3V- dry ice

Kevin McGovern

Kevin McGovern

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Jul 31, 2015
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Anyone have a recipe for 3v using dry ice for sub zero quench? Is dry ice even advantageous for this steel?
 
To know whether there is an advantage you have to know why you are doing a sub-zero treatment in the first place. Do you know by what mechanism a sub-zero quench changes properties of the steel?
 
If I knew that, I suppose I wouldn't be asking. In AEB-L, I do it to reduce retained austinite. I don't know the purpose of the cryo included in some 3v recipes I've seen. Hence, my question.
 
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Martensite finish is often below room temperature for high alloy steels, so instead of a full transformation to martensite there is some austenite left over, or “retained.” The transformation is more complete if you go to lower temperature, it could very well be complete above dry ice temperatures, though this depends on your austenitizing temperature, holding time, and alloy (in this case 3V). Therefore, if attempting to minimize austenite the lower in temperature you go after the quench the better.

There are a few potentially complicating factors; here are two of them:
1) Using an upper temper also helps to transform retained austenite. Sub-zero treatments may be less necessary when using an upper temper. However, I have seen papers where both were utilized and there was less austenite than upper temper alone.
2) Some research is indicating that a 24h or so cryo treatment (liquid nitrogen) increases the density of transition carbides during tempering which leads to greater wear resistance. I am not aware if this has been attempted with dry ice or other intermediate temperatures. The increase in wear resistance may also reduce toughness so this isn’t necessarily a universal good thing.
 
Yes it is. We have been using dry/ice sub zero as part of 3v heat treat with low temper for a long time. From my testing I prefer it to high temper. Butcher_block was the one who first mentioned it around here that I remember.
 
The question may be HOW beneficial. Dry ice apparently works fine for AEB-L, whereas the guy from B-U told me that it is not quite cold enough to the get full effect with steels like Elmax or M390. A few degrees too "warm.'
 
Kentucky said:
Yes it is. We have been using dry/ice sub zero as part of 3v heat treat with low temper for a long time. From my testing I prefer it to high temper. Butcher_block was the one who first mentioned it around here that I remember.
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Phillip, didn't the guys who developed the low temper regimen discover that cold/cryo was even more important than with the high temp method?
 
Yes it is from my understanding. Since the lower temper dosnt nothing to deal with the RA it's vital.
 
jdm61 said:
Phillip, didn't the guys who developed the low temper regimen discover that cold/cryo was even more important than with the high temp method?
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I haven’t experimented with 3v comparing dry ice to LN. With z-wear/cru-wear, cryo is worth a couple Rc points over sub sero. 3v is euctoid, where z-wear is hypereuctoid. That might be a big enough difference. I use full cryo now for all stainless or high alloy steels.

That said, I’ve used sub zero with 3v and S35VN in the past and had very good performing blades. Now that I use more higher alloy steels, I invested in a dewar.
 
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in the playing around that i have done (only cryo not dry ice) it can be a great benefit to higher alloy steels and steels that are known to be higher RA holders. the reason i had played around with 3v is due to the HT data is all worked around size change for tool and die work not knife work. the thought being that in knives that didnt matter as long as the RA was cleaned up and the steel matrix stabilized. i was already using cryo on cpm154 back then and after much reading and talking to some big brains in steel science it was confirmed that cryo will clean up the RA withought needing the high temp temper. as for how much difference with or withought cryo a knife maker asked me for a HT to use on cpm154 later he said he didnt want to fool with it for the few blades in SS he was doing so i HTed them. when he got them back he wass shocked at how much difference in grinding and sharpening his HT and my HT had
 
butcher_block said:
in the playing around that i have done (only cryo not dry ice) it can be a great benefit to higher alloy steels and steels that are known to be higher RA holders. the reason i had played around with 3v is due to the HT data is all worked around size change for tool and die work not knife work. the thought being that in knives that didnt matter as long as the RA was cleaned up and the steel matrix stabilized. i was already using cryo on cpm154 back then and after much reading and talking to some big brains in steel science it was confirmed that cryo will clean up the RA withought needing the high temp temper. as for how much difference with or withought cryo a knife maker asked me for a HT to use on cpm154 later he said he didnt want to fool with it for the few blades in SS he was doing so i HTed them. when he got them back he wass shocked at how much difference in grinding and sharpening his HT and my HT had
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I find I get more warping with cryo compared to high temper. Dimensional stability is not as good using cryo as part of the quench. For our purposes, that is easy enough to correct, and we get the benefits of more corrosi9n resistance, better fine edge stability, and eta carbides, if we soak long enough.
 
What do you mean dimensional stability isn't as good using cryo? Do you mean stability between pre-heat treat and post? Because cryo treated pieces should provide the most dimensional stability of a finished part, no?
 
kuraki said:
What do you mean dimensional stability isn't as good using cryo? Do you mean stability between pre-heat treat and post? Because cryo treated pieces should provide the most dimensional stability of a finished part, no?
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When I did plate quench and high temper, the knives came out straight was an arrow. When I had straight blades going into cryo, they come out a bit warped. The steel moves more than when using high temper.
 
Willie any detriments to using high temper and dry ice? I like the idea of using high temper as I can flirt with the temper more when I grind as I like to grind post heat treat?
 
Tin.Man said:
Willie any detriments to using high temper and dry ice? I like the idea of using high temper as I can flirt with the temper more when I grind as I like to grind post heat treat?
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I haven’t played with high temper and sub zero between tempers.

I grind post heat treat, as plate quenching is a bit faster than air cooling, which helps with optimum structures. I use cryo/low temper. I get my desired Rc hardness by adjusting the austenitizing temp, rather than tempering temp.
 
Willie71 said:
When I did plate quench and high temper, the knives came out straight was an arrow. When I had straight blades going into cryo, they come out a bit warped. The steel moves more than when using high temper.
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Ok, that's what I thought. Just confusion of terms. Dimensional stability usually refers to how stable a finished part will be, and cryo treated parts should be the most stable. I would imagine the reason they seem less stable during the heat treat process is the same reason they make the most stable finished parts, because of the greater conversion of RA.
 
only time i have had issue with warping is when i pur a handful of blades in a the tank too close together and they dont cool evenly and can get a warp i always try to shake the "straws" full of blades to keep the LN moving around the blanks till theyget most of the way cooled. the other times i have bone headed it by having a tang stickiing up out the top of the straw and having it contact the dewar neck and adding stress. all in all i find if they come out the kiln straight 95% chance it stays that way for me in cryo
 
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