Nb-Si-based in situ composites are receiving attention as a substitute for Ni-based alloys in aerospace,while poor toughness limits its application.In this work,the toughness of Nb_(4)FeSi-containing Nb-Si-based alloy...Nb-Si-based in situ composites are receiving attention as a substitute for Ni-based alloys in aerospace,while poor toughness limits its application.In this work,the toughness of Nb_(4)FeSi-containing Nb-Si-based alloys was improved by hot deformation.The different deformation behaviors of reinforcements from traditional alloys,including the eutectoid decomposition ofβ-Nb_(5)Si_(3),and the stacking faults(SFs)and reorientation-induced plasticity(RIP)effect of Nb_(4)FeSi,are revealed.During hot deformation,theβ-Nb_(5)Si_(3)phase undergoes the eutectoid decomposition to obtain theα-Nb_(5)Si_(3)and niobium-based solid solutions(Nbss)phases,whichα-Nb_(5)Si_(3)and Nbss satisfy the relationship{110}_(α)//{110}_(Nbss).The[110]SFs and lath-like reoriented variants are formed in the Nb_(4)FeSi phase,where the matrix and variants follow[001]_(m)//[111]v,(110)_(m)//(110)v.Furthermore,the interface between matrix and variant isΣ33c symmetrical tilt boundaries,manifested as(110)/60°.The fracture toughness of the deformed alloy reaches 18.31 MPa·m1/2 at 1300℃/0.005 s^(-1)/0.7,which is 49%higher than the initial alloy.展开更多
Understandings of the effect of hot deformation parameters close to the practical production line on grain refinement are crucial for enhancing both the strength and toughness of future rail steels.In this work,the au...Understandings of the effect of hot deformation parameters close to the practical production line on grain refinement are crucial for enhancing both the strength and toughness of future rail steels.In this work,the austenite dynamic recrystallization(DRX)behaviors of a eutectoid pearlite rail steel were studied using a thermo-mechanical simulator with hot deformation parameters frequently employed in rail production lines.The single-pass hot deformation results reveal that the prior austenite grain sizes(PAGSs)for samples with different deformation reductions decrease initially with an increase in deformation temperature.However,once the deformation temperature is beyond a certain threshold,the PAGSs start to increase.It can be attributed to the rise in DRX volume fraction and the increase of DRX grain with deformation temperature,respectively.Three-pass hot deformation results show that the accumulated strain generated in the first and second deformation passes can increase the extent of DRX.In the case of complete DRX,PAGS is predominantly determined by the deformation temperature of the final pass.It suggests a strategic approach during industrial production where part of the deformation reduction in low temperature range can be shifted to the medium temperature range to release rolling mill loads.展开更多
Ti-Cu eutectoid or near-eutectoid alloys were found to possess exceptional high strength owning to the nano-scale lamellar structure of Ti_(2)Cu andα-Ti after additive manufacturing,they are potential candidates for ...Ti-Cu eutectoid or near-eutectoid alloys were found to possess exceptional high strength owning to the nano-scale lamellar structure of Ti_(2)Cu andα-Ti after additive manufacturing,they are potential candidates for high-performance materials.To reveal the deformation and strengthening mechanisms,the molecular dynamics(MD)simulations and experimental analysis were carried out upon Ti-Ti_(2)Cu lamellae.In this work,we focused on revealing the interface dislocations(IDs)pattern and its effects on the dynamic evolution of the lattice dislocations(LDs)at the Ti/Ti_(2)Cu interface with(0001)α//(013)Ti_(2)Cu orientation relationship.Atomistic simulations depicted that the equilibrium Ti/Ti_(2)Cu interface contains three groups of partial dislocations which dictate two interfacial coherent structures with low stacking fault energy.Each ID consists of several segments,connected by atomic steps with identical direction.The nucleation sites of LDs under external loading locate at the intersection between the dislocation segment and the atomic step,which is related to the local high atom strain.Under compression deformation,the100{011}and331{103}slip systems in Ti_(2)Cu,and the112¯3{101¯1}slip system inα-Ti are activated,achieving a co-deformation mechanism in the Ti-Ti_(2)Cu multilayers.The dislocation-interface interactions are responsible for the deformation plasticity and in turn governs the mechanical strengthening.During nanoindentation tests,larger hardness(∼6.2 GPa)and smaller activation volume(∼12b3)were found in the Ti-Ti_(2)Cu lamellae,which is mainly ascribed to the presence of high-density lamellae interface and confined layer slip,resulting in interface-mediated dislocation annihilation/deposition and consequent high strain hardening.The MD simulations,nanoindentation tests and TEM investigations of interlayer dislocation activity support the strengthening mechanism of dislocation-interface interactions.展开更多
The morphology and structure of δ-eutectoid and the transformation of δ-eutectoidic austenite in high speed steel have been studied under SEM and TEM.The δ-eutectoid in as-cast high speed steel is rod-shaped eutect...The morphology and structure of δ-eutectoid and the transformation of δ-eutectoidic austenite in high speed steel have been studied under SEM and TEM.The δ-eutectoid in as-cast high speed steel is rod-shaped eutectoidic units with different orientations and is markedly surrounded by carbide shell.The eutectoidic carbide is rod-shaped M_6C of square eross section.The eutectoidic austenite may transform into pearlite structure during cooling.展开更多
