Toward superior fatigue and corrosion fatigue crack initiation resistance of Sanicro 28 pipe super austenitic stainless steel

Abstract

The present work deals with the fatigue and corrosion-fatigue crack initiation in cold-pilgered Sanicro 28 super austenitic stainless steel. Toward this end, the stress-controlled symmetric reverse bending fatigue tests were conducted in air and mixed acid aqueous solution under the stress amplitude of 200–570 MPa with the stress ratio of −1 and frequencies of 1 and 15 Hz at ambient temperature. The fatigue study was supplemented with electrochemical experiments and advanced microstructural analyses to explore the damage characteristics in detail. The planar character of dislocation substructure owing to the low stacking fault energy of the material, and formation of parallel slip bands led to a more homogenous distribution of the imposed strain which retarded the progress of damage accumulation. According to the X-ray photoelectron spectrometer results, the formation of the insoluble and stable MoO3 oxide increased the rate of repassivation. This sticky oxide resisted against breakdown rendered by the attack of aggressive chloride ions. The corrosion fatigue behavior of the experimented alloy under the various test frequencies was discussed relying on the synergistic effects of mechanical and environmental damages.