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The Study of Heat Treatment Effects on Chromium Carbide Precipitation of 35Cr-45Ni-Nb Alloy for Repairing Furnace Tubes

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Thai-French Innovation Institute, King Mongkut′s University of Technology North Bangkok, Bangsue, Bangkok 10800, Thailand
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Faculty of Engineering, King Mongkut′s University of Technology North Bangkok, Bangsue, Bangkok 10800, Thailand
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Department of Welding Engineering Technology, College of Industrial Technology, King Mongkut′s University and Technology North Bangkok, Bangsue, Bangkok 10800, Thailand
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Welding Engineering and Metallurgical Inspection, Science and Technology Research Institute, King Mongkut′s University and Technology North Bangkok, Bangsue, Bangkok 10800, Thailand
*
Author to whom correspondence should be addressed.
Academic Editor: Hugo F. Lopez
Metals 2016, 6(1), 26; https://doi.org/10.3390/met6010026
Received: 30 November 2015 / Revised: 11 January 2016 / Accepted: 13 January 2016 / Published: 19 January 2016
This paper presents a specific kind of failure in ethylene pyrolysis furnace tubes. It considers the case in which the tubes made of 35Cr-45Ni-Nb high temperature alloy failed to carburization, causing creep damage. The investigation found that used tubes became difficult to weld repair due to internal carburized layers of the tube. The microstructure and geochemical component of crystallized carbide at grain boundary of tube specimens were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM) with back-scattered electrons mode (BSE), and energy dispersive X-ray spectroscopy (EDS). Micro-hardness tests was performed to determine the hardness of the matrix and the compounds of new and used tube material. The testing result indicated that used tubes exhibited a higher hardness and higher degree of carburization compared to those of new tubes. The microstructure of used tubes also revealed coarse chromium carbide precipitation and a continuous carbide lattice at austenite grain boundaries. However, thermal heat treatment applied for developing tube weld repair could result in dissolving or breaking up chromium carbide with a decrease in hardness value. This procedure is recommended to improve the weldability of the 35Cr-45Ni-Nb used tubes alloy. View Full-Text
Keywords: ethylene pyrolysis; furnace tube; chromium carbide; heat treatment; carbide dissolution; carburization ethylene pyrolysis; furnace tube; chromium carbide; heat treatment; carbide dissolution; carburization
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Srisuwan, N.; Eidhed, K.; Kreatsereekul, N.; Yingsamphanchareon, T.; Kaewvilai, A. The Study of Heat Treatment Effects on Chromium Carbide Precipitation of 35Cr-45Ni-Nb Alloy for Repairing Furnace Tubes. Metals 2016, 6, 26.

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