The Truth about Cryo Tempering

H

Hesparus

Joined
Oct 31, 2004
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The subject line says it all. I have heard a lot about the benefits of cryo tempering in Ed Fowler's "Knife Talk" and other places. Everybody seems to have a different opinion about what it does. Everything from increasing tensile strength, increasing hardness, increasing cutting ability, to making the blade jump up and dance. So what's the deal, and is it worth the extra four bucks to have it done?

- Chris
 
It's a must if you're talking stainless steel. (It's the only way to ensure complete martensite transformation within your life time.)

Other steels have the debate. Even good ol' Fowler has found that on the beloved 52100 it isn't necessary if you have your quench dialed in.

One point that everyone agrees on - it doesn't hurt. Spend the $4.

Steve
 
Well I knew it wasn't going to make the knife any worse. But what kind of improvements can I expect from, say, 154cm?

- Chris
 
From the chapter in William Bryson's book, Heat Treatment, Selection, and Application of Tool Steels entitled "Cryogenics:"

In studying the heat treatment process you will discover that you can get 95% or 96% transformation of austenite into martensite only if you do exactly as the recipie calls out, and only if you use the proper timing at all phases, and only if your equipment is calibrated perfectly...This is the area in which cryogenics can really strut its stuff. The reason is that cryogenics is the only method known that can complete transformation to 100% martensite, or come at all close to it. Martensite...is the fine hardened grain structure that you strive for in the heat treat process.
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(Bill also wrote a whole book called Cryogenics and was a metallurgist at Crucible for some time. He's done extensive analysis on the cryo quenching process and is an authority on it.)

If your blade isn't completely transformed, it won't wear uniformly along its length. Little dings and outcroppings caused by uneven wear provide a foothold for further wear, and end up requiring deeper sharpening to get a smooth edge back.
 
Hesparus said:
Well I knew it wasn't going to make the knife any worse. But what kind of improvements can I expect from, say, 154cm?

- Chris
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30% + edge retention. :)
 
For some steels it's of no value. Bryson's book title is about "Tool Steels" there there might be a benefit. It must be done properly and for a steel like 154CM it will give you an increase of 2 points of RHc hardness .We used to just call it sub-zero quench, it's been around a long time !! But in the old days we just used it where needed without any hype.
 
Paul Bos has been doing cryo as part of his heat treating service, for 20+ years. He just never made a big deal about it. It was just something he did to give his customers the best service available.

I would never have it any other way with the air hardening steels I use(mostly stainless).
 
In the research I did for a college paper entitled "Crygenics: Fact or Snakeoil", I discovered that cryotreating m2 mill cutters for example could extended their wear life 400%. It really depends on how good the initial heat treat was(i.e. the percentage of martensite transformation) and the chemical make up of the steel. One of you brought up the point that Ed Fowler used to cryo treat. When I interviewed him for my series of papers on this, he concluded that for 52100 in particular, cryogenic treating provided no benefit(but thats coming from Ed, a man with over 40 years experience who continues to develop and expertise with ONE steel). Anyways, I think that cryogenics provides a benefit, particularly to the production knife/part that may be subject to not quite being in the "right" position of the HT oven. Irregardless, it is sort of a mute point for knives in my opinion. Do we really need a cryotreated knife? Probably not. Do companies that use thousands of drill bits and cutters benefit from cryotreated parts....absolutely.
 
Lukers said:
Do we really need a cryotreated knife? Probably not. Do companies that use thousands of drill bits and cutters benefit from cryotreated parts....absolutely.
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I'd say absolutely it should be done
it's the cheapest thing you can do to a knife with the biggest effect on it for the least money
I can do at least 10 blades for about $11.00 plus the trip

I think most if not all the high carbon ss's were meant to be cryo'd when designed as part of the heat treat process anyway.
 
With the work we have done with 52100, when cryo makes a big difference you can make it up by developing your heat treat to be more in harmony with the steel you are using and the puropse of the finished steel. The resultant blades from fine tuned forging methods and heat treat were better performers than those that were soaked in liquid nitrogen.
 
