| 摘要 |
Provided are a high strength hot-dip galvanized steel sheet and a high strength hot-dip galvannealed steel sheet, which are ideal as materials for automobile components and have a tensile strength (TS) of at least 1180 MPa and excellent spot-welding properties, impact resistance and bending workability, and a manufacturing method therefor. The amount of C is 0.15% or less; the ferrite area ratio is 10% or less, the bainitic ferrite area ratio is 2-30%, and the martensite area ratio is 60-98%; the residual austenite area ratio is less than 2%; the mean grain size of martensite that is adjacent to bainite is 15 µm or less; the proportion of massive martensite that is adjacent to bainite only in the total composition is 10% or less; and the value (ˆ†Hv) obtained by subtracting the Vickers hardness at a position that is 20 µm from the surface of the steel sheet from the Vickers hardness at the 100 µm position is at least 30. |
