Hot Plastic Working Research Articles

Modelling and simulation of dynamic recrystallisation based on multi-phase-field and dislocation-based crystal plasticity models

ABSTRACT The mechanical properties of metals used as structural materials are significantly affected by hot (or warm) plastic working. Therefore, it is industrially important to predict the microscopic behaviour of materials in the deformation process during heat treatment. In this process, a number of nuclei are generated in the vicinity of grain boundaries owing to thermal fluctuation or the coalescence of subgrains, and dynamic recrystallisation (DRX) occurs along with the deformation. In this paper, we develop a DRX model by coupling a dislocation-based crystal plasticity model and a multi-phase-field (MPF) model through the dislocation density. Then, the temperature dependence of the hardening tendency in the recrystallisation process is introduced into the DRX model. A multiphysics simulation for pure Ni is conducted, and then the validity of the DRX model is investigated by comparing the numerical results of microstructure formation and the nominal stress–strain curve during DRX with experimental results. The obtained results indicate that in the process of DRX, nucleation and grain growth occur mainly around grain boundaries with high dislocation density. As deformation progresses, new dislocations pile up and subsequent nucleation occurs in the recrystallised grains. The influence of such microstructural evolution appears as oscillation in the stress–strain curve. From the stress–strain curves, the temperature dependence in DRX is observed mainly in terms of the yield stress, the hardening ratio, and the change in the hardening tendency after nucleation occurs.

Peculiarities of Alloying Effect on the Eutectic Cementite Behavior Under Hot Rolling

Abstract Currently, cast iron remains one of the major modern casting materials in metallurgy and machine-building industry and is sure to take the lead in the future. Chilled cast iron has high hardness and wear resistance due to a large number of carbide phases in its structure. However, low ductility and impact hardness essentially limit its applicability in terms of processing. Hot plastic working, under which the eutectic net crushing is observed, appears to be one of the most effective means of the eutectic alloy products shape and microstructure transformation. Chilled cast iron properties fundamentally improve after hot plastic working: ductility, strength and impact hardness increase by 2-3 times on retention of the high hardness factor. Chilled cast iron ductility increase can be attained when using phase transformations in eutectic cementite under lean alloying with carbide forming elements. The purpose of the paper is to study alloying effect on the chilled cast iron ductility as well as eutectic cementite behavior under hot rolling. In the paper hardening and softening of the structural components in chilled cast iron under hot working have been studied. The deformation texture forming in eutectic cementite under hot rolling has been revealed, which is connected with the dynamic softening and depends on the degree and the nature of its alloying. The mechanism and regularities of the phase transformation effect in cementite on its behavior under plastic deformation and on the alloys ductility in general have been studied. In cementite chromium alloying initiates processes, that can be characterized as the pre-precipitation stage of the new phases, and this way it contributes to the cast iron ductility reduction and embrittles cementite. Carbide transformation, that occurs in eutectic cementite under alloying with vanadium, stimulates softening of the alloy and increases its ductility level. Moreover, the multiple glide planes {130},{011},{112} in cementite have been determined. It has been found out, that in supersaturated cementite vanadium carbides precipitation stimulates the extra glide plane {111} occurrence under hot rolling. The essence of the carbide transformation phenomenon is that under hot working there occurs the lubricating effect at the transition of the metastable iron carbide condition, which is strengthened with vanadium supersaturation and mechanical hardening, to a more stable condition due to precipitation of the proeutectoid constituents on the one hand, and because of the dynamic softening processes on the other hand. At that, the autocatalyticity effect is observed: there is precipitation of carbides with hardening and softening, similar to the processes that arise as a result of the superplastic effect induced by phase transformations.

