SRX Kinetics Research Articles

Combining crystal plasticity and phase field model for predicting texture evolution and the influence of nuclei clustering on recrystallization path kinetics in Ti-alloys

A three-dimensional computational framework has been developed combining a crystal plasticity (CP) and a phase-field (PF) approach that can efficiently simulate static recrystallization (SRX) and grain growth during the hot-forming in Ti-alloys. In the framework, the CP slip system parameters have been accurately calibrated by solving an inverse optimization problem from available experimental tension and compression stress–strain data through CP simulations performed via an orientation distribution function (ODF)-based computational model. Using the CP model, the evolution of inhomogeneous local deformation, deformed texture, and grain dislocation density have been simulated in the plastically deformed polycrystalline Ti-alloys. The PF model then predicts microstructure evolution and kinetics of SRX from CP-informed dislocation density during the annealing phase. Experimental information on microstructural heterogeneity in terms of the initial arrangement of nuclei distribution has been used to guide the development of the framework that can provide deeper insights into unique morphological evolution for various types of grain impingement as well as experimental validation of SRX kinetics. Finally, when the proposed model has been quantitatively validated through experimentally measured texture evolution and SRX path kinetics, excellent agreement is achieved. The current study highlights a systematic modeling framework that is capable of predicting crystallographic texture, microstructural evolution, and kinetics in the course of SRX for a clear understanding of the relationship between the mechanical properties, various microstructural descriptors, and thermo-mechanical process in the regime of material design.

Investigating the Static Recrystallization Behavior of 22MnB5 Manganese–Boron Steel through Stress Relaxation Analysis

A constitutive model was developed to characterize the static recrystallization (SRX) and evolution of the grain size of the industrially relevant press-hardening steel, 22MnB5, subsequent to the hot forming of sheet metal. Isothermal stress relaxation tests were conducted using the BAEHR 805 A/D thermomechanical simulator, encompassing a temperature range of 950 to 1050 °C, prestrain levels ranging from 0.01 to 0.1, and strain rates spanning from 0.01 to 0.8 s−1. The results obtained from the isothermal stress relaxation tests facilitated the formulation of an Avrami equation-based model, which aptly describes the kinetics of SRX in relation to the temperature, prestrain, and strain rate. Notably, an increase in temperature led to accelerated recrystallization kinetics, signifying temperature-dependent behavior. When the temperature increased from 950 to 1050 °C, the recrystallization time was reduced to approximately one-third. Additionally, the prestrain exhibited a positive influence on the acceleration of SRX kinetics. A quintupling of the prestrain from 0.01 to 0.05 resulted in a reduction of the static recrystallization duration to approximately one-fifth. Among the parameters studied, the strain rate had the least impact on the SRX kinetics, as doubling the strain rate from 0.01 to 0.8 only resulted in a halving of the recrystallization duration. Moreover, an analysis of the microstructural evolution in response to the forming parameters was undertaken. While the grain-size investigation post-isothermal stress relaxation tests provided results in line with the SRX kinetics calculations, the observed effects were comparatively subdued. Furthermore, a comprehensive examination was conducted using electron backscatter diffraction (EBSD) analysis, aiming to explore the effects of specific stress relaxation states on the morphology of martensite. The findings reveal fully recrystallized globulitic microstructures, characterized by relatively minor differences among them.

Initial grain orientation controls static recrystallization outcomes in cold-worked iron: Insight from coupled crystal plasticity/vertex dynamics modeling

