steel when heated, the surface layer of the carbon and oxygen in the medium, hydrogen, carbon dioxide and water vapor react, reducing the surface carbon concentration is called decarburization, the surface hardness of the steel after hardening off, fatigue strength and abrasion is lowered, and the surface forms a residual tensile stress crack mesh is easy to form a surface.

When heated, the surface layer of the steel and iron and alloy element or media as oxygen, carbon dioxide, water vapor and other phenomena occur in the reaction of the oxide film is called oxidation. After the high temperature oxidation of the workpiece dimensional accuracy and surface brightness deterioration of the oxide film having poor hardenability of steel prone to quenching soft spots.

In order to reduce oxidation and decarbonization measures to prevent are: surface coatings, stainless steel foil packet sealed heated salt bath heating, the use of protective atmosphere heated flame burner.