Tool Steel Color 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
Steel exhibits different colors depending on temperature. Temperatures above 800°F (427°C) produce incandescent colors; the atoms in the steel are so energized by heat that they give off photons. Temperatures below 800°F (427°C) produce oxidation colors. As the steel is heated, an oxide layer forms on the surface; its thickness (and thus the interference color as light is reflected) is a function of temperature. These colors may be used in tempering tool steel.
I hope this will help
Casey
