In the paper the application and properties of the new AHSS for automotive industry were presented. Will be carried out the analysis of properties changes and structure evolution, occurring at static and dynamic deformation of a Mn-Al austenitic steel with various strain rates. Especially strengthened in the result of mechanical twinning were presented for few selected grades of steel. After the static and dynamic deformation using a FWM and HPB methods, material characteristics and calculated value of the specific energy absorption SEA may be useful in application of the steels for structural elements used at crush zone of vehicles. On the base of results SEA value during the dynamic deformation, confirmed that the investigated steels has an ability for transmission of dynamic loads irrespective of its stress condition. Hardening of the 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 rate value. If the deformation rate and the deformation value increase, in the structure, we observed the dislocation transformation into the complex arrangement and simultaneously, increasing the share of mechanical twinning.
Schematic conceptualization of the relation of deformation processes parameters and the hardening mechanisms, and their influence on SEA of the analyzed steel was proposed.
The aim of the contribution is creation of transformation diagrams of hypoeutectoid 25CrMo4 steel that is used for tube production for the OCTG (Oil Country Tubular Goods) industry. For a comparison purpose, the CCT diagrams with and even without influence of previous deformation were assembled. In addition, the DCCT diagram (i.e. with previous deformation influence) was exposed to different austenitization conditions. The transformation diagrams were assembled on the basis of dilatometric tests which were confronted with the metallographic analysis and hardness measurement. Due to the influence of previous deformation and different austenitization conditions, peremptory movements of curves in the assembled transformation diagrams were occurred, which, of course, was reflected also on the structure and hardness, respectively. After the previous deformation, the structures of samples had considerably increased share of quenching phases, including of share of acicular ferrite. This, of course, was manifested by increased values of hardness.
In order to achieve an economic forming technology production, a well-developed lubrication technology is generally required. Within the scope of this work, further investigations on a novel self-lubricating forming process are presented. Powder metallurgical (PM) components were impregnated with lubricant in order to store the oil within their process-related porosity. In a subsequent forming process the induced pressure forces the oil to leak out lubricating the process.
In preliminary works it was found, that the maximum forming load can be reduced by up to 39 % applying the new lubrication method in comparison to unlubricated processes. In addition, relative densities up to 99 % were reached after deformation.
In this contribution optimised impregnation parameters regarding the initial porosity and impregnation time are presented. Compression tests were conducted and strain-stress-curves were recorded and analysed. In addition, friction factors were determined in order to characterise the lubrication behaviour. The optimised parameters lead to significantly higher strains and lower friction factors, compared to dry forming processes.
The paper deals with the unconventional way of making thin-walled circumferential rings produced by classical technology. The essence of the phenomenon is induction. The accumulated energy drains through the coil to produce a repulsive force that causes a dull thrust. Further, the theoretical process conditions are described. Figures illustrate the entire forming process. It is also described the studied process in terms of metal forming theory in order to distinguish the difference between this method and the magnetic field application technology. The drawbar is designed as a all-metal (non-magnetic) with a divided die, from which the finished work is removed and elapsed after completion of the process. First phase: Place a splinter of the appropriate size from which the container is to be made into the pulling tool. The drawingpiece is made in the conventional manner and remains in the pulling tool. In the second stage, the traction tool is placed in an electromagnetic field, which is formed by means of a coil which is located in the cavity of the extraction. This will increase the effect of the electromagnetic field. The electromagnetic pulse causes the necessary strain and forces to form peripheral rings on the drawingpiece. After disconnecting the DC stream and rejecting the coil from the drawingpiece, the divided die is scraped and the extraction is removed from the tool. In order to clarify the phenomenon of the experiment, it is necessary to analyse the case of magnetic induction on the solenoid axis. The drawingpieces were almost plastic deformation, but the magnetic field built up had to be considerably larger than that of the experiments. It turns out that such a forming process is directly dependent on the size of the supplied current, the built-up magnetic field, and the drawingpiece plate thickness. It is possible to expect a state where the drawingpieces can be formed even under the conditions of piece production just by applying the magnetic field to the process.
