ABSTRACT

An in-depth understanding of the role of non-metallic inclusions (NMIs) in the hydrogen-induced failure of structural materials is important in the manufacture and application of steels. In this paper we investigated the type, the amount and the distribution of NMIs in pipeline steels and their relation to the susceptibility to hydrogen-induced cracking (HIC). Scanning Electron Microscope (SEM) observation confirmed the interlinking of the microcracks formed at the inclusion-matrix interfaces. By combining with the nondestructive three-dimensional (3D) mapping of crack propagation paths, based on the synchrotron tomography technique, we obtained direct evidence that the cracking initiation at the NMIs and then interlinking on the (nearly) same plane are the main mechanism of HIC failure in X70 steels. We built an elastic-energy-based model, which can be applied to quantitatively predict the HIC-induced dependence of the fracture toughness on NMIs, based on statistical information of the NMIs. The theoretical results show a good agreement with the experimental observation. We proposed a criterion to determine the susceptibility to HIC by the observation of NMIs. We also developed a thermodynamics-based model to analyze the hydrogen trapping at the inclusion-matrix interface and its dependence on the strength of the steel matrix. For the first time, the direct relationship between NMIs and HIC-induced degradation of fracture toughness is obtained.

摘要

深入理解非金属夹杂物（NMI）在氢诱导的结构材料破坏中的作用对于钢的制造和应用很重要。在本文中，我们研究了管线钢中NMI的类型，数量和分布，以及它们与氢致裂纹敏感性（HIC）的关系。扫描电子显微镜（SEM）的观察证实了在夹杂物-基质界面处形成的微裂纹的相互联系。通过基于同步加速器层析成像技术，结合裂纹扩展路径的无损三维（3D）映射，我们获得了直接的证据，表明NMI处的裂纹萌生然后在（几乎）同一平面上互连是裂纹的主要机理。 X70钢的HIC失效。我们建立了一个基于弹性能量的模型，基于NMI的统计信息，可以将其用于定量预测HIC引起的断裂韧性对NMI的依赖性。理论结果与实验结果吻合良好。我们提出了通过观察NMI来确定对HIC的敏感性的标准。我们还开发了基于热力学的模型来分析氢在夹杂物-基体界面处的捕集及其对钢基质强度的依赖性。首次获得了NMI与HIC引起的断裂韧性降低之间的直接关系。我们提出了通过观察NMI来确定对HIC的敏感性的标准。我们还开发了基于热力学的模型来分析氢在夹杂物-基体界面处的捕集及其对钢基质强度的依赖性。首次获得了NMI与HIC引起的断裂韧性降低之间的直接关系。我们提出了通过观察NMI来确定对HIC的敏感性的标准。我们还开发了基于热力学的模型来分析氢在夹杂物-基体界面处的捕集及其对钢基质强度的依赖性。首次获得了NMI与HIC引起的断裂韧性降低之间的直接关系。