Thin AEB-L heat treating issues

H

Hubert S.

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Dec 14, 2019
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I heat treated two AEB-L blades yesterday, one 0.04" thick, the other 0.082". Both were only profiled and about 11" or so long. I did a prequench after twenty minutes at 1,725F and then 1,975F for ten minutes. Both blades seemed to bend under their own weight on the way from oven to quench plates. The thinner blade curled up at the ends shortly after I put it on the bottom quench plate and before I put the top plate on, the ends were about 1/2" off the bottom plate. I quenched the blades separately and left them between the plates for two minutes. The thicker blade was at 70F, the thinner one at 100F after that amount of time. I think the folds of the foil packet in the corners were actually thicker than the blade itself and I did not have good contact everywhere because of that. After plate quenching, I removed the blades from the foil packet and put them in a dry ice/denatured alcohol bath.

Both blades were pretty warped, so I clamped them to a piece of angle iron and tempered for two hours at 350F. The warp did not get noticeably better, so I shimmed and over-corrected the warp when clamping and tempered again at the same temperature for another two hours. This appeared to have helped a little bit, particularly on the thinner blade. The thicker blade is in the tempering oven again with a bit more aggressive correction applied.

Am I wasting my time trying to straighten the blades this way? Is there a better way to straighten them?

I want to cut out a few more blanks and try this again, but I am not exactly sure what I need to do differently to get better results. I did not have the quench plates mounted in a vise and just used my body weight. Next time, I will try the vise. How hard do I need to squeeze?

When sealing the foil packet, how many times do I need to fold the edges? I folded three times and the blades came out pretty clean, but I think the folds prevent the quench blade from making good contact with the thinner blade. Also, the foil stuck a little bit to one of the blades. Is there any way to prevent this?

Is there anything else I can do to minimize warping?
 
Try coating the blade in baby powder before wrapping it in stainless foil.
 
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HSC /// said:
Can u explain this...What for? What does this do?
Click to expand...
He said that he was experiencing issues where the blade was sticking to the aluminum foil pouch. I have heard that coating the blade in baby powder before placing it in the pouch for heat treating helps prevent sticking.
 
HSC /// said:
Can u explain this...What for? What does this do?
Click to expand...

I found a few posts about this, one by Darrin Sanders from 2012:

Darrin Sanders said:
A light dusting of cheap baby powder will stop the welding and you don't have to worry about the WD-40 flaming up or ballooning the package. Baby powder is Talc which is a rock in a powder form so it wont burn even at these temps.
Click to expand...
 
Hey Hubert,
Welcome to the joys of HT-ing AEB-L!

JTknives JTknives is the guy to ask about this, he does it professionally for a lot of the makers out there.

a couple things to ask, 1st are you profiling and bevel grinding before you try heat treating? if you are, stop. profiling is fine, but you will have tons of warp issues if you try HT after doing the bevels.

2nd are you laying your packages straight on the floor of the kiln? if so, you probably want to find some way of holding the knife edge up, or edge down in the kiln, so that you get more even heating. AEB-L is so finicky that you need to eliminate every variable that you can to ensure that you're getting everything as even as you possibly can.

if your packages are giving you problems in the plates, try making them bigger, so that the folded areas are outside the plates (i have no evidence for this, just a thought).

ask JTknives, he knows the deal for sure!
 
TheEdge01 said:
He said that he was experiencing issues where the blade was sticking to the aluminum foil pouch. I have heard that coating the blade in baby powder before placing it in the pouch for heat treating helps prevent sticking.
Click to expand...
It is a stainless steel foil pouch (309, I think).
 
A.McPherson said:
Hey Hubert,
Welcome to the joys of HT-ing AEB-L!

JTknives JTknives is the guy to ask about this, he does it professionally for a lot of the makers out there.

a couple things to ask, 1st are you profiling and bevel grinding before you try heat treating? if you are, stop. profiling is fine, but you will have tons of warp issues if you try HT after doing the bevels.

2nd are you laying your packages straight on the floor of the kiln? if so, you probably want to find some way of holding the knife edge up, or edge down in the kiln, so that you get more even heating. AEB-L is so finicky that you need to eliminate every variable that you can to ensure that you're getting everything as even as you possibly can.

if your packages are giving you problems in the plates, try making them bigger, so that the folded areas are outside the plates (i have no evidence for this, just a thought).

ask JTknives, he knows the deal for sure!
Click to expand...
I only profiled, no bevels. I had the pouches upright in the kiln, more or less. I had both blades in the oven at 1,725F, but did them individually at 1,975F.

I will make the packages bigger next time and see if that helps.

