The work presents the results of a study on drawability evaluation methodology of thin sheet metals of high strength. Materials of high strength are used for the construction of car and aircraft components. Those components are responsible for the safety of the construction of vehicles and thus for the safety of passengers. The high strength of the thin metal sheets creates limitations in their deformability. Due to the limited deformability, development of the drawability evaluation methodology is particularly desirable by designers and manufacturers. Automotive industries have many manufacturing problems with so-called advanced high-strength steels (AHSS), while the aerospace industries - with heat resistant and creep resistant alloys, and e.g. nickel superalloys. In these cases, the standard procedure for the qualification of stamping materials has been found to be insufficient. Due to this both industrial problems have been undertaken research on drawability evaluation of selected high-strength thin sheet metals made of DP steel (AHSS representative) and Inconel 625 (nickel superalloy representative). These studies allowed formulating guidelines to methodology of drawablity evaluation of high-strength thin sheet metals. In addition, previous experiences gained in the project N R15 0042 06 under the title: “Development of methods for computer-aided design process of stamping products for the aerospace industry”, financially supported by Polish The National Centre for Research and Development (NCBiR) in years 2009-2013 and conducted at the Institute of Material Technology of the Silesian University of Technology, have been added. The drawability of these sheet metals has been comprehensively defined by forming limit curves designation, while modern AutoGrid® digital local strain analyzer and the method of image analysis of deformed coordination nets has been applied. Hereby quantitative and qualitative drawability have been evaluated.
Forming limit diagrams (FLD) are used to determine process limitations in sheet metal forming, i.e. as a level of formability assisting in the estimation of stamping characteristics. This paper deals with experimental determination of a forming limit curve (FLC) using the Erichsen test. In this case, FLC of an austenitic stainless steel X5CrNi18-10 is obtained by performing the Erichsen test with different shapes of specimens. Furthermore, utilization of FLD for evaluation of a hydroforming process is shown in the second part of the paper.
Slab thermal homogenization during reheating in furnace is temperature and retention time dependent. Dissolution of microalloying element like niobium in austenite at soaking temperature is important; to achieve desired strength and toughness in final rolled product. Under soaking and low set temperature may not dissolve microalloying elements and on other hand over soaking and higher temperature may lead to austenitic grain growth. In both cases, it affects, strength and toughness of the final product. The optimum temperature and retention time allows micro-allying elements to dissolve in austenite and controls austenite grain growth. These conditions are favorable to achieve both high strength and toughness in the rolled strip.
Gleeble 3000 physical simulator was used to conduct trials with combination of various soaking temperatures and time. Prior austenitic grain size and dissolution of micro-alloying was evaluated. To validate experiment and check relevance of experiment with actual rolling during production, laboratory muffle furnace was used and same plant process conditions of soaking temperatures and time were used to simulate actual plant conditions. The results of validation trials were encouraging. Temperature of 1220°C and soaking for 15 and 30 Seconds in Gleeble experiments, had shown similar results, this was deciding factor for the optimizing retention time in reheating furnace. Based on laboratory trials results, plant trials were conducted with reduced furnace retention time of 160 minutes minimum against 170 minutes earlier. The test results of plant trials were satisfactory and meeting specification requirements. Special technique of micro etching was used to reveal prior austenitic grain size.
With 10 minutes reduction in retention time for group of steel grade, around 6% more time will be available for rolling, contributing to increment in production and financial benefits.
Examination of structure-forming processes of HSLA steel with 0.025 % Nb was performed in relation with rolling of the heavy seamless tubes in the Big Mannesmann mill. Based on the dilatometry data, a DCCT diagram after deformation 0.35 at temperature of 900 °C was designed. Hardness HV 30 of value 157 was determined for low cooling rate of 0.2 °C·s-1 and the structure was consisting mostly of ferrite and pearlite. For faster cooling with rate of 60 °C·s-1 the hardness was equal to 404 with entirely martensitic structure. Non-recrystallization temperature was determined by the rolling-cooling-quenching tests and metallography just above 850 °C. Finally, steel samples were subjected to temperature controlled rolling and cooling with the rate of 0.25°C·s-1 in the laboratory reversing mill with the working rolls’ diameter of 350 mm. Grain refinement as well as homogenization of the final microstructure was observed after lowering the finish rolling temperature in the interval from 990 to 850 °C. Greater effect of decreasing finish rolling temperatures was observed below 890 °C as a result of deceleration of the recrystallization kinetics due to the precipitation during the cooling phase and getting closer to non-recrystallization temperature. The smallest secondary grain size of 17 μm was achieved despite the initial coarse-grained structure (created by preheating at 1280 °C), low degree of material deformation and slow final cooling. Low-temperature finish rolling resulted in a significant increase in the roll forces – approximately by 50 % when comparing the results of experiments performed at temperatures of 990 °C and 850 °C.
