## 1 Introduction  
Welding, particularly of parts made of high-strength low-alloyed steels, is a very complex process. There are numerous parameters that make the welding process complicated. The high-strength low-alloyed steel (HSLA) producers usually prescribe the relevant welding parameters to be applied in welding of these steels. They are considered as conditionally weldable, which means that certain special measures must be applied that would provide for the successful execution of the welded joints. It is also a known fact that welding, due to changes in their microstructure, causes degradation of otherwise exceptional mechanical properties of those steels. The changes are especially prominent in the heat-affected zone (HAZ) of the welded joints. They cause increase of stiffness and brittle to ductile transition temperature, while simultaneously causing decrease of toughness. In addition, due to the fast cooling of the butt weld, it is possible for brittle phases to appear, as well as cracks within the welded metal, since the cooling is done within the temperature limits characterized by the largest instability of austenite. Due to all of these factors, it is necessary to consider all the aspects of the applied welding technology, with all the possible negative effects that it can cause. The impact toughness of a welded joint is defined as its ability to permanently deform while absorbing the energy before fracturing, i.e., it is the amount of energy the welded joint can take before cracking. The general objective is thus to increase the impact toughness of the welded joints, whichis influenced by several factors, namely the welding procedure parameters. The first is the filler metal, i.e., the properly chosen filler metal can provide for good impact toughness of the welded joint and minimize the extent and rate of cracking. Using such a filler metal, with an appropriately selected welding procedure, can prevent cracking of the welded structure altogether. Besides the adequate filler metal and the welding procedure, aninfluencing parameter is the shielding gas. The rule for obtaining satisfactory impact toughness of the welded joint is to use the shielding gas recommended by the manufacturer for the particular combination of the base and filler metal. The heat treatments are also very important factors. The preheating of the base metal, as well as maintaining the proper interpass temperatures during the welding, are of the utmost importance. The slow cooling rate of the welded joint can minimize the problems of inadequate microstructure of its different zones, which can negatively affect the impact toughness of the whole structure. The post-welding heat treatment is aimed at relieving the residual stresses that appeared during the welding. In this paper, the emphasis is on the influence of the welding procedure on impact toughness of the welded joint of the high-strength low-alloyed steel, i.e., the comparison was performed of the two combinations of the welding procedures for executing the single V butt multi-pass welded joints of such steels. Problems related to welding of steels were subjects of research of numerous authors. Here presented is only a brief survey of some of those research results, mainly related to the study of the impact toughnessof HSLA steel welded joints. Authors in [1] analyzed the influence of morphology of martensite-austenite constituents on impact toughness of HSLA steel welds in the inter-critically reheated coarse-grained heat-affected zones and concluded that slender constituents are more destructive to joint toughness than massive ones. Application of super-martensitic stainless steels (SMSS), characterized by good weldability, for fabrication of onshore and offshore pipelines, was considered in [2]. The welded areas of the SMSS pipes can be exposed to stress corrosion cracking. Apost-weld heat treatment was proposed consisting of holding the welded joint for 5 min at about 650 \({}^{\circ}\)C, to eliminate that risk.