Comparative Study of the Influence of Reversion- and Recovery- Annealing on the Mechanical Behavior of High-Manganese Steels with Varying Stacking Fault Energy

High-manganese steels are promising candidates for application in crash-relevant automobile components due to their outstanding mechanical properties. These properties result from the activation of additional plasticity effects, such as transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP). In the present study, we investigate the influence of thermomechanical treatment, specifically by reversion-annealing, on the mechanical properties. Three alloys with varying stacking fault energy (SFE) values are used: a X8Mn23 TRIP steel (SFE approximate to 5 mJ m(-2)), a X30Mn22 TWIP/TRIP steel (SFE approximate to 16.3 mJ m(-2)), and a X30MnAl22-1 TWIP steel (SFE approximate to 25 mJ m(-2)). The objective of the study is to combine the beneficial influences of the TWIP and TRIP effect to tailor the mechanical properties. Bimodal microstructures are generated by pre-deformation with subsequent reversion- or recovery-annealing to correlate the influence of the different microstructural features with the tensile behavior. During reversion-annealing at 350 degrees C for 2 min, the previously introduced epsilon-martensite is transformed to soft austenite. At the same time, dislocations and deformation-induced twin boundaries are thermally stable. Recovery-annealing at 550 degrees C for 30 min results in the annihilation of dislocations, but retention of deformation twins. These bimodal microstructures, comprised of strong and soft austenite, facilitate an improved yield strength-ductility combination. Reversion-annealing of the TWIP/TRIP steel results in a slightly higher yield strength with lower total elongation, but decreased work-hardening rates compare to the recovery-annealed TWIP steel.