Effect of Ce Addition on Inclusions and Primary Carbide Network in AISI 440C Bearing Steel

The effects of Ce on inclusions and the primary carbide network of AISI 440C bearing steel are experimentally and theoretically investigated. Adding Ce improves the cleanliness and refinement of primary carbide networks in AISI 440C bearing steel ingots. The addition of Ce substantially reduces the contents of total oxygen (T.O) and S in the steel, and MnS and Al 2 O 3 inclusions are modified into finer Ce‐containing inclusions (Ce 2 O 2 S and Ce 2 O 3 ). When Ce is added, the average equivalent diameter of the inclusions decreases from 1.82 to 1.33 μm, and the number of inclusions per unit area (mm 2 ) increases from 59 to 105. Moreover, the addition of Ce reduces the secondary dendrite spacing from 33.82 to 24.2 μm, and the proportion of primary carbide is reduced from 22.08% to 11.17%. The 2D lattice disregistry theory confirms that Ce 2 O 2 S and Ce 2 O 3 inclusions can be utilized as effective heterogeneous nucleation cores for γ‐Fe, thus refining the solidification microstructure and also the primary carbide. This study provides theoretical guidelines for the fabrication of domestic AISI 440C bearing steel ingots.