Black oxide finish
Black pickling is a chemical process to produce a thin iron oxide layer on steel surfaces, offering corrosion protection and darkening the appearance.
Physico-chemical Mechanism of Action
Black pickling forms through a chemical reaction between the steel and the air. The surface material iron reacts with oxygen to form iron oxide. This process can be accelerated by coating agents.
Metallurgical Relevance & Risks in Welding
The iron oxide layer protects the steel from corrosion and gives it a black color, hence the name. If applied incorrectly or at too high a concentration, the layer can become too thick and make the workpiece visually unattractive. Furthermore, it can cause difficulties during welding, as it acts as a barrier layer and hinders the bonding of metals.
Workshop Practice & Action Instructions
Use black pickling in the workshop for corrosion protection or optical alteration of steel. Make sure to control the concentration to produce a thin layer. When welding, it is important to clean the surface thoroughly beforehand and, if necessary, remove the iron oxide layer to ensure a clean bonding seam.