Effect of Hydrogen on the Tensile Behavior of Austenitic Stainless Steels 316L Produced by Laser-Powder Bed Fusion

Abstract

Hydrogen was doped in austenitic stainless steel (ASS) 316L tensile samples produced by the laser-powder bed fusion (L-PBF) technique. For this aim, an electrochemical method was conducted under a high current density of 100 mA/cm2 for three days to examine its sustainability under extreme hydrogen environments at ambient temperatures. The chemical composition of the starting powders contained a high amount of Ni, approximately 12.9 wt.%, as a strong austenite stabilizer. The tensile tests disclosed that hydrogen charging caused a minor reduction in the elongation to failure (approximately 3.5% on average) and ultimate tensile strength (UTS; approximately 2.1% on average) of the samples, using a low strain rate of 1.2 × 10−4 s−1. It was also found that an increase in the strain rate from 1.2 × 10−4 s−1 to 4.8 × 10−4 s−1 led to a reduction of approximately 3.6% on average for the elongation to failure and 1.7% on average for UTS in the pre-charged samples. No trace of martensite was detected in the X-ray diffraction (XRD) analysis of the fractured samples thanks to the high Ni content, which caused a minor reduction in UTS × uniform elongation (UE) (GPa%) after the H charging. Considerable surface tearing was observed for the pre-charged sample after the tensile deformation. Additionally, some cracks were observed to be independent of the melt pool boundaries, indicating that such boundaries cannot necessarily act as a suitable area for the crack propagation.

Significance of Melt Pool Structure on the Hydrogen Embrittlement Behavior of a Selective Laser-Melted 316L Austenitic Stainless Steel

“…The twins can help to maintain strain hardening at higher stress levels, resulting in higher ductility [ 40 ]. However, the sample with H did not form high-density twins, which could be an important reason for the reduction in UTS and ductility of the samples with H. The surface damage induced by hydrogen will cause mechanical property degradation [ 14 ]. As shown in the SEM pictures of the hydrogen charging sample ( Figure 3 d,e), the hydrogen-induced cracking along the MPBs, which will be conducive to generating high-stress concentration, resulting in faster failure.…”

“…Recently, some studies have investigated the hydrogen behavior of selective laser-melted austenitic stainless steel. Khaleghifar et al [ 14 ] found that SLM 316L SS has a slight reduction in elongation after H charging. Bertsch et al [ 15 ] systematically investigated the influence of hydrogen on the mechanical properties of SLM 316L SS, indicating that the presence of hydrogen leads to decreasing plasticity.…”

Effects of Wall Thickness Variation on Hydrogen Embrittlement Susceptibility of Additively Manufactured 316L Stainless Steel with Lattice Auxetic Structures

“…Whereas the thickest strut, T1.4, displayed fewer surface flaws, the mechanical properties were more affected by H-charging. This can be attributed to reversible trapping sites, such as dislocation cores [ 23 ], which are increased with increasing cross-section, as reported in the literature [ 38 , 39 ]. This is in an agreement with the mechanical properties illustrated in Table 2 .…”

“…There are two competing factors which affect the HE susceptibility of AM316L SS: the surface roughness and the hydrogen trapping sites [ 19 , 20 , 21 , 22 , 23 , 45 ]. Hydrogen atoms effectively diffuse into the rough surface as the surface flaws and other imperfections, such as pores, serve as entrances for the H atoms, as reported in the literature [ 24 , 44 , 45 , 52 ].…”

“…Various studies have been conducted on the HE susceptibility of 3D-printed 316L-SS [ 19 , 20 , 21 , 22 , 23 , 24 ]. These studies have found that volumetric defects, sub-grains in the cellular structure, and the melt pool boundaries present in selective laser melted (SLMed) 316L-SS act as potential trapping sites for H atoms.…”