TheTempest:
breakable with pleasure.
Wikipedia:
The steel is then tempered by heating between the ranges of 150–260 °C (302–500 °F) and 370–650 °C (698–1202 °F). Tempering in the range of 260–370 °C (500–698 °F) is sometimes avoided to reduce temper brittling. The steel is held at that temperature until the carbon trapped in the martensite diffuses to produce a chemical composition with the potential to create either bainite or pearlite (a crystal structure formed from a mixture of ferrite and cementite). When producing a truly bainitic or pearlitic steel the steel must be once again taken up to the austenite region (austenizing) and cooled slowly to a controlled temperature before being fully quenched to a low temperature.