Dynamic Softening Research Articles

On the Origin of Enhanced Tempering Resistance of the Laser Additively Manufactured Hot Work Tool Steel in the As-Built Condition

Abstract In laser additive manufacturing (AM) of hot work tool steels, direct tempering (DT) of the tool from as-built (AB) condition without prior conventional austenitization and quenching results in enhanced tempering resistance. To date, intercellular retained austenite (RA) decomposition, leading to a shift in secondary hardening peak temperature, and finer martensite substructure are reported to be responsible for such a behavior. In this work, authors aimed at studying the strengthening contributions by performing isothermal tempering tests for long times (up to 40 hours) at elevated temperatures (up to 650 °C) on DT and quenched and tempered (QT) specimens. The thermal softening kinetics and the microstructural evolution were evaluated with the support of computational thermodynamics. The results suggest that the main contributor to enhanced temper resistance in DT condition is the larger fraction of thermally stable and extremely fine (~ 20 nm) secondary (tempering) V(C,N) compared with QT. This could be explained by the reduction of available V and C in austenitized and quenched martensite for a later secondary V(C,N) precipitation during tempering, because of equilibrium precipitation of relatively large (up to 500 nm) vanadium-rich carbonitrides during the austenitization process. A complementary effect of the substructure refinement (i.e., martensite block width) in rapidly solidified highly supersaturated martensite was also quantified in terms of Hall–Petch strengthening mechanism. The significant effect of secondary V(C,N) was successfully validated by assessing a laser AM processed vanadium-free hot work tool steel in QT and DT condition, where no significant differences in strength and temper resistance between the two conditions were evident. Graphical Abstract

Subtle frequency matching reveals resonant phenomenon in the flight of Odonata.

In this work, we investigate the connection between the flight flapping frequency and the intrinsic wing properties in Odonata (dragonflies and damselflies). For such large flying insect species, it has been noted that the wingbeat frequency is significantly lower than the structural resonance of the wing itself. However, the structural resonance mechanism is often evoked in the literature for flying and swimming animals as a means to increase locomotion performance. Here, we show that the flight of Odonata is based on a nonlinear mechanism that strongly depends on the wingbeat amplitude. For large flapping amplitudes (as observed in natural flight), the resonant frequency of the wings decreases with respect to its value at low amplitudes to eventually match the wingbeat frequency used in flight. By means of this nonlinear resonance, Odonata keep a strong wing stiffness while benefiting from a passive energy-saving mechanism based on the dynamic softening of the wing.

The effects of deformation parameters on the second phases and softening behavior of Al–Zn–Mg–Cu alloys

This study investigates the effects of deformation parameters on the second phase and softening behavior of Al–Zn–Mg–Cu alloy. The results are as follows: Firstly, the area fraction of the intermetallic phase fluctuates between 0.704 ± 0.092% and 1.886 ± 0.231% with varying deformation parameters. Secondly, in the temperature range of 270 °C to 430 °C, the area fraction of the η[Mg(Zn, Al, Cu)2] phase first increases and then decreases with rising deformation temperature, and gradually increases with decreasing strain rate. The highest area fraction is 12.613 ± 0.340% at 350 °C/0.001 s−1, and the lowest is 0.366 ± 0.068% at 470 °C/0.001 s−1. Additionally, the coarsening and dissolution of the η[Mg(Zn, Al, Cu)2] phase accelerate the dynamic recovery softening of the alloy. The sample at 350 °C/0.001 s−1 shows a low-angle grain boundary (LAGBs) percentage of 97.83% and a minimum average dislocation density of 8.493 × 102 μm2. Furthermore, at 470 °C/0.001 s−1, the Al7Cu2Fe phase has a weaker effect on stimulating nucleation and recrystallization, while the most significant promotion occurs at 430 °C/0.001 s−1. In the range of 270 °C to 350 °C and 0.1 s−1 to 0.5 s−1, the Al7Cu2Fe phase mainly stimulates the formation of sub-grains. These findings offer valuable insights for refining the grain size of alloys by regulating the content of the second phase during hot deformation.

