Pyrometallurgical Cleaning
The thermally induced removal of oxides and contaminants on the metal surface immediately prior to the wetting process. This is often accomplished through reducing furnace atmospheres.
Pyrometallurgical cleaning is basically an annealing process under a reducing atmosphere. You heat the part in the furnace to temperature so that the oxides on the surface decompose and you get a clean, metallically bright surface for welding. This is especially important for heavily scaled or rusty parts, because you don't introduce contaminants into the weld. But be careful not to overdo the material. If you get too hot or the atmosphere isn't right, you'll alter the structure or burn off the alloying elements, and then you'll have a hard, brittle weld or a part that won't weld cleanly anymore. After annealing, you must work and weld the surface promptly, otherwise it will oxidize again.