Hot Deformation Process Research Articles

Hot deformation characteristics and processing map of Ti-25Al-14Nb-2Mo-1Fe alloy under hot working process conditions

The hot working process is a proven technique to manufacture special aviation components. However, a suitable working process window for Ti-25Al-14Nb-2Mo-1Fe alloy has not been established. In this work, the hot deformation characteristics of Ti-25Al-14Nb-2Mo-1Fe alloy was systematically studied. In addition, the processing map of the alloy was established to further analyze the inherent machinability properties. Through the processing map analysis and microstructural observation, the instability and stability domains were identified. The optimum working parameters for the alloy were obtained (950–970 ℃/0.001–0.01 s−1, 1015–1100 ℃/0.001–0.01 s−1), which is conducive to optimizing the hot working parameters.

Optimization of hot deformation processing parameters for as-extruded 7005 alloys through the integration of 3D processing maps and FEM numerical simulation

The hot deformation behavior and microstructure were investigated for as-extruded 7005 alloys, which is the same as the billet state in real applications in the commercial forging process. It provides a more accurate understanding of the hot deformation flow behavior and microstructure evolution of 7005 alloys for commercial forging processing engineers and mold designers. The compression tests were conducted in temperatures 300–550 °C and strain rates 0.001–1 s−1 using an isothermal hot compression test. The power dissipation efficiency (η) and instability parameter (ξ) were calculated according to the true stress-true strain data obtained from the thermal compression tests. 3D thermal processing maps including the true strains were generated for as-extruded 7005 alloys, and the optimal processing conditions were selected according to η, ξ, and microstructure. The results showed that η increased with increasing temperature but decreased with increasing strain rate. The size of the instability region expanded with decreasing temperature and with increasing strain rate. An η < 0.20 is generally designated an instability region. Microscopic defects such as micro cracks and flow localizations could be observed, and the microstructures of the stability regions showed fine recrystallized grains with η above 0.30. The optimal processing conditions were determined to be a processing temperature between 425 and 500 °C and a strain rate between 0.1 and 0.01 s−1. This study is the first to optimize the closed die forging processing parameters through integration of 3D processing maps and a numerical simulation for a hub based on its real workpiece appearance. A function for prediction of the microstructure evolution is provided using commercial simulation software to help mold designers and forging processing engineers reduce the trial time.

The Microstructure Evolution and Dynamic Recrystallization Mechanism of Cu-1.1–Ni-0.7–Co-0.45–Si-0.3Cr Alloys during High-Temperature Deformation

Copper alloys with a combination of good electrical conductivity and mechanical properties are widely used in automotive electronics, large-scale integrated circuits, and other fields. In this study, a new type of Cu–Ni–Si alloy with added trace elements of Co and Cr was fabricated. Hot compression tests of this alloy at different temperatures and strain rates were conducted using a Gleeble-1500D simulator. Then, the microstructure transformation and precipitation behaviors of the Cu-1.1–Ni-0.7–Co-0.45–Si-0.3Cr alloy were studied during a hot deformation process. The results show that the hot deformation behavior of the Cu-1.1–Ni-0.7–Co-0.45–Si-0.3Cr alloy includes continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX). The intensity of the texture in the microstructure is decreased, and the randomness of the texture in the microstructure is increased together with the recrystallization progress. The degree of recrystallization of the new Cu-1.1–Ni-0.7–Co-0.45–Si-0.3Cr alloy is increased when the hot deformation temperature rises. Additionally, the results indicate that there are two types of precipitates which are formed in the alloy during the hot deformation process. These two precipitates can pin dislocations and grain boundaries, and therefore, they significantly improve the hot compression resistance of the Cu-1.1–Ni-0.7–Co-0.45–Si-0.3Cr alloy.

