Is anyone familiar with hardening by freezing, or chrio freezing?
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  1. #1
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    Default Is anyone familiar with hardening by freezing, or chrio freezing?

    There is a company near me who does chriogenic hardening. Curious if this is good for die making? Wondering if with this type of hardening my dies wont need to be ground afterward.

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    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
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    I may be mistaken but I think you've got the wrong idea about cryogenic treatment of steel. My (limited) understanding is that it is an enhancement to the hardening process, more fully converting formation of Martensite, and not a replacement of the traditional hardening/tempering process of heat treating. Using cryogenic treatment also adds the risk of thermal stress cracking if not carefully controlled. If your primary goal is replacement of grinding then I think you need to do some more reading about cryogenics. I also would not trust a die section or punch/perforator to remain dead true after being subjected to cryogenic treatment until it was proved to be true, too much potential stress in the process. I'd probably dust the critical reference surfaces on the SG anyway just to maintain the geometry. What sort of dies are you considering this for? I've worked on a lot of stamping dies and enhancing performance always called for changes in tool steel and/or coatings. That doesn't mean cryogenics is wrong but it's expensive, has added risks, and the known properties of different tool steels and/or coatings was a more reliable/proven solution. In the 80's cryogenics had a lot of snake oil in the sales pitch so arm yourself with reliable information. This is all just my limited opinion, hope it helped.

    -My fingers are too slow and clumsy, Marcus has offered a more thorough explanation than I did.
    Last edited by AD Design; 09-09-2019 at 10:22 AM. Reason: Too slow

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    Cryogenic treatment is an extension of the quench process to eliminate "retained austenite".

    No retained austenite = no cryogenic treatment necessary.

    So the real question is do your parts have a sufficient amount of retained austenite after standard heat treating? The answer is, "it depends". Depends on the alloy, the cross sectional thickness, and how your local heat treater handled the process. There are plenty of ways to predict it, but ultimately if an application warrants the added cost, the only surefire way of knowing is to send samples to a lab for destructive testing. Retained austenite is visible under high powered microscopes.

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