The dynamic behaviour of a twinning induced plasticity steel

The influence of strain rate on the twinning behaviour and microstructure of an Fe–15Mn–2Al–2Si–0.7C twinning induced plasticity (TWIP) steel has been investigated. A Hopkinson pressure bar setup was used in addition to blast testing to perform the high strain rate testing. The yield stress exhibited a positive strain rate sensitivity with increasing strain rate. However, the failure strain of the material was relatively unaffected. Post-deformation microscopy indicated that deformation twinning was less profuse at higher strain rates. Electron backscatter diffraction also indicated the activation of multiple twin systems at strain rates below 1000 s⁻¹ although this did not occur at the higher strain rates tested. A large intragranular misorientation was found to exist in the material tested at lower strain rates indicating a relatively larger dislocation density existing in the material tested at lower strain rates. In addition selected grains in the blast tested material exhibited a 'wavy' structure which was determined not to be due to a phase transformation. It is suggested that this was caused by the complex loading experienced by the material during testing. High resolution transmission electron microscopy also indicated a large density of intrinsic stacking faults in the material subjected to blast testing.