Discussion in 'Heat Treating Forum on KnifeDogs' started by dadams, Mar 15, 2015.
Might be a silly question but do you have to cryo the stainless? And steels like d2? Thank Davey
It isn't an absolute necessity but it really helps. The purpose is to convert a greater percentage of Austenite to Martensite. Tempered Martensite is the phase of steel that makes the best knife blade and the greater the Martensite percentage, the better the blade.
Blades without a freeze/cryo can have as much as 15% retained Austenite and blades done with a freeze/cryo can have as little as 2%. Actual percentages vary widely depending on the steel and H/T procedure.
Thank you so much for the reply. I will get some dry ice and start doing it when I start with those steps
Actual cryo requires more than just dry ice.
Take a look at this post to see what difference the real world has between dry ice (-95ºF) and no freeze treatment:
Start at top, watch cutting test for freeze treated blade, then on down to video of test with non-freeze treated blade. Then read what the guy says. Understand, this is NOT a scientific test, but more what a person would experience in real life.
Thank you guys
It really depends on how optimal the maker wants the blade to be and the difference can be seen in testing.
Ideally the blades should be kept in LN2 for 24 hours before the tempering cycles begin.
However there are different thoughts on this as in to do it at all or not so opinions will vary, but if the maker want the highest performing blade possible then a proper CYRO is really needed.
Its generally though to improve things, but some users report non-cryogenically treated blades hold their dges longer. It's not a "have to" thing though.
Would depend on who actually made the blades I would suspect and if the knife maker really knew what they were doing or actually had the proper Heat Treating equipment and if they used dry ice or LN2 and actually did it right or not.
So things can vary.
All that comes into play. I'm thinking specifically of a tester on another forum who had a well known heat treater take care of several blades, which he then tested to see the effects of various things, one of which was cryogenic treatment. I'd have to assume the heat treater he used knows what they're doing, as they heat treat a lot of knives for a lot of makers. I would share the names, but I'm not sure it's okay since it's on another forum, and I don't think the guy's a member here. In any case, in a carefully controlled test, cryogenically treated blades outcut non-treated blades in less than half his trials. This was a huge undertaking and it's not done as far as I know. The micrographs and analysis are still in the works.
In terms of is cryogenic treatment necessary, about the only thing that can be said with great certainty is one has to try it out and see.
I'm so tired of people posting GARBAGE that influences people who don't know any better. I honestly don't know how much more I can take.
With my limited testing and experience I would say that it is something that should be done and I will continue to do it (sub zero) on my knives. If I can gain one point in hardness it's worth it. If it will improve the knife's ability to cut, I'll do it. I want to make the best performing blade that I can with the material that I am working with. I think I owe that to anyone who is willing to buy a knife that I make.
And that's really all that needs to be said right there.
When the steel companies are recommending that the blades go through some sort of Sub Zero in their data sheets there must be something to it or they wouldn't even mention it.
So yes I understand.
You know were I stand on CRYO treating and I make it pretty well known what I think about it.
So you know I am being nice here.
Would you care to elaborate?
Nothing to do with this thread, but I share your frustration. I think one of the problems is that people get an idea in their head and set out to prove it. In fact, the true test would be to set out to disprove it - blind. Only then has is passed any meaningful challenge.
Having said all that, only a few knife makers have the ability to evaluate something in isolation and without bias. Legends ensue.
I do believe just about everyone here offers their knowledge in good faith. The anecdotal is not to be entirely dismissed and the sharing of all experiences is appreciated. I just have to decide for myself if there are any useful lessons in that experience.
Darrin - I'm sure for a person with your knowledge and experience it can get frustrating at times. I felt the statement you made at start of this thread about cyro was so valid:
tells it pretty much like it is. Please don't get "too" fed up and quit sharing your knowledge and experience with the rest of us folks. It's folks like you 'n Ed Caffrey 'n Bruce Bump, and many other folks.... Rob - just too many to list that really help the rest of us novices learn.
i can't remember well, i'm sorry (not being too much involved in SS), but the deep freeze (short time, "moderate" under zero) and the LN procedure (24h, "deep" under zero, Cryo so to speak), are totally different beasts, and aim different specific targets, the latter being related to producing small carbides by diffusive process over time, the first just to reach Mf and so complete the quick shear type transformation.
Both of them work ok around the RA issue in high alloy ss steels, but the "superior outcome" in wear resistance claimed regarding the LN procedure i believe is still debated by metallurgists, where some study underlines diminished impact-resistance.
Thanks for the info Stezann - Your statement of "LN procedure ..... being related to producing small carbides. Sandvik says a true Cyro isn't required on their steels as they focus on having very small carbides already. Sandvik says a -95º is all that's required and would be explained because of the need "to reach Mf and so complete the quick shear type transformation".
I had wonder why Sandvik said a fully cyro didn't help, - do I understand this all correctly?
This is one of those threads that I usually try to steer away from-just not often enough. Remember that the thread started was dealing with D2, stainless steel, and other complex alloys and not something as relatively simple as even 52100. With some alloys, as indicated by their data sheets, cryo or even just cold treatment does make an improvement. Other steels you're just making cold. The formation of eta-carbides and their significance seems to be a area that is still under research and discussion.
As far as people putting their garbage out there, remember it goes both ways. I get frustrated at people who don't have the ability to isolate and test the variables involved reject decades of metallurgical science for their own pet theories and they get tired of me quoting Verhoeven and other authors of books on metallurgy. We just need to try real hard and treat each other with respect and know when to back off. Remember, never argue with an idiot. They'll drag you down to their level and beat you with experience.
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