The Modification of Aluminum Oxide Inclusions in Bearing Steel under Different Cleanliness Conditions by Rare Earth Elements.

The impact of rare earth treatment on the chemical morphology evolution of non-metallic inclusions in bearing steel under different initial cleanliness conditions was studied through simulation. Thermodynamic calculations indicate that at an oxygen content of 0.001%, the evolution route of inclusions with increasing Ce content was Al₂O₃ → CeAl₁₁O₁₈ + CeAlO₃ → CeAlO₃ + Ce₂O₂S → Ce₂O₂S → Ce₂O₂S + CeS. As the initial oxygen content decreases, the proportion of CeAlO₃ decreases, leading to easier conversion of CeAlO₃ to Ce₂O₂S. Vacuum induction furnace experiments demonstrated that with an oxygen content of 0.001%, an increase in Ce content results in a gradual rise in the proportion of inclusions in steel sized 1~2 μm. In contrast, the proportion of inclusions sized 2~5 μm decreases. Consequently, the overall content of inclusions in steel decreases, along with a reduction in both the number density and average size of inclusions. Introducing bearing steel melt with approximately 0.01% Ce rare earth to bearing steel with initial oxygen contents of 0.0005%, 0.001%, and 0.0015% showed an evolution of inclusions from Ce₂O₂S and CeS to Ce₂O₃, CeAlO₃, etc. The average inclusion size significantly increased from 0.7 μm to 2.16 μm. Morphologically, the transition of inclusions from precipitated to polymerized forms occurred as the initial oxygen content rose. High-temperature laser confocal microscopy experiments demonstrated that inclusions in low cleanliness conditions tend to agglomerate more than those in high cleanliness conditions, contributing to the increase in average size. [ABSTRACT FROM AUTHOR]