Studies of effect of glass/silicon powder coatings on clogging behaviour of submerged entry nozzles when using REM alloyed stainless steels

Abstract

The internal surfaces of modern submerged entry nozzles (SENs) were coated with a glass/silicon powder layer to prevent SEN graphite oxidation during preheating. The effects of the interaction between the coating layer and the SEN base refractory materials on clogging were studied. The results indicated that penetration of the formed alkaline rich glaze into the alumina/graphite base refractory occurs during preheating. More specifically, the glaze reacts with graphite to form carbon monoxide gas. Thereafter, dissociation of CO at the SEN/molten metal interface takes place. This leads to reoxidation of dissolved rare earth metals, which form 'in situ' rare earth metal oxides at the interface between the SEN and the molten steel. In addition, the interaction of the penetrated glaze with alumina in the SEN base refractory materials leads to the formation of a high viscous alumina rich glaze during the SEN preheating process. This, in turn, creates a very uneven surface at the SEN internal surface. The 'in situ' formation of the rare earth metal oxides together with the uneven internal surface of the SEN may facilitate the accumulation of the primary inclusions on the refractory walls.

Studies of the decarburisation phenomena during preheating of submerged entry nozzles (SEN) in continuous casting processes

“…Already stated [7], the temperature of the SEN should never be over 800°C after preheating. However, these high preheating temperatures enable an increase of the interaction between the refractory base material and the molten steel during casting [1]. Hence, it is of great importance to obtain knowledge about the SEN's behaviour during the preheating process.…”

“…This steel flow through the SEN can be disturbed by nonmetallic inclusions which accumulate on the SEN's internal surface and lead to clogging of the SEN. This in turn can result in halted production, production losses, impaired quality and therefore increased costs [1][2][3][4]. During steelmaking the molten steel has a temperature of around 1600°C and if the SEN is at room temperature before being put in contact with the steel there is a high risk for thermal shock and resulting damage of the refractory base material (RBM).…”

“…Also, the results suggested that the preheating of a SEN should be carried out at higher temperatures and during shorter holding times instead of at lower temperatures and longer holding times. Alkaline (Na 2 O and K 2 O) glass/silicon powder coatings are used for protection against a graphite oxidation of the SEN's internal wall during preheating, which leads to the formation of a dense and protective glaze [1,5]. During preheating experiments, Memarpour et al [1] found that a protective high viscous alumina rich glaze penetrated into the Al 2 O 3 -C RBM.…”

“…Alkaline (Na 2 O and K 2 O) glass/silicon powder coatings are used for protection against a graphite oxidation of the SEN's internal wall during preheating, which leads to the formation of a dense and protective glaze [1,5]. During preheating experiments, Memarpour et al [1] found that a protective high viscous alumina rich glaze penetrated into the Al 2 O 3 -C RBM. Besides that the alkalis in the glaze reacted with the graphite; the penetration resulted in an uneven surface where primary inclusions in the molten steel were found to agglomerate on the surface [1].…”

“…During steelmaking the molten steel has a temperature of around 1600°C and if the SEN is at room temperature before being put in contact with the steel there is a high risk for thermal shock and resulting damage of the refractory base material (RBM). To minimize this phenomenon, the SEN is preheated before a casting operation is initiated [1]. This preheating of the SEN can initiate a decarburisation of the RBM, which can influence the casting process.…”