Thermodynamic Formation and Three-dimensional Characterization of MnS–MgAl₂O₄ Composite Inclusions in Steel

Abstract

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.

Effect of Magnesium on Sulfide and Microstructure in Microalloyed Steel

“…In the range of 750-1400 °C, the mismatch degree value ranges from 7.8% to 8.5%, [16] and even lower than 7.0% when their planes are {110}. [17] The formation mechanism of MnS-MA composite inclusions has always been considered the result of heterogeneous nucleation, while the relationship between the state of the MnS-MA system and its formation mechanism has been ignored during the solidification process of steel. In this study, to improve the cutting performance of sulfides on medium carbon MAS, trace amounts of magnesium were added to the steel to explore the effect of magnesium on the morphology of sulfides.…”

“…In the range of 750–1400 °C, the mismatch degree value ranges from 7.8% to 8.5%, [ 16 ] and even lower than 7.0% when their planes are {110}. [ 17 ]…”