Metadynamic Recrystallization Behavior Research Articles

Construction of meta-dynamic recrystallization dynamic model of 316L stainless steel based on grain orientation spread during continuous variable rate thermal deformation

Because the deformation parameters (temperature, strain rate) in the actual manufacturing process are non-constant. We investigate meta-dynamic recrystallization behavior under the transient mutation state. First, based on a single-pass thermal deformation experiment and electron backscatter diffraction (EBSD) technique, this study establishes a quantitative calculation method for the volume fraction of meta-dynamic recrystallization under different deformation conditions, and find the GOS threshold basis for judging the occurrence of meta-dynamic recrystallization. Comparing the experimental results with the numerical simulation results, it is found that the MDRX behavior of the material could be accurately described. The meta-dynamic recrystallization evolution law of the material in the thermal deformation insulation stage under the variable strain rate state is investigated by continuous variable rate thermal deformation experiment and numerical simulation. It is observed that an increase of the average strain rate in the continuous variable strain rate state would promote the meta-dynamic recrystallization softening behavior of the material in comparison with the steady state deformation stage, and vice versa.

Metadynamic Recrystallization Behavior of Cr-Ni-Mo Alloy Steel

In order to study the metadynamic recrystallization behavior of 34CrNi3MoV steel, a double-pass isothermal compression experiment and a single-pass thermal interval experiment were designed and conducted to obtain the stress–strain curves under different deformation conditions and to explore the action law of deformation parameters during the compression process. The softening rate was calculated by the compensation method, and the grain size in the recrystallization region was measured. Based on the obtained data, the effects of deformation temperature (T), interval time (t), and strain rate (ε˙) on the softening rate and grain size of 34CrNi3MoV steel during metadynamic recrystallization were analyzed. The results show that increasing the deformation temperature, extending the interval time, and increasing the strain rate are all beneficial to the improvement of the metadynamic recrystallization softening rate and that fine and uniform new grains can be obtained under a high strain rate. However, in high-temperature conditions, mixed crystallization can easily occur, which is not conducive to grain refinement. Based on the true stress–strain data and experimental data on the grain size, a relevant model for metadynamic recrystallization of 34CrNi3MoV steel was established using mathematical analysis of regression equations. The average relative error AARE between the constructed dynamic model and the grain size model and the experimental results are 6.48% and 1.30%, respectively. This indicates that the model has high predictability.

The metadynamic recrystallization behavior of ultrahigh-strength stainless steel: effects of precipitates and shear bands

The metadynamic recrystallization behavior of Cr-Co-Ni-Mo ultrahigh-strength martensitic stainless steel was studied in a double-pass isothermal compression test, and a metadynamic recrystallization kinetics model for softening was established. The results showed that the metadynamic recrystallization softening rate of the steel not only depended on the deformation temperature and strain rate but was also related to the dynamic precipitation and the local shear bands in the steel. When the deformation temperature was below 1050 °C, the dynamically precipitated M6C carbides pinned the grain boundaries and hindered metadynamic recrystallization. When the steel was deformed at a deformation temperature of 1000∼1050 °C and a strain rate of 1.0∼5.0 s−1, a large number of local shear bands were generated. The local shear bands increased the number of nucleation sites for dynamic recrystallization and enhanced the softening rate of metadynamic recrystallization.

Study of meta-dynamic recrystallization behavior of GH5188 superalloy

Cobalt-based superalloys have good service performance in environments where nickel-based superalloys cannot work. A number of the studies focused on mechanical properties, microstructure evolution and hot deformation characteristics, but studies of meta-dynamic recrystallization (MDRX) behavior remain lacking. The MDRX behavior of GH5188 superalloy was investigated using two-stage hot compression tests. The kinetic model and grain size model were built to better describe the MDRX process. The good agreement between the predicted values and experimental values was verified. The effects of holding time, temperature, strain rate and intervals time on MDRX microstructure evolution were analyzed and discussed. The results show that by descending order of correlation was: intervals time, holding time, temperature and strain rate. The MDRX fraction and grain size increase with the increase of holding time, temperature, strain rate and intervals time. At low temperatures, MDRX grains grew up in the form of bowed grain boundaries. At high temperatures, the growth of MDRX grains was often accompanied by the generation of twinning bands. Twins were formed in the process of grain growth.

