THE LEVEL OF PLASTICITY OF THE PHASES IN NON-METALLIC INCLUSIONS WITH A COMPLEX STRUCTURE

Purpose. It is necessary to study of the effect of heterophase inclusions on the technological ductility of steels for various purposes. The goal of the work was to study of the nature and level of plasticity of multiphase inclusions in steels under conditions of hot and cold deformation. Methods. Comprehensive methods for the study of heterophase non-metallic inclusions (metallographic, petrographic, X-ray microanalysis methods) were used. Results. Plastic phases in multiphase inclusions of different types under conditions of hot and cold deformation of steels were investigated. It is shown that each type of multiphase inclusions, which are microcomposite formations in steels, is characterized by its laws of development of deformation processes, which are determined by their chemical and phase composition, structure, deformation ability of the phases of inclusions. Scientific novelty. Peculiarities of plastic behavior of multiphase inclusions of different types are established. The inhibitory effect of non-deformable phases of inclusions on the deformability of plastic phases in a wide range of steel deformation temperatures is established. Peculiarities of the nature of plasticity of multiphase inclusions having different compositions and structure are discussed. Practical significance. Using the results obtained will allow developing technologies for producing steels with regulated content and types of multiphase non-metallic inclusions, which will significantly increase their technological plasticity, as well as prevent the formation of various kinds of defects during the processing of steels by pressure.

ANALYSIS OF DIFFERENT ENVIRONMENTS INFLUENCE ON COPPER ALLOYS CORROSION RESISTANCE

Purpose of this work was to establish relationship between corrosion damages depending on chemical composition, as well as external factors affecting copper and copper alloys in different operating conditions corrosion. Methodology. Object of analysis was actual normative and technical database on standard and prospective copper-based alloys compositions for operation in aggressive environments (atmosphere, gases, salts and alkalis solutions, aqueous mediums). Comparative analysis method in order to substantiate the prospects of special bronzes implementation for manufacture of machines and mechanisms corrosion-resistant parts has been used. Results and discussion. Copper alloys behavior in different operating conditions has been analyzed and factors causing their destruction have been considered. Corrosion damaging relationships with chemical composition, as well as external factors affecting corrosion have been demonstrated. Information on copper alloys corrosion rate in different environments has been given. Issues of copper alloys rational uses in relation to parts and constructions peculiar working conditions have been presented. Relevant information on copper alloys products problem of reliability and durability increasing, one of which solving methods is purposeful choice of material for their manufacturing depending on operating conditions, has been given. Practical value. According to research results, effective practical using of technical copper, brasses, tin, silicon, aluminum, nickel bronzes have been substantiated in terms of their resistance to corrosion damages features. Conclusions. It has been established that copper alloys are characterized by high corrosion resistance in different environments. In marine and ocean environments aluminum bronzes corrosion resistance exceeds in some cases all other copper alloys resistance. It has been concluded that aluminum bronzes and copper-nickel alloys have the highest corrosion resistance among copper alloys.

THERMODIFFUSION SATURATION OF THE SURFACE LAYERS OF α-TITANIUM BY OXYGEN, NITROGEN, CARBON

The purpose of the study is to analytically assess the depth of the gas-saturated zone in the case of a single-component diffusion saturation of alpha-titanium with nitrogen, oxygen and carbon from a rarefied controlled gas environment. Results. Based on the analysis of the literature data, the work schematically shows the interaction of alpha titanium with the elements of implementation and presents the processes with the corresponding parameters that characterize. It is shown that the surface impurity concentration is equal to the equilibrium concentration and is established instantly and does not depend on time. Consequently, with the proposed generalized nonstationary boundary condition in the absence of diffusion of impurities into the volume of the metal, the time dependence of its surface concentration is given, determined by the intensity of surface processes. The dependence of the relative change in the microhardness in the diffusion zone of titanium due to dissolved nitrogen (without taking into account the contribution of nitride inclusions) is presented. Analytically calculated concentration profiles of nitrogen generally correlate well with the distribution of the corresponding relative changes in microhardness in the surface layer. Analytical calculations of the concentration profiles of oxygen, nitrogen and carbon in titanium at a saturation temperature of 700 °C are presented. Practical value. The results obtained will make it possible to preliminarily estimate the size of the fortified near-surface layer depending on the parameters of chemical-thermal treatment and select the optimal parameters of thermal diffusion treatment to ensure the formation of reinforced layers on products made of alpha-titanium based on elements of interstitial in order to increase the functional properties.

