The structure and characteristics of high-performance lightweight aggregates produced by high-carbon gasification slag were investigated by X-ray diffraction,scanning electron microscopy,thermogravimetry/differential ...The structure and characteristics of high-performance lightweight aggregates produced by high-carbon gasification slag were investigated by X-ray diffraction,scanning electron microscopy,thermogravimetry/differential thermogravimetr,differential scanning calorimetry-Fourier transform infrared,and mercury intrusion porosimetry,respectively.The experimental results show that the ceramsite undergoes two weightless stages in the calcining process.With the increase in the calcining temperature,a large number of pores are formed inside the ceramsite,its structure becomes denser,but the calcining temperature band of the ceramsite becomes narrow.The crystalline phase of the ceramsite changes at different calcining temperatures and the mineral phase changes from the earlieralbite,quartz,oligoclase,hematite,etc,to a silica-aluminum-rich glass phase.The 1130℃ is a more suitable calcining temperature,and the cylinder compressive strength of ceramics is 11.59 MPa,the packing density,apparent density,porosity,and water absorption are 939.11 kg/m^(3),1643.75 kg/m^(3),28.11%,and 10.35%,respectively,which can meet the standards for high-strength lightweight aggregates.展开更多
The effect of RE-modifier on the microstructure and mechanical properties of high carbon-medium manganese steel has been investigated in present work. The results showed that the RE-modifier can refine the crystalline...The effect of RE-modifier on the microstructure and mechanical properties of high carbon-medium manganese steel has been investigated in present work. The results showed that the RE-modifier can refine the crystalline grain of high-carbon medium-manganese steel. The shape and distribution of carbides are improved and the columnar grains and phosphide in grain boundary are eliminated. Consequently, the impact toughness of the steel is increased by more than one time, compared with no addition of RE-modifier.展开更多
As a crucial environmental reform system to realize“carbon peaking”and“carbon neutrality”,the pilot policy of low-carbon cities(LCCs)puts pressure and challenges on high-carbon emitting enterprises(HCEEs)while pro...As a crucial environmental reform system to realize“carbon peaking”and“carbon neutrality”,the pilot policy of low-carbon cities(LCCs)puts pressure and challenges on high-carbon emitting enterprises(HCEEs)while providing opportunities for these firms to take the path of independent transformation.Employing the data of Chinese listed enterprises from 2006 to 2016 and adopting a difference-in-differences(DID)model,we evaluated the impact of LCC construction on the upgrading of HCEEs and its mechanisms.The results indicate that LCC construction enhances the upgrading of HCEEs in the pilot cities.The conclusions remain stable after a series of robustness tests.The mechanism analysis reveals that LCC construction triggers the upgrading of HCEEs by promoting resource allocation efficiency,R&D investment,and green technology innovation.The heterogeneity results indicate that this positive effect is more pronounced for HCEEs in regions with more stringent environmental law enforcement.This study also observes that the upgrading impact is more promi‐nent for state-owned enterprises,enterprises with higher bargaining power,and enterprises whose managers have a long-term vision.The above results provide directions for upgrading HCEEs and replicable evidence for cities in developing economies to fulfill the win-win target of environmental protection and economic transfor‐mation.展开更多
In this study,the spheroidization process of large-deformed steel under various conditions was researched. Steel with a high carbon content(1.0% C)was first treated thermomechanically using multipass rolling.Then it u...In this study,the spheroidization process of large-deformed steel under various conditions was researched. Steel with a high carbon content(1.0% C)was first treated thermomechanically using multipass rolling.Then it underwent spheroidization treatments at different heating temperatures,using various heating times and cooling rates.Spheroidization processes with a lower heating temperature,shorter heating time,or faster cooling rate than those of the traditional process all showed good results,indicating that the spheroidization process was promoted significantly by the large deformation process.Grain refinement and fragmentation of cementite,along with the large deformation process,promoted this spheroidization process.展开更多
