Any cryo is better than no cryo
According to Dr. Larrin Thomas and at least 80 years of observation. I forget which knifemaker who wrote an article in Blade magazine in the 90s said that he noticed that his 52100 forged blades he left out in his shop in -30 F temps were tougher and harder. Larrin Thomas says that if you cannot immediately temper your knives after quench to put them in the freezer. Every steel can benefit from a cryo and Larrin tested knives from freezer to liquid nitrogen the steel always shows some improvement. (BTW not tempering a knife soon after quench allows austenite to 'set' and tempering doesn't change it to martensite or change a certain amount of brittleness.)
I can attest to simple freezer cryo as I worked for a metallurgist engineer who would always put his heat treated gears into a special -40 F freezer and would leave them there until he had a big enough batch to temper. Guy was a fanatic, but taught me how to tig weld gears without affecting their HT.
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