Warp during normalization

[Temujin H-Pinchers]

Last night I normalized an Old Hickory Hunting Knife blade, I want to change the handle scales to the old traditional 6 pin configuration but had to normalize to be able to drill new holes through the tang for the pins. I wrapped the blade in stainless foil and took it to 1650F in my Evenheat oven. After a 10 minute soak I took the blade out and buried it in a bucket of wood ash to cool slowly overnight. This morning I took the blade out the foil and noticed it had developed a significant warp and slight twist. When I was looking at the normalizing procedure for 1095, which this blade is made from, there were no instructions on whether to put the blade in the cold oven and ramp up, or to get to temp then put the blade in like I would usually do for austenizing. I ended up putting the blade in when my oven was at about 1000F. Was the warping due to when I put the blade in the oven or something else? I know these are relatively cheap and simple knives, stamped out of strip metal so I also wondered if the warp could be from residual stress during manufacture. Just looking for some advise and knowledge on this matter. Many thanks.

 

[weo]

I also wondered if the warp could be from residual stress during manufacture

It's my understanding that the answer is yes,

 

[samuraistuart]

It could be stress from the original heat treat. It could be when you placed it into the wood ash, as the steel would be austenite and bends quite easily. Even a side to side motion during a quench can warp a blade, especially a thin one.

Tip....for any heat treat operation (normalizing, cycling, austenitizing, tempering), you want your furnace to be at the target temp and then insert the blade.

Another tip....I have always been told that with hypereutectoid steels like 1095, the wood ash/vermiculite/slow cool is not ideal during normalizing, it's too slow of a cooling process, as it tends to put that proeutectoid cementite (carbides) in the grain boundaries, making for a more brittle blade after heat treatment. A simple air cool is what you want. With that said, if you just stuck the handle in the ash and left the blade sticking out in air, that would have softened your tang nicely, and been the ideal cooling rate for the blade.

If it were my knife, I would get the holes drilled and re-normalize the blade, just do an air cool, nothing slower than that.

 

[3fifty7]

You seem to be going about this the most difficult way possible. Maybe it’s the way you are familiar with or the tools available to you, I can’t say as I’m not in your position.

Could you not have spot annealed where you want to redrill for pins?

The hardness on old hickory knives usually plays out between the first and second rivet, so likely you would have only had to do 2 spots.

 

[Temujin H-Pinchers]

Didn't seem particularly difficult, inefficient maybe?

I don't have any gas for my torch atm so didn't have the facility to heat only the tang. Softening the whole blade will make it easier for me to re-profile the knife if I wish before re-hardening it. The tang is hardened the whole length on this knife at least, evidenced by the instant flattening of the tip of my centerpunch when attempting to mark a pinhole at the butt end of the tang.

You seem to be going about this the most difficult way possible. Maybe it’s the way you are familiar with or the tools available to you, I can’t say as I’m not in your position.

Could you not have spot annealed where you want to redrill for pins?

The hardness on old hickory knives usually plays out between the first and second rivet, so likely you would have only had to do 2 spots.