First-Principles Calculation and In Situ Observation on the Precipitation of Inclusions during Solidification of a High Sulfur Steel

The precipitation process of inclusions in the high sulfur steel with the cerium addition is observed using the high-temperature confocal scanning laser microscope (CSLM). Rare earth (Re) inclusions formed in the molten steel, and MnS inclusions precipitate along grain boundaries or on oxide cores at the end of solidification. With the addition of cerium, the average aspect ratio of inclusions in the steel decreases from 6.5 to 5.0, and the addition of cerium effectively modifies the elongated MnS. Thermodynamic calculations show the inclusion transformation during solidification, yet it lacked the formation of Ce₂O₂S and Re sulfides. According to the first-principles calculation, the priority of the inclusion formation was Ce₂O₃ > CeAlO₃, Ce₂O₂S > CeS > Ce₃S₄ > MnS. The stability of MnS inclusions is much lower than that of cerium-containing inclusions. It is in situ observed that the addition of cerium promotes the formation of cerium-containing inclusions and reduces the precipitation of MnS in the high sulfur steel.