Joe,

You are about to engage in some considerable cost for a dewar that large. Nitrogen is not all that expensive but the dewar can be. My question is why? There appears to be no evidence that cryogenic processes do anything more than reduce retained austenite. There is lots of talk that they do more and lots of commercial marketing about what they can do. Since you can reduce retained austenite through other means, why cryogenic?

curious!

Dan

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I was wondering if anyone's ever made a cryogenic tempering furnace for shop use. I've done some research into building one, but I can't seem to find anything that suites my taste. I'd be looking for something versatile and large enough to fit swords in (maybe 4" diameter by 5' tube or larger). Controlled, slow cooling is a must.

Any diagrams, websites, pictures, or ideas would be greatly appreciated. Thanks.

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Joe,

You are about to engage in some considerable cost for a dewar that large. Nitrogen is not all that expensive but the dewar can be. My question is why? There appears to be no evidence that cryogenic processes do anything more than reduce retained austenite. There is lots of talk that they do more and lots of commercial marketing about what they can do. Since you can reduce retained austenite through other means, why cryogenic?

curious!

Dan

Hey Dan,

Thanks for the input/questions! The are a number of reasons I'm looking into my cryo-treatment options. The main reasons are increased strength, wear resistance, and (like you said) reduce retained austenite. In the tool steel I'm using, it's not uncommon to get around 30-40% RA. 30% retained austenite in a sword is down-right deadly. Also, according to ASM Handbook volume 4, reaching the temperature of -310F will increase the wear resistance of most tool steels anywhere between 104-560% when performed directly after traditional heat treatment.

~Joe

Joe,

Is there any way you can put what ASM says up here? I'm asking because I don't have access to Volume 4 and my general understanding was freeze or cold treating (-95 F to -125F) would convert retained austenite to martensite with commensurate increase in hardness and strength... that cryo treating into the 310F range made little to no difference in conversion of retained austenite and it's directly associated hardness/strength gains.

Mike

Very good question Mike, I also would be interested in seeing that material. If it's source is the ASM Committee on Cryo I would understand, as that group... well lets just say they follow the beat of a different drum, and leave it at that. I would however be very disappointed in any other part of ASM putting forth numbers like 560% for anything other than the conversion of large amounts of RA. With the steels bladesmiths commonly work with, 10XX, W1, W2, 15n20, L6, O1, 5160, 52100, and other oil or water hardening alloys, anything exceeding 6% RA should be fixable by adjusting your initial heat treatments.

Mike,

Sure, I have the digital copies of ASM at work, so I should be able to post them tomorrow.

~Joe

The attached file is directly from ASM Volume 4 Heat Treating published 1991 and starting on page 203. The info I previously quoted comes from the section titled "Case Studies of Cryogenically Treated Steels". I copied this text from a digital version of the book, but I double checked and the hard copy is identical.

Now, I full heartedly understand that a single case study doesn't prove anything, but I know many industrial tool makers who use it and I figured it's worth investigating.

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The attached file is directly from ASM Volume 4 Heat Treating published 1991 and starting on page 203. The info I previously quoted comes from the section titled "Case Studies of Cryogenically Treated Steels". I copied this text from a digital version of the book, but I double checked and the hard copy is identical.

Now, I full heartedly understand that a single case study doesn't prove anything, but I know many industrial tool makers who use it and I figured it's worth investigating.

Thank you very much, Joe...

Started reading and ran out of time but will make time to finish.

Mike

Yes, thank you Joe, I know how time consuming posting information for people can be at times. I enjoyed reading the material and was very relieved and happy to see the information broken into two parts, traditional and proven cold treatments, followed by the more controversial cryogenic claims along with an appropriate disclaimer. My faith in ASM's commitment to responsible information remains intact.

There have been many studies and tests done concerning cryo, I am still looking for the one that is entirely free from an association or connection with those in the business of selling the service in some way, but here is one that seems to be the most objective and reasonable in its claims:

Cryogenic Quenching of Steel Revisited

In the "Cryo Quenching of Steel...", from the abstract, What does "Results confirm the cryo-treatment enhanched precipitation in the subsequent tempering step of what turns out to be 100-250 nm alloy-depleted carbides,..." mean?

Mike

Mike there are a group of ultra fine carbides that form during tempering which have very intimidating Greek alphabet names that will make you wonder if you are talking steel or college fraternity's. The most common are Epsilon carbides formed in the initial stages of tempering as the carbon locked in the matrix diffuses. If you think about it, all those carbon atoms locking the martensite in the BCT configuration have to go somewhere for things to relax a bit. However there are other more exotic carbides that will form over time or temperatures and the ones you want to look at to help understand what they refer to in the writing you point out would probably be Eta carbides. The cryo folks have a very keen interest in finding anything to explain the property gains they claim, and so when cryoed steel was found to contain a gain in Eta type carbides it became a big buzzword in that field. When I discussed one of the better known writings on the topic with a very respected metallurgist and researcher, he just chuckled and said that he knew, since it was some of his papers that they had borrowed the Eta carbide information from. He seemed to indicate that these carbides will eventually form over time and that the cryo process just sort of expedited things, he also felt that retained austenite quite adequately explained the gains in abrasion resistance and dimensional stability.

I personally think there could be something to the idea of improving the lattice stacking or arrangement by the crunch of extreme cold, but it is too bad that the people selling the process have resorted to claims so far over the top that the field has lost much of its credibility. Much like in our business where there are little tricks that can tweak a property here or there, but the outrageous claims, driven by the desire to be the maker of the best knives ever made, make it so that eventually you have to take any of it with a large grain of salt.

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I personally think there could be something to the idea of improving the lattice stacking or arrangement by the crunch of extreme cold, but it is too bad that the people selling the process have resorted to claims so far over the top that the field has lost much of its credibility. Much like in our business where there are little tricks that can tweak a property here or there, but the outrageous claims, driven by the desire to be the maker of the best knives ever made, make it so that eventually you have to take any of it with a large grain of salt.

Like... where there is smoke, there are mirrors?... =]

Thanks, Kevin.

Mike