The fatigue crack propagation (FCP) properties of AISI 4130 steel plates with a ferrite/pearlite (F/P) banded structure were evaluated both in air and electrolytic hydrogen charging environments. To understand the combined effects of hydrogen, directions of banding and elongated non-metallic inclusions on the FCP, specimens with six different orien- tations relative to the rolling direction were sampled and charged with hydrogen. When tested in air, the result reveals that the crack plane as related to the direction of banding, and the local stress concentration induced by elongated inclusions, largely affected the FCP rate. It also shows that the relative dominance of banding and inclusions depended on the direction of banding. For specimens after hydrogen charging, the results show the FCP rate was an order higher than that for the specimens tested in air. The enhancement of FCP rate was found to vary with respect to the main three directions (longitudinal, transverse and through-surface directions) as related to banding. For specimens where hydrogen can easily diffuse along the longitudinal direction into speci- mens and assisted crack propagation, they had the highest FCP rate. It was followed by the specimens in which hydrogen diffused along transverse direction. When bydrogen diffused through layers of ferrite

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