Critical Strain For Dynamic Recrystallization Research Articles

Hot compression behavior and microstructure evolution of Mg-Gd-Y-Zn-Zr alloy

In this work, the hot compression behavior and microstructure evolution of Mg-8Gd-3Y-xZn-0.6Zr (x = 0, 1.5) alloys were investigated by Gleeble-1500D thermal simulation test machine, SEM, EBSD and other equipment. The results showed that, prior to hot deformation, the grain size of Mg-8Gd-3Y-1.5Zn-0.6Zr (1.5Zn) alloy was smaller than that of Mg-8Gd-3Y-0.6Zr (0Zn) alloy. Both alloys exhibited weak texture strength with predominantly large angle grain boundaries. The true stress-strain curve of the 1.5Zn alloy distinctly revealed dynamic recrystallization features. Notably, the 1.5Zn alloy exhibited higher peak stress and thermal activation energy compared to the 0Zn alloy. Furthermore, the 1.5Zn alloy demonstrated a lower critical strain for dynamic recrystallization, suggesting a heightened likelihood and increased degree of recrystallization. After hot deformation, the Mg-8Gd-3Y-xZn-0.6Zr alloy experienced a notable reduction in grain size, particularly evident in the 1.5Zn alloy, where the grains were smaller compared to the 0Zn alloy. Moreover, the texture strength of 1.5Zn alloy was obviously weaker than that of 0Zn alloy. Dynamic precipitation and dynamic recrystallization were more likely to occur at grain boundaries. Simultaneously, the constitutive model, hot processing map and recrystallization kinetics model were constructed for Mg-8Gd-3Y-xZn-0.6Zr alloy.

On the capability of grain refinement during selective laser melting of AlSi10Mg alloy

This work focuses on the origin and capability of grain refinement in the microstructure of selective laser-melted AlSi10Mg alloy. The grains in printed microstructure have been oriented in a random manner and there is no sign of preferred micro-texture. In the molten pool, columnar grains have been formed aligned with the building direction, and stretched toward the center of the molten pool. The fraction of refined equiaxed grains by the size of fewer than 10 μm is considerable (∼40%) which have been formed (i) during solidification owing to high solidification rate to thermal gradient ratio, or due to (ii) the occurrence of dynamic recrystallization during the manufacturing process after completion of the solidification. These refined equiaxed grains have been differentiated through plotting Grain Orientation Spread maps. The numerous thermal cycles experienced by each layer cause considerable tensile or compressive micro-plastic strains and give rise to dynamic recrystallization. The presence of incomplete grains can be clearly traced which are ready to be evolved into the recrystallized grains. This, besides the extensive substructure development and sub-grain formation, are main proof for governing of continuous mechanisms of recrystallization mechanisms. Finally, selective laser melting has been approached as a thermomechanical processing route, and the calculated micro-plastic strain has been compared with a critical strain of dynamic recrystallization obtained from the hot compression testing method.

Influencing Mechanisms of Prior Cold Deformation on Mixed Grain Boundary Network in the Thermal Deformation of Ni80A Superalloy.

Within the grain boundary engineering (GBE) of alloys, a mixed grain boundary network with random grain boundaries interrupted by twin boundaries, contributes to enhancing the overall grain boundary-related properties. The higher density of twin boundaries is pursued herein. Furthermore, a two-stage deformation method, i.e., prior cold deformation followed by thermal deformation, was proposed for improving the mixed grain boundary network in the thermal deformation of Ni80A superalloy. The influence of prior cold deformation on the mixed grain boundary network was investigated through a series of two-stage deformation experiments. The analysis of the stress–strain curves shows that the critical strain for dynamic recrystallization (DRX) and peak strains decrease significantly under the effect of prior cold deformation. In comparison to the necklace-like microstructures that occur after a single thermal deformation, the microstructures apparent after a two-stage deformation are characterized by finer DRX grains with abundant Σ3n twin boundaries, with a significantly improved density of the Σ3n twin boundaries (BLDΣ3n) by a factor of around nine. With increasing prior cold strain, the grain size, after a two-stage deformation, decreases continuously, while the BLDΣ3n increases firstly and then decreases. The mechanisms for improving the mixed grain boundary network via two-stage deformation were uncovered. The sub-grain boundaries formed in prior cold deformation stimulate the nucleation of DRX grains and twins; meanwhile, the driving force for grain boundary migration is enhanced due to prior stored energy. Then, DRX is activated in advance and occurs more completely, thereby promoting the formation of Σ3n twin boundaries.

