| 摘要 |
PROBLEM TO BE SOLVED: To provide a low corrosion rate and high strength hot rolled steel sheet having tensile strength of >=590 N/mm2 and having excellent hole expansibility and ductility. SOLUTION: This steel sheet has a composition containing, by weight, 0.01 to 0.20% C, 0.05 to 1.5% Si, 0.5 to 2.5% Mn, 0.03 to 0.2% P, <=0.09% S, 0.1 to 1.0% Cu, 0.1 to 1.0% Ni, <=0.010% N, 0.0005 to 0.01% Mg, 0.002 to 0.07% Al and one or two kinds of 0.003 to 0.25% Ti and 0.003 to 0.04% Nb, and the balance iron with inevitable impurities. Also the steel sheet contains MgO whose particle size is within 0.005 to 5.0μm or multiple oxide containing the MgO and one or more kinds of Al2O3, SiO2, MnO and Ti2O3 by 1.0×103 to 1.0×107 pieces/mm2 by controlling the oxide and has a steel structure mainly consisting of ferritic structure and the balance bainitic structure.
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