| 摘要 |
Provided is a high-strength galvannealed steel sheet having a chemical composition to which expensive alloy elements are not actively added, excellent formability including elongation, bendability, and stretch flange formability, and a tensile strength of 900 MPa or more. A high-strength galvannealed steel sheet has a chemical composition containing, by mass%, C: 0.14% or more and 0.24% or less, Si: 0.8% or more and 1.8% or less, Mn: 1.0% or more and 3.0% or less, P: 0.020% or less, S: 0.0040% or less, Al: 0.01% or more and 0.1% or less, N: 0.01% or less, Ca: 0.0001% or more and 0.0020% or less, and the balance comprising Fe and incidental impurities, and a microstructure, in which the total area ratio of a ferrite phase and a bainite phase with respect to the whole microstructure is 30% or more and 70% or less, in which the area ratio of a tempered martensite phase with respect to the whole microstructure is 20% or more and 40% or less, in which the area ratio of a retained austenite phase with respect to the whole microstructure is 1% or more and 5% or less, in which the area ratio of a martensite phase with respect to the whole microstructure is 2% or more and 20% or less, and in which the total area ratio of cementite and a pearlite phase with respect to the whole microstructure is 10% or less. |
