Study on the utilization of supersaturation degree in Al deoxidation to improve cleanliness and control of Al2O3 inclusions in ultra-low carbon steel

Effects of supersaturation degree (S) in Al deoxidation on cleanliness and alumina inclusions in steel were studied. If enough Al was added to steel, higher initial dissolve oxygen before Al deoxidation resulted in higher steel cleanliness. In the experiments, with the rise of [mass% O] from 102 ppm to 340 ppm and 931 ppm, logS in steel melts were increased from 4.8, to 7.0 and 8.8, respectively. As a result, total oxygen (T.O) was decreased to 25 ppm, 22 ppm and 21 ppm, respectively. Based on the results, important influence of supersaturation degree on the formation of Al2O3 was revealed. At lower S, Al2O3 would be singular and smaller particles <= 5 mu m that was difficult to be removed. However, Al2O3 would exist as large clusters in steel at higher S, which can be efficiently removed. By utilizing the findings in laboratory, RH refining of ultra-low-carbon steel was optimized. Steel cleanness and control of inclusions were improved. As a result, surface defects in cold rolling sheets caused by Al2O3 inclusions were effectively minimized.