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Cryo with dry ice

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by Revolverrodger, Apr 16, 2018.

  1. Revolverrodger

    Revolverrodger Gold Member Gold Member

    Jul 23, 2007
    I am planning to make a camping knife from nitro-V.
    I would like to try to cryo with dry ice and denatured alcohol but never tried it before...

    Here is the HT protocol I was thinking about
    Heat to 1950 for 20 minutes in SS foil
    Plate quench (not sure how long I need)
    Dunk in dry ice / denatured alcohol (not sure how long)
    Temper at 400 for 2 hours twice

    What do you guys think ?
    Any suggestions ?
    Some people temper after plate quench and before cryo... What is best ?
     
  2. Russ Andrews

    Russ Andrews Knifemaker Knifemaker / Craftsman / Service Provider

    Nov 27, 2002
    Dry Ice isn't cryo. For Cryogenic processing, you need liquid Nitrogen.
    Dry ice is a continuation of the quench, for the purpose of completing transformation from
    austenite to martinsite.
    The steels that seem to benefit most from cooling to -100 to -105 are oil/air quenching steels...
    requiring a slow quench....Cool your blades slowly, and hold for the time recommended by the steel
    co.
     
    hugofeynman likes this.
  3. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    A sub-zero treatment with dry ice at -100°F reaches the Mf - Martensite Finish point.
    Cryo in liquid nitrogen is at -300°F, and sets up the steel to form eta carbides in the temper. It will at a point or two in hardness.
     
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  4. Revolverrodger

    Revolverrodger Gold Member Gold Member

    Jul 23, 2007
    Sorry for the mistake
    Should I do the sub-zero treatment directly after plate quench?
    Thanks
     
  5. Russ Andrews

    Russ Andrews Knifemaker Knifemaker / Craftsman / Service Provider

    Nov 27, 2002
    Yes.
     
    Revolverrodger likes this.
  6. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    The sub-zero is the end of the cooling curve. It should be as smooth and continuous as possible. This means getting down to room temp and then continuing down to -100F in a more or less unbroken curve. If the steel rests too long at room temp some of the austenite may stabilize.
     
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  7. Revolverrodger

    Revolverrodger Gold Member Gold Member

    Jul 23, 2007
    Thanks
    I will use dry ice and kerosene then
    Should the ice be added ti the kerosene or vice versa?
     
  8. LCoop

    LCoop

    294
    May 5, 2007
    I dump the DI in a container then add denatured alcohol. It' will be boil and fizz like a scary movie. When it settles down I add the blades. I take my foil wrapped blades out of the oven and straight to aluminum plates. I have the plates laying on my concrete garage floor. Place a foil wrapped blade on a plate, put another plate on top and step on them for pressure. Alternating between plates as I usually heat treat 5 or 6 blades at a time. Probably within 2 minutes they are cool enough to touch. I take them out of the foil and immediately put in DI alcohol bath. 10 minutes is probably long enough but I do 30 or if I'm busy let them stay till DI is gone. I immediately put in my tempering oven for the first cycle then. Hope this helps.

    So basically within 3 minutes my 440C blades have went from 1875 to -100. Fire and Ice!
     
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  9. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    As Coop said, it is simplest to bust up the DI into smaller chunks and slowly pour the alcohol (or kerosene) over it. It will settle down in a few minutes to a steady simmer, which indicates the bath is down to around -100F.
    Once the quenched blades have cooled off to room temp, put the blades in the DI bath and just leave them until all are in, or until the bath has quit bubbling ( about an hour). Let the blade sit at room temp for 10 minutes, then put in the temper oven.
     
    Last edited: Apr 19, 2018
    hugofeynman and Revolverrodger like this.
  10. Revolverrodger

    Revolverrodger Gold Member Gold Member

    Jul 23, 2007
    Thank you all for the very clear and practical instructions
     

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