Effect of deoxidation methods on inclusions in steel

In order to control the nitrogen content of liquid steel, two different deoxidation methods were applied:(Ⅰ) Al blocks were added for deoxidation when tapping; (Ⅱ) Si-Mn alloys without Al were added for deoxidation at first when tapping, and then Al wires were fed at the LF station. The oxygen content, nitrogen content and inclusions in steel deoxidized by the two methods were analyzed by gas analyzer and scanning electron microscopy (SEM). It is found that the total oxygen content of the final product is almost the same with the two deoxidation methods, while the method (Ⅱ) is more advantageous to control the nitrogen content and by using the deoxidation method the nitrogen content can decrease by about 5 × 10^-6. Both the deoxidation methods affect little the type and size of inclusions in the final product, and most of the inclusions are globular CaS and CaO-MgO-Al₂O₃ inclusions. The formation process of inclusions during Si-Mn deoxidation was inferred according to SEM observations and thermodynamics.