Seznam abstraktů 2023: POSTEROVÁ SEKCE B

The process of closing defects in 12X13 austenitic stainless steel by radial shear rolling on an RSP 10-30 mill was investigated. The advantage of radial shear rolling over other rolling methods is that it is an efficient way of achieving a high monotonic uniform deformation of the steel. The rolling sample was taken as an ingot of 12X13 steel with a diameter of 30 mm and a length of 150 mm. For mathematical research of the trough defects’ behavior in the radial-slide rolling mill calculation model was carried out in the software package Deform-3D. In the ingot were simulated transverse defects of different diameters and depths with a diameter d0 of 5 mm and 2.5 mm and a depth h0 of 5 mm and 2.5 mm and one through. The simulation aim was to compress the ingot from a diameter of 30 mm to a diameter of 15 mm with the step of rolling by 1.5-2 mm. Based on FEM modeling the evolution of defects in various intermediate stages of radial-shear rolling has been analyzed in order to investigate the possibility of defect closing.

The paper concerns the evaluation of the formability of sheet metal by means of the cylindrical cup drawing test, which belongs to the imitation tests of formability of sheet metal, and the influence of individual factors on the results of drawing. With the use of a special jig in the Department of Mechanical Technology, Faculty of Mechanical Engineering, VSB - Technical University of Ostrava, the experimental drawing of cylindrical stampings from a set of Cu-ETP copper sheet blanks was carried out with a deformation network formed with circular elements arranged in two mutually perpendicular directions passing through the centre of the circular blank. To determine the maximum size of the blank from which the stamping can be drawn without breaking, the individual diameters of the blanks were graduated in 1 mm increments. The chosen drawing tool was a drawing punch with a diameter of 49.5 mm and a radius of curvature of the drawing punch edge of 4.2 mm and a drawing die with an internal cylindrical bore of 52 mm and a radius of curvature of the drawing die edge of 7.3 mm. The maximum diameter of the blank at which a crack in the stamping would not yet occur during the drawing was experimentally determined to be 102 mm. Tensile tests of the Cu-ETP test bars were performed to determine the directional and average values of the mechanical properties, as well as the non-conventional formability criteria, that is, the strain hardening exponent (nm = 0.76) and the directional values of the plastic anisotropy coefficient (r0 = 0.54, r45 = 0,93 a r90 = 0,64). The experimentally obtained drawing results were verified in the Pam-Stamp Professional 2022 CAE programme using the finite element method. Using simulations and subsequent analysis of the drawability of the cylindrical stamping using the forming limit diagram of the Cu-ETP material used, the effects of various factors on the results of the cylindrical cup drawing test were then evaluated, which include the blank material, sheet thickness, the magnitude of holding force, lubrication, and radius of curvature of the punch drawing edge.

The steel with 0.3% C - 1.2% Mn - 0.8% Cr - 0.2% Mo is intended for the production of seamless pipes in the Mannesmann method, i.e. by piercing of the round billet by skew rolling and subsequent longitudinal rolling on a pilgrim mill. The heating and finishing temperatures are relatively high and it is therefore necessary to know the continuous cooling transformation (CCT) diagrams in a wider range of temperature conditions. At a heating rate of 0.167 °C/s, the temperature Ac3 = 824 °C was determined dilatometrically for the investigated steel. Subsequently, two different austenitizing temperatures were chosen for dilatometric tests. Continuous cooling transformation diagrams with previous deformation (DCCT) were constructed after the compressive true strain of 0.35 with the strain rate of 1 s-1, carried out at the appropriate austenitizing temperature of 860 °C and/or 1000 °C. Dilatometric curves were obtained after cooling at constant rates in the range of 0.1 - 35 °C/s. Their mathematical processing was combined with metallographic analysis and hardness measurement of selected samples. After cooling at rates lower than about 0.8°C/s, the structure consisted of ferrite, bainite and pearlite in varying proportions. Higher cooling rates led to an increasing share of martensite. In the high-temperature DCCT diagram, bainite plays a more significant role, and both the Ferrite-start and Pearlite-start curves are shifted towards longer times. This can be explained by the coarser initial austenitic grains after heating the samples to a temperature of 1000 °C.

