The effective operation of ageing coal-fired power plants requires routine damage assessment of critical component materials throughout their service history. Traditional post-exposure mechanical testing typically requires large amounts of material for each testing condition. This study introduces an accelerated (high stress and temperature) creep testing technique that employs digital image correlation for strain measurement over a non-uniform temperature field generated by a thermomechanical tester. When applied to different ex-service (exposed to service conditions within a power plant) 12% Cr piping steels, multiple accelerated creep curves at temperatures ranging from 550°C to 600°C are measured from a single specimen for each material condition. Higher creep damage in the steel due to longer service exposure and higher void densities is revealed by shorter rupture times, faster creep rates and tertiary-dominated creep curves when compared to the lower creep damage state. Microstructural study via quantitative electron microscopy confirms the dislocation creep-driven growth of subgrains in the specimen gauge regions relative to the grips. Larger subgrains and a weakening of precipitate distributions for the high damage material were also noted. Digital image correlation–measured strains are in good agreement with traditional techniques of creep testing with standard extensometry. On a comparative basis, the technique is shown to be a plausible form of damage assessment of 12% Cr piping steels with varying levels of service exposure and serve as a suitable mechanical complement to the traditional void replica methodology.

中文翻译：

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使用数字图像相关测量退役 12% Cr 钢的蠕变变形

老旧燃煤电厂的有效运行需要在其整个服务历史中对关键部件材料进行常规损坏评估。传统的暴露后机械测试通常需要为每个测试条件使用大量材料。本研究介绍了一种加速（高应力和温度）蠕变测试技术，该技术采用数字图像相关性在由热机械测试仪生成的非均匀温度场上进行应变测量。当应用于不同的服役期（暴露于电厂内的服役条件）12% Cr 管道钢时，在 550°C 至 600°C 的温度范围内，针对每种材料条件从单个试样测量多条加速蠕变曲线。与较低的蠕变损伤状态相比，更短的断裂时间、更快的蠕变速率和三次占主导地位的蠕变曲线表明，由于更长的使用时间和更高的空隙密度，钢中的蠕变损伤更高。通过定量电子显微镜进行的微观结构研究证实，相对于夹具，试样规格区域中亚晶粒的位错蠕变驱动生长。还注意到较大的亚晶粒和高损伤材料的析出物分布减弱。数字图像相关性测量的应变与使用标准引伸计进行蠕变测试的传统技术非常一致。在比较的基础上，