| 摘要 |
PURPOSE:To simply produce a steel sheet coated with Sn-based multilayered plating and having superior adhesion to paint by successively forming specified amts. of Ni-based underlayers by plating and Sn layers by tinning on the front and rear sides of a steel sheet, carrying out melting treatment by heating, and forming chromate layers. CONSTITUTION:A steel sheet is plated to form Ni-based underlayers on one side of the sheet corresponding to the inside of a can by 10-80mg/m<2> (expressed in terms of Ni) and on the other side corresponding to the outside of the can by 30-1,000mg/m<2>. The plated sheet is tinned to form Sn layers on the side of the sheet corresponding to the inside of the can by 500-1,500mg/m<2> and on the side corresponding to the outside of the can by <=1,000mg/m<2>. The sheet is then heated to carry out melting treatment. By this treatment, all the Sn on the side of the sheet corresponding to the outside of the can is alloyed to improve the adhesion to paint. Free Sn is left on the side corresponding to the inside of the can by the irreducible min. amt. required to obtain weldability and corrosion resistance. Chromate layers are further formed on the sheet by 1-50mg/m<2> (expressed in terms of Cr). Thus, a steel sheet for a welded can coated with Sn-based multilayered plating and having superior adhesion to paint, satisfactory weldability and corrosion resistance is obtd.
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