cryo times for 'complete' conversion

[shgeo]

The martensite transformation is a diffusionless shear-related recrystallization that moves at ~1 KM/sec through simple FeC steels. I have not seen figures for the phase transformation rates in high alloys, but I would expect it to be slower through the more complex systems.

Crucible and Bucorp (Bohler/Uddeholm, NA) both recommend cold treatments at dry ice temperatures (-110F to -112F) for 3 to 4 hours for tool and CPM steels. It will not hurt to go longer. The colder lN2 temperatures give a small extra amount of transformed retained Austenite, but the relationship is asymptotic as mentioned above.

I have not seen any published data that claims anything other than retained Austenite transformation for cryo treatment..other than from companies involved in cryo.

[Mike Stewart]

Over the years I have used a number of steels and all have had noticable benifit from Cryo-Treating.

I have used 1095,5160, 440A, 12C27,440C,52-100,0170-6, 154CM,S30V and A-2.

In side by side tests all the blades performed at a higher level of edge retention and lateral strength with the process.

Mike.........

[mete]

" cryogenically treating since 1987" ? that makes me feel 1000 years old. In the old days we called it subzero quench or treatment. Since Roger already quoted me I'll stand by my comment that 10 hours is more than enough.Much of cryo is nonsense ,at this point in time cryo has been proven to reduce retained austenite anything else is still conjecture . There is a research paper that talks about eta carbides and that has been quoted by many cryo companies who imply many things. If we are looking at edge retention and wear resistance we have the large carbides that haven't been dissolved in austenitizing [high carbon steels], smaller carbides from tempering martensite and still smaller eta carbides from cryo. Obviously the larger carbides will have a greater effect on wear. The existance and effect on eta still is in question. ......The use of cryo to make up for poor hardening is certainly not recommended - do it right the first time. Improper austenitizing will produce more retained austenite which cryo will reduce ,but do it right the first time.

[Mike Stewart]

Mete,

Good to see you have been doing the process that long. In the OLD days we all did sub-zero quench. I still do a sub-zero quench. I also do a 24 hour after the third temper and after the blades are ground.( I grind hard). I don't need to have a bunch of Cryo salesmen tell me anything and I agree with you that the guys who sell the service and the equipment imply a lot. I ask them nothing and just tell them what I want done. My favotire was the guy who told me that he was going to ultrasonically -magneto -wave length migrate my carbides. I'm just not sure how much snake oil is needed for that process. All I know is that my blades are stronger and hold an edge better the way I have them processed. That's really all I need to know.

Thanks,

Mike........

[mark23]

Originally Posted by Mike Stewart

... My favotire was the guy who told me that he was going to ultrasonically -magneto -wave length migrate my carbides. I'm just not sure how much snake oil is needed for that process. All I know is that my blades are stronger and hold an edge better the way I have them processed. That's really all I need to know.

Thanks,

Mike........

Mike, in case you have your knives processed this way, can you give further information on the "ultrasonically-magneto-wave length migration" of carbides? Do you happen to know whom to ask for further information?

Thanks!

Best regards

Mark23