Modeling of critical strain for dynamic recrystallization of niobium microalloyed steels

The critical strain for dynamic recrystallization (DRX) is most important in designing rolling schedules for the refinement of grain size by boundary-induced transformation mechanisms. Modeling of the critical strain for DRX from the stress-strain curves obtained from hot compression was physically built in this paper. The stress-strain behaviour of materials during hot deformation should be a combination of work-hardening and recrystallization softening. Before DRX occurred, the stress-strain behaviours could be described by a constitutive equation in which basic strain hardening and the effect of strain rate and temperature on stress-strain behaviour are included. Once DRX was promoted, obvious deviation between the experimental and calculated stress-strain curves appeared, which denoted the critical strain for DRX. The modeling in this work could be used not only to accurately calculate the critical strain for DRX but also to analyze the dynamic softening behaviours during hot deformation. To validate the calculated results, the stress-strain database was analyzed in the H beam sample deformed at 1000 °C with a strain rate of 0.1/s, and a critical strain of 0.22 was obtained by this novel method as an example. The calculated result is in good agreement with the experimental data obtained by micrographical observations.

Dynamic recrystallization behavior of 6082 aluminum alloy during hot deformation

The dynamic recrystallization behaviors of 6082 aluminum alloy in the temperature range of 623–773 K and strain rate range of 0.01–5 s−1 were studied by electron back scattered diffraction (EBSD) and transmission electron microscopy (TEM). According to the experimental results, dynamic recrystallization occurs during hot deformation of 6082 aluminum alloy, although the true stress-strain curve has no obvious single peak characteristic, and the degree of dynamic recrystallization is closely related to the Z parameter. Hot compression with lnZ = 24.9014 (723 K, 0.1 s−1) gives rise to the highest recrystallization fraction of 38.6%. The initial critical strain of dynamic recrystallization was determined by the work hardening rate. The quantitative relationship between the critical strain and Z parameters was established: [Formula: see text]. Based on the EBSD analysis and measurement results, dynamic recrystallization kinetics models of 6082 aluminum alloy during hot deformation were deduced. Microstructure analysis showed that the subgrain structure formed in the original grain is coarsened by grain boundary migration, and the orientation difference increases continuously until a large-angle grain boundary forms, resulting in dynamic recrystallization of grains. The likely mechanism is continuous dynamic recrystallization.

Flow Behavior and the Critical Strain of Dynamic Recrystallization for Mg-10.22Gd-2.31Y-0.1Zr Alloy

Flow Behavior and the Critical Strain of Dynamic Recrystallization for Mg-10.22Gd-2.31Y-0.1Zr Alloy

Effect of deformation parameters on microstructure of martensitic stainless steel during static recrystallization

In this paper, the static recrystallization behavior of X20Cr13 martensitic stainless steel was studied based on the hot compression test. The experimental results show that when the strain of the first pass is less than the critical strain of dynamic recrystallization, the main static softening mechanism is static recrystallization. The effects of prestrain, initial austenite grain size, deformation temperature and strain rate on the microstructure during static recrystallization were analyzed in detail.

Dynamic Softening Mechanism and an Improved Unified Constitutive Model for an Al–Cu–Mn–Fe–Zr Alloy during Warm Deformation

Deformation behavior of an Al–Cu–Mn–Fe–Zr alloy is investigated by plane strain compression tests at a warm deformation region. The flow stress first increases and then keeps steady, and the flow stress increases with reducing temperature or raising strain rate. However, the influence of strain rate on flow stress is weak at 100 and 150 °C. The dynamic recovery (DRV) mechanism is the dominant mechanism to balance the work hardening, and a larger number of dislocations are consumed at low strain rates. So, the deformed grains are difficult to reach the critical strain for dynamic recrystallization (DRX). When the strain rate is relatively high, the critical strain can be reached in a short time, which promotes the process of DRX. In addition, an improved unified constitutive model is built based on the evolution of dislocation density. The predicted flow stresses are in a close agreement with the measured results, proving that the built model can nicely reproduce the flow behavior.

