Hogue Blades - 154 CM Cryo-treated?

[Phil Wilson]

Jim, As I mentioned cryo treatment is controversial. Some Metallurgists’ will tell you that if the heat treat was done right in the first place then it is not necessary. My take is to do it right in the first place and use a sub-zero cycle to squeeze out the last bit of retained austenite and also as a final quality control measure. Multiple tempers at the “high” end-- 975 vs 400-- for example will do close to the same thing as cryo cycle in LN2 right after the quench. Problem is that the high end tempers also can have negative effects on corrosion resistance and ductility. So it depends on the steel you are working with and where you want to end up. Some tool makers want some retained austenite since it tends to cushion the force when a tool like a milling cutter is pushed hard.
Yes, the fact that this particular maker advertises and uses a cryo cycle does not automatically mean his 154 CM is better than someone else’s. In order to judge that we would have to know his process. In the end it is how the blade performs that is important. Phil

 

[Ankerson]

Jim, As I mentioned cryo treatment is controversial. Some Metallurgists’ will tell you that if the heat treat was done right in the first place then it is not necessary. My take is to do it right in the first place and use a sub-zero cycle to squeeze out the last bit of retained austenite and also as a final quality control measure. Multiple tempers at the “high” end-- 975 vs 400-- for example will do close to the same thing as cryo cycle in LN2 right after the quench. Problem is that the high end tempers also can have negative effects on corrosion resistance and ductility. So it depends on the steel you are working with and where you want to end up. Some tool makers want some retained austenite since it tends to cushion the force when a tool like a milling cutter is pushed hard.
Yes, the fact that this particular maker advertises and uses a cryo cycle does not automatically mean his 154 CM is better than someone else’s. In order to judge that we would have to know his process. In the end it is how the blade performs that is important. Phil

Thanks Phil for sorting that out for me.

 

[mete]

If 154CM has 30% retained austenite it has been IMPROPERLY HT'd !! If that's the case they are then using cryo to attempt to correct very poor HT. That's not the way it should be done !
That much RA means overheated steel which in turn means not only high amounts of RA but large grain size .Large grain size means lower toughness !

 

[Buck_110]

Again to yield full conversion to martensite, a very stressed condition. If the cryo cycle is done after tempers and it does in fact move some retained austentite to martensite then you have some untempered martensite, which is again adding stress to the blade if left in that state. Another temper is required to modify the martensite structure.

These three sentences drove it home for me. I was under the impression that machining was responsible for the majority of retained stress due to metal distortion. While I know the austenite to Martensite conversion creates stress, I was unaware that the conversion is responsible for the majority of it.

Thank you, Phil.

 

[warbird436]

You have to define what you are talking about. Some of you are talking about cold treatment which is basically treating metal down to about -120F. Then there is cryogenic treatment which means going down to -300 or below. Cryogenic treatment consists of a slow cool down with a hold at the low temperature and a slow warm up, usually followed by one or more tempering cycles. Also, you need to define how you are rating your results. Meat packing companies have found that cryogenically treated blades stay sharp longer. Yes, a lot of marketing departments like to use the phrase "cryogenically treated." And many of them have no idea about what a cryogenic treatment is. Also, recent research is showing that some metals need to be held at -300F for different times. Some alloys with cobalt in them should not be held at -300F for over 8 hours, while D2 likes 36 hours.

Cryo treating is becoming more like heat treating as the research shows us more and more about what is happening during the process. There are a lot more things happening than just the reduction of retained austenite. As the temperature drops, the solubility of the alloying elements in the iron matrix changes. This causes movement of atoms and vacancies. This causes the metal to change characteristics. If the temperature drops too quickly, there is a tendency to "freeze in" what existed at the higher temperatures.

My point is that unless you know how the part was treated you cannot make very many decisions on whether or not cryogenic processing was successful or not.