The abnormal prices of copper and aluminium over the last decade have led to increasing substitution of copper with aluminium. This is mainly possible due to the favourable relation of the strength properties of aluminium to its density with respect to copper. An aluminium conductor with the same length and the same resistance has twice the weight of a copper conductor. The main technological problem of substituting copper with aluminium lies in the technology of drawing small diameter aluminium wires and their annealing on-line. In recent years, this problem has been effectively solved by introducing dedicated aluminium alloy grades and a new generation of rod breakdown machines and multiwire machines that allow drawing aluminium using emulsions with simultaneous annealing of online wires in a way similar to annealing copper wires. Due to the high stacking fault energy of aluminium in relation to that of copper, the aluminium alloy is characterized by a recovered structure, which translates into low susceptibility of the aluminium wires to annealing. This problem is not observed with copper wires. The article includes the results of studies of the process of strengthening Cu-ETP copper wire rods and EN AW 1350 aluminium wire rods, and the annealing characteristics (softening curve) observed during the hour-long annealing process. The structures of wires after drawing and after annealing and their electrical properties are presented. The analysis of the studies shows that the temperature of recrystallization of aluminium wires is about 200°C higher than that of copper wires of the same deformation degree. There was a significantly different recrystallization kinetics of the studied wires (different angle of slope of the UTS = f (T) characteristic), which translates into the need for other current settings in the annealing line in production lines.
In the paper the problem of changes in structure and properties, occurring under the influence of cold deformation of a high-manganese austenitic steel with various rates, strengthened in the result of mechanical twinning were presented. The goal of the research carried out using static and dynamic FWM and HPB methods was to obtain material characteristics, and most of all a detailed analysis of changes occurring in the steel microstructure in a broad range of deformation rates and deformation magnitudes.
The results may be useful in application of the steel for structural elements under dynamic loads. The calculated high value of the absorbed deformation energy factor EABS confirms that the steel has an ability for transmission of dynamic loads irrespective of its stress condition. Both in tensile and compression tests using high rates, the calculated value of the EABS factor of the steel remains in the range of 0.4-0.47. Hardening of the X55MnAl25-5 steel while maintaining its high plasticity results from participation of two basic mechanisms of plastic deformation, i.e. glide and twinning, and their contributions depend on the deformation rate and magnitude. The results of structural investigations became a basis for development of original models of structural changes under conditions of both tension and compression, in which characteristic stages of structural evolution depending on the deformation parameters were distinguished. These models were developed taking into account the participation of the individual deformation mechanisms in the steel hardening process. Moreover, a schematic conceptualization of relation of parameters of the deformation processes and the deformational hardening mechanisms, and their influence on EABS of the X55MnAl25-5 steel was proposed. Two basic plastic deformation mechanisms participate in the hardening process, namely glide and twinning. As the deformation rate and the deformation value increase, the dislocation structure undergoes a transformation and simultaneously, the share of mechanical twinning increases. As a consequence, deformation of steel with high rates and high deformation values occurs in the result of mechanical twinning, and structural effect of the glide assume a form of advanced dislocation configurations, accompanied by effects of an intense cumulation of energy stored in the form of shearing bands.
Drawability data of a sheet material considering to its thickness is essential for tool and drawing step design to prevent the part failure during the deep drawing process. However, there is no direct procedures to determine material drawability, especially for recently developed high-strength alloys, One of the most commonly used procedures to compare drawability of different materials is determination of limiting draw ratio (LDR). LDR is the ratio of the maximum blank diameter to the punch diameter that can be drawn successfully without failure in one step.
