High-strength dual-phase steel sheet having a minimum tensile strength of 600 MPa, hot-rolled, precipitation-strengthened and crystal grains refined, and method for producing the same

摘要

The present invention relates to a method for producing a duplex steel sheet, wherein the chemical composition is such that, by weight%, C: 0.03 to 0.12, Mn: 0.8 to 1.5, Si: 0.1. , Cr: 0.3 to 0.7, S: maximum 0.008, P: maximum 0.025, Al: 0.01 to 0.1, N: maximum 0.007, Nb: 0.005 to 0.5. 035, V: a step of producing a molten steel having a maximum of 0.06, a step of continuously casting the molten steel into a slab, a step of hot-rolling the slab to a hot-rolled steel sheet at a finish rolling temperature (FRT) of 840 ± 30 ° C., Cooling the rolled steel sheet at a cooling rate of 40 to 70 ° C./s on a run-out table until a middle temperature (TINT) 720 ≦ TINT ≦ 650 is reached, a step of naturally cooling the hot-rolled steel sheet for 5 to 7 seconds, and a hot-rolled steel sheet At a cooling rate of 40-70 ° C to a winding temperature of less than 400 ° C. Comprising the step of transforming the carbon-enriched austenite into martensite remaining quenched to.