Physical Metallurgy and Heat Treatment of Metals

RESEARCH OF PRODUCTION TECHNOLOGY AND PROPERTIES OF THE BLADE IS MADE BY THE MINE WELDING METHOD

2023-10-20T19:33:20+03:00

Problem statement. One of the main requirements for the blade is to achieve significant indicators of corrosion resistance and elasticity, the ability to withstand lateral and contact loads. Thanks to the combination of high-carbon and stainless steels with the help of pit welding, the effect of zone hardening is achieved in the subsequent heat treatment. Zone hardening technology is a combination of different hardness indicators on one knife blade, which leads to a significant increase in the elasticity and durability of the blade, reduces the risk of hardening cracks. Mine welding allows you to combine into a composite steels that have a high content of carbon (С = 0,9…1 %, С = 0,4…0,45 %) and chromium (Cr = 13…14 %), which with an ordinary electric arc method is practically impossible to do. High carbon equivalent and chromium doping complicates existing welding processes. With the appropriate modes of thermoplastic deformation, we get in the zone of forge welding a monolithic connection of two steels at the atomic level, which in itself is already a composite (combination of two materials with different properties to obtain a third starting material). Materials and methods. Etching the blade in an acid solution. To obtain blanks for blacksmithing (pit welding), we took steel bar ШХ15Ш (ТУ141594 DSTU4738:007) Ø – 20 mm, length L − 80 mm for the cutting part of the blade, steel bar 40Х13 DSTU 7838:007, for covers Ø − 20 mm, L − 150 mm. The total weight of the package is 0,42 kg. The results of the experiment. When conducting four experimental attempts to determine the tempering temperature-time regimes for a composite knife blade (ШХ15Ш in 40Х13 facings), the following parameters were obtained: 1. heating temperature 260…270 °С; 2. exposure for 1,8…2 hours; 3. cooling − air. The hardness of the blade is 58−59 HRC, the cutting part is 52−54 HRC of the coating. With such indicators, the maximum indicators of wear resistance of the cutting edge and high indicators of blade elasticity were obtained. For steel n690: 1. heating temperature for tempering 200…220 °С; 2. exposure for 1 hour; 3. cooling − air. Conclusions. Knife blades are proposed to be made by manual forging, without the use of pneumatic and hydraulic hammers, to ensure the purity of the experiment. The work includes calculations of heat treatment regimes, analysis of the microstructures of the obtained monosteel and composite, economic feasibility, advantages and disadvantages of one method of obtaining a blade blade over another.

CALCULATION OF MATERIAL QUALITY CRITERIA USING FRACTAL THEORY

2023-10-20T20:24:46+03:00

Problem statement. Changing the parameters of standard technology can significantly change the properties of rolled iron in a wide range of values. Regulatory and technical industry documentation regulates only the hardness indicators of cast iron rolls, and the requirements for mechanical characteristics and wear resistance are not indicated due to the influence of many technological parameters. Therefore, an important aspect is the prediction for quality indicators of cast iron due to the use of mathematical modeling, in particular the theory of fractals. Materials and methods. Cast iron rolls with a pearlite matrix were studied. The mechanical properties of the working area for cast-iron graded rolled rolls produced by OJSC “Dniprovskyi zavod protnykhnykh valkov”, Dnipro, were determined on standard equipment using INSTRON and CD-40 machines, PSV 5 pendular digger, Shore hardness tester. The microstructure of the rolls was analyzed at a magnification of 200 times. The results of the experiment. As a result of the experiment, it was established that the best among analyzed sensitivity of mechanical properties to dimensional characteristics of carbides is observed for fractal, information and correlation dimensions. Therefore, it is advisable to use these dimensional estimates of carbides in the future to predict the mechanical properties of the working zone for rolled iron with lamellar graphite. To predict the mechanical properties of rolled cast iron with lamellar graphite, it is advisable to use dimensional estimates of graphite and carbides with an increase in the structure of ´200. Conclusions. The analysis of the obtained results showed the promise of using the theory of multifractals for the quantitative assessment of the structural elements of rolled cast iron rolls with a complex geometric shape. This approach makes it possible to use statistical estimates of the dimensions of graphite and carbides to predict and correct the quality indicators of roll metal according to the obtained equations (3-6) along with traditional methods of quantitative metallography, which evaluate their geometric characteristics: shape, distribution, dimensions (length, diameter) and content.

