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The temperature of a forming region has a gradient distribution characteristic in the belt heating incremental sheet forming process, in which the relation between the heating power and the temperature distribution is ambiguous in the pre-heating stage. The setup of the heating power is therefore challenging, and the whole forming efficiency might decrease due to the above issue. Therefore, this paper proposes a belt heating method for electric conduction heating and presents a temperature calculation model for the forming region of the plate in the preheating state based on the heat conduction model. The calculated accuracy of the model is analysed through physical experiments, and the thermal transfer efficiency of heating tubes is analysed in detail. Based on the result, the thermal transfer efficiency value for heating tubes is determined to improve the accuracy of the suggested model. In addition, the effect of the model slope on the calculated result is further analysed, and the setting method of the slope value for the model is proposed according to different accuracy requirements. [ABSTRACT FROM AUTHOR]

Since the hot forming of TC4 alloy after diffusion bonding has extensive applications in aerospace and medical industries, it is practically significant to explore the influence of diffusion bonding on the alloy's hot formability and identify the optimal forming parameters. Therefore, dual-stage diffusion bonding of aviation grade TC4 is carried out firstly at 900 °C for 1 h and then at 930 °C for 2 h under 2-MPa normal pressure in 5.0 × 10 - 3 -Pa vacuum atmosphere. Another block of the as-received alloy is subjected to the same thermal loading as the diffusion bonding process. The diffusion-bonded and heat-treated alloys are then subjected to uniaxial tensile tests at 750 - 900 °C and 0.0001 - 0.1 s - 1 . Based on the tensile test data, the constitutive and dynamic material models are developed to investigate diffusion bonding effects on the alloy's hot forming behavior and identify optimal forming conditions. The developed constitutive model showed good predictability. The apparent activation energy of diffusion bonded (440 - 510 kJ · mole - 1 ) and heat-treated (400 kJ · mole - 1 ) alloys indicated that dynamic recrystallization and recovery are the primary deformation mechanisms. The processing maps revealed that diffusion bonding expanded the instability domain and lowered the dissipation efficiency, limiting the safe working conditions of the alloy. The analysis of deformed microstructure validated the findings of processing maps. The optimal processing conditions of 800 °C /0.0001 s–1 and 850 °C /0.0001 s–1 are discovered for diffusion-bonded and heat-treated alloys, respectively. [ABSTRACT FROM AUTHOR]

Bi-axial state is the dominant stress state experienced by the sheet metal during various forming processes, which requires a thorough understanding and modelling for process designs. In this paper, effects of equal bi-axial stress-state on the hot deformation behavior of titanium alloys are thoroughly investigated using hot bulging tests, and is further compared to the uniaxial stress state. Firstly, a specific hot bulging test device enabling a uniform temperature field and constant control of strain rate was established, using which, systematic hot bulging tests at various temperatures (750–850 °C) and strain rates (0.001–0.1 s−1) of the near-alpha phase TA32 sheets were conducted to determine the hot equal bi-axial bulging behavior. Based on the testing data of force and geometry variations of bulged domes, the equivalent stress–strain curves were calculated. Secondly, a plane-stress visco-plastic plane-stress model of near-alpha TA32 sheets was developed for the first time, enabling both the uniaxial and biaxial flow behavior and forming limits to be precisely predicted. The prediction accuracies for uniaxial and biaxial cases are 93.5% and 89%, respectively. In the end, the uniform deformation resulting from the strain and strain rate hardening was determined, which contributes to the understanding of the stress-state effect on hardening preliminarily. The plane stress visco-plastic model provides an efficient and reliable material model for finite element (FE) simulations of hot forming titanium alloy sheets. [ABSTRACT FROM AUTHOR]

This paper presents a study of temperature conditions for the homogenization of a cast high-strength ZK60 alloy belonging to the Mg-Zn-Zr group of magnesium alloys. On the basis of a literature review, two-stage homogenization conditions were selected to improve the forgeability of the ZK60 casting. The effectiveness of this treatment was evaluated experimentally on the basis of structure and hardness tests and was found to be satisfactory. Plastometric tests were carried out for the samples made from the ingots after homogenization. These tests were performed in a compression test in hot forming conditions at three temperatures (350 °C, 400 °C and 450 °C) and four strain rates (0,01; 0,1; 1,0 and 10 s-1). The determined flow curves will be used to develop a material model of the cast magnesium alloy ZK60 for numerical simulations. [ABSTRACT FROM AUTHOR]

Hot forming process has been used more and more frequently in the production of body structures of modern ultralight passenger cars for several years. This, unlike the commonly used cold stamping, is a complicated process, combining heat treatment and plastic-forming methods. For this reason, permanent control at each stage is required. This includes, among others, measurement of the blank thickness, monitoring its heating process in the suitable atmosphere in the furnace, control of the forming process itself, measurement of shape-dimensional accuracy as well as mechanical parameters of the finished drawpiece. This paper discusses the method of controlling the values of production parameters during the hot stamping process of a selected drawpiece. For this purpose, digital twins of the production line and the stamping process, made in accordance with the assumptions of Industry 4.0, have been used. Individual components of the production line with sensors for monitoring process parameters have been shown. The system's response to emerging threats has also been described. The correctness of the adopted values is confirmed via tests of mechanical properties and the assessment of the shape-dimensional accuracy of a drawpiece test series. [ABSTRACT FROM AUTHOR]

Hardening is the core factor to determine deformation uniformity in sheet metal forming. Hot deformation of titanium alloy sheets encounters the coupled effects of strain hardening, strain rate hardening and softening, which makes the determination of forming parameters aiming for an enhanced hardening very difficult in practical processes. This paper presents a new model to quantify the hardening of Ti-6Al-4 V titanium alloy sheets under hot forming conditions based on the underlying correlation between uniform strain and hardening. Firstly, to precisely determine hot deformation characteristics of titanium alloy sheets, hot tensile uniaxial tests using Gleeble systems at various strain rates of 0.01–1 s−1 and temperatures of 973–1123 K were performed systematically. A newly developed volume-based correction method for stress–strain curves of Gleeble thermo-mechanical testing was proposed to eliminate the damaging effect of temperature gradients on strain calculations, which enables the strain hardening, strain rate hardening and softening to be determined precisely. Then, a simple unified formula of hardening components (n, m and s) was proposed to predict the achievable uniform strain at certain conditions efficiently. Using which, occupation of each hardening can be quantified and compared to facilitate the determination of process parameters. Finally, a phenomenological model based on the hardening and softening components was developed to predict the hot flow behaviour. The proposed quantitative model can provide an efficient and useful approach for process designers to design process parameters driven by the objective of enhancing hardening to maximize uniform deformation during hot forming of titanium alloy sheets. [ABSTRACT FROM AUTHOR]

