Dynamic Recrystallization Model Research Articles

Hot Deformation Behavior of Free-Al 2.43 wt.% Si Electrical Steel Strip Produced by Twin-Roll Strip Casting and Its Effect on Microstructure and Texture.

Twin-roll strip casting (TRSC) technology has unique advantages in the production of non-oriented electrical steel. However, the hot deformation behavior of high-grade electrical steel produced by TRSC has hardly been reported. This work systematically studied the hot deformation behavior of free-Al 2.43 wt.% Si electrical steel strip produced by twin-roll strip casting. During the simulated hot rolling test, deformation reduction was set as 30%, and the ranges of deformation temperature and strain rate were 750~950 °C and 0.01~5 s-1, respectively. The obtained true stress-strain curves show that the peak true stress decreased with an increase in the deformation temperature and with a decrease in the strain rate. Then, the effect of hot deformation parameters on microstructure and texture was analyzed using optical microstructure observation, X-ray diffraction, and electron backscattered diffraction examination. In addition, based on the obtained true stress-strain curves of the strip cast during hot deformation, the constitutive equation for the studied silicon steel strip was established, from which it can be found that the deformation activation energy of the studied steel strip is 83.367 kJ/mol. Finally, the kinetics model of dynamic recrystallization for predicting the recrystallization volume percent was established and was verified by a hot rolling experiment conducted on a rolling mill.

Determining the Hot Workability and Microstructural Evolution of an Fe-Cr-Mo-Mn Steel Using 3D Processing Maps.

The Laasraoui segmented and Arrhenius flow stress model, dynamic recrystallization (DRX) model, grain size prediction model, and hot processing map (HPM) of Fe-Cr-Mo-Mn steels were established through isothermal compression tests. The models and HPM were proven by experiment to be highly accurate. As the deformation temperature decreased or the strain rate increased, the flow stress increased and the grain size of the Fe-Cr-Mo-Mn steel decreased, while the volume fraction of DRX (Xdrx) decreased. The optimal range of the hot processing was determined to be 1050-1200 °C/0.369-1 s-1. Zigzag-like grain boundaries (GBs) and intergranular cracks were found in the unstable region, in which the disordered martensitic structure was observed. The orderly packet martensite was formed in the general processing region, and the mixed structure with incomplete DRX grains was composed of coarse and fine grains. The microstructure in the optimum processing region was composed of DRX grains and the multistage martensite. The validity of the Laasraoui segmented flow stress model, DRX model, grain size prediction model, and HPM was verified by upsetting tests.

A predictive mesoscale model for continuous dynamic recrystallization

Thermomechanical processing of titanium alloys often requires complex routes to achieve the desired final microstructure. Recent advances in modeling and simulation tools have facilitated the optimization of these processing routes. However, existing models often fail to accurately predict microstructural changes at large deformations. In this study, we refine the physical principles of an existing mean-field model and propose a calibration method that uses experimental results under isothermal conditions, accounting for the actual local deformation within the workpiece. This new approach improves the predictability of microstructural changes due to continuous dynamic recrystallization during torsion and compression experiments. Additionally, we integrate the model into the commercial FEM-based DEFORM™ 2D software to predict the local microstructure evolution within hot torsion specimens thermomechanically treated by resistive heating. Validation using non-isothermal deformation tests demonstrates that the model provides realistic simulations at high strain rates, where adiabatic heat modifies temperature, flow stress and microstructure. This study demonstrates the intrinsic correlation between microstructure, flow behavior, and workpiece geometry, considering the impact of deformation history in thermomechanical processes.

Effects of Y2O3 on the hot deformation behavior and microstructure evolution of Al2O3-cu/35Cr3TiB2 electrical contact composites

The Al2O3-Cu/35Cr3TiB2 and 0.5Y2O3/Al2O3-Cu/35Cr3TiB2 composites were prepared by a combination of fast hot compression sintering and internal oxidization. The effects of Y2O3 on the hot deformation behavior and microstructure evolution of the composites were investigated. According to the hot deformation data, the constitutive equations, hot processing maps, and critical dynamic recrystallization models were constructed for the two composites. The Y2O3 addition enhanced the flow stress, activation energy, and hot processing properties of the composites. This led to a reduction in the percentage of dynamic recrystallization structure from 25.3% to 19.4%, and decreased the amount of high-angle grain boundaries from 77.8% to 71.4%. Y2O3 was distributed at grain boundaries and phase interfaces, effectively impeding dislocation movement and grain boundary migration. Notably, the strain distribution within Y2O3 exhibited greater homogeneity compared to the Cu matrix. More twins and stacking faults were observed inside the 0.5Y2O3/Al2O3-Cu/35Cr3TiB2 composites, which synergistically strengthened the matrix.

