DRX Kinetic Model Research Articles

Experimental Study and Numerical Simulation of Dynamic Recrystallization Behavior of a High-Strength Steel

In this paper, to research the dynamic recrystallization (DRX) behavior of a high-strength steel (34CrNiMo6), hot compression tests were carried on Gleeble-1500D thermo-mechanical simulator within the different temperatures and strain rates. After hot compression tests, the microstructures of specimens were observed by optical microscope. Based on Kocks and Mecking mathematics model (KM), the DRX kinetic model was established by the flow stress curves during hot deformation. Meanwhile, a grain size model was established by measuring microstructure. Furthermore, combined with the material kinetic model and grain size model, a rigid–plastic finite element simulation was built to analyze the microstructural behavior of 34CrNiMo6 steel during the uniaxial hot compression. The results indicate that the simulation results are in good agreement with the experimental data. The DRX model had an accurately predictive capability for the hot compression process, which could provide a theoretical guidance and process optimization for metal forming processes.

Modeling of dynamic recrystallization volume fraction evolution for AlCu4SiMg alloy and its application in FEM

Abstract To improve the understanding of coupling effect between dynamic recrystallization (DRX) behaviors and flow behaviors of as-cast AlCu4SiMg, a finite element (FE) simulation equipped with the models of DRX evolution was implemented. A series of isothermal compression tests were performed primarily on a Gleeble−3500 thermo-mechanical simulator in a temperature range of 648−748 K and a strain rate range of 0.01−10 s −1 . According to the measured true stress−strain data, the strain hardening rate curves (d σ /d e versus σ ) were plotted to identify the critical strains for DRX initiation ( e c ). By further derivation of the related material constants, the DRX volume fraction equation and the strain for 50% DRX ( e 0.5 ) equation were solved. Accordingly, the aforementioned DRX equations were implanted into the FE model to conduct a series of simulations for the isothermal compression tests. The results show that during the evolution of DRX volume fraction at a fixed strain rate, the strain required for the same amount of DRX volume fraction increases with decreasing temperature. In contrast, at a fixed temperature, it increases with increasing strain rate. Ultimately, the DRX kinetics model of AlCu4SiMg alloy and the consequence of the FE analysis were validated by microstructure observations.

Comparison study of hot deformation behavior and processing map of AZ80 magnesium alloy casted with and without ultrasonic vibration

In order to compare the workability of AZ80 magnesium alloy casted with and without variable-frequency ultrasonic field (VUF), uniaxial hot compression tests were carried out in the temperature range of 523–673 K and the strain rate range of 0.001–1 s−1 on a Gleeble-3500D thermo-mechanical simulator. The flow stress, constitutive relation, DRX kinetic model and processing map were analyzed based on the experimental data. The results show that, the VUF samples have lower peak stress and peak strain than DC samples at low strain rates, while the opposite situation can be observed at high strain rate. The calculated activation energy Q and stress exponent n for DC samples are 192.38 kJ/mol and 7.30158, which are higher than the calculated values for VUF samples, showing the figures of 165.30 kJ/mol and 7.30158, respectively. The VUF casted samples start DRX earlier and easier, and can obtain complete DRX structure at high strain rate. The VUF samples have larger workability range but smaller instability region than DC samples. Dense and irregular bulges can be observed on side surfaces of DC samples after compression, while surfaces of VUF samples are smooth.

Modelling of dynamic recrystallization kinetics of 300M steel at high strain rates during hot deformation

The flow curves of 300M steel exhibit a transition from stress peak presence to stress peak absence as the strain rate increases. It is difficult to establish dynamic recrystallization (DRX) kinetics models suitable for strain rates where there are no stress peaks in the flow curves using the existing Avrami equation, and the optimal processing parameters for forging can be scarcely acquired. In this study, the high-temperature flow and DRX behavior of 300M steel are investigated by performing isothermal compression tests at temperatures between 1173–1423 K with strain rates between 0.001–50 s −1. Distinct stress peaks can be found in the flow curves at low strain rates, and the average grain size decreases with the increase in the strain rate at the same temperature. The DRX mechanism is a discontinuous DRX, and the grain boundary migration plays an important role in the DRX process. In contrast, no stress peak is observed in the flow curves at high strain rates, and the average grain size no longer decreases with the strain rate increase at the same temperature. The DRX mechanism in this case is a continuous DRX. The demarcated strain rate is calculated based on the characteristics of the obtained flow curves and grain sizes. The recrystallization volume fraction model and prediction grain size model at high strain rates are established. In combination with the existing DRX kinetics models at low strain rates, the processing parameters can be optimized to produce components with excellent mechanical properties.

