随着经济社会快速发展，能源消费结构持续优化，电力作为现代社会的核心能源，其需求量呈现稳步增长态势。从我国能源资源禀赋来看，煤炭资源储量丰富，分布广泛，这一特点决定了燃煤发电在电力供应体系中长期占据主导地位。由于用电负荷的不均匀性，火电机组的功能从以发电为主转变为以调峰为主，机组启动停止频繁以及通过变压实现的调峰模式，会导致主蒸汽管道瞬时负载变化过大；机组内温度的急剧变化也将导致主蒸汽管道易承受周期性变化的载荷和热应力的作用，即要承受循环疲劳载荷的作用，所以疲劳性能显得尤为重要。HT700P合金是由西安热工院自主研发的一种适用于先进超超临界（A-USC）主蒸汽管道的候选材料。已有的研究包含了该合金的氧化性能和焊接性能。本文在已有的工作基础上，进一步开展了试验研究，主要内容包括：650℃和700℃下不同时效时间对合金微观组织和静态力学性能（拉伸、冲击、硬度）的影响。以及合金中γ′相、MC碳化物和M₂₃C₆碳化物的析出规律；研究了650℃和700℃不同应力下持久性能的变化规律以及对微观组织的影响；研究了650℃和700℃不同应变幅下低周疲劳性能的变化规律以及对微观组织的影响。这些研究成果将为HT700P合金在超超临界机组中的应用提供重要的理论和实验依据。主要结论如下：

（1）HT700P合金经过标准热处理后呈现典型的γ/γ′两相组织特征。其中，基体相为面心立方结构的γ相[Fe(Ni)固溶体]，主要强化相为γ′相[Ni₃Al或Ni₃(Al,Ti)]。该合金主要形成MC型碳化物(TiC)以及次生M_23­C₆型碳化物。金相分析表明，固溶处理后的试样呈现均匀细小的等轴晶组织，这种微观结构特征有利于提升材料的力学性能。实验数据显示，该合金具有优异的抗拉强度，能够满足火力发电设备在高温高压服役环境下的使用要求。

（2）研究了长时时效对HT700P合金显微组织的影响。研究结果表明，随着时效时间的延长，晶界形态发生变化，由初始的弯曲状逐渐趋于平直状，同时晶界碳化物数量明显增多。在650℃、700℃长时时效试验中，γ′强化相呈现均匀的球状析出特征，颗粒尺寸半径的三次方和时效时间呈线性相关，其尺寸演变规律遵循LSW理论描述的粗化机制。

（3）HT700P合金在持久试验中，温度是影响持久寿命的关键因素。温度越高持久寿命显著降低。并且发现在650℃下，外加载荷会抑制γ′相的生长；在700℃高应力状态下，外加载荷会抑制γ′相的生长；而在低应力状态下，外加载荷会促进γ′相的生长。通过对断口形貌的观察发现，在同一温度下，随着应力的增加，试样的断裂模式从沿晶断裂逐渐过渡到穿晶断裂。

（4）HT700P合金在低周疲劳实验中，应变幅是影响疲劳寿命的主要因素。合金在不同应变幅下的低周疲劳过程主要变现为循环软化、循环硬化两个行为。HT700P合金疲劳断口主要由疲劳裂纹源区、疲劳扩展区和疲劳瞬断区组成。合金的裂纹主要起源于试样表面。在扩展区可以观察到大量的疲劳条带，并且垂直方向指向裂纹源。疲劳瞬断区主要为韧性断裂，并且随着应变幅的增加，韧性断裂逐渐转变为脆性断裂。通过对疲劳断口剖面观察发现，在650℃下，疲劳裂纹源区和扩展区主要为穿晶断裂，在700℃下，疲劳裂纹源区和扩展区主要为沿晶断裂。低应变幅下的样品，在晶内出现大量平行的滑移带，随着应变幅的增加，滑移带逐渐消失。通过对EBSD结果分析得知，随着应变幅的增加，HT700P合金的小角度晶界占比增多、变形程度增加、晶格畸变程度增大。