Morphological evolution and dissolution mechanisms of γ′ phase in a novel HIPed P/M superalloy in hot deformation process

Isothermal compressive tests of a new hot isostatic pressed (HIPed) powder metallurgy (P/M) superalloy are performed at diverse deformation amounts, strain rates, and elevated temperatures. The impacts of hot compression parameters on the morphological evolution and dissolution behavior of γ' phase are studied. Results show that the morphology of γ′ phase changes from the various initial shapes (irregular, split-off branch, dendrite, butterfly-like, and cauliflower) to spherical, due to the overlap of the γ'/γ interface energy and the coherent strain energy related to lattice misfit. Besides, the dislocation accumulation leads to the increased local stress and enhances the spheroidization behavior of γ' phase. Increasing temperature/true strain or decreasing strain rate, the dynamic dissolution behavior of γ' phase is obvious. It is because the dislocation/ vacancies-assisted element diffusion is rapid at high deformation temperatures/true strains, and the low strain rate can provide the enough time for element diffusion. The substantial dissolution of γ' phase at 1140 °C and 1170 °C is also related to the deformation temperature approaching and exceeding the γ' solvus temperature (1150 °C), respectively. Additionally, the decreased fraction of γ' phase is also related to the high γ'/γ interfacial energy. To quantitatively describe the dissolution behavior of γ′ phase, a dynamic dissolution kinetics model is proposed, and the correlation coefficient between the predicted and experimental values is 0.990. It indicates that the proposed model can precisely depict the dissolution behavior of γ′ phase. The findings in this work can provide the theoretical guidance to optimize deformation parameters, as well as control the morphology and fraction of γ′ phases.

Study on hot deformation behavior of homogenized Mg-8.5Gd-4.5Y-0.8Zn-0.4Zr alloy using a combination of strain-compensated Arrhenius constitutive model and finite element simulation method

Isothermal hot compression experiments were conducted on homogenized Mg-8.5Gd-4.5Y-0.8Zn-0.4Zr alloy to investigate hot deformation behavior at the temperature range of 673–773 K and the strain rate range of 0.001–1 s − 1 by using a Gleeble-1500D thermo mechanical simulator. Metallographic characterization on samples deformed to true strain of 0.70 illustrates the occurrence of flow localization and/or microcrack at deformation conditions of 673 K/0.01 s − 1, 673 K/1 s − 1 and 698 K/1 s − 1, indicating that these three deformation conditions should be excluded during hot working of homogenized Mg-8.5Gd-4.5Y-0.8Zn-0.4Zr alloy. Based on the measured true stress-strain data, the strain-compensated Arrhenius constitutive model was constructed and then incorporated into UHARD subroutine of ABAQUS software to study hot deformation process of homogenized Mg-8.5Gd-4.5Y-0.8Zn-0.4Zr alloy. By comparison with measured force-displacement curves, the predicted results can describe well the rheological behavior of homogenized Mg-8.5Gd-4.5Y-0.8Zn-0.4Zr alloy, verifying the validity of finite element simulation of hot compression process with this complicated constitutive model. Numerical results demonstrate that the distribution of values of material parameters (α, n, Q and ln A) within deformed sample is inhomogeneous. This issue is directly correlated to the uneven distribution of equivalent plastic strain due to the friction effect. Moreover, at a given temperature the increase of strain rate would result in the decrease of equivalent plastic strain within the central region of deformed sample, which hinders the occurrence of dynamic recrystallization (DRX).