The warm compression tests were performed on the eutectoid steel to investigate the evolution of cementite morphology. Several processing parameters, such as temperature, strain rate and reduction, were changed to ana...The warm compression tests were performed on the eutectoid steel to investigate the evolution of cementite morphology. Several processing parameters, such as temperature, strain rate and reduction, were changed to analyze the effect of each parameter on spheroidization of cementite. The results showed that the warm compression promoted the fragmentize and the spheroidization of lamellar cementites. When the specimen was compressed with reduction of 50% at 700 ℃ and in the strain rate of 0.01 s-1, the excellent spheroidized cementite was obtained. The mechanism of fragmentation and spheroidization of lamellar cementites during compression was discussed by using transmission electron microscope. The formation of spheroidized cementite was related to the time of compression process. The fragmentize of lamellar cementites was due to the extension of sub-grain boundary in the cementite. The spheroidization of cementite depended on the diffusion of carbon atoms at the tip of bended and breakup cementite.展开更多
Mssbauer spectrum and three dimensional atom probes（3DAP） were combined to investigate the mechanism of cementite dissolution in a cold-drawn eutectoid steel at a true strain of 2.89.The experimental results suggest...Mssbauer spectrum and three dimensional atom probes（3DAP） were combined to investigate the mechanism of cementite dissolution in a cold-drawn eutectoid steel at a true strain of 2.89.The experimental results suggest that the dislocations play an important role in the dissolution of the cementite by sweeping across the nano-scaled cementite,and transferring carbon from cementite to ferrite inducing cementite decomposition.The mechanism of cementite dissolution in the steel is discussed in association with the investigation of nonstoichiometric cementite structure after heavy deformation.展开更多
Based on current theories of diffusion and creep cavity closure at high temperature, a theoretical analysis of phase transformation diffusion bonding for T8/T8 eutectoid steel is carried out. The diffusion bonding is ...Based on current theories of diffusion and creep cavity closure at high temperature, a theoretical analysis of phase transformation diffusion bonding for T8/T8 eutectoid steel is carried out. The diffusion bonding is mainly described as two-stage process: Ⅰ The interfacial cavity with shape change from diamond to cylinder.Ⅱ The radius of the cylindrical cavity are reduced and eliminated gradually. A new theoretical model is established for the process of transformation superplastic diffusion bonding (TSDB) on the basis of a theoretical model for isothermal superplastic diffusion. The model can predict the bonding quality which is affected by technological parameters, such as limit cycling temperature, the compressive stress, the numbers of thermal cycles and temperature cycling through the phase transformation in the thermal cycling and so on. Results show that the maximum temperature, the compressive stress, the numbers of thermal cycles and the rate of temperature changing speed in the thermal cycling have an important influence on TSDB process. Meanwhile, reasonable technological parameters chosen from theoretical analysis is in good agreement with those obtained from experimental results.展开更多
The effect of dissolved niobium on the eutectoid transformation behavior in near-eutectoid high-carbon steels has been studied.Dissolved niobium is important in the eutectoid transformation behavior.It increases the e...The effect of dissolved niobium on the eutectoid transformation behavior in near-eutectoid high-carbon steels has been studied.Dissolved niobium is important in the eutectoid transformation behavior.It increases the eutectoid carbon content significantly（by^0.0477% per 0.00001% dissolved niobium）,increases the hardenability of steel markedly,yields finer,more uniform,polygonal proeutectoid ferrite,induces a transition in morphology of eutectoid cementite from lamellar to somewhat spheroidal,and increases the misorientation angle of pearlite colonies from being focused near 0°to near 60°.展开更多
Seeking high-performance computing methods to solve the problem of a large amount of calculation,low calculation efficiency,and small simulation scale on the traditional single central processing unit (CPU) platform i...Seeking high-performance computing methods to solve the problem of a large amount of calculation,low calculation efficiency,and small simulation scale on the traditional single central processing unit (CPU) platform is of great value to the simulation study of micro-structure.In this study,based on the three-dimensional multi-phase-field model of KKSO coupling phase-field and solute field,the open computing language (OpenCL) + graphics processing unit (GPU) heterogeneous parallel computing technology is used to simulate the eutectoid growth of Fe-C alloy and the end growth process of pearlite under pure diffusion.The effects of initial supercooling and different diffusion coefficients on the growth morphology of lamellar pearlite were investigated.The results show that ferrite and cementite are perpendicular to the front of the solid-solid interface and are coupled and coordinated to grow,and there is no leading phase under the initial supercooling degree of 20 K.With the continuous increase of the initial supercooling degree (19 K-22 K),the morphology changes of the eutectoid layer are as follows:cementite stops growing → slice amplitude increases → regular symmetric growth → oblique growth → layer merge.With the increase of the diffusion coefficient from 3×10^(-13) m^(2)·s^(-1) to 15×10^(-13) m^(2)·s^(-1),the growth rate of the microstructure of the lamellar pearlite increases linearly,and there is no obvious change in the frontal appearance of the pearlite.展开更多
