High-strength hot-rolled steel sheet for processing excellent in strength-hole expansion ratio balance and shape freezing property, and method for producing the same

摘要

PPROBLEM TO BE SOLVED: To provide a steel sheet which jointly has an excellent balance of strength-hole expansibility, an excellent balance of strength-elongation and shape fixability, i.e., a high strength steel sheet for working which has an excellent balance of strength-hole expansibility and shape fixability, and to provide a method for producing the same. PSOLUTION: The high strength steel sheet for working excellent in a balance of strength-a hole expansion ratio and shape fixability has prescribed chemical components. The microstructure in the cross-section of the steel sheet comprises one or two kinds selected from martensite and retained austenite by 3% in the total area ratio, and one or two kinds selected from ferrite and bainite by 80% in the total area ratio, and the balance pearlite, and further, the maximum length of the pearlite, martensite and retained austenite is 10 microns. Further, inclusions of 20 microns are present in the cross-section of the steel sheet by 0.3 pieces per mm. PCOPYRIGHT: (C)2004,JPO