Effect of rare earth on inclusion evolution in industrial production of HRB500E steel

The effect of rare earth (RE) on inclusion in HRB500E steel was studied based on plant trials. The results showed that S decreased by 47.6% after 0.0059% RE treatment. In samples without RE treatment, the inclusions change from Al 2 O 3 -MnO to ellipsoidal Al 2 O 3 -MnO-CaO complex inclusion, and the size of such inclusions is ≤ 2 µm and isolated strip MnS inclusion with the size of ≥ 2 µm. With RE treatment, Al 2 O 3 -MnO-CaO inclusions are transformed into spherical or ellipsoidal REAlO 3 and REAlO 3 -MnS. The size of such inclusions is ≈ 1.5 µm and single MnS inclusions were not found. The number density and size of inclusions changed significantly after RE treatment. Thermodynamic calculations show that the Gibbs free energy of RE inclusions is more negative and more stable. The transformation model of inclusions is established to illustrate the modification of inclusions during the smelting process.