the Niku from a blade would essentially ruin it.
One might add that the edge is polished sharp, not ground. This is important as for a chip to develop, there needs to be a micro chip to start the process. The smoother the edge, and almost total lack of grief lines, the less it is prone to chipping or cracking. This philosophy carries forward to Rockstead Knives today, that are hardened up to 67 Rockwell.
I also believe to have heard somewhere that the niku was sometimes segmented (kind of like a row of teeth) to keep cracks from spreading along its length.
Many just enjoy competition and winning in that particular competition. Japanese swords of apple seed grinding like Ichimonji school of Yoshindo still exist. And he enjoyed another fame of helmet cutting with such fatter edge. Certain tatami cutter use flat grinded blade for thinness and marvelous cutting ability with tatami. So, horses for causes. It is showmanship for many.
In my experience, the fatter shape cannot reduce chipping significantly. A sword/katana could fight a few warrior(like 7) before getting too blunt or chipped to kill more or cutting into more flesh. Killing enemies is an expensive business. So, the film 7 samurai expressed the need of using many swords in war.
Matt is correct that steels that are more hardened will be more brittle. You are correct that the comparison between Japanese and European blades is an over generalization.
Thanks for the breakdown, it's a good recap, but also there was a lot of new information for me to think about!
Suggestions: Korean weapons, or the sosun pattah sword (it looks like a recurve sabre, which is really intriguing to me!
Does the fact that the edges in euro swords would cool faster, thanks to them being both thinner and at the....edges of the sword cause them to be a bit harder than the spine and internal meat just by virtue of physics of cooling ?
Yes.
not absolutely no because they are not generally thin when quenched, much of that is ground in because quenching thin steel easily cracks or warps it
Yes, definitely. If the edge is thin when quenched it will cool much faster than a thicker spine or centre. 0.5mm thick vs 6mm thick can be the difference between 64HRC and 40 HRC, depending on steel alloy and quench medium.
@@andyc750 theyre not as thin when they quenche, but the edges are still nuch thinner than the core and the effect still applies.
@@louisvictor3473 not always no, depends on if bevels have been forged or ground in by then, many now grind them in after hardening to stop potential cracking and warping
Differential hardening can also be done by use of insertion or lamination, where differing carbon content steels are forge welded together, and the different carbon contents result in different as-quenched hardness, the whole tool then being uniformly tempered. This was common practice in American, UK, and Nordic scythe blades, where a laminate of high carbon steel comprising the edge and medium carbon spring steel comprising the back were clade in plain iron. This method had the extra benefit of taking advantage of the way that rigidity scales cubically with changes in thickness, which is why a high-hardness safety razor blade can flex so much without breaking when an only slightly thicker straight razor edge can chip from an accidental impact with a faucet. By having the high-hardness edge supported by iron you achieve both high hardness and excellent edge retention alongside excellent ductility/toughness, and the spring steel at the back of the blades helped them hold their proper shape instead of taking a set (which they still could do if used poorly--they're tools of finesse.)
Ah, yes, my favorite piece of bladesmith's equipment: the teapot.
Educational as always!
That’s a nice sword 0:52
Quick point of discussion. The kukri being differentially hardened, the back and belly being softer. do you think the “notch” at the base of the blade acts like a hinge, or a place for the shock from a strike to go into the softer steel instead of the hard brittle edge? I think this may be the the elusive purpose for the notch. Would like to hear from others.
I don't quite understand what you mean, maybe you have your terms mixed up.
Thanks, Phat Beastin'.
Matt, don’t forget to mention quenching in salt water! Salt water quenching is best for medium carbon steel. Too low of carbon will have no effect. To high carbon will cause warping cracking or breaking. From what I understand medieval steel tools like a draw knife or axe bit for example may have been medium steel quenched in salt water.
It might be worth noting the choice of what to quench with, depends a lot on how easily hardenable the steel is. As the carbon content goes down, you need a faster quench. So with modern high carbon steels, hardening in water can go right past sanely hard into warped, cracked, glassy junk.
Doubly so in tool steels. Some tool steels are even considered "air quenched". AKA you heat them up, and "quench" by letting them cool in the "not furnace".
The other thing of note is that you get differential hardness (not necessarily hardening) by having different steel/metal at different places. This is another technique common throughout the world, but again, one used by Japanese blades a lot. Katanas are typically 3 types of steel, the core soft steel, the edge hard steel, and a shell of something in between. Then forge welded together and differentially quenched. But, again, different steels isn't unique.
You can achieve different mmetal properties in different ways, the most common today, is actually case hardening. You pack the item in graphite or some other fine carbon, heat it, and the outside absorbs some of the carbon into the metal crystal structure, but only around the surface.
