Dynamic Recrystallization Model Research Articles

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.

Full field modeling of dynamic recrystallization in a CPFEM context – Application to 304L steel

In this work the recently proposed full field approach to model dynamic recrystallization [1] is applied to model 304L steel. The framework couples a CPFEM (crystal plasticity finite element method) model with a LS-FE (level-set finite element method) for grain boundary migration and phenomenological laws. 304L steel samples are subjected to thermomechanical tests and their flow behaviour is characterized, additionally Electron Back Scattered Diffraction (EBSD) is used to study microstructure evolutions. Part of the experimental data is used to calibrate the model parameters and describe their evolution as a function of the thermomechanical conditions. The calibrated model is used to predict the microstructural evolution of 304L steel, the results are compared with the remaining experimental measurements. The comparison shows that the model correctly predicts the flow behaviour and recrystallization fraction evolution. However the results also show that the use of classical phenomenological models limit the model capability to predict grain size evolution. Different approaches to improve the model grain size prediction are presented and compared, the results show significant improvements when compared with experimental data.

Monte Carlo simulation of grain refinement during friction stir processing

A procedure combining computational fluid dynamics modeling/Monte Carlo simulation was implemented to predict grain refinement during friction stir processing (FSP) of an Al–Mg alloy. Based on the critical parameters during FSP treatment such as rotational tool speed (w), and traverse velocity (v), the thermal and strain rate contours were simulated, and used as inputs for a statistical model of dynamic recrystallization. Afterward, the simulated grain structures were verified experimentally by electron backscattering diffraction analysis. FSP generated equiaxed grains with average sizes in the range of 3–10 µm depending on the heat input index in terms of w/v ratios in the range of 4–28 rev.min/mm. A correlation between simulated and experimentally validated grain structures is observed, with crystallographic textures consistent with shear strain induced preferred orientations with a dominant {112} component.

Phase field modeling of discontinuous dynamic recrystallization in hot deformation of magnesium alloys

A phase field model of discontinuous dynamic recrystallization (PF-DDRX) was employed to investigate grain structure evolution and its impact on mechanical response during thermomechanical processing of magnesium alloys. A set of isothermal compression experiments were conducted by thermo-mechanical simulator and used to calibrate the PF-DDRX model parameters such as the critical stress of recrystallization, the activation energy coefficient of dislocation, grain boundary mobility and recrystallization grain nucleation. The grain structure features of polycrystalline magnesium alloys were used to generate the initial grain structure for DDRX simulations. Simulation results show that 1) the ‘necklace’ microstructures, which are often observed in DDRX, form at the earlier stage of recrystallization; and 2) both predicted grain structure and mechanical response are in a reasonable agreement with experimental data. More importantly, the results demonstrate that the proposed methods enable one to establish the relationships between PF-DDRX model parameters and material properties for quantitative prediction and design of grain microstructures and material properties with thermomechanical processes.

Analytical mechanics modeling of residual stress in laser powder bed considering flow hardening and softening

Residual stress builds up during the fabrication of components via laser powder bed fusion (L-PBF) process which causes parts to fail due to the crack initiation and growth, low fatigue life, and fall outside of the specified dimensions. During the thermal loading, the grain size affected by strain hardening and flow softening is altered at the subsurface through dynamic recrystallization (DRx) and subsequent recovery. The yield strength of the alloys is largely determined by the size of nucleated grains, and it has a substantial influence on flow stress and residual stress build-up. In this work, a physics-based analytical model is proposed to predict the residual stress affected by the strain hardening, flow softening, and microstructural evolution during L-PBF process with IN718 as a material system for exploration. The temperature field is predicted using a transient moving point heat source approach. Due to the non-uniform heating, materials experience high thermal stress which may exceed the yield strength of the material. The thermal stress is obtained from Green’s functions of stresses due to the point body load. A material constitutive flow stress model known as Johnson-Cook is used to determine the yield surface. This flow stress model is modified to incorporate the effects of flow softening and grain size. The dynamic recrystallization and grain refinement models are used to calculate the grain size using recrystallized volume fraction from nucleation and growth rates. As a result of the cyclic heating and cooling and the fact that the material is yielded, the residual stress build-up is precited using incremental plasticity and kinematic hardening behavior of the metal according to the property of volume invariance in plastic deformation in coupling with the equilibrium and compatibility conditions. Results from the analytical residual stress model showed good agreement with X-ray diffraction measurements used to determine the residual stresses in the IN718 specimens built via L-PBF.

