Seznam abstraktů 2015: POSTEROVÁ SEKCE B

The aim of this paper is to determine the impact of heat treatment of steel pre-treated thermo-mechanically using Gleeble 3800 simulator on the structure and mechanical properties of investigated high-manganese austenite Fe-Mn-(Al, Si) steel, containing 25% of Mn, 3% of Si, and 3% of Al. Applying thermo-mechanical treatment using Gleeble 3800 simulator allow to obtain the conditions for a gradual grain refinement controlled mainly by dynamic recrystallization and also by a dynamic recovery in a whole temperature deformation range. The high-manganese TWIP steel after hot-deformation is characterized by a mixture of fine, recrystallized grains and some fraction of dynamically recovered grains with a mean diameter of about 5-7µm. Solution heat treatment of the specimens from a temperature 850°C cause that steel possesses fine-grained microstructure of austenite with grain sizes about 10µm. Increasing solution temperature from 850 to 1000°C results in a rapid grain growth up to about 17µm. Specimens were solution at time 900s, increasing solution time also cause a growth of austenite mean grain size in high-manganese Fe-25Mn-3Si-3Al TWIP steel.
The new developed high-manganese TWIP steels provide an extensive potential for automotive industries through exhibiting the twinning induced plasticity (TWIP) and transformation induced plasticity (TRIP) mechanisms. TWIP steels not only show excellent strength, but also have excellent formability due to twinning, thereby leading to excellent combination of strength, ductility, and formability over conventional dual phase steels or transformation induced plasticity TRIP steels.

In the paper the analysis of the gas turbine forging process made from highly alloyed steel NiCrMoV to power engineering application was done. Numerical analysis of material flow in following stages of forging process also effective strain distribution in forging was introduced. Industrial technology of forging process with numerical calculations results was compared.

Intensity of change in structure of the forged pieces at forging is usually determined in dependence on the degree of thickness reduction ratio. Degree of thickness reduction ratio at elongation is most often calculated with use of simple relations, which are based on the change of cross-section of the forged pieces. The intensity of development of structure is influenced not only by the simple change of cross-sections, but also by relative length of the stroke, magnitude of deformation in individual passes, manner of canting, temperature, friction and shape of anvils. The paper gives an analysis of influence of the relative length of the stroke on the degree of thickness reduction ratio.

Modern incremental metal-forming processes are developed in order to obtain products of specific shape and functional properties and/or to achieve new production opportunities and economical benefits. A definition of incremental metal forming processes has been presented in the paper as well as several examples of such processes reported in the literature or currently investigated by the authors. The main features of these forming methods, their potential benefits and possible application areas have been described.

In the article results of the influence of deformation parameters on the susceptibility to plastic forming for steels for rolling of wire rod type have been presented. Hot torsion test was performed on torsion plastometer at the temperature range 800 to 1100ºC and strain rate of 0.1, 1 and 10 s-1. The analysis of obtained results the flow curves in the flow stress – true strain system, was determined. Characteristic points: peak stress, strain of obtained curves were analyzed. The activation energy of plastic deformation was determined. They are indicating that influence of Zener-Hollomon parameter on peak flow stress and strain for both the steels can be presented in form of power function. Function of flow stress using selected form of Hensel-Spittel equations have been determined.

Development of technologies of production of ultra-fine grained (UFG) materials is at present accelerated very intensively. Apart from classical ECAP technology (the most used one at present) new technologies for sheet metal forming are being developed for industrial use, namely the techies DCAP and CONFORM. The paper analyses development of ultra-fine grained structure in a strip of sheet on a similar type of equipment called DRECE – Dual Rolling Equal Channel Extrusion. This equipment is at present being developed at the working site of Development of new technologies at the Faculty of Mechanical Engineering at the Technical University of Mining and Metallurgy in Ostrava (VŠB – TU Ostrava). The issues related to development of UFG structure in the strip of sheet made of non-ferrous metals with dimensions 58 x 2 x 1000 mm is described in greater detail. Moreover an analysis of structure and mechanical properties obtained after multiple plastic deformations is made with subsequent comparison of the obtained results with the properties of alloys and non-ferrous metals sheet in initial state. Investigations of structures and mechanical properties give a good premise for the use of the achieved results in practice.

