Influence of h-BN particle size on fracture behavior and thermal shock resistance of Al₂O₃–C refractories

h-BN can be applied in Al₂O₃–C refractories to substitute graphite due to their similar crystal structure and better resistance to molten steel and oxidation. The effects of h-BN particle size on the mechanical properties and fracture behavior of Al₂O₃–C refractories were investigated through wedge splitting test and microstructural analyses. The obtained results demonstrated that the addition of larger-sized h-BN was conducive to the growth of in situ formed SiC whiskers, which contributed to the highest flexural strength (42.63 ± 3.10 MPa) of specimen D10. In comparison, the smaller-sized h-BN can induce more crack propagation paths along the interface and within matrix, leading to more tortuous crack propagation paths, and thus the thermal shock-related parameters such as specific fracture energy, characteristic length, and thermal shock resistance were improved. Consequently, the residual strength ratio of Al₂O₃–C refractories was increased from 35.5% to 42.5% with decreasing the h-BN particle size from 10 to 0.1 μm.