The article presents the results of a study of the stress-strain state by several plastic deformation of workpieces in a closed die. Stress state study was performed by slip lines and simulation software Deform 3D.
Analysis of stress state research shows that the value of the stress components within the scope of the workpiece is increased by one cycle of deformation of 1.5-2.5 times. The prevalence of compressive stresses will contribute to refining metal structure with high-cycle alternating strain.
Manufacturing steel complex figurine parts remains a fundamental scientific challenge. This article suggests the solution of using hybrid methods that unite processes like combined rolling/stamping, rolling/plastic bending, and asymmetric rolling to produce steel complex figurine parts with wall thickness of 40-100 mm and diameter (width) up to 4000 mm. Traditionally, machine-building factories produce large-size bodies of rotations, with the help of an inefficient and rather costly process, using stamping or sheet-bending machines. These details are designed for usage as casings for various technological aggregates (converters, mixers, scrubbers, steel teeming ladles, etc.). The aim of the work is to develop a technology for obtaining large-sized parts with a curved surface in conditions of a plate rolling mill. The man objectives of the study:1) The choice and adaptation of the visco-plastic mathematical model for describing the new combined rolling and stamping and asymmetric rolling and plastic bending processes of production large-sized parts with a curved surface; 2) Numerical and experimental studies of the new combined processes with the study of the influence of various parameters on the geometry and mechanical properties of large-sized parts with a given curvature; 3) Determination rational process schemes and operating modes of the combined processes of production. large-sized parts with a curved surface. The chief features of new hybrid processes are identified. Results of theoretic and experimental investigations are provided. A technology of manufacture of converter housing parts at the 4500 PJSC "MMK" has been developed. Two cases were manufactured and installed in PJSC MMK. The economic effect was more than 1 million dollars.
In this study, effects of Friction Stir Processing (FSP) on the deformation behavior of Dual Phase (DP) 600 thin steel sheets under static and cyclic loading were investigated. Fatigue tests were performed on servo-hydraulic machine at a frequency of 15 Hz during repeated tension at a cycle asymmetry R=0 and 106 loading cycles. DP 600 steel reflected yield strength of about 300 MPa and reached to ultimate tensile strength (UTS) of about 620 MPa with uniform elongation of 21% and fractured after a total elongation of 34% elongation in its as-received condition. After FSP, it was observed that the yield strength increased to about 811 MPa and the tensile strength value reached to 1053 MPa. This effective strength enhancement brought about an acceptable decrease in ductility values of the DP 600 steel resulting in uniform elongation and elongation to failure of 6.3% and 13.0%, respectively. Based ductility values obtained, it can be considered that, FSPed DP 600 shows a deformation behavior that mostly dominated by the strain hardening. Static strength enhancement obtained by FSP of DP 600 steel also yielded a favorable effect on the fatigue behavior and stress level leading to transition to the infinite life. As a result of the fatigue tests, it was determined that the fatigue limit of the as-received DP 600 steel increased from 350 MPa to 480 MPa after the applied FSP process. Experimental results obtained in the study mainly indicate that, FSP is an easy to apply and practical procedure which provides significant enhancement on the mechanical performance of DP 600 steel under both static and cyclic loading conditions.
The effect of High-Temperature Thermomechanical Processing (HTMP) on the structure and mechanical properties of austenitic-ferritic steel has been studied. The dislocation structure observed in austenitic-ferritic stainless steels gave evidence that HTMP affected the strengthening and softening behaviour. Temperature - strain - time parameters are responsible for the substructure formation at the HTMP of duplex austenitic-ferritic steel. The effect of strain accumulation program in the formation of substructure and phase transformations as well and the relation between the changes in the crystal structure due to HTMP and the mechanical properties of steel are considered.
