Cold drawing is the final process of plastic deformation in the manufacture of precision steel seamless tubes. This particular technology is utilities by multiple drawing operations (sequences) with intermediate heat treatment. The different drawing methods are differentiate according specification of the inner diameter of the tube. Hollow sinking process is simply drawing the tube through and reducing the outside and inside diameters without using an internal support (tool). Plug drawing is used to achieve wall thickness and inner diameter. According to the shape it is possible to distinguish the plugs on the conical and cylindrical. A modern approach to solving complex technological issues is the use of numerical simulations based on the finite element method. In this paper, stress-strain states describing the flow of material will be analysed, as well as the geometry of tribological pairs of forming tools with respect to the drawing force. The results are verified in technology in order to improvement production and reduce economic costs.
This article presents the impact of continuous plastic deformation SPD with the DRECE technique on a structure and properties of low carbon IF steel. The impact of numbers of passes on a change of mechanical properties of tested steel, such as tensile strength TS and yield strength YS, was tested. Within the SPD techniques an unconventional method of deformation was used, which is DRECE - Dual Rolls Equal Channel Extrusion developed on VŠB - Technical University in Ostrava. This technique uses reproducible plastic deformation to refine the structure and improve the mechanical properties of a metal band [1]. Numerous changes in the structure and they were associated to evolution of a dislocation structure and grain refinement were observed. In the case of the tested steel the increase of resistance properties was confirmed after the DRECE process after first pass through the device. The biggest hardening of the material is observed after the fourth pass.
In the paper the results of investigation of drawing method including simple drawing and shear by computer simulation were presented. The simulation in Deform program was performed. As basic scheme of drawing the industrial variant of LLP “Kaz-Metiz” was chosen. Both two new variants were the schemes of step and alternating drawing proposed in Krakow University of science and technology. The parameters of stress-strain state (strain effective, average hydrostatic pressure) and also drawing load were studied. The comparison of all three models revealed that on the existing drawing equipment in LLP Kaz-Metiz the implementation of any of two offered drawing schemes is possible. The most optimal variant is the scheme of alternating drawing.
In bending of plates, unlike the case of sheet metal forming, a 3-D stress state is valid. Moreover, apart from the some very specific cases, the plane strain assumption is not appropriate either. Therefore; bending of thick ultra-high strength steel (UHSS) plates is a deformation process where 3-D stress and strain states exist in general. This study basically focuses on the prediction of the bending corner topology with non-linear finite element analysis method, since the laser-cut edges of the UHSS are particularly prone to edge cracking during bending operation. Within the scope of this study, an experimental set-up is designed which consists of bending tools and a servo mechanical press. The samples were bent by means of this set-up in an air-bending operation up to 90°. This experimental work was followed by optical scanning measurements. And finally, the FEA results and the scanning data were compared in 3-D space. The results showed good correlation. As a future study, the 3-D strain field of the bending corner will be tried to be measured by a professional digital image correlation (DIC) system which could probably give more precise data when combined with the data from FEA.
Company NETZSCH Gerätebau GmbH is a producer of the instruments for the Thermal Analysis of different materials including metals and metal alloys. Short description of the history and an overview of the product range. The values of specific heat capacities, coefficients of thermal expansion, melting and solidification temperatures or enthalpies, and characteristic thermal effects can be measured. Melting, crystallization, phase transitions and specific heat capacities are important chemical properties in metals and alloys that are measured by means of DSC or STA (simultaneous thermal analysis). With dilatometers and TMAs, the coefficient of thermal expansion can be precisely measured; DMA determines the modulus of elasticity and the damping values that are relevant in practice for components. With LFA, the thermal diffusivity and conductivity - even of molten metals - can be investigated.
COMTES FHT is a private research institute in the field of research and development of steels and other metallic materials. COMTES offers a wide range of activities from material analyses, numerical simulations of processes and design of manufacturing technologies to prototype manufacturing.
