Contribution of tundish slag entrainment, reoxidation, and refractory errosion, to the amount of large nonmetallic inclusions occurring during teeming in continuously cast slabs has been determined with tundishes of varying design equipped with different type of nozzles. Reoxidation taking place during teeming from ladle to tundish, travelling in tundish, and teeming through tundish nozzle, has also been evaluated separately. The fraction of large inclusions occurring from the entrainment of tundish-or mould-slag has been examined by use of La2O3 or CeO2 as tracer. Most of large inclusions has been found to be of exogenic origin arising mainly from air reoxidation and tundish slag entrainment.
On the basis of these observations, a combination of specifically designed tundish and tundish nozzle has been developed to virtually remove inclusion accumulation in the upper quarter thickness of continuously cast slabs for deep drawing-ironing strip steel and control-rolled high strength strip steels.
