Dynamic Recrystallization Model Research Articles

Subsurface microstructural dynamic recrystallization in multiscale abrasive wear

This paper evaluates various subsurface microstructures of Hadfield steel worn in different abrasion systems. The abrasion systems are defined according to their abrasion conditions related with the following scales: macro (cone crusher); meso (jaw crusher test) and micro (scratch test) in order to relate the industrial and laboratory conditions. The subsurface microstructures were evaluated by Scanning Electron Microscope, Electron Backscatter Diffraction, X-Ray Diffraction, Focused Ion Beam and Transmission Electron Microscope. The observed wear effects to the surface of the cone crusher mantle are characterized by indentations, grooves, intergranular cracks and grain detachment. The subsurface microstructure of the multiscale abrasive wear conditions was composed of a topmost layer with ultrafine grains, a layer with deformation twins and slip bands. In the cone crusher and the jaw crusher, changes in the shape of the subsurface deformed grains after plastic strain were not observed, leaving deformation twinning as the primary strain mechanism. The cone crusher subsurface microstructure showed dynamic recrystallization characterized by ultrafine-grains, small grains with continuous network carbides in the grain boundary, acicular carbides and annealed twin. The analysis of the ultrafine grains formation considers the energy release at the abrasive/material interface and in the subsurface by deformation as responsible for nucleation and growth of ultrafine grains. The scratch test in {111}//ND grain has the subsurface with ultrafine-grains and deformation twins. The nano-hardness results show that the regions with ultrafine-grains have a higher hardness than the regions with deformed grains, where the plasticity was restored and the hardness of the subsuperficial layer had improved. The models of dynamic recrystallization induced by severe plastic deformation are discussed and correlated to the ultrafine-grains formation.

Microstructure modeling of a sintered Al–4Si–0.6Mg alloy extruded at semi-solid temperature ranges

The microstructure evolution of sintered and extruded samples of Al–4Si–0.6Mg powder alloys at various semi-solid temperature ranges of 560 °C, 580 °C, and 600 °C, holding times of 600, 1200, and 1800 s, and strain rates of 0.1, 0.2, and 0.3 s−1 was studied. From the stress–strain curves and metallographic studies, Arrhenius grain growth model and Avrami dynamic recrystallization model have been formulated by means of linear regression. Parameters such as peak strain, critical strain, recrystallization fraction, and material constants have been found using the above equations. The experimental and calculated values of various material parameters agree with each other, indicating the accuracy of the developed model. Finite element method-based simulations were performed using DEFORM 2D software, and the average grain size obtained from experiments and simulations was validated by means of average grain size. The relative density of the compacted specimens as well as the extruded specimens was also simulated. The simulation results showed that large grains appeared at high temperatures and at the bottom of the specimen.

Hot deformation behavior and workfability of the homogenized Mg-5.8Zn-1.2Y–1Mn alloy containing I and W phases

In the present study, a thermo-mechanical simulator (Gleeble-1500D) is applied to conduct compression tests on homogenized Mg–6Zn-1.2Y–1Mn (wt.%) alloy and investigate features of this alloy in terms of flow behavior, dynamic recrystallization (DRX) evolution and hot workability. Different strain rates varying from 0.005 to 5 s−1 and different temperatures within the range of 200–400 °C are used in the experiments. An apparent mean deformation activation energy of 216.027 kJ/mol with a stress exponent of 10.88964 are achieved by regression analysis of Arrhenius type flow behavior equation. Using true stress-true strain data analysis, a kinetic model of dynamic recrystallization is presented as: XDRX=1−exp[−1.41((ε−εc)/ε∗)1.51]. Furthermore, the processing maps are developed and analyzed according to the dynamic material model (DMM). Based on the processing maps, the flow stability and instability domains are determined. It is found that the optimal hot working region of the alloy is temperature of 325–400 °C and strain rate of 0.005–0.05 s−1. Finally, a finite element analysis is carried out, and the reasonability of the optimal deformation parameters are verified.