With the rapid development of economy and society, the energy consumption structure continues to optimize, and the demand for electricity, as the core energy of modern society, shows a steady growth trend. From the perspective of China's energy resources endowment, coal resources are rich in reserves and widely distributed, which determines the long-term dominant position of coal-fired power generation in the power supply system. Due to the non-uniformity of the power load, the function of the thermal power unit is changed from generation to peak load. The frequent start and stop of the unit and the peak load mode realized through voltage change will cause the instantaneous load of the main steam pipeline to change too much. The rapid change of temperature in the unit will also lead to the main steam pipeline is easy to withstand the role of cyclic fatigue load and thermal stress, that is, to withstand the role of cyclic fatigue load, so the fatigue performance is particularly important. HT700P alloy is A candidate material independently developed by Xi 'an Thermal Engineering Institute for advanced ultra-supercritical (A-USC) main steam pipeline. The oxidation properties and weldability of the alloy have been studied. On the basis of the existing work, further experimental studies were carried out in this paper. The main contents included: the effects of different aging times at 650℃ and 700℃ on the microstructure and static mechanical properties (tensile, impact, hardness) of the alloy. And the precipitation law of γ 'phase, MC carbide and M₂₃C₆ carbide in the alloy; The changes of the durability properties and the effects on the microstructure under different stresses at 650℃ and 700℃ were studied. The variation of low-cycle fatigue properties and the effect on microstructure under different strain amplitudes at 650℃ and 700℃ were studied. These research results will provide important theoretical and experimental basis for the application of HT700P alloy in ultra-supercritical units. The main conclusions are as follows:

(1) HT700P alloy showed typical γ/γ' two-phase microstructure after standard heat treatment. Among them, the matrix phase is the face-centered cubic structure γ phase [Fe(Ni) solid solution], and the pig phase is the γ 'phase [Ni₃Al or Ni₃(Al,Ti)]. This process mainly forms MC type carbide (TiC) and secondary M₂₃C₆ type carbide. Metallographic analysis shows that the sample after solution treatment has a uniform fine equiaaxial crystal structure, which is beneficial to improve the mechanical properties of the material. The experimental data show that the alloy has excellent tensile strength, which can meet the requirements of thermal power generation equipment in high temperature and high pressure service environment.

(2) The effect of long aging on the microstructure of HT700P alloy was studied. The results show that with the extension of aging time, the grain boundary flattens gradually and the carbide at the grain boundary increases gradually. γ՛ phase was precipitated at 650℃ and 700℃ and grew up as uniform spherical particles. The cubic power of particle size radius was linearly correlated with the aging time, and its growth law was consistent with LSW theory.

(3) Temperature is the key factor affecting the long life of HT700P alloy in the long life test. The longer lasting life decreases significantly with higher temperature. It is found that the growth of γ 'phase is inhibited by external load at 650℃. Under high stress at 700℃, the growth of γ 'phase is inhibited by external load. In the low stress state, the external load will promote the growth of γ 'phase. According to the observation of the fracture morphology, the fracture mode of the sample gradually changes from intergranular fracture to transgranular fracture with the increase of stress at the same temperature.

(4) Strain amplitude is the main factor affecting fatigue life of HT700 alloy in low cycle fatigue test. The low cycle fatigue process of the alloy under different strain amplitudes is mainly manifested as cyclic softening and cyclic hardening. The fatigue fracture of HT700P alloy is mainly composed of fatigue crack source region, fatigue expansion region and fatigue transient fracture region. The crack of the alloy mainly originates from the specimen surface. A large number of fatigue bands can be observed in the spread region, and the vertical direction is toward the crack source. The fatigue transient fault zone is mainly ductile fracture, and with the increase of strain amplitude, ductile fracture gradually changes to brittle fracture. According to the observation of the fatigue fracture profile, it is found that at 650℃, the fatigue crack source and expansion zone are mainly transgranular fracture, and at 700℃, the fatigue crack source and expansion zone are mainly intergranular fracture. A large number of parallel slip bands appear in the samples under low strain amplitude, and the slip bands disappear gradually with the increase of strain amplitude. The EBSD results show that with the increase of strain amplitude, the proportion of small Angle grain boundary increases, the degree of deformation increases, and the degree of lattice distortion increases.