Impact of hydrogen-assisted cracking on the mechanical properties of 316L stainless steel produced by selective laser melting using an in-situ small punch test

This study investigates the impact of hydrogen-assisted cracking on the mechanical properties of 316L stainless steel (SS316L) produced by selective laser melting (SLM) using a small punch (SP) test. The relationships between the process parameters, specifically the scan speed, laser power, energy density, and strength characteristics of SS316L are explored, with a particular focus on the effect of hydrogen precharging. Experimental results demonstrate that increasing the scan speed and laser power improves the maximal peak load (P_m) and fracture displacement (δ_f) up to an optimal range. This improvement is attributed to enhanced microstructural properties, including better fusion and a reduction in grain size, which results in more uniform grain structures and contributes to higher mechanical strength. However, beyond this optimal range, the mechanical performance diminishes owing to the reduced energy density, leading to poorer microstructural integrity. These findings suggest that the optimal SLM parameters for achieving superior mechanical properties in SS316L lie within a specific range of scan speeds and energy densities. Hydrogen precharging, on the other hand, leads to a significant degradation in mechanical properties, with reductions in both P_m and δ_f compared to uncharged specimens. This degradation suggests the occurrence of hydrogen-enhanced localized plasticity (HELP). Geometrically necessary dislocations (GNDs) and twin density measurements are obtained from the stretched regions of the interrupted SP specimens. These measurements provide insights into the underlying hydrogen-induced damage mechanisms by which hydrogen precharging exacerbates material degradation.