对长期服役的乙烯裂解炉辐射段炉管进行金相检验和拉伸试验，研究了其渗碳区与非渗碳区的显微组织、碳化物尺寸、室温及高温力学性能，建立了碳化物宽度与炉管拉伸性能之间的定量关系。结果表明：炉管非渗碳区与渗碳区晶粒形貌、尺寸相近，前者由奥氏体基体、一次碳化物、G相以及NbC相组成，后者无G相，一次碳化物发生明显粗化，蠕变孔洞和微裂纹增多；炉管室温强度和塑性劣化严重，非渗碳区的高温拉伸性能基本满足要求，而渗碳区发生明显脆化；碳化物宽度随着距炉管外表面距离的增加而增大；炉管的抗拉强度和屈服强度与碳化物宽度呈正相关，断后伸长率与之呈负相关。

Metallographic examination and tensile test were carried out on the long-term service radiation section tube of ethylene cracking furnace, and the microstructure, carbide size, room temperature and high temperature mechanical properties of carburized and non-carburized zone were studied. The quantitative relationship between carbide width and tensile properties of furnace tube was established. The results show that the grain morphology and size of non-carburized zone and carburized zone of the furnace tube were similar. The former was composed of austenite matrix, primary carbides, G phase and NbC phase; the latter had no G phase, and its primary carbides were obviously coarsened. The carburized zone had more creep holes and microcracks. The room temperature strength and plasticity of the furnace tube were seriously deteriorated. The high temperature tensile properties of the non-carburized zone basically met the requirements, and the carburized zone was obviously embrittled. The carbide width increased with the distance from outer surface of furnace tube. The tensile strength and yield strength of the furnace tube were positively related to the carbide width, and the percentage elongation after fracture was negatively related to it.