Effect of Steelmaking Slag Additives on Mullitization and Phase Composition of Chamotte Refractories

Steelmaking produces large volumes of slag, a by-product with environmental risks due to accumulation and possible contamination. This study explores its use as a mineralizing agent in chamotte refractories. Slag rich in clinoferrisilite was added up to 5 wt.% to partially replace fine chamotte. Samples were shaped by semi-dry pressing and fired at 1350 °C. Chemical and phase composition, thermal behavior, microstructure, and physico-mechanical properties were analyzed. Results showed slag addition increased mullite content to 68 wt.% and promoted secondary magnesium–aluminosilicate phases (indialite, cordierite), indicating activation of reactions in the MgO-Al2O3-SiO2 system. DSC and TGA revealed thermal effects between 1298 and 1325 °C, confirming slag’s fluxing role and lowering the liquid-phase sintering temperature. Optimal properties were achieved with 5% slag and 10% clay, yielding compressive strength of 24 MPa and apparent density of 2.30 g/cm3, meeting GOST 390-96 requirements for grade SHA. However, excess liquid-phase components reduce thermal stability. Thus, steelmaking slag is an effective secondary raw material, enhancing mullitization and refractory performance when used within controlled limits.