By introducing aparameter of difference in ferrite formation temperature between binary Fe-C and multicomponent system,and referring to the thermodynamic model for Fe-C binary system,a simplified thermodynamic model f...By introducing aparameter of difference in ferrite formation temperature between binary Fe-C and multicomponent system,and referring to the thermodynamic model for Fe-C binary system,a simplified thermodynamic model for pro-eutectoid ferrite formation in Fe-ΣXiC multicomponent structural steels(Xi=Mn,Si,Mo,Cr,Ni or Ti,etc)was suggested.The comparison of the calculated Ae3 temperatures with the measured data of steels 42 shows that the relative standard deviation and root-mean-square(RMS)error between them are only 0.71% and 8.92 K,respectively.However,the deviations between the same measured data and the values calculated from the superelement model are as high as 1.86% and 23.83 K,respectively.It can be concluded that the simplified thermodynamic model for pro-eutectoid ferrite formation in multicomponent structural steels is acceptable and the calculated Ae3 temperatures are in good agreement with the experimental data.展开更多
This paper discusses the microstructure of nickel-aluminium bronzes con-taining（9-10）wt% Al and（0.1～5）wt% Ni,in which three eutectoids may exist.Themorphologies of α+γ<sub>2</sub> and α+β’<sub...This paper discusses the microstructure of nickel-aluminium bronzes con-taining（9-10）wt% Al and（0.1～5）wt% Ni,in which three eutectoids may exist.Themorphologies of α+γ<sub>2</sub> and α+β’<sub>2</sub> are similar but the latter is finer.In the α+β’<sub>2</sub>+γ<sub>2</sub>eutectoid structure β’<sub>2</sub> is mainly concentrated at the α/β boundaries,while γ<sub>2</sub> is distrib-uted inside prior B regions.Both K-S and N-W orientation relationships exist betweenα and β’<sub>2</sub>（or γ<sub>2</sub>）in alloys consisting of α+β’<sub>2</sub> or α+γ<sub>2</sub>.However,if the alloy consists ofα+β’<sub>2</sub>+γ<sub>2</sub> eutectoid,the lattices of β’<sub>2</sub> and γ<sub>2</sub> are parallel,both of them have the N-Worientation relationship with α.展开更多
The Al-Zn eutectoid alloy has been widely known as a typical superplastic metallic material, where fine-grained microstructure is usually obtained by heat treatment. Recently, thermo-mechanical controlled process has ...The Al-Zn eutectoid alloy has been widely known as a typical superplastic metallic material, where fine-grained microstructure is usually obtained by heat treatment. Recently, thermo-mechanical controlled process has also been reported to provide a fine-grained microstructure. In the present study, Al-Zn alloy ingots of 20 mm in thickness were homogenized and hot-rolled to a thickness of 2 mm under three processes： 1） the specimen was air-cooled after homogenization and hot-rolled; 2） the specimen was water-quenched after homogenization and hot-rolled; 3） the specimen was immediately hot-rolled after homogenization. Microstructural observation showed that, in processes l and 3, lamellar microstructure was formed after homogenization, and became fragmented to fine-grained microstructure as the hot roiling process proceeded. In process 2, fine-grained microstructure without lamellar microstructure was attained throughout the hot-rolling process. A minimum grain size of 1.6 μm was obtained in process 3. Tensile tests at room temperature showed that the elongation to failure was the largest in process 3.展开更多
The active eutectoid decomposition and its morphological evolution during slow cooling and isothermal holding were investigated in a Ru-containing Ti Al alloy. The fine τ 1/γ active eutectoid nodules precipitated at...The active eutectoid decomposition and its morphological evolution during slow cooling and isothermal holding were investigated in a Ru-containing Ti Al alloy. The fine τ 1/γ active eutectoid nodules precipitated at α grain boundary and interior during water quenching. The active eutectoid microstructure evolved from sheaf-like, granular to bulky net-like sluggish eutectoid morphology gradually with the decrease in quenching/holding temperatures. The active eutectoid reaction occurs from 1220 to 1290 ℃, while the beginning temperature of sluggish eutectoid locates at 1305 ± 5 ℃. The combination of the intact τ_(1) phase and immature nano-sized γ laths suggests a short incubation period of τ_(1) phase in the active type. Furtherly, the semiquantitative estimation shows that the growth velocity of active eutectoid is about ninety times higher than sluggish type. In addition, a representative feature of γ phase abruptly ripening along {111} crystallographic plane was also observed in the active eutectoid.展开更多