The contribution is aimed on appraisal of influence of previous deformation on spring steel CCT diagram. There were assembled based on dilatometric analysis of cooling curves, using by universal deformation simulator HDS-20, CCT and DCCT diagrams after austenitization at the temperature of 850 °C which were supported by metallographic analysis and hardness measurement HV30. Dilatometric tests were performed at different cooling rates in range of 12 – 0.16 °C/s. By this way assembled diagrams were compared with diagrams computed numerically by the specialized software QTSteel at the same conditions. The comparison of the experimentally obtained diagrams with the numerically computed confirms irreplaceability of physical experiments because of large differences against reality of numerically computed diagrams. The influence of previous deformation on anisothermal disintegration of austenite was manifested at each phase transformation, but in case of perlitic transformation was most outstanding because of significant acceleration.

The paper presents analysis of plasticity characteristics and microstructure of magnesium alloy with yttrium, zirconium an rare earths element in comparison to classical alloys from Mg-Al-Zn-Mn group. Susceptibility of magnesium alloy to cracking in high temperatures was tested on Gleeble3800 simulator zero resistance temperature was determined and zero plasticity was determined. Tests of fracture character were conducted with the use of scanning microscopy. Tests were conducted for assessment of susceptibility of tested alloys to hot plastic deformation. A tensile test was realized in temperature from 250 to 450 °C. Base on the results, ultimate tensile strength and reduction of area were determined for samples. A varied plasticity of tested alloys was found depending on aluminium content. Tests results will be useful in development of forging technology of chosen construction elements which serve as light substitutes of currently used materials.

The paper presents results of research concerning the impact of different values of friction coefficient on pressure during an uniaxial compression test. The study was conducted using a simulator of metallurgical processes Gleeble 3800 located at the Institute of Metal Forming and Safety Engineering in Czestochowa University of Technology. Cylindrical samples with dimensions of φ 10 x 12 mm were upset at 1100 °C with a deformation of 15, 30, 45 and 60%. During the test such parameters like: temperature, strain, stress and pressure were recorded. In order to perform numerical simulations the flow curves obtained in the form of a table were loaded into the program Forge 2011. In the numerical simulation the coefficient of friction was varied in the range 0,05 ÷ 0,4 and friction factor in the range 0,1 ÷ 0,8. The obtained results allowed to compare changes of barreling deformation of the sample and the pressure. The results allowed also to modify the plastometric curves and to continue the process of the numerical studies of real metal forming processes.

The paper presents research results aimed at determination of the best controlled cooling conditions for 16,5 mm in diameter wire rod. The examinations were carried out for 20MnB4 steel grade for cold upsetting.
In the first research stage the analysis of the currently wire rod rolling and cooling technology, especially controlled cooling process according to the Stelmor technology was done. The influence of the rolling technology for the microstructure and mechanical properties of the produced wire rod were determined. In the next research stage TTT and DTTT diagrams the for the investigated steel grade were elaborated The purpose of this research stage was determination of cooling rate for the microstructure formation of the analyzed steel grade.
Based on the obtained diagrams and metallographic investigations the changes of wire rod controlled cooling process were proposed. These modifications should to improve of final product microstructure and mechanical properties.