Hybrid modelling of dynamic softening using modified Avrami kinetics under Gaussian processes

This paper presents a new method of modelling that combines several approaches to anticipate the softening of nickel-niobium alloys during dynamic recrystallization (DRX). The study employs an extensive dataset obtained from hot torsion deformation tests conducted on high-purity nickel and six nickel-niobium alloys. The niobium concentration in these alloys varies from 0.01 to 10 wt % (Matougui et al., 2013). The hybrid technique integrates the Avrami model to provide early predictions about the kinetics of recrystallization and then uses mechanistic modelling to assess the progression of softening caused by dynamic recrystallization (DRX). The integrated technique is improved by using Gaussian process regression analysis, which investigates the softening properties and offers useful insights into the effects of niobium additions on dynamic softening behaviour. This unique hybrid framework combines multiple modelling tools to reveal intricate connections impacted by solute addition, therefore enhancing our comprehension of the physical events that take place during the hot deformation of superalloys. The use of empirical, mechanistic, and machine learning methods in this hybrid model provides a more thorough and detailed investigation of DRX processes in these alloys.

Microstructural evolution of GH4079 superalloy during hot deformation and heat treatment

Through hot compression and subsequent heat treatment experiments on GH4079 superalloy, the influence of different hot deformation and heat treatment conditions on the evolution of GH4079 superalloy microstructure was studied. The evolution of grains and γ′ phases under different thermomechanical conditions was investigated. The results indicate that at deformation temperatures above 1100 °C and strain rates ranging from 0.01 to 0.1 s−1, the primary mechanism of dynamic softening in the alloy is discontinuous dynamic recrystallization (DDRX). When the deformation temperature is below 1100 °C and strain rates range from 0.01 to 0.1 s−1, both continuous dynamic recrystallization (CDRX) and DDRX are the main dynamic softening mechanisms. Due to high strain energy accumulation, the samples deformed at lower temperatures (below 1100 °C) and then solution-treated at 1120 °C for 8 h exhibit significant increases in recrystallization volume fraction and recrystallization grain size. Conversely, the samples deformed at higher temperatures (above 1100 °C) and then solution-treated at 1120 °C for 8 h show minimal changes in recrystallization volume fraction and recrystallization grain size. After solution treatment at 1140 °C, the grain size of the alloy significantly increases. The samples deformed at higher strain rates exhibit the evolution of fine γ′ phases into elongated rod shapes during solution treatment, while larger γ′ phases undergo splitting processes.

Hot compression recrystallization and processing characteristics of 18 %Cr lean duplex stainless steel with Mn addition

The deformation differences of hot compression tests for 18 % Cr lean duplex stainless steels, alloyed with 3.1 and 5.8 wt% Mn concentrations were comparatively investigated. The deformed microstructure revealed that more Mn promoted the formation of austenitic dislocation cells, inhibited the occurrence of dynamic recrystallization (DRX), and resulted in a decrease in the number of refined austenite grains at lower temperatures and strain rates. Meanwhile, more Mn addition promoted ferrite DRX, and delayed austenite DRX initiation deformed at higher strain rates and lower deformation temperatures. The nearly complete refinement of austenite grains formed due to DRX deformation at 950℃/0.01 s−1 with 3.1 % Mn addition, while fine grains caused by ferrite DRX mainly occurred at 850℃/1 s−1 with 5.8 wt% Mn addition. The relationships between the Zener–Hollomon parameter (Z) and critical strain (stress) were established using the power law relation. The stability processing domains with high power efficiency greater than 0.34 narrowed with increasing Mn content, are located in the temperature range of 1000–1150℃ and strain rate range of 0.01–0.03 s−1, and austenite DRX plays a significant role in compression deformation improvement. At a low deformation temperature of 850 ℃, the work hardening rate in the initial strain increased with increasing Mn addition, and a lower strain rate and deformation temperature contributed to the dynamic deformation softening caused by austenite DRX, but ferrite DRX slightly contributed to the improvement of compression deformation. The DRX kinetics models show that the trend of the volume fraction of DRX as a function of processing variables is in good agreement with experimental data.

Thermo-mechanical processing characteristics and strain-rate-sensitive degradation properties of Mg-Er-Ni alloys

Hot deformation behavior, the corresponding microstructure evolution, and degradation properties of a weak-textured Mg-Er-Ni alloy containing a high-volume fraction of Ni-LPSO phases, have been investigated. Hot deformation behavior has been carried out in the temperatures range of 370 ∼ 460 °C and strain rates range of 0.001 ∼ 1 s−1. Flow stress-strain curves of high strain rate cases show a continuous increase trend without a steady or a peak stage, while that of low strain rate cases show an obvious dynamic softening after peak stress. Based on flow stress-strain curves, materials constants calculated by an Arrhenius-type constitutive equation, show a high n and Q compared to those of high-volume fraction α-Mg matrix Mg alloys. Optimal processing windows, based on the dynamic material model, is determined as high temperature domains. As for microstructure evolution, a complete recrystallization and dispersive Ni-LPSO fragments for high temperature & low strain rates while a restricted recrystallization and a streamline distribution LPSO phase for high temperature & high strain rates are observed. Varying degrees of continuous dynamic recrystallization, particle induced nucleation mechanism, as well as coordinated deformation of LPSO through kinking and bending account for the strain-rate-dependence hot deformation mechanism. As a result, dispersive Ni-LPSO fragments at low strain rates provide more degradation channels for the α-Mg matrix and thus possess better a degradation rate than the streamlined LPSO at high strain rates.

