The Submerged Entry Nozzle : A Study of how to Reduce Decarburization and Clogging

Abstract: During continuous casting the submerged entry nozzle (SEN) is one of the critical points. This since sequence casting is favourable, clogging of the SEN results in fever sequences or aborted castings. In this study the preheating of SEN has been evaluated at different steel plants. This since it earlier  has been found, preheating resulted in decarburisation of  the refractory base material (RBM)  which in turn resulted in clogging of the SEN. During the industrial preheating trials it was found that decarburisation of  the SEN is possible.The decarburisation results in a higher oxygen potential near the SEN wall. This in turn makes it possible for aluminum in the molten steel to form alumina particles. For low carbon aluminum killed steel grades, accretion of alumina clusters on the SEN internal wall result in clogging which hinder or reduces the steel flow through the SEN. For this reason, laboratory trials were performed to establish the formation of a liquid phase. Thus simulating the formation of liquid inclusions when alumina clusters attaches to the SEN wall, and which can be washed away by the steel flow. Formation of a liquid phase was indicated at the temperatures 1550-1600°C, and plasma coated nozzles were tried in pilot plant trials. The coating contained of 5-9 pct, 99.9 pct pure, calcium titanate (CaTiO3) mixed with yttria stabilized zirconia (YSZ).