Transient Behavior and Thermodynamics of Inclusions in Al-Ti-Deoxidized and Ca-Treated Steel

Abstract

Ti-alloyed steels have severe nozzle clogging problems, which are detrimental to the steel production process. However, little research on the Al-Ti-Ca-O complex inclusion in molten steel has been carried out. Based on that, experiments with different calcium additions were carried out in an Al2O3 crucible at 1873 K to investigate the variation of inclusions in Ti-bearing Al-killed steel in the current article. It was found that calcium treatment significantly influenced the morphology, composition distribution, and size of oxides in Ti-bearing Al-killed steel. Inclusions with a higher CaO or TiOx content were liquid at 1873 K (1600 °C), indicating that the inclusions in Ti-contained steel can be modified to liquid ones through the proper calcium treatment process. The appropriate amount of calcium should be added to the steel depending upon the aluminum and titanium contents. Thermodynamics of the inclusions in the Al-Ti-Ca-O molten steel system at high temperature and during the solidification process were comprehensively calculated, including all types of inclusions such as calcium oxide, aluminum oxide, titanium oxide, calcium aluminate, calcium titanate, and liquid inclusion. The thermodynamic calculations agree well with the experimental results and can precisely predict the formation of the inclusions in Al-Ti-Ca deoxidized steel.