Experimental Investigation of Heat-Affected Zone Development, Hardness Distribution and Mechanical Performance of Gas Metal Arc Welded Low-carbon steel under Variable Process Conditions

This study investigated the influence of three gas metal arc welding (GMAW) parameter combinations on heat-affected zone (HAZ) development, hardness distribution, and mechanical properties of mild steel. Weld integrity and mechanical performance were evaluated using macroscopic examination, tensile testing, Charpy impact testing, Vickers hardness testing, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDX). The results showed that the mean HAZ width increased from 2.5 to 3.8 mm (52%) across the investigated welding conditions as the calculated heat input increased. The highest mean ultimate tensile strength (UTS) was recorded at a heat input of 0.768 kJ/mm, whereas the highest individual UTS value occurred at 1.080 kJ/mm. The intermediate heat-input condition produced the highest mean Charpy absorbed energy (90.0 ± 5.0 J) and impact energy per unit fracture area (1.11 ± 0.06 J/mm²). Mean hardness increased slightly from 196.33 to 203.60 HV10 across the investigated conditions. SEM–EDX analysis revealed variations in surface morphology and local elemental composition between the HAZ and base metal, with iron remaining the predominant metallic constituent. Macroscopic examination revealed no visible gross weld defects. These findings demonstrate that the investigated GMAW parameter combinations produced measurable differences in HAZ width and mechanical performance. Within the experimental conditions examined, the parameter combination corresponding to 0.768 kJ/mm provided the highest mean tensile strength, while the intermediate heat-input condition exhibited the highest mean impact toughness indicator. However, because only three combined parameter settings were evaluated, the observed differences cannot be attributed exclusively to heat input or generalised to other welding conditions. The study highlights the importance of selecting appropriate GMAW parameters to balance tensile strength, impact resistance, and HAZ characteristics in mild-steel welded joints.