Well, having seen this question here a couple of times I had decided to ask my former boss of any benefits of cryo-treatment. (His degrees up to PhD are in metallurgy, UConn):
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Hey Ron,
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The heat treatment industry differentiates between cold treatment (-84°C) and cryogenic treatment (-190°C...liquid nitrogen
temperatures). The purpose of these treatments is to convert retained austenite to martensite. Austenite is a face-centered
cubic phase of steel which forms during solidification or heat treatment above 740°C. Martensite is a body-centered cubic
phase of steel which forms when austenite is quenched. However, some of the austenite doesn't get converted to martensite
during the quench, and is called retained austenite. Martensite is the desired phase in tool steels; the presence of
retained austenite can cause excessive wear, undesirable residual stresses, and cracks. Austenite is thermodynamically
unstable at room temperature, but the kinetics are slow; it would probably take a few hundred years to change. Cold
treatment and cryogenic treatment will accelerate the phase transformation to a few hours or a day.
Cold treatment of tool steels is pretty widely accepted in the metallurgical community---it works, and we know why.
Cryogenic treatment of tool steels has been under debate for years, mostly because the mechanism is not completely
understood. Some believe that the lower temperature produces a more complete phase transformation to martensite; others
believe that submicroscopic carbides form, reducing internal stresses. There is evidence that wear resistance of cryogenic
treated parts is better than cold treated parts; the degree of improvement depends on the alloy. I don't know if cracking
resistance improvement over cold treated parts has been documented.
That's a long-winded answer to a short question. Yes, cold treatment works. No, I'm not sure if cryogenic treatment is
worth the extra money. If you want more details, let me know. Good luck!
Barry
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So...what I gather from what he had written was some evidence suggests cryo does have, at most, a very slight benefit but whether if it is cost effective is up to the user.
- Ron V.
[This message has been edited by hksigwalther (edited January 24, 2000).]