Carbide precipitation behavior and mechanical properties of micro-alloyed medium Mn steel

The carbide precipitation behavior and mechanical properties of advanced high strength steel deformed at different temperatures are investigated by X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) equipped with an energy dispersing spectroscopy (EDS), and tensile tests. The medium Mn steel was subjected to controlled deformation up to 70% at 750 °C, 850 °C, 950 °C, and 1050 °C, and then quenched with water to room temperature, followed by intercritical annealing at 630 °C for 10 min. In comparison with the undeformed and quenched specimen, it can be concluded that acicular cementite precipitates during the quenching and cooling process, while granular NbC is the deformation induced precipitate and grows during the following annealing process. As the deformation temperature increases from 750 °C to 1050 °C, the product of strength and elongation increases at first and then decreases. The smallest average size of second phase particles (20 nm) and the best mechanical properties (32.5 GPa.%) can be obtained at the deformation temperature of 950 °C.