Enhanced performance of ultra-low carbon MgO-C bricks by the addition of special C/MgAl2O4 composite powders

Argon oxygen decarburization (AOD) refining as one type of secondary refining plays an important role in the steel industry. MgO-CaO and MgO-C bricks are widely used in AOD refining, and MgO-CaO bricks are easily hydrated. MgO-C bricks containing carbon easily pollute molten steel and have lower mechanical strength. In this study, ultra-low carbon MgO-C bricks containing C/MgAl2O4 composite powders used in AOD refining were explored. MgAlON as the strength phase was in situ generated in the composites (M3) containing 2 wt% C/MgAl2O4 composite powders. The samples were further compared with commercial MgO-CaO bricks (M1), which are currently used in the slag line of the AOD furnace, and the sample (M2) without the addition of C/MgAl2O4 composite powders. The hot modulus of rupture (HMOR) of M3 was the highest at 27.3 MPa, which increased 44% compared with that of M2 and increased 158% compared with that of M1. The number of thermal shock test cycles of M3 was 1.6 times that of M2. HMOR and cold crush strength (CCS) of samples after thermal shock resistance test were measured. The HMOR of M3 after 3 cycles of the thermal shock test was 2.1 times greater than that of M1. After 20 thermal shock cycles, the residual CCS ratio of M3 was highest, up to 94.6%. Improvement in the thermal shock resistance of the composites can be achieved by the addition of C/MgAl2O4 composite powders, which promote the generation of MgAlON. It was also found that the slag corrosion depth of M3 was the lowest at 64.7% of that of M2 and was 13% of that of M1. The internal micromorphologies researched by XRD and SEM and the corrosion mechanism revealed by thermodynamic calculations show that MgAlON was formed in situ after the corrosion test and endowed the composites with excellent properties.