HIGH-STRENGTH STEEL SHEET EXCELLENT IN IMPACT RESISTANCE AND MANUFACTURING METHOD THEREOF, AND HIGH-STRENGTH GALVANIZED STEEL SHEET AND MANUFACTURING METHOD THEREOF

摘要

The present invention provides a high-strength steel sheet excellent in impact resistance. The high-strength steel sheet contains predetermined contents of C, Si, Mn, P, S, Al, Ti, N, and O, with the balance being iron and inevitable impurities, and has a steel sheet structure in which, in a 1/8 thickness to 3/8 thickness region across 1/4 of a sheet thickness, 1 to 8% retained austenite is contained in volume fraction, an average aspect ratio of the retained austenite is 2.0 or less, an amount of solid-solution Mn in the retained austenite is 1.1 times an average amount of Mn or more, and TiN grains having a 0.5 µm average grain diameter or less are contained, and a density of AlN grains with a 1 µm grain diameter or more is 1.0 pieces/mm2 or less, wherein a maximum tensile strength is 900 MPa or more.