Effect of annealing time on microstructure and mechanical properties of Fe–C–Mn–Al–Si steel

Cold-rolled medium manganese steel (0.09C–7.23Mn–1.99Si–4.42Al wt-%) was investigated. The tested steel was treated by inter-critical annealing quenching and partitioning process. The effects of the annealing time on the microstructure and mechanical properties of the medium manganese steel were investigated by SEM, TEM, EBSD and XRD methods. The results show that, the tested steel consists of martensite, α-ferrite, δ-ferrite and retained austenite. The process has a significant effect on the diffusion of C/Mn elements and significantly changes the microstructure of the tested steel. At the same time, the austenite grain size and the degree of dispersion of its internal elements reach a balance, which is conducive to maintaining moderate stability of the massives retained austenite at room temperature.