Search

In recent years, severe plastic deformation has been one of the most popular methods of increasing the mechanical properties of bars. Obtaining an ultra or nanostructure in such bars provides high strength properties, but also reduces plasticity. This paper shows that gradient structure formation in carbon steel bars gives a simultaneous increase in strength properties and some decrease in plastic properties. A new combined technology is proposed for obtaining gradient microstructure. This technology consists of drawing medium carbon steel bars on a radial-shear broaching mill and subsequent drawing. Bars with 30 mm diameter were strained at room temperature to a diameter of 16 mm in 3 passes. As a result, during three straining cycles, the average value of microhardness in the central zone was 2085 MPa, in the neutral zone was 2505 MPa, and in the surface zone was 2915 MPa. This variation of microhardness confirms gradient microstructure availability. Also there was an increase in strength characteristics almost 2 times, plastic characteristics undergo reduction due to gradient microstructure obtained during straining, but remain at a fairly good level for steel AISI 1045. The validity of the results is confirmed by a large number of experiments using a set of standard and modern research methods, such as optical, scanning and transmission microscopy, EBSD analysis, microhardness changes, fractographic method and tensile tests of mechanical properties, as well as by the results reproduction in the joint use of methods.

Traditionally, structural wire is characterized by a homogeneous microstructure, where the average grain size in different parts of the wire is uniform. According to the classical Hall–Petch relationship, a homogeneous polycrystalline metal can be strengthened by decreasing the average grain size since an increase in the volume fraction of grain boundaries will further impede the motion of dislocations. However, a decrease in the grain size inevitably leads to a decrease in the ductility and deformability of the material due to limited dislocation mobility. Putting a gradient microstructure into the wire has promising potential for overcoming the compromise between strength and ductility. This is proposed a new combined technology in this paper in order to obtain a gradient microstructure. This technology consists of deforming the wire in a rotating equal-channel step die and subsequent traditional drawing. Deformation of copper wire with a diameter of 6.5 mm to a diameter of 5.0 mm was carried out in three passes at room temperature. As a result of such processing, a gradient microstructure with a surface nanostructured layer (grain size ~400 nm) with a gradual increase in grain size towards the center of the wire was obtained. As a result, the microhardness in the surface zone was 1150 MPa, 770 Mpa in the neutral zone, and 685 MPa in the central zone of the wire. Such a symmetrical spread of microhardness, observed over the entire cross-section of the rod, is a direct confirmation of the presence of a gradient microstructure in deformed materials. The strength characteristics of the wire were doubled: the tensile strength increased from 335 MPa to 675 MPa, and the yield strength from 230 MPa to 445 MPa. At the same time, the relative elongation decreased from 20% to 16%, and the relative contraction from 28% to 23%. Despite the fact that the ductility of copper is decreased after cyclic deformation, its values remain at a fairly high level. The validity of all results is confirmed by numerous experiments using a complex of traditional and modern research methods, which include optical, scanning, and transmission microscopy; determination of mechanical properties under tension; and measurement of hardness and electrical resistance. These methods allow reliable interpretation of the fine microstructure of the wire and provide information on its strength, plastic, and electrical properties.

This article presents the results of research on a new combined process involving multi-cycle wire-drawing and subsequent cryogenic cooling after each deformation stage. For theoretical research, modeling in the Deform software was performed. The analysis of temperature fields and the martensitic component in all models showed that for both considered thicknesses, the most effective option is a low deformation velocity and the conduct of a process without heating. The least effective option is to use an increased thickness of the workpiece at an increased deformation velocity and the conduct of a process without of heating to ambient temperature, which acts as a local cooling of the axial zone of the workpiece with an increase in the workpiece thickness. An analysis of laboratory studies on this combined process revealed that in the absence of intermediate heating of a wire between deformation cycles, 100% martensite is formed in the structure. However, if intermediate heating to 20 °C between deformation cycles is carried out, a gradient distribution of martensite can be obtained. And, since the wire has a circular cross-section, in all cases, martensite is distributed symmetrically about the center of the workpiece.