Recrystallization of metallic materials is an important metallurgical treatment to bring cold-worked alloys to a usable state. Static recrystallization (SRX) occurs after deformation, once the material has built up sufficient plastic strain energy to trigger grain boundary motion. However, we have very limited knowledge about the combined effects on recrystallization kinetics of temperature, amount of cold working, triple junction mobility, and level of recovery in the deformed microstructure. In particular, little is still known about the microstructural factors that control the onset of SRX. Here we develop a comprehensive physical model based on coupling crystal plasticity and grain boundary kinetics utilizing curvature and differential plastic strain energy as driving forces for SRX in polycrystalline iron. The model links finite-element polycrystal plasticity simulations with a two-dimensional vertex dynamics approach, and is used to probe the large parameter space influencing static recrystallization. Our main finding is that the initial texture (defined by the polycrystal’s grain orientation and size distribution) is the dominant feature triggering and controlling SRX kinetics. We find a direct correlation between the degree of dislocation density buildup and the relative grain orientation across a grain boundary at the beginning of the deformation phase. Indeed, analysis of our results points to the maximum Schmid factor of a grain as the best predictor for activation of its grain boundaries during the recrystallization phase. We also find that the amount of post-deformation recovery only has a limited effect on the evolution of the recrystallized microstructure. Finally, using a definition based on the rate of transformation of the material, we find a recrystallization temperature of 600 ∘C, consistent with experimental observations in high-purity iron specimens.

Recrystallization Behavior and Microstructure Evolution in High‐Manganese Austenitic Steel

Compression deformation experiments are conducted to investigate the recrystallization behavior during the dynamic recrystallization (DRX) and static recrystallization (SRX) of high‐manganese steel in terms of flow stress and microstructure morphology. The experimental results indicate that strain rate plays a key role on DRX style. A low strain rate promotes discontinuous dynamic recrystallization (DDRX), whereas a high strain rate encourages continuous dynamic recrystallization (CDRX). The steady‐state stress of DRX behavior decreases with increasing deformation temperature regardless of the true strain and strain rate. Deformation temperature is a vital factor in determining the softening fraction of SRX behavior. The effect of interpass time on austenite grain size is weak for SRX behavior. The SRX kinetics equation for the designed high‐manganese steel is proposed according to experimental results.

Cellular automata modeling of the kinetics of static recrystallization during the post-hydroforming annealing of steel tube

A modeling setup based on the cellular automata (CA) method was developed to model the kinetics of static recrystallization (SRX) in hydroformed steel tubes undergoing the annealing process. In addition, the impact of multiaxial deformations on the kinetics of SRX within the hydroformed steel tube was investigated. First, hoop and axial strains developing at the pole of the steel tube during hydroforming were obtained from the digital image correlation measurements. Then, an exact analytical solution was employed to calculate the corresponding hoop and axial stresses at the pole of the bulged tube. Using these biaxial stress–strain curves, the stored energy was calculated for the hydroformed tube specimen. Second, the actual grain topology and crystallographic orientation of grains in the deformed specimen were obtained with the electron backscatter diffraction. Third, the calculated stored energy as well as the microstructural and crystallographic data was incorporated into the CA model as initial conditions to predict the kinetics of SRX in the specimen during annealing. Finally, to assess the accuracy of the CA model, experimental and predicted results were compared in terms of grain topology data including the grain size and aspect ratio distributions, as well as the rate of recrystallization during annealing. A reasonable agreement between the experimental and CA predictions in partial and fully recrystallized specimens was achieved inferring the validity of the developed algorithm and the modeling setup to predict the SRX kinetics during the post-tube hydroforming annealing process.

In-situ observations and modeling of static recrystallization in 300 M steel

The study of static recrystallization (SRX) has been widely concerned for its importance in regulating the microstructure and mechanical properties of deformed materials. In the paper, the effects of SRX on the flow behaviors of 300 M steel are investigated by thermal compression experiments. The SRX mechanism of 300 M steel is investigated by high temperature laser scanning confocal microscopy (HTLSCM) setup. The variations in the flow behaviors and microstructure under different experimental conditions are discussed in detail. Also, the relationships between microstructure evolution and mechanical properties are analyzed. The SRX mechanism is detected by the analysis of microstructure. According to the statistical results of microstructure, the SRX kinetics models and the average recrystallization (RX) grain size model are proposed. It can be found that the flow stress increases with the increased strain rate and reduced deformation temperature. The yield stress is affected by both the softening mechanisms of static recovery and SRX. The main SRX mechanism of 300 M steel is strain-induced boundary migration (SIBM). Compared to the pre-strain rate, the insulation temperature has a more significant effect on the SRX rate, maximum SRX volume fraction and average RX grain size. And the effects of pre-strain rate on the RX grain size are negligible at low pre-strain rate. The comparison between the calculated and experimental results is consistent, which implies that the established models can describe the SRX process accurately. Besides, compared to the softening volume fraction calculated based on the stress-strain curves, the SRX volume fraction calculated based on the statistic results of microstructure can reflect the SRX process more precisely, which indicates the effectiveness of the research method used in the paper.

