Many years ago, plastic processing of metallic materials was treated as a process of giving products a specific shape, and while shaping them, specific mechanical properties were obtained. Very often, when carrying out these types of processes, especially under hot deformation conditions, it was necessary, for example, to perform intermediate post-heating of the deformed material, as well as finishing heat treatment. Currently, when designing plastic working processes, a lot of emphasis is placed on shaping the products with controlling their mechanical properties. In addition, the aim is to intensify the processes as much as possible, using certain features of the material's behavior under the conditions of plastic deformation.
Many years of research conducted in various research and development centers and scientific institutions have led to the development of new design solutions for devices in which an unconventional way of influencing the deforming material has been introduced. Cyclical changes in the stress state scheme and local intense plasticization of the material allow for an increase in the ultimate deformation and the use of large plastic deformations. A properly selected change of the deformation way causes softening of metal during deformation, which is a result of the destabilization of the material structure. These phenomena reduce the forces required to deform the material, and also affect the achievement of the desired structure that guarantees appropriate mechanical properties.
The presentation will show examples of technologies using the above-described phenomena. These technologies have been introduced into industrial practice in recent years or are characterized by a high implementation potential. Techniques based on intense shear deformations are characterized by particularly high applicability, including processes using the known method of pushing the material through the angular channel, methods using the oscillating movement of deformation tools, or segmental forming.
Temperature of the bloom during hot rolling is crucial factor for quality of final product. Heat losses during hot rolling affecting bloom temperatures were therefore experimentally investigated. Experiments were designed to simulate heat transfer on bloom surface during rolling when 1. the bloom does not move and is far from the work roll (heat transfer by radiation and natural convection in air), 2. the bloom moves far from the work roll (heat transfer by radiation and forced convection in air), 3. the bloom moves close to the work roll so the residual water from roll cooling falls on its surface (heat transfer by radiation and forced convection by residual spray from work roll cooling). Roll bite is excluded in this paper. Experiments were performed with austenitic steel plate embedded by thermocouples. The plate was firstly heated up to 900 °C and then moved by computer controlled mechanism repeatedly through section which simulated blooming line. Three different velocities of 1, 3, 5 m·s-1 were tested to observe velocity influence on the heat losses. Temperatures gathered during experiments are evaluated numerically by an inverse heat conduction task and analytically. The final results show that the highest heat loss is caused by radiation, its value is 171 W·m-2K-1 for 1100 °C. The heat loss due to residual water from work roll cooling is 81-88 W·m-2K-1 and the heat loss by forced air is found to be within 11-29 W·m-2K-1.
The paper deals with the use of a modified model of microstructure development in the design of a regime of controlled rolling of round bars rolled in Liberty Ostrava a.s. The combination of strain-induced precipitation (SIP) and recrystallization used in the model is presented here. The predictions of the model are verified by plastometric simulation using a plain strain compression test of the rolling regime of a round bar with a diameter of 100 mm. A comparison of the predicted and measured grain size for 4 rolling modes is performed. New model for prediction of mean flow stress is introduced. A new chemical composition of steel alloyed by Nb for supporting SIP is designed using the model.
Modern trends in the development of automation in the metallurgical industry are characterized by the widespread use of information technology. Automated control systems are used today at all modern enterprises of the metallurgical industry and the tendency of their implementation is increasing. The use of such systems allows to ensure uninterrupted operation of the equipment and minimize unplanned downtime. Automation also leads to an improvement in the quality of manufactured products due to the stability of processes, to an increase in productivity and minimization of the human factor in production.
The article contains a description of the main technological processes in rolling production and a proposal for the automation workpiece handling process. The main goal of the article is to show the use of digital image processing methods in the automation of rolling industry processes. It will involve the use of computer vision technology using a system of line lasers, digital cameras, and algorithms for digital image processing. The system will be used to manipulate the billet between the individual stands and rolling calibers within the rolling mill stands.
Due to their higher weight-specific and high-temperature strength, iron-aluminium alloys have a high potential to replace steel in various applications. The good availability of the two materials, the excellent recyclability, lower density with increasing aluminium content and the high corrosion resistance in sulphide- and sulphur-rich environments are further advantages. However, with increasing aluminium content, ductility of FeAl alloys decreases due to hydrogen embrittlement at room temperature. As a result, iron-aluminium alloys have been excluded from potential applications, particularly structural ones. Investigations on powder metallurgical produced iron-aluminium alloys show that fine-grained microstructures can lead to significant improvement in ductility. Assuming equal grain diameters, higher toughness is expected in case of metallurgical ingot production followed by hot forming. The present work deals with the mechanical properties of fine-grained microstructure in iron-rich iron-aluminium alloys, pre-processed through Equal Channel Angular Pressing. In order to characterize the mechanical properties, compression tests with the alloys Fe9Al, Fe28Al and Fe38Al are carried out at different temperatures. The flow curves determined are then compared with those from as-cast state. In addition, deformation capacity is examined optically on slopes of external cracks. In conclusion, the results are discussed based on the microstructure.