For the prototype manufacturing of novel and special alloys COMTES FHT is equipped with a unique metallurgical facility consisting of a small VIM furnace for melting and casting of small batches in the range of 50-500 kg. Furthermore a forging press, rolling mill, wire drawing line and other forming devices are available for further processing of alloys. Since 2018 a 3D printing laboratory for metals is available.
COMTES FHT continuously collaborates with many excellent industrial companies such as Skoda, Doosan, Benteler, Daimler, Bilstein, Sulzer and others.
The influence of the cooling rate immediately before hot working on the flow stress and microstructure of δ ferrite-austenite duplex stainless steel (25 % Cr duplex stainless steel) was investigated by a hot compression test at 1,000 - 1,200 °C with various strain rates (0.1 to 10.0 s-1). In spite of the fact that the compression temperature was the same, the condition of rapid cooling immediately before the hot compression test greatly reduced the maximum flow stress σmax and work-hardening coefficient n values. In addition, the stable stress at a slow strain rate of 0.1 s-1 under the rapid cooling condition gradually increased with increasing compression strain. The microstructure just after the compression test was investigated by EBSD (Electron Back Scatter Diffraction Patterns). As a result of a detailed crystal orientation analysis, it was found that supercooled δ ferrite produced by rapid cooling immediately before the hot compression test influenced the decrease in σmax and n. Furthermore, a slow strain rate condition promoted the strain induced austenite phase transformation from the supercooled δ ferrite phase during the hot compression test, and because the increased austenite phase during the hot compression test is harder than the δ ferrite phase, stable stress gradually increased together with progress of the austenite transformation.
The analysis of the causes of the ski-effect of the sheet in the hot rolling conditions in the plate mill 5000 was performed. Influence of kinematic, thermal and geometrical factors on the occurrence of the ski-effect of the sheet were investigated. Influence of the velocity asymmetry of work rolls on bending of the front end of a sheet was studied in detail. Influence of parameters of the rolling process and the velocity asymmetry of work rolls on the shape of the front end of the sheet for different passes were analyzed. Modes of asymmetric rolling alloy pipe steels in the plate mill 5000 were developed and simulated with using software DEFORM. The problem of flatness formation of the sheet was also studied. Industrial tests were performed in the plate mill 5000. Specific asymmetric rolling modes and recommendations for industry were developed. Results of research can be applied to any type of plate mill with independently adjustable velocity of the upper and lower work rolls.
This paper deals with the influence of die surface orientation of roughness and die surface excitation on friction in metal forming processes. A way to evaluate friction coefficients from the flattening of long rectangular specimen was used for aluminium specimens with different die surface orientation of roughness. At the same time, this method was also used to examine the influence of die surface lateral vibration to friction with different parameters, such as frequency, amplitude and orientation of the specimen. The experimental results show that the roughness and die vibration have significant effects on friction in bulk forming process of small components.
Creating of gradient structures with the grain size changing from microns to nano-scale through the thickness of processed metallic materials represents a new advanced strategy for producing a superior combination of high strength and good ductility. Severe plastic deformation with predetermined strain gradient can be considered as a mechanism of creating of gradient structures. Strain gradient through sheet thickness can be achieved by special rolling technique. A surface of work rolls consisted of small microscopic grooves with the depth of 25 µm, located in transverse to rolling direction. A ribbed surface can have certain advantages in terms of tribological use. When positioned in transverse to metal flow direction a ribbed surface of work rolls can increase the frictional force. The aim of the ribbed surface was to create high opposite frictional forces during rolling and to develop the severe plastic deformation method for producing of sheets and strips with gradient microstructure. This paper presents the distributions of the plastic strain through sheet thickness of pure aluminum processed by symmetric and asymmetric rolling. Effects of contact friction coefficient, thickness reduction per pass and rolls speed ratio were investigated by the rigid-plastic finite element analysis. Extremely high strain difference through sheet thickness was found during symmetric and asymmetric rolling. Finite element analysis of strain gradients can be used for development of the special rolling techniques for fabrication of metal sheets with gradient structures and improved properties.
