## 3 Results and Discussion
### Mechanical Properties  
The tensile test was performed on as-received base metals and the weld joints, two samples were tested in each condition and the average value was reported. The tensile test samples after test are shown in Figure 9. The tensile strength and elongation of the microscale flux weld sample was 630.8 MPa and 21.5%; and the tensile strength and elongation of the nanowire flux weld sample was 700.23 MPa and 34.1%, respectively. Whereas, the tensile strength and elongation of HMS base metal were measured as 850 MPa and 50%, respectively. It was observed that the strength of the nanowire flux weld sample was similar to the HMS base metal and had a much higher elongation parameter than the microscale flux welded sample.  
Figure 8: SEM microstructure of the fusion zone, HAZ and base material of nanoscale Fe\({}_{2}\)O\({}_{3}\) flux weldments: (**a**) fusion zone \(1\); (**b**) fusion zone \(2\); (**c**) fusion zone \(3\); (**d**) heat-affected zone (HAZ); (**e**) base metal.  
The joint efficiency of the microscale flux was calculated as:  
\[\text{Joint efficiency}=(\text{Strength of welding sample})/(\text{Strength of HMS})=630.8/850\times 100\%=74.2\%. \tag{3}\]  
The joint efficiency of the nanowire flux was calculated as:  
\[\text{Joint efficiency}=(\text{Strength of welding sample})/(\text{Strength of HMS})=700.23/850\times 100\%=82.38\% \tag{4}\]  
However, the percentage strain obtained for both welds was lower than the base metal. The increased tensile strength and reduced ductility of the A-TIG welds was attributed to the martensitic formation and larger grain size. Moreover, the hardness result (shown in Figure 10) is also in good agreement with the microstructure studies, as larger grains possess a lower hardness. The increased hardness (higher than base metal) in the A-TIG weld zone and part of HAZ was attributed to its microstructural transformation from austenitic to martensitic. The other part of HAZ has lower hardness due to the tempering of the existed martensite caused by the weld thermal cycle and absence of lath martensite.  
SEM images of the tensile test fracture surfaces among welding zone are shown in Figure 11. The fracture surface of the as-received base metal (Figure 11a), the TIG welding  
Figure 10: Microhardness profiles along X direction (nanowire flux).  
Figure 9: Tensile stress vs. tensile strain curve for the nanowire flux and microscale flux weld joint.  
joint without flux (Figure 11b), and the A-TIG with microscale Fe\({}_{2}\)O\({}_{3}\) flux and nanoscale Fe\({}_{2}\)O\({}_{3}\) flux weldments failed from the welding joint (Figure 11c,d) were found dissimilar in morphological nature. Multiple fine dimples were observed on the fracture surface from the base metal, which indicates strong tensile strength and elongation. The sizes of the dimples were calculated and proved to be different. First, the base metal had the finest size of dimples (average 3.52 \(\upmu\)m). As for the normal TIG welding without flux, it had a larger average dimple size (5.76 \(\upmu\)m) than the base metal, which may arise from the coarsening grain size in the welding zone. There are some fine dimple zones coexisting with big size dimples in the conventional TIG weld joints. For the A-TIG welding sample fracture surfaces with either micro- or nanofluxes, both have larger dimples than the TIG welding samples since the higher heat input increased the grain size among the welding zone. However, the nanoscale Fe\({}_{2}\)O\({}_{3}\) flux sample has finer average dimple sizes (6.02 \(\upmu\)m) than microscale Fe\({}_{2}\)O\({}_{3}\) flux sample (7.67 \(\upmu\)m). This is consistent with the data which the nanoscale Fe\({}_{2}\)O\({}_{3}\) flux welding sample has higher elongation compared with microscale one.