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

The invention is directed to providing, forapplication in automobiles, construction materials,household appliances and the like, high-strength sheetsexcellent in formability properties such as holeexpansibility and ductility, and also in fatigueresistance, characterized in comprising, in specifiedcontents expressed in mass%, C, Si, Mn, P, S, Al, N and Oand a balance of iron and unavoidable impurities, andhaving a steel sheet structure composed mainly of ferriteand hard structures, a crystal orientation differencebetween some ferrite adjacent to hard structures and thehard structures of less than 9°, and a maximum tensilestrength of 540 MPa or greater.