Recently,high-and medium-entropy alloys(HEAs and MEAs) have been found to exhibit excellent cryogenic mechanical properties,but most of them contain high-priced Co element.Therefore,developing HEAs or MEAs with high s...Recently,high-and medium-entropy alloys(HEAs and MEAs) have been found to exhibit excellent cryogenic mechanical properties,but most of them contain high-priced Co element.Therefore,developing HEAs or MEAs with high strength and ductility and relatively low cost is urgent.In this work,novel Cofree Fex Mn(75-x) Ni(10)Cr(15)(x=50 and 55 at.%) MEAs were developed,which exhibit a good combination of low cost,high strength and ductility at cryogenic temperature.It was found that the Fe(50)Mn(25)Ni(10)Cr(15)MEA exhibits a combination of cryogenic tensile strength of^0.98 GPa and ductility of^83 %.The excellent cryogenic mechanical properties were attributed to joint of twinning-induced plasticity(TWIP) and transformation-induced plasticity(TRIP) effects.The present study sheds light on developing low cost MEAs with high perfo rmance for cryogenic-tempe rature applications.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
A great deal of stabilized retained austenite can be obtained by means of austempering immediately after intercritical annealing in the low-carbon plain steel sheets which only contain alloying elements of silicon and...A great deal of stabilized retained austenite can be obtained by means of austempering immediately after intercritical annealing in the low-carbon plain steel sheets which only contain alloying elements of silicon and manganese. Transformation from retained austenite to martensite may be induced by strain at a temperature ranging from 50 ℃ to 400 ℃ during tension testing. Transformation-induced plasticity (TRIP) may occur. Alloying of silicon improves the stability of retained austenite. Mechanical properties of the present TRIP steels containing manganese increase with increasing silicon amount when the amount of silicon is less than two percent.展开更多
A new type of high strength steel containing a significant amount of stable retained austenite was obtained by austempering immediately after intercritical annealing.This sort of low carbon steel only contains alloyin...A new type of high strength steel containing a significant amount of stable retained austenite was obtained by austempering immediately after intercritical annealing.This sort of low carbon steel only contains alloying elements of silicon and manganese rather than nickel and chromium.Its mechanical properties were enhanced considerably due to strain-induced martensite transformation and transformation-induced plasticity(TRIP)of retained austenite when it was strained at temperatures between Msand Md,because retained austenite was moderately stabilized due to carbon enrichment by austempering.Austempering was carried out at different temperatures and 400 ℃ was found to be optimal.Tensile strength,total elongation and strength-ductility balance reached the maximum values and the product of tensile strength and total elongation exceeded 30 135 MPa % when the TRIP steel was held at 400 ℃ and strained at 350 ℃.展开更多
The effect of nitrogen on microstructural evolution and tensile properties of transformation-induced plasticity(TRIP)Fe_(50)Mn_(30)Co_(10)Cr_(10)HEAs was investigated.Nitrogen was fully introduced in solid solution by...The effect of nitrogen on microstructural evolution and tensile properties of transformation-induced plasticity(TRIP)Fe_(50)Mn_(30)Co_(10)Cr_(10)HEAs was investigated.Nitrogen was fully introduced in solid solution by pressure-induced melting technique.Nitrogen addition turned the TRIP alloy to a twinning-induced plasticity(TWIP)alloy,and simultaneously improved the strength and elongation.For the nitrogen-doped HEA,the high yield strength is mainly resulted from the friction stress via interstitial strengthening effect,and the high ductility is originated from retained high strain-hardening capability via the successive onset of dislocation accumulation and deformation twinning.The strain-hardening behavior and microstructural evolution at specified strains were revealed.展开更多
