CPM154 choil cracking

J

John L

Joined
Oct 28, 2004
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I make slipjoints. Using Aldos' CPM154 at oversized 3/32" I cut out blades and springs, roughly fit them up, cut choil, stamp, cut nick, and heat treat. I ramp to 1400 and hold for 15 minutes, ramp to 1950 and hold for 20 minutes, clamp between two pcs of 2" aluminum plate, cryo, and then temper. The last three times the choil, an inverted V for slipjoints has cracked. I have never had this problem with any steel other than his batch in more than 800 blades. Problem was this batch had 10 blades in it and they all cracked. I had forgotten about this problem but had the same problem three months ago. I had been using 52100 in the mean time. Very frustrating and quite time consuming to say the least. Steel problem, heat teat problem....? I can't figure out a good way to cut choil after heat treat.........Solutions? Thanks.

John Lloyd
 
Camera out of order but crack is about 3/32 long and starts at apex of V. Tempered back to 59 -60. I had dropped one of the ten blades and could not find it yesterday before tempering. I looked and looked this morning and finally found it and the crack was there before tempering if that helps at all. Thank you.
 
Vs are stress concentrators and heat treatment is a stress process. research stress riser geometry and you will see. Make sure that you round the bottom of your choil notch and your problem should go away. Also if your cut scratches run across the blade that can contribute especially at the bottom of a notch. If I cut a notch choil I use a diamond rotary bur and make it a round one

-Page
 
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John,

I cut my choils for the most part post heat treat with a little fixture I made up using a small cross slide assembly and a holder for a Foredom hand piece. I shape the cut off wheel with a diamond point dresser. If I remember correctly Mr Shadley shows a picture of a choil cutter in the book co-authored with Terry Davis.

I must say I have heat treated lots of CPM154 for springs and blades with all kinds of crazy sharp angles etc, and have not experienced any cracking.
 
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Thanks Ken....the thing is I have never had a problem before this batch of CPM154.....with any steel...be it 154, D2, ats34 or any high carbon steel. Time between cryo and tempering is just a couple of minutes or so after steel is to room temp. But cracking seems to be occuring during hardening.
 
I do a similar setup in my small lathe to the one Ken E. shows after hardening. That being said
I would be seriously concerned no matter when its cracking. I would also Rc test that batch
inside out.
Ken.
 
I spoke at length with Ken Erickson about the problem and he believes it is probably a bad batch of steel. Who knows? I may Rockwell test it but that may tell me nothing. Stamping may be the culprit but I stamp every blade I have made in the past and no problems. Until this batch of steel is used up I may cut choil in later even though it is a PIA for me. Hmmmmmmmmmmm? I certainly appreciate all the possible answers or things to check on from everyone. Thank you.
 
John could Aldo have shipped you some Cpm-D2 instead of the 154? It looks the same and I've had a hard time identifying which is which on my shelf. Heat treats almost the same but could it be enough to make the difference?
 
I grind large finger choils into my neck knives. I had a batch of 8 that cracked at the top of the choil- every one, to some degree.

I didn't anneal the batch. I didn't have much steel to grind, so I ground them after they had been normalized thrice. I thought they were soft and should have been under little to no stress, but I was obviously wrong.

I'm not positive that not annealing would cause this, but it was definitely the biggest detour that that group of blades took. I haven't made many knives yet, so I keep on tweaking things. This was by far my biggest disaster.

I use LN a lot, since I've only heard benefits, especially the "relaxation" of the steel. I didn't do anything differently with the cryo, but I wonder if I over-do it.

Next batch, I did anneal, and cut back on the cryo cycles. No problems.

If anyone has feedback about this, I would love to hear it.
 
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