High‐Cycle Fatigue Behavior of Duplex Stainless Steel Microstructures Obtained by Laser Beam Powder Bed Fusion Process

ABSTRACT

Conventionally fabricated duplex stainless steels (DSSs) are well‐known for their good fatigue, corrosion, and combined fatigue/corrosion performance. In laser beam powder bed fusion (PBF‐LB/M), their fabricability and tensile behavior are increasingly studied, though literature highlights process‐induced defects and the need for heat treatment to transform the fully ferritic as‐built microstructure into a duplex (ferrite/austenite) state. Heat treatment can tailor grain size and reduce defects. This work investigates the interplay between microstructure and defects in tensile and torsional high‐cycle fatigue of PBF‐LB/M DSS. Three microstructures are examined: fully ferritic, fine‐grained 50/50 duplex, and coarse‐grained 50/50 duplex, with comparison to a hot‐isostatically pressed condition to assess defect effects. The austenite‐free microstructure is highly defects‐sensitive, whereas duplex structures show reduced sensitivity, particularly under torsion. Fine grains enhance fatigue strength in both loading modes. These findings demonstrate how additive manufacturing‐enabled microstructural design mitigates defect‐sensitivity and inform heat treatment strategies for improved fatigue performance.