Reoxidation of Al-Killed Molten Steel by Fe2O3and Cr2O3in the Magnesia-Chromite Refractory

Abstract

In the present work, the reoxidation of Al-killed molten steel from the magnesia-chromite refractory was investigated. Firstly, the composition and the phases of magnesia-chromite bricks from three different steelmaking shops were analyzed. Secondly, the magnesia-chromite bricks were immersed in Al-killed molten steel for a determined time to observe the reaction mechanism. Finally, the reoxidation of Al-killed molten steel by the magnesia-chromite bricks was evaluated based on a comparison with the pure magnesia crucibles. The XRF showed the Fe2O3 content of the magnesia-chromite bricks is about 6 mass%, and the Cr2O3 content is in a range of 13–19 mass%. The XRD pattern showed the phases in the bricks are mainly MgO and (Mg,Fe)(Cr,Al,Fe)2O4. The fracture surface of magnesia-chromite bricks after immersion in Al-killed molten steel indicated that there exists a reacted layer, and the reacted layer formed after immersion in the low Cr steel is more obvious than that formed after immersion in the high Cr steel. The SEM–EDS of magnesia-chromite bricks showed that (Mg,Fe)(Cr,Al,Fe)2O4 in the reacted layer decreased after immersion in Al-killed molten steel, especially in the low Cr molten steel. Compared with steel melted in pure magnesia crucibles, the total oxygen of steel melt in magnesia-chromite crucibles showed a lower decreasing rate, and the rate of Cr increase and Al loss were much larger, especially in the low Cr molten steel.