what makes japanese chisel steel so much harder?

[Brian Holcombe]

Better late than never

Working on these one by one to savor the experience. The last three stones on this are Tsushima, Shinden suita then finally Nakayama Asagi. This was worked entirely freehand, but enough about that, you can see a difference in the weld line here. This chisel is Assab K120 steel, which is plain High carbon.



I realize this is a bit goofy, but what initially attracted me to this maker was the back hollow cut with a sen (metal scraper), not ground with a grinder.

I can tell from feedback on the stones that these chisels are very hard.

[Kees Heiden]

That's a beauty! And indeed, the transition is obvious. But I have really no idea if it really maters.

[Warren Mickley]

Mike mentioned something about Japanese chisel blades in the 1800's. Indeed, they were laminated. The technique is hundreds of years old.

Stan

Have you seen a Japanese chisel from the 17th or 18th century? I would be very interested in seeing a picture.

[Mike Henderson]

Mike has it right. Forge welding the two types and plates of steel together is a quick process. It is not difficult either. The videos below show some examples for various tools.

https://www.youtube.com/watch?v=n_jCTaUisN0

https://www.youtube.com/watch?v=rjXrJGh_idg

https://www.youtube.com/watch?v=6bI_q1gksII

The flux used varies by craftsman, and they all have their own formula. Most add steel fines. Some add sharpening stone mud. The purpose of the flux is simply to prevent a layer of oxidation between the two layers as they are forge welded. The heat and pressure does the actual welding.

Ms. Katsuki, in her book on blacksmiths in the Tosa region of Japan on Shikoku Island, documents an interview with an aged blacksmith who recalls when flux was introduced to his area from England, and became commonly available, and how much easier it made the blacksmith's job. My point is that, while the flux helps, it is not essential to the process.

Notice all the hammering going on. When done over repeated heats, and at the right temperature, the crystalline structure of the steel is improved considerably as carbides are reduced in size and distributed more thoroughly and evenly throughout the mass. While the videos show only heating, hammering, grinding and quenching, the blacksmiths are using their eyes, hands and experience to judge the temperature, heat time, carbon content, and crystalline structure achieved throughout the process. So while it appears to be rough and even careless work, in fact it is very delicate and precise. Experience, and learning from a good master, are critical. Without the master, the experience may never be obtained.

The two layers shine so differently in the polished blade shown by Brian simply because of the different crystalline structure of the two types of steel. Also, the sharpening process and stones used can make a big difference in the contrast.

In the rare laminated blade you may see garbage between the two layers. This is not good (although it probably doesn't harm the blades cutting performance) as it is indicative of sloppy work. I suggest you reject such blades. Certainly the blacksmith that let such a shoddy blade out the door of his shop was not paying attention..

Near the beginning of the 2nd video, it shows the edge of some rolled plate steel. if you look carefully, you can see a layer of steel laminated in the center. This layer is high-carbon steel, and the 2 outer layers are low-carbon steel. This material is called "rikizai" and is rolled in a factory. It is used by most manufacturers of kitchen knives in Japan. It is shown in this video to differentiate between the factory knife and hand-forged knife.

I've written about rikizai in this forum before. It is a good material, one that makes a good knife at a relatively inexpensive price, but it is not hand-forged, and a knife manufactured from it through the usual process of stamping, grinding, and heat treating in an automated oven will be inferior to a hand-forged knife made by an experienced and skilled blacksmith simply because of its crystalline structure.

There are also many manufacturers that sell plane blades mass-produced using this material as well. The result is good blade at a low price. But performance will probably match the price.

The problem is that, if you are not careful, you can end up paying a high price for a blade made using cheaper materials and without much handwork beyond decoration. Caveat Emptor, my friends.

Of the typical woodworking tools, the kiridashi knife is easiest to make, followed by the plane, even though these two types of tools demand relatively high prices.

The chisel is much much more difficult to produce due to the problems of warpage and shaping. Lots of time is required, as you can see.

The sawblade is by far the most difficult tool to make by hand. There are very few craftsmen left in the world that can hand forge a top-quality handsaw blade. Such blades cost a lot, and can't compete with inexpensive blades stamped out of Swedish steel sold on rolls.

Mike mentioned something about Japanese chisel blades in the 1800's. Indeed, they were laminated. The technique is hundreds of years old. I was once entrusted with a beautiful and rare laminated sword made by a famous smith that was over 700 years old. I still miss the seeing and holding of that sword.....

Stan

I don't remember saying anything about Japanese chisels from the 1800. Could have, but don't remember it. My interest and study has been about western steelmaking and western tools. I don't know much about antique Japanese tools.

I've encountered a bit in my studies about the making of Japanese swords and how the steel was made for those but that's about it.

Mike

[Kees Heiden]

Nice chisels!

The recrystalisation process. Allready heavilly investigated in the early 70ies, Miller and Grange are two names. To put it in simple words, the forging process damages the grain boundaries in the steel. Those damages are starting points for the growth of new crystals. New crystals start out small, so when you don't overheat the steel, the net result is finer grain. Exactly the same effect can be reached with a heat treating schedule of rapid heating and quenching for a few times, but that is probably quite risky for simple high carbon steels (warping and cracking). The effect depends on the amount of violence inflicted on the steel, the time and the temperature. As always in this kind of chemistry, heat is much more powerfull then time.

So, the rolling mill of an industrial process is not worse then the hammer on the anvil. Maybe even better because the rolling mill works uniformly and results in a more homogenous structure.

