Spheroidization: prolonged heating of iron-based alloys at a temperature slightly below the critical temperature range followed by relatively slow cooling, usually in air. Small objects of high carbon steel are more rapidly spheroidized by prolonged heating to temperatures alternately within and slightly below the critical temperature range.The purpose of this heat treatment is to produce a globular condition of the carbide.
Normalizing: heating iron-base alloys to temperatures approximately 50℃ above the critical temperature range followed by cooling in air to below the range.The purpose is to put metal structure in a normal condition by removing all internal strains and stresses given to the metal during some processing operation.
Annealing: A comprehensive term used for heat treatment, which can be used to relieve stress. Change the ductility, toughness, electrical, magnetic or other physical properties, improve the crystal structure; remove gas; or produce micro-structures. The treatment temperature and cooling rate depend on the purpose of treatment and the composition of the heat-treated material.
Hardening: heating and quenching certain iron-based alloys at or above the critical temperature range. The heating temperature and the length of time or "holding time" at this temperature depend on the composition of the material. The quenching medium used may depend on the hardness required for the composition and the complexity of the design.
Tempering: Harden the iron-based alloy to a temperature below the critical temperature range before heating, and then proceed to the required cooling rate. The purpose of tempering is to eliminate strain and reduce hardness and brittleness.