Effect of Cryo on Toughness

Shaw Blades said:
Fun to read and I feel like I understand most of it. But I'm wondering this...this indicates a .40 increase in toughness in D2. What does this translate into real world usability you know? I've seen firsthand a W2 knife heat treated and tempered with an oxy acetylene torch cleanly cut a rolling paper, chop through 5 pieces of seasoned oak as thick as a human leg, then come back and cleanly cut a rolling paper again...no edge deformation.

Is it wishful thinking at some point? I have sent a few blades out of more complicated steels like 3V and even some AEB-L and they have been cryo'd so I'm not saying I don't do it myself just wondering if anyone has ever done anything like side by side hemp rope slices to compare the two.

Thanks for posting this and opening up the discussion.
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This is the reason nowadays I prefer simpler to heat treat steels. My focus is on toughness, so now I much favor Knives in shock resistant steels and spring steels. They perform very well for my usage and don’t require super complex heat treatments that, if you miss a step, you compromise everything. Too much variables to control, in my opinion.
 
samuraistuart said:
When I first started to try and understand cryo and what it does for knife steels, I came across charts that claimed an enormous increase in wear resistance with steels that were cryo'd vs non cryo. I recall O1 (it may have been 52100) had a 400% increase in wear resistance. That's 4 times the wear resistance. I find that highly doubtful. Theoretically, it would take me 4 times as long to put a hand rubbed finish on a cryo 52100 blade vs non cryo, when in reality, there is no discernible difference. A lot of that "research", as it turns out, was funded by companies heavily vested in cryo processing. Getting real world data, especially for knife steels, is still in it's infancy.
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Yes those are good examples of the dubious nature of some cryo studies. I will be addressing all of that directly in Part 3 on wear resistance.
 
skillgannon said:
What kind of test could we do to shed a bit more light on this? My big plan is to be exploring some higher alloy tool steels. I'm kinda thinking this might take me little while. It would be nice to have some structure to be looking build off of.
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More tests like those Warren and I did would be nice. We may be able to learn something when it comes to edges when I am fully confident in my edge impact test setup. I also have a proposed CATRA study for Part 3.
 
Larrin said:
More tests like those Warren and I did would be nice. We may be able to learn something when it comes to edges when I am fully confident in my edge impact test setup. I also have a proposed CATRA study for Part 3.
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We have a standard for test pieces for the toughness test. Could we come up with a standard test blade? Something like a straight 3" blade made from 1/8" stock tapered to .010 or something similar? If we had something standardized as I work up a recipe I could run a extra test blade and send it off with the recipe attached.
 
I can’t stop thinking about this article. We definitely see improvements in steels like 3v, cru-wear/z-wear, and V4e with cryo/low temper. Now I’m curious if that’s true at all hardnesses, or are we lucking out in the range of hardnesses we prefer? I’m also curious to know if this will work with all steels that use a high temper, or is it alloy type or level specific? If the mechanism is prevention of the carbide precipitation in the secondary hardening, we can generalize that to a lot of steels. That seems to be the most obvious explanation.

I’m realizing I need to do a lot more heat treating of samples in different steels and different hardnesses to help tease this out.
 
I've definitely never seen anything in the literature generalizing that a low temper is superior. Sometimes the opposite claim is made. There are quite a few studies showing that an upper temper has lower toughness but that is usually blamed on retained austenite difference. Not many studies out there on cryo+low vs high temper.
 
Larrin - you sure are doing a GREAT service with these articles. While I personally am happy with "cookbook" info on HT'ing, I read thru each of your articles (some will get read several times) and I pick up nuggets of info to help me understand the "why" of the cookbook recipes.

