Abstract The determination of fracture behaviour of welds in presence of internal hydrogen is essential for the integrity assessment of CrMo vessels and pipes working under high hydrogen pressures. Homogeneous coarse-grain tempered bainitic/martensitic microstructures were obtained in 42CrMo4 and 2.25Cr1Mo steels by means of laboratory heat treatments in order to reproduce the coarse grain heat affected zone (CGHAZs) of real welds. Afterwards, the fracture toughness behaviour of the simulated CGHAZs was assessed under low displacement rate J-fracture tests, using pre-charged (in hydrogen gas) CT specimens. The hydrogen embrittlement (HE) experienced by the CGHAZs of both steels was considerably greater than in the base steels. The greater hardness, i.e. higher dislocation density, characteristic of the CGHAZ microstructures, explains the more strongly trapped hydrogen, and hence the sharper drop in the fracture toughness, also associated to an increase of intergranular fracture micromechanisms. Scanning electron microscopy examination of the fracture surfaces revealed the action of hydrogen-enhanced localized plasticity (HELP) mediated hydrogen-enhanced decohesion (HEDE) micromechanism, in which HELP took place first, providing enough hydrogen in the process zone to modify the local resistance, and eventually weakening the cohesion of the internal interfaces, HEDE.

中文翻译：

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内含氢调质铬钼钢粗晶热影响区的断裂韧性：断裂微观机制

摘要 确定焊缝在内部氢存在下的断裂行为对于在高氢压力下工作的 CrMo 容器和管道的完整性评估至关重要。通过实验室热处理在 42CrMo4 和 2.25Cr1Mo 钢中获得均匀的粗晶回火贝氏体/马氏体显微组织，以再现真实焊缝的粗晶热影响区 (CGHAZ)。然后，在低位移率 J 断裂试验下，使用预充（氢气）CT 试样评估模拟 CGHAZ 的断裂韧性行为。两种钢的 CGHAZ 经历的氢脆 (HE) 明显大于基础钢。更大的硬度，即更高的位错密度，CGHAZ 微观结构的特征，解释了更强的截留氢，因此断裂韧性急剧下降，这也与晶间断裂微观机制的增加有关。断口的扫描电子显微镜检查揭示了氢增强局部塑性 (HELP) 介导的氢增强脱聚 (HEDE) 微观机制的作用，其中 HELP 首先发生，在工艺区提供足够的氢来改变局部电阻，并最终削弱内部接口 HEDE 的凝聚力。