A continuously cast eutectoid Zn-Al alloy was extruded at about 250℃ and the complex microstructures of three phases (α. ε and η'E) were observed in the extruded eutectoid Zn-Al alloy.The fcc Al-rich α phase ...A continuously cast eutectoid Zn-Al alloy was extruded at about 250℃ and the complex microstructures of three phases (α. ε and η'E) were observed in the extruded eutectoid Zn-Al alloy.The fcc Al-rich α phase appeared as isolated particles with clear boundaries instead of the α phase occurring with diffuse boundary within the dendrites of the as-cast structure. A new unstable phase η'E was determined to have hexagonal close packed crystal structure. The decomposed β's, phase comprised the matrix. The new phase η'E decompoeed and a four phase transformation α+ε T'+η occurred afterwards during the isothermal holding. The extruded alloy tended to be stable after these two phase transformations. The early shrinkage and the following increase in dimension were related to the decomposition of the new phase η'E and the four phase transformation.展开更多
By means of rapid cool dilatometry, the influence of rare earths on kinetics of pre-eutectoid transformation of austenite of carbon-manganese clean steel was studied. While the content of rare earths were proper, the ...By means of rapid cool dilatometry, the influence of rare earths on kinetics of pre-eutectoid transformation of austenite of carbon-manganese clean steel was studied. While the content of rare earths were proper, the nucleation of pre-eutectoid ferrite on the grain boundary of austenite was accelerated and the incubation period of pre-eutectoid transformation was shortened. But while rare earths were excessive, opposite actions appeared. Rare earths decreased transformation velocity constant in the process of transformation from austenite to ferrite, which meant that the growth of per-eutectoid ferrite became slow. The reason above varieties was related to effect of rare earth on grain boundary constitution of austenite and diffusion of carbon element.展开更多
The phenomenon of anisotropism in most rolled products necessitates that the rolling direction that enhances desirable mechanical property is established. In this paper, the comparative deep drawability of as-received...The phenomenon of anisotropism in most rolled products necessitates that the rolling direction that enhances desirable mechanical property is established. In this paper, the comparative deep drawability of as-received and annealed mild steel containing about 0.1%C was investigated. The flat steel sample was divided into two and classified as as-received and heat treated respectively. The heat treated sample was obtained by annealing at 950°C after been soaked for 5 hours and deep drawn at ambient temperatures (35°C - 42°C). From both samples, circular specimens were machine- blanked parallel to the rolling directions inclined at 0°, 45° and 90° respectively and were prepared for deep drawability test while rectangular specimens were prepared for tensile test. Both specimens, as-received and annealed were then sub- jected to tensile, cupping and microstructural analyses. Results show that the contribution to increased formability at 90° rolling direction seems to have come from the spheroid-like pearlite grains induced during annealing while the sta- bility of spread observed was achieved through a modest increase in strength. Thus, the resistance of annealed eutectoid steel to cupping is quite minimal at 90° to the rolling direction. The desirable drawability characteristics developed by the annealed eutectoid steel specimen are: cup-height, 30 mm maximum and ear, 6.4% maximum.展开更多
The effect of austenite deformation on the pearlite microstructure of eutectoid steel w as investigated by hot uniaxial compression tests using a Gleeble 1500 thermo-mechanical simulator. The results show ed that the ...The effect of austenite deformation on the pearlite microstructure of eutectoid steel w as investigated by hot uniaxial compression tests using a Gleeble 1500 thermo-mechanical simulator. The results show ed that the deformation of the austenite phase accelerated the transformation of pearlite,leading to a smaller colony size and a smaller interlamellar space of pearlite; meanw hile,the orientation of pearlite lamellae became more heterogeneous,and the lamellar thickness decreased. Larger strain of austenite w as observed to accelerate the spheroidization process of carbides w ithin pearlite colonies.展开更多
The pearlitic transformation and the deformation behavior of lamellar cementite after cold rolling in eutectoid steels Fe-0.76%C-0.137%Mn(mass fraction) were studied by means of Formastor-F (Full Automatic Transformat...The pearlitic transformation and the deformation behavior of lamellar cementite after cold rolling in eutectoid steels Fe-0.76%C-0.137%Mn(mass fraction) were studied by means of Formastor-F (Full Automatic Transformation Testing Instrument) and field emission scanning electronic microscopy (FESEM) observation. Fine and coarse pearlite were obtained in the eutectoid steels austenitized at 900℃ for 15min, then hold at 620℃ for 90 s and 690℃ for 7 h, respectively. The deformation behavior of cold rolled lamellar cementite could be classified as: cleavage fracture, inhomogeneous slip, fragmentation, thinning or necking, and homogeneous bending. The cementite lamellae with the thickness of more than 100 nm could be deformed plastically.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52425401 and 52374384)the Foundation of National Key Laboratory for Precision Hot Processing of Metals(No.JCKYS2021603C001)the Fundamental Research Funds for the Central Universities(No.2023FRFK06014).
