Salt bath hardening

Molten salt baths have the benefit of very rapid heat transfer into the work piece and although a labour intensive method of heat treatment salt bath hardening is economical for treating small components. Capital cost is low but the cost of safe disposal of the used salt is expensive. Salt compositions are available for case hardening of low carbon steels and the neutral hardening of higher carbon and alloy steels, including tool steels. The method has greatly reduced in use due to environmental and health and safety considerations, as the operator is exposed to contact with the salt.

In order to provide a quicker alternative to the long cycle times required to develop gas or plasma nitrided case depths and to extend the range of ferrous alloys which may be treated, several salt bath treatments have been developed. Slightly higher temperatures are used, (550/ 570° C), and cycle times are mainly in the range of 2 to 4 hours. Although these processes can be applied to alloy nitriding steels with similar results as gas or plasma nitriding, they are generally applied to plain carbon and low alloy steels and cast irons