Abstract The microstructure in the heat affected zone of the multi-pass welds constructed using the 9% Cr tempered martensitic steels is complex and susceptible to premature creep failure. In the present research, a systematic investigation has been conducted after long-term creep exposure in the heat affected zone of a multi-pass weld on the 9% Cr Grade 92 steel to identify the sub-optimal microstructures with a high susceptibility to creep cavitation. The characterisation techniques employed include hardness mapping and a range of electron-based microscopy methods. The results provide quantitative data for microstructure and creep cavities. In this case, preferential creep cavitation has been confirmed in the regions within the heat affected zone that possesses a microstructure with an inhomogeneous distribution of the M23C6 carbides and a refined martensitic grain structure. Creep cavities have been observed on the secondary phase particles including the Al2O3, the MnS and the BN phases. The observations from the current research confirm that creep cavitation preferentially occurs in the partially-transformed zones that were subjected to thermal cycles associated with peak temperatures between the Ac1 and the Ac3 transus temperatures during weld fabrication.

中文翻译：

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长期高温蠕变过程中显微组织对92钢焊缝热影响区空化的影响

摘要 用9% Cr 回火马氏体钢构造的多道焊缝热影响区的显微组织复杂且易发生过早蠕变破坏。在本研究中，在 9% Cr 92 级钢的多道焊缝热影响区长期蠕变暴露后进行了系统调查，以确定对蠕变空化高度敏感的次优微观结构. 所采用的表征技术包括硬度映射和一系列基于电子的显微镜方法。结果提供了微观结构和蠕变腔的定量数据。在这种情况下，已经在热影响区内的区域证实了优先蠕变空化，该区域具有 M23C6 碳化物不均匀分布的显微组织和细化的马氏体晶粒结构。在包括 Al2O3、MnS 和 BN 相在内的二次相颗粒上观察到蠕变空腔。当前研究的观察结果证实，蠕变空化优先发生在部分转变区域，这些区域经历了与焊接制造过程中 Ac1 和 Ac3 转变温度之间的峰值温度相关的热循环。