This paper presents a systematic study of heating effects on the hot deformation and microstructure of dual-phase titanium alloy Ti-6Al-4V (TC4) under hot forming conditions. Firstly, hot flow behaviors of TC4 were characterized by conducting tensile tests at different heating temperatures ranging from 850 °C to 950 °C and heating rates ranging from 1 to 100 °C/s. Microstructure analysis, including phase and grain size, was carried out under the different heating conditions using SEM and EBSD. The results showed that when the heating temperature was lower than 900 °C, a lower heating rate could promote a larger degree of phase transformation from α to β, thus reducing the flow stress and improving the ductility. When the temperature reached 950 °C, a large heating rate effectively inhibited the grain growth and enhanced the formability. Subsequently, according to the mechanism of phase transformation during heating, a phenomenological phase model was established to predict the evolution of the phase volume fraction at different heating parameters with an error of 5.17%. Finally, a specific resistance heating device incorporated with an air-cooling set-up was designed and manufactured to deform TC4 at different heating parameters to determine its post-form strength. Particularly, the yield strength at the temperature range from 800 °C to 900 °C and the heating rate range from 30 to 100 °C/s were obtained. The results showed that the yield strength generally increased with the increase of heating temperature and the decrease of heating rate, which was believed to be dominated by the phase transformation. [ABSTRACT FROM AUTHOR]

Dynamic recrystallization is one of the main phenomena responsible for microstructure evolution during hot forming. Consequently, obtaining a better understanding of dynamic recrystallization mechanisms and being able to predict them is crucial. This paper proposes a full-field numerical framework to predict the evolution of subgrain structures upon grain growth, continuous dynamic recrystallization, and post-dynamic recrystallization. To be able to consider a subgrain structure, two strategies are proposed. One relies on a two-step tessellation algorithm to generate a fully substructured microstructure. The second strategy enables for the simulation of the formation of new subgrains during hot deformation. Using these tools, the grain growth of a fully substructured microstructure is modeled. The influence of microstructure topology, subgrain parameters, and some remaining stored energy due to plastic deformation is discussed. The results highlight that the selective growth of a limited number of subgrains is observed only when mobility is a sigmoidal function of disorientation. The recrystallization kinetics predicted with different criteria for discrimination of recrystallized grains are quantitatively compared. Finally, the ability of the framework to model continuous dynamic and post-dynamic recrystallization is assessed upon a case study representative of the hot extrusion of a zircaloy-4 billet ( T = 650 °C ; ε ˙ = 1.0 s − 1 ; ε f = 1.35 ). The influence of grain boundary properties and nucleation rules are quantified to evaluate the model sensitivity and suitability. Application of these numerical tools to other thermomechanical conditions and microstructures will be presented in an upcoming article. [ABSTRACT FROM AUTHOR]

The combination of complex geometry and martensitic microstructure, characterized by ultrahigh strength and hardness, can be obtained in a single hot stamping process. However, this technology requires a multifaceted approach, allowing for an effective and efficient design process that will ensure the elements with the desired properties and shape are produced because of the high tool cost. This paper presents a comprehensive case study of the design process, simulation and experimental evaluation of the hot forming of an automotive door beam. The U-shaped beam designed with CAD was analyzed using the finite element method in the Autoform v.10 software. The modeling process included: a shape definition of the flat blank; a FEM analysis and design of the die, punches, and clamps; and a forming and quenching simulation. The results covered visualization of the forming and quenching stages for different variables including a forming limit diagram; a distribution of the drawpiece thinning; and a diagram showing the hardness of the drawpiece and its microstructure. Based on the results, a full-size tool for hot stamping was first modeled in the CAD and next manufactured. The tool was used to produce an initial sample series that was used to investigate the conditions for continuous use of the tool. One of the produced hot-stamped products was investigated for its hardness and microstructure, which exhibited a beneficial and fully martensitic microstructure with high hardness of above 400 HV1. [ABSTRACT FROM AUTHOR]

The production of ultra-high strength automotive components requires a multi-directional approach. Hot stamping combines both forming and heat treatment processes to obtain a usually martensitic structure of complicated shaped automotive parts. The preparation for production using hot stamping must involve the latest methods of numerical analysis of both temperature changes and forming, which are applied for an increasing range of materials used. In this paper, the current state of knowledge about the basics of hot stamping, used technological lines, and the current state of material used with applied heat treatments and possible coatings have been reviewed. Moreover, the numerical modeling process has been described. The most important aspects of process automation, including the use of digital twins for simulation and optimization of operational kinetics of the robots accomplishing the production process, analysis and minimization of time of production cycles, and searching for weak operational points of the control systems and for real time visualization of operation of complete line, are considered. The digital twins and corresponding numerical models enable the symmetrical design of real production lines. The details of heat treatment profiles with so called tailored zone heat treatment are provided. Hot stamping is a dynamically developing technology as evidenced by the increasing range of materials used, also from the 3rd generation of advanced high strength (AHSS) steels. It starts to combine forming of symmetric or asymmetric elements with more complex heat treatment processes as required for dual phase (DP) stainless steels or the newest generation of high-strength and ductile medium-manganese steels. [ABSTRACT FROM AUTHOR]

• Unified backstress and stress sensitivity models covering creep and viscoplasticity. • Microstructure-based constitutive model to encompass diverse deformation states. • Tensile, creep and stress-relaxation are concurrently and accurately predicted. • The model greatly improves the prediction accuracy for hybrid forming of Ti alloy. A unified model to characterize the mechanism transitions in a wide range of strain rates at elevated temperatures of titanium alloys has been developed and validated in this study. Models of microstructure-based backstress and strain rate dependent stress sensitivity covering both creep and viscoplasticity domains have been proposed, so as to predict different deformation behaviors concurrently for hot forming. Systematical experiments, including hot tensile, creep, stress-relaxation, and corresponding loading-unloading tests have been designed and performed, to get the different deformation behaviors, as well as the evolution of backstresses of titanium alloys at elevated temperatures. Microstructural observations, such as electron backscatter diffraction (EBSD), have also been performed to assist the mechanisms characterization. Based on the microstructural and macro properties results, the developed unified model has been calibrated and further implemented for typical cases of hot stamping - stress-relaxation forming (HS-SRF). The developed model achieved an excellent accuracy for all the tensile, creep, and stress-relaxation behaviors concurrently, with an error of only about 4.9 %, and a comparative 71.8 % ∼ 90.8 % reduction in springback prediction error has been reported for hot forming of typical thin-walled titanium alloy components when compared with the conventional modelling strategy where a single deformation mechanism is considered. The potential of the proposed model for process design and optimizations has also been discussed. [Display omitted] [ABSTRACT FROM AUTHOR]