Nickel-chromium alloys are increasingly being used in the construction of the most loaded machine components including aircraft engines, therefore, determining the parameters of metal forming for those alloys is very important.
The hot deformation behaviour of Ni55Cr45 alloy with cast starting structure was investigated in the temperature range of 750 – 1150 °C and strain rate range of 1 – 100 s-1. The workability consists of two parts: the intrinsic workability and the State-of-Stress (SoS) workability.
Processing maps showing the intrinsic workability dependent on the material properties have been drawn on the basis of experimental data from compression tests carried out on the thermo-mechanical simulator Gleeble 3800 and based on the Prasad's approach.
Due to the significant influence of strain on the efficiency of power dissipation parameter  and the instability parameter , maps were drawn up for a true strain in a range of 0.2 - 0.9. The processing windows and the flow instability regions have been determined.
By using Lua scripts processing maps have been integrated with the commercial software based upon FEM – QForm V8 for numerical calculation, which made it possible to designate the distribution of the flow instability parameter  during forging.
In addition the strain rate, the strain rate sensitivity parameter m and the efficiency of power dissipation parameter  for the studied forgings have been determined.
Such an approach has allowed to integrate the intrinsic workability and the State-of-Stress workability and showed that it can be considered as an effective method of workability analysis.

The paper presents experimental results of diameter reduction in tubes with the angle of flare α=300. Tube diameter reduction was performed on the WPM-120 cold profile eccentric rolling machine. In the investigations, AISI MT 1020 (ASTM A513) steel tubes with the relative ratio s0/D=0.09 were used. The appropriate values of the eccentric and feed were chosen for the experiment. The coefficient of necking for the samples was K=D/d=1.46 (where d - smallest diameter in reducing tubes after rolling, D - initial outer tube diameter). The evaluation of the quality of the samples obtained in the experiment was based on the measurements of cylindricity and the wall thickness distribution in the longitudinal section of reducing tubes. The measurements of cylindricity were taken with the ZEISS PRISMO navigator, a coordinate measuring machine. The results obtained in the experiment might be used as guidelines to develop a technological process for manufacturing such type of reducing tubes with the WPM cold rolling method. They could also be helpful while applying the method to industrial practice.

Microalloyed steel P355NH or EN 10216-3, which is intended for the production of the seamless steel tubes for pressure purposes, and S355J2H or EN 10210-1 vary especially by the amount of the niobium (0.013 % in case of the steel P355NH and 0.037 % as for the S355J2H, respectively). Uniaxial hot compression tests performed on the Hot Deformation Simulator HDS-20 were utilized to compare the influence of the niobium amount on the hot flow stresses of these steels. There was investigated in case of both steels the temperature range from 700 °C to 1200 °C in combination with the nominal strain rate range from 0.1 s-1 to 100 s-1. The unique computing method was employed to correct the shape of the experimentally obtained hot flow stress curves influenced by the spreading of the test samples at high strains. Then it was possible to calculate with using the peak coordinates the value of the activation energy at hot forming 534.9 kJ•mol-1 in case of the steel P355NH and 554.3 kJ•mol-1 as for the S355J2H. Decrease of the temperature led to the increase of the hot flow stress. The same influence had the increase of the strain rate value. There was found out, the higher amount of the niobium has been mostly led to the increase of the hot flow stress. This means, the hot flow stress of the steel S355J2H is almost at each temperature higher against of the steel P355NH. Nevertheless, some different flow stress behavior was observed at small strain rates.

Nickel superalloys like Inconel are used for the production of aircrafts engine components exposed to high temperatures. These alloys are characterized by heat and creep resistance. One of the technique for producing is rotary forming. Due to the limited plasticity have been made attempts of forming at elevated temperature, or even hot. One way of heating is a laser heating. Aim of this study is to identify the components of the microstructure of material in initial state, and products made of nickel superalloys in the rotary forming process. The analysis is based of microstructure and mechanical properties study of material in initial state and after deformation.

