what makes japanese chisel steel so much harder?

[jamie shard]

This is a simple question, but when I try to find the answer via googling there is a low signal to noise ratio. My question is what makes the steel in japanese chisels have such a significantly higher rockwell hardness? Is it the elemental blend (more chrome, vandium, etc.) or is it the forging process which compacts the carbides or is it tempered less or is it something else entirely?

[Kees Heiden]

Most Japanese chisels are made from a low carbon body with a rather small bit of high carbon steel at the edge. Usually white paper steel which is a Japanese name for a very simple high carbon steel. It has about 1.2% carbon and the rest is mostly iron.

Like all high carbon steels it can be hardened to a rockwell C value around 66%. That is, directly after heating to 850 degrees Celsius (or thereabouts) and quenching it has such a high hardness. The disadvantage is that after quenching the steel is very brittle and full of stress. Therefore every tools steel is tempered. When you look up for example the tempering curve for 1095 steel you will see that a low tempering temperature (100 degree celsius) results in still very high hrc values. Higher tempering temperatures, like 200 or even 250 degrees brings the hrc value down to about 60. (All numbers from my head, so to be precise you must look it up).

Westeern chisels are almost always tempered to those values in the high 50's or low 60's. That gives a solid, relatively hard, but not brittle chisel that is easy to sharpen.

The Japanes smiths temper to much higher HRC values for their top of the line chisels. 63 or 64. The worst of the stress is now gone from the steel but it is still relatively brittle. It is the construction of the chisel, the low carbon body with the steel only a small part of it. The unhardened low carbon body takes the "beating". So the chisel won't break under hammering. But it still needs to be handled with care. Under prying loads you can easilly break small chips from the edge.

Oh, and before I forget, the smiths are great craftsman. They manage the heat treating and the forging so that the end result is a steel with very fine grain. The coarser the grain, the more brittle the steel is. So by paying attention to this detail, you can get away with more hardness. It is probably a trade secret how they do it exactly, but it is a matter of much experience anyway, it is not simply following a recipe.

[Stanley Covington]

My question is what makes the steel in Japanese chisels have such a significantly higher rockwell hardness? Is it the elemental blend (more chrome, vandium, etc.) or is it the forging process which compacts the carbides or is it tempered less or is it something else entirely?

Japanese chisels tend to be, but are not always, harder than Western style chisels because they are intentionally heat treated to be harder. This is easy to do, but hard to make practical.

They can tolerate the extra hardness partially because of the laminated structure of high-carbon steel and low carbon, relatively softer and therefore tougher, steel used to make chisel blades. A western style chisel blade made of uniform high-carbon steel structure would simply break if heat treated to the same hardness.

Another reason is that the steel is typically (but not always) of better quality, and if forged, will have a relatively more uniform crystalline structure less inclined to chip at higher levels of hardness.

None of this is rocket science or unique to Japan. Laminated chisels and even plane blades have a long history in the West, as does hand forged, high quality steel. The West just abandoned top-quality blade smithing with the industrial revolution. Some of the best-cutting and most durable laminated plane blades I have ever seen were made in Sheffield England in the 1800's, and branded "Cast Steel." The West simply abandoned the techniques still used in Japan.

After cutlery became commonly mass-produced in sweat shops, the really good blacksmiths could not compete anymore with factory products.

The mass industrialization of toolmaking in Western Europe, Northern Europe, and America lead inexorably forward to mediocrity. But in Japan, during this same period, a change in laws forbade the wearing of swords in public (the 'haitorei" 廃刀令 of 1876), thereby ruining the livelihood of tens of thousands of the arguably best blacksmiths in the world. Many of these artisans switched to tool making, and applied their excellent forging, heat treating, and shaping skills to woodworking tools.

In Japan, prior to this change in laws, the more mechanical gun never really replaced the elegant sword. In fact, the government bureacracy and aristocracy of Japan, unlike America and England, have always feared the common man (who until the 1800's were slaves in all but name) owning weapons, and fiercely opposed private ownership of firearms. Therefore, the sword has always been seen as the ultimate weapon. These extremely sharp, tough, and elegant blades have for many hundreds of years been iconic subjects of reverence and lust. This fanatic desire for sharp, tough cutting tools extended to woodworker's as well.

Consequently, while the average skill levels of tool blacksmiths dropped in the West, they dramatically improved on the average in Japan. It is no wonder Japan developed not only unique tool designs, but improved the quality and effectiveness of its woodworking tools. The West has never been as fanatic about sharpness and excellent steel as the Japanese.

I hope this helps.

