5. Surface hardening

The main aim of surface hardening processes is to improve the wear resistance of a machined surface, but other advantages also result, such as improved behavior with respect to certain corrosive environments and, above all, increased fatigue resistance. Indeed, these treatments most often generate compressive stresses which, like those caused by work-hardening (roller burnishing), can have significant effects in relieving local tensile stresses linked to certain stress modes, particularly in fillets connecting elements subjected to bending. As in the case of steels, martensitic surface hardening is carried out by spraying the previously austenitized surface with a flashlight or inductor, and the hardened layers are of the order of a few tenths of a millimetre or a few millimetres. As thermochemical hardening involves the penetration of chemical elements by diffusion at moderate temperatures,...