| 摘要 |
PURPOSE:To manufacture a tin-free steel sheet with superior adhesion to paint by specifying the concn. of sexivalent Cr in a base and the concn. of F in a compound contg. F as an auxiliary in electrolytic chromating. CONSTITUTION:A steel sheet is plated with metallic Cr by cathodic electrolysis in an aqueous soln. contg. Cr, and the Cr plated steel sheet is anodized (reversely electrolyzed) in the Cr plating soln. The reversely electrolyzed steel sheet is electrolytically chromated in an aqueous soln. contg. >=1 kinds of compounds selected among chromic anhydride, chromates and dichromates as principal components. At this time, the concn. of sexivalent Cr in the base in the bath is adjusted to 0.2-1.4mol/l in terms of CrO2, and a compound contg. F such as H2SiF6 or HBF4 is added as an auxiliary in 1/1,000-1/20 molar ratio of F<->/Cr<6+>.
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