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Thread: Cryo?

  1. #81
    Join Date
    Aug 2009
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    South Central Minnesota
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    7,981
    If you are using dry ice as a cryo, I'd suggest using RV anti-freeze rather than acetone. It's non-toxic and non-flammable and cheaper.
    Tracy Mickley
    Forum owner and administrator

    Mickley Knives www.Mickleyknives.com
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  2. #82
    Ted, there is nothing subjective about it. Take a steel and like A2 and do the "standard" HT, 1750F 30 minute soak, plate quench, then take a hardness reading. Then, do either a sub zero or a cryo treatment, and take your reading again. You will find, on average, a 2-3 point gain in hardness. The goal is to have the highest hardness you can attain post quench, then temper back. It's not subjective at all, it is actual material science. The reason the hardness gain happens is because the retained austenite in the steel is being converted over to untempered martensite (that then must be tempered). If your steel has no gain in hardness by sub zero or cryo, then there is probably no real benefit (other than the eta carbide precip with LN2....and data on that aspect is very scarce).

    I would say that LN2 is probably BETTER than sub zero (dry ice/denatured alcohol), especially if you're doing lots of knives, for a few reasons. And I don't do cryo, only sub zero on the steels that need it like A2 (I send off higher alloy to Peters). 1. You can be ensured of 99% of RA conversion on most any and all steel with LN2. 2. You get the benefit of eta carbide precip which is said to aid cohesion of the martensite/carbide matrix 3. It's a chunk of $$$ for the dewar up front, but generally lasts maybe 3 months and is ~$60 a fill, compared to ~$10 worth of dry ice every time you need to HT, and is evaporated in ~24 hours. Numbers are approx. Point being, it's probably more effecient for a knife maker, especially in quantity, to use LN2 over dry ice sub zero.

    Another example....a steel as simple as 1095. If you do the "right" HT for that steel (1475F, soak, fast oil quench), you will not see any gain in HRC reading by either sub zero or cryo. Why? Because you have 66-68 post quench, and thus, basically speaking, ALL of the austenite you put in solution is converted over to martensite during the quench. If you HT at a higher temp, say 1550, your post quench hardness will not be as high, maybe 64-65, and then to get back up to 66-68, you can do a sub zero or cryo treatment to convert the retained austenite (that caused the lower hardness) over to untempered martensite.

    What I find amusing is the charts out there claiming that "Wear Resistance" is increased 400% (like on O1 for example) by LN2. I find that laughable. That would translate to having to spend 4X the amount of effort in hand sanding a blade that has been cryo vs one that hasn't, and that is simply not the case.

    The idea is RA conversion, and tempering before sub zero or cryo will tend to stabilize RA, what we don't want to happen. With all that said.....if you find no improvement in the performance of your blades by employing said procedures, then I would say skip it. There are a few well known makers I can think of that use high alloy steels (steels that have excessive RA post quench), that do NOT employ ANY sort of sub zero/cryo, and their knives are raved about. Ponder that!

  3. #83
    Join Date
    Apr 2014
    Location
    North central montana
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    614
    Samuraistuart thank you for the excellent reply...and you also Ken! Boss, I am indeed trying the RV antifreeze for my first go around...I was hoping that by racking the knives, putting the ice on a grill just above the top of the blades (edge up) and slowly pouring the antifreeze into the cooler to create a ramp (if the consensus is that ramping a cold treatment is necessary).

    Samuraistuart...I do not think the science of the thing is subjective....I think the opinions and methods of guys making perfectly good knives are. things that I find subjective are things that are difficult to cross-examine with other techniques. I am not scientifically advanced enough to know which tip to reject in favor of another....that type of subjectivity is what you are pointing out in your post...400% improvement I can weed out!...lol. other stuff not so easy.

    When selling a knife made of A2 do you differentiate between LN and dry ice if both are effective?... or do you say the knife has had a cryogenic treatment?

    A few months back I saw an A2 recipe that went HT---temper 1---LN---warm to room---temper 2.(they were getting good results) Once again that is different than what I've learned recently (which makes more sense...cold after HT...keep them molecules a movin') I absolutely believe in the science behind it I just think different guys are hitting on a method that works that is different from other guys. So a noob like me is tempted to homogenize a bunch of different methods which is most likely unwise. It would probably be better to copy one persons HT/CT recipe and see if you can get similar results.

    Also...on anything requiring testing...the human bias creeps in almost unnoticed. our ability to almost subconsciously skew results towards our favored outcome is amazing.

    My notion now is to continue working with A2 as it seem to benefit from either method of cold treatment. I'll HT....cool to room/forced air? into dry ice/ RV antifreeze....soak for at least 8 hours. leisure warm to room temp...into temper 1...cold water quench and scrub.....temper 2....cool to room temp...do some grinding.(please pick this apart!) this would be for an edc not survival.

