Hydrogen Embrittlement Mechanism of Ultrafine-grained Iron with Different Grain Sizes

To investigate the effect of grain sizes on hydrogen embrittlement 4N-purity iron, miniature tensile tests were conducted after charging for ultrafine-grained specimens produced by high-pressure torsion and subsequent annealing. Hydrogen indexes defined from reduction area increased with decreasing size, shear-type fracture occurred fine dimples surface diagonally raptured specimen a smaller size. The formation growth microvoids at triple junctions boundaries ahead propagated cracks responsible such earlier because necking between adjacent more likely extensively occurred. In larger or without charging, other hand, local coalescence predominant due to longer distances junctions, resulting in void coalescence-type coarser dimple patterns. Therefore, atoms introduced are considered enhance deformation-induced vacancies finer