Hydrogen permeation into duplex steel under compressive and tensile stresses: Symmetric lattice swelling and asymmetric stress redistribution

A fundamental understanding of how mechanical stress influences hydrogen diffusion is essential for developing strategies to mitigate hydrogen embrittlement of structural materials. This study investigates the effect of externally applied stress on hydrogen uptake in 2205 duplex stainless steel, an industrially relevant material with a heterogeneous, dual-phase microstructure. A four-point bent sample is subjected to in-situ electrolytic hydrogen charging for four hours while being analyzed via high-energy synchrotron cross-sectional X-ray micro-diffraction, enabling time- and depth-resolved characterization of strain-free lattice parameters and internal stresses. The results reveal symmetric lattice expansion within the tensile- and compressively-stressed sample regions in both ferrite and austenite phases to a depth of ~100 µm. This lattice swelling shifts the in-plane stress components toward more compressive levels within the hydrogen-affected regions. As a result, tensile stresses are relaxed and compressive stresses moderately increase on respective sides of the sample, as verified by finite element simulations. The findings call into question models suggesting that the surface treatments and compressive residual stresses can be used to reduce hydrogen ingress into metals.