| 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 layer contg., as solid contents, 100 pts.wt. resin and 0.1 to 3000 pts.wt. silane coupling agent, and the surface is provided, further thereon, with an organic film layer as an upper layer. The galvannealing layer can moreover contain 0.01 to 2 wt.% Si, and the substrate treatment film layer can contain one or more kinds of, as solid contents, 1 to 2000 pts.wt. particulate silica and 0.1 to 1000 pts.wt. etching fluoride.
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