Improved thermal shock resistance of MgO-C refractories with addition of calcium magnesium aluminate (CMA) aggregates

Thermal shock resistance is of great importance for MgO-C refractories used in steelmaking process. In this study, calcium magnesium aluminate (CMA) aggregates were selected to replace partially fused magnesia aggregates in MgO-C refractories, and their effects on phase compositions, microstructure, thermal shock resistance and fracture behavior of MgO-C refractories were investigated. The results showed CMA aggregates partly disintegrated, and spinel particles and whiskers were observed together with Al4C3 phase in MgO-C specimens coked at 1400 degrees C. With the increase in coking temperature up to 1600 degrees C, CMA aggregates completely disintegrated to generate much liquid phase, which promote the formation of spinel whiskers apart from spinel particles and hexagonal AlN in MgO-C refractories. CMA aggregates containing MgO-C refractories coked at 1400 degrees C possessed higher thermal shock resistance because CMA aggregates had abundant micro-sized pores and lower thermal expansion coefficient. When reheating up to 1600 degrees C in coke bed after thermal shocks, they had higher recovery strength index than CMA-free refractories. Furthermore, MgO-C refractories containing CMA showed lower brittleness and better bearing capacity via wedge splitting test.