One of the most important causes of steel sections failures are the residual stresses. They are those stresses that are locked in the profiles without of application of any service or internal loads. They influence the material properties of rolled materials and as a consequence the propagation of cracks.
Three dimensional finite element modelling of the roller straightening process of H-section beams is presented in the paper. An explicit-dynamic method by using Abaqus solver was adopted to realize the feeding of H-sections into the intermeshed rolls by rotating the upper rolls and to accomplish the calculation under condition of frequent contact between H-section and roll interface. Realistic kinematic boundary conditions are implemented in the research; the longitudinal movement of the product through straightening machine achieved by the rollers and the (Coulomb) friction. For the constitutive equation of the material, elastic-plastic hardening low was used. The effect of the roll gap on the straightness of the chosen H-section after straightening process was examined. Equivalent stresses, strains in the H-section, forces and torques parameters were calculated as well.
Based on the received results, three dimensional finite element analysis of the roller straightening process of chosen H-section was found to be promising for the designing of optimal setting of each roll. Well known global effects eg. increasing of the web height during straightening, flapping of the H-section towards rollers occurs in the research as well. The residual stress can be reduced by reasonable straightening process and it contributes to improving the quality and secure life of H-sections.
With using of anizothermal plain strain compression tests, which were performed on the Hot Deformation Simulator HDS-20, the physical simulation of rolling and following cooling of seamless tubes from steel 42CrMo4 was performed. The aim was to simulate the thermomechanical conditions during piercing as well as rolling in a pilger mill of the seamless tubes with the final diameter of 273 mm (with the wall thickness of 6.3, 20 and 40 mm) and evaluate the influence of the finish rolling temperatures (chosen in the range from 820 to 970 °C) on microstructural and mechanical properties of the investigated steel. In the case of tubes with the wall thickness of 6.3 and 20 mm the highest hardness was reached at finish rolling temperature of 820 °C and the microstructure of samples was formed by majority share of martenzite and minority share of bainite. In the case of simulation of tube rolling with the wall thickness of 40 mm the chosen finish rolling temperatures did not fundamentally influence the hardness of deformed samples and final microstructure of all these samples was formed by the mixture of bainite, ferrite and pearlite.
Large sheet metal components are widely required in the manufacturing sector, which is the target sector. While conventional forming methods as deep or stretch drawing might be applicable in high volume production, they are not suitable for economic manufacturing of small batch sizes, because tooling costs for large parts and accordingly huge tools require an enormous number of parts to amortize. To solve this problem, electromagnetic forming offers a suitable solution. It only requires one forming tool and thus reduces the effort and the production costs. The electromagnetic forming combines the principles of conventional sheet metal forming to extend the boundaries of individual processes. This strategy uses a universal coil to shape the full geometry in several sequences. Mechanical field variables (e.g., displacement, gap, trajectory etc.), electromagnetic field variables (e.g. current density, discharge energy, etc.), and thermal field variables (e.g. temperature, heat transfer, etc.) have been modelled in sufficient detail - multiphysical simulations of the forming process rely on the coupling of finite element (FEM) and boundary element methods for the eddy current case of Maxwell's equations, FEM for contact mechanics of sheet metal, and FEM for heat analysis due to the Joule losses. Capacitors’ charging process has been optimized to shorten the charging time. Optimal scheme of capacitors connection and the optimal method charging/discharging control has been investigated. Special attention has been paid to finding components for higher frequencies of sequential work cycle.
The design of a very strong bainitic nano-structure opened a whole new field of research about a decade ago. Due to the very low transformation temperature leading to a highly refined structure (20-40nm ferrite lath thickness), it was possible to obtain a notable strength of ~2.3GPa with a ductility of ~30%. The austenite retained between the layers of bainitic ferrite accounts for the TRIP effect and hence the high ductility. The carbon rejection from ferritic laths and austenite stabilization are the major factors controlling the kinetics of phase transformation.