Effect of Sm on dynamic recrystallization of Mg-8Gd-0.5Zr alloy during hot compression

Mg-8Gd-0.5Zr (wt%) alloy and Mg-8Gd-3Sm-0.5Zr (wt%) alloy were prepared by casting method in this paper. The microstructures of the two alloys after hot compression at 350–500 °C and strain rate of 0.002–1 s−1 were studied, and the critical strain of dynamic recrystallization was calculated. It is found that the critical strain of dynamic recrystallization decrease because of Sm addition. Therefore, the Mg-8Gd-3Sm-0.5Zr alloy recrystallizes easily. Due to the addition of Sm, more dynamic precipitates (β) are produced in Mg-8Gd-3Sm-0.5Zr alloy during hot compression. The β phase increases the dynamic recrystallization nucleation rate and refines the dynamic recrystallized grains. The dynamic recrystallization mechanism of Mg-8Gd-3Sm-0.5Zr alloy are continuous dynamic recrystallization (CDRX) and particle stimulated nucleation (PSN).

Establishment of a two-stage constitutive model based on dislocation density theory for as-forged SA508 Gr.3Cl.1

The high-temperature deformation behavior of the SA508 Gr.3Cl.1 steel was investigated by the uniaxial isothermal compression tests at the deformation temperature from 1223 K to 1473 K and strain rate from 0.001s−1 to 1 s−1, which were carried out using Gleeble-1500 thermo-mechanical simulator. Based on the experimental data, the material parameters and active energy of hot deformation were determined according to the regression analysis method. The critical strain of dynamic recrystallization (DRX) was confirmed by simplified P-J method. Furthermore, the constitutive model for work hardening-dynamic recovery (WH-DRV) stage and DRX stage was established based on dislocation density theory and the kinetics of DRX. Finally, the flow stress calculated using the established model and experiment data was compared and the results showed that it is enough accurate to predict the flow stress during hot deformation for SA508 Gr.3Cl.1. Thus, the model will be beneficial for the accuracy of simulation by Finite Element Method (FEM) method.

Dynamic Behaviors and Microstructure Evolution of Iron–Nickel Based Ultra-High Strength Steel by SHPB Testing

Iron–nickel based ultra-high strength steel (wt. 18~20% Ni) is characterized by its high strength and low thermal conductivity, and is normally used to make key components by forming and machining processes. The optimization of these processes is based on a deep understanding of the mechanical and dynamic behaviors under high strain, high strain rate, and high temperature. In this paper, the relationship of stress to strain, strain rate, and temperature is systematically investigated by the dynamic compression tests combined with quasi-static compression tests, and the hardening and softening is associated with the transformation in microstructures. According to the analysis, dynamic recrystallization around 600 °C is assumed to be one important influencing factor, hence hot deformation equations are established and the critical strain for dynamic recrystallization and the volume fraction of the dynamic recrystallized grains are defined.

Effect of alloying additions on work hardening, dynamic recrystallization, and mechanical properties of Ti–44Al–5Nb–1Mo alloys during direct hot-pack rolling

There is significant gap in the understanding of the effect of alloying elements, particularly V and B, on the dynamic recrystallization (DRX) behavior, and the corresponding microstructure evolution in Ti–44Al–5Nb–1Mo-(V, B) alloys during uniaxial hot compression. In this regard, we have studied here the relationship of work hardening rate (θ) and critical strain of dynamic recrystallization (εc) on strain, deformation parameters. The θ values showed typical dynamic recrystallization characteristics, and were sensitive to temperature and strain rate. Deformation mechanism involving twinning-dislocation interactions and phase transformation contributed to characteristics of θ. DRX occurred in Ti–44Al–5Nb–1Mo–2V-0.2B alloys even at higher rolling speed and at ambient temperatures over a wide range, which implied a wider processing window during the direct hot-pack rolling process. Crack-free sheets were directly obtained from the as-HIPed alloys at 1250 oC with rolling speeds of 0.3 m/s, and 10%–20% reduction per pass. Their microstructure, high-temperature tensile properties and fracture mechanisms are discussed. As rolling progressed, Ti–44Al–5Nb–1Mo alloy was characterized by residual lamellae with locally dissolved α2 laths, broadening γ laths, and fine sub-grains. Dislocation-induced DRX and phase transformation of α2/γ lamellae were the primary deformation modes. In contrast, on the addition of V and B, deformation twinning was activated. Multi-phase microstructure was characterized by equiaxed grains of ~ 5–20 μm. The as-rolled sheets of both the alloys exhibited superior performance at 800 oC. Ti–44Al–5Nb–1Mo alloy showed a higher ultimate tensile stress of ~689 MPa, while superior ductility of greater than 75% was obtained for Ti–44Al–5Nb–1Mo–2V-0.2B alloy. The microstructure with different degree of dynamic recrystallization contributed to various aspects of high-temperature tensile properties.

