Abstract: By simulating the continuous annealing process of a cold rolled 980 MPa dual-phase steel by a Vatron Voestalpine thermal simulator, the effect of soaking temperature, slow cooling temperature, overaging temperature and the strip speed in continuous annealing on microstructure and mechanical properties of the dual-phase steel was studied by means of tensile testing machine, optical microscope and scanning electron microscope. The results show that with the increase of the soaking temperature in the range of 820, 840 and 860 ℃, the proportion of ferrite decreases and the yield strength increases. A certain amount of bainite appeares in the microstructure when the soaking temperature is increased to 860 ℃, which leads to the tensile strength reach the lowest value 1020 MPa. The slow cooling temperature can change the volume fraction of martensite and affect the mechanical properties of dual-phase steel. When the overaging temperature varies among 250, 270, 290, 310 and 330 ℃, with the overaging temperature increases, the degree of softening of the martensile increases, the tensile strength decreases and the total elongation of the tested steel increases. With the increase of overaging temperature above 310 ℃, the decomposition of martensite is promoted, and at the same time the precipitations of second phases are increased and the yield strength decreases first and then increases. Comprehensively considering the mechanical properties control of the cold rolled dual-phase steel under different annealing processes, the optimal annealing parameters are selected as soaking temperature of 840 ℃, slow cooling temperature of 680 ℃, overaging temperature of 250 ℃ and the strip speed of 120 m/min, under which the maximum value of the product of strength and elongation is 15.6 GPa·%.

Key words: dual-phase stee, soaking temperature, slow cooling temperature, overaging temperature, microstructure, mechanical properties