Evolution of microstructure, texture and formability of Al–Mg–Si alloys at different hot rolling finish temperatures

The impact of hot rolling finish temperature (HRFT) on the evolution of microstructure, texture, as well as formability—including deep drawability and bendability—of Al–Mg–Si alloy was studied in present work. The obtained results reveal that HRFT has a notable influence on the dynamic softening and dynamic precipitation behaviors during the hot rolling process of the investigated alloy. This leads to the volume fraction and number density of micro-sized Mg2Si particles increase as the increase of HRFT, those of nano-sized particles decrease, and the dislocation density decrease, in the hot-rolled sheets. These microstructural variations persist in the cold-rolled sheets, subsequently affecting the ultimate microstructure, texture, as well as formability of T4P sheets. The deep drawability improves as the HRFT rises, as indicated by the increase in normal anisotropy (r‾) and decrease in planar anisotropy (Δr). This is attributed to the weakening of texture intensity. The bendability, quantified by the minimum hemming factor (Rmin/t), deteriorates as the HRFT rises from 260 °C to 390 °C, attributed to the strengthening of P component along with the weakening of Cube component. Conversely, with the HRFT rises from 390 °C to 420 °C, the bendability improves dramatically due to the significant reduction in the average grain size. A combination of excellent deep drawability and bendability could be obtained by elevating the HRFT to 420 °C, attributed to the combined effect of weakened texture intensity and fine grains.

Research on the Dynamic Softening Mechanism of Dual‐Phase Structure During Warm Forming of Fe–8.5Mn–1.5Al Medium‐Manganese Steel

In this article, Fe–8.5Mn–1.5Al medium‐manganese steel is taken as the research object, and Gleeble 3500 thermal simulation testing machine is used to conduct isothermal compression at different deformation temperatures, strain rates, and strains in its austenite ferrite two‐phase zone. A constitutive model and a dynamic recrystallization volume fraction model for materials are established, and finite‐element method is used to simulate the temperature, equivalent strain, and dynamic recrystallization volume fraction distribution in different regions of the workpiece under different deformation conditions. By comparing and analyzing the microstructure, finite‐element simulation results, and hot working diagrams obtained from the experiment, the microscopic mechanism of dynamic softening of the material when ferrite and austenite coexist is explained; the transformation of the dynamic softening mechanism of the two phases with the hot deformation process is also explained. Early deformation mainly occurs in softer ferrite, which preferentially undergoes continuous dynamic recrystallization. Austenite has a lower stacking fault energy, and discontinuous dynamic recrystallization (DDRX) occurs when the dislocation density reaches a certain critical value. At the same time, when the strain reaches a certain level, the dynamic softening behavior of ferrite will also transform into DDRX. The optimal deformation conditions for Fe–8.5Mn–1.5Al medium‐manganese steel during warm processing in the two‐phase zone are a temperature of 720 °C, a strain rate of 0.01 s−1, and a large deformation zone.

Interaction between dynamic recrystallization and phase transformation of Ti-43Al-4Nb-1Mo-0.2B alloy during hot deformation

