Effect of annealing on the microstructure and mechanical properties of cold rolled Fe–24Mn–3Al–2Si–1Ni–0.06C TWIP steel

Abstract

Fe–24Mn–3Al–2Si–1Ni–0.06C TWinning Induced Plasticity (TWIP) steel was 42% cold-rolled and isochronally annealed at temperatures between 600 and 850 °C. Optical, secondary and transmission electron microscopy found that a majority of as cold-rolled grains contain a large fraction of primary twin densities and a smaller fraction of secondary twins. Partially recrystallised microstructures comprise a mix of recrystallised grains and annealing twins as well as remanent deformed grains with heavy dislocation substructures and deformation twins. Both deformation and annealing twins follow the {1 1 1}〈1 1 2〉 relationship. All partially recrystallised samples exhibited four work hardening regions and a decreasing twinning onset stress with greater percentage softening. A modification to the Hollomon–Ludwigson scheme is suggested to empirically account for the effect of strain on microstructural refinement.