Removal of surface oxide from steel after hot rolling. Steel at high temperatures reacts with the environment, producing a phenomenon of surface oxidation that results in the generation of ferrous oxide and ferric oxide on the surface of the pieces, generating a hard, fragile and abrasive layer that can produce damages in subsequent processes in cold.
Pickling can be mechanical or chemical.
In the mechanical pickling, the surface iron oxide layer is removed by bending and twisting methods which cause the oxide to peel off.
The chemical pickling consists of introducing the pieces into an acid bath (hydrochloric or sulfuric) until the oxide is removed.