Too Long in Liquid Nitrogen?

M

Marc Cooper

Joined
Apr 7, 2019
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60
Hey All

I am working with Nitro V steel and placing my steel in a Liquid Nitrogen dewar immediately after it cools from the plate quench.

I know I should let it sit in the Liquid Nitrogen dewar for at least an hour, but can I let it sit in there too long?

If I let it sit in the Liquid Nitrogen overnight will I damage the steel? (It is usually fairly late by the time I get to work in the knife shop, so letting it soak overnight in the Liquid Nitrogen Dewar then tempering the next night would streamline my process.)

Thanks All!
 
No, there is no real damage to be done by a long soak in LNM. 2 hours or 24 hours will be the same to the steel. I believe most folks shoot for 6 hours.
 
And some steels just need to get down to the required temp and don’t need a soak.
 
Like Roman Landes once explained, the process of converting the RA into (untempered) Martensite is hyperfast and it’s not time dependant, just Temperature dependant. So letting it 30 minutes it’s the same as 24 hours. I’m sure Larrin also explained this quite well in his articles.
 
Isn't there some ideas of ETA carbides when soaked in LN for several hrs?

Agreed from all I've read RA conversion is almost speed of sound type of speed? Don't remember for sure from reading, but it was FAST! My understanding for RA conversion soak long enough to reach desired temp in center of blade. I usually leave in dry ice solution for 30 minutes or so because it's there, and to be sure blades are an even temp.
 
Ken H> said:
Isn't there some ideas of ETA carbides when soaked in LN for several hrs?

Agreed from all I've read RA conversion is almost speed of sound type of speed? Don't remember for sure from reading, but it was FAST! My understanding for RA conversion soak long enough to reach desired temp in center of blade. I usually leave in dry ice solution for 30 minutes or so because it's there, and to be sure blades are an even temp.
Click to expand...

Nothing was proven until now, that I know of, and reputable Metalurgists think the same. Do you have access to Roman Landes recipe to heat treat cpm3v? He recommends two 30 minutes sub zero cycles. If eta carbides where a reality, he would recommend maybe 12 hours for first sub zero cycle! For him, anything below excellence is not an option.
 
to save wear on my kiln due to temp swings i plan my HTs so that im done early evening with quenching that way i can get my blades into the LN and let them sit over night as the kiln comes down to room temp slowly over night. next day i fire up the kiln nd pull blades out of cryo. about the same time the blades get to room temp my kiln has started to cycle at 400f. just makes things easy
 
butcher_block said:
to save wear on my kiln due to temp swings i plan my HTs so that im done early evening with quenching that way i can get my blades into the LN and let them sit over night as the kiln comes down to room temp slowly over night. next day i fire up the kiln nd pull blades out of cryo. about the same time the blades get to room temp my kiln has started to cycle at 400f. just makes things easy
Click to expand...
I often do something similar but I put in the blanks into the furnace cold so that it doesn't overshoot with having to open the door. Seems to take forever to get back down when using low tempering temperatures.
 
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