BTW, when you don't think there is a transition zone between the high carbon steel and the iron body in a laminated chisel, then read this article about a metalurgic investigation of some 18th century western tools. Maybe it will change your opinion. It's an interesting read anyway.
http://preserve.lehigh.edu/cgi/viewc...66&context=etd

[Kees Heiden]

Verhoeven, chapter 8: http://Metallurgy of Steel for Blade...nd Forge Steel
Miller: http://download.springer.com/static/...e89f64a75aa08d

Hey, I am never afraid to acknowledge when I am wrong about a subject. So, do you have anything to support the claim that handforging produces better steel then an industrial mill can do (if they choose to do so)? Or what does handforging accomplish beyond a fine grain size?

[Mike Krall]

Mike,

From knife making... pattern welded steel construction (also called "damascus" steel... maybe, technically, erroneous). From a Masters dissertation specific to carbon diffusion in pattern welding (typically many thin layers). Very short period of time to full diffusion of carbon. The steels used were both "high carbon", which I believe goes down to around 50 points (then medium, then low)... like 72 points of carbon for one steel and 95 for the other.

Would this be different for, say, thin (1/8", 1/4", 1/2") layers of 9 point carbon steel and 100 point carbon steel. No.

I would have liked to have been able to post the .pdf address for the dissertation on this. It was well written and much more informative than my explanation. It was available for a while, but now it can not be accessed.

I feel the answer is in the heat used... 2000 F to 2400 F. Atoms (all) excited to the extreme... carbon VERY willing to move... trying it's heart out to get onto the face of every iron crystal (a cube, so 6... from it's steady state of one carbon atom in the center of an iron crystal), and not at all particular as to which iron crystal. There is more to this than a few sentences... by quite a bit... but a multi-layer billet of 4" thick will diffuse carbon equally in the 30 - 45 minutes it takes to do the process. That does not include the time spent in the same heat to draw out the billet, re-layer it, re-draw, and on... and then the forging time at heat.

In your example of a simple two layer weld... the steels must be at a temperature where the weld will take. Certainly hot enough for carbon diffusion. The layers are welded, and even if that were the end of the process, the billet would be at high temp for quite a while (more than a few minutes). This type of chisel is then forged... more diffusion time. In the end, is carbon equally diffused in a Japanese laminated steel chisel? No... or I don't believe so. There may be (that's a maybe may be) some answer-ish aspect in the amount of carbon in the cutting edge steel. It's very high. Japanese #1 white paper steel has something like 1.4 to 1.6 percent carbon (140 to 160 points). A person could speculate some of the carbon leaving the cutting edge steel and still leaving plenty behind.

Mike Krall

[Vincent Tai]

Mike,



In your example of a simple two layer weld... the steels must be at a temperature where the weld will take. Certainly hot enough for carbon diffusion. The layers are welded, and even if that were the end of the process, the billet would be at high temp for quite a while (more than a few minutes). This type of chisel is then forged... more diffusion time. In the end, is carbon equally diffused in a Japanese laminated steel chisel? No... or I don't believe so. There may be (that's a maybe may be) some answer-ish aspect in the amount of carbon in the cutting edge steel. It's very high. Japanese #1 white paper steel has something like 1.4 to 1.6 percent carbon (140 to 160 points). A person could speculate some of the carbon leaving the cutting edge steel and still leaving plenty behind.

Mike Krall

Yes the carbon diffuses. No it is not even near equally diffused in a Japanese chisel. On some of my very first kannas I decided to do a few heats at forge welding or near forge welding temps and some forging at those temps just to have peace of mind that the weld was together. There was quite a noticeable transition, a 1/64 inch one of mild steel at the boundary that was shiny when polished on a Jnat. The scale of diffusion in a normal good forge welded tool is far far far smaller. A Japanese smith gets the weld set in one heat and go. Starts drawing out on the power hammer on the second. Also the mild steel is heated first, flux sprinkled on and the thin HC rested on top of the hot mild steel and flux. Back in the heat and it does not take long at all to get up to the right temp. Depending on the heat source, and size, couple-few minutes for most things. A bigger forge would keep the time the same for anything huge. My tiny forge heats a 2" wide weld in 3-5 min. 3-5 min is not spent at forge welding temps. Just to reach and equalize, soak a little. These tools aren't big Damascus billets getting folded and folded. The re-stacking and folding is the big difference. If I did that to a J tool billet for some reason that quick diffusion would be very apparent after 16 layers or even less. The Japanese also like to forge at ever descending temperatures and spend much of their time in low temperatures most western smiths would be afraid to, frown at, etc. This reduces the rate of diffusion greatly. 1-2 heats max at forge welding temperatures. From what I've seen it is really just 1 heat at a proper forge welding temp when the Japanese smiths do their thing. The second heat is still very high temp but a notch lower. So the actual time the billet is at forge welding temperature, is maybe what, 2 minutes at most. This is including the hammering time to weld. Maybe more with an undersized forge and if you need to wait for the heat to equalize in your piece because of said small forge. With all the careful descending temps; frankly at most non forge welding temps diffusion is just not really a huge issue so it's fine to work at higher temps that isn't a forge welding temp. Unless one likes to leave things sitting in the forge while they have lunch and a nap. Plenty of good laminated knives forged today at western standard higher temps.
Your point on that very high carbon content is right and all of the points mentioned means when they're combined a very high carbon content is where it matters. In Damascus often something like 15N20 and 1095 are paired, diffusion isn't a problem with that sort of pairing so high temps each weld and subsequent heats for drawing out is not an issue.

Vincent