Precipitation behavior of κ-carbides and its relationship with mechanical properties of Fe–Mn–Al–C lightweight austenitic steel

The effects of the aging process on the κ-carbide precipitation behavior and thus on the mechanical properties of an Fe-30.5Mn–8Al-1.0C lightweight austenitic steel were experimentally studied. The morphology of intragranular κ-carbide precipitation evolved from spherical to cuboidal and then to rectangular with increasing aging temperature and time, and intergranular κ-carbides precipitate in the high-temperature-aged steels and exhibit lath-like and lamellar morphologies. For steels with intragranular κ-carbide precipitation, the yield strength becomes significantly improved with the persisting aging owing to the enhanced dislocation shearing strengthening via κ-carbide growth, and the increase in yield strength exceeded the contribution of work hardening. Intergranular precipitation in higher-temperature-aged steel has a negative effect on the strength and ductility; it partly counteracts the strength increase due to intragranular precipitation. In summary, the studied steel aged at 550 °C for 1–2 h exhibited a better strength–ductility match.