Wavy warped edge on clay-quenched blades

[Leon Husock]

The last three blades I've quenched with clay on the spine the edge has done this thing where it wiggles back and forth. It's just the edge, not the spine, and it's so back and forth that there's no way to fix it in the temper. I take the edge down to .035", grind the scale off the blade, thermocycle, re-grind the scale off the blade, put the clay on and put it in a cold oven and bring it up to around 350/400 degrees and leave it for a bit so the clay can really dry out without popping off, then heat and quench. The only thing I've been doing differently lately is the part with the oven, but I can't imagine why that would be causing this. Has this happened to anyone else? Does anyone know why it might be happening?

Edit: the first time this happened my ashi lines in my clay weren't mirror images of each other and it seemed like the warping was caused by that, but the next two times I was careful to line my clay up on each side and it still happened. So *shrug*

 

[scott kozub]

I'm assuming w2 or 1095? How did you quench oil or water? Did you do a thin coat of clay over the whole blade? Heat treat oven or forge? Temperature and Soak time?

I just attempted my first hamons in w2. I left the edges at 0.03. One edge had a small wave and it was because I had a small thin spot there I didn't notice. 0.1 seems thick so id have a hard time seeing that warp. I have read that in water quenches the air forum by the vaporization of the water can cause bacon edge.

 

[Leon Husock]

I'm assuming w2 or 1095? How did you quench oil or water? Did you do a thin coat of clay over the whole blade? Heat treat oven or forge? Temperature and Soak time?

I just attempted my first hamons in w2. I left the edges at 0.03. One edge had a small wave and it was because I had a small thin spot there I didn't notice. 0.1 seems thick so id have a hard time seeing that warp. I have read that in water quenches the air forum by the vaporization of the water can cause bacon edge.

Hey sorry, yeah, W2, heated in a forge. I was going for 1475, but it was probably something like 1500, quenched in McMaster 11-second quench oil. Not much in the way of soak, I don't have a PID or anything. I don't do the thin coat of clay just because it's not how I was taught to do it. Also I just measured and the edge is .035, lol. I didn't have the knife on hand when I posted and I hadn't measured it before, just eyeballed (turns out I can judge whether it's the thickness I want it to be but I can't tell you what that thickness is, heh). I've edited the original post to reflect the actual measurement.

 

[Joshua Fisher]

Hey sorry, yeah, W2, heated in a forge. I was going for 1475, but it was probably something like 1500, quenched in McMaster 11-second quench oil. Not much in the way of soak, I don't have a PID or anything. I don't do the thin coat of clay just because it's not how I was taught to do it. Also I just measured and the edge is .035, lol. I didn't have the knife on hand when I posted and I hadn't measured it before, just eyeballed (turns out I can judge whether it's the thickness I want it to be but I can't tell you what that thickness is, heh). I've edited the original post to reflect the actual measurement.

To me it sounds like either the edge needs to be thicker before quench or the blade was too hot going into the quench, maybe try leaving the edge at .05 and make sure you are doing your ht with all the lights off so you have the best chance at reading the color of the piece since you are using a forge, I’d say if you wanted to leave the edge thin like you have it that a thin wash coat of clay would be the next best option, it may not be how you were taught but it is very common practice even for traditional smiths. If you did a thin wash coat then a thicker coating on the spine you may even be able to play around with a brine quench to see if you get an increase in activity in the hamon.

 

[Leon Husock]

Thanks, Josh. That's all super helpful, and I'll try it out. I'd suspected my edge was too thin, and it's extremely likely my blade is too hot considering right now I'm stuck working outside under a tent so I can't exactly turn the lights off. I've been saving up for a hydraulic press but now I'm thinking maybe a digital heat treat oven is the next piece of equipment I should get.

 

[Joshua Fisher]

Thanks, Josh. That's all super helpful, and I'll try it out. I'd suspected my edge was too thin, and it's extremely likely my blade is too hot considering right now I'm stuck working outside under a tent so I can't exactly turn the lights off. I've been saving up for a hydraulic press but now I'm thinking maybe a digital heat treat oven is the next piece of equipment I should get.

Try waiting to do the heat treat until dusk or when natural light is starting to go away, that’s what smiths would do traditional is wait until dark to heat treat, atleast from what I’ve seen of traditional Japanese methods. You can do a real quick torch temper just to relieve stress until you can do your full temper cycles the next day, or just do a short snap temper in a oven so you don’t end up with a cracked blade in the morning.

 

[JTknives]

Edge is to thin for carbon steel especially for clay coating, We call that bacon edge. Most times .03 can be ok for stainless steels, I personally think most stainless should be ground after heat treat. but on carbon steel you need to be around the thickness of a dime. The edge is hard and the spine is soft so the edge when quenched is actually longer now. This extra length has to go somewhere which is what gives that nice curve to Japanese swords. If the blade can’t curve up then the edge will buckle under the compressive stress and look like bacon. And actually Cooking bacon Does the same thing. There is fat usually in the middle of the bacon that shrinks down more then the meat the extra length of the meat has to go some where so it ripples.

 

[weo]

Nice explination and analogy, JT.

 

[Leon Husock]

Edge is to thin for carbon steel especially for clay coating, We call that bacon edge. Most times .03 can be ok for stainless steels, I personally think most stainless should be ground after heat treat. but on carbon steel you need to be around the thickness of a dime. The edge is hard and the spine is soft so the edge when quenched is actually longer now. This extra length has to go somewhere which is what gives that nice curve to Japanese swords. If the blade can’t curve up then the edge will buckle under the compressive stress and look like bacon. And actually Cooking bacon Does the same thing. There is fat usually in the middle of the bacon that shrinks down more then the meat the extra length of the meat has to go some where so it ripples.

Interesting. My understanding had always been that you only get the curve from a differential quench if you put clay on the spine itself instead of just on the sides (and use a sufficiently fast quench, of course). Hamons are pretty much the only time I grind before quench, so I don't have as much experience gauging an acceptable pre-quench thickness for the edge. I'll try to err on the side of slightly thicker in the future. I also think Josh was definitely right about going into the quench too hot, just based on some unscientific tests I did today of sprinkling salt on hot steel to see if it was at least 1475.