This is another one of those topics that come up, as if it had never been covered before, again and again very often. So often it is one of those that tend to burn seasoned posters out by typing the same explanations ad nauseum. I see the usual fine and leveled headed input here but, as always, have been just waiting to see some of those fervent believers in the process to pop in to let you know how fantastic this mystery cure all can really be, only to find out that these endorsements come almost universally by folks who...
offer cryo services ,reducing all of their valuable input to little more than cheap advertising.
The folks who say that retained austenite is just the tip of the iceberg in the miracles that this process can provide will also quickly point out how virtually any object made from any material will incredibly increase in any desired property you may wish. Women’s stockings will no longer run, tennis rackets will make you a winner at Wimbledon, golf clubs will hit like Tiger Woods is holding them, Trombones will sound sweeter than angel’s song after having their slides chilled... any body with any sort of common sense and caveat emptor radar should have some flags going up at this point. Tell me you have a process that will convert 10-20% more retained austenite to martensite in steels that have a low Mf and I may decide I could use your service. Heck, tell me that there may be some reordering of the crystalline lattice and some accelerated precipitation of secondary carbides with a 10% improvement in strength properties, and I may still give it a shot just to see. But start barking about how Dr. McGillicutty's magical cryogenic life tonic elixir will sudden solve all of life problems as evident in some testimonials from true believers, and I am going to have to ask you to give me a break! I can swallow it as an added step in quenching, but to many it seems to be the new “pyramid power”.
Ed nailed it quite well, if you are using simpler steels, 10xx, L6, O1, 5160, 52100, W1, W2 etc... and seeing a drastic increase in hardness after cryo, check your initial heat treatment, something wasn't quite right! If you get those results with richer alloys and stainless then cool that makes perfect sense and probably worth your money.
The amount of independent and objective information on this subject that has not been touched, influenced or outright funded by companies selling the same service is VERY small. This is particularly true of any article I have yet seen in a knife magazine on the topic. The knife enthusiast public really needs to come to grips with that fact that magazines are supported by, filled with, and entirely oriented around
advertising, and virtually everything one sees in them, particularly the articles, are a form of P.R. Also I know of no magazine in our business that utilizes a staff metallurgist to verify if anything they print makes any sense whatsoever. I have spoken with a number of very impressive material scientists, who were basically brains with legs when it comes to metallurgy, who would simply laugh when the subject went any farther than converting retained austenite.
In short (oops too late again
), it seems to be fact that we know cryo will indeed convert retained austenite and thus improve steel performance if that is an issue. Anything beyond that we don’t know for certain if it does anything at all and if somebody tells you they do, ask them if they happen to be involved with the cryo business in some way, if they are, please consider that when drawing your conclusions.
P.S. microscopic flat spots appearing on the edge
may be the results of overgrown carbides. Really coarse carbides will often present embrittlement problems and will give edge issues as they get pulled out of the surrounding material at such a fine interface. Cryo will not do much for this, but careful intitial heat treating, particularly pre-quench treatments (normalizing, annealing and austenitizing) will help greatly in this area.
