The question I have been trying to clarify is whether the retained austentite to martensite conversion during cryo is a rate or temperature dependent phenomenon. The fact that blades frozen in a freezer for several days will attain essentially the same hardness as a -100F cryo'd blade suggests it is rate dependent, and thus the need for LN or dry ice is not essential except for the time saving involved. There are tables on the net at commercial cryo sites that suggest, however, that the absolute temperature is also a determining factor, but they do not state whether this is an equal time at lowest temp or what. It is interesting to note, however, that one steel, 440C, performed better by their tests after a -100F cryo than after -300F. This is of very real importance to me as I am engaged in studying the HT of 440C at home to find if there is a better HT method available than the traditional conditions. I would appreciate anyone able to shed further light on the topic. Thanks.
PS Sorry to bring up that nasty "stainless" on your forum, Ed!
06-19-2002, 01:22 PM
Linear Mode