Keeping in mind the large scale production of bainitic steels by thermo-mechanical processing, we studied the effect of ausforming on the kinetics of formation, morphology and crystallography of low temperature bainite. The composition of the alloy steel studied was 0.79C, 1.51Si, 1.98Mn, 0.98Cr, 0.2Mo, 1.06Al, 1.58Co (wt. %) with Bs and Ms temperatures of 385oC and 155oC, respectively, ensuring low temperature bainite formation. Direct metallographic observations were made followed by volume fraction calculation and EBSD analysis for axisymmetric deformation at different temperatures and using different strains, keeping the isothermal transformation temperature constant at 350oC and strain rate of 0.1s-1. The high temperature deformation was performed on Servotest TMTS 500kN.
Although ausforming is known to increase the rate of transformation in case of upper bainite, it did not have the same effect on low temperature bainite. For every ausforming temperature there was a critical strain above which the mechanical stabilization of austenite took place, retarding the decomposition of austenite into bainitic ferrite. The value of this critical strain decreased with an increase in the deformation temperature. Further the accumulation of dislocation debris gave rise to thinner bainitic ferrite plates with lower final volume fraction of bainite. A correlation between the deformation temperature, strain and variant selection was also found.
Critical phase control MAF is also an important technique to produce the bulk size UFG components with better combination of mechanical properties as compared to the other SPD techniques. In the present study, single phase control multiaxial forging (MAF) was performed up to the maximum cumulative strain of 18 (0.4×3×15 cycles) for the microalloyed steel in 3 phase regimes (γ-region, γ→α transition region and pure α-region) separately. More than 4-fold increase in the YS (1027MPa) of the microalloyed steel specimen of after MAF (for 15 cycles at 650°C) as compared to that of the starting sample (251MPa) is ascribed to the development of submicron size (~280nm) ferrite grains and formation of nanosize (35nm) fragmented cementite (precipitated through repeated heating cycles) within the submicron size matrix grains. The formation of submicron size ferrite grain in the microalloyed (~280nm) steel sample by MAF is attributed to the mechanisms of formation of micro-shear bands in multiple directions, repeated change in the accumulated strain paths to promote dislocation activity, increase in the misorientation angle of grain boundaries and finally strain induced ferritic transformation with extensive recovery (confirmed by EBSD and TEM study). Furthermore, the best combination of the YS (1027MPa), ductility (8.3%) and fracture toughness (90MPa√m as per Kee) is achieved for the 15 cycles MAFed microalloyed steel samples. The complex microstructure of the sample is found to play the vital role to yield such high YS and fracture toughness with significant amount of ductility.
Light-weighting targets of the automotive sector requires to use of advanced high-strength steels (AHSS) with higher strength more extensively. However, as a common behavior, increasing strength levels of AHSS accompanied with decreasing ductility/formability levels. This behavior become more pronounced during secondary deformation of a blanked edge. To examine this concept, hole expanding (HE) test, that simulates the local formability of the edges after blanking operations, has been started to be widely used. In this study, deformation stages of the HE tests were examined by means of main characteristics and variations of F (force) - X (extension) curves and derivative of F with respect to the X (dF/dx) during the punch travel until cracking. In order to correlate variation in curve characteristics with deformation stages, high-resolution camera images of the tested samples concurrently collected during the whole test and main relationships between them were determined. Based on these relationships a new approach to predict “stop stroke” of the HE tests is proposed. Therefore, elimination of the visual inspection and decision making of an operator or an in-situ image processing software is aimed. Proposed approach was developed using DP600 steel with a thickness of 1.2 mm as a common steel grade that widely used in automotive industry. Also, validation of developed “stop stroke” criteria was tried in HE testing of thinner and thicker DP600 samples. Results showed that a good prediction of stop stroke can be achieved by using proposed approach.
