The bare steel should be treated with a metal cleaning liquid, Metal-Prep, Aluma-Prep, Galva-Prep as examples. These solutions clean the metal chemically and also etch the surface to increase adhesion. Apply the solution with a CLEAN/NEW brush, scratch pad, cotton rag. Watch the surface of the steel as you clean the area, you will be able to see the liquid bead up if the steel is still dirty, the solution will "sheet" when the surface is clean, then rinse with clean water.