A new numerical framework for the full field modeling of dynamic recrystallization in a CPFEM context

This work describes the coupling of a level-set (LS) based numerical framework for microstructural evolutions modeling with a crystal plasticity finite element method (CPFEM), in order to propose a new full field approach dedicated to dynamic recrystallization (DRX) modeling. These developments are proposed for 3D polycrystalline metals subjected to large deformations at high temperatures.CPFEM is one of the best available alternatives to model the evolution of dislocation densities and misorientation during plastic deformation. The dislocation density and misorientation is then used as input data for the recrystallization model. Grain boundary migration (GBM) is modeled by using a kinetic law which links the velocity of the grain boundaries, described by LS functions, with the thermodynamic driving pressures. The nucleation of new grains is modeled by using phenomenological laws, which define the number of nucleation sites as a function of the dislocation density and the misorientation. The link between the CPFEM and the GBM model gives an accurate description of the DRX phenomenon, which is intended to model industrial processes.In this work the methods and the coupling algorithm are presented, along with an analysis of the different numerical parameters and strategies to define nucleation. The calibration and validation of the model against experimental data for 304L steel will be presented in a future work.

Constitutive analysis and dynamic recrystallization behavior of as-cast 40CrNiMo alloy steel during isothermal compression

Casting-forging combination forming process is an advanced manufacturing technique which is applicable to manufacture the parts with both complex shape and high performance. As a fundamental research of casting-forging combination forming process, as-cast 40CrNiMo alloy steel is obtained through vacuum casting by using metal mold. The isothermal compression tests of as-cast 40CrNiMo alloy steel are implemented on a Gleeble-3800 thermal simulation machine at deformation temperatures of 800, 900, 1000 and 1100 ℃, with strain rates of 0.001, 0.01, 0.1, 1 and 10 s−1. The results indicate that the true stress-strain curves present typical dynamic recovery type under low deformation temperature and high strain rate. With the increases of deformation temperature or the decreases of strain rate, the true stress-strain curves gradually transform to dynamic recrystallization type. The Arrhenius-type constitutive equation with Zener–Hollomon parameter is determined for constitutive analysis. The kinetic model and kinematic model of dynamic recrystallization are deduced to describe the dynamic recrystallization behavior.

Mesoscale Modeling of Dynamic Recrystallization: Multilevel Cellular Automaton Simulation Framework

The main attraction of cellular automaton (CA) method used in computational material science lies on not only the simulation of recrystallization without the complicated differential equations calculation, but also the visualization of nucleation and grain growth during discontinuous recrystallization. In this work, by incorporating the idea of multilevel cellular space into the classical CA simulation framework and formulating cellular state transformation rules and data transfer rules between different levels of cellular space, the multilevel cellular automaton (MCA) model for dynamic recrystallization (DRX) is constructed for the first time. The developed MCA model includes a multilevel recrystallized nucleation (MRN) module and a full-field multilevel grain topological deformation (FMGTD) module. The thermal compression experiments of 316LN stainless steel are carried out, and the developed MCA model is applied to the numerical simulation of DRX for 316LN steel. The accuracy and reliability of this model are verified by comparing simulation results with experimental results. The influences of simulation parameters such as the number of levels N in the FMGTD module and the discrete strain increment on simulation results are discussed. The discrete cellular space area (i.e., grain topology mapping accuracy) in the MCA model increases with N but decreases with the discrete strain increment. The results show that the developed MCA model can not only describe the grain topological deformation in the DRX process more accurately but also more compatible with the physical mechanism of recrystallized nucleation. The calculation accuracy of the MCA model is higher than the existing CA model. Besides, the MCA model can be closer to the real deformation process while ensuring the high grain topology mapping accuracy and solve the problem of the loss of grain boundary area in the existing CA model.

Development of a Methodology for Strain Field Analysis during Orthogonal Cutting

Functionality of all machined parts depends on their dimensional tolerance, surface condition and subsurface characteristics, which are often summarized as surface integrity. Key aspects of surface integrity are a change of the residual stress state and white layer formation. Reasons for any workpiece modification of the surface rim zone can be found in the occurring high thermo-mechanical loads during the cutting process. Over the last years, many researchers published simulation based approaches to determine both thermo-mechanical loads and changes in workpiece microstructure induced by machining. Nevertheless, the direct measurement of relevant state variables such as plastic strain and temperature fields at relevant cutting conditions is still a key challenge. Directly obtaining those state variable fields from the process will enable the development of fast computing analytical models to in-process estimate surface integrity features. As a basis for later modelling of dynamic recrystallization during cutting, a methodology to calculate the accumulated equivalent plastic strains alongside one particle movement path throughout the shear zone is developed in this paper. Therefore, an orthogonal cutting test bench has been used to obtain high resolution images when cutting AISI 4140 which were then analyzed using Digital Image Correlation (DIC).

