Are my foil pouches CAUSING my warps?

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Grayzer86

Joined
Jan 15, 2012
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I have been making quite a few fillet blades, and have been using AEB-L, CPM154 and S35VN. Aside from the AEB-L, I haven’t had too many issues with warps in the hardened blades. What I am seeing though is that when I pull these thin blades from the kiln (evenheat KF22.5) they immediately take a massive warp when removed from the heat headed to the plates. Sometimes they curve 1/2 to a full inch or more. The plate quench typically straightens them, but sometimes they still have some residual curve when cooled. This doesn’t happen when I use 1/8 or thicker stock, just my 1/16 fillet stock. I have tried larger and smaller foil pouches, changing the direction I cut the foil off the roll, forward, backward, and end to end in the kiln, and it doesn’t seem to make a difference. Because it’s happening with different steels but only thin sections and only when wrapped, is it possible I am doing something wrong when I make up my foil pouches?

Edited to add that I have tried running subcritical anneal before heat treat and it doesn’t seem to help. All heat treating us done full thickness and bevels are ground after heat treat.
 
I've tried switching pouch fold directions and I tend to straighten out the folded areas before putting them in the kiln. I don't know if it helps. AEB-L is notoriously warpy, and we tend to use it for thinner stuff too. I currently plate-quench horizontally, but I think the weight of the blade and pouch may contribute to bending due to gravity, and would like to move to a veritcal plate-squeeze setup. The steel is really soft when it comes out at 1950F. I don't lay my pouches flat on the kiln floor, so why do I quench them that way? Don't think I want to anymore. Anyway, opportunity for more detailed setup is coming my way shortly.
 
Have you tried a 1200 stress relief cycle beforehand?
Do you stack the thin blades? Like 2 or 3 high?
Place the thin blade between thicker stock AEBL?

I have come to accept some warp and use a carbide chisel to peen straighten
 
HSC /// said:
Have you tried a 1200 stress relief cycle beforehand?
Do you stack the thin blades? Like 2 or 3 high?
Place the thin blade between thicker stock AEBL?

I have come to accept some warp and use a carbide chisel to peen straighten
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I have been doing a 1200 anneal. I believe I was using 1250 though (haven’t done any in like 6 months). The blades are vertical on the spine in my kiln rack. One blade per pouch is what I have been doing. It’s not so much an issue of them ending up warped. It’s more an issue of them warping severely coming out if the kiln. Like if I pull a blade out of the kiln, and just hold it horizontal with the tongs, spine down, I can watch it curve like crazy as it cools. This didn’t happen on the one piece I tried as a test without foil but I’m aware I can’t heat treat them unprotected.

As for the peining a hardened blade, that seems like something that would straighten it, but straighten it by creating a bunch of stress risers and internal stress in the blade. You can straighten a blade by selective sandblasting too, but but that seems to me like fighting internal stress with more stress.
 
Grayzer86 said:
As for the peining a hardened blade, that seems like something that would straighten it, but straighten it by creating a bunch of stress risers and internal stress in the blade. You can straighten a blade by selective sandblasting too, but but that seems to me like fighting internal stress with more stress.
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I always want to ask that .....Thanks for this :thumbsup: I would like to hear opinion of other member about this
 
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As soon as the blades come from the quench plates they are still fairly limber and can be straighten by hand pretty good. On AEB-L I also clamp the quenched blade between two pieces of 1/4" aluminum barstock while tempering to hold it straight. Even goes into LN clamped between two aluminum bars.
 
Ive been peening my AEBL straight with a carbide glass drill bit embedded in a hammer. Very light taps is all it takes. I brought this up in another forum recently and was shot down pretty quickly for adding stress into the blade. The thing is, wouldnt any form of straightening (stressing a blade past the plastic limit) also be putting stress into the blade? Unless you use a ton of heat and blow out you temper.

I'm really curious to hear what others think.
 
Cu
Ken H> said:
As soon as the blades come from the quench plates they are still fairly limber and can be straighten by hand pretty good. On AEB-L I also clamp the quenched blade between two pieces of 1/4" aluminum barstock while tempering to hold it straight. Even goes into LN clamped between two aluminum bars.
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Currently I am plate quenching, then into two pieces of 1/4x2 angle iron bolted tight for cryo and temper cycles.

I am pretty used to AEB-L warping, and my issue is not so much with steels being warped before or after heat treat, but rather why they are warping so badly in the foil pouch. If I pull an uncovered blade out of the kiln and just hold it there, it’s doesn’t seem to curve. If I pull an identical blade from the kiln at the same temp in the same steel, but in a pouch, in seconds it starts to curve radically on its own. I’m just trying to figure out why the pouch seems to be causing blades to curve wildly in still air while suspended with no other pressure and seemingly totally even cooling. I can’t figure out if it’s my foil, my pouches being too large or small, or some other factor I am missing that is causing this. Currently it happens with my 154 and S35VN as well. I have not tried it at lower temps with carbon steels.
 
I have seen a few posts about using an anti-scale compound instead of foil for stainless. The specific product is Condursal Z1100, which is produced in Nagold, Germany, just a few miles from where I grew up. I do not recall anybody mentioning that it reduces warping, but people seem to like it. The trouble is finding it, I have never seen it in stock anywhere, so I bought a roll of foil. I have the same warping issues on thin AEB-L.
 
Regarding the straightening , Isn’t this concern of stress induced in a blade a little over rated....? Anyone have any actual evidence or real world experience of a broken blade due to?
 