The two-dimensional task of isothermal rolling of aluminum sheet in the superplasticity conditions realized with a low angle of nip is considered. The solution of the task is based on the well-known mechanisms of the plastic flow in the wedge-shaped convergent canal. For the mathematical formulation of the task the theory of elasto-plastic processes ratios of the small curvature was attracted, and the state equation is suitable for the description of regularities of high-temperature deformation in the wide strain rate-rate interval including the conditions of superplasticity effect realization. The components of the movements rates vector, tensors of the stresses and strain rates are written down. The parameters summarized rate, geometrical contact factors in zones of backward and forward of rolling are determined. It is shown the existence of the angle of nip below which the center of deformation is considered only as forward of rolling zone.
The specific calculations of the roll force distribution corresponds to thermal superplasticity conditions and outside of its applied to industrial alloy EN AW 5083 was carried out and the results were compared. The experimental realization of the process has been realized in the approximate chemical composition alloy EN AW Alustar with the producing fine-grained structure in the rolled product.

A model of prediction of flow stress during hot rolling plates and wide strips of carbon, low alloy and micro-alloyed steels, especially deformation resistance which are not yet known, was developed. Method of L. V. Andreyuk was adopted for a basis of model, wherein each of thermomechanical factors represented as equations for the 13 chemical elements. The main limitations of the method (rolling temperature not less 800 °C, strain 0.05-0.3) are overcome by supplementing the known dependence factor, which takes into account the phase transformation, as well as a factor that compensates for the degree of error in the calculation and strain rate. These factors have reduced the lower limit of the confidence interval for the temperature to 700 °C and raise the upper limit of the confidence interval for the degree of deformation up to 0.5. The degree of conformity predicted and observed values of the flow stress is 82.6 – 94.7%.

The paper is aimed on the investigation of the deformation behaviour of two nickel alloys – IN 713 LC and MAR M-247 which are delivered in as-cast state. The goal was to physically determined the nil-strength temperatures and assembled 3D-maps of the plastic even strength characteristic of both alloys on basis of uniaxial tension tests. The determined nil-strength temperatures of the investigated materials are 1295 °C in case of the alloy IN 713 LC and 1310 °C as for the alloy MAR M-247. These values are almost by 100 °C lower than in case of common steels, which indicates higher susceptibility of these alloys to burn away at the heating before forming. The results of the high-temperature tensile tests of the given alloys correspond with the low nil-strength temperatures. The examined alloys would be possible processed by forming in the relatively narrow temperature range ca from 1000 to 1100 °C (IN 713 LC), ca from 1000 to 1200 °C (MAR M-247) respectively. The experiments were performed on the Hot Deformation Simulator HDS-20 that is operated in Regional materials science and technology centre on VŠB-TU Ostrava.

Development of materials with ultra-fine-grained structure belongs at present to the front-end areas of research of materials and forming technologies in the whole world. Technology of manufacture of semi-products (strips, round bars and sections) with ultra fine-grained structure is intensively developed namely in Korea, USA and Japan. Increase of the load transferred by structural elements made of these materials with simultaneous enhancement of safety of structures. Nano-structural materials in mechanical engineering, metallurgy, automotive, military and aerospace industry are applied. Used DRECE process belongs to the group of a progressive type of forming processes making use of severe plastic deformation (SPD). After this processing the materials exhibit in comparison with conventional structure materials significantly higher mechanical properties, especially yield strength, and in limited extent also ultimate tensile strength. Forming process DRECE is an extrusion technology with limited cross-sectional reduction to achieve high degree of deformation of the suitable selected material. DRECE machine can unequivocally contribute to implementation of new production technology for strips made of non-ferrous metals and steels (as semi-finished products), which have substantially higher mechanical properties with preservation of their formability.
Experiments with use of selected steels and brass were made on the DRECE machines to achieve grain refinement in the strip of sheet with dimensions 58 x 2 x 1 000 mm. A prototype of this equipment developed has been put on Department of Mechanical Technology, VSB-Technical University of Ostrava, Faculty of Mechanical Engineering. On the part of brass strip sheets after the first DRECE processing next heat treatment 400oC/15min/air has been made to obtain the behaviour of that materials after heat treatment with aim the next DRECE processing with changing conditions namely with obtaining grain refining. Metallographic analysis of structure was made on optical microscope NEOPHOT 2 and mechanical properties of studied samples by tensile test and Vickers hardness method were tested.