Flow modelling of Ti6Al4V under large strains

This work uses flow stresses obtained experimentally at different strain rates and temperatures to validate flow modelling results. Flow curves of Ti6Al4V are measured via torsion experiments with a Gleeble® 3800 up to effective strains of 8. A physically based model that describes the evolutions of microstructure and the flow stress in the β-phase field was developed. A model of continuous dynamic recrystallization (CDRX) based on the work of Gourdet and Montheillet [1] for aluminium alloys is combined in this work with elements taken from Kocks and Mecking [2]. The model consists of a detailed description of the microstructure, based on different dislocation density populations and grain boundaries. All these internal variables evolve according to a production and a recovery term correlated mathematically with the temperature and the strain rate. The modelled output variables besides the flow stress are the total, the interior and the wall dislocation densities as well as the subgrain and grain sizes developed by continuous dynamic recrystallization. The model describes the softening occurring during large strain deformations, which is partly produced by the formation of new high angle grain boundaries (HAGB). The fraction of HAGB was used to determine the recrystallization grade, validated with microstructural characterization.

Modeling and simulation of dynamic recrystallization for Mg/LPSO alloys based on multi-phase-field and dislocation-based crystal plasticity models

Modeling and simulation of dynamic recrystallization for Mg/LPSO alloys based on multi-phase-field and dislocation-based crystal plasticity models

Constitutive Model and Flow Behavior of B1500HS High-Strength Steel During the Hot Deformation Process

Hot compression tests were carried out on a Gleeble-3800 thermal mechanical simulator in the temperature range from 700 to 900 °C and strain rate range from 0.005 to 10 s−1 to investigate the hot deformation behavior of B1500HS high-strength steel. Softening mechanisms of B1500HS high-strength steel under different deformation conditions were analyzed according to the characteristics of flow stress–strain curves. By analyzing and processing the experimental data, the values of steady flow stress, saturated stress, dynamic recovery (DRV) softening coefficient, and other factors were solved and these parameters were expressed as functions of Zener–Hollomon factors. Based on the dislocation density theory and the kinetic model of dynamic recrystallization (DRX), constitutive models corresponding to different softening mechanisms were established. The flow stress–strain curves of B1500HS predicted by a constitutive model are in good agreement with the experimental results and the correlation coefficient is . The comparison results indicate that the constitutive models can accurately reflect the deformation behavior of B1500HS high-strength steel under different conditions.

Constitutive modeling of dynamic recrystallization and precipitation behavior of Nb and Ti of Q1030 high strength steel

The thermal deformation and precipitation behavior at 900-1100° and strain rate of 0.1-5s−1 were studied by Gleeble-3800 thermal simulator of Q1030 high strength steel. The activation energy of hot deformation in austenite region was determined by regression method, and the hot deformation equation of the Q1030 high strength steel was established. The critical strain and peak strain of dynamic recrystallization were predicted accurately by fitting the inflection point with cubic polynomial of curve of Q1030 high strength steel, and relationship between critical strain and Z parameter was established. Finally, the precipitation behavior of Nb and Ti particles during low strain rate deformation was studied, the results show that the precipitated phases in steel are rectangular TiN, quadratic (Nb, Ti) (C, N) carbonitride, elliptical (Nb, Ti) C carbide and NbC. Thermodynamic calculation shows that the order of precipitation of the second phase in steel is TiN, TiC, NbC and NbN.

Constitutive Equation of GH4169 Superalloy and Microstructure Evolution Simulation of Double-Open Multidirectional Forging

This paper presented a double-open multidirectional forging with relatively few deformation passes and a uniform deformation. The constitutive equation and dynamic recrystallization model of the GH4169 superalloy were identified based on a thermal compression test and imported into Deform simulation software. The microstructure evolution law of GH4169 superalloy undergoing double-open multidirectional forging was simulated. The evolution of the recrystallization volume fraction and recrystallized grain size of the GH4169 superalloy during double-open multidirectional forging was obtained. Both higher temperatures and more passes were found to produce more complete recrystallization and smaller recrystallization grain size. At the maximum temperature studied, 1000 °C, with nine passes, the recrystallization volume fraction exceeded 95%, and the recrystallized grain size reached 3–5.5 µm.

Critical conditions and grain growth model for dynamic recrystallization of Cu-Ni-Si alloy

Hot compression tests of Cu-Ni-Si alloy with high Ni and Si contents were performed at the deformation temperatures of 750–950 °C, and the strain rates of 0.01–10 s−1 on a Gleeble-3800 thermo-mechanical simulator. The critical conditions for dynamic recrystallization (DRX) of Cu-Ni-Si alloy were obtained by processing the collected data and combining with the inflection point of θ-σ curve with the minimum value criterion of −∂θ/∂σ-σ curve. There was a certain correlation between the critical strain (εc) and the peak strain (εp), that was, εc/εp = 0.723, and the functional relationship between εc and Z parameter was εc = 1.05 × 10−3Z0.059. The average recrystallized grain size under various deformation conditions was measured, and the DRX grain growth model of Cu-Ni-Si alloy was established as dDRX = 5650.4ε̇−0.12891exp(−73142/RT).

