Fatigue strength of additively manufactured 316L austenitic stainless steel

Study on Mechanism of Structure Angle on Microstructure and Properties of SLM-Fabricated 316L Stainless Steel

“…The average grain size of each sample was below 26 μm, and the volume fraction of finer grains was greater than 5% except for the 45° sample. Based on the Hall–Petch formula: where is the friction stress (≈188 MPa), k is the strength coefficient (275 MPa·μm1/2 for 316L steel), and dm represents the average grain size ( Li et al, 2018 ; Kumar et al, 2020 ). For most alloys, yield strength improves with a decreasing grain size.…”

“…where σ 0 is the friction stress (≈188 MPa), k is the strength coefficient (275 MPa•μm1/2 for 316L steel), and dm represents the average grain size (Li et al, 2018;Kumar et al, 2020). For most alloys, yield strength improves with a decreasing grain size.…”

A critical review on the effects of process-induced porosity on the mechanical properties of alloys fabricated by laser powder bed fusion

“…Fatigue cracks initiate from the surface under the high cycle fatigue regime but under the very high cycle fatigue regime, cracks initiated from internal unmelted particles, inclusions or LoF pores [127] 316L R = 0.1 Fatigue cracks initiate from internal LoF pores under high loads, but from the surface under low loads (transition occurred at * 10 5 cycles) [119] 316L R = 0.1 Machining can expose sub-surface/internal porosity that can become responsible for fatigue failure Small sub-surface LoF pores (contour area) can dominate over much larger internal pores [205] 316L R = -1 Porosity increases the scatter in fatigue results which can mask other factors that influence fatigue life [206] 316L R = -1 Fatigue cracks that initiate at sub-surface pores propagate without much resistance as the as-built microstructural features are unable to act as barriers to crack propagation or arrest cracks [176] 316L R = 0.1 Samples with high porosity performed worse in fatigue tests as the fatigue life was driven by porosity Fatigue life of dense samples (* 1% porosity, Archimedes method) was dictated by ductility under low-stress loading and by tensile strength at high-stress loading [207] 316L R = 0.1 Defects, sample orientation and surface quality are less influential in high-stress fatigue For low-stress fatigue, cracks initiate from sub-surface pores for machined or surface-treated samples [101] 316L R = -1 For low-stress amplitudes, vertically built samples have higher pore tolerance due to better hardening potential to withstand localized stresses At high-stress amplitudes, vertically built samples perform worse due to poor yield strength [208] 316L R = -1 Stress-relief can improve pore tolerance for horizontal samples to improve fatigue life, but this is effect is more limited on vertical samples [188] 316L R = 0.1 Horizontal samples perform better than vertical samples across all stress levels regardless of whether stress-relief treatment was done With machining, cracks initiated from sub-surface LoF pores. Otherwise, cracks initiated from the surface [209] 316L R = 0.1 Machining can improve fatigue life by reducing roughness, removing surface pores, and introducing compressive residual stresses [210] 316L R = 0.1 The presence of small LoF pores or gas pores are not critical for high-stress fatigue loading as this is microstructure-driven [147] 316L R = 0.1 A transition from porosity-driven fatigue failure (under fixed cyclic loading at 438 MPa) to a microstructural one was observed as density was improved from 98.88% to 99.92% A critical pore size causing this transition was proposed, which could be relative to the length scales of various localized microstructural features [211] 316L R = -1 Pore closure with HIP improves fatigue life at low-stress levels HIP limited fatigue improvements at higher-stress levels due to a substantial reduction in yield strength LoF pores are more detrimental to vertically built samples [216] AlSi10Mg R = 0.1 Porosity causes worse performance than cast AlSi10Mg…”

The Effect of a Slow Strain Rate on the Stress Corrosion Resistance of Austenitic Stainless Steel Produced by the Wire Laser Additive Manufacturing Process

“…This analysis revealed that the source of failure of the counterpart AISI 316L alloy was its relatively greater ductility vs. that of the WLAM alloy. This was manifested by the increased depth of the dimples in the fracture surface of the counterpart AISI alloy, indicating increased ductility [43,44].…”