In the present study, a quenching treatment prior to two-stage heat treatment was conducted on a Fe-0.28C-1.55Mn-2.06Al transformation-induced plasticity steel to tailor the final microstructure. Compared with the mic...In the present study, a quenching treatment prior to two-stage heat treatment was conducted on a Fe-0.28C-1.55Mn-2.06Al transformation-induced plasticity steel to tailor the final microstructure. Compared with the microstructure of the ferrite, bainite and blocky retained austenite obtained by conventional two-stage heat treatment, the microstructure subjected to quenching plus two-stage heat treatment was composed of the ferrite, lath bainite and film-like retained austenite. The corresponding tensile behavior and mechanical stability of retained austenite were investigated by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The results show that the mechanical stability of blocky retained austenite grains is lower and most of them transform to martensite during the tensile deformation, which leads to higher ultimate tensile strength and instantaneous work hardening exponent. Film-like retained austenite has relatively higher stability, which could cause sustained work hardening and high ductility as well as product of strength and elongation.展开更多
Different samples of TRIP （transformation induced plasticity） steel obtained by two different hot rolling schedules are investigated by using a SEM （scanning electron microscope）. The microstructure is characteriz...Different samples of TRIP （transformation induced plasticity） steel obtained by two different hot rolling schedules are investigated by using a SEM （scanning electron microscope）. The microstructure is characterized by using an OM （optical microscope） for phase distribution and by EBSD （electron backscatter diffraction） for texture and phase mapping. ODF （orientation distribution function） graphs are used to investigate the effect of recrystallization behavior of the hot-deformed austenite on phase transformation during the controlled cooling process. The mechanical behavior is interpreted in terms of the strength of both hard and soft phases, in combination with the quantity, loca- tion and transformation kinetics of the mechanically induced martensite （TRIP effect）. The results show that more austenite grains exist in the steels obtained at finishing rolling temperature （FRT） of 750 ℃, which inherited the de- formation structure after the hot-rolling process. The instantaneous n value （ni） of those steels is kept high during a large range of strain before failure, while the tensile strength and total elongation of the steels with respect to the dif- ferent finishing rolling temperatures do not show any significant differences.展开更多
In this study, the effect of cooling rates on microstructures and mechanical properties in a Al-bearing hot-rolled transformation- induced plasticity steel was investigated. The experiments were carried out using hot ...In this study, the effect of cooling rates on microstructures and mechanical properties in a Al-bearing hot-rolled transformation- induced plasticity steel was investigated. The experiments were carried out using hot simulation machine and hot rolling mill, where the samples were cooled at different cooling rates. The results showed that with the increase in cooling rates, film-like retained austenite gradually disappeared and only blocky retained austenite was retained at higher cooling rates. The volume fraction of retained austenite was 9-11% at cooling rates of 0.05-1 ℃/s and 4-6% at cooling rates of 5-10 ℃/s. In addition, martensite/austenite island was observed because of the heterogeneous carbon distribution. The samples cooled at 0.05℃/s and 0.5 ℃/s exhibited excellent mechanical properties, with tensile strengths of 712 MPa and 726 MPa, total elongations of 42% and 36% and strength and ductility balances of 29.91 GPa% and 26.15 GPa%, respectively. During plastic deformation, the instantaneous work hardening exponent of the sample cooled at 0.05 ℃/s increased continuously until it reached the maximum value, while the instantaneous work hardening exponent of the sample cooled at 0.5℃/s remained stable.展开更多
This paper examines older driver＇s automotive trip （abbreviation： trip） characteristics which include trip frequency, trip length, destination distribution, and non- home-based （NHB） trips. A two-month experimen...This paper examines older driver＇s automotive trip （abbreviation： trip） characteristics which include trip frequency, trip length, destination distribution, and non- home-based （NHB） trips. A two-month experiment of 108 participants was carried out to collect GPS tracking data in Aichi Prefecture, Japan. To identify the effect of living area, a comparative analysis between older drivers and others is conducted in densely inhabited district （DID, i.e., urban） and other areas （non-DID, i.e., suburban, rural, etc）, separately. The present study found that there was no sig- nificant difference between the trip characteristics of older drivers and others who were living in DID. Thus, we suggest that the education of safety driving and the rec- ommendation of public transportation should be given to DID-living older drivers. However, the results of non-DID reflected that older drivers＇ trip frequency, trip length, destination, and NHB trips rate were shorter and lower than others＇. This implies that electric vehicles may be suit- able for promotion among older drivers in suburban and rural area. Furthermore, the regression analysis confirmed that ＂older driver＂ was a significant independent variable on trip frequency, trip length, and NHB trips, and there were interaction effects between ＂older driver＂ and ＂living areas＂ on all trip characteristics.展开更多
基金financially supported by the National Natural Science Foundation of China (No. 51501031)the Natural Science Foundation of Liaoning Province (No. 20170520348)
文摘In the present study, a quenching treatment prior to two-stage heat treatment was conducted on a Fe-0.28C-1.55Mn-2.06Al transformation-induced plasticity steel to tailor the final microstructure. Compared with the microstructure of the ferrite, bainite and blocky retained austenite obtained by conventional two-stage heat treatment, the microstructure subjected to quenching plus two-stage heat treatment was composed of the ferrite, lath bainite and film-like retained austenite. The corresponding tensile behavior and mechanical stability of retained austenite were investigated by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The results show that the mechanical stability of blocky retained austenite grains is lower and most of them transform to martensite during the tensile deformation, which leads to higher ultimate tensile strength and instantaneous work hardening exponent. Film-like retained austenite has relatively higher stability, which could cause sustained work hardening and high ductility as well as product of strength and elongation.
