Cyclic deformation behavior and dynamic strain aging of 316LN stainless steel under low cycle fatigue loadings at 550 °C

High temperature low cycle fatigue tests at various strain amplitudes (+/- 0.5%, +/- 0.6%, +/- 0.8%, +/- 1.0%) and strain rates (0.5%/s, 0.05%/s, 0.005%/s) were performed at 550 degrees C. The stress decomposition method and microstructure characterization were used to analyze cyclic hardening and softening behavior. Results showed that increased back stress and the combined action of back and friction stresses were responsible for the pronounced cyclic hardening at the early and late stages of initial hardening, respectively. The decrease in friction stress resulted in cyclic softening until final fracture. Moreover, the evolution behavior of dynamic strain aging (DSA) activity was discussed, which showed a clear dependence on loading cycles and directions. Specifically, the DSA activity was firstly attenuated and then gradually intensified from the late stage of cyclic hardening, and it was stronger in the compressive plastic deformation regime of hysteresis loops than in the tension part.

Automated summary

High-temperature low-cycle fatigue tests were conducted at 550 degrees C with various strain amplitudes and strain rates. The results showed that cyclic hardening was caused by increased back stress and the combined action of back and friction stresses, while cyclic softening was attributed to a decrease in friction stress. Additionally, the evolution of dynamic strain aging activity exhibited a clear dependence on loading cycles and directions, with DSA activity being stronger in the compressive plastic deformation regime of hysteresis loops.