A systematic experimental and numerical study of the cooling rate effects on the post-formed strength and microstructure evolutions of a dual phase Ti-6Al-4V alloy under hot forming conditions was performed in this study. A series of cooling treatment tests were designed to achieve typical cooling scenarios in current hot forming processes, i.e. air cooling, water quenching and die quenching. The post-treated mechanical properties and phase volume fractions were characterized and quantified. The results show that higher temperatures and higher cooling rate would facilitate the β phase transformation and martensite transformation of α ′ phases, leading to the higher yield strength in the formed part. Based on the macro- and micro- properties relations and observed data, a unified model for the hot forming and cooling of Ti-6Al-4V was proposed and calibrated, enabling the accurate prediction of both the macro-strength and microstructures under different cooling conditions of the material. The proposed model was further implemented into FE simulation for practical forming process simulations. A typical hot gas forming process of a rectangular cross-sectioned titanium alloy hollow tubular part was investigated. Experiments of hot gas forming with different cooling conditions, i.e. forming temperatures and cooling rates, were carried out and used to validate the established material model and simulation model. Good prediction accuracy was obtained under all the tested conditions, with the maximum prediction errors of 5.55 % for macro-strength and of 9.79 % for average grain size. The results and the model developed in this paper provides an effective way to facilitate the process designs and optimization for hot forming titanium alloy parts in various applications. • Cooling rate effects on strength of hot formed Ti-6Al-4V are experimentally and numerically investigated. • Cooling induced strength changes is due to phase transformation and grain evolutions. • A unified model is developed to accurately predict cooling effects on microstructures and strengths. • The model in micro and macro properties prediction is validated by hot gas forming of typical components. [ABSTRACT FROM AUTHOR]

The aim of this work is to generate an advantageous compressive residual stress distribution in the surface area of hot-formed components by intelligent process control with tailored cooling. Adapted cooling is achieved by partial or temporal instationary exposure of the specimens to a water–air spray. In this way, macroscopic effects such as local plastification caused by inhomogeneous strains due to thermal and transformation-induced loads can be controlled in order to finally customise the surface-near residual stress distribution. Applications for hot-formed components often require special microstructural properties, which guarantee a certain hardness or ductility. For this reason, the scientific challenge of this work is to generate different residual stress distributions on components surfaces, while the geometric as well as microstructural properties of AISI 52100 alloy stay the same. The changes in the residual stresses should therefore not result from the mentioned changed component properties, but solely from the targeted process control. Within the scope of preliminary experimental studies, tensile residual stresses in a martensitic microstructure were determined on reference components, which had undergone a simple cooling in water (from the forming heat), or low compressive stresses in pearlitic microstructures were determined after simple cooling in atmospheric air. Numerical studies are used to design two tailored cooling strategies capable of generating compressive stresses in the same components. The developed processes with tailored cooling are experimentally realised, and their properties are compared to those of components manufactured involving simple cooling. Based on the numerical and experimental analyses, this work demonstrates that it is possible to influence and even invert the sign of the residual stresses within a component by controlling the macroscopic effects mentioned above. [ABSTRACT FROM AUTHOR]

The family of bulk forming technologies comprises processes characterised by a complex three-dimensional stress and strain state. Besides shape and material properties, also residual stresses are modified during a bulk metal forming process. The state of residual stresses affects important properties, like fatigue behaviour and corrosion resistance. An adjustment of the residual stresses is possible through subsequent process steps such as heat treatments or mechanical surface modification technologies, like shot peening and deep rolling. However, these additional manufacturing steps involve supplementary costs, longer manufacturing times and harmful effects on the product quality. Therefore, an optimized strategy consists in a targeted introduction of residual stresses during the forming processes. To enable this approach, a fundamental understanding of the underlying mechanisms of residual stress generation in dependence of the forming parameters is necessary. The current state of the art is reviewed in this paper. Strategies for the manipulation of the residual stresses in different bulk forming processes are classified according to the underlying principles of process modification. [ABSTRACT FROM AUTHOR]

Summary: The deformation behaviour of bimodal sized Al2O3/Al nanocomposites were investigated by hot compression tests conducted in the temperature range 350–500°C and strain rates of 0.001, 0.01 and 0.1 s–1. The dynamic recrystallisation behaviour of the nanocomposites strongly depended on the forming parameters. The bimodal sized Al2O3 particles played a crucial role in the recrystallised microstructure. The addition of bimodal sized Al2O3 particles led to a significant increase of activation energy of plastic deformation, corroborating the enhanced resistance of the nanocomposite to hot deformation. This was also reflected by the increased compressive yield strength in the nanocomposite due to both dislocation strengthening caused by n‐Al2O3 and preventing the grain growth due to the presence of μ‐Al2O3 at grain boundaries. It was found that with the decrease of Z values, local strain induced by deformation was released and the grain size of aluminium matrix gradually increased, indicating that the main softening mechanism of the bimodal sized Al2O3/Al nanocomposites was dynamic recrystallisation (DRX). The lower the Z value was, the easier the DRX occurred. The highly beneficial role of the bimodal sized Al2O3 reinforcement in improving the high‐temperature performance of aluminium matrix nanocomposite was discussed. [ABSTRACT FROM AUTHOR]

A new one‐step process for manufacturing press hardened steel–carbon fiber reinforced (thermoset) polymer hybrid parts with potential for reduced cycle time, infrastructure requirements, and energy consumption compared with traditional two‐ and three‐step processes is developed. The process combines and optimizes the press hardening and prepreg compression molding technologies, traditionally used in isolation for manufacturing press hardened steel and carbon fiber reinforced polymer parts, respectively, to produce hybrid parts in a one‐step, fully integrated process. Heat required for curing and bonding prepreg to steel is provided by residual heat of the steel part immediately following hot forming and interrupted die‐quenching of steel. Thermal conductivity of tool material is investigated to achieve the optimal balance between die‐quenching rate for martensite formation in steel and temperature maintenance for complete curing and bonding of prepreg. Addition of epoxy adhesive and thickness ratio between steel and prepreg are also investigated. Benchmarking is conducted against parts manufactured by the traditional two‐step process, in which the press hardened steel part is formed in isolation before joining with the carbon fiber reinforced polymer part. No sacrifice of part quality is found from the new one‐step process with no loss of mechanical performance, despite clear economic and environmental advantages. [ABSTRACT FROM AUTHOR]

