Effects of Laves Phase on Burst Behavior of GH3625 Superalloy Pipe During Hot Extrusion
CHEN Jianjun1, DING Yutian1(), WANG Kun2, YAN Kang1, MA Yuanjun1, WANG Xingmao1, ZHOU Shengming3
1.State Key Laboratory of Advanced and Recycling of Nonferrous Metals, Lanzhou University of Technology, Lanzhou 730050, China 2.The 404 Company Limited, China National Nuclear Industry Corporation, Jiayuguan 735100, China 3.State Key Laboratory of Nickel and Cobalt Resources Comprehensive Utilization, Jinchuan Group Company Limited, Jinchang 737100, China
Cite this article:
CHEN Jianjun, DING Yutian, WANG Kun, YAN Kang, MA Yuanjun, WANG Xingmao, ZHOU Shengming. Effects of Laves Phase on Burst Behavior of GH3625 Superalloy Pipe During Hot Extrusion. Acta Metall Sin, 2021, 57(5): 641-650.
GH3625 superalloy is a type of solid-solution strengthened nickel-based wrought superalloy having Mo and Nb as the main strengthening elements. Because of its excellent high-temperature mechanical properties and oxidation resistance below 650 oC, it can be used in harsh stress and atmosphere environments. It is mainly used as a pipe material for aeroengine fuel main pipe, nuclear power steam generator heat transfer pipe, and pressure pipe, etc. Owing to the high alloying degree of nickel-based superalloys, large deformation resistance, and narrow thermal processing temperature range, the pipe preparation process is complicated. In this study, the as-cast and homogenized pipe billets were used for a short-flow hot extrusion pipe preparation test using the same process. The homogenized pipe billet was extruded successfully, and the pipe burst occurred during the extrusion of the as-cast billet. The pipe burst behavior was studied by OM, SEM, and EBSD, with an EDS analysis. The results showed a considerable amount of Laves phases in the as-cast pipe billet, and the Laves phases and micro-segregation were essentially eliminated after homogenization. Adiabatic heating of the as-cast pipe billet leads to the Laves phase remelting during the hot extrusion process, which is the main reason for pipe bursting during a hot extrusion process. The cracking mode of the pipe burst is a quasi-cleavage fracture, combining brittle fracture and ductile fracture with the predominance of the brittle fracture.
Fund: National Key Research and Development Program of China(2017YFA0700703);National Natural Science Foundation of China(51661019);Program for Major Projects of Science and Technology in Gansu Province(145RTSA004);Program for State Key Laboratory Nickel and Cobalt Resources Comprehensive Utilization(301170503);Program for Hongliu First-Class Discipline Construction Plan of Lanzhou University of Technology
About author: DING Yutian, professor, Tel: (0931)2976688, E-mail: dingyt@lut.edu.cn
Fig.1 Flow chart of hot extrusion experiment for the GH3625 superalloy pipe
Fig.2 OM (a [ 25], c [ 8]) and SEM (b, d) images of as-cast (a, b) and as-homogenized (c, d) GH3625 superalloy billets
Fig.3 Cross section (a) and longitudinal section (b) EBSD images of successfully hot extruded pipe of GH3625 superalloy (The black, grey, and red lines in Figs.3a and b represent high angle grain boundaries, low angle grain boundaries, and twin boundaries, respectively), and OM images of burst pipe at outer wall (c), near the central fracture (d), and at inner wall (e)
Fig.4 SEM images and EDS analyses of strip structures of GH3625 superalloy
Fig.5 SEM image and EDS map scan of strip structure in square area of Fig.4c
Fig.6 SEM images of cracks in GH3625 superalloy burst pipe (a-c), and EDS analysis result along line across the crack showed in insert SEM image (d)
Fig.7 SEM image and EDS map scan of crack terminal in square area of Fig.6c
Fig.8 SEM fractographs of the GH3625 superalloy burst pipe
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