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
The microstructural evolution of pearlite during severe cold rolling in Fe-0.8C binary alloy and Fe-1Mn-0.8C ternary alloys was investigated by using SEM, TEM and XRD etc. The results show that the deformed pearlite c...The microstructural evolution of pearlite during severe cold rolling in Fe-0.8C binary alloy and Fe-1Mn-0.8C ternary alloys was investigated by using SEM, TEM and XRD etc. The results show that the deformed pearlite consists of irregularly bent lamella, coarse lamella with shear-band and fine lamella. As the rolling reduction increases, the proportion of fine lamella increases. The strong plastic deformation, amorphization and dissolution of cementite take place during the severe cold rolling. The maximum carbon content in ferrite reaches 0.15 mass% after 90% cold rolling.展开更多
To study the microstructural evolution of pearlite steel subjected to pure rolling and rolling-sliding contact loading,a hypoeutectoid pearlite steel with composition and microstructure similar to BS11 was designed an...To study the microstructural evolution of pearlite steel subjected to pure rolling and rolling-sliding contact loading,a hypoeutectoid pearlite steel with composition and microstructure similar to BS11 was designed and twindisc tests of this pearlite steel were performed to simulate the wheel/rail system.After a series of twin-disc tests,optical microscope（OM）observation,scanning electron microscope（SEM）observation,X-ray diffraction（XRD）,and micro-hardness tests were conducted to characterize the microstructure.Under the pure rolling contact condition,a large amount of reticular cracks emerged within 60μm below the contact surface of the samples after 120 000 revolutions.The largest deformation was approximately 200μm below the contact surface.Under the rolling-sliding contact condition,the nodularization of pearlite within 100μm below the contact surface was obvious.The microstructure and stress-strain distribution of the area within 2mm below the contact surface were investigated.The distribution of micro-hardness under the contact surface varied with contact conditions.Finite element method（FEM）was used to simulate the stress-strain distribution.The results of SEM,FEM,and micro-hardness tests indicated that under the pure rolling contact condition,the maximum plastic strain was approximately 200-400μm below the contact surface.Conversely,under the rolling-sliding contact condition,the maximum plastic strain emerged on the contact surface.Under the pure rolling contact condition,the distribution of micro-hardness was almost identical to that of the equivalent plastic strain.Under the rolling-sliding contact condition,the distribution of micro-hardness was affected by the equivalent plastic strain and tangential stress.展开更多
Three warm-rolled ferrite/pearlite microstructures were prepared by rolling at 500℃, and the austenitizing characteristics were discussed in conjunction with deformation during the heating stage. The results indicate...Three warm-rolled ferrite/pearlite microstructures were prepared by rolling at 500℃, and the austenitizing characteristics were discussed in conjunction with deformation during the heating stage. The results indicated that the final austenite grain size was sensitive to the deformation direction of the initial warm-rolled microstructure. The transient microstructure at a given temperature was the most important influencing factor on the austenitizing characteristic combined with deformation. Moreover, the hot-rolled mierostructure also had to be prepared in an optimal state because of its direct effect on the warm-rolled microstructure.展开更多
Using the methods of transmission electron microscopy, the carbide phase evolution in surface layers of the differentiallyquenched rails is studied after the passed tonnage of 691.8 million tons at the depth up to 10 ...Using the methods of transmission electron microscopy, the carbide phase evolution in surface layers of the differentiallyquenched rails is studied after the passed tonnage of 691.8 million tons at the depth up to 10 mm along the central axis andfillet of rail head. The action of two mutual supplement mechanisms of steel carbide phase transformation in surface layersat rail operation is established： （1） cutting mechanism of cementite particles with the following departure in the volume offerrite grains or plates （in pearlite structure）; （2） cutting mechanism and following dissolution of cementite particles,transfer of carbon atoms on dislocations （in Cottrell atmospheres and dislocation cores）, transfer of carbon atoms bymoving dislocations into ferrite grains volume （or plates） with the following repeated formation of nanosized cementiteparticles. The first mechanism is accompanied by the change in linear sizes and morphology of carbide particles. Cementiteelement composition change is not essential. Carbide structure change can take place during the second mechanism.展开更多
