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Research Papers: Materials and Fabrication

Evaluation of Fatigue Strength of Similar and Dissimilar Welded Joints of Modified 9Cr–1Mo Steel

[+] Author and Article Information
Shigeru Takaya

Mem. ASME
Japan Atomic Energy Agency,
4002 Narita,
O-arai, Ibaraki 311-1393, Japan
e-mail: takaya.shigeru@jaea.go.jp

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received December 3, 2014; final manuscript received June 15, 2015; published online August 26, 2015. Assoc. Editor: David L. Rudland.

J. Pressure Vessel Technol 138(1), 011402 (Aug 26, 2015) (9 pages) Paper No: PVT-15-1003; doi: 10.1115/1.4030932 History: Received December 03, 2014

This paper presents an evaluation method for the fatigue strength of similar and dissimilar welded joints of modified 9Cr–1Mo steel, which is a candidate structural material for demonstration of fast-breeder reactor being developed in Japan. The discontinuity of the mechanical properties across a welded joint causes a nonhomogeneous strain distribution, and this effect should be considered in the evaluation of the fatigue strength of welded joints. In this study, a “two-element model,” which comprises base metal and welded metal, was employed. First, the strain ranges of each element are calculated, and second, the fatigue lives of each element are evaluated. Finally, the shorter fatigue life is selected as the fatigue life of the welded joint. The failure position can be also estimated by this model. The evaluation results were compared with experimental data obtained at elevated temperature, and the results were in good agreement.

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Figures

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Fig. 1

Dimensions of test pieces (mm): (a) similar welded joint, (b) modified 9Cr–1Mo steel side partial dissimilar welded joint (type I), (c) modified 9Cr–1Mo steel side partial dissimilar welded joint (type II), (d) modified 9Cr–1Mo steel side partial dissimilar welded joint (type III), (e) SUS304 side partial dissimilar welded joint, and (f) welded metal taken from dissimilar welded joint

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Fig. 2

Fatigue life of similar welded joints of modified 9Cr–1Mo steel at 550 °C

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Fig. 3

Fatigue life of modified 9Cr–1Mo steel side partial dissimilar welded joints: (a) 400 °C and (b) 550 °C

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Fig. 4

Fatigue life of SUS304 side partial dissimilar welded joints: (a) 400 °C and (b) 550 °C

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Fig. 5

Evaluation procedure of fatigue life of welded joint based on two-element model

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Fig. 6

Determination of fatigue life curve and estimation of failure position for welded joint based on two-element method

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Fig. 7

Cyclic stress–strain curve for welded metal of similar welded joint at 550 °C

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Fig. 8

Fatigue life of welded metal of similar welded joint at 550 °C

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Fig. 9

Cyclic stress–strain curve for welded metal of dissimilar welded joint

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Fig. 10

Fatigue life of welded metal of dissimilar welded joint

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Fig. 11

Cyclic stress–strain equations for evaluation in this study: (a) 400 °C and (b) 550 °C

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Fig. 12

Fatigue failure equations for evaluation in this study: (a) 400 °C and (b) 550 °C

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Fig. 13

Evaluated fatigue life of similar welded joint at 550 °C

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Fig. 14

Comparison between observed and predicted fatigue lives of similar welded joint

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Fig. 15

Evaluation result for modified 9Cr–1Mo steel side dissimilar welded joint: (a) 400 °C and (b) 550 °C

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Fig. 16

Comparison between observed and predicted fatigue lives of modified 9Cr–1Mo steel side partial dissimilar welded joint: (a) 400 °C and (b) 550 °C

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Fig. 17

Evaluation result for SUS304 side partial dissimilar welded joint: (a) 400 °C and (b) 550 °C

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Fig. 18

Comparison between observed and predicted fatigue lives of SUS304 side partial dissimilar welded joint: (a) 400 °C and (b) 550 °C

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