The most of the research works have been completed with two doctoral dissertations, to wit, on the thermal influences upon the weld metal during the fusion welding of multi-pass welded joints in a Slovene high-strength low-alloy structural steel and on the effects of sub resonant vibrating applied during welding of the same kind of joints in the same steel. The results of the approved hypotheses and the drawn conclusions are independent contribution to the treasury of the world knowledge in the area of phenomena related to fusion welding. It was proven that the fracture properties of welded joints that cannot be imagined without imperfections because of peculiarities of welding processes used in the actual industry depend in different ways on the influences of welding itself and on the effects of the techniques for material relaxation used during welding. It is possible to improve considerably reliability of welded joints with little financing for improving knowledge of the people and diverse simple equipment. The load-carrying capacity of welded structures and the strength of machines manufactured by using welding in high-strength low-alloy structural steels depend on the reliability of welded joints. In the subprogram "Continuous casting of Ni-based superalloys" we have explained processes taking place during each cycle of the the continuous casting of several cast Ni-based superalloys and the influence of casting parameters for obtaining the designed microstructure. The new approach comprising the rapid solidification and internal carbonisation makes possible the fabrication of discontinuous Cu-C composites with submicron dispersion of graphite particles. The internal oxidation of the discontinuous Cu-C composites with submicron dispersion of C-particles caused the formation of submicron bubbles, which have greater specific volume than solid graphite, so they establish the compressive stresses in the Cu-matrix. Research results enable the broadening of fundamental knowledge in the field of the production of composites with very fine dispersion of reinforcing elements, the correlation between technology, microstructure and material properties. Our model for manufacturing of discontinuous metal-matrix composites by joining two or more semi-solid metallic alloys is, at our knowledge, worldwide the first one, employing more than one semi-solid component.