New grain formation during warm deformation of ferritic stainless steel

Microstructural evolution accompanied by localization of plastic flow was studied in compression of a ferritic stainless steel with high stacking fault energy (SFE) at 873 K (approximate to 0.5 Tm). The structure evolution is characterized by the formation of dense dislocation walls at low strains and subsequently of microbands and their clusters at moderate strains, followed by the evolution of fragmented structure inside the clusters of microbands at high strains. The misorientations of the fragmented boundaries and the fraction of high-angle grain boundaries increase substantially with increasing strain. Finally, further straining leads to the formation of new fine grains with high-angle boundaries, which become more equiaxed than the previous fragmented structure. The mechanisms operating during such structure changes are discussed in detail.