Steel Tempering Colors

The tempering process of hardening steel

tempering steel color

Tempering steel is a two-step process where the

1. The tool is forged and hardened

  • tool end is heated to bright red color and forged
TemperatureColor of Heated Carbon Steel
2192 1200  
2012 1100  
1922 1050  
1796 980  
1706 930  
1598 870  
1490 810  
1400 760  
1292 700  
1202 650  
1212 600  
  • tool quenched in cold water and cooled until touchable
  • tool is sharpened and polished

2. The tool is tempered

  • tool heated to tempering temperature as indicated below
TemperatureColor of Heated Carbon Steel 
600 316   Scrapers, spokeshaves
560 293   Screwdrivers, springs, gears
540 282   Cold chisels, center punches
520 271   Taps <= 1/4 inch
500 260   Axes, wood chisels, drifts, taps >= 1/ inch, nut taps, thread dies
480 249   Twist drills, large taps, knurls
460 238   Dies, punches, bits, reamers
450 232   Twist drills for hard use
440 227   Lathe tools, scrapers, milling, cutters, reamers
430 221   reamers
420 216   Knives, hammers
  • tool quenched in cold water

Note that oil baths and salt bats are also used extensively for tempering steel tools. Lead baths and sand baths are also used. 

If steel is heated in an oxidizing atmosphere - like air - a film of oxide forms on the surface and the color changes as the temperature increases. The colors are affected to some extent by the composition of the steel and the method may not be dependable.

Related Topics

  • Miscellaneous - Engineering related topics like Beaufort Wind Scale, CE-marking, drawing standards and more
  • Material Properties - Material properties for gases, fluids and solids - densities, specific heats, viscosities and more

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