Non-metallic inclusion entrapment by slags: laboratory investigation

Abstract Non-metallic inclusions that originate from secondary metallurgy treatments may provoke nozzle clogging during continuous casting and lead more or less directly to surface defects on final products. The amount of these non-metallic inclusions (oxides or nitride) in the solid or liquid steel is governed by the steelmaking practice and in particular by the different slags used in ladle, tundish or mould. One of the functions of the slag is the entrapment of non-metallic inclusions contained in the liquid steel. To study the rate of entrapment, a new experimental technique has been developed. It consists of melting the top of a steel rod together with a slag droplet in an induction furnace. The phenomenon of inclusion entrapment is directly observed on the surface of the liquid steel and recorded with a video camera. The rate of entrapment is measured using image analysis. The original laboratory results obtained have shown that one of the physical-chemical parameters which modifies the kinetics of oxide inclusion assimilation is the rate of dissolution in the slag. Slags with low viscosity and a low alumina activity are the more efficient to assimilate alumina inclusions, in agreement with literature results. Interaction of TiN inclusions with different slags appears to be more complex.