The hardening of ferrous materials (steel and cast iron) is an increase of its mechanical resistance by targeted modification and transformation of its microstructure. It can be achieved through heat treatment with subsequent quenching (sudden cooling). If a metal is plastically deformed, dislocations spread in the workpiece. In order to increase the strength, measures must be taken to hinder the movement of dislocations.
Quenching and Tempering
Quenching and tempering describes the combined heat treatment of metals, consisting of hardening and subsequent tempering. In general, this refers to the material steel, but this type of thermal microstructure formation and change is also common for non-ferrous metals such as titanium alloys.
Nitriding is a heat treating process that diffuses nitrogen into the surface of a metal to create a case-hardened surface. These processes are most commonly used on low-carbon, low-alloy steels. They are also used on medium and high-carbon steels, titanium, aluminium and molybdenu.