文摘Nb-Si-based in situ composites are receiving attention as a substitute for Ni-based alloys in aerospace,while poor toughness limits its application.In this work,the toughness of Nb_(4)FeSi-containing Nb-Si-based alloys was improved by hot deformation.The different deformation behaviors of reinforcements from traditional alloys,including the eutectoid decomposition ofβ-Nb_(5)Si_(3),and the stacking faults(SFs)and reorientation-induced plasticity(RIP)effect of Nb_(4)FeSi,are revealed.During hot deformation,theβ-Nb_(5)Si_(3)phase undergoes the eutectoid decomposition to obtain theα-Nb_(5)Si_(3)and niobium-based solid solutions(Nbss)phases,whichα-Nb_(5)Si_(3)and Nbss satisfy the relationship{110}_(α)//{110}_(Nbss).The[110]SFs and lath-like reoriented variants are formed in the Nb_(4)FeSi phase,where the matrix and variants follow[001]_(m)//[111]v,(110)_(m)//(110)v.Furthermore,the interface between matrix and variant isΣ33c symmetrical tilt boundaries,manifested as(110)/60°.The fracture toughness of the deformed alloy reaches 18.31 MPa·m1/2 at 1300℃/0.005 s^(-1)/0.7,which is 49%higher than the initial alloy.
基金financially supported by the National Natural Science Foundation of China(Nos.52293395 and 52293393)the Xiongan Science and Technology Innovation Talent Project of MOST,China(No.2022XACX0500)。
文摘Understandings of the effect of hot deformation parameters close to the practical production line on grain refinement are crucial for enhancing both the strength and toughness of future rail steels.In this work,the austenite dynamic recrystallization(DRX)behaviors of a eutectoid pearlite rail steel were studied using a thermo-mechanical simulator with hot deformation parameters frequently employed in rail production lines.The single-pass hot deformation results reveal that the prior austenite grain sizes(PAGSs)for samples with different deformation reductions decrease initially with an increase in deformation temperature.However,once the deformation temperature is beyond a certain threshold,the PAGSs start to increase.It can be attributed to the rise in DRX volume fraction and the increase of DRX grain with deformation temperature,respectively.Three-pass hot deformation results show that the accumulated strain generated in the first and second deformation passes can increase the extent of DRX.In the case of complete DRX,PAGS is predominantly determined by the deformation temperature of the final pass.It suggests a strategic approach during industrial production where part of the deformation reduction in low temperature range can be shifted to the medium temperature range to release rolling mill loads.
基金supports by the National Nature Science Foundation of China(No.52275354)the Na-tional Key R&D Program of China(No.2018YFA0702900).
