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Research Papers: Materials and Fabrication

Evaluation of Fracture Toughness of a SA580 Gr. 3 Reactor Pressure Vessel Using a Bimodal Master Curve Approach

[+] Author and Article Information
Jong-Min Kim, Seok-Min Hong, Bong-Sang Lee

Safety Materials Technology
Development Division,
Korea Atomic Energy Research Institute,
111, Daedeok-Daero 989 Beon-Gil,
Yuseong-Gu,
Daejeon 34057, Korea

Min-Chul Kim

Safety Materials Technology
Development Division,
Korea Atomic Energy Research Institute,
111, Daedeok-Daero 989 Beon-Gil,
Yuseong-Gu,
Daejeon 34057, Korea
e-mail: mckim@kaeri.re.kr

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received October 29, 2018; final manuscript received May 30, 2019; published online August 2, 2019. Assoc. Editor: Bostjan Bezensek.

J. Pressure Vessel Technol 141(6), 061403 (Aug 02, 2019) (8 pages) Paper No: PVT-18-1235; doi: 10.1115/1.4044263 History: Received October 29, 2018; Revised May 30, 2019

The standard master curve (MC) approach has a major limitation in that it is only applicable to homogeneous datasets. In nature, steels are macroscopically inhomogeneous. Reactor pressure vessel (RPV) steel has different fracture toughness with varying distance from the inner surface of the wall due to the higher cooling rate at the surface (deterministic material inhomogeneity). On the other hand, the T0 value itself behaves like a random parameter when the datasets have large scatter because the datasets are for several different materials (random inhomogeneity). In this paper, four regions, the surface, 1/8 T, 1/4 T, and 1/2 T, were considered for fracture toughness specimens of Korean Standard Nuclear Plant (KSNP) SA508 Gr. 3 steel to provide information on deterministic material inhomogeneity and random inhomogeneity effects. Fracture toughness tests were carried out for the four regions at three test temperatures in the transition region and the microstructure of each region was analyzed. The amount of upper bainite increased toward the center, which has a lower cooling rate; therefore, the center has lower fracture toughness than the surface so reference temperature (T0) is higher. The fracture toughness was evaluated using the bimodal master curve (BMC) approach. The results of the BMC analyses were compared with those obtained via a conventional master curve analyses. The results indicate that the bimodal master approach considering inhomogeneous materials provides a better description of scatter in the fracture toughness data than a conventional master curve analysis does.

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Figures

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Fig. 1

Investigated RPV block and locations of specimen extraction

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Fig. 2

OM and SEM images according to position

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Fig. 3

Variation of yield strength over the temperature range from room temperature to 196 °C

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Fig. 4

Standard MC reference temperature T0

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Fig. 5

Standard MC and measured KJC values at the surface

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Fig. 6

Standard MC and measured KJC values at 1/2 T and 1/4 T

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Fig. 7

Comparison of the bimodal and conventional MC analyses for all datasets corresponding to temperature dependence

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Fig. 8

Comparison of the bimodal and conventional MC analyses at various temperatures: (a) T = −100 °C, (b) T = −110 °C, and (c) T = −120 °C

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Fig. 9

Standard and bimodal MC with all measured KJC values

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