Non-metallic inclusions of non-oriented silicon steel in RH refining process

Prior to industrial trials, a 1:5 scale water model was established based on a 200 t ladle RH refining unit to investigate the effect of lifting gas flow rate in the upleg on slag entrapment under practical production conditions. The results show that stable and uniform slag entrapment occurs at a lifting gas flow rate of 120 m³/h, which is favourable for sufficient steelslag reactions. Industrial trials were then carried out on the RH degasser based on the water model results. Systematic sampling was conducted, and the number, size distribution and morphological evolution of non-metallic inclusions in non-oriented silicon steel with and without premelted refining slag treatment were analysed using a metallographic microscope, an image analyser and a scanning electron microscope. Quantitative comparison indicates that with the application of premelted slag, Al₂O₃ inclusions are modified into CaOAl₂O₃SiO₂MgO complex inclusions after RH refining, accompanied by a remarkable reduction in both the number and size of inclusions.