PRODUCTION OF SURFACE TREATED STEEL SHEET FOR WELDED CAN HAVING SUPERIOR WELDABILITY, ADHESION OF PAINT AND CORROSION RESISTANCE AFTER PAINTING

摘要

PURPOSE:To produce a surface treated steel sheet for welded cans having supe rior adhesion of paint and superior corrosion resistance after painting, by subjecting the surface of a steel sheet to Ni-Fe alloy plating, tinning and melting treatment and by depositing a chromate film under specified conditions. CONSTITUTION:The surface of a steel sheet is plated with an Ni-Fe alloy contg. 2-25wt.% Ni to form an Ni-Fe alloy layer by 50-400mg/m2 an Sn layer is formed on the alloy layer by tinning by =about 2,500mg/m2. After reflow treat ment is carried out, the steel sheet is immersed in a soln. contg. 10-200g/l chromic anhydride and 0.01-10.0g/l fluorine and sulfur compds. as auxiliary. In the soln., the steel sheet is cathodically treated at 1-200A/dm2 current densi ty to deposit a chromate film by 1-10mg/m2 (expressed in terms of Cr). Thus, a surface treated steel sheet for cans having superior adhesion of paint and improved seam weldability is obtd. even in case where the chromate film is thin.