Mesoscale modeling of continuous dynamic recrystallization in Ti-10V-2Fe-3Al alloy

Continuous dynamic recrystallization (CDRX) is the dominant restoration mechanism of near-β titanium alloys during hot deformation. But till now, there is seldom visual modeling of the process which limits its industrial application. Based on CDRX mechanisms characterized by low-angle grain boundaries (LAGBs) formed and partially transformed into high-angle grain boundaries (HAGBs), the present study established a cellular automata (CA) model to investigate the substructure evolution and mechanical response of Ti-10V-2Fe-3Al alloy. Besides, a new set of equations for subgrain rotation considering the effect of the α-phase was integrated into the CA model to improve its applicability in titanium alloy. The model was validated by experimental results and then applied to predict the substructure evolution during hot working. Simulation analysis revealed that, except for high strain rates and temperatures, a high fraction of α/β phase boundaries could also promote the development of CDRX. The proposed CA model provided an effective method for microstructure optimization in hot forging of the Ti-10V-2Fe-3Al alloy.

Improved dynamic recrystallization modeling in the high-speed machining of titanium alloy

Improved dynamic recrystallization modeling in the high-speed machining of titanium alloy

An improved cellular automaton model of dynamic recrystallization and the constitutive model coupled with dynamic recrystallization kinetics for microalloyed high strength steels

This study analyzed the deformation behavior of Nb–Ti microalloyed high strength steel at strain rates of 0.001–0.1 s−1 and deformation temperatures of 1050–1150 °C using hot compression tests. The deformation activation energy of 321.1 kJ/mol was calculated based on the stress-strain curve, and the characteristic points on the flow stress curve were extracted. In contrast, the relationship equation between the characteristic points and the Zener-Hollomon parameter was established. A modified dynamic recrystallization (DRX) kinetics model was proposed based on the stress-strain data, considering the strain rate and deformation temperature. A high-precision constitutive model was established based on the dislocation density evolution phenomenological model, which couples with the modified DRX kinetics model. Furthermore, an improved DRX cellular automaton (CA) model was constructed, which comprehensively took into account a series of processes such as dislocation density evolution, recrystallization nucleation, and grain growth. Notably, the model also embedded the pinning effect of second phase (SP) particles on the DRX process. The improved CA model can control the pinning force by adjusting the size and volume fraction of SP particles and can accurately predict the evolution characteristics of DRX and the average austenite grain size of Nb–Ti microalloyed high strength steels during thermal deformation. The development of an improved CA model can be extended to apply to the DRX evolution of other microalloyed steels, and the model provides a powerful tool and method for understanding the thermal deformation behavior and microstructural evolution of microalloyed steels.

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

Modeling CDRX and MDRX during hot forming of zircaloy-4

A recently developed full field level-set model of continuous dynamic recrystallization is applied to simulate zircaloy-4 recrystallization during hot compression and subsequent heat treatment. The influence of strain rate, final strain and initial microstructure is investigated, by experimental and simulation tools. The recrystallization heterogeneity is quantified. This enables to confirm that quenched microstructures display a higher extent of heterogeneity. The simulation results replicate satisfactorily experimental observations. The simulation framework is especially able to capture such recrystallization heterogeneity induced by a different initial microstructure. Finally, the role of intragranular dislocation density heterogeneities over the preferential growth of recrystallized grains is pointed out thanks to additional simulations with different numerical formulations.

Flow stress and dynamic recrystallization behavior and modeling of GH4738 superalloy during hot compression

