Tanto blade tempering

D

DruBokkens

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Jul 17, 2016
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Not sure if the question belongs in this section, but I'm curious about the tanto blades tempering process, specifically, how did they remain straight despite receiving differential heat treatment? On some antique examples I've seen a hamon, thus expecting the blade would gain a sorii when cooled, yet the mune was perfectly straight.

Also, was there a difference in lamination between tanto and katana? Did they just forge such short blades in maru if even kobuse and harden the edge, since I imagine there wasn't a need for a knife to stand up to the same stresses as a long blade? Hard to imagine a hira zukuri tanto blade laminated in soshu, or am I wrong?


Doing my homework in this area since I haven't had a chance to learn enough about forging differences between daito and tanto, figure 'got to start somewhere.
 
I know nothing, but I'd have imagined that the curving caused by cooling would be less pronounced in a shorter/smaller piece of steel.
I HAVE seen some items described to me AS tanto that did have the curve, as well.
S'probably wizards.
 
Good point. I've seen some tanto blades ever so slightly curved, barely noticeable, so likely quenching wouldn't be able to bend them so much due to short blades being much wider in proportion to length than long blades, so more material resisting and countering bending force. I guess they didn't bother so much trying to control the outcome shape and just let it happen naturally, whatever the end-result curvature. Looking at some older blades, I also assume they just clay-tempered the very edge (to lesser extent toward the shinogi than on long blades), since on tantos I've seen, hamon tends to be thinner, which also would reduce the steel stress during quenching.

That leaves lamination difference. I've read somewhere a long time ago that in tanto blades they only used basic lamination, kobuse being plenty sufficient on higher quality blades, or even more commonly maru. Curious if someone could expand on it.
 
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I have no experience working with traditional Japanese steels in a water quench, but I deal with negative sori on my quasi-Japanese style blades with an oil quench. Yes, the curve is much more noticeable on a longer piece. I have traced the curvature of the spine on my anvil with soapstone prior to the quench, then compared it afterward. The further you get from the blade/tang transition, the more the curve drops. So with shorter blades, there is less steel to curve and the effect is less obvious.
 
A negative curve was introduced, which would allow the blade to be straight after quenching. Any adjustment was done by hammering the spine afterwards, which would allow for a bit of adjustment. Shorter blades did undergo less curvature obviously, but this is/was still a factor that experience would overcome.
Many/most tanto did not have a core of softer steel due to the size. Still forged and folded though.
 
Thanks a lot for the info. Do you think lamination method influences the degree of curvature after quenching? Say, if they forged a tanto in shihozume or soshu, would the softer layers present there make it a bit less resistant to bending force during quenching, as opposed to maru of uniform hardness throughout the whole piece?
 
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I have an ooold tanto that appears to be a san mai with very coarsely laminated side panel construction, so they did do the complex builds now and again-I think that might have had more to do with conservation of material (core steel) rather than strength.
I think there's a big difference between clayed water quenched differential hardening and modern oil/oxyacetylene torch (or clayed) DH-the Japanese got positive sori, every single DH'd blade I've done that was not water/clay has negative sori (youcan also see it in seaxes of the Viking era in Scandinavian museums). The ones I've done in water with clayed hamon all went positive, up to and including ripping the hardened edge apart/off in one case. The contraction of the spine during cooling has a lot of leverage.
Also interesting to note-that old tanto of mine is nearly glass hard at the edge.
 
Then they must have relied on negative sori for the most part, to take the blade as close to straight as possible. However, if your tanto's blade is shinogi or similar, it could have been forged in honsanmai as a longer blade and cut down to tanto later on?
 
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Quenching a Tanto

[video=youtube;eb9ZCyvf8uQ]https://www.youtube.com/watch?v=eb9ZCyvf8uQ[/video]

Main thread in custom forum

I will post here when it's done
 
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