AEB-L warpage woes

[Hubert S.]

I heat treated eight AEB-L kitchen knife blanks yesterday and out of the eight, only one came out straight and the rest were warped to varying degrees. Four of them did not just warp side-to-side, but picked up a curve along the spine, like sori on a katana. I cannot think of anything I did differently compared to my last batch, where all the blades came out perfectly straight.

My process is as follows: 1,950°F for 15 minutes, aluminum quench plates for about 90 seconds, then dry ice/alcohol slurry. Prior to that, I used @DevinT's prequench followed by a subcritical anneal. These last two steps were done on separate days for four of the blanks each time. I tempered the blades at 325°F for a couple hours last night and left it at that.

Does anybody have any ideas what I might be doing wrong that would create the sori? I have another batch of knives I want to heat treat next week and would really like to avoid this problem.

The knives are all hidden tang and I can take a lot of the curvature out of the tang and nobody will ever know, so I am not too worried about that. But I have to figure out how to get rid of the side-to-side warp first. There has been some discussion recently about chisels and hammers with carbide inserts for straightening in this thread about straightening high-speed steels. How well do these tools work on AEB-L and how much of a warp can one expect to correct with them? Some of the blades I did yesterday have pretty minor warps, but a couple of the 0.06" thick blades have about a 1mm gap when I put them on the surface plate and they are only short little petty knives. Can a warp that bad be corrected with a carbide tipped hammer or a chisel? I've straightened minor warps with a sandblaster in the past, but I am pretty certain it will not work to correct some of the blades I did yesterday.

Are there any other methods for straightening AEB-L? I have tried straightening during tempering by overcorrecting the curvature in a jig a couple of times without success, so I don't think I'm going to bother trying that again. This method seems to only work on carbon steel knives for me. Any suggestions would be greatly appreciated.

 

[HSC ///]

The carbide chisel hammer works great. I use it all the time (unfortunately)

Mine always warp. I don’t know how to keep them straight out of the quench. So i am always straightening

grind the blade bevels down so the stocking is thinner than try straightening with the carbide chisel hammer. The steel moves easier.

but the .06” stock blades should straighten easily with the carbide chisel

btw when you say soak 15 mins, what’s the total time inside from door closing to door opening. Just curious.

lastly have you ever tried stress relieving the material when you get it from the supplier? Like 1200 and furnace cool.
You might try that

 

[bmilleker]

I have had good luck clamping them between angle iron AS SOON as they are finished plate quenching. They stay clamped when they go into the dry ice slurry and temper. After the first temper I check whether they are straight or not. 99% of the time they are. After the check, I reclamp, temper again, and they stay clamped until I am ready to surface grind. Which is usually a couple days later. This is my method for Nitro-V as well.

I just did 18 knives this way. All straight. I clamped them all together between the angle iron chunks.

 

[Hubert S.]

The carbide chisel hammer works great. I use it all the time (unfortunately)

Mine always warp. I don’t know how to keep them straight out of the quench. So i am always straightening

grind the blade bevels down so the stocking is thinner than try straightening with the carbide chisel hammer. The steel moves easier.

but the .06” stock blades should straighten easily with the carbide chisel

btw when you say soak 15 mins, what’s the total time inside from door closing to door opening. Just curious.

lastly have you ever tried stress relieving the material when you get it from the supplier? Like 1200 and furnace cool.
You might try that

I guess soak time was not really accurate. Fifteen minutes is the approximate total time in the oven. If I put two blades in, it takes about three minutes for the PID to go back to the set point. I used to peek inside to figure out how long it takes for the blades themselves to get up to temperature and that takes about another two minutes depending on size and thickness. The first blade comes out eight minutes later and second one two or three minutes after that. I am curious if other people use longer soak times as Larrin's book recommends 15 minutes, but Hoss's thread says 8 minutes total time in oven. I based what I do on Hoss's thread and did some coupons and hardness testing and it seemed to be spot on.

I have not tried stress relieving. Do you do that before profiling?

 

[Hubert S.]