European swords mostly stopped using a lot of these techniques, not because they were lazy or stupid of course. Once you have hardenable spring steel, you can just make the whole thing out of that. The ultimate hardness of the edge might go down a bit, but the trade off in every other blade property is well worth it. Depending on use case of course. Context context context.
I'll just be over here with my collection of tungsten carbide edged knives if anyone wants to claim katanas are absolutely the best of the best.
Hardenability has more to do with alloying elements like manganese, chromium, and molybdenum.
A modern steel like Hitachi White #2 has very high carbon at 1% but also needs a very fast quench because it only has 0.25% manganese.
@@FuckYouYouFuck yes, but there was only so much I wanted to fit in a RUclips comment.
Odd question but do we know approximately when oil began to be used? Just some randomness that jumped into my head while watching lol. Cheers!
Thanks for bringing this topic up. I have also seen fine temperlines along good wootz shamshirs (not all) exactly as you described. Any idea how a curved blade can be differentially tempered like that without clay? Have been looking for it in Persian sources, so far nothing found..
This is a figure from a book by Kamil Haydakov titled: "Shamshirs: Old sabers and the secrets of ancient sword making" published in Moscow, 2013. It shows the variation of heat treatment patterns on shamshir blades. Some may suggest usage of clay, but I am not sure.
drive.google.com/file/d/1b1PeZjdmB1zSqS0G2pIQq79puWxdfRWF/view?usp=sharing
All swords are differentially hardened to some extent, but you would need to take a cross-section of the blade to measure it.
The surface that's exposed to the oil or water will get harder than the core of the blade as it's cooled quicker. The thinner edge especially will cool much quicker. It's not going to be nearly double the Rockwell hardness as in Japanese swords, but I would expect to see a 15 or 20% difference throughout the cross-section (unless the blade is very thin).
Yes that's a fair point, though there is a big difference in the degree of 'differential'.
That katana has beautiful shiny blade. Thats the second nirvana shirt i seen you sportin...
I think.
will you also discuss differential tempering?
Saw a video years ago of some natives using some very very large kukri shaped weapons to chop heads off of cattle at the neck. Never could find any more information on those blades, I was wondering if you had any knowledge of this. One swing and that was all they needed, it was a clip from a nat geo documentary I believe
Probably made from old jeep or truck suspension leaf springs.
I have seen talloires hardened with a water-soaked sheepskin the process is to draw the hot blade Edge through the sheepskin quenching it I do not know how common the practice is however that would make it work and it uses the least amount of water which makes sense because we're talkin about desert people water is a precious commodity use as little as possible polluting it
I think part of why Japan emphasizes and is known for the hamon is that there was a time where swords were banned, so, craftsmen needed to show that they were making works of art, and not just weapons. So, the hamon became an artistic feature, so that they could maintain their craft.
In the talks I have seen by the owners of antique Japanese swords, the claim is made that the quenching water was always at uniquely cold. Is that an issue?
The blade that you're holding in the opening is very short. Are you able to share its dimensions and maybe some more details about it?
I have a strong interest in 'short katana' or kodachi, as they're the preferred sword of my martial style, but finding them is hard.
What do you make of the interaction of the differential hardening and the low[er] carbon back and high carbon jacket/edge? It seems to me that the clay and quench style stems from the construction method, and likewise, the swordplay from the characteristics of the blade.
I was going to point this out as well. Different carbon steels have different hardenability. It might be possible that clay was needed for Japanese style swords with different carbon steel pieces wielded together where as monosteel blades had no need for clay.
You can read Doctor Larrin Thomas's article about quenching that just came out in knife steel nerds. Modern makers use engineered quench oil that often quench nearly as fast as water. The difference is just the quench speed at certain times doesn't strain the blade as bad. Most antiques would have used very simple steels. Alloy let's a steel harden slower. Without alloy it is common to get what we in modern times call an auto hamon where the hamon forms because of the thickness of the blade does not allow for the thicker part to harden. When they happen they can be some of the most dramatic. What I have come across from sword makers they say it is likely that European swords were not fully through hardened since it is extremely difficult to even get 1/4" to through harden with very simple steels. If there were trace alloys if things like Manganese or Chromium then it would have been easier. The clay of a hamon is just painted on and that little bit is all that is needed to slow things down. If it is out in to thick the heat will creep back out to the edge and make it very shallow or have unhardened spots. Don't ask me how I found out. This heat creep is what is called and auto temper. Speaking of tempering.... Hardening in water can give you max hardness and it is needed for full conversion with ultra simple steel( carbon and iron is as simple as steel gets). So long as they understood tempering that is the way hardness should be brought down. To control it by under quenching has a lot of negative side affects. As far as I know the main reason European swords were more springy was that they had a lower carbon content. That is the best way to gain better toughness since high carbon steel will not be as tough as a medium carbon steel even if they are at the same hardness. The biggest advantages we have now is our ability for precision heat input. We can get more out of the carbon and alloy by holding it at just the right temperature to let everything desolve into solution without growing the grain more than necessary. The condition the steel is in makes a big difference as well. There is a reason that some of this stuff had myth and legend around it. Things like seeing shadows running through the steel show phase transition where the steel gets cooler as the phase changes even though it is still heating. The trained human eye is only good at telling temperature for about 200 degrees because of how our eyes adjust to light. Finding a spot to start paying attention and then things like a dark moonless night help get closer. 25 degrees can make a big difference in how a blade performs. With the limited tech ritual was how you made the best possible blade. Blades are still one of the highest performance uses if steel. A common blacksmith never built fine blades like in the movies.
