| 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, Mn: 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 (f gamma R) of retained austenite and a carbon concentration (C gamma R) of the retained austenite satisfies the equation: <DF NUM="(I)">(f gamma R x C gamma R) / C≥50 </DF> |
