| 摘要 |
PROBLEM TO BE SOLVED: To develop a technique by which the blackening of a steel sheet can effectively be improved without a treatment with an Ni/Co ion-containing solution and even if skinpass rolling is performed. SOLUTION: A continuously-annealed steel sheet is dipped into a galvanizing bath containing, by mass, 0.15 to 0.3% Al, and is galvanized. After that, the steel sheet is heated at 420 to 600 deg.C, and 0.25 to 1.0% Al and 0.5 to 6.0% Fe are incorporated into the plating film. Then, the steel sheet is subjected to the chromate treatment in which the ratio of trivalent chromium to the total Cr contents (Cr<3+> /T.Cr) is 35 to 60%, and coating weight is 10 to 100 mg/m<2> in terms of metal chromium.
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