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Thread: Cryo?

  1. #71
    Join Date
    Apr 2014
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    North central montana
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    I've read so many different opinions on cryo that I don't know quite what to think.

    If dry ice treatment is not the waste of time that some makers seem to think....it is probably closest to a controlled ramp (depending on how you setup)?
    Thanks,
    Smallshop (AKA Ted Hauser)


    ---------------------------------------------------------------------------------

    God puts the iron in the ground and the highlights in the wood....it's His stuff, we just get to work with it....make it nice.

  2. #72
    Join Date
    May 2012
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    creedmoor, nc
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    Quote Originally Posted by Blade-Runner View Post
    Ok, so I am not sure how much background everyone has on heat treatment and more specifically, cryogenics, but I have a little. I have read a few books - I know, not the real world, but...- and a few studies on the process. If you're interested look up "Cryogenics", by William E. Bryson. He also has some great books on "Heat Treatment, Selection, and Application of Tool Steels" is a great one that I am sure anyone/everyone on here would find relevant. I have also read this from Jay Fisher:

    "What is the specific rate of cooling for most of these steels? 4-5 degrees Fahrenheit per minute. That means in order to reach -100F, it should take about 40 minutes (from room temperature), and to reach -325F should take about an hour and a half (from room temperature). This is why simply dipping blades into cryogenic baths of dry ice and alcohol or liquid nitrogen is a huge and destructive error, yet knifemakers who are uneducated in this process frequently do this, and tell others that it's the proper way to quench! Sad, truly sad for the knife client. The cryogenic process cooling rate is absolute and critical." http://www.jayfisher.com/Heat_Treati...Quenching_Rate

    Which seems in line with what the books and studies say. So I am now "fishing" all the forums to see how other knifemakers are making this a reality....but so far, I have yet to find anything.

    I am super interested in hearing any feedback you might have.
    so much depends on the steel involved. the makers of basic stainless steel such as 12C27, 13C26, and AEB-L recommend a freezing treatment, cooling the blades to -95F, with no soak as part of the heat treat process.(http://smt.sandvik.com/en/products/s...ezing-70c-95f/)
    Crucible recommends freezing treatment, cooling to -100F, to reduce retained austenite when using CPM S35VN, CPM 154CM, and similar steels.
    Carpenter recommends freezing treatment, cooling to -100F, to reduce retained austenite when using B75P, BG42, 440C and similar steels.
    here is a study using A2, where some samples went from room temp directly into LN2 http://www.airproducts.com/~/media/F...3005019GLB.pdf
    Scott, just a tired old sailor
    see my knives and woodwork here
    https://www.etsy.com/shop/oldsailorsknives?ref=l2-shop-info-name

  3. #73
    Join Date
    Jan 2012
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    S. Baldwin Co., Alabama
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    Scott - good links you've posted. From my discussion with Sandvik engineer they have found there is NO improvement in LN treatment over dry ice treatment. He talked like they had tested pretty thoroughly to determine this.

    On the 2nd link - very interesting read there. Sounds like they did some good testing on A2 grade tool steel. Not sure their tests would apply to any other steel alloy. Two things stood out for me in their conclusions.
    *********
    1. Experimental heat-treatment schedules applied to A2 steelconfirmed that cryogenic quenching results in a moderateimprovement of wear resistance and hardness, at the cost ofimpact resistance.
    **********
    Note it's only a "moderate" improvement, and at the cost of impact resistance.

    ***************
    2. Results confirm that, in order to be effective, cryogenictreatments need to be carried out soon after martensiticquenching from austenitic temperatures and beforetempering
    ******************
    Note they are saying cryo must be done ASAP after quench.

    That paper confirms what I have read other places - need for cryo depends on the steel, and if you are going to do it, be sure it's right after quench.

    "IF" I remember cryo is for high alloys (tool steels, stainless, etc). Simple carbon steels (1080, 1084, 1095, etc) don't need it "IF" the HT/quench are done correctly. I do get things mixed up sometimes so please correct if this isn't a valid statement.

    Ken H>

  4. #74
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    May 2012
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    creedmoor, nc
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    with the steels I listed, they were all recommending about -100F. i would bet if we could find a complete CCT on these steels, the Mf or martensite finish temperature is somewhere around -70F, especially since they all say no soak. hardness improvement at expense of impact resist seems to be the story in all research I have been able to find. time to break the dry ice and everclear, maybe make some PJ when knives are done.
    Scott, just a tired old sailor
    see my knives and woodwork here
    https://www.etsy.com/shop/oldsailorsknives?ref=l2-shop-info-name

  5. #75
    Full on "Cryo" (LN2 -300F) is said to allow for the formation of small "greek letter" (it's all greek to me!) carbides that precipitate upon tempering (if the alloying is there). "Sub Zero" (dry ice -100F) is not cold enough to do this.

    The main reason to use "sub zero" or "cryo" is for the retained austenite conversion over to untempered martensite, however, and some of the more highly alloyed steels have Mf points below -100F (dry ice won't get it as well as LN2 will). That said.....Martensite finish temperature (Actual Mf) is, from my research, a point of diminishing returns (you never get there).

    Also....some steels like A2 have been shown to have their Mf well below -100F, D2 as well. Which I find interesting...as the data provided by the manufacturer of higher alloy steels say that Mf is -95F etc. You wouldn't think A2 would have that much RA after a standard quench, and I would think A2 would have all RA converted with sub zero (-100F) temps, but that's not necessarily the case....http://www.hypefreeblades.com/forum/....php?f=3&t=928

  6. #76
    Join Date
    Sep 2009
    Location
    Great Falls, Montana, USA
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    2,818
    ^Well put. I personally don't like or recommend the Acetone/dry ice thing, simply because I've done it, and when compared to using LN, there's a very noticeable difference in favor of LN (on those steels where "cold treatments" matter)


    www.caffreyknives.net
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    "Nobody cares what you know.....until they know you care."
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  7. #77
    Join Date
    Apr 2014
    Location
    North central montana
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    general questions/observations not in any specific order:

    The effects of cryo/cold treatments seem very subjective and possibly the best proof is anecdotal (not a bad thing but perhaps observable improvements are due to corrective ability of cold treatment over faulty heat treating)?

    dry ice is less effective than LN?

