A review on phase transformation mechanisms and process control for strengthening and toughening of V-microalloyed bainitic steels

: Vanadium microalloying has emerged as a key technological strategy for enhancing the overall performance of bainitic steels. However, the influence of vanadium on bainitic transformation kinetics remains controversial. This review systematically clarifies the "dual-role" regulatory effect of vanadium on bainitic transformation kinetics, revealing the existence of a temperature-dependent kinetic crossover point: above this point, vanadium suppresses the transformation, whereas below it, vanadium promotes the transformation. Building on this understanding, the key preparation processes for bainitic steels—including austenitization, continuous cooling, isothermal/quasi-isothermal treatment, thermomechanical controlled processing, and tempering—are critically reviewed. Furthermore, the strengthening and toughening mechanisms of vanadium-microalloyed bainitic steels are elucidated, and a synergistic strengthening–toughening system based on “nanoscale precipitation strengthening–multi-scale grain refinement strengthening–stabilization of retained austenite” is constructed. Finally, prospective research directions concerning integrated composition–process design and engineering applications in this field are outlined.