Sometimes cryo treatment is 'sold' as an almost magic treat-all but, as I understand it metallurgists view its application as much more limited with benefits only in certain narrow applications. Basically quenching 'freezes' the hard structure of a white hot steel, and tempering modifies that to give a hard, but not so brittle structure (ferrites, martensites etc in a different balance) these both finish off at room temperature, whereas cryo treatment can take them down further to well below -100C for a period of time, using liquid nitrogen or argon, supposedly further stabilising structure, I believe.
I don't remember from my dealing with special steels whether it should have much benefit for M42, one of the higher Cobalt HSSs but I do think that M42 should have several advantages over the standard M2, M4 often used for such HSS tools - and if the M42 were HIPped PM, this would further benefit its edge and other properties, maybe much more than being cryo treated.
Any specialist HSS metallurgists out there?