Innovative refractories for preventing nozzle clogging in continuously cast aluminum-killed steels

Nozzle clogging in submerged entry and tundish nozzles adversely impacts the productivity and quality of continuously cast aluminum-killed steels. The objective of the research conducted was to develop innovative refractories that are less prone to accretion formation than current materials.;Nozzle permeability has been theorized to affect nozzle clogging. However, until this work no experimental evidence had been collected to evaluate the merit of this theory. Casting simulation experiments that replicate industrial clogging behavior were conducted on laboratory alumina-graphite and magnesia nozzles with varying permeability levels. Nozzle permeability was found to have no significant effect on clogging behavior.;Static accretion experiments were conducted on calcium titanate, calcium zirconate, boron nitride, boron carbide, and silicon carbide with unkilled and aluminum-killed steels. The purpose of these experiments was to evaluate the stability of these materials with molten steel. All five materials reacted with the molten steel to varying degrees. The carbide and nitride materials were dramatically attacked by molten steel. There was also evidence of severe contamination of the steel with various dissolved elements. Calcium zirconate and calcium titanate reacted with alumina present in the molten steel. Both materials transformed the alumina to a calcium aluminate phase. Only calcium titanate appeared to transform the alumina to liquid calcium aluminates, which could dramatically reduce clogging.;Based on the static accretion experiments, casting simulations were conducted on calcium titanate, calcium zirconate, and a 2:1 calcium zirconate to calcium titanate blend. Nozzles were made from each material. Calcium titanate dramatically outperformed current refractories and the calcium zirconate and 2:1 mixture nozzles. Microscopy on spent simulation nozzles showed no accretion formation in the calcium titanate nozzles. The reduction in accretion formation was due to liquid phase formation at the nozzle wall, which prevented alumina accretion formation.