P92钢焊接接头细晶区高温蠕变中显微结构对微孔洞演化影响

The main steam tubes of ultra supercritical fossil-fired power plants are usually produced by P92 heat resistant steel, and in their fine-grained zone of welded joints creep damage badly restricts their service life. Based on the experiment test and theoretical analysis, the project characterizes the microstructure evolution in the fine-grained zone of P92 steel welded joints during high temperature creep. The analytical models are established to characterize grain boundaries (GBs) and their deformation in this process, and their influences on the evolution of multi-scale second phases are studied. The interaction of the microstructures, such as the actual configuration of dislocation, GBs and their deformation, multi-scale second phases, with the microvoid is systemically investigated, taking into account the size-dependent surface/interface effect and temperature-dependent sliding and diffusion. Their quantitative relativity of the features of the microstructures and temperature is estimated with microvoid evolution (formation and growth). The rational models representing the surface/interface (GB, phase boundary and microvoid surface) and their deformation are built to reflect the significant the multi-scale surface/interface effect, scale effect, temperature effect and time effect, etc. The main positions of high temperature formation of microvoids and the primary mechanism controlling their evolution are revealed. The origin of high temperature creep threshold stress is discussed in the fine-grained zone of second phase strengthened P92 steel welded joints. These studies have important scientific significance and practical value for revealing high temperature creep damage behavior and fracture failure mechanism from the perspective of microstructure.

超超临界发电机组主蒸汽管道采用P92耐热钢制造，其焊接接头细晶区蠕变损伤严重制约其使用寿命。本项目采用实验测试和理论分析相结合的方式，针对该细晶区高温蠕变过程中微观组织的演变，建立表征细晶区晶界及其变形的解析力学模型；研究晶界及其变形对多尺度第二相演化的影响规律；研究实际构型位错、晶界及其变形、多尺度第二相等显微结构与微孔洞的交互作用，包括尺度依赖的表/界面效应和温度依赖的滑移扩散效应，进一步揭示微结构参数以及温度与微孔洞演化（形核和长大）的定量关联；建立反映重要多尺度显微结构表/界面效应、尺度效应、温度效应和时间效应的合理表/界面（晶界、相界与微孔洞表面）及其变形模型；揭示微孔洞高温形核的主要位置和控制其演化的主要微观机制；探讨第二相强化细晶区高温蠕变门槛应力的途径。为从细微观结构角度揭示P92钢焊接接头高温蠕变损伤行为和断裂破坏机制提供科学依据。

超超临界发电机组主蒸汽管道采用P92耐热钢制造，其焊接接头细晶区蠕变损伤严重制约其使用寿命。本项目前期详细地进行了P92钢焊接接头高温蠕变实验，发现高温蠕变过程中微孔洞和微裂纹形核位置大多位于晶界上。因此先建立了理论模型研究纳米裂纹对晶界变形的影响，从而获得了纳米裂纹附近最先发生塑性变形的理论解析模型，揭示了纳米裂纹、晶粒及晶界等的微结构特征对塑性变形影响的临界特征。通过本研究的结论可知在P92钢细晶区纳米裂纹和晶界微观特征是如何阻碍裂纹扩展和促进塑性变形的，从而揭示了微结构特征对材料强韧化的影响规律。然后建立了研究纳米孔洞对晶界变形及其三叉晶开裂影响的理论模型，详细揭示了纳米孔洞、晶粒及变形的晶界等微结构对增强材料强韧化的影响机制。通过本研究可知在P92钢细晶区形核的纳米孔洞和晶界变形引起的塑性变形对纳晶材料断裂韧性的影响规律，从而揭示了不同微观结构是如何阻碍裂纹扩展和促进塑性变形的。最后基于高温蠕变过程中微孔洞大多形核在晶界的过程与晶界上碳化物有关，致使晶界及其变形、第二相等对细晶区的蠕变孔洞演化有重要影响。因此研究了纳晶粒和纳米第二相对晶界滑移以及纳米晶体材料屈服强度的影响，为分析纳米第二相对细晶区的蠕变孔洞和裂纹演化的影响规律做基础。通过本研究可知在P92钢细晶区不同微结构特征对材料强韧化的影响规律。