Nb-Ti-series 780MPa-class hot-rolled dual-phase steel and production method thereof

The invention discloses an Nb-Ti-series 780MPa-class hot-rolled dual-phase steel. The steel comprises the following chemical components in percentages by weight: 0.06-0.09% of C, 0-0.20% of Si, 1.30-1.60% of Mn, 0-0.015% of P, 0-0.004% of S, 0.020-0.060% of Als, 0.030-0.040% of Nb, 0.025-0.045% of Ti, and the balance of Fe and inevitable impurities. In a cooling step of a production method of the steel, a three-section type controlled cooling technology is adopted and comprises the following steps: controlling the cooling speed of a first section to be 130-180 DEG C/s, and cooling until the temperature reaches 610-740 DEG C; controlling the cooling speed of a second section to be 3-8 DEG C/s, and cooling until the temperature reaches 590-720 DEG C; and controlling the cooling speed of a third section to be 50-70 DEG C/s, cooling until the temperature reaches 50-150 DEG C, and controlling the temperature of cooling water to be 10-25 DEG C. The produced hot-rolled dual-phase steel of which the tensile strength is 780 MPa class can effectively acquire ferrite+martensite dual-phase tissues effectively, the lower yield strength of a steel plate reaches 380-635 MPa, the tensile strength is greater than or equal to 780 MPa, elongation A50mm can be greater than or equal to 16%, the steel is qualified if the transverse section bend test D is equal to 1.5a, the yield-tensile ratio is less than or equal to 0.60, and the product has the features of high strength and low yield-tensile ratio.