## 3 Results  
### Macrostructural Characteristics and Penetration Depth  
Macrostructural analysis was conducted to evaluate the weld bead geometry, fusion zone continuity, and penetration depth for the three arc stud welding methods investigated in this study. Representative macroetched cross-sections for the ARC CF (ceramic ferrule) process are shown in Figure 1. Sample 3-3 (S235)R + N) exhibits a well-formed, continuous fusion zone with deep penetration and no internal flaws. In contrast, the stainless-steel joint (Sample 3-5, X5 CrNi18-10) demonstrates good fusion but shows slightly higher sensitivity to heat input, emphasizing the importance of precise parameter control for austenitic alloys. The macro-sections of specimens 6-3 and 6-5, which correspond to arc stud welding utilizing shielding gas (SG), are depicted in Figure 2. These cross-sectional analyses were  
Figure 1: Macroetched cross-sections of welded joints: (**a**) sample 3-3 (S235)R + N, etched with 3% nital); (**b**) sample 3-5 (X5 CrNi18-10, electrochemically etched in 10% oxalic acid). conducted employing the same metallographic methodologies as those utilized for the preceding specimens, encompassing grinding, polishing, and etching--specifically, 3% nital for structural steel and 10% oxalic acid for stainless steel. Sample 6-3, composed of structural steel (S235 JR + N), displayed a slender yet uninterrupted fusion zone devoid of any discernible internal imperfections. The interface between the stud and the base metal was characterized by a smooth finish, with no indications of lack of fusion, porosity, or inclusions. Nevertheless, no critical defects were detected, and overall fusion quality was acceptable. Conversely, the macro-section of sample 6-5 (X5 CrNi18-10) exhibited a concentration of weld metal at the right margin of the fusion zone (highlighted in the image), likely attributed to the phenomenon of arc blow--a common occurrence in gas-shielded welding of austenitic steels. Notwithstanding this asymmetry, the joint demonstrated commendable penetration and an absence of observable defects such as cracks, porosity, or undercuts. The overall morphology suggests a robust weld that satisfies structural integrity standards, although enhanced arc control may be requisite for improved visual uniformity. The macro-sections of specimens 9-3 and 9-5, which were welded employing the arc stud welding technique in conjunction with a radially symmetric magnetic field (SRM) and shielding gas, are depicted in Figure 3. Consistent with the preceding samples, the metallographic preparation involved meticulous sectioning, polishing to achieve a metallic sheet, and etching utilizing suitable reagents. In the macro-section of specimen 9-3 (S235 JR + N), a slender yet uninterrupted fusion zone is discerned, characterized by a marginally increased central melting, presumably affected by the stabilization of the arc and the effects of gas shielding. The geometry of the weld indicates effective fusion with regulated penetration and the absence of discernible defects, such as porosity, inclusions, or undercuts. Conversely, the macro-section of specimen 9-5 (X5 CrNi18-10) manifests a predominantly uniform and well-established fusion zone; however, a minor gas pore is observable at the center (marked in red), situated within the fused area. This defect is likely attributable to the entrapment of shielding gas during the rapid solidification process, a well-documented hazard associated with the welding of stainless steels under inert gas environments. Notwithstanding this localized imperfection, the overall morphology of the joint remains within acceptable quality thresholds, exhibiting commendable metallurgical bonding and the absence of significant discontinuities. Figure 2: Macrostructure of welded joints: (**a**) sample 6-3 (S235 JR + N); (**b**) sample 6-5 (X5 CrNi18-10). Imperfections are highlighted with red circles.