780 Method for manufacturing thick hot-rolled steel sheets with tensile strength of 780MPa grade

摘要

PURPOSE: A method for manufacturing hot rolled steel plate with tensile strength of 780 MPa grade and thickness of 6 mm or more is provided which suppresses growth of fine grain boundary carbide by dipping the coiled steel plate into a dipping type water cooling furnace after coiling the steel plate. CONSTITUTION: The method comprises a step of finish hot rolling a steel slab comprising 0.06 to 0.10 wt.% of C, 0.20 wt.% or less of Si, 1.5 to 2.0 wt.% of Mn, 0.02 wt.% or less of P, 0.0005 wt.% or less of S, 0.010 to 0.050 wt.% of Al, 0.050 to 0.150 wt.% of Ti, 0.020 to 0.040 wt.% of Nb, 0.10 to 0.25 wt.% of Mo, 0.006 wt.% or less of N and a balance of Fe and other inevitable impurities at a temperature of 840 deg.C or more; a step of coiling the hot rolled steel plate in the temperature range of 580 to 620 deg.C; and a step of dipping the coiled steel plate into a dipping type water cooling vessel for less than 30 minutes.