Cryogenic Treatment effect on Hardness
Cryogenic Treatment effect on Hardness
(OP)
Let's say I have specimen of carburized 8620 steel, .020 case depth, 58RC hardness (89R15-N)at the surface of the case.
If this sample was cryogenically treated (soaked in liquid Nitrogen for 1 hour) would the case hardness increase as retained Austenite was converted to Martensite? If hardness increased about how much could I expect?
Many Thanks,
Bill
If this sample was cryogenically treated (soaked in liquid Nitrogen for 1 hour) would the case hardness increase as retained Austenite was converted to Martensite? If hardness increased about how much could I expect?
Many Thanks,
Bill





RE: Cryogenic Treatment effect on Hardness
RE: Cryogenic Treatment effect on Hardness
I have found cryo treatment beneficial in tool steels and high carbon high chromium grades castings.
RE: Cryogenic Treatment effect on Hardness
Normal carburizing of 8620 results in fairly low retained austenite, probably 10-20%. Subzero treatments will convert this and raise the hardness somewhat, but I do not have any data to indicate by how much. I would speculate that it might increase 1-2 HRC at the most. Perhaps Carburize can provide some information based on his experience.
RE: Cryogenic Treatment effect on Hardness
As mentioned above, any potential gain in hardness is minimal. If you really need some extra surface hardness, then maybe you should be looking for a different process like Nitriding or maybe the carbon potential in the carburizing atmosphere is low since you should max out in the low HRC 60's with max carbon percent without pushing into carbide network unless you have excessive mass/cross-section that your quench cycle is not achieving adequate quench rate.
If a tiny bit extra surface hardness will really work for you, the cryo treatment does not require an hour. Transformation to Martensite is not time dependent rather it is only temperature dependent.
RE: Cryogenic Treatment effect on Hardness
Thanks for the replies. Let me explain exactly what I am doing and why I am asking this question.
I have an 8620 lever arm that is spring loaded in a mechanism. At times the lever rotates through an arc and with a tip velocity of 13 fps it strikes a much more massive part. This lever is carburized to about 58 RC on the case, .015" RC50. I am getting wear on one location of the lever that rubs against another. I am thinking I need another 2-3 Rockwell points (lubrication, nitriding and hard coatings I can't consider). I was just wondering if I cryo treat I can get the extra hardness or do I need to perhaps increase the case depth a bit and temper to 60RC. I would love to use a through hardening alloy (like A2 or D2) but the part has some thin sections and I am worried about fracture failure; the part has to have impact resistance with a hard surface. I will test and let everyone know the results.
Bill
RE: Cryogenic Treatment effect on Hardness
RE: Cryogenic Treatment effect on Hardness
RE: Cryogenic Treatment effect on Hardness
My customer requested no lubrication. The application will be exposed to the elements and must work with little to zero maintenance.
JHossom, is the CPM-3V a powder metal product? I forgot to add that I am limited to the investment casting process in the part's fabrication.
Constraints can be a pain sometimes.
Bill
RE: Cryogenic Treatment effect on Hardness
RE: Cryogenic Treatment effect on Hardness
The wear area is sort of an internal feature and I thought PVD coatings need direct access as it is a thermal spray. This might be my ignorance talking.
I will look into your suggestion.
Bill
RE: Cryogenic Treatment effect on Hardness
RE: Cryogenic Treatment effect on Hardness
I agree that 8620 should not show any significant change in hardness due to a sub-zero treatment the case should be pretty well fully tranformed at room temperature and transformation of the remaining ~10% austenite will not produce any major increase in hardness. Even if there is a 1 or 2 point Rockwell increase this will be reduced by the temper needed after the sub-zero treatment.
RE: Cryogenic Treatment effect on Hardness
Does a part definitely need a post temper after sub-zero treatment? What happens if that step is forgone?
Bill
RE: Cryogenic Treatment effect on Hardness
If the cryo treatment is done to remove RA then definately, other wise teh untempered martinsite will cause problems.
RE: Cryogenic Treatment effect on Hardness
RE: Cryogenic Treatment effect on Hardness
Bill
RE: Cryogenic Treatment effect on Hardness
I'm not sure this would solve even your problem if you are showing wear at HRC58, it would seem you need to be much harder than even HRC65 to help much and since it is impact loading, Nitriding does not apear an option.
Can you redesign the lever to act like a spring and absorb energy so that the impact results in less contact (compressive) stress?