JPH05287551

PURPOSE:To form a sparingly soluble chromate coating film excellent in corrosion resistance on the surface of a steel sheet by applying a specific aqueous chromate solution on the surface of a zinc plated steel plate, drying at a specific temp. and cooling immediately with a solution of alcohols. CONSTITUTION:The aqueous chromate solution is applied on the surface of the zinc plated steel plate. The solution having 5-30g/l total chromium conc. and 40-80% chromium reducing ratio contains 10-200g/l phosphoric acid and 0.1-1.0g/l hydrofluoric acid. The steel sheet is dried so as to be 50-200 deg.C plate temp. as the maximum achievable sheet temp. after applying. Then, the steel plate is immediately cooled using the solution of alcohols having >=1.0% conc. as a cooling medium. The chromate coating film of 5-150mg/m per one side in total chromium quantity is formed on the surface. The chromate coating film is sparingly soluble and excellent in corrosion resistance, alkali resistance and coating property and high rust preventive treatment on the galvanized steel sheet is possible by forming this coating film.