THICK-WALLED, HIGH TENSILE STRENGTH STEEL WITH EXCELLENT CTOD CHARACTERISTICS OF THE WELD HEAT-AFFECTED ZONE, AND MANUFACTURING METHOD THEREOF

摘要

Provided are a heavy wall thickness high-strength steel plate with excellent low-temperature toughness (Charpy impact and CTOD properties of a weld bond) in a multilayer weld zone and a method for manufacturing the steel plate. The high-strength steel plate has a chemical composition containing, by mass%, a certain amount of C, Si, Mn, P, S, Al, Cu, Ni, Nb, Ti, N, O, and the like, and the balance being Fe and inevitable impurities, in which Ceq which is defined by relational expression (1) is 0.520% or less, in which Ti/N is 1.50 or more and 4.00 or less, in which a parameter relational expression regarding specified chemical elements for controlling the shape of sulfides in steel and the degree of center segregation is satisfied, and in which the hardness of a center segregation part of the steel plate is specified: Ceq = [C] + [Mn]/6 + ([Cu]+[Ni])/15 + ([Cr] + [Mo] + [V])/5 ... (1).