PSI - Issue 68

Mahmoud Khedr et al. / Procedia Structural Integrity 68 (2025) 1017–1023 Mahmoud Khedr / Structural Integrity Procedia 00 (2025) 000–000

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1. Introduction Gas tungsten arc welding (GTAW) is a widely used technique for joining similar and dissimilar metals, offering precise control overheat input and producing high-quality welds with minimal defects, as demonstrated by Khedr et al., (2024) and Mvola et al., (2015). In recent years, the demand for advanced welding techniques capable of effectively joining diverse materials has grown significantly, particularly in applications requiring a combination of high strength and ductility, as noted by Khedr et al., (2023). Among the materials frequently utilized in industrial applications, low carbon steel (LCS) and various types of stainless steel are particularly interesting due to their distinct mechanical and chemical properties, as reported by Abioye et al., (2019). LCS is renowned for its excellent weldability, cost-effectiveness, and mechanical properties, making it a popular choice in structural applications, as recommended by Kang et al., (2009). Conversely, austenitic stainless steels, such as Ni-Cr and low-Ni medium-Mn variants, offer superior toughness, and high-temperature performance, as shown by Eshkabilov, et al., (2021). However, Awad et al., (2021) displayed that welding dissimilar materials such as LCS with Ni-Cr austenitic stainless steel (NiCr-SS) or low-Ni medium-Mn austenitic stainless steel (MMn-SS) presents unique challenges due to differences in thermal expansion coefficients, melting points, and chemical compositions. The fluid motion in the weld pool circulates and mixes the molten base metals (BMs), resulting in a uniform distribution of alloying elements like Fe, Cr, and Ni throughout the weld zone, as shown by Bahrami et al., (2016). Huang et al., (2021) reported that these disparities can lead to the formation of brittle intermetallic phases and residual stresses, which may compromise the integrity and performance of the welded joint. Furthermore, Vashishtha et al., (2021) attributed that effect to the presence of intermetallic compounds like Cr 23 C 6 , which can deteriorate mechanical properties and lead to failure in the fusion zone (FZ). Therefore, the tensile strength of dissimilar joints is generally lower than that of the stainless-steel BM due to the inhomogeneous dendritic structure and Cr-carbides precipitation in the FZ, as concluded by Awad et al. (2021). From a metallurgical perspective, Bahrami et al., (2016) displayed that the FZ of dissimilar joints between LCS and stainless steel often exhibits a duplex structure of austenite and delta ferrite, with the lowest hardness observed in the FZ compared to the heat-affected zone (HAZ) and BM. The microstructure of these weldments can vary significantly depending on the heat input applied during the welding process, as reported by Mohammed et al., (2017) and Verma et al., (2017). Vashishtha et al., (2019) found that the lower heat inputs generally produce improved mechanical properties and result in a lathy ferrite morphology, whereas lower welding speeds tend to favor the formation of vermicular ferrite. Despite these insights, further comprehensive investigations of weldments between LCS and various stainless-steel grades such as NiCr-SS and MMn-SS, using a range of filler metals, are essential for optimizing welding parameters in industrial applications, as recommended by Maurya et al., (2021). The present study explores the weldability of LCS with Ni-Cr-SS and MMn-SS using the GTAW technique via employing ER309MoL filler metal, which is known for its excellent compatibility with carbon steel and stainless steel. Microstructural characteristics and mechanical properties of the processed dissimilar welded joints were studied. Specifically, the analysis focuses on the formed microstructures, hardness distribution, and tensile strength in the FZ of LCS/MMn-SS and LCS/NiCr-SS joints. Understanding the mechanical behavior of these dissimilar steels is crucial for advancing the application of hybrid metal systems in various engineering fields. This research provides valuable insights into the microstructural evolution and mechanical behavior of dissimilar welded joints, contributing to the development of more reliable and durable materials for structural, automotive, and aerospace applications. 2. Material and methods The experimental materials are metal sheets of thickness 2 mm from LCS, MMn–SS and LCS/NiCr-SS. Heterogeneous welding using ER309MoL filler metal was applied to manufacture tailored dissimilar butt joints from the metals under consideration. The chemical compositions of the steels and filler metal are listed in Table 1. The welding direction was perpendicular to the rolling direction. Welding was conducted using the GTAW technique (ESAB Tig 4300i AC/DC) with pure argon shielding gas (99.8% purity) at a flow rate of 15 l/min. No preheat or post weld heat treatment was applied to the specimens. Table 2 displays the welding parameters utilized in the GTAW process for the dissimilar welding of LCS/MMn-SS and LCS/NiCr-SS. The heat input was determined using Equation (1) as follows: