This study takes U26Mn2Si2CrNiMo bainitic austenitic steel as the object, and systematically investigates the micromechanical role and morphological evolution mechanism of inclusions in its tensile fracture behavior. The influence of the cooling process on the organization evolution is analyzed by establishing a temperature field model, and the variation rule of mechanical properties is revealed by combining room temperature and low temperature tensile experiments. The microstructural features are characterized by multi-scale microscopic techniques such as metallurgical microscopy, scanning electron microscopy and transmission electron microscopy. The results show that the normalizing final cooling temperature affects the distribution of grain boundary mismatch angle and residual austenite by regulating the degree of bainite phase transformation, which in turn changes the material toughness and toughness, and the full austenite organization is realized under the final cooling condition of 320℃. The La element addition caused the average size of inclusions to decrease and then increase, with H1, H2, and H3 varying to 0.62 μm, 0.43 μm, and 0.49 μm. The material strength and plasticity are synergistically enhanced under lowtemperature tensile conditions, and the pulse current treatment reduces the work-hardening capacity through softening effect. This paper provides a theoretical basis for the control of inclusions and process optimization of steel for railroad turnout heart rails.
