| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength multiple-layered steel sheet with good press formability and wettability to plating, a high strength hot-dip Zn based- galvanized multiple-layered steel sheet, a high strength alloyed hot-dip galvanized multiple-layered steel sheet, and their manufacturing method. SOLUTION: A base material has an inner layer which is composed of C: 0.05 to 0.15, Si: 0.4 to 2.0, Mn: 1.5 to 2.8, Al: 0.005 to 0.5 in mass % with Fe and inevitable impurities as the balance, satisfying the relationships (%Mn)/(%C)>=15, and (%Si)/(%C)>=4, where %C, %Si, %Mn are contents of C, Si, Mn respectively, while its surface layer is composed of C: 0.05 to 0.15, Si: 0.4 to 2.0, Mn: 1.5 to 2.8, Al: 0.005 to 0.5, Ni: 0.01 to 5.0, Cu: 0.01 to 5.0 in mass % with Fe and inevitable impurities as the balance. The high strength multiple-layered steel sheet with good wettability to plating and high press formability is characterized in the above multiple-layers.
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