HIGH-STRENGTH STEEL SHEETS WHICH ARE EXTREAMELY EXCELLENT IN THE BALANCE BETWEEN BURRING WORKABILITY AND DUCTILITY AND EXCELLENT IN FATIGUE ENDURANCE, ZINC-COATED STEEL SHEETS, AND PROCESSES FOR PRODUCTION OF BOTH

摘要

The invention is directed to providing, for application in automobiles, construction materials, household appliances and the like, high-strength sheets excellent in formability properties such as hole expansibility and ductility, and also in fatigue resistance, characterized in comprising, in specified contents expressed in mass%, C, Si, Mn, P, S, Al, N and O and a balance of iron and unavoidable impurities, and having a steel sheet structure composed mainly of ferrite and hard structures, a crystal orientation difference between some ferrite adjacent to hard structures and the hard structures of less than 9°, and a maximum tensile strength of 540 MPa or greater.