Change of stress-strain hysteresis loop and its links with microstructural evolution in AISI 316L during cyclic loading

Abstract

The cyclic deformation behaviour of an austenitic stainless steel and its links with microstructure are examined by analysing changes in the stress-strain hysteresis loop characteristics and dislocation condition with increasing cycle number. In terms of peak tensile stress, AISI 316L exhibits a hardening stage followed by a softening stage, and finally a stable response stage, during strain-controlled cyclic loading. During the hardening stage, dislocation density increases, mainly in the form of planar structures, i.e. stacking faults, pile-ups. Dislocations then rearrange to form walls and channels during the softening stage, which further develop to become a cellular structure later in this stage and during the final stable response stage. An analysis of the change in hysteresis loop shape during cyclic loading shows that the increase in dislocation density is responsible for an increase in effective stress. In addition, the long range internal stress (back stress), which is strongly sensitive to dislocation distribution and dislocation structure, is mainly responsible for the cyclic deformation response. The loop shape parameter and other quantities derived from the stress-strain hysteresis loop also evolve along with the development of the dislocation condition.