Influence of the PWR environment on low cycle life fatigue of 304 L stainless steel

The 304L austenitic stainless steel is used to fabricate reactor components, notably primary circuit cooling tubes. In this application, the material is submitted to cyclic solicitations associated with thermal transients like reactor stopping and restarting. In order to understand the phenomena occurring for this material, a study of the low cycle fatigue behaviour of this alloy has been performed in different environments: air, primary water of a PWR, and secondary vacuum. Tests are performed with an imposed total deformation, with a triangular signal, and at 300 C. Three strain rates are used. The material behaviour is analyzed in terms of stress response and life duration. Deformation and damage mechanisms are studied by scanning electronic microscopy observations of samples at various stages of their life duration