Influence of slag composition on desulfurization and cleanliness of silicon steel

To clarify the effect of CaO saturated slag on desulfurization mechanism and steel cleanliness during the secondary refining process of non-oriented silicon steel, slag-steel reaction experiments at 1873K were conducted to systematically analyze the variations in the sulfur partition ratio, the average size of MnS-containing inclusions, and the sulfur distribution in the slag. The results show that the CaO–Al 2 O 3 –CaF 2 –MgO slag containing saturated CaO can effectively reduce the sulfur content in steel to below 15 ppm. An increase in both the initial addition amount of CaF 2 and the CaO/Al 2 O 3 ratio in the liquid slag significantly increases the sulfur partition ratio. When the CaO/Al 2 O 3 ratio in the liquid slag is maintained at around 2.1, the growth time of MnS inclusions is effectively shortened, and the cleanliness of the steel is notably improved. A clear threshold effect of slag liquid fraction on desulfurization was observed. Optimal sulfur partition ratio was achieved when the liquid fraction was maintained at approximately 60 %. Below this value, the main phase of the slag changed from 12CaO·7Al 2 O 3 ·CaF 2 (CaS) to CaO·Al 2 O 3 ·CaF 2 (CaS), while the decrease in liquid phase fraction increased viscosity, causing sulfur distribution in the liquid slag to shift from homogeneous to discrete point-like dispersion.