Coexistence of two distinct fatigue failure mechanisms in Super304H welded joint at elevated temperatures

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING

卷:819

Article

Song, Geun Dong^1,2  Hwang, Jeong Ho^1,2  Kim, Dae-Woong^1,2  Park, Byong Chon¹  Hahn, Junhee^1,2  Hong, Seong-Gu^1,2,3 

[1] Korea Res Inst Stand & Sci, Interdisciplinary Mat Measurement Inst, Daejeon 34113, South Korea

[2] Korea Inst Energy Res, Future Energy Plant Convergence Res Ctr, Daejeon 34129, South Korea

[3] Univ Sci & Technol, Dept Nano Sci, Daejeon 34113, South Korea

关键词: Super304H welded joint;    Fatigue failure mechanism;    Thermal aging effect;    Chromium carbide precipitation;    Elevated temperatures;   

DOI  :  10.1016/j.msea.2021.141465

来源: Elsevier

【 摘 要 】

Super304H steel is a promising candidate for boiler tube materials in thermal power plants operating under ultrasupercritical conditions, and the fatigue properties of its welded joint play a key role in the structural reliability of the thermal power plants. Herein, we report that there is a transition in the fatigue failure location (i.e., fatigue failure mechanism) from the base metal at a high strain amplitude ( -0.4%) to the weld metal at a low strain amplitude (<-0.3%) at a constant temperature in the operating range of 500-700 degrees C, and this leads to a significant reduction in the fatigue resistance of the welded joint as compared to that of the base metal. We found that a longer fatigue test time at a low strain amplitude induces a thermal aging effect that promotes different microstructural evolutions in the base metal and weld metal, deepening material inhomogeneity in the welded joint, and thereby triggering strain localization in the weld metal. With increasing fatigue test time (i.e., thermal aging time), Cr23C6 carbides precipitated in the interdendritic region of the weld metal and at the austenitic grain boundary of the base metal, and Nb (C, N) phases precipitated in the interior of austenitic grain in the base metal, which increased local hardness, whereas there was no significant microstructural change in the dendrite core of the weld metal, retaining its initial hardness. The intensified local hardness inhomogeneity caused the softest zone in the welded joint, wherein strain localization occurred, serving as a crack nucleation site and propagation path, to shift from the base metal to the weld metal (dendrite core). This induced a shift in the fatigue failure location from the base metal to the weld metal with decreasing strain amplitude.

【 授权许可】

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