| 摘要 |
PURPOSE:To obtain a tin-free steel sheet for a welded can having superior corrosion resistance and weldability by successively forming a specified amount of metallic Cr layer and a specified amount of a nonmetallic Cr layer on the surface of a steel sheet and by projecting part of the metallic Cr. CONSTITUTION:The surface of a steel sheet is degreased, pickled and plated with Cr in an aqueous soln. contg. Cr<6+>. Electrolysis is then carried out in the same soln. using the steel sheet as an anode, and the steel sheet is treated as a cathode in an aqueous soln. contg. a Cr plating assistant and Cr<6+>. Thus, 40-150mg/m<2> metallic Cr layer and 5-25mg/m<2> nonmetallic Cr layer are successively formed on the surface of the steel sheet. Part of the metallic Cr has projections. The metallic Cr layer is not porous and covers the entire surface of the steel sheet, so the corrosion resistance before painting is improved. The projections improve the weldability.
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