| 摘要 |
<p>An object of the present invention is to provide a high tensile strength hot rolled steel sheet having sufficiently high strength and excellent formability (elongation and stretch-flange ability), as well as a method for manufacturing the hot rolled steel sheet. Specifically, the present invention provides a high tensile strength hot rolled steel sheet having tensile strength of at least 980 MPa and excellent formability, comprising: a composition including by mass %, C: 0.07% to 0.13% (inclusive of 0.07% and 0.13%), Si: 0.3% or less, Mn: 0.5% to 2.0% (inclusive of 0.5% and 2.0%), P: 0.025% or less, S: 0.005% or less, N: 0.0060% or less, Al: 0.06% or less, Ti: 0.08% to 0.14% (inclusive of 0.08% and 0.14%), V: 0.15% to 0.30% (inclusive of 0.15% and 0.30%), Solute V: 0.04% to 0.1% (inclusive of 0.04% and 0.1%), Solute Ti: 0.05% or less, and remainder consisting of Fe and incidental impurities; (ii) microstructure with fine carbides dispersion precipitated therein, the fine carbides containing Ti and V and having the average particle diameter of less than 10 nm, as well as volume ratio with respect to the entire microstructure of at least 0.007; and matrix as ferrite phase having area ratio with respect to the entire microstructure of at least 97%, wherein contents of C, Ti, V, S and N satisfy formula (1) and formula (2) below. Ti ‰¥ 0.08 + N / 14 × 48 + S / 32 × 48 0.8 ‰¤ Ti / 48 + V / 51 / C / 12 ‰¤ 1.2
In formulae (1) and (2), "C", "Ti", "V", "S" and "N" represent contents (mass %) of corresponding elements, respectively. Bending properties of the hot rolled steel sheet is further improves by setting the total content of the solute V and the solute Ti to be at least 0.07 mass %.</p> |