A Dynamic Recrystallization (DRX) Constitutive Model for Elevated Temperature Flow Behavior of Cu-0.5Cr-0.1Zr Alloy

In order to obtain the high-temperature flow behavior of Cu-0.5Cr-0.1Zr alloy more accurately, the hot compression test of Cu-0.5Cr-0.1Zr alloy was performed at the strain rates from 0.001 to 1.0 s−1 and the deformation temperatures from 600 to 750 °C on a Gleeble-3800 thermo-simulation machine. The results show that the high-temperature flow stress and dynamic recrystallization behavior of Cu-0.5Cr-0.1Zr alloy are affected by strain rate and temperature. The peak stress is obvious under the condition of high temperature and low strain rate, and the flow stress curve shows a clear dynamic recrystallization phenomenon. On the contrary, there is no obvious peak stress at the low temperature and high strain rate, and dynamic softening behavior is mainly based on dynamic recovery. The high-temperature flow stress of Cu-0.5Cr-0.1Zr alloy is expressed as a result of multiple stress actions, such as work hardening, dynamic recovery softening, and dynamic recrystallization softening. The thermal deformation activation energy of this alloy can be calculated as 244.94 kJ/mol. The relationship between the critical stress and the critical strain of dynamic recrystallization and the Z parameter was established through the cubic linear fitting of the work hardening rate curve. Based on the stress–dislocation relation and kinetics of dynamic recrystallization, the constitutive equations before and after critical strain of Cu-0.5Cr-0.1Zr alloy were developed. The predicted stresses of the established DRX constitutive model agree well with the experimental stresses.

Constitutive modeling and critical strain of dynamic recrystallization in SA508Gr.4N steel for advanced pressure vessel materials

Using a Gleeble–1500D thermal–mechanical simulator, the hot-deformation behavior and critical strain in the dynamic recrystallization of SA508Gr.4N steel were investigated by compression tests from 1050 to 1250 °C with strain rates from 0.001 to 0.1 s−1. Stress–strain curves were fitted by a nonlinear fitting method. Based on these tests, the flow stress constitutive equations of the work-hardening dynamical recovery period and dynamical recrystallization period were established for SA508Gr.4N steel. The stress–strain curves of SA508Gr.4N steel predicted by the established models are in a good agreement with the experimental ones. Curves of lnθ − e and − ∂(lnθ)/∂e − e (where θ is the work-hardening rate and e is true strain) were plotted from experimental data. A critical strain (ec) and a peak strain (ep) of dynamic recrystallization were obtained and exhibited a linear relationship, i.e., ec = 0.386ep. The predicted model of ec could be described by the equation of ec = 1.604 × 10−3Z0.127.

Effect of Nb Content on the Hot Deformation Behavior of S460ML Steel

The hot deformation behavior of S460ML steel with different Nb contents was investigated by single-pass compression experiment on the Gleeble-1500 thermo-machine simulator at deformation temperatures ranging from 900 to 1200 °C and strain rates from 0.1 to 5.0 s−1. The critical strain of dynamic recrystallization (DRC) under different conditions was determined by using working hardening rate-strain curves. The relationship between critical strain and peak strain of DRC was discussed. By means of regression analysis method, the hot deformation activation energy of steels and the mathematical model for predicting DRC critical strain were calculated and established, respectively. The results showed that DRC occurred during hot deformation. As the deformation temperature increased and strain rate decreased, the critical strain of DRC decreased. The critical strain (εc) showed linear relationship with peak strain (εp). As Nb content increased, the needed deformation temperature for occurring DRC increased, while the needed strain rate for it decreased. The activation energy for hot deformation of S460ML steel increased with increasing Nb content.