A continuous dynamic recrystallization model to describe the hot deformation behaviour of a Ti5553 alloy

A physical based model is developed to describe recrystallization phenomena of titanium alloys during hot working of the β phase. Continuous dynamic recrystallization is attributed as the restoration mechanism based on the progressive transformation of low angle boundaries (subgrains) into high angle boundaries (grains). The model describes both, the microstructure, and the flow stress evolutions during hot deformation with large strains. The microstructure is conceived as been formed by three different populations of dislocations, and high as well as low angle grain boundaries. Evolution rates of all microstructural features are determined based on the effects of generation, interaction and annihilation of dislocations during deformation due to dynamic recovery, continuous dynamic recrystallization and static recovery. Continuous dynamic recrystallization is modelled and is considered to occur homogeneously within the microstructure. The model is able to predict the formation of subgrains from a fully annealed microstructure and the progressive formation of high angle grain boundaries. The subgrain and grain sizes are also obtained as output of the model. The model was applied to describe the hot compression behaviour of a Ti5553 alloy deformed between 880°C to 920°C and strain rates from 0.001 s−1 up to 10 s−1. The model is validated with flow curves and microstructural characterisation of hot deformed, and with microstructural information of non-deformed samples. The critical strain rate increases with increasing strain rate and decreasing temperature, similar to the discontinuous dynamic recrystallization phenomenon. The model can be implemented to simulate the microstructure and predict flow stresses of titanium alloys in industrial processes.

Cellular automaton modeling of dynamic recrystallization of Ni–Cr–Mo-based C276 superalloy during hot compression

Abstract

Hot Deformation Behavior of Q345 Steel and Its Application in Rapid Shear Connection.

The high-temperature deformation behavior of Q345 steel is detected by a Gleeble-3800 thermal simulator. The Arrhenius constitutive equation for high-temperature flow stress and the dynamic recrystallization model are constructed. With the secondary development technology, customized modifications are made on existing Deform-3D software. The constructed constitutive model and dynamic recrystallization model are embedded into Deform-3D to realize the secondary development of Deform-3D. The grain size and volume percentage distribution of dynamic recrystallization are obtained by simulating the shear connection process at high temperature and high speed. The results show that the constitutive equation and the dynamic recrystallization model constructed in this paper can be used to predict the evolution of the microstructure. The difference between the prediction results and the experimental data is about 3%. The accuracy of Arrhenius constitutive equation, dynamic recrystallization model and the feasibility of software secondary development are verified.

Modeling and simulation of dynamic recrystallization for Inconel 718 in the presence of δ phase particles using a developed cellular automaton model

The dynamic recrystallization (DRX) behavior of Inconel 718 superalloy containing second phase particles (δ phase) was investigated through isothermal compression deformation tests under the deformation temperatures of 960 °C–1000 °C and strain rates of 0.01, 0.1, 1 s−1. A developed cellular automaton (CA) model was established to describe the DRX process, considering the ellipsoid particle effects of particle stimulated nucleation and pinning grain boundary mobility. The comparisons of average grain size evolution and DRX kinetics were carried out between the studied superalloy with and without a δ phase. The results show that the δ phase could reduce the critical strain triggering DRX, average grain size at steady state and peak stress while increase the value of the Avrami exponent. And the effects of δ phase on average grain size is more and more obvious with the increase of strain rate. A great agreement between the simulated and experimental results was obtained, which indicates that the developed CA model considering the δ phase effects could well describe the DRX process of the studied superalloy.

An optimization method of upsetting process for homogenized, nickel-based superalloy Udimet 720Li ingot considering both cracking and recrystallization

The fracture prediction model and dynamic recrystallization (DRX) model for homogenized Udimet 720Li are investigated utilizing high temperature tensile tests in a temperature range of 1070–1220 °C and hot compression tests in a temperature range of 1130–1190 °C, respectively. The accuracy of the models is verified using the finite element method (FEM). Furthermore, the FORTRAN language is used to program updates into the Deform-3D software in order to effectively illustrate the fracture prediction model and the DRX model in the double-cone compression simulation. The calculated cracking and microstructural results conform well to experimental ones, which indicates the reliability and feasibility of the models. With the two models, an optimization method is put forward which can determine a perfect upsetting window in the aim of no cracks, high fraction of DRX and fine DRX grains for homogenized U720Li during the upsetting process.