Benefit of cryo for D2

[Nathan the Machinist]

Thanks for that Nathan. I wasnt aware that only some tool steels could get grain refinement through multiple heat treating cycles. Do you have some sources of info so I can learn more about this?

I read that in ASM "Tool Steels", George Adam Roberts, George Krauss, Richard L. Kennedy, 1998.

 

[cotdt]

help me with this chart it cant possibly mean that cryo 52100 is 4.6 x more wear resistant than regular
or that cryo m2 is 15.8 x more wear resistant then regular 52100?!?!

try this its really long and takes sume sifting through, but there is good information
http://books.google.com/books?id=cYzNYwMtQHcC&pg=PA238&lpg=PA238&dq=cryo+heat+treating+M4&source=bl&ots=6z3P8nWfrY&sig=XRBDjd-c0-x9aU2NvNrlAf6oVec&hl=en&ei=3szDSt-GIsXM8Qb-hu3fCQ&sa=X&oi=book_result&ct=result&resnum=1#v=onepage&q=&f=false

Those numbers look ridiculous if it is wear resistance. But in the case that the cryo'ed steel is 2-3 rc points harder than non-cryo, then of course the wear resistance would be a lot better.

That book is very interesting though. Cryo treatment made a measured improvement for A2/D2 but none for CPM M4. Then again, they used the high temper for CPM M4, which has similar effects as the cryo treatment (converting retained austenite and carbide refinement). If they are going to cryo CPM M4, they should use the low temper instead.

As expected, the book showed that cryoing after the steel is already tempered made zero difference. I don't understand why this is still a standard practice.

 

[Nebulae]

there seems no point in cryoing M4 if the point of cryo treating is to transform all of the austenite to martensit, but that can be done at a high temper with out ruining the heat treat seems to me that would be safer, however if you could temper significantly lower one might gain a point or two, but at the sacrifice of some toughness right?
(feel fre to insert a couple of these ....)

 

[cotdt]

there seems no point in cryoing M4 if the point of cryo treating is to transform all of the austenite to martensit, but that can be done at a high temper with out ruining the heat treat seems to me that would be safer, however if you could temper significantly lower one might gain a point or two, but at the sacrifice of some toughness right?
(feel fre to insert a couple of these ....)

Yeah that's the idea. But in S30V the low temper and high temper produce different kinds of carbides (so performance is different even at the same hardness), so it might be in the case of CPM-M4 as well, who knows. Most knifemakers use the low temper for S30V now, the high temper was found to be more brittle and less stain resistant.

 

[Nebulae]

seems a mute point for HSS, oh and by the way this is related I swear.
some steel with really high nickle and manganese content have a criticle point so low that if you want any martensite at all you need to cryo, if not you can get a completly austenetic,and therefore nonmagnetic finished knife, or whatever just a fun fact