Dynamic recrystallization behavior and microstructure evolution of low-density high-strength Fe–Mn–Al–C steel

The hot deformation behavior of low-density high-strength Fe–Mn–Al–C steel at T = 900–1150 °C and ε˙ = 0.01–10 s−1 is studied using the Gleeble-3500 thermo-mechanical simulator. The rheological stress curve characteristics of the steel are analyzed through experimental data and the dynamic recrystallization activation energy is calculated. The critical strain/stress, peak strain/stress and steady-state strain/stress models of dynamic recrystallization are characterized by introducing the dimensionless parameter Zener-Hollomon. The microstructure evolution is analyzed and the dynamic recrystallization state diagram of the steel is drawn. The results indicated that the steel is a negative temperature-sensitive and a positive strain rate-sensitive material. The dynamic recrystallization activation energy is 669.844 kJ mol−1. With the decrease of ε˙ or the increase of T, the Z parameter decreases gradually and the dynamic recrystallization behavior is more likely to occur; however, its grain size increases accordingly. The fine and uniform grain structure can be obtained by hot working in the range of 950–1000 °C/0.01–0.1 s−1 and 1050–1100 °C/1–10 s−1. Finally, the prediction model for the dynamic recrystallization average grain size is established, and the correlation coefficient (R) of the prediction model is 0.996; therefore, the model has a high prediction accuracy.

Multiscale modeling of discontinuous dynamic recrystallization during hot working by coupling multilevel cellular automaton and finite element method

Discontinuous dynamic recrystallization (dDRX) is considered an effective way to obtain fine grain microstructures during hot working of materials with low-to-medium stacking fault energy (SFE). However, to date, investigation and modeling of dDRX in complex hot working processes are not appropriately performed, which hinders further control of the microstructure and forming quality of products during hot working. In this study, a multiscale modeling framework, namely the MCAFE-dDRX model, was constructed by coupling the multilevel cellular automaton (MCA) and finite element (FE) method. The data acquired via the FE method was used as an input for MCA simulation by discretizing the increment in FE time to consider the deformation history of materials. Compared to previous studies where only the effects of constant strain rate and temperature on the deformation of materials are analysed, the MCAFE-dDRX model can evaluate the dDRX microstructure evolution at different Zener-Hollomon levels, which has been validated by hot extrusion in this study. The developed simulation framework facilitates the prediction of microstructure evolution during heterogeneous and non-isothermal deformation of materials.

Modeling and simulation of dynamic recrystallization in super austenitic stainless steel employing combined cellular automaton, artificial neural network and finite element method

A cellular automaton (CA) model for dynamic recrystallization (DRX) is established by employing Moore’s neighboring rule to predict flow stress, DRX grain size (DDRX) and DRX fraction (XDRX). The CA model has been optimized for super austenitic stainless steel at different strain rates (0.001–10 s−1) and temperatures (1173–1423 K) under isothermal deformation conditions. The output of the CA simulation has been used for establishing ANN-based constitutive models. The trained ANN-based constitutive models have been further implemented in FEM software (ABAQUS 6.14) to evaluate flow behavior and microstructure response of the alloy under various non-isothermal deformation conditions. The conventional CA (CAC) model has failed to provide a good depiction of the microstructure evolution, as it revealed a very low correlation coefficient (R) for XDRX (R ~ 0.75) and DDRX (R ~ 0.8). This inaccuracy of the model could be related to its inherent inability to consider the effect of solute drag on grain growth and DRX kinetics. Therefore, a modified cellular automata (CAM) model has been developed by introducing a new temperature-strain rate-dependent mobility parameter for numerically considering the solute drag effect. Employing non-isothermal simulations, the CAM model has revealed a higher correlation coefficient than the CAC model for predicting XDRX (R ~ 0.95) and DDRX (R ~ 0.98). Moreover, the developed CAM model has also predicted the flow behavior of the alloy in the entire domain investigated, revealing a higher correlation coefficient (R ~ 0.987) and a low average absolute relative error (8.6%).

Kinetic model of dynamic recrystallization of DP1000 steel for auto body structures

Hot compression tests were performed in DP1000 steel under a temperature range of 950 ∼ 1150 °C with corresponding strain rate of 0.05 ∼ 10 s−1 to investigate the kinetic model of dynamic recrystallization (DRX) on a Gleeble 3800 thermal simulation test machine. The characteristic parameters such as critical stress/strain (σ c/ε c), peak stress/strain (σ p/ε p), maximum softening stress/strain (σ m/ε m) and steady-state stress/strain (σ ss/ε ss) were acquired according to the stress-strain data. The beginning of DRX was found from the inflection point of the cubic spline θ-σ curve. The Zahiri model was used to calculate the DRX percentage. The revised MZ DRX model based on multiple characteristic parameters was developed, and the prediction value had good agreement with the experimental results.

