Assessing Creep–Fatigue Interactions in Wrought and LP-DED-Processed 316 Stainless Steel

Abstract This study examines the low-cycle fatigue (LCF) and creep–fatigue (CF) behavior of wrought 316L and 316H stainless steels to develop acceptance criteria for accelerated testing of additively manufactured (AM) stainless steels. New LCF and CF data were generated between 550 and 700 °C, focusing on the impact of temperature, control mode, and hold time on fatigue life. Life assessment methods, including time fraction (TF), ductility exhaustion (DE), and stress-modified DE (SMDE), were evaluated for their applicability to nuclear code cases. Results highlight that conventional accelerated CF tests often lead to fatigue-dominated failures due to insufficient hold times. DE and SMDE models correlated more effectively with experimental data than TF, particularly when non-damaging viscous strains were excluded. Testing laser powder-directed energy deposition (LP-DED) 316H revealed non-conservative life predictions across all models, contrasting with the conservative predictions for wrought 316L and 316H, despite comparable LCF and creep properties. These findings underscore the need to refine accelerated CF test protocols to better capture damage mechanisms in AM materials.