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Open AccessArticle

The Mechanism for HAZ Liquation of Nickel-Based Alloy 617B During Gas Tungsten Arc Welding

by Shanlin Li 1,2, Kejian Li 1,2,*, Mengjia Hu 1,2, Yao Wu 3, Zhipeng Cai 1,2,4,5,* and Jiluan Pan 1,2
1
Department of Mechanical Engineering, Tsinghua University, Beijing 10084, China
2
Key Laboratory for Advanced Materials Processing Technology, Ministry of Education, Beijing 100084, China
3
Tianjin Research Institute for Advanced Equipment, Tsinghua University, Tianjin 300300, China
4
Collaborative Innovation Center of Advanced Nuclear Energy Technology, Tsinghua University, Beijing 10084, China
5
State Key Laboratory of Tribology, Tsinghua University, Beijing 10084, China
*
Authors to whom correspondence should be addressed.
Metals 2020, 10(1), 94; https://doi.org/10.3390/met10010094
Received: 26 November 2019 / Revised: 26 December 2019 / Accepted: 2 January 2020 / Published: 6 January 2020
(This article belongs to the Special Issue Microstructure and Properties of Metallic Heat-Affected Zones)
The mechanism for HAZ (heat-affected zone) liquation of alloy 617B during gas tungsten arc welding (GTAW) was investigated. Welding thermal simulation work was conducted to investigate the effects of thermal parameters (peak temperature, holding time, and thermal cycle numbers) on M23C6 carbides’ evolutionary behavior in nickel-based alloy 617B. OM (optical microscopy), SEM (scanning electron microscopy), TEM (transmission electron microscopy), and SIMS (secondary ion mass spectrometry) were employed to characterize HAZ carbides. It was found that the constitutional liquation of M23C6 carbides is responsible for HAZ liquation in alloy 617B. Rapid heating meant that solute atoms released from partially dissolved M23C6 carbides did not have enough time to sufficiently diffuse into the matrix, resulting in eutectic reaction M23C6 + γ → liquid in the temperature range from 1250 °C to 1300 °C. In the following cooling process, the liquid phase transformed into γ and M23C6 (or M6C) carbides simultaneously, creating a eutectic microstructure. Subsequent thermal cycles with peak temperature 1100 °C and proper holding time brought about a tempering effect to precipitate fine M23C6 carbides from the Cr supersaturated zone around the eutectic microstructure. Boron was found to be enriched in carbides and was expected to promote HAZ liquation by two mechanisms. No cracking caused by HAZ liquation has been found, indicating that GTAW is a suitable method for joining alloy 617B. View Full-Text
Keywords: nickel-based alloys; welding; thermal simulation; constitutional liquation; M23C6 carbides nickel-based alloys; welding; thermal simulation; constitutional liquation; M23C6 carbides
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Li, S.; Li, K.; Hu, M.; Wu, Y.; Cai, Z.; Pan, J. The Mechanism for HAZ Liquation of Nickel-Based Alloy 617B During Gas Tungsten Arc Welding. Metals 2020, 10, 94.

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