| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength high ductility steel sheet excellent in strength-ductility balance, capable of securing tensile strength (TS)×elongation (EL)×elongation flanging (λ) of 500000 MPa % % or more at tensile strength (TS) of 1180 MPa or more.SOLUTION: There is provided a high strength high ductility steel sheet having a component composition containing, by mass%, C:0.40 to 0.60%, Si+Al:0.5 to 2.0%, Mn:1.0 to 4.0%, P:0 to 0.05%, S:0 to 0.01% and the balance iron with inevitable impurities and a steel structure consisting of, by area percentage based on the total structure, retained austenite of 20 to 40% and the balance one or more of bainite, martensite, tempered bainite and tempered martensite and, in terms of carbon concentration in the retained austenite, an average carbon concentration is 0.9 to 1.2 mass%, a standard deviation of carbon concentration distribution is 0.29 mass% or more and an area with a carbon concentration of 1.5 mass% or more is 2.0% or more by area percentage based on the total structure.SELECTED DRAWING: None |
