Hydrogen-induced softening and embrittlement in 316L stainless steel fabricated using laser-powder bed fusion

To investigate the effects of hydrogen (H) on the mechanical properties of 316L austenitic stainless steel (316L) additively manufactured using laser-powder bed fusion (L-PBF), tensile, nanoindentation, and micropillar compression tests were performed on samples in both the as-built (AB) and H-charged (HC) conditions. Microstructural characterization revealed that the electrochemical H charging exerted marginal effects on grains, phases, and overall dislocation densities of L-PBF 316L. However, the dislocation networks inherent to L-PBF 316L appear to disentangle upon H charging and are distributed more homogeneously through the matrix. Mechanical test results showed that H charging results in a marginal reduction in hardness and strength, indicating H-induced softening, possibly due to the elastic shielding effects of H that weaken the interactions between dislocations. The elastic shielding effect and the enhanced slip planarity, facilitate the H accumulation along slip bands and twins, promote H-enhanced localized plasticity, resulting cracking when a critical H concentration is reached. This, in turn, aids in H embrittlement mechanism that results in a significant loss in ductility upon H charging. A detailed discussion of all these micromechanisms is presented.