Accumulative roll bonding (ARB) is one of the severe plastic deformation methods of producing ultrafine grained laminated metal composites (LMCs). In order to obtain one‐body solid material, the rolling in ARB is not only a deformation process but also a roll-bonding process. ARB technique can be applied to generate LMCs consisting of layers of the same one material or several dissimilar materials. This paper is focused on LMCs consisting of dissimilar metal system of aluminum alloys 1050/6061 and 1050/6061/1050. One difficulty of roll bonding dissimilar materials is obtaining of elevated strain at the interface of the composite in order to provide the ultrafine grain structure and superior bonding strength between the stacked layers. Compared to conventional ARB the asymmetric accumulative roll bonding is more appropriate for the production of dissimilar metal composites. This paper presents the results of the finite element simulation and comparison of interface strain behavior during conventional and asymmetric ARB of 1050/6061 and 1050/6061/1050 Al composites. Influence of rolls speed ratio and contact friction on strain distribution through composite thickness, especially on interface between the 1050 and 6061 layers, during asymmetric ARB were analyzed by FEM in details. The FEM results of investigation can be useful for the development of the improved ARB process of Al composites with UFG structure and high bond strength.
This paper describes issues related to the process of cutting with a punch with internal heating. The theoretical part explains the effects related to thermal expansion, conduction and transfer of heat in the body of punches. The experimental part refers to the design of a tool with an internally heated punch. Experimental results are summarised and the process is analysed in the discussion.
Due to the unique set of functional properties, copper alloys are widely used in electrical engineering. It was found during previous studies that proper heat treatment (solutionizing and aging) followed by subsequent severe plastic deformation enable to increase mechanical properties while maintaining high electrical conductivity of the investigated copper alloys. In this study, two various sequences of heat treatment and SPD processing were taken into account. In the first variant, samples after solution treatment were subjected to rolling with transverse rolls motion (one of the SPD technique) and then aged. In the second variant, solutionizing, SPD rolling and aging were followed by another SPD rolling. Microstructural effects of the applied thermo-mechanical process conditions, as well as hardness and electrical conductivity of the deformed samples, were compared with those obtained in previous studies.
The article presents the results of the study of the microstructure and mechanical properties of austenitic stainless steel AISI-321 after radial-shear rolling. The studies carried out in this work allowed to prove the possibility of obtaining the ultra-fine-grained structure in long-length blanks of austenitic stainless steel AISI-321 after radial-shear rolling, as well as to achieve a significant increase in the initial mechanical properties of this steel. Thus, in the course of experimental studies, bars from AISI-321 steel with a diameter of 13 mm with a grain size of 300-600 nm were obtained, while having an inhomogeneity in the cross section of the bar. The mechanical properties and microhardness of steel AISI-321 were increased more than 2 times compared to the original values.
Based on dilatometry tests, the effect of various values of previous deformation on the kinetics of austenite transformations during the cooling of P620Q steel has been studied. Dilatometry tests have been performed with the use of the optical dilatometry module of the plastometer Gleeble 3800. The obtained results were confronted with the metallographic analyses and hardness measurements HV30. Uniaxial compression deformations were being chosen as follows: 0, 0.15, 0.35, 0.7, 1, and 2; note, these are true (logarithmic) deformations. The strain rate of 1/s was used in each case. It was verified, an increasing deformation value causes the growth of the ferrite and pearlite start-temperatures - especially in the areas of higher cooling rates. Based on this, the assumption of acceleration of by-diffusion-driven transformations through the previous deformation has been again verified. With the increasing of previous deformation, a bainite-start temperature was being proportionally growing in the entire range of cooling rates. Nevertheless, the effect of the increasing previous deformation was in the case of a martensite-start temperature entirely opposite.