Cr-Ni-Mo-V steam-turbine rotors have been widely used as key components in power plants. In this study, a coupled thermomechano-metallurgical model was proposed to simulate the phase transformation and transformation-...Cr-Ni-Mo-V steam-turbine rotors have been widely used as key components in power plants. In this study, a coupled thermomechano-metallurgical model was proposed to simulate the phase transformation and transformation-induced plasticity (TRIP) of a 30Cr2Ni4MoV steam-turbine rotor during a water-quenching process, which was solved using a user defined material mechanical behavior (UMAT) subroutine in ABAQUS. The thermal dilation, heat generation from plastic work, transformation latent heat, phase transformation kinetics, and TRIP were considered in the model. The thermomechanical portion of the model was used to predict the evolution of temperature, strain, and residual stress in the rotor. The phase transformation that occurred during the quenching process was considered. Constitutive models of phase transformations (austenite to pearlite, austenite to bainite, and austenite to martensite) and TRIP were developed. Experimental data were adopted and compared with the predicted results to verify the accuracy of the model. This demonstrates that the model is reliable and accurate. Then, the model was utilized to predict the temperature variation, dimensional change, minimum austenitization time, residual stress, TRIP, and volume fractions of each phase. It is concluded that this model can be a useful computational tool in the design of heat-treatment routines of steam-turbine rotors.展开更多
The effect of thermomechanical control processing（TMCP）on microstructure and mechanical properties of Fe-0.2C-1.44Si-1.32Mn hot rolled TRIP steel was investigated through experiments.Strain-induced transformation an...The effect of thermomechanical control processing（TMCP）on microstructure and mechanical properties of Fe-0.2C-1.44Si-1.32Mn hot rolled TRIP steel was investigated through experiments.Strain-induced transformation and transformation-induced plasticity behavior of retained austenite were analyzed.The results show that with multipass deformation,reduction per pass of more than critical deformation in austenite recrystallization region and total reduction of more than 58% in non-recrystallization region and high temperature section of two-phase region,austenite can be refined before γ→α transformation.It is beneficial to obtain refined ferrite grain in final microstructure.To obtain fine and uniform microstructure and excellent strength-ductility balance,a three-stage cooling process（laminar cooling-air cooling-ultra-fast cooling）after hot rolling was conducted.The ultimate tensile strength and elongation of the investigated steel can reach 663 MPa and 41%,respectively.展开更多
High-strength bainitic steels have created a lot of interest in recent times because of their excellent combination of strength,ductility,toughness,and high ballistic mass efficiency.Bainitic steels have great potenti...High-strength bainitic steels have created a lot of interest in recent times because of their excellent combination of strength,ductility,toughness,and high ballistic mass efficiency.Bainitic steels have great potential in the fabrication of steel armor plates.Although various approaches and methods have been conducted to utilize the retained austenite(RA)in the bainitic matrix to control mechanical properties,very few attempts have been conducted to improve ballistic performance utilizing transformationinduced plasticity(TRIP)mechanism.In this study,high-strength bainitic steels were designed by controlling the time of austempering process to have various volume fractions and stability of RA while maintaining high hardness.The dynamic compressive and ballistic impact tests were conducted,and the relation between the effects of TRIP on ballistic performance and the adiabatic shear band(ASB)formation was analyzed.Our results show for the first time that an active TRIP mechanism achieved from a large quantity of metastable RA can significantly enhance the ballistic performance of high-strength bainitic steels because of the improved resistance to ASB formation.Thus,the ballistic performance can be effectively improved by a very short austempering time,which suggests that the utilization of active TRIP behavior via tuning RA acts as a primary mechanism for significantly enhancing the ballistic performance of high-strength bainitic steels.展开更多
