Transformation plasticity in ceria-stabilized tetragonal zirconia poly- crystals due to the stress-induced tetragonal-to-monoclinic martensitic transforma- tion under tension and bending is studied by moire interferom...Transformation plasticity in ceria-stabilized tetragonal zirconia poly- crystals due to the stress-induced tetragonal-to-monoclinic martensitic transforma- tion under tension and bending is studied by moire interferometry. The whole fringe patterns including u fields and v fields are acquired. According to these patterns, the distributions of transformation plasticity in transformation zones are obtained, and the phenomenon of plastic flow localization for transformation is revealed. The above work provides a significant experimental foundation for establishing transformation constitutive relations展开更多
With the two sublattices model, equilibrium compositions of ferrite (α) and austenite (γ) phases, as well as the volume percent of austenite (γ) in different TRIP steels are calculated. Concentration profiles of ca...With the two sublattices model, equilibrium compositions of ferrite (α) and austenite (γ) phases, as well as the volume percent of austenite (γ) in different TRIP steels are calculated. Concentration profiles of carbon, manganese, aluminum and silicon in these steels are also estimated under the lattice fixed frame of reference so as to identify if the equilibrium state is obtained. Through the comparison between the profiles after different time diffusion, the distribution of elements in phases is exhibited and the complex effect due to the mutual interaction of the elements on diffusion is discussed.展开更多
The Luders deformation behavior in a medium Mn transformation induced plasticity （TRIP） steel is investigated at different temperatures ranging from 25 to 300 ℃. It demonstrates that the Ltiders band appears at all...The Luders deformation behavior in a medium Mn transformation induced plasticity （TRIP） steel is investigated at different temperatures ranging from 25 to 300 ℃. It demonstrates that the Ltiders band appears at all testing temperatures but with varied Luders strains which do not change monoton ically with temperature. The martensitic transformation is simultaneously observed within the Ltiders band in varying degrees depending on the testing temperature. It is well verified that the martensitic transformation is not responsible for the formation of Luders band, and a reasonable explanation is given for the non-monotonic variation of Luders strain with increasing temperature.展开更多
The weldability of 0.28C-2.0Mn-0.93Al-0.97Si(wt.%)transformation induced plasticity(TRIP)steels was investigated using a 2.5 kW CO2 laser at the welding speeds of 2,2.5 and 3 m/min.The welded joints were characterized...The weldability of 0.28C-2.0Mn-0.93Al-0.97Si(wt.%)transformation induced plasticity(TRIP)steels was investigated using a 2.5 kW CO2 laser at the welding speeds of 2,2.5 and 3 m/min.The welded joints were characterized in terms of hardness,tensile properties and microstructure.High-quality welded joints of TRIP steels with the carbon equivalent of 0.7 were obtained.Lower loss of ductility,nearly unvaried hardness of the fusion zone(FZ)and tensile strength equal to the base metal were observed with increasing welding speed.Lath martensite and lower bainite formed in FZ and the microstructure of FZ varied little with welding speed.Weld thermal simulations of heat-afected zone(HAZ)were carried out using a quenching dilatometer,and the microstructures of dilatometric samples revealed the carbon diffusion-controlled transformations in HAZ.The microstructure distribution of HAZ could be influenced by the welding speed due to the significant temperature gradient over the narrow HAZ.展开更多
Thermomechanical controlled processing （TMCP） was conducted by using a laboratory hot rolling mill. Austempering in the salt bath after hot rolling was investigated. The effect of isothermal holding time on mechanic...Thermomechanical controlled processing （TMCP） was conducted by using a laboratory hot rolling mill. Austempering in the salt bath after hot rolling was investigated. The effect of isothermal holding time on mechanical properties was studied through examining of the microstructure and mechanical properties of the specimens. The mechanism of transformation-induced plasticity （TRIP） was discussed. The results show that the microstructure of these steels consists of polygonal ferrite, granular bainite, and a significant amount of stable retained austenite. Strain-induced transformation to martensite of retained austenite and TRIP occur in the hot rolled Si-Mn TRIP steels. Excellent mechanical properties were obtained for various durations at 400℃. Prolonged holding led to cementite precipitation, which destabilized the austenite. The mechanical properties were optimal when the specimen was held for 25 min, and the tensile strength, total elongation, and strength ductility balance reached the maximum values of 776 MPa, 33%, and 25608 MPa.%, respectively.展开更多