I have had good luck clamping them between angle iron AS SOON as they are finished plate quenching. They stay clamped when they go into the dry ice slurry and temper. After the first temper I check whether they are straight or not. 99% of the time they are. After the check, I reclamp, temper again, and they stay clamped until I am ready to surface grind. Which is usually a couple days later. This is my method for Nitro-V as well.

I just did 18 knives this way. All straight. I clamped them all together between the angle iron chunks.

Interesting. Do you put the blades into the dry ice one at a time, or do you stack them and clamp them between the angle iron as they come out of the plates and then put them in dry ice all together once they are all plate quenched?

I am curious what you do with the 1% of blades that are not straight after the first temper.

 

[HSC ///]

I guess soak time was not really accurate. Fifteen minutes is the approximate total time in the oven. If I put two blades in, it takes about three minutes for the PID to go back to the set point. I used to peek inside to figure out how long it takes for the blades themselves to get up to temperature and that takes about another two minutes depending on size and thickness. The first blade comes out eight minutes later and second one two or three minutes after that. I am curious if other people use longer soak times as Larrin's book recommends 15 minutes, but Hoss's thread says 8 minutes total time in oven. I based what I do on Hoss's thread and did some coupons and hardness testing and it seemed to be spot on.

I have not tried stress relieving. Do you do that before profiling?

I use considerably longer soak times than what is usually written or others use. Quite a bit longer.

stress relieving - as soon as u get the material in, stick it in the furnace in the evening at 1200 and overnight furnace cool

 

[Hubert S.]

I have had good luck clamping them between angle iron AS SOON as they are finished plate quenching. They stay clamped when they go into the dry ice slurry and temper. After the first temper I check whether they are straight or not. 99% of the time they are. After the check, I reclamp, temper again, and they stay clamped until I am ready to surface grind. Which is usually a couple days later. This is my method for Nitro-V as well.

I just did 18 knives this way. All straight. I clamped them all together between the angle iron chunks.

Another question I have about this approach is the amount of dry ice you go through. I did a few blades this way about a year ago and very quickly ran out of dry ice. The eight blades I did yesterday used 3.5 lbs of dry ice and there was a good bit of solid ice left at the end. The dry ice is cheap enough around here, I might try clamping the blades on the next batch.

 

[Bob Duguay]

I am curious as well.. I will HT Abel for the first time this week. As recommended by others I will plate quench then clamp ( bolt at each end) each knife between 1/4”x2” aluminum plate. I will leave them like that in dry ice and through temper. We will see what happens. I have also seen some clamp 5 or 6 blades together then temper. I have wondered if all the blades will receive equal heat so as to get the same tempering results? What are your thoughts on that?

 

[Hubert S.]

I am curious as well.. I will HT Abel for the first time this week. As recommended by others I will plate quench then clamp ( bolt at each end) each knife between 1/4”x2” aluminum plate. I will leave them like that in dry ice and through temper. We will see what happens. I have also seen some clamp 5 or 6 blades together then temper. I have wondered if all the blades will receive equal heat so as to get the same tempering results? What are your thoughts on that?

I have been clamping a stack of several blades to angle while tempering. I do two two-hour tempering cycles. Good luck with your first attempt at AEB-L! If you haven't used dry ice before, a couple of safety tips. Be careful when you put the chunk of aluminum into the dry ice slurry, it can start boiling violently and spray solvent around. Also, don't put the solvent back into a sealed container before it is back at room temperature and had some time to release the carbon dioxide, it can burst the container. One time I had a container bulge even though I waited a whole day before pouring the alcohol back. Luckily, I caught it in time and now I only put the lid on loosely.

 

[Hubert S.]

I am going to try to make a hammer similar to the one S Scaniaman showed here. I ground a piece of 1/4" carbide, but maybe it has too much of a flat spot. What do you guys think?

 

[Scaniaman]

It looks pretty round to me. Roll it against something flat against a light and see how the two surfaces meet.

