Microstructural factors dictating the initial plastic deformation behavior of an ultrafine-grained Fe-22Mn-0.6C TWIP steel

While leading a great strain hardening capability, carbon-containing twinning-induced plasticity (TWIP) steels exhibit serrations on their stress-strain curves, resulting in barriers to commercial development. Although grain refinement is believed to suppress the serrations, how the grain size, particularly in the ultrafine-grained (UFG) range, and its orientation impacting on the serrations and plastic deformation mechanism are overlooked. Here, we compared the plastic deformation behavior in fine-grained (2 mu m) and ultrafine-grained (0.86 mu m) specimens, in both macroscopic and microscopic behavior, using digital image correlation (DIC) and scanning transmission and transmission electron microscopy (S/TEM) techniques. Our results showed that the dominant plastic deformation mode was changed from dislocation gliding and tangling to stacking faults and deformation twin- ning in the grains equal to or smaller than 1 mu m (ultrafine grains). This alteration is also strongly influenced by the grain orientation, i.e., the maximum resolved shear stress for slip versus twinning. The enhancement of strain localization and the inhibition of the serrations in the UFG specimens are discussed.

Automated summary

Carbon-containing TWIP steels, which have a great strain hardening capability, suffer from serrations on the stress-strain curves, hindering their commercial development. The impact of grain size, especially in the ultrafine-grained range, and its orientation on the serrations and plastic deformation mechanism has been overlooked. This study compared the plastic deformation behavior in fine-grained and ultrafine-grained specimens and found a change in the dominant deformation mode when the grain size was equal to or smaller than 1 μm. The alteration was strongly influenced by the grain orientation and resulted in the enhancement of strain localization and the inhibition of serrations in the ultrafine-grained specimens.