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Microstructural Evolution of Inconel 625 and Inconel 686CPT Weld Metal for Clad Carbon Steel Linepipe Joints: A Comparator Study

The Effect of Iron Dilution on the Elemental Segregation of Alloying Elements in Nickel Based Filler Metals

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Microstructural evolution of Inconel 625 and Inconel 686CPT filler metals, used for the fusion welding of clad carbon steel linepipe, has been investigated and compared. The effects of iron dilution from the linepipe parent material on the elemental segregation potential of the filler metal chemistry have been considered. The results obtained provide significant evidence to support the view that, in Inconel 686CPT weld metal, the segregation of tungsten is a function of the level of iron dilution from the parent material. The data presented indicate that the incoherent phase precipitated in the Inconel 686CPT weld metal has a morphology that is dependent on tungsten enrichment and, therefore, iron dilution. Furthermore, in the same weld metal, a continuous network of finer precipitates was observed. The Charpy impact toughness of each filler metal was evaluated, and the results highlighted the superior impact toughness of the Inconel 625 weld metal over that of Inconel 686CPT.

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This work was supported by the Pipeline Production Group division of Subsea 7. The author would also like to gratefully acknowledge the support and expertize of the AMRL department of the University of Strathclyde.

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Correspondence to Charles A. Maltin.

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Manuscript submitted May 25, 2013.

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Maltin, C.A., Galloway, A.M. & Mweemba, M. Microstructural Evolution of Inconel 625 and Inconel 686CPT Weld Metal for Clad Carbon Steel Linepipe Joints: A Comparator Study. Metall Mater Trans A 45, 3519–3532 (2014).

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  • Weld Metal
  • Impact Toughness
  • Filler Metal
  • Interdendritic Region
  • Fusion Line