 

[JTknives]

Welcome to the world of AEBL. We use to fight it and fight it. Sometimes clamping in the freezer would keep it straight and other times it wouldn’t. Clamping it straight for tempering does just about nothing. We do not have time to futz around with individual blades so we do our best to keep them straight from the get go. We have found out that aebl has to be treated very gently after coming out of the quench plates. It will bend by hand VERY EASY. Think of the blades as if made out of soft copper. So do not set them on any cold surface after you take them out of the foil. Be very gentle cutting the foil off. Also I will say this. Resist the urge to straighten the blades by hand at this point. It can easily be done as the steel is still very soft. But you create worse problems for your self after the cold treatment and tempering. For some reason if you straighten by hand it still bows back after the tempering and it’s worse and gets a kind of kink like bow to it.

honestly your best bet is to let the blade do what it want to and then straighten it after it’s been cold treated and double tempered. Straightening only takes us a few min as we surface peen The inside of the bow. We use a Starrett straight edge and work the blade in different areas to get the blade as flat as is practical.

The issue I have found with AEBL is how it’s manufactured which It’s cold rolled and coiled. So the radius of the section of the coil that your sheet came from affects the amount of warp your blade has. Now if you cut your blades across the grain the warping just about disappears. I’m not saying you should cut blades from Across the grain. But I have done a few tests and it’s clearly a HUGE difference.

 

[JTknives]

I am going to try to make a hammer similar to the one S Scaniaman showed here. I ground a piece of 1/4" carbide, but maybe it has too much of a flat spot. What do you guys think?

Way to flat. The max you want is a perfect 1/8” radius. On the surface peening hammers we make and sell we have tried a few different radius sizes. The amount of force you have to use goes up substantially as the radius gets bigger.

 

[Hubert S.]

It looks pretty round to me. Roll it against something flat against a light and see how the two surfaces meet.

There is definitely a flat spot when I roll it. I'll work it some more. Thank you. How did you attach the carbide to the hammer? I was thinking JB weld.

 

[Hubert S.]

Way to flat. The max you want is a perfect 1/8” radius. On the surface peening hammers we make and sell we have tried a few different radius sizes. The amount of force you have to use goes up substantially as the radius gets bigger.

Thank you.

 

[Hubert S.]

I put a much more aggressive point on it.

 

[Scaniaman]

There is definitely a flat spot when I roll it. I'll work it some more. Thank you. How did you attach the carbide to the hammer? I was thinking JB weld.

I drilled a hole same size as the bit and squeezed the bit in with some G-flex.
I just checked mine for roundness. Maybe there is a tiny flat like 1/2 square mill. Works great.
Here's a small knife I heat treated last night. AEB-L's younger sister 14c28n, also a warping steel. Warp seen in first pic. Then pretty much done in second. You can see the marks in the third pic. Not a lot of force needed here. 2 mm stock st 61 Hrc.

 

[bmilleker]

I clamp them all together between the angle iron. When doing a larger batch, each knife is plate quenched, and then added to the clamped knives. This means the first knife plate quenched might not hit the dry ice for 30 minutes or so. But that would be the longest.

I typically buy 3 to 5kg of dry ice.

Maybe its not required to keep them clamped after the dry ice, but I honestly don't want to risk it. My method has been working great for me. Going on 75+ knives now.

 

[Scaniaman]

With all the shim-clamp-tempering and carbide hammer whacking, we shouldn't forget about good old fashing bending. It can fix a lot. I had 180 mm nakiri (2.5 mm 14c28n 61 hrc) come out like a steel colored banana a while back. The vast majority of that warp was fixed by sticking the blade in the vice, jaws slightly open, and then pulling on the tang multiple times. The warp was mostly in the tang/blade junction and the curve was long. With shorter curve warps towards the tip, I think the carbide hammer works best.

 

[Hubert S.]

I drilled a hole same size as the bit and squeezed the bit in with some G-flex.
I just checked mine for roundness. Maybe there is a tiny flat like 1/2 square mill. Works great.
Here's a small knife I heat treated last night. AEB-L's younger sister 14c28n, also a warping steel. Warp seen in first pic. Then pretty much done in second. You can see the marks in the third pic. Not a lot of force needed here. 2 mm stock st 61 Hrc.

Thank you, this is very encouraging. It looks like about the same amount of warp I have, maybe 1mm give or take.