Effect of intercritical annealing temperature on microstructure and mechanical properties of V-Ti-Mo microalloyed medium Mn steel

The effect of intercritical annealing temperature on the microstructure and mechanical properties of V-Ti-Mo microalloyed medium Mn steel were investigated using a scanning electron microscope, electron backscatter diffraction, X-ray diffraction and transmission electron microscope. The results showed that the microstructure of the experimental steel in the hot rolled state and after annealing at different temperatures consisted of martensite and reverted austenite. As the annealing temperature increased, the content of reverted austenite increased linearly and reached a maximum value of 29.08 % after annealing at 650 degrees C. It was difficult to occur austenitic reverted transformation at an annealing temperature of 580 degrees C. In addition, block-like reverted austenite appeared after annealing at 600 degrees C, and the austenite size had the largest after annealing at 650 degrees C. With the increase of annealing temperature, the mass fraction of M3C particles decreased gradually, while that of MC particles increased progressively. Specifically, the mass fraction of 1-5 nm sized MC particles increased first and then decreased, indicating the precipitation strengthening effect was enhanced initially and then weakened. As the annealing temperature rose, the yield strength and tensile strength of the steels decreased gradually, whereas the elongation and impact energy gradually increased. The steel annealed at 650 degrees C exhibited optimal comprehensive mechanical properties, with a strength-ductility product reaching 26.8 GPa %.