Numerical investigation of the evolution of microstructure of nickel-based alloys during plastic working

The paper considers the process of hot plastic working of a large metal billet, which causes its upsetting to a dimension specified by the manufacturing technique and the average axial deformation of 32.5%. The billet was made of heat-resistant nickel alloy Waspalloy widely used in the aircraft industry. The structural condition of the deformed alloy and, consequently, its mechanical properties depend on many factors: the degree of deformation, the rate of deformation, recrystallization in the process of deformation. This generates a need for a comprehensive study of the plastic flow in the examined material and the influence of the deformation parameters on its characteristics. The paper presents the results of a numerical investigation of the deformation and temperature states of the billet that allowed us to analyze changes occurring in the structure of nickel alloy during plastic deformation at different upsetting rates (50 and 100 mm/s). The shape of billet lateral surface and the forces required to complete the process of free upsetting are calculated as well. The numerical simulation was performed by the finite element method using the DEFORM-2D/3D software package. The average grain size and the fraction of recrystallized grains in the body of the billet were determined based on the Johnson-Mehl-Avrami-Kolmogorov model (JMAK). The results of numerical modeling showed that the greatest change in the microstructure of the alloy occurs in the region of intense plastic strains. The upsetting rate of 100 mm/s leads to the formation of structure with finer grains compared to the structure formed at the upsetting rate of 50 mm/s.

Controlling behavior of δ-ferrite in nitrogen-containing chromium–nickel–manganese steels

This article discusses the behavior of δ-ferrite upon crystallization, solidification, and subsequent cooling of solid nitrogen-containing stainless steel of various compositions on the basis of thermodynamic simulation. The results are confirmed experimentally and can be applied for selection of the steel composition as well as its production at all stages, including hot plastic working and welding, where δ-ferrite can be useful provided that its content is controlled. These results can be applied also for selection of temperature modes of austenitization aiming at the most complete dissolution of δ-ferrite in the final metal.

Microstructure and Plastic Properties of Mg-Li Alloys Smelted in Vacuum Induction Furnaces after Hot Working

AbstractThe paper analyses the characteristics of plasticity and microstructure of magnesium alloys with lithium meant for hot plastic working with different lithium content. The alloys were prepared in conditions of vacuum smelting. Achieved ingots were subject to hot extrusion. Tests on Gleeble simulator were conducted to assess the susceptibility of tested alloys to plastic forming in conditions of hot plastic working. For tested alloy the activation energy was marked for hot plastic deformation and plasticity characteristics in function of Zener-Hollomon parameter. After the analysis of the influence of temperature on the deformability of tested alloys it was stated that the alloy containing 8%Li (LAZ831) has better susceptibility to plastic treatment than alloy containing 4%Li (LAZ431), but higher than in case of classic magnesium alloys - AZ31.

The characteristic of deformability and quantitative description of the microstructure of hot-deformed Ni-Fe superalloy

Abstract The paper presents the results of research concerning the influence of hot plastic working parameters on the deformability and microstructure of a Ni-Fe superalloy. The research was performed on a torsion plastometer in the range of temperatures of 900-1150°C, at a strain rates 0.1 and 1.0 s-1. Plastic properties of the alloy were characterized by the worked out flow curves and the temperature relationships of flow stress and strain limit. The structural inspections were performed on microsections taken from plastometric samples after so-called “freezing”. The stereological parameters as the recrystallized grain size, inhomogenity and grain shape have been determined. Functional relations between the Zener-Hollomon parameter and the maximum yield stress and the average grain area have been developed and the activation energy for hot working has been estimated.

The Structure and Properties Formation of the NiTi Shape Memory Rods after Hot Rotary Forging

Shape memory effects, the course and characteristic temperatures of phase transitions and mechanical properties and surface properties of NiTi alloys strongly depend on the chemical composition, the production process used and the plastic working and thermomechanical treatment as well as surface treatment. The test alloy was obtained by vacuum metallurgy by melting the components in a graphite crucible and casting into a graphite ingot mould. In order to obtain the rods in the process of hot plastic working, hot forging was applied using a smith hammer and rotary hot forging on a swaging machine. The resulting rods were subjected to an appropriate heat treatment and thermo mechanical treatment to obtain, at room temperature, a parent phase structure B2.The paper presents the results of the research of NiTi rods after hot rotary forging. The phase composition of the samples of the tested alloy after different heat treatments were determined by X-ray powder diffraction technique. It was found that at room temperature, depending upon the processing the samples had a structure parent phase with a small amount of martensite. The courses of phase transitions and the changes of the temperature characteristic were determined on the basis of the recorded DSC curves. It was found that the test rate after aging in the temperature range of 400-500 °C transitions take place involving the rhombohedral R phase. The temperature ranges of shape recovery of samples after various heat treatments were determined by recording the recovery of the shape during heating, in tests performed according to the standard ASTM 2082-06.

