| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength hot rolled steel sheet having a tensile strength of 1,180 MPa or higher and a yield ratio of 80% or higher and also having excellent notch elongation properties, and a method for producing the same.SOLUTION: A steel slab comprising, by mass, C of 0.1 to 0.5%, Si of 0.5% or lower, Mn of 1.5% or lower, P of 0.03% or lower, S of 0.03% or lower, Al of 0.1% or lower and N of 0.1% or lower, and further comprising one or more kinds selected from Ti of 0.1 to 2.0%, Nb of 0.05 to 2.0% and Zr of 0.05 to 2.0% is cooled from a solidification point to 1,300°C at 300°C/min or lower and is reheated at 1,150 to 1,300°C for 40 min without being cooled to below 900°C, and hot finish rolling is finished at 820°C or higher to obtain a hot rolled steel sheet having a steel structure of a ferrite single phase, the maximum diameter of carbides precipitated in the grains of 100 nm or lower, and a tensile strength of 1,180 MPa or higher and a yield ratio of 80% or higher. |
