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Pursuit of perfection: The Japanese swordsmith

 
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Tornadoes28
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PostPosted: Fri Feb 10, 2012 2:17 pm    Post subject: Pursuit of perfection: The Japanese swordsmith Reply with quote
An article from the publication "Humans Invent: Innovation, Craftsmanship & Design"

http://goo.gl/obelA
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PostPosted: Fri Feb 10, 2012 3:42 pm    Post subject: Re: Pursuit of perfection: The Japanese swordsmith Reply with quote
I looked at the article:
Quote:
The traditional Samurai sword is made from specialist Japanese steel, Tamahagane, which is made up of combinations of hard, high carbon steel, and tough, low carbon steel. The idea is that the high carbon steel is harder and able to form the shape of the sword, while the low carbon steel is more brittle and could break during combat. Having a small amount of carbon allows the sword to absorb impact and be more malleable, becoming blunt but not breaking during any form of combat.
I know absolutely nothing about sword-making, so I am trying to learn something, but did some sentence there get backwards? Like, is low carbon brittle and breakable and yet tough?
When they say "having a small amount of carbon allows the sword to absorb impact" are they comparing it with steel with no carbon, so a small amount is good, or do they mean "having only a small amount allows the sword to absorb impact" so low-carbon as opposed to high-carbon? What are the Japanese names for high- and low-carbon steel?
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PostPosted: Fri Feb 10, 2012 4:02 pm    Post subject: Reply with quote
It's definitely not very welll written, but my assumption is that low carbon steel, while brittle alone, adds malleability and flexibility when combined with the high carbon steel. But we'll wait for an expert to drop some knowledge here.
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nagaeyari
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PostPosted: Fri Feb 10, 2012 4:46 pm    Post subject: Reply with quote
In a nutshell, carbon is the major difference between iron and steel.

Higher carbon content (in most Japanese texts, this is just written as 炭素量が多い・少ない, although since carbon content is the major difference between iron and steel, those terms are preferred, it seems) = harder, but more brittle.

Lower carbon content = more malleable.

You will find a higher carbon content in cast iron, as carbon lowers the melting temperature. In lower-carbon iron, you will need to hammer out impurities from the spongy, soft mass called the bloom.

And now I have taught you all I know.... Laughing

http://www.ksky.ne.jp/~sumie99/ironandsteel.html
http://www.anselm.edu/homepage/dbanach/h-carnegie-steel.htm
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PostPosted: Fri Feb 10, 2012 5:12 pm    Post subject: Reply with quote
That is one of the facets that make the Nihonto a good sword. There are many ways to construct one, but, simply it is a lower carbon steel wrapped in a higher carbon steel. The higher carbon steel in the hardening quench (yaki-ire) which forms the cutting edge is cooled faster to create the hard martensite needed to hold an edge. The back of the blade cools slower and is composed of ferrite and pearlite which can absorb the shock of cutting allowing the blade resistance to shattering. The edge can be too hard and require tempering to reduce the hardness and built in stresses.Early swords even have iron as the core steel. Some swords have a monosteel (kobuse) that obtains this hard soft construction by only the differential hardening process. This is simplified, but, basically the process. John
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PostPosted: Fri Feb 10, 2012 7:14 pm    Post subject: Reply with quote
Great conversation and information on the swords guys. It's information like this which is why I love coming here. I am not very knowledgeable on sword construction either but I do know about the general differences that nagaeyari described. What was interesting to me from the article was the different eras of swordmaking in Japan.

Quote:
The history of the Samurai sword is divided into four periods – Koto (Pre 1596), Shinto /Shinshinto (1597 to 1876), Gendai (1877 to the end of world war II), and Shinsaku (modern).


Interesting how the first era goes up to 1596 with the remaining eras up through modern times.
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PostPosted: Fri Feb 10, 2012 8:28 pm    Post subject: Reply with quote
nagaeyari wrote:
In a nutshell, carbon is the major difference between iron and steel.

