Dry ice & acetone slurry

I cannot give first hand experience as I have not done this myself as yet, but this is what I know. Take apx. 1 pound of dry ice, crush, place into container. Slowly add acetone. Wait a few mins. then immerse blade. The mixture will produce super cold temps. & should get at least 1-4 rockwell more from blade. Leave blade in about 30 secs. then remove & allow to warm to room temp. & temper as usual. DO-NOT add the dry ice to the acetone. This is dangerous! This is the best I can do at this time. Hopefully someone with more experience will answer. How it actually works, I'm not sure, but guess that it's a chemical reaction of some kind. The only reason I have not tried it myself is that I live on another planet, & can't get dry ice easily & without laying out a bunch of money. Anyway, good luck.
 
Heat treating is not my forte but from what I understand what this basically does is to "chill" the blades down to -100 degrees F. This sub-zero quench tends to remove all or most of the retained austensite from the steel and transforms it to martinsite. This is intended to enhance edge holding properties.

This is, or should be a standard procedure to properly treat some steels, 440C and ATS34 or 154CM come to mind.

There are some heat treat facilities that will take it down even further to -300 degrees F but the dry ice and acetone slurry will never reach that temperature. Is -300 degrees F necessary? I don't know. Any answers to that one?

CLWilkins
 
Interesting. When you say to temper as usual after using the slurry, does that mean that this is done between the initial hardening and the "draw" or temper? I don't know much about heat treat myself but I'd like to try it this summer if possible, and if this would help I'd love to try it too.

I can second the part about adding acetone SLOWLY--my friends used to use any number of substances to make dry ice "bombs." Fun in an empty parking lot, not in a workshop!
 
There seams to be some debate on if the cold side of the process should be done before or
after the first temper.
The way I see it is doing a temper first can’t hurt and most of the steel company
metallurgists I have asked have said do a temper or stress relieve first.
I do a stress relieve 100-200f below the final tempering temp for 1hr
and I also do a stress relieve after final grinding at 50F below the temper temp for two hr.
ED
 
The acetone is used so there is full contact with the blade. If dry ice itself was used, some parts of the blade would be in contact with the ice while other parts would be in contact with the warmer air. The dry ice chills the acetone down to about -70 degrees F (or whatever temp. CO2 sublimes at under normal atmosperic pressure) and, therefore, no warm spots.
All that I've heard about the metallurgical reaction is that the cold temp. allows any retained austenite (due to the high alloy content) to convert to martensite. Normally, the austenite wouldn't, or would very slowly, convert to martensite when it is sitting at room temp.

Matt Janiga
 
A few years ago I believe I was told that you could use dry ice and alcohol for a slurry mix on baldes. Has anybody heard of this before, I think they said it would cool down to 150 below 0, Chris.
www.toptexknives.com

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Dry ice and Kerosene is actually the safest of the bunch-acetone is dangerous, due to the low flash point. I used the kerosene/dry ice combo before I bought my Liquid Nitrogen set up. Dry ice isn't cheap, and the kerosene was messy/smelly and hard to dispose of afterwards. I believe you can get down to -100-120 this way. And you are right, the liquid is there so that the whold tool is cooled evenly.

LN2 gets you down to -320 or so, which is just that much better. It is also a lot cleaner to use, as it turns into Nitrogen gas and just goes away.

What you are doing here is taking the steel down to below, or very near the finish temperature for the Martensite transformation, which is often well below room temp-it gets lower as the alloy content of the steel increases.
There are additional, documented benefits of reduced grain size, carbide size and distribution, all of which make the steel very happy and a better cutting tool.

Many heat treaters still do this cryo treatment right after the quench, believing that, if the transformation is allowed to stop for any length of time, the retained Austenite will stabilize, and not convert to Martensite during the subsequent cryo treatment. This is what I was taught in college.
Recently, it has been documented that this is not correct, and that it is preferable to temper once before cryo treatment, with the result being smaller grain size and thus more toughness. You should always temper again after cryo treatment, so that the new Martensite gets tempered.

Either way, cryo treatment will improve the quality of the steel's structure. It may or may not increase the hardness-the better the primary heat treatment is, the less hardness increase you get with cryo.
If the initial treatment was off- oversoaked, for example, then the cryo will make the hardness increase, because of the large amounts of retained austenite left in the steel from the poor heat treatment.

Hope this hasn't been just long and boring. Honestly, the coolest thing is looking into my Dewar's flask at the clear liquid in there, and realizing it is so frieking cold-it blows the mind!! minus 320!! WOW

If you are interested in having this done, check out the post by Advisor in Metals, here on Bladeforums. He taught me all this cool stuff as it applies to knife blades.

RJ Martin
 
If you ever get the chance to play with N2(l)* try quenching a small piece of steel in it. I've always wondered what would happen, just be really careful!
Aaron
*time for the chemist in me to be nit-picky, chemical formula(N2) followed by state(l)
smile.gif


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Why did you stab that girl?
You won't believe this, but I had too much coffee!
-Edmond by David Mamet
aaronm@cs.brandeis.edu
 
I use the acetone dry ice method after initial heat treat. I was taught to do this as a continuation of the cooling after heat treat. I use it on both 440-C and ATS-34. I would probably use liquid nitrogen if I had a flask. I did not do "scientific" testing, but I can notice a definite difference in the blades treated this way. They are harder. I have tempered after the deep freeze in the past, but I will try to temper before to see if there is a difference. I hold both my 440-C and ATS in the bath for 6 hours. I have a tin box wrapped in an old sleeping bag and then inserted in an old ice chest that I use. I pay $.75 per pound for the dry ice and a couple of pounds will last the 6 hours in the chest.

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Ron Ruppé
www.ruppe.com/Knives/index.htm
 
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