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Multiple tempering (high and low)

Posted by CliffStamp 
Multiple tempering (high and low)
August 29, 2015 05:24PM
This is the first time I have heard someone do this :

- [www.google.com]

It is part of a process of how to harden a D2 type steel, here is the interesting part :

Quote

(a) pre-heating the steel for at least 20 minutes between 1400° F. to 1500° F.;
(b) austenitizing the steel at a temperature of from 1925° F. to 1975° F.;
(c) gas quenching the austenitized steel;
(d) tempering as follows:
(1) heating at between about 900° F. to 950° F.;
(2) freezing at from -120° F. to -150° F. for at least 16 hours; and
(3) heating at from 400° F. to 550° F.

Note the tempering part of hitting the secondary hardness maximum, then using cryogenics, then hitting the low tempering point for maximum strength. There is no materials data on the steel that results however I have not even heard of anyone doing this and I am not sure on what exactly is trying to be gained.
Re: Multiple tempering (high and low)
August 31, 2015 03:17AM
Quote
CliffStamp

Note the tempering part of hitting the secondary hardness maximum, then using cryogenics, then hitting the low tempering point for maximum strength.

First time I have seen this being done. In my years of talking to many makers and reading I have never read or heard of that being done.
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