The β solidified γ-TiAl alloy holds important application value in the aerospace industry, while its complex phase compositions and geometric structures pose challenges to its microstructure control during the thermal-mechanical process. The microstructure evolution of Ti-43Al-4Nb-1Mo-0.2B alloy at 1200 °C/0.01 s−1 was investigated to clarify the coupling role of dynamic recrystallization (DRX) and phase transformation. The results revealed that the rate of DRX in α2+γ lamellar colonies was comparatively slower than that in βo+γ mixed structure, instead being accompanied by intense lamellar kinking and rotation. The initiation and development rates of DRX in α2, βo, and γ phases decreased sequentially. The asynchronous DRX of the various geometric structures and phase compositions resulted in the uneven deformed microstructure, and the dynamic softening induced by lamellar kinking and rotation was replaced by strengthened DRX as strain increased. Additionally, the blocky α2 phase and the terminals of α2 lamellae were the preferential DRX sites owing to the abundant activated slip systems. The α2→βo transformation within lamellar colonies facilitated DRX and fragment of α2 lamellae, while the α2→γ transformation promoted the decomposition of α2 lamellae and DRX of γ lamellae. Moreover, the varied βo+γ mixed structures underwent complicated evolution: (1) The γ→βo transformation occurred at boundaries of lamellar colonies, followed by simultaneous DRX of γ lamellar terminals and neighboring βo phase; (2) DRX occurred earlier within the band-like βo phase, with the delayed DRX in enclosed γ phase; (3) DRX within the βo synapses and neighboring γ phase was accelerated owing to generation of elastic stress field; (4) Dispersed βo particles triggered particle stimulated nucleation (PSN) of γ phase. Eventually, atomic diffusion along crystal defects in βo and γ phases caused fracture of band-like βo phase and formation of massive βo particles, impeding grain boundary migration and hindering DRXed grain growth of γ phase.

Hot deformation behavior and dynamic recrystallization of 2195 Al–Li alloy with various pre-precipitation microstructures

In this work, 2195 Al–Li alloys with various precipitation microstructures were obtained by homogenization treatment followed by air-cooling (AC), discontinuous cooling (DC), and furnace-cooling (FC), and then tested by hot compression at different temperatures. The results show that the flow stresses of all specimens decrease with temperature and the peak stresses of AC, DC and FC specimens decrease in order at the same temperature. For FC samples, coarse pre-precipitates diminish the deformation resistance due to the reduction of solid solution strengthening and precipitation strengthening. Dynamic softening at low temperatures is significantly greater than that at high temperatures, except for the anomalous softening of the FC specimen at 520 °C due to stress release by cracks. At 370–420 ​°C, the dynamic softening of the AC specimen is more significant than the other samples, resulting from dynamic precipitation and precipitate coarsening. Furthermore, there is considerable dynamic recrystallization (DRX) in FC samples and not in AC and DC samples, although their precipitates coarsen to similar levels at low temperatures. This suggests that DRX is associated with the particle-stimulated nucleation mechanism by regularly arranged precipitates. The banded or regularly arranged precipitates divide the Al matrix into multiple confined units, hindering dislocations and (sub)grain boundary movement, and thus promoting the development of sub-grains and DRX.

Effect of TiB2 particles on dynamic recrystallization in TiB2-reinforced Al–Zn–Mg–Cu–Zr during hot compression

We investigated the microstructure evolution of a 6 wt% TiB2-reinforced Al–Zn–Mg–Cu–Zr composite subjected to hot compression at temperatures within the range 370 °C–490 °C, at strain rates between 0.001 s−1 and 10 s−1. The microstructure evolution was characterized by electron backscatter diffraction and transmission electron microscopy. Dynamic recovery and dynamic recrystallization mechanisms were analyzed, with a focus on nucleation at original grain boundaries and TiB2 particles. The results show that recovery is the main dynamic softening mechanism due to the high dislocation mobility in the Al matrix. However, low temperature and high strain rate results in a large number of small recrystallized grains, whereas high temperature and low strain rate results in a few large recrystallized grains. Dynamic recrystallization is mainly attributed to particle-stimulated nucleation occurring near TiB2 particles/clusters, especially TiB2 particles/clusters at grain boundaries. Relations between the observed dynamic recrystallization and the Zener-Hollomon parameter are discussed.

Hot compression deformation behavior and microstructure evolution of Al-0.5Mg-0.4Si alloy

The hot compression tests for as-cast Al-0.5Mg-0.4Si alloy were performed on Gleeble-3500 thermo-mechanical simulator under temperatures of 350–500 °C and strain rates of 0.01–10 s−1. Based on the experimental data, a strain-compensated Arrhenius constitutive model was established by exponential function coupling strain. The hot processing map of Al-0.5Mg-0.4Si alloy was established, and the reasonable processing parameters were obtained. The microstructural evolution and dynamic softening mechanisms of the alloy were analyzed using electron backscatter diffraction (EBSD). A detailed description of the evolution of dislocation and the dislocation density during the deformation process was provided. The results indicate that the softening mechanisms of Al-0.5Mg-0.4Si alloy are dynamic recovery (DRV) and continuous dynamic recrystallization (CDRX). The dynamic recovery mechanism is related to the cross slip of the screw dislocation. High temperature and low strain rate are conducive the occurrence of CDRX. This study provides comprehensive guidance for the hot processing of Al-0.5Mg-0.4Si alloy from both macroscopic and microscopic perspectives.

