Heat treatment is the process of using heat to modify the physical and chemical properties of a material. There are various synonyms for heat treatment that have been used over the years. These include annealing, tempering, quenching, normalizing, and hardening. Annealing is a process that involves heating a material until it reaches a specific temperature and then cooling it slowly. Tempering is a process that involves heating a material to a specific temperature and then cooling it quickly. Quenching, on the other hand, is a process in which a material is heated and then rapidly cooled to increase its hardness. Normalizing involves heating a material to a specific temperature and then allowing it to cool in still air. Hardening is a process that involves heating a material until it reaches a specific temperature and then cooling it rapidly to increase its hardness and strength.