Influence mechanism of rare earth (RE) on inclusion modification in non-oriented silicon steel

Effects of rare earth (La+Ce) on inclusions in hot-rolled band of 3.0 similar to 3.3%Si-0.8 similar to 1.0%Al non-oriented silicon steel was studied using industrial trials, scanning electron microscope (SEM) and thermodynamic analysis. Furthermore, combining Heterogeneous Nucleation Theory with Edge-to-Edge Matching (E2EM) model, the formation mechanism of complex inclusions was also investigated. Rare earth (La+Ce) would promote the spheroidization and coarsening of inclusions, and then transform into regular and near circle morphology composite inclusions of rare earth. The low content of rare earth (21 ppm) mainly deoxidized and modified Al2O3 inclusions, and formed (La,Ce)AlO3 inclusions. Increasing of rare earth (29-45 ppm) would promote the formation of (La,Ce)AlO3-(La,Ce)2O2S and (La,Ce)2O2S inclusions, reduce the sulfide precipitation, and promote a gradual transformation of the core of composite inclusions from (La,Ce)AlO3 to (La,Ce)AlO3-(La,Ce)2O2S and (La,Ce)2O2S, which agreed well with the thermodynamic analysis. However, rare earth (29-45 ppm) had a weak metamorphic effect on Al2O3 inclusions generated by temperature drop and secondary oxidation. LaAlO3, CeAlO3, La2O2S and Ce2O2S could be the heterogeneous nucleation core of AlN, Al2O3, MgO-Al2O3, typical composite inclusions with (La,Ce)AlO3 and (La,Ce)2O2S as the core would ultimately form.