Hot Deformation Behavior and Processing Map Considering Strengthening Effect for Al–10.0Zn–3.0Mg–2.8Cu Alloy

In this paper, a hot processing map that takes into the strengthening effect into account is optimized for the Al-10.0Zn-3.0Mg-2.8Cu alloy, mainly considering the crushing and dissolving behavior of the insoluble phase. The hot deformation experiments were performed by compression testing with strain rates ranging from 0.001 to 1 s-1 and the temperature ranging from 380 to 460 °C. The hot processing map was established at the strain of 0.9. It exhibits that the appropriate hot processing region is located at the temperature from 431 to 456 °C and its strain rate is within 0.004-0.108 s-1. The recrystallization mechanisms and insoluble phase evolution were demonstrated using the real-time EBSD-EDS detection technology for this alloy. It is verified that the work hardening can also be consumed by the coarse insoluble phase refinement with the strain rate increasing from 0.001 to 0.1 s-1, besides the traditional recovery and recrystallization, but the effect of the insoluble phase crushing was weakened when strain rate increased over 0.1 s-1. Better refinement of the insoluble phase was around strain rate in 0.1 s-1, which exhibits adequate dissolving during the solid solution treatment, leading to excellent aging strengthen effects. Finally, the hot processing region was further optimized, so that the strain rate approaches 0.1 s-1 instead of 0.004-0.108 s-1. This will provide a theoretical support for the subsequent deformation of the Al-10.0Zn-3.0Mg-2.8Cu alloy and its' engineering application in aerospace, defense and military fields.

Dynamic recrystallization and constitutive equation of 15Cr-10Mn-Ni-N steel under hot deformation

Hot working as one of the indispensable processes for all metal materials can effectively refine the grain to improve the material properties. However, the study on the hot-deformation process of low-Ni austenitic stainless steel is scarce. In this study, we conducted single-pass compression tests to explore the dynamic recrystallization process of a low-Ni austenitic stainless steel with the chemical compositions of 15Cr-10Mn-Ni-N during deformation at various temperatures and strain rates. According to the experimental data, the true stress-strain curves are drawn and constitutive equation is established to predict the variations of stress and strain, accompanied with high accuracy. The microstructural characterizations show that the increase of deformation temperature leads to the occurrence of recrystallization in spite of the enhanced softening effect. In particular, the increase of strain rate promotes the refinement of grain size, and the average grain size significantly decreases from 200 µm to 20 µm under the compression condition of 1100 ℃ and 10 s−1. The decreasing grain size can compensate the sacrificing strength due to the reduction of Ni addition. The peak stress of 15Cr-10Mn-Ni-N austenitic stainless steel is 186 MPa at 1000 °C and 0.1 s−1, which is basically similar with the conventional austenitic stainless steel. Evidently, the austenitic stainless steel in this study has a cost-effective advantage because of its low Ni addition, i.e., we have the advantage of reducing material costs while maintaining the identical mechanical properties. Here the recrystallization process of 15Cr-10Mn-Ni-N austenitic stainless steel provides a basis for the selection of thermal processing parameters and a general understanding of the microstructure evolution.

Hot deformation constitutive analysis and processing maps of the as-cast and wrought Mg–2.5Gd–0.5Zr alloy

Hot deformation behavior and constitutive analysis of the as-cast and extruded Mg–2.5Gd–0.5Zr alloy were compared, using the shear punch testing (SPT) method in the temperature range of 623–723 K and shear strain rate range of 2.8 × 10–3–2.2 × 10–2 s–1. The respective hyperbolic-sine exponents of 2.67 and 2.59 as well as activation energies of 183 and 275 kJ mol–1 obtained for the as-cast and extruded alloy suggested grain boundary sliding as the prevailing deformation mechanism. Surprisingly, regardless of the instability domains, the efficiency of power dissipation exceeded 30% in most areas in the processing maps of both cast and wrought conditions. The safe and instability domains were rather similar in both processing maps. The relatively high potential of the as-cast alloy for hot deformation, despite its initial coarse grain size of about 150 µm, can be ascribed to the severe dynamic recrystallization (DRX) during hot deformation caused by Zr. This could be economically advantageous, as there would be no need for homogenization of the as-cast material before deformation processing. The most noticeable optimum window occurred in the temperature range of 673–723 K for both as-cast and extruded conditions with a vaster strain-rate range for the extruded one (5.6 × 10–3–1.4 × 10–2 s–1), owing to its initial finer grain size. The instability domains, however, took place for both conditions in the temperature range of 648–673 K and strain rates of about 5.6 × 10–3 s–1, manifested by cracking in the deformed zone, and also at temperatures higher than 673 K and medium to high strain rates.