[Warren Mickley]

As mentioned by others, before tempering high carbon steel tools are hard and brittle whether Japanese or English. We deliberately temper the tools at a higher temperature because we prefer them that way and we know how to handle a tool that is heat treated this way. I think the English tools made in the early 19th century are fantastic. I have had only one 18th century tool and it was also very fine. These older tools are also laminated. I have been fanatic about sharpness and steel for over fifty years.

[jamie shard]

At the risk of oversimplifying, it sounds like the critical feature is the lamination which allows for more brittle steel to be used at the cutting edge. The quality of the steel is enhanced by the forging. The steel itself is basic high-carbon steel.

[Brian Holcombe]

The lamination is critical, it allows support of the hard steel by softer low carbon steel or plain iron ( chisel or plane ). Japanese do have alloy steels, in fact some makers are quite famous for their various special blend alloys, such as Tasai or Kengo.

I prefer plain HC for my purposes, but it's worth a mention.

[Warren Mickley]

At the risk of oversimplifying, it sounds like the critical feature is the lamination which allows for more brittle steel to be used at the cutting edge. The quality of the steel is enhanced by the forging. The steel itself is basic high-carbon steel.

I would not say that. My chisels and plane irons were all made in England or America. The majority are laminated; I would say the better ones are laminated. We prefer higher tempering for these tools and have for over three hundred years.

[Stanley Covington]

At the risk of oversimplifying, it sounds like the critical feature is the lamination which allows for more brittle steel to be used at the cutting edge. The quality of the steel is enhanced by the forging. The steel itself is basic high-carbon steel.

That's the nutshell summary,

The steel is not typically plain high-carbon steel nowadays. More alloys with chrome, moly, and some tungsten, among other additives to improve heat treatment characteristics and QC are used. These additives help significantly to reduce warping during heat treatment and to widen the range of successful temperatures for quenching and tempering. Fewer rejects, better productivity.

You can imagine what chrome and tungsten do for sharpening, though. Not an improvement, but certainly tolerable.

[Kees Heiden]

There are a few big differences between the old English chisels and the Japanese one. The Japanese like to advertise with HRc of 64 or 65. That is hardly tempered at all, just enough to relieve the stress in the steel from the quench. I don't think English ones ever were beyond 61 or 62 (outliers not counted). The English bench chisels were often a lot thinner. Japanese chisels are relatively thick. The Japanese chisels are also shorter. I think both these factors help the stability of the chisel and thus allow a harder steel bit too.

Some old English chisels were not laminated. Especially the smaller sizes were often made entirely from cast steel. The Seaton chest has two sets that are almost the same but one set is not laminated and is marked "cast steel". The other set is laminated in the larger sizes and is probably made of wrought iron with a blister steel edge.

[Mike Henderson]

Don't get too excited about a chisel marked "cast steel". In old tools, the words "cast steel" actually means "crucible steel", steel that was melted in a relatively small crucible. Prior to the Bessemer process, the only way to melt steel was in a small crucible and that steel was marked as "cast steel" to distinguish it from blister steel. Cast steel was much more homogeneous than blister steel.

The crucible process continued after the Bessemer process became popular because it could produce better steel than the Bessemer process (that wasn't saying much, because Bessemer steel was not very consistent batch to batch:)). Today, the electric arc furnace has replaced the crucible process.

But the steel that came out of a crucible depended on what went into the crucible and different batches were often different. About the best that can be said of crucible steel (or cast steel) is that it may be about as good as some of the modern carbon steel. Beyond that, a lot depended on the processing of the steel into a tool.

But the important take-away from my posting is that there's nothing special about "cast steel" - it's just plain carbon steel, often with poorly controlled impurities.

An excellent book on crucible steel is "Steelmaking Before Bessemer, Volume 2, Crucible Steel" by K.C. Barraclough, published by the Metals Society. Volume 1 on Blister steel is also good.

Mike

[Kees Heiden]

It is very hard today to find pure carbon steel. Even 1095 has about 0.5% manganese. Now, don't get me wrong, I think manganese in steel is not a bad idea, because it binds suplhur and helps with the hardening of the steel. But it is not quite the same as a pure Japanese white paper steel that only has a tiny bit of silicon added. Some people think any addition makes the steel less perfect, so for those people nothing else is good enough.

About cast steel, Its production was of course difficult to control. Everything depended on the skill of the foundry men. Chisel makers with an intend to make the best were often intimately connected to their steel supplier or were even making their own steel. Only then they could rely on a steady supply of good stuff. Even then, it is a bit of a miracle that they were able to produce such good tools in an environment like that.

