The structure characteristics and mechanical properties of as-cast and carburized HPNb alloy tubes were investigated in this paper. Through magnetism test by the vibrating sample magnetometer, we find that the paramagnetic structure of as-cast HPNb alloy tubes has changed into ferromagnetic structure after carburization. Electron back-scattered diffraction (EBSD) and X-ray diffraction (XRD) analyses show that the M₂₃C₆ type carbide transformed into M₇C₃ type carbide in carburization zone. Due to the coarser primary carbides and blocky-shaped secondary carbides after carburization, the ductility and toughness of the ethylene cracking furnace tubes are very low and become brittle. At high temperature, the tensile strength and yield strength of carburized tube are higher than those of as-cast tube, but the tensile elongation is lower. Owing to the microstructure degradation, the creep strength of HPNb alloy decreased after carburization. Hence, the carburization also could lead to the decrease of the remnant life of the pyrolysis furnace tubes.

研究了铸态渗碳HPNb合金管的结构特征和力学性能。通过振动样品磁强计的磁测试，我们发现铸态HPNb合金管的顺磁结构在渗碳后已转变为铁磁结构。电子背散射衍射（EBSD）和X射线衍射（XRD）分析表明，M ₂₃ C ₆型碳化物转变为M ₇ C ₃型碳化物在渗碳区。由于渗碳后较粗的一次碳化物和块状二次碳化物，乙烯裂解炉管的延展性和韧性非常低，并且变脆。在高温下，渗碳管的抗拉强度和屈服强度高于铸态管，但拉伸伸长率较低。由于组织的退化，渗碳后HPNb合金的蠕变强度降低。因此，渗碳也可能导致热解炉管的剩余寿命缩短。