Regenerated MgO-CaO brick samples containing 80wt%, 70wt%, and 60wt% MgO were prepared using spent MgO-CaO bricks and fused magnesia as raw materials and paraffin as a binder. The bricks were sintered at 1873 K for 2 h under an air atmosphere and under an isolating system. The microstructure, mechanical properties at room temperature, and hydration resistance of the regenerated samples were measured and compared. The results indicated that the isolating sintering generated a strongly reducing atmosphere as a result of the incomplete combustion of paraffin, and the partial oxygen pressure was approximately 6.68 × 10^-7 Pa. The properties of the regenerated bricks sintered under air conditions were all higher than those of the bricks sintered under a reducing atmosphere. The deterioration of the bricks was a result of MgO reduction and a decrease in the amount of liquid phase formed during sintering under a reducing atmosphere.
Because CaSi core wire was not fed in external refining process for 26CrMo4S/2 steel making, it was found that the molar ratio of calcium versus alumina was very low and subsequently resulted in generation of much more non-metallic inclusions. Hence, it was reasonable to sugguest feeding appropriate amount of Ca core wire. Before the performance, the thermodynamic calculation had been carried out to obtain the theoretical amount of Ca wire to be fed. According to the practical data from steel plant and the thermodynamic data, it was calculated that only when 5 2/34.97 10 [%Al]T-≥×4 2/31.38 10 [%Al] [%Ca]T T-×≥≥in molten steel the Al2O3 inclusions could be properly modified.
