The Influence of High Internal Hydrogen Content on the Evolved Microstructure During Fatigue-Crack Growth in 316L Stainless Steel
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The link between the microstructural states following uniaxial fatigue loading in the absence (4 mass ppm of hydrogen) and presence of hydrogen (104 mass ppm of hydrogen) has been made using type 316L austenitic stainless steel. The fracture surface morphology was first examined using scanning electron microscopy and then samples were extracted using focused-ion beam machining from regions containing striations. Microstructures were assessed using conventional diffraction contrast and zone-axis scanning transmission electron imaging conditions. The high internal hydrogen content led to a 22.3% reduction in fatigue life. Later stages of crack growth show hydrogen affecting the depth and degree of refinement near the fracture surface, measured by the degree of curvature of a twin variant. Findings are discussed in terms of the effect of hydrogen on the collective behavior of dislocations, deformation twinning, and mode of fracture.