Effect of the structural parameters of refractories on their slag impregnation in the units used for vacuum refining of steels

Abstract

Extensive studies on the mechanism of the wear of the linings of the vacuum units used for refining of steels have revealed splitting (shear failure) of the products during thermal cycling and erosion of their working layer owing mainly to the characteristics of the process of interaction of the refractories with the metal and the slag (the characteristics such as the depth of impregnation and the quantity of the liquid phase accumulated in the material). In particular, splitting (chipping) of the refractories can occur because of the difference in the coefficients of thermal expansion of the impregnated and the unaffected zones or due to the modifying transformations of the infiltrate that are accompanied by volumetric expansion. The rate of the erosive wear of the refractories is determined to a large extent by the extent of the structural changes occurring in the material adjacent to the working layer owing to the increase in the content of the liquid phase and by the depth of occurrence of these changes that adversely affect the mechanical properties of the material. Table 1 shows comparative data with respect to the total thickness (depth of impregnation) of the reaction zone and the transitional zone in the specimens of the products after their service in the slag belt of a ladle of an ASEA-SKF unit and in the branch pipe (nozzle) of a VP-130 batch-output vacuum installation and, also, the average wear rate and the quality parameters of the refractories.With respect to open porosity and strength, the imported products do not differ significantly from the Soviet products; however, they are subjected to impregnation and wear to a considerably less extent (the insignificant depth of impregnation of the PShKV products is not to be taken as an indicator of quality because of their intensive wear).In order to delineate the reasons underlying such a significant difference in the depth of the impregnated portion, we carried out a comparative study of the pore structure of the refractories, the wetting characteristics with respect to the ladle slag and the steel processed in an ASEA-SKF unit.