Abstract
The creep deformation behavior of virgin and long-term service-aged (77000 h) T91 steel of superheater tubes in a power plant was assessed via creep tests along with microstructure examination. A series of miniature tensile creep tests were conducted at 590 °C under applied stresses ranging from 120.0 to 224.1 MPa for both material types. The creep behavior was examined in terms of variations in the microstructural properties correlated with creep rupture life and ductility. X-ray diffraction, optical microscopy, field-emission scanning electron microscopy, hardness measurements, and image analyses were used to analyze the shape and morphology of the existing δ-ferrite, tempered martensite microstructure, and precipitates in both the virgin and long-term service-aged materials. The presence of larger residual δ-ferrite in the virgin microstructure was one of the causes of creep rupture strength reduction in the virgin material. On the contrary, the synergistic effect of the tempered martensite lath microstructure and additional precipitation strengthening of fine precipitates had beneficial effects translating to retention of the creep rupture strength of the long-term service-aged material.
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Abbreviations
- A :
-
Creep coefficient
- C :
-
Larson-Miller constant
- LMP :
-
Larson-Miller parameter
- n :
-
Creep exponent
- T :
-
Temperature (K)
- t r :
-
Time to rupture (h)
- σ :
-
Applied stress
- \(\dot \varepsilon \) :
-
Creep strain rate
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This work was supported by the KETEP (No. 2016 1110 100090), granted financial resource from the Ministry of Trade, Industry & Energy (MOTIE).
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Vanno Lok received his B.S. in Industrial and Mechanical Engineering from Institute of Technology of Cambodia. He received M.S. in Mechanical Engineering from Chung-Ang University. He is currently a Ph.D. candidate in Chung-Ang University. His research interests are stress analysis problem in pressure vessel & piping application in power plant and microstructural analysis of high temperature fracture mechanics to structural materials in life assessment.
Thi Giang Le received her B.S. in Metallurgical Engineering from Hanoi University of Science and Technology. She received M.S and Ph.D. in Mechanical Engineering from Chung-Ang University. Her research interest is creep behavior and aging characteristics of the high temperature alloy materials.
Jong Min Yu received his M.S. in Mechanical Engineering from Chung-Ang University. He is currently a Ph.D. candidate in Chung-Ang University. His research interest is life and integrity assessment of facilities in power and process plants. He is also interested in creep fracture of additive manufactured components.
Young Wha Ma received his Ph.D. degree in Mechanical Engineering from Chung-Ang University, Korea in 2007. After that, he worked at Georgia Institute of Technology, U.S.A. as a postdoc. Dr. Ma is currently Senior Research Engineer at Doosan Heavy Industries & Construction. His research interest is application of high temperature fracture mechanics to residual life assessment of structural materials including single and directionally solidified superalloys such as gas turbine blade.
Vinh Phu Nguyen received his B.S. degree in Material Technology from Bach Khoa University, Ho Chi Minh City, Vietnam, in 2014, and M.S. degree in Mechanical Engineering from University of Ulsan, Ulsan, Korea. In 2016 he joined and is currently Ph.D. candidate at Chung-Ang University. His research fields are molecular dynamics, fracture mechanics and high temperature creep deformation.
Seung Tae Choi received his Ph.D. degree from Korea Advanced Institute of Science and Technology. He is currently a Professor at Chung-Ang University. His current research interests include multiscale analysis of deformation and fracture of polycrystalline materials and development of ferroelectric polymer sensors and actuators.
Kee Bong Yoon received his B.S. in Mechanical Engineering from Seoul National University, M.S. from KAIST and Ph.D. from Georgia Institute of Technology. He is currently a Professor at Chung-Ang University. His research interests are high temperature fracture and risk based management of energy plants and semiconductor plants. He is extending research to fracture of additive manufactured materials.
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Lok, V., Le, T.G., Yu, J.M. et al. Changes in creep property and precipitates due to aging of T91 steel after long-term service. J Mech Sci Technol 34, 3283–3293 (2020). https://doi.org/10.1007/s12206-020-0720-4
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DOI: https://doi.org/10.1007/s12206-020-0720-4