| 摘要 |
PURPOSE:To manufacture inexpensively the titled steel sheet superior in thread rust resistance, by applying suitable quantities of metallic chromium plating and tin plating on steel sheet, then applying heat treating, further suitable chromate treatment or electrolytic chromic acid treatment to said sheet. CONSTITUTION:Metallic chromium plating is applied on steel sheet at 10-150mg/m<2> per one side surface. Next, tin is plated at 0.1-1.0g/m<2> while removing remaining hydrated chromium oxide. Thereafter, plated steel sheet is heated to 240-350 deg.C to melt tin. By this way, tin layer is made to island state and discontinuous cover having good adhesive property. Further the steel sheet is chromate treated to form hydrated chromium oxide of 2-20mg/m<2> calculated in chromium, or electrolytically chromic acid treated to form 3-30mg/m<2> metallic chromium and hydrated chromium oxide of 2-20mg/m<2> calculated in Cr.
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