The high productivity high intensity steel sheet and its production mannered null mass which possess the basic material and the welding thermal effect section

摘要

PROBLEM TO BE SOLVED: To provide a thick steel sheet which has superior weldability and toughness, has a high strength of a 570 N/mm² grade, and can be manufactured in a short period of time at a low cost, and to provide a manufacturing method therefor.;SOLUTION: A steel slab comprises, by mass%, 0.03 to 0.12% C, 0.05 to 0.50% Si, 1.60 to 3.00% Mn, 0.015% or less P, 0.001 to 0.010% S, 0.05 to 0.30% Cu, 0.05 to 0.60% Ni, 0.001 to 0.050% Al, 0.05 to 0.30% Mo, 0.005 to 0.030% Ti, 0.005 to 0.100% Nb, 0.0025 to 0.0060% N, and the balance iron with unavoidable impurities. The method for manufacturing the steel plate comprises the steps of: heating the above steel slab at 1,050°C to 1,200°C; hot-rolling it with a cumulative rolling reduction of 40% or higher in a non-recrystallizing temperature region; finishing hot rolling at 720°C or higher; and cooling the plate to 550°C or lower from a temperature of 700°C or higher, at a cooling rate of 5°C/s or higher.;COPYRIGHT: (C)2008,JPO&INPIT