We introduce a non-equiatomic Fe_(61)Mn_(18)Si_(11)Cr_(10) medium entropy alloy designed by subjecting it to transformation-induced plasticity upon deformation at room temperature. Microstructure characterization carr...We introduce a non-equiatomic Fe_(61)Mn_(18)Si_(11)Cr_(10) medium entropy alloy designed by subjecting it to transformation-induced plasticity upon deformation at room temperature. Microstructure characterization carried out using scanning electron microscopy(SEM), electron backscatter diffraction(EBSD), transmission electron microscopy(TEM) and X-ray diffraction(XRD) shows a homogeneous solid solution FCC + BCC structured dual phase. Investigations on the deformation substructures at specific strain levels via EBSD reveal the deformation-induced transformations of γ→α′ and γ→ ε. The strengths, particularly yield strength, of the designed alloy are found to be higher than these of the well-studied five component FeMnNiCoCr system for the introduction of the hard phase( α′-martensite). When tensile tests are performed at different strain rates of 10^(–4)s^(-1), 10^(–3)s^(-1), 10^(–2)s^(-1), the tested material exhibits a slightly negative strain rate sensitivity and work hardening rate sensitivity.展开更多
An ultrafine-grained(UFG) low-carbon medium-manganese steel was fabricated by the heavily warm rolling(HWR) and subsequent quenching, and the effects of annealing temperatures on microstructure and mechanical properti...An ultrafine-grained(UFG) low-carbon medium-manganese steel was fabricated by the heavily warm rolling(HWR) and subsequent quenching, and the effects of annealing temperatures on microstructure and mechanical properties of the UFG HWRed steel were investigated. The results show that the HWRed steel exhibits simultaneous improvements in strength,uniform elongation and work hardening, which is mainly attributed to the refinement of martensitic microstructures. The HWRed steels comprise only a-phase when annealing at lower temperatures below to 550 °C and at higher temperatures above to 700 °C. Whereas, UFG c-austenite is formed by reverse transformation when the HWRed steel was annealed at intermediate temperatures from 550 to 700 °C and the volume fraction increases with increasing annealing temperatures,consequently resulting in a dramatic increase in ductility of the annealed HWRed steels. It was found that the transformed UFG austenite and ferrite remained ～500 nm and ～800 nm in size when the HWRed steel was annealed at 650 and700 °C for 1 h, respectively, showing an excellent thermal stability. Moreover, the HWRed steel annealed at 650 °C exhibits high strength-ductility combinations with a yield strength of 906 MPa, ultimate tensile strength(UTS) of1011 MPa, total elongation(TEL) of 51% and product of strength and elongation(PSE: UTS 9 TEL) of 52 GPa%. It is believed that these excellent comprehensive mechanical properties are closely associated with the UFG austenite formation by reverse transformation and principally attributed to the transformation-induced plasticity(TRIP) effect.展开更多
Intercritical annealing（IA） at various temperatures followed by quenching and partitioning（IAQP） treatments was conducted on a cold-rolled Fe-0.2C-1.42Si-l.87Mn（wt%） sheet steel.Optimized microstructure and enha...Intercritical annealing（IA） at various temperatures followed by quenching and partitioning（IAQP） treatments was conducted on a cold-rolled Fe-0.2C-1.42Si-l.87Mn（wt%） sheet steel.Optimized microstructure and enhanced mechanical properties were achieved through appropriate adjustment of IA temperatures.The steel which was annealed at1,033 K for 600 s,then quenched to 573 K and partitioned at 693 K for 20 min,designated as 1033 QP steel,exhibits maximum 16.3 vol% retained austenite（RA） with good mechanical properties（ultimate tensile strength 886 MPa and total elongation 27%）.It was found that the thermal and mechanical stabilities of RA are mainly influenced by the combined effect of its average carbon content and amount of adjacent martensite.Furthermore,the transformation-induced plasticity effect increased the peak n-values observed at the second stage of the work hardening of IAQP steels.展开更多
The room-temperature stability of the retained austenite against strain-induced martensitic transformation, its deformation behavior, the response to the bainitic isothermal treatment, the appearance of yield point el...The room-temperature stability of the retained austenite against strain-induced martensitic transformation, its deformation behavior, the response to the bainitic isothermal treatment, the appearance of yield point elongation and other peculiarities of plastic flow, and the mechanical properties of transformation-induced plasticity（TRIP） steel were tailored based on the chemical homogeneity and the relative distribution of the retained austenite, bainite, and ferrite in the microstructure. The presence of ferritic-pearlitic banded structure in the initial microstructure resulted in an inhomogeneous TRIP microstructure, in which the retained austenite and bainite were confined to some bands and it was found to be responsible for the resultant inferior mechanical properties. The appearance of discontinuous yielding for the chemically inhomogeneous material was related to the martensitic transformation of unstable retained austenite at the initial stage of tensile deformation. These results are essential for better understanding of the behavior of advanced high-strength steels and their applications.展开更多