[Warren Mickley]

Kees, you mentioned the cast steel chisels in the Seaton chest. I believe that for some time in the 18th century the craftsmen had trouble forge welding cast steel to the rest of the chisel; it took some years to solve the technical problems, but later cast steel chisels were laminated. I have never seen a Japanese chisel from the 18th century; I don't know what the Japanese were doing at the time.

I have used cast steel tools for forty years now. I feel like I am lucky to have them. I can thank some 19th century craftsmen who were willing to pay a premium for quality.

[Bill McNiel]

Forget all the mumbo-jumbo, the real answer is "oriental magic"

[Steve Voigt]

I cannot prove it, but I think the traditional explanation given--that lamination cushions the steel and keeps it from chipping at high RC--is not true. Chips on a chisel, unless it's seriously defective or seriously mistreated, are usually a few thousandths to maybe a 64th deep. Laminations, especially on a japanese chisel, are at least 3/32-1/8 thick. Looking at the geometry, I think the soft steel (or wrought iron) is just too far away from the edge to have any effect. I think if a japanese chisel were made entirely out of White or Blue paper steel, it would still work as well.
I had an O1 plane iron made by Steve Knight that was very similar in feel to japanese blades. It was so hard I could barely sharpen it on oil stones, yet it didn't chip. I think that the most important factors are high quality steel, properly hardened and tempered by someone who knows what they're doing. Laminating is important for tradition, and because the white or blue steel is very expensive--I bought one stick this summer when I was in Germany, it was almost $40.

[Kees Heiden]

I think we must now start to look at the stress-strain diagram. Bear with me, this is all new stuff for me too and I haven't quite grabbed it all either.

http://i.stack.imgur.com/kIOJo.png

This diagram pictures how steel behaves when it is pulled apart in a special machine. The machine tries to make the steel rod longer and meassures the elongation and the force. The most important part of the curve is the first rise until the yield point. This is the springy part of the curve, when the force is released before the yield point the steel springs back to its original shape. Above the yield point the steel deforms permanently until it breaks. hardened steel doesn't reach very far beyond the yield point, it snaps long before the top of this curve.

The same kind of steel can be hardened to several different hardness levels. A spring steel, hardened to 50 HRc will have a much lower yield point then a steel hardened to 60 HRc, but with much more elongation. It also won't snap as easilly beyond the yield point.

Here is a diagram describing how I think it works with tool steels. The little stars are the break points. (This is just a quicky diagram, nothing is to any kind of scale, imperial or metric :D).

http://i290.photobucket.com/albums/ll266/Kees2351/temp/Stress-strain_zpsucw1rzc1.gif (http://s290.photobucket.com/user/Kees2351/media/temp/Stress-strain_zpsucw1rzc1.gif.html)
More hardness makes the curve steeper, raises the yield point (more pressure neccessary to stretch the steel), but also reduces the elongation and it makes the steel more brittle, it snaps quicker when you go beyond the yield point. When you manage to reduce the grain size of the steel during the heat treatment, then you make the steel stronger (higher yield point) and tougher (more elongation until you reach the yield point). A steel with very high hardness can withstand a lot of stress, but it is very brittle so it snaps just a little beyond the yield point and it elongates hardly at all before it breaks.

How do we translate this to chisels? A chisel with low hardness is perfect for rough work. A bit of prying is no problem, the chisel won't break easilly when mistreated. But the edge isn't very hard. When mistreated the edge will give rather quickly and may even fold over.

A very hard chisel is always at risc when being bend to break in two parts. It is telling that 5 (!) chisels from the Seaton chest are broken or cracked! That is where the lamination comes in. The hard steel is very well supported by the much tougher iron body of the chisel. But when we look at the edge, then things are a little different. When you hammer a chisel into a piece of hard wood, you want to stay below the yield point. A very hard edge has a much higher yield point, so it won't deform as easilly. In the direction of the length of the chisel, this edge is very well supported and thus very strong. But in a prying direction the support of the edge is much less, and it will be easier to pass beyond the yield point resulting in a chipped edge.

So the lamination helps to avoid a total failure of the chisel. The hardness plays a role in the stability of the edge in the cutting direction, but high hardness makes it vulnerable for chipping when a force perpendicular acts on the edge.

[Kees Heiden]

BTW, I don't think that White paper steel is excessively expensive. I bought a rod of silver steel last week and it was also 25 euro. Silver steel is our kind of drill rod, but it has a little bit of chrome and vanadium.

The white steel from Dictum: 500x45x3 mm for 30 euro.
My silver steel rod: Round 10mm x 1000 mm for 25 euro.

