Effect of Mo on precipitation behavior and tensile properties of Fe26Mn8Al1.2C–xMo lightweight austenitic steels

The effect of Mo on dual-phase precipitation behavior and tensile properties of Fe26Mn8Al1.2C–(2–3.5 wt.%) Mo lightweight austenitic steels after annealing at 700 °C was investigated by electron backscatter diffraction, transmission electron microscopy, hardness and tensile tests. Alloying with Mo in the steels promotes the precipitation of Mo₂C carbides while inhibits the precipitation of κ-carbides. The addition of Mo exceeding 2.5 wt.% facilitates the precipitation of intragranular Mo₂C carbides, whereas with up to 2.5 wt.% Mo, only intergranular Mo₂C carbides precipitate. With containing more Mo in the steels, the strength increases due to enhancement of precipitation strengthening and solid solution strengthening, while ductility gradually decreases. 3Mo steel exhibits excellent overall mechanical properties, with the synergistic increase in strength, ductility, and work-hardening rate, which can be attributed to the precipitation of fine intragranular Mo₂C distributed uniformly in the matrix and the suppression of the formation of coarsened κ-carbides. However, in 3.5Mo steel, abundant coarsened Mo₂C precipitation strongly interacts with dislocations to promote crack propagation along non-coherent interfaces, leading to a high initial work-hardening rate but severe ductility loss.