SURFACE-TREATED STEEL SHEET FOR SEAM WELDING CAN HAVING EXCELLENT WELDABILITY

摘要

PURPOSE:To provide a titled surface-treated steel sheet provided with corrosion resistance and adhesion of a coated film after painting by forming adequately a metallic tin layer having many projecting parts on the surface and forming further an adequate chromate film layer thereon. CONSTITUTION:A metallic tin layer having many projecting parts is formed on the surface of a degreased and pickled steel sheet and is so adjusted that the area of the respective projecting parts mentioned above is 1-800,000mum<2>, the area per cent occupied by the projecting parts is 20-80% and the thickness of the metallic tin in the projecting parts is 0.007-0.70mum. A chromate film layer consisting of chromium oxide hydrate or metallic chromium and chromium oxide hydrate is formed on the top layer of said metallic tin and is so adjusted that the total chromium weight in the chromate coating layer is <=30mg/m<2> and the chromium oxide hydrate weight is 3-25mg/m<2>. The above-mentioned projecting parts are formable by a method for electrodepositing tin or the like by electroplating via a masking sheet having fine holes.