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Effect of Keyhole Gas Tungsten Arc Welding and Post-welding Heat Treatment on Microstructure and Hardness of Inconel 740H

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Abstract

Keyhole mode gas tungsten arc welding (GTAW) is used to obtain crack-free full-penetration welds in Ni-base superalloy Inconel 740H. Associated spatial variation in microstructure and microhardness are correlated. Local softening in the heat-affected zone (HAZ) is observed after welding. This cannot be explained by changes in grain size, twin fraction or heterogeneous strain distribution, but instead can be attributed to the dissolution of ultra-fine grain boundary carbides. Fusion zone microstructure consists of large, columnar \(\gamma\) dendrites and Ti- and Nb-rich carbides at the interdendritic region. The relatively large grain size in the FZ results in a reduction in hardness compared to the base metal. Elemental partitioning during solidification is estimated from composition measurements in the FZ and compared against existing reports for conventional GTAW. The effect of different post-weld heat treatments (PWHTs) on the precipitation of \(\gamma^{\prime}\), disappearance of the dendritic microstructure, composition homogenization and spatial variation of microhardness is also investigated. Specifically, grain growth in the HAZ is observed after two-step PWHTs, and not for the single-step direct aging, which could have important implications for the creep response of the material.

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Acknowledgments

Authors gratefully acknowledge the financial support received under the grant TMD/CERI/CleanCoal/2017/034 (IIT H) and Prof. G. Phanikumar, IIT Madras, for his help with the procurement of the IN740H plates.

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  1. Department of Materials Science and Metallurgical Engineering, Indian Institute of Technology Hyderabad, Sangareddy, Telangana, India

    K. S. Athira & S. Chatterjee

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Athira, K.S., Chatterjee, S. Effect of Keyhole Gas Tungsten Arc Welding and Post-welding Heat Treatment on Microstructure and Hardness of Inconel 740H. J. of Materi Eng and Perform (2023). https://doi.org/10.1007/s11665-023-08831-3

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