If you ever wanted to do a steel theory video I think there is a good chance that you could get Larrin Thomas on your show. He does other podcast and RUclips videos and is the best expert in blade steel out there right now. I posted your Seax video and he was one if the first to respond. If not I would crowd source info on the forums from sword makers. I know most of them well enough to sift and could put together a list of info for you or better yet give you an interduction and I bet they would help you out. A lot of those guys have done some serious research and have made real wootze and pattern welded stuff and would love it if someone was putting good info out there. You would have the best researched thing out there on any well followed format. You are great at making it understandable and you have the historical "Context" to put the whole package together. You can reply back to this or find me as StormW on Blade Forums in the makers area. I can tell you a fair bit of modern theory and how stuff works but I'm not a true expert although I know more than most. I am still open to make you something out if modern steel as payment for all the hours of enjoyment I have received. Interest in what you talk about has even shaped what I did for a living and my hobbies of bow and knife making.
Were I making a sword using modern steels I'd consider air hardening tool steel like S7 specifically to avoid breaking the blade during the quench.
10:18
To make things clear, China was the one to bring the folding and differential hardening to Japan.
It went from China to Korea and then to Japan. China and Korea were very tight with each other and this will be important later. In around the 9th century, japan caught word of China and Korea making stronger blades. They the imported many smiths from both lands to teach their smiths how to do it. In the following centuries, japan would improve on the technique and would end up making better swords in this style.
Fast forward to the Imjin war (1590s), Japan is beating Korea on the land but not at sea. The Koreans beat the Japanese through naval technology but then imported Japanese smiths to teach them how to make better swords. They realized Japanese swords were of better quality and they had not improved the folding method because China didn’t either. It turns out, the Koreans were only folding 2-3 time opposed to the Japanese who innovated and were folding over 10 times. I speculate that the method of folding from the 9th century only did a few folds but since then, the Japanese figured out more folds mean less impurities. Hence why Korea and China then had to learn the Japanese style of forging all those centuries after China introduced Japan to it.
Differential hardening was actually indigenously developed in Japan, it was the folding of steel that was imported. Differential hardening would inevitably curve the blade, and during the time period in which the Japanese were importing sword technology from China, all Japanese and Korean swords were universally straight, while the Chinese blades of the time that were curved were made as such during forging, not quenching. Much later, after the Japanese developed differential hardening, the Koreans imported that technology through trade, and long before the Imjin wars, at that.
@@Vlad_Tepes_III Didn't the Danes also use differential hardening on their axes?
Some Japanese school do not understand purity of steel. On the whole Art sword appreciation enjoys areas of great difference in concentration and composition to make interesting pattern in/on the sword body.
From museum antique it can be seen that the earliest example of Chinese and Japanese swords have many folds. Modern Pilipino blades still have very few folds. People fold steel to obtain interesting visual pattern often. Some (cheap?) Chinese swords have added hard edge and no metal folding.
Some European antique and modern Western blades have beautiful geometric pattern.
Japanese sword polishing has improved greatly. Some fine patterns the smiths of old induced into their blades could not be seen at their time. It is an enjoyment to see quality steel pattern. I have blades that look like cold ice and blades that look oily(muji hada). Some Japanese did not care about sword body patterns. The use of Western imported steel frequently produce swords that do not show steel pattern. They are known or coded as mirror pattern. Some of these can show a hada or grain pattern with great modern Japanese polishing.
With modern abortion culture, lots of people enjoy throwing their babies out together with their bath water.
Therefore perhaps we have a flying baby culture or 2.
@@MtRevDr All this was nice to know, for the most part, but how was that last bit about abortion relevant?
@@alexsitaras6508 They did, and they laminated their axes as well. A harder, but more brittle, higher-carbon steel core sandwiched between two tougher lower-carbon steel laminates, with the central layer being larger and protruding out from the laminates out in front. It is this core that was hardened and sharpened to form the edge, while the lower-carbon steel laminates protected the brittle core from torsion and impacts.
Weren't some swords from Viking Era and Migration Era also differentially hardened?