The development of tools in bulk metal forming for the production of steel components consists of an iterative development process and requires a large number of test tools, resulting in high costs as well as increased production time. The simulation of process steps on the basis of the finite element method is an established technique for tool design and provides a significant contribution to the optimization of processes in the development phase. Thermally and mechanically induced deviations from the desired component geometry occur due the forging process. The approximation of the actual to the target geometry of the component must be worked out in several iteration loops by adapting the process conditions, or by modifying the forming tools. A newly developed process-accompanying compensation strategy helps to reduce the deviations by modifying the forming tool and process conditions within the virtual product development phase. In that regard, the numerical investigation of a forging process has been carried out in this study. The influence of different process conditions and their influence on the workpiece deviation are investigated. For this purpose, first of all the material data such as flow curves and coefficients of thermal expansion are determined in experimental tests. The coefficients for an analytical flow curve approach called GMT, which is implemented in the commercial software simufact.forming are computed for the investigated steel grades 16MnCr5 and 42CrMo4. Finally, the flow curve approach was validated by comparing numerical and experimental results of a uniaxial compression test. Also the numerical results of the forging process with different initial forging temperatures are compared with each other and the deviations of the workpiece are discussed.
The present paper does not have in view the impact of metallurgical industry on the environment. We have in view some thermal models, used in the case of solid bodies like for example the steel, in order to analyze similar phenomena in the nature and the effect on the climate changes. But, in the case of a natural system, it is more complicate, having in view the properties of the rocks and of the air.
In the case of the conductivity of the steels, it is used the Laplace equation for the bidirectional conductivity and the theory of Debay and Einstein regarding the stream of the electrons. But, is it applicable in case of the rocks and of the soils? This is not very sure. In the article are used some experimental data regarding the temperature in soils and the temperature of the air. The data are obtained at research centre Abisko located near the Arctic Circle, Sweden. Tables and graphics are obtained and the results are analyzed. Some conclusions regarding the heat transfer from the interior levels of the rocks are presented. However, the conclusions are not the final conclusions and more data and mathematical models are necessary. Therefore, we propose to follow the researches in two directions. It means, the theory of heat transfer in solid bodies, and the second direction regard the data of heat transfer from the soil surface to the air. It can be employed a quantitative approach, including numerical solution and theoretical aspects of heat transfer.
The study focused on numerical and experimental investigations of steel head restraint produced via the technology of cold rotary swaging. The analyses were carried out via finite element modelling and experimental swaging; the whole study was supplemented with 3D scanning. The experimentally swaged work-piece was scanned and eventually compared with the final product from the simulation. The results showed a good correlation of the swaged and predicted shape of the final head restraint. The numerical simulation focused especially on the distribution of equivalent imposed strain and a possible increase in temperature due to the development of deformation heat. The experimental part was supplemented with examinations of mechanical properties, and microstructure observations.
The effect of rolling temperature (800-1000 °C) - strain accumulation (number of rolling passes: 3÷5) - cooling rate (8.6 - 250C/s) parameters at the High Temperature Thermomechanical Processing (HTMP) on the microstructure, mechanical properties at the room and low temperatures of C-Ni-Nb and C-Ni-V steels intended for the usage as a high- strength material for production of the shelf constructions, strips and other special welded products has been studied. Experiment planning method (EPM) has been used to study the effect of the mentioned above parameters on the mechanical properties. By results of experiments the regression equations described the qualitative and quantitative effect of HTMP parameters on the mechanical properties of steel are constructed. The analysis of microstructure and SEM analysis of the fracture at +200C and -400C temperatures has been carried out. It was shown that the highest strength (YS = 987 MPa) in combination with a high impact strength (W = 154 J) has a Ni-Nb-bearing steel with lower bainite structure formed result in maximum passes and highest deformation temperature and cooling rate realization. The best cold resistance has steel with low bainite structure transformed at the accelerate cooling from the fine fragmented hot deformed austenite.
