<p>This investigation focuses on the characteristics of single, large-sized, spherical D-type inclusions within the ultra-high clean bearing steel. The compositions and diameters of single, large-sized, spherical D-type inclusions are investigated through the comparative analysis of inclusion data derived from three different plants. The findings elucidate that single, large-sized, spherical D-type inclusions predominantly belong to the CaO–SiO₂–Al₂O₃ type which contains Si content ranging from 1 to 10 mass pct. Large-sized inclusions exceeding 60&#xa0;<i>μ</i>m exist within specific ranges associated with Si content and the mass ratio of Ca/Al of the inclusions. As the Ca/Al or Si content in the inclusions increases, the diameter of inclusion follows an ascending and subsequently descending trend. When the Al₂O₃/(Al₂O₃&#xa0;+&#xa0;CaO) ratio in inclusions falls within the range of 48.9 to 53.3&#xa0;mass pct, their average size reaches its peak. These characteristics are primarily influenced by the Ca/Al ratio and Si content’s effect on the melting point of inclusions. The large-sized inclusions discussed in this study are all in a pure liquid state at 1600&#xa0;°C. The melting point of inclusions directly impacts their size. The lower the melting point, the more likely these inclusions will remain in a pure liquid state during the smelting process, thus staying in the molten steel. The Ca/Al ratio in inclusions plays a critical role in determining both their melting point and size. Although Si has less direct influence on the melting point, it serves as an indicator of Al’s reactivity and the early incorporation of Ca during the competitive oxidation of Ca, Si, and Al in molten steel.</p>