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Sialon–ZrN powders were synthesized from low-grade bauxite using a zirconite additive by carbothermal reduction nitridation (CRN). The as-synthesized Sialon–ZrN powders were subsequently used as SiC-based free-fired refractories. Their phase compositions and microstructures of the powders were determined using X-ray diffraction and scanning electron microscopy. The physical properties and blast furnace (BF) slag resistance of the SiC–Sialon–ZrN free-fired refractories were also studied. The results show that the low-grade bauxite and zirconite powders were transformed to β-Sialon and ZrN by the CRN process at 1600°C. The phenolic resin provided a strongly bonded interface between the Sialon–ZrN matrix and SiC particles and thus enhanced their combined strength after drying at 150°C. The strength increased as the temperature was elevated from 1000°C to 1500°C. As the ZrN content increased, the slag erosion rate of the SiC–Sialon–ZrN free-fired refractories initially decreased and then increased after being heated at 1500°C. The presence of ZrO2 in the slag (oxidized from ZrN) revealed that the ZrO2 did not react with other oxides in the BF slag to form low melting point phases. This may play a crucial role in its BF slag erosion resistance. The corrosion mechanism of the BF slag towards the as-prepared SiC–Sialon–ZrN free-fired refractories was determined to be oxidation-erosion-dissolution-penetration. [ABSTRACT FROM AUTHOR]