Microstructure and mechanical properties of hot-rolled Nb-V-Ti microalloyed TRIP steel based on dynamic transformation of undercooled austenite

The influence of the state of prior austenite grains before dynamic transformation on the multi-phase microstructure and mechanical properties of hot-rolled Nb-V-Ti microalloyed TRIP steel based on dynamic transforma-tion of undercooled austenite (DTUA) was investigated by uniaxial hot compression test, scanning electron microscopy, and X-ray diffraction. In comparison with that prior anstenite grains are equiaxed before DTUA, when prior austenite grains are elongated before DTUA, the volume fraction of ferrite obtained by DTUA is higher, the volume fractions of bainite and martensite are lower, and the average size of bainite packets is smaller in the final multi-phase microstructure. But the volume fraction of retained austenite and the carbon content of retained austenite are similar in both cases. Compared with hot-rolled TRIP steel based on DTUA without micro-alloying elements, hot-rolled Nb-V-Ti microalloyed TRIP steel based on DTUA demonstrate higher yield strength and tensile strength, but lower elongation.