    For an outdoor knife maybe skip the cold treatment because of : For A2 tool steel note they also say at bottom of page #5: "applied to A2 steel confirmed that cryogenic quenching results in a moderate improvement of wear resistance and hardness, at the cost of impact resistance"? A2 already has pretty good wear resistance and hardness so perhaps cold not needed? This is where determining yes/no feels subjective...HOW MUCH cost of impact resistance...was it worth a "moderate" increase in hardness and wear resistance that didn't really net a 400% increase...lol?


    Thanks for all the help guys.

    Sorry if I let too much frustration bleed through my earlier post.
    Last edited by Smallshop; 03-18-2017 at 01:02 PM.
    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.

  4. #84
    Ha! Ted, believe it or not, last night I was loosing sleep over my comment to you! You corrected me, and rightly so, that you weren't questioning the science...but rather some of the claims being made. How right you are on that, too. Not just cryo treatments!

    When selling a knife in A2, personally (this is just my opinion, others may disagree) I wouldn't even bother with putting "cryo" in the description. Why? To me, the science and data is there to support the fact that A2 "should" be receiving some sort of sub zero or cryo treatment as part of the quench. Sort of like, this is a given! It's A2? Oh, then it at least had a sub zero treatment, without having to ask or advertise. The RA% is too high, in my understanding and opinion, for the type of knife/edge/apex/performance I am after. Have I done a side-by-side comparison of A2 with and without? No I have not, but I know London is there, tho I've never been. However, the way I see it, talking the steels we knife makers commonly use from 1080 thru the ***"V" series "super" steels as they are called, there is a fairly clear distinction of which steels "should" receive at least the subzero (dry ice) quench. 1080, 1095, W2, 52100, O1, O7, and the like....no. There is not enough retained austenite in these steels (after a correct HT) for subzero to do anything substantial to improve performance, or LN2 (I'll leave the carbide precipitation of LN2 out of this discussion...as I understand it, any steel that has an LN2 quench will have the benefit of some of these super small carbides precipitated upon tempering....but the data on that, and the actual real world benefits of that...hard to source). Move on up in alloying, and especially looking at the hardening temperature (1750F for example with A2), you can bet that the RA% in that steel is going to be higher than what we want. And any steel with more alloying and higher hardening temps than A2, like D2 and AEBL and up thru S110V, you can bet the RA% is just too high to not address it. Let me throw in the fact that the "traditional" way of dealing with excessive RA in these steels is the secondary hardening tempers, in the 1000F range. These high temp tempers also do a great job in reducing RA, however, they also allow carbide precipitation, which robs more carbon from the martensite matrix to form these carbides, not ideal for what we are(or at least not ideal for what I am) after. Wear resistance is said to improve with the SH tempers, but at the expense of toughness. I can only speak for myself. Some makers may WANT RA in their blades!!!! I think there are some out there that know that the RA is there, and choose to leave it in, and they "may" have a good reason to do so. It's just not the type of knife/heat treatment I want, or what I "think" I "know" to make a good/better/best blade. Some special applications, RA may be OK to have in some small dose, I think impact resistance may be one...but not the best way to have "impact resistance".

    Get off your box, Stuart. I will....hold on! There is nothing wrong at all with selling a knife in A2 and labeling it as having been "cryo" treated (whether that was dry ice OR LN2), the public doesn't care so much about the science, but they hear "cryo" and images of suspended animation and such run thru their heads!

    Your A2 procedure looks A2-OK to me! harden, quench, sub zero, temper, temper. Quench during tempers if you like, I do as well. I'll throw this out to confuse you more, my understanding of the formation of martensite is that is happens at the speed of sound (literally), once the piece reaches that temperature. Soaking 8 hours in dry ice would probably be 7 (or maybe 7.5 hours?) longer than necessary. I may be wrong on this, but the same with LN2. Once the piece hits the temperature at which that retained austenite wants to be converted to martensite, it happens at the speed of sound, and soaking (for RA reduction only), does little. However, when talking about the additional benefits LN2 offers with the carbide precip, I think that is where the soak comes in play. Please don't quote me on that, tho. That is my understanding, and it may be wrong. You've got it all nailed down, right? Quiz tomorrow.

    To address your last paragraph, that is the way I would understand things. For a small knife that needs to be hard and wear resistant....do the cryo. For a large knife, the same exact HT, but you can temper it back more for more toughness (59 instead of 62). But my thought, choose different steel if more toughness is needed. S7 has LOTS of impact resistance, and its wear resistance is no slouch. Simply leaving high RA% in a steel for added impact resistance is not the ideal road to take. There is always a give and take. Strength vs toughness.
    Last edited by samuraistuart; 03-19-2017 at 02:11 PM.

  5. #85
    Join Date
    Apr 2014
    Location
    North central montana
    Posts
    614
    "You've got it all nailed down, right? Quiz tomorrow."

    HAHAHA!!! I wish I did. Thanks for the reply...absolutely no need to apologize.

    My instinct on the long cold soak times with dry ice and RV AF is that if the cold does not actually hurt the blade, you buy time to begin the warm up and temper....which may be after nappy time for the night...or whatever is convenient. So, an AM start on tempering is nice...rather than a late night because you hard to fish the blade out right after hitting temp. Which brings up another thought...I don't believe I could adequately find the temp/time of lowest temp/conversion....safer to just let it get as cold as possible for as long as you have dry ice?