The hot deformation behavior and microstructure evolution of high manganese transformation induced plasticity steel(Fe - 20Mn - 3Si - 3Al) were investigated by using hot compression test in a temperature range from 80...The hot deformation behavior and microstructure evolution of high manganese transformation induced plasticity steel(Fe - 20Mn - 3Si - 3Al) were investigated by using hot compression test in a temperature range from 800℃to 1 050℃and strain rate ranging from 0.01 s^(-1) to 5.0 s^(-1).The effects of temperature,strain rate,and true strain on the flow behavior and microstructures of high manganese transformation induced plasticity steel were discussed.The results show that the dynamic recrystallization occurs only at higher temperature and lower strain rate.Hot deformation behaviors of high manganese transformation induced plasticity steel were sensitive to temperature and strain rate.The apparent stress exponent and the apparent activation energy of the investigated steel were about 4.280 and 463.791 kJ/mol, respectively.The apparent activation energy of the high manganese transformation induced plasticity steel was approached to the austenitic stainless steel(400 -500 kJ/mol).The hot working equation is obtained. Hot deformation peak stress increased with increasing of the value of lnZ.Peak stress and InZ exhibits a linear variation,the linear correlation coefficient was 0.988 9.The results show that the dynamic recrystallization was prone to occur when lnZ≤43.842 26 and Z≤1.098×10^(19),and better hot deformation properties would be obtained under this condition.展开更多
To obtain a better understanding the thermal stress of a rail,the thermal simulator was used to measure the expansion curves of different stresses loaded during the continuous cooling process of U75V rail.The transfor...To obtain a better understanding the thermal stress of a rail,the thermal simulator was used to measure the expansion curves of different stresses loaded during the continuous cooling process of U75V rail.The transformation plasticity model was established.The experimental results show that stress can accelerate the transformation process of pearlite.While the same cooling rate is accelerated with the increase of stress,the transformation process of pearlite is accelerated,and the proportion of plastic strain transformation in total strain increases.At the same stress,the process of transformation of pearlite decreases with the increase in cooling rate,and the proportion of transformation plastic strain in total strain decreases.When considering the transformation plasticity,the axial residual stress is more consistent with the actual working condition,the accuracy of the transformation plasticity model is higher;during the continuous cooling process,and the loading stress has a significant influence on the structure.When the stress increases,the orientation of the pearlite lamellae becomes disordered,the pearlite lamellae are bent,the lamellae spacing is no longer uniform,and the hardness is improved.展开更多
As a representative of the third generation advanced high-strength steels(AHSSs),medium Mn steels(MMS)have broad development prospects in the field of automobile manufacturing.MMS with typical austenite reversion trea...As a representative of the third generation advanced high-strength steels(AHSSs),medium Mn steels(MMS)have broad development prospects in the field of automobile manufacturing.MMS with typical austenite reversion treatment have a soft duplex microstructure,i.e.ferrite+austenite,presenting a high ductility but a low yield strength.Here we show that a flash heating and cooling after austenite reversion treatment can replace the ferrite with strong martensite,which greatly enhances the yield strength of a 0.25C-4Mn steel by about 461–886 MPa.By adjusting the reversion temperature before the flash treatment,the C and Mn concentrations of reverted austenite can be altered,which determine the fraction of reverted austenite surviving the flash treatment.In addition,the mechanical stability of final retained austenite is also linked to the reversion temperature,resulting different work hardening behaviors due to transformation induced plasticity(TRIP)effect.By tweaking the reversion temperature before the flash treatment,an optimized combination of strength and ductility can be achieved.The micromechanical differences caused by the replacement of the matrix are also investigated via in-situ digital image correlation method.展开更多
In order to reveal the cavitation erosion mechanisms of Fe_(50)Mn_(30)Co_(10)Cr_(10)coating prepared by laser melting deposition(LMD)technique,the phase composition evolution,microstructure,microhardness,cavitation er...In order to reveal the cavitation erosion mechanisms of Fe_(50)Mn_(30)Co_(10)Cr_(10)coating prepared by laser melting deposition(LMD)technique,the phase composition evolution,microstructure,microhardness,cavitation erosion resistance and failure mechanisms were investigated.The results demonstrate that the amount of martensite HCPεphase of the coating surface increased by a factor of 2.43,and the microhardness increased from HV 270 to HV 410 after 20 h of cavitation erosion test in distilled water.The cumulative volume loss of the coating was approximately 55%less than that of AlCoCrxCuFe(x=2.0),and the cumulative mean depth of erosion(MDE)was 9%that of FeCoCrAlNiTix(x=2.0).The surface strength and plasticity of the coating were further strengthened in the process of cavitation erosion due to the back stress strengthening and work hardening mechanism caused by the heterogeneous structure,which effectively improved the cavitation erosion resistance of the coating.展开更多
