Dry Ice - Probably Good Enough

[SteveS]

I was making a knife making tool and needed a hardened part. I chose S30V, but I'm out of LN. So, I thought I'd run a dry ice test.

2 pieces of steel: S30V and ATS34. I set my oven to 2020 degrees (which I believe gives me about 1990). Put the steel in a cold oven ran up to 1800, with a 10 minute rest. Then a 20 Minute soak at ~1990. Quench with plates.

The S30V came out at 63HRC and the ATS34 at 56HRC. Well those are the expected numbers based on the data sheets.

Then I placed them on a block of dry ice for 3 hours. No acetone or anything, just set them there.

The S30V block rose to 63.5 - that's what I usually get with LN and my process - not much change.

------ATS 34 block went from 56 to 62. Again that's on par with the data sheets.

Obviously, the dry ice was capable of transforming a large percentage of retained austentite. Maybe doesn't transform all of it. Maybe requires longer soak times than LN. But it certainly works.

Steve

[RJ Martin]

Steve: Yes, dry ice is cold enough to benefit both of those steels greatly. LN2 is still better, because it's a lot colder. How much better? I'm not going to argue that........

Just a suggestion-rather than equalizing at 1800F, try 1550/1600 for S30V and 1500 for ATS34. A brief hold at these temps will set these alloys up for a better transformation later on.

[millironknives]

how cold do you think dry ice will get with acetone added?

[fitzo]

The mixture is the same temperature as the dry ice, -78C.

[millironknives]

many thanks for the info

[SteveS]

I think the reason folks use the acetone thing is to get a better thermal transfer. But steel being what it is and these thin strips we use, I don't think it's an issue.

It sure works in a pinch.

Steve

[RJ Martin]

Stay away from Acetone! Highly flammable and noxious vapors. Kerosene or alcohol is a much better choice. Yes, the liquid is just for more even thermal conductivity.

[TexasJack]

Isopropyl alcohol will make a pretty nice "slush" with dry ice. It's not as volatile as acetone, but it does make everything smell like a doctor's office. As far as acetone being "noxious", it's not one of the more toxic solvents. (Fingernail polish remover is acetone.)

If using a solvent/dry ice mix, cover it (if possible) to minimize water condensing into it, but don't seal it closed.

[tonn]

I use a cold spray - gives instantly -55C.