Internal Erosion in Submerged Entry Nozzles of Continuous Steel Casters as a Function of Al, Si and Ca Concentrations in Nozzle Wall

摘要

This paper presents the causes of scab formation on the inside wall of submerged entry nozzles (SEN) in continuous steel casters. X-ray fluorescence spectrometry(XRF) of the wall of the graphite-alumina SEN after the continuous steel casting process revealed a change in the Al, Si and Ca concentrations in the SENs of one series. Measurement results showed that the SEN wall thickness had decreased, irrespective of the scab thickness, due to internal erosion. In addition, the Al, Si and Ca concentrations in the SEN-steel contact zone of the wall were found to have changed. The increase in Al and Si concentrations in the contact zone compared to the rest of the wall is the result of diffusion on the steel side of the SEN wall. At the same time, the Ca concentration was lower in the contact zone of the SEN wall than in the rest of the wall. The examination results have shown that the Al and Si concentrations increase with increasing internal erosion in the SEN, while the Ca concentration in the contact zone of the SEN wall decreases. The significance of this relationship also confirms the high values of correlation indexes. The drop in Ca concentration in the contact zone of the SEN wall can be explained by the increase in the Ca content in the scab. As internal erosion in the SEN wall increases, the Ca concentration in the contact zone of the SEN wall decreases, while the CaO content in the SEN scab increases. At the same time, this changed concentration and diffusion were not registered in the walls of the other SEN series. The wall thickness of the nozzles in the other series also remained unchanged, which confirms that no internal erosion has occurred. The relationship between internal erosion and Al, Si and Ca concentrations in the SEN wall could be established only after complex research of both the SEN scab and the SEN wall. The research had to be done on a large number of samples from nozzles used in a continuous rounds caster.