Study on microstructure evolution and hot deformation behaviour of Cu–6.5Fe–0.3Mg alloy

The hot deformation behaviour and microstructure evolution of the Cu–6.5Fe–0.3Mg alloy were explored. The optimum hot working temperature of the alloy was 950°C and the strain rate was 10 s−1. The alloy underwent dynamic recovery (DRV) and dynamic recrystallisation (DRX) behaviour during hot compression. The density of the Fe phase particles increased significantly, and they were all aligned along the vertical compression direction. The α-Fe phase transformed to γ-Fe phase at 950°C. A large amount of α-Fe and γ-Fe phases effectively inhibited the DRX behaviour of the Cu–6.5Fe–0.3Mg alloy and significantly improved its thermal stability. The research on the hot deformation behaviour of the Cu–6.5Fe–X alloys had a theoretical guiding role in determining its hot working process. Highlights The optimal hot deformation process of Cu–6.5Fe–0.3Mg alloy was clarified. Constitutive equations and thermal working diagrams of the alloys are constructed Thermal deformation significantly increases Fe particle density, optimising its distribution. the transformation of α-Fe phase to γ-Fe phase during the hot compression at 950°C. The increasing in Fe phase significantly inhibits the dynamic recrystallization of the alloy.

EBSD Analysis of Hot Deformation Behavior of Oxide-Doped Molybdenum Alloys

Hot compression tests of Mo–1.5 wt% Al2O3/ZrO2 molybdenum alloys were carried out using the Gleeble–1500 simulator at 0.01 s−1−5 s−1 strain rates and 1000–1500 °C deformation temperatures. The microstructural changes of the alloy at 1000–1500 °C were studied. The changes in the hot deformation process for the Mo−1.5 wt% Al2O3/ZrO2 molybdenum alloys were analyzed by means of EBSD. The ZrO2 particles had a greater effect on improving the thermal deformation resistance of molybdenum alloys than did the Al2O3 particles. The activation energy of the molybdenum alloy doped with ZrO2 (403.917 kJ/mol) was lower than that of the molybdenum alloy doped with Al2O3 (440.314 kJ/mol). Due to the occurrence of recrystallization, the intensity of {100} the texture first increased and, then, dropped down with increase in the temperature, while the change law of {111} texture was the opposite. Above 1200 °C, the higher deformation temperature made the texture more random by lowering the texture intensity. The dislocation density was sacrificed to promote recrystallization. When dynamic recrystallization occurred, the sub–grain boundaries absorbed dislocations and transformed them into high–angle grain boundaries, resulting in a decrease in dislocation density and an increase in high–angle grain boundaries at high temperatures and low strain rates. At 0.01 s−1 strain rate, the average grain size of Mo–1.5 wt% ZrO2 alloy increased from 2.38 μm to 4.67 μm, and the proportion of large angle grain boundaries increased from 59.8% to 86.6%.

Deformation Mechanisms and Processing Maps for High Entropy Alloys (Presentation of Processing Maps in Terms of Zener-Hollomon Parameter): Review.

