Case hardening is a thermochemical diffusion process in which carbon diffuses into the surface of the material. The carbon can be supplied by means of a gas or liquid. The resulting material has a shallow (typically .015” to .100” thick) surface layer with much higher carbon content and hardness than the remaining base material. The process for case hardening is to heat the material in a carbon rich atmosphere at high temperature (typically around 1700 oF).

The time held at this temperature determines how deep the case depth will be. Typical hold times vary from 1 to 7 hours. After the desired hold time is reached the part is immediately quenched (usually in oil) and then tempered to the desired hardness. This process is typically applied to lower strength materials to generate high surface hardness (typically 55 to 60 Rc) for improved wear resistance without sacrificing toughness.

Typical applications – 1018, 1026, 4320, 4820, and 8620 but the process can be applied to other lower carbon steels