Abstract: Inclusions are one of the main factors that deteriorate the soft magnetic properties of high-grade non-oriented silicon steels. Reducing the number of inclusions and coarsening the size of inclusions through rare earth treatment can help alleviate the harm of inclusions to the soft magnetic properties. The current study conducted LaCe misch metal treatment on a high-grade non oriented silicon steel, and sampled from refining, casting, continuous casting slabs, hot-rolled plates, and final products. The steel composition and inclusion characteristics were detected, and the formation process of inclusions was analyzed based on thermodynamic calculation. The following conclusions were drawn: after adding misch metal for 3 minutes, the total mass fraction of rare earth in the steel was 64×10^-6, which gradually decreased during the subsequent refining process until the tundish molten steel was 25×10^-6. The decrease in sulfur content and increase in magnesium content in the refining process were mainly due to the desulfurization effect of CaO-CaF₂ desulfurizer and its erosion effect on refractory materials. Rare earth treatment slightly reduced sulfur content and increased magnesium content, but its effect was smaller than that of desulfurizer. After the addition of misch metal, MgO·Al₂O₃ in non-oriented electrical steel was modified into rare earth oxide sulfides and rare earth sulfides. The proportion of lanthanum and cerium in rare earth inclusions was related to their size. The atomic proportion of lanthanum and cerium in inclusions larger than 3 μm was almost equal, and these inclusions extended into a string like morphology after cold rolling; Inclusions smaller than 3 μm, possessed more cerium element and hardly deformed after rolling. Thermodynamic calculations showed that rare earth lanthanum had a stronger ability to modify inclusions than cerium. When using misch metal to modify inclusions in non-oriented electrical steel, rare earth elements tended to preferentially modify MgO·Al₂O₃ in the steel, and then reacted directly with dissolved oxygen, sulfur, and other elements in the steel to form rare earth inclusions.

Key words: misch metal, inclusions, non-oriented electrical steel, thermodynamics