High-temperature MgO-C-Al refractories-metal reactions in high-aluminum-content alloy steels

MgO-C-Al refractories were used in this study to evaluate high-temperature refractory-metal reactions with molten Fe-Mn-Al alloys. Dynamic reaction tests at 1570 degreesC and static reaction tests at 1500 degreesC and 1600 'C, respectively, were used. MgAl2O, and Al4C3 phases were observed in the refractory bulk, and a large amount of protective MgAl2O4 phase formed due to the decomposition of Al4C3 phases on the refractory-metal reaction interface of the MgO-C-Al brick to retard the high-temperature attack of Fe-Mn-Al alloy melts. The oxygen partial pressure was substantially reduced by the oxidation of graphite in the MgO-C-Al brick during high-temperature test. This resulted in the nitridation of aluminum in molten Fe-Mn-Al alloy. White aluminum nitride (AlN) with the shape of whisker-like powder was formed and adhered to the surface of the MgO-C-Al brick. Aluminum was depleted from the Fe-Mn-Al alloy by nitridation or the oxidation reaction by CO gas. The alloy would also be carburized due to the absorption of CO gas or the reaction between aluminum and CO gas, which was produced by the oxidation of graphite in the MgO-C-Al refractory after static reaction test. It is argued that the MgO-C-Al refractory is not suitable to be used in the melting of Fe-Mn-Al alloys with high aluminum contents.