Phase and formation mechanism of the brittle layer of ASC castable in blast furnace hearth

An Al2O3-SiC C castable BF was dissected and investigated in the present work. The phase composition and microstructure of the brittle layer of castable and the original castable after service were analyzed by XRD, chemical analysis, and SEM-EDS. The results show that a brittle layer of castable with a thickness of about 50-300 mm is found at the bonding surface between the carbon brick and castable on the sidewall of the hearth. Zn enrichment was found in the brittle layer of castable. In the high-temperature environment of the furnace sidewall, the evaporation of water and formation of mullite phase in the process of phase transformation at high-temperature lead to the formation of pores and microcracks in the castable. Stress concentration in the joint area of the castable and carbon brick was produced due to their different expansion coefficient, and the microcracks in the castable gradually develop and expand under the action of thermal stress. In addition, the diffusion of CO, alkali metal steam, and Zinc vapor in the blast furnace hearth and the expansion caused by the reaction product with the original phase of castable accelerated the propagation of microcracks in castable and finally formed the macro-brittle layer.