In this review paper, the hot compressive deformation mechanisms and processing maps of high-entropy alloys (HEAs) with different chemical compositions and crystal structures are analyzed. The stress exponent (n1) values measured from the series of compression tests for the HEAs performed at different temperatures and strain rates are distributed between 3 and 35, and they are most populated between 3 and 7. Power law breakdown (PLB) is found to typically occur at T/Tm ≤ 0.6 (where T is the testing temperature and Tm is the melting temperature). In AlxCrMnFeCoNi (x = 0-1) and AlxCrFeCoNi (x = 0-1) HEAs, n1 tends to decrease as the concentration of Al increases, suggesting that Al acts as a solute atom that exerts a drag force on dislocation slip motion at high temperatures. The values of activation energy for plastic flow (Qc) for the HEAs are most populated in the range between 300 and 400 kJ/mol. These values are close to the activation energy of the tracer diffusivity of elements in the HEAs ranging between 240 and 408 kJ/mol. The power dissipation efficiency η of the HEAs is shown to follow a single equation, which is uniquely related to n1. Flow instability for the HEAs is shown to occur near n1 = 7, implying that the onset of flow instability occurs at the transition from power law creep to PLB. Processing maps for the HEAs are demonstrated to be represented by plotting η as a function of the Zener-Hollomon parameter (Z = expQcRT, where R is the gas constant). Flow stability prevails at Z ≤ 1012 s-1, while flow instability does at Z ≥ 3 × 1014 s-1.

Hot Tensile Deformation Behavior and Constitutive Models of GH3230 Superalloy Double-Sheet.

In this paper, the hot tensile deformation of a GH3230 superalloy double-sheet was conducted under deformation temperatures ranging from 1123~1273 K and strain rates ranging from 0.001~0.2 s-1. The flow behavior of the GH3230 superalloy double-sheet was analyzed in detail. The hot tensile deformation process of the GH3230 superalloy double-sheet includes four stages of elastic deformation, strain hardening, steady state and fracture. The true stress decreases with the increasing deformation temperature and decreasing strain rate. The variation of the strain rate sensitivity index and strain hardening index with processing parameters were discussed. The average apparent activation energy for hot tensile deformation is 408.53 ± 46.96 kJ·mol-1. A combined Johnson-Cook and Hensel-Spittle model considering the couple effect of strain hardening, strain rate hardening and thermal softening was established to describe the hot tensile behavior of the GH3230 alloy double-sheet. Compared to Johnson-Cook model and Hensel-Spittle model, this model has the highest predicting accuracy. The average absolute relative error of true stress between the experimental and the predicted is only 2.35%.

Hot Workability of the Multi-Size SiC Particle-Reinforced 6013 Aluminum Matrix Composites.

The size and distribution of ceramic particles in aluminum matrix composites have been reported to remarkably influence their properties. For a single ceramic particle, the particle size is too small and prone to agglomeration, which makes the mechanical properties of the composites worse. When the ceramic particle size is too large, the particles and alloy at the interface are not firmly bonded, and the effect of dispersion distribution is not achieved, which will also reduce the mechanical properties of the composites. The multi-size ceramic particles are expected to improve this situation, while their effect on hot workability is less studied. In this study, the hot deformation behavior, constitutive model, processing map and SEM microstructure were investigated to evaluate the hot workability of multi-size SiC particle-reinforced 6013 aluminum matrix composites. The results showed that the increased deformation temperature and decreased strain rate could decrease flow stresses. The flow stress behaviors of the composites can be described by the sine-hyperbolic Arrhenius equation with the deformation activation energy of Q = 205.863 kJ/mol. The constitutive equation of the composites is ε&amp;nbsp;˙=3.11592×1013sinh0.024909σ4.12413exp-205863RT. Then, the hot processing map of the SiCp/6013 composites was constructed and verified by SEM observations. The rheological instability zone was in the region of a high strain rate. The optimal processing zone for composites was 450~500 °C and 0.03~0.25 s-1. In addition, the strain level was found to increase both the Q value and the area of the instability zone.