Incremental sheet forming is a sheet forming process for small lot sizes due to its dieless principle. One of its process variants includes local heating of the sheet to counteract some of the process restrictions (formable materials, forming forces, achievable deformations). Although forming at elevated temperatures provides various advantages, the geometric accuracy of the formed part remains low due to shrinking effects caused by local heating and cooling. This publication presents a data-driven approach where process data is gathered and used in regression learning to predict the geometric accuracy resulting from the shrinking effects. To successfully apply regression learning, a big amount of process data is needed covering a wide range of possible process states. Therefore, a specific experimental series, consisting of 54 individual forming experiments, is designed and carried out. Based on the 3D digitization of the formed parts, a process database is built up comprising 408,296 records, each representing a toolpath point. This process database is used to train 19 different regression models. The performance of their ability to predict the geometric deviations is investigated. A compensation approach is presented that improves the geometric accuracy through a prediction-based modification of the toolpath. Validation experiments demonstrate the improvement of the geometric accuracy of the formed part and the generalizability of the approach. [ABSTRACT FROM AUTHOR]

The paper covers the research on the process of solutionizing of 7075 aluminum alloy in cold tools during the stamping of a high-strength structural element (B-pillar's base). For technological reasons, in order to obtain high strength parameters of the 7075 alloy, it is necessary to carry out a solutionization process, which allows to obtain dispersion strengthening during ageing process. Properly performed heat treatment of the alloy increases the strength of the material to approx. 600 MPa. The combination of the process of solutionization with simultaneous shaping is aimed at improving and simplifying technological operations of aluminum alloy stamping, shortening the duration of the manufacturing process and reducing production costs. The manufactured lower part of the B-pillar will be used for the verification of the validity of the developed method. During the experiment, a series of stamping tests were carried out, in which the lubricants, pressure and position of the upper and lower blankholders were the variables. The obtained results allow to estimate the influence of the cooling conditions on the strength of the drawpieces obtained after the process of artificial ageing. In order to verify and analyse the results more quickly, a numerical simulation was carried out. [ABSTRACT FROM AUTHOR]

To investigate the impact of the variations of different input parameters in the multi-stage hot forging process of a shackle, an analysis is carried out through numerical simulations of the whole manufacturing process. Due to the complexity of the process and the large number of factors influencing the thermo-mechanical forming process, the investigation is focused on the workpiece positioning, the temperature of the tools, the transportation time and the contact-friction conditions. The analysis is narrowed down to the key stages of the process that are closed-die forging and ram bending. Coupled with experimental measurements, a comparison of forging loads, functional dimensions and shackle geometry is presented. It is shown that the conformation of shackle geometry to the industrial specifications depends mainly on the workpiece positioning and the transportation time. The dispersion measured in the forging load and in the main dimensions can thus be explained and these observations can be used to improve the manufacturing process for shackles. [ABSTRACT FROM AUTHOR]

A modified iron-based superalloy is studied regarding its hot formability. The microstructure contained particles of titanium carbides, carbonitrides and nitrates. Torsion tests at high strain rate at temperatures ranging from 800 to 1200°C were conducted. Results of these tests were correlated by means of the Garofalo hyperbolic sine creep relation. An optimum forming temperature of 1260°C at 10 s−1 is obtained. This temperature is strongly dependent on the strain rate. An activation energy for plastic deformation close to that for the activation energy for lattice diffusion in austenitic stainless steels and a stress exponent near 5 were obtained. These values suggest that plastic deformation is controlled by a dislocation climb mechanism. [ABSTRACT FROM AUTHOR]

In this work, a hot forming procedure is developed using computer-aided engineering (CAE) to produce thin Ti-6Al-4V sheet components in an effective way. Traditional forming methods involve time- and cost-consuming furnace heating and subsequent hot sizing steps. A material model for finite element (FE) analyses of sheet metal forming and springback at elevated temperatures in Ti-6Al-4V is calibrated and evaluated. The anisotropic yield criterion proposed by Barlat et al. 2003 is applied, and the time- and temperature-dependent stress relaxation behavior for elastic and inelastic straining are modeled using a Zener–Wert–Avrami formulation. Thermo-mechanical uniaxial tensile tests, a biaxial test, and uniaxial stress relaxation tests are performed and used as experimental reference to identify material model parameters at temperatures up to 700 °C. The hot forming tool setup is manufactured and used to produce double-curved aero engine components at 700 °C with different cycle times for validation purposes. Correlations between the predicted and measured responses such as springback and shape deviation show promising agreement, also when the forming and subsequent holding time was as low as 150 s. The short cycle time resulted in elimination of a detectable alpha case layer. Also, the tool surface coating extends the tool life in combination with a suitable lubricant. [ABSTRACT FROM AUTHOR]

The formability of high strength AA7075 aluminum alloy under elevated temperatures is vital in guiding the fabrication of automobile structural parts. The ductile fracture forming limit of AA7075 at elevated temperatures is essentially governed by thermal damage evolution. In this paper, the hot tensile test (300ºC-450 °C, strain rate 0.1s−1-0.001s−1) for AA7075 was conducted and the corresponding flow behavior was fitted by Hensiel-Spittel (HS) constitutive equation. The GTN mesoscopic damage model was implemented to take account of the damage evolution phenomenon of AA7075 at elevated temperatures. The temperature-dependent damage void volume fractions (VVF) were identified accurately based on a novel inverse identification procedure, named the CCD parameters design-FEM inverse simulation-genetic algorithm (CCD-FEIS-GA) optimization method. Subsequently, the thermal forming limit diagram (TFLD) was calculated based on the GTN damage parameters and further validated by hot Nakajima-type bulging experiment. The corresponding damage evolution behaviors and effects of critical forming parameters were discussed in detail. The comparison of experimental and numerical results showed that the formability of AA7075 firstly increases and then decreases with the increasing forming temperature, the TFLD 0 reaches its maximum value when the temperature is 400 °C, and the formability also increases with the increasing strain rate and the decreasing surface coefficient of friction. The proposed simulated strategy coupled with mesoscopic GTN approach conduces to the accurate prediction of TFLD and damage fracture behavior of AA7075 in the hot forming process. Image 1 • Thermal mechanical behavior and damage characteristics of AA7075 were discussed. • The GTN damage fractions were identified by a novel inverse optimization procedure. • The TFLD of AA7075 was predicted by the GTN model and validated. • The effects of hot forming parameters of AA7075 were analyzed and discussed. [ABSTRACT FROM AUTHOR]

