| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel sheet applicable to members requiring hole expansibility such as automobile members and brockets, and to provide its production method. SOLUTION: This high strength steel sheet excellent in formability and hole expansibility has a composition containing, by mass, 0.05 to 0.2% C, 1 to 2.5% Si, 0.5 to 2.5% Cu and 0.5 to 3.0% Mn and further containing 0.01 to 2.5% Al and/or at least one or more kinds selected from <2.0% Ni, <0.2% Mo, <1.0% Cr, <0.3% V, <0.01% B, <0.06% Ti, <0.06% Nb, <0.05% Ca and <0.05% Mg, in which the hardness of a ferritic phase is also 150 to 240 by Hv, and further, the volume ratio of retained austenite in the steel structure is 2 to 20%.
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