GH4738 superalloy is a key material for gas turbine engines, yet its relatively poor thermoplasticity and narrow temperature range for hot working deteriorate grain structure uniformity and thereafter service performance. Employing hot compression experiments and finite element analysis (FEA), the present study examined the thermoplasticity of the GH4738 alloy and proposed a fast approach to establishing its dynamic recrystallization (DRX) model. The hot working conditions were considered in the 1000–1160 °C temperature range under strain rates of 2–26 s−1 up to a true compressive strain of 0.69. Friction- and temperature-corrected stress-strain curves were obtained, based on which the efficiency of power dissipation and constitutive equations were constructed. It reveals that DRX is the dominant softening mechanism in the GH4738 alloy, where the sensitivity of flow softening positively correlates with lower temperatures and higher strain rates. The appropriate hot working condition for the alloy is temperatures around 1040–1080 °C and a strain rate larger than 8 s−1. The final grain sizes (d) and fractions of DRX (Xdyn) were minimized using the stochastic gradient descent algorithm based on 120 sets of data within the framework of the Avrami equation. It is shown that the formulated model and its integration into the FEA not only yield satisfactory agreement with the experiment but effectively avoid the complexity involved in the traditional method. The study provides key inputs for predicting the flow behavior and grain structure of the GH4738 superalloy, which shall be critical for process development and optimization of industrial manufacturing processes.

A High-Temperature Strain-Compensated Arrhenius-Type Constitutive Model and an Improved Avrami-Type Dynamic Recrystallization Model of 40CrNiMo

A High-Temperature Strain-Compensated Arrhenius-Type Constitutive Model and an Improved Avrami-Type Dynamic Recrystallization Model of 40CrNiMo

Hot Deformation Behavior and Dynamic Recrystallization of a Medium Carbon Cr–Mo Steel for Class 16.8 Bolts

AbstractThis study investigates the hot workability of medium carbon Cr–Mo steels for manufacturing ultra-high strength bolts. The main purpose of this research is to establish a constitutive equation and a kinetic model of dynamic recrystallization of the material for industrial applications. Hot torsion tests were conducted at temperatures of 1173, 1273, and 1373 K and strain rates of 0.1, 0.5, 1.0, and 2.0/s. Strain rate sensitivities and work-hardening coefficients of the material were calculated at various strain rates and temperatures using the Fields–Backofen equation. Results indicated that the material’s strain rate sensitivities and work-hardening coefficients generally increased with temperature. Stress–strain curves showed a general variation depending on the strain rates and the deformation temperatures, with higher strain rates and lower temperatures resulting in increased flow stresses. However, peak stresses were not clearly observed due to the presence of Nb in the material. A constitutive equation for flow stresses was derived, with a thermal activation energy for deformation of 238.57 kJ/mol. Zener–Hollomon parameter was used to analyze the relationship between peak strains and critical strains, finding that the critical strains being about 0.17 times the peak strains. The volume fractions of dynamic recrystallization were estimated using an Avrami form of the kinetic equation, and the Avrami constants $$k$$ k and $$m$$ m were 0.84 and 6.89, respectively. The kinetic model of dynamic recrystallization that we developed can be applied to arbitrary deformation conditions, enabling the optimization of the hot rolling process for this material. Graphic Abstract

Physical metallurgy guided machine learning to predict hot deformation mechanism of stainless steel

This study proposes a novel approach to address the limitations of traditional experimental and mathematical statistical methods in predicting the deformation mechanism of materials. Specifically, a physical metallurgy-guided machine learning method is proposed to achieve fast and accurate prediction of the thermal deformation mechanisms of antibacterial stainless steels with varying Cu contents. First, the Arrhenius and the dynamic recrystallization model were developed utilizing experimental data for the preliminary prediction of the effect of Cu content on the thermal deformation behavior of antibacterial stainless steel. Then, the calculated intermediate parameters were incorporated into the original data set as additional input features to construct a physical metallurgy (PM) guided least squares support vector machine (LSSVM) prediction model, and the optimization of the prediction model is performed through utilization of a particle swarm optimization (PSO) algorithm. The results indicate that the addition of Cu content influences the rheological stress of antibacterial stainless steel at low temperatures and high strain rates. Furthermore, the increase of Cu content reduces the thermal deformation activation energy, inhibiting the dynamic recrystallization of antibacterial stainless steel, while an increase in deformation temperature or a decrease in strain rate promotes recrystallization. The proposed PM-PSO-LSSVM model is in good agreement with experiments, providing theoretical guidance for optimizing the composition and process parameters of antibacterial stainless steel.

Finite Element Analysis of Dynamic Recrystallization Model and Microstructural Evolution for GCr15 Bearing Steel Warm-Hot Deformation Process.