A new front-tracking Lagrangian model for the modeling of dynamic and post-dynamic recrystallization

A new method for the simulation of evolving multi-domains problems has been introduced in previous works and further developed in parallel in the context of isotropic grain growth (GG) with no consideration for the effects of the stored energy (SE) due to dislocations. The methodology consists in a new front-tracking approach where one of the originality is that not only interfaces between grains are discretized but their bulks are also meshed and topological changes of the domains are driven by selective local remeshing operations performed on the finite element (FE) mesh. In this article, further developments and studies of the model will be presented, mainly on the development of a model taking into account grain boundary migration (GBM) by SE. Further developments for the nucleation of new grains will be presented, allowing to model dynamic recrystallization (DRX) and post-dynamic recrystallization (PDRX) phenomena. The accuracy and the performance of the numerical algorithms have been proven to be very promising in Florez et al (2020). Here the results for multiple test cases will be given in order to validate the accuracy of the model taking into account GG and SE. The computational performance will be evaluated for the DRX and PDRX mechanisms and compared to a classical FE framework using a level-set formulation.

Constitutive modeling of dynamic recrystallization coupled to viscoplasticity

AbstractDuring thermomechanical processing the microstructure is subject to drastic changes. These changes relate to various physical mechanisms such as recrystallization, recovery, grain growth and phase transitions, heavily affecting material properties in engineering components. This enables the targeted adjustment of microstructures and the gradation of macroscopic mechanical properties. During thermomechanical processing the modeling of dynamic recrystallization is of major importance. Thus, we present a thermodynamically consistent framework based on an existing continuum mechanical model. Major improvements, including derived recrystallization volume fractions and clean distinction of true microstresses and nominal microstresses, have been made in comparison to the original model.

Cellular automaton modeling of dynamic recrystallization in Al-Mg alloy coating fabricated using the friction surfacing process

In this study, the dynamic recrystallized microstructure of the friction-surfaced Al-Mg alloy coating was predicted using a cellular automaton model. To realize this objective, using the temperature and strain rate results obtained from a 3D thermo-mechanical finite element model combined with a cellular automaton model, the microstructure of the coating was predicted by taking into account the effects of the secondary phase particles during the coating process. Based on the results, it was observed that the percentage of error in estimating the grain size when considering the effects of secondary phase particles was much lower than the case where the effects of secondary phase particles were not considered. In addition, by considering a rotational speed in the range of 600–3000 rpm, a traverse speed in the range of 50–750 mm/min, and an axial feeding rate in the range of 100–820 mm/min, it is observed that with a simultaneous increase in the rotational and traverse speeds as well as a simultaneous increase in the axial feeding rate and the traverse speed, the grain size of the coating decreases; however, it bounces back up after reaching the minimum value. Based on the results predicted by the microstructural model, the minimum grain size of the coating (1.8 μm) was obtained at the rotational speed of 1400 rpm, the axial feed rate of 400 mm/min, and the traverse speed of 400 mm/min.

Constitutive Model and Microstructure Evolution Finite Element Simulation of Multidirectional Forging for GH4169 Superalloy

This study investigates three processes of multidirectional forging (MDF), namely, closed MDF (CMDF), single-open MDF, and double-open MDF, by using a constitutive equation and a dynamic recrystallization model of hot deformation of the GH4169 superalloy. The microstructure evolution of the three processes is simulated and compared. Among the three processes, the double-open MDF obtains the highest recrystallization degree, followed by the CMDF and the single-open MDF under the same reduction. The recrystallization degree of CMDF reaches 99.5% at 1000 °C and 9 passes, and the average recrystallized grain size is small, which is approximately 8.1 μm. The double-open MDF can obtain a fine grain size of forgings at 9 passes and 1000 °C, and it is easy to obtain forgings with the single-open MDF with uniform performance. The temperature is 850 °C–1000 °C, the compression rate is 0.15–0.2, and the pass is 5–9, which are the suitable parameter selection ranges for the CMDF. The temperature is 950 °C–1000 °C, the compression rate is 0.1–0.2, and the pass is 7–9, which are the suitable parameter selection ranges for single-open MDF. The temperature is 850 °C–1000 °C, the compression rate is 0.1–0.2, and the pass is 6–9, which are the suitable parameter selection ranges for the double-open MDF.

