## 3 Results
### Macrostructural Characteristics and Penetration Depth
Across all analyzed samples, deformations in the shape of the welded circular flanges were minimal, and internal defects observed in the macro-sections were either absent or within acceptable limits. The fusion zones were continuous, with no critical flaws such as cracks, incomplete fusion, or significant porosity. Based on both visual and macrostructural evaluations, it can be concluded that the welds in all samples meet the required quality standards, confirming the effectiveness of the selected arc stud welding parameters and processes. All the macro-sections confirmed continuous fusion zones, minimal deformation of the welded collars, and only minor imperfections, all within acceptable tolerances. According to ISO 5817:2014, all welds meet Quality Level C (Intermediate), with maximum undercut depths below 0.5 mm, no detected cracks or lack of fusion, and only minor acceptable surface irregularities. This level is appropriate for general structural applications where robust, reliable joints are required. Such welds are widely used for general structural steelwork, bridges, buildings, machinery, ship structures, and similar applications where good but not flawless welds are acceptable. The penetration depth (d) of the welded joints was measured from the prepared macro-sections using ImageJ 1.54f software, a validated tool for digital image-based dimensional analysis. Penetration depth was defined as the maximum depth from the stud tip into the base material, as observed in the etched cross-sections. The measured values are listed in Table 6.  
The results show that the ARC CF (ceramic ferrule) method consistently produced the greatest average weld penetration depth. For stainless steel, the maximum penetration reached 3.547 mm, while for structural steel, it was 2.679 mm, confirming the effective heat confinement provided by the ferrule. \begin{table}
\begin{tabular}{l l l l} \hline \hline
**Macro-Section** & **Welding Type** & **Material** & **d [mm]** \\ \hline
3-3 & ARC CF & Steel 1.0038 (S235 JR + N) & 2.679 mm \\
3-5 & ARC CF & Steel 1.4301 (X5 CrNi18-10) & 3.547 mm \\
6-3 & ARC SG & Steel 1.0038 (S235 JR + N) & 1.632 mm \\
6-5 & ARC SG & Steel 1.4301 (X5 CrNi18-10) & 2.383 mm \\
9-3 & ARC SRM & Steel 1.0038 (S235 JR + N) & 2.001 mm \\
9-5 & ARC SRM & Steel 1.4301 (X5 CrNi18-10) & 1.232 mm \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Measured weld penetration geometry of the samples. Figure 3: Macroetched cross-sections of SRM-assisted welded studs: (**a**) sample 9-3 (S235 JR + N, etched with 3% mital); (**b**) sample 9-5 (X5 CrNi18-10, electrochemically etched in 10% oxalic acid), with a visible gas pore circled in red. The ARC SG (shielding gas) method achieved moderate penetration depths with smoother bead contours but lower fusion than ARC CF, due to less arc confinement. The ARC SRM (radially symmetric magnetic field) process produced the most uniform and symmetrical fusion zones but showed the shallowest penetration depths. The stabilizing effect of the magnetic field concentrates the arc at the stud tip and limits excessive heat spread into the base material, resulting in a narrower heat-affected zone (HAZ), which is beneficial for thin plates or heat-sensitive applications. The magnetic field assists in stabilizing arc motion, concentrating heat at the stud tip [26]. Figure 4 presents a boxplot that summarizes the measured penetration depths for each method and material. This visualization highlights the central tendency and variability for each technique. The plot confirms that ARC CF provides the deepest penetration, ARC SG delivers moderate and consistent results, and ARC SRM shows the lowest but most uniform penetration, which aligns with the macrostructural observations and measured values. Heat input and cooling rate control are key to avoiding undesirable phase transformations in the weld metal [27]. These findings indicate that stud welding with a ceramic ferrule yields the greatest weld penetration, enhancing joint strength through deeper fusion with the base material.