Creep-fatigue properties and deformation mechanism of 316L steel fabricated by laser powder bed fusion (PBF-LB/M)

Abstract

To ensure the structural integrity of components manufactured by laser powder bed fusion method at extreme service condition, the creep-fatigue interaction (CFI) properties of PBF-LB/M materials need to be investigated. As a common structural material in nuclear plants, 316L stainless steel is chosen and fabricated to samples using PBF-LB/M method. A series of CFI tests at 550 °C are undertaken on PBF-LB/M 316L to investigate its deformation behavior and microstructural evolution, specifically focusing on the effects of varying tensile holding time on fatigue-creep competition mechanism. The creep voids formation, coarsen of cellular sub-structure, texture evolution and σ-phase formation are observed in PBF-LB/M 316L after cyclic deformation. PBF-LB/M 316L exhibits a fatigue life 35 % superior to that of traditional 316L under LCF loading. Nevertheless, with an increase in tensile holding time to 600 s, the fatigue life of PBF-LB/M 316L diminishes by 17 % compared to traditional 316L. The fatigue cracks induced by CFI tests are all initiated from lack-of-fusion defects at the sub-surface and propagate intergranularly.