Oxidation: Oxidation in its original sense is the chemical reaction of a substance with oxygen (formation of oxides).

Scaling: Oxidation process above approx. 500°C, in which the atmospheric oxygen reacts with the red-hot material to form iron oxide Fe3O2 - "scale".

Scale forms where oxygen has free access to the tool cutting edge, i.e. the ends on the free, rake face. But oxidation can also occur on the workpiece surface.

Again, oxidation occurs at temperatures exceeding the hot strength of some tool materials (tool and high speed steels).