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The deformation behavior and microstructure of 25CrMo4 axle steel was systematically investigated by thermal compression deformation. The hot-compression test of a 25CrMo4 axle steel sample was carried out on a Gleeble-3800 thermal mechanical simulation tester. The flow behavior of the alloy was studied at the deformation temperature (900–1200 °C), strain rates (0.01; 0.1; 1.0) s–1 and the maximum deformation of 60 %. The flow curves under different deformation conditions were obtained, and the effects of the deformation temperature and strain rate on the appearance of the flow curves are discussed. The true stress-strain curve obtained by experiment is modified by friction. Based on the corrected experimental data, the activation energy determined by the regression analysis was Q = 311 kJ/mol, and the constitutive model was constructed. The high-temperature flow behavior of the 25CrMo4 axle steel was described by the Zener-Hollomon parameter. The optimum hot-deformation process parameters were determined based on the hot processing maps, followed by the analysis of the microstructure characteristics of the alloys under optimum hot working. The results show that the suitable hot-deformation process parameters of the alloy are as follows: deformation temperature is 1050–1200 °C, and strain rate is 0.01 s–1 to 0.14 s–1.

Directional solidification (DS) processing parameters have significant influence on microstructure of ZL114A alloy. Therefore, it is necessary to optimize DS processing parameters to control its properties. This work is aimed at studying the effect rule of DS processing parameters on microstructure of ZL114A alloy. The specimens of this alloy were prepared using high-vacuum DS equipment. In the process of DS, temperatures change from 700 °C to 800 °C, and pulling rates increase from 100 μm/s to 200 m/s. Microstructure of specimens was investigated using scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). Mechanical properties of specimens were measured by means of universal tension tester and microhardness tester. Effects of melt temperatures and pulling rates on the microstructures and mechanical properties were studied and discussed. Experimental results show that the microstructure can be improved with the decrease in melting temperatures and the increase in pulling rates. However, the microstructure became coarser when the pulling rate is too higher. Therefore, a set of processing parameters were optimized as melting temperature of 700 °C and pulling rate of 150 μm/s to improve the microstructure of ZL114A alloy.

Direct deformation spheroidization (DDS) of carbides in warm conditions can improve the microstructure and performance of bearing steel. In this study, based on the carbide spheroidization mechanism, a set of multiaxial constitutive equations was developed to predict the microstructure evolution of bearing steel 52100 during warm skew rolling (SR). The derived multiaxial constitutive equations were implemented in DEFORM-3D software through a user subroutine. FE simulation of warm SR was performed to predict the formation and microstructure evolution of bearing steel balls (BSBs). The distribution of the normalized dislocation density, carbide phase transformation fraction and carbide spheroidization fraction within BSBs was predicted via FE simulation of warm SR. To validate the FE simulation results, warm SR experiments were conducted to produce BSB specimens with 30 mm diameter. The microstructure of BSB specimens was observed to analyze their microstructure distribution in the longitudinal and transversal sections. The predicted and experimental results were compared, and the results show that the predicted carbide spheroidization distribution agrees well with the experimental results. This indicates that the formation and microstructure of BSB during warm SR can be predicted well using the derived multiaxial constitutive equations.

In this paper, the mechanical behaviour and microstructure evolution of TC4 titanium alloy during high temperature plastic deformation are studied. The compression experiment was carried out on the Gleeble-3800 thermal simulator at the deformation temperature ranging from 900℃~1100℃ and at the strain rate of 0.1/s~10/s. The experimental results show that the flow softening mechanism of TC4 titanium alloy is dynamic recrystallization under condition of high temperature deformation. As the deformation temperature increases, the volume fraction and size of the β-transformed tissue become larger, and more acicular martensite appears in the β-transformed tissue. With the increase of strain rate, the grain size is reduced. Moreover, under the condition of high-temperature deformation, TC4 titanium alloy has obvious discontinuous yield phenomenon, and the higher the deformation temperature is, the more obvious the discontinuous yield phenomenon is. At low strain rate, TC4 titanium alloy has a slight strain hardening in a small strain rage, then it exhibits the characteristic of continuous softening flow, and it eventually tends to steady state. At high strain rates, TC4 titanium alloy exhibits wave yielding phenomenon.