The additional temper did not do anything to straighten the blade any further, even though I doubled up on the shims.
 
often you really have to go further than you think you should with the shims... you might also try raising the temps by 25-50 degrees each time you temper. of course you can't go too far with that or you'll get your RC lower than you would like.
 
I went a lot further with the shims than I thought I should already. I think it was about 5mm. Do you think it is worth trying again with more?

I tried peening the surface and that seemed to help. It got about half the warp out. The trouble is I don't have the right tool, just an improvised tool from an old tap. Initially, it left nice little dimples but got less effective pretty quickly. I guess the blade is hard. I think this method will let me straighten the blade with a bit more effort, but I think when I start grinding the bevels, the blade is going to go straight back to the warped shape.
 
I have never tried the hammering technique, but from what others have said, it's effective even after you sand out the divots.

also when you start grinding your bevels, your gonna get more warp, it's just the nature of AEB-L. as you grind just do a pass or two on one side, then a pass or two on the other to keep it even.
 
Welcome to the world of aebl. Everything your experiencing is normal for aebl. Only double fold the edges. If and when you get a leak it won’t be from a fold it will be from the bottom edge that is sitting in the oven floor. When ever I have a foil packet fail that’s where it fails. Your going to need more weight then just standing on it unless you weigh 400-800 pounds. My plates are mounted to 9” wood workers vises with a quick release. Aebl has to evenly cool or it warps, and even then it will still try and get away from you. The thing is that aebl is cold rolled (most thicknesses) and coiled. Even if you get it straight out of the quench and temper it’s going to warp and bow as you grind it. I have not found clamping during tempering to help with straightness. Clamping and counter bending on plates while tempering works really good with carbon steel but does not really phase aebl. I find the best way to deal with warps is to get all your heat treating and annealing done and out of the way. Then surface peen to correct the bows. You can surface peening a blade as you grind it as well if you need to. I made a filet knife for my mother-in-law for Christmas’s abs as I was hallow grinding it the tip kept wanting to bow one direction. Just gently peened it on the inside of the bow and back to grinding. It came out perfectly straight.

AEBL is a steel that you will HATE heat treating at first but as you do it more and more it won’t bother you as much as you slowly die inside from all the stress. Once you’re fully dead inside you will fly through the heat treating with out batting an eyelash.

oh and .040 aebl can be a royal pain in the ass. It’s so thin it cools all mostly instantly so it has to get into the plates and clamped with in seconds. When clamped you have to make sure your plates are clamped square and perfectly parallel. If not then you not cooling the blade evenly.
 
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That sounds encouraging, I guess? I will try again this weekend. If I have to die inside, better get it over with quickly!

I appreciate all the advice. I have a 7" quick release wood workers vise that I will mount the plates to.

I went to your website and saw that straightening hammers will be coming soon. How soon is soon and what could I use in the meantime to try and fix the warped blades I have?
 
I just did a couple .040 AEBL fillet and pairing knives this weekend. Like all AEBL they came out warped. I've never had luck trying to bend them straight. Recently I got some bead media for my sandblaster and in less than 1 hour I had 15 blades straight ranging in thickness from .040 to .118. The thin stuff straightens really fast.

Jts advice is as good as it gets.
 
Thank you, Scott. It's good to know I am not the only one with warping issues. I will not try to bend the thin blade straight any longer. It did not really get any straighter, and then I broke of part of the tang!

I tried the sandblaster on the 0.082" blade and it was an improvement, but I could not get all of the warp out with it. I have pretty fine abrasive in it, maybe that is not ideal.

The way I see it, I now have two blades to practice grinding on. With your and JT's advice, I hope my next set of blades will be better.
 
Keep at it. AEBL is a pain but makes beautiful blades. Especially for the kitchen. Make sure they're as cool as possible before going into cryo or sub zero. If they do warp out of the plates you have a minute or so while they are really soft and can be bent straight or bent warped if not careful. I find they tend to warp in the cold treatment but it seems to help to keep then vertical. Why I tried laying them down in dry ice they warped like crazy.
 
Yeah, 1/16" or thinner tends to be thinner than the foil folds, which is problematic between plates. I carry my blades in a vertical orientation from the kiln to the plates, but I think the thin ones still warp under their own weight. Vertical plates would be better.

The baby powder trick is key. Doesn't take much.

One thing I've learned is to NOT correct warps between plates and sub-zero steps. Sure, the steel is cool enough to touch, but still tantalizingly pliable... you'll be sorry. Let it finish all it's warping.

I warm to tempering temp for an hour at least, then bend between wooden vise jaws. Often takes several cycles. Key is to not let the blade cool too much during each attempt, or *snap*.
 
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