The white steel is 67500 mm3.
Silver steel is 78500 mm3

So the price difference is about 40%. That is not excessive for steel adorned with oriental magic!

[jamie shard]

Sounds like the lamination basically ensures that the force experienced by the hard steel is all in compression.

[Warren Mickley]

I don't think this is well thought out, Kees. Your diagrams suggest that the softer steel has more strain for a given stress and then you claim this material "supports" the stiffer steel. If you want to support the steel you need something stiffer not more springy.

[Kees Heiden]

Yes and no. Large scale (meassured in cm's) yes. But at the very edge, in those last few micrometers before the chisel ceases to exist, the steel is flopping around. There it is only supported in compression in the cutting direction, while in the prying direction it is in tension.

Of course we shouldn't pry with our chisels, but you have to be a much better craftsman then me to completely prevent any misaligned force under the mallet.

[Kees Heiden]

I don't think this is well thought out, Kees. Your diagrams suggest that the softer steel has more strain for a given stress and then you claim this material "supports" the stiffer steel. If you want to support the steel you need something stiffer not more springy.

You need something tougher. The lamination makes it stiff. Together they are stiffer and tougher then either alone.

[Kees Heiden]

There is another test for measuring toughness. They make a kerf in a bar of steel and then hit it hard enough to break at that point. The impact force and the way how the steel breaks is a good indicator for the toughness. Because this is an impact test in state of the static elongation test, it is a better test.

Don't quite know yet how to translate that one to chisels.

[Brent Ring]

So, in the long and short, which steel is best to look for when shopping for Japanese Chisels?

[Stanley Covington]

Very entertaining. What Kees has shown in his diagram is entirely true, but is very elementary, and does not address some important factors.

The fact is that the stress, bending and shear diagrams for the various force vectors potentially acting on a chisel in this case are more complicated than what he could show in this limited medium, and the interaction between the low carbon and high-carbon layers in a chisel is too complicated and boring for this forum. I think we should stick to layman's terms and avoid deep discussions of materials science and static analysis.

The high-carbon layer of steel in a Japanese chisel is relatively thin. If the chisel was made thick, perhaps 12mm thick, for instance, and from a solid piece of uniform high-carbon steel of perhaps HRC67, instead of a laminate with a high carbon steel layer of the same hardness, it would be quite strong in bending and shear. It would even be more resistant to impact forces. But the materials cost would be much higher, it would be heavier, and clumsy to use, and it would be very difficult to sharpen. If enough force was applied, however, it would still break dramatically and suddenly. It would not be at all flexible. Sudden catastrophic failure is acceptable in window glass, but not in a chisel.

The fact is that high-quality high-carbon steel has, for almost all of human history, been a mystery, difficult to make and very expensive. Cost reduction is one reason why laminations in chisel and plane blades were SOP for so long. The same lamination concept has proved very effective in Japanese swords, middle eastern damascus swords (the real thing, not the decorative, silly, and overpriced stuff popular today), and even some varieties of scandinavian swords. It makes blades tougher, without sacrificing cutting potential.

Window glass is a good parallel. You can heat treat glass to make tempered glass, and it will be much much stronger, and tougher, than standard glass. It will be much more difficult to break than regular glass. But when it fails, it is totally destroyed fracturing into a million small fragments. This sort of catastrophic failure is not acceptable in a chisel blade much less a sword blade. But, on the other hand, take two pieces of the same tempered glass, and laminate them together with a piece of relatively soft but very flexible plastic sandwiched in between to make "safety glass," and even if the glass fractures, the window will remain in one piece. Hanging together and staying in once piece even after failure is the essential definition of toughness.

The importance of toughness, and the absolutely critical need to avoid catastrophic failure, is why structural steel as used in building frames is relatively soft and of relatively low tensile strength. You can literally bend a quality I beam into a pretzel, either slowly or using impact forces, and it simply will not break. The I beam will absorb a tremendous amount of energy (measured by some as the area under the curve in Kee's diagram) in the process and stretch the process of ultimate failure over a much longer period of time. This saves lives. While a stronger, stiffer, harder beam can absorb a higher ultimate force prior to failing (yield point), it is not nearly as tough, and when it does rupture, it will shear right off. Obviously a fatal mistake in material selection for a building.

Looking at the laminated chisel again, the thicker softer layer does allow the thinner harder layer to deform and bend well past its yield point, without cracking or failing. And even if it does fail and crack, the soft layer will hold the chisel together. This is where the diagrams become complicated, but it is an indisputable, provable, and verifiable scientific fact.