Grayzer86 said:
Cu

Currently I am plate quenching, then into two pieces of 1/4x2 angle iron bolted tight for cryo and temper cycles.

I am pretty used to AEB-L warping, and my issue is not so much with steels being warped before or after heat treat, but rather why they are warping so badly in the foil pouch. If I pull an uncovered blade out of the kiln and just hold it there, it’s doesn’t seem to curve. If I pull an identical blade from the kiln at the same temp in the same steel, but in a pouch, in seconds it starts to curve radically on its own. I’m just trying to figure out why the pouch seems to be causing blades to curve wildly in still air while suspended with no other pressure and seemingly totally even cooling. I can’t figure out if it’s my foil, my pouches being too large or small, or some other factor I am missing that is causing this. Currently it happens with my 154 and S35VN as well. I have not tried it at lower temps with carbon steels.
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I tend to buy AEB-L in 12x24" sheets. I cut all my blade out lengthwise. Often they warp while being cut out on the bandsaw. There's a lot of stress in these sheets.

Is it possible that the warping while in the oven is due to placement? If you have multiple blades in there one side may be exposed to the elements on the side of the over while one isn't or one side is closer to to an element and each time they turn on one side is heating faster than the other? Just spit balling here.

HSC /// said:
Regarding the straightening , Isn’t this concern of stress induced in a blade a little over rated....? Anyone have any actual evidence or real world experience of a broken blade due to?
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I'd be really curious to hear about this as well.
 
Grayzer - out of curiosity ... do you see any difference in surface appearance on one side of the blades versus the other side? Is there consistency in terms of the direction of warp versus location of fold or closure of the foil? Can you post a photo of what your wrap looks like ?

I know people are not really hearing the question you are asking - warp in wrapped versus no warp in unwrapped blades. That is ... interesting. I am wondering about maybe a slight difference in surface oxidation on one side versus the other due to air getting in through gaps in the foil closure. Very slight differences in surface composition could easily create a stress difference from one side to the other...
 
Cushing, I have noticed no difference in surface texture or color from side to side on the blades, or inside or outside the foil pouch. I have not determined yet if the bend is always to the same side of the foil pouch or not but I believe it is from memory. It’s been about 6 months since I ran any blades this thin and just brought this up because I will need to do another batch in the next month or so. I am double folding and hammering all of my pouch folds, basically folding the edges over, hammering, and then rolling them over again and tapping that seam flat again. I may try doing a triple fold with the last fold being rolled the opposite way to see if my folds are causing the curve. Being that it only seems to happen to wrapped blades, I’m just assuming it’s an issue with the pouches and not uneven heating. Out of habit I always fold my pouches the same direction and place the knives in the same. For my next batch I will make my folds to the opposite side and see if the warps follow the fold direction. If they don’t, my pouches may be a red herring.
 
Grayzer86 said:
Cushing, I have noticed no difference in surface texture or color from side to side on the blades, or inside or outside the foil pouch. I have not determined yet if the bend is always to the same side of the foil pouch or not but I believe it is from memory. It’s been about 6 months since I ran any blades this thin and just brought this up because I will need to do another batch in the next month or so. I am double folding and hammering all of my pouch folds, basically folding the edges over, hammering, and then rolling them over again and tapping that seam flat again. I may try doing a triple fold with the last fold being rolled the opposite way to see if my folds are causing the curve. Being that it only seems to happen to wrapped blades, I’m just assuming it’s an issue with the pouches and not uneven heating. Out of habit I always fold my pouches the same direction and place the knives in the same. For my next batch I will make my folds to the opposite side and see if the warps follow the fold direction. If they don’t, my pouches may be a red herring.
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Could your hammering the foil closure be setting up a slight stress on that side different from the other side?????
 
This sounds like an opportunity to run a controlled experiment and determine the cause for yourself. Wrap half your blades your normal way and half the mirror opposite. That should provide a fairly conclusive result, but my expectation is that the blades will all bend the same way regardless of how they're wrapped.
 
Darn, I'd never thought about that, but when using really thin blade stock (.040" to .063") that fold crease could surely become an issue, especially with tri-folds folks talk about.
 
Ken H> said:
Darn, I'd never thought about that, but when using really thin blade stock (.040" to .063") that fold crease could surely become an issue, especially with tri-folds folks talk about.
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Yeh, don't ask how I know
 
I’ve run into the seam being thicker than the knife, especially the top corners where you have 2 seams overlapping. I try to make my pouches a little bigger to make sure I don’t get a seam under the blade while clamping. As others have said AEBL is notorious for warping. I handle slight warps in thin knives as follows. First I go ahead and grind the bevels. Next I take a bead blaster to it to straighten it out. Last I have sand it and finish the blade. Works well for me and I’ve had zero issues using this method. I mostly do it on filet knives and they get a lot of flex.
 
I will sometimes quench with the corner of the plate across the bend of the foil (not the seams) if the blade is thin stock.
Also, I learned that straightening warps between plate and sub-zero doesn't net you anything, as it's likely to move in sub-zero/cryo too. Might as well wait until it's done and then fix it after. I get blades up to tempering temp for an hour and then straighten them between wooden jaws in the vise. Gotta be careful about not letting them cool while you're flexing them... Sometimes I'll reheat the spine w/ a plumbing torch if I don't get it right away, but always back into the oven for more tempering after bending/straightening.
 
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