文摘Ti-Cu eutectoid or near-eutectoid alloys were found to possess exceptional high strength owning to the nano-scale lamellar structure of Ti_(2)Cu andα-Ti after additive manufacturing,they are potential candidates for high-performance materials.To reveal the deformation and strengthening mechanisms,the molecular dynamics(MD)simulations and experimental analysis were carried out upon Ti-Ti_(2)Cu lamellae.In this work,we focused on revealing the interface dislocations(IDs)pattern and its effects on the dynamic evolution of the lattice dislocations(LDs)at the Ti/Ti_(2)Cu interface with(0001)α//(013)Ti_(2)Cu orientation relationship.Atomistic simulations depicted that the equilibrium Ti/Ti_(2)Cu interface contains three groups of partial dislocations which dictate two interfacial coherent structures with low stacking fault energy.Each ID consists of several segments,connected by atomic steps with identical direction.The nucleation sites of LDs under external loading locate at the intersection between the dislocation segment and the atomic step,which is related to the local high atom strain.Under compression deformation,the100{011}and331{103}slip systems in Ti_(2)Cu,and the112¯3{101¯1}slip system inα-Ti are activated,achieving a co-deformation mechanism in the Ti-Ti_(2)Cu multilayers.The dislocation-interface interactions are responsible for the deformation plasticity and in turn governs the mechanical strengthening.During nanoindentation tests,larger hardness(∼6.2 GPa)and smaller activation volume(∼12b3)were found in the Ti-Ti_(2)Cu lamellae,which is mainly ascribed to the presence of high-density lamellae interface and confined layer slip,resulting in interface-mediated dislocation annihilation/deposition and consequent high strain hardening.The MD simulations,nanoindentation tests and TEM investigations of interlayer dislocation activity support the strengthening mechanism of dislocation-interface interactions.
文摘The morphology and structure of δ-eutectoid and the transformation of δ-eutectoidic austenite in high speed steel have been studied under SEM and TEM.The δ-eutectoid in as-cast high speed steel is rod-shaped eutectoidic units with different orientations and is markedly surrounded by carbide shell.The eutectoidic carbide is rod-shaped M_6C of square eross section.The eutectoidic austenite may transform into pearlite structure during cooling.
基金Item Sponsored by National Natural Science Foundation of China(50271060)Natural Science Foundation of Hebei Province of China(503291)
文摘The warm compression tests were performed on the eutectoid steel to investigate the evolution of cementite morphology. Several processing parameters, such as temperature, strain rate and reduction, were changed to analyze the effect of each parameter on spheroidization of cementite. The results showed that the warm compression promoted the fragmentize and the spheroidization of lamellar cementites. When the specimen was compressed with reduction of 50% at 700 ℃ and in the strain rate of 0.01 s-1, the excellent spheroidized cementite was obtained. The mechanism of fragmentation and spheroidization of lamellar cementites during compression was discussed by using transmission electron microscope. The formation of spheroidized cementite was related to the time of compression process. The fragmentize of lamellar cementites was due to the extension of sub-grain boundary in the cementite. The spheroidization of cementite depended on the diffusion of carbon atoms at the tip of bended and breakup cementite.
基金supported by the National Natural Science Foundation of China(No.50371057)
文摘Mssbauer spectrum and three dimensional atom probes（3DAP） were combined to investigate the mechanism of cementite dissolution in a cold-drawn eutectoid steel at a true strain of 2.89.The experimental results suggest that the dislocations play an important role in the dissolution of the cementite by sweeping across the nano-scaled cementite,and transferring carbon from cementite to ferrite inducing cementite decomposition.The mechanism of cementite dissolution in the steel is discussed in association with the investigation of nonstoichiometric cementite structure after heavy deformation.
文摘Based on current theories of diffusion and creep cavity closure at high temperature, a theoretical analysis of phase transformation diffusion bonding for T8/T8 eutectoid steel is carried out. The diffusion bonding is mainly described as two-stage process: Ⅰ The interfacial cavity with shape change from diamond to cylinder.Ⅱ The radius of the cylindrical cavity are reduced and eliminated gradually. A new theoretical model is established for the process of transformation superplastic diffusion bonding (TSDB) on the basis of a theoretical model for isothermal superplastic diffusion. The model can predict the bonding quality which is affected by technological parameters, such as limit cycling temperature, the compressive stress, the numbers of thermal cycles and temperature cycling through the phase transformation in the thermal cycling and so on. Results show that the maximum temperature, the compressive stress, the numbers of thermal cycles and the rate of temperature changing speed in the thermal cycling have an important influence on TSDB process. Meanwhile, reasonable technological parameters chosen from theoretical analysis is in good agreement with those obtained from experimental results.