Establishment of a novel constitutive model considering dynamic recrystallization behavior of Ti-22Al-25Nb alloy during hot deformation

Abstract The hot deformation behavior of Ti-22Al-25Nb alloy fabricated by hot compressed sintering was investigated under various conditions of compression tests in the deformation temperature range of 975-1075 °C with 20 °C intervals and the strain rate range of 0.001-1.0 s−1. Based on the experimental data, a novel constitutive relation combining a series of models was developed, including Zener-Hollomon parameter (Z), DRX critical model and kinetics model. The results show that the hot-deformed activation energy Q is calculated to be 410.172 kJ/mol, the ratio of critical strain (ec) to peak strain (ep) is a constant value of about 0.67. The predicted stress obtained by the established constitutive equations matches well with the true stress from experimental data. Despite large errors occur at the stage where strain rate is 0.1 s−1 and the values of true strain are less than 0.1, the stage of large strain should be more concerned during plastic forming. Furthermore, the predicting accuracy with the DRX kinetics model was testified by an electron back-scattered diffraction (EBSD) technique.

Evaluation of Hot Deformation and Dynamic Recrystallization Behaviors of Advanced Reduced-Activated Alloy (ARAA)

The hot deformation behavior of advanced reduced-activation alloy (ARAA) was investigated using hot torsion tests. The flow stress decreased as deformation temperature increased and as strain rate decreased. The flow behavior demonstrated the typical dynamic recrystallization (DRX). Based on the constitutive analysis of peak stress, the activation energy for hot deformation was found to be 330.3 kJ mol−1. Peak stress was analyzed as a function of the Zener–Hollomon parameter, and calculated and experimental values were in good agreement. A DRX kinetic model for ARAA was derived with deformation conditions based on the Avrami-type model. It was confirmed that the volume fraction of dynamically recrystallized grains increased as deformation temperature increased and as strain rate decreased. The necklace structure and grain boundary bulging were observed in the deformed microstructure of ARAA. The suggested DRX mechanism for ARAA during hot working is discontinuous DRX.

Dynamic recrystallization behavior of upward continuous casting Cu-0.19Cr-0.1Ag alloy

The flow and dynamic recrystallization (DRX) behaviour of the Cu-0.19Cr-0.1Ag alloy was systematically investigated by hot compression tests using a thermal simulation testing machine. The results showed that dynamic recovery and partial dynamic recrystallization occured at the strain rate of 10 s−1 in the entire temperature range tested, and at strain rates varying between 0.01 s−1 and 10 s−1 below 850 °C. Complete dynamic recrystallization occured when the deformation temperature was higher than 900 °C. The maximum softening rate strain (ε*) and the variable Z were introduced in the DRX kinetic model developed for the Cu-0.19Cr-0.1Ag alloy, obtaining an Avrami constant of 1.88.

Study of dynamic recrystallization behavior of T2 copper in hot working conditions by experiments and cellular automaton method

The dynamic recrystallization (DRX) behavior of T2 copper was studied by experiments and cellular automaton (CA) simulation during hot compression. The hot compression deformation of T2 copper was performed by isothermal hot compression tests over a wide range of temperatures (400–900 °C) and strain rates (0.001–10 s−1). The experimental results show that the deformation temperatures and strain rates have a profound influence on the DRX behavior. The characteristic parameters for the DRX behavior of T2 copper were obtained and a DRX kinetics model based on the modified Avrami equation was proposed to describe the DRX behavior of T2 copper. The average DRX grain size of the copper was estimated on the basis of metallography observation, and a power law function of Zener-Hollomon parameter was established to predict the grain size under different deformation conditions. A mesoscopic cellular automaton model was established to simulate the DRX behavior of T2 copper. The comparison between experimental and simulation results indicates that the recrystallization fraction and the average DRX grain size can be accurately predicted by the present CA model. It suggests that the developed CA model can be used to take control of the DRX process for the copper during hot working.

