Assessment of the Contribution of Internal Pressure to the Structural Damage in a Hydrogen-charged Type 316L Austenitic Stainless Steel During Slow Strain Rate Tensile Test

The aim of this study is to provide a quantification of the internal pressure contribution to the SSRT properties of H-charged Type-316L steel tested in air at room temperature. Considering pre-existing penny-shaped voids, the transient pressure build-up has been simulated as well as its impact on the void growth by preforming JIc calculations. Several void distributions (size and spacing) have been considered. Simulations have concluded that there was no impact of the internal pressure on the void growth, regardless the void distribution since the effective pressure was on the order of 1 MPa during the SSRT test. Even if fast hydrogen diffusion related to dislocation pipe-diffusion has been assessed as a conservative case, the impact on void growth was barely imperceptible (or significantly low). The effect of internal pressure has been experimentally verified via the following conditions: (I) non-charged in vacuum; (II) H-charged in vacuum; (III) H-charged in 115-MPa nitrogen gas; (IV) non-charged in 115-MPa nitrogen gas. As a result, the relative reduction in area (RRA) was 0.84 for (II), 0.88 for (III), and 1.01 for (IV), respectively. The difference in void morphology of the H-charged specimens did not depend on the presence of external pressure. These experimental results demonstrate that the internal pressure had no effect on the tensile ductility and void morphology of the H-charged specimen.