A modified cellular automaton model is developed to depict the interface evolution inside the cementite plus ferrite lamellar microstructures during the reaustenitization of a pearlite steel. In this model, migrations...A modified cellular automaton model is developed to depict the interface evolution inside the cementite plus ferrite lamellar microstructures during the reaustenitization of a pearlite steel. In this model, migrations of both the austenite- ferrite and austenite-cementite interfaces coupled with the carbon diffusion and redistribution are integrated. The capil- laxity effect derived from local interface curvatures is also carefully considered by involving the concentration given by the phase diagram modified by the Gibbs-Thomson effect. This allows the interface evolution from a transient state to a steady state under different annealing conditions and various interlamellar spacings to be simulated. The proposed cellular automaton approach could be readily used to describe the kinetics of austenite formation from the lamellar pearlites and virtually reveal the kinematics of the moving interfaces from the microstructural aspect.展开更多
The austenite transformation characteristics for various warm-rolled pearlite during rapid heating were investigated. The results indicate that the start temperature （Ts） is sensitive to the microstructural feature ...The austenite transformation characteristics for various warm-rolled pearlite during rapid heating were investigated. The results indicate that the start temperature （Ts） is sensitive to the microstructural feature of pearlite, whereas the dislocation plays an important role in the transformation rate; at the same time, the uniformity of austenite grains is more or less affected by the amount of spheroidized pearlite. A critical effect on the state of austenite grain is created through the influence of initial microstructures on the start temperature of transformation.展开更多
In order to further reveal the influence of abnormal segregation band on mechanical properties of hot rolled ferrite/pearlite steel plate, especially on laminated tensile fracture, the experimental method of delaminat...In order to further reveal the influence of abnormal segregation band on mechanical properties of hot rolled ferrite/pearlite steel plate, especially on laminated tensile fracture, the experimental method of delamination tension was adopted. In this paper, the thin tensile samples with 3 mm thickness from the surface, 1/4 positions and center along the thickness orientation of test plate were measured, also the relationship between microstructure and mechanical properties was probed. The results show that the center region of hot rolled ferrite/pearlite steel plate exists granular bainite and ferrite mixed grains, which leads to lower plasticity and toughness of this region. During the tensile process, microcracks are generated and extended at the center of steel plate due to the inconsistency of deformation and fracture on the adjacent structures, finally leading to laminated fracture of steel plate.展开更多
The flow stress of ferrite/pearlite steel under uni-axial tension was simulated with finite element method (FEM) by applying commercial software MARC/MENTAT. Flow stress curves of ferrite/pearlite steels were calculat...The flow stress of ferrite/pearlite steel under uni-axial tension was simulated with finite element method (FEM) by applying commercial software MARC/MENTAT. Flow stress curves of ferrite/pearlite steels were calculated based on unit cell model. The effects of volume fraction, distribution and the aspect ratio of pearlite on tensile properties have been investigated.展开更多
The pearlite transformation in a Mo-containing iron alloy was investigated under 12 T magnetic field. The pearlite transformation was accelerated owing to the application of a strong magnetic field. Pearlite was of de...The pearlite transformation in a Mo-containing iron alloy was investigated under 12 T magnetic field. The pearlite transformation was accelerated owing to the application of a strong magnetic field. Pearlite was of degenerated morphology without the presence of a strong magnetic field; but the degeneracy of pearlite is reduced when a strong magnetic field was applied, which may be attributed to the effect of strong magnetic field on faster carbon diffusion and less molybdenum segregation caused by a strong magnetic展开更多
The continuous cooling transformation (CCT) diagrams of 86CrMoV7 steel samples including hot deformed and not hot deformed were constructed by dilatometry, metallography and transmission electron microscopy (TEM). The...The continuous cooling transformation (CCT) diagrams of 86CrMoV7 steel samples including hot deformed and not hot deformed were constructed by dilatometry, metallography and transmission electron microscopy (TEM). The results showed that hot deformation accelerated pearlite transformation and fine pearlite microstructure. Moreover, the undissolved carbides became the nucleating sites of pearlite, accelerated pearlite formation and fine pearlite if the steel had been deformed at high temperature. In contrast, undissolved carbides did not make any influence on pearlite transformation if the steel had not been deformed at high temperature.展开更多