Hot Deformation Behavior and Processing Map of Cu-Bearing Ship Plate Steels

Hot Deformation Behavior and Processing Map of Cu-Bearing Ship Plate Steels

Ductile fracture prediction of ZK61M high-strength magnesium alloy sheet during hot deformation process

To predict the ductile fracture behavior of a ZK61M high-strength magnesium alloy sheet during hot deformation, experiments and numerical simulations were performed under specific conditions. According to the stress state parameters and fracture strain data obtained for different specimens, the undetermined coefficients of four fracture models were solved using the particle swarm optimization algorithm. According to the error evaluation results, the modified Wilkins model was the most accurate. This model was introduced into a finite element, and the results were compared with experimental results. The results indicated that the mean relative errors of the fracture displacement and fracture load of the tensile parts were <15%, and the mean relative error of the forming depth of the cylindrical parts was 13.88%. The established finite element model can accurately simulate the experimental process and predict the fracture position.

Proper (Nb,Fe) co-alloyed TiAl-based alloy with good hot deformation processing capability

In order to develop a proper (Nb,Fe) co-alloyed TiAl-based alloy with excellent hot deformation processing capability, avoiding the heavy alloying induced damage of service properties, the Ti–44Al–4Nb-0.5Fe-0.1B and Ti–44Al–2Nb–2Fe-0.1B alloys are designed and prepared. This paper mainly focuses on whether and why the hot deformation processing capability of the new alloys are improved. In view of this, thermo-compression experiments are carried out, hot deformation behavior is studied, constitutive equations are derived, hot processing maps are drawn, and hot deformation microstructure is studied. The results show that the Ti–44Al–2Nb–2Fe-0.1B alloy has lower true stress, moderate diffusion activation energy, lower stress exponent and larger hot processing window. Especially, the large hot processing window of Ti–44Al–2Nb–2Fe-0.1B alloy covers almost all the tested range of 1100 °C–1250 °C and 0.001 s−1-1.0 s−1, and meanwhile, the its power dissipation factor is higher. At lower temperatures of 1100 °C and 1150 °C, relatively more B2 phase in the Ti–44Al–2Nb–2Fe-0.1B alloy plays a good stress-strain coordination effect in the hot deformation process. At higher temperatures of 1200 °C and 1250 °C, the Ti–44Al–2Nb–2Fe-0.1B alloy is in the higher temperature phase region. Moreover, the compressed Ti–44Al–2Nb–2Fe-0.1B alloy has relatively lower dislocation density and more adequate dynamic recrystallization. In conclusion, all these results demonstrate that the Ti–44Al–2Nb–2Fe-0.1B alloy meets the design expectations, that is, this alloy with a proper (Nb,Fe) addition still has a very good hot deformation processing capability. At the same time, the Ti–44Al–2Nb–2Fe-0.1B alloy has a typical near-lamellar structure, rather than containing too much B2 phase or even containing lots of τ2 phase, so the good service properties can be expected.

Preparation of Anisotropic Nanocrystalline NdFeB Magnets from Amorphous Powders by One‐Step Hot Deformation

The preparation of nanocrystalline anisotropic NdFeB permanent magnets generally includes two steps, hot pressing (HP) and hot deformation (HD). Herein, one‐step HD process is proposed to fabricate NdFeB magnets using amorphous powders. The effects of deformation ratio on the microstructure, magnetic properties, and corrosion resistance are investigated. Compared to traditional HP and HD process, one‐step HD can significantly reduce the volume fraction of coarse‐grain zone in the magnet. The increase of deformation ratio can promote the formation of the textured platelet‐shaped grains and uniform grain boundary phase. The magnetic properties, temperature stability, and corrosion resistance of the magnets increase with increasing deformation ratio until 80%. The best magnetic properties with intrinsic coercivity Hcj = 930 kA m−1, remanence Jr = 1.17 T, and maximum energy product (BH)max = 263 kJ m−3 have been achieved for the magnet prepared by one‐step HD, which are comparable to those obtained by conventional HP/HD. In addition, different Co element segregations are observed in the magnets with different deformation ratios, which have important effects on the Curie temperature and thermal stability of the magnets. The results suggest that, by replacing HP/HD process and using amorphous powder, one‐step HD can simplify the process while maintaining good properties.

