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Microstructure-performance relationships in gas tungsten arc welded Hastelloy X nickel-based superalloy

Ghasemi, A ; Sharif University of Technology | 2020

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  1. Type of Document: Article
  2. DOI: 10.1016/j.msea.2020.139861
  3. Publisher: Elsevier Ltd , 2020
  4. Abstract:
  5. This study aims at understanding the metallurgical and mechanical response of Hastelloy X nickel-based superalloy to the thermal cycle of gas tungsten arc welding (GTAW), post welding solution treatment (ST), and aging. In the as-weld condition, the weldment was characterized by the formation of the M6C carbide, sigma phase, and micro-solidification cracks in the interdendritic zones of the weld metal, and constitutional liquation of M6C carbide in the heat-affected zone. It is demonstrated that neither the weld metal nor the heat-affected zone could adversely affect mechanical properties of the welded joint in as-weld condition. However, to alleviate the microstructural heterogeneity, tensile residual stresses, and non-equilibrium microstructure developed due to the welding thermal cycle, the weldment was subjected to the solution treatment cycle (1177 °C/5 min) as post-weld heat treatment. The post-weld heat treatment enabled complete elimination of sigma phase. The tensile and creep properties of the weldment after the solution treatment cycle were compared to that of the as-weld condition. Despite the 8% decrease in the strength of the weldment after the ST cycle, the sample not only still met the minimum mechanical requirements but also benefited from a homogenized and nearly equilibrium microstructure. Microstructural observations of the weldment after the aging cycle (800 °C/8h), as well as its mechanical response, revealed that the formation of continuous Cr-rich carbides at the grain boundaries of the base metal deteriorates the room temperature ductility and creep life of the joints. © 2020
  6. Keywords:
  7. Fusion welding ; Hastelloy X ; Microstructure ; Post weld heat treatment ; Stress-rupture ; Tensile properties ; Carbides ; Chromium compounds ; Creep ; Gas metal arc welding ; Grain boundaries ; Heat affected zone ; Heat treatment ; Nickel ; Nickel alloys ; Nickel metallurgy ; Superalloys ; Thermal cycling ; Tungsten ; Constitutional liquation ; Equilibrium microstructures ; Micro-structural observations ; Microstructural heterogeneity ; Microstructure performance ; Nickel- based superalloys ; Non-equilibrium microstructure ; Room-temperature ductility ; Gas welding
  8. Source: Materials Science and Engineering A ; Volume 793 , 2020
  9. URL: https://www.sciencedirect.com/science/article/abs/pii/S0921509320309333