In recent years, severe plastic deformation has attracted the most attention as a way to improve the mechanical properties of steel bars. Obtaining ultrafine grains and nanostructures in such bars leads to a strong increase in strength properties but strongly reduces their plastic properties. This study shows that the formation of a gradient microstructure allows simultaneous improvement in the strength and plastic properties of carbon steel bars, taking into account the symmetry of the microstructure distribution from the center of machining. A new combined technology is proposed to obtain such a microstructure. This technology consists of drawing bars from medium carbon steel on a radial-displacement rolling mill and carrying out subsequent drawing. Steel bars with a diameter of 30 mm were strained in three passes to a diameter of 16 mm at room temperature. The results show that the average value of microhardness in the center, neutral, and surface areas for the three straining cycles were 1890 MPa, 2335 MPa, and 2920 MPa, respectively. This symmetrical distribution of microhardness confirms the gradient microstructure. Strength characteristics also increased almost twofold: the yield strength increased from 330 to 735 MPa, and the ultimate strength increased from 600 MPa to 1025 MPa. Relative elongation decreased from 18 to 14 MPa, and relative reduction decreased from 40 to 31%, but remained at a fairly good level for AISI 1045 steel. The validity of all results was confirmed through numerous experiments using a set of traditional and modern research methods, which included optical, scanning, and transmission microscopy. EBSD analysis allowed precise positioning of the field of vision for studying microstructural changes across the entire bar cross-section. All of these methods used together, including tensile testing of the mechanical properties and the fractographic method, allow us to assess changes in microhardness and the reproduction of results.

The paper studies the evolution of microstructure and mechanical properties of copper wire during a new combined straining process. The main point of the technological process is to strain the wire in a rotating equal-channel step die and subsequent drawing. The die rotates around the wire axis and thereby creates tension due to equal-channel angular pulling and twisting in the die. Transmission electron microscopy and EBSD analysis, as well as tensile testing and microhardness determination investigated the strained copper wire. Ultra-fine grain gradient microstructure with a high component of high-angle grain boundaries was obtained as a result of straining. The tensile strength of the strained copper wire compared to the unstrained one increases more than twice from 302 to 635 MPa, and the yield strength increases from 196 to 406 MPa. The use of such hardened copper wire in construction will reduce the weight of the structure due to the reduction of diameter.

A traditional use of high cumulative reduction ratios is not effective for manufacturing wire with high performance and mechanical properties, since cold plastic deformation reduces the wire diameter, while hot deformation has its own limitations. Thus, thermomechanical treatment of rolled steel has a huge potential to reduce costs and improve product quality when used in the construction industry. Such processing allows metalworking industries to increase the economic effect due to a more complete satisfaction of the requirements for the mechanical properties of finished rolled products. The article developed a new technology for thermomechanical processing of stainless steel wire, consisting of preliminary heat treatment to obtain an austenitic structure and traditional drawing followed by cryogenic cooling. As a result of such treatment, an ultrafine-grained structure was obtained, consisting of a mixture of austenite and α-martensite, with high strength and plastic properties. To analyze the features of the obtained microstructures, modern methods of metallographic analysis were used, such as scanning electron microscopy, transmission electron microscopy, and analysis of backscattered electron diffraction patterns. The microstructure is obtained after deformation at both temperatures and consists of a mixture of α-martensite and austenite. A structure with an average grain size of 0.5 µm was obtained by drawing using cryogenic cooling, and a microstructure of 1 µm was obtained at room temperature. The results obtained allow us to expect an increase in the performance and durability of stainless steel wire, which can be used for various purposes.

This study describes the evolution of the microstructure and mechanical properties of bimetallic aluminum-copper rods during straining by Equal channel angular pressing-drawing (ECAP-drawing). The study was conducted by means of a transmission electron microscope, EBSD analysis, tensile tests and determination of microhardness. The paper shows that an ultrafine-grained copper-aluminum composite with a gradient structure is formed during straining by ECAP-drawing. Microhardness of copper shell during 4 cycles of straining by ECAP-drawing increased from 57 to 165, and hardness of aluminum rod increased from 25 to 75 HV. This is associated with grain refinement and hardening of their boundaries by increasing the density of dislocations. Tensile test diagrams analysis has shown that straining leads to an increase in strength properties of bimetallic wire by 2 times, and as a result the plastic properties are also reduced by almost 2 times, but remain at a level applicable for further use. Application of such bimetallic rods in construction will allow reducing specific quantity of metal per structures without reduction of strength properties.

