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

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 degrees 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. (C) 2011 Elsevier B.V. All rights reserved.