School me on cryo via acetone and dry ice please

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godogs57

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Apr 16, 2004
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I have limited experience with cryo. Until now, I had used liquid N with good results after I learned to cryo immediately after cool down. To put it bluntly, the welding supply near me doesn't really want to accommodate me with filling my container any more and are discouraging me by charging out the ying yang for the product. We don't have dry ice here and never have for some reason. Just last week our local grocer has started stocking it!

How do I mix acetone and dry ice?
Could I use my large Yeti thermos to do it, like I did with the liquid N?
How long to cryo once I've mixed up the solution? I used to immerse one to two hours with N.....no idea how long with acetone and dry ice.

Any helpful hints would be most appreciated. Probably using on NItro V and/or S35VN.

Thanks in advance.
 
DI/ acetone is used a lot in chem labs.
Wearing gloves you break the DI into small pieces. You can pound on the paper it usually comes in and then pour it into a cooler. Slowly pour the acetone over the DI and it will bubble a little at first as it chills and then settle down. Once it has settled, you can add a few pieces of DI if you wish. The mixture is cold as long as you see solid DI in there. You can add a little periodically.
When you are finished, you can recover the acetone to use again. You shouldn't lose much at these temps.
 
Tracy Mickley has suggested using anti-freeze. It will get very thick but it avoids the fears and dislikes people hold toward acetone.
 
Hubert S. said:
Mine comes in a metal tin. Acetone does not dissolve all plastics, but some like PVC, CPVC, acrylic and probably others.
Click to expand...
Ours came in big plastic bottles, but good point, it will certainly dissolve some.
I ruined a CD case with just a quick wipe.
 
If the greasy aspect of kerosene won't bother you use that, it's less volatile and will last longer, if you don't want the oily mess use denatured alcohol, that still is less volatile than acetone and will last longer.
 
I like to use denatured alcohol. It won't damage plastics, it's not too volatile so it doesn't evaporate out of the bath too quickly, but it's volatile enough to evaporate off of a blade as it warms up without leaving any residue. And it's widely available quite cheaply. Just don't drink it! Denatured alcohol has methanol in it which is toxic and can be absorbed through the skin.
 
The denatured alcohol we bought from Ace contains methyl isobutyl ketone (MIBK) as one of the denaturants, or so my nose tells me. It may not be so plastic friendly, so test the plastic first before committing.
 
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My last batch of AEB-L was cryo treated with the dry ice and 100% acetone method. I measured the temp at around -119F. It did absolutely nothing to raise my hardness level from a batch done without dry ice cryo.

I'm not saying nothing happened inside the steel structurally, but there was no increase in my HRC at all. Note I have a calibrated tester that's within .3-.5 HRC of my calibrated test discs.

I won't be going through that mess again. I may invest in Liquid Nitrogen, but no time soon. I'm getting 62HRC consistently with my current heat treat procedures.
 
CDHumiston said:
My last batch of AEB-L was cryo treated with the dry ice and 100% acetone method. I measured the temp at around -119F. It did absolutely nothing to raise my hardness level from a batch done without dry ice cryo.

I'm not saying nothing happened inside the steel structurally, but there was no increase in my HRC at all. Note I have a calibrated tester that's within .3-.5 HRC of my calibrated test discs.

I won't be going through that mess again. I may invest in Liquid Nitrogen, but no time soon. I'm getting 62HRC consistently with my current heat treat procedures.
Click to expand...
That's interesting. I've found an increase in hardness when using an appropriate austenitizing temperature with a dry ice treatment. What temperature did you use?

Also, I recommend reading this article. It's a very throrough exploration of the topic: https://knifesteelnerds.com/2022/01/11/how-cold-for-cryo/
 
I suppose it depends on the steel for sure. BUT I just two days ago heat treated some AEB-L . I heat treated like i was going to do cyro and that may have been a mistake after rereading Larrin's awesome post. His valuable intel says if your not doing cyro to heat treat at a lower temp. Bottom line I ran and soaked at 1970 degrees soaked 10 minutes. Plate quenched then IMMEDIATELY put in ice water. Then went in household freezer for 1 hour. After a single tempering cycle of 300 degree actual RH come out at 62. My second batch came in lower as I put them in and waited to temp read 1970 then begin timer for 10 minutes. Wished I had let them soak longer. They came out in the 59 RH range. FYI
 
CallumRD1 said:
That's interesting. I've found an increase in hardness when using an appropriate austenitizing temperature with a dry ice treatment. What temperature did you use?

Also, I recommend reading this article. It's a very throrough exploration of the topic: https://knifesteelnerds.com/2022/01/11/how-cold-for-cryo/
Click to expand...

1950 for 15 minutes, plate quench in aluminum plates with a little compressed air on the plates. Straight into the dry ice mixture for about 2 hours. Tempered at 350 for 2 two-hour cycles. Blades tested 61 HRC

Previous batch was done at 1950 for 15 minutes same procedure but 1 hour in my freezer instead of the dry ice. Blades tested 62 HRC

I have read that article and many others by Larrin. I also have his book.
 
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CDHumiston said:
1925 for 15 minutes, plate quench in aluminum plates with a little compressed air on the plates. Straight into the dry ice mixture for about 2 hours. Tempered at 350 for 2 two-hour cycles. Blades tested 61 HRC

Previous batch was done at 1950 for 15 minutes same procedure but 1 hour in my freezer instead of the dry ice. Blades tested 62 HRC

I have read that article and many others by Larin. I also have his book.
Click to expand...
I've been using 1975˚F for 10 minutes, plate quenched, then into a dry ice and alcohol bath for ~30 minutes before tempering twice for two hours at 325˚F. My understanding is that if you're using dry ice or liquid nitrogen then you should be using a higher temperature than 1925˚F. Stealing some figures from Larrin Larrin : https://knifesteelnerds.com/2022/01/11/how-cold-for-cryo/

aeb-l-300F-cold-treatments.jpg

aeb-l-tempering-350f.jpg
 
CallumRD1 said:
I've been using 1975˚F for 10 minutes, plate quenched, then into a dry ice and alcohol bath for ~30 minutes before tempering twice for two hours at 325˚F. My understanding is that if you're using dry ice or liquid nitrogen then you should be using a higher temperature than 1925˚F. Stealing some figures from Larrin Larrin : https://knifesteelnerds.com/2022/01/11/how-cold-for-cryo/

aeb-l-300F-cold-treatments.jpg

aeb-l-tempering-350f.jpg
Click to expand...

I understand. I just looked at my oven settings and I was actually at 1950. I see on the chart that 1975 would have been better.

I just have come to the conclusion for my personal knife making that the trouble is not worth the reward.

Even if I had increased 1 HRC it was just not worth the extra steps and mess it made. Not to mention the added cost.

My knives are holding a very good edge for a nice long while. They are easy to sharpen and my wife and other users are very happy with them.

This is and always will be a hobby for me. I sell to the occasional friend to try and recoup some of my expenditures, but that's as far as it will ever go.

Thanks for the info, I know it will be very helpful to those who choose to use dry ice!
 
Remember that the two different manufacturers of “AEB-L” respond differently to heat treatment which changes the peak austenitizing temperatures.
 
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