IanB Posted March 29, 2012 Report Share Posted March 29, 2012 Further to the above quotations above on armour plates. A relatively small amount of microscopic analysis on armour plates was in fact done by Dr. David Starley and myself on some four or five pieces of armour plate I had accumulated over the years. One was a plate from a dou that was undoubtedly Momoyama in date and it consisted of ferrite. We did notice that the sample was remarkably free from impurities. Similar results were obtained from the other samples with one exception. This was a truly awful quality shikoro that judging by the shape was probably 18th century. The armourer must have worked miracles with multiple coatings of filler to make it look decent when lacquered. Surprisingly the plates of this neck guard were composite, the inner side being ferrite with a thin skin of steeled metal on the outside. Kozan describes this process in Chukokatchu Seisakuben as a means of making bullet resistant armour. Obviously such a small sample means little, but I suspect a lot of armour was in fact iron and it was the shape and work hardening during forging that gave pieces such as masks and helmets their strength. This is particularly obvious with 62 plate suji bachi. As the plates approach the tehen at the top, they twist and are almost on edge around the tehen giving the top of the bowl a considerable thickness even though the plates themselves are relatively thin. Ian Bottomley Link to comment Share on other sites More sharing options...
Ford Hallam Posted March 29, 2012 Author Report Share Posted March 29, 2012 Hello Ian, thank for that input, it does add a little to the picture, I think When you sat ferrite I assume you mean essentially iron with very low levels of carbon? The 18th cent. steel/iron laminate neck guard is very interesting too. Link to comment Share on other sites More sharing options...
cabowen Posted March 29, 2012 Report Share Posted March 29, 2012 I think there are a couple of misconceptions here: first, steel does not work harden when forged at temperature. It work hardens when worked cold, but anyone who has pounded on steel with hand tools knows how well this works.... Secondly, experiments have shown that when forge welding at temperature, carbon diffusion takes place which homogenizes the carbon content in the work piece. As a result, there are no local areas of high carbon or low carbon and thus "bones" should be neither higher nor lower in carbon that the plate itself. Link to comment Share on other sites More sharing options...
Lee Bray Posted March 29, 2012 Report Share Posted March 29, 2012 Hi Chris, Carbon diffusion takes place at welding heat but not to the degree that the entire piece is homogenous otherwise what would be the point of shingane, kawagane and hagane in a sword? Edit - I just noticed your use of the word 'local' which could invalidate my point but then recall the So Tsutomu hamon. There was a clear demarcation between the two different carbon content steels and they reached welding heat. Link to comment Share on other sites More sharing options...
cabowen Posted March 29, 2012 Report Share Posted March 29, 2012 I have raised that same point but research seems to indicate that at the critical temp, carbon diffuses rather rapidly and homogeneously throughout the workpiece. The demarcations seen in forge welded material is said to arise more from compositional differences between the adjoining layers as well as the simple physical boundary between the layers. I have a paper here published in "Materials Characterization", 41:183-191 (1998) by Verhoeven and Clark titled "Carbon Diffusion Between the Layers in Modern Pattern Welded Damascus Blades".....I actually spoke with Howard Clark about this last weekend..... Link to comment Share on other sites More sharing options...
Mark Green Posted March 29, 2012 Report Share Posted March 29, 2012 Yes sorry, I should have qualified as ' Bones like effects'. Most of the old Samurai armor I have played wit,h did seem very thin, as far as the metal parts. A lot of orerlaping was used, and of course, the thick lacquer added quite a bit of strength. Most of the parts, seemed to be a softish iron like metal. A lot of the body armor parts you could just about bend with your fingers, with a good bit of pressure. Mark G Link to comment Share on other sites More sharing options...