In this paper, drawability of Hynes 230 alloy which is a high-strength superalloy, evaluated using Swift cup test to determine its limiting draw ratio (LDR). Evaluation of the impact of Punch and Die corner radius on limiting draw ratio (LDR) is the next section of this paper. The results shows that increasing parameters of the Punch corner radius and the Die corner radius increase the limiting draw ratio (LDR).
The evolution of the new microstructures produced by under hot deformation conditions is reviewed. The Finite Element Method (FEM) and Experimental Planning Method (EPM) has been used for the examination of the combined effect of the temperature-strain parameters of structural steels and super alloys during rolling and forging metal forming technique. It is shown that simulation of dynamic recrystallization for the definite cross-section of profile by FEM on the base of the data obtained by EPM allowed to predict structure and mechanical properties and to develop computer modelling for the different cross-section of finished profile.
The contribution deals with an unconventional way of the connection of steel pipes with a thin wall. In the introduction, the one of methods of the electromagnetic forming tubes is described. The induction is the essence of this phenomenon. The accumulated energy is lost through the coil, thereby resulting a repulsive power that causes strain times. Further, the theoretical conditions of the process and the three possible transition phenomenon in electromagnetic circuits are described. For the following experiments the suitable state is, when the current is damped at the aperiodicity limit.
The experimental section deals with the real design solution of the forming equipment for the electromagnetic forming tubes. According to the equation (1) referred in the text of this contribution the number of coil turns was determined. By means of this coil experimental works were carried out, thus linking the two tubes. Figures in the text of this contribution illustrate the entire forming process. In experimental verification there was found that the length of the associated parts is an important point. The pipe walls thickness is also of particular importance. Decreasing the thickness of the walls is in direct dependence with increasing diameter of the hole, i. e. the coil may have higher parameters, as they are determined by calculation, which is the one of the important conditions for the success of the process after making experiments in the connection parts.
The aim of our study was to investigate the cold rotary swaging on the Ti6Al4V alloy with a finite element modeling (FEM) and subsequently by experimental verification of the model predictions. The experimental examination was evaluated both cast and swaged material states. A FE analysis was performed to describe the rotary swaging from a 7.5 mm round bar diameter with the total reduction of 27% in cross-section. The numerical simulations were focused on the investigation of swaging force, distributions of strain, stress state, temperature and plastic flow of material. Subsequent experimental verification such as microhardness, tensile properties, and microstructure observations validated the predicted results. The one of experimental analysis was dedicated on measurement of swaging force during RS by using KOMAFU S600 dynamical force measuring system. After comparison between predicted and experimentally obtained data a good agreement was found. Among others there was observed same trend between microhardness profile and imposed strain distribution throughout the cross section of swaged billet.
Owing to its versatility and the ability to provide the final products with advantageous characteristics, rotary swaging is widely used in automotive industry for production of various components. The focus of this study was to perform numerical prediction of rotary swaging of a steering tube. The predicted results were subsequently evaluated with data gained from experimental swaging. The analyses carried out on the experimentally swaged model included measurements of microhardness and surface roughness, as well as scanning electron microscopy observations. To evaluate reliability of the simulation, the simulated swaged component was compared with a 3D-scanned real product. As shown by the results, the parameters of the dies and processing conditions defined in the simulation corresponded very well with the real process and thus the designed numerical model can be considered as an accurate one. The swaged product featured a very smooth surface and small equiaxed grains, 80% of which were smaller than 1 µm, with no prevalent grains orientation.
Ecological and economic reasons become more and more important by energy efficiency and resources savings. Especially for the automotive and transport industry – but also for all other industrial branches dealing with accelerated masses – lightweight design is a key issue for achieving this goal. Higher process stability, improved material exploitations, and general shortening of process chains are the most important aims of Fraunhofer IWU. The requirements of the future car achieve the lightweight construction concepts, in which materials, design and manufacturing process harmonize optimally. A target-oriented design helps to save weight by using optimally adapted structures. To enable the design of the structuring, the influence of structures manufactured by different forming technologies including electromagnetic forming (EMF) and forming by elastomer tools, was systematically analyzed through complementing numerical and experimental investigations. Knowledge about the influence of the structuring technology and the process parameters on the resulting structure and the part performance allows conclusions regarding the optimization of the part functionality via a suitable selection and design of the process. The sequential forming is a good way by flexible manufacturing of big 3D-sheet metal parts.
