CPM 3V Heat Treat

J. Oeser

J. Oeser

Joined
May 13, 2009
Messages
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I've decided to make a few bushcraft blades with 3V and have searched through numerous threads. I've talked to a few people that have had real difficulty heat treating the stuff so I wanted to post what I have gathered so far and get a little directions from those in the know.

I plan to make a knife with a 5" blade and 4 1/2" handle at about .140" thick or there abouts. I am currently planning on this recipe.

Preheat to 1500 F for 5 mins, soak at 1975 for 30 mins, plate quench on aluminum plates 1 1/2" x 6" x 18". Once cooled to room temp straight to dry ice over night (I don't have LN2 so I can't do it but figured dry ice would be better than nothing). Then temper at 400 F 3 x 2 hrs.

I think that should give me about 60-61 which is where I would like it.

I know that recipes are highly subjective and my oven may be a little different etc., but if there is something I am doing dramatically wrong or that I could change to get better results please let me know.


Thanks everyone in advance!
 
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That's part of my concern. The data sheet says one thing but quite a few of the threads showed people tempering at 950 or higher and having problems. Then they tempered at 400 with success.

I'm hoping to hear from those that have done the HT themselves.
 
in a nutshell you need to take care of RA if you do it with cryo you can use the lower temp temper (400) if no cryp you woudl be better off at high temper (950-1000)
i didnt do any destructive testing of non cryo and 400 temper so thats on you but since its all aobut the RA i never even tried this combo
 
I dry ice after plate quench and still temper at 1000. I have yet to have any issues with a knife I have heat treated.
I test a sampling of each batch and consistently get a 59-60 Rc.
I let the oven ramp up, at 1500 I put the blades in, austenize at 1980, plate quench to room temp, dry ice for a couple hours or until my oven cools to 1000, then back in for 2 hrs 3 times.
 
Ok, now this is exactly what I needed to find out. So Butch, you are tempering at 400 when using LN, and it sounds like you have tempered at 1000 when using dry ice? So am I to understand that correctly that dry ice is not cold enough to complete take care of the RA?

Is there anyone that has used the 400 degree temper and dry ice that has had good results?
 
I have been told by a couple steel guys that if you are using quench plates that there is really no benefit in the cryo. The cryo benefits larger sections of steel that do not cool as fast as knife blades, like those used in tooling and mold industry. That said I still do both. Dry ice is around -100 degrees and the RA transformation takes place at -95. Dry ice is cold enough, it just has to soak a little longer is how I understand it. I am having some testing done as we speak on two 3V knives with identical heat treats, but one was cryoed and the other was not. It is a blind test as well so the tester has no advantage to know which should perform better.

All this is why heat treating is till such a mystery, IMHO. Ask 5 people and you get 5 similar but different responses.
 
I don't know who those "steel guys" are, but I can tell you with some certainty that this is incorrect. The rapid quench is helpful, but it is no substitute.

There is a kernel of truth. The thick sections still get "under the nose", meaning there is no pearlite. But enough carbon leaks back out of solution on a slow quench that you have reduced strain energy which causes problems with RA. So for sure, thick sections make the problem worse. But being thin and achieving a rapid quench is not enough to do the trick on any RA sensitive alloy that I know of. You still need -100 as a part of the quench.

As an aside: I've come to the conclusion over the years that the data sheets are not the last word. There is a misconception that "hey it's their steel, they're the experts, go by the literature". Unfortunately, this is not necessarily true. They may be experts at making steel, but developing the optimum heat treat for that steel for a particular application is not truly their core competency.
 
That's right Nathan , but we do need some experimental room otherwise life is no fun. I've also come across too mant examples of the standard HT working poorly or not at all'
 
Kevin Cashen told me a while back that with some steels, you "get what the chemistry will give you" as far as certain physical/structural characteristics go. But he also said that some steels can be played with more extensively. i think that the current lower temperature methods for austenizing 52100 and low temperature tempering of high alloy and stainless steels like 3V are a good examples. The shorter and more even austenizing/soak cycles permitted by high temp salts combined with faster quenching(bumping the as quenched hardness up a point of two) and the reduction of RA through cold/cryo are perhaps other ones. When talking about the "factory specs" for heat treat, I think that we can teach old dogs new tricks because sometimes we are using materials in applications different from the ones for which they were originally designed.
 
