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 has an aspect ratio of prior austenite grains of ≤20, precipitates and/or inclusions of ≤1,000 particles/μm³, an average particle diameter of cementite of not more than 60 nm, an integration degree of {110} planes raging from 0.3 to 1.8 at a quarter thickness position of a steel sheet, an accumulation degree of {211} planes ranging from 0.9 to 2.4 at a quarter thickness position of the steel sheet, and the steel comprises, in terms of mass%, C, Si, Mn, Al, N, P, S and O, and if necessary, one or more elements 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 to hot rolling at a rolling reduction of ≤70% in a unrecrystallized region, then cooled to a temperature of ≤350°C at an average cooling rate of not less than 2°C/sec from the Ar₃ transformation point or higher, and tempered to a temperature of ≥400°C and equal to or lower than the Ac₁ transformation point at an average temperature elevation rate of ≥1°C/sec.;COPYRIGHT: (C)2010,JPO&INPIT