Based on a series of related investigations,a mechanism for the formation of longitudinal surface cracks on a continuous casting slab of high-carbon steel was investigated. High-temperature tensile tests performed on ...Based on a series of related investigations,a mechanism for the formation of longitudinal surface cracks on a continuous casting slab of high-carbon steel was investigated. High-temperature tensile tests performed on slab samples,metallographic and scanning electron microscopy studies,as well as heat flux and shell thickness in continuous casting predicted on the basis of a mathematical model were conducted. The results showed that highcarbon steel exhibited a much lower liquidus temperature and a wider brittle temperature range immediately after solidification compared with those of low-carbon steel. Concentrations of elements K and Na,which are contained in the mold fluxes,were not observed in the cracks during this study. The calculated results showed that the heat flux and the shell thickness were uneven along the mold width and that the shell was thinner and close to the center line of the slab surface. The longitudinal cracks were observed in situ using confocal laser scanning microscopy,to first occur close to the solidification front,where the ductility was extremely low;in addition,the shell growth was slower than in other regions,which led to a thinner shell and depressed shrinkage owing to a lack of lubrication by the mold fluxes below the meniscus. Furthermore,the pouring temperature of high-carbon steel is ~ 100 ℃ lower than that of low-carbon steel,so the formation of a stable liquid flux near the meniscus within a short time at the beginning of casting is difficult. The amounts of liquid slag film and crystalline slag film were insufficient to provide adequate lubrication between the shell and the mold,which resulted in greater friction force that induced or aggravated cracks. Therefore,the homogeneity of mold fluxes and initial solidification in the mold should be improved to reduce the concentration of slab surface defects.展开更多
The patenting process of three hot-rolled steels with carbon mass contents of 0. 70%-0. 90% was studied.The effect of the quenching temperature on the cementite lamellar distance in the steel was evaluated on the basi...The patenting process of three hot-rolled steels with carbon mass contents of 0. 70%-0. 90% was studied.The effect of the quenching temperature on the cementite lamellar distance in the steel was evaluated on the basis of microstructural characterization and mechanical property tests. The patenting treatment of high-carbon hot-rolled strip and its application in springs were discussed.展开更多
The effects of rare earths（RE）-Mg-Ti compound modification on the structures and properties of high-carbon high speed steel（HSS） were researched.The impact toughness（αk）,the fracture toughness(K1c)and threshold...The effects of rare earths（RE）-Mg-Ti compound modification on the structures and properties of high-carbon high speed steel（HSS） were researched.The impact toughness（αk）,the fracture toughness(K1c)and threshold of fatigue crack growth(ΔKth)are tested.The thermal fatigue test is done on a self-straining thermal fatigue tester,the wear test is done on a high temperature wear test machine.The results show that the matrix can be refined by the RE-Mg-Ti compound modification,the eutectic carbides are inclined to spheroidicize and are distributed evenly,the morphology and distribution of eutectic carbides are improved by appropriate RE-Mg-Ti complex modification.After RE-Mg-Ti compound modification,a little effects can be found on the strength,hardness and red hardness,but the fracture toughness(K1c) and threshold of fatigue crack growth(△Kth) are improved in the meantime,the impact toughness （αk） is increased by over one time,and the resistance to thermal fatigue and wear resistance at an elevated temperature are remarkably improved.展开更多
