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If you austentize O1 at the higher than recommended temp of 1475, as in 1525+, yes RA becomes an issue. However, if you harden at 1475F, recommended temp, then RA is negligible, and the sub zero dry ice isn't going to do much of anything.
Try it yourself. Take coupons, and harden them at 1425, 1450, 1475, 1500, 1525, 1550. You will notice RC will drop about 1 point every 25 degrees (give or take) each side of 1475F. Once you go above 1475, and the hardness drops...then you can take that coupon and cryo or sub zero, and watch the RC bump back up to max. That is the RA being converted back over to martensite. (untempered martensite technically).
Again, the idea with knife steel is to put just enough carbon in solution to attain max RC, leaving the rest of the excess carbon tied up in the carbides...for added wear resistance. Most don't realize...the steel received annealed actually has a higher percentage of carbides than hardened.
I've seen all the cryo studies before, usually funded and put out by.......cryo companies that sell their services.
If you're seeing vast improvements on O1 by employing sub zero/cryo....go back and rethink the HT you are doing.
Wear resistance does not equal edge stability/edge retention. It is but one factor.
D2 is a different story. Same with A2. Your austenitizing temperature is so high that RA is most certainly an issue. Hence the recommended sub zero with these steels....and any and all higher alloy steels. Even AEBL loves to be at least sub zero.
Now full on cryo, LN temps and soak time, it gets a little different. It isn't solely about RA reduction. The LN temps will permit the formation of so called epsilon, or eta, carbides, upon tempering, that would not otherwise be formed in a standard quench, or even sub zero quench. There is very little info about the formation of these super small carbides that, frankly, is WAY more interesting than the straightforward concept of RA reduction.
If O1 were to be improved by 400% by a simple sub zero soak, I promise you, every single knife maker would be doing it. If it offered 10% increase in performance, I promise you every single knife maker using O1 would do it. It simply does not.
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