[samuraistuart]

The point of the cryo LN2 (and even sub zero dry ice slurry) is to minimize retained austenite in a steel after it is quenched. What does that mean to us as makers? Put simply, a slight boost in hardness. Usually 1-3 points HRC. When making knives, it is always advisable to get as much martensite as possible during the quench, and then temper down to desired hardness.

If one were to quench 440C without using the sub zero or LN2 quench continuation, then the max HRC you're likely to get is around 59HRC or so (if memory serves me right). That's a good hardness, no doubt, and quite serviceable. However, there is going to be some amount of retained austenite in that blade, and RA is a soft generally undesirable structure in blade steel. If one were to add the sub zero or cryo post quench (before any tempers), then the RA will be minimized, and the final HRC will be several points higher. 62 or 63. You could leave it at that hardness, or temper down as desired.

I had some kitchen knives from Boker (Prestidges or some weird name like that). They had 440c, and I was impressed with their performance. MUCH MUCH better than the other "generic" stainless steels out there like 440a or X50 whatever from China. 440c is no slouch.

(Some steels that are VERY highly alloyed will not have decent RA conversion even with extended soaks in LN2!!!! They need the secondary hardening tempers (~1000°f) to eliminate the RA, but that causes different issues for a knife blade. Think steels like T15. I sure wouldn't want to be the guy putting a hand rubbed finish on steels like that! Count me out. CPM M4 is bad enough!)