Development of high-performance phase transformation electrodes in lithium ion batteries requires comprehensive studies on stress-mediated lithiation involving migration of the phase interface. It brings out many coun...Development of high-performance phase transformation electrodes in lithium ion batteries requires comprehensive studies on stress-mediated lithiation involving migration of the phase interface. It brings out many counter-intuitive phenomena, especially in nanoscale electrodes, such as the slowing down migration of phase interface, the vanishing of miscibility gap under high charge rate, and the formation of surface crack during lithiation. However, it is still a challenge to simulate the evolution of stress in arbitrarily-shaped nanoscale electrodes, accompanied with phase transformation and concurrent plastic deformation. This article gives a brief review of our efforts devoted to address these issues by developing phase field model and simulation. We demonstrate that the miscibility gap of two-phase state is affected not only by stress but also by surface reaction rate and particle size. In addition, the migration of phase interface slows down due to stress. It reveals that the plastic deformation generates large radial expansion, which is responsible for the transition from surface hoop compression to surface hoop tension that may induce surface crack during lithiation. We hope our effort can make a contribution to the understanding of stress-coupled kinetics in phase transformation electrodes.展开更多
During quenching, the residual stresses are affected by the crystallographic orientation of martensite, because the nonuniform thermal stresses affect the crystallographic orientation of the lathshaped martensite and ...During quenching, the residual stresses are affected by the crystallographic orientation of martensite, because the nonuniform thermal stresses affect the crystallographic orientation of the lathshaped martensite and induce the anisotropic expansion. To simulate this process, the model of anisotropic transformation induced plasticity（TRIP） was built using the WLR-BM phenomenological theory. The equivalent expansion coefficient was introduced considering the thermal and plastic strains, which simplified the numerical simulation. Furthermore, the quenching residual stresses in carbon steel plates were calculated using the finite element method under ANSYS Workbench simulation environment. To evaluate the simulative results, distributions of residual stresses from the surface to the interior at the center of specimen were measured using the layer-by-layer hole-drilling method. Compared to the measured results, the simulative results considering the anisotropic expansion induced by the crystallographic orientation of martenstic laths were found to be more accurate than those without considering it.展开更多
To provide data for improved modelling of the behaviour of steel components in a simultaneous forming and quenching process, the effects of plastic deformation and stresses on dilatation during the martensitic transfo...To provide data for improved modelling of the behaviour of steel components in a simultaneous forming and quenching process, the effects of plastic deformation and stresses on dilatation during the martensitic transformation in a B-bearing steel were investigated. It was found that plastic deformation of austenite at high temperatures enhances ferrite formation significantly, and consequently, the dilatation decreases markedly even at a cooling rate of 280'C/s. The created ferritic-martensitic microstructure possesses clearly lower hardness and strength than the martensitic structure. Elastic stresses cause the preferred orientation in martensite to be formed so that diametric dilatation can increase by nearly 200% under axial compression.展开更多
The incubation period of proeutectoid ferrite transformation for Si-Mn transformation induced plasticity (TRIP) steel has been calculated by the Aaronson's incubation period model for transformation.The influences...The incubation period of proeutectoid ferrite transformation for Si-Mn transformation induced plasticity (TRIP) steel has been calculated by the Aaronson's incubation period model for transformation.The influences of chemical compositions and hot deformation of austenite on the incubation period have been taken into consideration in the calculation,and some parameters have been proposed and validated with the measured time temperature transformation (TTT) curves from dilation tests.The calculation results show that it is essential to take into account of the effect of solute atoms on the interfacial energy in the austenite grain boundaries.For hypoeutectoid steel,the incubation period of ferrite transformation increases with the increase of C and Mn contents,and C has a greater impact than that of Mn,while the incubation period of ferrite transformation decreases with the increase of Si content.Hot deformation shortens the incubation time and promotes austenite to ferrite transformation.展开更多
2Y-PSZ/TRIP steel composites have been sintered by hot-pressing method. Their microstructure and mechanical properties were investigated by means of SEM, TEM, XRD and static tension, split Hopkinson pressure bar metho...2Y-PSZ/TRIP steel composites have been sintered by hot-pressing method. Their microstructure and mechanical properties were investigated by means of SEM, TEM, XRD and static tension, split Hopkinson pressure bar method. The results showed that the strength and elastic modulus of 2Y-PSZ/TRIP steel composites at room temperature decreased with the increase of 2Y-PSZ content. The main reason was that the combining strength was quite weak between the grains of ZrO2. Distortion induced martensite transformation and plasticity during the dynamic loading increased the strength and distortion capability of the composites. The transformation was carried out mainly through twins formation. The shape of martensite induced by distortion was lamellate with substructures of twins. The habit plane was near {259}T with no mid-ridge and no explosion phenomena. The interface was straight between the austenite and martensite induced by distortion. The increase of 2Y-PSZ content, on the one hand, made the composite dynamic flow stress improved. Thereby, the fracture strength was improved. On the other hand, it depressed both the distortion capability and the martensite transformation induced by distortion. This resulted in the decrease of dynamic fracture strength.展开更多
