Quenching and tempering (quenching and drawing) is a conventional process used to harden or strengthen steel or ferrous alloys. In the first step, the ferrous alloy is transformed to austenite and then quenched in water, brine water, air or oil. During the quenching step, the austenite is converted to martensite in a diffusionless shear reaction. Martensite is very hard, but too brittle for practical use in the untempered state. The quenched alloy is then tempered (drawn) or heated at an intermediate temperature to transform the brittle martensite into a very fine dispersion of cementite (iron carbide) phase in an iron ferrite matrix. Tempered martensite or tempered steel is the product of a conventional hardening process. The martensite transformation is a diffusionless reaction that proceeds rapidly (at the speed of sound) as a shear wave through the material. Careful control is required to avoid or reduce any distortion and cracking that may occur due to the rapid martensite transformation. In some cases, a martempering process is advisable to avoid cracking.
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