Local overheating during grinding that either retempers the hardened surface and drops its hardness or, when severe, takes it above the critical temperature so it rehardens as untempered martensite over a softened zone. Both leave tensile residual stress and can start grinding cracks. Burn is found by nital etch inspection or Barkhausen noise, and if it shows as visible discoloration it is already severe.
Etch shows grinding burn on half the cams, the wheel was loaded and they were hogging 0.002 a pass.
Also heard as
- grind burn
- grinding abuse
- temper burn
Related terms
Nital etch
An etch of nitric acid in alcohol that reveals steel microstructure and grinding damage.
White layer
The thin, hard compound layer of iron nitrides that forms on the surface during nitriding.
Tempering
Reheating hardened steel below its lower critical temperature to trade some hardness for toughness.