Instantaneous Transition of Composition and Morphology of Inclusions with An Initial Al2O3 Composition in the Molten Steel during Calcium Treatment

The instantaneous morphological transition of triangular Al2O3 particles with various sizes in the molten Ca-treated steel was observed using a confocal scanning laser microscope at the steelmaking temperature. And the composition of inclusions at different times was analyzed using scanning electron microscope-energy dispersive spectroscopy. The shape evolution of particles was characterized by the shape parameter of overall regularity. It was found that the overall regularity of particles gradually increased with time during the calcium treatment. The geometry of the particle tends to be more rounded and regular as the overall regularity increases during the modification process. An empirical formula was proposed to predict the composition of Al2O3 particles based on their overall regularity during the calcium treatment. When the CaO/Al2O3 ratio was larger than 0.451, the irregular Al2O3 inclusion changed to an ideal spherical calcium aluminate inclusion. The smaller particle size promoted the transformation of Al2O3 inclusions to spherical calcium aluminates during the calcium treatment.