Scale-Induced Segregation
Local concentration changes at the material surface caused by selective oxidation of certain alloy constituents at high temperatures. This sustainably alters the near-surface chemical composition.
Scaling segregation occurs when certain alloying elements are oxidized away at the surface during heating. This changes the composition there, and the surface can cause problems during subsequent welding – such as poorer wetting or porosity. It becomes particularly critical when the edge zone becomes brittle or reacts differently than the rest of the workpiece. Make sure to clean the surface before welding and avoid unnecessary heat input. If the scaling is too heavy, you have to grind or mill it off beforehand, otherwise the weld won't hold cleanly.