Never heard of that before. Can you post a link?
@@avd-wd9581 I don't know where I heard that, so I'm not sure - that's why I was asking in the first place.
The only serious info I could find is this study:
A METALLURGICAL STUDY OF SOME VIKING SWORDS
core.ac.uk/download/pdf/268620377.pdf
From what I've read, some swords were fully made of steel, others of iron with added steel edges, and some may have been hardened.
In some cases it states that the edges have been hardened - but often there is no sample analysis from the interior of the blade.
I'm also not competent enough to properly interpret on my own the results of the metalurgical analysis.
For an example, look at pages 10 and 11 of the PDF (130 and 131 of the study).
@@XCodes Yeah, it wasn't pure iron, it had impurities, including carbon.
Perhaps the term "iron alloy" should be used instead of steel, the same way "copper alloy" is now often used instead of bronze.
Love me a differentially hardened blade.
Why though?
@@FuckYouYouFuck cuz in a katana guy
@@erichusayn I'm a modern high tech alloy katana guy. Once you've had 2.75% vanadium you'll never go back.
@@FuckYouYouFuck I own quite a few of those modern ones as well, but definitely like the traditional looking hamon and hada to appreciate
There's art of European medieval art of differential tempering of double edged blades by placing red hot bars down the centre of the blade. Tempering lessens the hardness slightly and allows a more durable/springy steel to recrystalise.
Could you apply a thin layer of clay so the back cools only slightly slower? Giving it alittle more flexibility but keeping it spring tempered?
From what i know, traditional tamahagane katanas have steels with less carbon at the spine and sides ? Not sure if that could be tempered to a spring temper ? Thats why they had to be so thick there, to make up for that.
@@vedymin1 AIUI blades made of different steels were a relatively late development in Japan, with edges, backs and sides of the blade forge-welded of different steels specifically to obtain different hardness and "toughness" in different parts of the blade. (Whether using different steels began in Japan or wherever is AFAIK unknown.)
Allegedly toward the end of traditional sword making in Japan they had advanced to coating blades thickly with clay at the back and less on the edge to allow the edge to cool quicker than the rest but not "instantly" as it would with no clay. That took some of the hardness from the edge but also made it less brittle.
There are so many conflicting sources, and so much "lore" touted as fact that it's difficult to know for sure, but the physics does make sense.
What I find fascinating is that traditional sword makers everywhere for centuries discovered all of this though trial and error, refining their techniques without needing to know any of the modern details of alloy content and the thermodynamics of crystal formation in iron alloys, doing things like identifying critical stages in quenching by eye. How was tempering developed? Who first took a forged and quenched blade and thought "if I heat this back up not quite to redness and let it cool by itself it will be stronger", or was it accidental i. e. storing quenched blades near enough the forge to temper them and discovering later that they were stronger?
Cheers interesting video
Is quenching swords in snow only thing in fantasy, or was it done somewhere for real?
This could be a modern thing, but i have seen swords quenched in narrow trough, allowing the smith to lower the hot blade lengthways into the water/oil edge-first, where they hold it for a while so that only the edge is in the liquid, before they finally plunge the entire thing into the now somewhat warmer water/oil to quench the rest too.
Here in some parts of the Philippines, it is called SUGBO or SUGBU method. I am not sure if it's a modern way but I think it is most likely a traditional method.
@@oxvendivil442 Thanks, I can look that up now :)
What about quenching in blood?
I’m trying to make a knife and was told I would get a harder steel that way
Blacksmiths in Europe have differentially hardened and tempered tools for a terribly long time. It's one of the first things an apprentice learns when making punches, chisels, and other tools. It only makes sense that the same technique would be applied to specialized cutlery.
What type of steel is on the lk chen sword? There are a few choices and i like the shine on yours.
Similar to the Nepalese method of partial blade quenching is the SUGBO method. In some parts of the Philippines it's called (sugbo) method and I think it is due to Chinese, Indian, and Middle eastern influences; dipping the edge on the quenching tub first and letting the whole blade cool a little before dipping the whole blade. I think as far as China is concerned they started with a similar process to the sugbo(classical period like han dynasty) and then developed the clay insulating method during (medieval period like sui and t'ang dynasty) which latter got to Japan, after that China returned to the sugbo method in the period that they were influenced by steppe sword designs ( like song, yuen, ming, and qing dynasty) and after a while some copied Japanese sword designs and clay quenching again (during ming dynasty I think). I think china had spring steel, differentially hardened(sugbo), and Differentially hardened(clay) blades pretty much all at the same time, the only difference is the predominance of one or two types/methods at a given time and for certain types of blades. An example is during the T'ang dynasty, they had spring steel and differentially hardened(clay) swords predominantly and at the same time had swords and other tools using (sugbo)like methods on a lesser extent/amount. Korea probably followed Chinese trends but adopted less steppe influence in their sword/sabre designs(maintaining older Chinese designs while changing it a little bit and with some Japanese design influence). The (sugbo method) was less controlled, less artistic than the clay method and produced more utilitarian looking but just as good blades, something the Chinese needed when arming a large imperial army with munitions grade weapons.
