2) During deoxidation, the dissolved oxygen in molten steel is precipitated as oxides due to the addition of elements with high oxygen affinity. Primary inclusions are formed under isothermal conditions during the deoxidation process while secondary inclusions are generated during solidification and cooling. 1) To accomplish either of these entails a thorough understanding of the origin, phases, morphology and composition of inclusions in all the stages of steelmaking from ladle treatment and casting to the final stages of rolling.ĭepending on their thermal origin, inclusions can be classified as primary or secondary. Recent approaches to this problem involve modifying the inclusions to optimize the properties of the steels or minimizing the amount of inclusions to nullify their detrimental effects on the steel. One of the unavoidable and persisting challenges to steel production is the control of harmful non-metallic inclusions that form during the steelmaking process. From this, the inclusions formed in Si–Mn deoxidized alloys held isothermally at the solid-liquid equilibrium temperature were of three types: primary MnO–SiO 2 inclusions, secondary SiO 2 inclusions and complex inclusions with both primary MnO–SiO 2 inclusions and precipitated secondary SiO 2 inclusions. The general mechanism of inclusion formation observed in this study can be divided into three steps: 1) the formation of primary MnO–SiO 2 inclusions above the liquidus temperature when the steel is in a completely molten state as a result of the deoxidation process 2) the nucleation of secondary inclusions as the molten steel becomes supersaturated with the solute elements while holding at the solid-liquid equilibrium temperature and 3) the growth and coalescence of inclusions due to natural convection in the molten alloy. The changes in the composition of the inclusions depended on the manganese and silicon contents in the metal. With isothermal holding at the solid-liquid equilibrium temperature, formation of a secondary SiO 2-rich inclusion phase occurred. The typical inclusions found in the alloy were MnO–SiO 2 based, spherically shaped and homogeneously distributed. In this study, the formation of complex inclusions in Si–Mn deoxidized steel after isothermal holding at the solid-liquid equilibrium temperature (T S) was investigated. However, besides the temperature conditions during steelmaking or continuous casting, other factors contributing to changes in the morphology and composition of inclusions during solidification are still unknown. Morphology and composition of inclusions change with temperature.
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