Ed Fowler said:
With the work we have done with 52100, when cryo makes a big difference you can make it up by developing your heat treat to be more in harmony with the steel you are using and the puropse of the finished steel. The resultant blades from fine tuned forging methods and heat treat were better performers than those that were soaked in liquid nitrogen.
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if I could add
keeping high carbon separate from SS in this matter of topic
because cryo was meant to be done on the SS so it has to be used for full treatment.

as said the others, as in the High carbons has little effect on it as ED said properly heat treated High carbon steel it makes cents what you are saying here ED for sure..
kind of like,,,
you can replace a piston in a chain saw but if you don't find out why it went bad in the first place you'll be replacing it again very soon.. :(

cryo should not be used a fix but be used as an enhancement and part of the treatment of the SS keeping in mind what it was used for and it's place in knife making using either steels...if I'm making any cents :confused: :)
 
Mike Hull said:
Paul Bos has been doing cryo as part of his heat treating service, for 20+ years. He just never made a big deal about it. It was just something he did to give his customers the best service available.

I would never have it any other way with the air hardening steels I use(mostly stainless).
Click to expand...

That speaks volumes. I just have a hard time when other treaters charge extra for cryo when it SHOULD be part of the standard process.

If you are sending in one or two blades, no big deal, I guess. :rolleyes:
But as far as from a business standpoint, if you are paying extra for it then ask your customer first if they want it (if an ordered knife) and pass that cost to them. Why should you eat the cost?

There are some steels that do not benefit much, if at all from cryo but if you are talking 440C and 154CM then by all means the potential is there for improvement.

Craig
 
Except for a few steels we like to use, if you can do it DO IT. Regardless, if available to you - do it. Do a snap temper before hand and get it into deep cryogenics IMMEDIATELY upon assuming room temperature after snap temper. Afterwards and the steel has warmed to room temperature immediately perform the first tempering.

Your chances of 100% austenite transformation without deep cryogenic treatment is about as well as Howdie Duddies's wooden ass surviving in Hell. I have on occassion, once or twice here, read where cryo just won't raise the HRc. Well, I'll tell you I've done that too and it has been because of over austenitizing either by too high a temperature or too long a soak or a combination. It says nothing to little about retained austenite but can say a lot about edge chipping.

RL
 
I haven't made near the the number or quality of blades that most of you here have, but I'll bet I've done more research on metals......40 years of it. Not having any initials by my name doesn't give me expert status, but here's my opinion, anyway.....

The difference between a Rockwell hardness of 56 and 62 is like like difference between a firecracker and an an h-bomb, in terms of edge holding.

(except for the specialty matrix). Then, watch your wallet, and buy plenty belts.

Cryo is the only way to get most SS into the realm of suitable cutlery steel. And then, it's marginal..........440C (A6) is barely abrasion resistant BEFORE tempering.............afterwards, it's very marginal for blades...

Everybody else is correct. It only serves to age the martensite and overcome any problems with the HT.........

Which is why (and this will get me in hot water, I suppose), I have never seen, nor heard of, any current marketable SS that will cut/hold an edge, as well as plain old O1, D2, A2, 1095, 5160, 52100 series stuff).. Properly HT, of course........no cryo needed.



Mike
 
I'll enter that contest if anyone else wants to. I'll put up a stainless - not 440C though. I'll put up one of several stainless.

RL
 
rlinger said:
I'll enter that contest if anyone else wants to. I'll put up a stainless - not 440C though. I'll put up one of several stainless.

RL
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Not wanting to start a fued, but in the interest of science, I applaud your zeal :p

To do this properly, we need a judge(s). We need 2 blades. We need to spec the qualifiers (no specialty pieces, for example). I know that most ABS Smiths qualify using 5160, because of the bend tests........What specs do you think are fair? Who will judge, and what type blade do you propose for the test?

Mike
 
I don't care how its made or by whom. I'll stock remove and HT. I will not make a finished knife though. I will not do that. Too busy for that just for a blade test.

There is no fued and none will occur.

RL
 
I have looked back through this thread and can not find the challenge - ?
I will however offer to test the blades for what ever you want them tested for under the conditions that you not tell me anything about the blades, only what you want them tested for and how you want them sharpened between tests. There will be no rockwell tests, only cut. Edge flex if you want to know.

Should any wish to come to the Willow Bow Ranch shop for a visit and the test that would be OK.
 
Warrant said:
Cryo is the only way to get most SS into the realm of suitable cutlery steel. And then, it's marginal..........440C (A6) is barely abrasion resistant BEFORE tempering.............afterwards, it's very marginal for blades...


Mike
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Are you trying to say that 440C is the same thing as A6?
 
Ed,

It is very recent, only a couple / three posts above you that that occured and it was my doing. Our friend challenged stainless as too inferior for my liking. It did not settle well with me so I offered a not yet ground entry. I stand by all my above words on that.

RL
 
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