The present study investigates the performance of four selected PVD coating materials in application near hot-forming procedure of Al-Si coated 22MnB5 steel sheets. These are: a Ti 0.57 Al 0.43 N/Mo-Si-B multilayer, a TiN base layer having a Mo-Si-B top layer, a DLC, and an Al-Cr-O coating. We determined the amount of adherent material (after the hot-forming procedure) by 3D topographical analysis and characterised the build-up volume as well as the coating/build-up interface constitutions with respect to the diffusivity of the participating elements. The smallest build-up volume could be identified for the Ti 0.57 Al 0.43 N/Mo-Si-B multilayer as well as the DLC coating, whereas the highest adhesive wear peak-value during the whole testing sequence was detected for the Al-Cr-O coating. Based on detailed TEM analysis of the diffusion zones (between build-ups and coating materials), we can conclude that the smallest adhesive wear is obtained, if the interface formation (between build-up and coatings) is narrow and Fe-free or at least Fe-lean. • Wear behaviour of PVD coated forming tools. • Hot-forming of AlSi coated UHS steel sheets. • 3D topographical adhesive and abrasive wear analysis. • TEM based interfacial diffusion study of the build-up/coating interface. • Correlation between adhesive wear and Al and Fe inter-diffusion. [ABSTRACT FROM AUTHOR]

Single point incremental forming (SPIF) is an emerging forming process for rapid prototyping and manufacturing of complex components from sheet metals. Recently, the use of electric current for the local resistance heating of the deformation area has attracted much attention in SPIF. In order to further study the electric hot incremental sheet forming (EHISF), in the present research, the effect of utilizing various lubricants on the formability of Ti-6Al-4V, AA6061, and DC01 sheet metals is experimentally investigated by forming a truncated cone under different feed rates, vertical pitches, and electric currents. To this end, the Taguchi design of experiment (DOE) and the analysis of variance (ANOVA) are employed. The results showed that the formability of Ti-6Al-4V and AA6061 sheets can be improved using the EHISF. For both the sheets, the lubricant and the electric current have significant effects on the maximum achievable forming depth. In addition, the formability of the DC01 sheet is highly affected by the lubricant and the feed rate. The results of the DC01 sheet showed that at the considered wall angle, the maximum forming depth in the EHISF does not change, compared to the cold SPIF, but the thickness distribution of the formed part at a higher temperature is more uniform. [ABSTRACT FROM AUTHOR]

Chromium nitride (CrN) coating is considered as one of the best candidates for wear protection in many forming application where adhesive wear and galling dominate. However, its relatively high coefficient of friction against soft metals hinders its applicability. Vanadium nitride (VN), on the other hand has attracted increasing interest as VN is easily oxidized to form Magneli phase vanadium oxides with easy slipping shear planes, on one hand leading to self-lubricating properties but also to deteriorated wear resistance. This can be overcome by forming CrVN coatings. However, there is a lack of information how such coatings perform in terms of galling resistance and V-concentration in typical forming conditions and against soft metals. Therefore, the aim of this work was to study friction properties of nano-layered PVD (Cr,V)N coatings at room and elevated temperature and how V-content influences on friction and galling resistance against typical work materials. Nanolayered (Cr,V)N coatings with V in concentrations from 15 to 30 % were deposited by industrial DC magnetron sputtering system and tested using Load-Scanner against AA2024 aluminum alloy and low-carbon steel at room and elevated temperature of 300 °C and 600 °C, respectively. Results were evaluated in terms of coefficient of friction level and stability, critical loads for galling initiation and volume of adhered work material. Results show that (Cr,V)N coatings do not necessarily improve galling resistance, being strongly dependent on V concentration and contact temperature. For forming Al alloys positive results are obtained with coatings containing 20–25 at.% V and for low-carbon steels above 25 at.%, with marked improvement obtained only at elevated temperatures. [Display omitted] • Nanolayered (Cr,V)N coatings with different V content were deposited on tool steel. • High temperature friction and galling resistance were studied. • For forming Al alloys V concentration between 20 and 25 at.% provides improvement. • High V contents (> 25 at.%) improve high temperature forming of low-carbon steels. [ABSTRACT FROM AUTHOR]

Abstract Forming at elevated temperatures can significantly increase the ductility of aluminium alloys enabling the manufacture of complex-shaped panel components from sheets. This study describes and investigates two elevated temperature forming processes: Hot Form Quench (HFQ®) (Lin et al., 2008) and conventional hot forming (HF) of aluminium alloys, with various material condition and processing parameters in order to advance the understanding of forming characteristics and post-formed strength. High temperature uniaxial tensile tests of AA7075 under HFQ® and HF conditions were performed to compare the stress-strain behaviors, ductility, and post-formed hardness. The results have shown that the ductility for HFQ® condition was greater than that for the HF condition when forming temperature was below 400 °C. In addition, typical microstructural evolution, such as the low-melting phase of HFQ® and precipitation of HF, were identified using fracture morphology observations and used to explain ductility differences exhibited in these processes. Post-formed hardness resulting from HF with different initial alloy temper and forming conditions were determined and compared with those from HFQ®. Severe reduction in hardness was found for HF using both high quench-sensitive alloy AA7075 and low quench-sensitive alloy AA6082. For the first time, the effects of a variety of influencing factors are investigated systematically, including heating rate, initial alloy, temperature and strain rate, on the high temperature deformation and post-formed strength of heat-treatable aluminium alloys, which contributes to the thorough understanding of the correlation between forming conditions and microstructural evolutions. [ABSTRACT FROM AUTHOR]

• The hot tensile and the forming limit experiments of AA7075 were conducted. • A modified continuum damage model was proposed. • The forward Euler method with NSGA-Ⅱalgorithm for parameters calibration was executed. • The thermal forming limit diagrams (TFLD) of AA7075 were predicted and compared. • The effects of multi-axial damage parameters on the computed TFLD were discussed. The formability of high strength Al-Zn-Mg-Cu (7000 series) aluminum alloys can be significantly improved at elevated temperatures, which has been paid more attention in recent decades. The formability of high strength aluminum alloys at elevated temperatures is essentially governed by thermal-damage evolution. In this paper, the main purpose is to propose a modified continuum damage model to describe the damage evolution and predict the fracture behavior of AA7075 at elevated temperatures (300–400°C). Firstly, the thermal-mechanical behavior and forming limit of AA7075 alloy sheet were experimentally investigated using a series of isothermal uniaxial tensile tests and Nakajima tests at different temperatures and strain rates. A set of uniaxial continuum damage constitutive equations (CDCEs) coupling continuum damage mechanics (CDM) with unified viscoplastic theory was proposed to describe the uniaxial tensile behavior of AA7075. Subsequently, the uniaxial equations were extended into a set of multi-axial CDCEs by introducing a multi-axial damage correction formula to predict the TFLD of AA7075. Besides, the forward Euler method was employed to integrate the proposed CDCEs, and the corresponding material constants of CDCEs were further calibrated by the non-dominated sorting genetic algorithmⅡ(NSGA-Ⅱ). The results illustrate that the thermal flow behavior and the TFLD of AA7075 alloy can be predicted successfully by the proposed damage model. Detailed discussions about the effects of corresponding parameters on the computed TFLD indicate the established multi-axial CDCEs are flexible and beneficial to the application potential in numerical simulation of hot sheet metal forming. Image, graphical abstract [ABSTRACT FROM AUTHOR]