The bore expansion test represents one of basic technological tests for determination preparation technologies influence on the maximal strain value. The most frequently it is used to determine material limit stage at comparison blanking and e.g. nonconventional cutting methods (abrasive water jet, laser and so on). Regarding the great development of contact-less optical methods for measuring deformation it is subsequently very suitable to use photogrammetry also at measurement and evaluation the bore expansion test. As an advantage there is e.g. very transparent graphical display of strain distribution around the bore without necessity to manually measure final bore diameter, information about strain change course during the whole test or also possibility to display strain gradient in any direction. On the other hand among disadvantages of contact-less optical deformation measurement is mainly purchase price, necessity of their precious adjustment before measurement (calibration of cameras, setting of shutters and so on) and also requirement for special surface treatment of sample (stochastic pattern). Within the experimental part of this paper there was measured the bore expansion test by contact-less optical system ARAMIS. As a tested material was chosen the phosphated deep-drawing material DC06. The purpose was to find out for six different initial diameters (from 5 mm up to 30 mm á 5 mm) strain distribution around bore for the last stage before the fracture and subsequently to evaluate strain gradient change in radial direction. After that final data were processed statistically and graphically, mutually compared to determine strain gradient change influence.

During the last years there is a strong tendency of automotive industry to achieve suitable compromise between effort to lower environmental load at car operation by lowering its weight (thus to lower thickness of used parts) and on the other hand there is tendency to still increase safety of passengers by utilization ultra-high strength materials. That is why these days are more and more important strength materials and alloys based e.g. on aluminium or magnesium. However industrial processing of these materials reveals quite a lot of problems. Thus these days there is a great demand for high-quality computational models within the numerical simulations for processing these materials because quite great portion of producing problems can be eliminated by pre-producing phase using numerical simulations (FEA). For precious numerical simulations computation is, beside geometry of part and tool, very important selection and accuracy of material input data subsequently regarding also selection of own computational model. During the last years there were developed a lot of computational models which within the metal forming regard yield criterions. One of these yield criterions is also anisotropic computational model named as Vegter model. The purpose of this paper is not only to describe such computational model but mainly to show procedure of measurement the most important input material data for stainless material to be computed by Vegter model. Such measurement is not only about static tensile test but there is used also the hydraulic bulge test to determine so-called bi-axial point in Vegter model.

These days there can be observed still increases requirement about products quality at keeping low price level. Such contending claims of market environment force producers in every branch of engineering industry to innovate their technological procedures and to process new progressive materials with specific utility properties. Regarding great development of numerical simulations there is not only use of computation methods but also qualitatively higher level of modeling technological processes where PCs behave as computational models on which it is possible to simulate also such processes which would be very difficult to carry out on the real part under operating conditions. Numerical simulations results are greatly influenced by knowledge and quality of input data. There are mainly boundary conditions which characterize simulated process, knowledge of the stress and deformation behavior of forming material and last but not least also selection of the proper computational model. For the most used computational models is material deformation behavior described only by static tensile test in combination with normal anisotropy coefficients. However for specific materials, thus also titanium alloys, is such characterization insufficient and is obvious that results from numerical simulations observed from this measurement do not agree with the real forming processes (mainly stamping). In this paper is described possibility to use advanced computational models for drawing process numerical simulation by software PAM STAMP 2G and method how to obtain input parameters for the material definition of the formed material. Results from the numerical simulation are compared with experiment ones.

