MANUFACTURE OF TIN-FREE STEEL WITH SUPERIOR RESISTANCE TO RETORTING

PURPOSE:To obtain the titled steel for a can by subjecting a steel sheet to reverse electrolysis using the sheet as an anode between a Cr plating stage and an electrolytic chromating stage while restricting the current density and the quantity of electricity. CONSTITUTION:A steel sheet is plated with metallic Cr by cathodic electrolysis in an aqueous soln. contg. Cr as the principal component. The plated sheet is subjected to anodizing (reverse electrolysis) in the soln., and it is electrolytically chromated in an aqueous soln. contg. >=1 kinds of compound selected from chromic anhydride, dichromates and chromates to obtain a tin-free steel (TFS). Said reverse electrolysis is carred out while satisfying equations I -III [where x is current density (A/dm ), and y is the quantity (C/dm ) of electricity].