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.

中文翻译：

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离心铸造35Cr45NiNb+MA炉管服役过程中的组织与性能研究

摘要 在本研究中，研究了 35Cr45NiNb+MA 乙烯裂解炉管在使用过程中的微观结构演变及其对性能的影响。结果表明，在服役初期，骨架M7C3和蠕虫状NbC分别转变为块状M23C6和G相（Ni16Nb6Si7），并伴有许多分散的M23C6二次碳化物。随着使用时间的延长，晶界上的M23C6碳化物转变为具有高堆垛层错结构的M7C3并粗化，块状G相转变为粒状NbC。时效炉管的屈服强度和极限抗拉强度下降了9%-18%，而断后伸长率从10.0%-14.0%明显下降到3.0%-5.0%。在1100℃、16MPa的试验条件下，渗碳管渗碳区硬度提高10%-17%，断裂时间降低45%-75%。最后总结了进化图。