Case hardening, also referred to as surface hardening is the process of hardening a surface of a metal. It is done by surfacing the metal surface with a layer of metal on top of it, in order to harden it.

Case hardening or surface hardening is the process of hardening the surface of a metal, often a low carbon steel, by infusing elements into the material's surface, forming a thin layer of a harder alloy.

It is a process for case hardening stainless steel.

The term means "hardening" of the "drum". In this case, it is meant that the inner ear is calcified.

mostly is the hardening done by induction hardening machine, I know also manufactures that do this using the flame hardening method.