Case hardening is a thermo-chemical process. Within the framework of this process, the surface layer of components is enriched with carbon (carburisation) or carbon and nitrogen (carbonitriding), in order to improve the mechanical properties of the component surface layer. For both process variants, various plant technologies, such as chamber furnaces, through-type furnaces, salt baths, low pressure systems etc., are available.
As a rule, case hardening comprises three working steps. In the first step, the workpieces are exposed to a carbon or carbon and nitrogen rich environment at a temperature of 800 to 1,050 °C. In the second step, the quenching (hardening) may take place either directly from the application temperature or after intermediate cooling and reheating to a material-specific hardening temperature. The third step, the annealing treatment serves essentially to relieve the highest stresses in the material structure and to reduce sensitivity to grinding cracks..
Steels suitable for case hardening are unalloyed or alloyed steels with a carbon content below approx. 0.25%. Before quenching, the surface layer of these steels must be carburised or carbonitrided.
Case hardening steel (C ≤ 0.25 %)
Core zone (C ≤ 0.25 %)
Surface layer (C = 0.70…0.90 %)
Partial case hardening is possible, thanks to suitable insulation techniques.