| 摘要 |
PURPOSE: To obtain the steel sheet excellent in corrosion resistance, particularly in contaminant rust resistance. CONSTITUTION: This steel sheet is obtained by coating a plated steel sheet with a chromate solution contg. Cr<3+> ions in a 30 to 80% ratio, organic and inorganic phosphoric acids in amounts to provide a ratio of the total concn. of these phosphoric acids to the chromic acid concn. of 0.5 to 3.0 and 1.0 to 150g/l of a water-soluble organic high polymer and thereafter, further subjecting the resulting steel sheet to organic thin film coating with an epoxy resin, urethane resin or the like. Thus, by adding the organic phosphoric acid and the water-soluble organic high polymer to the chromate solution, a chromate coating film excellent in chromium dissolution resistance and rust resistance is formed on a plated steel sheet and by further subjecting the resulting steel sheet to organic thin film coating, the objective steel sheet excellent in corrosion resistance (particularly in contaminant rust resistance) can be obtained.
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