Cryo tempering

dirtyphil

dirtyphil

Joined
Mar 19, 2014
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165
What is it and why? I'm sending off my first batch of knives to get heat treated...52100 and 1084. Is it worth it for these steels, or am I polishing a turd? The blades are puukko knife blades, hidden tang. What is the benefit, what does it do? Thanks, Phil
 
Bout to open a huge can of worms on the carbon steel cryo debate.Good discussion though..Personally,just in my opinion carbon steels benefit so little if any at all from cryo that its not worth doing it..Cryo isn't "tempering", its a continuation of the quench process to transform all retained austenite to martensite. Also some other small/moderate benfits regarding eta carbides but finishing the quench for stainless/high alloy steels is the jist of it. for instance aeb-l out of the plate quench may hit 62rc,after sub-zero quench or Ln it will hit 64rc because of the retained austenite being taken care of by the cryo.
If its part of the service sure go ahead and have it done. cant hurt.
 
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I can't speak for carbon steels but for stainless steels generally speaking it increases the HRC by about 1~2 points.
 
Kentucky said:
Bout to open a huge can of worms on the carbon steel cryo debate.Good discussion though..Personally,just in my opinion carbon steels benefit so little if any at all from cryo that its not worth doing it..Cryo isn't "tempering", its a continuation of the quench process to transform all retained austenite to martensite. Also some other small/moderate benfits regarding eta carbides but finishing the quench for stainless/high alloy steels is the jist of it. for instance aeb-l out of the plate quench may hit 62rc,after sub-zero quench or Ln it will hit 64rc because of the retained austenite being taken care of by the cryo.
If its part of the service sure go ahead and have it done. cant hurt.
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Well.............

standard punch made of S5 steel is capable of producing roughly 4,000,000 tablets while a cryogenically treated punch is capable of producing roughly 64,000,000 tablets
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What does quenching achieve?
Like all matter, metals exhibit thermal motion at any temperature above absolute zero, -459.67 degrees F (0 degrees Kelvin).

“At any temperature above absolute zero, things move around in metal, or any material,” said Frederick Diekman, Controlled Thermal Processing. “At room temperature the motion is slow, and because it’s at random, metal objects don’t change shape.” Heating the metal increases the amount of thermal motion; quenching slows this process markedly, but doesn’t stop it.

“Heat treating really is all about the quench, and the quench doesn’t magically stop because the planet happens to be at 72 degrees F,” said Pete Paulin, 300° Below. It continues in a process known as aging.

If the material is steel and it has some retained austenite, the austenite will continue to convert to martensite at room temperature. Because the martensitic structure is slightly larger than the austenite it replaces, the material actually changes size. The change is small and it occurs slowly, but it is measurable.

“Any tool- and diemaker can tell you that a die that has sat on a shelf for five years will have grown,” Paulin said. “If you put a micrometer on it, you can measure the change. That’s aging, or age-hardening, which is a very slow process.”

It also changes size as internal stresses relieve, Diekman said.

Cryogenic processing accelerates these processes.

“We speed that up—we do about 20 years of age-hardening in about 20 hours,” Paulin said. “You can leave a cryogenically treated die on a shelf for a decade, pull it out and mic it, and it will not have grown. It’s done. Cryogenic treatment is an extra step, but you’d rather have it grow in a cryogenic chamber than on the shelf, especially if you have mission-critical tolerances.”

Paulin added that sub-ambient quenching processing has expanded the number of tool steels useful in industry.