Thanks guys! I'm going to go with what Butch and Chris are suggesting and temper at around 1000 F.

Nathan, I have to say, since we talked a while back I have used the dry ice treatment immediately after quenching on plates for all my CPM 154CM with a significantly noticeably difference. I was really surprised after destroying a few blades at how much better the HT was and how nice the grain structure looked especially compared to older broken blades. I am absolutely convinced, at least in the case of CPM 154 and the like, that dry ice is essential.
 
i have never used dry ice. the times i did the 1K f temper there was no cold treatment. im in the better safe then sorry (i never had any problems with the no cryo + 1000f temper BTW)
 
Thanks again for all the help everyone! I finally HTed some 3V and it seems to have turned out great. I tempered at 975 and they came out at just shy of 61RC which is right where I wanted them. Now to take one and beat the snot out of it.
 
Hi All,
Just researching some HT methods as I'm keen to start doing my own HT. So please forgive me if I ask something dumb.

Jared you previously say that for CPM154, cryo (dry ice) is essential during the quench, this will reduce the Retained Austinite so a lower temper (400F) can be used and avoid the second hardening hump.
But then your last post (for 3V) you decided to try tempering at 975F - I'm wondering if you got the chance to compare the high and low tempers (with similar steels)?

Big Chris mentions that he did a blind test regarding 2 blades - one with cryo and one not, but sadly no followup on the results - I'd also like to know if this was tempered high or low.

I have read Nathan's 3V testing thread and it's leading me along the path of cryo as a part of the quench and lower temper cycles.
Does anyone think that plonking the blades back in cryo between tempers is worth anything?
And it also seems that dry ice is "adequate' for cryo, is it worth the effort ($$$) to upgrade to LN.

I'm asking because I feel that correct HT is the ESSENTIAL part of making a knife - I've had knives professionally HT'd and am, quite frankly, disappointed in the result with either tips breaking (overheated) or edges smooshing during use (over tempered?).

Knowledge is the key and I'm just trying to get schooled up before I start playing and spending $$$ on HT at home.
But I'm inclined to think that Jared is on the money with his recipe in the OP.

Preheat to 1500 F for 5 mins.
Soak at 1975 for 30 mins, plate quench on aluminum plates.
Once cooled to room temp, straight to dry ice over night. (Needs to get into the dry ice pretty rapidly, don't pause here).
Then temper at 400 F 3 x 2 hrs. (is there any benefit in re-cryo between tempers?)
 
Wow , I can say this twice in one day !
Dry ice reduces RA.called "sub-zero quench "
Cryo [liquid nitrogen] reduces RA further but ALSO permits the formation of fine eta carbides on tempering !! That's for max performance ! Stick to the 400 F temper. The higher temperatures 900 + F are used for dimensional stability which is not needed in knives .
Yes 3V is nice stuff !
 
Thankyou mete. I apologize for the cryo/sub-zero error. I have seen you make that distinction elsewhere.

Can anyone please explain to me about the following....
In quite a few posts, there seems to be the opinion that "room temperature" means nothing to steel during HT. It's best to incorporate sub zero/cryo in as a continuation of the quench.
So how come cycling between room temp and temper temp is ok? If it's making changes at temper temp, why not just keep it there for longer or take it back down to sub-zero in between?

I understand that a lot of this is worked out by trial and error, and if you got better results by wearing a tutu during HT and no one could tell me why, then I'd do it. But I'm curious if any passing metallurgist's or other learned people could give me an explanation regarding the tempering questions
 
I don't have a tutu .You should always look at your whole process .The low temperature process ,sub-zero or cryo , that reduces RA is a fast martensitic transformation. In cryo the additional action is a diffussion type requiring longer time .In any case when you transform RA you must then temper !!
The earlier steps of quenching are to to be done quickly To insure complete transformation to martensite .The stresses produced add to the hardness too. But too much stress and Ping !
Anyway find out what you are getting at each stage and ask is that what you want ??
 
Thanks again for sharing your knowledge Mete.
I'll order a HT oven (it'll only take a few months to arrive here in Aus) and start playing. It'll be fun.
 
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