In this paper a concept of 'leading probability' is presented. The difference in the leading probability between ferrite and cementite depends mainly upon the difference between their driving forces at the beg...In this paper a concept of 'leading probability' is presented. The difference in the leading probability between ferrite and cementite depends mainly upon the difference between their driving forces at the beginning of precipitation. The results of theromdynamic calculations showed that the leading probability of cementite increased with the increase of carbon concentration of austenite, and the decrease in transformation temperature was favourable to cementite's being the leading nucleus during pearlite transformation.展开更多
This paper presents the results obtained, deductions made from solidification behaviour and a series of micro structural studies such as pearlite content, eu-tectic cell count and grain size of hypoeutectic gray cast ...This paper presents the results obtained, deductions made from solidification behaviour and a series of micro structural studies such as pearlite content, eu-tectic cell count and grain size of hypoeutectic gray cast iron which was sand cast (CO2 moulding) using metallic, nonmetallic, water cooled and subzero (cryogenic) end chills. Hypo-eutectic cast irons containing C 3.42, Si 2.4 and Ni 1.5 with impurity contents (S, P, Mn etc.) were solidified unidirectionally in an American Foundrymen Society (AFS) standard mould, the end of which was provided with different end chills to study the effect of chilling during solidifi-cation. The melts were inoculated with 0.3% Fe-Si to promote graphitization. It was observed that the transition from one structure to another is more gradual than normally obtained in the structure of cast irons solidified mul-ti-directionally in a sand mould at room temperature. Austenite dendrite interactions were shown to be a major factor in determining the microstructure, in which the higher dendrite reaction leads to changes in DAS, ECC and GS. It is observed that, the number of eutectic cells is an index of graphite nucleation and the effect of these on structure, since the eutectic cells are developed on the graphite nuclei during solidification.展开更多
The microstructure evolution and its effects on the mechanical performance of 2000 MPa bridge cable steel wires were investigated by transmission electron microscope(TEM),electron backscatter diffraction(EBSD),X-ray d...The microstructure evolution and its effects on the mechanical performance of 2000 MPa bridge cable steel wires were investigated by transmission electron microscope(TEM),electron backscatter diffraction(EBSD),X-ray diffractometer(XRD)and mechanical tests.Experimental results reveal that,with the increasing strain from 0 to 1.42,a fiber structure and a<110>fiber texture aligned with the wire axis are gradually developed accompanied by cementite decomposition and the formation of sub-grains;the tensile strength increases linearly from 1510 to 2025 MPa,and the reduction of the area is stable with a slight decline from 44%to 36%.After annealing at 450℃for different times,pronounced changes in the microstructure occur.Cementite lamella fragment into coarser globules corresponding to a remarkable spheroidization process,while ferrite domains recover and recrystallize,and this process is associated to modifications in the mechanical properties.Furthermore,based on the observations on dislocation lines crossing through cementite lamellae,a possible mechanism of cementite decomposition is discussed.展开更多
As the rapid development of railway transportation,the wear damage between wheels and rails is increasingly severe,significantly impacting the safety and efficiency of train service.A novel heavy-haul wheel(NW)steel w...As the rapid development of railway transportation,the wear damage between wheels and rails is increasingly severe,significantly impacting the safety and efficiency of train service.A novel heavy-haul wheel(NW)steel with superior rolling-slide wear resistance is presented.Additionally,the microstructure evolution and hardening mechanisms of the wheel steel after wear were analyzed by various characterization methods.The results indicate that NW wheel steel,characterized by finer pearlite lamella and low content of proeutectoid ferrite,demonstrates exceptional wear resistance under axle loads of 200 and 400 kN.Compared to CL65 steel,the wear rate of NW wheel steel is reduced by 28%and exceeds that of most reported wheel steels.After wear,the surface material of the wheel steel experiences significant deformation,forming a gradient strain layer with microstructure and hardness exhibiting gradient changes along the depth direction.The topmost material undergoes refinement and dislocation multiplication,leading to a substantial increase in surface hardness.Moreover,NW steel exhibits more severe surface dislocations and increased hardness at higher axle loads.Therefore,by controlling the pearlite content and reducing the lamellar spacing,a gradient strain layer with enhanced hardening capabilities can be achieved,thereby improving the wear resistance of the wheel material.展开更多