Study on Static Recrystallization Behavior of Medium-Carbon Cr-Ni-Mo Alloyed Steel During Hot Deformation

A series of two-pass hot compression tests were conducted on Gleeble-1500 thermo-mechanical simulator to investigate the static recrystallization (SRX) behavior of a medium-carbon Cr-Ni-Mo alloyed steel 34CrNiMo. The compression tests were performed at a deformation temperature range of 950-1150 °C, a strain rate range of 0.1-3.5 s−1, and an interval time range of 1-100 s. The experimental flow stress curves and microstructural observation indicate that deformation temperature, pass interval time, strain rate, and pre-strain have significant influences on the recrystallization behavior of 34CrNiMo steel. It is identified that the softening fraction increases with the increasing deformation temperature, pre-strain, and interval time, while it decreases with the increasing strain rate. Based on the experimental data, the SRX kinetics equations of 34CrNiMo steel were developed. And the calculated results are in good agreement with the experimental ones, which demonstrates that the established equations can be used to describe the SRX behavior of 34CrNiMo steel at elevated temperatures.

Study of static recrystallization behavior in hot deformed Ni-based superalloy using cellular automaton model

A cellular automaton model (CA) with probabilistic state switches is developed to simulate the microstructural evolution in a Ni-based superalloy during static recrystallization (SRX). The kinetics of SRX is formulated on a mesoscale level. SRX nuclei grow under the driving pressure resulting from the reduction of stored energy and grain boundary energy. It is found that SRX grain size can be well predicted by the developed CA model. Solute elements of the studied superalloy have a drag effects on grain boundary motion. But, this solute drag effect is not obvious at high deformation temperatures. Nucleation rate of the SRX grain increases with the increase of strain, strain rate, and deformation temperature. Besides, the inhomogeneity of grain size first increases, then decreases with the increase of SRX fraction. The changes of inhomogeneity mainly result from the evolutions of the primary and SRX grain sizes.

Computational inverse analysis of static recrystallization kinetics

Accurate static recrystallization (SRX) models are necessary to improve the properties of austenitic steels by thermo-mechanical operations. This relies heavily on a careful and accurate analysis of “the interrupted test data” and conversion of the heterogeneous deformation data to the flow stress. A “computational-experimental inverse method” was presented and implemented here to analyze the SRX test data, which takes into account the heterogeneous softening of the post-interruption test sample.Conventional and “inverse” methods were used to identify the SRX kinetics for a model austenitic steel deformed at 1273K (with a strain rate of 1s−1) using the hot torsion test assess the merits of each method. Typical “static recrystallization distribution maps” in the test sample indicated that, at the onset of the second pass deformation with less than a critical holding time and a given pre-strain, a “partially-recrystallized zone” existed in the cylindrical core of the specimen near its center line. For the investigated scenario, the core was confined in the first half of the gauge radius when the holding time and the maximum pre strain were below 29s and 0.5, respectively. For maximum pre strains smaller than 0.2, the specimen did not fully recrystallize, even at the gauge surface after holding for 50s. Under such conditions, the conventional methods produced significant error.