The equation which reflects the relationship between the retained austenite and strain has been proposed and clear TRIP can be obtained while the S value (An index of retained austenite stability) is less than 6.5 for...The equation which reflects the relationship between the retained austenite and strain has been proposed and clear TRIP can be obtained while the S value (An index of retained austenite stability) is less than 6.5 for Silicon-Manganese TRIP steel展开更多
The mechanical properties of transformation induced plasticity （TRIP） steel are strongly affected by the conditions of iso-thermal bainitic processing. The multiphase microstructure of TRIP steel under different con...The mechanical properties of transformation induced plasticity （TRIP） steel are strongly affected by the conditions of iso-thermal bainitic processing. The multiphase microstructure of TRIP steel under different conditions of isothermal bainitic processing was investigated using OM,SEM,XRD and TEM. The volume fraction of retained austenite and the carbon content in austenite were determined quantitatively using X-ray diffraction patterns. The relationship between mechanical properties and isothermal bainitic processing parameters was investigated. The stability of retained austenite was analyzed by the volume fraction of retained austenite and the carbon content in retained austenite. The experimental results show that the multiphase microstructure consists of ferrite,bainite and metastable retained austenite.To obtain good mechanical properties,the optimal conditions of isothermal bainitic temperature and holding time are 410-430°C and 180-240 s,respectively. After isothermal bainitic processing under the optimal conditions,the corresponding volume fraction of retained austenite is 5vol%-15vol%,which can provide enough retained austenite and plastic stability for austenite with high carbon content.展开更多
Bead-on-plate CO2 laser welding of 1 000 MPa grade transformation induced plasticity （TRIP） steel was conducted under different welding powers, welding speeds and shield gases. The macrostructural and microstructura...Bead-on-plate CO2 laser welding of 1 000 MPa grade transformation induced plasticity （TRIP） steel was conducted under different welding powers, welding speeds and shield gases. The macrostructural and microstructural features of the welded joint were investigated. The increase of welding speed reduced the width of the weld bead and the porosities in the weld bead resulting from the different flow mode of melted metal in weld pool. The decrease of welding power or use of shield gas of helium also contributed to the reduction of porosity in the weld bead due to the alleviation of induced plasma formation, thus stabilizing the keyhole. The porosity formation intimately correlated with the evaporation of alloy element Mn in the base metal. The laser welded metal had same martensite microstructure as that of water-quenched base metal. The welding parameters which increased cooling rate all led to fine microstructures of the weld bead.展开更多
The high-manganese steels are important structural materials,owing to their excellent toughness at low temperatures.However,the microstructural causes for their unusual properties have not adequately been understood t...The high-manganese steels are important structural materials,owing to their excellent toughness at low temperatures.However,the microstructural causes for their unusual properties have not adequately been understood thus far.Here,we report a reversal relationship between impact toughness and grain size in a high-manganese steel and its unrevealed microscopic mechanisms,which result in an excellent low-temperature toughness of the steel.Our investigations show that with increasing grain size the impact toughness of the steel can be improved drastically,especially at low-temperatures.Advanced electron microscopy characterization reveals that the enhanced impact toughness of the coarse-grained steel is attributed to the twinning induced plasticity and transformation induced plasticity effects,which produce large quantities of deformation twins,ε_(hcp)-martensite andα'_(bcc)-martensite.Inversely,in the fine-grained steels,the formation of deformation twins and martensite is significantly inhibited,leading to the decrease of impact toughness.Microstructural characterizations also indicate thatε_(hcp)-martensite becomes more stable thanα'_(bcc)-martensite with decreasing temperature,resulting in characteristic microstructures in the coarse-grained samples after impact deformation at liquid nitrogen temperature.In the coarse-grained samples under impact deformation at-80℃,ε_(hcp)-martensite transformation,α'_(bcc)-martensite transformation and deformation twinning all occur simultaneously,which greatly improves the toughness of the steel.展开更多