In order to investigate the influence of different deformation routes of equal channel angular pressing (ECAP) on mechanical properties and microstructure of AA6063 alloy at room temperature. The specimens were processed with angle of 120°regarding processing routes A, BA, BC, BC-UD2 and C. Then the macro morphology of specimens was analyzed, the strength and hardness were measured, and the microstructure was observed by SEM. The results show that, after four passes, the deformation of route A is the most inhomogeneity, while route BC-UD2 is the most homogeneity. Route BC deformation is relatively uniform and not easy to generate cracks on up-surface. The increase of tensile strength of route BC and route C is the most. The ductility of route BA and route BC keep best. Route BC can not only improve the strength of the material, but also maintain the plasticity of the material. The hardness improvement and the deformation uniformity show negative correlation under in all routes. The hardness improvement is most obvious after route BA, and the deformation is most homogeneous after route BC-UD2. The microstructure of route C and route BC is equiaxed grain. The average grain size of specimens is smaller after route C.

Equal channel angular pressing (ECAP) is one of the methods to prepare ultrafine-grained materials by sever plastic deformation. The materials with large grain size can be extruded at room temperature. The present work investigates the influence of different deformation routes on microstructure evolution and electrical conductivity at room temperature of ECAP processed AA6063 sample. Samples were processed with four different routes (A, BA, BC and C) in the ECAP die. The microstructure and electrical conductivity of the specimen after ECAP were measured. The results show that with the increase of extrusion passes, ECAP can fragment the large AlFeSi phase to small particles (length (1−3)μm) and homogenize the small particles. After four passes of ECAP, the grain of the sample is refined, and the grain size is about 0.55μm. The order of average grain size from small to large is C BC > C.

A high-performance titanium alloy requires a fine and homogenous microstructure. The rational deformation process parameters of the Ti-3Al-5Mo-4.5V (TC16) titanium alloy can contribute to achieving this important microstructure. Hot-compression experiments were performed at temperatures in the range 100–800 °C and at strain rates of 0.1 s–1 to 10.0 s–1. The effects of deformation temperatures and deformation rates on the mechanical behaviour and microstructure evolution were analysed and discussed. The softening mechanism of the Ti-3Al-5Mo-4.5V alloy at an elevated deformation temperature was revealed. Experimental results showed that 500 °C is the critical deformation temperature to distinguish the warm-deformation region of 100–400 °C and the hot-deformation region of 500–800 °C. The softening mechanism is dominated by -phase spheroidization in the temperature range 100–400 °C with a higher strain rate of 10.0 s–1. The softening mechanism is dominated by a local temperature rise in the temperature range 500–800 °C with a lower strain rate of 0.1 s–1.

The phase component, microstructure and compressive properties of a novel 3d transition metal high entropy alloy, AlCoCrCuTi, in as-cast and annealed conditions were investigated. The phases of the as-cast AlCoCrCuTi alloy are composed of primary phase AlCo2Ti (L21), eutectic structure {AlCo2Ti (L21)+ Al3Cr7 (BCC)} and interdendritic phase AlCu2Ti (L21). Through annealing, a rosette feature of the as-cast AlCo2Ti + Al3Cr7 eutectic structure is deteriorated due to the lath-like Al3Cr7 changed to finely-divided one. In mechanics performance, the as-cast alloy exhibits a balanced synergy in hardness (593±37 HV) and ultimate strength (745 MPa), while the hardness of the annealed alloy slightly increases to 647±23 HV at the expense of the ultimate strength. Moreover, the alloy either in as-cast or annealed conditions unfortunately display a typically brittle character. The deficiency of elongation might stem from the diversified brittle and hard phases incorporated, such as AlCo2Ti + Al3Cr7.

Microstructure evolution and hot deformation behaviors of bearing steel SAE 52100 were investigated by hot compression test at temperatures from 950°C to 1160 °C and strain rates from 0.1s−1 to 10.0s−1. The effects of process parameters (strains, strain rates and temperatures) on recrystallization behavior and plastic flow behavior were discussed. A set of unified visco-plastic constitutive model was built using internal state variables modeling method to predict microstructure evolution and flow stress of bearing steel SAE 52100 during hot deformation. Material parameters within constitutive model were determined using genetic algorithm (GA) optimization technology. The developed model was validated using experimental average grain size, recrystallized fraction and effective stress. Good agreements have been obtained for the predicted and experimental results. It indicates that the derived constitutive model is reliable. Microstructure evolution of SAE 52100 steel in hot metal forming was analyzed using the derived model.

Direct deformation spheroidization of bearing steel can produce a fine and homogeneous microstructure. Warm-compression experiments were performed to investigate the carbide spheroidization behavior of 52100 bearing steel at temperatures of 650 °C to 750 °C and strain rates of 0.1 to 10.0 s−1. A set of mechanism-based unified constitutive equations was developed using the internal state variable method to describe the carbide spheroidization and metal flow behaviors of 52100 steel under warm deformation. The carbide spheroidization fraction, dislocation density, and phase transformation were modeled and correlated with unified constitutive equations. Material parameters in the constitutive equations were determined using genetic algorithm optimization techniques. The developed constitutive equations were validated by comparing the predicted and experimental results. Good consistency between these results indicated that the carbide spheroidization and metal flow behavior could be predicted using these constitutive equations.

