| 摘要 |
<p>A low cost, a high strength steel sheet which exhibits excellent chipping resistance, low YP, high BH and high El and, further, exhibits a small change in material quality in a coil, and a method for manufacturing the steel sheet are provided. A high strength steel sheet is formed of steel having the composition containing by mass% over 0.015% and less than 0.100% C, less than 0.50% Si, over 1.0% and less than 2.0% Mn, 0.05% or less P, 0.03% or less S, 0.01% or more and 0.3% or less sol. Al, 0.005% or less N, less than 0.35% Cr, 0.0010% or more and 0.0050% or less B, less than 0.15% Mo, less than 0.030% Ti, and iron and unavoidable impurities as a balance, wherein the steel satisfies 2.1‰¤[Mneq]‰¤3.1, the microstructure of the steel includes a ferrite and a second phase, a volume fraction of the second phase is set to 2.0 to 12.0%, a total ratio of a volume fraction of martensite and a volume fraction of retained ³ to the volume fraction of second phase is 60% or more, and the number of carbides which are present within ferrite particles, have an aspect ratio of 3.0 or less and have a diameter of 0.25 to 0.90µm is set to 10000 pieces/mm 2 or less. Here, [Mneq]=[%Mn]+1.3[%Cr]+3.3[%Mo]+8[%P]+150B*, B * = % B + % Ti / 48 × 10.8 × 0.9 + % Al / 27 × 10.8 × 0.025 ,
and B * = 0.0022 when B * satisfies B * ‰¥ 0.0022.</p> |
