Strengthing Mechanism of Cryo Treating
11-18-2003, 08:18 AM
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Strengthing Mechanism of Cryo Treating
I was wondering how the strengthing mechanisms of cryo treating worked. The two possibilites I can come up with are:
1. The low temp of the liquid nitrogen causes the part to reduce in size due to thermal expantion. The stress caues from this does some form of work hardening/increases the number of dislocations. If this were true, then cryo treating a forged part might have less of an affect as cryo treating a cast part made of the same metal.
2. The nitrogen reacts chemicly with the part and alters the chemical compisiton some how.
Any ideas/theorys are appreciated
-Jon
1. The low temp of the liquid nitrogen causes the part to reduce in size due to thermal expantion. The stress caues from this does some form of work hardening/increases the number of dislocations. If this were true, then cryo treating a forged part might have less of an affect as cryo treating a cast part made of the same metal.
2. The nitrogen reacts chemicly with the part and alters the chemical compisiton some how.
Any ideas/theorys are appreciated
-Jon
11-18-2003, 09:26 AM
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Cryo treating involves transforming austenite to a more stable martensite structure.
The nitrogen itself doesn't react with the part. The cold causes the transformation. Nitrogen is simply the means to achieve the cold.
The nitrogen itself doesn't react with the part. The cold causes the transformation. Nitrogen is simply the means to achieve the cold.
11-18-2003, 09:54 AM
#3
Chiung is correct.
When you heat treat a ferrous metal (steel, cast iron, etc), the elevated temperature transforms the microstructure to austenite. There is a chart called the "Time Temperature Transformation Curve" which shows what the microstructure will become if you cool the metal down at various rates given a specific chemistry. If you cool the material down to cryogenic temperatures instead of room temperature, the percent of martensite transformation is increased significantly. Also, the faster you cool it down, the greater the transformation.
With the added strength you gain from a cryogenic heat treatment, you also get significant residual stresses. But a subsequent "temper" (smaller elevation of temperature) gives you excellent toughness by removing much of the residual stresses without reducing the amount of martensite.
Slower quenches and room-temperature quenches will result in a larger percentage of ferrite, and with cast iron, pearlite. These phases are relatively soft and ductile.
When you heat treat a ferrous metal (steel, cast iron, etc), the elevated temperature transforms the microstructure to austenite. There is a chart called the "Time Temperature Transformation Curve" which shows what the microstructure will become if you cool the metal down at various rates given a specific chemistry. If you cool the material down to cryogenic temperatures instead of room temperature, the percent of martensite transformation is increased significantly. Also, the faster you cool it down, the greater the transformation.
With the added strength you gain from a cryogenic heat treatment, you also get significant residual stresses. But a subsequent "temper" (smaller elevation of temperature) gives you excellent toughness by removing much of the residual stresses without reducing the amount of martensite.
Slower quenches and room-temperature quenches will result in a larger percentage of ferrite, and with cast iron, pearlite. These phases are relatively soft and ductile.
11-18-2003, 01:05 PM
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So basically the cryo treatment is just a way to rapidly quench the part in order to acheive the critical cooling rate to form the martensite in that perticular steel.
Thanks for your help
-Jon
Thanks for your help
-Jon
11-19-2003, 12:47 AM
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Originally posted by Road Rage
OT:
I write for a high end audio mag (well, two) and there are wackos who believe cryogenically treating a CD will make it sound better!
OT:
I write for a high end audio mag (well, two) and there are wackos who believe cryogenically treating a CD will make it sound better!
LOL!
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11-19-2003, 04:47 AM
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Originally posted by Road Rage
OT:
I write for a high end audio mag (well, two) and there are wackos who believe cryogenically treating a CD will make it sound better!
OT:
I write for a high end audio mag (well, two) and there are wackos who believe cryogenically treating a CD will make it sound better!
How much strength does a CD gain from doing this? Is it martenistic plastic after it has been cryogenically treated.Actually I purchased some 4:77 gears and want to have them treated with this process.How much stronger is martenistic steel?