Dynamic Material Model Research Articles

Investigation of the Hot Deformation Behavior and Mechanism of a Medium-Entropy CoCr0.4NiSi0.3 Alloy

The CoCrNi-based medium-entropy alloys (MEA) have been extensively investigated due to their exceptional mechanical properties at both room and cryogenic temperatures. To investigate the hot deformation behavior and the recrystallization mechanism of the CoCr0.4NiSi0.3 medium-entropy alloy, a series of deformation tests was conducted using the MMS-100 thermal simulation tester, with deformation conditions of 0.001–1 s−1/850–1150 °C. During the hot deformation process, the flow stress initially increases up to its peak value before gradually decreasing towards a steady state level. Higher flow stress levels are observed with increasing strain rate and decreasing deformation temperature. The estimated activation energy for hot deformation of this alloy is approximately 423.6602 kJ/mol. The Arrhenius-type constitutive equation is utilized to establish a modified model while incorporating power dissipation theory and the instability criterion of a dynamic material model to construct power dissipation maps and instability maps. By superimposing these maps, hot processing maps with strains of 0.4, 0.5, and 0.7 are derived. In this investigation, it is observed that regions of instability exclusively occur when the true strain exceeds 0.4. These regions of instability on the hot processing map align well with experimental findings. The suitable range of parameters for hot-working decreases as the true strain increases. The microstructure was analyzed using electron backscatter diffraction and transmission electron microscopy (TEM) techniques. The volume fraction of dynamic recrystallization (DRX) decreases with increasing strain rate but diminishes with rising temperature. The TEM characterization elucidated the mechanism of DRX in this MEA. The presence of the long-period stacking ordered (LPSO) phase was observed in both the face-centered cubic matrix and hexagonal close-packed recrystallized grains under different deformation conditions. The LPSO phase originates from the matrix at a low strain rate, whereas it is generated during recrystallization at a high strain rate. The observed increase in flow stress of the as-cast MEA is primarily attributed to the synergistic effects arising from the interaction of the dislocation with twins and the second phase. The onset of instability is effectively suppressed within a limited range through the formation of coherent second phases such as L12, LPSO, and superlattice structures resulting from phase transitions. These second phases serve as nucleation sites for recrystallization and contribute to the strengthening of dispersion. Furthermore, their interaction with dislocations and twins significantly influences both flow stress behavior and recrystallization kinetics under hot deformation. These findings not only deepen our understanding of the underlying deformation mechanisms governing MEA but also offer valuable insights for designing CoCrNi-based alloys with improved mechanical properties at elevated temperatures.

Dynamic recrystallization behavior and microstructure evolution of high-Mn austenitic steel for application in a liquefied natural gas carrier

The hot-working behavior of high-Mn austenitic steel for liquefied natural gas carriers at the deformation temperature in the range of 1073–1273 K and the strain rate in the range of 0.01–10 s−1 was studied on a Gleeble-3800 thermomechanical simulator using a compression test. Electron backscatter diffraction was used to study the microstructure after deformation. Under each deformation condition, a peak stress appears in the stress-strain curve, which conforms to traditional dynamic recrystallization hot-working flow stress curves. A hyperbolic sine-law-type constitutive equation was established to predict the peak stress. The thermal deformation activation energy was 414.19 kJ/mol, and the stress index n was 4.94. The texture of the deformed grains consisted of strong <110> and weak <100> fibers along the compression direction. The main recrystallization mechanism was discontinuous dynamic recrystallization. The grain size of the discontinuous dynamic recrystallization grains tended to increase with increasing deformation temperature or decreasing strain rate. Processing maps were drawn based on the dynamic material model. At high deformation temperatures, the power consumption factor of dynamic recovery was greater than that of dynamic recrystallization, whereas at low deformation temperatures, the power consumption factor of discontinuous dynamic recrystallization was greater than that of dynamic recovery. There are two flow instability regions in the processing maps, 1243–1273 K/1-10 s−1 and 1073–1203 K/0.05–10 s−1. The formation of a ‘necklace microstructure’ was the main cause of deformation instability. The optimized process parameters for industrial production were 1243–1273 K/1-10 s−1.

