Tempering

Tempering is a heat treatment that reheats hardened steel below its transformation temperature. It reduces brittleness and adjusts hardness by changing the steel’s microstructure.

Martensite: A hard, brittle steel microstructure formed when austenite transforms rapidly during quenching. Tempering modifies the martensite produced by hardening, reducing its brittleness.
Heat treatment: The controlled heating and cooling of a material to change its structure and properties. Tempering is one stage in the broader family of heat treatments.
Tool steel: A family of alloy steels designed to retain hardness and resist wear during cutting, forming, or machining. Tempering tunes tool steel hardness while limiting brittleness in service.
Annealing: A heat treatment that softens a material and improves ductility by heating and controlled cooling. Annealing generally softens steel more extensively than tempering hardened steel.
Tempered martensite: A steel microstructure formed when martensite decomposes during tempering into ferrite and fine carbide particles. It is the characteristic product of tempering hardened steel.
Austenitizing: Heating steel until its structure becomes predominantly austenite before a subsequent cooling treatment. Hardened steel is commonly austenitized before quenching and later tempering.
Spring steel: Steel formulated and processed to undergo elastic deformation and return to its original shape. Tempering helps springs combine strength with resistance to fracture.
Normalizing: A steel heat treatment involving austenitizing followed by cooling in still air. Normalizing resets steel’s structure from austenite, while tempering starts with hardened steel below transformation.
Carbide precipitation: The formation of solid carbide particles from carbon dissolved in a metal matrix. Fine carbides form as carbon leaves martensite during tempering.
Quenching: Rapidly cooling a heated material to produce a desired structure or suppress slower transformations. Quenching creates the hard, brittle structure that tempering then modifies.

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