Cryogenic processing

Rick Baum

Rick Baum

Joined
Mar 14, 2000
Messages
509
Thanks to Bill Burke and Ed Fowler, I have a new passion to consume my time... Deep Cryogenic Processing. It seems that the internet has a lot of information that really amounts to very little. Is this something that is relatively new to the knifemaking crowd? Has anyone done side-by-side comparisons of their own, besides Bill and Ed? I found an article that gives a very shallow explanation of a process called "Cryotune". It talks about "new structures being formed called N-Carbides during the deep freeze. They theorize that these new carbides are allowed to form because electrical energy is reduced due to the extreme temperatures, and this allows electrons to slow down enough that the atoms can form molecules that would otherwise be unable to form. Is it necessary to go to -320 degrees for this or can I get the same results with acetone and dry ice with a longer soak? It sounds to me that this process is definitely a way to improve the perfomance of a knife. If I remember correctly, Bill and Ed have gone from 100 or so cuts on a hemp rope to just over 400 cuts before the edge quit biting!

Anyone done their own tests?
 
The process has been around for at least 50 years, in the cutlery industry. I'm not positive which firm, Cattaraugus, or Queen started doing this, but one of them was the first to use it in cutlery. I have been making knives for over twenty years, and all mine have gotten the cryo treatment.
In the steels I use,stainless, large amounts of austenite are retained in the as quenched structure. A great percentage of this can be transformed by subzero cooling, immediately after quenching. Followed by two or more complete tempering cycles, for maximum transformation. I drew in part from a Paul Bos brochure for the description, as it is far better than I could do.
I remember that it was determined that one did not have to go to -320 degrees, but you do have to get to at least -150 degrees to be really useful.
I hope this helps a little.
PS; Cryo helps almost any steel, axles, gears, gun barrels, knives etc. All will see some improvement over no cryo.
 
Thanks Mike. Just wondering, have you done any side by side testing with a cryo treated blade and an untreated blade? If so, what were your results?

Does anyone know what temperature the acetone/dry ice treatment reaches?

Thanks,
Rick
 
Bill Bryson includes specification of the use of a dry ice bath in his book 'Heat Treatment, Selection, And Application Of Tool Steels'.

Dry ice is at about -109 F. I have achieved about -100 F with a kerosine bath.

You are right in your presumption. This lower temperature should be used for a longer time. I have gotten almost 48 hours out of dry ice/kerosine by putting the cooler in a freezer. BE CAREFUL - kerosine will destroy styrofoam - leaving quite a dangerous mess.

I have not done a comparison of the same heat treat with and with out cryo. I am firmly convinced of its advantage and your explanation of why makes good sense to me. The common belief is that it helps transform remaining austinite into martensite and this process is refered to as 'aging'. Your electrical properties explaination is the first I have read as to why this is accomplished. I wonder if it is correct.

Another very interesting result of properly cryo treated steel is that the steel will be soft for a very shallow depth of about 1 or 2 thousandths. Therefore, it is advisable to sharpen the edge after cryo instead of before.

Roger
 
One assumption was that cryo treatment was especially beneficial on steels with chromium in them (stainless steels, and, to a lesser extent, 52100 and 5160), due to their propensity to retain austenite. Tim Zowada (and you should contact him directly for any details beyond my hearsay) mentioned to me that he has cryo treated other tool steels as well and found a considerable increase in performance. All in all, it seems cryo is a worthwhile step--you may not gain much, but you stand to gain something without losing anything (unless of course you truly don't believe and feel you are wasting time and money and the process itself....)

John
 
Thanks everyone for all of the input so far.
John, do you have any contact info for Mr. Zowada?

I've notice a couple of things so far:
1 - Nobody seems to be doing any side-by-side comparisons between a cryo treated blade and non-treated blade to "scientifically" see what the benefits are.
2 - It seems that we really don't know what is truely happening to the steel and why. We all seem to be going on assumptions.

I agree that from what I have read, that a knife would probably benefit from the cryo treatment, but I would really like to find some facts about what is happening and why during the cryo treatment. Does anyone have some links or a recommendation on a book?

Sorry if I seem unappreciative. I'm not, I really just want to get a "Meat and Taters" kind of a thread going that we can all benefit from. Keep it comming guys!

Thanks,
Rick
 
I'm not sure off the top of my head, but a search should do the trick. I believe his name is in the URL.


As for what is going on in the steel, parts of it, at least, are fairly clear. Retained austenite is being converted into martensite. It is not a tempering process, but a completion of the quenching/hardening process. Tempering also converts some retained austenite to untempered martensite (this is why triple tempering is a good idea) but not nearly as thoroughly as cryo. Some makers even up their tempering temps by 25 or 50 degrees following cryo in order to compensate for the increased hardness.

All other things being equal, the blade that begins with the higher Rockwell number will be better. In other words, take two identical blades, harden one to 59 Rc (not so thorough a quench, no cryo) and the other to 63 Rc (good quench, full cryo) (These numbers are purely hypothetical and just to make a point). Now temper both to 58 Rc, a general working hardness for many forged carbon steel blades. You have two knives of the same steel, forged and ground the same way and both at 58 Rc--on paper, and to many customers, these are the same knife. But the one that started at 63 will be superior. It began with more martensite, and full martensite tempered to the desired hardness will be a superior performer.

One more thing. When I say "superior performer," I mean as a cutting implement. It will not bend 10 times 90 degrees without breaking. It may snap at about 45 degrees BUT you may not be able to bend it to 45 degrees without a 4 foot cheater bar!

Sorry so long winded,

John
 
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