Effect of matrix recrystallization on morphology, crystallography and coarsening behavior of vanadium carbide in austenite

The effect of matrix recrystallization on the morphology and crystallography of B1-type vanadium carbide (VC) formed in austenite (γ) was studied in an Fe-12Mn-0.3V-0.8C (mass%) alloy by transmission electron microscopy. With direct aging at 1173 K after solutionizing, without cold rolling, VC precipitates display a cube-cube orientation relationship with respect to γ. In the early stage of aging, the morphology of VC is octahedral with {111}_γ facets, but with prolonged aging, {001}_γ facets with lower boundary energy replace the preexisting {111}_γ facets, resulting in a change in VC morphology from octahedral to tetra-kai-decahedral. After the γ matrix containing these VC precipitates is recrystallized, the morphology and crystallography of the VC change significantly, exhibiting no specific VC/γ orientation relationship as well as no specific morphology. Coarsening of VC is significantly accelerated after γ recrystallization, presumably due to an increase in VC/γ boundary energy and short-circuit diffusion during passage of the γ grain boundary over the VC particles during grain growth.