HIGH-STRENGTH STEEL SHEET AND GALVANIZED STEEL SHEET HAVING VERY GOOD BALANCE BETWEEN HOLE EXPANSIBILITY AND DUCTILITY, AND ALSO EXCELLENT IN FATIGUE RESISTANCE, AND METHODS OF PRODUCING THE STEEL SHEETS

摘要

Provided are high-strength steel sheets which are excellent in workabilities such as burring workability and ductility and in fatigue characteristics and which are suitable for automobiles, building materials, domestic electrical appliances, and so on. A high-strength steel sheet having a composition which contains C, Si, Mn, P, S, Al, N and O in prescribed amounts by mass% with the balance being Fe and unavoidable impurities and a structure which is mainly composed of ferrite and a hard phase, characterized in that the difference in crystal orientation between the hard phase and some ferrite adjacent thereto is less than 9° and that the sheet has a maximum tensile strength of 540PMa or above.