Modeling of the Dynamic Recrystallization Kinetics of a Continuous Casting Slab Under Heavy Reduction

Heavy reduction (HR) is used to implement a large reduction amount to improve the internal quality and refine the microstructure of continuous casting billets with large section sizes. In this paper, microstructural evolution and dynamic recrystallization (DRX) kinetic models for continuous casting slabs under HR were investigated for an experimental temperature range from [1173 K to 1573 K (900 °C) to (1300 °C)] and strain rates of 0.001 to 0.1 s−1. Based on the experimental data, various DRX kinetics models for a continuous casting slab as functions of the strain rate, strain, initial austenite grain size, and temperature were established to predict DRX-induced softening behaviors. A comparison of the new modified model, with Laasraoui and Jonas’s model, the modified Yoda’s model, and Liu’s model, revealed that the new modified model is the most suitable model for a continuous casting slab under HR. Based on this research, constitutive models with the characteristics of DRX and dynamic recovery (DRV) were established to predict the flow stress curve with the parameters of the strain rate ( $$ \dot{\varepsilon } $$ ), deformation temperature (T), and the initial austenite grain size (d0). Moreover, the microstructural evolution of a tested slab after hot compression tests was investigated by optical microscopy and a DRX grain size model under different deformation conditions was established.

New insights on the relationship between flow stress softening and dynamic recrystallization behavior of magnesium alloy AZ31B

The dynamic recrystallization (DRX) behavior of magnesium alloy AZ31B with large initial grain size was investigated. Two methods were applied to establish the DRX kinetics model. One is based on the values of DRX volume fraction evaluated by true stress-strain curves (Model 1). The other is based on the values of DRX volume fraction evaluated using optical micrographs (Model 2). It is found that the predicted DRX volume fraction by Model 1 is significantly larger than that by Model 2. It indicates that the value of DRX volume fraction (Xdrx) cannot be calculated by the true stress-strain curves for the magnesium alloy AZ31B with large initial grain size. To understand the phenomenon, the reason was analyzed and discussed. We found that the main reason can be attributed to the strong fine-grain strengthening (FGS) effect of magnesium alloy AZ31B. For the studied material, the flow behavior will be mainly affected by two factors during DRX: 1) the decrease of average dislocation density which gives rise to the decrease of flow stress; 2) the decrease of average grain size which results in the increase of flow stress. The latter causes that the DRX volume fraction evaluated by the true stress-strain curves is obviously larger than the real one. The research results will be good references for the evaluation of DRX volume fraction of other FGS materials with large initial grain sizes.

Investigation of dynamic recrystallization and modeling of microstructure evolution of an Al-Mg-Si aluminum alloy during high-temperature deformation

The dynamic recrystallization (DRX) behavior and microstructure evolution of an Al-Mg-Si aluminum alloy (AA6N01) during hot deformation are investigated by experiments and mathematical modeling. Based on hot compression tests under different strain rates and temperatures, the type of dynamic recrystallization are firstly investigated by EBSD analysis. It is observed that DRX occurs under all examined conditions, however, the type of DRX is associated with the deformation temperature at the strain level of about 1.5. Then considering the deformed and recrystallized behaviors, a grain size evolution model is established to predict the microstructure evolution during hot deformation. (1) According to the dislocation work hardening theory, the DRX kinetic model is built to predict the distribution of DRX. (2) Taking the effects of deformation temperature and strain rate into account, the DRX grain size model is built to predict the equiaxed recrystallized grain size. (3) By combining the experimental observations with numerical simulation, the deformed grain size model is established to predict the elongated grain size evolution. Finally, by integrating above three models, the grain size evolution model is established to predict the microstructure evolution of AA6N01 during high-temperature deformation and is validated by comparing the predicted grain size with experimental observations during hot compression and hot extrusion, respectively.

Dynamic recrystallization kinetics and microstructure evolution of an AZ91D magnesium alloy during hot compression

The flow behavior of as-cast AZ91D magnesium alloy was evaluated by isothermal compression tests within the temperatures of 220 °C, 260 °C, 300 °C, 340 °C, and 380 °C, and the strain rates of 0.001, 0.01, 0.1, 1 and 10s−1. Based on the stress-strain curve and hyperbolic sine function, the thermal activation energy and the strain rate sensitivity of the material were determined to be 142.2726 kJ·mol−1 and 0.142, respectively. The S type evolution of the dynamic recrystallization with the increasing strain that dynamic recrystallization (DRX) model obtained from stress and strain data. There was a good consistency between the proposed DRX kinetics model and microstructure observation results. Combining isothermal compression specimens with finite element and scanning electron microscopy (SEM) analysis indicated that the sample can be divided into rarely recrystallized region, partially recrystallized region and completely recrystallized region, which falls within the dense deformation zone, free deformation zone and severe deformation zone, respectively. The different forms of the β-Mg17Al12 phase induced by compression tests were confirmed by SEM. Nucleation mechanisms of the DRX were discussed with reference to the transmission electron microscope (TEM) analysis results.

