Effect of nitrogen content and cerium treatment on the characteristics of inclusions in non-oriented silicon steel

The electric arc furnace (EAF) short process is an important technical path for the future production of green steel, while the higher nitrogen content limits the production of high-grade steel plates, represented by non-oriented silicon steel (NOSS). Under this background, the influence of nitrogen content and cerium treatment on the characteristics of inclusions in NOSS was investigated. Thermodynamic analysis reveals that increasing nitrogen content raises both the initial precipitation temperature and the mass fraction of AlN. NOSS with varying nitrogen contents were smelted in a resistance furnace by top-blowing nitrogen gas (simulating high nitrogen content NOSS produced using EAF), and then cerium treatment was performed on the high nitrogen content NOSS. The inclusions were qualitatively and quantitatively characterised by scanning electron microscope (SEM, Sigma 300). The results indicate that as nitrogen content increases from 0.0013 to 0.0043 wt%, the number density of submicron-sized inclusions, which are more harmful to NOSS properties, increases from 95.43 to 126.64 mm⁻². These inclusions are mainly pure MnS and nitrides (AlN and AlN + MnS). After cerium treatment, the modification of sulphides and coarsening of AlN resulted in a decrease in the number density of submicron inclusions. With 0.0086 wt% cerium, the lowest observed number density of submicron-sized inclusions is 14.58 mm⁻². The heterogeneous nucleation between AlN and Ce-S was confirmed using the edge-to-edge matching model combined with electron backscattered diffraction.