Crystallization Behavior of the CaO-SiO2-Al2O3-MgO System Inclusions

The crystallization process of low melting point CaO-SiO2-Al2O3-MgO system inclusions during the continuous casting and hot rolling process greatly affects the deformability of inclusions. The effect of Al2O3 and MgO contents on the crystallization characteristics of CaO-SiO2-Al2O3-MgO system melts representing the typical oxide inclusions in Si-Mn deoxidized steels is systematically investigated. The continuous cooling transformation and time-temperature transformation experiments are carried out. The results reveal that the increase of Al2O3 contents restrains the crystallization process of the melt, whereas the crystallization tendency of the melt is promoted with the increase of MgO contents. The precipitated phases are predominately 2CaO<middle dot>MgO<middle dot>2SiO(2) and 3CaO<middle dot>MgO<middle dot>2SiO(2), and the primary crystalline phase is unaffected by the changes of Al2O3 and MgO contents. To obtain low melting point plasticized inclusions with limited crystallization ability, it is recommended to control the Al2O3 and MgO contents greater than 15 wt% and below 5 wt%, respectively. The isothermal treatment is suggested to be controlled within a proper temperature range (1175-1250 degrees C) to decrease the crystallization kinetics. The oxide system's viscosity change is the limiting kinetic factor in the crystallization process, and it can be utilized to predict the system's crystallization tendency.