Submerge entry Nozzles based on alumo-graphite refractory material in the process of continuous steel casting

Abstract

Submerge entry Nozzles are parts made of refractory material and are utilized for steel casting in the continuous casting process. Steel is cast from the tundish into the crystallizer through the Submerge entry Nozzle (SEN). The role of the SEN is to protect steel from oxidation and to provide a uniform flow of steel during casting[1][2]. SEN are manufactured from refractory material with diverse composition. At the beginning of application of SEN, when introducing the continuous casting process, white SEN, based on melted quartz, were utilized. White SEN were utilized primarily for casting one steel grade. Alumo-graphite SEN are another type of SEN that are utilized for casting all steel grades. They are sensitive to thermal shocks, so before use they must be heated in special heating facilities at the temperature ranging from 1000°C-1100°C. Alumo-graphite SEN are manufactured by special isostatic pressing process. These are used successfully today. During casting, the SEN are in contact with steel on the internal side of the wall, and on the external side of the wall with casting powder and slag formed in the crystallizer. Internal erosion sometimes appears at the contact with steel on the internal side of the wall of alumo-graphite SEN, but build-up is formed more often. The SEN erosion occurs on the external side of the SEN wall, which originated due to the effect of casting powder and slag. All three phenomena affect SEN durability. External erosion reduces the thickness of SEN wall and causes SEN cracking. On the other hand, the formed build-up reduces the diameter of SEN orifice (aperture) leading to reduction of steel flow and excluding the SEN from the exploitation process. Depending on the steel grade being cast, mineralogical composition of casting powder, quality of alumo-graphite SEN, SEN design, technological parameters and technological process itself, the internal, external erosion or build-up will appear on the internal wall of the alumo-graphite SEN. Each of enumerated phenomena affects the lifetime of the alumographite SEN. This scientific paper aimed at presenting and explaining the phenomena and causes of reduced lifetime of the alumo-graphite SEN on a few characteristic examples.