Influence of rare earth Ce on hot deformation behavior of as-cast Mn18Cr18N high nitrogen austenitic stainless steel

The hot deformation behavior of Mn18Cr18N and Mn18Cr18N+Ce high nitrogen austenitic stainless steels at 1173-1473 K and 0.01-1 s^(-1) were investigated by thermal compression tests.The influence mechanism of Ce on the hot deformation behavior was analyzed by Ce-containing inclusions and segregation of Ce.The results show that after the addition of Ce,large,angular,hard,and brittle inclusions(TiN-Al_(2)O_(3),TiN,and Al_(2)O_(3)) can be modified to fine and dispersed Ce-containing inclusions(Ce-Al-O-S and TiN-Ce-Al-O-S).During the solidification,Ce-containing inclusions can be used as heterogeneous nucleation particles to refine as-cast grains.During the hot deformation,Ce-containing inclusions can pin dislocation movement and grain boundary migration,induce dynamic recrystallization(DRX)nucleation,and avoid the formation and propagation of micro cracks and gaps.In addition,during the solidification,Ce atoms enrich at the front of solid-li-quid interface,resulting in composition supercooling and refining the secondary dendrites.Similarly,during the hot deformation,Ce atoms tend to segregate at the boundaries of DRX grains,inhibiting the growth of grains.Under the synergistic effect of Ce-containing inclusions and Ce segregation,although the hot deformation resistance and hot deformation activation energy are improved,DRX is more likely to occur and the size of DRX grains is significantly refined,and the problem of hot deformation cracking can be alleviated.Finally,the microhardness of the samples was measured.The results show that compared with as-cast samples,the microhardness of hot-deformed samples increases signific-antly,and with the increase of DRX degree,the microhardness decreases continuously.In addition,Ce can affect the microhardness of Mn18Cr18N steel by affecting as-cast and hot deformation microstructures.

Hot deformation behavior of Fe–27.34Mn–8.63Al–1.03C lightweight steel

Hot compression tests were performed to investigate the hot deformation behavior of Fe–27.34Mn–8.63Al–1.03C lightweight steel and optimize the hot workability parameters. The temperature range was 900–1150℃ and the strain rate range was 0.01–5 s^(-1)on a Gleeble-3800 thermal simulator machine. The results showed that the flow stress increased with decreasing deformation temperature and increasing strain rate. According to the constitutive equation, the activation energy of hot deformation was 422.88 kJ·mol^(-1). The relationship between the critical stress and peak stress of the tested steel was established, and a dynamic recrystallization kinetic model was thus obtained. Based on this model, the effects of strain rate and deformation temperature on the volume fraction of dynamically recrystallized grains were explored. The microstructural examination and processing map results revealed that the tested steel exhibited a good hot workability at deformation temperatures of 1010–1100℃ and strain rate of 0.01 s^(-1).

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 of novel high-strength Mg-0.6Mn-0.5Al-0.5Zn-0.4Ca alloy

The hot compression behavior of as-extruded Mg-0.6Mn-0.5Al-0.5Zn-0.4Ca alloy was studied on a Gleeble-3500 thermal simulation machine.Experiments were conducted at temperatures ranging from 523 to 673 K and strain rates ranging from 0.001 to 1 s^(-1).Results showed that an increase in the strain rate or a decrease in deformation temperature led to an increase in true stress.The constitutive equation and processing maps of the alloy were obtained and analyzed.The influence of deformation temperatures and strain rates on microstructural evolution and texture was studied with the assistance of electron backscatter diffraction(EBSD).The as-extruded alloy exhibited a bimodal structure that consisted of deformed coarse grains and fine equiaxed recrystallized structures(approximately 1.57μm).The EBSD results of deformed alloy samples revealed that the recrystallization degree and average grain size increased as the deformation temperature increased.By contrast,dislocation density and texture intensity decreased.Compressive texture weakened with the increase in the deformation temperature at the strain rate of 0.01 s-1.Most grains with{0001}planes tilted away from the compression direction(CD)gradually.In addition,when the strain rate decreased,the recrystallization degree and average grain size increased.Meanwhile,the dislocation density decreased.Texture appeared to be insensitive to the strain rate.These findings provide valuable insights into the hot compression behavior,microstructural evolution,and texture changes in the Mg-0.6Mn-0.5Al-0.5Zn-0.4Ca alloy,contributing to the understanding of its processing-microstructure-property relationships.

