Heating a metal or alloy to such a high temperature that its properties are impaired. When the original properties cannot be restored by further heat treating, by mechanical working, or by a combination of working and heat treating, the overheating is known as burning.
Failure of tools and components in heat treatment can arise through overheating. This may be caused due to quenching from a temperature too high for the type of steel involved. Overheating is evidenced by cracking, grain-coarseness, erratic surface hardness and pitting.