What is quenching and tempering?

Quenching and tempering are processes that strengthen and harden materials like steel and other iron-based alloys. The process of quenching or quench hardening involves heating the material and then rapidly cooling it to set the components into place as quickly as possible. The process is tightly controlled, with the heating temperature, cooling method, cooling substance and cooling speed all dependent upon the type of material being quenched and the desired hardness. A typical heating range is between 815 and 900 degrees celcius, with extra care being taken to keeping the temperature as stable as possible. Variances in the degree of heat being applied during the process can result in distortion in the resultant metal.

Likewise, the temperature of the cooling element needs to remain constant or the edges of the metal can wind up brittle. Different cooling elements have come into prominence over the years, naturally starting with water and moving onto mineral oils and even inert gases like nitrogen or helium.

After the material has been quenched to its hardest state, the process of tempering is used to achieve greater toughness and ductility by decreasing hardness. Tempering is achieved by heating the quenched material to below the critical point for a set period of time, then allowing it to cool in still air. Both the temperature and heating time depend on the composition of the material and will determine the amount of hardness removed.