Supposing carbon contents of ferrite phases in pearlite precipitating from austenite in multicomponent steel at temperature T and in Fe-C ystem at T' are the same the pearlite formation temperature diference, can ...Supposing carbon contents of ferrite phases in pearlite precipitating from austenite in multicomponent steel at temperature T and in Fe-C ystem at T' are the same the pearlite formation temperature diference, can be calculated from the FeX phase diagrams and the equilibrium temperature Al. Using Tp and Fe-C binary thermodynamic model, the driving forces for phase transformation from austenite to pearlite in multicomponent steels have been successfully calculated. Through the combination of simplified Zener and Hillert's model for pearlite growth with Johnson-Mehl equation, using data from known TTT diagrams, the interfacial energy parameter and activation energy for pearlite formation can be determined and expressed as functions of chemical composition in steels by regression analysis. The calculated starting curves of pearlitic transformation in some commercial steels agree well with the experimental data.展开更多
The ultra-fast cooling technology of large section bars and the microstrueture for different cooling patterns were studied by optical microscope, transmission electron microscope and energy spectrometer. The results i...The ultra-fast cooling technology of large section bars and the microstrueture for different cooling patterns were studied by optical microscope, transmission electron microscope and energy spectrometer. The results indicated that the large section bars were passed through the zone of secondary carbide precipitation quickly by ultra-fast cooling technology （UFC） at instantaneous cooling rate of about 200 ℃/s and the finishing cooling temperature was higher than Ms. The lamellar spacing of pearlite decreased and the microhardness increased with decreasing the rereddening temperature. The precipitation of network carbide was restrained when re-reddening temperature was 690 ℃. And fine laminated pearlite was obtained through transformation of pseudopearlition that induced the reduction of the diameter of pearlite grain and refinement of the lamellar spacing of pearlite, so ideal microstructures of promoting spheroidizing annealing were obtained.展开更多
The microsturctural transformation of austenite grain, pearlite interlamellar spacing, and lamellar cement ite thickness of spring steel 60Si2MnA for railway were studied in the hot-rolled and reheated states. Further...The microsturctural transformation of austenite grain, pearlite interlamellar spacing, and lamellar cement ite thickness of spring steel 60Si2MnA for railway were studied in the hot-rolled and reheated states. Furthermore, the effect of microstructural characterization on its final mechanical properties was discussed. The results showed that as far as 60Si2MnA, the pearlite interlamellar spacing determined the hardness, whereas, the austenite grain determined the toughness. Compared with microstructure and mechanical properties in the hot rolled state, after reheating treatment at 950 ℃, its average grain sizes are apparently fine and the pearlite interlamellar spacing and lamellar cementite thickness coarsen to some extent, but both hardness and impact toughness increase to HRC 48 and 8.5 J, respectively. In the course of making spring, the optimum reheating austenitizing temperature for the 60Si2MnA steel is 950 ℃.展开更多
The microstructural banding in steels is often found in hot rolling strips, which plays a very important role in mechanical properties. Much work has been done to investigate how the microstructural banding is formed ...The microstructural banding in steels is often found in hot rolling strips, which plays a very important role in mechanical properties. Much work has been done to investigate how the microstructural banding is formed during hot rolling. In the present study, the microstructure of hot rolling strips was examined in term of optical microscopy and transmission electron microscopy. Electron probe microanalysis was also used to decide the distribution of microchemical bands, by this means, the phases in these strips were found to be ferrite and pearlite. The average distance between the carbon lamellas in pearlite is about 0.06-0.1μm. It is also shown that microstructural banding in hot rolled carbon steel was closely related to the segregation of manganese and silicon into those bands. Based on the transformation kinetic, the simulated results pointed out that the thermodynamic stability of austenite would increase with the increasing of Mn, which led to a decrease of ferrite growth rate. The effect of Mn on the decomposition of austenite is attributed to segregation of Mn atoms along the ferrite/austenite phase boundary which causes a strong solute drag effect. The addition of Mn to steel decreases the activity of austenite, thereby it is beneficial to the formation of non-equilibrium phase, such as degenerate pearlite. The formation of banded structure on the hot rolled process was discussed.展开更多
