Three-stage deformation behaviors of a austenitic Fe-Mn-Al-C low-density steel: slip bands–twinning–shear bands

Abstract

This study presents a systematic investigation of microstructure evolution and the mechanical response of a low-density steel during cold rolling with the thickness reduction of up to 90 %. With the strain increase, a three-stage deformation microstructural evolution from slip bands, to deformation twins, and eventually to shear bands has been observed based on detailed microstructure characterization. At the first stage (rolling reduction < 30 %), dislocation slip bands are the dominant deformation microstructure, due to the planar slip of dislocations. As strain increases, the band spacing is progressively refined with a saturation of ∼50 nm. These slip bands gradually evolved into microbands as a result of strain localization and plastic instability. At the second deformation stage (30 %–50 % rolling reduction), deformation twinning is activated, which was seldom reported in low-density steel due to its high stacking fault energy. The deformation twins were found to be preferentially nucleated in the grains with orientations approaching 〈001〉 // rolling direction and 〈111〉 // rolling direction. At the last deformation stage (60 %–90 % rolling reduction), the deformation was mainly controlled by the formation of shear bands, generated in the areas with orientations close to$〈111〉$ // normal direction. In the mechanical response aspect, the strength was progressively increased with increasing rolling reduction. The formation of deformation twins and shear bands could notably enhance the strength, exhibiting a distinct three-staged mechanical behavior during cold rolling. This research provided a thorough understanding of the distinct microstructure evolution and mechanical response of the low-density steel during cold rolling.