When steel is heated with a carburizing flame, it becomes red, and as the heating continues, the color of the steel becomes progressively lighter, until the thin carbonized surface layer begins tomelt.This takes place at approximately a white heat, about 1200°C (2200°F). The welding rod is then melted and flowed over this sweating surface with the flame of the torch. No attempt should be made to puddle with the rod. It will flow and spread like solder when the surface is properly heated, and will adhere to the base metal, resulting in a weld that is actually stronger than the alloy itself.