Transformation behavior in low carbon Si Mn TRIP steel was investigated by means of microstructural ob servation and computer modelling. A transformation model in which transformation is controlled by carbon diffusion...Transformation behavior in low carbon Si Mn TRIP steel was investigated by means of microstructural ob servation and computer modelling. A transformation model in which transformation is controlled by carbon diffusion was suggested, which well described the volume fractional change of ferrite, pearlite, and bainite during continuous cooling. The influence of Si content and austenite grain size was thoroughly investigated. The calculated results indicated that Si retards pearlite transformation, accelerates polygonal ferrite transformation, refines the austenite grain, and increases the ferrite transformation rate.展开更多
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The financial support of the Iron and Alloy Institute of Japan is gratefully acknowledged.One of the authors(Wantang Fu)appreciates the support from the National Natural Science Foundation of China(No.50271061).
文摘The microstructural evolution of pearlite during severe cold rolling in Fe-0.8C binary alloy and Fe-1Mn-0.8C ternary alloys was investigated by using SEM, TEM and XRD etc. The results show that the deformed pearlite consists of irregularly bent lamella, coarse lamella with shear-band and fine lamella. As the rolling reduction increases, the proportion of fine lamella increases. The strong plastic deformation, amorphization and dissolution of cementite take place during the severe cold rolling. The maximum carbon content in ferrite reaches 0.15 mass% after 90% cold rolling.
基金Item Sponsored by National Basic Research Programs of China(2015GB118001,2015CB654802)
文摘To study the microstructural evolution of pearlite steel subjected to pure rolling and rolling-sliding contact loading,a hypoeutectoid pearlite steel with composition and microstructure similar to BS11 was designed and twindisc tests of this pearlite steel were performed to simulate the wheel/rail system.After a series of twin-disc tests,optical microscope（OM）observation,scanning electron microscope（SEM）observation,X-ray diffraction（XRD）,and micro-hardness tests were conducted to characterize the microstructure.Under the pure rolling contact condition,a large amount of reticular cracks emerged within 60μm below the contact surface of the samples after 120 000 revolutions.The largest deformation was approximately 200μm below the contact surface.Under the rolling-sliding contact condition,the nodularization of pearlite within 100μm below the contact surface was obvious.The microstructure and stress-strain distribution of the area within 2mm below the contact surface were investigated.The distribution of micro-hardness under the contact surface varied with contact conditions.Finite element method（FEM）was used to simulate the stress-strain distribution.The results of SEM,FEM,and micro-hardness tests indicated that under the pure rolling contact condition,the maximum plastic strain was approximately 200-400μm below the contact surface.Conversely,under the rolling-sliding contact condition,the maximum plastic strain emerged on the contact surface.Under the pure rolling contact condition,the distribution of micro-hardness was almost identical to that of the equivalent plastic strain.Under the rolling-sliding contact condition,the distribution of micro-hardness was affected by the equivalent plastic strain and tangential stress.
基金supported by the National Natural Science Foundation of China(No.50527402).
文摘Three warm-rolled ferrite/pearlite microstructures were prepared by rolling at 500℃, and the austenitizing characteristics were discussed in conjunction with deformation during the heating stage. The results indicated that the final austenite grain size was sensitive to the deformation direction of the initial warm-rolled microstructure. The transient microstructure at a given temperature was the most important influencing factor on the austenitizing characteristic combined with deformation. Moreover, the hot-rolled mierostructure also had to be prepared in an optimal state because of its direct effect on the warm-rolled microstructure.
