Experimental Investigation of the System Nonmetallic Inclusion-Molten Steel-Refractory System at High Temperatures

In continuous casting, the buildup of particles in the flow control system is called clogging. Clogging may be caused by preexisting nonmetallic inclusions attached to the refractory wall, interrupting or disturbing the fluid flow conditions. The interfacial properties of the nonmetallic inclusion-molten steel-refractory system are believed to play a key role in the clogging tendency of selected steel grades in contact with ceramics. The combination of a high-temperature laser scanning confocal microscope (HT-LSCM), which is employed for in situ observation of inclusions’ behavior in the liquid steel or at the steel/ceramic interface, and a high-temperature drop shape analyzer (HT-DSA), which is utilized for contact angle measurements, enabled the investigation of reactions and interactions in the described system at experimental temperatures of approximately 1600 °C. The objective of this study was to develop a method to obtain qualitative information on the deposition of nonmetallic inclusions (NMIs) in the submerged entry nozzle (SEN) during casting. The behavior of solid NMIs from a calcium-treated steel at the interface between liquid steel and Al₂O₃ or MgO was investigated by means of HT-LSCM. During the test evaluation, inclusions were found to separate at the steel/ceramic interface due to an attractive force. This force increased with the NMIs’ size as well as with the ceramic particle change. The HT-DSA provided contact angle data between molten steel and the ceramic used for implementation into the theoretical capillary force model. A clear correspondence between the estimated and calculated capillary forces was observed. The change in the wettability of the system, as induced by the change in the ceramic from MgO to Al₂O₃, showed a reduction of the attractive forces, indicating a weaker separation toward the SEN for the same inclusion type. This study confirmed the strong potential of wettability investigations to predict the clogging tendency of certain steel grades.