As Kees and others have clearly observed, however, the cutting edge is not protected or cushioned in any way by the softer body (jigane) and will chip and break if abused. This means one must be careful to not pry with Japanese chisels to avoid chipping the edge. This tendency to chip can be greatly reduced by using a more obtuse bevel angle. But that makes the chisel more blunt, and it will not cut as well. As in all things, a balance must be reached. With quality Japanese chisels, however, the critical balance between hard and soft, tough and strong, sharp and fragile, ease of sharpening and edge longevity is commonly achieved. They are a simple, but elegant solution to a difficult problem.

I am saddened that these techniques, once common in the West, were so totally discarded and forgotten. I am heartened that they still remain in the hands and minds of a few blacksmiths in the islands of Japan, at least for a few more years.

I hope this rambling tome helps.

[Stanley Covington]

So, in the long and short, which steel is best to look for when shopping for Japanese Chisels?

It depends:D

Blue Paper steel is a solid, reliable choice. It is relatively easy to heat treat, and quality problems are fewer. You really must have serious sharpening skills, excellent stones, and refined senses to detect the differences in sharpness between White Paper steel and Blue Paper Steel. Most people can tell the difference in ease of sharpening, and with experience, most guys find the White Paper steel quicker and more pleasant to sharpen. But is is not enough of a difference for most people to worry about, in my humble, but very experienced, opinion.

White Paper steel, as a material, is cheaper than Blue Paper steel, but much more difficult to work with. White Paper steel warps like a SOB, cracks easily when quenched, and has a much narrower range of acceptable temperature for effective heat treatment. Therefore, QC is much more difficult. But a blacksmith that routinely and successfully uses White Paper steel is a master on a higher level in his field. And his products will cost more.

On the other hand, when people swear that Blue Paper Steel is superior to White, understand that they are either misinformed, have swallowed a marketing ploy hook, line, and sinker, or, if they do know the facts, are speaking from the viewpoint of the manufacturer rather than the end user. Blue Paper steel as a material is more expensive because of the expensive additives. But the labor required to make high-quality blade, as well as the number of rejects due to warping, cracks, and hardness problems is much less. Therefore, it saves the manufacturer greatly in labor costs.

There are other steels available. I would avoid SK steel for chisels and planes, as well as Yellow Paper steel.

I would also avoid, like the plague, Blue Paper Super steel unless abrasion resistance is a big deal for you. Lots of tungsten, and difficult to sharpen. But for those that like D2 steel, Blue Super will be an improvement.

Due drachma

[Jim Koepke]

I hope this rambling tome helps.

Even if it doesn't help, it was an interesting read. Thanks to all for taking the time.

jtk

[Kees Heiden]

Another little detail, there isn't an abrubt transition from high to low carbon steel in a laminated blade. A good forge weld gives a gray inbetween area where the carbon content gradually decreases from the toolsteel to the wrought iron. Carbon movement in the steel is a diffusion proces, so the carbon atoms really want to move from the steel to the iron. But diffusion is a relatively slow process, which is accelerated with high temperatures. Forge welding happens at very high temperatures, close to the melting point, so the diffusion happens relatively quickly. Afterwards the chisel is heated up a few more times, to finish the forging and to heat treat the steel.

Damascus steel for example is made up of layers of usually two different kinds of steel. To make the damascus package it needs to be forge welded and drawn out several times. The end result is a very even distribution of the carbons atoms throughout the entire blade. A laminated chisel is only forge welded one time, so it doesn't end up completely homogenous.

I think this transition zone also helps to moderate shockloads in the steel.

[Brian Holcombe]

Kees,

I think the forge line is fairly thin, I can make it out on some chisels;
http://i27.photobucket.com/albums/c181/SpeedyGoomba/E60D43C2-9419-4C27-9044-3624EAAA4340_zpsvca2ddg3.jpg (http://s27.photobucket.com/user/SpeedyGoomba/media/E60D43C2-9419-4C27-9044-3624EAAA4340_zpsvca2ddg3.jpg.html)
http://i27.photobucket.com/albums/c181/SpeedyGoomba/CE173077-CAFF-4449-B13C-D7934CE9F955_zpsftwniy4o.jpg (http://s27.photobucket.com/user/SpeedyGoomba/media/CE173077-CAFF-4449-B13C-D7934CE9F955_zpsftwniy4o.jpg.html)http://i27.photobucket.com/albums/c181/SpeedyGoomba/DE325BE7-E17E-456D-AAB8-973EA173CD56_zpsgxdezyw6.jpg (http://s27.photobucket.com/user/SpeedyGoomba/media/DE325BE7-E17E-456D-AAB8-973EA173CD56_zpsgxdezyw6.jpg.html)

