HIGH-TENSILE STEEL EXCELLENT IN BENDING WORKABILITY AND LOW-TEMPERATURE TOUGHNESS, AND METHOD FOR MANUFACTURING THE SAME

摘要

PROBLEM TO BE SOLVED: To provide a high-tensile steel excellent in bending workability and low-temperature toughness, which is suitable for a steel having a tensile strength of ≥600 MPa, and to provide a method for manufacturing the steel. SOLUTION: The steel material has an aspect ratio of prior austenite grains of not more than 20 in a microstructure of a steel sheet, precipitates and/or inclusions of ≤1,000 particles/μm3, an integration degree of ä110} planes ranging from 0.3 to 1.8 at a quarter thickness position of the steel sheet, an accumulation degree of ä211} planes ranging from 0.9 to 2.4 at a quarter thickness position of the steel sheet, and the steel material comprises, in terms of mass%, C, Si, Mn, Al, N, P, S and O, and if necessary, one or more of Mo, Nb, V, Ti, Cu, Ni, Cr, W, B, Ca, REM and Mg, and the balance Fe and inevitable impurities. The steel having the above components is subjected, after casting, to hot rolling at a rolling reduction of ≤70% in a unrecrystallized region to obtain a predetermined plate thickness, subsequently cooled from the Ar3transformation point or higher down to a temperature of ≤350°C at an average cooling rate of ≥2°C/sec, and tempered to a temperature equal to or lower than the Ac1transformation point at the center of the plate thickness. COPYRIGHT: (C)2010,JPO&INPIT