Hot deformation behavior and microstructure evolution of Be/2024Al composites

The high temperature compression test of Be/2024Al composites with 62wt%Be was conducted at 500–575℃ and strain rate of0.003–0.1 s^(-1).The strain-compensated Arrhenius model and modified Johnson–Cook model were introduced to predict the hot deformation behavior of Be/2024Al composites.The result shows that the activation energy of Be/2024Al composites was 363.364 k J·mol^(-1).Compared with composites reinforced with traditional ceramics,Be/2024Al composites can be deformed with ultra-high content of reinforcement,attributing to the deformable property of Be particles.The average relative error of the two models shows that modified Johnson–Cook model was more suitable for low temperature condition while strain-compensated Arrhenius model was more suitable for high temperature condition.The processing map was generated and a hot extrusion experiment was conducted according to the map.A comparation of the microstructure of Be/2024Al composites before and after extrusion shows that the Be particle deformed coordinately with the matrix and elongated at the extrusion direction.

Modeling of hot deformation behavior and prediction of flow stress in a magnesium alloy using constitutive equation and artificial neural network(ANN)model

The aim of the present study was to investigate the modeling and prediction of the high temperature flow characteristics of a cast magnesium(Mg-Al-Ca)alloy by both constitutive equation and ANN model.Toward this end,hot compression experiments were performed in 250-450℃and in strain rates of 0.001-1 s^(−1).The true stress of alloy was first and foremost described by the hyperbolic sine function in an Arrhenius-type of constitutive equation taking the effects of strain,strain rate and temperature into account.Predictions indicated that unlike low strain rates and high temperature with dominant DRX activation,in relatively high strain rate and low temperature values,the precision of the models become decreased due to activation of twinning phenomenon.At that moment and for a better evaluation of twinning effect during deformation,a feed-forward back propagation ANN was developed to study the flow behavior of the investigated alloy.Then,the performance of the two suggested models has been assessed using a statistical criterion.The comparative assessment of the gained results specifies that the well-trained ANN is much more precise and accurate than the constitutive equations in predicting the hot flow behavior.

Mechanical Behaviors and Microstructural Characteristics of TC11 Alloy during Hot Deformation

The mechanical behaviors and the microstructural characteristics of TC11 alloy with quenched martensite microstructure during hot compressive deformation were investigated. It shows that at various temperatures and strain rates, the stress strain curves firstly exhibit strain hardening, then strain softening and finally reach the steady deformation state; in the meanwhile, the initial lamellar microstructure is transformed into the equiaxed and uniform one through dynamic recrystallization. It shows that the present TC11 alloy has different Z D relationships in relatively lower temperature (RLT) range and relatively higher temperature (RHT) range, which is believed to be due to different deformation activation energies. During RHT deformation, dynamic recrystallization occurs in both α phases and β phases, but during RLT deformation, dynamic recrystallization only occurs in α phases and in the meanwhile β phases undergo a process of precipitation and growth.

Analysis of the hot deformation of ZK60 magnesium alloy

Hot deformation of cast-homogenized and extruded(in both the extrusion and transverse directions)ZK60 magnesium alloy was conducted using the Gleeble®3500 thermal-mechanical simulation testing system.A new approach to model the high temperature constitutive behavior of the alloy was done using two well-known equations(i.e.hyperbolic sine and Ludwig equations).For this approach,the deformation conditions were divided into regimes of low and high temperature and strain rate(four regimes).Constitutive model development was conducted in each regime and the material parameters(P)were evaluated as strain,strain rate and temperature-dependent variables;P(ε,ε,T).Using this approach,the flow curves were predicted with high accuracy relative to the experimental measurements.Moreover,detailed information on the evolution of hot deformation activation energy was obtained using the modified hyperbolic sine model.Using the modified Ludwig equation,details of strain hardening and strain rate sensitivity of the ZK60 material during hot deformation were obtained.

