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Open AccessArticle

Microstructural Changes and Impact Toughness of Fill Pass in X80 Steel Weld Metal

1
School of Mathematics and Physics, University of Science and Technology Beijing, Beijing 100083, China
2
Pipeline Institute, China Petroleum Pipeline Engineering CO., LTD., Langfang 065000, China
3
School of Energy and Environmental Engineering, University of Science and Technology Beijing, Beijing 100083, China
4
College of Science, China Three Gorges University, Yichang 443002, China
*
Authors to whom correspondence should be addressed.
Metals 2019, 9(8), 898; https://doi.org/10.3390/met9080898
Received: 27 July 2019 / Revised: 11 August 2019 / Accepted: 14 August 2019 / Published: 16 August 2019
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PDF [58632 KB, uploaded 16 August 2019]
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Abstract

Multi-pass welding is used in high-pressure and thick-walled pipes in natural gas and oil pipelines. When a welding layer of a welded joint is subjected to different welding thermal cycles, its microstructure and properties change, thereby affecting the overall welding performance. In this study, the temperature and microstructural variations of the fill pass 2 (FP2) in the entire welding process were investigated by combining the thermal cycle with the cascade welding method. The original FP2 and FP2 after double thermal cycles had the worse deformation ability by tensile test. The toughness of FP2 improved after a single thermal cycle, decreased after double thermal cycles, and improved again after triple thermal cycles. The content of martensite–austenite (M–A) constituents and the average grain size of FP2 in the cascade samples were inversely proportional to FP2 toughness. Massive M–A constituents and their unique distribution at the inter-critical temperature were harmful to weld metal toughness. Controlling the size and fraction of M–A constituents can improve weld metal toughness. View Full-Text
Keywords: weld metal; thermal cycle; M–A constituent; impact toughness; grain size weld metal; thermal cycle; M–A constituent; impact toughness; grain size
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Bai, F.; Ding, H.; Tong, L.; Pan, L.; Wang, L. Microstructural Changes and Impact Toughness of Fill Pass in X80 Steel Weld Metal. Metals 2019, 9, 898.

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