Investigation of the Effects of Al₂O₃ Content and Cooling Rate on Crystallization in Fe₂O₃–CaO–Al₂O₃ System Using In Situ Confocal Laser Scanning Microscopy

Sinter is a major Fe source, that is, used extensively in blast furnace processes worldwide. The chemical and physical properties of sinter are crucial factors that affect the operating stability of blast furnaces. The quality of sinter is largely determined by the phase fraction of the silico-ferrite of calcium and aluminum (SFCA), which is a low-melting-point bonding phase formed during sintering. Calcium ferrite (CF)-containing alumina is known to be the structural basis for SFCA and SFCA-1, and provides basic information regarding the influence of Al₂O₃ on the formation of CF solid solutions. In this work, experiments are conducted to investigate the crystallization behaviors of an Fe₂O₃–CaO–Al₂O₃ system based on its Al₂O₃ content and cooling rate. The effects of Al₂O₃ additions are used to analyze changes in the phase formation temperature, phase ratio, and rate of decrease by using an in situ confocal laser-scanning microscope, optical microscope, electron probe micro analyzer, and horizontal tube furnace. The temperatures at which the primary phase forms for various Al₂O₃ contents and cooling rates differ from the equilibrium temperatures, and the phase-formation temperature ranges vary with the cooling rate.