The effect of vanadium micro-alloying on the microstructure and the tensile behavior of TWIP steel

The effect of V addition on the microstructure and the tensile behavior of Fe-17Mn-0.45C-1.5Al-1Si-xV TWIP steel was investigated. The V additions contributed to a reduction of the grain size and an increase of the yield strength of the TWIP steels. The size distribution of various precipitates in the V-added steel, i.e. VC, TiC-VC co-precipitates and TiC, was investigated. The yield strength of the V-added steel was modelled by considering the effect of the Peierls lattice friction, solid solution strengthening, grain size refinement strengthening and precipitation hardening by the Ashby-Orowan mechanism. Electron backscattering diffraction (EBSD) microstructure analysis and constitutive modeling revealed a slight difference of the twinning behavior in the V-free and V-added steel. While a higher twinning activity was observed in the V-added steel in the early stages of deformation, more twinning was observed in the V-free steel at higher strains. It is argued that the smaller grain size in the V-added steel leads to higher localized stresses at the grain boundaries as compared to the coarser grained V-free steel, and that these higher stresses facilitate grain boundary nucleation of deformation twins in the V-added steel.