Determination of Hot Workability of 5Cr5MoSiV1 Steel Based on Hot Processing Map

The evaluation of the hot workability of 5Cr5MoSiV1 steel with high deformation resistance is crucial for the controllability of the hot forging process. Based on the isothermal compression at deformation temperature of 950–1200 °C and strain rate of 0.01–10 s−1, the flow behavior of 5Cr5MoSiV1 steel is demonstrated. As the strain rate increases, the typical characteristics of the true stress–strain curve indicate that the dynamic softening mechanism changes from dynamic recrystallization to dynamic recovery. Moreover, the hot working window determined by the hot processing map from the modified J–C constitutive model is constructed for the forging process of the material. Through microstructure verification, the optimal hot working window is within the range of deformation temperature from 1000 to 1185 °C and strain rate from 0.01 to 0.202 s−1. Furthermore, the forging upsetting tests of the large cylindrical specimens are used to confirm the insecurity of hot deformation parameters outside the optimum hot working window. The implementation of this study can provide a theoretical basis for the determination of hot forging process parameters for 5Cr5MoSiV1 steel.

Delineating the role of dynamic and static recrystallization during hot working of nickel-based superalloy (IN600)

In the presented research, the dynamic working of nickel-based (IN600) superalloy was performed and the micro-mechanisms affecting the deformation behaviour were closely monitored, particularly the role of static and dynamic recrystallization. Hot deformation flow stress response indicated an increase in the true stress value with an increase in strain rate and decrease in temperature. The constitutive calculations indicated that deformation progressed mainly due to dislocation climb motion. The hot workability map indicated a peak power dissipation efficiency (PDE) of 0.39 in two working domains. The microstructural evolution in the hot deformed specimens depicted a consistent increase in dynamic softening at temperature ≥ 1000 °C, whereas, a steady decline in the extent of dynamic softening is observed with increase in strain rate from 0.01 s−1 to 1 s−1. The mechanism for microstructural evolution in this range (0.01–1 s−1) was identified as discontinuous dynamic recrystallization (DDRX). Moreover, at the highest strain rate of 10 s−1, a sudden surge in the recrystallization fraction was observed, which was attributed to the combined effect of DDRX and static recrystallization (SRX). Additionally, this study shows that the presence of twin boundaries (TBs) contributes to dynamic softening by serving as sites for nucleation of strain-free grains.

A study on the collaborative deformation mechanisms of continuous and discontinuous dynamic recrystallization under low strain rates for the Ti6455x alloy with a low activation energy

To reveal the collaborative dynamic recrystallization mechanisms occurring only at low strain rates, the Ti6455x titanium alloy was designed and prepared by hot deformation. The microstructure, activation energy, and the dynamic recrystallization (DRX) process under different strain rates and temperatures were investigated, with a corresponding mechanism revealed for the first time. Results show that at low strain rates of 0.01 and 0.001 s-1, as temperature from 1173 to 1223 K, the grain size decreases, jagged bumps appear at the grain boundaries and new small grains are produced. The activation energy of Ti6455x titanium alloy is 128.63 kJ/mol. Quantitative calculations revealed that the thermal deformation mechanisms depend on the dissipation efficiency factor, η. With an increasing value of η, the dynamic softening mechanism changes from dynamic reversion (DRV) to DRV and continuous dynamic recrystallization (CDRX). While with a high η value, CDRX and discontinuous dynamic recrystallization (DDRX) occur at a temperature of 1223 K, and a strain rate of 0.001 s-1. The collaborative deformation process proceeds because: low activation energy titanium alloys facilitate the rotation of sub-grain boundaries, while dislocations can easily migrate. This condition enables CDRX to occur, leading to the refinement of grains and producing jagged grain boundaries. Then, CDRX provides nucleation sites for DDRX, promoting grain boundary migration and breaking down grains. This mechanism can significantly refine the grain size and improve mechanical properties. It is shown that both the design of low activation energy alloys and controlling hot processing conditions are effective in the development of high-strength titanium alloys.

