Characterization of tensile and torsional fatigue behaviors of additively manufactured super duplex stainless steel SAF 2507

Abstract Super duplex stainless steels (SDSSs) are well known for their good mechanical properties and corrosion resistance inherited from the dual-phase microstructure with equivalent proportion of ferrite and austenite. The development of additive manufacturing has given rise to the use of more diversified material than usual metallic alloys such as SDSSs. Nevertheless, this material is fully ferritic in the as-built state from laser powder bed fusion process. Despite this phase ratio difference with conventional processes, literature has demonstrated that the monotonic tensile properties are higher than wrought material, and with an equivalent corrosion behavior. Given these observations, it is interesting to determine the influence of process parameters on the fatigue behavior of single phase SDSS. Hence, two batches of dense specimens were built with two different set of process parameters. The respective defect populations and microstructures were characterized by means of X-ray computed tomography, electron backscattered diffraction, X-ray diffraction, and transmission electron microscopy. Based on these features, the monotonic tensile behavior, and fully-reversed tension and torsion fatigue properties of the specimens obtained with the two batches are analyzed. Defects of equivalent size between the two batches were obtained but the difference in defect density resulted in crack initiation scatter. With defect size, in the range of the grain size, tension and torsion fatigue behavior were not similarly affected. Tension fatigue behavior and strength were different depending on crack initiation phenomena: surface defect or grain. However, behavior in torsion loading is not affected by the change of crack initiation phenomena.