| 摘要 |
A high tensile strength steel sheet excellent in processibility which can satisfy a strength, a total elongation, and stretch-flanging property (hole enlarging rate) at a further high level and comprises a matrix microstructure of tempered martensite or tempered bainite and, if necessary, ferrite, and a second phase of retained austenite, wherein (1) the steel comprising C: 0.10 to 0.6 mass %, Si: 1.0 mass % or smaller, Mu: 1.0 to 3 mass %, Al: 0.3 to 2.0 mass %, P: 0.02 mass % or smaller, S: 0.03 mass % or smaller, (2) a volume rate of retained austenite obtained by a saturated magnetization measuring method is 5 to 40% by area (whole field is 100%), and (3) a relationship of a carbon amount (C: weight %) in the steel, a volume rate (fgammaR) of retained austenite and a carbon concentration (CgammaR) of the retained austenite satisfies the equation: <?in-line-formulae description="In-line Formulae" end="lead"?>(fgammaRxCgammaR)/C>=50 (I) <?in-line-formulae description="In-line Formulae" end="tail"?>
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