Chinese cities need the appropriate administration system and governance model to support the implementation of low carbon eco-city projects, and to effectively scale up this urban development model across the nation....Chinese cities need the appropriate administration system and governance model to support the implementation of low carbon eco-city projects, and to effectively scale up this urban development model across the nation. Currently, local planning authorities are piloting the implementation of these low carbon eco-city projects through the statutory Regulatory Plans system(the local district zoning plans system). However, the focus has been put primarily on the use of the relevant technologies and the control through design approval. There is a lack on research and study on the establishment of an effective planning administration and governance environment for the subsequent promulgation of this development model. This situation is affecting the speed in the scaling up of the implementation of low carbon ecological projects in Chinese cities. This paper argues that while technology applications and design issues are important factors, attention shall be put to setting up innovative planning administration and governance models for the statutory Regulatory Plan to facilitate the implementation of the low carbon eco-city projects. This paper puts forth an analysis framework on the administration and governance system which includes 4 governance components:(1) Administration platform and local capacity;(2) Planning conditions and approval process;(3) External public policy context;(4) Developers involvement and participation. A case study was undertaken based on Taihu New City eco-city project located at Wuxi, China. Based on research and analysis of the project implementation process, the study examines the challenges faced by the local planning offi cials and development companies during the implementation stage of the low carbon eco-city project. Finally this paper puts forth initial recommendations that could lead to further research in this important area.展开更多
After reviewing the development of energy-saving construction and green buildings in China,the author suggests that in order to develop low carbon cities in China,efforts should be put into both green buildings constr...After reviewing the development of energy-saving construction and green buildings in China,the author suggests that in order to develop low carbon cities in China,efforts should be put into both green buildings construction and low carbon ecologic city development.The paper divides the low-carbon ecologic cities into four categories and summarizes the experiences gained from the ecologic city development in Sino-Singapore Ecologic City in Tianjin and Caofeidian in Tangshan.In addition,it also introduces the general idea for low carbon city development in China and the particular requirements for the planning and construction,as well as the critical techniques for low carbon ecologic city development.展开更多
Dry sliding friction and wear test of Nb containing low carbon microalloyed steel was carried out at room temperature,and the effect of Nb on the wear behavior of the steel,as welll as the mechanism was studied.Scanni...Dry sliding friction and wear test of Nb containing low carbon microalloyed steel was carried out at room temperature,and the effect of Nb on the wear behavior of the steel,as welll as the mechanism was studied.Scanning electron microscopy(SEM) and energy dispersive spectrometry(EDS) were employed to analyze the morphology and composition of the worn surface,and the structure evolution of the plastic deformation layer.The carbide content and type in the steel were analyzed by the electrolytic extraction device and X-ray diffraction(XRD).The experimental results demonstrate that the addition of 0.2% Nb can refine the grain and generate Nb C to improve the wear resistance of the steel.By enhancing the load and speed of wear experiment,the wear mechanism of the test steel with 0.2% Nb changes from slight oxidation wear to severe adhesion wear and oxidation wear.Compared with the load,the increase in the rotation speed exerts a greater influence on the wear of the test steel.展开更多
The construction of relevant standards for building carbon emission assessment in China has just started,and the quantitative analysis method and evaluation system are still imperfect,which hinders the development of ...The construction of relevant standards for building carbon emission assessment in China has just started,and the quantitative analysis method and evaluation system are still imperfect,which hinders the development of low-carbon building design.Therefore,the use of intelligent energy management system is very necessary.The purpose of this paper is to explore the design optimization of low-carbon buildings based on intelligent energy management systems.Based on the proposed quantitative method of building carbon emission,this paper establishes the quota theoretical system of building carbon emission analysis,and develops the quota based carbon emission calculation software.Smart energy management system is a low-carbon energy-saving system based on the reference of large-scale building energy-saving system and combined with energy consumption.It provides a fast and effective calculation tool for the quantitative evaluation of carbon emission of construction projects,so as to realize the carbon emission control and optimization in the early stage of architectural design and construction.On this basis,the