| 摘要 |
A high-strength hot-rolled steel sheet which contains, in terms of mass%, 0.050-0.200% C, 0.01-1.5% Si, 1.0-3.0% Mn, 0.0002-0.0030% B, and 0.03-0.20% Ti, has P, S, Al, and N contents reduced to 0.05% or less, 0.005% or less, 0.5% or less, and 0.009% or less, respectively, and contains one or more of 0.01-0.20% Nb, 0.01-0.20% V, and 0.01-0.20% Mo, with the remainder comprising Fe and unavoidable impurities and in which the ratio of the length of small-angle crystal grain boundaries that are boundaries having a crystal orientation angle of 5º or larger but less than 15º and the length of large-angle crystal grain boundaries that are boundaries having a crystal orientation angle of 15º or larger is 1:1 to 1:4 and the total amount of C and B segregated in the large-angle crystal grain boundaries is 4-20 atoms/nm2. The steel sheet has a tensile strength of 850 MPa or higher and a hole expansion ratio of 25% or higher. |
