A comparative assessment of fatigue deformation behavior of 316 LN SS at ambient and high temperature

Abstract

In this study, the low cycle fatigue deformation of 316 LN stainless steel has been assessed and compared for relatively low and high temperatures. Low cycle fatigue tests were carried out on the steel at 298K and 873K employing strain amplitudes ranging from ±0.3% to ±1.0% at a strain rate of 3×10−3s−1. At both the temperatures, the material exhibited initial hardening followed by gradual softening to the saturation stage and final failure. Comparison of hysteresis loops at saturation revealed that the material exhibited Masing behavior at lower strain amplitudes and non-Masing behavior at relatively higher strain amplitudes at 298K whereas a reverse trend was observed at 873K. Manifestation of Masing and non-Masing behavior was reflected in the dual slope cyclic stress- strain relationship. The change from Masing to non-Masing behavior and vice versa depending on the temperature and strain amplitude has been corroborated with the transmission electron microscopic and electron backscattered diffraction investigation. The dislocation substructure was found to depend on the temperature and strain amplitude. At 298K, pile-up in the planar slip and tendency to develop cell structure was observed at lower and higher strain amplitudes, respectively. However, dislocation pinning resulting from DSA and well developed cell structure was observed at lower and higher strain amplitudes, respectively at 873K. The fatigue life has been predicted based on the hysteresis energy approach considering both the Masing and non-Masing behavior and it was observed that the non-Masing analysis predicts the fatigue life more accurately than the Masing analysis.