基金financially supported by the National Natural Science Foundation of China (Nos. U1832203, 11975202, U1704159 and 51701183)the Key Research & Development and Promotion of Special Project of Henan Province (Science & Technology) (No. 192102210006)。
文摘Recently,high-and medium-entropy alloys(HEAs and MEAs) have been found to exhibit excellent cryogenic mechanical properties,but most of them contain high-priced Co element.Therefore,developing HEAs or MEAs with high strength and ductility and relatively low cost is urgent.In this work,novel Cofree Fex Mn(75-x) Ni(10)Cr(15)(x=50 and 55 at.%) MEAs were developed,which exhibit a good combination of low cost,high strength and ductility at cryogenic temperature.It was found that the Fe(50)Mn(25)Ni(10)Cr(15)MEA exhibits a combination of cryogenic tensile strength of^0.98 GPa and ductility of^83 %.The excellent cryogenic mechanical properties were attributed to joint of twinning-induced plasticity(TWIP) and transformation-induced plasticity(TRIP) effects.The present study sheds light on developing low cost MEAs with high perfo rmance for cryogenic-tempe rature applications.
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.
文摘A great deal of stabilized retained austenite can be obtained by means of austempering immediately after intercritical annealing in the low-carbon plain steel sheets which only contain alloying elements of silicon and manganese. Transformation from retained austenite to martensite may be induced by strain at a temperature ranging from 50 ℃ to 400 ℃ during tension testing. Transformation-induced plasticity (TRIP) may occur. Alloying of silicon improves the stability of retained austenite. Mechanical properties of the present TRIP steels containing manganese increase with increasing silicon amount when the amount of silicon is less than two percent.
基金Sponsored by National Natural Science Foundation of China(50334010)
文摘A new type of high strength steel containing a significant amount of stable retained austenite was obtained by austempering immediately after intercritical annealing.This sort of low carbon steel only contains alloying elements of silicon and manganese rather than nickel and chromium.Its mechanical properties were enhanced considerably due to strain-induced martensite transformation and transformation-induced plasticity(TRIP)of retained austenite when it was strained at temperatures between Msand Md,because retained austenite was moderately stabilized due to carbon enrichment by austempering.Austempering was carried out at different temperatures and 400 ℃ was found to be optimal.Tensile strength,total elongation and strength-ductility balance reached the maximum values and the product of tensile strength and total elongation exceeded 30 135 MPa % when the TRIP steel was held at 400 ℃ and strained at 350 ℃.
基金financially supported by the National Natural Science Foundation of China(Nos.U1960203,51774074,51434004 and U1435205)the Fundamental Research Funds for the Central Universities(No.N180204015)+1 种基金the Shanxi Municipal Major Science&Technology Project(No.20181101014)the Fundamental Research Funds for the Central Universities(No.N172512033)。
文摘The effect of nitrogen on microstructural evolution and tensile properties of transformation-induced plasticity(TRIP)Fe_(50)Mn_(30)Co_(10)Cr_(10)HEAs was investigated.Nitrogen was fully introduced in solid solution by pressure-induced melting technique.Nitrogen addition turned the TRIP alloy to a twinning-induced plasticity(TWIP)alloy,and simultaneously improved the strength and elongation.For the nitrogen-doped HEA,the high yield strength is mainly resulted from the friction stress via interstitial strengthening effect,and the high ductility is originated from retained high strain-hardening capability via the successive onset of dislocation accumulation and deformation twinning.The strain-hardening behavior and microstructural evolution at specified strains were revealed.