High-performance bearing steel requires a fine and homogeneous structure of carbide particles. Direct deformation spheroidizing of bearing steel in a dual-phase zone can contribute to achieving this important structure. In this work, warm compression testing of 52100 bearing steel was performed at temperatures in the range of 650–850°C and at strain rates of 0.1–10.0 s−1. The effect of deformation temperatures on mechanical behavior and microstructure evolution was investigated to determine the warm deformation temperature window. The effect of deformation rates on microstructure evolution and metal flow softening behavior of the warm compression was analyzed and discussed. Experimental results showed that the temperature range from 750°C to 800°C should be regarded as the critical range separating warm and hot deformation. Warm deformation at temperatures in the range of 650–750°C promoted carbide spheroidization, and this was determined to be the warm deformation temperature window. Metal flow softening during the warm deformation was caused by carbide spheroidization.

As ductile damage has a severe impact on the performance of bearing steel-balls (BSB), it is necessary to apply the ductile damage evolution model for predicting the distribution of ductile damage in BSB. A new ductile damage model was developed using physically-based internal state variables method by considering the effect of two important stress state parameters: stress triaxiality and relative ratio of max principal tension stress, on the ductile damage evolution. The newly developed ductile damage model was implemented into the commercial FE code, DEFORM-3D, via a user defined subroutine and cold forging simulation was operated. BSB formation tests were carried out and the microstructure and micro-damage were examined from the tested samples. FE simulation results of ductile damage were compared with those of tested samples. Good agreements have been achieved, which proves that the newly developed ductile damage model enables micro-damage evolution during cold forging to be well predicted. Some constructive suggestions have been obtained to improve the quality of BSB during cold forging.

The high-temperature deformation behavior of 5Cr21Mn9Ni4N heat-resistant steel was studied using a Gleeble-1500D thermal simulation test machine for high-temperature compression tests. The deformation temperatures ranged from 1273 K to 1393 K, and the strain rates ranged from 0.1 s −1 –10 s −1 . The height reductions were 20%, 40%, and 60%. The flow stress of 5Cr21Mn9Ni4N increased with increasing strain rate, whereas it decreased with increasing temperature. The high-temperature deformation of 5Cr21Mn9Ni4N began from the strain-hardening stage to the steady-state deformation stage. The characteristics of the stress–strain curves were determined through the interaction of work hardening, dynamic recovery, and dynamic recrystallization. The relationship between microstructure and processing parameters was analyzed. A set of unified viscoplastic constitutive equations based on changes in dislocation density, volume fraction of dynamic recrystallization, and grain size was established to predict deformation behavior and microstructure during a high-temperature working process. The average relative error between the calculated and experimental flow stress was 4.8%. This finding indicated that the constitutive equations could be used to predict the flow behavior of 5Cr21Mn9Ni4N accurately during high-temperature deformation.

The hot deformation behavior of 4Cr9Si2 heat-resistant steel was investigated by hot deformation compression tests in the deformation temperature range of 950–1180 °C with strain rates of 0.1–10 s−1. The constitutive equation of 4Cr9Si2 heat-resistant steel was established to describe the peak stress as a function of the deformation temperature and strain rate. The deformation characteristics of the cross wedge rolling (CWR) process of preform hollow valves are analyzed. By using DEFORM-3D software for finite element simulation tools, the process of CWR forming hollow valves was analyzed. According to the finite element simulation results, which reveal the influence of different process parameters on the inner diameter of the hollow valve blank, changing the stretching angle of the die design method effectively improves the position wedge reaming of the workpiece.

Different constitutive modeling methods lead to different prediction accuracy of stress-strain relationships for hot metal forming. The aim of this work is to establish constitutive model using two methods of double multiple nonlinear regression model (DMNR) and strain-compensated Arrhenius-type constitutive model (SACM) to describe the material flow behaviour of TC16 titanium alloy under hot compression in the strain rate range of 0.1 s − 1 ∼ 10.0 s − 1 and temperature range of 973 K ∼ 1373 K . A comparative study has been conducted on the prediction capability of DMNR model and SACM model under different temperature ranges, and their prediction accuracy was quantified by using standard statistical parameters such as correlation coefficient ( R ), average absolute error ( A A R E ) and root mean square error ( R M S E ). The results showed that the DMNR model has a better prediction accuracy to describe the stress-strain relationship than SACM model at temperature range of 973 K ∼ 1373 K . It indicates that DMNR model is more suitable in a wider range of deformation temperature. When the constitutive models of TC16 titanium alloy were developed at temperature range of 1173 K ∼ 1373 K , SACM model has more excellent predictability than DMNR model. It indicates that SACM model is more suitable to describe the stress-strain relationships in a narrow range of deformation temperature.

