The distribution and morphology of inclusions in steel have an important effect on the quality of steel. It has been proved that the oxide inclusions can be modified into small and dispersed spinel inclusions by adding proper amount of Mg in steel. The MnS-MgAl 2 O 4 composite inclusions are formed with the core of MgAl 2 O 4 inclusions during the solidification process of molten steel, which has deforming ability and can improve the properties of materials steel. However, the investigation of the control of the composite inclusions is limited by the lack of understanding structure of the inclusions. In this study, the Mg treated steel samples were prepared by induction furnace in this study. In the experiment, SEM-EDS was used to characterize the samples, and thermodynamic calculations were used to describe the evolution mechanism of inclusions and MnS-MgAl 2 O 4 composite inclusions formed in steel samples with different Mg contents. The atomic mismatch calculated between MnS and MgAl 2 O 4 proves that they can nucleate effectively. The threedimensional (3D) morphology of the composite inclusion of MnS-MgAl 2 O 4 in steel samples were observed by using the X-ray Micro-CT in the beamline of BL16U2 at Shanghai Synchrotron Radiation Facility (SSRF). It is proved that MnS and MgAl 2 O 4 phases exist in the form of coassociated, which is valuable for the control of composite inclusions in steel. The current work provide a powerful method to analyze the detailed structure of the composite inclusions in the steel.
The complex inclusions of Al 2 O 3 -SiO 2 is a common inclusion in the steel, which leads to the stress concentration in the steel products. The formation of MnS on the surface of Al 2 O 3 -SiO 2 could reduce the stress concentration due to the high plasticity of the MnS. In this study, the formation of MnS-Al 2 SiO 5 complex inclusions is investigated at the atomic level by using first principles calculation based on the density functional theory (DFT). The adsorption energy of the atoms of Mn and S on the Al 2 SiO 5 (110) surface was calculated with various initial positions and sequence. The interaction among the atoms was calculated to analyze the stable structures after the adsorption of the Mn and S on the Al 2 SiO 5 (110) surface. The formation of the MnS on the surface of Al 2 SiO 5 was proved by analyze the structure formed by the adsorbed atoms that shows the similar tetracyclic structure of the MnS crystal.
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