Pilot plant study of nozzle clogging mechanisms during casting of REM treated stainless steels

Abstract

A pilot scale bottom teemed high frequency furnace with a nominal capacity of 600 kg and an adjustable nozzle temperature was used to study clogging of rare earth metal (REM) treated stainless steels. The influence of the following variables on the clogging was studied: amount of REM, fraction of oxide clusters, total oxygen content in the steel, reoxidation, aluminium additions before REM additions and silicon additions during casting. Overall, the results show that, during the present experimental conditions, mainly two typical clogging rates could be identified, fast and slow clogging. Two main differences could be detected between the fast and slow clogging rates. Steel containing mainly small single inclusions clogged faster than steel containing mainly large inclusion clusters. The reason was believed to be that the small inclusions could stick to the nozzle wall at narrow passages where the steel flow velocity was high while the larger ones could not. The source of the small inclusions was believed to be reoxidation. It was also found that the main part of the nozzle accretion was caused by agglomeration of inclusions and inclusion clusters, while only a thin oxide film along the nozzle wall was caused by oxide precipitation at the nozzle wall.

Turbulent Flow Phenomena and Ce2O3 Behavior during a Steel Teeming Process

“…After experiment, the steel left in ladle must be tapped out making it difficult to get a sample of solidified steel at that region. However, supporting the model results is the comparable experiments reported by Kojola,40) demonstrating that clogging also frequently occurs in the upper part of the nozzle. Both the simulation and experiment show that the transition region of geometry, or flow field, is the sensitive region for an inclusion deposition, as well as for clogging.…”

“…Although a lot of inclusions exist at the straight pipe nozzle wall, they are not the vital reason for the interruption of teeming. In Kojola et al study,40) clogging at the upper part of the nozzle near the connection region between the nozzle and ladle bottom was also found. …”

“…Kojola et al 40) showed the pictures of inclusion network near the nozzle wall and the nozzle center in their research. Inclusion compositions in steel and in clogged nozzle were also compared.…”

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

“…Furthermore, in channel 6 the seat is initially heated to a higher temperature in comparison to the other measurement positions. Since the clogging in the seat is the flow limiting factor in the SEN, it is of most importance to have a controlled preheating process [15]. Even though torches in the tundish lid were used, the lower temperature in channel 6, compared to the highest measured temperature, indicates that the temperature contributions from the torches in the tundish lid to the SEN were lower than from the torches at the SEN outlet.…”

Three Dimensional Evaluations of REM Clusters in Stainless Steel

“…1) Further studies [2][3][4][5][6] reported that rare earth metals reduce the degree of undercooling for nucleation, refine the as-cast structure, and limit solidification segregation in steels. However, the addition of a mischmetal to liquid steel often leads to formation of REM clusters and nozzle clogging, [7][8][9] which is a serious problem during continuous casting in the steel industry. Kojola et al 7) found that the main part of the nozzle accretion was caused by agglomeration of Ce inclusions and clusters.…”