PSI - Issue 68

Liesbet Deconinck et al. / Procedia Structural Integrity 68 (2025) 1074–1080 Liesbet Deconinck et al./ Structural Integrity Procedia 00 (2025) 000–000

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Figure 1: SEM micrograph from (a) SR and (b) HIP L-PBF 316L. The building direction is oriented horizontally in both cases.

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Figure 2: EBSD figures of (a) SR and (b) HIP L-PBF 316L. The building direction is oriented horizontally in both cases.

The effect of hydrogen charging on the different microstructures was first evaluated with XRD. The XRD patterns of both post-processing conditions are given in Figure 3, before and after electrochemical hydrogen charging. The face centered cubic austenite phase was present in all conditions. Comparing the uncharged materials reveals that the peaks of uncharged HIP L-PBF 316L are narrower than for uncharged SR L-PBF 316L. This observation confirms that the HIP treatment reduces the quantity of residual stresses compared to the SR treatment, due to the additional cycle at high temperature and high pressure. Upon hydrogen charging, the characteristic peaks broaden with respect to the uncharged condition, and slightly shift to lower 2θ angles. The observed peak broadening indicates that hydrogen introduces non-uniform stresses in the microstructure. Considering the charged microstructure micrographs in Figure 4 with slip bands, the broader peak appearance upon hydrogen charging can also be related to the scattering of the coherently diffracting slip bands, in combination with dislocation scattering. Besides, the slight peak shift to the left upon hydrogen charging indicates an expansion of the lattice constant due to the introduction of interstitial hydrogen atoms. No additional phases were observed with XRD after hydrogen charging. In contrast, conventionally manufactured 316L steel typically undergoes a partial phase transformation into martensite upon hydrogen charging (Metalnikov et al., 2022).