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

Steels which are utilized in the manufacturing of specific parts of military technology such as crankshafts of engines in heavy-duty vehicles or barrels of guns must be subsequently modified by heat treatment according to the requirements of customers. Despite the hard surface of martensitic structure obtained by hardening process, steels have a low wear resistance and high values of coefficient of friction. To improve these parameters and due to the fact that many of steels which are utilized for manufacturing of mentioned parts are also categorized as Nitralloy steels, in this paper, the improvement in these properties of chosen steels by the application of plasma nitriding has been studied. The steel equivalent 17Ni4CrMo (i.e., CSN 41 6720) and equivalent 42CrMo4 (i.e., CSN 41 5142) were chosen for the study. The chemical composition of chosen steels was verified by optical emission spectrometry. The microstructure and the diffusion layer were observed by optical microscopy due to the evaluation of layer parameters important for the lifetime. ZWICK ZHU 2.5 was used for a measurement of the universal hardness of the surface and values of graphs of microhardness were obtained by the device LM 247AT LECO from a cross-section of samples. The coefficient of friction was determined by Bruker CERT-UMT-3 with a ball-on-disc method. The parameters of wear paths were obtained by Talysurf CLI 1000. After the application of plasma nitriding technology, the hardness of both steels was rapidly increased in comparison with non-nitrided samples. According to the comparison of coefficients of friction with respect to the parameters of the measurement, the coefficient of friction of nitrided samples decreases with increasing temperature, which is essential knowledge for the weapon industry, especially the construction of bore barrel.

This paper deals with the effect of selected cutting parameter values in machining of OCHN3MFA steel on AFM and SEM microstructural analysis, cutting forces, nanohardness, 2D and 3D surface roughness, and material removal rate of surface layers after machining. OCHN3MFA steel was selected and used to perform experiments. Firstly, the selected steel was investigated before machining tests, due to the checking of the initial microstructure and chemical composition. The microstructure was performed on the Tescan Vega TS 5135 scanning electron microscope (SEM) with the X-ray microanalyzer Noran Six/300, and the Oxford Instruments MFP-3D Infinity atomic force microscope (AFM). Chemical composition was analyzed on Tasman Q4 surface analyzer. All machining tests of the used samples were performed under the selected cutting parameters in the SU 50A lathe machine tool with the CNMG 120408-M5 cementite carbide cutting insert clamped in the suitable DCLNR 2525M12-M cutting tool holder. During the machining process of testing samples, individual components of cutting forces were measured on a Kistler 9257B piezoelectric dynamometer with their subsequent evaluation using software Dynoware. Other experiments following the machining process were performed, evaluating the effect of selected cutting parameters on surface hardening. Surface hardening after machining of testing samples was subsequently measured on Hysitron TI950 Triboindenter with a Cube Corner measuring tip and evaluated by software Triboscan. 2D and 3D surface roughness and material removal rate (MRR) were finally performed on Talysurf CCI Lite and evaluated by software TalyMap Platinum.

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 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.

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.

CoCrMo alloys have been used for biomedical implants for a number of years. One of the important parameters which influences durability of the coating and thus whole implant are parameters of surface texture, namely Ra and Rt, which are determined by standards ISO 7206-2:2011 and ISO 7207-2:2011. Three duplex surface systems were applied to improve mechanical properties. The combination of plasma nitriding and subsequent deposited thin films of the nACo 3 ®, DLC and ZrN were used as a duplex treatment. Plasma nitriding was implemented under these conditions: duration time 10 hours, the ratio of gases H 2 :N 2 =3:1, process temperature 450 °C, 500 °C and 550 °C. The surface texture parameters were measured on the polished surface of the CoCrMo alloy at first, then on the polished surface after plasma nitridation process and finally on the polished surface of deposited coating. It has been demonstrated that deposition of the selected coatings on the nitride surface influences the surface texture parameters Ra and Rt.

This paper deals with possibilities of acoustic emission method utilization as an online surveillance tool for improvement of identification of structural damage onset in composite materials. With employment of AE method we are able to localize the degraded areas in stressed components and subsequently estimate the extent of degradation. In experimental part the piezoelectric sensor was employed for continuous record of emission signals, continuous processing and analysis of measured data and monitoring of stressed material feedback on applied mechanical load in real time. Partial results from distinctive areas of conducted research were implemented in this method, especially detection of emission signals and analysis of recorded signals in both frequency and temporal zones. Samples were reinforcement of 6 layers aramide-carbon weave 0/90° of specific mass 180 g/m2.In total 7 samples were tested in monoaxial tension on universal testing apparatus ZDM 5/51 with acoustic emission measurement recording in course of testing.