IMPROVING THE WEAR RESISTANCE OF ECONOMICALLY ALLOYED STEELS

2023-10-20T21:16:59+03:00

Problem statement. The influence of wear on the formation of a “white band” in metastable austenitic, martensitic-austenitic and secondary hardening steels of the Cr−Mn−Ti system, additionally alloyed with Mo, B, V, is studied. The influence of structure and phase composition on the wear resistance of economically alloyed metastable and secondary hardening steels is shown. Results. Surfacing of the studied materials was conducted in copper molds with different rates of forced cooling. Metastable austenitic, martensitic-austenitic and secondary hardening steels of the Cr−Mn−Ti system additionally alloyed with Mo, B, V are studied. Additional alloying of these steels with titanium in an amount of 2...5 % contributed to the prevention of spalling along the fusion zone. Near the fusion line there is a base metal zone with a width of 7...15 µm. After testing at the volume temperature of the working part of the specimen Т_V= 553…573 K in the contact volumes for deposited metal of the 30Cr2W8V type, broadening of the grain boundaries, shear lines, finer grains compared to the underlying layers are revealed. Outside the zone of plastic deformation, the size of the grains corresponds to their sizes before the start of testing, the grain boundaries are relatively thin. The number and location of carbides observed at X430, X80O magnifications are also similar to the structural characteristics for deposited metal of the 30Cr2W8V. At close values of the contact pressure in the friction pair, the time of formation of a crack of critical length increases with an increase in the effective surface energy γе (including the energy of plastic deformation). Thus, the crack resistance indices (CR, j-integral, δ_С) and, consequently, the wear resistance of maraging steels are higher than those of metastable and tool steels. Conclusions. The conducted studies confirm the possibility of the formation of a "white band" both in alloys with a high concentration of elements − austenitizers (Mn, C, Ni), and when alloyed with carbide-forming elements with a relatively low affinity for carbon (V, Mo). The crack resistance indices (CR, j-integral, δ_С) and, consequently, the wear resistance of maraging steels is higher than those of metastable and tool steels.

ON COMPETING PROCESSES AT THE INCLUSION – MATRIX BOUNDARIES DURING STEEL ROLLING

2023-10-20T21:34:02+03:00

Purpose of the work – to study of the processes that determine the interaction of non-metallic inclusions and the steel matrix during steel rolling. Methods. The behavior of inclusions was studied during hot rolling of steels 08Yu, 08T, 08kp, NB-57, 08GSYUTF in the temperature range of 1 200...900 °C and cold rolling with degrees of deformation of 35...75 %. The study of hot slipping along the boundaries of the inclusion − matrix was observed during high-temperature (900...1 200 °C) deformation by stretching in a vacuum on the IMASH-5S installation with a gripper movement speed of 1 680 mm/min. According to the study of slipping, steel samples were stretched in a vacuum at temperatures of 25...900 °С on the IMASH-5S installation with a gripper movement speed of 2 000 mm/min. On the surface of the samples, using the PMT-3 device, reference points were applied near the 0° and 90° inclusion poles on both sides of the inclusion − matrix boundary. Research methods are given in works [10; 11]. Identification of inclusions was carried out by metallographic (Neophot-31), petrographic and micro-X-ray spectral (MS-46 Cameca) methods. Results. It is shown that during plastic deformation, there is an interaction between non-metallic inclusions and the steel matrix, which determines their joint plastic shape change and is associated with the development of competing processes at the inclusion − matrix interphase boundaries: interphase friction and slipping (hot or cold depending on the deformation temperature). The mechanisms of these processes are determined depending on the deformation conditions and the level of plasticity of non-metallic inclusions and the steel matrix. Scientific novelty. The peculiarities of interphase friction and hot and cold slipping along the inclusion − matrix interphase boundaries of steel under different conditions of plastic deformation have been established. It is shown that the mechanisms of each of these processes depend on the temperature regime of deformation, the level of plasticity of the inclusions and the steel matrix, as well as on the structure of the inclusion − matrix boundaries, which determines the possibilities of movement and interaction of interfacial defects. It is shown that the specified processes determine the level of plasticity of the inclusion − matrix boundaries and significantly affect the nature of the change in shape of the inclusions and their redistribution in the steel matrix during steel rolling, which inevitably affects the technological plasticity of steels. Practical significance. The use of the results obtained will make it possible to develop technologies for producing steels with regulated types of nonmetallic inclusions, which will significantly increase their technological characteristics, as well as prevent the formation of various kinds of defects during the processing of steels by pressure of products.

