Strain rate dependence on the evolution of microstructure and deformation mechanism during nanoscale deformation in low carbon-high Mn TWIP steel

Abstract

We elucidate here the strain rate dependence on the deformation behavior and accompanying deformation mechanism in Fe-30Mn-0.3C TWIP steel via nanoscale deformation experiments and post-mortem microscopy of the deformed region. The nanoindentaion hardness increased with increased strain rate from 0.01 s-1 to 1 s-1, and exhibited a positive strain rate sensitivity of 0.095 with an activation volume of 18b3. At a low strain rate, dislocations dominated the deformation behavior with a high density of 2.7 × 1016 m-2. With increased strain rate, the dislocations decreased and the stacking faults and nanotwins gradually increased. However, nanotwins with secondary twins were the dominant deformation process at high strain rate of 1 s-1. The deformation behavior was significantly impacted by the interplay between strain rate, stacking fault energy and deformation mechanisms. A critical theoretical analysis suggested that the strain rate influenced the critical shear stress for twinning and dislocation slip, resulting in the change in deformation mechanism from dislocation slip to twinning.