| 摘要 |
PROBLEM TO BE SOLVED: To obtain the surface treated steel sheet for welded can by successively forming an iron-Ni alloy layer, an iron-Ni-tin alloy layer with Ni concentration gradient, an iron-Ni-tin alloy layer without Ni concentration gradient, an island-like or granular tin layer, and a chromate film layer, in respectively specified amounts, on the surface of a steel sheet. SOLUTION: After the surface of a steel sheet 1 is subjected to (20 to 200)mg/m<2> Ni quantity of Ni plating or iron-Ni alloy plating, heat treatment is performed is a nonoxidizing atmosphere to form an iron-Ni alloy layer 2 and temper rolling is carried out and an iron-Ni alloy plating of 10-30% Ni content and (5 to 50)mg/m<2> Ni quantity is applied. Subsequently, tin plating of (500 to 2000)mg/m<2> tin quantity in applied and an island-like or granular layer 5 of (100 to 1500)mg/m<2> coating weight is formed by means of reflowing treatment, and also, between the layer 5 and the layer 2, an iron-Ni-tin alloy layer 3 composed essentially of iron-tin alloy, having 0.01-0.3μthickness and also having an Ni concentration gradient in which Ni concentration is decreased with the approach to the layer 2, and a similar iron-Ni-tin alloy layer 4 of 0.001-0.1μthickness, without Ni concentration gradient, then, chromate layer of 10-50mg/m<2> is depositted, are formed. Then, a chromate film layer of (10 to 50)mg/m<2> coating weight is formed.
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