Hot deformation behavior and microstructural evolution of Mg–Zn–Ca–La alloys

Abstract

A New Method for Optimizing Hot Processing Parameters of Mg-6.0Zn-0.5Mn-0.5Er Alloy Based on Kinetic Model of Dynamic Recrystallization and Processing Map

Hot deformation behavior of the cast-homogenized Mg-6.0Zn-0.5Mn-0.5Er alloy was studied using dynamic recrystallization (DRX) kinetic model and processing map. The compressing tests were conducted in the temperature range of 250-450 °C and strain rates of 0.001-1 s−1. According to the evolution of microstructures, under lower strain rates, the main DRX mechanism of Mg-6.0Zn-0.5Mn-0.5Er alloy is continuous DRX (CDRX); twinning induced DRX (TDRX) and CDRX both become the main DRX mechanism under higher strain rates. The DRX kinetics model of Mg-6.0Zn-0.5Mn-0.5Er alloy is calculated as $$X_{\text{DRX}} = 1 - \exp \left[ { - 1.9463\left( {\frac{{\varepsilon - \varepsilon_{\text{c}} }}{{\varepsilon^{*} }}} \right)^{1.4608} } \right]$$ , which is corresponding to the microstructure evolutions of DRX under different deformation conditions. The contour map of DRX was proposed based on the calculation results of DRX kinetics model. The processing maps are constructed to predict processing parameters of the alloy, and the predictability was evaluated combining with the contour map of DRX and dynamic materials model (DMM) processing map. It is deduced from the microstructures evolution and processing map that the optimum processing domain is mainly at 380-450 °C and 0.01-0.001 s−1, and 410-420 °C and 0.01-1 s−1.

Optimum parameters and kinetic analysis for hot working of a solution-treated Mg-Zn-Y-Mn magnesium alloy

The flow behavior, dynamic recrystallization (DRX) evolution and hot workability of the solution-treated Mg94Zn2.5Y2.5Mn1 (at%) alloy were investigated by hot compression tests. Compression tests were performed in the temperature range of 350–500 °C and the strain rate range of 0.001–1 s−1 on a Gleeble-1500D thermo-mechanical simulator. Using regression analysis for the constitutive equation of the flow behavior, the average activation energy of deformation and the stress exponent were determined to be 302.22 kJ/mol and 8.60452, respectively. The flow stress of the Mg94Zn2.5Y2.5Mn1 alloy predicted by the proposed models well agrees with experimental results. The kinetic model of DRX was proposed based on the analysis of true stress-strain data, which can be described as XDRX=1−exp[−2.15((ε−εc)/ε∗)1.51]. The DRX kinetic model was validated by means of microstructure observation. Furthermore, processing maps were developed and analyzed based on the dynamic material model (DMM). The flow instability regions and stability regions were identified based on the processing maps; the optimum domain for hot working of the experimental alloy are temperatures ranging from 400 °C to 450 °C and strain rates ranging from 0.001 s−1 to 0.01 s−1. Finally, a hot extrusion test was performed according to the optimum deformation parameters. The deformed sample exhibited a good surface quality and excellent mechanical properties, which verified the reasonability of the optimal deformation parameters.

Analysis of dynamic recrystallization behaviors in resistance heating compressions of heat-resistant alloy by multi-field and multi-scale coupling method

The deep understanding of the dynamic recrystallization (DRX) behaviors by grain morphology analysis in an electrical–thermal–mechanical coupling process for a heat-resistant alloy involves a multi-field and multi-scale dynamic coupling issue. As for SNCrW austenitic heat-resistant alloy, based on the true stress–strain data the DRX volume fraction evolution kinetics including a modified Avrami type equation, and a modified version of meso-scale cellular automaton (CA) method with Laasraoui-Jonas hardening and recovery models were solved. The multi-field and multi-scale coupling finite element (FE) model was developed by implanting the solved DRX kinetics model and CA model into the electrical–thermal–mechanical multi-field coupling method. Following which, a series of simulations corresponding to different strain rates and temperatures were implemented. The simulated results show that the mean grain size and DRX volume fraction increase with the increase of temperature, and decrease with the increase of strain rate. The microstructural evolution during the whole forming process were illustrated and described numerically. Finally, the simulated grain morphology was validated by metallography observations. The average relative deviation of grain size between experiment and simulation results is limited in 7.47%.

