The resistance of steels against hydrogen embrittlement can be assessed with the standardized NACE-A test, in which a tensile specimen is exposed to a sour medium at a constant mechanical load corresponding to 85% of its yield strength. In this presentation, the influence of hydrogen on fracture in martensitic steels is studied with a micromechanical model in which the martensitic microstructure is represented in a simplified way. Hydrogen diffusion is explicitly taken into account, enabling the investigation of the local hydrogen concentration as function of residual stresses within the microstructure. This micromechanical model is embedded within a macroscopic model mimicking the boundary conditions of the NACE-A test.

The presence of hydrogen is assumed to locally influence the cohesive strength of grain boundaries and, thus, cause the nucleation and growth of cracks. Based on this model, the influence of microstructure, local plastic relaxations and hydrogen diffusion on the lifetime of a material under NACE-A conditions can be studied. Furthermore, it is demonstrated how such micromechanical models can be augmented by insight and data gained from fundamental atomistic models that are used to quantify the influence of hydrogen on the mechanical properties of interfaces and grain boundaries.