STEEL PLATE WITH EXCELLENT LOW-TEMPERATURE TOUGHNESS AND WELDED JOINT FRACTURE TOUGHNESS, AND ITS MANUFACTURING METHOD

摘要

PURPOSE: A steel plate with superior low-temperature toughness and welding joint fracture toughness and a manufacturing method thereof are provided to enable application to a marine structure in a deep-sea region or a cold region. CONSTITUTION: A steel sheet comprises C of 0.02-0.10 mass%, Si of 0.5 mass% or less, Mn of 1.0-2.0 mass%, Ni of 0.10-1 mass%, Nb of 0.005-0.03mass%, Ti of 0.005-0.02mass%, N of 0.0030-0.065 mass%, P of 0.02mass% or less, S of 0.015 mass% or less, Al of 0.01-0.06 mass%, and Fe and inevitable impurities of the remaining amount. The tensile strength of the steel sheet is 470MPa or greater. [Reference numerals] (AA) VTre t/2 C direction(C); (BB) Acicular ferrite fraction difference(area%)