Improving the as-cast structure and semi-macro segregation in bearing steel through cerium inclusions

The modification effect of the rare earth Ce on inclusions in 100Cr6 bearing steel was investigated through theoretical calculations and experimental analysis to clarify its role in refining the solidification structure and reducing semi-macro segregation. The results show that the stability of rare earth inclusions formed after Ce addition in high-carbon chromium bearing steel follows the sequence: CeAlO 3 → Ce 2 O 2 S → Ce 2 O 3 . The lattice misfit calculations indicate that the lowest matching interfaces are (111) CeAlO3 //(111) γ-Fe , (0001) Ce2O2S //(100) γ-Fe , and (0001) Ce2O3 //(100) γ-Fe , demonstrating that these inclusions serve as heterogeneous nucleation sites for the primary γ-Fe phase. With increasing Ce content (0, 48, 130, and 190 ppm), the inclusion modification sequence evolves as follows: MgAl 2 O 4 → CeAlO 3 → Ce 2 O 3 → Ce 2 O 2 S. High-temperature melting experiments show that the Ce-free control group exhibits an equiaxed ratio of 31.2 %, characterized by coarse secondary dendrites in the core zone and a maximum spot segregation size of 178.2 μm. When Ce content reaches 48 ppm (forming CeAlO 3 ) and 190 ppm (forming Ce 2 O 2 S), the refinement of the solidification structure remains limited, resulting in moderate increases in the equiaxed ratio to 39.6 % and 44.0 %, respectively, with minimal reduction in spot segregation size. However, when Ce content is 130 ppm, the formation of Ce 2 O 3 inclusions significantly refines the solidification structure, increasing the equiaxed zone to 71.7 %, producing a uniform and fine equiaxed dendritic, and reducing the maximum spot segregation size to 148.6 μm. These results indicate that optimizing Ce content to promote Ce 2 O 3 inclusion formation can significantly refine the solidification structure of high-carbon chromium bearing steel. Such structural refinement benefits the improvement of banded carbides during subsequent rolling, thereby improving overall product homogeneity.