A new concept of stability of materials is introduced by defining the optimum hot forming temperature for any given strain rate. This temperature is obtained through forming maps that are based on Lyapunov concepts and the introduction of a Garofalo equation in the Lyapunov criterion. This new approach is applied to a magnesium alloy AZ61. Torsion tests were carried out in the temperature range 574-734 K and strain rate range 0.7-8.7 s−1 and the microstructures were determined using optical microscopy. Using the peak stress, optimum workability at 630 K is obtained at 12 s−1. The results and the maps are compared with data and maps of other authors for AZ61 alloys in various states. [ABSTRACT FROM AUTHOR]

We have investigated the effect of introducing hot deformation and bainite isothermal treatment to the quenching-partitioning process for steel on the mechanical properties. The results indicate that the number of bainite-nucleation sites increase and the total elongation improves by deforming the steel and subsequently refining the martensite sheaves. Following this process, an excellent strength-elongation product of 27.5 GPa% is obtained. [ABSTRACT FROM AUTHOR]

On the basis of simulation with the help of the QFORM VX software, we study the CONFORM process with an aim to eliminate the delamination defects of products in the course of subsequent heat treatment. In the first stage of the solution, it is necessary to determine the stress-strain state in the deformation zone in the billet and to analyze the behavior of the flow of metal and the appearance of the zones of hindered deformation. [ABSTRACT FROM AUTHOR]

Although traditional hot forming parts are designed to have high strength to satisfy the requirement of lightweight and crash safety, its plasticity is too low to meet the need of part regional property. To overcome this shortcoming, the selective cooling process is a solution for properties regional distribution of part design. In this paper, the simulation is used to analyze the non-uniform temperature field and hot forming process. The results predict the microstructure of the slow cooling zone can obtain ferrite and pearlite that of the rapid cooling zone can get martensite. Experiments verified simulations by metallographic, tensile strength tests, and elongation measurement. The analysis of the metallography draws the same conclusion as the simulation. The tensile strength of the rapid cooling part can reach 1500MPa while that of the other is just 680MPa. The elongation of the slow cooling part can reach 11.2%, which of the rapid one is about 7.0%. The method of selective cooling could realize regional distribution of properties and different microstructure of materials. It provides a new direction for further research on distribution of properties and hot forming technology. [ABSTRACT FROM AUTHOR]

This work introduces a novel forming process, named Quench-form and In-die Creep Age (short for QICA). It integrates a hot stamping by warm dies (named quench-form) with a fast in-die creep age to significantly improve the dimensional accuracy of the formed part with maintained post-form mechanical properties and reduced total processing time. The process principle and underlying mechanisms were revealed by experimental forming tests, tensile tests, TEM observations. The optimum processing temperature range has been determined, and the processing window for industrial significance has been discussed. Results showed that under a heat treatment condition of 240 °C × 5 min followed by 175 °C × 4 h, the panel spring-back is significantly reduced by 75%, from 21′ to 5′, compared to that under the T6 forming condition. The total processing time is also dramatically reduced from the conventional 12–4.5 h, increasing the overall production efficiency by 62.5%. From industry perspective, an 80 °C temperature operation window, from 160 °C to 240 °C, is suggested to guarantee a yield strength of > 280 MPa (93% of the T6 strength). The effectiveness of the process has also been verified by forming an aircraft engine inlet lip part. The maximum clearance between the formed part and die was reduced from 7.00 mm to 2.01 mm by replacing the HFQ® technique with the QICA technique. The proposed novel process delivers an alternative energy-efficient method to produce high-accurate extra-large parts that are beneficial for aircraft and aerospace OEMs. [Display omitted] • A novel Quench-form and In-die Creep Age technique for forming large 2xxx parts. • The optimum processing conditions is 200–220 °C × min + 170–180 °C × 4 h. • Up to 71% spring-back reduction and 62.5% reduction in process time are achieved. • Two types of precipitates coexist in the QICA-formed parts. [ABSTRACT FROM AUTHOR]

In this work, a general elasto-viscoplastic constitutive model incorporating a finite strain viscoplastic flow law, the Kocks-Mecking dislocation density evolution, work hardening, stress softening due to dynamic recovery and dynamic recrystallization (DRX), and the Johnson-Mehl-Avarmi-Kolmogorov (JMAK) DRX kinetics was established for modeling the deformation and microstructure evolution of a near- α Ti alloy. A full-implicit stress integration scheme was proposed to implement the constitutive model into the commercial FEM solver ABAQUS/Standard. Isothermal hot compression experiments under various deformation conditions and detailed microstructure characterizations were conducted to study the deformation and DRX behaviors of the alloy, as well as to validate the developed material model. The alloy exhibits a typical discontinuous DRX behavior, macroscopically sensitive to various deformation conditions and microscopically strongly affected by the orientation of prior grains. The simulation results regarding the macroscopic flow stress curves and the local volume fractions of DRX in various regions in the specimen agree well with the experimental results. The proposed material model and the robust numerical implemental scheme can be extended to consider more physical deformation mechanisms and microstructure evolution of advanced structural metals and alloys. [ABSTRACT FROM AUTHOR]

The electric assistance incremental forming technology is usually adopted to form hard-to-form sheet metals. Recently, the local heating method by current is used to fabricate specimens with these materials due to low costs and simple setups. However, the heating method has four natural defects: inhomogeneous temperature distribution, arc burns for the sheet and the tool, unsuited for multistage forming, and complex lubrication processes. In this work, a novel heating design, directly making current flow from the one side of the sheet into the other side of the sheet, was proposed to form specimens with TC4 Ti alloy. Meanwhile, different current values were adopted in numerical simulation and experiments, which demonstrated that a current value of 500 (A) should be selected to fabricate the specimen with TC4 Ti alloy. In addition to this, some forming results, such as temperature variations, roughness, and tool damage, obtained respectively by local and integral electric heating incremental forming processes were analyzed further. [ABSTRACT FROM AUTHOR]

