Microstructure Evolution and Mechanical Properties of Dissimilar Material Diffusion-Bonded Joint for High Cr Ferrite Heat-Resistant Steel and Austenitic Heat-Resistant Steel
HUA Yu1, CHEN Jianguo2, YU Liming1, SI Yonghong2, LIU Chenxi1(), LI Huijun1, LIU Yongchang1()
1.State Key Laboratory of Hydraulic Engineering Simulation and Safety, School of Materials Science and Engineering, Tianjin University, Tianjin 300354, China 2.Tianjin Special Equipment Inspection Institute, Tianjin 300192, China
Cite this article:
HUA Yu, CHEN Jianguo, YU Liming, SI Yonghong, LIU Chenxi, LI Huijun, LIU Yongchang. Microstructure Evolution and Mechanical Properties of Dissimilar Material Diffusion-Bonded Joint for High Cr Ferrite Heat-Resistant Steel and Austenitic Heat-Resistant Steel. Acta Metall Sin, 2022, 58(2): 141-154.
High Cr ferrite heat-resistant steel has excellent geometric structure stability, low radiation swelling rate, and good corrosion resistance of liquid metal. TP347H austenitic heat-resistant steel is based on the traditional 18-8 austenitic steel with the addition of a certain amount of Nb and a small amount of N to precipitate MX-type carbonitride, which results in superior high-temperature properties. Steam with high temperature and pressure flowing through supercritical thermal power units may exhibit heterogeneous connections between high Cr ferrite and austenitic heat-resistant steel components in the supercritical thermal power units. In this study, the vacuum diffusion-bonding of dissimilar materials between high Cr ferritic and TP347H austenitic heat-resistant steel was performed, the effects of diffusion-bonding time and post weld heat treatment (PWHT) process on the microstructural evolution and mechanical properties of the diffusion-affected zone was examined. The results indicated that with the extension of diffusion-bonding time, the interfacial bonding rate gradually increased. The interaction due to the difference in deformation storage energy and dislocation slips resulted in dynamic recrystallization, and the fine grains formed at the diffusion-bonding interface evolved into a serrated interface. Fine and dispersed MX and M23C6 phases were precipitated in the austenite grain boundaries and at the grain boundaries of the diffusion-bonding zone. After PWHT, the grains in the diffusion-bonding zone were further refined, dislocations were stable, dislocation density reduced, small-angle grain boundaries increased, and element diffusion was more sufficient. Tensile tests at different temperatures showed that the fractured sites were all in the matrix, which indicates that high-quality diffusion-bonding joints of dissimilar materials were achieved.
Fund: National Natural Science Foundation of China(52034004);Tianjin Natural Science Foundation(18JCQNJC03300)
About author: LIU Chenxi, associate professor, Tel: (022)85356410, E-mail: cxliu@tju.edu.cnLIU Yongchang, professor, Tel: (022)85356410, E-mail: ycliu@tju.edu.cn
Table 1 Chemical compositions of materials for experiments
Fig.1 Sketch diagrams for the process curves
Fig.2 Schematics of tensile specimen (unit: mm, Ra—roughness)
Fig.3 OM images of the parent metals for diffusion-bonding
Fig.4 Low (a1-e1) and high (a2-e2) magnified OM images and SEM images (a3-e3) showing the microstructures of the diffusion-bonding joints with the bonding temperature of 1050oC and bonding stress of 15 MPa, for the different bonding time
Fig.5 Interfacial bonding percentage as a function of the diffusion-bonding time
Fig.6 SEM images of the diffusion-bonding joints with the bonding temperature of 1050oC, bonding stress of 15 MPa, and the bonding time of 120 min after PWHT
Fig.7 EBSD analyses of the diffusion-bonding joint area before PWHT
Fig.8 EBSD analyses of the diffusion-bonding joint area after PWHT
Fig.9 TEM analyses of the diffusion-bonding joints before PWHT
Fig.10 TEM analyses of the diffusion-bonding joints after PWHT
Fig.11 EDS line scanning results of the diffusion-bonding joint after PWHT
Specification
Temperature / oC
Average tensile strength / MPa
Rp0.2 / MPa
Elongation / %
Shrinkage / %
Before PWHT
25
601.68
263.56
33.05
50.66
600
322.45
153.79
21.79
47.62
After PWHT
25
558.82
249.37
24.74
31.69
600
290.45
153.38
12.26
29.34
Table 2 Tensile test results of the diffusion-bonding joints before and after PWHT
Fig.12 Physical drawing of tensile fracture specimen
Fig.13 Engineering stress-strain curves of the diffusion-bonding joints before and after PWHT under testing temperatures of 25oC (a) and 600oC (b)
Fig.14 Low (a, c) and high (b, d) magnified tensile fracture morphologies of the diffusion-bonding joints at 25oC before (a, b) and after (c, d) PWHT
Fig.15 Low (a, c) and high (b, d) magnified tensile fracture morphologies of the diffusion-bonding joints at 600°C before (a, b) and after (c, d) PWHT
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