STRUCTURE AND PROPERTIES OF ROLLED STEEL AFTER SKIN-ROLLING ACCORDING TO DIFFERENT TECHNOLOGICAL PRODUCTION SCHEMES

Problem statement. Development of an effective technology for the skin-rolling will allow the production of hot-rolled sheet products with quality indicators that meet the requirements of standards for cold-rolled sheets. Consumers with significant economic benefits will be able to use relatively inexpensive hot-rolled sheets instead of expensive cold-rolled sheets. The purpose of the article: establishment of the effect of skin-rolling to various technological schemes for the production of hot rolled fine and thickness rolled for cold stamping on the structure and properties of the metal. Conclusion. The patterns of the formation of the structure and properties after skin-rolling of hot rolling sheet steel and plate steel for cold stamping are established. It is shown that with an increase in the degree of deformation during skin-rolling in the unit cutting unit, there is a decrease in the plasticity of hot-rolled plate steel strips of low carbon steels. As a result of heat treatment and skin-rolling on a separately located mill of hot rolled, thin-sheet low carbon steel, the plasticity of the metal rises and a homogeneous structure is formed in accordance with the requirements of ДСТУ 2834-94. Obtaining hot-rolled thin-sheet steel with quality indicators at the level of requirements for cold-rolled metal will allow the use of hot-rolled steel instead of cold-rolled one, which will ensure an increase in labor productivity and savings electricity.

SMOOTH AND REDUCED OIL AND GAS PIPES WITH INCREASED CORROSION RESISTANCE

Formulation of the problem. Corrosion of pipes used in the oil and gas industry leads to significant economic losses, therefore, increasing their corrosion resistance and durability is an urgent task. Purpose: generalization of results of developments of technologies of manufacturing and research of qualitative characteristics of oil and gas pipelines (smooth) and pump-compressor (threaded) pipes of the increased and high corrosion resistance and giving recommendations on their application in oil and gas industry in environments of various corrosion aggressiveness. Methodology. The microstructure of tubular steels and protective coatings was studied by light metallography and electron microscopy. Complex corrosion studies included laboratory tests of samples in model chloride and hydrogen sulfide-containing media, the resistance to sulfide corrosion cracking under stress (SCCS) and hydrogen cracking (НС) according to the methods of NACE TM 0177 and NACE TM 0284 as well as operational tests at the oil fields of Ukraine. Mechanical properties for stretching and impact bending of samples by standard methods. Results. The results of the development of production technologies and the study of the qualitative characteristics of oil and gas pipelines and tubing with increased and high corrosion resistance in aggressive oil and gas production environments are summarized. The influence of the chemical composition of steels and protective coatings, as well as pipe manufacturing technologies on their microstructure, corrosion resistance in various media, and mechanical properties is shown. Scientific novelty. For the first time, the presence of special low-energy boundaries in the ferrite of low-alloy ferrite-pearlite and high-alloy ferritic-austenitic steels was established, their number and energy level were estimated. The high operational reliability of threaded pipes with a protective coating is substantiated. Practical value. The results of the work and recommendations for the rational use of oil and gas pipes with increased corrosion resistance can be used to increase the economic efficiency of production in the oil and gas industry.

INVESTIGATION OF THE CAUSES OF UNSATISFACTORY RESULTS OF ULTRASOUND CONTROL OF EXPERIMENTAL FORGES FROM AUSTENITE HIGH-ALLOY STEEL

The purpose of the work is to establish the main causes of defects by ultrasonic testing (UST) of experimental forgings made of high-alloyed austenitic steel 08Kh18N10T on the basis of comprehensive comparative studies of samples of defective and suitable forgings. Techniques. Chemical analysis of forgings was performed on a high-sensitivity spectrometer "SPECTROMAX" company "SPECTRO", Germany; studies of macro- and microstructure (liquation heterogeneity, grain boundary structure, non-metallic inclusions, excess phases, etc.) were carried by the methods: metallographic and electron microscopic with micro-X-ray spectral analysis; tests of forgings for durability against intergranular corrosion (IGC) were carried out by the methods of AMU, GOST 6032. Results. It was established that experimental forgings rejected by UZK, in contrast to suitable forgings, were characterized by: the presence of areas of liquation inhomogeneity of steel, including high content of δ-ferrite; local defects of the macrostructure in the form of flocs; areas with anomalous multi-grained microstructure with a grain size of –2 to 8 points according to GOST 5639; release of chromium carbides at the boundaries of austenitic grains; susceptibility to intergranular corrosion (ICC). All forgings contained non-metallic inclusions within the permissible limits according to GOST 1778, as well as titanium carbides. Scientific novelty. For the first time on the basis of complex researches it is proved that the main reason of unsatisfactory results of UZK of experimental forgings from high-alloyed austenitic steel, is the anomalous multigrain structure connected with the unstable temperature-deformation mode of forging of ingots. Practical significance. Recommendations for improving the structure and improving the quality characteristics of industrial forgings made of high-alloy austenitic steels in terms of industrial production have been developed.