基金supported by Russian Scientific Foundation(Project No.15-12-00010)
文摘Using the methods of transmission electron microscopy, the carbide phase evolution in surface layers of the differentiallyquenched rails is studied after the passed tonnage of 691.8 million tons at the depth up to 10 mm along the central axis andfillet of rail head. The action of two mutual supplement mechanisms of steel carbide phase transformation in surface layersat rail operation is established： （1） cutting mechanism of cementite particles with the following departure in the volume offerrite grains or plates （in pearlite structure）; （2） cutting mechanism and following dissolution of cementite particles,transfer of carbon atoms on dislocations （in Cottrell atmospheres and dislocation cores）, transfer of carbon atoms bymoving dislocations into ferrite grains volume （or plates） with the following repeated formation of nanosized cementiteparticles. The first mechanism is accompanied by the change in linear sizes and morphology of carbide particles. Cementiteelement composition change is not essential. Carbide structure change can take place during the second mechanism.
基金financially supported by the National Natural Science Foundation of China (Nos. 51371169 and 51401214)
文摘A modified cellular automaton model is developed to depict the interface evolution inside the cementite plus ferrite lamellar microstructures during the reaustenitization of a pearlite steel. In this model, migrations of both the austenite- ferrite and austenite-cementite interfaces coupled with the carbon diffusion and redistribution are integrated. The capil- laxity effect derived from local interface curvatures is also carefully considered by involving the concentration given by the phase diagram modified by the Gibbs-Thomson effect. This allows the interface evolution from a transient state to a steady state under different annealing conditions and various interlamellar spacings to be simulated. The proposed cellular automaton approach could be readily used to describe the kinetics of austenite formation from the lamellar pearlites and virtually reveal the kinematics of the moving interfaces from the microstructural aspect.
基金Item Sponsored by National Natural Science Foundation of China (50527402)
文摘The austenite transformation characteristics for various warm-rolled pearlite during rapid heating were investigated. The results indicate that the start temperature （Ts） is sensitive to the microstructural feature of pearlite, whereas the dislocation plays an important role in the transformation rate; at the same time, the uniformity of austenite grains is more or less affected by the amount of spheroidized pearlite. A critical effect on the state of austenite grain is created through the influence of initial microstructures on the start temperature of transformation.
文摘In order to further reveal the influence of abnormal segregation band on mechanical properties of hot rolled ferrite/pearlite steel plate, especially on laminated tensile fracture, the experimental method of delamination tension was adopted. In this paper, the thin tensile samples with 3 mm thickness from the surface, 1/4 positions and center along the thickness orientation of test plate were measured, also the relationship between microstructure and mechanical properties was probed. The results show that the center region of hot rolled ferrite/pearlite steel plate exists granular bainite and ferrite mixed grains, which leads to lower plasticity and toughness of this region. During the tensile process, microcracks are generated and extended at the center of steel plate due to the inconsistency of deformation and fracture on the adjacent structures, finally leading to laminated fracture of steel plate.
文摘The flow stress of ferrite/pearlite steel under uni-axial tension was simulated with finite element method (FEM) by applying commercial software MARC/MENTAT. Flow stress curves of ferrite/pearlite steels were calculated based on unit cell model. The effects of volume fraction, distribution and the aspect ratio of pearlite on tensile properties have been investigated.
基金support for this research from State Ministry of Education (No.NCET-05-0680)support from Natural Science Foundation of Hubei Province (No.2006ABB037)
文摘The pearlite transformation in a Mo-containing iron alloy was investigated under 12 T magnetic field. The pearlite transformation was accelerated owing to the application of a strong magnetic field. Pearlite was of degenerated morphology without the presence of a strong magnetic field; but the degeneracy of pearlite is reduced when a strong magnetic field was applied, which may be attributed to the effect of strong magnetic field on faster carbon diffusion and less molybdenum segregation caused by a strong magnetic
文摘The continuous cooling transformation (CCT) diagrams of 86CrMoV7 steel samples including hot deformed and not hot deformed were constructed by dilatometry, metallography and transmission electron microscopy (TEM). The results showed that hot deformation accelerated pearlite transformation and fine pearlite microstructure. Moreover, the undissolved carbides became the nucleating sites of pearlite, accelerated pearlite formation and fine pearlite if the steel had been deformed at high temperature. In contrast, undissolved carbides did not make any influence on pearlite transformation if the steel had not been deformed at high temperature.