A continuous dynamic recrystallization constitutive model combined with grain fragmentation and subgrain rotation for aluminum alloy 2219 under hot deformation

The large temperature gradient resulted from rapid heat dissipation and a long process period in the hot deformation of aluminum alloy causes complex microstructure evolutions. Accurate constitutive models describing the evolution of the microstructures over a wide temperature range are acquired. Thus, a physically-based continuous dynamic recrystallization constitutive model combined with grain fragmentation and subgrain rotation was established in this investigation. Uniaxial hot compression tests for aluminum alloy 2219 were conducted at temperatures of 250 °C–450 °C and the evolution of microstructures were analyzed via metallographic technique. Then internal state variables were proposed to describe the migration of grain boundary, dislocation density, average grain boundary misorientation, and subgrain/grain size. The net torque on the grain is introduced to precisely describe the progressive subgrain rotation mechanism. Moreover, geometrically necessary dislocations are considered to reasonably simulate the rise in flow stress associated with grain fragmentation. The results show that continuous dynamic recrystallization (CDRX) and dynamic recovery are the main softening mechanisms. The CDRX mechanism is gradually changed from grain fragmentation to subgrain rotation due to the increase in temperature. The new constitutive model may precisely predict the flow stresses, subgrain/grain size, and average misorientation in the wide temperature range. Comparing with the existing continuous dynamic recrystallization model which only considers subgrain rotation, the overestimate of the grain size in the low-temperature range is avoided in the new constitutive model. Furthermore, the contributions of the grain fragmentation to the increase in strain hardening can reasonably be covered.

Hot deformation characteristics and kinetics analysis for Ni‐based corrosion resistant alloy

AbstractThe hot deformation characteristics of Nickel‐based corrosion resistant alloy was studied in the temperature range of 1050°C to 1200°C and the strain rate range of 0.001 to 0.1 second−1 by employing hot compression tests. The results show that the peak stress increases with decreasing temperature and increasing strain rate, and the apparent activation energy is about 409 kJ/mol. Based on the Avrami equation through using the critical strain (εc) and the strain for 50% DRX (ε0.5), a kinetic model for dynamic recrystallization (DRX) was established, where the model parameters could be obtained using the modified Zener‐Hollomon parameter (Z*). Applying the model, the predicted value of the steady‐state strain (εss) and the strain for maximum softening rate (εm) agree well with the experimental results. Accordingly, the relationship between εm and ε0.5 is established, which is mainly dependent on the Avrami exponent (n). When n < 3.25, εm becomes less than ε0.5 and the difference in between decreases with increasing the strain rate or decreasing the deformation temperature. Finally, through observing DRX microstructure under different deformation conditions, a power law relation between DRX grain size (Ddrx) and Z*, with an exponent of −0.36, was found.

Dynamic Recrystallization Modeling and Mechanisms in Inconel 690 Alloy during Hot Compressive Deformation

The dynamic recrystallization (DRX) behavior of INCONEL 690 (IN690) alloy was studied using electron backscatter diffraction (EBSD) and transmission electron microscopy. Isothermal compression tests were performed on a Gleeble-3500 simulator under temperatures 950-1100 °C, strain rates 0.01-1 s−1, and the maximum true strain 0.8. An Avrami-type model was developed to investigate the DRX behavior of IN690; it was found to be extremely sensitive to the processing parameters of temperature, strain rate, and true strain. As temperature increased and strain rate decreased, the activation energy increased, thus accelerating movement of dislocation and migration of grain boundaries, causing DRX behavior acceleration. The DRX behavior is accompanied by dislocation rearrangement and annihilation. The DRX mechanism of IN690 is dominated by discontinuous dynamic recrystallization (DDRX) and supplemented by continuous dynamic recrystallization (CDRX). A key characteristic of DDRX is grain-boundary bulges, while CDRX features progressive sub-grain rotation, leading to migration of low-angle grain boundaries to high-angle grain boundaries. A series of constitutive models were embedded into finite-element method software to study the DRX behavior of IN690. The results show that the microstructure evolution regularity obtained by the simulation method is consistent with the experimental values, which provides a basis for computer simulations of the hot machining process.