Does anyone know of any good books on this matter? I see the edge quenching is abundant in Southeast Asia.
I’m interested in doing it on a small knife. As far as I understand, After the edge is quenched in the water, the residual heat in the blade tempers it. And I see them consistently putting the edge back into the water lest it tempers it too much. Thanks in advance.
Differential Hardening with Clay(Chinese:覆土燒刃) is originated in China, not unique in Japan.
Many Chinese swords also have differential hardening, the oldest ones can be traced back to Han dynasty. You can also ask LK Chen if you like.
Clay tempering did not begin until about the mid-Kamakura period with only at the end of the period did it start to resemble what people recognized today, recommend to look up" 唐刀不算日本刀祖先 但中国古刀不逊任何日本刀".
Kukri is also quenched differentially and in the water
Japan has a quite unique way to do differential hardening. They utilise clays to control the exact pattern on the blade. I wonder if similar techniques had been practiced elsewhere or not.
I think the Chinese taught the Japanese clay differential hardening method, but the Chinese preferred the "suguha" type(straight pattern and not wavy) of "hamon" on their blades, probably partly due to the way Chinese T'ang era sabers's bevels were designed making the hamon less visible to begin with, so making fancy patterns was useless; while the Japanese treat the suguha pattern as very old and traditional.
@@oxvendivil442 no it's a Japanese development.
Edit required; Japanese blades are fully coated in a clay mix prior to heating and quenching,thinner along the edge where the swordsmith also adds adds clay in fine lines to create activities like 'ashi'.
The hardened edge section of the blade is the 'yakiba'.
The 'hamon' is the outline of the 'yakiba'.
Your description is not accurate or well researched.
The Japanese method also gives their blades that iconic curve..
The curve comes when it's quenched it warps the blade giving it that curve.
@@jeremynedrow7003 what did I say that was different??
@@nimrodthewise836 Nothing, he wasn't refuting you, merely elaborating on what you said.
@@Vlad_Tepes_III it wasn't an elaboration, it was iteration..
I wasn't saying you were wrong just adding my two sense 😂.I think you took it the wrong way.
Thats an actual antique katana ? If so....nice :)
I have a Bhutanese pata(n)g that looks like it may have been edge hardened as well.
is there a benefit to differential hardening?
With historical weapons and lower quality steel, yes, maybe. It could make for a hard cutting edge and tough spine, which is more important with low quality steel. It would allow the sword to bend, and stay bent, rather than snap. The other approach is to fully harden the blade to a lower hardness so it is not as hard but very elastic.
With modern steels there is no real advantage to differential hardening and is mostly done for aesthetic reasons.
@@FuckYouYouFuck thank you!
What is the difference between mono steel blades, and poly steel ( and/or steel and soft Iron blades(( ie. The Indonesia Kriss ect.)) And water quenching?
It's a bit self-explanatory. Mono-steel is a blade of one alloy of steel. Laminated steel has different alloys forge welded together, most commonly a high carbon steel for the cutting edge and lower carbon steel or wrought iron for the spine or cheeks of the blade. This is typically done for lower cost or in some tools ease of sharpening. In some blades like a katana the different alloys may be used to impart toughness.
What is the misconceptions about Knife/Sword making in medieval period?
If I understand your description of Nepalese kukri hardening, it should actually be less severe than the Japanese process, not more. The kukri's spine isn't being quenched at all, and there's a transition from hard (at the edge) to less hard (just past the edge) to not especially hardened, with more time built in. The Japanese process stresses the entire blade at once, and has a single, defined boundary between the edge hardening and the rest.
The kukri method does tend to warp the blades though. Thinner wider blades more and thicker narrower (sirupati type) less. Also the tip and edge of the blade near the handle is left softer.
I differential harden chopper knives all the time.
Can you differential harden and spring temper? Oh shit...sorry you just mentioned it
I like to compare katana with smallswords for both their social status/wealth indicators and tools of 1v1 duel culture.
I always had the belief that medieval europe used blood or a tea like infusion of water and leaves to quench? but I might be mistaken
More often than not axes are not so much differentially hardened as they are made of two different materials usually a high carbon and a low carbon steel so that when quenched the high-carbon steel turnstep spring steel and the low carbon steel remains Steel or soft Steel in this case both steals our quench hardened it's just the high-carbon steel takes on a spring steel qualities will the low carbon steel does not have enough carbon to harden as hard I've never seen high carbon and super high carbon because well the super high-carbon would simply shatter I do believe it is be called because high carbon steel is considered spring steel super high carbon steel is either considered glass or Pig
Steel metallurgist (and hobby bladesmith/blacksmith) here. Matt - Please take a class or two about metallurgy. I think it will help you a lot.
