| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel sheet having excellent fatigue crack propagation resistance. SOLUTION: The steel sheet has a composition containing 0.03 to 0.30% C,≤0.5% Si, 0.8 to 2% Mn, 0.01 to 0.1% Al,≤0.010% N,≤0.03% P and≤0.01% S, and the balance Fe with inevitable impurities, and in the position of the depth t/4(t=sheet thickness) viewed from the Z direction (sheet thickness direction), residual austenite is present by 1.0 to 10.0% by an area fraction, and the number density of the residual austenite is 4,000 to 50,000 pieces/mm<SP>2</SP>. COPYRIGHT: (C)2008,JPO&INPIT
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