Cyclic deformation behavior in a nitrogen-alloyed austenitic stainless steel in terms of the evolution of internal stress and microstructure

In order to understand the physical nature of cyclic deformation behavior in 316LN under uniaxial loading, the evolution of dislocation structure and density was explored by transmission electron microscopy (TEM) observation on specimens loaded with different cycles. Particular attention was paid to the evolution of internal stress which was evaluated by partitioning the hysteresis loops, and further decomposed into intergranular and intragranular components by taking into account quantitatively the heterogeneous dislocation structure. For medium and high strain amplitudes, planar dislocation structures were observed in most grains during the initial hardening stage, in which the intergranular internal stress dominates the cyclic hardening behavior. The activation of cross slip in the following softening stage not only acts to reduce intergranular internal stress, but also promotes the formation of heterogeneous dislocation distributions which acts to improve the intragranular internal stress. For low strain amplitude, no dislocation rearrangement was observed and the evolution of internal stress was determined only by its intergranular component throughout the entire cycling process.