[Kees Heiden]

If you can see it then it is huge on an atomic scale :)

[Mike Henderson]

Another little detail, there isn't an abrupt transition from high to low carbon steel in a laminated blade. A good forge weld gives a gray inbetween area where the carbon content gradually decreases from the toolsteel to the wrought iron. Carbon movement in the steel is a diffusion proces, so the carbon atoms really want to move from the steel to the iron. But diffusion is a relatively slow process, which is accelerated with high temperatures. Forge welding happens at very high temperatures, close to the melting point, so the diffusion happens relatively quickly. Afterwards the chisel is heated up a few more times, to finish the forging and to heat treat the steel.

Damascus steel for example is made up of layers of usually two different kinds of steel. To make the damascus package it needs to be forge welded and drawn out several times. The end result is a very even distribution of the carbons atoms throughout the entire blade. A laminated chisel is only forge welded one time, so it doesn't end up completely homogenous.

I think this transition zone also helps to moderate shockloads in the steel.
I'm not sure that's true. The diffusion of carbon into steel is a very slow process. When Blister steel was made, for example, they ran the furnace for a week or more to diffuse carbon into the wrought iron. I think the total process, including the cooling of the furnace, was more like two weeks. The diffusion resulted in a gradient of carbon in the wrought iron which was a problem for certain uses of the resulting metal. After the blister steel was produced, they would fold the resulting ingots to produce shear steel. If they were folded more than once, it was known as double shear steel.

Laminating of high carbon to low carbon steel is a very quick process, much too quick to see much diffusion of carbon. All of the laminated tools I've examined, both western laminated (cast steel) tools and Japanese chisels, have a very defined, sharp line between the two types of steel. Note that Stanley plane irons produced up until maybe 1920 were laminated. I don't know the date when they went to non-laminated blades - just guessing 1920.

Mike

[Brian Holcombe]

Stanley, I appreciate the tomes, these are quite insightful.

[Kees Heiden]

Well, I am absolutely sure about the Damascus steel. When they make that from high and low carbon steel, they end up with a medium carbon steel throughout. But there still are very definitive color differences between the layers, due to other elements in the steel that don't diffuse so easilly around. Wrought iron contains a lot of sulphur while white steel doesn't, for example, but I don't know if that explains the color difference.

There is a very interesting study about 18th century woodworking tools available online:
http://preserve.lehigh.edu/cgi/viewcontent.cgi?article=1266&context=etd

They meassured the hardness along the length of several chisels. In the area where the steelbit starts they measured a gradual increase of the hardness over a length of 2.25 mm (average). I don't know how quickly the hardness increases over the thickness of the chisel, but there is one image (nr. 16) that clearly shows this transition zone.

BTW, I think that the making of blister steel takes so long because the carbon has difficulty to jump the gap between the steel and the charcoal.

[Mike Henderson]

Well, I am absolutely sure about the Damascus steel. When they make that from high and low carbon steel, they end up with a medium carbon steel throughout. But there still are very definitive color differences between the layers, due to other elements in the steel that don't diffuse so easily around. Wrought iron contains a lot of sulphur while white steel doesn't, for example, but I don't know if that explains the color difference.

There is a very interesting study about 18th century woodworking tools available online:
http://preserve.lehigh.edu/cgi/viewcontent.cgi?article=1266&context=etd

They meassured the hardness along the length of several chisels. In the area where the steelbit starts they measured a gradual increase of the hardness over a length of 2.25 mm (average). I don't know how quickly the hardness increases over the thickness of the chisel, but there is one image (nr. 16) that clearly shows this transition zone.

BTW, I think that the making of blister steel takes so long because the carbon has difficulty to jump the gap between the steel and the charcoal.

Antique wrought iron was not excessively high in sulphur. Sulphur makes wrought iron "hot short (https://en.wikipedia.org/wiki/Red-short)" (or "red-short") meaning that the iron would get brittle when heated to forging temperature.

Our ancestors did not have knowledge of chemistry but they could see the result of different ores. The ores from Sweden were very low in sulphur and were sought after for production of iron and steel. Bessemer had trouble with his process because of the ores used. He developed the process with Swedish ores but after he sold licenses for the process to others, they tried to use it with English ores which were high in sulphur and the process would not produce decent steel.

I don't think the migration of carbon is affected to any great degree by the origin of the carbon. The carbon was in intimate contact with the iron in the blister steel furnaces. I've not heard of any reports of rapid migration of carbon within iron. In fact, if it would migrate quickly once it was in the metal, we would not see the high gradient of carbon within blister steel. Once the carbon was in the iron, if it had high migration, carbon would migrate through the ingots (which were quite thin). But that's not what we see.