    You cannot lower blades into LN slow enough to be considered any kind of "Ramp"...merely break prevention?

    cold treatment and heat treatment are vastly different. NO-ONE soaks their blades in a furnace for twenty hours. Perhaps ramping is less critical in a cold treatment?

    If you were a mfg of commercial freezers you would push the necessity of cold ramping since that is something joe garage dude cannot do? (yes, cynical... I know...)

    perhaps cold treatments are being done just to say they were done as a fine blade can be made without them if HT is dialed in? But if customers want something....?

    dry ice has no effect on a blade?

    dry ice is very effective on a blade?

    Once you try LN you never go back to dry ice?

    Everybody agrees that heat treating and tempering a blade correctly makes it a better blade?

    opinions vary greatly as to cold treatment making a better blade? (and likely will for years to come?)
    Last edited by Smallshop; 03-17-2017 at 11:41 AM.
    Thanks,
    Smallshop (AKA Ted Hauser)


    ---------------------------------------------------------------------------------

    God puts the iron in the ground and the highlights in the wood....it's His stuff, we just get to work with it....make it nice.

  8. #78
    Join Date
    Jan 2012
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    S. Baldwin Co., Alabama
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    Ted, if you go back and read the posts (I know they are confusing) you will notice that everyone (almost anyway) says the need for cold treatment depends on the steel being used, with simple alloys not really needing any cold treatment. It's the higher alloy steels (tool steels, SS, etc) that benefit from cold treatment.

    Dry Ice bs LN? Well, again it depends on the steel. I do think the knife steel manuf's have a decent idea if their steel requires LN, or if dry ice is sufficient. If a person is setup for LN, then it surely won't hurt for any high alloy steel, nor should it "hurt" a simple alloy.

    Sandvik for example says they have tested their blade steels with LN and find no benefit over dry ice. When I say "dry ice" I'm referring to a dry ice/alcohol slurry, not acetone. There are other manuf's who recommend LN treatment.... all depending on the steel alloy.

    Yes, a decent blade can be made without any cold treatment, but cold (DI or LN) does seem to have higher alloy steels.

    On the idea of ramping down - never really heard that mentioned before for knife blades. I do like Ed's idea of laying them on top of LN in the vapor to allow cooling before dunking in LN.

    I do think it's generally agreed you should come from quench, allow to cool to room temperature, then direct to cold (DI or LN) treatment with as little time lag as possible.

    Ken H>

  9. #79
    Join Date
    Apr 2014
    Location
    North central montana
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    Thanks Ken. I have read so much stuff the last couple years on certain topics that some of it becomes a jumble of opinions. I have kind of gotten to where I learn here and at the hypefreeblade site. (that is mostly reading archives not interacting like here). The reason is I have gotten to where I don't have time to vette out 300 people for veracity. the tone here seems serious/friendly. anyway....

    I'm planning on using A2 and 440C and was hoping to do dry ice/alcohol treatment. I really want to do things that matter not just appease potential customers because they demand something that provides marginal benefit. If LN is what really makes the difference I should be heading that way.

    Yet even the the A2 doc looked like leaving the blade in air for 24hrs before LN gave the best blade. I think that was N2? ( And of course I ask WHY does it seem like everybody quenchs A2 in oil??) If you do a batch of blades and you're pulling them out one at a time to oil quench how over-soaked is the last blade? Wouldn't a rack of blades being air quenched be an advantage over the chronology of one at a time in oil?

    Sometimes I read the cryo stuff and my head swims....Maybe because I'm still dialing in heat treating. Often when I get to really read stuff it's late and the brain is gone. And by stuff I mean technical stuff where vocab is unfamiliar and requires more thinking than telling someone "beautiful knife!"...I must be getting old...lol.

    the LN fumes to pre-cool seem excellent. I also wonder if just putting the blade in a freezer and then in the fumes would help slow the "ramp". That'll get you to -20 and maybe slower that hovering over LN. though enough distance would give you good control there. The data on ramp speed seems like the goal is slower than easily achieved?

    feeling old and tired today....
    Thanks,
    Smallshop (AKA Ted Hauser)


    ---------------------------------------------------------------------------------

    God puts the iron in the ground and the highlights in the wood....it's His stuff, we just get to work with it....make it nice.

  10. #80
    Join Date
    Jan 2012
    Location
    S. Baldwin Co., Alabama
    Posts
    1,857
    Ted, take a look at the top of page #5, and you can see it's actually better to go from quench to LN. Because of the way it works on a molecular level you want a constant drop of temperature from quench to LN with no pauses between.

    For A2 tool steel note they also say at bottom of page #5: "applied to A2 steelconfirmed that cryogenic quenching results in a moderateimprovement of wear resistance and hardness, at the cost ofimpact resistance"

    That's only a moderate improvement in wear resistance, but at the cost of some impact resistance. I think in chopper knives I might prefer to sharpen a bit more often and not worry about chipping so much. In a slicer the loss of impact resistance wouldn't be a problem.

    440C I won't comment on - I've not done enough reading to give a good idea of importance of LN.

    LN vs Dry Ice - consider the amount of improvement vs the number of knives you expect to make per month.... and cost.

    Ken H>

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