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
Effect of austempering on the transformation induced plasticity （TRIP） of hot rolled multiphase steel was investigated. Polygonal ferrite, granular bainite, and a large amount of stabilized retained austenite could ...Effect of austempering on the transformation induced plasticity （TRIP） of hot rolled multiphase steel was investigated. Polygonal ferrite, granular bainite, and a large amount of stabilized retained austenite could be obtained in the hot rolled multiphase steel. Strain induced martensite transformation （SIMT） of retained austenite and TRIP effectively occur under straining owing to austempering after hot rolling, and mechanical properties of the present steel remain at a relatively high constant value for austempering at 400℃. The mechanical properties of the steel exhibited a good combination of tensile strength （791MPa） and total elongation （36%） because the stability of retained austenite is optimal when the steel is held for 20min.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
On the basis of continuum mechanics and the Mori-Tanaka mean field theory, a micro-mechanical flow stress model that considered both the transformation-induced plasticity （TRIP） effect and the inelastic strain recov...On the basis of continuum mechanics and the Mori-Tanaka mean field theory, a micro-mechanical flow stress model that considered both the transformation-induced plasticity （TRIP） effect and the inelastic strain recovery behavior of TRIP multiphase steels was presented. The relation between the volume fraction of constituent phases and plastic strain was introduced to characterize the transformation-induced plasticity effect of TRIP steels. Loading-unloading-reloading uniaxial tension tests of TRIP600 steel were carried out and the strain recovery behavior after unloading was analyzed. From the experimental data, an empirical elastic modulus expression is extracted to characterize the inelastic strain recovery. A comparison of the predicted flow stress with the experimental data shows a good agreement. The mechanism of the transformation-induced plasticity effect and the inelastic recovery effect acting on the flow stress is also discussed in detail.展开更多
Effects of deformation temperature on the mechanical properties and microstructure of lean duplex stainless steels B2102 and S32101 have been investigated. It was found that the strength decreased continuously with in...Effects of deformation temperature on the mechanical properties and microstructure of lean duplex stainless steels B2102 and S32101 have been investigated. It was found that the strength decreased continuously with increases in temperature from -60 ℃ to 100 ℃. The strength of S32101 was higher than that of B2102 owing to its higher nitrogen content. Plasticity of B2102 increased with an increase in deformation temperature from - 60 ℃ and reached the optimal elongation ratio of 49% - 54% after deformation at 20 - 50 ^（2. Martensite transformation was observed during deformation due to the transformation-induced plasticity effect. The optimal elongation was achieved at deformation temperatures close to the Md（3O/50） temperatures of 62 ℃ and 6 ℃ for B2102 and S32101. respectively.展开更多
The transformation behavior and tensile properties of an ultra-high-strength transformation-induced plasticity （TRIP） steel （0.2C-2.0Si-I.SMn） were investigated by different heat treatments for automobile applicat...The transformation behavior and tensile properties of an ultra-high-strength transformation-induced plasticity （TRIP） steel （0.2C-2.0Si-I.SMn） were investigated by different heat treatments for automobile applications. The results show that F-TRIP steel, a tradi- tional TRIP steel containing as-cold-rolled ferfite and pearlite as the original microstructure, consists of equiaxed grains of intercritical ferrite surrounded by discrete particles of M/RA and B. In contrast, M-TRIP steel, a modified TRiP-aided steel with martensite as the original mi- crostlucture, containing full martensite as the original microstructure is comprised of lath-shaped grains of ferrite separated by lath-shaped martensite/retained austenite and bainite. Most of the austenite in F-TRIP steel is granular, while the austenite in M-TRIP steel is lath-shaped. The volume fraction of the retained austenite as well as its carbon content is lower in F-TRIP steel than in M-TRIP steel, and austenite grains in M-TRIP steel are much finer than those in F-TRIP steel. Therefore, M-TRIP steel was concluded to have a higher austenite stability, re- sulting in a lower transformation rate and consequently contributing to a higher elongation compared to F-TRIP steel. Work hardening be- havior is also discussed for both types of steel.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
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
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
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supported by the National Natural Science Foundation of China(No.50334010)the Doctor Degree Thesis Subsidization Item of Northeastern University(No.200302).
