Comparative study on the evolution behavior of non- metallic inclusions in Fe-1.5%Al and Fe-4%Si steels

Abstract

The effect of the reaction between alloy elements and slag on the production behavior of non-metallic inclusions in molten steel from non-directional electric steel sheets was investigated at 1873K (1600°C). Aluminum added to the molten steel produces an alumina- rich inclusion by reaction with oxygen, and it reduces FeO by interfacial reactions between CaO-Al2O3-FeO-SiO2-MgO slag to increase the alumina content of the slag.On the other hand, silicon added to the molten steel increases the silica content of the slag by interfacial reactions between slag and causing aluminum pick-up from the liquid slag into the molten steel, which changed the existing silica-rich inclusion into aluminum- rich inclusions. The addition of each of the two alloying selements produced alumina-rich inclusions, and the two series of existing alumina inclusions were modified with MgAl2O4 spinel inclusions by picking up magnesium equally from the slag and the molten steel.Through a population density function (PDF) analysis of inclusions, we confirmed that inclusion growth occurred by diffusion of magnesium and aluminum in steel with 1.5%Al or 4.0% Si. As a result of calculating the supersaturation for alumina inclusions, the 1.5% Al-added steel and 4.0% Si-added steel continued to decrease as the reaction time increased. As a result, dendrite or spherical alumina inclusions were observed in both series at 1 minute of deoxidation, and small, independently present polygonal alumina inclusions were mainly observed at 30 minutes of deoxidation. The inclusion removal rate as a function of the reaction time was compared to evaluate the cleanliness by converting the two-dimensional (2D) inclusions observed on the metal surface into three-dimensional (3D) inclusions.