Abstract: Effect of grain size on hydrogen damage behavior in 99% pure iron was investigated by controlling grain size through different annealing processes. Two types of pure iron with different grain sizes were subjected to electrochemical hydrogen charging. The hydrogen-induced damage was characterized by using scanning electron microscopy, while thermal desorption spectroscopy was employed to analyze hydrogen desorption behavior. The X-ray diffraction was utilized to examine lattice distortion caused by hydrogen charging. The results show that hydrogen-induced cracks primarily initiate at grain boundaries in the surface layer. As the cracks propagate, the surface region is extruded, forming hydrogen blisters. The size of hydrogen blisters show a positive correlation with grain size, whereas the amount of hydrogen desorption decreases with the increase of grain size. The X-ray diffraction analysis reveals that hydrogen charging causes a shift in diffraction peaks towards lower angles, indicating lattice expansion, which may significantly influence hydrogen damage in pure iron. These findings elucidate the effect of grain size on hydrogen damage behavior in pure iron and provide experimental evidence for improving hydrogen embrittlement resistance.

Key words: pure iron, grain size, hydrogen damage, hydrogen desorption