evaluation,analysis and calculation method of building structure based on carbon reduction target is proposed,combined with the carbon emission quota management standard proposed in this paper.Taking small high-rise residential buildings as an example,this paper compares and analyzes different building structural systems from the perspectives of structural performance,economy and carbon emission level.It provides a reference for the design and evaluation of low-carbon building structures.The smart energy management system collects user energy use parameters.It uses time period and time sequence to obtain a large amount of data for analysis and integration,which provides users with intuitive energy consumption data.Compared with the traditional architectural design method,the industrialized construction method can save 589.22 megajoules(MJ)per square meter.Based on 29270 megajoules(MJ)per ton of standard coal,the construction area of the case is about 8000 m2,and the energy saving of residential buildings is 161.04 tons of standard coal.This research is of great significance in reducing the carbon emission intensity of buildings.展开更多
Low carbon landscape development is an emerging approach of landscape design,which aims to promote sustainable development,and reduce energy consumption and environmental impact by reducing carbon emissions.As an impo...Low carbon landscape development is an emerging approach of landscape design,which aims to promote sustainable development,and reduce energy consumption and environmental impact by reducing carbon emissions.As an important component of low carbon landscape construction,the construction of urban pocket park system based on mini-parks plays a crucial role in improving the urban greening level,increasing the urban green space,alleviating the urban pressure,improving the living and healthy environment of urban residents,and promoting the urban ecological balance.Taking Chaowai district of Beijing as an example,this paper calculates the ecological value of trees including energy contribution,carbon sequestration,ability to improve rainfall runoff and aesthetic value by collecting the information of trees and the plot on which the trees are located through the i-Tree platform,which provides important reference value for the urban pocket park system planning to create low carbon comprehensive benefits.展开更多
Considering the growing prominence of global environmental issues,a low-carbon economy has emerged as a crucial direction for economic development across various countries.As the world’s second-largest economy,China ...Considering the growing prominence of global environmental issues,a low-carbon economy has emerged as a crucial direction for economic development across various countries.As the world’s second-largest economy,China has also witnessed the influence of a low-carbon economy on its international trade development.This article aims to commence with an exploration of the development background,meaning,and significance of a low-carbon economy.Subsequently,it delves into an in-depth analysis of the impact that a low-carbon economy has on China’s international trade.The article concludes by proposing pertinent countermeasures and suggestions.展开更多
With the continuous implementation of national measures related to carbon neutrality strategy,the concept of a low-carbon economy has been deeply rooted in people’s hearts.Low-carbon tourism has gradually become an i...With the continuous implementation of national measures related to carbon neutrality strategy,the concept of a low-carbon economy has been deeply rooted in people’s hearts.Low-carbon tourism has gradually become an inevitable trend,and the tourism industry is also undergoing orderly transformation and upgrading.To promote the sustainable development of the tourism industry,the tourism and hotel industry should also shift towards a low-carbon and green model.Hotel activities can easily bring related environmental issues,such as energy consumption,garbage generation,ecological pollution,etc.Therefore,building a green hotel will bring huge social and economic benefits to the low-carbon tourism industry.This article will address the above issues and take a low-carbon economy as the starting point,proposing sustainable development strategies and suggestions for green hotels from both the internal and external environment of the hotel,creating a low-carbon management atmosphere,and promoting the low-carbon operation of the green hotel industry.展开更多
Electron microscopic investigation on low carbon steel strips produced by the CSP process has been carried out. Large number of oxide dispersive precipitates have been observed in the ferrite matrix of the steel strip...Electron microscopic investigation on low carbon steel strips produced by the CSP process has been carried out. Large number of oxide dispersive precipitates have been observed in the ferrite matrix of the steel strips. Dimension of them is about 10~20 nm. Electron diffraction study showed that the structure of these precipitates consists with cubic system spinel structure. Their lattice parameter is about 0.83 nm. The results implied that they should be complex oxides of Fe, Al et al. Small sulfide particles with 100-300 nm in size have also been observed. Remarkable strengthening and grain refinement effects can be obtained by the precipitations. The oxygen and sulfur in steels could play beneficial role under certain conditions.展开更多
