Phase equilibria of the Al2O3–CaO–SiO2-(0%, 5%, 10%) MgO slag system for non-metallic inclusions control

AlO–CaO-(MgO–SiO) inclusions are one of the dominant inclusions in Al-deoxidized spring steel, the compositions changes of which are closely related to refining slags and deoxidization process. The AlO–CaO–SiO–MgO system can represent the primary ingredients of the AlO–CaO inclusions. According to analyzed compositions and predicted liquidus temperature ranges of inclusions and refining slag, equilibra experiments under high temperature, water quenching technique and subsquent electron probe X-ray microanalysis (EPMA) has been conducted to ascertain detailed thermodynamic database for inclusions control. Liquidus temperatures within the dominant phase fields of CaSiO, CaSiO, CaAlO, CaAlO, spinel and MgO with the intervals of 20 °C from 1350 to 1560°C were identified. To further promote inclusions control, the influences of mass ratios of Mass(Al2O3)Mass(Al2O3+SiO2+CaO) and MgO contents on equilibrated phases and liquidus temperature changes have been explored. To further enhance modification levels of AlO–CaO-(MgO–SiO) system inclusions, it is suggested that refining time could be suitably prolonged.