HIGH-STRENGTH STEEL SHEET HAVING EXCELLENT DUCTILITY AND LOW-TEMPERATURE TOUGHNESS, AND METHOD FOR PRODUCING SAME

摘要

A high-strength steel sheet of the present invention is a steel sheet satisfying a predetermined component composition. A metal structure of the steel sheet is composed of polygonal ferrite, high-temperature region generated bainite, low-temperature region generated bainite and retained austenite each having a predetermined area percent, and a distribution using each average IQ of predetermined crystal grains determined by electron backscatter diffraction satisfies Equations (1) and (2) below. According to the present invention, a high-strength steel sheet having excellent ductility and low-temperature toughness can be realized even at a tensile strength of 780 MPa or more. IQave ˆ’ IQmin / IQmax ˆ’ IQmin ‰¥ 0.40 ÃIQ / IQmax ˆ’ IQmin ‰¤ 0.25