The goal of case hardening is to enrich the surface layer of low-carbon case-hardening steels with carbon up to a defined depth so that surface layer properties such as a high degree of hardness, compression strength, and resistance to wear are obtained following hardening. The core of the component, which is not enriched with carbon during hardening, obtains a structure that is highly ductile and resistant to bending with a comparatively low degree of hardness due to its low carbon content. This results in an increased bending resistance of the component.

Case hardening is a thermochemical process that consists of a number of sub-processes: Carburizing, hardening, and relaxing. During carburizing, the material being treated is exposed to a carbon-emitting atmosphere at temperatures between 850 °C and 950 °C for a defined period of time, which may be up to over 100 hours depending on the carburizing depth. Due to the set concentration gradient of carbon between the atmosphere of the furnace and the component, the carbon penetrates into the surface of the component and diffuses into the inside of the workpiece. Hardening refers to the sub-process in which the material being treated is quenched following carburization – typically in oil, depending on the material.

During the subsequent tempering and relaxing process, the desired surface hardness is established by warming the material again.