## 3 Results
### Secondary Phases  
The as-deposited GMAW passes with higher-than-recommended arc energy (GH) showed the lowest presence of nitrides and no nitrides in some cases, despite having remained longer times at the critical temperature ranges. The as-deposited GMAW passes with recommended arc energy (GR) showed the highest presence of nitrides and the FCAW with recommended arc energy was in between. The root pass (GTAW) in the GR weld contained significant amounts of nitrides after only 6 s in the critical temperature range (Figure 10; Left). By far this pass showed most nitrides in the as-deposited pass compared to any other experiment. The first pass in the FR and GH welds presented a nitride-free microstructure despite the fact that they experienced longer times in the critical range. The cooling rate (based on the cooling time t\({}_{12/8}\)) of the root GTAW pass was the same as the cooling rate of the  
Figure 8: Ferrite content (Y-axis) measured by magnetic permeability pass by pass to evaluate the influence of the successive reheating on the ferrite content. A progressive reduction in ferrite content was observed in the weld metal. For better clarity of the reduction in ferrite, dotted lines show a linear regression of ferrite content in specific weld metal passes (Weld Pass 1 in the GH and GR welds and Weld Pass 4 in the FR weld). “WM pX” means the weld metal deposited in Weld Pass X.  
Figure 9: Micrographs of Weld Pass 1 in the GH weld. (**Left**) As-deposited. It shows Widmansätten austenite laths within the ferrite matrix. (**Right**) After six reheating cycles. Widmansätten austenite laths grew (an average of 4 μm thicker) and secondary austenite (small needle-shaped) was formed in the intragranular areas of the ferritic matrix. second GMAW weld pass (38 \({}^{\circ}\)C/s), which did not present nitrides (Figure 10; Right). However, the average size of the ferrite grains in the second GMAW weld was 87 \(\upmu\)m +/\(-\)12 \(\upmu\)m, whilst in the root GTAW pass it was 147 \(\upmu\)m +/\(-\)35 \(\upmu\)m.  
Regarding the HAZ, nitrides were found in the HAZ of all the passes. In the low-temperature heat-affected zone (LTHAZ), they were concentrated at a distance from the intergranular austenite, but also along the primary ferrite grain boundaries and in the \(\delta\)/y boundaries (Figure 11). The largest LTHAZ was found in the GTAW pass (root pass) of the GR weld, with nitrides found up to 2 mm from the fusion line. In the high-temperature heat-affected zone (HTHAZ), nitrides were mainly seen in the ferrite. Secondary austenite was only found in the reheated HTHAZ of the GH weld produced with higher-than-recommended arc energy. In that case, the secondary austenite was found in the former nitride locations (Figure 12). Figure 11: Preferential locations for precipitation of nitrides in the HAZ: primary ferrite grain boundaries, \(\delta\)/y boundaries and in the ferrite grains. Figure 10: Influence of the grain size on the nitrides precipitation. First and second passes in GR weld cooled at the same cooling rate (38 \({}^{\circ}\)C/s). (**Left**) Root pass (GTAW) showing significant amounts of nitrides after only 6 s in the critical temperature range. Average ferrite grain size was 147 \(\upmu\)m. (**Right**) Second pass (GMAW) not presenting nitrides after 6 s in the critical temperature range. Average ferrite grain size was 87 \(\upmu\)m.  
One general trend observed in all the experiments was that only one reheating cycle was enough to promote the formation of secondary austenite regardless of the time that the material was experiencing temperatures higher than 500 \({}^{\circ}\)C. What seems to be a key factor in the secondary austenite formation was the previous presence of nitrides in the ferrite matrix of the as-deposited pass and the number of reheating cycles experienced, which in turn was connected to the weld pass sequence layout (Figure 1), described in Section 3.5.