HIGH STRENGTH HOT ROLLED STEEL SHEET HAVING EXCELLENT ELONGATION PROPERTY, STRETCH FLANGE PROPERTY AND TENSILE FATIGUE PROPERTY, AND ITS PRODUCTION METHOD

摘要

PROBLEM TO BE SOLVED: To provide a high strength hot rolled steel sheet having a high strength satisfying TS≥780 MPa, and also having excellent elongation properties, stretch flange properties and tensile fatigue properties.;SOLUTION: The steel sheet contains, by mass, 0.03 to 0.2% Ti and 0.03 to 0.5% Mo as essential components, and has a steel structure, by occupancy ratio to the whole structure, 40 to 96% ferrite, 4 to 15% retained austenite, and the balance substantially bainite, and in which precipitates composed of Ti, Mo and C are precipitated into ferrite, the average diameter of the precipitates is controlled to ≤20 nm, and the average spacing between the precipitates is controlled to ≤60 nm.;COPYRIGHT: (C)2006,JPO&NCIPI