“Before we had the ability to put tooling into liquid nitrogen, metalworkers figured out that the maximum amount of carbon [in steel] would be about 0.4 percent to get a martensitic transformation,” Paulin said. “This is because the one variable they couldn’t manipulate was ambient temperature. Any steel with a carbon content greater than 0.4 percent needs a sub-ambient quench.”
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http://research.ijcaonline.org/iccia/number9/iccia1068.pdf
 
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..Industry standard heat treats often leave massive ammounts of RA..many of the heat treats we use do not or we have changed them to take care of that RA..D2 is a prime example. "
..take for instance W2..i can already get 67rc out of it buy using a 1465° aust temp..No more hardness will be gained by using a cryo treatment(I know hardness is not the point but Im using as a point that there is a very small amount of RA in simple carbon steels compared to complex high alloy steels). Ive tried..Im sure some carbide formation comes into play but just how much of a gain are we talking about with simple carbon steels..
Im willing to bet 99%(probably higher) of the folks out there will never tell the difference in a W2 blade that has cryo and one that dosnt..I have access to cryo in our shop but after testing Ive seen little real world gain from it on simple carbon steels..
Maybe Im thinking about it too simply, but Im approaching it from a view of every day use and testing..
 
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Well ........... what about this ?

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D2,A2,M2 of course they are high alloy steels..All three will have as much as 20% RA if its not taken care of... but O1, I just have not seen it for myself..More than double wear resistance? I kinda think that as long as you don't get to much carbon into solution you will keep your MF point well above room temp then no need for cryo. That's why I like about 1475° for o1 instead of 1500°+ that's often called for..
What Im saying is if you are going to do high alloy steels then yes they need a sub zero or cryo treatment depending on the steel.. If you are doing simple carbon steels there is no need to spend hundreds of dollars on a dewar full on Ln..If its provided by a service as part of the package sure go ahead and get it..Im sure you will get some benefits..I just highly doubt you will notice those benefits when your elbow deep in deer or elk carcasses though..
 
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To be honest there is a lot of contention about 52100 and cryo out there..I don't feel confident enough to make a hard opinion..I can say this, I use Kevin Cashens heat treat on 52100..With it you can consistently get 66-67 right out of the quench and its a awesome performer..I like the lower aust. temps on 52100 too.
Im no expert here, Im sure not trying to act like one..I hope no one thinks that..Just stating opinions ;)
 
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Some of this went right over my head but thanks for the responses. I'm using TrueGrit heat treat and it's 4$ per knife for cryo tx. Thanks, Phil
 
If it's optional per blade try one of each, if you're sending that many. Whether it helps or not is very steel specific, even for high alloy steels. It is also heat treat specific, as some heat treat procedures get more benefit from it than others. For those steels, it can't hurt, but if try both of you can.
 
Pretty much everything I heat treat goes in the liquid. I'm not saying it's necessary for carbon steels, but I've never heard anyone say it hurts. It doesn't really cost me anything to let them soak for awhile.
 
There is sub zero (which is dry ice temperature of around -100F), then there is cryo (LN2 temps of -300F). Sub zero will do one thing.....take care of retained austenite. Cryo will take care of retained austenite PLUS 2 other things...the allowance of the formation of eta carbides upon tempering, and a tightening or added cohesion of the overall matrix. Industry standard HT of even 52100 steel will result in somewhat unacceptable levels of retained austenite. Hence the sub zero (or cryo) to deal with the RA. The HT we (or at least many of us here) use for 52100 does not allow for much RA. So sub zero isn't going to help much. We know this because we routinely get 67+ out of the quench, and a sub zero or cryo treatment will not add 2 HRC points on top of 68 to get 70. However, 52100 with industry standard HT will reach about 65, maybe 66. Do a sub zero or cryo, and this will bump it back up to 67+.
 
Sorry to inject a noob question.

If cryo is a rapidly accelerated age hardening does that mean I could dump any blade into liquid N even if the heat treat was done a year ago?
 
dirtyphil said:
Just don't really get the physics and science behind the whole thing...I just need to keep reading the forums to understand. Thanks again for the info, Phil
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Oh, well that is pretty broad. Any specific questions?
 
me2 said:
Cryo is not a rapidly accelerated age hardening.
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Cool (pun) Thank you.
What happens if I cryo a blade long after HT? Some improvement or nothing benefitial at all or even harmful as in risking to widen a microcrack for example?
Thanks.
 
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