Hot Deformation Behavior and Dynamic Recrystallization Model of 6082 Aluminum Alloy in High Temperature

By high temperature compression experiment, true stress vs true strain curve of 6082 aluminium alloy are obtained at the temperature 460°C -560°C and the strain rate 0.01s-1-10s-1. The effects of deformation temperature and strain rate on the grain evolution are investigated; Critical strain of dynamic recrystallization of 6082 aluminium alloy model is obtained. The results show lower strain rates are beneficial to increase the volume fraction of recrystallization, the average grain size is coarse; High strain rates are beneficial to refine average grain size, the volume fraction of dynamic recrystallization is less than that in low strain rates. High temperature cause coarse grains. Dynamic recrystallization grain evolution model and model of DRX fraction can effectively predict recrystallization grain size and recrystallization fraction of 6082 aluminium alloy thermal deformation.

Effect of the Rate of Hot Compressive Deformation on the Kinetics of Dynamic and Static Recrystallization of Novel Medium-Carbon Medium-Alloy Steel

Dynamic and static recrystallization occurring under hot deformation at a rate of 1 and 100 sec – 1 in high-strength medium-carbon wear-resistant steels developed at CRISM “Prometey” for die forming of parts of driven elements of tillage machines is studied. The critical strain of dynamic recrystallization and the threshold temperatures and times of finish of static recrystallization are determined for the studied deformation rates at various temperatures.

Microstructural Evolution and Dynamic Recrystallization Behavior of β–γ TiAl‐based Alloy during Hot Compression

In this paper, the hot deformation behavior of a TNM TiAl‐based alloy (Ti–44.45Al–3.80Nb–1.01Mo–0.29Si–0.14B) is investigated via isothermal compression tests. The experimental results demonstrate that the critical strain for dynamic recrystallization gradually decreases with increasing deformation temperature. At the initial stage of the low‐temperature deformation process, the deformation is mainly caused by dislocation glide in the γ and β phases. When the deformation reaches a certain level, dislocation glide in the β and the DRX γ phases dominates the deformation. In the high‐temperature deformation process, the deformation is the result of dislocation glide in the α and β phases.

Study of the processing map and hot deformation behavior of a Cu-bearing 317LN austenitic stainless steel

Abstract The hot-working behavior of a Cu-bearing 317LN austenitic stainless steel (317LN–Cu) was investigated in the 950–1150 °C temperature and 0.01–10 s − 1 strain rate range, respectively. The effects of different deformation parameters and optimum hot-working window were respectively characterized through analyzing flow stress curves, constitutive equations, processing maps and microstructures. The critical strain for dynamic recrystallization (DRX) was determined by the inflection point on θ - σ and −∂ θ /∂ σ - σ curves. The peak stress was found to increase with decrease in temperature and increase in strain rate. Typical signs of DRX over a wide range of temperatures and strain rates were observed on the flow stress curves. The power dissipation maps in the strain range of 0.1–0.4 were basically similar, indicating the insignificant effect of strain on the power dissipation maps of 317LN–Cu. However, the instability maps showed strong strain sensitivity with increasing strain, which was attributed to the flow localization. The optimum hot-working window for 317LN–Cu was obtained in the temperature range 1100–1120 °C and strain rate range 0.01–0.018 s − 1 , with a peak efficiency of 38%. Microstructural analysis revealed fine and homogenized recrystallized grains in this domain.

Investigation on critical strain of dynamic recrystallization for SiCp/Al-Cu composite

Using Gleeble-1500D simulator, the critical strain of dynamic recrystallization of SiCp/Al-Cu composite were investigated at 623-773 K with strain rate of 0.01-10 s-1. The results show that the main softening mechanism is the dynamic recrystallization through the stress-strain curves of SiCp/Al-Cu composite, the activation energy is 272.831 KJ/mol. lnθ-ε and (-∂(lnθ)/∂ε)-ε) curves were plotted based on the experimental data to further obtain the critical strain and steady strain of DRX. Then the critical strain model and the steady-state strain model of DRX were set up. Furthermore, the dynamic recrystallization volume fraction of SiCp/Al-Cu composite was investigated.