During the production of Ti-bearing Al-killed ultra-low-carbon(ULC) steel, two different heating processes were used when the converter tapping temperature or the molten steel temperature in the Ruhrstahl–Heraeus(RH)...During the production of Ti-bearing Al-killed ultra-low-carbon(ULC) steel, two different heating processes were used when the converter tapping temperature or the molten steel temperature in the Ruhrstahl–Heraeus(RH) process was low: heating by Al addition during the RH decarburization process and final deoxidation at the end of the RH decarburization process(process-Ⅰ), and increasing the oxygen content at the end of RH decarburization, heating and final deoxidation by one-time Al addition(process-Ⅱ). Temperature increases of 10°C by different processes were studied; the results showed that the two heating processes could achieve the same heating effect. The T.[O] content in the slab and the refining process was better controlled by process-Ⅰ than by process-Ⅱ. Statistical analysis of inclusions showed that the numbers of inclusions in the slab obtained by process-Ⅰ were substantially less than those in the slab obtained by process-Ⅱ. For process-Ⅰ, the Al_2O_3 inclusions produced by Al added to induce heating were substantially removed at the end of decarburization. The amounts of inclusions were substantially greater for process-Ⅱ than for process-Ⅰ at different refining stages because of the higher dissolved oxygen concentration in process-Ⅱ. Industrial test results showed that process-Ⅰ was more beneficial for improving the cleanliness of molten steel.展开更多
A suitable carburized microstructure with fine granular dispersed carbides in hypereutectoid zone,ultra fine martensite in matrix and recrystallized austenite to be refined to the grain size of 12~14 has been obtaine...A suitable carburized microstructure with fine granular dispersed carbides in hypereutectoid zone,ultra fine martensite in matrix and recrystallized austenite to be refined to the grain size of 12~14 has been obtained by a new process,which is a high carbon concentration carburizing with rare earth element at low temperature(860~880℃)in a discontinuous gas carburization furnace.There was not much difference for the microstructure in eutectic zone between this and conventional process.Forming mechanism of granular carbides has been also studied in this paper.展开更多
Utilizing Gleeble-1500 thermomechanical simulator, the influences of hot deformation parameters on continuous cooling bainite transformation in Nb-microalloyed low carbon steel were investigated. The results indicate ...Utilizing Gleeble-1500 thermomechanical simulator, the influences of hot deformation parameters on continuous cooling bainite transformation in Nb-microalloyed low carbon steel were investigated. The results indicate that bainite starting temperature decreases with raising cooling rate and increases with increasing deformation temperature. Deformation has an accelerative effect on the bainite transformation when the specimens are deformed at 950 ℃. When the deformation temperature increases, the effect of deformation on bainite starting temperature is weakened. The amount of bainite is influenced by strain, cooling rate, and deformation temperature. When the specimens are deformed below 900 ℃, equiaxed ferrites are promoted and the bainite transformation is suppressed.展开更多
The decarburization behaviors of ultra low carbon steel in a 210-t RH vacuum degasser were investigated under practical operat- ing conditions. According to the apparent decarburization rate constant (Kc) calculated...The decarburization behaviors of ultra low carbon steel in a 210-t RH vacuum degasser were investigated under practical operat- ing conditions. According to the apparent decarburization rate constant (Kc) calculated by the carbon content in the samples taken from the hot melt in a ladle at an interval of 1-2 min, it is observed that the total decarburization reaction period in RH can be divided into the quick decarburization period and the stagnant decarburization period, which is quite different from the traditional one with three stages. In this study, the average apparent decarburization rate constant during the quick decarburization period is 0.306 min^-1, and that of the stagnant period is 0.072 min^-1. Increasing the initial carbon content and enhancing the exhausting capacity can increase the apparent decarburization rate constant in the quick decarburization period. The decarburization reaction comes into the stagnant decarburization period when the carbon content in molten steel is less than 14× 10^-6 after 10 min of decarburization.展开更多
Hot deformation experiments were carried out on Gleeble 1500 thermo-mechanical simulator. The bainite transformation after deformation was investigated by optical microstructure analysis. The results indicated that th...Hot deformation experiments were carried out on Gleeble 1500 thermo-mechanical simulator. The bainite transformation after deformation was investigated by optical microstructure analysis. The results indicated that the deformation accelerated the bainite transformation when the deformation was carried out at high temperature and no or little ferrite was precipitated before bainite transformation; when the deformation was carried out at low temperature, the deformation hindered the bainite transformation because a lot of ferrite precipitated before bainite transformation.展开更多
