Hydrogen absorption in structural alloys can induce degradation through mechanisms that depend on its transport, distribution, and interaction with microstructure. Yet, these processes have been accessible only through indirect, bulk-averaged, or post-mortem measurements. Here, we present an operando high-energy X-ray diffraction microscopy approach that enables the quantification of hydrogen solubility and diffusivity from real-time lattice-strain evolution with micrometre-scale spatial resolution. The method, demonstrated on a double precipitation-hardened martensitic steel, provides spatiotemporal maps of hydrogen ingress across entire specimens, enabling simultaneous determination of local concentration and transport kinetics from a single experiment. Complementary electrochemical permeation measurements reveal analogous multi-stage transients, directly visualising the transition from lattice-fast to trap-controlled regimes and validating the diffraction-derived diffusivity hierarchy. The results show that hydrogen diffusivity is not a fixed material property but rather evolves during uptake. Precipitation-rich microstructures confine hydrogen near the surface, whereas precipitation-free martensite permits rapid penetration, establishing hydrogen transport as a state-dependent, time-variant process. Hydrogen absorption in steel can cause degradation, yet the underlying processes are typically only accessible through indirect, bulk-averaged, or post-mortem measurements. This paper uses operando high-energy X-ray diffraction to quantify hydrogen solubility and diffusivity by the real-time tracking of lattice-strain on the micrometer scale.
Aksoy et al. (Tue,) studied this question.