cryo with dry ice and aceton, steps to prefrom?

L

LCoop

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I'm about to try my first 440C cryo treatment using dry ice and acetone. I've searched but couldn't find specific steps to accomplish this. I guess my questions are what type and size cooler are you using? How much dry ice to acetone? etc. I have a small 12" square Styrofoam cooler that I think I could use as my knives are only 9" long, will this work or should I think bigger? Thanks in advance.
 
If my memory is correct, the acetone will dissolve the styrofoam very quickly. So I think you need to rethink your container.

Ric
 
Just a FYI, what you are doing is a cold treatment. Cryogenic treatment doesn't actually start until around liquid nitrogen temperatures.

I would be leery of any plastic container holding acetone. Test it first in a safe place.
 
Use alcohol. It won't dissolve most plastics, is cheaper and evaporates slower. Acetone can be toxic and is highly flammable.
chip Kunkle
 
With dry ice you will just perform a complete martensite transformation, minimizing the RA.
You won't need much time at that temperature to complete the transformation, just enough time to ensure even temperature in the piece.
Any container capable to withstand the chemical used for the bath (alchool or acetone...) is thus suitable, it could be even steel if you want, since when the dry ice is sublimated you have already reached your target.

Forget snap tempering! The continuos cooling is very important from quench to dry ice....tempering comes after that or you will be get the retained austenite stabilized !

liquid nitrogen long soaks are meant to also promote small carbide precipitation, but with dry ice is a simpler story
 
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Half a gallon of denatured alcohol (comes in gallon cans at the hardware store) and 5 pounds of dry ice. Either get pelletized dry ice or smack the bag with a wooden mallet or a 2X4 to break it up into small chunks. It pretty much powders as you smack it. Put the DI in a metal container ( aluminum baking pan) and add the alcohol. It will "boil" for a minute and then calm down. After the cooling the knife in quench plates, let the blade drop to room temp and then place in the dry ice slurry. Leave there for a few minutes ( ten is more than enough) and remove. Let warm back up to room temp and immediately temper twice.


This is called a sub-zero quench, and is the bottom of the cooling curve for stainless steels. It is around -100°F
Cryo is a different kind of treatment done with liquid nitrogen at -400°F.
 
Acetone will definitely melt through Styrofoam. It's one of our pranks we like to pull on the new guys with a Styrofoam coffee cup. Shoot towards the bottom of the cup an watch.
 
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After the DI has all sublimate ( the next morning) put the alcohol back in the can to reuse again and again. I give it a shake to release any dissolved CO2, and then cap it up. I labile that can "HT".
 
I always used acetone but put in a metal can. never had any problems but made sure to keep in ventilated area away from flame..Ive checked it with a thermocouple many times and Ive read it down to -106° often..We always used acetone because it has the lowest freeze point but Im not sure a extra few degrees will make any difference.
 
The alcohol DI slurry should get within a few degrees of the acetone. Besides being cheaper, it lasts longer, and is less hazardous to breathe. I can't say it it was an impression or a fact, but the acetone used to seem like it carbonated more than the alcohol does. After I switched from acetone, I never looked back.

Since I do so few stainless HTs anymore (I send most to Peter's in batches), I never fill the LN dewar. A few bucks of DI takes care of a batch of six blades with no problem. Frankly, ( on many stainless steels) the blades seem to preform the same when done in DI as they do with an LN cryo. I think austenitization temp is far more important.
 
Thanks it's been very helpful reading all the responses! I've looked at a bunch of on line references for tempering 440C after alum plate quench and or after cyro. They seem to be all over the place. So now I've learned that DI sub zero quench isn't the same as LN cryo does anyone have suggestions on tempering temps and cycles after a DI treatment?

Once again I want to thank everyone for their responses. As you can probably tell I've been a user of this forum for years but hardly ever post as I can usually learn answers to my questions by reading all the old threads on here. A bunch of knowledge goes through this board and I try to soak it up! I'm only a hobby knife maker and don't get to spend near as much time making knives as I'd like. However after a sudden unexpected bypass heart surgery I find myself in great shape, a warm garage and time to pursue one of my favorite things to do! Thanks again!
 
The tempering procedure is a bit different also.

DI: as Stacy underlined, you just aim to get rid of RA by continuos cooling evenly the steel to the bottom of the cooling curve for alloyied steels, like SS are. Tempering afterward only lets you lower the hardness down to the desired HRC, let's say 385-450 °F.

LN: Since you soak for long time at -300°F you not only get rid of RA, BUT also set up things for the precipitation of epsilon carbides in the subsequent tempering, BUT those carbides will only precipitate by tempering up to the 2nd "bump", that's around 800°F. Some peaople swear that's the better deal, but i'm not agreeing (just my own feeling).
Another option is tempering still in the 400°F range, and it's worth noting that some hyper alloyied steel have their natural cooling curve so low that LN would be suited better just to reach the bottom of the curve anyway, just to minimize the huge tendency to have RA.
 
I agree with Stezann - I temper at 400-425F with ether DI or LN. The austenite to martensite conversion is the same in either one.

The "e" carbides increase wear resistance, but my main goal for the blade is a sharp edge. Wear resistance isn't much of a problem with the stainless steels I use. Minimum RA is the main goal for me.
 
stezann said:
The tempering procedure is a bit different also.

DI: as Stacy underlined, you just aim to get rid of RA by continuos cooling evenly the steel to the bottom of the cooling curve for alloyied steels, like SS are. Tempering afterward only lets you lower the hardness down to the desired HRC, let's say 385-450 °F.

LN: Since you soak for long time at -300°F you not only get rid of RA, BUT also set up things for the precipitation of epsilon carbides in the subsequent tempering, BUT those carbides will only precipitate by tempering up to the 2nd "bump", that's around 800°F. Some peaople swear that's the better deal, but i'm not agreeing (just my own feeling).
Another option is tempering still in the 400°F range, and it's worth noting that some hyper alloyied steel have their natural cooling curve so low that LN would be suited better just to reach the bottom of the curve anyway, just to minimize the huge tendency to have RA.
Click to expand...

Interesting. I just finished reading some work with carbide precipitation during tempering at 450 to 500 F. Is that for specific steels, or maybe just the one I read about?
 
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