| 摘要 |
PROBLEM TO BE SOLVED: To provide a galvannealed steel sheet having a tensile strength (TS) of 780 MPa or more and a yield ratio (YR) of 0.45 to 0.85.SOLUTION: A steel sheet contains a chemical composition containing, by mass%, C:0.05% to 0.25%, Si:0.5% to 3.0%, Mn:1.5% to 5.0%, P:0.05% or less, S:0.01% or less, sol.Al:0.001% to 2.5%, Bi:0.0001% to 0.010% or less an N:0.01% or less, and a steel structure containing 70% or less of ferrite and 5% to 25% of retained austenite, by an area ratio. |