Hot deformation behavior of a Fe3Al–Ta alloy in the B2-order regime

In the present work, the hot deformation behavior and the corresponding microstructure evolution of an Fe–25Al-1.5Ta (at.%) alloy in the B2-phase field were investigated. Uniaxial compression tests were carried out in a strain rate range from 0.0013 s−1 to 1 s−1 and in a temperature range from 800 °C to 850 °C, where an ordered B2–FeAl matrix phase along with a C14 - (Fe, Al)2Ta Laves phase was confirmed by X-ray diffraction. A dynamic material model was applied to predict the safe and damaging processing windows. The underlying flow softening mechanisms were characterized using scanning electron microscopy and electron-backscatter diffraction. The flow stress-strain curves mostly showed a broad maximum followed by a slight decrease in stress until a steady stress was reached. The optimum processing window for the studied alloy was located at 850 °C/0.0013 s−1, where the efficiency of power dissipation (η) and strain rate sensitivity (m) reached 50% and 0.25, respectively. The processing map also showed a domain of flow instability, resulting from cracking, in the range of lower temperatures and higher strain rates (800 °C/1 s−1). The microstructural analyses confirmed a combination of dynamic recovery (DRV) and dynamic recrystallization (DRX) over the entire range of deformation conditions tested. The current study reveals a well-suited parameter range to achieve a high degree of hot deformability in Fe–Al alloys at significantly lower temperatures than those typically used. This may contribute to optimizing the thermomechanical processing of Fe–Al alloys and reducing energy consumption in industrial forging operations.

Deformation Behavior and Processing Map of AlCoCrFeNiTi0.5 High-Entropy Alloy at High Temperature

AlCoCrFeNiTi0.5 high-entropy alloy (HEA) shows excellent properties in hardness and corrosion resistance. AlCoCrFeNiTi0.5 HEA was prepared using a non-consumable vacuum arc furnace. Hot-deformation behavior of AlCoCrFeNiTi0.5 HEA was explored under 1073–1373 K with a strain rate between 0.001 and 1 s−1 using a Gleeble-3800 thermomechanical simulator. The constitutive equation was established using the Arrhenius model, and the deformation activation energy and material constant were obtained. The processing map of HEA within 0.3–0.6 deformation was drawn according to dynamic material model (DMM). The results show that the hot-deformation process of HEA is dominated by work hardening combined with dynamic recovery, and dynamic recrystallization. The flow stress of HEA is significantly affected by deformation temperature and strain rate. The constitutive equation was constructed and verified, and the correlation coefficient of R2 = 0.9873 indicated that the constitutive equation can be used to accurately predict the flow stress of HEA. The processing map of HEA shows that the optimal hot-working process parameters are in the range of temperature 1150–1300 K and strain rate 0.002–0.05 s−1. This work will provide theoretical guidance for the hot-processing of HEA, which effectively promotes the application of the HEA in industry.

Effect of masonry infill on the response of reinforced concrete frames subject to in-plane blast loading

This paper presents a numerical study investigating the effect of masonry infill on the response of reinforced concrete (RC) frames subject to in-plane blast loading. Three-dimensional single-bay single-story masonry infilled reinforced concrete (MIRC) frames were modeled, in which a simplified micro-modeling approach was adopted for the masonry infill. The surface-based cohesive model was employed between the expanded brick units by adopting the traction-separation law. A non-integral modeling approach was considered with an appropriate contact algorithm between the infill wall and bounding RC frame. The dynamic material models with explicit dependency on strain rate were incorporated in the finite element (FE) models and validated against the experimental test data. The developed FE models of bare RC and MIRC frames were subjected to surface blasts with variable scaled distances representing the far-field, near-field, and close-in blasts. The effect of masonry infill on the response of RC frames subject to in-plane blast loading was investigated using the general-purpose FE software ABAQUS without employing user-defined subroutines. The blast response was characterized using displacements, energy dissipation, strain localization and accumulation, stiffness degradation, and damage modes. Results highlight the beneficial influence of masonry infill in reducing the local deformation and altering the failure modes of RC frames subject to in-plane blasts. However, results suggest that the effects of infill on the overall structural response, including axial, flexural, and shear demands, must be considered during the design of bounding RC frames. Furthermore, parametric studies were carried out based on varying masonry bonding patterns and wall thickness, number of bays and stories, and masonry infill heights, and provided conclusive remarks.

Constitutive Modeling of Hot Deformation Behaviors and Processing Maps of Mg–4.83Gd–2.36Nd–0.21Zr Alloy

Accurately assessing the hot workability and flow behavior is crucial in the preparation of high‐performance wrought Mg–rare earth (RE) alloys. The hot deformation behaviors and workability of Mg–4.83Gd–2.36Nd–0.21Zr alloy are examined via Gleeble 3500 thermosimulation tests across a range of deformation temperatures from 350 °C to 450 °C and strain rates ranging from 0.001 to 1 s−1. The experimental results reveal that the flow stress of the experimental alloy decreases as the temperature increases and the strain rate decreases. The activation energies for deformation (Q) of the experiment alloy are calculated by the hyperbolic constitutive equation and range from 186.78 to 234.97 kJ mol−1. Strain compensation is incorporated in constitutive modeling, resulting in the correlation coefficient (R) of 0.9865 and the average absolute relative error (AARE) of 5.4639%. Further, the processing maps are constructed at different strains based on dynamic material models, from which the feasible processing window of the experimental alloy is determined in the areas of deformation temperatures of 425–450 °C and strain rates of 0.01–0.1 s−1.

Revealing the hot deformation behavior of AZ42 Mg alloy by using 3D hot processing map based on a novel NGO-ANN model

The hot deformation behavior of AZ42 alloy was observed using thermal compression tests at a temperature scope of 250–400 °C and strain rate scope of 0.001–1 s−1. True stress-strain curves exhibited a combination of work hardening and dynamic softening features. A Northern Goshawk algorithm (NGO)-optimized artificial neural network (ANN) model was proposed. The established NGO-ANN model demonstrated impressive prediction accuracy, achieving a high determination coefficient of 0.991, a mean absolute percentage error of 3.51 %, and a root mean square error of 2.73. Subsequently, three-dimensional (3D) hot processing map based on the dynamic material model (DMM) theory was created. There were three different regions within the processing maps: the flow instability region (region A: 250–260 °C, 0.02–1 s−1, and region B: 300–400 °C, 0.01–0.1 s−1), high-power dissipation coefficient region (region C: 350–400 °C, 0.001–0.02 s−1, and region D: 300–350 °C, 0.5–1 s−1), and low power dissipation efficiency safety region (region E: the rest ones). Microstructural analysis revealed significant local plastic flow features in the flow instability region and a combination of coarse initial deformation grains and fine dynamic recrystallization (DRX) grains in the low power dissipation efficiency safety region. Fine and uniform grains were observed in the high-power dissipation efficiency region with DRX degree VDRX as high as 85.6 %, resulting in the best mechanical properties. Based on the established 3D hot processing map, the optimal process domains were determined.

Application of processing maps and numerical modelling for identification of parameters and limitations of hot forging process of 80MnSi8-6 steel

The processing maps developed by dynamic material modelling (DMM) method are now widely used in the design of hot forming processes. However, this applies to those processes that are relatively fast or are carried out under isothermal conditions, when it is possible to maintain the deformation parameters within the processing window. In the case of multi-stage free forging, the temperature successively decreases during subsequent operations and is increased during inter-process reheating. Under such conditions, processing maps in direct form are not applicable. The proposed solution is to implement the data obtained by the DMM method into calculations carried out by the finite element method (FEM). This approach leads to obtain the distributions of DMM parameters in the volume of the feedstock at successive forging stages. Selected results of a combined DMM/FEM analysis of a multi-stage hot forging process of 80MnSi8-6 steel are presented. The starting data for the analysis were the flow curves of this material, determined from compression tests. The processing maps were developed and processing windows were determined. The results of the DMM analysis were verified by microstructure observations. Data from the DMM analysis were implemented into QForm software using LUA scripts. An integrated FEM/DMM numerical analysis of the process of a multi-step hot free forging of an example product was performed. The geometry of the tools and a sequence of operations were developed. The distributions of the DMM parameters and the hot deformation activation energy in the forging volume after successive forging sequences were analyzed.

Microstructural and constitutive relationship in process modeling of hot working: The case of a 60Mg-30Pb-9.2Al-0.8B magnesium alloy

Hot compression tests in the temperature range of 493-653 K and strain rates of 0.01-10.00 s−1 were used to evaluate the hot deformation behavior of 60Mg-30Pb-9.2Al-0.8B alloy. In order to optimize the hot working parameters, the Arrhenius constitutive equation and processing map with strain compensation were established on the dynamic material model (DMM). The results show that the stress-strain curves have three different stages of rising, peaking, and steady state during the hot compression with typical characteristics of work hardening (WH), dynamic recovery (DRV), and dynamic recrystallization (DRX). In addition, the improved Arrhenius strain compensation constitutive model has a higher precision than the traditional constitutive model. By dividing the processing map into three typical regions for analysis, the maximum power efficiency is obtained at ε = 0.4. The optimum hot working parameters are temperature range of 573K∼653K, and strain rate range of 0.01 s−1∼0.1 s−1. Instability usually occurs in the region with high strain rate and low temperature, and the main form of instability is cracking.

Hot deformation behavior and microstructure characterization of AlCrFe2Ni2(MoNb)0.2 high entropy alloy

The hot deformation behavior and microstructure evolution of AlCrFe2Ni2(MoNb)0.2 eutectic high entropy alloy at deformation temperatures of 900 °C–1100 °C and strain rates of 0.001 s−1∼1 s−1 were systematically investigated by hot compression tests. The principal structure equations of AlCrFe2Ni2(MoNb)0.2 high entropy alloy were constructed using the Arrhenius equation modified by Zener-Hollomon parameters. The decrease of strain rate and the increase of deformation temperature can enhance the continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) processes simultaneously. The power dissipation and instability diagrams were constructed according to the power dissipation theory and instability criterion, and the hot processing diagrams with strains of 0.3–0.6 were obtained by combining with the Dynamic Material Model (DMM) theory. According to the analysis of power dissipation rate and processing safety zone, the optimal hot processing parameters were found to be ε = 0.6 for the true strain, T = 1050–1100 °C, ε˙ = 0.0037–0.031 s−1.

Hot deformation behavior of Ni61Fe10Cr10Al17Mo2 high-entropy alloy with hierarchical structure

The Ni61Fe10Cr10Al17Mo2 high-entropy alloys (HEAs) with low density have been developed with great potentials for applications. The forging process is one of the important methods for fabricating components. Accordingly, the study of the deformation behavior of HEAs is the essence in the processing and molding of this material for using in industry. Moreover, there are multiple phases with hierarchical structures in the as-cast Ni61Fe10Cr10Al17Mo2 alloys, with the face-centered cubic (FCC) phase as the matrix phase accompanied with hard body-centered cubic (BCC) B2 phase. Here, the hot deformation behaviors of the homogenized Ni61Fe10Cr10Al17Mo2 alloy were investigated at strain rates ranging from 0.001 to 1.0 s−1 and temperatures ranging from 1000 to 1200 °C via isothermal compression tests. The true stress-strain curves were used to reveal the relationship between the flow stress and the deformation temperature and strain rate. The constitutive equations describing the correlations between the flow stress and hot compression parameters were constructed. At the same time, the dynamic material model and instability criterion were used to plot the hot processing map. Furthermore, the deformed microstructures and the dynamic recrystallization of alloy were investigated. Combined with the processing map, the optimal processing route is obtained.

Thermal deformation behavior and microstructure evolution of Fe−8.5Mn−1.5Al light−weight medium manganese steel

In this paper, Fe−8.5Mn−1.5Al light−weight medium Mn steel is used as the research object, and the hot compression test is conducted by Gleeble−3500 thermal simulation tester. The dynamic reversion and dynamic recrystallization (DRX) processes are analyzed according to the true stress−strain curve; the θ−σ work−hardening rate curve is plotted by P−J double differential method to analyze the influence law between work−hardening and dynamic reversion and recrystallization softening effect of the material; the DRX critical strain model is established to analyze the influence law of deformation parameters on DRX; Based on the dynamic material model theory, the hot working diagram and three−dimensional power dissipation diagram are constructed, and the best hot working area is determined by combining the microstructure of the material. Finally, based on the above research content, a systematic overview of the dynamic softening effects of DRX and dynamic recovery (DRV) will be provided.

Hot Working of an Fe-25Al-1.5Ta Alloy Produced by Laser Powder Bed Fusion

In the present work, hot working was used as a post-processing method for Fe-25Al-1.5Ta (at.%) alloy built using laser powder bed fusion (LPBF) to refine the undesirable columnar microstructure with heterogeneous grain sizes and strong textures in the build direction. The hot deformation behavior and workability were investigated using constitutive modeling and the concept of processing maps. Uniaxial compression tests were conducted up to a true strain of 0.8 at 900 °C, 1000 °C, and 1100 °C with strain rates of 0.0013 s−1, 0.01 s−1, and 0.1 s−1. The constitutive equations were derived to describe the flow stress–strain behavior in relation to the Zener–Hollomon parameter. Processing maps based on a dynamic materials model were plotted to evaluate the hot workability and to determine the optimal processing window as well as the active deformation mechanisms. The microstructure of the deformed specimens was characterized by scanning electron microscopy equipped with an electron backscatter diffraction detector. The results indicated a high degree of hot workability of the LPBF builds without flow instabilities over the entire deformation range tested. The epitaxially elongated grains of the as-built alloys were significantly refined after deformation through dynamic softening processes, and the porosity was reduced due to compressive deformation. The current study revealed a well-suited parameter range of 1000–1080 °C/0.004–0.012 s−1 for the safe and efficient deformation of the LPBF-fabricated Fe-25Al-1.5Ta alloys. The effectiveness of the process combination of LPBF with subsequent hot forming could be verified with regard to microstructure refinement and porosity reduction.

