Clogging in submerged entry nozzles

Abstract

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 Al killed steels the high Mn (> 3000 ppm) and high C (> 500 ppm) grades cause less clogging than Al killed steel grades with low Mn content (< 3000 ppm) and that Al/Si killed steel grades cause less clogging when compared to Al 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.