Microstructures and mechanical properties of Nd ： YAG laser welded transformation induced plasticity （TRIP） steel with tensile strength of 645 MPa were studied. Due to high cooling speed of laser welding, the weld ...Microstructures and mechanical properties of Nd ： YAG laser welded transformation induced plasticity （TRIP） steel with tensile strength of 645 MPa were studied. Due to high cooling speed of laser welding, the weld metal mainly consists of martensite different from the base metal, which is composed of ferrite matrix with bainite and a little retained austenite. Therefore, the weld metal has maximum hardness at welded joint. The yield strength and tensile strength of welded specimens tested perpendicular to weld line were almost equal to those of the base metal. But the yield strength and tensile strength of welded specimens tested parallel with weld line were a little higher than those of the base metal. The formability of laser welded TRIP steel was decreased compared with that of the base metal.展开更多
基金The project supported by the National Natural Science Foundation of China
文摘Transformation plasticity in ceria-stabilized tetragonal zirconia poly- crystals due to the stress-induced tetragonal-to-monoclinic martensitic transforma- tion under tension and bending is studied by moire interferometry. The whole fringe patterns including u fields and v fields are acquired. According to these patterns, the distributions of transformation plasticity in transformation zones are obtained, and the phenomenon of plastic flow localization for transformation is revealed. The above work provides a significant experimental foundation for establishing transformation constitutive relations
文摘With the two sublattices model, equilibrium compositions of ferrite (α) and austenite (γ) phases, as well as the volume percent of austenite (γ) in different TRIP steels are calculated. Concentration profiles of carbon, manganese, aluminum and silicon in these steels are also estimated under the lattice fixed frame of reference so as to identify if the equilibrium state is obtained. Through the comparison between the profiles after different time diffusion, the distribution of elements in phases is exhibited and the complex effect due to the mutual interaction of the elements on diffusion is discussed.
基金support from the Steel Joint Funds of the National Natural Science Foundation of China(Grant No.U1560204)Research Grants Council of Hong Kong(Grant Nos.HKU719712E,HKU712713E)Small Project Funding of HKU(Grant No.201409176053)
文摘The Luders deformation behavior in a medium Mn transformation induced plasticity （TRIP） steel is investigated at different temperatures ranging from 25 to 300 ℃. It demonstrates that the Ltiders band appears at all testing temperatures but with varied Luders strains which do not change monoton ically with temperature. The martensitic transformation is simultaneously observed within the Ltiders band in varying degrees depending on the testing temperature. It is well verified that the martensitic transformation is not responsible for the formation of Luders band, and a reasonable explanation is given for the non-monotonic variation of Luders strain with increasing temperature.
基金the Technology Innovation Program of Shanghai Research Institute of Materials(19SG-06)The authors gratefully acknowledge Ansteel Group Corporation for providing the materials,and the authors also acknowledge the support from Instrumental Analysis and Research Center of Shanghai University for the microstructural characterizations.
文摘The weldability of 0.28C-2.0Mn-0.93Al-0.97Si(wt.%)transformation induced plasticity(TRIP)steels was investigated using a 2.5 kW CO2 laser at the welding speeds of 2,2.5 and 3 m/min.The welded joints were characterized in terms of hardness,tensile properties and microstructure.High-quality welded joints of TRIP steels with the carbon equivalent of 0.7 were obtained.Lower loss of ductility,nearly unvaried hardness of the fusion zone(FZ)and tensile strength equal to the base metal were observed with increasing welding speed.Lath martensite and lower bainite formed in FZ and the microstructure of FZ varied little with welding speed.Weld thermal simulations of heat-afected zone(HAZ)were carried out using a quenching dilatometer,and the microstructures of dilatometric samples revealed the carbon diffusion-controlled transformations in HAZ.The microstructure distribution of HAZ could be influenced by the welding speed due to the significant temperature gradient over the narrow HAZ.
基金This work was financially supported by the National Natural Science Foundation of China (No.50334010).
文摘Thermomechanical controlled processing （TMCP） was conducted by using a laboratory hot rolling mill. Austempering in the salt bath after hot rolling was investigated. The effect of isothermal holding time on mechanical properties was studied through examining of the microstructure and mechanical properties of the specimens. The mechanism of transformation-induced plasticity （TRIP） was discussed. The results show that the microstructure of these steels consists of polygonal ferrite, granular bainite, and a significant amount of stable retained austenite. Strain-induced transformation to martensite of retained austenite and TRIP occur in the hot rolled Si-Mn TRIP steels. Excellent mechanical properties were obtained for various durations at 400℃. Prolonged holding led to cementite precipitation, which destabilized the austenite. The mechanical properties were optimal when the specimen was held for 25 min, and the tensile strength, total elongation, and strength ductility balance reached the maximum values of 776 MPa, 33%, and 25608 MPa.%, respectively.