Hot deformation behaviors and dynamic softening mechanism of 6%Si high-silicon austenitic stainless steel

The hot deformation behaviors and softening mechanism of 6%Si high-silicon austenitic stainless steel were investigated under deformation conditions of 1000–1200 °C/0.01–10 s−1. The constitutive equation was established based on the stress-strain curves, and the processing maps were drawn based on the Dynamic Material Model (DMM) at different strain levels. The results show that the activation energy(Q) of hot deformation is 368.555 kJ/mol. The peak region of the hot processing maps is 1130–1170 °C/0.01–0.03 s−1 at the strain of 0.7, the η value is 0.47, indicating that the best hot workability can be achieved in this region. At high strain rates (1000–1200 °C/0.66–10 s−1), the material is easily destabilized, while in the non-destabilized zone, η values are greater than 0.3, excluding the processing danger zone, and a better microstructure can be obtained. The accuracy of the processing maps established in this paper was verified by combining the microstructural morphology of different regions with the processing maps. Under the deformation conditions of 1200 °C/0.01 s−1, the χ phase and a small amount of δ ferrite are precipitated. The second phases induce the occurrence of a fracture along the grain while refining the grain size. Therefore, processing should be avoided in the range of second-phase precipitation. Crystallographic information analyses showed that the softening mechanism of high-silicon austenitic stainless steel is mainly discontinuous dynamic recrystallization (DDRX), and continuous dynamic recrystallization (CDRX) occurs in the softening mechanism between 1100 and 1150 °C.

Hot Deformation Behavior and Dynamic Softening Mechanism in 7B50 Aluminum Alloy.

The hot deformation behavior and dynamic softening mechanism of 7B50 aluminum alloy were studied via isothermal compression experiments in the range of 320-460 °C/0.001-1.0 s-1. According to the flow curves obtained from the experiments, the flow behavior of this alloy was analyzed, and the Zener-Hollomon (Z) parameter equation was established. The hot processing maps of this alloy were developed based on the dynamic material model, and the optimal hot working region was determined to be 410-460 °C/0.01-0.001 s-1. The electron backscattered diffraction (EBSD) microstructure analysis of the deformed sample shows that the dynamic softening mechanism and microstructure evolution strongly depend on the Z parameter. Meanwhile, a correlation between the dynamic softening mechanism and the lnZ value was established. Dynamic recovery (DRV) was the only softening mechanism during isothermal compression with lnZ ≥ 20. Discontinuous dynamic recrystallization (DDRX) becomes the dominant dynamic recrystallization (DRX) mechanism under deformation conditions of 15 < lnZ < 20. Meanwhile, the size and percentage of DDRXed grains increased with decreasing lnZ values. The geometric dynamic recrystallization (GDRX) mechanism and continuous dynamic recrystallization (CDRX) mechanism coexist under deformation conditions with lnZ ≤ 15.

Exploring hot deformation behavior of equimolar CoCrFeNi high-entropy alloy through constitutive equations and microstructure characterization

In present study, hot deformation behavior of equimolar CoCrFeNi HEA have been carried out through hot compression with strain rate from 10−3 s−1 to 1 s−1 and temperature between 1123 K and 1373 K. The predicted flow stress were are esitmated using constitutive analysis. The hot working efficiency is plotted in the processing maps using dynamic materials model. The contour map shown the well hot deformed region with the value of power dissipation parameter of 0.3 is located at the conditions of 1223 K and 10−3 s−1. The map provides CoCrFeNi HEA for guidance of hot deformation behavior, and is helpful for others HEA as well as the prediction of material workability in hot forging process. Moreover, the microstructural observations were consistent well with the contour map. At the best region, the highest recrystallized fraction and lower texture intensity is observed. The present study conducted a more in-depth investigation of the application and reliability of the hot processing map.

