Formation of Interface Layers between Corundum-Based Refractory Ceramics with Carbon Additions and Molten 42CrMo4 Steel

The formation of reaction layers between corundum-based (Al2O3 + C) filter materials covered with functional Al2O3-C coatings having different carbon contents and molten steel 42CrMo4 is investigated at the reaction temperature of 1600 degrees C. Within the first 60 s, an amorphous reaction layer is formed at the interface between the original filter surface and the molten steel. This layer consists mainly of Fe and O with small, varying amounts of Al and Si. After a longer contact time (120 s), nanocrystalline phases, which are identified as iron-based oxides, formed within this amorphous interlayer. After 5 min, the amorphous interface layer is replaced by a dense corundum layer, on which thin corundum platelets are attached. The formation of the amorphous interface layer, its transformation to dense corundum, and the effect of the carbon content in the functional Al2O3-C coating on the nucleation and growth of the corundum platelets are discussed. The reaction experiments are carried out in a spark plasma sintering device to avoid liquid metal convection and as immersion tests in a steel casting simulator to obtain relevant information about the filtering process.