Microstructure Evolution and Work Hardening Behavior of Hot-Rolled DP780 Ferrite/Bainite Dual-Phase Steel

In this article, by optimizing the alloy composition, the DP780 grade hot-rolled duplex steel was obtained by TMCP (thermo-mechanical control process) combined with medium temperature coiling procedure. The microstructure evolution and mechanical properties of the experimental steel were analyzed by means of optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), room temperature tensile experiment, and low-temperature impact experiment. When the coiling temperature was 540°C, the yield strength, tensile strength, and elongation of the experimental steel were 663 MPa, 785 MPa, and 23%, respectively, and the product of the strength and elongation was as high as 18.1 GPa%, which accords with the mechanical properties of the national standard for DP780 dual-phase steel. The experimental steel exhibits significant work hardening effect at higher strain, and can still guarantee a certain work hardening index and good formability. When the coiling temperature was high (570°C), the strength of the experimental steel decreased and the work hardening effect was also weakened due to the coarsening of microstructure. The results of this article provide theoretical guidance for the production of DP780 dual-phase steel by hot rolling.