A Ti+Nb bearing ultra-low carbon bake hardening sheet steel hot-rolled in the conventional austenite region and in the ferrite region with lubrication was experimentally studied. Subsequent cold rolling and continuou...A Ti+Nb bearing ultra-low carbon bake hardening sheet steel hot-rolled in the conventional austenite region and in the ferrite region with lubrication was experimentally studied. Subsequent cold rolling and continuous annealing processes were also conducted. The results show that microstructures of ultra-low carbon bake hardening hot strips at room temperature are basically irregular polygonal ferrites. The yield strength, ultimate tensile strength, n value, and r value of the No.2 specimen hot-rolled in the ferrite region with lubrication are 243 MPa, 364 MPa, 0.29, and 1.74, respectively, which are similar to those of the No.1 specimen hot-roiled in the conventional austenite region. The elongation rate and bake hardening value of No.2 specimen are 51% and 49.4 MPa, respectively, which are greater than those of No. 1 specimen. The No.2 specimen hot-rolled in the ferrite region with lubrication exhibits good mechanical properties and relatively excellent baking hardening performance. Therefore, the hot rolling experiment of Ti+Nb bearing ultra-low carbon bake hardening steel in the ferrite region with lubrication is feasible and can be considered in the future industrial trial production.展开更多
A dilatometer was used to study the kinetics of bainite-to-austenite transformation in low carbon microalloyed steel with the initial microstructure of bainite during the continuous reheating process. The bainite-to-a...A dilatometer was used to study the kinetics of bainite-to-austenite transformation in low carbon microalloyed steel with the initial microstructure of bainite during the continuous reheating process. The bainite-to-austenite trans- formation was observed to take place in two steps at low heating rate. The first step is the dissolution of bainite, and the second one is the remaining bainite-to-austenite transformation controlled by a dissolution process. The calculation result of the kinetics of austenite formation shows that the two steps occur by diffusion at low heating rate. However, at high heating rate the bainite-to-austenite transformation occurs in a single step, and the process is mainly dominated by shear. The growth rate of austenite reaches the maximum at about 835℃ at different heating rates and the growth rate of austenite as a function of temperature increases with the increase in heating rate.展开更多
The characteristics of nanosized precipitates in steels depend on the heat-treatment parameters. The effects of characteristics of vanadium precipitates formed during isothermal heat treatment on the hardness of the f...The characteristics of nanosized precipitates in steels depend on the heat-treatment parameters. The effects of characteristics of vanadium precipitates formed during isothermal heat treatment on the hardness of the ferrite matrix in low-carbon vanadium-alloyed steel were investigated through analysis of transmission electron microscopy images and microhardness measurements. The results show that, during isothermal holding in the temperature range from 675 to 750℃, only interphase precipitation occurs, whereas only random precipitation occurs in the ferrite matrix during holding at 600℃. Furthermore, during isothermal heat treatment between 600 and 675℃, both random and interphase precipitates occurred in the ferrite. Nanoscale vanadium carbides with different atomic ratios of vanadium(V) and carbon(C) were the dominant precipitates in the random and interphase precipitates. The sizes of random precipitation carbides were smaller than those of interphase ones. Also, the sample isothermally heat treated at 650℃ for 900s exhibited a higher hardness with a narrower hardness distribution.展开更多
文摘Chinese cities need the appropriate administration system and governance model to support the implementation of low carbon eco-city projects, and to effectively scale up this urban development model across the nation. Currently, local planning authorities are piloting the implementation of these low carbon eco-city projects through the statutory Regulatory Plans system(the local district zoning plans system). However, the focus has been put primarily on the use of the relevant technologies and the control through design approval. There is a lack on research and study on the establishment of an effective planning administration and governance environment for the subsequent promulgation of this development model. This situation is affecting the speed in the scaling up of the implementation of low carbon ecological projects in Chinese cities. This paper argues that while technology applications and design issues are important factors, attention shall be put to setting up innovative planning administration and governance models for the statutory Regulatory Plan to facilitate the implementation of the low carbon eco-city projects. This paper puts forth an analysis framework on the administration and governance system which includes 4 governance components:(1) Administration platform and local capacity;(2) Planning conditions and approval process;(3) External public policy context;(4) Developers involvement and participation. A case study was undertaken based on Taihu New City eco-city project located at Wuxi, China. Based on research and analysis of the project implementation process, the study examines the challenges faced by the local planning offi cials and development companies during the implementation stage of the low carbon eco-city project. Finally this paper puts forth initial recommendations that could lead to further research in this important area.
