Heat Treatment

Heat treatment is used in the steel industry for a number of uses. There are a few types of heat treatments. These heat treatments include the processes of annealing, tempering, quenching and normalization.

Annealing is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. This is done by heating the steel and then cooling it again.

Tempering is a process of heat treating, which is used to increase the toughness of steel. Tempering is usually performed after hardening, to reduce some of the excess hardness. This is done by heating the metal to a much lower temperature than what was used for hardening.

Quenching is the rapid cooling of a work piece to obtain certain material properties. It is most commonly used to harden steel. In this process steel is heated and then rapidly cooled.

Normalization is an annealing process in which a metal is cooled in air after heating, in order to relieve stress. This process improves the ductility and toughness of the steel.

Steel Colour vs Temperature

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Temperature °F Colour Temperature °C
2000°F Bright yellow 1093°C
1900°F Dark yellow 1038°C
1800°F Orange yellow 982°C
1700°F Orange 927°C
1600°F Orange Red 871°C
1500°F Bright Red 816°C
1400°F Red 760°C
1300°F Medium Red 704°C
1200°F Dull Red 649°C
1100°F Slight Red 593°C
1000°F Very slight red, mostly grey 538°C
0800°F Dark Grey 427°C
0575°F Blue 302°C
0540°F Dark Purple 282°C
0520°F Purple 271°C
0500°F Brown/Purple 260°C
0480°F Brown 249°C
0465°F Dark Straw 241°C
0445°F Light Straw 229°C
0390°F Faint Straw 199°C

Hardness vs Temperature

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Temperature°F Aproximate Hardness Rc Temperature °C
300°F 63/65 149°C
350°F 62/64 177°C
400°F 61/63 204°C
450°F 60/62 232°C
500°F 58/60 260°C
600°F 55/57 316°C
700°F 51/53 371°C
800°F 48/40 427°C
900°F 44/47 482°C
1000°F 40/44 538°C