Microstructural evolution and flow behavior greatly affect the hot forming process of IN718. In this research, hot deformation behaviors of IN718 were investigated by performing hot compression tests at temperature range of 1000–1100 °C with strain rates of 0.1–20.0 s−1. By incorporating physically based internal state variables such as dislocation density, volume fraction of dynamic recrystallization, and grain size, a set of unified viscoplastic constitutive equations were developed to predict the microstructural evolution and flow behavior of IN718. The material constants were determined using a genetic algorithm (GA)-based optimization method. Comparisons of the computed and experimental results indicate that the constitutive equations established in this study can accurately describe the hot deformation behavior and microstructural evolution of IN718.

The mechanical properties of 25CrMo4 steel for high-speed railway axles depend on its microstructural evolution during hot cross wedge rolling (CWR). In this paper a set of mechanism-based unified constitutive equations has been determined for the prediction of elastic-viscoplastic material behaviour and microstructural evolution of the 25CrMo4 steel during hot CWR processes. Hot compression tests were conducted using a Gleeble thermo-mechanical simulator at temperatures in a range of 1223–1433 K and at strain rates in a range of 1.0–10.0/s. A set of equations was determined from experimental data of static grain growth, grain refinement and viscoplastic flow using a genetic algorithm (GA) method. Good agreements between the experimental and predicted data were obtained. The determined constitutive equations were implemented into the commercial FE code, DEFORM-3D, via a user defined subroutine and CWR processes were modelled. CWR tests were also carried out and microstructure examinations were conducted. FE simulation results, such as grain size, were compared with those of CWRed parts. Good agreements have been obtained, which shows that the determined constitutive model enables microstructure evolution in CWR processes to be well predicted.

Hot tensile tests were conducted using a Gleeble 1500, at the temperature range of 623 K to 823 K (350 °C to 550 °C) and strain rate range of 0.1 to 10 s−1. Flow stress is significantly affected by temperature and strain rate. As strain increases; the flow stress first rapidly increases, subsequently maintains a steady state, and finally drops sharply because of damage evolution. The features and mechanism of the damage were studied utilizing a scanning electron microscope. Micro-void nucleation, growth, and coalescence result in the failure of the hot-formed specimen. A damage equation based on continuum damage mechanics and damage mechanism in hot metal forming was proposed. A unified viscoplastic damage model coupled with strain, strain rate, temperature, dislocation, hardening, damage, damage rate, and so on was developed and calibrated for AA6111 using Genetic Algorism Tool in three steps. This model can be used to describe viscoplastic flow behavior and damage evolution at various temperatures and strain rates. The model was implemented into the finite element (FE) model in ABAQUS platform via the variable user material subroutine. Thus, the FE model could be employed to study the damage distribution and the effects of blank holder force (BHF) and forming velocity on hot cylindrical deep drawing. It is revealed that lower BHF and higher velocity are beneficial for drawability. A good agreement between simulated and experimental results has been achieved.

Microstructure and ductile damage have a significant influence on the deformation behavior of high-speed railway axles during hot cross wedge rolling (CWR) and its final performance. In this study, based on the continuum damage mechanics, a multiaxial constitutive model coupling microstructure and ductile damage was established to predict the evolution of microstructure and ductile damage of 25CrMo4 during hot CWR processes. Material constants within the multiaxial constitutive model were determined by Genetic Algorithm (GA) optimization techniques from thermo-mechanical test data. The derived multiaxial constitutive model was embedded into the DEFORM-3D software through a user subroutine. FE simulation of CWR was performed to predict the microstructure evolution and ductile damage. CWR experiments were also carried out to validate the proposed model. The predicted grain size and ductile damage agree well with the experimental results. Good agreements indicate that the derived multiaxial constitutive model is reliable and can be used to predict the evolution of microstructure and ductile damage during CWR process.

Electro hydraulic proportional pressure-flow compound valve (P-Q valve) is a new type of energy saving combination valve. The velocity and output force of the actuator can b e proportionally controlled by the P-Q valve in dif ferent working state. The author puts forward a new scheme that the hydraulic elevator applies the P-Q valve to hydraulic driving control system. The author also makes theoretic analysis and builds a m odel of the elevator mechanical drive system and hydraulic driving system, according to which the system is simulated by computer. The results show that: the hydraulic driving control system which is based on P-Q valve of the hydraulic elevator has the advantage of smooth starting, high control precision and sm all impact in the case of emergency stop.