Metallurgy

 

Color Temperatures of Carbon Stee

The approximate temperatures at which various colors appear as carbon steel is heated or cooled are shown in the following table.

Note: There is some variation in the temperature ranges, depending on the exact composition of the steel. There is also considerable variation in the temperatures and color-designation terminology used in various sources. The informaton provided in the table should be considered as a guide.

 

Color Temperatures

Color	Fo	Co	Comments
White	2200	1205
Light Yellow	1975	1080
Lemon	1830	1000
Orange	1725	940
Salmon	1652	900	At 912 degrees C/1674 degrees F alpha-iron transforms to gamma-iron (austenite). This is the usual temperature at which iron is forged.
Bright Red	1544	840
Cherry or Dull Red	1375	745
Medium Cherry	1275	690
Dark Cherry	1175	635
Blood Red	1075	580
Faint Red	930	500
Black Heat	788	420
Light Blue	640	338	Faint Straw through Light Blue is the tempering range for carbon steel. These colors are due to a very thin oxide layer that forms on the steel. The temperatures at which the colors appear will vary for alloy steel. Some higher alloys of steel show no temper colors. Note: Colors may appear different, depending on the lighting. These colors should be observed under a dim light, but never a flourescent light, which completely misleads color judgement.
Full Blue	590	310
Peacock	540	282
Bronze	520	271
Deep Straw	475	246
Straw	440	227
Faint Straw	400	204