Effect of vanadium microalloying on the deformation behavior and strain hardening of a medium Mn steel

Abstract

Microalloying is a well-established approach for tailoring the mechanical properties of conventional steels, yet its effects on the mechanical properties and the underlying deformation mechanism for medium Mn steels remain elusive. Here, we report a thorough investigation of deformation behavior in the intercritically annealed medium Mn steels, both with and without the 0.1 wt.% V microalloying. The V-alloyed steel exhibits comparable yield strength and uniform elongation, but higher ultimate tensile strength and enhanced strain hardening, as compared to the V-free counterpart. Our analysis indicates that the V microalloying preferentially reacts with C atoms to form VC precipitates, which affect the subsequent ferrite to austenite transformation mainly by reducing the C content in the initial ferrite phase rather than impeding the phase interface migration. We reveal that the similar yield strengths originate from the increased strength of ferrite due to refined grain size being offset by the decreased strength of austenite arising from the reduced C content. Furthermore, for the first time, we quantitatively resolve the origins of strain hardening in the V-alloyed and V-free steels, where the transformation-induced plasticity (TRIP) effect, stress partitioning, and dislocation activities make fundamentally different contributions in the two steels. On this basis, we uncover that the extra strain hardening in the V-alloyed steel is ascribed to the rapid TRIP effect, enhanced stress partitioning, and active dislocation accumulation mainly facilitated by statistically stored dislocations. The present findings provide mechanistic insights into the role played by microalloying in modulating the deformation behavior and strain hardening of medium Mn steels.