I guess you refers to Peters HT who specialize on heat treating high alloy steel for knife. I mean ordinary HT company who HT tool part are mostly overlooks these process.
Is Cryo Really Necessary?
- Thread starter SLC_Blades
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I guess you refers to Peters HT who specialize on heat treating high alloy steel for knife. I mean ordinary HT company who HT tool part are mostly overlooks these process.
Willie71
Warren J. Krywko
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- Feb 23, 2013
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Most steels need to go to about -100-110f. Some like V4e or z-wear need about -130-140f, which are my go to steels now (V4e is newer, but I’m sure I’ll be using a lot of it.). Cryo is overkill to about -300f. I was thinking of eta carbides when I got the dewar, but the testing we have done hasn’t shown changes in toughness, and the literature makes bizarre claims that fall apart with scrutiny. Dry ice/acetone is -90-100f. (I’m doing these numbers from memory, so I might be out by a few degrees.) Dry ice/acetone is pretty close for many steels. For me it’s inconvenient. I have to drive 45 minutes, one way to get it, and it lasts less than 24h. Cryo needed the dewar, which cost me nearly $800.00cdn, cry once type deal. I fill the dewar every 5 months. I have it on hand for whenever I need it, so I don’t have to plan batches asdiligently as I used to. It’s also been great for the charpy samples. I know I’m getting cold enough, not close enough.
I see sub-zero/cryo in similar light to having a kiln versus forge, or canola oil vs parks 50. You might make a serviceable blade without it, but why pay extra for steel that you won’t get max performance out of? Do it right, or pick different steel. If you make knives for yourself, do what you want. If you sell them, do it right.
I see sub-zero/cryo in similar light to having a kiln versus forge, or canola oil vs parks 50. You might make a serviceable blade without it, but why pay extra for steel that you won’t get max performance out of? Do it right, or pick different steel. If you make knives for yourself, do what you want. If you sell them, do it right.
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Yes, good post, Warren. The way I see it, for the type of blades that I make (hunting knives, EDC knives, kitchen knvies), I don't care to have any retained austenite in them. If I were making blades that saw more impact applications, I wouldn't be too concerned about RA reduction. For me and my knives, the goal is always maximum HRC post quench. For "certain" steels, this requires at least sub zero (-100F). For "most" steels I use, including all the low alloy carbon steels like 1084, 80CrV2, 1095, W2, 52100, O1, O7, CFV.....these steels will not benefit at all from any sub zero or cryo quench, and the reason is straightforward....I am getting maximum HRC post quench right from the oil, and the sub zero or cryo quenches will not add any hardness. It is like Kevin Cashen once said, "If you are using those steels, and you do see a hardness increase after sub zero or cryo, you need to rethink your heat treatment." I 100% agree with that.
But once you move up in alloy, and I like to think of A2 as that threshold, and you're making fine cutting instruments, then my philosophy is you need to be "continuing the quench". As I said, I don't want to settle for 63-64 post quench when it could be 65-66 post quench. Larrin has talked about how hardness is directly related to wear resistance and "strength". Is 63HRC post quench good enough for you and the application? Then don't bother with it! If you want more strength and more wear resistance....then IMHO you "should" be doing it. Are you trying to make the "Best" knives you can, or is it "good enough"? Another point, if a steel has an Mf temperature of -130F, a -100F quench is "good enough" in my book. I wouldn't worry too much about that last 30°. Martensite finish temperatures are variable to some degree, and probably rarely is 100% RA conversion done on a blade steel. But the way I see things, if the steel has a low martensite finish temperature, and dry ice is at my local grocer, I am using it.
About the eta carbide precip that has been claimed with LN2 cryo, that isn't a concern for me. My goal is just max hardness/minimizing RA.
And if we want to make the best cutting instruments we can, all we have to do is know the martensite finish temperature (or Mf90 or whatever we want to call it, I guess we could say "as much martensite conversion as you can get at that temp) for any given steel. It would be extremely helpful to have a chart that listed the steel, and then list the Mf or Mf90 next to it.
But once you move up in alloy, and I like to think of A2 as that threshold, and you're making fine cutting instruments, then my philosophy is you need to be "continuing the quench". As I said, I don't want to settle for 63-64 post quench when it could be 65-66 post quench. Larrin has talked about how hardness is directly related to wear resistance and "strength". Is 63HRC post quench good enough for you and the application? Then don't bother with it! If you want more strength and more wear resistance....then IMHO you "should" be doing it. Are you trying to make the "Best" knives you can, or is it "good enough"? Another point, if a steel has an Mf temperature of -130F, a -100F quench is "good enough" in my book. I wouldn't worry too much about that last 30°. Martensite finish temperatures are variable to some degree, and probably rarely is 100% RA conversion done on a blade steel. But the way I see things, if the steel has a low martensite finish temperature, and dry ice is at my local grocer, I am using it.
About the eta carbide precip that has been claimed with LN2 cryo, that isn't a concern for me. My goal is just max hardness/minimizing RA.
And if we want to make the best cutting instruments we can, all we have to do is know the martensite finish temperature (or Mf90 or whatever we want to call it, I guess we could say "as much martensite conversion as you can get at that temp) for any given steel. It would be extremely helpful to have a chart that listed the steel, and then list the Mf or Mf90 next to it.