Case microstructure in induction surface hardening of steels: an overview

The microstructure and resultant mechanical properties of the hardened case produced in steels by induction surface hardening are discussed. The development of the final structure is followed throughout its characteristic evolutionary stages; its dependence on heating and cooling rate, maximum temperature of the treatment, composition, and initial microstructure is described in detail. Gradients of microstructure, composition, and hardness brought about by induction surface hardening inside the case are studied and explanations about their origin are proposed. The properties of the hardened case completely rely upon its microstructure, whose control is then a key factor for engineering applications.