Obtaining square cups with the radius at the bottom corner lower than the thickness of original plate via a single-step hot forming process is a challenge. In this paper, a processing way was proposed by combining local-thickened plate and friction control, to manufacture square cups with small corner radii. Through finite element (FE) simulations, the metal flow during hot forming of square cups was optimized by varying the shape of the local thickened section and adjusting the friction conditions at the interfaces between blank and tools. It was found that the filling ratio of the bottom corner can be significantly improved by increasing the friction coefficient at the interfaces between the blank and the upper punch, and that between the blank and the central zone of counter punch. The established flow dividing surface (FDS) model is capable for describing the variation of metal flow with the friction coefficients. Base on the simulation results, hot forming experiments were also carried out, and square cups with small radii of 2 mm at the bottom corners were successfully manufactured. [ABSTRACT FROM AUTHOR]

Hollow blades which have large size and complex surface are difficult to control springback and dimensional accuracy in hot forming. The forming molds only have upper and lower die that it cannot control the material flow effectively. So, a new hot forming process has been proposed. In this paper, a blade back arc that is used in nuclear steam turbine stator and formed through hot drawing with binder is chosen as the research object. After optimizing the forming parameters, numerical simulation technology is used to forecast the forming quality, and the part trial test agrees with the simulation results. The thickness of part meets the requirements, and the springback results show that springback of part is beyond the tolerance range in small area. According to the test result, die surface is compensated. After that, springback is controlled into an acceptable range. Compared with former hot forming process, the new hot forming process controls the material flow effectively, and blade back arc has small springback and high accuracy. [ABSTRACT FROM AUTHOR]

The present work aims at evaluating and understanding the mechanical behavior of a Ti-6Al-4 V alloy under hot and superplastic forming conditions. Tensile tests were performed at temperature range from 650 °C to 950 °C, at strain rates between 10-2 s-1 and 10-4 s-1. Three equiaxed microstructures, each characterized by a different starting grain size (4.9 μm, 3.0 μm and 0.5 μm), are compared to better understand the microstructural evolutions under hot and superplastic forming conditions and their influence on the mechanical behavior. Hence, an accurate model with microstructural considerations is proposed. The model capabilities consider the grain size evolution that is influenced by the temperature and deformation. The computed flow stresses strongly depend on the strain rate and on the considered initial grain size. Temperature and strain rate conditions may lead to a strain hardening phenomenon in some cases. The comparison between the model response and experiment shows a good agreement for all the tests carried out on Ti-6Al-4 V. [ABSTRACT FROM AUTHOR]

Titanium parts can be very expensive or can be a good compromise between cost and efficiency especially when expected cost and weight reduction is reached or exceeded. Titanium properties are always well desired but the high level of material cost and the cost of manufacturing are not appreciated. Applicable forming processes for sheet metal parts range from conventional cold forming of commercially pure titanium with subsequent separate annealing up to hot forming processes like hot bending, hot calibration, hot deep drawing and superplastic forming with in-process annealing. Each process has limitations and/or special advantages. There are big differences in material waste, cycle time, process cost, overweight from minimum wall thickness requirements and tool design. Suitable choice of process and the technical feasibility is mostly depending on part geometry also in respect of constant wall thickness and type of alloy. The paper describes decision guidelines to find the right process for a given inquiry concerning alloy, service loads, number of load cycles, temperature, quantity, optical appearance, etc. The total picture has to include the following assembly processes. Some representative solutions are described. [ABSTRACT FROM AUTHOR]

Hot forming (quenching and forming at the same time) makes the steel surface oxidation and decarburization. Stamping parts formed in this technique shows low hardness in the exterior and high hardness in the interior. The material properties exhibit the continuous functionally gradient distribution in the thickness direction. The exterior hardness and strength is low, while the interior hardness and strength is high. So, the new type of multi-layer metal composite materials is formed. The microstructure, hardness, strength and plasticity of this new metal composite material is analyzed and taking the reinforced beam for example, the three-point bending experiment is implemented. To investigate the crashworthiness of the new metal composite materials, the finite element analysis (FEA) model of the reinforced beam is established on the basis of the metallographic and three-point bending experiments. To compare the crash force and energy absorption between the metal composite materials and each phase material in the interior, it is found that the metal composite materials have the comprehensive performance of every single-phase material. So, it is a good alternative material in application of bearing impact and absorbing energy. [ABSTRACT FROM AUTHOR]

Deforming nickel base superalloys under the γ′ solvus retards dynamic recrystallisation (DRX) by hampering grain boundary motion; this is an efficient way of refining grain size during forging and other hot working processes. A previously proposed model for describing the kinetics of DRX in nickel alloys is here further developed to account for the influence of γ′ intermetallics, allowing predicting microstructural evolution during subsolvus deformation. The model incorporates alloy composition and initial grain size, as well as temperature and strain rate. It is calibrated with data for both supersolvus and subsolvus deformation. Plotting the calculated steady-state grain size as a function of the strain necessary to complete DRX allows visualising both processing and compositional trends, which are relevant to materials engineering and can be used for design. It is shown that efficient grain refinement cannot be achieved with a limited amount of strain if process or alloy optimisation alone is performed. Instead, it appears that this may only be reached by joint design of the forming process (strain rate and temperature) and composition. [ABSTRACT FROM AUTHOR]

Five hardness grades of 22MnB5 are considered, covering the full strength-range from 600 MPa in the ferritic/pearlitic range to 1500 MPa in the fully hardened, martensitic state. These five grades form the basis for a hardness-based material model for the heat-affected zone found around resistance spot welds in tailor hardened boron steel. Microhardness measurements of resistance spot welds in all five grades are used to determine the location and shape of the heat-affected zone and for mapping of the hardness distributions into FE-models of the specimens used for model calibration. For calibration of the strain hardening of the heat-affected zone, a specially designed asymmetric uni-axial tensile specimen is used that features a well-defined strain field up to fracture initiation. Both the measured force–displacement curves and the strain fields are used as input for an inverse FEM optimization algorithm that identifies suitable strain hardening model parameters by minimizing the differences between experimental and simulated results. A strain-based fracture model is calibrated using a hybrid experimental/numerical approach, featuring two additional specimens in which fracture initiates in the HAZ under different stress states. Strain hardening and fracture strains are assumed to be linearly related to the as-welded material hardness. The calibration and modeling approach are validated by comparing measured and predicted force–displacement curves and strain fields of welded coupon tensile tests. [ABSTRACT FROM AUTHOR]

