| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-tensile-strength hot-dip galvanized steel sheet consisting of a complex metal structure superior in formability for an extension flange, a strength-ductility balance and strain age-hardening properties, having a TS of 440 MPa or higher, and to provide a manufacturing method therefor. SOLUTION: The steel sheet includes 0.01 to 0.10% C, 0.0050 to 0.0250% N, 0.05 to 1.0% Mo, while N/Al is 0.3 or more, and 0.0030% or more dissolved N, and satisfies the expression 12(C+N)+Mn-Si among C, N, Mn and Si so as to be 0.5 to 2.0. The manufacturing method comprises the sequential steps of: heating the above steel slab; rough-rolling and finish-rolling it; hot-rolling it and winding a steel sheet at 750°C or lower; cold-rolling the steel sheet; annealing the steel sheet including heating between(Ac<SB>3</SB>-50°C) and (Ac<SB>3</SB>+50°C) and subsequent cooling it in two stages; removing a component densified layer; hot-dip galvanizing the sheet including both of annealing it before plating which heats the sheet at a temperature between Ac<SB>1</SB>and (Ac<SB>1</SB>+50°C), and hot-dip galvanizing it; or further an alloying the sheet. COPYRIGHT: (C)2004,JPO&NCIPI
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