The article presents the influence of the metallurgical process condition on the parameters of drawing M95 brass rods obtained in the continuous casting process. This work has investigated the effect of input material composition (scrap selection), diversified casting speed (various feeding and stopping time) to allow for crystallization and cooling intensity on cast quality, including solid particles removal. Studies were conducted on cast made of M95 brass and included the research on: mechanical and electrical properties, elastic constants and also comparison of density of particular casts. Casts obtained in process were subject to deformability tests in the drawing process. The drawing process was carried out on samples with the diameter range of 9.5 to 4.45mm. The research produced the flow curves for the tested materials. Comparison of this curves allows to determine the influence of metallurgical synthesis parameters of M95 brass on flexibility and force parameters in drawing process.
The cylindrical samples of AISI 1018 steel were subjected to loading by the shock wave of the bicyclo octogen explosion. Phase and structural transformations were investigated by methods of metallography and micro-hardness measurements. The ferrite-pearlite structure changes at high-speed plastic deformation, hydrodynamic flow effects, including formation of adiabatic shear bands were investigated. The microhardness changes in different parts of the loaded sample were analysed.
The process of spall fracture is divided into several stages: nucleation and growth of micro-defects under the influence of tensile stresses, the merger of neighboring developed defects in macrocrack, metal separation, the formation of free surfaces.
With the explosive charge mass increasing, the amplitude of leaving the free surface shock wave pressure increase, which created conditions for spalling observation σ_tens≥σ_frac.
The loaded samples were observed for adiabatic shear band and localized flow caused by the powerful influence of a shock rarefaction wave.
In the study, changes in microhardness after the shock wave loading, the following patterns were found. At a distance of 250 µm from the loading surface micro hardness increases up to 430 HV and abruptly falls off at a distance of 500 µm up to 160 HV.
Increased hardness of adiabatic shear bands caused by the fine-grained structure, which was formed by dynamic recrystallization, accompanied by a significant rise in temperature.
Thus, the nucleation and growth of cracks in samples of the investigated alloys is determined by the conditions of shock-wave loading: the action of primary and reflected stress waves, the properties of the sample material, their macro- and microstructure.
The reason for the increase in hardness and other related mechanical properties after the impact of high-speed deformation by the shock wave of the explosion is spatial changes in the characteristics of the microstructure. That is, the formations of martensite and adiabatic shear bands.
In the field of boiler tubes in the energy sector, it is becoming necessary to define characteristics of the boiler tube more precisely, not only from the perspective of material properties, but more importantly, to focus on the inner tube surface. The primary importance of the inner tube surface is to ensure the flow of the heat transfer medium in the most efficient manner. In addition to reducing the effect of friction parameters, most of the customers and tube producers for energy sector focus nowadays on the shape of the inner surface as it ensures better flow of the medium as well as more efficient transfer of heat energy.
In this article we deal with optimizing the production of tubes with multi-rifled inner surface in terms of the stability of the geometric dimensions of the produced tube as well as the impact of tool wear on the production cycle. For these analyses, optical 3D scanning devices were used in order to ensure precise measurement of dimensions of multi rifled tubes drawn in the experiment. The experiment was performed at the production of Železiane Podbrezová a.s.
Forging die inserts used in the industrial hot forging processes characterize in a relatively low hardness, which directly translates to both the quality and the cost of the forging production. The mutual relations of the particular degradation mechanisms of forging tools significantly vary and depend mainly on the operation conditions under which the forging process is conducted. Usually, during semi-free die forging (upsetting, flattening, etc.), the tools are not lubricated due to the complicated flow of the deformed material. This case is different from the one of typical die forging, during which the application of a lubricant is required in order to minimize the friction, aiming at precise filling of the working pattern of the tool by the deformed material. During the operation of upsetting, scale is removed (periodically cleaned off by the forger), which also can affect the durability. This makes the operation conditions for non-lubricated, and thus non-cooled, tools to be different from the ones for lubricated tools. A little different case is with forging tools which are not lubricated or cooled, for which the typical degradation mechanism is abrasive wear and plastic deformation [3,5,7]. The research performed by the authors concerning the analysis of the surface layer of forging tools showed that, in the case of forging processes conducted at elevated temperatures, for typical tool work conditions (lubrication and cooling), the percentage of abrasive wear as the dominant degradation mechanism decreases, and the participation of thermo-mechanical fatigue significantly increases, this process being the one which accelerates the visible and easily measured abrasive wear, as a result of which the tools are removed from production.
