n.
Heat-treating of metal alloy s, particularly steel , to reduce brittleness and restore ductility .
In tempering, steel is slowly heated to a temperature between 300 and 1,300 °F (150 and 700 °C), depending on desired properties, in an oil or salt bath and held for about two hours and then allowed to air cool. As steel is physically worked (e.g., rolling , wiredrawing , hammering), hardening takes place, and it grows progressively more brittle. Similarly, but more deliberately, heating and quenching increase hardness. Combined quench-and-temper heat-treating is applied at many different cooling rates, holding times, and temperatures and is a very important means of controlling the properties of steel.