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<p>This study investigates the effect of various filler compositions on the microstructure and mechanical properties of dissimilar metal welds between austenitic stainless steel AISI 304H and the Ni-based superalloy Inconel 617 (IN617). These materials are used in the production of boiler components that operate at moderately high temperatures in advanced ultra-supercritical (AUSC) power plant units, with the aim of reducing overall costs and improving the structural integrity of the welded joints. The dissimilar welded joint is fabricated using the gas tungsten arc welding (GTAW) process, utilizing four different filler materials: austenitic filler SS 308H, Inconel 82 (ERNiCr-3), Inconel 617 (ERNiCrCoMo-1), and Inconel 625 (ERNiCrMo-3). Both macroscopic and microscopic examination of the welded joints showed no evidence of cracking in the weld metal for any of the filler materials used. SEM and optical microscopy confirmed the presence of an austenitic microstructure in the weld metal, characterized by a dendritic structure and segregation of alloying elements. The composition of the weld metal matrix and its structure were observed to vary along the welded joint, from the weld metal near interface to the central region of the bulk weld metal. The microstructural study of the interfaces revealed macrosegregation, characterized by features such as island and peninsula formations, along with an unmixed zone. Additionally, diffusion of the elements was observed across the interfaces. The welds made with Inconel 617 showed the highest ultimate tensile strength and total elongation at room temperature, with failure in the region of the AISI 304 base metal. For the Ni-based fillers, failure was observed in the AISI 304H base metal, while for the SS 308H filler, failure occurred in the weld metal region. For high-temperature tensile testing at 650&#xa0;°C and 700&#xa0;°C, the UTS ranged from 290 to 318&#xa0;MPa and 244–252&#xa0;MPa, respectively, with failure occurring in the AISI 304H base metal for all the fillers. These values were close to the UTS of the AISI 304H base metal, which was 322&#xa0;MPa at 650&#xa0;°C and 261&#xa0;MPa at 700&#xa0;°C, but significantly lower than the UTS of the Inconel 617 base metal at both temperatures, making them suitable for AUSC power plant boiler applications. Charpy impact testing revealed that all specimens exhibited ductile fracture. The maximum Charpy toughness of 125&#xa0;J was observed for the Inconel 82 filler, while the minimum toughness of 79&#xa0;J was recorded for the SS 308H filler. The microhardness study of the weldments revealed that the maximum hardness of the weld metal was 246 ± 10 HV for the Inconel 617 filler weld, while the minimum hardness was 204 ± 7 HV for the SS 308H filler weld. Additionally, a trend of increasing hardness was observed, ranging from the AISI 304H base metal to the Inconel 617 base metal through the weld metal for all the fillers. Among all the filler metals evaluated, Inconel 617 filler metal exhibited the most favorable performance in fabricating a dissimilar weld between Inconel 617 and AISI 304H, as confirmed by comprehensive microstructural analyses and mechanical testing.</p>

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Tailoring weld integrity for AUSC applications: a filler metal perspective on dissimilar AISI 304H and Inconel 617 joints

  • 期刊论文

  • 发表日期：

    2025年8月16日

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  • Abhinav Garga,
  • Hirshikesh,
  • Chandan Pandey

摘要

This study investigates the effect of various filler compositions on the microstructure and mechanical properties of dissimilar metal welds between austenitic stainless steel AISI 304H and the Ni-based superalloy Inconel 617 (IN617). These materials are used in the production of boiler components that operate at moderately high temperatures in advanced ultra-supercritical (AUSC) power plant units, with the aim of reducing overall costs and improving the structural integrity of the welded joints. The dissimilar welded joint is fabricated using the gas tungsten arc welding (GTAW) process, utilizing four different filler materials: austenitic filler SS 308H, Inconel 82 (ERNiCr-3), Inconel 617 (ERNiCrCoMo-1), and Inconel 625 (ERNiCrMo-3). Both macroscopic and microscopic examination of the welded joints showed no evidence of cracking in the weld metal for any of the filler materials used. SEM and optical microscopy confirmed the presence of an austenitic microstructure in the weld metal, characterized by a dendritic structure and segregation of alloying elements. The composition of the weld metal matrix and its structure were observed to vary along the welded joint, from the weld metal near interface to the central region of the bulk weld metal. The microstructural study of the interfaces revealed macrosegregation, characterized by features such as island and peninsula formations, along with an unmixed zone. Additionally, diffusion of the elements was observed across the interfaces. The welds made with Inconel 617 showed the highest ultimate tensile strength and total elongation at room temperature, with failure in the region of the AISI 304 base metal. For the Ni-based fillers, failure was observed in the AISI 304H base metal, while for the SS 308H filler, failure occurred in the weld metal region. For high-temperature tensile testing at 650 °C and 700 °C, the UTS ranged from 290 to 318 MPa and 244–252 MPa, respectively, with failure occurring in the AISI 304H base metal for all the fillers. These values were close to the UTS of the AISI 304H base metal, which was 322 MPa at 650 °C and 261 MPa at 700 °C, but significantly lower than the UTS of the Inconel 617 base metal at both temperatures, making them suitable for AUSC power plant boiler applications. Charpy impact testing revealed that all specimens exhibited ductile fracture. The maximum Charpy toughness of 125 J was observed for the Inconel 82 filler, while the minimum toughness of 79 J was recorded for the SS 308H filler. The microhardness study of the weldments revealed that the maximum hardness of the weld metal was 246 ± 10 HV for the Inconel 617 filler weld, while the minimum hardness was 204 ± 7 HV for the SS 308H filler weld. Additionally, a trend of increasing hardness was observed, ranging from the AISI 304H base metal to the Inconel 617 base metal through the weld metal for all the fillers. Among all the filler metals evaluated, Inconel 617 filler metal exhibited the most favorable performance in fabricating a dissimilar weld between Inconel 617 and AISI 304H, as confirmed by comprehensive microstructural analyses and mechanical testing.