Generally speaking with blades, when we talk about hardening we are looking for a change in phase, specifically looking to form martensite. This is a very hard and brittle phase, and when tempered becomes less brittle at the expense of some of it's hardness. When we talk about softer spines we are not (typically) talking about martensite with more of a temper, but in fact a phase that is not martensite. Typically this softer phase we want to be pearlite, but bainite is also a good one to have. Both pearlite and bainite can also be tempered, but being much softer (lower stress) than martensite, it is not as critical. Quenching in water vs oil does not change the hardness of the martensite (at least in an appreciable way). What it changes is the amount of martensite formed. If one were to look up the TTT (or CCT) diagram for a given alloy you will see that you have a set amount of time to cool from the critical temperature (different for every alloy; "non-magnetic" is not good enough as critical is often above the Curie Temperature) to the martensite start temperature, or at least past the curve of the TTT diagram. Things like 1095 have less than 1 second to get down to below the curve in the TTT, but alloys with more Mn and Cr (among other elements) can take several seconds, or even minutes to pass the curve and still form 100% martensite. This is what can lead to great differential hardening. An alloy matched with a quench media and blade geometry that allows the edge material to "beat the nose of the curve" but not the spine. This can even happen without adding any clay or quenching just the edge, if the spine is thick enough to retain heat long enough to miss the nose of the curve you can get an "auto-hamon". Obviously the subject can get a lot more in depth, but there is a little more information for anyone wanting to read this.
The Curie point thing makes me wonder; we know all of this due to modern science, but did ancient smiths ever use lodestones (natural magnets) to test their steels while working them?
I suspect they did not, because it isn't actually reliably helpful. Recalescence and decalescence, on the other hand, show you exactly what you need to know, even if you don't know (as they wouldn't) that you were actually seeing the steel pass through the critical temperature.
@@markfergerson2145 They probably did not. A good smith can use the glowing color to determine the proper temperature. I had some training in smithing. The instructor could see from 10 yards away when the steel was not hot enough for the quench.
Modern performance tool steels often are less forgiving. Keeping proper temperatures and cooling curves is crucial. Typically they are not hand forged or heat treated in a simple forge.
Is it possible to reduce the brittleness that results from a water quench through the tempering?
By for instance tempering at a slightly higher temperature?
Sort of - the tempering almost completely overrides the quench, so you don't need to adjust. Japanese swords were not tempered. Highly skilled American blacksmiths and cutlers making the tools for the Industrial Revolution typically used water quenches for most things except for small/thin items. I'd imagine the Europeans did the same. The thickness of the steel affects the quench just like the quench medium does. If you're going to temper it, the quench medium is only really important to stop warping or breaking (which small items like springs are prone to in a water quench, and long thin items like a European sword can warp a bit if you aren't careful and lucky.
Water quenching doesn't increase brittleness. Water quenching has inherent risks of cracking a blade, especially with modern steel alloys. If the blade survives the quench it doesn't need to be tempered differently because it was water quenched.
Japanese swords were tempered immediately after quenching, by reheating to a lower temperature over the forge. I see some modern bladesmiths do this and flick water on the blade to see when it gets hot enough that water droplets skip off with the leidenfrost effect, around 200°C.
@@FuckYouYouFuck well, doesn't it though? It cools the steel faster, making it form a harder metal structure. Which is also more brittle.
@@gustavchambert7072 Yes and no. All else being equal, 67 HRC as quenched W2 steel is just as hard and brittle whether it was quenched in oil or water. Water doesn't increase brittleness, it increases the hardening response, which may or may not be an issue, but is more likely to be an issue than using a slower quench medium. Though with the slower quench medium, you may have an issue with inadequate cooling rate, depending on the steel alloy.
@@FuckYouYouFuck Mmmf, right and wrong both. The thing is if you water-quench the same steel vs. oil quench, you will get both more hardness (HRC) and more brittleness in the water than the oil. If you specify HRC 67, you are specifying the result, not the means to produce it. You can't quench the same piece in oil and water and get the same Rockwell Hardness with both quenching liquids and the same steel thickness and composition.
Cambodia still dose water quench
I always thought the clay was used during heat treatment not the quench. Why would you do that?
Quenching is part of heat treatment. Clay the blade, heat to 800°C, quench in water, reheat the blade to ~200°C to temper it. With a modern steel and process you would heat the blade to 200°C and hold it at that temperature for 2 hours, then cool it off, then repeat the process of heating it to 200°C for 2 hours.