The use of hybrid semi-finished products made of aluminium and steel enables the production of components with locally adapted properties, i.e. high strength and wear-resistance with reduced weight. In the scope of this work, different impact extrusion processes for the forming of friction-welded hybrid semi-finished products consisting of steel (20MnCr5) and aluminium (EN AW 6082) were developed and experimentally implemented. The resulting material flows were intended to enable different joining zone geometries as well as to evaluate the influence of a thermo-mechanical treatment during the impact extrusion process on the quality of the joining zone. For this purpose, a full-forward extrusion, cup-backward extrusion, combined cup-backward-full-forward extrusion and a hollow-forward extrusion process were investigated. The evaluation of the resulting component quality was carried out based on metallographic images, which provide microstructural information about the forming-related influence on the friction welded joining zone. Based on the characteristic values determined, a correlation between the reproducibility and quality of the joining zone properties and the type of impact extrusion process is deduced. The backward extrusion processes have proven to be the best processes in terms of influencing the joining zone geometry. Further, the effect of forward extrusion showed no significant influence on the joining zone geometry, even resulting in a reduction of the joining zone formation in the combined cup-backward-full-forward extrusion process.
This work deals with the study of structure and physical properties of 316 L austenitic stainless steel prepared by additive manufacturing and subsequently processed by the technology of rotary swaging. The semi-finished products were printed on a Renishaw 3D printing machine using the SLM (Selective Laser Melting) method, during which the metal powder is gradually sintered via cladding of individual layers using a powerful laser. Subsequently, room temperature rotary swaging was applied to enhance the structure and properties of the SLM-manufactured semi-product. The structural analyses showed that the swaging process imparted significant refinement of the average grain size, which decreased down to approx. 12.5 µm (measured as the maximum feret diameter). As regards the physical properties, the density of the as-printed, as well as swaged, samples were measured using a pycnometer. As a result of forming, better material properties, such as increased density and improved microhardness, were achieved. To confirm the advantages of the proposed approach consisting of a combination of 3D printing and deformation processing, all the results were compared with those acquired for an identical stainless steel prepared by conventional casting.
The paper focuses on the formation of cavities in metal samples. The main part is the results of experimental work, which are presented in the form of summary knowledge about the process of forming cavities. Lead plates into which the shapes of the mandrels, in this case punches with apex angles of 60 ° and 90 °, were pressed as samples were used. The cavities in the samples can generally be made with a radius or a point. The presented contribution follows on from the authors' published contribution at the Metal conference last year, where the results obtained during the embossing of the radius punch were published. The experimental work was carried out using a magnetic shock application, the great advantage of which is that the shaping process implemented in this way does not place an enormous burden on the environment. The actually used experimental equipment for laboratory work is also presented. The text of the paper is supplemented by tables with summary results of experiments, graphs and photographs of cavities. The aim of the paper was mainly to verify the possibilities of applying a special tool in the formation of cavities in metal samples.
Tube and tube systems are very critical to fulfill the design requirement of applications. Especially bending radius is most important issue in tube bending.
In tube bending, as the bend ratio (bending radius/outer diameter of tube) and wall thickness of the tube material decrease, the risk of encountering defects such as wrinkles, ovality, wall thinning and crack increases. Rotary draw bending process is generally preferred for bending tubes with small bend ratio and thin wall thickness. In this bending process, elements such as bend die, clamp die, clamp insert, pressure die, wiper die and mandrel are used. For the minimum bending radius value that can be obtained in this process, there are many parameters such as material properties and geometry of tube, die geometries, position and geometry of mandrel, wiper die angle, pressure value of pressure die and bending speed are taken into consideration. Trying to determine the limits by trial and error, bending for different tube materials with many process parameters would result in waste of time and money. In this proposed study the effects of different mandrel positions, ball diameter and pitch distance of mandrel on minimum bending radius value for AA 2024 material are investigated by PAM-STAMP program. The results will be compared with the results in literature.
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Hot forming tools are exposed to cyclically changing thermal loads. These conditions are caused by heat exchange between tool and billets while forming and the consecutive spray cooling and can lead to crack initiation. A continuous cooling with Heatpipes (HP) inside the active tool components could prevent this. HP use a circular flow of a cooling fluid inside a closed tube, often made of copper. Previous studies showed an influence of connection by thermal paste between the forming die and the HP, its orientation, as well as its inner surface structure. The use of paste proved essential for closing the contact by filling the microscopic air pockets between the surfaces. Bonding by means of deformation leads to the limitation to sintered internal surfaces, since the others are damaged in the process. This research paper deals with the influence of the geometrical and force connection between die and HP. To test the impact, HP were connected with heated model dies on one side and an aluminum block on the other. Thermocouples were used to monitor the temperature of both, the aluminum block and the model dies. Temperature, weight and thermal capacity of the aluminum block allow the calculation of the heat flow. Different inner surface structures of HP were varied in addition to their fitting type with the model die. The best heat transfer was achieved by using HP with sintered inner structure and pressure closed connection, resulting in nearly full-surface contact.
