## 4 Conclusions  
Welding of the high-strength low-alloy steel S690 QL was considered in this paper, namely the influence of the welding procedure on some properties of the welded joints of this steel. Application of steel of this grade in the welded structurescan be observed from two aspects: its mechanical behavior in exploitation, and applied technology for execution of the welded joints. The latter aspect was considered here by analyzing the two different procedures for the butt multiple-pass welding with a V-groove configuration, which is usually applied for welding of thicker plates. Actually, the welding plan combined three procedures in order to determine which combination of the two of them would provide essentially favorable microstructures, which is a basis for structural integrity and response to loads of the whole welded structure. The selected procedures represent welding procedures ordinarily used in industrial practice; the MIG or MMA processes were used for the root passes, combined with the MAG process that was used for the filling and covering passes. Each of the two combinations of procedures was characterized by metallographic testing of the relevant samples. Mechanical characteristics and responses to load during the impact toughness tests point to a significant deterioration of mechanical properties of the observed S690 QLsteel as a result of the applied welding procedures. Microstructures of specific zones of welded joints, assessed by metallographic methods, were expected and are in agreement with theoretical observations. Experimentally determined values of the fracture energy of samples with a notch in the fusion zone were higher for the MMA/MAG weld than for the MIG/MAG welds. This is a consequence of different welding groove geometry, taking into account that all the other parameters were the same. However, the shape of the groove did not have such a prominent influence for the other cases of the notch position, i.e., for the other zones of the welded joint. The mechanical response to load of samples with a notch in the zones of fusion for both the MMA/MAG and MIG/MAG welds is in mutual accordance during the crack initiation, formation and growth until the final fracture. As the fracture energies of both considered MMA/MAG and MIG/MAG welds, for samples with a notch in the HAZ, were approximately equal, it can be concluded that the welding procedure had no influence on the fracture energy of those test samples in the researched conditions. Experimentally obtained values of the fracture energy of those samples were smaller than values obtained for samples without the welded joints, made of the parent metal. This confirms the fact that welding causes a decrease of the fracture energy of the parent metal. The mechanical characteristics during the fracture of samples with a notch in the HAZ of the considered MMA/MAG and MIG/MAG welds were in mutual accordance until the final fracture as well. In the case of the MMA/MAG welding procedure, values of fracture energy of samples with a notch on the root pass side were higher than the corresponding values experimentally obtained on the test samples with the MIG/MAG weld. Thus, it can be concluded, concerning this aspect, that applying the MMA/MAG welding provided joints with more favorable characteristics. However, obtained values of the fracture energy of samples with the MMA/MAG and MIG/MAG welds were smaller than the fracture energy obtained for samples made of the parent metal. The fracture energy values for both considered welded joints were nearly equal; accordingly, it can be concluded that the welding procedure did not influence the fracture energy of samples with a notch in the HAZ on the side of the root pass, under the testing conditions. The samples with the MIG/MAG welded joints did not express the termination zones of the fast crack growth during the testing, as it was observed for samples with the MMA/MAG welded joints. Experimentally obtained results correspond to the relevant literature sources [28; 29; 30; 31; 32].