PSI - Issue 68

Ibrahim R. Awad et al. / Procedia Structural Integrity 68 (2025) 1024–1030 Ibrahim R. Awad / Structural Integrity Procedia 00 (2025) 000–000

1025

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particular, the comparison between gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW) reveals important differences in terms of mechanical properties and weld integrity, with studies indicating that SMAW welds often exhibit superior tensile characteristics when compared to GTAW welds (Mushthofa et al., 2023; Singh and Grover, 2015; Z. Afriansyah, 2024). Interestingly, the enhancements observed in the tensile properties of SMAW welds may be attributed to the effects of post-weld heat treatment, which has been demonstrated to significantly improve the mechanical properties of the welds produced using this technique (Ghosh and Singh, 2004). Additionally, the unique thermal cycles associated with each welding process can have a profound influence on the microstructural and mechanical properties of the welded joints, where the controlled heat input in SMAW can result in reduced softening of the weld region compared to GTAW welding (Fikrie et al., 2022; Ghosh and Singh, 2004). Therefore, GTAW is preferred for thinner materials ( ≤ 2 mm) due to its ability to produce fewer defects and superior weld quality compared to SMAW (A. Sharma, 2024; Arandjelovic et al., 2024; Ibrahim et al., 2021; Khedr et al., 2024). While GTAW offers precision and reduced defects, SMAW remains valuable for its versatility and effectiveness in various applications (A. Sharma, 2024). The choice between these methods often depends on specific project requirements and material characteristics. Therefore, the choice between GTAW and SMAW welding for S275JR low-carbon manganese steel should be carefully considered, as the particular application and performance requirements will largely dictate the optimal welding technique. Furthermore, the flexibility of SMAW allows for better adaptability to varying joint configurations and positions, often resulting in a more robust and durable weld for complex assemblies, especially when evaluating the overall cost-effectiveness and time efficiency of the welding process in a manufacturing setting. S275JR steel is known for its good weldability and strength, making it a preferred choice in construction. Its microstructure typically consists of ferrite and pearlite phases, influenced by its carbon content (Brnic et al., 2013; Rahimi et al., 2019). A study by (Elmas et al., 2024) examined the microstructure and mechanical properties of both similar and dissimilar joints of S275JR using Gas Metal Arc Welding (GMAW). The findings showed a microstructure composed of acicular ferrite, Widmanstätten ferrite, and pearlite. The tensile strength of similar S275JR welds was 507.3 MPa, achieving a welding efficiency of 99.76%. (Çevik, 2018) investigated the effects of GMAW and flux cored arc welding (FCAW) on the mechanical and microstructural properties of S275JR. Their results revealed that the weld metal and coarse-grained regions exhibited grain boundary ferrites, polygonal ferrites, Widmanstätten ferrites, and acicular ferrites. Additionally, the hardness in the fusion zone (FZ) was higher than in both the heat affected zone (HAZ) and base metal (BM) across all welding parameters. The highest tensile and bending strengths were observed in samples welded with FCAW, with fractures occurring in the transition region between the weld metal and coarse-grained areas. However, comparisons of as-welded joints by GTAW and SMAW (without post-heat treatment) are limited. Thus, the present study reveals the microstructure and mechanical behavior of S275JR joints welded by GTAW and SMAW, by assessing microstructure evolution, hardness, and tensile properties, which is vital for construction and industrial applications. 2. Material and methods In this study, the utilized base metal is a commercial low-carbon manganese steel, designated as S275JR, supplied by the EL-Temsah factory in Cairo, Egypt. Table 1 shows the chemical composition of the investigated BM.

Table 1. Chemical composition of the base metal.

Element

C

Si

Mn

V

Cr

Mo

Ni

Al

Co

S

Fe

Wt.%

0.091 0.035

1.24

0.069

0.061

0.12

0.08

0.02

0.011

<0.0005

Bal.

Welding was processed via GTAW and SMAW techniques, employing ER70S6 and E7018 filler metals, respectively. GTAW was carried out at a current of 65 A, a voltage of 12.6 V, and a welding speed of 1.53 mm/s, whereas SMAW was conducted at a current of 60 A, a voltage of 28.5 V, and a welding speed of 4.21 mm/s. The welding heat input (HI) was calculated according to equation (1), as follows (Ibrahim et al., 2021; Khedr et al., 2023):