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<p>The study investigates the microstructural evolution, iron dilution, and intermetallic carbide formation in Inconel-625 (IN-625) weld overlays on medium-carbon steel (AISI 4140) substrates using synergic MIG welding. A three-layer IN-625 overlay was applied with varying heat inputs (214&#xa0;J/mm and 385&#xa0;J/mm) to examine their effects on dilution, microstructure, and mechanical properties. Metallurgical analysis revealed a significant microstructure variation, including coarse- and fine-grained heat-affected zones, columnar dendrites, and equiaxed grains across different weld layers. The first weld layer exhibited the highest iron dilution (~30%), which decreased in subsequent layers, maintaining surface integrity. SEM/EDS analysis confirmed the formation of niobium–carbide (NbC) intermetallic carbides due to carbon migration from the substrate, while XRD analysis primarily identified a <i>γ</i>-phase Ni-rich matrix. Microhardness analysis showed a peak of ~ 300 HV<sub>0.2</sub> in the heat-affected zone, raising concerns about potential cracking. Despite variations in dilution, the weld overlay exhibited a uniform hardness distribution, making it suitable for surface modification applications. The electrochemical behavior of both weld overlays was analyzed using linear sweep voltammetry, showing better corrosion resistance for the sample with lower heat input. The findings contribute to optimizing welding parameters for enhancing the performance and durability of IN-625 overlays on medium-carbon steels in industries such as aerospace, marine, and oil &amp; gas.</p>

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Microstructural Evolution and Iron Dilution in Synergic Metal Inert Gas-Welded IN-625 Overlays on AISI 4140 Steel: Effect of Heat Input

  • 期刊论文

  • 发表日期：

    2025年8月25日

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  • Ashutosh Bagchi,
  • Qasim Murtaza,
  • K. Srinivas

摘要

The study investigates the microstructural evolution, iron dilution, and intermetallic carbide formation in Inconel-625 (IN-625) weld overlays on medium-carbon steel (AISI 4140) substrates using synergic MIG welding. A three-layer IN-625 overlay was applied with varying heat inputs (214 J/mm and 385 J/mm) to examine their effects on dilution, microstructure, and mechanical properties. Metallurgical analysis revealed a significant microstructure variation, including coarse- and fine-grained heat-affected zones, columnar dendrites, and equiaxed grains across different weld layers. The first weld layer exhibited the highest iron dilution (~30%), which decreased in subsequent layers, maintaining surface integrity. SEM/EDS analysis confirmed the formation of niobium–carbide (NbC) intermetallic carbides due to carbon migration from the substrate, while XRD analysis primarily identified a γ-phase Ni-rich matrix. Microhardness analysis showed a peak of ~ 300 HV0.2 in the heat-affected zone, raising concerns about potential cracking. Despite variations in dilution, the weld overlay exhibited a uniform hardness distribution, making it suitable for surface modification applications. The electrochemical behavior of both weld overlays was analyzed using linear sweep voltammetry, showing better corrosion resistance for the sample with lower heat input. The findings contribute to optimizing welding parameters for enhancing the performance and durability of IN-625 overlays on medium-carbon steels in industries such as aerospace, marine, and oil & gas.