750℃级电站锅炉用合金组织演化规律及持久寿命预测方法的研究

Final superheater/reheater is one of the critical boiler components in 700℃ ultra supercritical thermal power units (A-USC). The high temperature strength (100000h rupture strength) of alloys developed for such component must exceed 80-100MPa at 750℃, and therefore precise performance prediction of the alloys during long-term service is of great significance to realize the reliable operation of units. However, previous prediction models are primarily based on high-temperature short-term test data, without consideration of microstructure evolution under the interaction of temperature and stress and its effect on creep rupture life. Hence, the accuracy of these prediction models is doubtful. In this study, the creep behavior and evolution of gamma prime of Inconel 740H (Ni-based) and HT-700T alloys (Ni-Fe based) at simulated and non-simulated service environment will be investigated and the effect of stress during the process will be illustrated. The relationship between microstructure evolution and creep property will be identified. Based on these results, microstructure characteristics in several key stages during creep can be obtained by changing temperature and/or time through initial heat treatment or heat exposure and the following creep property can be predicted more quickly. The achievements of this program will promote the reasonable assessment of long-term creep rupture life for such kind of superalloys.

锅炉末级过/再热器是700℃先进超超临界机组的关键部件之一，其所用材料必须满足750℃/80-100MPa下的持久寿命大于10万小时。准确预测合金在服役过程中的持久寿命对实现机组可靠运行至关重要。以往的预测大部分基于高温短时试验数据，对温度和应力交互作用下组织的演化及其对合金持久寿命的影响了解甚少，因此预测准确性存疑。本课题通过表征两种析出强化候选合金（Ni基Inconel 740H和Ni-Fe基HT-700T）经非服役（热处理/不加载热暴露）和模拟服役（蠕变：加载热暴露）处理后的蠕变行为和主要强化相的分布特征及其演变规律，揭示应力在组织演变中所起的作用；获得修正非服役和模拟服役处理制度间组织和性能演化差异的关联模式；确立通过非服役处理获得具有不同蠕变关键节点和临界点组织特征的手段，进而确认该阶段和临界点后的性能变化趋势；为快速准确预测服役状态下此类合金的持久寿命打基础。

锅炉末级过 / 再热器是700℃先进超超临界机组的关键部件之一，其所用材料必须满足750℃ / 80-100MPa下的持久寿命大于10万小时。准确预测合金在服役过程中的持久寿命对实现机组可靠运行至关重要。以往的预测大部分基于高温短时试验数据，对温度和应力交互作用下组织的演化及其对合金持久寿命的影响了解甚少，因此预测准确性存疑。本课题表征了两种析出强化型候选合金（Inconel 740H和HT-700T）经非服役（初始热处理 / 长期时效：不加载热暴露）和模拟服役（持久 / 蠕变：加载热暴露）处理后主要强化相'的分布特征及其演变规律，揭示了温度、时长及应力在其中所起的作用。结果表明，随着时效/蠕变时间的延长，In 740H及HT-700T合金中'相的形貌、分布、数量、尺寸等相参量均发生了不同程度的变化，其中尺寸的变化最为显著且最易准确定量表征；外加应力的存在对'相的粗化没有明显的促进，有、无应力状态下其粗化规律均符合LSW理论；在此基础上，通过MH参数法建立了非服役和模拟服役处理制度间'演化规律与持久性能的关联模式，进而提出了一种快速准确预测服役状态下此类合金持久寿命的可行性方法。