Study on microstructure and properties of centrifugal casting 35Cr45NiNb+MA furnace tubes during service |
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| Authors: | Biao Hu Xuedong Chen Chunjiao Liu Xiaoming Lian Tao Chen |
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| Affiliation: | 1. Institute of Process Equipment and Control Engineering, Zhejiang University of Technology, HangzhouP. R. China;2. National Engineering and Technical Research Center on Pressure Vessels and Piping Safety, Hefei General Machinery Research Institute Co., Ltd., HefeiP. R. China330156262@qq.com;4. National Engineering and Technical Research Center on Pressure Vessels and Piping Safety, Hefei General Machinery Research Institute Co., Ltd., HefeiP. R. China;5. National Engineering and Technical Research Center on Pressure Vessels and Piping Safety, Hefei General Machinery Research Institute Co., Ltd., HefeiP. R. China |
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| Abstract: | In the present study, the microstructure evolution of 35Cr45NiNb+MA ethylene cracking furnace tubes during service and its effect on the properties were investigated. According to the results, in the early stage of service, the skeletal M7C3 and vermicular NbC were transformed into blocky M23C6 and G phase (Ni16Nb6Si7), respectively, accompanied with many dispersed M23C6 secondary carbides. With the extension of service time, M23C6 carbides on the grain boundaries were transformed into M7C3 with high stacking fault structure and coarsened, and the blocky G phase was transformed into granular NbC. The yield strength and ultimate tensile strength of the aging furnace tubes decreased by 9%-18%, yet the elongation after fracture decreased significantly from 10.0%-14.0% to 3.0%-5.0%. The hardness of the carburized zone of the carburized tubes increased by 10%-17%, and the rupture time decreased by 45%-75% under the test condition of 1100℃ and 16MPa. Finally, the evolution map was summarized. |
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| Keywords: | 35cr45ninb+MA high?-temperature ageing M23C6 M7C3 carburi?sing microstructure evolution properties map |
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