文摘Effect of austempering on the transformation induced plasticity （TRIP） of hot rolled multiphase steel was investigated. Polygonal ferrite, granular bainite, and a large amount of stabilized retained austenite could be obtained in the hot rolled multiphase steel. Strain induced martensite transformation （SIMT） of retained austenite and TRIP effectively occur under straining owing to austempering after hot rolling, and mechanical properties of the present steel remain at a relatively high constant value for austempering at 400℃. The mechanical properties of the steel exhibited a good combination of tensile strength （791MPa） and total elongation （36%） because the stability of retained austenite is optimal when the steel is held for 20min.
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supported by the National Natural Science Foundation of China (No.50705067)the Ph.D. Programs Foundation of the Ministry of Education of China (No.20070247013)
文摘On the basis of continuum mechanics and the Mori-Tanaka mean field theory, a micro-mechanical flow stress model that considered both the transformation-induced plasticity （TRIP） effect and the inelastic strain recovery behavior of TRIP multiphase steels was presented. The relation between the volume fraction of constituent phases and plastic strain was introduced to characterize the transformation-induced plasticity effect of TRIP steels. Loading-unloading-reloading uniaxial tension tests of TRIP600 steel were carried out and the strain recovery behavior after unloading was analyzed. From the experimental data, an empirical elastic modulus expression is extracted to characterize the inelastic strain recovery. A comparison of the predicted flow stress with the experimental data shows a good agreement. The mechanism of the transformation-induced plasticity effect and the inelastic recovery effect acting on the flow stress is also discussed in detail.
基金sponsored by the Project of Shanghai Industrial Application of New and HighTechnologies in 2009
文摘Effects of deformation temperature on the mechanical properties and microstructure of lean duplex stainless steels B2102 and S32101 have been investigated. It was found that the strength decreased continuously with increases in temperature from -60 ℃ to 100 ℃. The strength of S32101 was higher than that of B2102 owing to its higher nitrogen content. Plasticity of B2102 increased with an increase in deformation temperature from - 60 ℃ and reached the optimal elongation ratio of 49% - 54% after deformation at 20 - 50 ^（2. Martensite transformation was observed during deformation due to the transformation-induced plasticity effect. The optimal elongation was achieved at deformation temperatures close to the Md（3O/50） temperatures of 62 ℃ and 6 ℃ for B2102 and S32101. respectively.
基金financially supported by the National Natural Science Foundation of China (No. 51271035)The financial support of the Beijing Laboratory of Metallic Materials and Processing for Modern Transportation
文摘The transformation behavior and tensile properties of an ultra-high-strength transformation-induced plasticity （TRIP） steel （0.2C-2.0Si-I.SMn） were investigated by different heat treatments for automobile applications. The results show that F-TRIP steel, a tradi- tional TRIP steel containing as-cold-rolled ferfite and pearlite as the original microstructure, consists of equiaxed grains of intercritical ferrite surrounded by discrete particles of M/RA and B. In contrast, M-TRIP steel, a modified TRiP-aided steel with martensite as the original mi- crostlucture, containing full martensite as the original microstructure is comprised of lath-shaped grains of ferrite separated by lath-shaped martensite/retained austenite and bainite. Most of the austenite in F-TRIP steel is granular, while the austenite in M-TRIP steel is lath-shaped. The volume fraction of the retained austenite as well as its carbon content is lower in F-TRIP steel than in M-TRIP steel, and austenite grains in M-TRIP steel are much finer than those in F-TRIP steel. Therefore, M-TRIP steel was concluded to have a higher austenite stability, re- sulting in a lower transformation rate and consequently contributing to a higher elongation compared to F-TRIP steel. Work hardening be- havior is also discussed for both types of steel.
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.
