Dislocation plasticity reigns in a traditional twinning-induced plasticity steel by in situ observation

To twin or not to twin? The critical doubt emerges recently on the dominant role of deformation twinning in contributing to strain hardening and plasticity, which has been long taken for granted specifically in twinning-induced plasticity (TWIP) steels. Here, the dynamic deformation process was in situ studied in a typical Fe-30Mn-3Si-3Al (wt. %) TWIP steel by using transmission electron microscopy. It is found that dislocation activities, instead of twinning, reigns over the whole plastic process, including planar slips and especially cross-slips of dislocations, leading to strong interaction of dislocations. An unexpected generation of nanograins is visible because of dislocation activities ahead of the crack tip. Moreover, the dominant dislocation plasticity continues straight down to cryogenic temperatures. The present results evidence the key role of forest dislocation hardening and shed insights into deformation physics in TWIP steels, contrary to our conventional understanding.