Forging is currently one of the most economical processes for the manufacture of parts for industry. Product quality and production costs are very significant factors for manufacturers today and determines their competitiveness. The design of preforms, together with determination of the required number of transforming stages used in forging processes is an important aspect for improving the quality and reducing the costs.
This paper presents a new possibility to design preforms for closed die hot forging using a simple moving average smoothing technique. Like examples, the preform design of axisymmetric forgings is performed. A computer simulation of the forging processes in the preform and final forging stages was carried out. The results are compared and analyzed.

Grade 20MnCrS5 is a structural alloy steel for surface hardening. Despite the low carbon content, it exhibits good wear resistance after hardening. The material can be hardened to a depth of about 40 mm. Sulphur in the content of 0.020 - 0.040% improves machinability. The material is commonly used for the production of moderately stressed parts of motor vehicles and machine parts intended for cementation with higher strength in the core (e.g. transmission gears, axles, pinions and camshafts). Continuous cooling transformation diagram of steel grade 20MnCrS5 was constructed after the compressive true strain of 0.35 with the strain rate of 1 s-1. Based on the experimentally determined value of Ac3 = 829 °C, the austenitization temperature of the dilatometric samples was chosen to be 880 °C. Samples cooled at a constant nominal rate of 0.1 - 35 °C/s were subjected to structural analyses (optical and scanning microscopy) as well as hardness measurements. Even at the highest applied cooling rate, trace amounts of ferrite were detected. Martensite and bainite appeared in the structure after cooling at a rate of at least 0.7 °C/s. Continuous cooling transformation diagrams are valuable from the point of view of optimizing the cooling regimes after hot bulk forming and/or at the heat treatment of the final products.

In the article, the authors presented the technological assumptions for the production of a helical metal expansion joint. Currently produced expansion joints have bellows or lens shapes. A helical metal expansion joint is a new type of expansion joints that can compensate for torsional deformations of industrial pipelines. The authors presented a method of mechanically assisted laser forming, which was used as a manufacturing technology for this type of element. Experimental results obtained during the manufacturing of metal helical metal expansion joints are presented. Mainly, the results are presented and discussed, such as: obtained geometry, forces needed to manufacture the element, processing temperature, strain rate and others. ACKNOWLEDGEMENTS: The research reported herein was supported by a grant from the National Centre for Research and Development. Program title: Lider XI, grant title: "Development of new type metal expansion joints and their manufacturing technology", contract number: LIDER/44/0164/L-11/19/NCBR/2020.

Equal-channel angular pressing (ECAP) is one of the main ways of refinement the structure of metals into a fine-grained and nanostructured state. Regardless the great prevalence and high knowledge of the method, the issues of optimization and improvement of the design and geometry of the working tool still relevant. A number of simulations of the geometry of the channels of the matrix with a spherical cavity of the junction of the channels were carried out in order to study the regularities of the stress strain state formed in the channel. The study was carried out for different angles of the junction of the matrix channels using the example of a zirconium alloy Zr-2,5%Nb. Due to the spherical cavity, a back pressure is formed, as a result of which the nature of the accumulation of deformation in the alloy changes. Using die with spherical cavity, it is possible to achieve a more complex of shear deformations scheme in comparison with the conventional method and to increase the treatment of metal in the axial zone of the billet. However, this type of ECAP is characterized by a more heterogeneous distribution of the accumulated strain in the cross section of the billet, as well as an increase in the pressing force in all cases (about 1.7 times).

This article focuses on the influence of simplification of thermophysical properties on computational modeling of heating process of steel billets in pusher-type reheating furnaces. The objective is to investigate the impact of the simplification of thermal conductivity and heat capacity on the temperature gradient within the material surface and the center. The pusher-type reheating furnace is widely used in the steel industry for the reheating of steel billets before they are processed further. The heating process is complex, involving the transfer of heat from the combustion gases to the steel billets, and the temperature distribution within the material plays a critical role in determining the final quality of the product. The study uses a computational fluid dynamics (CFD) model to simulate the heating process of the steel billets, and the effects of simplification of thermophysical properties are analyzed. The results show that the simplification of thermal conductivity and heat capacity leads to a significant misprediction of the temperature at the material surface, resulting in a higher temperature gradient between the surface and the center of the billet. The simplified models also show a weaker correlation with the experimental data. The study concludes that the simplification of thermophysical properties can result in significant errors in the computational modeling of the heating process of steel billets in pusher-type reheating furnaces. It is therefore recommended to use more accurate thermophysical property models to improve the accuracy of the simulation results. The study also highlights the importance of experimental validation of the computational models to ensure their accuracy and reliability in predicting the temperature distribution within the material.

