Effect of rare earth cerium on inclusions and hot ductility of high-strength steel for construction machinery

The effect of cerium on inclusions and hot ductility was studied by adding rare earth alloy to high-strength steel for construction machinery. The type, quantity, and size of inclusions were analyzed by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), automatic detection system of non-metallic inclusion, and thermodynamic calculation, respectively. The hot ductility of the experimental steel was measured using a Gleeble1500 thermal simulation tester, and the tensile fracture morphology and microstructure were observed with an optical microscope (OM) and scanning electron microscope. The results show that the addition of Ce modifies the inclusions in the steel from irregular complex inclusions consisting of Al₂O₃, MnS, and Al₂O₃+MnS to spherical or ellipsoidal Ce₂O₂S and CeS, with an increase in quantity and a decrease in size of 37.64%. The reduction in cross-sectional area of Ce-containing steel within the range of 650-1 050 °C is higher than that of Ce-free steel, indicating better hot ductility. This is attributed to the fact that the small spherical rare earth inclusions generated by the Ce treatment reduces the stress concentration, coordinates the deformation with the matrix, and induces the intragranular ferrite nucleation, ultimately improving the hot ductility of steel.