Quenching from 800°C makes the blade very hard, say 65 on the Rockwell C hardness scale, but also very brittle. Tempering relaxes the steel reducing its hardness and making it tough and elastic, say 60 HRC.
@@FuckYouYouFuck I always thought the Japanese would quench the sword then after it cooled put the clay on the blade and temper the sword that way
🤠👍🏿
So, historically, is there any evidence for differential tempering? It's used in modern blades to produce a harder edge and softer body, I think my sword was treated that way.
The maker through hardens the blade, and then during the tempering process heats part of the blade to a higher temperature that the edge, so that part becomes slightly softer.
Is that a modern thing?
"So, historically, is there any evidence for differential tempering?" Yes :-) I don't know where you got the idea that this is a modern thing.
@@quintoblanco8746 I got the idea it was modern from the descriptions I've read of the process.
The blade his heated in a precise way in one area, say the spine, with a gas torch until the steel begins to change color to blue. As the blue color from the heating moves through the blade, the smith watches until it reaches a certain point, maybe just before it touches the edge, and then removes the blade from the heat and allows it to cool. The result is a blade which is differentialy hard, softer at the part of the blade which was more exposed to the heat, and harder towards the edge.
I'm curious, do you know of any pre modern cultures who did this? It seems like it would be difficult without modern equipment like a blowtorch.
I don't honestly know the answer, but I don't know how they would have done it before the blowtorch was invented.
@@johnhanley9946 What you are describing is a specific type of differential hardening that is sometimes used in the making of chisels.
The more common method is differential tempering by the methods described in the video.
The results are essentially the same.
Obviously people did not always have gas torches, but I have seen traditional tool makers position the blade in a way where it's possible that the blunt part of the machete acts like a heatsink (dissipates heat to the air) and the edge gets hotter than the back of the blade because it's thinner and closer to the fire.
Whether or not that actually does something meaningful, I don't know. The resulting tools weren't very hard.
To my mind the water pouring method is more precise.
@@scholagladiatoria Residual heat in the core can be used for that. After the quench the forging scales are removed to watch the color of the oxide layer. The color turns from yellowish to gray. When the edge has the proper color, the blade is cooled completely. It´s not easy. Timing is crucial. I have seen it done.
I did always wonder why some were quenched in oil or water
Quenching causes a change in the crystal structure of the steel. Depending on the content of the steel and the desired product you need to have a certain cooling curve (if you you want to go into more detail "the iron - carbon phase or equilibrium diagram" is the place to look). Cooling too slowly will leave the steel softer. Cooling too fast will cause stress for the material and potentially cause cracks. In "Forged in Fire" the usually use steels that need to be quenched in oil and they make thick blades which are are more critical because the outer layers contract and the core still is hot and expanded.
Fun facts:
Some modern tool steels even quench in air. Cooling them after anealling need to be really slow (e. g. in hot sand).
Steels that are not magnetic at room temperature cannot be hardened by quenching.
Some Caucasian qama/kindjal have clay added to the blade before quenching
According to al-kindi, differential hardening was known to the arabs as far back as the 9th century
Are you sure that sword is 17th century? It has rather less sori than would be typical of the time.
On the contrary, Kanbun era swords are almost straight and quite tapered, hence the attribution of this one. Greater sori was found before and after the Kanbun period, though the sori was located in different regions of the blade before than after, in general. To confuse matters, in the late Edo, many swords were made to look like older blades, and could come in any of the earlier styles.
You can see some good examples of this technique on "Forged in fire".
Am I early ?
Most of your heat treating information is wrong...
Selection of quench media is solely a product of your alloying elements and phase diagram. Oil hardening a water quenching steel will result in an incomplete hardening or no hardening. Harder materials are usually oil or air quenched because of their alloy content. Tool steels and high speed steels are typically air quenched or vacuum gas quenched. If you tried to water or oil harden them they would crack.
D2 is a good example of a material that is air hardened, which will substantially outperform any carbon steel in terms of hardness and cannot be water quenched.
Similarly, high speed steels, which substantially outperform anything you're likely to be familiar with, are gas quenched and maintain hardnesses above 60 Rc (up to 68+) whilst maintaining toughnesses higher than annealed carbon steels etc.
Similarly the quench has pretty well nothing to do with the toughness of the blade, this is primarily associated with the following tempers.
For the most part differential hardness used as a bit of a crutch for poor performing steels (poor quality etc).
Very good information!
Except on D2. Plenty of carbon steels can get as hard or harder than D2. It seems to top out at around 64HRC as quenched with liquid nitrogen cryo. Most 1% carbon low alloy steels can get to 66 or 67HRC as quenched. None of the simple carbon steels will have wear resistance/edge retention as good as D2 though.