Dynamic Recrystallization Behavior of 7056 Aluminum Alloys during Hot Deformation

To investigate the dynamic recrystallization behavior of 7xxx aluminum alloys,the isothermal compression tests were carried on the 7056 aluminum alloy in the temperatures range of 320-440℃and in the strain rates range of 0.001-1 s^(-1).In addition,the microstructure of samples were observed via electron back scanning diffraction microscope.According to the results,true stress and true strain curves were established and an Arrhenius-type equation was established,showing the flow stress increases with the temperature decreasing and the strain rate increasing.The critical strain(ε_(c))and the critical stress(σ_(c))of the onset of dynamic recrystallization were identified via the strain hardening rate and constructed relationship between deformation parameters as follows:ε_(c)=6.71×10^(-4)Z^(0.1373) and σ_(p)=1.202σ_(c)+12.691.The DRX is incomplete in this alloy,whose volume fraction is only 20%even if the strain reaches 0.9.Through this study,the flow stress behavior and DRX behavior of 7056 aluminum alloys are deeply understood,which gives benefit to control the hot working process.

Anisotropic NdFeB Magnet Fabricated by Single Stroke Hot Deformation

The general hot deformation process consists of two steps, hot pressing and die-upsetting in order to obtain the anisotropic NdFeB magnet. This is the first report that the high anisotropy NdFeB magnets can be fabricated by single stroke hot deforming the isotropic magnet. The magnetic properties of those materials are: coercivity _iH_c -11 kOe, remanence B_r-12 kG, and the maximum energy product (BH)_max-28 MG.Oe.

Effect of Hot Deformation on Microstructure and Hardness of In-situ TiB_2/7075 Composite

Hardness of the TiB2/7075 composite increased with increasing deformation temperature In the annealed TiB2/7075 composite, a great amount of fiber-like MgZn2 phases (about I μm in length) and small MgZn2 phases (about 100 nm in size) were precipitated nearby the grain boundaries where the TiB2 particles exist. After deformation at 3000 C, some of the large pre- cipitates and all the small precipitates in these area dissolved into the matrix, meanwhile, fine precipitates were formed in grains. After deformation at 450℃, all the precipitates in the an- nealed composite dissolved into the matrix, and new phases were precipitated in grains. The dissolution of the large fiber-like precipitate makes the saturation level of the matrix increased and leads to an increased solution hardening and natural aging, which contribute much to the hardening effect.

Texture analysis of ultra-high coercivity Sm_(2)Co_(7) hot deformation magnets

Bulk anisotropic Sm_(2)Co_(7) nanocrystalline magnets were successfully prepared by hot deformation process using spark plasma sintering technology.The coercivity of the isotropic Sm_(2)Co_(7) nanocrystalline magnet is 34.76 kOe,further,the ultra-high coercivity of 50.68 kOe is obtained in the anisotropic hot deformed Sm_(2)Co_(7) magnet when the height reduction is70%,which is much higher than those of the ordinarily produced hot deformed Sm_(2)Co_(7) magnet.X-ray diffraction(XRD)analysis shows that all the samples are Sm_(2)Co_(7) single phase.The investigation by electron backscatter diffraction indicates that increasing the amount of deformation is beneficial to the improvement of the(001) texture of Sm_(2)Co_(7) magnets.The Sm_(2)Co_(7) nanocrystalline magnet generates a strong c-axis crystallographic texture during large deformation process.

