No 9 (147) (2023)

The topicality of the research is occasioned by exaggeration of working conditions of products used at high temperatures and made of heat-resistant sheet alloys, including in particular austenitic chromium-nickel steels. When steel parts under load are operated in an oxidizing atmosphere and aggressive environments, besides resistance to electrochemical and gas corrosion, they require increased strength, hardness, and heat resistance. The increase in the characteristics of these proper-ties is achieved by three-dimensional and surface hardening techniques, which include the nitration process. The applica-tion of traditional technologies of furnace gas nitriding for chromium-nickel steels is complicated due to the problems of the low rate of the nitrogen saturation, which significantly increases the process time, and the formation of chromium nitrides, which negatively affects corrosion and heat resistance. The development of new technologies for nitrogen hardening of high-alloyed chromium-containing steels is carried out in the direction of saturation process intensification and regulation of the phase composition of the nitrided layer to minimize the formation of chromium nitrides. The article is aimed at defin-ing rational technological options and modes of gas austenitic nitriding of austenic steel, making it possible to increase strength characteristics at RT and higher temperatures without sacrificing its heat resistance. Thermodynamic modeling of the phase composition based on the CALPHAD technique shows that primary ways for minimizing the release of chromium nitrides on the nitrided surface are to increase the concentration of titanium in steel and to reduce the activity of the saturat-ing gas atmosphere, which is achieved by inert gas dilution of nitrogen. Experimental studies were carried out on sheet samples of 1.5 mm thick austenic steel of the type X18N10T with a standard (0.5%Ti) and increased (1%Ti) titane content. The experiments were carried out on a laboratory installation for high-temperature nitriding (900.1200 °); pure nitrogen and mixtures of nitrogen with argon were used as saturating media. Two-stage processes consisting of nitrogen hardening in nitrogen followed by argon afterburning were also investigated. Metallographic analysis showed that at the same nitrid-ing temperature, the amount of chromium nitrides decreases in experimental steel with an increased titanium content, and dilution of nitrogen with argon reduces the temperature of chromium nitride release. According to the study of saturation process kinetic, the time of through-the-thickness nitriding of a sheet sample under different saturation modes was deter-mined, as well as the duration of de-nitriding annealing, calculated on the basis of the known thickness of the chromium nitride zone. It was found that the dispersion hardening of the zones of internal nitriding with titanium nitrides leads to an increase in the strength characteristics of steels both at RT and higher temperatures compared to the characteristics of base steel 08X18N10T after typical heat treatment, while the greatest hardening effect is achieved due to through-the-thickness nitriding of steel with 1%Ti. Recommended options for the processes of through-the-thickness nitriding of 1.5 mm sheet of experimental steel: tn=1050 ℃, N2, 16 h; tn= 1100 ℃, 50%N2 + 50%Ar, 22 h; tn=1100 ℃, N2, 5 h + tann=1200 ℃, Ar, 9 h. The temporary passive hardness of nitrided steel at RT increases by 45...50%, and when tested at 800 ℃ - by 40... 65%, de-pending on the process mode. Through-the-thickness nitriding makes it possible to raise the working temperature of steels by 100.150 ° with the same long-term strength. The heat resistance at 900 ℃ remains at the level of non-carbonated steel after two-stage processes that ensure maximum chromium nitrides removal from the surface at the annealing stage.