Critical Dynamic Recrystallization Model and Nucleation Mechanisms of an Alumina-Forming Austenitic Stainless Steel during Hot Deformation

The hot deformation behavior of an alumina-forming austenitic (AFA) stainless steel was investigated on a Gleeble-3500 simulator. Moreover, the critical dynamic recrystallization model was established, and the critical stress was determined. Microstructural characterization was analyzed using electron backscattered diffraction (EBSD) and transmission electron microscope (TEM). The microstructure evolution showed that the degree of dynamic recrystallization (DRX) and the content of high-angle grain boundaries increased significantly with the increasing temperature and the decreasing strain rate. For recrystallization mechanisms, the bulging mechanism was found dominating, while the sub-grain rotation mechanism played an assisting role. Furthermore, discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) coexisted during the hot deformation.

Dynamic recrystallization analysis of reduction pretreatment process by multi-phase field method

The reduction pretreatment (RP) process is an effective method to improve billet quality, and the deformation recrystallization plays an important role in the process. Exploring the RP process parameters, a dynamic recrystallization model of GCr15 steel was established by the phase-field method and physical simulation. The recrystallization kinetics and flow stress curves during hot compression were simulated by using this mode. The effects of deformation parameters and initial grain size on the dynamic recrystallization were investigated. Moreover, by using the results obtained by Finite element method (FEM), dynamic recrystallization during the RP process was investigated though this model. It was found that increasing the deformation temperature, deformation rate and decreasing the initial grain size can promote the dynamic recrystallization kinetics. Large Zener-Hollomon parameters can enhance recrystallized grain refinement, while the recrystallized grain size was not affected by the initial grain size. During the RP process, when the reduction is insufficient (10%), partial recrystallization occurs in the billet. With the increase of reduction from 10% to 16%, the area of complete recrystallization increases gradually. When the reduction is the same, the recrystallization in the billet center increases with the decrease of casting speed. When the reduction is 10%, partial recrystallization occurs in the billet center at a casting speed of 0.7 m min−1, and fully recrystallization occurs in the billet center with a casting speed of 0.5 m min−1. Thus, when the reduction is difficult to increase further, the recrystallization in the billet center can be improved by decreasing the casting speed.

Flow Stress of Duplex Stainless Steel by Inverse Analysis with Dynamic Recovery and Recrystallization Model

Flow Stress of Duplex Stainless Steel by Inverse Analysis with Dynamic Recovery and Recrystallization Model

Study on Dynamic Recrystallization Models of 21-4N Heat Resistant Steel

Study on Dynamic Recrystallization Models of 21-4N Heat Resistant Steel

Hot Deformation Behavior of V–Ti Microalloy Steels

Hot deformation behavior of V–Ti microalloyed steel is carried out using Gleeble1500. The results show that the flow stress curve is mainly characterized by work hardening and high‐temperature deformation softening mechanisms. Herein, the combination of strain hardening rate–stress curve and stress–strain–temperature dynamic recrystallization 3D model can be used to determine the temperature and strain corresponding to the beginning and end of dynamic recrystallization. The recrystallization activation energy and hot deformation constitutive equation are calculated by austenite recrystallization kinetic regression. Comparing three constitutive equation models with different fitting accuracies, the hyperbolic sine equation with fitting accuracy of 0.99178 is obtained, and the thermal deformation activation energy is determined to be 286.897 kJ mol−1. It is close to the self‐diffusion activation energy of austenite 281 kJ mol−1, so the rate control mechanism under this deformation condition is the dislocation climbing of diffusion control. The combination of the 3D model of dynamic recrystallization and the constitutive equation can not only obtain the flow stress curve under a certain deformation condition, but also obtain the structure evolution information. The mutual verification of the two makes it possible to study the hot deformation behavior under different deformation conditions more comprehensively.

Modeling and simulation of dynamic recrystallization behavior for Q890 steel plate based on plane strain compression tests

AbstractIn view that the traditional dynamic recrystallization (DRX) model cannot effectively predict the DRX process in the hot deformation process of sheet metal, DRX behavior modeling and simulation of q890 steel plate based on the plane strain compression test are designed. The plane strain thermal simulation tests were performed at 1,223–1,373 K and the strain rates of 1–50−1 on Gleeble-3500 thermal–mechanical simulator. The flow stress curves were well smoothed. The stress–strain data were investigated for the analysis of the dynamic recrystallization in the process of thermal deformation. The activation energy of DRX was calculated as Q = 394.53 kJ/mol by the simulation data. The equation of peak strain was developed with the flow stress data by the Zener–Hollomon parameter. The DRX transformation fraction of Q890 steel was studied, and the DRX kinetics equation was developed by the Avrami equation. The experimental data are in good agreement with the calculated values, which proves the reliability of the DRX model and can be widely used in real life.