High strength hot-rolled steel sheet for welded steel line pipe having excellent souring resistance, and method for producing same

Abstract

A steel material containing 0.01% to 0.07% C, 0.40% or less Si, 0.5% to 1.4% Mn, 0.1% or less Al, 0.01% to 0.15% Nb, 0.1% or less V, 0.03% or less Ti, and 0.008% or less N on a mass basis, Nb, V, and Ti satisfying Nb+V+Ti<0.15, Cm satisfying 0.12 or less, is heated to a heating temperature of 1,100° C. to 1,250° C., finish-rolled in such a way that the accumulative rolling reduction at a temperature of 930° C. or lower is 40% to 85% and the finished rolling temperature is 760° C. to 870° C., cooled to a cooling stop temperature of 500° C. or lower in terms of surface temperature at an average cooling rate of 30° C./s to 200° C./s in terms of thickness-wise center temperature, naturally cooled for more than 10 s after cooling is stopped, and coiled at a coiling temperature of 400° C. to 620° C.