AEB-L warpage woes

Hubert S. said:
I heat treated ten more blades, all but one had small warps. The carbide tipped hammer is absolutely amazing. For most of the blades, it takes just a few taps to straighten them. I overdid it on one, but that was quickly fixed by hammering on the other side. The ones I've ground so far stayed straight after the dimples were ground out.

This time, I put every blade on the surface plate to make sure the spine was straight before I put them in the stainless steel pouch. On two of them, the tang was kicked up slightly after heat treat as illustrated below. It's not a big deal and I can grind it straight, but I would really like to know what might be causing this. If anybody has any idea, please let me know.

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Dunno why, but maybe use your hammer on the spine?
 
Natlek said:
Maybe because tang cool much faster then rest of knife ...............?
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As I understand it, Japanese swords pick up their curve during quenching, so I think it has to be something like that, or maybe a temperature gradient in my oven. I thought maybe it's because the tang is always near the furnace door and it might be cooler there. But the odd thing is that this warp is most severe on short little petty knives that are far inside the oven.
 
Hubert S. said:
As I understand it, Japanese swords pick up their curve during quenching, so I think it has to be something like that, or maybe a temperature gradient in my oven. I thought maybe it's because the tang is always near the furnace door and it might be cooler there. But the odd thing is that this warp is most severe on short little petty knives that are far inside the oven.
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Japanese swords pick up their curve during quenching because of differential hardening , martensite change/increase volume while spine not and that make that curve ...........They use clay on spine
 
Natlek said:
Japanese swords pick up their curve during quenching because of differential hardening , martensite change/increase volume while spine not and that make that curve ...........They use clay on spine
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I don't really understand all the mechanisms at play. There is an interesting online article here where they did some computer modelling. It is not really all that clearly written, but the way I read it is that the direction of bending changes during the quench due to thermal and phase transformation effects and the final curvature is created by thermal shrinkage of the spine. From the article:
In the successive stage of cooling, hot ridge side shrinks gradually because of thermal contraction, and finally, the normal bending can be obtained.
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Does unground AEB-L still warp when heat treated? IE just profiled and pin holes drilled? 3/32" thick stock?
 
Taz said:
Does unground AEB-L still warp when heat treated? IE just profiled and pin holes drilled? 3/32" thick stock?
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I no longer grind my AEB-L flat before heat treat per JT's suggestion and still get warps. I've had problems with pin holes in 0.04" stock, 0.08" seems to be ok for me, but I have not done a lot of full tangs.
 
Like I have said quite often, AEBL will warp almost 100% of the time no mater what. It’s less on unprofiled blades. It’s best to leave them between the quench plates till thy are cool. If you pull them out while still warm it will be much worse. What’s funny is our process does not change but blades come out with differing amounts of bows depending on what sheet it was cut from. All the knives cut from the same sheet will have the same amount of bow. But another sheet of a different thickness or batch will have a different bow. This is what makes me think it has to do with the cold rolling and coiling that is done to this alloy for transport.
 
Ok, so I may just drill the holes in the AEB-L and do all of the profiling/bevel grinding for after they come back then!
 
Taz said:
Ok, so I may just drill the holes in the AEB-L and do all of the profiling/bevel grinding for after they come back then!
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Yeah just drill the holes and grind the profile. Save the edge bevels for after the heat treat. Also don’t grind the factory finish off the flats. Once you grind test it seams to Make warping worse. Just leave the steel as is from the factory and profile the blade.
 
Had a batch of AEB-L I heat treated yesterday, all straight, even the thin ones. I follow JTknives suggestion and only profile and drill tang holes. I keep the blanks clamped in quench plates for about 2 minutes and carefully remove from foil.

I also do a stress relieving step, 1200 Fahrenheit degrees for 2 hours, that seems to really help with other steels as well.
 
Seedy Lot said:
Had a batch of AEB-L I heat treated yesterday, all straight, even the thin ones. I follow JTknives suggestion and only profile and drill tang holes. I keep the blanks clamped in quench plates for about 2 minutes and carefully remove from foil.

I also do a stress relieving step, 1200 Fahrenheit degrees for 2 hours, that seems to really help with other steels as well.
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I am a bit jealous. JT mentioned above that the amount of warpage you get depends on the batch of steel and I think he is right about that. A year ago I heat treated several batches without any warping to speak of, now most every blade warps for me. Maybe the few that stayed straight in my recent batches were from steel I bought over a year ago, but I have no way of checking that. If the steel gets coiled like JT says, it could well be that there is a big difference depending on whether your steel came from the inside or the outside of the coil.
 
I use to get a lot of warpage in aeb-l when I first started with it. I tweaked my procedures a little and and with some tips from Devin I havnt had a warped one in a while. Now Im getting ready to heat treat some .078 stock this week and may eat my words,LOL
 
Hubert S. said:
I am a bit jealous. JT mentioned above that the amount of warpage you get depends on the batch of steel and I think he is right about that. A year ago I heat treated several batches without any warping to speak of, now most every blade warps for me. Maybe the few that stayed straight in my recent batches were from steel I bought over a year ago, but I have no way of checking that. If the steel gets coiled like JT says, it could well be that there is a big difference depending on whether your steel came from the inside or the outside of the coil.
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Have you been using a stress relieving step? I find a stress relieving step to be a game changer for me with most of the steels I use.
 
Seedy Lot said:
Have you been using a stress relieving step? I find a stress relieving step to be a game changer for me with most of the steels I use.
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I did stress relieving on the last few batches. I am using Devin's prequench, then stress relief. I do this over the course of a few weeks whenever I get a chance until I have a stack of blades and a free weekend day to heat treat a batch. Since I've been doing the stress relief, I have seen more warpage, but I think that is a coincidence and probably related to other factors. I suspect the warpage is more likely to a new order of steel, which coincided with the change in procedure to include a stress relief.
 
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