Higher carbon content (in most Japanese texts, this is just written as 炭素量が多い・少ない, although since carbon content is the major difference between iron and steel, those terms are preferred, it seems)
Also "Early swords even have iron as the core steel."

So does "iron 鉄" have less carbon than "steel 鋼", or do I have the wrong terms? It seems like steel is between wrought iron and cast iron, so I am not sure.

If I understand what has been said, it seems that that original quote should be rewritten as something like: "High carbon steel is harder and able to form the shape of the sword, but it is more brittle and could break during combat. So low carbon steel which is malleable, not brittle, is also use. Having a core of steel with only a small amount of carbon allows the sword to absorb impact and be more malleable, becoming blunt but not breaking during any form of combat."

Shin no Sen: "[Nihon-to] is simply it is a lower carbon steel wrapped in a higher carbon steel." So, when they talk about how many layers are in a sword, does that mean the core is (usually) made of layers of wrought (hammered out) iron?
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PostPosted: Fri Feb 10, 2012 8:54 pm    Post subject: Reply with quote
Apparently,
carbon content 2~0.1%: steel
carbon content <0.1%: wrought iron
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PostPosted: Sat Feb 11, 2012 4:32 pm    Post subject: Reply with quote
Bethetsu wrote:
So, when they talk about how many layers are in a sword, does that mean the core is (usually) made of layers of wrought (hammered out) iron?


So if you want any kind of iron out of the iron sand, as I understand it, there will need to be some kind of hammering and folding that will go on. It is just a matter of how much and the base materials used.

-Josh
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PostPosted: Sat Feb 11, 2012 6:58 pm    Post subject: Reply with quote
When the iron bearing ore (iron sand or other type of ores) is smelted (in the tatara) there is a mixture of steel and iron of varying carbon content. Tamagahane (jewel steel) the most coveted is not pure from the smelt. Further work is done to make the steel more homogenous and specific. Folding and hammering does this as well as expressing impurities. The Japanese were not the only people to do this and this was not the only method to homogenise steel. The Chinese and Koreans for the most part smelted cast iron and used decarburising methods to produce wrought iron or steels from that. John
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PostPosted: Sun Feb 12, 2012 5:39 am    Post subject: Re: Pursuit of perfection: The Japanese swordsmith Reply with quote
Bethetsu wrote:
I know absolutely nothing about sword-making, so I am trying to learn something, but did some sentence there get backwards? Like, is low carbon brittle and breakable and yet tough?


No. They got some things mixed up. Higher carbon content makes the steel harder, stiffer, and more brittle. Lower carbon content makes the steel softer, more flexible, and more bendable. I'm not clear on the names for the different carbon steels themselves, but the higher carbon steels are formed into kawagane "jacket steel" and the lower carbon steels are formed into shingane "core steel". The kawagane holds an edge better and looks prettier. From what I understand, until the Kamakura era swords were mostly made out of pure kawagane. Then it was discovered that by making the core out of softer, more flexible shingane, the swords would break less. You can't make a sword out of pure shingane because the edge would blunt very quickly and your sword would constantly be bending out of shape. However, by making the core soft and keeping the jacket hard, you could get the best of both worlds.
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PostPosted: Tue Feb 14, 2012 5:20 am    Post subject: Reply with quote
I thought this might explain a little more. John


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PostPosted: Tue Feb 14, 2012 3:44 pm    Post subject: Reply with quote
shin no sen wrote:
I thought this might explain a little more. John
Thank you. On the right page, those are 5 different methods of making swords? It seems that there are three different metals- the iron core 心, the steel jacket (skin) 皮 and then the blade 刃. Is the blade of even a higher higher carbon than the jacket? Which method is used for the classic Nihon-to? I cannot see the page well enough to read it. In no. 4, the jacket seems to run into the blade. Is the blade in that case made by cooling, not by different content?
Earlier I asked about Nie. You said it was the individual particles of martensite.The dictionary said it was 刃と地肌との境目に銀砂をふりかけたように輝いているもの. Is the blade made of martensite formed by cooling and the nie is seen when the blade is sharpened with a whetstone?