ABOUT TECHNOLOGICAL FEATURES OF PRODUCTION OF REINFORSING BARS FROM PEARLITE GRADE STEELS

Formulation of the problem. In the production of coiled rolled products from perlite grade steels, metallurgical enterprises encounter with the sorting of some batches of continuously cast billets or commercial products due to non-compliance with regulatory requirements. One of the alternative ways of using such blanks can be their reassignment for the production of thermally hardened reinforcing bars. In accordance with the edition of GOST 5781-82, it was possible to produce hot rolled reinforcing bars from steel grade 80C (carbon content 0,74…0,82 %), and according to TU 14-15-339-94 – thermally hardened with a carbon content of 0,50…0,85 % C. In world practice, reinforcing bars of a strength class similar to classes A800…A1000 (DSTU 3760:2019) are made mainly of high-carbon steels. The main type of stressed reinforcement in the EU, USA, Canada and Great Britain are rods with a nominal diameter of 26…40 mm of strength class 835…1030 MPa and 26…36 mm of strength class 1080…1230 MPa. An analysis of the requirements for reinforcing bars according to various regulatory documents shows that in the standards of Canada, the USA and the UK, the carbon content is not standardized, but according to the standards of Japan and Ukraine it is 0,45…0,80 % and 0,13…0,37 % respectively. According to the requirements of international standards, the minimum values of the yield strength and strength correspond to the reinforcing bar A800 (DSTU 3760:2019). Therefore, for the possibility of producing reinforcing bars from high-carbon steels, it is necessary to establish rational temperature-time conditions for heat hardening modes, which will ensure that the finished metal products comply with the requirements of DSTU 3760:2019. Purpose. Determine the influence of the parameters of the technology of thermal hardening on the features of the formation of the structure and mechanical properties of reinforcing bars made of steels with a carbon content of 0,50…0,90 %. Results. The possibility of producing reinforcing bars of strength classes А800 and А1000 from steels С56DВ, C70DВ, C80DВ and C82DВ (EN 16120-2:2017) using intermittent and interrupted quenching methods has been scientifically proven. In accordance with the results obtained, the industrial production of reinforcing bars of strength classes A800 and A1000 from these steels is expedient, since it will contribute to the improvement of technical and economic indicators in the production of coiled steel from perlite grade steels intended for high-strength products (cold-worked rebar, metal cord, bead wire, spring wire, reinforcing ropes, etc.). Based on the results of industrial experiments, a technical agreement was developed and approved for the production of pilot batches of thermally hardened reinforcing bars of strength classes A800 and A1000 from steels containing 0.50...0.90 % carbon.