Advanced high strength steels contribute reducing the weight of the cars by enabling the using of thinner sheets. However, cold forming of steels with a higher strength may cause problems such as springback, buckling, and crack of the parts during forming operation. Hence, press hardening process gain importance in recent years by minimizing the risks arises from forming. Thus, the press hardened steels make possible to obtain higher tensile strength compare to other advanced high strength steels.The press hardening process is carried out at high temperatures and therefore, temperature resistance coatings such as Al-based coatings are required for press hardening. Press hardening temperature causes the melting of zinc. After application of metal forming stress, the segregation of liquid zinc can be observed in the grain boundaries in steels. Grain boundary segregation of zinc leads to Liquid Metal Induced Embrittlement and delayed fracture. On the other hand, zinc coating is more attractive for automotive industry, because galvanic or cathodic corrosion resistance is not provided by Al-based coatings contrary to Zn coatings. In this study, endurance limit of zinc coating versus press hardening temperature is tried to be understood by using Zn coated 22MnB5. Press hardening process is carried out at temperatures, 745°, 755°, 775° and 950°C with applying 30% deformation. After the press hardening, samples were examined by Scanning Electron Microscope. Grain boundary segregation of Zn is observed at samples press hardened at 950°C. However, no grain boundary segregation was observed for samples press hardened at 745°, 755°, 775°. It was concluded that there is a potential for using Zn coated steels for press hardening with lowering the process temperature.
With using of tension tests, which were performed on universal plastometer Gleeble 3800, the influence of grain size on hot formability medium-carbon steel was investigated. From investigated steel were prepared 2 sets of samples, while the booth sets were made from the same melt. The first set of samples was made from hot rolled bars. The second set of samples was made from the subsurface area of the continuously cast billet. It can be assumed that the samples prepared from a cast billet should have a relatively coarse grain structure, whereas samples made from hot rolled bars should have relatively homogenous fine grain structure. The samples with initial deformed structural state were heated directly to the selected deformation temperatures, whereas samples with initial cast structural state were uniformly austenitized by temperature 1300 °C and then were controlled cooled down to selected deformation temperatures. All hot tensile tests were performed at uniform tension rate 1000 mm•s-1. The samples from initial deformed structural state exhibited, with comparison of samples from initial cast structural state, the higher contractual hot strength and smaller hot ductility. The interesting results of hot ductility were obtained in two-phase low temperature region. In case of samples from initial cast structural state the ductility at low temperature two-phase area decreased, whereas in case of sample from initial deformed structural state the ductility unexpectedly increase.
The procedure to determine unambiguously the material constants K, m for standard power law of superplasticity σ=Kξ^m from the results of constant pressure bulge trials is developed. The mathematical modeling is carrying out using the principal equations of thin shell theory. The boundary value problem in mechanics of solids is stated in terms of the theory of creep. Finite element modeling is effected using ANSYS software. Unlike of known approaches the solution of inverse problem is found taking into consideration the influence of entry radius of the die used. The procedure to calculate the pressure-time cycle of forming is also suggested. The results of finite element calculations are compared with corresponding analytical solutions as well as with available experimental data, a good agreement being found for titanium-based alloy VT6 (Ti-6Al-4V) and aluminum based alloy AMg6 (Al-Mg-Mn).
Deformation characteristics of carbon steel are studied in the temperature range 900-1200 ° C and strain rates 0.1-100 s-1 on the plastometr Gleeble using compression test on cylindrical samples. Processed a single dissipation maps in the field of forming are developed on the basis of changes in the effectiveness of dissipation, depending on temperature and deformation resistance, taking into account the strain rate. Strass-strain curves under different deformation conditions were used. Map of absorption of energy reveals that peak efficiency of strain rate sensitivity parameter is achieved of m values of 0.21 and from that the energy dissipation efficiency η is calculated with purpose to find the optimal forming conditions. At the same time to the contour dissipation map, the map of an instability criterion ξ has been added. The instability forming mode is recorded lower values of ξ, in the present case, however, it is not a dramatic slump, only a warning on the possibility of defects. Behavior analysis indicated that there were a dynamic recrystallization at higher temperatures and in all conditions forming since the value 0.2 deformation (deformation at lower strain rates there) and always above 0.2 to 0.4 even at high strain rates.
