Iron and steel thermal processing terms explained
Iron and steel thermal processing is an important aspect of the manufacturing process for many products. It is important to understand the various aspects of this process in order to properly produce a quality product.
Annealing: Annealing is a heat treatment process that is done in order to soften the steel and make it more workable. It occurs by heating the steel to near its recrystallization temperature and then cooling it very slowly in order to relieve the internal stresses that were generated by prior cold working or even welding.
Normalizing: Normalizing is a heat treatment process that is done in order to refine the crystal structure within the microstructure of the steel and to improve its mechanical properties. It occurs by heating the steel to a specific temperature, typically above the Ar1 transition temperature, and then cooling it in the air.
Quenching: Quenching is a heat treatment process used to increase the hardness of the steel by introducing a specific cooling rate to the steel. The cooling rate is either fast, known as a martensitic transformation, or slow, known as a precipitation hardening transformation.
Stress relieving: Stress relieving is a heat treatment process used to reduce the internal stresses caused by welding or cold working. It typically occurs by heating the steel to just below its austenitic transformation temperature and allowing it to cool slowly in an inert environment.
Tempering: Tempering is a heat treatment process used to increase the wear resistance of the steel by introducing a specific cooling rate to the steel. The cooling rate is typically slower than that used for quenching and creates a softer microstructure that is more resistant to wear.
Carburizing: Carburizing is a heat treatment process used to increase the surface hardness of the steel by introducing carbon into the surface. It typically occurs by heating the steel to a specific temperature, usually near its austenitic transformation temperature, and then introducing carbon in the form of a gas or liquid.
Austempering: Austempering is a heat treatment process used to increase the toughness of the steel by introducing a specific cooling rate to the steel. It typically occurs by heating the steel to a specific temperature, usually above its Ar1 transformation temperature, and then cooling it at a rate slower than that used for quenching.
Induction hardening: Induction hardening is a process used to heat the steel to a specific temperature, usually above the Ar3 transformation temperature, and uses an assisting medium (either gas or liquid) to transfer heat to the steel. It is typically used to produce a hard and wear resistant surface on the steel.
Heat treatment: Heat treatment is a process that affects the chemical and physical structure of the steel by introducing a specific temperature, time, and atmosphere to the steel. It is used to create a desired microstructure, hardness, and strength and to improve the dimensional stability of the steel.
Vacuum carburizing: Vacuum carburizing is a process used to increase the surface hardness and wear resistance of the steel by introducing carbon in a controlled, vacuum environment. The process is used to allow for better control of the carburization rate, temperature, and atmosphere and is typically used for components that need high surface hardness and wear resistance.
Nitriding: Nitriding is a heat treatment process used to increase the hardness of the steel by introducing nitrogen into the surface. It typically occurs by heating the steel to a specific temperature, usually near its austenitic transformation temperature, and then introducing nitrogen in the form of a gas or liquid.
Salt bath nitrocarburizing: Salt bath nitrocarburizing is a process of introducing nitrogen and carbon into the steel in a liquid bath five at a specific temperature, typically above the Ar2 transformation temperature. It is typically used to increase the surface hardness and wear resistance of the steel while minimizing distortion of the part.
Cryogenic treatment: Cryogenic treatment is a heat treatment process used to increase the toughness and wear resistance of the steel by introducing a controlled cooling rate to the steel. It occurs by cooling the steel to -320°F and holding it there for 8-48 hrs before allowing it to slowly come back to room temperature. This process creates a more uniform and consistent microstructure throughout the steel and improves its mechanical properties.