Knowledge of deformation limit states is the basic presumption for the proposal of all forming operations at stampings production. Deformation limit states of given material are greatly influenced by forming temperature, stress state and strain rate. Regarding the fact that common types of steel sheets are not formed under higher temperatures, size of limit deformation depends mainly on the stress state and the strain rate. For the technical community is the dependence of deformation limit states on the stress state commonly marked as forming limit diagram (FLD) and there are many experimental and numerical methods how to obtain so-called forming limit curve (FLC). Problem about strain rate on the deformation limit state is not so frequently discussed and in mostly cases it is just focused only on the research zone for uni-axial stress state. In this paper is evaluated influence of strain rate on the deformation limit state of TRIP steel at different stress states (from uni-axial up to bi-axial stress state). At experiment there is used pneumatic device which was designed and assembled at TU of Liberec and which makes possible to achieve the impact velocity of punch up to 30 m·s-1. Deformation analysis of tested samples was carried out by modern contact-less system ARAMIS in combination with high-speed (HS) cameras Photron SA3 which enables to scan processes under frequency up to 100 kHz. Results of experiments are presented by forming limit diagrams for chosen strain rates and by examples of deformation distribution on tested samples.

The paper presents the results from experimental studies of the combined extrusion of parts made of ENAW-1050A alloy. The studies were divided into three stages depending on the relative strain value of the material extruded in forward direction, 1: 0.77, 0.69 and 0.59. For each value of the relative strain 1, different values of relative strain of material extruded in backward direction were used, 2: 0,36, 0,46, 0,58. On this basis, the influence was determined of the relative strain level in the material extruded in forward and backward directions on the die pressure value. It was demonstrated that the values of die pressure in the combined extrusion increase with the levels of relative strain of material extruded in forward and backward directions. For combined extrusion, the pressure forces are smaller than during the forming of the extrusions in two procedures where in the first procedure, the cylindrical part is extruded in forward direction and in the other procedure, the sleeve part is extruded in the backward direction. Combined extrusion reduces the effort necessary to manufacture a product and the cost of manufacturing the tools whose durability is additionally enhanced due to lower values of exerted pressure.

Shear deformation of subsurface layers in wire drawing leads to marked non-uniformity of strain across the wire cross section. In wires intended for products operating under dynamic loads, such as ropes and springs, the variance in work hardening level across the cross section may cause fatigue fractures. In this paper we used physical modelling in an attempt to show how the non-uniformity of strain in drawing can be reduced by changing key process parameters. For this purpose, a full factorial experiment involving three factors was undertaken. (The factors included the approach angle 2α, single pass strain Qd or the number of passes n and type of scales removing (pickling or 2 axis bending + brushing.) The simulation involved drawing of 2.5 mm C78DP steel wire from 5.5 mm thick rolled rod. Single wire drawing block Koch with rotating die holder was used for the modelling. In this paper we evaluate the influence of factors on final plastic properties of the wire (number of torsion to fracture). The test was conducted in accordance with the ČSN ISO 7800 standard Metallic Materials - Wire - Torsion test.

This article is devoted to the problem of forming of axisymmetric elements of hard-to-deform material. The first stage was the deep drawing process of metal discs. Then the blanks were formed by the method of flow forming. Numerical simulations of both the processes were realized in Kraków at AGH University. Numerical verification of both processes was carried out using finite element models implemented with the help of commercial analysis system on basis of conducted in Poznań experimental shaping tests.
The use of modern computer technology has become an integral part of the development of innovative flow forming technologies. The use of software tools in the forming of numerical analysis systems based on the finite element method speeds up the design and optimization of processes.
This article summarizes example results of both numerical and experimental forming of products made of hard-to-deform material.

The Zn-Mg coatings are considered as the next generation of steel covering to be used in automotive industry since they improve the corrosion resistance of the base material. The weakness of this coating lies in its higher hardness and lesser ability of plastic deformation as compared to the purely zinc coatings. The Zn-Mg coatings break out and by higher deformation even flake off, which can influence the corrosion properties of the material. The experiment described in this article analyses the properties of the Zn-Mg coating in the dependence on the extent of deformation by different temperatures. The specimens were gradually deformed until their total rupture. Subsequently, the coating of deformed specimens was analysed by using electron microscope and the x-ray diffraction method. Y-ray diffraction methods are used for the evaluation of qualitative changes in the real structure of polycrystalline material. This method helps to find suitable technologies that do not cause cracking of the Zn-Mg coating.