【作者】 刘静；

【导师】 毛雪平；

【作者基本信息】 华北电力大学(北京) ， 动力工程（专业学位）， 2016， 硕士

【摘要】 提高电站锅炉蒸汽参数是提高其效率和减少煤耗的主要途径,蒸汽参数的提高对电站锅炉材料提出了更加严格的要求。T92钢由于具有优良的抗高温腐蚀、抗高温蠕变等性能,成为超超临界电站锅炉主要的候选材料。为了保证机组运行的安全性,有必要对其高温蠕变行为进行深入的研究。本文研究了T92钢在高温和多轴应力条件下的蠕变特性,进行650℃不同应力水平下T92钢标准及缺口蠕变试验。为了研究T92钢在多轴应力状态下微观组织的变化以及析出物对其蠕变强度的影响,借助SEM、TEM等观察了其断口形貌、截面显微组织形貌及析出相的变化,利用EDS分析了析出相的成分组成。经历长期的蠕变过程后,材料的硬度会发生一定的变化,利用维氏硬度计对断裂后的试样进行硬度检测。通过对应力场的有限元模拟,结合微观结构的变化以及硬度的变化规律,研究分析应力的分布对T92钢蠕变特性的影响。研究结果表明：缺口的存在使得以颈缩为标志的塑性变形减弱,缺口越尖锐,塑性变形越小；缺口试样断口截面的韧窝尺寸较小,深度较浅；缺口试样与光滑试样的断裂机制不相同；T92钢在蠕变过程中的主要析出物为Laves相、M23C6型碳化物、MX型碳氮化物,缺口的存在有助于Laves相的析出；光滑试样硬度分析截面从中心到边缘硬度呈上升趋势,缺口试样从中心到边缘硬度呈下降趋势。Von-Mises应力是蠕变孔洞形核的原因,从而导致裂纹的萌生,进一步发生断裂。更多还原

【Abstract】 The main way to improve the efficiency and reduce the coal consumption is improving steam parameters of the power plant boiler. More strict requirements are put forward for power plant boiler material. T92 steel becomes the main candidate material of ultra-supercritical utility boiler for its excellent high-temperature corrosion resistance and high-temperature creep resistant performance. In order to guarantee the safety of the unit operation, the law of high temperature creep should be studied.The creep tests of T92 steel on both smooth and notched specimens were carried out under different stress levels at 650℃ to research the creep properties of the steel under high temperature and multiaxial stress state. In order to research the change of microstructure and the influence of precitipates on creep strength, SEM and TEM are used to observe the fracture morphology and the microstructure and precipitates transformation. The composition and transformation of precipitates were analyzed by means of EDS. Through long-term creep process, certain changes will happen to the hardness of material. Hardness tester is used to detect the hardness of material after creep. Finite element analysis is adopted to study the influence of multiaxial stress state on creep behavior. The results show that the presence of notch weaken plastic deformation of steel, with the increase of notch acuity ratio, the deformation is smaller. The notched specimens and smooth specimens have different fracture mechanism. The main precipitates consist of M23C6 carbides, MX carbonitrides and Laves phase during creep process. The presence of notch contributes to the precipitation of Laves phase. The hardness value in smooth specimens is on a rise as a whole from the center to the edge, while on a decline in the notched specimens. Von Mises stress seems to be the primary cause of cavities nucleation, thus leading to the initiation of crack and further to fracture.更多还原