Adding low thermal expansion materials containing zirconia such as alumina zirconia or zirconia mullite is considered one of the most effective method to improve spalling resistance of sliding nozzle plates (SNP). Zircoma containing materials change their structure of crystal at about 1,000℃ and this creates the volume change of the refractories. And this volume change improves the spalling resistance of refractories. Generally, this volLIme change is considered to improve the spalling resistance of refractories. We investigated the influence of zircoma containing materials on the microstructure of refractories and the spalling resistance of SNP. As the results, we found that the higher the content of monoclinic zirconia in raw materials, the larger the volume change of refractories. And consequently microcracks in the microstructure will be increased. Microcracks will lower the elasticity of refractories and as the result, will improve the spalling resistance of SNP. However, on the other hand, microcracks will lower the strength of SNP at the same time. Therefore, we believe it is necessary to select appropriate zirconia containing material to control the amount of microcracks and improve the total performance of refractories.

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Magnesia carbon bricks, which are widely lined in converter as a working lining, are used under continuous heat cycles in real plants. This study investigated the effect of heat cycles on the corrosion resistance of MgO-C bricks in the offline experiments. The apparent porosity increased and elastic modulus decreased as the number of heat cycle increased, indicating the significant microstructure change and a decrease of the corrosion resistance of the MgO-C bricks. The microstructure after used in converter was almost the same as in the offline experiments. The results m those experiments were therefore validated by the results in real plants. Heat cycles during operation in real plants, which changes the microstructure of MgO-C bricks, must be taken into account in the offline evaluation.

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