Ford Hallam Posted March 29, 2012 Author Report Share Posted March 29, 2012 I'd have to suggest that the notion that "carbon diffuses rather rapidly and homogeneously throughout the workpiece." is unreliable by reference to the well observed and documented practice of case hardening. This is a procedure specifically designed to impart carbon into the surface of a piece of low carbon steel yet despite the best current procedures this process only produces a relatively shallow penetration by the carbon. References to 'Modern Pattern Welded Damascus Blades' are, realistically speaking, not really relevant to the discussion with respect to what steel makers and tsuba-ko were doing 500 years ago...I feel. Link to comment Share on other sites More sharing options...
cabowen Posted March 29, 2012 Report Share Posted March 29, 2012 I'd have to suggest that the notion that "carbon diffuses rather rapidly and homogeneously throughout the workpiece." is unreliable by reference to the well observed and documented practice of case hardening. This is a procedure specifically designed to impart carbon into the surface of a piece of low carbon steel yet despite the best current procedures this process only produces a relatively shallow penetration by the carbon. Case hardening, or carburizing, places the workpiece in basically a carbon "bath". The carbon migrates into the workpiece because of the diffusion process however, since the carbon is not already in the steel matrix, I would suspect that the diffusion would not be as rapid or as homogeneous. References to 'Modern Pattern Welded Damascus Blades' are, realistically speaking, not really relevant to the discussion with respect to what steel makers and tsuba-ko were doing 500 years ago...I feel. You would have to read the paper to draw any meaningful conclusions. Has the process of forge welding steel through heating in a fire changed that much in the last 500 years? Link to comment Share on other sites More sharing options...
Ford Hallam Posted March 29, 2012 Author Report Share Posted March 29, 2012 Chris, my point was that the diffusion of carbon though iron is something that pretty well documented and understood...to the point data sheets exist in industry that detail the variables. Your suspicions may wall be correct but we should perhaps stick to what we can say with some degree of certainty, don't you think? We are already labouring under the confusion resulting from years of unsubstantiated supposition...we don't need any more And no, forge welding is still forge welding but working bloom steel/iron from a tatara is in no way analogous to working a billet of modern processed steels that have been piled up and arc welded together at the ends. Nor can we draw any parallels in terms of how carbon might distribute. I haven't read the paper you cite but I'd be interested to see a copy... I do have all of Verhoeven and Pendray's papers though. Fascinating stuff, I personally regard Al Pendray as a true pioneer in his field, a real gentleman and extremely generous with his knowledge to boot. Link to comment Share on other sites More sharing options...
Lee Bray Posted March 30, 2012 Report Share Posted March 30, 2012 Thanks for the explanation, Chris. O MiMi's knowledge is second to none so food for thought. I'm not entirely convinced though, as it still seems to me that compete carbon migration would negate any value of soft core steel to hard edge steel. Link to comment Share on other sites More sharing options...
runagmc Posted March 30, 2012 Report Share Posted March 30, 2012 Lee brought up the So Tsutomu blade... If carbon diffusion took place to that extent, how could you end up with such a different degree of hardening between the edge steel and skin steel. Isn't it the carbon difference that causes the almost pure martensite structure in the edge steel, while the skin steel part of the yakiba has very little martensite. Or I guess you could say the edge steel becomes all nie, while the skin steel in the yakiba is mostly nioi. If the diffusion took place quickly, I wouldn't think the demarcation between the steels would be so distinct. Link to comment Share on other sites More sharing options...
Soshin Posted March 30, 2012 Report Share Posted March 30, 2012 Hi Everyone,I think the data and the comparison between the Yamakichibei tsuba example I provided with many "iron bones" tekkotsu and details of carbon migration in Nihonto may not be a valid comparison due to differences is forging methods. It think the initial comparison with Momoyama Period armor provided most recently by Ian Bottomley and first by Andy M. even with the short comings pointed out by Ford is a more valid one give that many of the techniques used to forge the plate of the tsuba were adapted from armor making.Attached is photos of a tsuba made by a documented swordsmith. The signature mei (銘) from right to left top to bottom of nakago hitsu-ana is: Sagami (no) Kami (相模守), Yoshimichi (義道). This swordsmith who worked in the city of Kyoto ((京都) in Yamashiro Province (山城國) also made tsuba. Two generations are recorded in both W. Hawley's Japanese Swordsmiths (First Edition ID# Y0920) with a 10 point score and R. E. Haynes's Index of Japanese Sword Fittings and Associated Artists (ID# H 11843.0). This tsuba was made by the second generation that signed his work using Sagami (no) Kami (相模守) circa 1750. The plate surface shows no hammer marks only a polished smooth surface migaki-ji (磨地). The rim is square in shape and lacks any tekkotsu "iron bones'. The rim does show some lamination folds with one coming to the surface on the ura (裏) side. The only openwork design on this tsuba is the single enlarged udenuki ana (腕貫穴) used to prevent the sword from being drawn accidentally. Based upon the large size of the nakago-ana and overall weight of the tsuba I think this was likely mounted on a katana (刀) or o-wakazashi (大 小刀) even with the diameter of the tsuba being relatively small at 7.0 cm X 6.5 cm with a thickness at the rim of 5.5 mm. The analysis of this type might be helpful.P.S. Nice work Mark Green I love your tsuba that posted. Keep up the good work! :DYours truly,David Stiles Link to comment Share on other sites More sharing options...
