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Old 08-27-2004, 12:38 AM
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rlinger rlinger is offline
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Join Date: Jan 2003
Location: WV
Posts: 140
The book (figurative) says yes it can cause micro cracking and advises when doing with liquid nitrogen to introduce it slowly to the steel (some form of heat exchange that can vary from simply entering drops of LN into the cavity to more elaborate methods). I have read posts of real experience where bringing the steel very slowly down to cryogenic temperature is more beneficial. We ol'knife makers normally can not afford such equipment expense. I certainly can not. I have toiled over two schools of thought on how to hand lower a blade into a LN dewar. Some think it best to go very slowly. I prefer to put her in there as quickly as possible so that all the surface gets the shock at pretty much the same time. To my knowing, I have yet had one crack or warp. I think it much more likey to crack than warp and the cracking may be so small as not to notice before the knife is delivered.

It is important to remember that cryogenic treatment is not a seperate procedure outside the heat treat but instead is a component of it. A heat treat can be done without it but if it is incorporated it is part of it and not something that is done in addition to it.

Complete martensite obsorbtion (not the correct term, I am sure) is about 0.80 percent carbon. I believe any steel containing enough carbon content can benefit from cryogenic treatment regardless of how well the initial part of heat treat went, up to and including quench. I say this because it is so difficult to achieve a perfect heat treat. As stated above, some lower carbon steels, such as 5160 as an example, most probably will not benefit at all. I have tried it with such steels with no noticable difference. Even though they are specified as high carbon they are low by comparison.

Triple quenching appears to refine grain and therefore popularly refered to as giving credit to the quench. Actually, the grain is refined during soak - not the quench. I am still at school here reading you guy's stuff about triple quench however, I think multiple soaks followed by quench may better refine grain if each and every set are done correctly. In other words: I'll stick with a proper single soak but will not close any doors behind me concerning this.

RL


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Last edited by rlinger; 08-27-2004 at 01:13 AM.
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