Hot deformation behavior of 309L stainless steel

Hot compression tests were carried out on 309 L austenitic stainless steel at different deformation temperatures (900–1100 ℃) and different strain rates (0.01–10 s−1). Based on the stress-strain curve, three constitutive models, Modified Johnson-Cook, Modified Zerilli–Armstrong and Strain Compensation Arrhenius, are constructed, and it is found that the Strain Compensation Arrhenius model has the highest accuracy. Besides, the Arrhenius model and the dynamic material model were adopted to construct the activation energy map and power dissipation map of 309 L stainless steel with different strains. In the region with high temperatures and high strain rates, low activation energy Q value and high power dissipation η value were shown. According to the microstructure, the deformation of ferrite and austenite phases was uniform at 1050 and 1100 ℃/10 s−1, the level of recrystallization fraction was high, and the grains were fine and uniform. However, at 900 ℃/10 s−1, the microstructure suffered serious distortion, the ferrite was significantly elongated, and cracking occurred at the phase boundaries. A conceptual processing map was built through the prediction of activation energy map, power dissipation map and analysis of microstructure in combination. The optimal hot working range was 1025–1100 ℃/2.7–10 s−1, and the instability region was 900–958 ℃/0.28–10 s−1.

HOT-DEFORMATION BEHAVIOR AND PROCESSING MAP OF 22MnB5 HIGH-STRENGTH STEEL

In order to explore the hot formability of 22MnB5, a hot-tensile test of 22MnB5 high-strength steel plate was carried out using a Gleeble-1500 hot-tensile-testing machine. The stress-strain curves at 850 °C to 950 °C and 0.01 s–1 to 10 s–1 were obtained. The results show that 22MnB5 has an obvious positive-strain-rate sensitivity, and its peak stress decreases with the increase of temperature. The mechanical constitutive equation of 22MnB5 was established by using the improved Johnson-Cook model, and the fitting value was compared with the experimental value. Based on the dynamic material model, the hot-processing map of 22MnB5 was established and analyzed. The hot-processing process was determined as follows: deformation temperature 880 °C to 930 °C, strain rate 0.01 s–1 to 1 s–1.

Hot working processing and microstructure characterisation of as-cast high manganese TWIP steel

ABSTRACT The hot compression of the as-cast Fe-21Mn-0.7C–0.1Si twinning induced plasticity (TWIP) steel was investigated at the deformation temperature range of 950–1100 °C and strain rates of 0.01–5 s−1, using a GleebleTM thermo-mechanical simulator, to determine the hot deformation behaviour and analyse the recrystallisation mechanism. The results showed that the flow curves were characterised by yield-point-elongation (YPE) and dynamic recrystallisation (DRX) as the principal restoration mechanisms. The activation energy (Q) was calculated to be 394.975 KJ mol−1, which implies that the recrystallisation is sluggish in the whole range of the deformation conditions. Furthermore, the processing maps were generated according to the dynamic material model (DMM). The processing map was subdivided into different domains for the microstructural observations. The ideal hot deformation parameters of as-cast high Mn TWIP steel were obtained in the deformation condition range of 1087–1098 °C/10−1.2-10−0.17 s−1. Moreover, the microstructure analysis revealed that the DRX grains were twinned and nucleated through the bulging mechanism at the serrated grain boundaries, accompanied by twin boundaries migration created in the DRX grains by growth accidents, which contributed significantly to the growth of the DRX.

Hot Deformation Behavior of 301L Stainless Steel and Dissolution Behavior of δ‐Ferrite During Heat Treatment

The hot deformation behavior of 301 L stainless steel is investigated at 1000–1250 °C and 0.1–50 s−1. Deformation characteristics are studied through compressive stress–strain curves and constitutive equations. According to the dynamic material model and a series of diffusion annealing experiments, the hot processing map of 301 L stainless steel is established to determine the suitable processing domain. The results show that the stable domain is located in 1085–1240 °C and high strain rate range of 4.5–50 s−1, and the strain rate is the main factor affecting the machinability. Based on the hot compression tests, δ‐ferrite gradually forms a network structure with the increase of temperature; however, it can be inhibited at high strain rate. Therefore, it is necessary to reduce the temperature and increase the strain rate in the actual processing of the machinable area. It is found that diffusion annealing can reduce the content of δ‐ferrite from 12% to 0.67%, and the dissolution of δ‐ferrite is controlled by the diffusion of Cr and Ni, especially noticeable at the interface between γ and δ phase. Finally, the optimum diffusion annealing process parameter is determined at 1300 °C and 10 min.