| 摘要 |
PROBLEM TO BE SOLVED: To produce a chromium-free precoated steel sheet excellent in the corrosion resistance of its worked part and small in environmental loads. SOLUTION: The surface of a steel sheet is provided with a galvannealing layer having a compsn. contg., by weight, 1 to 10% Mg and 2 to 19% Al and the balance Zn, and in which Mg and Al also satisfy Mg(%)+Al(%)<=20%, as a lower layer, the surface is provided, thereon, with a substrate treatment film layer contg., as solid contents, 100 pts.wt. resin and 0.2 to 50 pts.wt. tannine or tannic acid, and the surface is provided, further thereon, with an organic film layer as an upper layer. Preferably, the galvannealing layer moreover contains 0.01 to 2 wt.% Si, the substrate treatment film layer is furthermore incorporated with particulate silica by 10 to 500 pts.wt. as solid contents, the organic film layer is composed of an under coat contg. rust preventive pigment and of a colored finish coat, and an Ni plating layer is provided below the galvannealing layer.
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