文摘The effect of dissolved niobium on the eutectoid transformation behavior in near-eutectoid high-carbon steels has been studied.Dissolved niobium is important in the eutectoid transformation behavior.It increases the eutectoid carbon content significantly（by^0.0477% per 0.00001% dissolved niobium）,increases the hardenability of steel markedly,yields finer,more uniform,polygonal proeutectoid ferrite,induces a transition in morphology of eutectoid cementite from lamellar to somewhat spheroidal,and increases the misorientation angle of pearlite colonies from being focused near 0°to near 60°.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51661020,11504149 and 11364024)the Postdoctoral Science Foundation of China(Grant No.2014M560371)the Funds for Distinguished Young Scientists of Lanzhou University of Technology(Grant No.J201304)。
文摘Seeking high-performance computing methods to solve the problem of a large amount of calculation,low calculation efficiency,and small simulation scale on the traditional single central processing unit (CPU) platform is of great value to the simulation study of micro-structure.In this study,based on the three-dimensional multi-phase-field model of KKSO coupling phase-field and solute field,the open computing language (OpenCL) + graphics processing unit (GPU) heterogeneous parallel computing technology is used to simulate the eutectoid growth of Fe-C alloy and the end growth process of pearlite under pure diffusion.The effects of initial supercooling and different diffusion coefficients on the growth morphology of lamellar pearlite were investigated.The results show that ferrite and cementite are perpendicular to the front of the solid-solid interface and are coupled and coordinated to grow,and there is no leading phase under the initial supercooling degree of 20 K.With the continuous increase of the initial supercooling degree (19 K-22 K),the morphology changes of the eutectoid layer are as follows:cementite stops growing → slice amplitude increases → regular symmetric growth → oblique growth → layer merge.With the increase of the diffusion coefficient from 3×10^(-13) m^(2)·s^(-1) to 15×10^(-13) m^(2)·s^(-1),the growth rate of the microstructure of the lamellar pearlite increases linearly,and there is no obvious change in the frontal appearance of the pearlite.
基金Item Sponsored by National Natural Science Foundation of China(50075053)
文摘By introducing aparameter of difference in ferrite formation temperature between binary Fe-C and multicomponent system,and referring to the thermodynamic model for Fe-C binary system,a simplified thermodynamic model for pro-eutectoid ferrite formation in Fe-ΣXiC multicomponent structural steels(Xi=Mn,Si,Mo,Cr,Ni or Ti,etc)was suggested.The comparison of the calculated Ae3 temperatures with the measured data of steels 42 shows that the relative standard deviation and root-mean-square(RMS)error between them are only 0.71% and 8.92 K,respectively.However,the deviations between the same measured data and the values calculated from the superelement model are as high as 1.86% and 23.83 K,respectively.It can be concluded that the simplified thermodynamic model for pro-eutectoid ferrite formation in multicomponent structural steels is acceptable and the calculated Ae3 temperatures are in good agreement with the experimental data.
文摘This paper discusses the microstructure of nickel-aluminium bronzes con-taining（9-10）wt% Al and（0.1～5）wt% Ni,in which three eutectoids may exist.Themorphologies of α+γ<sub>2</sub> and α+β’<sub>2</sub> are similar but the latter is finer.In the α+β’<sub>2</sub>+γ<sub>2</sub>eutectoid structure β’<sub>2</sub> is mainly concentrated at the α/β boundaries,while γ<sub>2</sub> is distrib-uted inside prior B regions.Both K-S and N-W orientation relationships exist betweenα and β’<sub>2</sub>（or γ<sub>2</sub>）in alloys consisting of α+β’<sub>2</sub> or α+γ<sub>2</sub>.However,if the alloy consists ofα+β’<sub>2</sub>+γ<sub>2</sub> eutectoid,the lattices of β’<sub>2</sub> and γ<sub>2</sub> are parallel,both of them have the N-Worientation relationship with α.
文摘The Al-Zn eutectoid alloy has been widely known as a typical superplastic metallic material, where fine-grained microstructure is usually obtained by heat treatment. Recently, thermo-mechanical controlled process has also been reported to provide a fine-grained microstructure. In the present study, Al-Zn alloy ingots of 20 mm in thickness were homogenized and hot-rolled to a thickness of 2 mm under three processes： 1） the specimen was air-cooled after homogenization and hot-rolled; 2） the specimen was water-quenched after homogenization and hot-rolled; 3） the specimen was immediately hot-rolled after homogenization. Microstructural observation showed that, in processes l and 3, lamellar microstructure was formed after homogenization, and became fragmented to fine-grained microstructure as the hot roiling process proceeded. In process 2, fine-grained microstructure without lamellar microstructure was attained throughout the hot-rolling process. A minimum grain size of 1.6 μm was obtained in process 3. Tensile tests at room temperature showed that the elongation to failure was the largest in process 3.