In modern engineering, the possibility of predicting the behaviour of processed material by means of numerical simulation is increasingly used. Knowledge of this issue is important to ensure the stability of the pressing process. Achieving higher process stability leads to a reduction in the number of correction loops for forming tool optimisation, and lower production rejects, and time and financial savings in tool and die shops. However, with respect to increasing productivity, there is instability in the pressing process, which may be related to the material’s behaviour when the deformation rate changes. There is a change in tool temperature due to friction between the tool and the material and heating of the material due to deformation. Therefore, it would be interesting to see whether the mechanical properties of the material change with temperature. The thermal effects in the cold forming process should be implemented in the numerical simulations. This work aims to carry out a heating design that will allow heating to temperatures corresponding to those of the pressing process. The specimen should be visible for the possibility of deformation analysis, e.g. by the ARAMIS system, which works on the principle of digital image correlation. The functionality of the designed device will be tested in tensile tests. Different temperatures from ambient to 160 °C will be measured to cover the continuous heating process in real forming.

The 3D printing method is a widely used technology for industrial and domestic applications. This paper deals with the design of forming tools for sheet metal drawing made of PLA plastic, produced by the FFF 3D printing method and used to create a lock cover part from DX56 sheet metal of 0.7 mm. First, a virtual model was created based on the pattern provided by company KERVAL a.s., which was used to design the tools' geometry and the input sheet's shape. In addition, tensile and compression tests were performed on the PLA samples to determine their properties. The results of these tests were used to build a material model to simulate tool deformation. Then, a numerical simulation was created in the Simufact Forming software to verify the manufacturability of the part, and the suitability of the tooling geometry, and to rule out damage to the blank. In the numerical simulation, rigid and deformable tools were considered. The tools were then printed and used to verify the real pressing process. The results showed that the deformable tools were able to press the lock cover part to the required quality; however, during the forming process, there was significant damage to the tool. In conclusion, the causes of this result and recommendations for possible solutions to the problem are analysed. The use of FFF 3D printing technology can significantly reduce the development time and cost of prototype forming tools.

Lightweight vehicles save on carbon emissions but still require strength to maintain their crashworthiness. Boron steel meets several needs of a rapidly changing automobile industry.1500 MPa press hardening steel (PHS), and 2000 MPa PHS are 2nd generation boron steels that are press hardening. Press hardening steels are able to be simultaneously quenched and formed using specials tools. In some cases, boron steels can be quenched to exhibit strengths of 2 GPa or more. However, ultra-high-strength steel is susceptible to brittle failure with a fully martensitic microstructure. The PHS most used in automotive body-in-white applications is 22MnB5 steel. In this study 1500 MPa press hardening steel (PHS), and 2000 MPa PHS used and compare with using same die part geometry and mechanical properties.

During the pressing of sheet metal parts, cracks may form around the holes that weren't predicted by numerical simulations. These cracks are caused by the partial depletion of the forming capacity at the edges of the hole due to the preparation technology used, most often shearing. The aim of this article is to refine the simulation models by introducing boundary conditions to describe this condition. The Hole Expansion Test (HET), described in ISO 16630 and currently the only worldwide standardised method for determining the sensitivity of a material to edge crack formation, is used to determine the limiting deformation at the edge of the material. Materials commonly used in the automotive industry were chosen for the experiment. Holes were made in samples of each material according to ISO 16630 by shearing, laser cutting, and electro-erosive machining. The testing was carried out according to ISO 16630 at room temperature and the specimens were evaluated manually just before failure. The results obtained were evaluated and compared with theoretical premises. By refining simulation models and introducing boundary conditions that account for the depletion of forming capacity at the edges of holes, manufacturers can better predict and prevent the formation of cracks during the pressing of sheet metal parts. This can improve the quality and durability of automotive parts and ultimately lead to safer and more reliable vehicles.

The low-temperature toughness of a 2205 DSS produced by the deference thermal processing histories was investigated. In order to compare the influence of an accelerated cooling immediately before working on low temperature toughness, specimens with three different microstructures were prepared by using different thermal histories. The heat treatment process was carried out by high temperature heating of 1300 °C to induce grain growth. The air cooling and the accelerated cooling process were applied with different cooling rates of 0.1 and 30.0 °C/s from the holding temperature of 1300 °C to the working temperature of 1 000 °C. Coarse microstructures were observed with the heat treatment and the air cooling process, while the microstructure achieved by the accelerated cooling process consisted of fine austenite grains. The accelerated cooling process resulted in a higher low temperature toughness and lower ductile-brittle transition temperature. Based on an investigation of the relationship between the fractography and instrumentation Charpy test results, it was concluded that the fine austenite grains produced by the accelerated cooling process have the function of preventing crack initiation.

