| Summary: | Al<sub>2</sub>O<sub>3</sub> substrate is widely used as a lining refractory material throughout the blast furnace (BF) process. Accordingly, the erosion of Al<sub>2</sub>O<sub>3</sub> refractory by molten slag has a negative influence on the running cost and smooth operation of BFs. The effect of the erosion behavior of BF primary slag containing FeO-CaO-SiO<sub>2</sub>-MgO-Al<sub>2</sub>O<sub>3</sub> on Al<sub>2</sub>O<sub>3</sub> substrate refractory was fundamentally investigated using the high-temperature contact angle method and FactSage thermodynamic software based on the composition of BF primary slag in a typical iron and steel enterprise of China. The results showed that the primary slag mentioned above was easily wetted with Al<sub>2</sub>O<sub>3</sub> substrate, and the observed contact angles were 24.5° and 22.0°, when the FeO mass fraction (<i>w</i>(FeO)) was maintained at 10% and 15% of the primary slag, respectively. Moreover, the starting melting temperature of the primary slag with high FeO content, of 1263 °C, was lower. The erosion thickness between the slag and Al<sub>2</sub>O<sub>3</sub> substrate increased from 19.23 to 23.17 μm as the added <i>w</i>(FeO) increased from 10% to 15%. In addition, it was observed via SEM-EDS analysis that the interface layer was formed, and high-melting-point compounds were generated during the wetting process. This was attributed to the interaction between the molten slag and Al<sub>2</sub>O<sub>3</sub> existing in the substrate, which may have inhibited the continuous dissolution of the Al<sub>2</sub>O<sub>3</sub> in the substrate into slag. Good surface wettability and the dissolution of the Al<sub>2</sub>O<sub>3</sub> substrate refractory into the primary slag of the BF are two dominant factors leading to the erosion of the refractory.
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