文摘The hot deformation behavior and microstructure evolution of high manganese transformation induced plasticity steel(Fe - 20Mn - 3Si - 3Al) were investigated by using hot compression test in a temperature range from 800℃to 1 050℃and strain rate ranging from 0.01 s^(-1) to 5.0 s^(-1).The effects of temperature,strain rate,and true strain on the flow behavior and microstructures of high manganese transformation induced plasticity steel were discussed.The results show that the dynamic recrystallization occurs only at higher temperature and lower strain rate.Hot deformation behaviors of high manganese transformation induced plasticity steel were sensitive to temperature and strain rate.The apparent stress exponent and the apparent activation energy of the investigated steel were about 4.280 and 463.791 kJ/mol, respectively.The apparent activation energy of the high manganese transformation induced plasticity steel was approached to the austenitic stainless steel(400 -500 kJ/mol).The hot working equation is obtained. Hot deformation peak stress increased with increasing of the value of lnZ.Peak stress and InZ exhibits a linear variation,the linear correlation coefficient was 0.988 9.The results show that the dynamic recrystallization was prone to occur when lnZ≤43.842 26 and Z≤1.098×10^(19),and better hot deformation properties would be obtained under this condition.
基金Funded by the Inner Mongolia Science and Technology Major Project(No.ZDZX2018024)the Natural Science Foundation of Inner Mongolia(No.2019LH05016)+1 种基金the Research Program of Science and Technology at Universities of Inner Mongolia Autonomous Region of China(No.NJZY20089)the Innovation Fund of Inner Mongolia University of Science and Technology(No.2019QDL-B06)。
文摘To obtain a better understanding the thermal stress of a rail,the thermal simulator was used to measure the expansion curves of different stresses loaded during the continuous cooling process of U75V rail.The transformation plasticity model was established.The experimental results show that stress can accelerate the transformation process of pearlite.While the same cooling rate is accelerated with the increase of stress,the transformation process of pearlite is accelerated,and the proportion of plastic strain transformation in total strain increases.At the same stress,the process of transformation of pearlite decreases with the increase in cooling rate,and the proportion of transformation plastic strain in total strain decreases.When considering the transformation plasticity,the axial residual stress is more consistent with the actual working condition,the accuracy of the transformation plasticity model is higher;during the continuous cooling process,and the loading stress has a significant influence on the structure.When the stress increases,the orientation of the pearlite lamellae becomes disordered,the pearlite lamellae are bent,the lamellae spacing is no longer uniform,and the hardness is improved.
基金National Key R&D Program of China(Grant Nos.2022YFE0110800 and 2022YFB3705300)the National Natural Science Foundation of China(Grant Nos.52104380 and 52171123)for grant and financial support.
文摘As a representative of the third generation advanced high-strength steels(AHSSs),medium Mn steels(MMS)have broad development prospects in the field of automobile manufacturing.MMS with typical austenite reversion treatment have a soft duplex microstructure,i.e.ferrite+austenite,presenting a high ductility but a low yield strength.Here we show that a flash heating and cooling after austenite reversion treatment can replace the ferrite with strong martensite,which greatly enhances the yield strength of a 0.25C-4Mn steel by about 461–886 MPa.By adjusting the reversion temperature before the flash treatment,the C and Mn concentrations of reverted austenite can be altered,which determine the fraction of reverted austenite surviving the flash treatment.In addition,the mechanical stability of final retained austenite is also linked to the reversion temperature,resulting different work hardening behaviors due to transformation induced plasticity(TRIP)effect.By tweaking the reversion temperature before the flash treatment,an optimized combination of strength and ductility can be achieved.The micromechanical differences caused by the replacement of the matrix are also investigated via in-situ digital image correlation method.
基金supported by the Innovative Research Team Development Program of Ministry of Education of China(No.IRT_17R83)State Key Laboratory of Materials Processing and Die&Mould Technology,Huazhong University of Science and Technology,China(No.P2021-018).
文摘In order to reveal the cavitation erosion mechanisms of Fe_(50)Mn_(30)Co_(10)Cr_(10)coating prepared by laser melting deposition(LMD)technique,the phase composition evolution,microstructure,microhardness,cavitation erosion resistance and failure mechanisms were investigated.The results demonstrate that the amount of martensite HCPεphase of the coating surface increased by a factor of 2.43,and the microhardness increased from HV 270 to HV 410 after 20 h of cavitation erosion test in distilled water.The cumulative volume loss of the coating was approximately 55%less than that of AlCoCrxCuFe(x=2.0),and the cumulative mean depth of erosion(MDE)was 9%that of FeCoCrAlNiTix(x=2.0).The surface strength and plasticity of the coating were further strengthened in the process of cavitation erosion due to the back stress strengthening and work hardening mechanism caused by the heterogeneous structure,which effectively improved the cavitation erosion resistance of the coating.
