Enhancement of the strength-ductility combination of twinning-induced/transformation-induced plasticity steels by reversion annealing

The aim of the present study was to combine the beneficial influences of both Twinning-Induced Plasticity (Twn.) and Transformation-Induced Plasticity (TRIP) effects on the mechanical properties and to adjust the contribution of both effects by suitable thermo-mechanical processing. Two high-manganese TRIP/TWIP steels were studied. In order to correlate the influence of the microstructural features to the mechanical properties, four specific conditions were set, i.e. pre-deformed, reversion-annealed, recovery-annealed and fully recrystallized. After pre-deformation, the alloys had different volume fractions of epsilon-martensite (5-24%). During reversion annealing at low temperature (350 degrees C) for 2 min, the epsilon-martensite was transformed to soft austenite. Recovery annealing (550 degrees C/5 min) resulted in annihilation of dislocations in addition to epsilon-martensite transformation. The corresponding bimodal microstructures were comprised of strong austenite with a high fraction of deformation twins and dislocations on the one hand and soft reverted austenite on the other hand. Due to the strong austenite, the high yield strength was retained and the soft austenite facilitated an improved work-hardening capacity.