The process of carefully heating the steel to a high temperature followed by cooling to room temperature under controlled conditions is called heat treatment of steel.
- Quenching of steel: When a steel is heated to high temperature of about 650oC, then the suddenly cooled by plunging into water, it becomes very hard and brittle. This process is called quenching of steel.
- Annealing of steel: In this process, steel is heated to bright red and allowed to cool slowly. The steel becomes very soft. Thus process is called annealing of steel.
- Tempering of steel: In this process, the steel is heated to a temperature of about 300oC and cooled slowly. This process is called tempering of steel. After tempering, steel becomes hard but lost its brittleness.