<i>In-situ</i> Observation of Inclusion Formation Behavior in Ultra-Low Carbon Steel with Al–Ti Complex Deoxidation

This research investigates the formation mechanisms of inclusions in ultra-low carbon steel with Al-Ti complex deoxidation. Al2O3-TiOx-(FeOx) complex inclusions can induce nozzle clogging and surface defects. Many studies have examined the formation of Al2O3-TiOx-(FeOx) complex inclusions in molten steel, and considerable effort has been made due to the difficulty in distinguishing between thermodynamic equilibrium and transient states. The primary focus is on confirming the effects of thermodynamically stable inclusions in the RH process with Al-Ti complex deoxidation using sampling techniques and high-temperature confocal microscopy. The samples were analyzed using SEM-EDS and SEM-FIB techniques for precise analysis, and the inclusions were extracted for SEM-EDS analysis. The inclusions analyzed in the RH samples with low oxygen potential, melted under deoxidized Ar gas conditions in a high-temperature microscope, were Al₂O₃, which is consistent with the results of the equilibrium phase diagrams reported by many researchers. Utilizing in-situ high-temperature confocal microscopy, this study confirms the formation of Al2O3-TiOx-(FeOx) complex inclusions during the reoxidation process. The results indicate that these Al2O3-TiOx-(FeOx) complex inclusions are not formed under thermodynamic equilibrium in the RH process but are instead a product of reoxidation. This results provides grounds for preventing reoxidation to reduce the formation of Al2O3-TiOx-(FeOx) complex inclusions, which cause nozzle clogging and surface defects in the steelmaking process.