Study of Static Recrystallization Behavior of a Nitrogen-Alloyed Ultralow Carbon Austenitic Stainless Steel by Experiment and Simulation

Static recrystallization (SRX) behavior of a nitrogen-alloyed ultralow carbon austenitic stainless steel was studied on a Gleeble-1500D thermal-simulator by two-step hot compression tests. Deformation temperatures of 1173-1473 K, deformation strains of 0.051-0.105, strain rates of 0.01-1 s−1, and inter-step times of 1-100 s were selected as the deformation conditions to investigate the effects of deformation parameters on SRX behavior. Besides, the influences of initial grain size on SRX behavior were studied. The results show that deformation temperature and strain have greater influences on SRX behavior than strain rate and initial grain size. Based on true stress-true strain data obtained from the experiments, SRX kinetics equation was determined. In addition, the established SRX kinetics equation was introduced into finite element simulation software DEFORM-3D to perform the two-step compression deformation. Furthermore, SRX kinetics equation was modified for improving the accuracy of finite element simulation, and the modified SRX kinetics equation was verified.

High-Temperature Flow Stress and Recrystallization Characteristics of Al-Bearing Microalloyed TWIP Steels

In this study, the effects of microalloying (Nb,V) and aluminum on the constitutive flow behavior and static recrystallization (SRX) characteristics of microalloyed TWIP steels (Fe-20Mn-0.6C-Al-(Nb,V)) have been investigated under hot deformation conditions. Compression tests in a Gleeble simulator, including the double-hit technique, enabled the acquisition of flow stress and recrystallization data. These were analyzed to determine the powers of strain and strain rate as well as the activation energies of deformation and recrystallization (Q def and Q rex). Aluminum increased the flow stress and activation energy of deformation and delayed the onset of dynamic recrystallization of microalloyed TWIP steels. While microalloying with V up to 0.3 pct seems to have little or no effect on the SRX kinetics, microalloying with 0.026 pct Nb significantly slowed down the SRX rate, similarly as in the case of low C-Mn steels. Addition of high aluminum (4.9 pct) marginally retarded the SRX kinetics in comparison with the steels with low aluminum (1.5 pct), with or without microalloying with V.

Coupling of Crystal Plasticity Finite Element and Phase Field Methods for the Prediction of SRX Kinetics after Hot Working

The conventional approach to model static recrystallization (SRX) kinetics is to use the well‐known Kolmogorov–Johnson–Mehl–Avrami (KJMA) equation. However, the validity of KJMA kinetics depends on whether the real recrystallization process follows the assumptions made in the derivation of the KJMA kinetics, which are a random distribution of nucleation sites, isotropic growth and a constant growth velocity. When these assumptions are violated the KJMA kinetics loose their physical meaning and turn into an empirical formula with limited predictive capability. In such cases, phase field (PF) method can be an alternative to the KJMA model, since it is based on irreversible thermodynamics. An effective strategy to apply the PF method to static recrystallization problems is coupling it to a deformation model though which the prior deformation process is simulated. For that purpose crystal plasticity finite element method (CPFEM) can be employed. In this work, an example of a weak coupling strategy was applied to a steel grade of commercial interest (X60Mn23 TWIP steel) for which KJMA equation is invalid. Deformation of a Voronoi type representative volume element was modeled using a Crystal plasticity finite element formulation after determining the material parameters of a strain hardening model from macroscopic experiments. Afterwards, the deformed structure was transferred on to a finite difference grid with a dedicated mapping scheme, which was then used as input for phase field simulation. Finally, the simulation results were compared with the results of stress relaxation tests. It was found that although the grain morphology of the simulation differed from the experimental results, the coupled simulation strategy was able to mimic the main features of the static recrystallization (SRX) kinetics.

