Effect of Vanadium on Microstructure and Properties of Alloyed Bainitic Ductile Iron

0.3wt% vanadium (V) was added in the Mo-Ni-Cu-Cr alloyed bainitic ductile iron, then the effects of V addition on the microstructure and mechanical properties of the bainitic ductile iron were investigated. The equilibrium phase diagram of the bainitic ductile iron containing 0.3wt%V was calculated by the thermal-calc thermodynamic software and the precipitation behavior of V was analyzed. The results show that with the addition of 0.3wt% V, the needle-like bainite in the microstructure of the ductile iron became finer; the amount of residual austenite and cementite increased; the nano-scaled VC particles distributed dispersedly in the matrix of bainite. Comparing to the ductile iron without V, the hardness of the ductile iron with 0.3wt%V increased slightly and the impact energy and wear resistance had more than doubled. The main strengthening mechanisms were the fine grain strengthening and precipitation hardening. The wear mechanisms of the ductile irons with and without V were both plastic deformation fatigue and micro-cutting.