基金Foundation Item:Item Sponsored by National Natural Science Foundation of China(50804005)Central Collegiate Basic Scientific Research Bursary of China(FRF-TP-11-005B)
文摘Different samples of TRIP （transformation induced plasticity） steel obtained by two different hot rolling schedules are investigated by using a SEM （scanning electron microscope）. The microstructure is characterized by using an OM （optical microscope） for phase distribution and by EBSD （electron backscatter diffraction） for texture and phase mapping. ODF （orientation distribution function） graphs are used to investigate the effect of recrystallization behavior of the hot-deformed austenite on phase transformation during the controlled cooling process. The mechanical behavior is interpreted in terms of the strength of both hard and soft phases, in combination with the quantity, loca- tion and transformation kinetics of the mechanically induced martensite （TRIP effect）. The results show that more austenite grains exist in the steels obtained at finishing rolling temperature （FRT） of 750 ℃, which inherited the de- formation structure after the hot-rolling process. The instantaneous n value （ni） of those steels is kept high during a large range of strain before failure, while the tensile strength and total elongation of the steels with respect to the dif- ferent finishing rolling temperatures do not show any significant differences.
基金support from the National Natural Science Foundation of China (No. 51504063)
文摘In this study, the effect of cooling rates on microstructures and mechanical properties in a Al-bearing hot-rolled transformation- induced plasticity steel was investigated. The experiments were carried out using hot simulation machine and hot rolling mill, where the samples were cooled at different cooling rates. The results showed that with the increase in cooling rates, film-like retained austenite gradually disappeared and only blocky retained austenite was retained at higher cooling rates. The volume fraction of retained austenite was 9-11% at cooling rates of 0.05-1 ℃/s and 4-6% at cooling rates of 5-10 ℃/s. In addition, martensite/austenite island was observed because of the heterogeneous carbon distribution. The samples cooled at 0.05℃/s and 0.5 ℃/s exhibited excellent mechanical properties, with tensile strengths of 712 MPa and 726 MPa, total elongations of 42% and 36% and strength and ductility balances of 29.91 GPa% and 26.15 GPa%, respectively. During plastic deformation, the instantaneous work hardening exponent of the sample cooled at 0.05 ℃/s increased continuously until it reached the maximum value, while the instantaneous work hardening exponent of the sample cooled at 0.5℃/s remained stable.
基金partially supported by the Center of Innovation Program from Japan Science and Technology Agency, JST
文摘This paper examines older driver＇s automotive trip （abbreviation： trip） characteristics which include trip frequency, trip length, destination distribution, and non- home-based （NHB） trips. A two-month experiment of 108 participants was carried out to collect GPS tracking data in Aichi Prefecture, Japan. To identify the effect of living area, a comparative analysis between older drivers and others is conducted in densely inhabited district （DID, i.e., urban） and other areas （non-DID, i.e., suburban, rural, etc）, separately. The present study found that there was no sig- nificant difference between the trip characteristics of older drivers and others who were living in DID. Thus, we suggest that the education of safety driving and the rec- ommendation of public transportation should be given to DID-living older drivers. However, the results of non-DID reflected that older drivers＇ trip frequency, trip length, destination, and NHB trips rate were shorter and lower than others＇. This implies that electric vehicles may be suit- able for promotion among older drivers in suburban and rural area. Furthermore, the regression analysis confirmed that ＂older driver＂ was a significant independent variable on trip frequency, trip length, and NHB trips, and there were interaction effects between ＂older driver＂ and ＂living areas＂ on all trip characteristics.