Asymmetric cryorolling is a technique that combines the features of asymmetric rolling and cryorolling, and can be used to produce ultrafine grained aluminum sheets. The problem with asymmetric cryorolling is the heat generated in the roll gap by high contact friction and the plastic deformation. Prediction of temperature rise during asymmetric cryorolling is very important. The temperature rise can be as large as to increase the sheet temperature above the cryogenic temperature. Therefore it is necessary to estimate the actual sheet temperature during the asymmetric cryorolling for a precise control of recovery, and hence of the grain size. This paper presents the results of the finite element simulation of heat transfer during asymmetric cryorolling of aluminum alloys. The effects of thickness reduction, rolling velocity and friction coefficient on the deformation heating and temperature field of aluminum alloys were found. The results of investigation are useful for the development of the optimal treatment process of aluminum alloys by cryogenic severe plastic deformation to obtain the ultrafine grain structure and high strength properties.
In this study, we will examine the phenomenon of precipitation that appears in the aluminum alloy AGS wires. Since the studied wires are drawn, we will try to see also the effect of the deformation on this phenomenon.
The precipitation was believed to be the main cause of hardening in the AGS 6101 wire rod. The hardening appears in this wire, after a period of storage, and causes the elevation of its hardness from 07% to 18% and its maximum tensile load from 04% to more than 22% depending on storage times.
Microstructural analysis of wire rod and drawn wires shows the existence of precipitates in the microstructures. Optical microscopy reveals the presence of two precipitates of different sizes and colors: whitish and dark gray. Under the scanning electron microscope, three types of precipitates appear: white, light gray and dark gray, ranging from 03 to 12 μm.
X-ray diffraction analysis did not reveal the presence of precipitates, observed by light microscopy and scanning electron microscopy. The EDS analysis allowed the measurement of the chemical composition of the light gray precipitates that were identified as the Mg2Si intermetallic compound.
Note that the effect of deformation on precipitation in AGS 6101 alloy was not found in this study. Because the wires used in this study were part of the same batch as the wire rod. However, in previous studies the effect of the deformation on precipitation after a heat treatment has been found.
The EN.I.CAB company in Biskra uses the cold drawing process on several types of wires rod of different materials and grades. Our study was carried out on an AGS (AA6101) type aluminum alloy wire rod, the most used by the ENICAB company in the manufacture of electrical energy transmission cables. The purpose of this work is to understand the evolution of the deformation texture and the energy stored in the grains during cold drawing of aluminum wire for industrial applications, as well as the combined influence of deformation and annealing temperature at 400°C during deferent holding time on recrystallization kinetics and evolution of local and global crystallographic texture during recrystallization annealing of drawn aluminum wires. For this study several experimental techniques of measurement and characterization allowed us to carry out this work. These are Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Back Scattered Electron Diffraction (EBSD), X-ray diffraction, Neutron diffraction, Vickers microhardness and Chemical analysis by EDAX, some of which have allowed to correlate the microstructure to the texture.
This work presents the evolution of the Cu2O eutectic oxides during the drawing process in terms of shape, size and quantity in the area of deformation of wires in various diameters. The main research hypothesis assumes that even a low oxygen content in copper (around 150 – 200 ppm) after its cold deformation creates structures of a specific Cu-Cu2O composite with a very large quantity of very small Cu2O particles the size of a fracture of a micrometer. The basis for this reasoning is the experimental observation which shows that in a typical copper containing about 200 ppm of oxygen there are about 1800 grams of Cu2O oxides the size of a micrometer, however, after their fragmentation during the deformation process their density can reach up to 500 000/mm3 of material. The analysis was conducted for selected particle diameters, different for different drawing machines due to the progressive fragmentation of particles during the drawing process. The estimated quantity of the particles is related to the size of the gap for the thick wire, medium-size and micro-wire drawing machines. The analysis shows that in a single drawing gap (micro-wire drawing machine) where the volume of the deformed material is 1000th parts of a cubic millimeter there are millions of Cu2O particles. The analysis assumes that all oxygen is chemically involved in the formation of the Cu2O oxides, both primary and secondary, so the presented calculations constitute the upper assessment of the content of Cu2O oxides and the upper assessment of the quantity of particles in the deformation gap. In fact, it may turn out that some oxygen is involved in the formation of oxides or conglomerates of oxides of other, more electropositive elements than copper.
