Role of grain size and anisotropy of neighboring grains in hydrogen-assisted intergranular fatigue crack initiation in austenitic stainless steel

This study explores the impact of microstructural features on fatigue crack initiation in poly-crystalline materials, emphasizing hydrogen-induced complexities. Grain anisotropy, misorientations, grain size variations, and elastic–plastic inhomogeneities concentrate stress at grain boundaries, making them susceptible to crack initiation during fatigue loading. The presence of hydrogen compounds this process, due to complications of characterization of local hydrogen content and activating embrittling mechanisms. Building upon a model for nickel, this research investigates 316L austenitic stainless steel specimens with varying grain sizes, both uncharged and hydrogen-charged. In situ low-cycle fatigue loading experiments establish correlations between fatigue crack initiation and microstructural features. The study reveals specific combinations of features crucial in the initiation process, undergoing alterations in the presence of hydrogen. A proposed qualitative model links microstructural features with accumulated plastic shear strain during fatigue and prevalent hydrogen embrittlement mechanisms like hydrogen-enhanced local plasticity and hydrogen-enhanced decohesion.