文摘After reviewing the development of energy-saving construction and green buildings in China,the author suggests that in order to develop low carbon cities in China,efforts should be put into both green buildings construction and low carbon ecologic city development.The paper divides the low-carbon ecologic cities into four categories and summarizes the experiences gained from the ecologic city development in Sino-Singapore Ecologic City in Tianjin and Caofeidian in Tangshan.In addition,it also introduces the general idea for low carbon city development in China and the particular requirements for the planning and construction,as well as the critical techniques for low carbon ecologic city development.
文摘Dry sliding friction and wear test of Nb containing low carbon microalloyed steel was carried out at room temperature,and the effect of Nb on the wear behavior of the steel,as welll as the mechanism was studied.Scanning electron microscopy(SEM) and energy dispersive spectrometry(EDS) were employed to analyze the morphology and composition of the worn surface,and the structure evolution of the plastic deformation layer.The carbide content and type in the steel were analyzed by the electrolytic extraction device and X-ray diffraction(XRD).The experimental results demonstrate that the addition of 0.2% Nb can refine the grain and generate Nb C to improve the wear resistance of the steel.By enhancing the load and speed of wear experiment,the wear mechanism of the test steel with 0.2% Nb changes from slight oxidation wear to severe adhesion wear and oxidation wear.Compared with the load,the increase in the rotation speed exerts a greater influence on the wear of the test steel.
基金supported by“Key Technology Research on Operational Performance Improvement of the Green Building”(2020YFS0060)Key Project of Science and Technology Department of Sichuan Province+2 种基金supported by“Creative VR Teaching and Learning Research Based on‘PBL+’and Multidimensional Collaboration”(JG2021-721)“Reform in the Mode and Practice of Architecture Education with the Characteristics of Geology”(JG2021-672)Education Quality and Teaching Reform Project of Higher Education in Sichuan Province in 2021–2023.
文摘The construction of relevant standards for building carbon emission assessment in China has just started,and the quantitative analysis method and evaluation system are still imperfect,which hinders the development of low-carbon building design.Therefore,the use of intelligent energy management system is very necessary.The purpose of this paper is to explore the design optimization of low-carbon buildings based on intelligent energy management systems.Based on the proposed quantitative method of building carbon emission,this paper establishes the quota theoretical system of building carbon emission analysis,and develops the quota based carbon emission calculation software.Smart energy management system is a low-carbon energy-saving system based on the reference of large-scale building energy-saving system and combined with energy consumption.It provides a fast and effective calculation tool for the quantitative evaluation of carbon emission of construction projects,so as to realize the carbon emission control and optimization in the early stage of architectural design and construction.On this basis,the evaluation,analysis and calculation method of building structure based on carbon reduction target is proposed,combined with the carbon emission quota management standard proposed in this paper.Taking small high-rise residential buildings as an example,this paper compares and analyzes different building structural systems from the perspectives of structural performance,economy and carbon emission level.It provides a reference for the design and evaluation of low-carbon building structures.The smart energy management system collects user energy use parameters.It uses time period and time sequence to obtain a large amount of data for analysis and integration,which provides users with intuitive energy consumption data.Compared with the traditional architectural design method,the industrialized construction method can save 589.22 megajoules(MJ)per square meter.Based on 29270 megajoules(MJ)per ton of standard coal,the construction area of the case is about 8000 m2,and the energy saving of residential buildings is 161.04 tons of standard coal.This research is of great significance in reducing the carbon emission intensity of buildings.
基金Sponsored by General Project of Natural Science Foundation of Beijing City(8202017)Youth Talent Support Program of 2018 Beijing Municipal University Academic Human Resources Development(PXM2018_014212_000043).
文摘Low carbon landscape development is an emerging approach of landscape design,which aims to promote sustainable development,and reduce energy consumption and environmental impact by reducing carbon emissions.As an important component of low carbon landscape construction,the construction of urban pocket park system based on mini-parks plays a crucial role in improving the urban greening level,increasing the urban green space,alleviating the urban pressure,improving the living and healthy environment of urban residents,and promoting the urban ecological balance.Taking Chaowai district of Beijing as an example,this paper calculates the ecological value of trees including energy contribution,carbon sequestration,ability to improve rainfall runoff and aesthetic value by collecting the information of trees and the plot on which the trees are located through the i-Tree platform,which provides important reference value for the urban pocket park system planning to create low carbon comprehensive benefits.