In the pursuit to produce the best product at the lowest cost, much can be done to reduce the cost of production. One of these methods, which is nowadays inseparable from the development part of production, is numerical simulation. However, the real world cannot be accurately modelled. The use of simplified models for numerical simulation can lead to different results between reality and simulation. One of these models is a coefficient of friction used in sheet metal forming simulations. Nowadays modern simulation software used for simulating the sheet metal forming process uses simplified model of friction coefficient using variables including surface roughness, topography, lubrication, and others. One of the variables not included in these models is temperature. In deep drawing, local temperatures of sheet metal can be over 120°C. Temperature can greatly change tribological properties, thus changing the friction between the tool and the sheet metal. The aim of this paper is to review a method of measurement of tribological properties in sheet metal forming and to design a modified tribometer for strip drawing test, focusing on the effect of temperature on tribological properties, predominantly for materials used in the automotive industry.

The authors presented the ideas and assumptions with regard to manufacturing and application of a new kind metal expansion joints. Mechanically assisted laser forming manufacturing technology was briefly discussed. Metal tube with appropriate diameter and wall thickness are used to manufacture metal expansion joints. The concept assumes using a CO2 laser to implement such expansion joints. The incidence of laser beam on selected surface of the rotating tube, heating it. After reaching the plasticising temperature, the actuator compresses the tube. As a result, a bellow-lens shape is formed at the plasticization area. Initial experimental studies confirmed the validity of the concept. The bellow-lens metal expansion joint was obtained as a final result.
ACKNOWLEDGMENT: The research reported herein was supported by a grant from the National Centre for Research and Development. Program title: Lider XI, grant title: "Development of new type metal expansion joints and their manufacturing technology", contract number: LIDER/44/0164/L-11/19/NCBR/2020.

Complex concentrated alloy (CCA) with designed nominal composition (CoCrFeNi)93Al3Ti4 (in at.%) was prepared by vacuum induction melting in a ceramic crucible and tilt cast into the cylindrical ceramic mould. The alloying elements Al and Ti were added to the basic quaternary CoCrFeNi system to promote the formation of L12 phase in the FCC (face-centred cubic) matrix during heat treatments. The as-cast ingot was subjected to solid solution annealing, which was followed by free hot forging to refine the coarse columnar grain structure of the as-cast CCA ingot. The forged alloy was subjected to annealing at temperatures ranging from 800 to 900 °C for various times ranging from 2 to 100 h. The properties of the CCA were studied with light microscopy (LM), energy dispersive spectroscopy (EDS), differential thermal calorimetry (DSC), and microhardness measurements. The CCA solidifies through FCC primary solidification phase. The as-cast microstructure of the alloy consists of columnar dendritic grains growing from the surface towards the centre of the cylindrical ingot. Solution annealing leads to a full chemical homogenization of the alloy and the formation of single-phase coarse columnar grains. Forging leads to the recrystallisation process and formation of equiaxed grains in the forgings. The annealing in the temperature range of 800-900 °C leads to significant hardening of the studied alloy, which is associated with the precipitation of secondary phases in the FCC matrix.

This study is carried out as part of a scientific collaboration with the national wire drawing and welding products manufacturing company (TREFISOUD) of El-Eulma, Sétif. The aim of this research work is to highlight the relationship between microstructural evolution and the mechanical properties of medium carbon steel drawn wires (C68D-2 and D45-2) intended for the manufacture of spring mattresses. The study was mainly oriented on the evolution of the crystallographic texture as a function of the deformation resulting from the industrial wire drawing process. This, in fact, will make it possible to establish a relationship between the microstructure and the variation in the mechanical properties of the wires and therefore to identify the problem of breakage of the wire during the use of these two medium carbon steel wires obtained by wire drawing and used in the manufacture of spring mattresses and also to save the losses generated and to qualitatively satisfy the users. A variety of experimental measurement and characterization technics are used in this work. These are optical microscopy, scanning electron microscopy (SEM), X-ray diffraction, back scattered electron diffraction (EBSD), tensile and torsional tests and micro-hardness measurements, some of which have allowed correlate the microstructure with mechanical properties.