Hi MetalArtistCandy:
Cryogenic hardening follows conventional heat treatment.
In simplistic terms it "finishes" the conversion of Austenite to Martensite and acts to "improve" the physical properties of steels that have already been hardened by conventional processes.
What that means is that freezing annealed steel will not magically harden it...you have to heat treat it first.
The heat treat step is what distorts it...when you harden it, you change the arrangement of the atoms within the atomic lattice of the steel by getting it hot, and then you lock that new atomic arrangement in place by cooling it suddenly.
That strains the internal structure, and those locked in internal strains are what makes it hard.
That's also what makes it distort.
That is a super simplistic description of what occurs, but it describes what you are up against.
There is a way to minimize that problem, and that is to alloy the steel with elements that will promote a different hardening mechanism called carbide precipitation and also allow the conversion and retention of Martensite at a slower rate of cooling...slow enough in fact to allow quenching in air as opposed to oil or water.
Such steels are referred to as "air hardening steels" and there are many alloys available.
A popular one for diemaking is D-2, another less popular (but easier to grind) one is A-2.
A-2 is very stable in heat treat and gets very hard...up to 65 Rockwell C right after the quench.
If you really don't want to have to post heat treat re-work the dies and punches, it's a good choice for modest production volumes and it's easy enough to harden that you can do it successfully in a potter's kiln or a jeweler's burnout furnace.
From your PM handle (MetalArtistCandy) I assume you are a jeweler or an artist, making pancake dies for blanking out artistic shapes to use as jewelery motifs or sculpture motifs.
If that assumption is correct, you may well get away with using a precipitation hardening steel that can be hardened at low temperature.
The most common is 17-4 PH...it will get up to about RC45 when hardened to "Condition H900" which is good enough to make runs of parts from soft metals in the hundreds rather than in the millions.
It also distorts very little during hardening; principally because the hardening mechanism is carbide precipitation rather than crystal lattice reorganization, and it occurs at (relatively) low temperature.
So that's it in a nutshell...hopefully all that babble was of some use to you.
Cheers
Marcus
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