Microstructural evolution in deformed duplex stainless steels

Abstract The present research is part of a project concerning texture and microstructure evolution upon deformation and annealing in a series of various duplex stainless steels. This article shows a comparison of deformation behavior in two grades of duplex steels subjected to cold-rolling over a wide range of reductions. Both steels under examination showed clear differences in chemical composition and their preliminary treatment included different processes of hot plastic working. Optical microscopy was used to examine changes in morphology and formation of a ferrite–austenite band-like structure upon cold-rolling. Transmission electron microscopy was applied to analyze microstructural evolution and deformation behavior within the ferrite and austenite bands. Additional research included texture measurements for both component phases. Special attention was paid to the ferrite–austenite co-deformation and the structural effects resulting from strain localization at high rolling reductions.

Effect of the Ceramic Dispersion in the Nickel Matrix Composite Coatings on Corrosion Properties after Plastic Working

Coatings of metal and ceramic composite were applied on the steel specimens using the subsonic process of flame spraying. The specimens were then subjected to both cold and hot plastic working by rolling and also cold pressing by the hydraulic press. Plastic working is an alternative to machining, as the method of finishing of coats applied by flame spraying. The article presents the findings of the research into the possibility of using plastic working (hot and cold rolling and pressing) to obtain the corrosion properties of the flame sprayed Ni-Al alloy coatings and Ni-Al-Al2O3composite coatings. The alloy coatings had a single-phase structure, of the maximum 10% aluminium solubility in the crystal lattice of nickel, whereas in the composite coatings the volume content of non-metallic material Al2O3was 15% and 30 %. After finishing the adhesion reduction, cracks on the surface and cross-sections of coatings was not observed. The largest value of strain hardening of alloy coating Ni-5%Al was stated after pressing. The composite coatings obtain by flame spraying be characterized by big surface roughness (Ra= 13.3 µm). The plastic working caused decrease surface roughness. Minimum value of Raparameter was observed after hot rolling. It was found that maximal roughness was presented after pressing. The corrosion tests were performed in 0.01 M H2SO4solution by potentiokinetic technique. The article presents the effect of dispersion phase of Al2O3on corrosion properties of composite coatings on the nickel base. The corrosion rate was dependent on method of plastic working. The increasing drafts resulted in rise corrosion current density and decrease in value of corrosion potential.

Development of re-crystallized W–1.1%TiC with enhanced room-temperature ductility and radiation performance

Ultra-fine grained (UFG) W–TiC compacts fabricated by powder metallurgical methods utilizing mechanical alloying (MA) are very promising for use in irradiation environments. However, the assurance of room-temperature ductility and enhancement in surface resistances to low-energy hydrogen irradiation are unsettled issues. As an approach to solution to these, microstructural modification by hot plastic working has been applied to UFG W–TiC processed by MA in a purified Ar or H 2 atmosphere and hot isostatic pressing (HIP). Hot plastically worked compacts have been subjected to 3-point bend tests at room temperature and TEM microstructural examinations. It is found that the microstructural modification allows us to convert UFG W–1.1%TiC to compacts exhibiting a very high fracture strength and appreciable ductility at room temperature. The compacts of W–1.1%TiC/Ar (MA atmosphere: Ar) and W–1.1%TiC/H 2 (MA atmosphere: H 2) exhibit re-crystallized structures with approximately 0.5 and 1.5 μm in grain size, respectively. It is shown that the enhancement of fracture resistance by microstructural modifications is attributed to significant strengthening of weak grain boundaries in the re-crystallized state. As a result the modified compacts exhibit superior surface resistance to low-energy deuteron irradiation.

