The purpose of this study was to evaluate the microstructural evolution of softened zones after cyclic plastic deformation (CPD) and the effect of CPD on the mechanical properties of X60 reeled-pipeline welded joints. The results showed that the existence of softened zone caused the deformation to be mainly concentrated in this area during CPD process. The minimum hardness of softened zone was 18 HV less than the base metal (BM). As the global strain of the welded joints increased from the initial state without CPD to 5% strain, the kernel average misorientation of inter-critical HAZ related to the geometrically necessary dislocation slightly increased from 0.66° to 0.87°, resulting in a slight rise in hardness. Despite the presence of softened zones in HAZ, the location of tensile fracture was at BM, which was attributed to the combined effect of the work-hardening effect in softened zones, the groove type, and the constraining effect of the welded joint, regardless of the CPD strain levels. The decrease in ductility of welded joints was due to the stress concentration caused by dislocation pile-ups during the CPD process and then leading to the early formation of microvoids.

中文翻译：

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循环塑性变形后X60盘管焊接接头软化区组织和力学性能的EBSD分析

这项研究的目的是评估循环塑性变形（CPD）后软化区的微观结构演变，以及CPD对X60盘管焊接接头力学性能的影响。结果表明，在CPD过程中，软化区的存在导致变形主要集中在该区域。软化区的最低硬度比贱金属（BM）低18 HV。随着焊接接头的整体应变从没有CPD的初始状态增加到5％应变，与几何必要位错相关的临界HAZ的核平均取向错误从0.66°略微增加到0.87°，导致硬度。尽管HAZ中存在软化区，但拉伸断裂的位置在BM，这归因于在CPD应变水平下，软化区中的加工硬化效应，坡口类型以及焊接接头的约束效应的综合作用。焊接接头的延展性降低是由于在CPD过程中位错堆积引起的应力集中，然后导致了微孔的早期形成。