cryo for beginners

T

T. J.

Joined
Jul 27, 1999
Messages
228
Ok, I'm looking for info on cryo treatment of blades for the beginner. If anybody knows of a site out there that goes into the why's and wherefores that would be great. Of those of you that do cryo, do you use a liquid nitrogen bath, or some type of microprocessor controlled freezer to control ramp down and up times? Benefits or drawbacks of either method?
Thanks; James
 
TJ,
I got started with cryo treating about a year ago with my knives and have been using liquid nitrogen at work for years. In the latest issue of Knives Illustraded (October 99) Tim Zowada's Q&A collumn disusses Cryo treating D2 and gives names of suppliers for dewars. Thats not the Scotch! It's what you need to put you liqid nitrogen in! I would recommed the best one you can afford! I had a cheepie and paid the price in lost "COLD"!
I would go by his recommendations as I am only working with and have confidence in cryo treating D2...
I don't know anything about freezers. I do know that, that is the way to go for the ultimate cryo, but I'm sure it's big bucks!
Tim gives his adress and website at the end of the article for questions and comments. I don't think he would mind if you got in touch with him.

tzowada@unnet.com
 
You can try dry ice and acetone. It won't get as cold as some of the other liquid gasses, but it will get WAY sub-zero. It's a great alternative for those of us that don't have access to the really cold stuff. I haven't tried this, I got it from "The Complete Bladesmith". I do have some D2 that I intend to try it on, though. I'll let you know how it goes when I do.
Oz

[This message has been edited by Osbourn (edited 01 September 1999).]
 
just got back from a week long class at Trinidad Junior College with Steve Rollert..

he used dry ice and rubbing alcohol.. it works fine..

 
Rubbing alcohol would make sense, too. Anything that has a really low freezing point should do the trick. I have just GOT to try this...
Oz
 
Okay dry ice and acetone or alcohol for how long and when do I freeze it right after the hardening process before the first temper? And which steels does this help out the most? Would it help with A2 ?
Thanks Steve

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BOHICA !
 
Been some discussion of this very subject over on the Knife-List.
Seems that there are new discoveries in the way that cryo is to be done....ramping down in temperature a set number of degrees per minute/hour, along with soak times at -300F. Very similar to HT specs for high alloy steels..... but in reverse.
Testing is being done at this very minute, and will probably be made public sometime next year.
 
What you do by cryo is to carry on with quenching. this means that you transform austenite into tetragonal martensit. steels with a high amount of chromium and other things inside high alloy grades tend to lower Ms martensite start herewith martensite finish Mf temperatur. this means that not all of the austenit will be transformed when you quench down to room temp..to carry on with transforming you just keep on "quenching" by supercooling it. the transformation is a tilt over thing that goes fast (supersonic speed). there is a maximum transforming around -100°C for almost every steel. the cryo has to be done within two hours after quench, to prevent the austenit from stabilising. a soak time 1/2 up to 24h is recommended. for steel used in knife application the first cryo I make is 1h soak then low temper 1h and then cryo and temper again to get rid of the most possible retaining austenite and untempered martensite.
refering to the steelgrade A means airhardening witch comes from the amuont of chromium inside. witch leads us back to the beginning.
Harry Jensen, testing has been done several years ago
Roman

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