In the present study, the effect of cerium content in the range of 0~0.0676% on oxygen and sulfur content, as well as the quantity, size, distribution, and type of inclusions in C104Cr saw wire steel, were investigated using thermodynamic analysis, metallographic examination, SEM-EDS, and component analysis. The results showed that conducting a vacuum carbon pre-deoxidization process is helpful in preventing the formation of Ce₂O₃ inclusions in a smelting experiment, and cerium has a beneficial effect in terms of modifying inclusions. When the content of cerium in steel is 0.0136% or 0.0277%, the main inclusions in the steel are Ce₂O₂S and CeS, and when the content of cerium is 0.0389% or above, the inclusions in the steel are Ce₂O₂S, CeS, Ce–S–O–P(As), Ce–O–P, and Ce–P(As). The calculation of the segregation model showed that the precipitation of CeP and CeAs in steel takes place at the end of solidification. According to the element mapping distribution diagram of Ce–S–O–P(As) and the layered Ce–O–P inclusions found in steel with high cerium content, two possible mechanisms for the formation of Ce₂O₃ inclusions distributed in the outer layer of cerium composite inclusions are proposed. The first mechanism suggests that Ce₂O₃ inclusions are generated from the combination of [Ce] and [O] directly, and the second suggests that Ce₂O₃ is the product of an oxidization reaction after the formation of CeP.

The effect of Ce on the microstructure, mechanical properties and corrosion resistance of 27Cr-3.8Mo-2Ni super-ferritic stainless steel were investigated by FactSage 7.2. The results reveal that when the Ce content increases from 0.00 wt-% to 0.0498 wt-%, Al₂O₃ inclusions wrapped by irregular (TiNb)N are gradually modified into spheroidal CeAlO₃, Ce₂O₃, Ce₂O₂S and Ce-O-P complex inclusions, the rare earth inclusions are smaller than 1.0 × 10⁻⁶ m (1.0 μm) and dispersedly distributed. The diameter of recrystallized ferrite grain is decreased, the mechanical properties of super-ferritic stainless steels are well improved, impact fracture appearance transforms from pre-dominant cleavage to ductile fracture at 298 K (25°C), and the cleaving step of the fracture becomes smaller at 243 K (−30°C), the uniform corrosion resistance to H₂SO₄ of steels with is enhanced especially in 40 vol.-% H₂SO₄ at 333 K (60°C). In addition, the microstructure and properties could not be further improved with 0.0744 wt-% Ce content.

To clarify the effect of sulfur on inclusions and mechanical properties of Ce-Mg treated resulfurized SCr420H steel. Laboratory experiments were conducted to prepare steels with sulfur contents as 0.01%, 0.06%, and 0.132%. Inclusion evolution in liquid steel, MnS precipitation during solidification, and tensile test results of steel after quenching and tempering were investigated. The results showed that due to the limitation of mass transfer in molten steel, composite inclusion that Ce-O-S wrapped by Ce-Ca-Mg-Al-Si-O, which was named transition state inclusions, can form quickly after adding Ce-Mg lump to the molten steel. As the homogenization of molten steel, the difference of sulfur content in steel can lead to the transition state inclusions transformed into different inclusions. With the increase of sulfur content, the quantity of MnS increased significantly, and the morphology of MnS transformed from “stick” to “dendritic + fishbone”, and then to “fishbone”. Tensile test results and fracture analysis indicate that the decline of inclusion spacing as the increase of sulfur content leads to a shorter physical path of crack propagation in steel. Therefore, the increase of sulfur content can bring about a decrease in the strength and plasticity of the steel. From the perspective of inclusion control, making the MnS inclusion precipitate more dispersive and increasing the distance between inclusions can be considered as a method for preventing the decline of mechanical properties in steel with high sulfur content.