Planar dislocation structure during creep-fatigue interactions of TP347H heat-resistant austenitic steel at 600 °C

The low-cycle fatigue (LCF) and creep-fatigue (CF) interaction tests of TP347H austenitic stainless steel are carried out in air under a fully-reversed strain amplitude of 1.0% at 600 degrees C. A 10 min tensile dwell is applied in CF interaction testing. The influences of dwell on dislocation structures and fracture behavior have been evaluated. It is found that CF interaction life is lower than LCF one. The fatigue fracture mode changes from transgranular crack under LCF to transgranular plus intergranular fracture with tensile dwell. A lot of dislocation planar slip bands (PSBs) were found under CF interaction condition. PSB interacts with PSB of another slip system, twins, grain boundary (GB), and triangular GB. Strongly PSB-GB interaction causes stress concentration at GB, creating cavities and crack initiation, causing intergranular fracture. The stress concentration within the PSBs will also cause cracks, resulting in transgranular fracture morphology with fatigue striation.