Currently, the direction of materials’ research, in which the martensitic transformations are observed, is intensively developed. This is due to the fact that, in the martensitic-transformation process, various defects of crystal structure (twins, dislocations, packaging defects, etc.) are formed in many materials, which together with grain fragmentation lead to a significant increase in the strength properties. The widespread occurrence of martensitic transformations has led to the study of the defective microstructure features and changes in the mechanical properties in the martensitic transformation process. This allowed the theory of martensitic transformations to occupy a key place in the science of the structure and properties of crystalline bodies. The operating temperature range of steels of this class is limited from below by their tendency to low-temperature embrittlement (cold breaking) under radiation effects, and from above, by the level of long-term strength (heat resistance). In this regard, today, the increased attention of specialists in the field of condensed matter physics to ferritic–martensitic steels is caused by the need to identify the mechanisms for the formation of microstructures and functional properties of steels stable at operating temperatures, as well as to search for reserves to increase their heat resistance, while maintaining a sufficient plasticity level.

This article investigates the effect of a new processing technology on the change in microstructure and mechanical properties of bimetallic aluminum-copper wire. This technology makes it possible to produce a new generation of wire for use in the construction of new overhead lines and reconstruction of old ones. The study was conducted using a transmission electron microscope, EBSD analysis, tensile tests, and determination of microhardness and electrical conductivity. The results of the study show that an ultrafine-grained copper-aluminum composite with a gradient structure is formed during straining by ECAP-drawing. Annealing after straining at 200 °C increases the strength of the interfacial connection between Cu and Al and improves the strength characteristics of the bimetallic aluminum-copper wire. The use of such aluminum-copper wires for overhead transmission lines allows to reduce the wire cross-section and, accordingly, wind loads, as well as to increase the strength properties without an additional increase in the total weight of the wire.

We study the influence of thermomechanical processing, namely, severe plastic deformation by high-pressure torsion and cryogenic cooling, on the change of the microstructure and mechanical properties of the piston rings made of AISI-316 stainless steel. The deformation of the annular workpieces is carried out in a tool of a new design, the key feature of which is a double helix system. In the first part of the experiment, an estimation simulation of the high-pressure torsion process is carried out in a new matrix design. To estimate the process possibility, the main technological parameters of the process are varied in order to determine the most optimal conditions. Parameters such as the workpiece heating temperature, the upper striker vertical speed, and the friction coefficient at the contact of the workpiece with the tool are selected. The stress–strain state of the annular workpiece during deformation is also studied. At the second stage of the study, a laboratory experiment on the annular blanks deformation is performed. The microstructure evolution and mechanical properties of deformed workpieces after 8 cycles of deformation by high-pressure torsion at cryogenic temperature are studied. All the metallographic studies are carried out using the modern methods such as transmission electron microscopy and analysis of diffraction patterns of back-reflected electrons. As a deformation result, a nanocrystalline structure with a size of 30–40 microns with a large number of large-angle boundaries and a high complex of mechanical properties is obtained. The tensile strength rises from 595 MPa to 1965 MPa, while the yield strength rises from 320 to 1280 MPa. The plasticity value decreases from 55% to 24% as compared to the initial state, but it remains at a sufficient level to be applied.

Traditionally, structural wire is characterized by a homogeneous microstructure, where the average grain size in different parts of the wire is uniform. According to the classical Hall–Petch relationship, a homogeneous polycrystalline metal can be strengthened by decreasing the average grain size since an increase in the volume fraction of grain boundaries will further impede the motion of dislocations. However, a decrease in the grain size inevitably leads to a decrease in the ductility and deformability of the material due to limited dislocation mobility. Putting a gradient microstructure into the wire has promising potential for overcoming the compromise between strength and ductility. This is proposed a new combined technology in this paper in order to obtain a gradient microstructure. This technology consists of deforming the wire in a rotating equal-channel step die and subsequent traditional drawing. Deformation of copper wire with a diameter of 6.5 mm to a diameter of 5.0 mm was carried out in three passes at room temperature. As a result of such processing, a gradient microstructure with a surface nanostructured layer (grain size ~400 nm) with a gradual increase in grain size towards the center of the wire was obtained. As a result, the microhardness in the surface zone was 1150 MPa, 770 Mpa in the neutral zone, and 685 MPa in the central zone of the wire. Such a symmetrical spread of microhardness, observed over the entire cross-section of the rod, is a direct confirmation of the presence of a gradient microstructure in deformed materials. The strength characteristics of the wire were doubled: the tensile strength increased from 335 MPa to 675 MPa, and the yield strength from 230 MPa to 445 MPa. At the same time, the relative elongation decreased from 20% to 16%, and the relative contraction from 28% to 23%. Despite the fact that the ductility of copper is decreased after cyclic deformation, its values remain at a fairly high level. The validity of all results is confirmed by numerous experiments using a complex of traditional and modern research methods, which include optical, scanning, and transmission microscopy; determination of mechanical properties under tension; and measurement of hardness and electrical resistance. These methods allow reliable interpretation of the fine microstructure of the wire and provide information on its strength, plastic, and electrical properties. [ABSTRACT FROM AUTHOR]