My image of sword-making based on various scenes in books, opera, kabuki, etc. (the equivalent of reel history), is of someone(s) hammering out a sword. Would this be especially the hammering out that makes the different metals stick together, or an earlier hammering, or since it occurs many times is this just a conventional way of describing making a sword?
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PostPosted: Tue Feb 14, 2012 5:27 pm    Post subject: Reply with quote
There is a multitude of sword construction methods. See http://home.earthlink.net/~steinrl/laminate.htm
When the different steels are heated and hammered they weld together, sometimes fukure (kizu-flaw) appear later where they didn't weld properly. There is some discussion still about fluxes and their use. Maru uses only one type of steel to make the sword, but, it must have the required carbon content to make the type of hard crystallised steel required for a hard edge holding blade. Kobuse is the most common. Nie and nioi show when the blade is polished and for the most part in the habuchi, the area of transition between the hard edge and the softer body of the sword. Oh, in the link is a spelling error, the soft core should be spell 'shingane'. John
Click on some interesting "cross-sections".
See actual blade cross sections of Japanese swords,
courtesy of Ted Tenold, Harvey Stearn and Mike Christianson
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PostPosted: Wed Feb 15, 2012 4:16 am    Post subject: Reply with quote
Bethetsu wrote:
Is the blade of even a higher higher carbon than the jacket?


Sometimes. If you look at the link Shin no sen provided, you will see that sometimes a separate piece is used for the actual edge. When this is done it is a higher carbon steel called hagane. However, the ones where the same edge metal extends all the way up the sides, the diagram is incorrect and that metal should be kawagane, not hagane.

In addition, the edge is further hardened through rapid cooling by quenching. Since you have other questions about folding, I'll go through the whole process in summary and you'll see the extra hardening at the end. I will leave out many of the steps which have nothing to do with hardening.

Tamahagane is full of impurities and the carbon is very inconsistent. Folding and hammering helps push out the impurities and more evenly distribute the carbon. The hammering must be done carefully to make sure the layers weld together and do not form pockets of air between the layers. However, you also loose steel and carbon through the process. Most smiths use somewhere in the range of 15-20 folds for the kawagane, which reduces the weight of the metal to about 1/4 of the original and the carbon density by about 1/2 (~1.4% -> ~0.7%).

Shingane is also steel, not iron. Shingane starts with a carbon content of about 1/3 of the beginning kawagane, but is only folded about 10 times and so winds up with about 1/2 the carbon content of the final kawagane (~0.5% -> ~0.3%).

In the kobuse-gitae method (the most common), the kawagane is then formed into a U and the shingane is placed in the middle. Through a different type of hammering, the block is extended into a long sword-shaped piece of steel. The smith then uses another hammering technique to form the features of the sword.

Finally, the entire sword is coated in clay. Thickly on the sides and back and very thinly on the edge. The pattern of clay helps form the shape of the hamon. The sword is re-heated in a way that heats the edge more. It is then plunged into water which causes the areas with thin clay to cool very quickly (called quenching). This quick cooling causes martensite to form through the steel making it much harder. Nie are, in fact, pockets of martensite that form in the transitional area. By the way, this hardening can be un-done by reheating the sword and letting it cool slowly. Also, as the steel which was coated in thick clay cools more slowly, it shrinks more and a curve appears in the sword. The curve can also be effected by the shape created before quenching and through various techniques after hardening.

Thus, though the edge and the sides are often made of the same metal, the edge is made harder than the sides through quenching.

The big sledgehammers often seen in popular depictions are from making the metal through folding. The methods for shaping the sword are made with smaller, less impressive hammers. Sometimes in popular depiction, you will also see the quenching since this is often considered the moment that the metal actually becomes a sword. It can be very dramatic with the smith suddenly moving from the furnace to the water and lots of steam and sound.

I hope I have done justice to the process and that it helps you.

Jeremy
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PostPosted: Thu Feb 16, 2012 3:47 pm    Post subject: Reply with quote
Thank you. That will be useful in trying to fit the various parts together.
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