Abstract Hydrogen embrittlement (HE) is widely believed to be harmful to engineering structures made of ferritic steel, particularly in the presence of pre-cracks. However, in this study, the ultimate tensile strength (UTS) of shallow pre-cracked cylinder specimens made of interstitial-free (IF) steel, which represents a standard microstructure of ferritic steel, does not always decrease in the hydrogen environment. Namely, the fracture characteristic is sensitive to hydrogen, but UTS is not under specific conditions. This influence of HE contrary to the common-sense understanding is attributed to the following: (1) the crack propagation assisted by hydrogen-enhanced localized plasticity (HELP) is stable before the onset of plastic instability because of exceedingly-high fracture instability toughness; and (2) the plastic strain localization at the pre-crack tip and secondary crack tips resisted the onset of plastic instability. Additionally, this effect calls into question the general applicability of conventional investigation of HE susceptibility that mainly focuses on the variation of fracture characteristic, which is often defaulted to cause changes in mechanical properties. Here, HE susceptibility is deduced to be depended mainly on geometric properties (geometric HE susceptibility) for shallow pre-cracked structures, while that for deep pre-cracked structures depends mainly on material properties (metallurgic HE susceptibility). Subdividing HE susceptibility helps identify conditions under which plastic strain localization caused by HE susceptibility is beneficial for UTS in fail-safe design.

中文翻译：

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在单调张力下区分由无间隙钢制成的预裂结构中的几何和冶金氢脆敏感性

摘要 氢脆（HE）被广泛认为对由铁素体钢制成的工程结构有害，特别是在存在预裂纹的情况下。然而，在本研究中，由代表铁素体钢标准微观结构的无间隙 (IF) 钢制成的浅层预裂纹圆柱体试样的极限抗拉强度 (UTS) 在氢环境中并不总是降低。即，断裂特性对氢敏感，但 UTS 不是在特定条件下。HE的这种与常识相反的影响归因于以下几点：（1）氢增强局部塑性（HELP）辅助的裂纹扩展在塑性不稳定开始之前是稳定的，因为断裂不稳定韧性非常高；(2) 预裂纹尖端和二次裂纹尖端的塑性应变局部化抵抗了塑性失稳的发生。此外，这种效应对 HE 敏感性的常规研究的普遍适用性提出了质疑，该研究主要关注断裂特征的变化，这通常被默认为导致机械性能的变化。这里推导出浅层预裂结构的HE磁化率主要取决于几何特性（几何HE磁化率），而深预裂结构的HE磁化率主要取决于材料特性（冶金HE磁化率）。细分 HE 敏感性有助于确定由 HE 敏感性引起的塑性应变定位有利于 UTS 故障安全设计的条件。