CALCULATION OF A MONOLITHIC COLUMN FOUNDATION FOR A REINFORCED CONCRETE COLUMN OF A MULTI-STOREY BUILDING IN LVIV

Problem statement. In modern construction of residential and commercial buildings, bridges and other structures, columns are often the main load-bearing elements. Different in the way they are manufactured and in their characteristics, these building elements serve as the basis of the framework on which all other building structures are placed. However, in order to have a strong, durable and, most importantly, correct construction of the whole structure, the columns should be installed with minimum deviations from the design values. This is why a great deal of attention is paid to the foundations in the design and implementation of the project. The purpose of the article is to develop a calculation of a monolithic column foundation for a reinforced concrete column of a multi-storey building in Lviv based on theoretical research. The design is based on theoretical studies and is based on the design of a monolithic column foundation for a multi-storey building in Lvov, taking into account the dimensions of the foundation, the soil characteristics, the self-weight of the foundation and the longitudinal reinforcement coefficient. Analysis of publications. Studying not only foreign, but also domestic current theoretical developments and practical experience will allow the objective to be achieved. There are examples among European countries that largely meet the current requirements. Results of the study. The most common soils in Lviv are chernozem, eluvial and peat-bog soils. The climate in Lviv is moderately continental with mild winters and warm summers. With these data, the dimensions of the monolithic columnar foundation for a multi-storey building are calculated and its reinforcement is determined. The strength of the monolithic columnar foundation for the reinforced concrete column of the multi-storey building is tested for the punching strength. Based on the results of the calculations, it is determined that the foundation is sufficiently strong under the column.Conclusions. In this article, the characteristics of soils and climatic conditions of the construction area in the city of Lviv were investigated. The dimensions of the foundation's underside, all dimensions of the foundation and the pressure on the ground under the underside from the design load were calculated. The reinforcement area of the foundation footing was selected and the strength of the foundation was tested for push-through.

Mechanism for choosing organizational and technological solutions based on integrated management of the construction process

Problem statement. The introduction of new requirements for rationing in the construction industry provides for changes in the rationing methodology, through the use of a predominantly parametric method. This stimulates the use in management of modern approaches, methods and mechanisms, technologies, innovative organizational and technological solutions to improve the quality and volume of construction, which in turn can accelerate the recovery from the crisis and the development of the construction industry as a whole.The use of the parametric method, in addition to the certain advantages indicated above, creates new challenges for the efficiency of management in the construction industry. On the one hand, there is an increase in the alternatives of possible managerial and organizational and technological solutions; identification of the list and consequences of risks for each alternative; improvement of the procedure and processes for predicting the consequences of each of the alternatives; putting forward new requirements for the information necessary for decision-making, the possibilities of its analysis and interpretation.On the other hand, the use of such a selection mechanism and the lack of clear requirements and orders can increase the costs of achieving the declared quality and reliability requirements of the construction object, and accordingly increase financial and organizational and technological risks. This creates the preconditions for the use of integrated management with the use of appropriate organizational and technological solutions that can satisfy both the requirements of quality management and risk management in construction. Purpose of the article − describe and substantiate the possibility of applying the mechanism for choosing organizational and technological solutions aimed at achieving parametric criteria as target indicators for managing construction processes in conditions of uncertainty using a functional model of a system-integrated approach. Conclusion. It has been substantiated that for an effective process of managing construction processes within an integrated approach, in conditions of uncertainty, it is necessary to use a system-wide algorithmic mechanism, which will ensure the coordination of control functions, their parallel and continuous execution within individual processes, the choice and decision-making in emergency situations for a minimum possible time period.This requires the compliance of each organizational and technological solution with the established criteria and the possibility of their comparison, in order to select the most effective in terms of leveling risk, achieving efficiency − in relation to their cost; and criteria for feasibility, assessment of the impact on quality indicators, implementation in time, competence and technological feasibility − in relation to their ability to implement. Keywords: construction process management; rationing; parametric method, integrated approach; processapproach; situational approach; a mechanism for choosing organizational and technological solutions

Principles of certification of metals for susceptibility to brittleness by the criterion of critical strength

Problem definition. Existing evaluation system of liability to brittle fracture is based on specifying the critical temperature Tc of ductile/brittle transition for specimens with stress concentrator (SC) and uses relative values of impact toughness (KCV, KCU) and widening (ψк). Thus the Tc becomes relative and it is not possible to measure brittleness or embrittlement degree for specimens with SC. Paper purpose. Neutralize the system faults of evaluation system of liability to brittle fracture of constructional alloys with SC. The concept is to change the KCV (KCU) or ψк parameters by critical strength parameter (ϭ0,2с at Tc). Conclusions. Fracture of the specimen with SC (ϭNF) on YTS (ϭ0,2с) at Tc (or room TR) as embrittlement criterion is proposed instead of relative values of (KCV, KCU) and (ψк). The ϭNF / ϭ0,2 = BrNF ratio is a degree of reliability for specimen with SC (BrNF > 1) or embrittlement measure (BrNF < 1). The BrNF value is a quantitative measure of the fracture resistivity of the specimen with SC or crack. Correlation ratio between Br and BrNF for each type of SC has been found. It allows to use the calculation of embrittlement liability based on metal strength for test of metals without full scale tests of metal specimens with SC. Keywords: embrittlement; fracture degree; fracture resistivity; critical temperature; critical strength; strengthreliability of the specimen with SC