Ratchetting process in the stainless steel AISI 316L at 300 K: an experimental investigation

The cyclic creep behaviour of austenitic stainless steel (316L) was studied at room temperature. Particular attention has been paid to the effect of peak stress (Σmax) and mean stress (Σm) on the ratchet strain rate. Threshold stress (230 MPa) for the transition from retardation to acceleration in the cyclic creep has been observed and interpreted as a transition between planar slip to wavy slip. The effect of stacking fault energy on this threshold stress is also studied. The cyclic creep rate increases as a function of Σmax. The influence of maximum stress has been considered as an effect of tensile plastic strain history. This has been previously characterised in terms of back stress and effective stress. In particular, three domains have been identified—R0, RI and RII—where the cyclic mechanisms are different. The slip mode and long-range internal stress state is at the origin of the three cyclic creep domains. Moreover, the evolution of internal stress states during cyclic creep test has been studied.