## 3 Discussion of Results  
The microhardness distribution along all the three considered directions, as well as micro-photography of the pre-existing microstructure states, for welds obtained by both procedures are shown in Figures 5 and 6. Figure 4: Position of the notch on samples for the impact toughness testing: (**a**) along the weld axis; (**b**) in the fusion zone; (**c**) in the HAZ. According to diagram of the microhardness distribution in all directions, for the MMA/MAG procedure sample (Figure 5), it is evident that the microhardness measured values did not exceed the critical values of the brittle structure formation, which is in accordance with the fact that no brittle structures of microstructural states were recorded in the micrographic analysis. The fine-grain and coarse grain zones were present in the HAZ along all the directions and are common for a large number of welding procedures by melting. In direction _I-I_ the coarse grain bainite microstructure with quenched martensite was registered at the spots close to the fusion zone. In the HAZ, close to the parent metal, a favorable fine-grain ferrite-pearlite structure with bainite was registered. The slightly higher microhardness was registered in the weld metal as compared to the microhardness measured in the HAZ, while the microstructure was assessed as the coarse grain bainite with a higher share of martensite, which correlated with measured microhardness values (Figure 5b). The measured microhardness values in direction _II-II_ were lower than those in specific zones in direction _I-I_ and didnot exceed the critical values relevant for the brittle microstructural states. The lower microhardness values resulted from the microstructure relief due to the heat input from the filling passes of the multiple-pass welding. The coarse grain microstructure of the HAZ in direction _III-III_ of metallographic samples was bainite without bold acicular structures. The root pass metal weld remained non-erosive during the preparation of metallographic samples due to the high-alloyed filler material used for the root pass, as presented in Figure 5a. The transient zone between the weld metal and the HAZ was characterized as bainite microstructure without acicular tendency, in compliance with the lowest microhardness measured in this zone, as compared to the related values in direction _II-II_[17]. Figure 5: Microhardness distribution and microstructure of the MMA/MAG samples: (a) zone of transition between the weld metal and HAZ; (b) weld metal. Values of the cooling time \(\mathfrak{t}_{8/5}\) were obtained within a range of 5.2 to 12.1 \(s\). Different theoretical formulas predict values that could range from 4 \(s\) (Ito-Bessyo formula) to 65 \(s\) (formula of limited thickness) [24], so the experimentally obtained values were in compliance with theoretically predicted ones. Observed microstructures for the MIG/MAG procedure sample (Figure 6) in direction \(I\)-\(I\) were similar to the corresponding microstructures of the metallographic sample with the MMA/MAG weld. That implies the dominant impact of the filling passes were the same for both group of samples, namely the MIG/MAG and MMA/MAG welds. The microstructure in the fine-grain HAZ along direction \(I\)-\(I\), as in the case of the MMA/MAG welded joint, was fine-grain pearlite with a possibly smaller share of bainite. In the coarse grain HAZ, the dominant was coarsened grain bainite microstructure with a possible share of a quenched martensite. The microstructural state in the coarsened grain HAZ along direction \(III\)-\(III\) for the MIG/MAG procedure was assessed as bainite microstructure without expressed acicular orientation (Figure 6,b). The position of the fusion zone of the weld metal of the root and filling passes pointed to the largerheight of the root pass in the MIG/MAG weld than in the MMA/MAG one, whichwas adequate for the geometry of the welding grooves and common practices.