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

1026

3

HI = η × I × V

(1)

where I and V are current in ampere (A) and V is voltage in volt (V), S is the welding speed in m/s, while η is the efficiency of welding arc taken as 0.6 and 0.75 for GTAW and SMAW, respectively, according to BS EN 1011-1 (Weman, 2012). HI measured 321.18 and 304.63 J/mm for GTAW and SMAW, respectively. The microstructures of the weld metal were investigated by using an optical microscope (Olympus PMG 3, Waltham, MA, USA). A Vickers hardness test was performed on the transverse section of the weldment using a Shimadzu HMV-G series Vickers hardness tester. During the test, a constant load of 10 kg was applied for 15 seconds, and an average of five readings was recorded. The tensile tests were carried out at room temperature on a hydraulic universal testing machine (UH-F1000kNI SHIMADZU, Tokyo, Japan) at a quasi-static strain rate of 1 × 10 -3 s -1 . 3. Results and discussion 3.1. Microstructure evolution The microstructures of welded joints produced by GTAW and SMAW are shown in Figures 1 and 2, respectively. In Figure 1 (a), the FZ-HAZ interface of the GTAW welded joints is depicted, while Figure 1 (b) highlights the HAZ, where grain coarsening is observed due to the heat input effect, particularly in areas closest to the weld metal during the welding processing (Türkmen et al., 2020). Grain boundary ferrite and Widmanhatten ferrite were reported to form during solidification in the weld metal and transition region, agreeing with the literature (Çevik, 2018). The weld metal microstructure comprises various structures such as acicular ferrite, ferrite, and pearlite, which develop during solidification, as illustrated in Figure 1 (c). The proportions of these phases vary depending on the cooling rate following the fusion welding of low-carbon steels. Similarly, Figure 2 (a) shows the FZ-HAZ interface of the SMAW welded joints, with grain coarsening in the HAZ of the SMAW joint visible in Figure 2 (b). The microstructure of the SMAW weld metal also consists of acicular ferrite, ferrite, and pearlite, as illustrated in Figure 2 (c).

Figure 1. Microstructure of GTAW welded joint via optical microscopy: (a) FZ - HAZ interface, (b) microstructure of HAZ, (c) microstructure of FZ.