To reveal the mechanism of ferrite nucleation induced by Y₂O₂S inclusion in steel, the work of adhesion, interfacial energy, structure stability and electronic properties of Fe(111)/YY₂O₂S(001) interfaces with various terminations were first investigated using the first-principles calculations. Secondly, the steels with and without yttrium were prepared, while the rare earth yttrium-based inclusions in low carbon steel were characterized using an electron probe micro-analyzer, and the grain size of steel was analyzed using a scanning electron microscope with electron backscattered diffraction. The results show that the bonding strength of Fe/Y₂O₂S interfaces with S- and Y-terminations is stronger than that of the interface with O-terminations. The Fe–hcp–S interfaces with S-termination have the highest work of adhesion (4.01 J/m²) and the lowest interface distance (1.323 Å ). The Fe–hcp–S interface exhibits the highest stability, and its interfacial bonding force is mainly attributed to the strong hybridization of Fe-3d and S-2p orbitals in the energy range of - 7.5–0 eV. Moreover, the interfacial energy of Fe–hcp–S is substantially lower than those of the ferrite(s)/Fe(L) interface and the ferrite–austenite interface, suggesting that Y₂O₂S inclusions in steel can efficiently promote ferrite nucleation. The experimental observations demonstrate that the ferrite grain size of steel containing 0.03 wt.% Y is much more refined than that of the steel without yttrium, and the average grain size of steel with and without Y is 102 and 258 μm, respectively. This indicates that the results of our calculations match with experimental findings.

To reveal the mechanism of ferrite nucleation induced by Y₂O₂S inclusion in steel, the work of adhesion, interfacial energy, structure stability and electronic properties of Fe(111)/YY₂O₂S(001) interfaces with various terminations were first investigated using the first-principles calculations. Secondly, the steels with and without yttrium were prepared, while the rare earth yttrium-based inclusions in low carbon steel were characterized using an electron probe micro-analyzer, and the grain size of steel was analyzed using a scanning electron microscope with electron backscattered diffraction. The results show that the bonding strength of Fe/Y₂O₂S interfaces with S- and Y-terminations is stronger than that of the interface with O-terminations. The Fe–hcp–S interfaces with S-termination have the highest work of adhesion (4.01 J/m²) and the lowest interface distance (1.323 Å ). The Fe–hcp–S interface exhibits the highest stability, and its interfacial bonding force is mainly attributed to the strong hybridization of Fe-3d and S-2p orbitals in the energy range of - 7.5–0 eV. Moreover, the interfacial energy of Fe–hcp–S is substantially lower than those of the ferrite(s)/Fe(L) interface and the ferrite–austenite interface, suggesting that Y₂O₂S inclusions in steel can efficiently promote ferrite nucleation. The experimental observations demonstrate that the ferrite grain size of steel containing 0.03 wt.% Y is much more refined than that of the steel without yttrium, and the average grain size of steel with and without Y is 102 and 258 μm, respectively. This indicates that the results of our calculations match with experimental findings.