文摘Considering the growing prominence of global environmental issues,a low-carbon economy has emerged as a crucial direction for economic development across various countries.As the world’s second-largest economy,China has also witnessed the influence of a low-carbon economy on its international trade development.This article aims to commence with an exploration of the development background,meaning,and significance of a low-carbon economy.Subsequently,it delves into an in-depth analysis of the impact that a low-carbon economy has on China’s international trade.The article concludes by proposing pertinent countermeasures and suggestions.
文摘With the continuous implementation of national measures related to carbon neutrality strategy,the concept of a low-carbon economy has been deeply rooted in people’s hearts.Low-carbon tourism has gradually become an inevitable trend,and the tourism industry is also undergoing orderly transformation and upgrading.To promote the sustainable development of the tourism industry,the tourism and hotel industry should also shift towards a low-carbon and green model.Hotel activities can easily bring related environmental issues,such as energy consumption,garbage generation,ecological pollution,etc.Therefore,building a green hotel will bring huge social and economic benefits to the low-carbon tourism industry.This article will address the above issues and take a low-carbon economy as the starting point,proposing sustainable development strategies and suggestions for green hotels from both the internal and external environment of the hotel,creating a low-carbon management atmosphere,and promoting the low-carbon operation of the green hotel industry.
文摘Electron microscopic investigation on low carbon steel strips produced by the CSP process has been carried out. Large number of oxide dispersive precipitates have been observed in the ferrite matrix of the steel strips. Dimension of them is about 10~20 nm. Electron diffraction study showed that the structure of these precipitates consists with cubic system spinel structure. Their lattice parameter is about 0.83 nm. The results implied that they should be complex oxides of Fe, Al et al. Small sulfide particles with 100-300 nm in size have also been observed. Remarkable strengthening and grain refinement effects can be obtained by the precipitations. The oxygen and sulfur in steels could play beneficial role under certain conditions.
基金Financial support from the Chinese Academy of Sciences and National Natural Science Foundation of China (No.50071061)Conseil Regional de Champagne Ardenne France is appreciated.
基金financially supported by the National Natural Science Foundation of China (No.51404022)
文摘During the production of Ti-bearing Al-killed ultra-low-carbon(ULC) steel, two different heating processes were used when the converter tapping temperature or the molten steel temperature in the Ruhrstahl–Heraeus(RH) process was low: heating by Al addition during the RH decarburization process and final deoxidation at the end of the RH decarburization process(process-Ⅰ), and increasing the oxygen content at the end of RH decarburization, heating and final deoxidation by one-time Al addition(process-Ⅱ). Temperature increases of 10°C by different processes were studied; the results showed that the two heating processes could achieve the same heating effect. The T.[O] content in the slab and the refining process was better controlled by process-Ⅰ than by process-Ⅱ. Statistical analysis of inclusions showed that the numbers of inclusions in the slab obtained by process-Ⅰ were substantially less than those in the slab obtained by process-Ⅱ. For process-Ⅰ, the Al_2O_3 inclusions produced by Al added to induce heating were substantially removed at the end of decarburization. The amounts of inclusions were substantially greater for process-Ⅱ than for process-Ⅰ at different refining stages because of the higher dissolved oxygen concentration in process-Ⅱ. Industrial test results showed that process-Ⅰ was more beneficial for improving the cleanliness of molten steel.
文摘A suitable carburized microstructure with fine granular dispersed carbides in hypereutectoid zone,ultra fine martensite in matrix and recrystallized austenite to be refined to the grain size of 12~14 has been obtained by a new process,which is a high carbon concentration carburizing with rare earth element at low temperature(860~880℃)in a discontinuous gas carburization furnace.There was not much difference for the microstructure in eutectic zone between this and conventional process.Forming mechanism of granular carbides has been also studied in this paper.
基金Item Sponsored by High Technology Development Programof China (863) (2001AA332020) and National Natural ScienceFoundation of China (50271015)
文摘Utilizing Gleeble-1500 thermomechanical simulator, the influences of hot deformation parameters on continuous cooling bainite transformation in Nb-microalloyed low carbon steel were investigated. The results indicate that bainite starting temperature decreases with raising cooling rate and increases with increasing deformation temperature. Deformation has an accelerative effect on the bainite transformation when the specimens are deformed at 950 ℃. When the deformation temperature increases, the effect of deformation on bainite starting temperature is weakened. The amount of bainite is influenced by strain, cooling rate, and deformation temperature. When the specimens are deformed below 900 ℃, equiaxed ferrites are promoted and the bainite transformation is suppressed.