And while sulphur makes iron hot-short, phosphorus makes iron cold-short. That is, brittle when cold.

Mike

[Reinis Kanders]

Brian,

What chisel is this? Seems like a handy one for the corners of the half blinds.

Thanks.


Kees,

I think the forge line is fairly thin, I can make it out on some chisels;

http://i27.photobucket.com/albums/c181/SpeedyGoomba/DE325BE7-E17E-456D-AAB8-973EA173CD56_zpsgxdezyw6.jpg (http://s27.photobucket.com/user/SpeedyGoomba/media/DE325BE7-E17E-456D-AAB8-973EA173CD56_zpsgxdezyw6.jpg.html)

[Roger Davis IN]

The conjectural diagram above (with the stars) could not be more wrong. As the first diagram notes, Young's Modulus is equal to the slope of the linear part of the graph. Young's Modulus is about 29,000,000 psi for anything that will rust, period. A publication from the National Bureau of Standards in 1966, "Heat Treatment of Steel," notes explicitly:

"The modulus of elasticity of steel is the same as that of iron (about 29,000,000 psi). It is not affected by heat treatment or by the addition of alloying elements. Since stiffness, or the resistance to deformation under load, is a function of the modulus of elasticity, it follows that the stiffness of steel cannot be changed by heat treatment or by alloying elements, provided that the total stress is below the elastic limit of the steel in question. Either heat treatment or alloying elements can raise the elastic limit and thus apparently improve the stiffness in that higher allowable unit stresses may be imposed on the steel."

"Elastic limit" is the Yield Strength in the first of the diagrams above. Comparison of the 50 HRc curve and the 64 HRc curve would suggest that the softer steel has a Young's Modulus of about 14-15,000,000 psi. This is nonsense; if it rusts it's about 29 million. Note that this constancy also implies that the soft back of a laminated chisel has exactly the same resistance to bending as the hard steel as long as you don't exceed its yield strength, which is to say, bend it. The two constituents will move together quite happily since their response to bending and compressive stresses will be identical unless you go so far as to induce a permanent bend. Heat treating changes yield strength, impact strength (toughness) and hardness. Throw in grain size and you've about covered it.

[Allan Speers]

So, in the long and short, which steel is best to look for when shopping for Japanese Chisels?

IMO:

Top quality white for paring.

Blue for mortising.

Your choice for bench chisels, depending on your preference for sharpness or durability.

[Kees Heiden]

Thanks for the explanation Roger. Glad you joined in and share your knowledge. Like I wrote, this is all new for me, and no wonder I get things mixed up.

When I put a length of hardened steel in a vise and try to push it over, bending it, that wil take a lot of force to reach a small deflection. If I do the same with a piece of spring steel, it is easier to bend it a larger distance. At least that was my train of thought. Can you explain where I went wrong?

[Roger Davis IN]

Put a hardened bar and an annealed (dead soft) bar of the same stuff and the same size and shape in your vise. Hang the same weight on each, and they will droop exactly the same amount, UP TO A POINT! At some point as you increase the load, you will see the soft bar bend farther than the hard one, and when you unload them, the soft bar will not return to its original shape. The hard one will come back to its original shape with the same load because its yield strength was increased by heat treatment. At some higher load, it, too, will fail to return to its original shape. The load which causes permanent deformation (and breaks the linearity of the stress-strain relationship) is the yield strength (elastic limit) of that bar, and can be converted to a universally applicable stress value by knowing the geometry of the bar and how the load was applied (complicated beyond this forum). If you were to test these bars for impact strength, you would find that the harder one can absorb less energy before snapping than the soft one can; this is the tradeoff between hardness and toughness one always faces with heat treatment. Note that all the data points for both bars would lie along the same line as long as you are below the yield point of the softer one. They have the same Young's Modulus (as above), and that is the slope of the linear stress-strain relationship. The harder bar would simply go farther up the same line before deviating at its (higher) yield point. Note the use of "apparently" in the last sentence of the passage I quoted. That is the key.

I've been planning to set up a demo of this for my blacksmithing club, as I have heard a lot of nonsense bandied about regarding the effect of heat treating on stiffness there.

[Roger Davis IN]

Kees:

Note that the increase in yield strength between the annealed bar and the hardened one can be really large, like a factor of 5 or 6 in some cases.

[Kees Heiden]

Thanks for explaning. It's always good to know when you are wrong about something.

