Tuesday, March 24, 2009

Heat Treating

I heat treated two blades tonight, a wakizashi and an integral bowie. Tanto is 14 inches, the bowie is now 3 pieces of very hard cementite. I held the bowie in the quench too long. This caused a spectacular crack near the handle. I think both were forged too thin for my liking.
14 inches is too big for a tanto. I should keep them down to a usable size. There is nothing too remarkable about the shape of this one. It is hira-zukuri. The spine is not thick enough at the machi for my liking, it is 0.23" I think. Its also flat, there are no ridges on the spine. This is unusual I think, but I'm not sure why. I would expect to see more hira-zukuri with flat spines from times when there were lots of wars. They are just extremely simple, and there is only one surface on each side to polish rather than 3 or more.
The clay pattern was simple with some lateral ashi. I wanted to maybe cross the ashi, but that takes much more time as one layer has to dry before the next is applied. So straight ashi, nothing complicated.
On the bowie I made a very risky and flashy pattern which was almost certain to cause problems with 1095 quenched in water.
Oh well. It would have been nice to see it at least stay in one piece.
It is a rainy, windy night, around 53 F. I let the forge get up to some heat before laying the blades on the floor and letting them come up to heat. This forge is not suitable for heat treating. I've been modifying it to reduce interior volume and increase heat for welding. I think it is the last time I will attempt to heat treat long blades with this one, but it is still good for forging.
There are hot spots around the burner, which makes it difficult or impossible to heat blades evenly. If they come up to heat unevenly, there are definitely going to be problems with warping or cracking. If these problems don't show up right away, I think the structure of the steel will all over the place.
I used tap water to at around 110F to quench.
The bowie went in the water first. I put it straight in edge first, held it until the color was gone, drew it out and went in again still spitting and vibrating. This of course is a bad idea, and so it cracked. All of the factors involved were against this one succeeding. The geometry of the blade was weird, the clay pattern, etc.
So the wakizashi I figured had a little better chance because of the simple clay pattern, and now the water was a few degrees warmer. I held it just until the color was gone, then removed it. If its going to harden, it will harden within the first second or so. I don't see any reason to put it back in the water once the color has gone to black. Actually the best idea would probably be to put it right into a tempering oven for an hour before anything is done to it. 1095 has to be treated carefully. It's not as forgiving as stuff in the .50 to .70 range.

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