STRUCTURAL STEEL FOR WELDING EXCELLENT IN BRITTLE FRACTURE PROPAGATION ARRESTING CHARACTERISTIC

摘要

PURPOSE: To remarkably improve brittle fracture propagation arresting property while obviating the necessity of expensive alloy elements by subjecting a steel plate to heat treatment under specific temp. conditions. ;CONSTITUTION: A steel plate having a composition consisting of, by weight, 0.02-0.20% C, 0.01-1.0% Si, 2.0% Mn, 0.001-0.20% Al, 0.020% N, ≤0.01% P, ≤0.01% S, and the balance Fe is cooled rapidly from a temp. not lower than the Ac₃ at ≥5°C/ sec cooling rate through the region of ≥0.02×tomm from the surface in the plate thickness direction of the steel plate when to represents the plate thickness at the time of water cooling in the course of rolling, by which the fraction of ferrite structure is regulated to ≥50%. Successively, hot rolling is started at the point of time when the surface layer reaches a temp. not lower than the Ar₃ point and then cooled at least down to the Ar₃ temp. at ≥2°C/sec cooling rate without recuperation to a temp. between (Ac₃-50)°C and the Ac₃ point. By this method, the structure composed essentially of ferrite of ≥3μm average circle equivalent grain diameter or bainite and constituted of spheroidal carbide phase of ≤0.6μm average circle equivalent grain diameter can be formed in the range of at least 2% or more of the plate thickness from the surface layer.;COPYRIGHT: (C)1993,JPO&Japio