文摘Cr-Ni-Mo-V steam-turbine rotors have been widely used as key components in power plants. In this study, a coupled thermomechano-metallurgical model was proposed to simulate the phase transformation and transformation-induced plasticity (TRIP) of a 30Cr2Ni4MoV steam-turbine rotor during a water-quenching process, which was solved using a user defined material mechanical behavior (UMAT) subroutine in ABAQUS. The thermal dilation, heat generation from plastic work, transformation latent heat, phase transformation kinetics, and TRIP were considered in the model. The thermomechanical portion of the model was used to predict the evolution of temperature, strain, and residual stress in the rotor. The phase transformation that occurred during the quenching process was considered. Constitutive models of phase transformations (austenite to pearlite, austenite to bainite, and austenite to martensite) and TRIP were developed. Experimental data were adopted and compared with the predicted results to verify the accuracy of the model. This demonstrates that the model is reliable and accurate. Then, the model was utilized to predict the temperature variation, dimensional change, minimum austenitization time, residual stress, TRIP, and volume fractions of each phase. It is concluded that this model can be a useful computational tool in the design of heat-treatment routines of steam-turbine rotors.
基金Item Sponsored by National Fundamental Project of Science and Technology of China(ZZ0113A0101)
文摘The effect of thermomechanical control processing（TMCP）on microstructure and mechanical properties of Fe-0.2C-1.44Si-1.32Mn hot rolled TRIP steel was investigated through experiments.Strain-induced transformation and transformation-induced plasticity behavior of retained austenite were analyzed.The results show that with multipass deformation,reduction per pass of more than critical deformation in austenite recrystallization region and total reduction of more than 58% in non-recrystallization region and high temperature section of two-phase region,austenite can be refined before γ→α transformation.It is beneficial to obtain refined ferrite grain in final microstructure.To obtain fine and uniform microstructure and excellent strength-ductility balance,a three-stage cooling process（laminar cooling-air cooling-ultra-fast cooling）after hot rolling was conducted.The ultimate tensile strength and elongation of the investigated steel can reach 663 MPa and 41%,respectively.
基金supported by the Agency for Defense Development(grant No.UE161030GD)the Korea University Grant for Dr.S.S.Sohnthe BK21 Plus Project for Center for Creative Industrial Materials。
文摘High-strength bainitic steels have created a lot of interest in recent times because of their excellent combination of strength,ductility,toughness,and high ballistic mass efficiency.Bainitic steels have great potential in the fabrication of steel armor plates.Although various approaches and methods have been conducted to utilize the retained austenite(RA)in the bainitic matrix to control mechanical properties,very few attempts have been conducted to improve ballistic performance utilizing transformationinduced plasticity(TRIP)mechanism.In this study,high-strength bainitic steels were designed by controlling the time of austempering process to have various volume fractions and stability of RA while maintaining high hardness.The dynamic compressive and ballistic impact tests were conducted,and the relation between the effects of TRIP on ballistic performance and the adiabatic shear band(ASB)formation was analyzed.Our results show for the first time that an active TRIP mechanism achieved from a large quantity of metastable RA can significantly enhance the ballistic performance of high-strength bainitic steels because of the improved resistance to ASB formation.Thus,the ballistic performance can be effectively improved by a very short austempering time,which suggests that the utilization of active TRIP behavior via tuning RA acts as a primary mechanism for significantly enhancing the ballistic performance of high-strength bainitic steels.
