Japanese Swords, Layers, and Carbon Migration

[darrylburke]

in several place's I've read about the "wrapping" of a softer metal around the harder "core" of a japanese sword, as well I've also seen some refrences to how "pattern welding" works with regards to two different steels (higher and lower carbon). and how the "carbon migration" essententualy evens out the level of carbon in both steels .

the questions I have is. is this true with the japanese swords as well.. I know that the inner layers were folded for working out the impurities (same metal folded on itself), but how much "migration" would happen on the "inner" and "outer" layers.. I assume that the more layers of wrapping around would cause more migration of the carbon, but how much would a single layer. Are the claims of the "harder core" as accurate as the say?
(or does the theory of carbon migration contradict this claim)

[DimeNickel]

Hi Darryl

there is a study on carbon mig done by Howard Clark... basically it takes about 5 weld heats and alot of the carb is distributed..

when the steel becomes non-mag.. the carbon goes into solution and will tend to move into low concentrated areas..
- elements like Ni, P, tend to stop or slow this down..

- as for the soft and hard steel in katanas... i'm not convinced of this... -but the clay quench makes for a soft spine and hard edge..

Greg

[Ray Rogers]

I don't know about the 'hard core' method that you mentioned either but I believe that some swords were made in a 'San Mai' fashion. This is simply taking a thin, hard piece of high quality blade steel and sandwiching it between two other pieces of mild steel. In effect, this creates a hard core that is thin enough to have some flex when supported by the softer wrapper. Done this way, there is probably only one or two welds required and migration wouldn't be a serious concern. In fact, I don't think migration is even a serious concern in damascus unless you are trying for hundreds of layers (which requires a lot of folding and heating).........

[Mail4Tim]

Just a bit of trivia for you. The term "San Mai" is actually Japanese for 3 flat things. San is Japanese for 3 and Mai is a counter. It is used for counting flat things, such as paper or sheets of steel.

Like I said, it's not really related to the topic it's just one of those fun facts. Hey, four years of living in Japan has taught me a little...

Tim