cabowen Posted March 30, 2012 Report Share Posted March 30, 2012 How would the forging of steel for tsuba be different that forging steel for swords? How would forging modern steels and iron be different that forging older steels and iron? Formation of martensite depends on cooling rate. The ultimate hardness of the martensite depends on carbon content. Link to comment Share on other sites More sharing options...
Soshin Posted March 30, 2012 Report Share Posted March 30, 2012 How would the forging of steel for tsuba be different that forging steel for swords? Hi Chris, The point of my post was to state that my original Yamakichibei tsuba was that the techniques used to forge the plate was of armorsmiths origin. I think tekkotsu are independent of carbon content and its movement during the forging process. The Tosho tsuba who I think is made of steel with what I think has high carbon content show no tekkotsu along the rim just evidence that it was forged folded. Yours truly, David Stiles Link to comment Share on other sites More sharing options...
paulb Posted March 30, 2012 Report Share Posted March 30, 2012 Chris, just for my own clarification I want to be sure I understand what you are saying about martensite. My understanding is that it is formed when Iron is heated in the presence of carbon to a temp of between700-800 degrees centigrade. If allowed to cool naturally it decomposes back to the original pearlite form. Rapid cooling does not create martensite but it does arrest its decomposition and retains it within the steel structure. Is this your understanding also or have I misunderstood? Regards Paul Link to comment Share on other sites More sharing options...
cabowen Posted March 30, 2012 Report Share Posted March 30, 2012 I think it would be very interesting to get Adrian to do some analysis with that nifty equipment he has access to....He could test the carbon content of various tsuba at various points, including the tekkotsu. It would also be interesting to cross section a blade of multipiece construction and test the carbon content at various points on the interior to see if there is any variation in carbon content through the interior... Link to comment Share on other sites More sharing options...
cabowen Posted March 30, 2012 Report Share Posted March 30, 2012 Chris,just for my own clarification I want to be sure I understand what you are saying about martensite. My understanding is that it is formed when Iron is heated in the presence of carbon to a temp of between700-800 degrees centigrade. If allowed to cool naturally it decomposes back to the original pearlite form. Rapid cooling does not create martensite but it does arrest its decomposition and retains it within the steel structure. Is this your understanding also or have I misunderstood? Regards Paul Pardon me for speaking loosely. Martensite is a structure that forms at a certain temperature. It is "frozen" in place by cooling at a certain rate. How much is retained depends on the cooling rate and subsequent processing. Hardness depends on carbon content. Link to comment Share on other sites More sharing options...
paulb Posted March 30, 2012 Report Share Posted March 30, 2012 thanks Chris, Just wanted to make sure I hadn't been working on misinformation over the years (wouldnt be the first time ) your comments confirm my understanding Link to comment Share on other sites More sharing options...
runagmc Posted March 30, 2012 Report Share Posted March 30, 2012 How would the forging of steel for tsuba be different that forging steel for swords? How would forging modern steels and iron be different that forging older steels and iron? Formation of martensite depends on cooling rate. The ultimate hardness of the martensite depends on carbon content. True, but the point is, on the blade in question, the cooling rate would be basically the same inside the yakiba, so that would't cause the difference of martensite in the edge and skin steel inside the yakiba. It would have to do with carbon content, or some other difference of composition. Anyway... I'm not trying to start another argument... it was just an observation. Link to comment Share on other sites More sharing options...