文摘In this paper a concept of 'leading probability' is presented. The difference in the leading probability between ferrite and cementite depends mainly upon the difference between their driving forces at the beginning of precipitation. The results of theromdynamic calculations showed that the leading probability of cementite increased with the increase of carbon concentration of austenite, and the decrease in transformation temperature was favourable to cementite's being the leading nucleus during pearlite transformation.
文摘This paper presents the results obtained, deductions made from solidification behaviour and a series of micro structural studies such as pearlite content, eu-tectic cell count and grain size of hypoeutectic gray cast iron which was sand cast (CO2 moulding) using metallic, nonmetallic, water cooled and subzero (cryogenic) end chills. Hypo-eutectic cast irons containing C 3.42, Si 2.4 and Ni 1.5 with impurity contents (S, P, Mn etc.) were solidified unidirectionally in an American Foundrymen Society (AFS) standard mould, the end of which was provided with different end chills to study the effect of chilling during solidifi-cation. The melts were inoculated with 0.3% Fe-Si to promote graphitization. It was observed that the transition from one structure to another is more gradual than normally obtained in the structure of cast irons solidified mul-ti-directionally in a sand mould at room temperature. Austenite dendrite interactions were shown to be a major factor in determining the microstructure, in which the higher dendrite reaction leads to changes in DAS, ECC and GS. It is observed that, the number of eutectic cells is an index of graphite nucleation and the effect of these on structure, since the eutectic cells are developed on the graphite nuclei during solidification.
基金Funded by the National Key R&D Program of China(No.2017YFB0304801)
文摘The microstructure evolution and its effects on the mechanical performance of 2000 MPa bridge cable steel wires were investigated by transmission electron microscope(TEM),electron backscatter diffraction(EBSD),X-ray diffractometer(XRD)and mechanical tests.Experimental results reveal that,with the increasing strain from 0 to 1.42,a fiber structure and a<110>fiber texture aligned with the wire axis are gradually developed accompanied by cementite decomposition and the formation of sub-grains;the tensile strength increases linearly from 1510 to 2025 MPa,and the reduction of the area is stable with a slight decline from 44%to 36%.After annealing at 450℃for different times,pronounced changes in the microstructure occur.Cementite lamella fragment into coarser globules corresponding to a remarkable spheroidization process,while ferrite domains recover and recrystallize,and this process is associated to modifications in the mechanical properties.Furthermore,based on the observations on dislocation lines crossing through cementite lamellae,a possible mechanism of cementite decomposition is discussed.
基金supported by the Key Project of Science and Technology in Anhui Province(No.202003a05020038)the Major Consulting Project of Chinese Academy of Engineering(No.ZGZ201812–03)。
文摘As the rapid development of railway transportation,the wear damage between wheels and rails is increasingly severe,significantly impacting the safety and efficiency of train service.A novel heavy-haul wheel(NW)steel with superior rolling-slide wear resistance is presented.Additionally,the microstructure evolution and hardening mechanisms of the wheel steel after wear were analyzed by various characterization methods.The results indicate that NW wheel steel,characterized by finer pearlite lamella and low content of proeutectoid ferrite,demonstrates exceptional wear resistance under axle loads of 200 and 400 kN.Compared to CL65 steel,the wear rate of NW wheel steel is reduced by 28%and exceeds that of most reported wheel steels.After wear,the surface material of the wheel steel experiences significant deformation,forming a gradient strain layer with microstructure and hardness exhibiting gradient changes along the depth direction.The topmost material undergoes refinement and dislocation multiplication,leading to a substantial increase in surface hardness.Moreover,NW steel exhibits more severe surface dislocations and increased hardness at higher axle loads.Therefore,by controlling the pearlite content and reducing the lamellar spacing,a gradient strain layer with enhanced hardening capabilities can be achieved,thereby improving the wear resistance of the wheel material.
