INTERACTION BETWEEN MOLTEN STEEL AND MgO-BASED TUNDISH LINING: A POTENTIAL SOURCE OF NON-METALLIC INCLUSIONS

Interactions between the molten steel and the refractory linings are of fundamental importance for the steelmaking industry. During the casting process the steel cleanliness can get worse because of the oxygen pick up of the liquid steel in contact with the atmosphere and the reoxidation of the molten steel caused by top slag and the refractory materials with high oxygen potential. In the industrial trials, three tundish refractory linings (pre-formed boards and two kinds of gunning masses, all MgO based refractories) were used in order to evaluate the interactions among the refractories and the molten steel. Due to small dimension of the tundish (5 ton) used in the continuous casting at Villares Metals SA, after casting, the chilled steel was cut in order to show us in a single section the stopper rod, submerged entry nozzle (SEN), MgO ramming and the work refractory lining. Cross sections of samples from steel/refractory interface were investigated by means electron probe microanalysis (EPMA). Three major aspects were observed at the steel/refractory interface: (1) steel infiltration into the tundish refractory lining, mainly in the gunning masses; (2) a steel oxidized layer formed at the steel/refractory lining interface and; (3) many particles were found in the steel phase, near to steel/refractory interface, being a potential source of non-metallic inclusions.