復雜應力下電站部件蠕變損傷及微觀組織演變的研究
[Abstract]:With the global energy tension, environmental degradation, climate warming and other issues increasingly prominent, the development of low energy consumption, low emissions, low pollution low-carbon technology has become a consensus. Supercritical generating units have high generation efficiency and low pollutant emission, which is one of the important components in the development of low-carbon technology in China's power industry. However, the large capacity and high parameter units mean that the service conditions of the components of the power station are worse. Due to the influence of geometry, load type and environment, the actual components are mostly affected by the complex stress state. According to statistics, creep is one of the main reasons for the failure of superheater, reheater and its header. For its excellent weldability, high temperature strength and creep properties, P92 steel has become one of the most common steels for supercritical coal-fired generating sets. The study of creep damage propagation and microstructure evolution of P92 steel under complex stress is a key part in predicting the life of high temperature components of coal-fired generating units, which is of great significance to the safe and economical operation of generating units. In this paper, the creep damage propagation and microstructure evolution of P92 steel under complex stress state are studied by means of creep test at high temperature, creep constitutive model and finite element numerical simulation. The specific work of this paper is as follows: firstly, uniaxial creep tests of standard smooth specimens at different temperatures and different stress levels are completed, and creep fracture mechanism of smooth specimens is analyzed from a microscopic point of view, and Norton-Bailey and Kachanov-Robotnov creep constitutive model is established. The method of determining the parameters of the model is defined, and its validity is verified, which provides the basic database for further research. Secondly, the multiaxial creep test and model are studied. The creep test of two notches under different stress and notch acuity was completed, and the creep results were analyzed from macroscopic and microscopic scales, and the creep damage process of notched specimens of P92 steel was predicted by modified Kachanov-Robotnov model, and the creep damage of P92 steel notched specimens was predicted by using the modified Kachanov-Robotnov model. Based on strain exhaustion theory, the concept of ductility depletion is introduced to combine the theory of continuous damage mechanics with the theory of pore growth to establish a ductile depletion model which can describe the creep behavior of P92 steel. The effects of multiaxiality on fracture toughness, micropore and hardness distribution of P92 steel were compared and analyzed by combining the microscopic results of creep test and the results of finite element numerical simulation. Thirdly, based on the damage mechanism of high temperature creep of P92 steel, the creep constitutive model of multiple damage variables based on microscopic mechanism is established, and the validity of the model is verified. The creep interruption tests of smooth and double notched specimens of P92 steel were carried out, the precipitated phases and voids in creep process were quantitatively counted, and the creep damage evolution of notched specimens of P92 steel was predicted by the model. The predicted damage value is in good agreement with the test results of P92 steel, which further proves the validity of the model. Finally, the design of full-scale pipe bend creep test, has now completed most of the preparatory work before the start of the test, such as strain, temperature measurement, using finite element numerical calculation software to explore the unequal wall thickness, The influence of initial ellipticity on creep damage propagation of pipe elbows is expected to provide a data basis for subsequent creep tests of full-scale pipe bends.
【學位授予單位】:華北電力大學(北京)
【學位級別】:博士
【學位授予年份】:2017
【分類號】:TM621
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