Wierd cryo question.

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skillgannon

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Apr 27, 2009
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I have a box of 15n20 that I got from JD. I think I might do a run of knives with it. I have had great success with it just using my atlas forge. Now that I have a oven I want to up my heat treatment quality. I don't have parks 50 and so I will use the old canola oil. This got me to thinking, if you have a simple carbon steel and are not giving it a fast enough quench, will cryo possibly help complete the conversion process?
 
skillgannon said:
I have a box of 15n20 that I got from JD. I think I might do a run of knives with it. I have had great success with it just using my atlas forge. Now that I have a oven I want to up my heat treatment quality. I don't have parks 50 and so I will use the old canola oil. This got me to thinking, if you have a simple carbon steel and are not giving it a fast enough quench, will cryo possibly help complete the conversion process?
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Larrin would be better to answer this, but before I had my oven, I was using dry ice and acetone with 15n20, regardless! You would get less retained austenite with a cold quench, so it’s worth using in my opinion. If you have it, I would suggest using it!
 
You won't get enough additional conversion with that mix. The use of LN and the formation of eta carbides are more suited for higher carbon ,higher alloying types .
 
I believe the point of the quenching fast enough is that you need to lower the temperature of the austenite to below the martensite start temp within the time window of the steel or else it will end up forming pearlite instead. Sub-zero or cryo won't turn pearlite into martensite. More knowledgeable metallurgy people should correct me if this is wrong...

Edited to add: Canola is fast enough for 15N20. Also 15N20 is almost always only available in thin pieces so should quench faster than really thick material.
 
milkbaby said:
I believe the point of the quenching fast enough is that you need to lower the temperature of the austenite to below the martensite start temp within the time window of the steel or else it will end up forming pearlite instead. Sub-zero or cryo won't turn pearlite into martensite. More knowledgeable metallurgy people should correct me if this is wrong...

Edited to add: Canola is fast enough for 15N20. Also 15N20 is almost always only available in thin pieces so should quench faster than really thick material.
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You mean the pearlite "nose" rather than martensite start. Slow cooling below the nose can stabilize austenite, which I think is what the OP is referring to. Cryo would help with transforming stabilized austenite. How much is stabilized and how much is then transformed with cryo is hard to guess.
 
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