Hot-bath burnishing is a chemical method in which an iron oxide layer ((Fe3O4) is applied on the surface of the workpieces to be treated (approx. 0.002 mm).
After the treatment, the components show a decorative dark grey/black appearance.
The surface is protected against corrosion to a certain extent. Increased corrosion protection is achieved, if a suitable anti-corrosion oil is used in addition.
Since there is only a substrate conversion resulting from the oxidic reactions of the burnishing salt with the component surface under heat, changes in the geometry cannot occur.
Burnishing layers are resistant to greases and oils and most additives making them ideal for tribological stresses. Any existing passivation layers must be removed prior to oxidation.
It is possible to burnish unhardened, hardened and nitrated surfaces.