Pursuit of perfection: The Japanese swordsmith

[Tornadoes28]

An article from the publication "Humans Invent: Innovation, Craftsmanship & Design"

http://goo.gl/obelA
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[Bethetsu]

I looked at the article:

[kitsuno]

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]

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....

http://www.ksky.ne.jp/~sumie99/ironandsteel.html
http://www.anselm.edu/homepage/dbanach/h-carnegie-steel.htm

[shin no sen]

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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知恵は時間及びエネルギーである

[Tornadoes28]

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.

[Bethetsu]

[nagaeyari]

Apparently,
carbon content 2～0.1%: steel
carbon content <0.1%: wrought iron

[JLBadgley]

[shin no sen]

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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知恵は時間及びエネルギーである

[jdmcowan]

[shin no sen]

I thought this might explain a little more. John


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知恵は時間及びエネルギーである

[Bethetsu]

[shin no sen]

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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知恵は時間及びエネルギーである

[jdmcowan]

[Bethetsu]

Thank you. That will be useful in trying to fit the various parts together.