High-strength hot-rolled steel sheet and method for producing the same
摘要:
Provided is a high-strength hot-rolled steel sheet containing, by mass %, C: 0.050 to 0.200%, Si: 0.01 to 1.5%, Mn: 1.0 to 3.0%, B: 0.0002 to 0.0030%, Ti: 0.03 to 0.20%, P: limited to 0.05% or less, S: limited to 0.005% or less, Al: limited to 0.5% or less, N: limited to 0.009% or less, and one or more of Nb: 0.01 to 0.20%, V: 0.01 to 0.20%, and Mo: 0.01 to 0.20%, with the balance being composed of Fe and inevitable impurities. In the high-strength hot-rolled steel sheet, a ratio of a length of small-angle crystal grain boundaries that are boundaries having a crystal orientation angle of 5° or more but less than 15° to a length of large-angle crystal grain boundaries that are boundaries having a crystal orientation angle of 15° or more is 1:1 to 1:4, an total segregation amount of C and B in the large-angle grain boundaries is 4 to 20 atoms/nm2, tensile strength is 850 MPa or higher, and a hole expansion ratio is 25% or more.
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