COATED STEEL SHEET EXCELLENT IN CORROSION RESISTANCE

摘要

PROBLEM TO BE SOLVED: To produce a coated steel sheet which is subjected to rust preventive treatment with a chrome-free substrate treating agent to take place of chromic acid treatment and phosphate treatment and has excellent corrosion resistance. SOLUTION: This coated steel sheet having the excellent corrosion resistance is obtained by forming a film consisting of the substrate treating agent containing (A) an aqueous liquid containing at least one kind of a titanium compound selected from a hydrolyzable titanium compound, a low condensate of the hydrolyzable titanium compound, titanium hydroxide and a low condensate of the titanium hydroxide (B) at least one kind of a compound selected from a phosphoric acid-base compound, metal hydrofluoric acid and a metallic hydrofluorate and (C) an aqueous organic high-molecular compound stable at a pH <=7 on the surface of a substrate metallic material and forming a finish coating film through or without through a primer coating film on the surface treated film.