In this work the high-pressure torsion process of AISI-316 stainless steel in cryogenic conditions is studied by means of finite element simulation. The stress and strain distributions are analyzed and compared with the ones obtained for ambient temperature. It is shown that the cooling to cryogenic temperature do not affect the equivalent strain distribution significantly. At the same time, the stress values are significantly different - with cryogenic cooling, the level of compressive stresses increases by about 20 %. The simulation of microstructure evolution in Deform-3D program showed that the use of cryogenic cooling makes it possible to further grind the original structure.

This article presents the results of research on a new combined process involving multi-cycle wire-drawing and subsequent cryogenic cooling after each deformation stage. For theoretical research, modeling in the Deform software was performed. The analysis of temperature fields and the martensitic component in all models showed that for both considered thicknesses, the most effective option is a low deformation velocity and the conduct of a process without heating. The least effective option is to use an increased thickness of the workpiece at an increased deformation velocity and the conduct of a process without of heating to ambient temperature, which acts as a local cooling of the axial zone of the workpiece with an increase in the workpiece thickness. An analysis of laboratory studies on this combined process revealed that in the absence of intermediate heating of a wire between deformation cycles, 100% martensite is formed in the structure. However, if intermediate heating to 20 °C between deformation cycles is carried out, a gradient distribution of martensite can be obtained. And, since the wire has a circular cross-section, in all cases, martensite is distributed symmetrically about the center of the workpiece. [ABSTRACT FROM AUTHOR]

One of the promising and little-studied methods for obtaining an ultrafine-grained structure and enhanced mechanical properties is the so-called cryogenic deformation - deformation at temperatures below 120K. It is assumed that low deformation temperatures suppress recovery processes, thus contributing to the accumulation of an extremely high dislocation density and increase internal stresses, as well as activate deformation twinning, which together will accelerate grain refinement. In this regard, in this work, we studied the drawing of steel wire under cryogenic cooling in liquid nitrogen. The results of the laboratory experiment show that the application of cryogenic deformation treatment after wire drawing improves mechanical properties compared to conventional wire drawing. In this case, after two cycles of deformation, the relative contraction after stretching decreases by 8 %, the ultimate strength increases by 40 %, and the conditional yield strength by 26 %. The results show that the deformation conditions during cryogenic drawing are an additional factor for the realization of structural resources of steel wire physical and mechanical properties optimizing. [ABSTRACT FROM AUTHOR]

A new combined deformation technology combining radial-shear broaching and drawing technology is developed in this work, which makes it possible to improve the mechanical and operational properties of carbon-steel bars. As a result, during three straining cycles, the average value of microhardness in the central zone is of 2085 MPa, in the neutral zone, it is of 2505 MPa, and in the surface zone, it is of 2915 MPa. In addition, the strength properties are increased by almost 2 times, the plastic characteristics are reduced not much, but remain at a fairly good level for steel 45 due to obtaining gradient microstructure during straining. [ABSTRACT FROM AUTHOR]

In recent years, severe plastic deformation has attracted the most attention as a way to improve the mechanical properties of steel bars. Obtaining ultrafine grains and nanostructures in such bars leads to a strong increase in strength properties but strongly reduces their plastic properties. This study shows that the formation of a gradient microstructure allows simultaneous improvement in the strength and plastic properties of carbon steel bars, taking into account the symmetry of the microstructure distribution from the center of machining. A new combined technology is proposed to obtain such a microstructure. This technology consists of drawing bars from medium carbon steel on a radial-displacement rolling mill and carrying out subsequent drawing. Steel bars with a diameter of 30 mm were strained in three passes to a diameter of 16 mm at room temperature. The results show that the average value of microhardness in the center, neutral, and surface areas for the three straining cycles were 1890 MPa, 2335 MPa, and 2920 MPa, respectively. This symmetrical distribution of microhardness confirms the gradient microstructure. Strength characteristics also increased almost twofold: the yield strength increased from 330 to 735 MPa, and the ultimate strength increased from 600 MPa to 1025 MPa. Relative elongation decreased from 18 to 14 MPa, and relative reduction decreased from 40 to 31%, but remained at a fairly good level for AISI 1045 steel. The validity of all results was confirmed through numerous experiments using a set of traditional and modern research methods, which included optical, scanning, and transmission microscopy. EBSD analysis allowed precise positioning of the field of vision for studying microstructural changes across the entire bar cross-section. All of these methods used together, including tensile testing of the mechanical properties and the fractographic method, allow us to assess changes in microhardness and the reproduction of results. [ABSTRACT FROM AUTHOR]

