The internal surfaces of modern submerged entry nozzles (SENs) were coated with a glass/silicon powder layer to prevent SEN graphite oxidation during preheating. The effects of the interaction between the coating layer and the SEN base refractory materials on clogging were studied. The results indicated that penetration of the formed alkaline rich glaze into the alumina/graphite base refractory occurs during preheating. More specifically, the glaze reacts with graphite to form carbon monoxide gas. Thereafter, dissociation of CO at the SEN/molten metal interface takes place. This leads to reoxidation of dissolved rare earth metals, which form 'in situ' rare earth metal oxides at the interface between the SEN and the molten steel. In addition, the interaction of the penetrated glaze with alumina in the SEN base refractory materials leads to the formation of a high viscous alumina rich glaze during the SEN preheating process. This, in turn, creates a very uneven surface at the SEN internal surface. The 'in situ' formation of the rare earth metal oxides together with the uneven internal surface of the SEN may facilitate the accumulation of the primary inclusions on the refractory walls.

The rate of dissolution of solid MgO–C into liquid CaO–Al2O3–SiO2–MgO slag at different temperatures was studied under conditions of forced convection by rotating cylindrical refractory specimens in a stationary crucible containing molten slag. The corrosion rate was calculated from the change in diameter of the cylindrical refractory specimens. The specimens were rotated for 15–120 min at a speed of 100–400 rpm in the molten slag. The rate of corrosion was found to increase with an increase in temperature and rod rotation speed, and to decrease when the slag was nearly saturated with MgO. The experimental results support the assumption that the diffusion of magnesium oxide through the slag‐phase boundary layer controls the corrosion process. The corrosion mechanism seems to be the dissolution of refractory material into the slag followed by penetration of pores and grain boundaries and dispersion of the grains into the slag.

The conditions of formation of inclusions in steel during ladle refining in MgO‐C lined ladles have been investigated in laboratory experiments at 1873 K in MgO‐C crucibles with 50 g iron. From both the experimental results as well those of a thermodynamic study conducted in parallel, the following conclusions can be made about the reaction mechanism between the MgO‐C refractory and aluminium deoxidised molten steel: At steelmaking temperature an internal oxidation‐reduction occurs in the MgO‐C refractory. The formation of a thin oxide layer at the interface is due to the reaction between magnesium vapour and aluminium dissolved into the molten steel and the CO(g) generated by the reaction between MgO and C in the crucible walls. The oxide inclusions formed in the steel have been shown mainly to consist of MgO, Al2O3 or mixture of them. Some of the finest inclusions are considered to be formed as secondary inclusions during cooling and solidification of the steel and they are connected only with the diffusion of magnesium from the crucible to the molten steel. The thermodynamic calculations indicate that during vacuum refining, as the pressure decreases, the chemical compatibility of carbon‐bonded magnesia for ladle lining decreases.

PostprintThis is the accepted version of a paper published in Ironmaking & steelmaking. This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination.Citation for the original published paper (version of record):Svensson, J., Memarpour, A., Brabie, V., Jönsson, P. (2016) Studies of the decarburisation phenomena duringpreheating of submerged entry nozzles (SEN) incontinuous casting processes. Decarburisation of the submerged entry nozzles (SEN) during the preheating process was investigated based on plant trials and thermodynamic modelling at three different steel plants. During the trials the preheating processes were mapped, the temperature profiles were registered and post mortem studies of the SENs with scanning electron microscopy (SEM) were performed. Typically, the glass/silicon powder will form a dense and protective layer inside the SEN when heated over 1100°C. However, this study found that the temperature distribution inside the SEN did not always reach this critical temperature. Thus, decarburisation of the SEN was found at all steel plants. The overall results illustrate that the control of the pre-heating process needs to be improved at all steel plants. It is suggested that future research should be focused on the development of new coating materials to prevent decarburisation of the RBM, which would decrease the chances of clogging during casting. Ironmaking