Innapropriate quenching mediums...

Osbourn

Osbourn

Joined
Jun 27, 1999
Messages
804
I read a previous post on cryo treating and the reasons for doing so. The main reason that I understood was for full martensitic conversion, as it's usually only partial conversion for most chrome-bearing steels. Wouldn't a more violent quench solve this problem, at least partially? Basically, if oil isn't getting the steel cold fast enough, the next step would be a lighter oil, then heavy brine, with an interrupted quench to prevent breaking. I think preventing warpage can be handled in other ways, keeping the blade intact is the first concern. The other concern is, would it work? Is it not even worth the experiment? Will I waste my 52100 trying?

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Oz

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I'll give an answer a try. The way I understand the cryo treatment is the same as you. It will help to speed up the conversion of retained autenite to martensite. In high alloy steels the alloys prevent some of this from happening at a normal quench. To be able to obtain a complete conversion would, as you pointed out, be destructive to the blade material. If I read my book right, retained austenite will eventually turn into martensite with time. This is believed to be the reason some very old blades seem to cut better etc. Taking a blade below -120F speeds this process up. Ed Fowler did a test on some of his blades and it improved the performance dramatically. My heat treat book also agrees that the performance of some materials can be improved by more than 300% with a cryogenic treatment.
I don't know if this does any good as an explanation but it is the way I understand it.
 
That's very helpful, actually. It tells me I'm not nuts in my interpretation, and that if the brine quench doesn't destroy the blade, it will end up a better piece. I'm no stranger to destroying blades in heat treating processes, I've killed plenty of otherwise fine tanto in clay water quenching, so it doesn't scare me that much. I'll give it a try. Thanks.

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Oz

Now, what other news did I have? Oh yes, IT'S A GIRL!!!
See her and my latest blades @
http://www.freespeech.org/oz/
 
Chuck :

retained austenite will eventually turn into martensite with time.
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Which will be untempered martensite having a very different structure than martensite (it is very brittle) and will cause localized stresses in the blades.

Cryo treatment does other things besides drop the temp down low enough for full martensite conversion. It also changes the carbide structure to enhance wear resistance and refine the grain structure for increased toughness.

-Cliff
 
How long would retained ausenite take to turn to full martensite?
When you say it refines the structure, does this mean that you end up with a smaller grain, or does it change the nature of the microstructure entirely?
Can it be explained in words HOW it does this, or is it something that visuals would be needed for?
Is there an online reference I can check to find out more?
Thanks,

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Oz

Now, what other news did I have? Oh yes, IT'S A GIRL!!!
See her and my latest blades @
http://www.freespeech.org/oz/
 
Obburn :

How long would retained ausenite take to turn to full martensite?
Click to expand...

Good question, wish I knew the answer. The transformation rate will be enhanced by cold working so you will probably see it at the edge first.

does this mean that you end up with a smaller grain
Click to expand...

Yes.

does it change the nature of the microstructure entirely?
Click to expand...

Yes, it causes a change in the carbides formed increasing wear resistance.

Is there an online reference I can check to find out more?
Click to expand...

I have some journal references, I'll post them up later.

-Cliff
 
Sean Perkins does a VERY violent quench of A-2, clay tempered, into ice water! It works, though, I'll tell you that much. I don't know how many blades he loses this way, but the ones that survive are damn good. Dunno if that info is hepful to you or not...

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