Cpm 154

Rob! said:
Be careful about focussing to much on boil off rates. a 1" neck will be very efficient but also very hard to stick a bowie knife through.;)

Rob!
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You are absolutely correct about those 1" necks! The Intl Cryo necks have 2.25 inch I.D. necks. Oh, and my boil off rate was wrong for the 10 liter, it was .15 liter, even better than what I said earlier.
 
I used dry ice for years and put the blades between two layers of solid dry ice. I never had one warp.

New information that I posted here in other threads has convinced me that while cryo raises the hardness, it lowers the toughness of tool steels. Now I have gone back to just tempering, but doing a third one to convert the max retained Austenite.
 
I believe it only lowers the toughness if you don't temper afterwards, otherwise I think it actually makes it tougher because you get rid of the retained austenite.
 
mrstenoien said:
I believe it only lowers the toughness if you don't temper afterwards, otherwise I think it actually makes it tougher because you get rid of the retained austenite.
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I used to think that, too. Almost everything that you see on the web about cryo is published by the companies involved.

Check out this independent study of cryo effects on A2:
http://www.airproducts.com/NR/rdonl...019GLB.pdf#search="cryogenic quenching steel"

The Control in this study was double tempered to HRC 58 and it was tougher than all of the cryoed samples including one at HRC 60. A2 quenched and tempered at HRC 60 is at its peak in toughness and is above the charpy value of the control.

The micrographs in the study identify the small secondary (eta?) carbides in the cryoed samples as FeCs which may be where the Carbon in the retained Austenite goes in the cryo process. Thorough tempering will convert retained Austenite to Martensite. What you have left is a trade off between a slight increase in hardness and a decrease in toughness. With the properties of most tool and stainless steels, I vote for getting my HRC 60 with the best toughness.
 
Be careful about drawing conclusions from this. It is a single study and he begins by acknowledging his results differ from others who have examined the issue. He's working with one steel - A2 - and makes unsupported suggestions that results would also apply to other tool steels as well as stainless. He has only applied one of many possible 'toughness' tests.

Note also that in every case, the cryo'ed samples ended up harder and more wear resistant than the control by a good margin. This study focussed on wear resistance primarily, using the 440C ball, the diamond scratch and a surface hardness test converted to RHC.

If someone were to draw conclusions about cryo's effect on steel, I would suggest a more exhaustive review of the research as well as a review of manufacturers literature and 'pers. comm.' from expert sources like this forum.

Mr Stenoien rightly poses the question that should have been examined if this study related to toughness.

Look at the crucible data sheet for A2. That charpy toughness curve is not exactly typical of other steels we use.

Rob!
 
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