Cryogenic cooling has actually been around for centuries. There are stories of the ancient Norse bladesmiths who were said to take their sword blades and leave them buried in snowbanks for the long winters before finishing them. Also, back during the ninteenth century, steel from Siberian railroad tracks was advertised as a superior steel for knives, gun barrels etc. The Siberian winters are of course famous for their icey cold temperatures. These days, most cryogenic cooling occurs between temperatures of -100F to -305F. Liquid nitrogen is the cooling source used in commercial cryo, with dry ice/acetone(extemely dangerous!!!) used by some others. There are a number of folks(me included) who also place carbon steel blades in their freezers(set for 0 F) for a number of days to accomplish something similar. The latter treatmeant tends to cause a bit of an argument(understatement) among folks, but I find it works to improve the quality of the occassional file knife I make. Cryo is not limited to knives. Cryo treating gun barrels, and I think, actions has also become somewhat popular. It also has it's uses in industry to toughen/harden steels for certain applications. About two years ago there was an intense, long term discussion at the Custom Knife Forum about cryo, and I wish I could remember all that was said by some excellant knifemakers. The gist of why cryo is used, it seems to have a greater affect on stainless than on high carbon steel; although both are affected, is as follows:
What cryogenic cooling accomplishes is somewhat similar to what happens when steel is forged(hammered). Grain shrinkage occurs, along with grain alignment....almost like a magnetic thing. This is similar to the "packing" which occurs when steels are hammered and the grains are forced closer together. It(cryo) also increases the Rockwell C rating by at least one point. This of course results in a denser, stronger steel matrix; which in turn results in a stronger, tougher blade. All this assuming the steels are treated correctly in all other aspects also. This toughness allows stainless steels to have a bit more flex to them and off course being harder/denser hold a bettre edge. Certain steels such as 154CM/ATS-34(and most other stainless) don't really reach their full toughness/hardness/edgeholding potential until cryo'd. All the stainless knives I make are cryo'ed by the heat treaters and folks are often amazed at how long the durn things stay sharp, especially if they are used to factory/non-cryo'd blades. I wouldn't buy a ATS-34 type blade UNLESS it was treated as such. If you spend money for what is considered a premium steel, it should have the treatment that makes it premium. Hope this helps.