In this study the bonding and debonding properties of three layer-clad aluminium sheets are investigated. The bonding was performed between AlMn1Si0.8 and AlSi10 alloys using hot rolling (a VON ROLL experimental duo mill). The experimental temperatures were 460, 480 and 500 °C. The goodness of bonding was tested by tensile test and T-peel test. T-peel test provided a good description about the quality of bonding. Structure analysis was also performed by light microscopy to detect typical bonding faults. The aim of this investigation is modelling the bonding conformation in experimental conditions. Further aim of this investigation is to produce some typical bonding faults and find the cause of formation. The influence of the rolling temperature and surface roughness on the bonding was also analysed. Rolling schedule and the role of first pass on the development of perfect bonding were experimentally determined.
Aluminum wires used for overhead power lines are in a different state of strengthening and are characterized by the structure of a reinforced material saturated with a large number of defects. Typical chemical composition of aluminum used for electrical purposes contains, depending on the species, from 0.3 to 0.5% by mass. silicon and iron. These elements form different fragile phases of Fe-Si and Al-Fe-Si type, which are places of stress concentration in deformed wires. In particular, their presence on the surface of the drawn wire evokes a network of surface microcracks during the drawing process. Macroscopically this is manifested, among other things, by the lower fatigue life of wires and lead to shorter service life.
The article presents the results of research on the influence of the strain hardening on the formation of fatigue strength of aluminum wires. Based on the results of experimental studies Wöhler curves of wires was developed which shown us relationship between the number of cycles to failure and the real deformation of wires was determined. In addition the character of fatigue fractures of wires was analyzed using scanning microscopy and light microscopy.
ACKNOWLEDGEMENTS: The project was financially supported by The Polish National Centre for Research and Development (PBS3/B5/34/2015).
A method of determining the plastic properties of the material under the conditions of microforming at elevated temperatures was presented. This involves performing the process of upsetting a cylindrical micro sample between flat tools of different temperatures. As a result of the heat flow in the volume of the sample the non-uniform temperature distribution is observed. It causes uneven distribution of deformations and a shape similar to the truncated cone is obtained. Based on the measurement of the sample side contour and the known temperature distribution, it is possible to determine the dependence of the plastic resistance on the temperature within the given range. Dependence is derived from one experiment. This method is recommended for studies where the number of samples for analysis is limited. The method allows to quickly determine the temperature characteristics of a material. A sample analysis of selected material was presented.
The range of applications for parts made of light metals (magnesium, aluminium or titanium) is constantly expanding. This could lead to a replacement of the parts made of steel by the ones manufactured from light metal parts. However, magnesium and aluminium parts in particular reach their technical limits when exposed to high tribological, mechanical or thermal stress. For this reason, often the so called metal-matrix-composites (MMC), which possess the advantages of light metal (low weight and high ductility) as well as of the reinforcing phase (high hardness, high strength and good wear resistance), are used.
This paper provides the initial findings of a fundamental investigation of the specific forming behaviour and the mechanical material properties for partially particle-reinforced powder metal parts. For this purpose, cylindrical raw parts are produced by powder pressing and further compacted in a subsequent sintering process. These parts consist of aluminium powder and an MMC material (ceramic powder) with concentric layer arrangement. The raw parts produced in this way form the basis for an examination where the existing residual porosities are to be reduced by subsequent upsetting and extrusion processes. The effects of the different process parameters (pressing force and forming temperature) on the material flow of the partially particle-reinforced material system and the structural strength of the formed parts are investigated. In this contribution, numerical simulations are performed to analyse the pore development during the above mentioned forming processes in order to determine the influence of porosity on the deformation behaviour of the considered material. The findings of this research work help to evaluate the dependence of the change in the residual porosity of sinter-forged parts on the prevailing forming mechanisms.
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).