| 摘要 |
PROBLEM TO BE SOLVED: To provide a surface treated galvanized steel sheet having excellent corrosion resistance equal to that by chromate treatment. SOLUTION: On the surface of a galvanized layer or a galvannealed layer, a film of a molybdenum compd. of 10 to 120 mg/m2 coating weight expressed in terms of Mo, a phosphoric compd. of 0.2 to 2 as the weight ratio expressed in terms of P/Mo and an organic compd. having an oxycarboxylic acid group by the coating weight of 5 to 300 mg/m2 is formed. The Mo-contg. film is formed by coating a galvanized steel sheet or a galvannealed steel sheet with a water base treating soln. contg. molybdate ions of 1 to 100 g/l expressed in terms of Mo, phosphate ions of 0.2 to 2 by the weight ratio expressed in terms of P/Mo and oxycarboxylic acid of 1 to 300 g/l and contg., and need, oxalic acid of 1 to 300 g/l in total with the content of oxycarboxylic acid by 10 to 120 mg/m2 coating weight expressed in terms of Mo, and, without executing water washing, it is dried under heating at 50 to 200 deg.C sheet temp.
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