Effects of varied levels of cerium(28×10-6,65×10^(-6) and 150×10^(-6))on inclusions in a high-carbon chromium bearing steel at different stages(before adding cerium,after adding cerium for 1,5,10 min an...Effects of varied levels of cerium(28×10-6,65×10^(-6) and 150×10^(-6))on inclusions in a high-carbon chromium bearing steel at different stages(before adding cerium,after adding cerium for 1,5,10 min and ingot)were studied using laboratory experiments.An automatic scanning electron microscope system with energy-dispersive spectroscopy was used to analyze the amount,composition,size and morphology of inclusions in the steel at different stages.When the cerium content in the molten steel increased from 0 to 150×10^(-6),the evolution sequence of inclusions was as follows:Al_(2)O_(3)→CeAl11O18→CeAlO_(3)→Ce_(2)O_(2)S.After 28×10^(-6) cerium was added,Al_(2)O_(3) inclusions were modified into CeAl_(11)O_(18) inclusions in the molten steel and then were further transformed into Al2O3 and CeAlO3 inclusions in the solid steel during cooling.With the addition of 65×10^(-6) cerium,inclusions in the molten steel were modified into CeAlO_(3) and a small number of Ce2O2S inclusions.When the addition amount of cerium increased to 150×10^(-6),inclusions were transformed to Ce_(2)O_(2)S.The size of inclusions in the molten steel decreased obviously with cerium addition.On the other hand,the size of inclusions increased during the cooling process in solid steels of No.1 steel(with 28×10^(-6) cerium)and No.2 steel(with 65×10^(-6) cerium).During the cooling process,unmodified MnS inclusions were precipitated in the solid steel of No.1 steel and wrapped outside the Al2O3 and CeAlO_(3) inclusions to form large complex inclusions.During the cooling process of No.2 steel,the inclusion size of CeAlO_(3) increased due to the collision and polymerization.In the No.3 steel(with 150×10^(-6) cerium),the average size of inclusions decreased rapidly and remained at a lower size during the cooling process,which was beneficial to improving the fatigue life of the steel.展开更多
High-carbon chromium bearing steels with different rare earth (RE) contents were prepared to investigate the effects of RE on inclusions and impact toughness by different techniques. The results showed that RE additio...High-carbon chromium bearing steels with different rare earth (RE) contents were prepared to investigate the effects of RE on inclusions and impact toughness by different techniques. The results showed that RE addition could modify irregular Al2O3 and MnS into regular RE inclusions. With the increase of RE content, the reaction sequence of RE and potential inclusion forming elements should be O, S, As, P and C successively. RE inclusions containing C might precipitate in molten steel and solid state, but the precipitation tem perature was significantly higher than that of carbides in high-carbon chromium bearing steel. For experim ental bearing steels, the volume fraction of inclusions increased steadily with the increase of RE content, but smaller and more dispersed inclusions could be obtained by 0.018% RE content compared with bearing steel without RE, whereas the continuous increase of RE content led to an increasing trend for inclusion size and a gradual deterioration for inclusion distribution. RE addition could improve the transverse impact toughness and isotropy of bearing steel, and for modified highcarbon chrom ium bearing steel by RE alloying, the increase of RE content continuously increased both transverse and longitudinal im pact toughness until excessive RE addition.展开更多
基金Funded by the National Natural Science Foundation of China (Z20180222)the Independent Research and Development project of State Key Laboratory of Green Building in Western China (LSZZ202021)+1 种基金the Natural Science Foundation of Shaanxi Provincial Department of Education (20JY041)the Qingyuan Science and Technology Plan Project (No.2020KJJH040)。
文摘The structure and characteristics of high-performance lightweight aggregates produced by high-carbon gasification slag were investigated by X-ray diffraction,scanning electron microscopy,thermogravimetry/differential thermogravimetr,differential scanning calorimetry-Fourier transform infrared,and mercury intrusion porosimetry,respectively.The experimental results show that the ceramsite undergoes two weightless stages in the calcining process.With the increase in the calcining temperature,a large number of pores are formed inside the ceramsite,its structure becomes denser,but the calcining temperature band of the ceramsite becomes narrow.The crystalline phase of the ceramsite changes at different calcining temperatures and the mineral phase changes from the earlieralbite,quartz,oligoclase,hematite,etc,to a silica-aluminum-rich glass phase.The 1130℃ is a more suitable calcining temperature,and the cylinder compressive strength of ceramics is 11.59 MPa,the packing density,apparent density,porosity,and water absorption are 939.11 kg/m^(3),1643.75 kg/m^(3),28.11%,and 10.35%,respectively,which can meet the standards for high-strength lightweight aggregates.
