Effect of nano-ZrO2 addition on heterogeneous nucleation behavior and morphology control of MnS inclusions in steel

The morphology of MnS inclusions significantly affects the mechanical properties of steel. In this study, the morphology and size of MnS inclusions were refined by introducing nano-ZrO 2 particles into the molten steel. As the ZrO 2 content increased, the number of Al 2 O 3 –MnS inclusions decreased, while ZrO 2 –MnS inclusions became predominant core-shell inclusions. Simultaneously, MnS inclusions transformed from elongated shapes to fine spherical particles with an average area of 0.963 μm 2 and a sphericity of 0.805 at a ZrO 2 content of 0.0126 wt.%. Although both Al 2 O 3 and ZrO 2 acted as heterogeneous nucleation sites for MnS, first-principles calculations revealed that ZrO 2 exhibited stronger nucleation capability, with the adsorption ability showing a clear gradient: monoclinic ZrO 2 exhibiting the strongest adsorption, followed by tetragonal ZrO 2 , and finally α-Al 2 O 3 . Based on the experimental observations and theoretical results, a mechanism for ZrO 2 -facilitated heterogeneous nucleation of MnS was proposed. These findings provide valuable theoretical insights and technical guidance for spheroidization of MnS inclusions during steelmaking process.