The article presents test results concerning the structure of welds made of high strength low-alloy steel 14HGNDC which, in the molten state, was provided with nanoparticles of various refractory compounds including oxides, carbides and nitrides (TiC, TiN, SiC, VC, NbC, TiO₂, Al₂O₃, MgO and ZrO₂). The performed tests revealed the effective use of the nano-oxides of titanium (TiO₂) and zirconium (ZrO₂) enabling the obtainment of high mechanical properties of the weld metal (R_m -708 MPa and 621 MPa, KCV_-20 - 60 J/cm² and 72,9 J/cm², a – 21 and 19%). The use of a Gleeble 3800 welding cycle simulator made it possible to determine the dependence between temperature ranges of transformations, amount of structural constituents and types of modifying nanoparticles.