The effect of stress state on the initiation of damage for leaded free cutting steel has been investigated under hot rolling conditions. Double notched (DN) circumferential tension samples were designed and used to simulate damage development at different stress states and deformation conditions using a Gleeble (3800) thermal-mechanical testing system. Two DN sample geometries with varying notch profiles were used to account for different states of stress. To simulate the conditions of hot rolling the samples were tested at high temperatures (900–1200 °C) and moderate strain rates (0.1–1 s−1). After testing to failure, which normally occurs at one notch of the specimen, the unfailed notch of each sample was sectioned to examine the sites where damage occurs since the material has been captured in a state very close to failure. Two of the cases examined have shown definitive damage paths occurring from ‘outside–in’ for a sharp notch deformed atT = 900 °C and from ‘inside–out’ for a blunt notch tested atT = 1200 °C for the same strain rate of 0.1 s−1. The experimental results of the failure initiation sites were compared with computed values of the stress fields around the notch profiles, obtained from FE analysis using a set of viscoplastic constitutive equations calibrated for free cutting steel. The temperature profiles from high temperature mechanical testing were used in the FE calculations of the stress state. [ABSTRACT FROM AUTHOR]

Hot stamping of sheet metal is an established method for the manufacturing of light weight products with tailored properties. However, the generally-applied continuous roller furnace manifests two crucial disadvantages: the overall process time is long and a local setting of mechanical properties is only feasible through special cooling techniques. Hot forming with rapid heating directly before shaping is a new approach, which not only reduces the thermal intervention in the zones of critical formability and requested properties, but also allows the processing of an advantageous microstructure characterized by less grain growth, additional fractions (e.g., retained austenite), and undissolved carbides. Since the austenitization and homogenization process is strongly dependent on the microstructure constitution, the general applicability for the process relevant parameters is unknown. Thus, different austenitization parameters are analyzed for the conventional high strength steels 22MnB5, Docol 1400M, and DP1000 in respect of the mechanical properties. In order to characterize the resulting microstructure, the light optical and scanning electron microscopy, micro and macro hardness measurements, and the X-ray diffraction are conducted subsequent to tensile tests. The investigation proves not only the feasibility to adjust the strength and ductility flexibly, unique microstructures are also observed and the governing mechanisms are clarified. [ABSTRACT FROM AUTHOR]

Results are presented from the use of numerical modeling to perform an empirical assessment of the effect of the initial process parameters in hot die forging (the temperatures to which the deforming tools and semifinished product are heated) on the temperature field in the semifinished product during deformation. A series of numerical experiments is performed on the basis of the finite-elements method, the resulting data are analyzed, and relationships between the parameters are established and explained. [ABSTRACT FROM AUTHOR]

In this article, an inverse FEM optimization strategy is proposed for identification of the strain hardening parameters of boron alloyed steel 22MnB5 in five different hardness grades. In the proposed elasto-plastic constitutive model, the strain hardening is represented by a nonlinear combination of the Swift hardening law and a modified version of the Voce law. Initial fits of these two classical strain hardening equations are constructed based on experimental data from uni-axial tensile tests up to the point of diffuse necking. The strain hardening response beyond the point of diffuse necking is determined from a 3D strain field analysis of notched tensile and equibiaxial tension tests. Both the measured force–displacement curves and the strain fields are used as inputs for the optimization algorithm that identifies suitable material model parameters by minimizing the differences between experimental and simulated results. In order to show the contribution of the different parts of the elasto-plastic model for representing the real material response, three simplified versions of the proposed model and the parameter identification procedure are applied on two selected hardness grades, confirming the importance of a flexible strain hardening law, suitable yield criteria and accurate experimental data up to high plastic strains. The calibrated model was shown to accurately capture the elasto-plastic response of 22MnB5 in different hardness grades, with an excellent representation of the strain fields up to the point of fracture. [ABSTRACT FROM AUTHOR]

Based on the analyses of how stress state influences the microstructure, thickness distribution and mechanical properties, rapid cooling pretreatment is proposed to solve the cracking issues of hot stamped AHSS (advanced high strength steel) parts with complex shapes. Rather than stamping the part right after the blank is fully austenitized at around 900–950 °C as in the traditional hot stamping process, the proposed process cools the blank rapidly to around 700 °C then followed by forming and quenching. The rapid cooling pretreatment not only enables the AHSS to have a higher hardening exponent n value so as better formability in tension dominant areas, but also increases the probability of additional nucleation of martensite in austenitic parent phase that helps obtain a dense microstructure and improved strength and toughness in compression dominant areas. Experiments show the rapid cooling prior to forming does help form AHSS parts without cracking. The process also leads to a microstructure with refined martensitic phase arrangement and uniformly distributed macro hardness. The rapid cooling method is thereby proved scientific and effective. It breaks through the bottleneck of the cracking problem in hot stamping very complex AHSS parts and establishes the theoretical foundation for the massive production intent manufacturing process. [ABSTRACT FROM AUTHOR]

A metallurgical material description of the flow behavior for finite element (FE) simulations was developed. During hot compression tests, the dynamic microstructure evolution is modeled on the example of high-strength martensitic steel MS-W 1200. Compression tests at 900-1000 °C with a strain rate of 0.1 s-1 on fine-grain and coarse-grain samples were performed. An analysis of the flow behavior identified a strong correlation between the dynamic recrystallization kinetics and the initial microstructure. The regression analysis has been used to determine correction factors of the new model to describe the dynamic recrystallization. A good agreement between FE simulation and measurement shows the validity of the new model. [ABSTRACT FROM AUTHOR]

High-strength boron steel used in auto body can not only achieve automobile lightweight, but also improve the crashworthiness. Hot punching process is the advanced manufacturing technology for forming high strength steel. At high temperature, it can improve the formability of sheet metal, reduce the spring back of forming part, and ensure the forming precision. With the finite element numerical simulation, it can effectively predict the forming process of sheet metal, and can greatly reduce high costs and long development cycle of traditional 'trial' method. In the paper, taking the B pillar of a car with '22MnB5' for example, had the thermal-mechanical coupling analysis for it. And then, the temperature distribution in sheet metal forming process and the change rate of thickness and thickness distribution after sheet forming were obtained. Having the simulation for hot forming products with thermal coupling conditions can provide effective help for the product design and process design of the punching die. [ABSTRACT FROM AUTHOR]