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.

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.