| 摘要 |
PROBLEM TO BE SOLVED: To stably provide a high strength hot rolled steel plate excellent in workability, having a strength-and-ductility balance satisfying [tensile strength(TS)×[total elongation(T.El)]>=24,000MPa%. SOLUTION: This hot rolled steel plate has a composition which consists of, by weight, 0.09-0.22% C, 2.0-4.0% Si, 1.5-2.5% Mn, <=0.02% P, <=0.01% S, 0.001-0.10% Al, <=0.01% N, and the balance iron with inevitable impurities and in which the contents of Si and Mn satisfy Si/Mn>=1.3. Further, this hot rolled steel plate has a structure composed essentially of ferrite in >=50% by volume occupancy and retained austenite including >=3.0% retained austenite free from strain induced transformation even at the time of application of 10% strain and having the balance consisting of bainite or martensite or both of them.
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