Question for those that do their own cryo...

Daniel Koster

Daniel Koster

www.kosterknives.com
Knifemaker / Craftsman / Service Provider
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Oct 18, 2001
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Before or after first temper?

I'm looking at setting up a cryo outfit for 10xx, 5160 and 52100 steels (as well as stainless, of course).


There's an article in a recent Knives Illustrated mag about cryo treatment...hence the question.

Just wondering what you guys do.
 
Dan, I'm no expert but I do a 1 hr. temper at 325 on my 52100 blades before I do the nitrogen plunge, It might not need it, but thats one drastic change going from 1500 to room temp and then to -300. so it does help relieve some of my stress.

How did that can billet you did at Duncans hammer in come out????

Good luck,

Bill
 
Haven't seen the article . Normal tempering stabilizes retained austenite .There is some risk in going direct from quench to cryo but that can be dealt with by a "snap temper" which is at 300-350 F .That will not stabilize the retained austenite .A 400 F temper ,or higher, will stabilize it ! Lower carbon [5160] and lower alloy steels will not benefit from cryo. 52100 and of course the stainless steels will benefit....There is a thread where Roger Linger experiments with before, after, snap temper that illustrates this perfectly !!!
 
The more time between the quench and the cryo the more stabilized the austenite will be and you won't get as much benefit like mete said. A snap temper might be a good compromise, but the most effective is straight in to the cryo after quenching.
 
B . Buxton said:
Dan, I'm no expert but I do a 1 hr. temper at 325 on my 52100 blades before I do the nitrogen plunge, It might not need it, but thats one drastic change going from 1500 to room temp and then to -300. so it does help relieve some of my stress.
Click to expand...

I'm with you, Bill, except I usually do the pre-cryo temper at 300. Also, FWIW I only cryo stainless stuff. I don't like the hardness I get with carbon, and usually draw it out a little more in temper cycles anyway. :)
 
I made a couple San Mai 52100 cored blades that I went from quench to cryo. As I emersed the blade into the Nitrogen I heard this sickening crack. The blade butterflied. They split from the edge down the middle of the 52100. Tempering generates untempered micro carbides. The blade should be tempered again after cryoing...Take Care...Ed
 
Daniel, Here is what I do: Quench blade down to 150 degrees or so, imerse in water to cool down to about 60 degrees, dry off and direct into the liquid nitrogen. The objective is to keep the process moving, with out a pause so the retained austenite will not have a chance to stabilize. When you slide the blade to the LN2 do it in one quick fluid motion. I use 154CM, S30V, S90V, 10V and 420HC. I have never had a blade crack or ever seen evidence of any incipient cracking. Leave the blade in the LN2 for at least 2 hours, more will not hurt anything and does not seem to help either. I have left them for as much as 24 hours. If you have blades with a very thick flat section next to a very thin ground section or have San Mail like Ed Shemp reported then the snap temper would be a good idea, but you will not get the full benifit of the process. The higher the soak temp you run the more retained austenite you will end up with, as much as 30% in some cases. You can resolve the RA by tempering but it would have to be at higher temperatures to be the most effective. The objective then is to resolve the RA by the subzero and then you can temper at lower temps for maximun toughness and corrosion resistance. I have used this method for fillet knives which must flex even when at high hardness. At RC 60 with S30V I can bend the blade past the elastic limit, where it will not spring back and then restore it back to normal by bending the other direction. Phil
 
It's a real long ramp down to -300, a sustained time there, then a rapid ramp up to temp. All taking 24-72 hrs total.
I've got a chamber at work, but the amount of LN2 required is substantial, and unless you've got many blades to be done at the same time, it would be cost-prohibitive.
One of those big dewars on wheels, solenoid valves to feed it, and an efficient chamber are not within the means of the home user...even if you could get the dewar delivered...
 
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