In the current study, the modification behaviours of the SiO2–MnO inclusions by the additions of three types of ferrosilicon including low Al and Ca ferrosilicon, high Al ferrosilicon, and high Ca ferrosilicon were investigated by the lab experiment and thermodynamic calculation. The SiO2–MnO inclusions change little after the low Al and Ca ferrosilicon addition. The high Al ferrosilicon significantly promotes the formation of Al2O3-rich inclusions in 18Cr–8Ni stainless steels. The high Ca ferrosilicon can modify SiO2–MnO inclusions to larger Al2O3–SiO2–CaO particles, indicating that the source of large Al2O3–SiO2–CaO inclusions in the molten steel is not only the entrapment or emulsification of the slag but also the modification of inclusions by Ca in the ferrosilicon. Thermodynamic calculated results have a similar tendency with observed experimental results. The low Al and Ca ferrosilicon is suggested to be used for alloying process in the ladle furnace.
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