文摘The effect of RE-modifier on the microstructure and mechanical properties of high carbon-medium manganese steel has been investigated in present work. The results showed that the RE-modifier can refine the crystalline grain of high-carbon medium-manganese steel. The shape and distribution of carbides are improved and the columnar grains and phosphide in grain boundary are eliminated. Consequently, the impact toughness of the steel is increased by more than one time, compared with no addition of RE-modifier.
基金This paper was supported by the Fundamental Research Funds for the Central Universities[Grant number:JBK2202018].
文摘As a crucial environmental reform system to realize“carbon peaking”and“carbon neutrality”,the pilot policy of low-carbon cities(LCCs)puts pressure and challenges on high-carbon emitting enterprises(HCEEs)while providing opportunities for these firms to take the path of independent transformation.Employing the data of Chinese listed enterprises from 2006 to 2016 and adopting a difference-in-differences(DID)model,we evaluated the impact of LCC construction on the upgrading of HCEEs and its mechanisms.The results indicate that LCC construction enhances the upgrading of HCEEs in the pilot cities.The conclusions remain stable after a series of robustness tests.The mechanism analysis reveals that LCC construction triggers the upgrading of HCEEs by promoting resource allocation efficiency,R&D investment,and green technology innovation.The heterogeneity results indicate that this positive effect is more pronounced for HCEEs in regions with more stringent environmental law enforcement.This study also observes that the upgrading impact is more promi‐nent for state-owned enterprises,enterprises with higher bargaining power,and enterprises whose managers have a long-term vision.The above results provide directions for upgrading HCEEs and replicable evidence for cities in developing economies to fulfill the win-win target of environmental protection and economic transfor‐mation.
文摘In this study,the spheroidization process of large-deformed steel under various conditions was researched. Steel with a high carbon content(1.0% C)was first treated thermomechanically using multipass rolling.Then it underwent spheroidization treatments at different heating temperatures,using various heating times and cooling rates.Spheroidization processes with a lower heating temperature,shorter heating time,or faster cooling rate than those of the traditional process all showed good results,indicating that the spheroidization process was promoted significantly by the large deformation process.Grain refinement and fragmentation of cementite,along with the large deformation process,promoted this spheroidization process.
文摘Based on a series of related investigations,a mechanism for the formation of longitudinal surface cracks on a continuous casting slab of high-carbon steel was investigated. High-temperature tensile tests performed on slab samples,metallographic and scanning electron microscopy studies,as well as heat flux and shell thickness in continuous casting predicted on the basis of a mathematical model were conducted. The results showed that highcarbon steel exhibited a much lower liquidus temperature and a wider brittle temperature range immediately after solidification compared with those of low-carbon steel. Concentrations of elements K and Na,which are contained in the mold fluxes,were not observed in the cracks during this study. The calculated results showed that the heat flux and the shell thickness were uneven along the mold width and that the shell was thinner and close to the center line of the slab surface. The longitudinal cracks were observed in situ using confocal laser scanning microscopy,to first occur close to the solidification front,where the ductility was extremely low;in addition,the shell growth was slower than in other regions,which led to a thinner shell and depressed shrinkage owing to a lack of lubrication by the mold fluxes below the meniscus. Furthermore,the pouring temperature of high-carbon steel is ~ 100 ℃ lower than that of low-carbon steel,so the formation of a stable liquid flux near the meniscus within a short time at the beginning of casting is difficult. The amounts of liquid slag film and crystalline slag film were insufficient to provide adequate lubrication between the shell and the mold,which resulted in greater friction force that induced or aggravated cracks. Therefore,the homogeneity of mold fluxes and initial solidification in the mold should be improved to reduce the concentration of slab surface defects.
文摘The patenting process of three hot-rolled steels with carbon mass contents of 0. 70%-0. 90% was studied.The effect of the quenching temperature on the cementite lamellar distance in the steel was evaluated on the basis of microstructural characterization and mechanical property tests. The patenting treatment of high-carbon hot-rolled strip and its application in springs were discussed.
