Steven Smets

Behaviour of magnesia-carbon refractories in vacuum-oxygen decarburisation ladle linings

Abstract Magnesia–chromite bricks are commonly used in the working lining in vacuum–oxygen decarburisation ladles. However, they are expensive and potentially environmentally-unfriendly. The possibilities of employing magnesia–carbon refractories were investigated through industrial testing combined with post-mortem assessments, thermodynamic calculations and mechanical considerations. Pitch bonded magnesia materials cannot be used in the slagline owing to the MgO–C reaction and extrinsic oxidation of carbon by reducible slag components (mainly CrOx), resulting in carbon removal, slag infiltration and direct MgO corrosion. Combined with turbulent slag motion this leads to hot erosion. Direct carbon burnout and the MgO reaction are the main causes for their failure in the freeboard. However, pitch bonded magnesia refractories are able to compete with magnesia–chromite bricks in the ladle bottom and in the lower metal bath region, where levels of turbulence and slag infiltration are limited. Simultaneously, both the MgO–C reaction and the extrinsic oxidation of carbon are restrained by, respectively, the inhibiting effect of a mechanical barrier and the non-wetting behaviour of steel towards the magnesia refractory component.

Measurement of ladle slag oxygen activity using electrochemical sensor

Abstract The oxygen activity of the ladle slag may be measured in situ with an electrochemical sensor. The measurement principle of this sensor needs further clarification. An experimental and computational study has been carried out of the contribution of specific components to the oxygen activity of the slag and of the factors that influence oxygen activity measurement with the sensor. Experiments on an industrial and on a laboratory scale show that FeOx, SiO2 and MnO exert a measurable influence on the results. The measurements also show a marked influence of the dissolved oxygen content in the steel. The oxygen activity of the slags has been calculated thermodynamically and compared with the sensor measurements. A systematic difference is observed. A hypothesis on the working principle of the sensor and on the cause of occasional problematic measurement values is proposed.