Al 2 O 3 -carbon composite submerged entry nozzles (SEN) are used for continuous casting of steels. Although this material has excellent mechanical and thermal properties, it frequently leads to clogging. The purpose of our research is to find a suitable refractory material that can be used to coat SENs. This paper reports on the chemical compatibility of a number of potential refractory materials: Al 2 O 3 , ZrO 2 , Al 2 O 3 -carbon, SiO 2 and MgO with liquid steel, an amount of simulated inclusions and synthetic slag. For this purpose, an experimental laboratory procedure was optimised to simulate the nozzle behaviour during continuous casting. Al 2 O 3 was found to give satisfactory results, and therefore a Al 2 O 3 plasma coated Al 2 O 3 -carbon material was also tested in the laboratory with good results.

Casting high quality steel grades requires the use of a submerged entry nozzle (SEN) to prevent oxygen and nitrogen pick-up and to achieve favourable steel flow conditions in the mould. Clogging of the SEN leads to instability of the casting operation as well as to a decrease in slab quality. To understand the interactions between liquid steel and the SEN, 156 nozzles from the Sidmar steel plant were investigated with respect to the amount of clogging. A linear relation between the clogging volume and the clogging weight was observed. This indicates that the clogging material's density remains constant during the clogging process for the different steel grades. A distinct relationship was also found between the amount of clogging and the cast steel weight. No relation between the amount of clogging and the superheating of the steel nor the steel flow rate was noticed, however. It was also concluded that for AI killed steels the high Mn (> 3000 ppm) and high C (> 500 ppm) grades cause less clogging than AI killed steel grades with low Mn content « 3000 ppm) and that AI/Si killed steel grades cause less clogging when compared to AI killed steel grades. When comparing these different steel grades with respect to their total oxygen concentration in the ladle, it appears that steel grades, which have a low total oxygen concentration, cause less clogging in the SEN. Based on these observations three combinations SEN/steel grade were selected for further analysis with electron microscopy. Verstopfung vonTauchrohren in StranggielJanlagen. Beim Stranggie!Jen hochwertiger Stahlsorten ist die Benutzung eines Tauchrohres (submerged entry nozzle -SEN) erforderlich, um die Aufnahme von Sauerstoff und Stickstoff zu vermeiden. Ein anderer Grund besteht darin, gOnstige Stremungsbedingungen in der Kokille einzustellen. Um die Wechselbeziehung zwischen FIOssigstahl und SEN besser zu verstehen, wurden 156 Tauchrohre des Stahlwerks der Sidmar auf ihre Neigung zum Zusetzen untersucht. Bei den untersuchten SEN konnte ein Zusammenhang zwischen dem Volumen und dem Gewicht der Partikel, die die Tauchrohre verstopfen, sowie zwischen deren Gre!Je und der durch das Tauchrohr vergossenen Stahlmenge festgestellt werden. Zwischen der Menge dieser Partikel und der Oberhitzung des Stahls, bzw. der Gie!Jgeschwindigkeit lieB sich keine Beziehung feststellen. Statistisch wurde ermittelt, da!J aluminiumberuhigte Stahlsorten mit hohem Mangangehalt (> 3000 ppm) und hohem Kohlenstoffgehalt (> 500 ppm) in geringerem MaBe zum Zusetzen neigen als aluminiumberuhigte Stahlsorten mit niedrigem Mangangehalt « 3000 ppm). Mit Aluminium und Silicium beruhigte Stahlsorten wirken ebenfalls weniger verstopfend als aluminiumberuhigte Stahlsorten. Auf der Basis dieser Ergebnisse konnten drei Kombinationen SEN/Stahlsorte festgelegt werden. FOr jede Kombination wurden mikroskopische und elementare Analysen durchgefOhrt.