Method for producing high-tensile hot-rolled steel strip having ferrite + bainite structure

摘要

PROBLEM TO BE SOLVED: To provide a method for producing a high tensile hot rolled steel strip having a ferritic + bainitic structure capable of obtaining uniform characteristics in the steel strip. SOLUTION: This method is provided with a process in which a rough bar or a thin slab of steel contg., by weight, 0.003 to 0.15% C, =1.5% Si, 0.5 to 2.5% Mn, =0.1% P, =0.01% S, 0.005 to 0.08% sol.Al and =0.008% N is produced, a process in which the rough bar or thin slab is heated to control a finishing temp. in the steel strip within a temp. range from the Ar3 transformation point to (the Ar3 transformation point + 50 deg.C) and to carry out finish rolling, a process in which the steel strip after the finish rolling is cooled to the temp. range of 550 to 750 deg.C at a cooling rate of =5 deg.C/s to be intermediately held for =1 sec and a process in which the steel strip after being intermediately held is cooled at a cooling rate of =5 deg.C/s and is coiled within the temp. range of 300 to 550 deg.C.