Hot stamping has become an established technology for the production of high strength steel parts in the automotive industry. The sheets are heated up to temperatures over austenitization temperature and held in order to obtain a fully austenised microstructure, formed and subsequently quenched. A locally optimized time-temperature-profile during heating provides the possibility to produce tailored parts, with locally varying microstructure and thus locally adapted mechanical properties. In order to determine an appropriate partial heating strategy, the heating as well as the cooling process has to be analyzed. In this paper a numerical model of a partial heating process is investigated in LS-DYNA comprising the heating process as well as the subsequent cooling phase. In order to describe the heating process, a new material model in LS-DYNA is used, which is suited for modeling arbitrary phase transformation processes of multiple phases with help of different transformation equations. The parameters of the numerical model are determined by means of experimental tests. The numerical findings are validated by comparison with experimental masking test.
Tools in hot forging processes undergo high thermal and mechanical loads and thus experience corresponding fatigues. Mechanical fatigue can be reduced by design optimization, but process related changes are needed in order to minimize the thermal fatigue. Especially the control of the ground temperature is important since it influences a large number of tool attributes e.g. strength and ductility, peak temperature and temperature difference. The use of an active cooling system allows a targeted control of the tool ground temperature thus leading to a reduction in process interruptions as well as maintenance time. In comparison to common straight drilled cooling channels, tool-specific cooling systems are known to remarkably take influence on an individual tool design, thus improving tool durability. The current study deals with the numerical investigation of a forging die with an oil based integrated cooling system. Different parameters like the coolant temperature and the mass flow rate were considered in order to evaluate the behaviour of the system during application. The results were compared with the temperature distribution in the forging die without integrated cooling. The findings of this work will help to further optimize the hot forging die and in return lead to more efficient forging processes.
The paper deal with experience with the introduction of production of ribbed wire from B500B steel on the cold stretching line KOCH in ArcelorMittal Ostrava. The basic principle of work hardening during cold stretching is introduced. Distribution of mechanical properties along the wire length of both hot rolled and cold stretched wire were performed. Statistical analysis has shown that there is a definable cause affecting the manufacturing process. Because of this, the yield strength, tensile stress and elongation to fracture values showing a trend along the wire length. It has been proven by measuring of the temperature of the wire at the conveyor by thermovision, that cooling of the wire rod on the chain conveyor is this definable cause. Different parts of the wire are cooled with varying intensity due to different densities of wire loops stacking on the conveyor. This fact directly affects the mechanical properties of the wire. Higher cooling rates result in higher yield strength and tensile stress values and lower elongation to fracture values. The effect of cold stretching on the change in the trend of mechanical properties over the length of the wire was also investigated. Interestingly, the variability of mechanical properties after cold stretching has increased.
In this study we present an analysis of the evolution of the texture of a mild steel welding rod from the initial state to the welded state. And thus show the effect of drawing on the texture of the welded metal.
The analysis of the initial state reveals the presence of a slight texture of the ferritic phase at the periphery. Several hypotheses are emitted but the main cause of the presence of the fiber <110> has not yet been identified.
The first deformation leads to the development of the fiber <110> over the entire section of the drawn wire. At this deformation level, the pearlitic phase does not appear to undergo any apparent deformation and the quantitative analysis shows a homogeneous distribution of the texture between the core and the periphery of the wire. After the second deformation, the perlite undergoes a very visible deformation under the light microscope and the fiber <110> becomes more intense in the core than on the periphery of the wire.
The examination of the texture of the welded state exhibits another texture composed of three <100>, <110> and <111> fibers whose ratios vary according to the observed angle. The chemical analysis reveals presence of elements of coating of a rod in a matrix of welded metal. It has been found that the drawn state of the rod and the manner in which welding is performed influence the texture of the deposited metal, but their separate effects need to be more inspected.
