| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength steel sheet having excellent stretch flange formability. SOLUTION: The high strength steel sheet having excellent stretch flange formability has a composition comprising, by mass, 0.03 to 0.3% C, 0.1 to 2.0% Si, 1.0 to 3.5% Mn,≤0.05% P,≤0.01% S, 0.0005 to 0.01% N,≤0.01% acid soluble Al, <0.005% acid soluble Ti, one or two kinds selected from Nd and Pr by 0.0002 to 0.02% in total, and the balance iron with inevitable impurities. The steel comprises inclusions of one or two kinds selected from Nd oxides and Pr oxides by 2 to 70% in total, 2 to 60% SiO<SB>2</SB>, and≤70% Al<SB>2</SB>O<SB>3</SB>as average inclusion compositions. COPYRIGHT: (C)2008,JPO&INPIT
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