cabowen Posted March 30, 2012 Report Share Posted March 30, 2012 Not sure what your comment pertains to- the sword shown has a seam along the edge which is the boundary between two different steels. There is martensite on both sides of the seam....??? Link to comment Share on other sites More sharing options...
runagmc Posted March 30, 2012 Report Share Posted March 30, 2012 The comment pertains to the idea that carbon diffuses rapidly and homogeneously throughout the workpiece. Something's causing much heavier nie in the edge steel here. Since we know it's not due to cooling rate, it seems it would have to be due to composition of the steel itself. Link to comment Share on other sites More sharing options...
cabowen Posted March 30, 2012 Report Share Posted March 30, 2012 I don't see any nie within the yakiba where you have labeled "heavy nie". In fact, the only nie I can see is maybe along the seam and in the peaks of the gunome in the far right of the picture....Nie usually occurs along the habuchi, not within the yakiba proper. There is a definite cooling rate gradient from the edge to the mune. The cross sectional area in combination with the clay jacket are the factors which influence this cooling rate.... Link to comment Share on other sites More sharing options...
ROKUJURO Posted March 30, 2012 Report Share Posted March 30, 2012 Dear NMB members,may I use this fascinating thread to present myself as new on board? I am greeting all members!Still learning, I am in contact with Japaneses arms since nearly forty years. As an active knife and traditional tool smith I have some experience with steel. A few years ago I began to research about TEKKOTSU, discussing the theories with other TSUBA collectors. Some were in opposition to my own knowledge and practice with the properties and the 'behavior' of steel.I have been reading quite a while here in the forums and as the discussion in this thread turned to TEKKOTSU I thought it might be helpful to add my personal observations and ideas to this subject. To start with, I want to say that I fully agree with what Ford Hallam said about it. As long as no scientifical examination has been made, one has to accept what is known about steel, and belief or even conviction are not helpful.Let me start with the article from Andy M. where I found this contradiction (among others which have already been cited).I cite:.....Tekkotsu may be defined as segregated areas of high carbon content, formed as a result of a process of successive episodes of heating, folding and hammering of an iron plate. Generally speaking, increasing the carbon content in iron results in decreased ductility......The last phrase is correct, but then the less ductile hard steel in a TSUBA would not protrude between layers of softer iron as to form TEKKOTSU. Working on the anvil, steel and iron can be well differentiated even at higher forging temperatures. Steel would not be 'squeezed' out between layers of iron. Imagine a steak instead of a hamburger in a BigMac.....Most of the members here have probably seen TSUBA with sword cuts on them. These are fine, sharp edged grooves. Try to do that with a hardened TSUBA! On the other hand I have yet to see TSUBA with chips that could lead to the conclusion that a blade hit a hardened metal obstacle.The description of 'dense, hard steel' is misleading. You cannot densify steel by hammering or any other technique, the density is always 7,85 (roughly). Of course you can hammer down a piece of TAMAHAGANE and densify it's structure, eliminating any voids that occurred in the process of production. But there is no such thing as 'dense iron'. The surface of a TSUBA may well give an impression of more or less structure, but this has nothing to do with the metal's physical properties.It was mentioned that acid treatment might eat away some superficial parts of the material and thus leave TEKKOTSU on the surface. I believe that this is correct, and if so, it supports Ford's theory that TEKKOTSU is more likely iron (or low carbon content steel) because the acid works best on high carbon steel. If on the other hand TEKKOTSU was indeed high carbon steel, we would find hollowed out grooves and lines in TSUBA MIMI instead of TEKKOTSU standing out.Relating to the etching processes I may add that all metals used in TSUBA were chemically treated or patinated with the exception of gold. In some places, silver was also left untouched. I do not mean that all TSUBA were treated, but these patinations were not only applied for aesthetic purposes but as well for corrosion protection. As examples, the well known SABIJI on iron or the 'foxes' red' on copper are very durable coatings, and not all recipes are yet known, as far as I know.In an attempt to prove my ideas to myself I made some samples with different layers of iron and steel. After forge welding them I ground them smooth at the sides and hammered them down at usual forging temperatures. The results were as expected: it was the softer iron that came visibly out at the sides.Going back to the production of steel one hast to remember that rather impure TAMAHAGANE had (and still has) to be processed with repeated folding and welding to become a refined and usable sheet material. It has nothing to do with intended production of layered steel material for improved impact stopping capacities as mentioned in the article. The fact that the production process is sometimes still visible in the workpiece has - at least in my understanding - more likely to do with a typical Japanese attitude found in many artistic and crafts fields such as metalwork, SUMI-E, pottery, and some woodwork.One word to the subject of carbon diffusion. This is influenced greatly by time, temperature and the way to travel , e.g. the thickness of layers. It ist quite well possible to create a decorative Damascus steel from high carbon steel and carbon free iron without having considerable carbon diffusion. This needs as few weldings as possible and thick layers.When it comes to longer periods of forge welding and folding, the overall time of heat application gets longer and the layer diameter diminishes, ending in a balanced carbon content in all layers. An obstacle to carbon diffusion is a layer of pure nickel.To increase research on the forming of TEKKOTSU we could also ask those TSUBASHI who are still able to produce TEKKOTSU, as I heard. But I am afraid there will be no satisfying reply for Westerners, when the artists answers: I use the same material as my ancestors and the techniques my master taught me, and the results are as expected.....Regards,Jean Link to comment Share on other sites More sharing options...
