Influence of Vanadium on Microstrain Partitioning and Evolution of Microstructural Damage in DP1300 Steel

We have investigated the effect of vanadium addition on a DP1300 ferrite-martensite steel, particularly in terms of microstructure, deformation, and damage behavior at the microscopic level. DP steels with and without vanadium addition were given slightly altered heat treatments to produce similar martensite content and ultimate tensile strength in both steels. The addition of 0.14wt% vanadium to the reference alloy yields a dispersion of nano-scale vanadium carbonitrides throughout the microstructure along with a pronounced grain refinement. Microscopic digital image correlation (μDIC) was employed to analyze the local strain partitioning between ferrite and martensite at the grain level. It was found that the addition of V increases the mechanical compatibility between ferrite and martensite. The consequent enhanced mechanical homogeneity and reduced strain gradients at the ferrite-martensite interface suppresses damage, thus enhancing ductility of the V-added alloy. Interrupted tensile tests coupled with X-ray computed tomography confirm that microstructural damage growth is slower in the V-added steel during post-uniform elongation prior to fracture.