The investigation of strain state and microstructure evolution of AISI-316 austenitic stainless steel during highpressure torsion process in the new stamp design was performed. The study using Deform-3D program was conducted. The deformation was carried out at ambient temperature. The results of strain state study showed that after 4 passes the processed workpiece is obtained the level of equivalent strain more than 5. But the distribution of strain has a gradient view in the cross section. The simulation results of the microstructure evolution showed that after 4 passes of deformation the initial grain size of 12 μm can be reduced up to 0,8 μm. But the distribution of grain size in the cross section also has a non - uniform gradient view.

The changes in the properties of copper and its alloys as a result of severe plastic deformation (SPD) are reviewed. The literature review shows that contemporary materials science is aimed at solving the problem of producing ultrafine-grained materials with high-angle grain boundaries. With using of the methods of severe plastic deformation, it is possible to obtain so-called bulk nanostructured materials with grain sizes of 0.1-0.2 microns and specific substructures containing the lattice and grain-boundary dislocations. Such structures are characterised by large elastic distortions of the crystal lattice. It is believed that such fine-grained structures should simultaneously provide a high level of plastic and strength characteristics due to special stressed high-angle grains. The article discusses SPD methods such as torsion with shear, equal-channel angular pressing, screw extrusion, all-round forging, rolling with shear, etc. Among the most significant results of SPD, it is worth highlighting the increase in strength, fatigue resistance and elastic properties of the material. These changes make copper and its alloys subjected to SPD very attractive for use in many industries, including electrical engineering, aviation, medicine, etc. [ABSTRACT FROM AUTHOR]

This work studies evolution of copper microstructure during a combined deformation process. The essence of this process is in deformation of copper wire in a rotating equal-channel stepped matrix with subsequent drawing. Deformed wire is examined using transmission electron microscopy and EBSD analysis. After three cycles of deformation, an ultrafine-grained gradient microstructure with a high component of high-angle grain boundaries is obtained. [ABSTRACT FROM AUTHOR]

One of ways of high-quality processing of metal billets is drawing of a lengthy wire. But at modern technology of processing total reductions during the drawing of billet into a wire are rather big (up to 99.2 %) that demands carrying out additional intermediate heat treatments. Therefore, increase in strength and plastic properties of metal without intermediate heat treatment with saving of necessary final characteristics of a wire at improvement of already existing technologies is the perspective direction of development of metal working. In this paper, the deformation of a wire made of Fe37-3FN steel by ECAP-drawing is carried out. It is shown that as a result of large deformations, the grain structure of the metal reached the UFG level, and the wire itself was highly textured, both due to a very high level of deformations, and due to the lack of intermediate annealing, the latter is dictated by energy and resource saving. It was found that after deformation by the ECAP-drawing method, the wire has an increased reserve of plasticity in comparison with the traditional drawing process, which allows its further processing with high degrees of deformation without intermediate annealing. [ABSTRACT FROM AUTHOR]

Copyright of Eurasian Physical Technical Journal is the property of E.A. Buketov Karaganda University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The effect of high-pressure torsion process in a new die on the structure and mechanical properties of corrosionresistant steel AISI 316 was studied. Deformation was carried out at room temperature, the number of deformation cycles was 7. In the process of high-pressure torsion, the structure of samples is considerably refined to nanostructured, so steel AISI 316 with an average grain size of 30 µm after deformation is refined to 80 - 100 nm. The tensile strength and yield strength values increase in seven passes from 595 to 1590 MPa and from 320 to 870 MPa, respectively. Relative elongation changes from 55 to 25 %, but remains at a sufficient level for an application. The initial structure of nondeformed steel has good ductility and demonstrates typical signs of ductile fracture. But with increasing HPT cycles the fracture mechanism changes from ductile to brittle, indicating a decrease in ductility of stainless steel AISI 316. [ABSTRACT FROM AUTHOR]

Copyright of Progress in Physics of Metals / Uspehi Fiziki Metallov is the property of G.V. Kurdyumov Institute for Metal Physics, N.A.S.U and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)