Low cycle fatigue behavior of additive manufactured 316LN stainless steel at 550 °C: Effect of solution heat treatment

Abstract

Heat treatment is used to change the microstructure and improve the low-cycle fatigue (LCF) performance of additive manufactured (AM) 316LN stainless steel (SS) in this work. Strain-controlled low cycle fatigue tests were performed on the as-built (AB) and heat-treated (HT) AM 316LN SS at 550 °C with strain amplitudes ranging from 0.4 % to 1.0 %. The AB material presents a cyclic softening behavior while HT material demonstrates an initially cyclic hardening followed by softening behavior, which is thoroughly analyzed based on the cyclic stress decomposition and microstructure characterizations. The crack nucleates at the specimen surface or near-surface defects in both AB and HT materials. The HT material presents a stronger resistance to crack propagation in comparison to AB material due to the modified microstructures after heat treatment. Correspondingly, the fatigue life of HT material is longer than AB material.