@@FuckYouYouFuck I can't see the point in considering pre tempering hardness, because, especially with carbon steels, you can't use them without tempering because they're about as fragile as glass. Pre tempering all of these things shouldn't be miles off each other in terms of hardness because we're talking about precipitated carbides. The point of high alloy materials is retained hardness, not pre temper hardness... That being said, you can get high alloy materials which will demonstrate substantially higher hardnesses post temper than carbon steels will demonstrate pre temper... ie; in the order of 70Rc but I've never seen a knife made out of them... Not much point I guess, something like an M4HSS blade is nearly pointlessly high performance already and D2 is perfectly adequate for pretty much anything IMO.
@@drew79s Post-tempering hardness or potential hardness is proportional. Working hardness for D2 is typically 58-61 HRC, I'm not afraid to leave it at 62 HRC with liquid nitrogen cryo. Most production knives in carbon steels are fairly soft, 57-61 HRC, very rarely 62 HRC.
Well made carbon steel knives can be harder, a high-end kitchen knife in Hitachi White or Blue, 26C3, 52100, or W2 might be 63-65 HRC. They're not especially tough and not intended for chopping through bone, but they will stand up to routine use. The carbon steel outdoors knives I used to make I would aim for a working hardness of 62 HRC. They can be hammered through nails or thrown tip first into concrete. They're not sharp afterwards but they're not broken.
The main point of high alloy steels is carbides. Carbides are extremely hard relative to the steel matrix that is holding them. CPM M4 tempered back to 58 HRC is full of 84-89 HRC tungsten and vanadium carbides that give it great wear resistance/edge holding. No point going that soft though, CPM M4 is better left as ~64 HRC, excellent toughness and even better edge holding.
There's only a handful of custom makers world wide using super hard exotic steels like CPM Rex 121, Maxamet, Hap 40, S390, etc. and they're more commonly 66-68 HRC, very rarely as high as 70 HRC. Very few makers know how to use it and far fewer are willing to grind it.
6:54 LOL No they couldn't put oil in the teapot. Not unless the enjoyed their tea "oily".
There are oil pots ( with long mouth piece of course) for cooking and for the dining table.
@@MtRevDr
Too expensive to risk. Hand crafted, and probably pride pieces to be displayed to guests.
We're not talking nobility here. In Asia crafts people were, in some places still are, considered just a step above merchants,who are just a step from those who handle dead bodies. Not exactly rich people.
This is assuming they were going to continue using the teapot for tea.
@@ollimoore
Forgo tea? Blasphemy!
Use water. it should be morning urine from a redhaired boy. after a night when it was a full moon :)
was urine used to quench swords?
Horse urine, yes. Blood and fat too, of any animals or human. But it have nothing to do with science, it just a mystical belief, pseudo-science.
@@MizanQistina You have to remember that traditional smiths did not start with degrees in metallurgy and thermodynamics; they experimented with whatever was available, remembered what worked and passed it down to their apprentices who repeated the cycle often with materials their teachers dd not have. Yes, they often used alchemical "reasoning" to do their testing; "Horses are strong and urine has a strong smell, so maybe using horse urine will lend that strength to the steel". Sounds silly to us maybe, but there's also the fact that hot steel will absorb nitrogen from materials like leather or urine producing a slightly harder, tougher, rust-resistant "case hardened" nitrided surface. This was apparently discovered using similar alchemical "reasoning".
@@markfergerson2145 Proper chemistry had to start somewhere, after all. The only difference between science and screwing around is writing down the results.
@@anthonylamonica8301 Well, for pre-literate (or illiterate) people, oral history is usually a viable substitute... ;>)
@@markfergerson2145 It is the world where the people believe the earth is flat...a world based on belief over reason.
First ;)
Third :)
Work hardened by peening the edge when sharpening.
3:15 Differential edge hardening with clay unique to Japan. I thought you had done your research on Chinese swords, Matt. Very disappointed. :(
When watching Hema channels talking about Japanese swords expect most of the info to be wrong, a wise person once said.
@@eagle162 Very true. High expectations are the fastest route to disappointment. Damn, now that that sunk in, I really should take my own advice and not be so invested or so critical.
@@Philxia66 well to be fair it was a Japanese development.
@@eagle162 Proof? Sources? As I understand it the "Japanese development" was wavy or irregular hamon shapes, not the use of clay differential hardening. Chinese swords were using clay to produce straight hamon long before the Japanese, as early as the Han Dynasty (206 BCE-220 CE)
@@Philxia66 using clay was in the ming Dynasty most likely thanks to do Japanese influence, look up 唐刀不算日本刀祖先 但中国古刀不逊任何日本刀
People need to understand that geniuses are a myth. Ideas come from your surroundings and if something makes sense multiple people will come up with it.
China copied somebody else's good ideas?
Where and when have I heard about that before? oh yeah always from everywhere
joking aside if someone is doing something better than you it's best to learn from them to improve