A two-stage constitutive model of X12CrMoWVNbN10-1-1 steel during elevated temperature

In order to clarify the competition between work hardening (WH) caused by dislocation movements and the dynamic softening result from dynamic recovery (DRV) and dynamic recrystallization (DRX), a new two-stage flow stress model of X12CrMoWVNbN10-1-1 (X12) ferrite heat-resistant steel was established to describe the whole hot deformation behavior. And the parameters were determined by the experimental data operated on a Gleeble-3800 thermo- mechanical simulation. In this constitutive model, a single internal variable dislocation density evolution model is used to describe the influence of WH and DRV to flow stress. The DRX kinetic dynamic model can express accurately the contribution of DRX to the decline of flow stress, which was established on the Avrami equation. Furthermore, The established new model was compared with Fields-Bachofen (F-B) model and experimental data. The results indicate the new two-stage flow stress model can more accurately represent the hot deformation behavior of X12 ferrite heat-resistant steel, and the average error is only 0.0995.

Flow Behavior and Dynamic Recrystallization of BT25y Titanium Alloy During Hot Deformation

Abstract The high-temperature plastic deformation and dynamic recrystallization behavior of BT25y alloy were investigated within the deformation temperatures of 1,213–1,293 K and strain rates of 0.001–1.0 s–1 on a Gleeble-1500 thermo-mechanical simulator. Results showed that the dynamic recrystallization (DRX) mechanism played an important role in the hot deformation of BT25y alloy. Based on the regression analysis of the true stress–strain data, the stress exponent and deformation activation energy of BT25y alloy were calculated to be 3.4912 and 288.0435 kJ/mol, respectively. The θ-σ and dθ/dσ–σ curves were plotted to further obtain the critical stress and critical strain for the occurrence of DRX. Based on the analysis results, the DRX kinetic model was established. The model was validated by the comparison between predicted and experimental volume fraction of DRX. As the DRX evolution was sensitive to deformation temperature and strain rate, quantities of dynamically recrystallized grains appeared at higher temperatures and lower strain rates.

Analytical Descriptions of Dynamic Softening Mechanisms for Ti-13Nb-13Zr Biomedical Alloy in Single Phase and Two Phase Regions

AbstractDynamic softening behaviors of a promising biomedical Ti-13Nb-13Zr alloy under hot deformation conditions across dual phaseα+βand single phaseβregions were quantitatively characterized by establishing corresponding dynamic recovery (DRV) and dynamic recrystallization (DRX) kinetic models. A series of wide range hot compression tests on a Gleeble-3500 thermo-mechanical physical simulator were implemented under the strain rate range of 0.01-10 s−1and the temperature range of 923-1173 K. The apparent differences of flow stress curves obtained in dual phaseα+βand single phaseβregions were analyzed in term of different dependence of flow stress to temperature and strain rate and different microstructural evolutions. Two typical softening mechanisms about DRV and DRX were identified through the variations of a series of stress-strain curves acquired from these compression tests. DRX is the dominant softening mechanism in dual phaseα+βrange, while DRV is the main softening mechanism in single phaseβrange. The DRV kinetic model for single phaseβregion and the DRX kinetic model for dual phaseα+βregion were established respectively. In addition, the microstructures of the compressed specimens were observed validating the softening mechanisms accordingly.

Dynamic Recrystallization Behavior of Vanadium Microalloyed Cryogenic Fine Grain Structural Steel Pipe at High Strain Rate

AbstractDynamic recrystallization (DRX) behavior of a vanadium microalloyed steel pipe was systematically investigated at temperatures range of 850–1,200 °C and a strain rate of 5 s−1 on a Gleeble-3800 thermo-simulation machine. Constitutive equation was obtained by characteristic points of DRX which derived from the strain hardening rate and stress curves. DRX kinetics model was established for determining the recrystallization volume fraction (X). Effect of dynamic precipitation of V(C, N) imposed on DRX at temperatures from 850–1,000 °C was analyzed. Results show that true stress-strain curves exhibited no clearly defined stress peaks with typical dynamic recovery behavior. X increased from 43.9 % to 100 % with increasing deformation temperature, which was in reasonable agreement with the observation of microstructure. Moreover, the calculation pinning force of V(C, N) precipitates was weaker than the recrystallization driving force, revealing that V(C, N) precipitates could effectively retard rather than prevent the progress of DRX.