STRUCTURE AND PROPERTIES OF THE ETRINGITE PHASE

2023-10-20T22:08:35+03:00

Problem statement. Aluminate and sulfoaluminate cements are not produced in Ukraine, despite a rather significant need for binders of this class. The use of imported raw materials is limited by the high cost and certain disadvantages occurring during exploitation including rapid hardening, significant heat generation, which is associated with instability of some sulfoaluminates. At the same time, it is possible to highlight the following problems in the direction of expanding possibilities of using special cements of this type: stabilization over time and operating conditions of the hydrosulfate phase based on alumina cement, as well as modification of the compositions of mineral binders based on calcium sulfate dihydrate (CaSO₄·2H₂O) and development of binders of this class based on secondary production products. The main factor is that during hydration of sulfoaluminates and aluminates in the presence of gypsum (CaSO₄·2H₂O), a hydrosulfoaluminate phase is formed, which makes it possible to obtain a hardened cement paste structure with special properties. Then monocalcium hydrosulfoaluminate turns into hydrosulfoaluminate of the low-sulfate form С₃А·СaSO₄·12H₂O with the release of gibbsite Al₂O₃·3H₂O. Also, ettringite С₃А·СaSO₄·nH₂O and 2(С₂S)·nH₂O is formed and hydrated calcium silicate CSH(B) can be formed. When gypsum is added to cement, ettringite is formed in this system. Etringite is one of the components. It is not formed initially, but through intermediate structures. During hydration reactions, ettringite is rearranged, neoplasms are formed, which can lead to gypsum corrosion. Etringite loses its stability. Herewith, the problem of primary and secondary ettringite arises. Primary ettringite creates conditions for strength. Secondary ettringite is formed already in the hardened system and leads to internal stresses. Formation of secondary ettringite can have both positive and negative consequences. The purpose of the atrticle is to investigate structure and properties of the ettringite phase. Conclusions. The hydration process depends on the Gibbs surface energy. Change in surface energy depends on the CaO/Al₂O₃ ratio. It was established that the surface energy increases with an increase in the CaO/Al₂O₃ ratio. The paper has studied influence caused by the ettringite phase on the main characteristics of alumina cement and gypsum in a modified gypsum binder. Studies have been conducted on formation of the maximum amount of ettringite phase. We have calculated the maximum amount of the ratio of alumina cement and gypsum to obtain the maximum amount of mineral – 70 % alumina cement and 30 % gypsum. The highest effect is achieved during the simultaneous use of С₆АṤ₃Н₃₂ and АН₃, which occurs during hydration of С₄А₃Ṥ. Taking into account the above, it is advisable to obtain clinker containing calcium sulfoaluminate and cements based on it.

FEATURES OF THE STRESS-DEFORMED STATE OF VERTICAL CYLINDRICAL TANKS UNDER EXTERNAL PRESSURE

2023-10-20T22:25:17+03:00

The paper investigates the features of the stress-deformed state of cylindrical shells under wind pressure, taking into account its actual distribution on cylindrical structures. The purpose of the work is to obtain a qualitative picture of the distribution of stresses and deformations in the cylindrical wall of the tank under wind load, to determine the effect of wind load on both the strength and stability of the tank. Practical significance. It is known that the stresses caused by the action of the wind load, due to their small value, are safe from the point of view of strength, at the same time, obtaining quantitative values of the stress-deformed state main components of the tank under wind load has a certain practical significance. The task is to solve the problem of deformation of the cylindrical shell under external uneven pressure of the wind type. Content of research. The solution of the deformation problem was performed in a linear formulation for cylindrical shells with geometric parameters corresponding to the geometric parameters of vertical tanks with a volume of 1,000…30,000 m³. The solution of the problem was carried out for several loads of the shell with wind pressure of different intensity q = (0,2…1,2) q_crw. Such formulation of the problem made it possible to investigate the features of the stress-deformed state of cylindrical shells under wind pressure both at small values of the external load and at pressure values close to the critical ones, which is important from the standpoint of shell stability. Conclusions. The static calculation of the shells under wind pressure showed that membrane stresses in the annular direction prevail. Membrane stresses in the meridional direction are the second largest. The distribution of these stresses along the perimeter of the shell corresponds to the wind pressure plot. The main feature of the bending stress graphs is their wave character along the perimeter of the shell. Plots of radial displacements w and deformed shells also have a wave character. The size of such wave deviations is insignificant, but their length is close to the length of the waves of the shell protrusion when it loses its stability. Thus, the process of deformation of cylindrical shells under wind pressure is generally stable. The wind load itself is safe from the strength point of view. However, the obtained nature of the deformation, namely the wave deviations of the surface of the shell, can significantly affect the stability of the shell, which requires additional research.