Rare earth permanent magnets prepared by hot deformation process

Hot deformation is one of the primary methods for fabricating anisotropic rare earth permanent magnets. Firstly,rapidly quenched powder flakes with a nanocrystal structure are condensed into fully dense isotropic precursors using the hot-pressing process. The prepared isotropic precursors are then hot-deformed to produce high-anisotropy uniaxial bulk rare earth permanent magnets and a highly textured structure is produced via this process. The resulting magnets possess many advantages such as near-net-shape, outstanding corrosion resistance, and ultrafine-grain structure. The influence of the preparation parameters utilized in the hot-pressing and deformation processes on the magnetic properties and microstructure of the permanent magnets are systemically summarized in this report. As a near-net-shape technique, the hot deformation process has notable advantages with regard to the production of irregular shapes, especially for radially oriented ringshaped magnets with high length-diameter ratios or thin walls. The difficulties associated with the fabrication of crack-free,homogeneous, and non-decentered ring-shaped magnets are substantially resolved through an emphasis on mold design,adjustment of deformation parameters, and application of theoretical simulation. Considering the characteristics of hotdeformed magnets which include grain shape and size, anisotropic distribution of intergranular phases, etc., investigation and improvement of the mechanical and electric properties, in addition to thermal stability, with the objective of improving the application of hot-deformed magnets or ring-shaped magnets, is of practical significance.

Hot Deformation Behavior of Aluminum Alloy 5083 for Automotive and Aviation Applications

This article concentrates on the investigation of hot deformation behavior of conventionally rolled commercial grade AA5083 alloy( Al-4. 5Mg),for automotive and aviation applications. The superplastic response of the alloy was investigated at high strain rates( ≥10- 3s- 1),and a temperature range of 400 ℃ to 550 ℃. An elongation to failure of 201% was achieved at low temperature( 425 ℃) and high strain rate( 10- 2s- 1),which indicates sufficient ductility under hot deformation for manufacturing of extremely complex shapes using superplastic forming technology. Furthermore,the alloy exhibited a maximum elongation of about 470% at strain rate of 10- 3s- 1and a temperature of 525 ℃. The deformation and failure mechanisms at both the critical conditions were studied as a function of strain rate and temperature. The contributions of strain-rate sensitivity and strain hardening were analyzed in relation to the observed tensile ductilities. Deformation mechanism of the alloy was also investigated with reference to Strain rate sensitivity index( m) and Activation energy( Q) for the given test condition. Empirical calculations reveal that dominant deformation mechanism responsible for hot deformation of the alloy is grain boundary sliding( GBS),which is further supported by deformed surface examination using scanning electron microscopy( SEM). Fracture surfaces of the samples deformed to failure,at relatively higher and lower strain rates,was examined to investigate the micromechanisms governing failure. Phenomenon of cavity nucleation,growth and coalescence was observed to be the failure mechanism in the investigated alloy.

Hot ductility of DSS and its microstructure observation during hot deformation

<正>selecting several typical DSS 00Cr22Ni5Mo3N,00Cr21Ni2Mn5N and 00Cr25Ni7Mo4N as research materials,hot ductility characteristic of DSS was studied and microstructure evolution during hot compression was observed.The results show that the optimum hot ductility temperature range of DSS is 1 050~1 200℃.00Cr25Ni7Mc4N exhibits the worst hot ductility and 00Cr21Ni2Mn5N has similar hot ductility to 00Cr22Ni5Mo3N.During hot compression,austenite of DSS mainly occurs dynamic recovery,the ferrite of 00Cr22Ni5Mo3N,00Cr21Ni2Mn5N can perform dynamic recovery and recrystallization,but only dynamic recovery can be observed in the ferrite of 00Cr25Ni7Mo4N.

Microstructure and Hot Deformation Behavior of Mg-9Al-3Si-0.375Sr-0.78Y Alloy

Using Gleeble-3500 thermal simulator,the high temperature plastic deformation behavior and microstructure evolution of Mg-9Al-3Si-0.375Sr-0.78Y alloy are investigated at the temperature of 523 K?673 K and the strain rate of 10^(-3)s^(-1) 10 s^(-1).True strain-true stress curves show the characteristics of the typical dynamically recrystallization process.The Arrhenius constitutive equation of the hyperbolic model is established.The average activation energy and the strain rate sensitivity index are,respectively,221.578 kJ·mol^(-1) and 0.137.The result shows that theα-Mg phase exhibits dynamic recrystallization (DRX)characteristics obviously.But no DRX occurs in the β-Mg_(17)Al_(12) phase.Hot deformation does not affect the primary Mg_(2)Si phase.Under the conditions of low temperature (523 K?673 K) and high strain rate(1 s^(-1) 10 s^(-1)),the flow instability and macro-defects such as crack appear in the specimens.However,there are finer recrystallization grains.Under the conditions of high temperature(≥673 K)or low strain rate,the microstructure of the alloy shows good homogeneity.The size of the primary Mg_(2)Si phase is uniform,the size of the β-Mg_(17)Al_(12) phase is small,and the distribution of the β-Mg_(17)Al_(12) phase is uniform.

