Corrosion Mechanism of A Density-Reduced Steel Ladle Lining Containing Porous Spinel-Calcium Aluminate Aggregates

Refractory monolithics for steel ladle linings are typically products with low porosities and high bulk densities. They achieve high temperature, penetration, and corrosion resistance. Despite the high density of these products, which is due to the low porosity of the aggregates, their matrices still exhibit a high amount of pores. Since calcium magnesium aluminate (CMA) has already proven its resistance to penetration and corrosion as a binder in the matrix, this paper investigated if alumina spinel refractories containing microporous calcium magnesium aluminate aggregates can withstand conditions that occur in a steel ladle wall. The objective was to reduce the castable density with the advantage of a lower material requirement for a ladle lining and reduced heat and energy losses. This was achieved by replacing dense alumina aggregates by up to 38% of porous CMA aggregates (grains with 30 vol% porosity), which resulted in a bulk density reduction from 3.1 g/cm3 for the dense alumina castable to 2.8 g/cm3 for the 38% CMA aggregates containing castable. However, the despite the higher porosity, penetration, and corrosion resistance and thermomechanical properties were not impacted negatively for a model alumina spinel castable. A postmortem investigation was conducted on a newly developed dry-gunning mix that was installed in a steel ladle wall on top of a slag penetrated castable and that achieved a service life of 31 heats versus only 18 heats for the reference mix that contained dense alumina and spinel aggregates. This new repair mix contained the newly designed porous CMA aggregates, which in this case partly replaced the dense alumina and spinel aggregates. These porous aggregates consisted of magnesium aluminate and calcium aluminate micro-crystals. The postmortem study revealed two important phenomena that can explain the improved performance: at the hot face in contact with steel and slag, a thin densified zone was observed that blocked the slag penetration into the porous matrix and the porous aggregates. Iron oxides were almost completely blocked from penetration, and only some manganese oxide was observed in the penetrated zone together with some silica and lime from the slag. Clusters of calcium aluminate (CA6) and magnesium aluminate (MA) spinel build the refractory back-bone on the hot side of the material and gussets filled with mostly glassy calcium aluminum silicates close to the hot face and gehlenite further inside the penetrated zone.