文摘The decarburization behaviors of ultra low carbon steel in a 210-t RH vacuum degasser were investigated under practical operat- ing conditions. According to the apparent decarburization rate constant (Kc) calculated by the carbon content in the samples taken from the hot melt in a ladle at an interval of 1-2 min, it is observed that the total decarburization reaction period in RH can be divided into the quick decarburization period and the stagnant decarburization period, which is quite different from the traditional one with three stages. In this study, the average apparent decarburization rate constant during the quick decarburization period is 0.306 min^-1, and that of the stagnant period is 0.072 min^-1. Increasing the initial carbon content and enhancing the exhausting capacity can increase the apparent decarburization rate constant in the quick decarburization period. The decarburization reaction comes into the stagnant decarburization period when the carbon content in molten steel is less than 14× 10^-6 after 10 min of decarburization.
文摘Hot deformation experiments were carried out on Gleeble 1500 thermo-mechanical simulator. The bainite transformation after deformation was investigated by optical microstructure analysis. The results indicated that the deformation accelerated the bainite transformation when the deformation was carried out at high temperature and no or little ferrite was precipitated before bainite transformation; when the deformation was carried out at low temperature, the deformation hindered the bainite transformation because a lot of ferrite precipitated before bainite transformation.
基金supported by the"11th five" National Science and Technology Support Project of China (No.2006BAE03A13)
文摘A Ti+Nb bearing ultra-low carbon bake hardening sheet steel hot-rolled in the conventional austenite region and in the ferrite region with lubrication was experimentally studied. Subsequent cold rolling and continuous annealing processes were also conducted. The results show that microstructures of ultra-low carbon bake hardening hot strips at room temperature are basically irregular polygonal ferrites. The yield strength, ultimate tensile strength, n value, and r value of the No.2 specimen hot-rolled in the ferrite region with lubrication are 243 MPa, 364 MPa, 0.29, and 1.74, respectively, which are similar to those of the No.1 specimen hot-roiled in the conventional austenite region. The elongation rate and bake hardening value of No.2 specimen are 51% and 49.4 MPa, respectively, which are greater than those of No. 1 specimen. The No.2 specimen hot-rolled in the ferrite region with lubrication exhibits good mechanical properties and relatively excellent baking hardening performance. Therefore, the hot rolling experiment of Ti+Nb bearing ultra-low carbon bake hardening steel in the ferrite region with lubrication is feasible and can be considered in the future industrial trial production.
文摘A dilatometer was used to study the kinetics of bainite-to-austenite transformation in low carbon microalloyed steel with the initial microstructure of bainite during the continuous reheating process. The bainite-to-austenite trans- formation was observed to take place in two steps at low heating rate. The first step is the dissolution of bainite, and the second one is the remaining bainite-to-austenite transformation controlled by a dissolution process. The calculation result of the kinetics of austenite formation shows that the two steps occur by diffusion at low heating rate. However, at high heating rate the bainite-to-austenite transformation occurs in a single step, and the process is mainly dominated by shear. The growth rate of austenite reaches the maximum at about 835℃ at different heating rates and the growth rate of austenite as a function of temperature increases with the increase in heating rate.
文摘The characteristics of nanosized precipitates in steels depend on the heat-treatment parameters. The effects of characteristics of vanadium precipitates formed during isothermal heat treatment on the hardness of the ferrite matrix in low-carbon vanadium-alloyed steel were investigated through analysis of transmission electron microscopy images and microhardness measurements. The results show that, during isothermal holding in the temperature range from 675 to 750℃, only interphase precipitation occurs, whereas only random precipitation occurs in the ferrite matrix during holding at 600℃. Furthermore, during isothermal heat treatment between 600 and 675℃, both random and interphase precipitates occurred in the ferrite. Nanoscale vanadium carbides with different atomic ratios of vanadium(V) and carbon(C) were the dominant precipitates in the random and interphase precipitates. The sizes of random precipitation carbides were smaller than those of interphase ones. Also, the sample isothermally heat treated at 650℃ for 900s exhibited a higher hardness with a narrower hardness distribution.