Metadynamic recrystallization behavior of 5083 aluminum alloy under double-pass compression and stress relaxation tests

The static softening behavior of A5083 aluminum alloy was studied through two thermomechanical tests, namely double-pass compression test and stress relaxation test. Metadynamic recrystallization and the further conventional static recrystallization cannot achieve complete recrystallization, which means that in the stress relaxation test, the traditional method used to determine the recrystallized fraction is no longer applicable. Hence, a new method is proposed based on the sigmoidal relationship between the relaxation stress and the recrystallized fraction. The order of the effects of the forming parameters on the metadynamic recrystallization, from strong to weak, is as follows: strain rate, temperature, and first-pass strain. External stress plays a significant role in retarding metadynamic recrystallization, thereby amplifying the effects of the forming parameters on the metadynamic recrystallization. Interestingly, metadynamic recrystallization, which is considered to occur immediately, has an incubation time of approximately 1 s in the studied aluminum alloy. The evolution of the microhardness and microstructure studied through microhardness tests and electron backscatter diffraction confirmed these conclusions. In addition, the phenomena of stress hardening and yield stress drop, caused by strain aging, were observed only under special experimental conditions.

Microstructure Evolution and Meta-Dynamic Recrystallization Behavior of Ti-45Al-8.5Nb-0.2W-0.2B-0.3Y Alloy during Inter-Pass Annealing after Deformation

The effect of processing parameters on meta-dynamic recrystallization (MDRX) and the microstructural characteristics evolution of TiAl alloy with high Nb containing during annealing period were studied through double-pass hot compression tests. The results indicated that the occurrence of MDRX had a strengthening effect to flow behavior of the present alloy, resulting in grain equalization. And the high temperature and large strain were beneficial for the occurrence of MDRX, resulting in the increase of recrystallization grains. For the present alloy, MDRX rate is low, hence, enough annealing time is needed for MDRX during inter-pass annealing. Besides, dislocation density is consumed with the occurrence of MDRX.

Simulation of Dynamic and Meta-Dynamic Recrystallization Behavior of Forged Alloy 718 Parts Using a Multi-Class Grain Size Model.

Dynamic and meta-dynamic recrystallization occur during forging of alloy 718 aircraft parts and thus change the microstructure during a multistep production route. Since the prediction of the resulting grain structure in a single grain fraction is not able to describe microstructures with bimodal or even multimodal distributions, a multi-class grain size model has been deployed to describe the recrystallization mechanisms during thermomechanical treatments and predict the resulting grain size distributions more accurately. As forging parameters, such as temperature, strain rate and maximum strain influence the flow curve and consequently the recrystallization behavior, a series of double cone compression experiments has been carried out and used to verify and adapt the material parameters for the multi-class grain size model. The recrystallized fractions of the numerical and experimental results are compared and differentiated in view of the recrystallization mechanism, i.e., dynamic and meta-dynamic recrystallization. The strong dependence of the recrystallization kinetics on the initial grain size is highlighted, as well as the influence of different strain rates, which shall represent typical forging equipment.

Modeling of Metadynamic Recrystallization Kinetics and Recrystallization Mechanisms of V-Containing 12Cr Rotor Steel

In order to study the metadynamic recrystallization (MDRX) behavior of 12Cr rotor steel, the double-hit hot compression tests were performed on a Gleeble1500D thermal simulator with temperatures of 1273-1373 K, strain rates of 0.001-0.05 s−1 and inter-pass times of 5-60 s. Based on the true stress–strain curves obtained at different deformation conditions, the effects of different deformation parameters on the MDRX softening behavior are discussed. Meanwhile, the microstructure was observed using an optical microscope, electron backscatter diffraction and transmission electron microscopy. Analysis showed that recovery was the main softening mechanism, followed by recrystallization. And the bulging at the grain boundary was the fundamental nucleation mechanism for MDRX. Furthermore, the kinetics model for MDRX of 12Cr rotor steel was established, which was verified to have an accurate capability of predicting MDRX softening behavior with a correlation coefficient of R = 0.9956.

Metadynamic recrystallization behavior of β-solidified TiAl alloy during post-annealing after hot deformation

The metadynamic recrystallization (MDRX) of β-solidified TiAl alloy and its effects on microstructural homogeneity were investigated in the present work. Based on the comprehensive microstructure characterizations in terms of scanning electron microscope in back-scattered electron (BSE) mode and electron back scattered diffraction (EBSD) technique, it is found that the occurrence of MDRX during the post-annealing process after hot compression leads to the decomposition of lamellar colonies, grain equalization and reduction of geometrically necessary dislocation. The MDRX in present alloy during interpass annealing process has a hardening effect on the subsequent flow behavior, while it is restricted due to the phase transformation γ to α when annealing at 1200 °C. Moreover, the occurrence of MDRX can reduce the microstructure heterogeneity among various areas induced by the different strains and stain rates, thus, to result in the microstructural homogenization. Through investigating the MDRX behavior, the present work supports important information for optimizing forged microstructure of TiAl alloys.

