First-principles investigation of MnS inclusion adsorption on MgAl ₂ O ₄ surfaces in EH40 steel

Oxide metallurgy is a critical technique for enhancing the welding performance of hull steel in high-heat-input welding applications. Its fundamental principle involves controlling the formation of beneficial composite inclusions and ensuring their uniform distribution within the steel matrix to facilitate grain refinement. In this study, EH40 hull steel with a multi-element Mo-Nb-Al-Mg-Ti system was investigated. The production process required ladle refining and magnesium–titanium treatment. The atomic-scale adsorption mechanism of MnS on the MgAl 2 O 4 surface was examined through a combination of first-principles calculations and microscopic characterization. A 10 × 10 × 10 mm steel plate sample was prepared for scanning electron microscopy (SEM) analysis, while a transmission electron microscope (TEM) sample was extracted using an FEI Scios focused ion beam system. SEM and TEM observations revealed that the complex inclusions consisted of an MgAl 2 O 4 core with attached Ti 2 O 3 precipitates, while MnS encapsulated the outer surface. The adsorption interface between MgAl 2 O 4 and Ti 2 O 3 was identified, with some Mn atoms bonding to titanium oxide. A bulk model with space group Fd-3 m, a lattice parameter of 0.8075 nm, and 56 atoms was constructed using Findit software. The adsorption energy, structural configuration, and electronic interactions of S and Mn atoms on the MgAl 2 O 4 (100)-Mg surface were analyzed through a two-step computational approach, considering different initial positions and adsorption sequences. The results confirmed that the TO1 site was the most favorable adsorption site for MnS on the MgAl 2 O 4 (100)-Mg surface, with an adsorption energy of −9.2 eV. The MnS growth mechanism involved the initial adsorption of Mn atoms onto the MgAl 2 O 4 (100)-Mg surface, followed by vertical growth into a cross-quaternary ring crystal structure.