The surface layer of hot working tools is subject to alternating thermo-mechanical loads during forging. It experiences a fast increase in temperature on contact with the pre-heated billets, followed by a steep temperature decline during application of the spray-coolant. This can lead to a cyclic surface rehardening of the tool surface layer due to the formation of a martensitic structure, which can either delay or accelerate tool failure. The microstructural changes in the tool surface layer mainly depend on the thermal, mechanical and tribological loads during forging. The investigation of the influence these loads have is of particular interest to understand the effect of cyclic surface rehardening.
The goal of this research is to investigate the influence of cooling parameters on microstructural changes in the tool surface layer during die forging. Mechanical and tribological loads are kept constant while cooling parameters are varied. Three internal thermocouples are applied to forging tools to measure the base tool temperature. To keep the amount of lubricant in each forging cycle at constant levels, cooling and lubrication are separated by use of boron nitride as lubricant, which is applied by electrostatic adherence. For cooling, the duration of water application is varied while maintaining pressure and spray patterns. Four tools with different tool base temperatures are investigated and the influence of the thermal loads on the wear behaviour displayed.
This study deals with new generation of ODS alloys strengthened with a high-volume fraction of Y-nanooxides of 4 %. The ODS alloy is produced using powder metallurgy consisting of mechanical alloying of input powders followed by hot consolidation of canned powder using rotary swaging technology and secondary recrystallization to provoke coarse-grained microstructure. We focus on the microstructure characterization after individual processing steps and measurement of mechanical properties after consolidation and after secondary recrystallization at room temperature and 1100 °C. The mechanical properties of the studied ODS alloy are compared with those of a conventionally produced alloy as INCONEL718.
Despite its relatively high cost, copper is still the most popular electroconductive material. Its electroconductivity can be affected via structure modifications introduced by shear mixing, i.e. deformation processing, and/or thermomechanical treatment. Being an industrially applicable method of intensive plastic deformation, advantageously used to impart shear mixing, rotary swaging is favourable for production of long electroconductive wires. This study is focused on assessment of the effects of thermomechanical treatment on structural phenomena within copper conductors; the treatment consisted of room temperature rotary swaging and subsequent annealing. The results showed that the deformation ratio introduced via swaging was sufficient to impart homogenization of structure as the differences between the grain sizes and texture orientations within the peripheral and axial regions of the conductor were minimal. On the other hand, the swaged and annealed conductor featured slight inhomogeneity between the peripheral and axial regions, especially as regards structure regeneration and the occurrence of twinning, which was more pronounced in the axial region of the thermomechanically processed conductor (the volume fraction of <111> 60° twin boundaries was higher than 60 % within this sample). Interestingly, the electroconductivity was higher than 100 % IACS (International Annealed Copper Standard) for the swaged conductor, and even slightly increased up to 104.4 % IACS due to the structure modifications imparted by the applied heat treatment.
During cold forming of metastable austenitic steels, a strength-increasing phase transformation induced by externally superimposed stresses occurs in addition to strain hardening. The effect of deformation-induced martensite formation has so far not been utilised industrially in the area of bulk forming, but could be suitable for the production of highly-loaded components in oxidative atmospheres. The aim of this study is the attainment of local phase transformations in metastable austenitic steels in the boundary layer of bulk formed components. For this purpose, the relationship between the process conditions occurring during bulk metal forming and the resulting martensitic phase fraction can be determined. Cylinder compression tests are carried out in which the influence of various process parameters can be investigated. These include forming temperature, true plastic strain, forming speed and the influence of individual alloying elements through the selection of different materials. In addition to a quantitative measurement by means of a magnetic induction process, local martensite formation is determined optically in light metallographic analyses and hardness measurements are carried out. The recorded flow stress curves are implemented in the numerical simulation. Furthermore, the influence of different tool surface topographies on the contact conditions of the workpiece-tool system is characterized by means of ring compression tests. With the numerical simulations and experimentally obtained results, a surface hardening process for bearing rings is designed. The relationship between local true plastic strain and deformation-induced martensite development is explained by material flow simulations, taking into account the process route for manufacturing the bearing ring and the varying friction factors.
The paper presents the results of the effect of deformation parameters on the hot-deformation behavior of the newly developed multi-phase steel assigned for production of forged machine parts. Continuous and interrupted compression tests of the samples after the given deformation were carried out with the use of the Gleeble 3800 thermomechanical simulator. The samples were tested in the temperature range from 900°C to 1100°C at the rate of 0.1s-1, 1s-1 and 10s-1. Basing on the analysis of the form and the course of curves obtained in the compression test, it was found that in the studied range of parameters of hot plastic deformation, the decrease of strain hardening of studied steel is caused by the process of dynamic recovery. This is also confirmed by calculation results of activation energy of plastic deformation process. Executed hot compression tests will contribute to establishing conditions of forging of newly developed multi-phase steel with the method of thermo-mechanical treatment.