极端环境承压设备安全性能测试仪研发、应用与产业化
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1.Carbide transformation in carburised zone of 25Cr35NiNb+MA alloy after high-temperature service
- 关键词:
- 25Cr35NiNb+MA alloy; Carburisation; M7C3; M23C6; Dislocation wall;MICROSTRUCTURE
- Liu, Chunjiao;Chen, Xuedong;Chen, Tao;Nie, Defu;Wang, Lu
- 《MATERIALS AT HIGH TEMPERATURES》
- 2016年
- 33卷
- 1期
- 期刊
Microstructure evolution due to carburising of a 25Cr35NiNb+MA ethylene pyrolysis furnace tube was investigated after service for approximately 4 years. The microstructure of 25Cr35NiNb+MA alloy was examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) equipped with energy-dispersive X-ray spectroscopy and high-resolution transmission electron microscopy (TEM). The results revealed that M23C6 carbides of the 25Cr35NiNb+MA alloy had coarsened and transformed to M7C3 carbides with a heavily faulted structure during carburising. The content of M7C3 carbide increased closer to the inner wall. A large number of dislocations had been observed surrounding the carbides and some formed dislocation walls. The carbide transformation mechanism and the effect of the dislocation walls are discussed.
...2.Carburization of Ethylene Pyrolysis Furnace Tube in a Petrochemical Plant
- 关键词:
- 25Cr35NiNb; carburization; diffusion; Cr7C3; Cr23C6; segregation;TEMPERATURE; MICROSTRUCTURE; DEGRADATION; PHOSPHORUS; SERVICE
- Chen, Tao;Chen, Xuedong;Liu, Chunjiao;Ye, Juan;Nie, Defu
- 《JOURNAL OF PRESSURE VESSEL TECHNOLOGY-TRANSACTIONS OF THE ASME》
- 2015年
- 137卷
- 6期
- 期刊
Carburization phenomena of the ethylene pyrolysis furnace tube made of 25Cr35NiNb alloy were investigated after service for approximate 30,000 h in a petrochemical plant. Three different zones, namely, oxidation zone, carburization zone, and aging product zone, were observed in the cross section of furnace tube by microscopic analysis. The oxidation zone near the inner surface has a thickness of about 700 mu m and possesses the characterization of many loose pores and voids. The inner surface has a continuous thin Cr2O3 layer and the grain boundaries near the inner wall are mainly composed of mixed oxides of Cr2O3 and SiO2. In addition, segregation of impurities S and P was detected at grain boundaries. The dark gray SiO2 distributes in the front of the oxidation zone. Carbides distribute at grain boundaries in the carburization zone with lots of voids and micro cracks. The width of grain boundary is broadened. According to the experimental results, the initiation of cracks may be promoted by carbides at grain boundaries. The uneven distribution of the Cr element was found in the carburization zone, and direct experimental evidence of Cr element diffusion was detected. In the aging product zone, the carbides evolution was observed. The chromium carbides are composed of Cr7C3 and Cr23C6. The microstructure and composition evolutions of the furnace tube and their effects on service life of ethylene pyrolysis furnace tube were also discussed.
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