Static recrystallization simulations by coupling cellular automata and crystal plasticity finite element method using a physically based model for nucleation

This study presents a 2D cellular automata simulation of static recrystallization (SRX) arising from the subgrain growth in single-phase material following cold deformation by coupling with a crystal plasticity finite element (CPFE) method. The spatial distribution of the stored deformation energy was obtained by CPFE simulation, based on which the initial deformed microstructure consisting of nonuniformly distributed subgrains was predicted. To simulate grain/subgrain growth during annealing, a curvature-driven mechanism was used, in which the grain/subgrain boundary energy and mobility were misorientation-dependent. On the SRX nucleation, a physically based model using critical subgrain size as criterion was adopted, which could provide better insight into the recrystallization nucleation mechanism involving grain boundary bulging. Simulations under different pre-deformation conditions were performed, and the influence of strain rate and strain on the SRX microstructure evolution and the transformation kinetics were investigated. Results show that deformation at higher strain rate can accelerate the SRX kinetics, and the SRX behavior depends more on the deformation state of individual grain than the nominal strain due to the relatively small computational domain.

Static Recrystallization and Precipitation Behavior of a Weathering Steel Microalloyed with Vanadium

The static recrystallization (SRX) and precipitation behavior of a weathering steel microalloyed with vanadium were investigated through double-pass compression tests under controlled conditions using the MMS-300 thermal-mechanical simulator. The deformation temperatures ranged from 800 °C to 1000 °C, and the inter-pass time from 1 s to 500 s. The simulation results showed that SRX occurred after 5–10 s at the first compression deformation. The softening fraction of SRX was found to increase with increasing the deformation temperature and the pre-strain. However, the softening fraction scarcely changed during the process of strain-induced precipitation. In addition, the kinetics of SRX was described by the Avrami equation, and the Avrami exponent appeared to be closely associated with the deformation temperature. The microstructure evolution was investigated at the initiation and completion of recrystallization. The amount and distribution of the precipitates were analyzed. The relationship between the driving force of SRX and the pinning force of precipitation was discussed. Besides, the recrystallization inhibition was detected at the early stage of precipitation, and the pinning forces were found to be of a magnitude comparable to the driving force. Moreover, the pinning forces were found to increase with the degree of precipitation and reach a peak at the intermediate stage of precipitation, and finally reduce as the particles coarsened.

Texture weakening and static recrystallization in rolled Mg–2.9Y and Mg–2.9Zn solid solution alloys

The microstructure and texture evolution in the Mg–2.9Y and Mg–2.9Zn solid solution alloys were investigated following rolling and subsequent isothermal annealing. The Mg–2.9Y alloy was hot rolled, and the Mg–2.9Zn alloy was rolled at room temperature in order to evaluate the possibility of attaining texture weakening by the suppression of dynamic recrystallization (DRX) and promotion of static recrystallization (SRX). It was found that texture weakening can be attained in Mg even in the absence of Y when there is no DRX, and SRX occurs during annealing. In solid solution, Y suppresses DRX during hot rolling, and retards the kinetics of SRX and grain coarsening in Mg. In the two alloys, the orientation of statically recrystallized grains at bands/twins (TSRX grains) is close to that of double and compression twins, exhibiting a much more evenly distributed and slightly wider orientation than that of basal parent grains and twins. In both Mg–2.9Zn and Mg–2.9Y alloys, a continuous texture weakening is observed with the progress of SRX, which results in a bimodal microstructure consisting of small TSRX grains and larger ones. With the increase in grain size during coarsening, the maximum intensity of basal pole figures rises linearly, with the slope of the lines being nearly identical in the two alloys. This texture strengthening was ascribed to the consumption of small TSRX grains by larger ones.

Static Recrystallization of Cold Rolled Intermetallic Fe17Al4Cr0.3Zr Alloy

The final microstructure of cold rolled intermetallic disordered alloy Fe17Al4Cr0.3Zr was rebuilt during the annealing at moderate temperatures in the range of 800 to 900 °C. The time necessary to obtain recrystallized structure was determined at several annealing temperatures to optimize the processing technology of the plates. The phases present in the material during this process were identified. The grain growth (grain boundary movement) during static recrystallization (SRX) is connected with the interaction with an array of the Laves phase λ1(Fe,Al)2Zr and ZrC particles. The Avrami-based phenomenological model describing kinetics of SRX was developed. The activation energy for recrystallization was estimated.

