Effect of vanadium on modification of inclusions in Mn- and Si-deoxidized steel during heat treatment at 1473 K

The effect of vanadium (V) on the modification of oxide inclusions in steels with different concentrations of Mn, Si, and V was determined before and after heat treatment at 1473 K. Changes in the morphology, size, and composition of these inclusions were analyzed. Equilibrium relations between the inclusions and steels at 1873 K and 1473 K were calculated using available thermodynamic data to roughly approximate the stable oxide inclusions in the steels. The results revealed that the concentrations of V and Si in the steel are critical for controlling the modification of the inclusions during heat treatment at 1473 K. MnO-SiO₂-type oxide inclusions gradually transformed into MnO-V₂ O₃-type or Mn-SiO₂- and MnO-V₂O₃-type inclusions in low-Si high-V steels heat-treated for 60 min. In addition, the morphology of the inclusions changed from spherical to irregular. A Si-accumulated zone and a V-depleted zone formed close to the interface in the steel matrix. The experimental and calculation results indicated that, during the heat treatment, an interface chemical reaction occurred between the Fe-Mn-Si-V steel and the MnO-SiO₂-type oxide inclusion.