Case hardening is defined as carburization, hardening, and tempering of a workpiece made of steel.
The method of case hardening is used when a tough core and at the same time a wear-resistant surface is required in a workpiece. To this end, the surface layer of the workpiece (case hardening steel) is carburized and subsequently quenched (hardened). Case hardening is generally performed at temperatures between 880 and 980°C. In this way the surface of the component is enriched with carbon by means of diffusion.
The average case hardening depths are between 0.1 and 2.5 mm (s.a. Hardness penetration capacity). After hardening the component is tempered. Tempering is required to minimize the stresses generated within the component and to achieve the required strength for use. Hardening and tempering induce great surface hardness and strength of the component, while the core remains in a though and resistant condition.
Case hardening is performed either in gas flow or in a salt bath. Salt baths provide the possibility of partial hardening without having to previously isolate specific sections of the workpiece. Suitable materials are various case hardening steels (approx. 0.1 - 2.5 % carbon content). Typical case-hardened machine parts, i.e. components with hard, wear-resistant surfaces and tough cores, are shafts, bearings or bearing journals.
Electron beam hardening
Salt bath furnace