Effect of Cryo on Wear Resistance and Edge Retention

This was quite enlightening. Going forward, one hour in cryo on charpy samples?

I have to admit I was a bit surprised that there was no difference once hardness was accounted for, but the results are what they are.
 
Willie71 said:
This was quite enlightening. Going forward, one hour in cryo on charpy samples?

I have to admit I was a bit surprised that there was no difference once hardness was accounted for, but the results are what they are.
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30-60 min cryo is what my father has used with all of the toughness samples he has made for me.
 
I had a feeling this would be the results since you mentioned in the past the changing ideas about eta carbides or transition carbides in cryo. The samples I made to have you charpy test had a number of 1 hour cryo and 12 hour cryo for the same alloy/aus temps to see if there was a difference in toughness (to perhaps evidence greater carbide formation in the longer cryo pieces).

I haven't sent them because the hardness of a couple samples did not turn out as expected for reasons unknown. I'll send them now anyway, maybe they'll provide some decent data.
 
kuraki said:
I had a feeling this would be the results since you mentioned in the past the changing ideas about eta carbides or transition carbides in cryo. The samples I made to have you charpy test had a number of 1 hour cryo and 12 hour cryo for the same alloy/aus temps to see if there was a difference in toughness (to perhaps evidence greater carbide formation in the longer cryo pieces).

I haven't sent them because the hardness of a couple samples did not turn out as expected for reasons unknown. I'll send them now anyway, maybe they'll provide some decent data.
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We did the same in z-wear. No changes in the samples regardless of time in cryo.
 
Sounds like a case of increased hardness and then "tough enough" kicks in.

With these recent articles and winter coming around, would cryo help extend the life of hard use knives/machetes in the cold as it would compensate for the increased hardness and reduced toughness from the lower temps because tempering would happen after the cold treatment? I suppose this applies just as much to axes and saws as well since they are also made from steel and can take a beating from cold, frozen or partially frozen wood.
 
kuraki said:
I know. I was curious of that was specific to the alloy or not at the time.

It'll be interesting to see how tough 58 RC 4V is :confused:
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I’m doing one soft sample to see. It’s in cryo right now actually. (Is it 4v, or V4e? I’d have to look at my cheat sheet.) I wouldn’t ever make a knife like that, but it’s a datapoint.

Once we see a trend with three plus steels, we can start generalizing and create specific tests to tease out more refined data.
 
bikerector said:
Sounds like a case of increased hardness and then "tough enough" kicks in.

With these recent articles and winter coming around, would cryo help extend the life of hard use knives/machetes in the cold as it would compensate for the increased hardness and reduced toughness from the lower temps because tempering would happen after the cold treatment? I suppose this applies just as much to axes and saws as well since they are also made from steel and can take a beating from cold, frozen or partially frozen wood.
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You must have seen my Instagram promotion:
winter-is-coming-promotion.jpg
 
Larrin, i sincerely appreciate all the work and effort you’ve put into these articles. I know a lot of research has been done by your effort on our behalf! Thanks so much!

Learning what cryo can or can’t do for knife steels is such a “cool” subject!

Ha ha! I’ll be here all night folks.

But seriously......

So I get the physics behind hardness increase (RA to untempered martensite that gets tempered). Which would be my main goal for cryo (or sub zero) treatment. My goal with cryo would be nothing more than an increase in hardness by the mechanisms you outlined. (If there is more to be gained besides an increase in hardness....awesome).

I understand increased wear resistance with the “eta” carbide precip (or rather n-carbide precip, smaller than eta carbide) upon tempering.

Did you come across anything in your research concerning a better “cohesion” between the carbides and the matrix these carbides reside in?

I think there are claims that “cryo” not only adds to wear resistance by “eta” or “n” carbides, but also a better “cohesion” between carbides and their bond with the surrounding matrix.

Is this something you have come across in your research?

(To recap, my understanding about cryo holds is:

1. Increase in hardness due to more martensite conversion (RA)
2. “Eta” or “n” carbides that precip upon tempering that add wear resistance.
3. A better “cohesion” or maybe to say a “tighter bond”, between the carbides and the matrix that surrounds them. )

I think think the RA conversion is pretty straightforward and understandable, resulting in higher hardness.

I think transition carbides can be fairly easily understood, if indeed that is the mechanism happening.

About the mechanism of the bond between carbides/martensite matrix is what I wonder about. And maybe I am all wet and off base? I defer to your thoughts. (Cryo makes stronger bonds between Aus grain or aus/carbide grain).



Thank you again, Larrin!
 
Natlek said:
I don t know about steel in knife but Cryougenic Treated brake rotors last much longer ............and I know that in first hand .

http://iopscience.iop.org/article/10.1088/1757-899X/171/1/012152/pdf
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Less RA, better wear resistance (Martensite is much better to wear resistance than austenite). Brake rotors suffer from friction, correct (so a martensite Steel structure is better, because gives the steel much better wear resistance, so the brake rotor should last more), not by impact (austenite (or bainite) would be better, because is much tougher than Martensite).
 
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The bond between carbides and the matrix is controlled by the carbide type and size, primarily. It loses coherency as it grows in size. Adding a cryo step wouldn't add back "cohesion."
 
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