kusunokimasahige Posted March 30, 2012 Report Share Posted March 30, 2012 To ask a mixed question which came up when reading this very interesting topic, Since the Japanese swordsmiths and polishers loved Hamon in their swords, are there any examples existing of a forged tsuba with a Hamon in the rim ? By that I mean the same process to make hamon in swords being used on a forged tsuba. KM Link to comment Share on other sites More sharing options...
Lee Bray Posted March 31, 2012 Report Share Posted March 31, 2012 Hardened steel is brittle. Unhardened steel is tough and malleable. Why any warrior would want a hardened, high carbon tsuba next to his fingers is beyond me. Link to comment Share on other sites More sharing options...
cabowen Posted March 31, 2012 Report Share Posted March 31, 2012 Hardened steel is brittle. Unhardened steel is tough and malleable.Why any warrior would want a hardened, high carbon tsuba next to his fingers is beyond me. Depends on the amount of carbon and the heat treatment. You can harden steel so that it is not brittle.... Link to comment Share on other sites More sharing options...
kusunokimasahige Posted March 31, 2012 Report Share Posted March 31, 2012 Lee, do you consider the cutting edge of a NihonTo brittle ? Apart from that, an unsharpened sword can just as well have a hamon as a sharpened one if it has gone through the Hamon forging process of clay in variable layers, reheating and quenching, so why not a Tsuba rim ? KM Link to comment Share on other sites More sharing options...
Lee Bray Posted March 31, 2012 Report Share Posted March 31, 2012 Depends on the amount of carbon and the heat treatment. You can harden steel so that it is not brittle.... Isn't that just tempering, reducing the hardness with heat? I'm wondering why high carbon steel would be considered for a tsuba. High carbon steel would have been reserved for swords. It makes little sense to me that HC steel would be used in tsuba but maybe it was. Henk - Of course it's brittle otherwise it wouldn't chip, it would roll. Link to comment Share on other sites More sharing options...
kusunokimasahige Posted March 31, 2012 Report Share Posted March 31, 2012 I see what you mean Lee. To me brittle means something which crumbles and breaks easily, like cast iron and not hardened steel. Lost in translation so to speak... Btw, I asked whether such a tsuba type ever existed, not if a tsuba like that would have been made often. I see it more as a probable/likely/possible experiment in aesthetics by either tsubako or swordsmiths with too much time on their hands... KM Link to comment Share on other sites More sharing options...
cabowen Posted March 31, 2012 Report Share Posted March 31, 2012 Isn't that just tempering, reducing the hardness with heat? I'm wondering why high carbon steel would be considered for a tsuba. High carbon steel would have been reserved for swords. It makes little sense to me that HC steel would be used in tsuba but maybe it was. Tempering is the usual method to reduce brittleness but if you start with a lower carbon content and cool at the right rate, you can get a hardened piece that is not brittle like a high carbon steel that has been cooled very quickly.... I agree that high carbon steel doesn't make much sense for tsuba.... Link to comment Share on other sites More sharing options...
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