The Effect of the Ceramic Dispersion on the Nickel Matrix Composite Coating Properties after Plastic Working

The paper presents the effect of dispersion phase of Al2O3 on selected potential properties of composite coatings on the nickel base. Coatings of Ni-Al-Al2O3 were applied on the steel specimens using the subsonic process of flame spraying. The specimens were then subjected to both cold and hot plastic working by rolling and also cold pressing by the hydraulic press. Plastic working is an alternative to machining, as the method of finishing of coats applied by flame spraying. The paper presents the findings of the research into the possibility of using plastic working (hot and cold rolling and pressing) to obtain the selected properties of the flame sprayed Ni-Al alloy coatings and Ni-Al-Al2O3 composite coatings. The alloy coatings had a single-phase structure, namely boundary solution α , of the maximum 10% aluminium solubility in the crystal lattice of nickel, whereas in the composite coatings the volume content of non-metallic material Al2O3 was: 0, 15, and 30 %.

Constitutive Relationship of IN718 Alloy for Thermoviscoplastic and Microstructure Evolution Coupled Analysis

The interaction between thermomechanical parameters and microstructure evolution is so intense that it must be considered during the finite element method (FEM) simulation of the hot plastic working process, for materials that are difficult to deform. Taking the microstructure evolution into account, a novel type of constitutive relationship has been put forward for the IN718 alloy. The microstructure evolution model was first established for the dominant microstructure evolution processes. Then the microstructure evolution models and the method to determine the local flow stress of the corresponding microstructure for current thermomechanical parameters and deformation history were presented. Once the local flow stresses of different structures and their volume contributions were defined, the apparent flow stress of the material could be determined as the weighted sum of the local flow stresses and volume contributions. To validate the proposed method, a thermoviscoplastics and microstructure evolution coupled analysis for a forging process of a critical IN718 disk forging was performed. The predicting results were in close agreement with the experimental data.

Protective process coatings for hot plastic working of steels and alloys

A technology for dispersion doping of glass matrices for creating superplastic coatings, permitting isothermal deformation of alloys without the use of special equipment, has been developed. The protective glassy and glass-ceramic process coatings which have been developed possess a strong internal structure and high film-forming ability and they withstand substantial impact and tension loads with high strain (above 40%).

The Individual and Cumulative Effect of C and N on the Hardening and Structure of High-Nitrogen Hot Plastic Worked Steels

Investigation into the effect of carbon and nitrogen contents of steels with an addition of chromium, nickel and manganese on their structure and properties after thermoplastic treatment has been carried out within the present study. For the physical modeling of thermoplastic treatment processes, a DIL 805A/D dilatometer with a deformation capability and a Gleeble 3800 simulator were used. The effect of carbon and nitrogen contents and the sum of these elements (C+N) on the hardening of the material during hot plastic working. The softening of the material depends on the C/N element ratio. The influence of the constituents under analysis on the dynamics of removal of cold work effects is different; C speeds up, while N slows down this process. The influence of the sum of the elements C and N depends on the type of nonmetallic phase precipitates. The structure and properties of such steels are determined by quenching and tempering cycles.

Changes in the structure of alloy on the matrix of FeAl intermetallic phase after primary crystallization and homogenizing treatment

In this work are presented results of examinations of the influence of the structure after primary crystallization and after homogenizing treatment. The performed structural examinations of alloy on FeAl intermetallic phase matrix had proved, that after a primary crystallization it has a coarse grain structure. Application of homogenizing treatment at temperature 1050 °C during 72 h leads to decay of growth twins, changes the distribution of dislocation in a manner enabling a hot plastic working.

