Experimental Study On The Acoustic Emission Characteristics Of Q345R Steel Creep Process

In the actual industrial production, a lot of pressure vessels are working in a high temperature and pressure environment for a long time, most failures of which are caused by creep damage. The occurrence of creep damage will result in the degradation of material organization and mechanical performance, by which load capacity will reduce greatly and then which will creates a great potential safety hazard for industrial production extremely. Therefore, it has an important practical significance to understand the creep damage deeply of Q345 R steel for the normal running and accident prevention of high temperature and pressure vessel. The paper is based on the material damage evolution theory and supported by Open Research Fund Program of Key Laboratory of Safety Science of Pressurized System, Ministry of Education "Experimental Study on the Acoustic Emission Characteristics of Heat Resistant Steel Creep Process". Acoustic emission testing technology was used to monitor the Q345 R steel creep process and obtain the creep damage characteristics. The following results are acquired.(1) At first, the research background, purpose and meaning are introduced and then a variety of existing theories of creep damage are discussed. According to the chapter, the mechanism of creep damage is understood deeply with the production process of acoustic emission phenomenon. Meanwhile, the feasibility analysis of the paper content is conducted and the research route is determined in the chapter.(2) Implicit creep strain is selected to simulate the Q345 R creep process in different temperature or stress in order to study the influence of temperature and stress. It is found that temperature and stress affect the creep greatly and the higher temperature and stress, the greater creep deformation, the more serious creep damage.(3) Energy release model is established by analyzing the load and deformation in material creep damage process. Combining the stress wave release theory with the model is used to simulate the acoustic emission generation and transmission during the Q345 R creep process. The results show that the transient stress wave will release from creep damage source and attenuate during the spreading process. When the wave arrives at the sensor location, displacement and time curve will be obtained which is similar to the typical acoustic emission signal waveform.(4) The creep experiment scheme is formulated, basing on which testing machine fixture is modified. The experiment is conducted with the fixture and some typical acoustic emission parameters are used to describe the creep damage process, such as counts, energy and amplitude. The results show that the acoustic emission activities at the beginning of creep are relatively active but leveling off. As the creep, acoustic emission activities turn into the plateau and signals appear constantly, but the semaphore is few and amplitude is low relatively. Cumulative counts and energy curve appear a step with increasing in a low speed. When Q345 R specimens enter into the later stage of creep, damage with acoustic emission activities is more active and the signal amplitude and energy achieves maxima at the time of creep rupture. With the aid of the macro and micro fracture analysis of creep specimen, the material performance of Q345 R is understood further, which also verifies the acoustic emission results in another way.