Cpm 154 warping

B

Bob Biggs

Joined
Jun 13, 2022
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2
Hello all. I'm new to using forums, so please excuse me if I'm doing this wrong. I've made 3 blades out of CPM 154 and all have warped! I'm using the standard heat treatment- I start with a cold oven, ramp up to 1450F for 15 minutes, ramp afap to 1950F and soak for 30 minutes. Then I air cool clamped between aluminum plates using compressed air aimed into the opening in the plates. I then have put them on my machinists style surface grinder and take about .002" passes. when removed from the magnetic chuck, There is a warp. I was able to correct the warp slightly by flipping the blade over and grinding the other side, but it's hard to judge how much to grind to correct the warp. I then cryo treat with Ln2 overnight and temper twice @ 300f for a hardness of 60-61 RHC. The last blade was a filet knife. It actually bowed like a Japanese sword would do. I wonder if the compressed air is at fault. Any help would be greatly appreciated!
Bob
 
You should go right from quench to cryo to temper then worry about any warping I think. Additionally your recipe seems a little off from the recommended. I also do the recommended, blades into oven cold. Fast ramp to 1400, hold 10, fast ramp to 1950, hold 30, cryo 2 hours +, double temper 400 for 61 - 62 hrc. Generally zero warping issues. I make small slip joint folders.
 
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I have had the same issue with AEB-L where some blades warped not only side to side, but also ended up with sori like on a Japanese sword. I asked in the thread linked below, and while I got a lot of useful information about how to deal with the side to side warp, I do not think anybody replied with a possible explanation for the sori. It keeps happening some times, but I have not been able to isolate what causes it. Most of the warp in that direction seems to occur at the ricasso and by the time I grind in the shoulders on the tang, there is very little sori left to grind away on the spine of the blade. I'd still like to know what causes it, but it is not really a big deal for the type of knives I make.

AEB-L warpage woes

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...
www.bladeforums.com www.bladeforums.com
 
Bob Biggs said:
Hello all. I'm new to using forums, so please excuse me if I'm doing this wrong. I've made 3 blades out of CPM 154 and all have warped! I'm using the standard heat treatment- I start with a cold oven, ramp up to 1450F for 15 minutes, ramp afap to 1950F and soak for 30 minutes. Then I air cool clamped between aluminum plates using compressed air aimed into the opening in the plates. I then have put them on my machinists style surface grinder and take about .002" passes. when removed from the magnetic chuck, There is a warp. I was able to correct the warp slightly by flipping the blade over and grinding the other side, but it's hard to judge how much to grind to correct the warp. I then cryo treat with Ln2 overnight and temper twice @ 300f for a hardness of 60-61 RHC. The last blade was a filet knife. It actually bowed like a Japanese sword would do. I wonder if the compressed air is at fault. Any help would be greatly appreciated!
Bob
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I failed to mention that the grinding is usually done after the cryo-treatment and tempering. The last blade, I used argon in my oven instead of stainless steel foil. The blade came out very clean but was warped like a Japanese sword as I said before.
 
Surface grinding is my nemesis so I might need to be scrutinized here… are you saying your depth of cut on the SG is .002 on heat treated steel? If so, seems excessive for that thin of stock. The warpage might be due to that.
 
I agree you should cryo right after plate quench.
I use three methods to tackle blade warps. The first is during tempering, I clamp the warped blade on a piece of angle iron with a shim in the middle so that blade is bent just past straight. I leave it clamped for both tempers and then let cool. If there's still a warp i use a carbide tipped hammer to peen it straight. (There have been a couple of good threads on this subject here in shop talk, just google "peening warps in knife blades")
Lastly I'll take out small warps with my surface grinding attachment if necessary.
One other point is that you might want to consider modifying your heat treating protocol. Here's a good article by Larrin Thomas, our resident expert metallurgist.
https://knifesteelnerds.com/2020/03/16/how-to-heat-treat-cpm-154-toughness-experiments/#:~:text=Optimum%20heat%20treating%20of%20CPM-154%20was%20found%20to,quench%20and%20cryo%20followed%20by%20a%20300°F%20temper.
 
Signalprick said:
I've heard that about certain steels, D2 for instance. Never CPM154. I've never NOT put them in cold and I've yet to have a warping issue.
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Also you make slipjoint folders. In terms of warping there’s a huge difference between a 3.5” folder blade and a 9” thin kitchen knife. Warping is part of the kitchen knife game.

Anyway yes you definitely want to put the steel into the furnace at the hardening temperature and not cold
 
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