基金financially supported by the National Natural Science Foundation of China(No.51774238)the 2018 joint Foundation of Ministry of Education for Equipment Preresearch(No.6141A020332)。
文摘The active eutectoid decomposition and its morphological evolution during slow cooling and isothermal holding were investigated in a Ru-containing Ti Al alloy. The fine τ 1/γ active eutectoid nodules precipitated at α grain boundary and interior during water quenching. The active eutectoid microstructure evolved from sheaf-like, granular to bulky net-like sluggish eutectoid morphology gradually with the decrease in quenching/holding temperatures. The active eutectoid reaction occurs from 1220 to 1290 ℃, while the beginning temperature of sluggish eutectoid locates at 1305 ± 5 ℃. The combination of the intact τ_(1) phase and immature nano-sized γ laths suggests a short incubation period of τ_(1) phase in the active type. Furtherly, the semiquantitative estimation shows that the growth velocity of active eutectoid is about ninety times higher than sluggish type. In addition, a representative feature of γ phase abruptly ripening along {111} crystallographic plane was also observed in the active eutectoid.
文摘A continuously cast eutectoid Zn-Al alloy was extruded at about 250℃ and the complex microstructures of three phases (α. ε and η'E) were observed in the extruded eutectoid Zn-Al alloy.The fcc Al-rich α phase appeared as isolated particles with clear boundaries instead of the α phase occurring with diffuse boundary within the dendrites of the as-cast structure. A new unstable phase η'E was determined to have hexagonal close packed crystal structure. The decomposed β's, phase comprised the matrix. The new phase η'E decompoeed and a four phase transformation α+ε T'+η occurred afterwards during the isothermal holding. The extruded alloy tended to be stable after these two phase transformations. The early shrinkage and the following increase in dimension were related to the decomposition of the new phase η'E and the four phase transformation.
基金the Ministry of Science and Technology of China (2002BA315A-5)
文摘By means of rapid cool dilatometry, the influence of rare earths on kinetics of pre-eutectoid transformation of austenite of carbon-manganese clean steel was studied. While the content of rare earths were proper, the nucleation of pre-eutectoid ferrite on the grain boundary of austenite was accelerated and the incubation period of pre-eutectoid transformation was shortened. But while rare earths were excessive, opposite actions appeared. Rare earths decreased transformation velocity constant in the process of transformation from austenite to ferrite, which meant that the growth of per-eutectoid ferrite became slow. The reason above varieties was related to effect of rare earth on grain boundary constitution of austenite and diffusion of carbon element.
文摘The phenomenon of anisotropism in most rolled products necessitates that the rolling direction that enhances desirable mechanical property is established. In this paper, the comparative deep drawability of as-received and annealed mild steel containing about 0.1%C was investigated. The flat steel sample was divided into two and classified as as-received and heat treated respectively. The heat treated sample was obtained by annealing at 950°C after been soaked for 5 hours and deep drawn at ambient temperatures (35°C - 42°C). From both samples, circular specimens were machine- blanked parallel to the rolling directions inclined at 0°, 45° and 90° respectively and were prepared for deep drawability test while rectangular specimens were prepared for tensile test. Both specimens, as-received and annealed were then sub- jected to tensile, cupping and microstructural analyses. Results show that the contribution to increased formability at 90° rolling direction seems to have come from the spheroid-like pearlite grains induced during annealing while the sta- bility of spread observed was achieved through a modest increase in strength. Thus, the resistance of annealed eutectoid steel to cupping is quite minimal at 90° to the rolling direction. The desirable drawability characteristics developed by the annealed eutectoid steel specimen are: cup-height, 30 mm maximum and ear, 6.4% maximum.
文摘The effect of austenite deformation on the pearlite microstructure of eutectoid steel w as investigated by hot uniaxial compression tests using a Gleeble 1500 thermo-mechanical simulator. The results show ed that the deformation of the austenite phase accelerated the transformation of pearlite,leading to a smaller colony size and a smaller interlamellar space of pearlite; meanw hile,the orientation of pearlite lamellae became more heterogeneous,and the lamellar thickness decreased. Larger strain of austenite w as observed to accelerate the spheroidization process of carbides w ithin pearlite colonies.
文摘The pearlitic transformation and the deformation behavior of lamellar cementite after cold rolling in eutectoid steels Fe-0.76%C-0.137%Mn(mass fraction) were studied by means of Formastor-F (Full Automatic Transformation Testing Instrument) and field emission scanning electronic microscopy (FESEM) observation. Fine and coarse pearlite were obtained in the eutectoid steels austenitized at 900℃ for 15min, then hold at 620℃ for 90 s and 690℃ for 7 h, respectively. The deformation behavior of cold rolled lamellar cementite could be classified as: cleavage fracture, inhomogeneous slip, fragmentation, thinning or necking, and homogeneous bending. The cementite lamellae with the thickness of more than 100 nm could be deformed plastically.