The problem of mechanical technology design for machining parts in granulated media in the conditions of digital produc-tion is viewed. The peculiarities of part process in abrasive media and with steel balls (finish- machining and strengthening treatment techniques) are shown. Dependences for determining the parameters of a single interaction of a medium particle with the surface of a part during processing in granulated media are obtained. Dependences for depth maximizing in cases of particle penetration into the surface of the machined part, the parameters of a single trace, surface roughness, processing time are found. For finish- machining and strengthening treatment techniques for granulated working media, dependences for determining the depth of the hardened layer and the degree of deformation are also obtained. The obtained theoretical dependences have been tested for adequacy through drawing an analogy with the results of experimental studies. During the research, it was found that the developed system of models does not take into account the peculiarities of various processing methods and their dynamics, and shape of the particles of the medium. To account all these parameters, the Rocky DEM ap-plication software package is used. The package allows modeling the processing chamber, the dynamic parameters of the machining process, the number of particles in the working space according to their mass, the shape and dimensions of the particles, the mass and shape of the machined part and its location in the processing chamber, the material of the machined part, the ratio of the mass of the part and the mass of the abrasive medium, some physical properties of the material of the processed part, slip coefficient of the abrasive medium on the part surface, process liquid properties and other parameters. The package made it possible to refine theoretical models and obtain results closer to production conditions. Based on the research carried out and being aimed at their introduction into modern digital production, the design technique of techno-logical processes has been developed and a software product has been proposed allowing to select possible working meth-ods in granulated media (in order of preference) according to the characteristics of the part, and to determine the technolog-ical modes for each of them and characteristics of working environments.

An urgent problem for improving the efficiency and machining operation quality for new polymer composite materials (PCM) based on carbon fiber in the operation of rocket and space equipment and aircraft engineering parts is solved in the article. One of the breakthroughs of the Russian domestic engineering is the introduction of wing elements of the new MS-21 civil airliner, the production of noise suppression bodies, compressor blades and other parts of gas turbine engines made of carbon fiber, requiring high-quality and productive machining. Machining operation of these products involves difficulties caused by the requirements of the design documentation to ensure the necessary degree of roughness, soundness of the machined surface and high strength of the finish-machined component. This article presents the results of a study of the application of high-performance technology of sequential blade-abrasive processing of carbon fiber-based PCM products. This article presents the results of a study of the application of high-performance technology of sequential blade-abrasive operation of carbon fiber-based PCM products. The rational geometry of the blade cutting tool for primary machining of the PCM is determined. An adequate empirical mathematical model of cutting modes influence on the surface layer roughness in the milling operation has been developed, as well as rational processing modes have been determined. The results of experimental studies of the abrasion of PCM with rigid grinding wheels made of white electrocorundum, green silicon carbide and elborum are presented. The dependences of the surface layer roughness on the grinding modes are given. According to the research results and the developed mathematical model, the rational characteristics of grinding wheels and processing modes are determined. For the first time, the issues of the influence of machining defects on the strength of PCM are viewed. Comparative tensile and tear strength tests of samples made by traditional edge cutting machining and sequential edge-cutting-abrasive operation are presented. The increase in tensile and tear strength of PCM parts manufactured according to the technology of sequential edge-cutting-abrasive operation by 20.30% compared to traditional edge-cutting operation has been proved.

. Technological aspects of digitalization of machine-building production at the stage of pre-production engineering process (PEP) are viewed. Research methods: an exhaustive study of the basic concepts of the PEP defined by standardized documentation - national standards forming the basis of a unified system of technological documentation. It is shown that the formal transition to digital production chains the phenomenon of transformation of basic concepts - the main emphasis is on the modeling technologies at the price of production technologies. As a result of the analysis of EP stages in accordance with standardized documents, the EP digitalization peculiarities are shown. Research results: for the main design tasks of the technological content, the problems of PEP caused by production digitalization are presented: rational choice problems for processing machinery selection; problems of rational choice of processing methods; rational determination of process specification of production work. It is shown that in the conditions of production, equipped with programm support and hardware facilities for technological equipment control, it is necessary to improve feedback systems for the implementation of operational diagnostics and active control of process system elements for guaranteed product quality assurance. It is shown that the process, methods and means of PEP should be adapted to the conditions of a particular production. It is shown that the tasks of PEP related to the rational choice and assignment of processing conditions should be implemented directly at the operating step. It will allow taking into account in a timely manner the material properties variability for the workpiece and the cutting tool being in the intraprocess. Conclusions: the rational application of the principles of digitalization will allow treating the hardware/ software complex for technological design and control of processing machinery as technological artificial intelligence – the accumulated experience and knowledge of specialists of technological services adapted to the conditions of a particular enterprise.