The impact of intercritical annealing temperature on microstructure and mechanical properties of an ultra-low carbon medium manganese heavy steel plates

This study examines how varying intercritical annealing temperatures influences the microstructure and mechanical properties of 30 mm thick ultra-low carbon medium manganese steel plates. The results indicate that annealing at 650 degrees C produced superior mechanical characteristics that include yield strength of 680 MPa, tensile strength of 871 MPa, elongation of 38.2%, and impact energy of 135 J at -60 degrees C. The microstructure consisted of lath-like ferrite and austenite in both film-like and blocky forms. With an increase in annealing temperature, a rise in the volume percentage of austenite and its transition from a film-like to a blocky structure were observed. The enhancement in mechanical properties can be ascribed to the formation of reverted transformation austenite during intercritical annealing. Furthermore, enhanced stability of the reverted austenite contributed to improved ductility in fracture behavior.