Thank you and all the rest of the knowledgeable folks who so freely share info with us "chefs" {grinning}

KenH>
 
Larrin said:
I've definitely never seen anything in the literature generalizing that a low temper is superior. Sometimes the opposite claim is made. There are quite a few studies showing that an upper temper has lower toughness but that is usually blamed on retained austenite difference. Not many studies out there on cryo+low vs high temper.
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I think I recall from my latest conversation with Fredrik Haakonsen that he wasn’t much excited about using low temper treatment (with cryo) in Vanadis 4 extra, he asked me if people using this procedure has examined the steel for RA conversion (lab analysis) or they are only having empirical observations about toughness gains. He uses this steel for years in his hunting knives. In his survival ones, he prefers A8mod and L6 (this one for economic reasons, I think).
 
hugofeynman said:
I think I recall from my latest conversation with Fredrik Haakonsen that he wasn’t much excited about using low temper treatment (with cryo) in Vanadis 4 extra, he asked me if people using this procedure has examined the steel for RA conversion (lab analysis) or they are only having empirical observations about toughness gains.
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I'm not sure I understand. He was saying that more conversion of retained austenite would lead to a toughness improvement, and asked if anyone had measured the RA?
 
To help with this question, I’ll do V4e in two hardnesses with high temper, plus four hardnesses in cryo/low temper. According to the datasheet, 1875f has the lowest retained austenite, so I’ll do that with low and high temper too. Damn, it would be interesting to play with one hardness and use different austenizing/temper combinations too. I’ll be cutting out a lot of V4e/4v this weekend. :eek:
 
Larrin said:
I'm not sure I understand. He was saying that more conversion of retained austenite would lead to a toughness improvement, and asked if anyone had measured the RA?
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No, I think what I understood from his words was that cryo plus low temper doesn’t remove so much RA as a high temper and that toughness increase that some people notice from some tests are due to that RA excess. Please take my word with a grain of salt, I really enjoy talking with Metallurgists, but I’m sure I always miss something. This could be my interpretation of what he said.
 
Related to these conversations, here is some Vanadis 4 Extra data. No information on whether any were given a cold temperature treatment. However, the wear resistance and toughness does not appear to be different between the high and low temperature tempering.
Vanadis-4-extra-wear-resistance.jpg

Vanadis-4-extra-toughness.jpg
 
Willie71 said:
To help with this question, I’ll do V4e in two hardnesses with high temper, plus four hardnesses in cryo/low temper. According to the datasheet, 1875f has the lowest retained austenite, so I’ll do that with low and high temper too. Damn, it would be interesting to play with one hardness and use different austenizing/temper combinations too. I’ll be cutting out a lot of V4e/4v this weekend. :eek:
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You are the best!

To make things even more interesting, here http://kniver.blogspot.com/2007/08/herding-med-fredrik-jeg-har-ikke-lest.html?m=1 you have a description of Fredrik Haakonsen’s V4e heat treatment (sorry, it’s in Norwegian, maybe Larrin and google translator can give a good help understanding).
 
Larrin said:
Related to these conversations, here is some Vanadis 4 Extra data. No information on whether any were given a cold temperature treatment. However, the wear resistance and toughness does not appear to be different between the high and low temperature tempering.
Vanadis-4-extra-wear-resistance.jpg

Vanadis-4-extra-toughness.jpg
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You’re right, minor differences, but low temper has a slightly impact toughness increase (more RA present in the steel?). Maybe the high temper gives a slightly wear resistance increase and this is what Fredrik’s is after in his hunting knives. I’m sure he tested this steel extensively, he uses it from way before people knew his existence (the steel).
 
hugofeynman said:
You’re right, minor differences, but low temper has a slightly impact toughness increase (more RA present in the steel?). Maybe the high temper gives a slightly wear resistance increase and this is what Fredrik’s is after in his hunting knives. I’m sure he tested this steel extensively, he uses it from way before people knew his existence (the steel).
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I also question the carbide volume as a contributor to the difference. Ra is not good for fine edge stability, but does help toughness. If low temper has improved fine edge stability, I suspect carbide volume is at play too.

I also suspect there is a level of alloying that will not do a full conversion to martensite so cryo will no longer work. At the extreme end I have some rex121 for testing. It’s ridiculous in its alloy content.
 
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