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High‐nitrogen stainless bearing steel (HNSBS) is the most representative third‐generation aviation bearing steel, and the cleanliness and microstructure characteristics of bearing steel are crucial to its high performance and long service life. In this work, the effect of cerium addition on the cleanliness and microstructure characteristics of as‐cast HNSBS was systematically studied by combining microstructural characterization and thermodynamic analysis methods. The results show that with increasing Ce content, the cleanliness of steel first improved and then decreased, and Ce2O2S, Ce2O3 and CeN inclusions were generated successively. The Ce content should be controlled to ≈0.012 wt% to ensure that all Al2O3, MgO · Al2O3, and MnS inclusions were modified, and minimize the formation of large‐size Ce‐bearing inclusions. Furthermore, cerium addition refined the dendrite structure due to more nucleation sites for γ‐Fe and the enrichment of Ce in the liquid phase at solidifying front. The finer and more dispersed distribution in precipitates was ascribed to the reduction of growth space and Cr segregation, as well as the increase in effective nucleation sites. These results can offer theoretical guidance for inhibiting the formation of harmful inclusions in high‐nitrogen alloy systems and refining the microstructure of alloy systems containing M23(C, N)6 and M2(C, N) precipitates. [ABSTRACT FROM AUTHOR]

Based on the analysis of thermodynamic driving force and solidification kinetics under pressure, the influence mechanism of solidification pressure on columnar‐to‐equiaxed transition (CET) of high‐nitrogen steel is clarified. It is observed that increasing the solidification pressure from 0.5 to 2 MPa results in a shift of the CET positions toward the center. This is attributed to the fact that higher solidification pressure can promote the growth of columnar dendrites by increasing the solidification rate, temperature gradient, and cooling rate. Meanwhile, increasing the solidification pressure shortens the length of the diffusion zone ahead of the advancing columnar front and reduces the supercooling. As a result, it becomes more difficult for equiaxed dendrites to nucleate ahead of the advancing columnar front, leading to CET positions closer to the center. This indicates that the main influencing factor for the change in CET caused by changing solidification pressure is solidification kinetics, that is, changes in the nucleation and growth environment of equiaxed dendrites, while thermodynamic driving forces are not the primary factor causing CET position changes. [ABSTRACT FROM AUTHOR]