Hot-dip galvannealed steel sheet with ultra-high strength and high formability, and manufacturing method therefor

Abstract

Disclosed are a hot-dip galvannealed steel sheet with ultra-high strength and high formability, and a manufacturing method therefor. In an exemplary embodiment, a hot-dip galvannealed steel sheet include: a base steel sheet; and a hot-dip galvannealed layer formed on the surface of the base steel sheet. The base steel sheet includes an amount of 0.05 to 0.15 wt % of carbon (C), an amount greater than 0 and less than or equal to 1.0 wt % of silicon (Si), an amount of 4.0 to 9.0 wt % of manganese (Mn), an amount greater than 0 and less than or equal to 0.6 wt % of aluminum (Al), an amount greater than 0 and less than or equal to 0.02 wt % of phosphorus (P) in, an amount greater than 0 and less than or equal to 0.005 wt % of sulfur (S), an amount greater than 0 and less than or equal to 0.006 wt % of nitrogen (N), and the balance of iron (Fe) and other inevitable impurities. The base steel sheet has a microstructure consisting of ferrite and retained austenite; the grain size of the microstructure is 3 μm or less; and the hot-dip galvannealed steel sheet has a yield strength (YS) of 800 MPa or greater, a tensile strength (TS) of 980 MPa or greater, an elongation (EL) of 25% or greater, and a hole expansion ratio (HER) of 20% or greater.