Deformation and recrystallization behavior of the new Ni-Co based superalloy ingot material prepared by electron beam smelting layered solidification

The hot deformation behavior of a Ni-Co based superalloy prepared by electron beam smelting layered solidification (EBSL-Ni-Co superalloy) was studied by hot compression tests under the temperature range of 1070–1180 °C and the strain rate range of 0.001–1 s−1 with a true strain of 0.693. The results show that the flow stress increases with the increase of strain rate and the decrease of deformation temperature, and the friction effect and adiabatic heating effect make the measured value of material flow stress higher than the real value. The hyperbolic sine Arrhenius equation was developed based on the γ' phase solution temperature, and the plastic flow stress model of the EBSL-Ni-Co superalloy was established. The deformation activation energies of the alloy in the γ + γ′ dual-phase and γ single-phase regions were 621.6 kJ/mol and 368.6 kJ/mol, respectively. The processing map of the superalloy was constructed based on the dynamic material model (DMM). Combined with the variation of microstructure, the optimum hot deformation processing conditions of the superalloy were determined. The increase of strain rate and the decrease of deformation temperature, the proportion of low-angle grain boundaries (LAGBs), and the reduction of recrystallization. Additionally, the hot deformation behavior of the EBSL-Ni-Co superalloy was found to be greatly influenced by the coarsening of γ' phase solution temperature.

Texture development and grain boundary phase formation in Ce- and Ce-La-substituted Nd-Fe-B magnets during hot-deformation process

In this study, the influence of Ce- and Ce-La-substitution for Nd in Nd-Fe-B magnets on their magnetic and microstructural changes in the course of the hot-deformation process was investigated to gain insight into further reducing the Nd content in fine-grained Nd-Fe-B hot-deformed magnets. We found that the [001] texture and microstructure of the RE-rich grain boundary phases, which are the factors that determine the remanence and coercivity of hot-deformed magnets, were deteriorated by the Ce- and Ce-La-substitution. This is because the volume fraction of the RE-rich liquid formed in the grain boundaries during the hot-press and hot-deformation decreased due to the Ce- and Ce-La-substitution, thereby increasing the friction between the 2:14:1 grains while the c-axes of grains were aligned by grain rotation and decreasing the RE concentration of grain boundary phases. In particular, the Ce-La-co-substitution further prevented the liquid formation within the grain boundaries of the magnets during hot-press and hot-deformation because the wettability of the RE-rich liquid on the 2:14:1 grains became poor when La was substituted for Nd in the 2:14:1 grains. These results indicate that there is room for further improvement in both the remanence and coercivity of the Ce- and Ce-La-substituted magnets by introducing additional liquid into the grain boundaries prior to hot-press and hot-deformation. By applying the Nd-Cu infiltration process to the melt-spun ribbons (intermediate infiltration, I-infiltration), both the remanence and coercivity of the Nd-saving (Nd0.7Ce0.3)-Fe-B and (Nd0.7Ce0.225La0.075)-Fe-B hot-deformed magnets were successfully improved.

Static Recrystallization Behavior of Low-Carbon Nb-V-Microalloyed Forging Steel

Static recrystallization is a method of tailoring the microstructure and mechanical properties of steels, which is important for microalloyed forging steels as the hot deformation process significantly affects their mechanical properties. In this paper, the static recrystallization behavior of a low-carbon Nb-V-microalloyed forging steel was investigated by double-pass hot compression tests at deformation temperature of 800–1100 °C and interruption time of 1–1000 s. The static recrystallization fractions were determined using the 2% offset method. The static recrystallization activation energy and the static recrystallization critical temperature (SRCT) of the experimental steel were determined. When the deformation temperature was higher than the SRCT, the recrystallization fraction curve conformed to the Avrami equation. When the deformation temperature was below the SRCT, the recrystallization curve appeared to plateau, which was caused by strain-induced precipitation. Before and after the plateau, the static recrystallization kinetics still obeyed the Avrami equation.