HIGH STRENGTH WITH A HIGH RATIO OF YIELD STRENGTH TO YIELD STRENGTH OF STEEL SHEET, HIGH STRENGTH W

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PROBLEM TO BE SOLVED : To provide a high yield ratio type high strength steel sheet having high strength and a high yield ratio and having excellent formability, and the like.SOLUTION : A high yield ratio type high strength steel sheet has a componential composition including, by mass, 0.03 to 0.20% C, ≤1.0% Si, >1.5 to 3.0% Mn, ≤0.10% P, ≤0.05% S, ≤0.10% Al and ≤0.010% N, and including one or more kinds selected from Ti, Nb and V by 0.010 to 1.000% in total content and the balance Fe with inevitable impurities, and has a structure including ferrite and a second phase as a microstructure. The ferrite has an area ratio of ≥50% and the average crystal grain size of ≤18 μm. The second phase includes martensite of 1 to <7% by area ratio, and the thickness of a band-shaped structure formed by the second phase satisfies a prescribed relational expression.