Investigation of Hot Deformation Behavior of SNCM8 Alloy Steel

Plastic flow behavior of the SNCM8 steel was investigated by performing hot compression tests within the temperature range of 850˚C to 1200˚C and strain rates of 0.01 s−1 to 10 s−1. Constitutive modeling based on dynamic recrystallization was established, in which Cingara equation was applied to represent work hardening up to peak stress and Avrami equation to describe dynamic softening beyond peak stress up to steady state. It was found that stress-strain responses predicted by the combined model fairly agreed with experimentally resulted curves for the particular conditions. The correlation coefficient (R) of 0.9485 and average absolute relative error (AARE) of 2.3614% was calculated for the modeled flow curves.

Hot Deformation and Modeling of Flow Stress for a Ti-containing HSLA Steel

单个舞台和双阶段打断了热耐压试验因为模仿热滚动为包含 Ti HSLA 钢(10Ti ) 被执行了。热滚动的物理模拟在进行中在 850-1150 度 C 和 0.1-60 s * 的种类率正在利用一个 Thermecmastor-Z 模拟器 * 减 **1。为剩余种类比率 lambda 的一个模型被设计，并且就剩余紧张而言的流动应力的一个模型被获得了。以各种各样的种类率的热变丑行为也被学习了。(编辑作者摘要) 13 个裁判员。

Hot Compressive Deformation Characteristics of Al-9.3Zn-2.4Mg-1.1Cu Alloy

To understand the hot compression deformation characteristics of the self-developed Al-9.3Zn-2.4Mg^(-1).1Cu alloy,the hot compression tests of Al-9.3Zn-2.4Mg^(-1).1Cu alloy were investigated by Gleeble 1500 thermo-mechanical simulator to determine the best hot processing conditions.The hot deformation temperatures were 300,350,400,and 450℃,and the strain rates were 1,0.1,0.01,and 0.003 s^(-1),respectively.Based on the experimental results,the constitutive equation and hot processing maps are established,and the corresponding strain rate and temperature-sensitive index are analyzed.The results show that Al-9.3Zn-2.4Mg^(-1).1Cu alloy has a dynamic softening trend and high strain rate sensitivity during the isothermal compression process.The hot deformation behavior can be described by an Arrhenius-type equation after strain compensation.The temperature has a negligible effect on the hot processing properties,while a low strain rate is favorable for the hot working of alloy.The processing maps and microstructure show that the optimal processing conditions were in the temperature range of 400-450℃and strain rate range of 0.003-0.005 s^(-1).

Adverse effect of niobium and boron on hot deformation behavior of sulfur-containing steel

The hot deformation behaviors of sulfur-containing gear steel 20MnCr5 containing three different contents of Nb and B(0,0.021%Nb,and 0.024%Nb-0.0022%B)were investigated.Hot compression and tenssion tests were carried out by Gleeble3800 at the austenite region from 850 to 1150℃and the adverse effects of Nb and B were analyzed by the fracture,microstructure and precipitate observations.Hot compression tests showed that the proportions of instable area in hot processing maps of 0.021%Nb and Nb-B steels were higher and the deformability of Nb free steel was better.The tensile deformation experiments showed that the reduction areas of Nb free,0.021%Nb and Nb-B steels were 92%-99%,84%-98%and 67%-97%,respectively.The addition of Nb or Nb and B inhibited the dynamic recrystallization during hot deformation,and consequently,more deformed grains were then formed in 0.021%Nb and Nb-B steels thus to obtain the microstructure with worse uniformity and then deteriorate the deformability.In addition,the interaction between inclusions and microalloyed elements was also significant.NbC particles of 0.021%Nb and Nb-B steels dynamically precipitated during deformation and precipitated together with MnS thus to worsen the deformability,resulting in the decrease of reduction area.