| 摘要 |
PURPOSE:To obtain a chemically treated steel sheet having a chromate surface layer ensuring improved corrosion resistance and adhesion to paint by treating a zinc (alloy) plated steel sheet with a treating soln. contg. Cr and P to form a first coating film and by treating the film with a treating soln. contg. P and Si to form a second coating film. CONSTITUTION:A steel sheet plated with zinc or a zinc alloy such as Zn-Ni is treated with a treating soln. contg. Cr and P, e.g., an aq. soln. contg. chromic anhydride and phosphoric acid to form a first coating film satisfying Cr/P=0.1-10 and Cr+P>=5 mg/m<2>. The corrosion resistance of the film is further improved by adding a water-soluble or water-dispersible org. resin to the treating soln. The film is then treated with a treating soln. contg. P and S to form a second coating film satisfying P/Si=0.1-10 and P+Si>=0.5 Mg/m<2>. Since the second coating film contains no Cr, the adhesion to paint and the resistance to leaving of fingerprints can be especially improved. |
