Stress relief for 15N20 - will it help with warping issues?

Heikki

Heikki

KNIFE MAKER
I've been doing some research on AEB-L recently because I want to start working with stainless steel this coming year. I came across a discussion of doing a stress relief cycle to reduce chances of warpage- basically soaking at 1200 F and letting cool overnight in the HT oven.

My question is would that same process work with 15N20 to help reduce warping? I'm working on a set of kitchen knives and have had some issues with 15N20 warping in the past.
 
You might want to consider a normalizing cycle. Per Dr. Larrin Thomas, this should help with warping. The difference is that you heat to austenizing temperature then air cool. His book is a wealth of information but, it gets into a lot of deep science.
 
Get yourself one of Kyle Daily’s straightening hammers. I pretty much only make chefs knives, and unfortunately, warping is the name of the game. I use 52100, so a little different from 15n20. Seems like I always have a little warp after HT, but what I started doing is quenching past the nose, and then immediately clamping it between my quench plates to come to room temp. You aren’t going to hurt it by doing a long anneal like that, but no matter what thermal treatment I do, there is always a little. I start a lil thicker than I want in the end so I can grind any little wiggles out.
 
I made a punch version. I had plenty of 1" brass rod laying around so I drilled one end and JB Welded some carbide rod in. I used 3/8" carbide rod and rounded it on the grinder after it was all glued up. I wanted to know how much pounding it would take to fracture the carbide (or the JB Weld), so I went cro-magnon with it on a banana shaped fillet blade and it ended up cracking my tempered blade... so don't go all cro-magnon with the smackety-smack. But the carbide will hold up if you're wondering.

Mine works within reason, but it's not going to take out a 1/4" warp unless I'm just doing it wrong. Anyhoo, there's an easy solution for AEBL and other such stainless...

Great piece of advice I got from Steve Miller (Bladegrinder) on here a long time ago: Stainless takes a lot longer to fully harden than you think. It is NOT like carbon steel where it comes out of the quench glass hard. When you pull AEBL out of the quench plates and you can hold it with gloves, if it's warped you can gently bend it for a very long time. You can literally straighten it with your gloved hands, and it's easy- so be gentle.

If the steel is that prone to warping that it comes out of the plates and warps, it's going to try to warp over and over again. Straighten it when it comes out of the plates. Then, and only then, clamp it to some bar stock or something before you do cryo / freezer. Keep it clamped all the way through the cryo and all the way through the temper cycle. It will stay straight then. It may pick up the tiniest bit of warp after it tempers but by then it's truly hard and the warp should be so minor that you can center scribe it and grind a straight blade out of it.

If you straighten it after the plates and then try to cryo without clamping it, my experience is that it will go banana shaped in cryo (and then fully harden) and the only way to straighten it then is with a torch and your vise. Maybe you'll get lucky and it will be minor enough to use the carbide hammer/punch.
 
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I noticed the same thing John pointed out about AEBL. Blades were so bendy out of the plate quench that I thought they didn’t harden. I tried oil quenching, same result, then out of frustration I quenched it in water. It didn’t crack, but it was quite bendy after that even. They stiffened up in cryo, and also warped badly in cryo, since I didn’t have them clamped in cryo. I ended up breaking all 5 blades, and went back to CPM154. It’s a bit better behaved.
 
Edwardshandmadeknives said:
I noticed the same thing John pointed out about AEBL. Blades were so bendy out of the plate quench that I thought they didn’t harden. I tried oil quenching, same result, then out of frustration I quenched it in water. It didn’t crack, but it was quite bendy after that even. They stiffened up in cryo, and also warped badly in cryo, since I didn’t have them clamped in cryo. I ended up breaking all 5 blades, and went back to CPM154. It’s a bit better behaved.
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You aren't kidding about doubting that it even hardened. It's dead soft out of the plates and that really freaked me out when I discovered that. Steve's advice calmed me down. I'm no metallurgist but I do a fair bit of research, and up until then I had not even heard it mentioned that it doesn't actually harden in the quench. You'd think somebody might have pointed that out before.

