HOT-ROLLED STEEL SHEET AND MANUFACTURING METHOD THEREOF

摘要

Provided are a high-strength hot-rolled steel sheet having reliable low-temperature toughness as well as exceptional stretch flangeability due to control having been maintained over the structural fractions and difference in hardness between structures, and a method for producing the high-strength hot-rolled steel sheet. A hot-rolled steel sheet characterized in containing 0.01 to 0.2% of C, 0.001 to 2.5% or less of Si, 0.10 to 4.0% or less of Mn, 0.10% or less of P, less than 0.03% of S, 0.001 to 2.0% of Al, less than 0.01% of N, (0.005+48/14[N]+48/32[S]) to 0.3% inclusive of Ti, 0 to 0.06% of Nb, 0 to 1.2% of Cu, 0 to 0.6% of Ni, 0 to 1% of Mo, 0 to 0.2% of V, 0 to 2% of Cr, 0 to 0.01% of Mg, 0 to 0.01% of Ca, 0 to 0.1% of REM, and 0 to 0.002% of B; having an aggregate structure in which mean X-ray random intensity ratio for the sheet-surface {100}<011> to {223}<110> orientation group is 6.5 or less, and the mean X-ray random intensity ratio for the {332}<113> crystal orientation is 5.0 or less in a sheet thickness center located 3/8 to 5/8 the distance from the surface of the steel sheet in the thickness direction; and having a microstructure in which the total surface area of tempered martensite, martensite, and lower bainite exceeds 85%, and the mean crystal grain size is 12.0 µm or less.