A simple method to produce austenite-based low-density Fe-20Mn-9Al-0.75C steel by a near-rapid solidification process

Austenite-based low-density steels are promising structural materials due to their excellent mechanical properties with reduced densities, whereas it is normally hard to produce such steels with high Mn and Al contents because of their relatively low thermal conductivities and high deformation resistance. In this paper, a new attempt has been made to produce the austenite-based low-density steels by a near-net shape method. Near-rapidly solidified strips, in 2 mm thickness of Fe-20Mn-9Al-0.75C low-density steel, were directly obtained from liquid metal by injection casting. Microstructural analyses revealed that there were mainly duplex phases composed of γ austenite and δ ferrite in as-cast strip, with ordered DO3 nanoparticles in δ, and ordered κ carbides in γ matrix, respectively. Some of the mechanical properties were found to be similar, and some of them were found to be even better than those steels with similar compositions but prepared by traditional methods with multiple heat treatments and rolling processes reported in literature. Annealing at 400 °C and 600 °C promoted the precipitation of ordered nano-sized DO3 and κ. As the ordering of κ carbides prevent dislocation and planar defects gliding, giving rise to decreased elongation while enhanced yield strength, ultimate tensile strength and micro-hardness. An eutectoid transformation (γ → α+κ) occurred when the annealing temperature reached 800 °C; as a consequence, the coarsened granular κ carbides drastically declined the total elongation. The present work demonstrated that a simple effective way to produce high-performance low-density steels.