Fabrication of composition-controlled TiNi shape memory wire using combustion synthesis process and the influence of Ni content on phase transformation behavior

TiNi intermetallic compounds were manufactured on an industrial scale using a combustion synthesis process that exploits the heat of formation between Ti and Ni. In this paper we investigate the influence of Ni content on the phase transformation temperature. The TiNi shape memory intermetallic compounds manufactured are homogeneous, show no gravity segregation, and have low oxygen content. Hot and cold plastic working can be carried out without difficulty. The martensitic (Ms) transformation temperatures of specimens that were solution-treated and heat-treated for aging fall rapidly with increased Ni content. However, the transformation temperature bottoms out at 51.4 at.% Ni and begins to rise again at 51.7 at.% Ni. The reason why the Ms temperature, etc., of the specimens heat-treated for aging rise more than for solution-treated specimens is that the Ti3Ni4 precipitates, causing the Ni content of the matrix to fall. The pattern of change in transformation temperature as a function of Ni content in the present experiment agrees with other researchers’ data in spite of the combustion synthesis process fundamentally different from the conventional melting process.© 2003 Elsevier Ltd. All rights reserved.

Production and characteristics of AgO-CuO composites powders

To avoid the troubles deriving from the conventional recycling process, an alternative process has been created, where chips of Al and its alloys are cut or milled convected directly by hot plastic working into final products. In the paper, the production of composites by the direct convertion of Al and AlMg2-alloy granulated chips with tungsten powder into final products by hot extrusion are described. The following extrusion parameters are the most important for the obtainment of high densities: (i) a high extrusion temperature, which enables the plastic flow of an extremely plastic matrix into pores and voids; and (ii) relatively low extrusion rates, which extend the time of plastic flow of the matrix material into the pores and voids and also the time for diffusional transport. The hardness and mechanical properties of Al and AlMg2 base composites are slightly lower than those of metallurgically-produced materials. The direct convertion method does not have any harmful effects on the environment and the material produced can be further processed by other plastic working methods such as forging and rolling.

Influence of the structure of the composite: ‘nitrided layer/PVD coating’ on the durability of tools for hot working

The paper presents research results of the influence of the ‘nitrided layer/PVD coating’ composite on the durability of tools for hot plastic working. Four structures of the composite differing in the PVD coating material were investigated. They were: TiN, CrN, (Ti,Cr)N and Ti(C,N). The composites investigated were created by means of the surface ‘duplex’ treatment method in a two stage separable cycle (the nitriding process and the PVD coating deposition were carried out with different devices). The nitriding process was executed with the use of the regulated gas nitriding method, whereas the PVD coating was executed by means of the arc-vacuum method. The tools tested were forge dies made of ISO steel 35CrMoV5 (0.4%C, 0.4%Mn, 1.0%Si, 5.0%Cr, 1.3%Mo, 0.3%V) designed for the plastic working of automotive half-shafts.The paper presents the results of maintenance investigations, executed under manufacturing conditions, obtained for tools used for hot forging which were covered with different composites. The investigations proved that the best durability was achieved for tools covered with the composite ‘nitrided layer/CrN coating’, for which the increase in durability was almost 90%. The smallest durability was noted for tools covered with the composite ‘nitrided layer/TiN coating’. The results obtained proved that a proper choice of the composite ‘nitrided layer/PVD coating’ structure may increase the durability of tools considerably for hot plastic working.

Production of composites from Al and AlMg2 alloy chips

To avoid the troubles deriving from the conventional recycling process, an alternative process has been created, where chips of Al and its alloys are cut or milled convected directly by hot plastic working into final products. In the paper, the production of composites by the direct convertion of Al and AlMg2-alloy granulated chips with tungsten powder into final products by hot extrusion are described. The following extrusion parameters are the most important for the obtainment of high densities: (i) a high extrusion temperature, which enables the plastic flow of an extremely plastic matrix into pores and voids; and (ii) relatively low extrusion rates, which extend the time of plastic flow of the matrix material into the pores and voids and also the time for diffusional transport. The hardness and mechanical properties of Al and AlMg2 base composites are slightly lower than those of metallurgically-produced materials. The direct convertion method does not have any harmful effects on the environment and the material produced can be further processed by other plastic working methods such as forging and rolling.

Welding on contact surfaces in different technological variants of the hot plastic working of P/M materials

Welding on contact surfaces in different technological variants of the hot plastic working of P/M materials