Investigation on hot deformation behavior and microstructure evolution of superaustenitic stainless steel S31254 during elevated temperature compression testing

The study thoroughly investigated the hot deformation behavior and microstructure evolution of superaustenitic stainless steel S31254. Hot compression tests were conducted at temperatures ranging from 950 °C to 1200 °C and strain rates of 0.01–10 s−1. The flow behavior of S31254 is influenced by adiabatic heating, particularly at high strain rates. The critical conditions of dynamic recrystallization for various deformation conditions were calculated based on the “double differential method.” An rise in deformation temperature or a reduction in strain rate reduces critical stress. Using the Arrhenius equation and Zener-Hollomon parameter to represent the deformation parameters, a linear connection between peak stress and dynamic recrystallization critical conditions was determined. Electron backscattering diffraction and transmission electron microscopy were used to characterize the microstructure under various deformation conditions. The dynamic softening of superaustenitic stainless steel is mainly achieved through dynamic recrystallization. The recrystallized grains are driven by distorted energy to nucleate preferentially at high-angle grain boundaries and grow towards high misorientations. Discontinuous dynamic recrystallization characterized by grain boundary bowing out is the main recrystallization mechanism in S31254. However, at high temperatures and low strain rates (1200 °C, 0.01 s−1), the dynamic recrystallization process shifts from discontinuous to continuous, with subgrain coalescence serving as the nucleating mode.

AlNbTiVZr refractory high entropy alloy combining exceptional high-temperature performance and excellent ductility fabricated by laser direct energy deposition

In this study, a new refractory high entropy alloy (RHEA) AlNbTiVZr is fabricated by laser direct energy deposition (LDED), and an investigation is conducted to explore the hot deformation. The body-centered cubic (BCC) phase structure and a small number of close-packed hexagonal Laves intermetallic phases of RHEA are predicted by combining XRD with the calculation of empirical parameters. Compression tests are carried out at different temperatures, and the results show that no fracture occurs when the strain reaches 50% at any of the temperatures tested while exhibiting a high yield stress. The dynamic softening effect is enhanced as the temperature increases and the yield stress decreases significantly. A slight hardening trend is observed during the steady-state flow stage of the stress-strain curve. The softening of RHEA is mainly caused by dynamic reversion (DRV) and assisted dynamic recrystallization (DRX), where the atomic mobility at the grain boundaries increases with temperature, promoting the creation of recrystallized grains.

Effects of service stress on the deformation behavior and microstructures of Zn-0.5Mg-0.05Fe alloy from ambient to high temperatures

To overcome challenges in the traditional melt casting process of zine alloys, such as oxidative burnout, compositional segregation, and grain coarsening, this study carried out hot compression deformation tests on Zn-0.5Mg-0.05Fe alloys prepared by powder metallurgy. The results show that increasing deformation temperature and decreasing strain rate reduce rheological stress. The hot compression deformation process exhibits three phases, as rheological stress increases, work hardening, dynamic softening, and steady-state fluidization are observed, respectively. An intrinsic equation for the hot compression process is derived as = 1.334 × 1010 × [sinh(0.0053σ)]7.62947exp(-109.931691/RT). Processing conditions for Zn-0.5Mg-0.05Fe alloy are determined from a processing map, suggesting that a safe zone of 25°C–130 °C deformation temperatures with 0.13s−1-0.36s−1 strain rates, and 120°C–200 °C deformation temperatures with 0.01s−1-0.6s−1 strain rates. Electron Back-scattering Patterns (EBSD) and Transmission Electron Microscope (TEM) results show both discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) during the hot deformation compression process. DRX reduces deformation resistance, refines the grains, and improves the mechanical properties of the alloys. This study provides theoretical insights and process guidance for preparing degradable zinc alloys with excellent mechanical properties.

Quantification of static softening process and its effects on work hardening characteristics of a typical high strength steel during multi-pass deformation

Heavy components of 300 M steel are usually manufactured by multi-pass forging. It is necessary to study the flow characteristics of 300 M steel during multi-pass deformation, which helps to regulate the flow behaviors during the actual forging process. In the study, multi-pass compression experiments are conducted on the Gleeble-3500 device to mimic the forging process of 300 M steel. Results show that the deformation parameters and inter-pass holding parameters can affect the work hardening rate significantly. It can be ascribed to coupling effects of dynamic softening and static softening behaviors. A unified static softening kinetics model is established to evaluate the coupling effects of static recovery, static recrystallization, and metadynamic recrystallization on the static softening behaviors. The established static softening kinetics model shows high prediction accuracy with a reliability of 0.99605. Furthermore, a new constitutive model is established to describe the effects of dynamic softening and static softening on the flow stress during multi-pass deformation. The prediction accuracy of the new constitutive model is 0.98897 with a mean absolute error of 4.075%, which demonstrates that the established constitutive model is reliable.