文摘Supposing carbon contents of ferrite phases in pearlite precipitating from austenite in multicomponent steel at temperature T and in Fe-C ystem at T' are the same the pearlite formation temperature diference, can be calculated from the FeX phase diagrams and the equilibrium temperature Al. Using Tp and Fe-C binary thermodynamic model, the driving forces for phase transformation from austenite to pearlite in multicomponent steels have been successfully calculated. Through the combination of simplified Zener and Hillert's model for pearlite growth with Johnson-Mehl equation, using data from known TTT diagrams, the interfacial energy parameter and activation energy for pearlite formation can be determined and expressed as functions of chemical composition in steels by regression analysis. The calculated starting curves of pearlitic transformation in some commercial steels agree well with the experimental data.
基金Sponsored by National Natural Science Foundation of China(50334010)
文摘The ultra-fast cooling technology of large section bars and the microstrueture for different cooling patterns were studied by optical microscope, transmission electron microscope and energy spectrometer. The results indicated that the large section bars were passed through the zone of secondary carbide precipitation quickly by ultra-fast cooling technology （UFC） at instantaneous cooling rate of about 200 ℃/s and the finishing cooling temperature was higher than Ms. The lamellar spacing of pearlite decreased and the microhardness increased with decreasing the rereddening temperature. The precipitation of network carbide was restrained when re-reddening temperature was 690 ℃. And fine laminated pearlite was obtained through transformation of pseudopearlition that induced the reduction of the diameter of pearlite grain and refinement of the lamellar spacing of pearlite, so ideal microstructures of promoting spheroidizing annealing were obtained.
基金Item Sponsored by Science Council of Beijing of China(D0404001040221)
文摘The microsturctural transformation of austenite grain, pearlite interlamellar spacing, and lamellar cement ite thickness of spring steel 60Si2MnA for railway were studied in the hot-rolled and reheated states. Furthermore, the effect of microstructural characterization on its final mechanical properties was discussed. The results showed that as far as 60Si2MnA, the pearlite interlamellar spacing determined the hardness, whereas, the austenite grain determined the toughness. Compared with microstructure and mechanical properties in the hot rolled state, after reheating treatment at 950 ℃, its average grain sizes are apparently fine and the pearlite interlamellar spacing and lamellar cementite thickness coarsen to some extent, but both hardness and impact toughness increase to HRC 48 and 8.5 J, respectively. In the course of making spring, the optimum reheating austenitizing temperature for the 60Si2MnA steel is 950 ℃.
基金This work was supported by the National High Technical Reasearch and Development Programme of China(No.2001AA339030)Shenyang Ligong University Foundation(No.3200903).
文摘The microstructural banding in steels is often found in hot rolling strips, which plays a very important role in mechanical properties. Much work has been done to investigate how the microstructural banding is formed during hot rolling. In the present study, the microstructure of hot rolling strips was examined in term of optical microscopy and transmission electron microscopy. Electron probe microanalysis was also used to decide the distribution of microchemical bands, by this means, the phases in these strips were found to be ferrite and pearlite. The average distance between the carbon lamellas in pearlite is about 0.06-0.1μm. It is also shown that microstructural banding in hot rolled carbon steel was closely related to the segregation of manganese and silicon into those bands. Based on the transformation kinetic, the simulated results pointed out that the thermodynamic stability of austenite would increase with the increasing of Mn, which led to a decrease of ferrite growth rate. The effect of Mn on the decomposition of austenite is attributed to segregation of Mn atoms along the ferrite/austenite phase boundary which causes a strong solute drag effect. The addition of Mn to steel decreases the activity of austenite, thereby it is beneficial to the formation of non-equilibrium phase, such as degenerate pearlite. The formation of banded structure on the hot rolled process was discussed.
基金Item Sponsored by National Natural Science Foundation of China(50334010)
文摘Transformation behavior in low carbon Si Mn TRIP steel was investigated by means of microstructural ob servation and computer modelling. A transformation model in which transformation is controlled by carbon diffusion was suggested, which well described the volume fractional change of ferrite, pearlite, and bainite during continuous cooling. The influence of Si content and austenite grain size was thoroughly investigated. The calculated results indicated that Si retards pearlite transformation, accelerates polygonal ferrite transformation, refines the austenite grain, and increases the ferrite transformation rate.
