Is Cryo Really Neccesary?

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huntingsgr8

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May 25, 2015
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I'm somewhat experienced in the realm of knife making, but I have yet to use stainless steel. One of the reasons I'm hesitant to acquire some, is that everywhere I've looked into heat treating stainless a cryo session is part of the process. Not having the money to afford the equipment to undertake it, I won't be able to do it. Is it really that important to the integrity of the knife? Is it necessary at all, or just an enhancement? If so how much would I be missing out on by skipping it?
 
Probably should have posted this over in the knifemakers section, perhaps a mod can move it...?

Short answer: if the specific steel calls for cryo, it should be done, or you'll end up with lots of retained austenite (this is bad).
 
Yes, this would be better over in shoptalk.

Crucible's data sheet for CPM154 indicates dry ice is sufficient, but also suggests that thin sections quench more easily (unsurprising) than large pieces, and hit the general hardness levels easily. I have no idea how to test for retained austenite, but started dry-icing my 154CM/CPM-154 for good measure. I'd like to know I've done the best heat-treatment I can, even if testing it precisely is beyond my current equipment. Dry ice is fairly accessible. A bare blade on a block of dry ice reads off the bottom of my infrared thermometer (-40F) very quickly. It makes sense to do several at once and amortize the cost/inconvenience of ice across several pieces.

And that doesn't really answer your question. :)
 
Short answer, no. If you can't cryo, go ahead anyway. The difference is so small it's almost impossible to detect in everyday performance, i.e., skinning game, whittling, cutting paper, etc., etc.. Under a microscope, yes, you see a difference.
 
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David Stifle said:
Short answer, no. If you can't cryo, go ahead anyway. The difference is so small it's almost impossible to detect in everyday performance, i.e., skinning game, whittling, cutting paper, etc., etc.. Under a microscope, yes, you see a difference.
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Darn, that's basically what I said. :( Can I undelete my post? ;)
 
Patrice Lemée;14814690 said:
Darn, that's basically what I said. :( Can I undelete my post? ;)
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Sure, Pat, go ahead.:) I'm not saying it's not a good thing, but I've worked with both cryo'ed and un-cryo'ed blades on everyday tasks, like skinning deer, cutting rope, etc., and I did not notice a difference between the blades. I know it makes a difference, but not one I noticed in everyday performance.
 
Some steels get a huge benefit from cryo. The Uddeholm metallurgist told me AEB-L gains up to 30% better edge holding from cryo.

Chuck
 
If you run a quick search, you'll find out that sub-zero cooling has 2 paths.
1) Overcome the alloying elements bad attitude to reinforce the austenite and stabilize it at room temperature...generally a slurry of dry ice and acetone/alchool is capable enough to allow the complete martensite transformation at -90°F more or less... just hit that low temperature and call it good, no soak required because it's just the end of your quench.
2) The second path is the LN route, and something else is supposed to happen at long soaks (many hours) at -280°F, something debated, related to the precipitation of eta carbides during tempering after said cryo temperature soak. Of course a LN bath will also take care of the conversion of stubborn austenite into martensite, but for just that a soak isn't required.

Given your alloy you have the choice to choose your path, and for simpler SS like 14c28n, 12c27, AEB-L... even a trip to your freezer will help converting enough austenite to get a very nice blade, especially if you use the lower end of the austenitizing temp. range, and dry ice will do the best for the higher end of the aust.temp. range.
Someone pointed out that dry ice will last for 24 h, while LN a couple of weeks into a Dewar and that is also a good point. And some alloys are so stubborn that will stay austenite no matter what (austenitic 300 series), everything else in between.
 
huntingsgr8 said:
As far as steels go, I was considering 440C, AST34, 154CM, and maybe some AEB-L or CMP154 at some point.
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If you decide to go with any of those steels, it's not that expensive to send them to a heat treating house. They also do the cryo as needed.
 
Some steels need dry ice to reduce RA and some need to be cooled further In liquid nitrogen. Some high alloy tool steels can be high tempered to reduce the RA %. Steels with higher RA % will be softer then a more complete martensitic blade. For example, an AEB-L blade without sub zero or cryo can be as much as 3-4 points lower on the Rockwell scale with same HT.
 
I'm not doubting cryo makes a difference, what I am doubting is if it makes enough of a difference for the average guy, doing average knife things, to notice a difference. I didn't, I skinned deer, cut rope, etc., with cryo'ed knives, and with others that were not. I didn't abuse the knives, just used them, I'm sorry, but I could not tell any difference at all. None of them, by the way, were AEB-L.
 
I agree with what David is saying, the average knife user is not likely to know the difference. I still do it myself but we all have our reasons and logic behind what we do.

If you are concerned get a steel that will hit its maximum potential with dry ice like AEB-L and use that. If you don't have anything you can buy a cheap plastic tub, gallon of alcohol and dry ice for under $20 locally.
 
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