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

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

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

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