Formation Mechanisms and Three-dimensional Characterization of Composite Inclusions in Low Aluminum Steel Deoxidized by Silicon

Silicon deoxidized steel takes a large proportion in addition to aluminum deoxidized steel, since aluminum deoxidation may cause many problems, such as nozzle clogging and low toughness. In this paper, a low aluminum silicon deoxidized steel was prepared in the laboratory. The inclusions in steel mainly include MnS and composite inclusions made of MnS and oxides. The formation of MnS and composite inclusion was discussed based on the thermodynamic calculations. It was clarified that the MnS precipitate during the solidification process of steel. In addition, the formation mechanism of the composite inclusions was illustrated from the perspective of thermodynamics and lattice mismatch. The composite inclusions in steel were reconstructed by Micro-CT and the three- dimensional (3D) morphologies were analyzed in details. This method avoids artifacts and misleading of the two-dimensional observation on the cross sections of the steel samples. Meanwhile, the 3D observation by Micro-CT is an innovation way to characterize the different phases of the inclusion simultaneously, which paved a way for the analysis of the composite inclusions in the steel.