    On the higher alloys like AEB-L and D2 will the dry ice still be sufficient or only LN. My reason is that I haven't found LN close but have found that the Budweiser distributor 30 miles away does carry dry ice.
    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.

  6. #86
    Join Date
    Jan 2012
    Location
    S. Baldwin Co., Alabama
    Posts
    1,844
    Ted, as I mentioned before, Sandvik's engineer claims there is no benefit to LN over Dry Ice treatment. He says in all their tests the -95F provided by dry ice does all the changing of RA that can be done. It seems that everybody insists AEB-L is exactly the same as Sandvik's 13C26 - if so, then dry ice should be just as good as LN for AEB-L. Sandvik also claims a long soak is not required, only enough time to bring metal down to full -95F, say 30 minutes or so? Longer soak doesn't hurt, but has no benefit.

    The above is NOT "my" knowledge, but what was told to me by a Sandvik engineer in a phone call.

    Ken H>

  7. #87
    As far as AEBL goes, which indeed Sandvik copied as their 13c26 steel, the Mf point is around -95F, so dry ice slurry would finish the martensite transformation for that steel. I think many of the higher alloy stainless steels and tool steels have their Mf point around the dry ice slurry temp of roughly -100F. Steels like 110V or 10V, I'm thinking their Mf point is lower than -100F. I have a tech paper on CPM M4 that says the Mf for that alloy is -130F. So the dry ice slurry would get most of the retained austenite converted for M4 steel, but not 100%. They use X Ray diffraction to detect RA levels, and I don't think that they can detect anything under 2%...guessing that to be the case anyway. As far as soak.....longer won't hurt at all. I leave mine in over night, actually. Once the dry ice has evaporated, I pour the denatured alcohol back in it's can for next session! (Leaving the cap a little loose, sometimes there might be some residual dry ice left in there....don't want a bomb in the garage going off!)

    Again, with D2, the tech data on the paper I cited ("Heat Treating, Including Steel Heat Treating in the New Millennium, An International Symposium in Honor of Professor George Krauss" (ASM Heat Treating Society) 2000) seems to indicate that sub zero slurry is cold enough. -100F= <2% RA (less than detectable).

    Hold your horses......what I find VERY odd, is that A2 and -100F still leaves 9% RA. And honestly, I wonder if the paper got their wires crossed on that one. It makes no sense to me whatsoever. How does D2, with 1.5% carbon and 12% chromium, with a hardening temperature of 1850f, have LESS RA than A2, which only has 1.05% carbon and only 5% chromium and a hardening temp of 1775f (after -100F sub zero)???? Both samples oil quenched...so quench rate variable is not there. Seems to me the numbers are crossed, and that D2 would have 9% RA and A2 would be 2% or less. I wonder.....
    Last edited by samuraistuart; 03-20-2017 at 10:17 AM.

  8. #88
    Join Date
    Apr 2014
    Location
    North central montana
    Posts
    614
    Thanks guys. Ken sorry to make you repeat...It seems as I age I retain less info than a perfect HT/CT retains austenite.....I should be re-reading before re-asking...sorry again.

    Samuraistuart....the last point you make might be a Kevin Cashen question?

    So, is everyone in agreement that leaving blades in cold treatment till you feel like working on them again is NOT harmful?

    And...why do people oil quench A2? Isn't an air or plate quench less violent? or maybe the question to ask is ...what is the advantage of ANY air-hardening steel over oil quench or oil-hardening steel?

    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.

  9. #89
    Join Date
    Jan 2012
    Location
    S. Baldwin Co., Alabama
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    1,844
    The advantage of air hardening steel over one that does require oil hardening is the use of aluminum plates to prevent warping. Aluminum plates REALLY help with warp problems. Any steel that can be plate quenched is MUCH easier to work with than one requiring oil quench - from my view anyway.

    Ted - don't worry about forgetting, I do it all the time!

  10. #90
    The reason people are oil quenching steels that are traditionally air cooled/plate quenched is that it is said to actual allow for LESS retained austenite, and any unwanted precipitates. In other words....a more complete quench from austenite to martensite. Maybe splitting hairs here, or even atoms. I oil quench A2 in 90F canola oil. Plate quenching is actually a faster quench than many realize, and an oil quench (medium speed...not fast oil like P50) is not a whole heck of a lot faster. If warping is a concern/issue, you can use plates strictly, or go to the plates after an oil quench.

    Oh yeah, almost forgot...not to worry on leaving the blades in the cold treatment, especially sub zero. Now I'll throw a wrench in that. There is a post on the Spyderco forum made some time ago by Cliff Stamp. In this post there are a few links to research into cryo with LN2, and the effects of leaving a blade in the LN2 for certain time intervals (I don't recall exactly, but like 4 hours, 8, 12, 24, 48, etc), and the results are very very odd.
    Last edited by samuraistuart; 03-21-2017 at 10:09 AM.

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