AEBL is very very warpy in my experience. A lot of people have also pointed out that what we get from Aldo may or may not be true AEBL and acts funnier than it should. The stuff from Aldo is most definitely cut from a coil because I get some in that looks like a leaf spring. That means it was pulled from a coil, went through a straightener before the shear, and still decided to coil up again. When you get a piece like that you better put your straightening boots on, because it's going to want to warp at every step of the process. I bought a LOT of it and I'm still working through it.

At this point I'm so used to the warp tendency that I have worked out my process to account for the warpiness (is that a word?) such that it no longer presents a problem. I just expect it to warp and so I handle it as described above. Real AEBL or not, it makes truly fantastic blades. I use the stuff for literally everything I make unless I get a special request.
 
John Wilson said:
You aren't kidding about doubting that it even hardened. It's dead soft out of the plates and that really freaked me out when I discovered that. Steve's advice calmed me down. I'm no metallurgist but I do a fair bit of research, and up until then I had not even heard it mentioned that it doesn't actually harden in the quench. You'd think somebody might have pointed that out before.

AEBL is very very warpy in my experience. A lot of people have also pointed out that what we get from Aldo may or may not be true AEBL and acts funnier than it should. The stuff from Aldo is most definitely cut from a coil because I get some in that looks like a leaf spring. That means it was pulled from a coil, went through a straightener before the shear, and still decided to coil up again. When you get a piece like that you better put your straightening boots on, because it's going to want to warp at every step of the process. I bought a LOT of it and I'm still working through it.

At this point I'm so used to the warp tendency that I have worked out my process to account for the warpiness (is that a word?) such that it no longer presents a problem. I just expect it to warp and so I handle it as described above. Real AEBL or not, it makes truly fantastic blades. I use the stuff for literally everything I make unless I get a special request.
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The stuff from Aldo isn’t “real” AEBL, it’s some other stuff that’s real similar. If you look at the material certs he has, it says what it actually is. I treated it like AEBL.
 
I know this isn’t really the answer you are looking for, but if you do have consistent warping issues with any steel, you can try what I do. Especially when I am working asymmetric blades (yanagiba) they warp badly in one direction. I harden the blade, then stand it on edge on my anvil and trace the curve of the blade. I anneal/normalize/etc, then bend the blade in the opposite direction of the warp enough that when it is hardened the second time, it will warp back straight. It works pretty darn good, usually a little bit uneven but not to where I can’t straighten it out pretty easily. Might be an option?
 
John Wilson said:
You aren't kidding about doubting that it even hardened. It's dead soft out of the plates and that really freaked me out when I discovered that. Steve's advice calmed me down. I'm no metallurgist but I do a fair bit of research, and up until then I had not even heard it mentioned that it doesn't actually harden in the quench. You'd think somebody might have pointed that out before.

AEBL is very very warpy in my experience. A lot of people have also pointed out that what we get from Aldo may or may not be true AEBL and acts funnier than it should. The stuff from Aldo is most definitely cut from a coil because I get some in that looks like a leaf spring. That means it was pulled from a coil, went through a straightener before the shear, and still decided to coil up again. When you get a piece like that you better put your straightening boots on, because it's going to want to warp at every step of the process. I bought a LOT of it and I'm still working through it.

At this point I'm so used to the warp tendency that I have worked out my process to account for the warpiness (is that a word?) such that it no longer presents a problem. I just expect it to warp and so I handle it as described above. Real AEBL or not, it makes truly fantastic blades. I use the stuff for literally everything I make unless I get a special request.
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Not AEB-L. Similar German steel. At least one heat treater says tell them if it is Aldo steel because it requires a slight modification in the process. I suspect that 13C26 is the same because it is also slightly different. The stuff from Alpha is supposedly not from a coil.
 
I dont use AEB-L at all but i was wondering if it still warps if you harden and temper before grinding........also if it is left clamped in the aluminum quench plates till it is cold? I grind everything post heat treat when using stainless
 
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