Investigation on the meta-dynamic recrystallization behavior of Inconel 718 superalloy in the presence of δ phase through a modified cellular automaton model

The Meta-dynamic recrystallization (MDRX) behavior of Inconel 718 superalloy containing second phase particles (δ phase) was investigated through the isothermal two-stage compression deformation tests under the deformation temperatures of 960–1000 °C,the strain rates of 0.01, 0.1, 1, 5s−1 afterwards to the strain of 0.2, holding time of 0s, 10s, 20 s at the deformation temperature, and then to the accumulated strain of 0.4. A developed cellular automaton (CA) model was built to better describe the MDRX process, with both considering the δ phase particles effects of particle stimulated nucleation (PSN) and pinning MDRX grain growth. The reasonable functions of driving force and nucleation rate were developed for predicting the MDRX process during the multi-pass deformation process in the developed CA model. The simulated microstructures indicate a good consistency with the experimental results, which shows the developed CA model could well describe the MDRX process of the studied superalloy. The effects of holding time, strain rate, temperature and δ phase on MDRX were analysed and discussed through the developed CA model.

Investigation on metadynamic recrystallization behavior in SA508-Ш steel during hot deformation

The metadynamic recrystallization (MDRX) behavior of SA508-Ш steel was investigated by isothermal double-hit hot compression tests at forming temperatures of 950–1250°C, strain rates of 0.001–0.1s−1 and the inter-stage delay time of 1–300s. Experimental results show that the effects of forming temperature and the strain rate are significant, while the pre-strain and initial grain size are less on metadynamic recrystallization behavior of SA508-Ш steel. Based on the experimental results, the kinetic equations and the grain size model for metadynamic recrystallization of SA508-Ш steel were established. Comparisons between the experimental and predicted results were carried out. The predicted results agree well with the experimental data, which indicates that the proposed kinetic equations can give a reasonable estimation of the softening behavior for this steel. Furthermore, by implementing the established kinetics and microstructural evolution equations of MDRX into commercial FE software, the hot forging process of SA508-Ш steel can be designed and optimized through numerical simulation.

An Investigation on the Softening Mechanism of 5754 Aluminum Alloy during Multistage Hot Deformation

Isothermal interrupted hot compression tests of 5754 aluminum were conducted on a Gleeble-3500 thermo-mechanical simulator at temperatures of 350 °C and 450 °C, and strain rates of 0.1 s−1 and 1 s−1. To investigate the metadynamic recrystallization behavior, a range of inter-pass delay times (5–60 s) was employed. These tests simulated flat rolling to investigate how softening behaviors respond to controlled parameters, such as deformation temperature, strain rate, and delay times. These data allowed the parameters for the hot rolling process to be optimized. The dynamic softening at each pass and the effect of metadynamic recrystallization on flow properties and microstructural evolution were analyzed in detail. An offset yield strength of 0.2% was employed to calculate the softening fraction undergoing metadynamic recrystallization. A kinetic model was developed to describe the metadynamic recrystallization behaviors of the hot-deformed 5754 aluminum alloy. Furthermore, the time constant for 50% recrystallization was expressed as functions related to the temperature and the strain rate. The experimental and calculated results were found to be in close agreement, which verified the developed model.

The kinetics and microstructural evolution during metadynamic recrystallization of medium carbon Cr–Ni–Mo alloyed steel

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Metadynamic recrystallization of Nb–V microalloyed steel during hot deformation

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A new method to predict the metadynamic recrystallization behavior in a typical nickel-based superalloy

The metadynamic recrystallization (MDRX) behaviors of a typical nickel-based superalloy are investigated by two-pass hot compression tests and four conventional stress-based conventional approaches (offset stress method, back-extrapolation stress method, peak stress method, and mean stress method). It is found that the conventional stress-based methods are not suitable to evaluate the MDRX softening fractions for the studied superalloy. Therefore, a new approach, ‘maximum stress method,’ is proposed to evaluate the MDRX softening fraction. Based on the proposed method, the effects of deformation temperature, strain rate, initial average grain size, and interpass time on MDRX behaviors are discussed in detail. Results show that MDRX softening fraction is sensitive to deformation parameters. The MDRX softening fraction rapidly increases with the increase of deformation temperature, strain rate, and interpass time. The MDRX softening fraction in the coarse-grain material is lower than that in the fine-grain material. Moreover, the observed microstructures indicate that the initial coarse grains can be effectively refined by MDRX. Based on the experimental results, the kinetics equations are established and validated to describe the MDRX behaviors of the studied superalloy.