基金financially supported by the Fundamental Research Funds for the Central Universities (No. 2020MS058)。
文摘We introduce a non-equiatomic Fe_(61)Mn_(18)Si_(11)Cr_(10) medium entropy alloy designed by subjecting it to transformation-induced plasticity upon deformation at room temperature. Microstructure characterization carried out using scanning electron microscopy(SEM), electron backscatter diffraction(EBSD), transmission electron microscopy(TEM) and X-ray diffraction(XRD) shows a homogeneous solid solution FCC + BCC structured dual phase. Investigations on the deformation substructures at specific strain levels via EBSD reveal the deformation-induced transformations of γ→α′ and γ→ ε. The strengths, particularly yield strength, of the designed alloy are found to be higher than these of the well-studied five component FeMnNiCoCr system for the introduction of the hard phase( α′-martensite). When tensile tests are performed at different strain rates of 10^(–4)s^(-1), 10^(–3)s^(-1), 10^(–2)s^(-1), the tested material exhibits a slightly negative strain rate sensitivity and work hardening rate sensitivity.
基金financially supported by the National Major Science and Technology Project of China (No. 2014ZX07214-002)
文摘An ultrafine-grained(UFG) low-carbon medium-manganese steel was fabricated by the heavily warm rolling(HWR) and subsequent quenching, and the effects of annealing temperatures on microstructure and mechanical properties of the UFG HWRed steel were investigated. The results show that the HWRed steel exhibits simultaneous improvements in strength,uniform elongation and work hardening, which is mainly attributed to the refinement of martensitic microstructures. The HWRed steels comprise only a-phase when annealing at lower temperatures below to 550 °C and at higher temperatures above to 700 °C. Whereas, UFG c-austenite is formed by reverse transformation when the HWRed steel was annealed at intermediate temperatures from 550 to 700 °C and the volume fraction increases with increasing annealing temperatures,consequently resulting in a dramatic increase in ductility of the annealed HWRed steels. It was found that the transformed UFG austenite and ferrite remained ～500 nm and ～800 nm in size when the HWRed steel was annealed at 650 and700 °C for 1 h, respectively, showing an excellent thermal stability. Moreover, the HWRed steel annealed at 650 °C exhibits high strength-ductility combinations with a yield strength of 906 MPa, ultimate tensile strength(UTS) of1011 MPa, total elongation(TEL) of 51% and product of strength and elongation(PSE: UTS 9 TEL) of 52 GPa%. It is believed that these excellent comprehensive mechanical properties are closely associated with the UFG austenite formation by reverse transformation and principally attributed to the transformation-induced plasticity(TRIP) effect.
基金financially supported by the National Natural Science Foundation of China (No. 51174251)the National Basic Research Program of China (No. 2010CB630803)
文摘Intercritical annealing（IA） at various temperatures followed by quenching and partitioning（IAQP） treatments was conducted on a cold-rolled Fe-0.2C-1.42Si-l.87Mn（wt%） sheet steel.Optimized microstructure and enhanced mechanical properties were achieved through appropriate adjustment of IA temperatures.The steel which was annealed at1,033 K for 600 s,then quenched to 573 K and partitioned at 693 K for 20 min,designated as 1033 QP steel,exhibits maximum 16.3 vol% retained austenite（RA） with good mechanical properties（ultimate tensile strength 886 MPa and total elongation 27%）.It was found that the thermal and mechanical stabilities of RA are mainly influenced by the combined effect of its average carbon content and amount of adjacent martensite.Furthermore,the transformation-induced plasticity effect increased the peak n-values observed at the second stage of the work hardening of IAQP steels.
文摘The room-temperature stability of the retained austenite against strain-induced martensitic transformation, its deformation behavior, the response to the bainitic isothermal treatment, the appearance of yield point elongation and other peculiarities of plastic flow, and the mechanical properties of transformation-induced plasticity（TRIP） steel were tailored based on the chemical homogeneity and the relative distribution of the retained austenite, bainite, and ferrite in the microstructure. The presence of ferritic-pearlitic banded structure in the initial microstructure resulted in an inhomogeneous TRIP microstructure, in which the retained austenite and bainite were confined to some bands and it was found to be responsible for the resultant inferior mechanical properties. The appearance of discontinuous yielding for the chemically inhomogeneous material was related to the martensitic transformation of unstable retained austenite at the initial stage of tensile deformation. These results are essential for better understanding of the behavior of advanced high-strength steels and their applications.