But now I am unsure how all this relates to laminated chisels. Is the total toughness of the laminated bar increased beyond the toughness of the hardened steel part?

[Brian Holcombe]

Brian,

What chisel is this? Seems like a handy one for the corners of the half blinds.

Thanks.

Reinis, That one is by Kikuhiromaru, it's hooped for striking as well. Very handy for half blinds.

[Roger Davis IN]

Kees:

I think that's clearly a true statement. I haven't really given a lot of thought to the effects of lamination.

[Kees Heiden]

I probably learned more from this thread then anyone else. I'll shut up for now (sleeping time) and again, many thanks Roger for your information. I wish your blacksmith club was a lot closer.

[Stanley Covington]

Antique wrought iron was not excessively high in sulphur. Sulphur makes wrought iron "hot short (https://en.wikipedia.org/wiki/Red-short)" (or "red-short") meaning that the iron would get brittle when heated to forging temperature.

Our ancestors did not have knowledge of chemistry but they could see the result of different ores. The ores from Sweden were very low in sulphur and were sought after for production of iron and steel. Bessemer had trouble with his process because of the ores used. He developed the process with Swedish ores but after he sold licenses for the process to others, they tried to use it with English ores which were high in sulphur and the process would not produce decent steel.

I don't think the migration of carbon is affected to any great degree by the origin of the carbon. The carbon was in intimate contact with the iron in the blister steel furnaces. I've not heard of any reports of rapid migration of carbon within iron. In fact, if it would migrate quickly once it was in the metal, we would not see the high gradient of carbon within blister steel. Once the carbon was in the iron, if it had high migration, carbon would migrate through the ingots (which were quite thin). But that's not what we see.

And while sulphur makes iron hot-short, phosphorus makes iron cold-short. That is, brittle when cold.

Mike

Great information, Mike.

Swedish iron ore is still listed as the purest commercially available in the world. Least sulfer, least phosphorus, less silica. I have it on good authority that Hitachi Metal's better products begin with it. And there are tool steels produced in Sweden today that are equal to (and some say better than) Hitachi's products. Harder to work with though, my blacksmith friends tell me.

Stan

[Stanley Covington]

Brian,

What chisel is this? Seems like a handy one for the corners of the half blinds.

Thanks.

Its called a "bachi" chisel from the tool used to pluck the strings on shamisen.

http://i.ytimg.com/vi/V-j-f_1uzVk/hqdefault.jpg

[Brian Holcombe]

Yessir!

I recieved some Konobu tsuki's and the weld line looks more like that of Yokoyama plane blade than most chisels I've come across. I'll post up a close up later on tonight.

[Brian Holcombe]

Better late than never :D

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.
http://i27.photobucket.com/albums/c181/SpeedyGoomba/D76357BE-8545-4DC7-9E99-5B5F8F879CBD_zpszqxf6gwk.jpg (http://s27.photobucket.com/user/SpeedyGoomba/media/D76357BE-8545-4DC7-9E99-5B5F8F879CBD_zpszqxf6gwk.jpg.html)
http://i27.photobucket.com/albums/c181/SpeedyGoomba/EDA36766-4996-4F22-BB5E-1912156C89C3_zpsyr0wugpl.jpg (http://s27.photobucket.com/user/SpeedyGoomba/media/EDA36766-4996-4F22-BB5E-1912156C89C3_zpsyr0wugpl.jpg.html)http://i27.photobucket.com/albums/c181/SpeedyGoomba/1A41B437-19ED-4F61-9CE2-6FBDCC9B1D01_zpsxj3pbtrf.jpg (http://s27.photobucket.com/user/SpeedyGoomba/media/1A41B437-19ED-4F61-9CE2-6FBDCC9B1D01_zpsxj3pbtrf.jpg.html)

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/viewcontent.cgi?article=1266&context=etd

[Kees Heiden]

Verhoeven, chapter 8: http://Metallurgy of Steel for Bladesmiths & Others who Heat Treat and Forge Steel
Miller: http://download.springer.com/static/pdf/872/art%253A10.1007%252FBF02647665.pdf?originUrl=http% 3A%2F%2Flink.springer.com%2Farticle%2F10.1007%2FBF 02647665&token2=exp=1448623011~acl=%2Fstatic%2Fpdf%2F872%2F art%25253A10.1007%25252FBF02647665.pdf%3ForiginUrl %3Dhttp%253A%252F%252Flink.springer.com%252Farticl e%252F10.1007%252FBF02647665*~hmac=b1e73f53de03528 90fe6b7ecfd0c068d32e04f01fd88fe0d45e89f64a75aa08d

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