Warm deformation is a plastic-forming process that differs from traditional cold and hot forming techniques. At the macro level, it can effectively reduce the problem of high deformation resistance in cold deformation and improve the surface decarburization issues during the hot deformation process. Microscopically, it has significant advantages in controlling product structure, refining grain size, and enhancing product mechanical properties. The Gleeble-1500D thermal-mechanical physical simulation system was used to conduct isothermal compression tests on GCr15 bearing steel. The tests were conducted at temperatures of 600-1050 °C and strain rates of 0.01-5 s-1. Based on the experimental data, the critical strain model and dynamic recrystallization model for the warm-hot forming of GCr15 bearing steel were established in this paper. The model accuracy is evaluated using statistical indicators such as the correlation coefficient (R). The dynamic recrystallization model exhibits high predictive accuracy, as indicated by an R-value of 0.986. The established dynamic recrystallization model for GCr15 bearing steel was integrated into the Forge® 3.2 numerical simulation software through secondary program development to simulate the compression process of GCr15 warm-hot forming. The dynamic recrystallization fraction was analyzed in various deformation regions. The grain size of the severe deformation zone, small deformation zone, and difficult deformation zone was compared based on simulated compression specimens under the conditions of 1050 °C and 0.1 s-1 with the corresponding grain size obtained with measurement based on metallographic photos; the relative error between the two is 5.75%. This verifies the accuracy of the established dynamic recrystallization and critical strain models for warm-hot deformation of GCr15 bearing steel. These models provide a theoretical basis for the finite element method analysis and microstructure control of the warm-hot forming process in bearing races.

Hot compression behavior of Mg–Zn–Y–Mn–Ti magnesium alloy enhanced by lamellar LPSO phase and spherical W phase

The hot compression experiments of the solution-treated Mg93.5Zn2.5Y2.5Mn1Ti0.5 alloy were carried out using a Gleeble-1500D thermal simulator under the conditions of a temperature of 350∼500 °C, a strain rate of 0.001–1 s−1 and a strain of 0.9. According to the stress-strain curve, the characteristics of flow stress were analyzed. Moreover, the constitutive equation of flow stress, the kinetic model of dynamic recrystallization, and the processing map were established. The results show that the flow stress of the alloy decreases as the deformation temperature increases or the strain rate decreases. The constitutive equation of flow stress can be expressed as a hyperbolic sine function: ε˙=4.27115×1019[sinh(0.01153σ)]8.493×exp(2.856×105/RT). With the increase of the deformation temperature or the decrease of the strain rate, the volume fraction and grain size of dynamic recrystallization of the alloy increase continuously. Its dynamic recrystallization volume fraction can be expressed by the Avrami equation as: XDRX=1−exp[−2.05((ε−εc)/ε∗)1.42]. The instability region of the alloy increases with the increase of strain. The first instability region is (350–410 °C, 0.12–1 s−1), the second one is (450–500 °C, 0.001–1 s−1), and the optimum domain for the hot processing of this alloy is (380–450 °C, 0.001–0.01 s−1).

Microstructural evolution and dynamic recrystallization model of extruded homogenized AZ31 magnesium alloy during hot deformation

Abstract Using a thermal simulation testing machine, hot compression experiments were carried out on extruded homogenized AZ31 magnesium alloy, and the hot deformation behavior was analyzed. Based on this, the constitutive equation of the alloy is constructed to explore the evolution law of microstructure during hot deformation of the alloy, which could provide theoretical guidance for the reasonable selection of parameter ranges during hot compression of extruded homogenized AZ31 magnesium alloy. The experimental result indicated that the flow stress of the alloy during the hot deformation decreases with increasing temperature, increases with the strain rate increasing, and the real stress–strain curves during deformation show dynamic recrystallization curves. According to the experimental results, the deformation activation energy Q is 126.882 kJ mol−1 and the stress exponent n is 4.36 calculated by the constitutive equation under the given parameters, which confirmed that the glide and climb of dislocations in the climb-controlled regime is the deformation mechanism in this work. Decreasing the compression temperature and increasing the strain rate are helpful to reduce the Zener–Hollomon parameter, control the dynamic recrystallization occurring, and refine grain size to improve the mechanical properties effectively. Moreover, the dynamic recrystallization model of the alloy was constructed using the work hardening rate method and regression method, including dynamic recrystallization critical condition model, dynamic model and grain size model.