文摘The effects of rare earths（RE）-Mg-Ti compound modification on the structures and properties of high-carbon high speed steel（HSS） were researched.The impact toughness（αk）,the fracture toughness(K1c)and threshold of fatigue crack growth(ΔKth)are tested.The thermal fatigue test is done on a self-straining thermal fatigue tester,the wear test is done on a high temperature wear test machine.The results show that the matrix can be refined by the RE-Mg-Ti compound modification,the eutectic carbides are inclined to spheroidicize and are distributed evenly,the morphology and distribution of eutectic carbides are improved by appropriate RE-Mg-Ti complex modification.After RE-Mg-Ti compound modification,a little effects can be found on the strength,hardness and red hardness,but the fracture toughness(K1c) and threshold of fatigue crack growth(△Kth) are improved in the meantime,the impact toughness （αk） is increased by over one time,and the resistance to thermal fatigue and wear resistance at an elevated temperature are remarkably improved.
基金support from the Natural Science Foundation of Hebei Province(Grant No.E2021203062)S&T Program of Hebei(Grant No.20311006D)the High Steel Center(HSC)at North China University of Technology,Yanshan University and University of Science and Technology Beijing.
文摘Effects of varied levels of cerium(28×10-6,65×10^(-6) and 150×10^(-6))on inclusions in a high-carbon chromium bearing steel at different stages(before adding cerium,after adding cerium for 1,5,10 min and ingot)were studied using laboratory experiments.An automatic scanning electron microscope system with energy-dispersive spectroscopy was used to analyze the amount,composition,size and morphology of inclusions in the steel at different stages.When the cerium content in the molten steel increased from 0 to 150×10^(-6),the evolution sequence of inclusions was as follows:Al_(2)O_(3)→CeAl11O18→CeAlO_(3)→Ce_(2)O_(2)S.After 28×10^(-6) cerium was added,Al_(2)O_(3) inclusions were modified into CeAl_(11)O_(18) inclusions in the molten steel and then were further transformed into Al2O3 and CeAlO3 inclusions in the solid steel during cooling.With the addition of 65×10^(-6) cerium,inclusions in the molten steel were modified into CeAlO_(3) and a small number of Ce2O2S inclusions.When the addition amount of cerium increased to 150×10^(-6),inclusions were transformed to Ce_(2)O_(2)S.The size of inclusions in the molten steel decreased obviously with cerium addition.On the other hand,the size of inclusions increased during the cooling process in solid steels of No.1 steel(with 28×10^(-6) cerium)and No.2 steel(with 65×10^(-6) cerium).During the cooling process,unmodified MnS inclusions were precipitated in the solid steel of No.1 steel and wrapped outside the Al2O3 and CeAlO_(3) inclusions to form large complex inclusions.During the cooling process of No.2 steel,the inclusion size of CeAlO_(3) increased due to the collision and polymerization.In the No.3 steel(with 150×10^(-6) cerium),the average size of inclusions decreased rapidly and remained at a lower size during the cooling process,which was beneficial to improving the fatigue life of the steel.
基金financially supported by the National Natural Science Foundation of China (Nos. U1508215 and U1708252)the National Key Research and Development Program (No. 2016YFB0300401)
文摘High-carbon chromium bearing steels with different rare earth (RE) contents were prepared to investigate the effects of RE on inclusions and impact toughness by different techniques. The results showed that RE addition could modify irregular Al2O3 and MnS into regular RE inclusions. With the increase of RE content, the reaction sequence of RE and potential inclusion forming elements should be O, S, As, P and C successively. RE inclusions containing C might precipitate in molten steel and solid state, but the precipitation tem perature was significantly higher than that of carbides in high-carbon chromium bearing steel. For experim ental bearing steels, the volume fraction of inclusions increased steadily with the increase of RE content, but smaller and more dispersed inclusions could be obtained by 0.018% RE content compared with bearing steel without RE, whereas the continuous increase of RE content led to an increasing trend for inclusion size and a gradual deterioration for inclusion distribution. RE addition could improve the transverse impact toughness and isotropy of bearing steel, and for modified highcarbon chrom ium bearing steel by RE alloying, the increase of RE content continuously increased both transverse and longitudinal im pact toughness until excessive RE addition.
