The chemical composition of the steel is one of the primary characteristics that influence the mechanical properties of high-stressed machine parts such as barrels of small arms weapon. Heat treatment is the most important technology to reach requested mechanical properties. By a suitable combination of mechanical and tribological properties, it is possible to improve the surface of highly stressed parts as to improve the wear resistance of barrel surface. Thus, surface technology is next step for obtaining new properties as tribological properties or preferable mechanical properties. Due to obtain suitable microstructure and wear resistance the samples of C35, 34Cr4, 37Cr4 and 42CrMo4 were heat-treated with following chemical heat treatment by gas nitriding process, for 6 hours. This paper deals with the influence of alloying elements of structural steels on surface microhardness and depth of diffusion layer. The gas nitriding process caused the creation of a compound layer on the surface of the steel. This layer leads to significant improvement in wear resistance. The concentration of alloying elements was analysed by OES methods. The technology of nitriding was applied to annealed, tempered and quenched steels. After chemical heat treatment, new surface morphology was created. The surface layers of the samples were analysed by microhardness method; surface morphology was evaluated by SEM method. Experimental part concerns structural steels with a concentration of alloying elements to 1 wt.%. In experimental part, the influence of alloying elements on the diffusion process in Fe-C system and the microhardness of the surface was proved.K e y w o r d s : gas nitriding, microhardness, chemical composition, diffusion, barrel

This paper deals with basic methodology of surface evaluation of functional surfaces, which were prepared by various machining methods (turning, milling and grinding). Here are the basic 2D (profile) parameters and 3D (spatial) parameters and their properties in relation to the machined surface. Parameters of machined surfaces were obtained by CCI Lite Coherence Correlation Interferometer from Taylor Hobson and evaluated using the TalyMap Platinum software. The article further demonstrates the inappropriateness of the surface structure assessment with only the parameter Ra (mean arithmetic deviation of the profile), which is the most common method in technical practice. This methodology extends the possibilities of a comprehensive assessment of exposed surfaces of machine parts.

The present article examines special steels used for the production of injection screws in the plastic industry, with a glass fiber content of up to 30%. Experimental materials, M390 and M398, are classified as tool steels, which are produced by powder metallurgy-HIP methods (hot isostatic pressing). The main goal of the presented paper is to propose the optimal tempered temperature of M398 steel and also to compare the tribological properties of both materials and to determine the degree of their wear depending on their final heat treatment. Partial results refer to the analysis of hardness, roughness, the overall wear mechanism, the change in the volume of retained austenite due to the tempering temperature, and the EDS analysis of the worn surfaces in individual contact pairs. A ceramic ball Al2O3 in the α phase was used as the contact material, which had a diameter of 6.35 mm. The ceramic ball performed a rotational movement on the experimental material surface at an elevated temperature of 200 °C using the dry ball-on-disk method. It was experimentally shown that the new M398 material can fully replace the M390 material because it exhibits significantly better tribological properties. The M398 material showed more than a 400% reduction in wear compared to the M390 material. The ideal heat treatment consisted of cryogenic quenching to −78 °C and a tempering temperature of 400 °C. At tempering temperatures of 200 and 400 °C, adhesive wear occurred, which was combined with abrasive wear at a tempered temperature of 600 °C. The averaged coefficient of friction (COF) results show that the M398 material presents less resistance in the friction process and its values are approximately 0.25, while the M390 material showed a COF value of 0.3 after the cryogenic hardening process. The friction surface roughness of the M398 materials also showed lower values compared to the M390 material by approximately 35%. Both of these results are related to the content of M7C3 and MC carbide particles based on Cr and V in the bulk of the material, which are in favor of the M398 material.

The current development of chemical-heat treatment technologies is aimed at increasing the utility properties of components and improving the quality of the produced surface. A prerequisite for a quality produced surface is the selection of a suitable method of surface machining before the application of chemical-heat treatment technology. Due to the requirements for functional areas of special technology, grinding is chosen in most cases. The present paper deals with the effect of nitriding in plasma and gas on the geometric accuracy of parts made of 42CrMo4 steel. This steel is widely used in special technology for the production of barrels, breech-block cases, ball screws and gears. On the ground steel samples, the 3D measurement on the coordinate measuring machine analyzed the change of dimensions after the application of nitriding in plasma and gas. Furthermore, the surface texture change was evaluated using 2D surface roughness parameters and 3D parameters of area. After nitriding in both plasma and gas, the dimensions increased by 0.034 mm in diameter. After the nitriding processes, the values of 2D and 3D surface roughness parameters decreased. A change in surface texture was observed when evaluating 3D parameters in both chemical-heat treatment processes. Increasing the dimensions and changing the texture of the surface affects the subsequent function of the components.

This article deals with the chemical composition and mechanical properties of plasma nitrided layers after chemical-heat treatment process. Experiments are focused on the creation of clusters of nitrogen on the surface of evaluated material. The peculiarity of this experiment is established sophisticated technological process suitable for creation of nitride layers inside cavities with really small diameters. The conditions of the process are designed to provide strictly defined nitride layers with defined parameters. In this case, the nitrided layers were applied to bars of steel 32CrMoV12-10 that were subsequently evaluated by metallographic, GDOES, XRD microanalysis and microhardness methods. The results of measurement showed trends of the chemical composition of alloying elements after chemical-heat treated process through the length of the cavity. Plasma nitriding process was applied for increasing the surface hardness of material in deep cavities. In the evaluation of surface structure the new typical marks on the surface of material after plasma nitriding process were found. Mechanical properties of evaluated material were significantly improved.