The effect of Ti-Mo-Nb on the microstructures and tensile properties of a Fe-Mn-Al-C austenitic steel

An investigation was performed to evaluate the effect of the Ti-Mo-Nb co-addition on the microstructure and the tensile behavior of a Fe-26Mn-8Al-1.5C austenitic steel after aging at temperatures from 500 to 600 degrees C. The co-addition of Ti-Mo-Nb in the steel refines grains, increases the sizes and volume fractions of kappa-carbides, and forms inter- and intra-granular (Ti,Mo,Nb)C particles. The promotion effect of Ti-Mo-Nb on the kappa-carbides precipitation varies with different aging temperature. The steel with co-addition of Ti-Mo-Nb possesses higher yield strength due to the combination of grain refinement, more kappa-carbides precipitation, and the formation of fine (Ti, Mo,Nb)C particles distributed uniformly within the grains, but has lower ductility ascribed to the coarseness of kappa-carbides with larger volume fraction and the existence of micron-sized inter-granular (Ti,Mo,Nb)C particles along the grain boundaries. With aging temperature increasing, the strength increases but the ductility decreases for both steels with and without microalloying. In addition, the strengthening mechanisms were analyzed quantitatively. The results show that the precipitation hardening is the dominant strengthening mechanisms for both steels.