基金supported by the National Natural Science Foundation of China (Grant no. 11472262)the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant no. XDB22040502)+1 种基金the Collaborative Innovation Center of Suzhou Nano Science and Technologythe Fundamental Research Funds for the Central Universities
文摘Development of high-performance phase transformation electrodes in lithium ion batteries requires comprehensive studies on stress-mediated lithiation involving migration of the phase interface. It brings out many counter-intuitive phenomena, especially in nanoscale electrodes, such as the slowing down migration of phase interface, the vanishing of miscibility gap under high charge rate, and the formation of surface crack during lithiation. However, it is still a challenge to simulate the evolution of stress in arbitrarily-shaped nanoscale electrodes, accompanied with phase transformation and concurrent plastic deformation. This article gives a brief review of our efforts devoted to address these issues by developing phase field model and simulation. We demonstrate that the miscibility gap of two-phase state is affected not only by stress but also by surface reaction rate and particle size. In addition, the migration of phase interface slows down due to stress. It reveals that the plastic deformation generates large radial expansion, which is responsible for the transition from surface hoop compression to surface hoop tension that may induce surface crack during lithiation. We hope our effort can make a contribution to the understanding of stress-coupled kinetics in phase transformation electrodes.
基金Funded by the Creative Research Groups of National Natural Science Foundation of China(No.51221004)the National Natural Science Foundation of China(Nos.51375443,50675200)
文摘During quenching, the residual stresses are affected by the crystallographic orientation of martensite, because the nonuniform thermal stresses affect the crystallographic orientation of the lathshaped martensite and induce the anisotropic expansion. To simulate this process, the model of anisotropic transformation induced plasticity（TRIP） was built using the WLR-BM phenomenological theory. The equivalent expansion coefficient was introduced considering the thermal and plastic strains, which simplified the numerical simulation. Furthermore, the quenching residual stresses in carbon steel plates were calculated using the finite element method under ANSYS Workbench simulation environment. To evaluate the simulative results, distributions of residual stresses from the surface to the interior at the center of specimen were measured using the layer-by-layer hole-drilling method. Compared to the measured results, the simulative results considering the anisotropic expansion induced by the crystallographic orientation of martenstic laths were found to be more accurate than those without considering it.
文摘To provide data for improved modelling of the behaviour of steel components in a simultaneous forming and quenching process, the effects of plastic deformation and stresses on dilatation during the martensitic transformation in a B-bearing steel were investigated. It was found that plastic deformation of austenite at high temperatures enhances ferrite formation significantly, and consequently, the dilatation decreases markedly even at a cooling rate of 280'C/s. The created ferritic-martensitic microstructure possesses clearly lower hardness and strength than the martensitic structure. Elastic stresses cause the preferred orientation in martensite to be formed so that diametric dilatation can increase by nearly 200% under axial compression.
基金the Scientific and Technical Supporting Program of China during the 11th Five-Year Plan(No.2006BAE03A08)
文摘The incubation period of proeutectoid ferrite transformation for Si-Mn transformation induced plasticity (TRIP) steel has been calculated by the Aaronson's incubation period model for transformation.The influences of chemical compositions and hot deformation of austenite on the incubation period have been taken into consideration in the calculation,and some parameters have been proposed and validated with the measured time temperature transformation (TTT) curves from dilation tests.The calculation results show that it is essential to take into account of the effect of solute atoms on the interfacial energy in the austenite grain boundaries.For hypoeutectoid steel,the incubation period of ferrite transformation increases with the increase of C and Mn contents,and C has a greater impact than that of Mn,while the incubation period of ferrite transformation decreases with the increase of Si content.Hot deformation shortens the incubation time and promotes austenite to ferrite transformation.
文摘2Y-PSZ/TRIP steel composites have been sintered by hot-pressing method. Their microstructure and mechanical properties were investigated by means of SEM, TEM, XRD and static tension, split Hopkinson pressure bar method. The results showed that the strength and elastic modulus of 2Y-PSZ/TRIP steel composites at room temperature decreased with the increase of 2Y-PSZ content. The main reason was that the combining strength was quite weak between the grains of ZrO2. Distortion induced martensite transformation and plasticity during the dynamic loading increased the strength and distortion capability of the composites. The transformation was carried out mainly through twins formation. The shape of martensite induced by distortion was lamellate with substructures of twins. The habit plane was near {259}T with no mid-ridge and no explosion phenomena. The interface was straight between the austenite and martensite induced by distortion. The increase of 2Y-PSZ content, on the one hand, made the composite dynamic flow stress improved. Thereby, the fracture strength was improved. On the other hand, it depressed both the distortion capability and the martensite transformation induced by distortion. This resulted in the decrease of dynamic fracture strength.
