Dry Ice Sub-Zero Quench

Stacy E. Apelt - Bladesmith

Stacy E. Apelt - Bladesmith

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I was doing the HT on the blade for Brian A. today, and decided to shoot a few shots of the dry ice slurry. It is five pounds of dry ice and two quarts of denatured alcohol. I pound the slab of dry ice in a cloth bag, and dump it into the alcohol slowly. Then I mix for a few minutes. The crushed DI ranges in size from fine snow to chunks up to the size of a walnut. The steel canister sits in a nest of insulation in an old cooler, but I took it out for the photos. It reads about -90F. The blade will sit in there overnight and then have a double temper. I get about six hours of sub-zero cooling from a slurry like this.


Note:
Edited to change the word "cryo" to "sub-zero", which is the correct term for -100F blade cooling. Thanks, mete.
 

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what steel are you working with for this batch? I don't know much about steel, but do understand the most basic of concepts involved with HT. Do simple steels, 10XX etc., Benefit from this as well?


-Xander
 
Yeah, that's pretty much what it looks like when I do it too.

I use acetone, and a lower ratio of liquid. Oh, and my container is red. But yeah, looks about the same as your setup.

I see the primary benefit of this process being the conversion of RA. And in theory, that happens instantaneously (non-diffusive process), but I still leave it in for about 4 hours. Call me crazy.

The magical wonders of -300 LN cryo (true cryo) have never had any noticeable effect beyond dry ice as far as I've been able to tell, but my mind is still open on that subject. I have arranged to have a few blades subject to LH cryo (a few deg above 0K), I'm not expecting much, but again I'm keeping an open mind.

However the effects of completing a quench (approaching Mf by using dry ice as a part of the quench) have been very evident in my eyes. Complex steels with an Mf below room temperature can leave a lot on the table if the freeze is skipped.
 
Its about a 2&1/2 hour round trip for me to go get dry ice. My question is should I get the ice before I start my H/T or can I go get it after I put the blade/blades between the plates? I guess what I'm really asking is what is the maximum reccomended time between the plate quench and the dry ice slurry? Thanks.

Darrin
 
Darrin I freeze my plates, keep them outside in the winter up here, or in the freezer in
the summer. When I quench in the frozen plates and cut the envelope open the blade
is as white (silver) as when I put it in. I don't dawdle getting it into the dry ice alcohol
or LN after that though- kind of keeping with "part of the quench" as opposed to after
the quench. I'd sure get it ahead of time if you can.
Ken.
 
Please use proper terms !
Cryo -- liquid nitrogen [LN] , -300 F
Sub-zero -- Dry ice [Solid CO2] ,-100 F

Most benefit is with high carbon steel, 1 % carbon or more. Complex blade steels such as the stainless ones like 154CM will benefit more. Expect about 1-2 points higher HRc with cryo.
 
Depends on the semantics:
Cryogenic liquids are any liquefied gas with a boiling point below -150C

Cryo refers to any freezing/cooling at very low temperature process.

The steel in the sub-zero/cryo tank is CPM-154. I austenitized at 1925 for 30 minutes, plate quenched, and immediately went to the DI/alcohol slurry. I pick up the DI before I even start the HT oven. Just stick the DI block in the freezer until ready to add it to the alcohol. A few hours is not a problem. It doesn't sublimate all that much until it goes into the liquid.

I realize that the process is complete when the blade gets to the bottom of the temp drop, but since it is there, unless I have other blades or things to do with the slurry, I leave the blade in till morning.
 
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Dry ice is -112°, when mixed with alcohol it should be around -87°. A lot of heat is gained when the dry ice is sublimated.

Why use the alcohol? Crucible specs their data sheet with just dry ice at -112°, not alcohol. In a proper insulating container the steel should be the same temp as the dry ice, -112°. Wouldn't the alcohol give about 1 pt. HRC lower than without?
 
Nathan,

Supposedly, the benefit of LN over dry ice is that, in addition to conversion of RA, LN causes some micro carbides to form.

I can send you references to the (long) papers that discuss this if you are interested.

Tait
 
bladsmth said:
Depends on the semantics:
Cryogenic liquids are any liquefied gas with a boiling point below -150C

Cryo refers to any freezing/cooling at very low temperature process.

The steel in the sub-zero/cryo tank is CPM-154. I austenitized at 1925 for 30 minutes, plate quenched, and immediately went to the DI/alcohol slurry. I pick up the DI before I even start the HT oven. Just stick the DI block in the freezer until ready to add it to the alcohol. A few hours is not a problem. It doesn't sublimate all that much until it goes into the liquid.

I realize that the process is complete when the blade gets to the bottom of the temp drop, but since it is there, unless I have other blades or things to do with the slurry, I leave the blade in till morning.
Click to expand...

Thanks Stacy thats exactly what I was wondering about.
 
Tait is correct .Tait would you please send me at least the titles of the papers .I have one that explains it but the search was long ! But it is recent info.
The lower temperature creates slight changes in crystal structure that permit formation of small eta carbides on tempering.
That's why we should make a distinction between cryo and sub-zero.
 
zaph1 said:
Why use the alcohol? Crucible specs their data sheet with just dry ice at -112°, not alcohol. In a proper insulating container the steel should be the same temp as the dry ice, -112°. Wouldn't the alcohol give about 1 pt. HRC lower than without?
Click to expand...

Interesting question! Any thoughts, guys?

Tait said:
Supposedly, the benefit of LN over dry ice is that, in addition to conversion of RA, LN causes some micro carbides to form.

I can send you references to the (long) papers that discuss this if you are interested.
Click to expand...

I'd be interested in that too.
 
Tait said:
Nathan,

Supposedly, the benefit of LN over dry ice is that, in addition to conversion of RA, LN causes some micro carbides to form.

I can send you references to the (long) papers that discuss this if you are interested.

Tait
Click to expand...


Tait could you send a copy to me as well, thanks.
 
Tait said:
Nathan,

Supposedly, the benefit of LN over dry ice is that, in addition to conversion of RA, LN causes some micro carbides to form.

I can send you references to the (long) papers that discuss this if you are interested.

Tait
Click to expand...

Oh, I don't doubt it. I've read the papers. And the application to something like disk brakes is an obvious one. But I have not seen any performance improvements in a knife edge by the presence of these nano carbides. Some cryo proponents argue that there is also a smoothing out or rounding of primary carbides (I'm not sure what the mechanism is supposed to be) and that the temporary contraction of the matrix encourages atoms to slip into voids and imperfections in the matrix such as commonly occur around carbides, making a more homogeneous structure.

There are lots of cool things that happen at low temperatures (ha, I made a pun) but I am still trying to see their effects translate into a better performing knife edge. To date, the only effect I have seen from going cold occurs at dry ice temperatures (in knife blades).

But, my mind is wide open...
 
Nathan, AWESOME sigline.

Everyone else, I AM SORRY!

When I last looked at these papers, they were free to download, so I would have been comfortable sending them around. It now appears they are available by subscription only; since I rely on publication myself for part of my career advancement, I respect their request for compensation for the publications. For those very serious about this stuff, or willing to try and see if some other free option is available:

Cryoprocessing of cutting tools

Cryogenically treated tool steel

Warning: They are dense reading!

Tait
 
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