The use of nozzle refractories in the continuous casting process has resulted in significantly higher productivity and increased stability in steel production. Nozzle refractories are considered critical components in the steel-making process, particularly submerged nozzles. Their stable performance and high durability are essential to the final stage of steel production. The enhanced performance of nozzle refractories is the result of many important improvements that have extended the life of the nozzles. Most significant is the improvement in the corrosion resistance of the material in the powder line zone, where the outer surface of the nozzle contacts the reactive fused casting powder and can result in the fatal corrosion of the nozzle. Recently, ZrO_2-Graphite (hereinafter known as "ZG"), has been used in the powder line zone due to its excellent corrosion resistance. It is generally known that the addition of zirconia (ZrO_2) to ZG improves its corrosion resistance although it may not improve its overall performance if ZrO_2 content is greater than 80%. This paper will explore the relationship between ZG's apparent porosity and its corrosion resistance and will clarify the reason why corrosion resistance deteriorates when ZrO_2 content exceeds 80 %. This paper will also examine how the durability of ZG materials can be improved. Thermal spalling resistance will be studied because resistance to thermal spalling deteriorates when ZrO_2 content is increased in ZG materials. This report will further examine how the properties of ZG materials change when a unique resin binder is added and microstructures such as carbon fiber are produced by carbonization through thermal processing. It will be shown that the addition of the unique resin improves both corrosion resistance and thermal spalling resistance in dense ZG materials of relatively high ZrO_2 content.
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