High Temperature Fatigue of Aged Heavy Section Austenitic Stainless Steels.

This work investigates two austenitic stainless steels, Sanicro 25 which is a candidate for high temperature heavy section components of future power plants and Esshete 1250 which is used as a reference material. The alloys were subjected to out-of-phase (OP) thermomechanical fatigue (TMF) testing under strain-control in the temperature range of 100 ∘C to 650 ∘C. Both unaged and aged (650 ∘C, 3000 h) TMF specimens were tested to simulate service degradation resulting from long-term usage.

Study of crack initiation or damage in very high cycle fatigue using ultrasonic fatigue test and microstructure analysis.

Fatigue damage behaviors of four metal materials in the very high cycle fatigue (VHCF) regime have been studied using ultrasonic fatigue test and microstructure analysis. The results show that the fatigue crack initiation in VHCF regime could occur at subsurface non-defect fatigue crack origin (SNDFCO), where the accumulated cyclic strains or damage in the specimens were highly localized, especially in the materials with some softer phase, where the local maximum strain can be eight times higher than the average strain value in the specimen. This high strain localization can cause a local plasticity exhaustion that leads to a stress concentration and consequently fatigue crack initiation, and finally the formation of SNDFCO.