Cryogenic Tempering

Cryogenic treatment of metals to improve wear characteristics is a relatively new engineering field, and little has been reported on the basic mechanisms by which the technique operates.

Industrial Cryogenic Enterprises Ltd. provides industry with a controlled, dry, cryogenic process that will produce considerably longer wear life for almost any tool or dynamic part subject to wear and abrasion.

Background to Cryogenic Treatment

The use of cryogenic temperatures (below about -240° F) in metal treating is a relatively new application in the realm of the ultra-cold. Some work was done during the 1940’s in which the metal parts were quenched in liquid nitrogen (-321° F). However, the investigators found that the very rapid quench produced thermal stresses which caused problems with the materials. Because of this early work and the problems associated with the rapid quench in liquid nitrogen, little interest was shown in the cryogenic process until the late 1960’s.

In order to avoid the problems associated with the rapid quench process, researchers tried to cool the machine elements in cold gaseous nitrogen. Dramatic improvements in the wear life were found for several machine elements, the wear life for machine elements involving tool steels can be improved by factors of 2 to 6, in most cases.

The Cryogenic Treatment Process

There are three important elements of the cryogenic treatment process, as determined by research conducted in the Mechanical Engineering Department at Louisiana Tech University. These elements are:

1. A very slow cooldown from ambient temperature to cryogenic temperatures. By cooling the parts at a very slow rate, thermal stresses are avoided, and the problems encountered during the early cryogenic tests in the 1940’s are eliminated.
2. A long soak at cryogenic temperatures. It was found that a soak of 20 to 24 hours was needed to take full advantage of the cryogenic treatment. In addition, the wear resistance was improved more if the parts were soaked at temperatures on the order of -310° F, in comparison with the treatment at dry-ice temperatures (on the order of -120° F).
3. A triple heat temper after the cryogenic treatment. This tempering process was carried out at temperatures on the order of +300° F. The temper reduced any brittleness caused by formation of martensite during the cryogenic treatment process.

Frequently treated materials are alloys of steel, copper alloys, aluminum and magnesium.