Thermochemistry of Steel-Refractory Interactions in Continuous Casting Nozzles

Accretions on the inner walls of submerged entry nozzles (SENs) can be formed or modified by interactions between molten steel and refractory materials. Thermochemical reactions that qualitatively explain these interactions were modeled using Facility for the Analysis of Chemical Thermodynamics (FACT) thermodynamic software. The predicted phases were compared with results from high temperature static experiments. In these experiments, steels with and without aluminum were melted in refractory crucibles fabricated from various oxide refractories with and without graphite. Samples of the refractory-metal interface were characterized using cathodo-luminescence (CL) microscopy, reflected light (RL) microscopy and scanning electron microscopy (SEM) to understand the interactions and establish the effects of refractory and steel composition on accretion formation. Both microscopy data and thermo-dynamic predictions indicated that graphite-containing refractories, especially magnesia-graphite and alumina-silica-graphite, resulted in the greatest degree of interaction with steels. All of the carbon-free and impurity-free materials resulted in significantly fewer interactions