The medium carbon steel drawn wires are used in wide variety of applications, such as bridge cables, tire cord and springs. Wire drawing is a cold working process. It issued for reducing the cross-section (the diameter) of a wire by plastic deformation, in the presence of a dry lubricant powder, called soap. An electron backscatter diffraction (EBSD) was developed which allow non-destructive evaluation of crystallographic orientation distribution in materials has been used in this study.
This present research paper focuses on the characterization of the texture, microstructural evolution and mechanical properties behaviour (hardness and torsion) of medium carbon steel wires obtained by wire drawing process at Tréfissoud (Company used for the manufacturing of the spring mattress). The study was carried out respectively on the two states of the wires, wire rod and drawn wire (47 % and 56 % of deformation level), using the scanning electron microscopy (SEM) for examination of the microstructure, the electron backscatter diffraction (EBSD) for crystallographic orientation distribution analysis, the hardness and torsion to follow the curing of the studied wires.
Comparison of (D)CCT diagram of studied steels. Selected steels are used for manufacturing seamless tubes. Compared materials are steels 4130, X70 and P620Q. Diagrams were compared based on phases and their position. Metallographic analysis and hardness measurements were also made. Main focus of the study was dilatometric tests with(DCCT) and without(CCT) previous deformation. Third set of tests were performed to evaluate the effect of high austenitization temperature on resulting structure. Samples were heated with a constant rate to austenitisation temperature and then cooled with selected cooling rates in case of CCT and deformed before cooling in case of DCCT. Effects of the high austenitization temperature were much larger than that of deformation alone. Hardness tests showed very similar values for the samples with a deformation difference and more significant difference in the case of high austenitization temperature. Tests were made on plastometer Gleeble 3800 with optical module in VSB-Technical University of Ostrava.
Steel products like hot rolled steel plates or strips are widely used in industry or in other fields of human activity. Prediction and control of cooling during hot rolling are necessary to obtain the desired mechanical properties of the hot rolled steel. Spray and laminar cooling are common ways of cooling of the hot rolled strip on a run-out table in many steel industries today. Disadvantage of water cooling is remaining water on the surface of the steel strip that is accumulated and forms a water layer on upper surface. Due to the presence of the water layer, jets do not impact on the steel surface directly and the cooling intensity is changed. In this article, simulations of top and bottom cooling of the steel strip on the run-out table during hot rolling are performed using experimentally obtained boundary conditions. The experiment for obtaining boundary conditions is also described. Simulation with remaining water on the surface and simulation where the effect of the water layer was neglected are compared and the influence of the remaining water on the final temperature of the steel strip, which is an important parameter to control the quality of the final product, is investigated.
The present contribution deals with numerical investigations of a challenging forming process called thixoforming. This technology takes advantage of the semi-solid material state in order to produce geometrically complex parts. The reliability of numerical investigations of such processes depends on the accuracy of the used input data. Current commercial FEA software packages provide material databases with a great amount of material properties for diverse materials. However, material properties valid for temperature ranges exceeding the solidus temperatures are often insufficiently described or at times not available at all. Since thixoforming of steel requires the aforesaid temperature ranges a material model, consisting of two sections, has been developed for the numerical description of thixoforming processes. The first one describes the material behaviour below the solidus temperature and comprises an approach from structure mechanics, whereas the second section model describes the thixotropic behaviour above the solidus temperature based on the Ostwald-de Waele power law. An appropriate material description enables the investigation of the life cycle of tools by calculating local thermal and mechanical stresses more accurately. In this context numerical calculations of the thermo-mechanical tool loads during thixoforging were carried out. The Sehitoglu’s fatigue model has been implemented in the commercial FE software Simufact.forming by means of user-defined subroutines. In addition low-cycle fatigue as well as thermo-mechanical fatigue tests were performed in order to calibrate the model.