ACADEMICINS OLEKSANDR PETROVYCH CHEKMAREV AND KYRYLO FEDOROVYCH STARODUBOV – OUTSTANDING INTELLECTUALS OF TECHNICAL THOUGHT OF THE DNIPRO REGION

2023-10-20T23:29:25+03:00

Problem statement. Ukrainian academicians O.P. Chekmaryov and K.F. Starodubov is known not only in the Dnipro region, but also in Ukraine, Europe and the world. The achievements of their intellectual genius are relevant to this day. The purpose of the article. Is to demonstrate the importance of the creative heritage of scientists in our time using the example of the analysis of the patent funds and technical department of the regional library. Conclusions. Intellectuals of technical thought, academicians O.P. Chekmaryov and K.F. Starodubov left quite a legacy to the next generation of national scientists. In particular, in the patent funds and technical department of the Dnipropetrovs’k Regional Library, more than 100 security documents are freely available, which testify to the depth of the technical genius of scientists in the form of copyright certificates and patents. However, only funds since 1967 have been open to the general public. And even in this somewhat limited form, the legacy of scientists is impressive in its scale. The material presented in this article will primarily be useful for those interested in the history of the development of the national metallurgical science.

MODELLING THE INFLUENCE OF WELDING MODES ON THE MECHANICAL PROPERTIES OF WELDED JOINTS

2023-10-21T12:00:09+03:00

Introduction. Welding is one of the most common and effective methods of joining metal structures, which is used in many industries, from the automotive to the oil industry. However, in the process of welding, the joints are subjected to significant thermal and mechanical loads, which can lead to defects and a decrease in the mechanical properties of welded joints. The main part. Modelling the influence of welding modes can be performed using various methods, such as mathematical modelling based on the laws of physics and mechanics, experimental studies of welded joints and their analysis, or a combination of these methods. Basically, finite element methods, boundary element method, finite difference method, and hybrid modelling method can be applied, where, for each individual element of influence on welding, the most effective method of mathematical modelling is used. It is considered what software can be used for modelling a mathematical model. The methods of experimental research used to determine the mechanical properties of a welded joint are analyzed. The methods of comparing experimental data to the mathematical model are also analyzed. Conclusions. The basic methods of mathematical modelling of welding, methods of experimental research, and comparison of the obtained data of the mathematical model with the conducted research have been considered. Based on the comparison, it is possible to find out how a particular welding mode will affect the quality of the welded joint.

INVESTIGATION OF THE STRUCTURE AND PROPERTIES OF FERROUS NICKEL ALLOYS AFTER MOLDING BY SELECTIVE LASER MELTING

2023-10-21T12:22:43+03:00

Problem statement. The selective laser melting method is a promising technology for the production of parts from heat-resistant alloys. Traditional methods of manufacturing such parts require additional technological equipment and processing, which increases the time of production preparation and, as a result, to the creation of a large number of raw materials. Selective laser melting allows you to produce parts of a complex configuration without the need for additional equipment. Molding of parts using additive technologies, which ensure a reduction in product preparation time, mechanical processing operations, and an increase in the efficiency of material use. Their application in the technological cycle of manufacturing products is an urgent task today. However, before the introduction into the technological process of forming products from heat-resistant alloys by the selective laser melting method, it is necessary to carry out a comprehensive analysis of the mechanical and technological characteristics of the material and its microstructure, which affects the final properties of the parts. The purpose of the article. Investigation of the possibility of implementing the selective laser melting method for the production of parts from strong alloys, analysis of the mechanical characteristics of the material, as well as the microstructure, which affects the final properties of the parts. Conclusions. Studies have shown that the selective laser melting method is effective for the production of complex parts from heat-resistant alloys. The obtained data on the mechanical properties after heat treatment of the Inconel718 alloy demonstrate its compliance with the requirements of the AMS 5662 standard and its suitability for working under extreme conditions. In the microstructure, highlighted features are revealed, which are characteristic of the selective laser melting method, as well as the presence of visible tracks and a special texture − elongated grains in the direction of growing parts. Research points to the potential of additive technologies in improving technological processes and properties of alloys for the production of heat-resistant alloy parts.