The processes leading to hydrogen-related fracture in X80 pipeline steel with a stress concentration have been investigated comprehensively through observations of fracture surfaces and subsidiary cracks, stress analyses, crack initiation and propagation analyses and crystallographic analyses of fracture surfaces. Fracture morphology showed quasi-cleavage (QC) fracture under various amounts of hydrogen. It was found that QC cracks initiated in hydrogen-charged specimens in an area ranging from the notch tip to 100 µm inside based on interrupted tensile tests until just before fracture strength. A fracture surface topography analysis (FRASTA) revealed that QC cracks initiated at the notch tip. A finite element analysis indicated that the equivalent plastic strain was maximum at the crack initiation site at the notch tip. A backscattered electron image showed that nanovoids of 50–250 nm in diameter were present near the initiation site. Regarding the crack propagation process, field emission scanning electron microscopy (FE-SEM), electron backscattered diffraction (EBSD) and FRASTA results indicated that some microcracks in ferrite grains coalesced in a stepwise manner and propagated. Trace analyses using EBSD revealed that the QC fracture surface consisted of {011} slip planes, {001} cleavage planes and non-specific index planes. These findings indicate that QC fracture initiated at the notch tip due to the interaction between dislocations and hydrogen associated with local plastic deformation, and propagated in a stepwise manner by coalescence through vacancies, nanovoids and microcracks on various planes associated with/without plastic deformation in ferrite grains.

通过对X80管线钢的断口及副裂纹观察、应力分析、裂纹萌生与扩展分析、断口晶体学分析，综合研究了X80管线钢在应力集中导致氢致断裂的过程。断裂形态显示在不同量的氢气下准解理 (QC) 断裂。发现在充氢试样中从缺口尖端到 100 µ的区域内产生 QC 裂纹m 内部基于间断拉伸试验直到断裂强度之前。断裂表面形貌分析 (FRASTA) 显示 QC 裂纹始于缺口尖端。有限元分析表明，等效塑性应变在缺口尖端裂纹萌生部位最大。背散射电子图像显示在起始位点附近存在直径为 50-250 nm 的纳米空隙。关于裂纹扩展过程，场发射扫描电子显微镜（FE-SEM）、电子背散射衍射（EBSD）和 FRASTA 结果表明，铁素体晶粒中的一些微裂纹以逐步方式聚结并扩展。使用 EBSD 的痕量分析表明 QC 断裂面由 {011} 滑移面、{001} 解理面和非特异性指数面组成。