International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

It is well known that there are several ways to make a butt weld depending on the thickness of the plates to be welded. This paper shows how important it is to prepare the surfaces to be joined by welding. In this paper, the 15 mm thick plates, made of mild steel S235JR, were welded face-to-face with a K-weld using the MIG welding method. The preparation of the plates before welding was not satisfactory, according to empirical instructions, and the resulting weld has defects. Four plates were welded face to face, resulting in two welds. The welds cooled in different ways after welding, one was cooled more slowly in air, and the other was cooled more quickly in water. After welding and cooling the welds, a metallographic analysis of the microstructures of the welds was carried out, and then their hardness was measured using the Vickers method. The conducted metallographic tests concluded that the heat-affected zone has a fine-grained structure, and the melting zone has a cast structure. After the hardness measurement, it can be seen that the hardness values in both the melting zone and the heat-affected zone increase from the root to the surface of the weld. Finally, a strength calculation was performed to determine how much static and dynamic alternating force the realized welded K-joint can withstand compared to the ideal value with good surface preparation

Investigations of wear resistance and tensile strength of steel products with diffusional zinc coating obtained in zinc powders with a nanocrystallized surface of powder particles were carried out. The effect of the structural state of the coating on the wear resistance and adhesive grasping with a steel counterbody was established. The prospects of the nanogalvanizing process to improve the strength of steel products are shown.

The development of technologies in modern machine building aims at improving the mechanical and technological properties of the materials. The present study presents an improvement in the mechanical properties of low carbon steels by thermoffusion coatings with nanofibers obtained under different heat treatment regimes. Depending on the type of heat treatment and the size of the zinc particles, different gradient layers can be obtained in depth. This of course reflects positively on the chemical resistance of the material. In addition, it positively affects the mechanical properties of the material by increasing mechanical strength and technological properties by improving the resistance to plastic deformation. With these first studies, there is an impetus for another look to improve the properties of low-carbon steels that are widely applicable in the field of machine building.

For many years casting alloys are widely used in dental applications. Among them, titanium and its alloys reveal the best properties for this purpose. However, the casting is difficult but it may be improved by alloying. This research deals with titanium-based alloys with zirconium additions. Investigated alloys were prepared by melting and casting in an electro-arc furnace under argon atmosphere. In order to identify the phases present in alloys, structural analysis was performed by X-ray diffraction method. It was showed two-phases microstructure of alloys. Further, zirconium addition in higher percentage contributes to formation of the beta phase of titanium which possesses more adequate properties then alpha titanium. Microstructural observations by scanning electron microscopy and energy-dispersive spectrometry showed that phases have similar chemical composition. Measured Vickers hardness values were lower than for pure titanium and are acceptable for dental applications.