High tensile strength hot rolled steel sheet having excellent formability and method for manufacturing the same

摘要

Described is a high tensile strength hot rolled steel sheet having high strength and formability, and a manufacturing method. It has tensile strength ≧980 MPa and excellent formability, and specifically identified ranges by mass % of C, Si, Mn, P, S, N, Al, Ti, V, Solute V, and Solute Ti; (ii) microstructure with fine carbides dispersion precipitated therein, the fine carbides containing Ti and V and having the average particle diameter <10 nm, as well as volume ratio with respect to the entire microstructure ≧0.007; and matrix as ferrite phase having area ratio with respect to the entire microstructure ≧97%. C, Ti, V, S and N satisfy (1) Ti≧0.08 +(N/14×48+S/32×48) and (2) 0.8≦(Ti/48+V/51)/(C/12)≦1.2, where “C”, “Ti”, “V”, “S” and “N” represent contents (mass %) of corresponding elements, respectively.

主权项

1. 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, andremainder consisting of Fe and incidental impurities;the total content, by mass %, of the solute V and the solute Ti being at least 0.07%; 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):
Ti≧0.08+(N/14×48+S/32×48)  (1)0.8≦(Ti/48+V/51)/(C/12)≦1.2   (2)where C, Ti, V, S, and N represent contents (mass %) of corresponding elements, respectively.