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

摘要

PROBLEM TO BE SOLVED: To provide a high strength hot rolled steel sheet having a high strength satisfying a TS (tensile strength) of ≥780 MPa, having excellent elongation properties, stretch flange properties and tensile fatigue properties, and further having impact resistance at a strain rate of 10/s for checking the deformation of an automobile cabin.;SOLUTION: In Ti-Mo compositely added steel, the steel structure of, by volume occupancy to the whole structure, 40 to 93% ferrite, 4 to 15% retained austenite, 3 to 12% martensite, and the balance bainite is formed, and also, the average diameter of precipitates composed of Ti, Mo and C precipitated in the ferrite is controlled to ≤20 nm, and the average spacing between the precipitates is controlled to ≤60 nm.;COPYRIGHT: (C)2006,JPO&NCIPI