Effect of carburization (pyrolysis furnace tube main failure factor) on the microstructure and properties of HPNb alloy tube. (September 2020)

• Record Type: Journal Article
• Authors: Guo, Jingfeng; Cao, Tieshan; Cheng, Congqian; Meng, Xianming; Zhao, Jie
• Is Part Of: Engineering failure analysis. Volume 115(2020)
• Publication Date: 2020-09
• Subjects: Carburization -- Carbide -- HPNb alloy -- Ferromagnetic structure -- Creep strength; System failures (Engineering) -- Periodicals; Fracture mechanics -- Periodicals; Reliability (Engineering) -- Periodicals; Pannes -- Périodiques; Rupture, Mécanique de la -- Périodiques; Fiabilité -- Périodiques; Fracture mechanics; Reliability (Engineering); System failures (Engineering); Periodicals; Electronic journals; 620.112
• DOI: 10.1016/j.engfailanal.2020.104610
• Languages: English
• ISSNs: 1350-6307

Abstract

Highlights: The paramagnetic structure of HPNb alloy change into ferromagnetic after carburization. The M23 C6 carbides are replaced by carbon-rich M7 C3 carbides in carburization zone. The carburized tube furnace tubes become brittle after carburization. Carburization reduced the high temperature creep strength of HPNb alloy tube. Abstract: 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 M23 C6 type carbide transformed into M7 C3 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.