Evolution mechanism of inclusions and microstructure in low-alloy cast steel with cerium addition

Rare earth (RE) elements not only modify inclusions but also refine the steel's microstructure. This study investigates the evolution mechanism of cerium on inclusions and microstructure in low-alloy cast steel through experimental and thermodynamic analyses. After cerium is added to the steel, strip-like inclusions transform into spherical ones, accompanied by a reduction in size. The evolution path of inclusions follows MnS + MnS–Al₂O₃→Ce₂O₂S–Ce₂S₃–MnS + CeAlO₃–Ce₂S₃–MnS with cerium addition. Notably, Ce₂S₃ and Ce₂O₂S exhibit an orientation relationship, with [$\bar{1}$ 22]_Ce2S3//[01 $\bar{1}$ 1]_Ce2O2S and (02 $\bar{2}$)_Ce2S3//($\bar{1}$ 011)_Ce2O2S. Compared to Ce-free steel, the Ce-0.06 steel shows a reduced grain size and the absence of needle-shaped Widmanstätten structures, which may be mainly attributed to rare earth inclusions as heterogeneous nucleation of δ-Fe. This work can provide a theoretical basis for improving the overall mechanical properties of low-alloy cast steel by adding cerium.