In situ diffraction characterization on microstructure evolution in austenitic stainless steel during cyclic plastic deformation and its relation to the mechanical response

Abstract

Diffraction line profile analysis was performed to qualitatively evaluate the change in the microstructure of austenitic stainless steel during 250 cycles of plastic deformation. The dislocation density increased with increasing number of cycles until 50 cycles but thereafter decreased. The cycle number corresponding to this maximum point differed depending on whether it was evaluated as the total dislocation density or was deconvoluted into edge and screw dislocation densities. At the initial state, edge dislocations were predominant; however, screw dislocations greatly increased at the first stage of cyclic loading. Afterwards, edge dislocations formed cell walls and screw dislocations annihilated. The cycle number at which the singularity was reached depended on the development of the dislocation structure. When the cell structure developed and the cell wall became sharp, the arrangement of dislocations on average decreased and the crystallite size increased. The flow stress of the austenite phase increased and decreased, reflecting the dislocation density during cyclic loading. However, after αʹ-martensite was generated as the number of cycles increased, the contribution of the transformed martensite to the total flow stress could increase.