Japanese Sword Quenching
 

Hi Folks,

A very informative paper: http://www.shibuiswords.com/tatsuoinoue.htm

Cheers
Chris

Rather neat to see this type of work being carried out, even though the final results may not have revealed anything major. I'm not so sure if I really agree on the heat transfer coefficients being "paradoxal" though, not too hard to see how the clay coat both provides better nucleation possibilities for the steam (helping cooling) and insulation through its thickness, resulting in just the behaviour they measured.

Hi Kisak,

Steam is generally considered the enemy of heat transfer because it is a thermal insulator relative to water. For this reason, if a very fast quench (cooling) is desired, salt is added to the water to minimize the stem envelope that otherwise would form around the blade. I haven't read that article in full, only raced through it as I have major construction works on my house to oversee.

Cheers
Chris

From what I can recall the salt helps through increasing nucleation, no?

Hi Kisak,

I took a little time out to read that paper, though only the sections dealing with the clay and cooling rates.

The aim of covering a Japanese blade in clay is primarily to slow down the cooling rate in the parts of the sword relative to that of the edge. This is so that the edge can transform to the hard martensite desired and the rest of the blade into the more ductile ferrite + pearlite, with a transition zone in between.

Salt is put into quenching water to help break up the water vapour barier that otherwise would envelop the steel and slow down its cooling rate. From that paper, it would seem that a thin coating of clay over the edge region has a similar effect, whereas over the rest of the blade, where the clay is applied more thickly, the cooling is slowed down and hence the paradox referred to..

Cheers
Chris