文摘The equation which reflects the relationship between the retained austenite and strain has been proposed and clear TRIP can be obtained while the S value (An index of retained austenite stability) is less than 6.5 for Silicon-Manganese TRIP steel
文摘The mechanical properties of transformation induced plasticity （TRIP） steel are strongly affected by the conditions of iso-thermal bainitic processing. The multiphase microstructure of TRIP steel under different conditions of isothermal bainitic processing was investigated using OM,SEM,XRD and TEM. The volume fraction of retained austenite and the carbon content in austenite were determined quantitatively using X-ray diffraction patterns. The relationship between mechanical properties and isothermal bainitic processing parameters was investigated. The stability of retained austenite was analyzed by the volume fraction of retained austenite and the carbon content in retained austenite. The experimental results show that the multiphase microstructure consists of ferrite,bainite and metastable retained austenite.To obtain good mechanical properties,the optimal conditions of isothermal bainitic temperature and holding time are 410-430°C and 180-240 s,respectively. After isothermal bainitic processing under the optimal conditions,the corresponding volume fraction of retained austenite is 5vol%-15vol%,which can provide enough retained austenite and plastic stability for austenite with high carbon content.
文摘Bead-on-plate CO2 laser welding of 1 000 MPa grade transformation induced plasticity （TRIP） steel was conducted under different welding powers, welding speeds and shield gases. The macrostructural and microstructural features of the welded joint were investigated. The increase of welding speed reduced the width of the weld bead and the porosities in the weld bead resulting from the different flow mode of melted metal in weld pool. The decrease of welding power or use of shield gas of helium also contributed to the reduction of porosity in the weld bead due to the alleviation of induced plasma formation, thus stabilizing the keyhole. The porosity formation intimately correlated with the evaporation of alloy element Mn in the base metal. The laser welded metal had same martensite microstructure as that of water-quenched base metal. The welding parameters which increased cooling rate all led to fine microstructures of the weld bead.
基金supported by the National Natural Science Foundation of China[Grant Nos.5180106051831004+6 种基金1142780651671082]the China Postdoctoral Science Foundation(grant number 2019M652756)the National Key Research and Development Program of China(grant number 2016YFB0300801)the China Scholarship Council(grant number 201606130008)the financial support from Austrain Science Fund(FWF)(grant number P 32378-N37)BMBWF(grant number KR 06/2020)。
文摘The high-manganese steels are important structural materials,owing to their excellent toughness at low temperatures.However,the microstructural causes for their unusual properties have not adequately been understood thus far.Here,we report a reversal relationship between impact toughness and grain size in a high-manganese steel and its unrevealed microscopic mechanisms,which result in an excellent low-temperature toughness of the steel.Our investigations show that with increasing grain size the impact toughness of the steel can be improved drastically,especially at low-temperatures.Advanced electron microscopy characterization reveals that the enhanced impact toughness of the coarse-grained steel is attributed to the twinning induced plasticity and transformation induced plasticity effects,which produce large quantities of deformation twins,ε_(hcp)-martensite andα'_(bcc)-martensite.Inversely,in the fine-grained steels,the formation of deformation twins and martensite is significantly inhibited,leading to the decrease of impact toughness.Microstructural characterizations also indicate thatε_(hcp)-martensite becomes more stable thanα'_(bcc)-martensite with decreasing temperature,resulting in characteristic microstructures in the coarse-grained samples after impact deformation at liquid nitrogen temperature.In the coarse-grained samples under impact deformation at-80℃,ε_(hcp)-martensite transformation,α'_(bcc)-martensite transformation and deformation twinning all occur simultaneously,which greatly improves the toughness of the steel.
文摘Microstructures and mechanical properties of Nd ： YAG laser welded transformation induced plasticity （TRIP） steel with tensile strength of 645 MPa were studied. Due to high cooling speed of laser welding, the weld metal mainly consists of martensite different from the base metal, which is composed of ferrite matrix with bainite and a little retained austenite. Therefore, the weld metal has maximum hardness at welded joint. The yield strength and tensile strength of welded specimens tested perpendicular to weld line were almost equal to those of the base metal. But the yield strength and tensile strength of welded specimens tested parallel with weld line were a little higher than those of the base metal. The formability of laser welded TRIP steel was decreased compared with that of the base metal.
