Mechanism of HCF-creep interaction in a type 316LN stainless steel

HCF-creep interaction in type 316LN stainless steel is investigated at 923 K by conducting HCF tests well below the endurance limit with high mean stress (high R-ratio). High mean stress inflicts creep damage at 923 K, which when imposed on a small alternating stress, leads to significant HCF-creep interaction. Depending on the magnitude of mean stress (R-ratio), three distinct regimes are identified, viz. (a) HCF regime (b) HCF-creep interaction regime and (c) creep regime. Detailed fractographic investigation revealed distinct fracture characteristics pertaining to each of the three regimes. HCF-creep interaction regime is marked by significant intergranularity at low values of mean stress which changes to predominantly dimpled fracture with increasing mean stress. The above observations are corroborated through detailed EBSD investigations which bring out the underlying deformation mechanisms responsible for failure under HCF-creep interaction.