Recrystallization, Precipitation Behaviors, and Refinement of Austenite Grains in High Mn, High Nb Steel

Through a series of experiments conducted on three kinds of high Mn steels with different Nb content, including stress relaxation tests, physical metallurgical modeling, and observation of prior austenite grains and precipitates, the effect of Nb on recrystallization and precipitation behaviors were investigated. The results indicate the existence of a novel deformation temperature range for grain refinement resulting from complete static recrystallization (SRX) in high Mn, high Nb steel, whereas slow SRX kinetics can be accelerated by a finer initial grain size. In this deformation temperature range, the effect of precipitation is too weak to prohibit SRX nucleation efficiently, but solute drag is still large enough to slow down growth rate. As a consequence, shorter incubation and homogeneous recrystallized nucleation can be realized at relative low temperature, and the coarsening rate of grains is much slower because of the high solute drag effect in the rolling of low C high Mn, high Nb line pipe steel.

Recrystallization behavior of a Nb-microalloyed steel during hot compression

Using a Thermecmastor-Z hot simulator, dynamic recrystallization (DRX) and static recrystallization (SRX) behavior of a Nb-microalloyed steel was investigated by single-hit compression tests and double-hit compression tests, respectively. The experimental results show that DRX will more easily occur at higher deformation temperature and lower strain rate. The deformation activation energy and stress exponent for the Nb-microalloyed steel are calculated to be 379.29 ± 23.56 kJ/mol and 5.76 in temperature range of 950 °C to 1100 °C by regression analysis, respectively. Furthermore, a semi-empirical model is developed to identify the peak stress and strain for DRX. It is found that SRX kinetics follows Avrami’s law, and the softening fraction predicted by the model agrees well with experimental results.

Microstructure and Mechanical Properties in Hot-Rolled Extra High-Yield-Strength Steel Plates for Offshore Structure and Shipbuilding

Key parameters for a thermomechanically controlled processing and accelerated cooling process (TMCP-AcC) were determined for integrated mass production to produce extra high-yield-strength microalloyed low carbon SiMnCrNiCu steel plates for offshore structure and bulk shipbuilding. Confocal scanning microscopy was used to make in-situ observations on the austenite grain growth during reheating. A Gleeble 3800 thermomechanical simulator was employed to investigate the flow stress behavior, static recrystallization (SRX) of austenite, and decomposition behavior of the TMCP conditioned austenite during continuous cooling. The Kocks–Mecking model was employed to describe the constitutive behavior, while the Johnson–Mehl–Avrami–Kolmogorov (JMAK) approach was used to predict the SRX kinetics. The effects of hot rolling schedule and AcC on microstructure and properties were investigated by test-scale rolling trials. The bridging between the laboratory observations and the process parameter determination to optimize the mass production was made by integrated industrial production trials on a set of a 5-m heavy plate mill equipped with an accelerated cooling system. Successful production of 60- and 50-mm-thick plates with yield strength in excess of 460 MPa and excellent toughness at low temperature (213 K (–60 °C)) in the parent metal and the simulated coarse-grained heat affected zone (CGHAZ) provides a useful integrated database for developing advanced high-strength steel plates via TMCP-AcC.

A neural network model for prediction of static recrystallization kinetics under non-isothermal conditions

This paper presents a new scheme to apply artificial neural network (ANN) in prediction of static recrystallization (SRX) kinetics. Firstly, based on empirical data of SRX kinetics, a mathematical model is suggested to construct a neural network. Then, an appropriate neural network is trained on the basis of the first and the second derivatives of recrystallized fraction with respect to time. Finally, a thermo-mechanical finite element analysis is coupled with the proposed ANN to predict static recrystallization kinetics in hot rolling process of AA5083. To verify the model, the predicted results and the experimental data are compared and it is observed that there is a good consistency between the two sets of results.