## 4 Discussion  
This research comprehensively investigated the performance of three arc stud welding techniques--ARC CF (ceramic ferrule), ARC SG (shielding gas), and ARC SRM (radiallysymmetric magnetic field)--applied to structural steel (1.0038) and stainless steel (1.4301). An integrated approach combining macrostructural examination, hardness testing, visual inspection, and non-destructive evaluation was used to characterize weld quality, penetration geometry, and defect formation. Weld pool behavior directly reflects the combined effects of process parameters and material thermal conductivity [33]. The main conclusions are as follows:  
1. Penetration depth and fusion quality: The ARC CF method achieved the greatest penetration depths (2.679-3.547 mm) due to effective arc confinement by the ceramic ferrule. ARC SG produced moderate penetration (1.632-2.383 mm) with stable fusion, while ARC SRM yielded the shallowest but most uniform fusion zones (1.232-2.001 mm), minimizing thermal impact.
2. Surface quality and visual defects: Visual inspection confirmed process-dependent surface features: \"hot welds\" in ARC CF due to high heat input, and \"cold welds\" in ARC SG linked to arc blow or gun misalignment. ARC SRM produced the cleanest weld collars with minimal spatter, ideal for applications requiring high surface quality and low post-processing effort.
3. Hardness distribution: Vickers HV10 testing verified that higher penetration correlated with increased weld metal hardness: ARC CF reached up to 295 HV10, ARC SRM up to 256 HV10, and ARC SG up to 235 HV10. These results confirm controlled energy input without undesirable hardness gradients or brittle phases [34].
4. Defects and compliance: Non-destructive liquid penetrant testing, performed in accordance with EN ISO 3452-1:2021, confirmed the absence of surface-breaking defects. Visual and radiographic inspections verified that all welds complied with ISO 5817:2014 Quality Level C, with only minor, acceptable imperfections.
5. Process selection recommendations: \(\circ\) ARC CF is best suited when maximum joint strength and deep fusion are priorities, but demands careful ferrule handling and spatter control. \(\circ\) ARC SG balances adequate penetration and cleaner post-weld surfaces, but requires precise alignment to avoid cold welds. \(\circ\) ARC SRM offers the highest process stability and best surface finish with low heat input, making it highly suitable for thin sections or applications sensitive to heat distortion. Future research should expand on these findings as follows:
* Assessing the fatigue life and cyclic loading behavior of welded studs, especially for ARC SRM specimens [25; 35];
* Refining SRM parameters (current control, shielding gas composition) to increase fusion depth while minimizing porosity formation [36; 37];
* Investigating alternative material combinations and larger stud diameters to validate scalability;
* Applying advanced numerical methods such as finite element modeling to simulate thermal cycles, residual stresses, and phase transformations more accurately [36; 37].  
These directions will deepen understanding of arc stud welding process mechanics and guide further optimization for diverse industrial applications.  
Short cycle arc stud welding also benefits from process optimization strategies similar to those discussed here [25].  
Further parameter optimization could improve fusion depth and reduce defect formation, especially in high-strength steels [38].