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利用旋转弯曲疲劳试验机,进行超超临界汽轮机CrMoW转子钢在常温与600℃条件下超高周疲劳行为的研究。采用透射电子显微镜TEM和扫描电子显微镜SEM分析试样疲劳前后显微结构及试样的表面与断口。研究结果发现,常温下的S-N曲线在疲劳寿命为5×106周次处出现拐点,但600℃条件下,S-N曲线呈现连续下降趋势;高温疲劳后材料的显微组织仍为典型的马氏板条体结构,但马氏体组织退化明显,出现板条碎化,板条界移动或者吞灭,位错密度下降,碳化物粗化、球化以及链状分布等现象。SEM分析表明,高温试样表面产生氧化膜,降低了试样的疲劳性能;常温与600℃环境条件下,疲劳裂纹主要萌生于试样表面;高温下试样裂纹萌生区发现夹杂,其裂纹萌生是表面裂纹起源和亚表面夹杂物相耦合的结果。
The use of rotating bending fatigue testing machine for supercritical steam turbine CrMoW rotor steel at room temperature and 600 ℃ ultrahigh cycle fatigue behavior. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to analyze the microstructures and the surface and fracture of specimens before and after fatigue. The results showed that SN curve at room temperature showed an inflection point at a fatigue life of 5 × 106 cycles, but the SN curve showed a continuous decreasing trend under the condition of 600 ℃. The microstructure of the material after high temperature fatigue was still a typical Mashi plate However, the degeneration of martensite is obvious, and there are some phenomena such as the shredding of slats, the movement or swallowing of slats, the decrease of dislocation density, the coarsening of carbides, the spheroidization and the distribution of chains. The SEM analysis shows that the oxide film is formed on the surface of the high temperature specimen, which reduces the fatigue property of the specimen. Under normal temperature and 600 ℃, the fatigue crack mainly occurs on the surface of the specimen. Crack initiation It is the result of the coupling between the origin of surface cracks and subsurface inclusions.