Arrhenius constitutive model and dynamic recrystallization behavior of 18CrNiMo7-6 steel

In order to analyze the thermal deformation and dynamic recrystallization behavior of 18CrNiMo7-6 steel, the isothermal compression tests are carried out on Gleeble-3500 thermal simulator machine at deformation temperatures 973.15 K–1273.15 K with strain rates 0.001 s−1–1 s−1. Based on the true stress σ0.3, the Arrhenius constitutive models are constructed by using characterization parameters and physical base parameters, and the determination coefficients between the predicted values of the two models and the measured values are 0.98378 and 0.97613, respectively. The constitutive models of characterization parameters and physical base parameters considering strain effect are also constructed, and a comparative analysis is made. The results show that the predicted values of the characterization parameters constitutive model is closer to the measured values in the low strain region. After reaching the peak strain, the predicted values of the two constitutive models are close to the measured values, and both have high prediction accuracy. The dynamic recrystallization models are established to characterize the recrystallization behavior. The recrystallization activation energy of 18CrNiMo7-6 steel is 169.6793 kJ mol−1, the ratio of critical strain to peak strain is about 0.47074, and the ratio of critical stress to peak stress is about 0.94059. The activation energy of 50% dynamic recrystallization is 29.9844 kJ mol−1. The dynamic recrystallized grain size increases with increasing deformation temperature or decreasing strain rate, and the activation energy of grain growth is −49.9237 kJ mol−1.

Microstructural evolution and hot-compressive behavior of Waspaloy forged bolts: experimental and finite element simulation

This study aims to present the optimum technological parameters of the hot forging process of aerospace bolts. Deformation-related parameters were determined according to the relevant conditions for commercial production of bolts. Deformation behavior and evolution of the microstructure of Waspaloy were systematically studied at temperature in the range of 1000–1120 °C and strain rate in the range of 0.01–10 s−1. The obtained results revealed the sensitivity of the flow stresses to the deformation parameters and stresses increased when deformed at lower temperatures or higher strain rates. At the high strain rates of 5–10 s−1, the flow curves exhibited a pronounced flow softening. The curves demonstrated a dynamic equilibrium at the low strain rates of 0.01–0.1 s−1. A constituent model of Waspaloy was established to describe the flow characteristic of Waspaloy. The microstructures showed that the grain refinement of DRX at low temperature (1000–1040 °C) was the main mechanism for microstructural evolution, while the grain growth kinetic was the dominant mechanism at high temperature (1080–1120 °C). The DRX kinetic model of this superalloy was established. Also, the constitutive and dynamic recrystallization models were used in the Deform-3D software for validation. The obtained results revealed that the simulation results matched well with the experimental results of grain sizes at different regions of the bolt specimens. The study can provide guidance to optimize technological parameters and predict the microstructure for commercial bolt forging.

Dynamic recrystallization behavior and processing maps of 5CrNiMoV steel during hot deformation

Hot deformation tests of 5CrNiMoV steel were performed at deformation temperatures of 700 to 870 °C and strain rates of 0.001 to 0.1 s−1 using the DIL 805D thermomechanical simulator. The critical strain and volume fraction models of Dynamic Recrystallization (DRX) were constructed based on the work hardening theory. The results showed that the critical strain of DRX decreases with increasing deformation temperature and decreasing strain rate, which implies that DRX occurs easily at higher temperatures and lower strain rates. The average DRX grain size model was established to predict grain size changes during hot deformation. Based on the hot processing maps that were constructed using the Dynamic Material Model (DMM) and microstructure observation, the optimum hot working parameters for 5CrNiMoV steel are a deformation temperature of 800 °C–870 °C, a strain rate of 0.001–0.05 s−1.

Thermal Deformation Behavior and Microstructure Evolution of GH4151 Alloy

Herein, an as‐cast GH4151 alloy is subjected to thermal compression at different temperatures and strain rates by a thermal simulation testing machine. The constitutive equation, dynamic recrystallization (DRX) model, and hot processing map are obtained from the stress–strain curves. The results show that the optimal heat processing conditions are 1100–1120 °C, 0.001–0.01 s−1 and 1100–1135 °C, 0.001–0.1 s−1. Electron backscatter diffraction (EBSD) and scanning electron microscopy (SEM) show that the recrystallization mechanism of GH4151 alloy is mainly discontinuous DRX (DDRX) and is supplemented by continuous DRX (CDRX). Deformation dislocations are eliminated by the phagocytosis mechanism of dislocations during recrystallization, and the subgrains and low‐angle grain boundaries are transformed into high‐angle grain boundaries, which finally form equiaxed grains. In addition, due to the pinning effect of γ′ phase on grain boundaries, the redissolution of γ′ phase during DRX greatly affects grain growth.