Metadynamic recrystallization behavior and workability characteristics of HR3C austenitic heat-resistant stainless steel with processing map

The metadynamic recrystallization (MDRX) behavior and workability characteristics of HR3C austenitic heat-resistant stainless steel during double-hit hot compression was studied by modeling the kinetic equations of MDRX and developing the hot processing maps. Hot compression experiments were conducted over a deformation temperature range of 950–1150°C, a strain rate range of 0.01–1s−1 and an inter-pass time range of 1–30s on Gleeble-1500 thermo-mechanical simulator. The kinetic equations were established to predict the MDRX behavior of hot compressed HR3C steel. The analysis shows that the results based on the kinetic equations can predict the experimental data precisely at high deformation temperatures, i.e., 1050–1150°C, however, the predicted kinetics of MDRX is much faster than the experimental kinetics at 950°C. The hot processing maps of double-hit hot compressed HR3C steel were developed. There is one stability domain existing in the region of the deformation temperature of 1150°C and the strain rate of 0.1–1s−1 at the strain of 0.6. According to the hot processing map, the large-strain compression should be performed at the domain when the inter-pass time is 15s in HR3C steel.

Metadynamic Recrystallization Behavior of As-cast 904L Superaustenitic Stainless Steel

The metadynamic recrystallization (MDRX) behavior of as-cast 904 L superaustenitic stainless steel was investigated by double pass isothermal compression tests at temperatures of 950 — 1150 °C, strain rates of 0.05 — 5 s−1 and interval of 1 — 100 s. The effects of working parameters (deformation temperature, strain rate, pre-strain and interval time) on the flow curves and microstructural evolution were discussed. The MDRX fraction increased obviously with the increase of deformation temperature, strain rate and interval time. The MDRX softening was controlled by the migration of grain boundary, annihilation of dislocation and dynamic recrystallization. Moreover, the kinetic model was established for the prediction of MDRX behavior of as-cast 904 L superaustenitic stainless steel based on the experimental data. A good agreement between the predicted and the experimental values was achieved (correlation coefficient R2=0.98), indicating a satisfactory accuracy.

The Kinetics of Metadynamic Recrystallization in a Ni-Cr-Mo-Based Superalloy Hastelloy C-276

The metadynamic recrystallization (MDRX) behavior of a typical Ni-Cr-Mo-based superalloy Hastelloy C-276 was investigated using two-stage isothermal compression tests on a Gleeble thermal-mechanical simulator in the temperature range of 1050-1200 °C, the strain rate range of 0.1-5.0 s−1, the strains of 0.32, 0.45, and 0.6 at the first stage of compression, and the interval times of 0.5-30 s. The results show that the microstructure and the stress-strain relation of the studied superalloy vary during the interruption period due to the occurrence of MDRX. The MDRX softening fraction and recrystallized grain size increase rapidly with the increasing of interval time, deformation temperature, and strain rate. The effect of strain at the first stage of compression on MDRX is less pronounced. The kinetics of MDRX softening was established based on the flow stress curves, and the apparent activation energy of MDRX of Hastelloy C-276 is evaluated as 241 kJ/mol.

Meta-Dynamic Recrystallization Behavior of SCM435 Steel

The meta-dynamic recrystallization behavior of SCM435 steel was studied on the MMS-200 thermal simulation machine through the double-pass compression experiment. The effects of the deformation temperature, the strain rate, and the initial austenite grain size on meta-dynamic recrystallization were analyzed. Based on the test result, the kinetics model of the meta-dynamic recrystallization of SCM435 steel was established, and the obtained activation energy was 242.3kJ/mol. The results showed that the meta-dynamic recrystallization fraction Xm of SCM435 steel increased as the deformation temperature and the deformation rate increased, decreased as the initial grain size increased, and increased as the time interval increased.

Metadynamic Recrystallization Kinetics of Twin Roll Cast AZ31 Alloy during Hot Deformation

Metadynamic recrystallization takes place during isothermal annealing of materials in which an incomplete dynamic recrystallization occurred. In magnesium alloys this question has been investigated less until now. The metadynamic recrystallization behavior of twin-roll-cast and annealed AZ31 strip after hot deformation was investigated under conditions corresponding to hot strip rolling process of twin-roll-cast Mg coils. Plane strain compression tests were performed using double hit compression tests at temperatures of 250 - 400 oC, strain rates of 0.1 - 5 s-1 and interpass time of 0.5 – 10 s. Based on the experimental results, the kinetic equations and grain size model were established. Results show the effects of deformation parameters, including forming temperature and strain rate, on metadynamic recrystallization softening fractions and grain size in the two-pass hot deformed AZ31 alloy. Results also reveal that the pre-strain (beyond the peak strain) has little influence on the metadynamic recrystallization behavior in AZ31 alloy. Comparisons between the experimental and the predicted results were carried out. A good agreement between the experimental and the predicted results was obtained.