Heavy seamless tubes are produced by the Big Mannesmann Rolling Mill in Třinecké železárny plant. Their final microstructures and properties are not only given by steel chemistry, they are also largely influenced by cooling conditions after finish-rolling. Continuous cooling transformation (CCT) analysis of various steel grades has been increasingly an object of the researchers' attention. Nevertheless, the phase transformations are also affected by the initial microstructure (e.g. austenite grain size) and previous deformation (ratio of residual hardening and softening). For that reason the DCCT diagrams (including the influence of defined deformation e = 0.35) of the HSLA steel X70 were designed for two states of the initial microstructures. In rough outline, the tested steel has the following chemical composition: 0.16 C – 1.0 Mn – 0.2 Cr – 0.05 V – 0.03 Nb (in wt. %). Phase transformations in the course of cooling were studied by dilatometer tests (performed in the Gleeble 3800 hot deformation simulator, to wide cooling rates range, from 0.15 °C/s to 80 °C/s), metallographic analysis and hardness as well as micro-hardness measurement. Coarse gamma grains (G = 3) were produced by high-temperature preheating (1280 °C) of the dilatometer samples made from the continuously cast bloom with diameter of 400 mm. Fine initial microstructure (G = 11) was obtained by severe laboratory hot rolling of the cast material and normalizing. Lower temperature of austenitization(900°C) has been set in the dilatometer to make such samples from the normalized material. Great transformations were observed, some coarse-grain samples containing acicular ferrite, whereas mixture of martensite and austenite appeared in the fine-grain samples cooled with rates of at least 12 °C/s. Lower heating temperature substantially accelerated the gamma/alpha transformation at high cooling rates.
Transformation kinetics of austenite during cooling is influenced by several factors as chemical content or thermomechanical parameters (temperature, dwell time, deformation, strain rate, cooling rate) and initial structure state, consequently initial austenite grain size. The aim of this article was just assess the effect of initial structure state (casted, deformed, purposely extremely roughened) on transformation kinetics of austenite during cooling of steel C10, which was moreover deformed uniaxial compression. This comparison was done on the basis of construction of three transformation diagrams type DCCT (deformation continuously cooling temperature) for different initial structure state of hypoeutectoid steel C10. DCCT diagrams were constructed on the basis of combination dilatometric tests with an influence previous deformation, metallographic analyses and measurements of Vickers hardness. For the execution of the experiment, the new optical dilatometric module of the plastometer Gleeble 3800 was used. The experiment demonstrated, that in the case of hypoeutectoid and low alloyed steels and in the case of slowly cooling rate (under 10°C/s) area of ferrite and pearlite formation were not dramatically shifted influence different initial grain size. In the case of higher cooling rate are already evident temperature shifts in areas of ferrite and pearlite. The obtained results show that the finer grain size shifted temperature border area of formation of ferrite and pearlite upward towards higher temperatures. Moreover in the case of purposely extremely roughened structure metallographic analyses obtained formation of acicular ferrite after cooling of cooling rate 35 °C/s.
In this study, we will try to follow the evolution of some properties of the drawn wire of the alloy AGS 6101 and also try to see the effect of a heat treatment at high temperature.
Micrographic observation of MO and SEM shows a homogeneous fibrous microstructure of the cross-section. However, the EBSD analysis shows that the distribution of the two main fibers <111> and <001> is not homogeneous on the cross-section of the wire drawn. And as the deformation increases, it has been found that the fiber <111> tended to form more at the core of the wire and the fiber <001> was distributed at its periphery. In similar previous studies on wire drawn copper and steel, we have found similarities in certain behaviors, but this phenomenon has not been observed. We have also found that in the established texture, the dispersion of the orientation of the grains (in particular the majority fibers) decreases when the deformation increases.
A heat treatment at high temperature (400 ° C.) for this alloy, which leads to a recrystallization, never modifies the texture established by drawing and the two fibers <111> and <001> remain the majority. More importantly, the treatment appears to reduce the dispersion of grain orientation and thus improves the sharpness of the texture around the drawing line. However, treatments beyond 20 minutes lead to heterogeneity in the size of the recrystallized grains between the core and the periphery of the wires.