Quantitative prediction of the hydrogen-induced crack initiation remains challenging, partially due to the difficulties in directly measuring the hydrogen gas pressure in the crack cavity. Through detailed cross-sectional observations, this study shows that the structure of the internal cracks beneath the surface blisters, i.e., the ratio of crack depth/length, can be significantly influenced by the hydrogen charging conditions. This is attributed to the change of hydrogen gas pressure in the crack cavity at different hydrogen contents, supported by the formation of stepwise cracks near the specimen surface as well as the hydrogen concentration measurements. The post-failure crack geometry is considered a useful indicator of the level of internal gas pressure to quantitatively assess the hydrogen-induced cracking sensitivity. The mechanisms of crack initiation and propagation at different hydrogen concentrations are discussed.

氢致裂纹萌生的定量预测仍然具有挑战性，部分原因是难以直接测量裂纹腔中的氢气压力。通过详细的横截面观察，本研究表明，表面气泡下方的内部裂纹结构，即，裂纹深度/长度的比值受充氢条件的影响很大。这是由于在不同氢含量下裂纹腔中氢气压力的变化，由试样表面附近阶梯裂纹的形成以及氢浓度测量支持。失效后裂纹几何形状被认为是内部气压水平的有用指标，可定量评估氢致裂纹敏感性。讨论了不同氢浓度下裂纹萌生和扩展的机制。