Quote:
Originally Posted by Seraphim
I'm not a mettalurgist, nor a blade forger, but I did have an opportunity to use a cryo treatment for a investigation project here at work (I work at an R&D lab).
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I had thougt cryo was just for stainless (ala Friodurs, etc.) but it looks as if carbon steel would also greatly benefit from this process.
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And a good question too.
To keep things simple, divide steels into two basic types. There are low alloy steels like the 10xx simple steels. There are high alloy steels which are more complex mixtures of basic steel plus alloying elements. Stainresistant steels fall into the high alloy category.
If a low alloy steel is heat treated correctly within it's specified parameters, there should be a minimum of retained austenite. If there is an excess of carbon (greater than 0.77%) even low alloy steels may have some retained austenite, but more likely from a poor heat treatment regimen. Essentially this means that all the possible martensite has been converted to the limit of the carbon carrying capacity of the material and what cannot be converted during the quench is leftover as retained austenite. This increases the brittleness of the material because the ideal would be to have only martensite and no retained austenite and then temper the martensite to improve toughness without losing hardness.
Practically all high alloy steels contain retained austenite to some percentage. There are graphs that will predict how much out there.
To convert retained austenite to martensite reducing the temperature will kick the RA over into martensite. This is best accomplished at the same time as the traditional quenching with the metal being in the metastable state during heat treatment. Then immediately tempered to convert the fresh martensite into tempered martensite according to the proper heat treatment regimen. Remember, this requires tempering after cryo, otherwise the untempered martensite is a weak point just waiting to crack.
If cryo is required to improve a low alloy steel, I have questions about the basic heat treatment regimen being used. It just isn't necessary for the most part.
Cryo will improve high alloy steels. It will reduce RA in most steels but I know of some alloys that just refuse to give up RA no matter what. Some of it you just have to live with.
Now, the biggest criticism, that I and a few others have, of this whole process is the not very well hidden conflict of interest. The PhD types who are writing these articles, are also heavily invested in the selling of the process.
And, I know of several folks well experienced in the tool and die industry who say that there is a statistical improvement in cutting ability, but, there may not be any practical recovery of the cost of the treatment in the sale of the product. It's expensive enough to make blades and sell them without adding several hundreds of dollars in equipment and then keeping a rapidly evaporating product contained long enough to be useful, then replacing it every month.
If you want to do it, go for it.
Just my simplified thoughts.
Cryo treatment
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