HEAT TREATMENT TERMINOLOGY

AUSTENITE - The solid solution of iron and carbon achieved by heating to high temperatures above the upper critical temperature. Known as the austenitizing temperature, this temperature must be attained to obtain the proper 
microstructure and full hardness of steel in heat treating. Austenitizing temperature varies with different grades of carbon, alloy and tool steels.

BAINITE - A product of austenite, this term is used by metallurgists to describe a particular structure of steel when the steel is polished, etched and examined with a microscope.

ANNEALING - A term that refers to softening metals by treating with sustained heat at the required temperature, followed by cooling at a controlled rate, while at the same time, producing desired results in other properties or microstructure. Annealing generally refers to slow cooling in carbon and allow steels, with the focus usually being on removing stresses; inducing softness; altering ductility, toughness, electric, magnetic or other physical and mechanical properties; changing the crystalline structure; and finally producing a definite microstructure.

CARBURIZING - Adding carbon to the surface of ferrous alloys to facilitate hardening by quenching directly from the carburizing temperature, or by cooling then reaustenitizing and quenching.

CASE HARDENING - A term referring to a combination of heat treatments of steel involving processes that change the chemical composition of the surface layers by absorption of carbon, nitrogen, or a mixture of the two. The end result is a surface that is substantially harder. The processes are known individually as carburizing, cyaniding, carbo-nitriding and nitriding.

CYANIDING - Surface hardening of steel by carbon and nitrogen absorption through heat treating at a specific temperature while in contact with cyanide salt, and following with quenching.

DECARBURIZATION - Loss of carbon from the surface layer of a carbon-containing alloy when the metal is subjected to high temperatures. The loss of carbon at the surface reduces the strength of the part.

INDUCTION HARDENING - A surface-hardening process in which only the surface layer of a ferrous metal is heated by electromagnetic induction and immediately quenched.

TEMPERING - Also know as drawing, this process involves reheating previously hardened or quenched steel to a temperature below the lower critical temperature, and followed by cooling. Tempering temperatures range from 300° to 1100° F.