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Cryogenic heat treatment and it's importance.
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Thread: Cryogenic heat treatment and it's importance.

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    Cryogenic heat treatment and it's importance.

    I am interested in all you KnifeNuts and most especially custom makers thoughts on heat treatment methods and the importance or lack theroff of a Cryogenic stage in the heat treat process, after talking to many custom makers it seems that this an important part of the process however I am also of the understanding that Cryo treatment is rare and/or seldomly used in the process from the Japanese makers, just curious on thoughts and opinions on this and what are the benefits if any of a heat treatment with a Cryo stage?? Cheers CB

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    I really don't know much about this, but as I understand it some steels require a cooling to cryo temps to complete the transformation of grain structure from austenite to martensite. I'm not sure if Japanese makers commonly use steel which requires this treatment.

    Their habit of leaving forged knives sitting for a couple of years before finishing them may be their solution to the problem.

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    Marko Tsourkan's Avatar
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    I think Devin is a great source to explain the benefits of cryo, having worked many steels in mono and san mai construction.


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    Senior Member quantumcloud509's Avatar
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    Thats really interesting about Jknife makers leaving their knives to sit for a couple years before full development.
    Amat Victoria Curam Fortune favors the prepared.
    "A human being is primarily a bag for putting food into." -George Orwell

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    Thanks for the input guys, judging by the feedback i can only assume that this is a topic that is not fully understood and or realised by many knife users but is probably fairly simple stuff to knife makers, so i welcome their input,please find below comments from a well regarded maker.

    Any steel benefits from cryo, particulaly steels with chromium and other alloys. The biggest benefit - increased transformation from austenites to martensites - increased hardness, more uniform structure (because you don't have soft spots in your steel matrix), ductability, better edge retention, ease of sharpening, etc. If you ever heard of wire-edge, resilient-burr expressions, these are examples of retained austenites - stuff (trying to explain in plain english) that didn't converted to full hardness during cooling, and they cause trouble.
    Cheers CB

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    Generally it's done on high carbon high alloy stainless steels for slight improvement in hardness and toughness. Low alloy high carbon steels gain little if any benefit from cryogenic treatment.

    I believe leaving the blades to rest is to allow stresses formed during the quench/temper to dissipate.

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    The rest is done for laminate blades that continue to move after heat treatment.

    https://www.youtube.com/watch?v=_6uTzsoUBMk

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    Quote Originally Posted by orangehero View Post
    Generally it's done on high carbon high alloy stainless steels for slight improvement in hardness and toughness. Low alloy high carbon steels gain little if any benefit from cryogenic treatment.

    I believe leaving the blades to rest is to allow stresses formed during the quench/temper to dissipate.
    Gaining 1.5-2 point Rockwell hardness in alloyed steel is no "slight" improvement.

    All steels benefit from cryo, some in more converted austenites (hardness, wear resistance, sharpenability), and some in a better ductability. Toughness depends more on HT the temperatures.

    San mai construction doesn't bode well with cryo because of the inner stresses, that might be one reason not many san mai makers use cryo, another is cost. Liquid nitrogen or dry ice/acetone is not cheap and need to be constantly replenished as it evaporates.

    And yes, there is absolutely no benefit to cryo if it is done the next day - heard about some makers doing it to minimize possibility of cracking.


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    Doesn't higher hardness (strength) and higher ductility translate to higher toughness? I didn't realize the increase in hardness was so great, but I suppose every steel is different.

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    Marko Tsourkan's Avatar
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    Higher hardness doesn't necessarily translates into higher toughness, in fact can be the opposite - micro-chipping is a result of an over-hardened steel (or inadequately tempered).

    Improved ductability does translated to better toughness, but toughness overall will be determined by carbide size of the elements in the steel, and the grain size of the heattreated steel, so all these factors have to be taken into account.


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