A novel droplet solidification technique was developed to emulate sub-rapid solidification and facilitate the formation of deposited films during the strip casting of silicon steels(w(Si):2.5 and 3.5 wt.%).With the in...A novel droplet solidification technique was developed to emulate sub-rapid solidification and facilitate the formation of deposited films during the strip casting of silicon steels(w(Si):2.5 and 3.5 wt.%).With the increasing number of droplet ejection experiments,the peak heat fluxes between droplet and substrate decreased firstly(1rd–5th ejection),then increased(5th–7th ejection),and finally decreased again(>7th ejection).In the first five experiments,the interfacial thermal resistance between the droplet and the substrate improved with increasing film thickness.However,at the onset of the 6th droplet ejection experiment,the deposited film initiated its melting process due to the accumulated thermal resistance,which has the potential to eradicate the cavity or air space existing between the droplet and the substrate.Consequently,the interfacial contact condition was improved gradually with the increasing melting area from 5th to 7th droplet ejection experiments,leading to an increase in heat fluxes.Increased SiO_(2) content in deposited films for 3.5 wt.%Si steel led to lower peak heat fluxes than for 2.5 wt.%Si steel.The solidification structure of the 2.5 wt.%Si steel droplet sample comprised a fine grain zone at the base,a columnar grain zone in the center,and an equiaxed grain zone at the top.However,the solidification structure of the 3.5 wt.%Si steel droplet only contained columnar grains and equiaxed grains,with a larger average grain size due to the lower interfacial heat flux.展开更多
Typical Q235 low-carbon steel samples with different hydrogen contents(0.0004,0.0008,and 0.0013 wt.%)were prepared by adjusting the environment humidity and moisture.The effects of hydrogen on interfacial heat transfe...Typical Q235 low-carbon steel samples with different hydrogen contents(0.0004,0.0008,and 0.0013 wt.%)were prepared by adjusting the environment humidity and moisture.The effects of hydrogen on interfacial heat transfer,contact behavior,and microstructure evolution were investigated using a novel droplet solidification technique.The results revealed that when the hydrogen content increases from 0.0004 to 0.0013 wt.%,the maximum heat flux between the molten steel and cooling substrate decreases from 8.01 to 6.19 MW/m^(2),and the total heat removed in the initial 2 s reduces from 10.30 to 8.27 MJ/m^(2).Moreover,the final contact angle between the molten steel and substrate increases from 103.741°to 113.697°,and the number of pores on the droplet bottom surface increases significantly from 21 to 210 with the increase in hydrogen.The surface roughness of the droplet bottom surface increases from 20.902 to 49.181 pm.In addition,the average grain size of the droplet increases from 14.778 to 33.548 pm with the increase in the hydrogen content.The interfacial contact condition becomes worse due to the escape of hydrogen from the steel matrix during the cooling process,which leads to the reduction in the interfacial heat transfer and the increase in the grain size.展开更多
Microstructure evolution, dynamic recrystallization, high temperature oxidation and hot ductility of 1.4 % Si non-oriented electrical steel sheets were investigated to reduce edge cracking. The causes of cracking were...Microstructure evolution, dynamic recrystallization, high temperature oxidation and hot ductility of 1.4 % Si non-oriented electrical steel sheets were investigated to reduce edge cracking. The causes of cracking were found to be coarse as-cast microstructure, grain boundary oxidation in reheating furnace, lack of dynamic recrystallization during hot rolling and increase of temperature, resulting in reduced hot ductility in strip edge region. Countermeas- ures against the edge crack are proposed accordingly. Lowering reheating temperature and reducing holding time re- duced oxidation and decarburization. Hot charging temperature was increased to decrease reheating temperature. And using an edger can refine microstructure in strip edge region. Finally, edge heater can be added to increase edge re- gion formability by inducing dynamic reerystallization and ductility by increasing temperature.展开更多
Sub-rapid solidification has the potential to enhance the columnar structure and the magnetic property of electrical steels.However,research on the hot deformation behavior of sub-rapid solidified non-oriented electri...Sub-rapid solidification has the potential to enhance the columnar structure and the magnetic property of electrical steels.However,research on the hot deformation behavior of sub-rapid solidified non-oriented electrical steel,particularly at varying strain rates,has yet to be fully understood.The effect of thermal compression on the microstructure and mechanical properties of 3.15 wt.%Si non-oriented electrical steel strips produced through a strip casting simulator was systematically investigated.The findings reveal that increasing the deformation temperature enhances grain recrystallization,while the peak stress decreases with higher temperature.Furthermore,a lower strain rate favors dynamic recrystallization and reduces thermal stress.It can be seen that sub-rapid solidification can effectively reduce the thermal activation energy of non-oriented electrical steel,and the thermal activation energy is calculated to be 204.411 kJ/mol.In addition,the kinetic models for the dynamic recrystallization volume fraction of the studied 3.15 wt.%Si non-oriented electrical steel were established.展开更多
The modified precipitation theory was employed to directly predict the multi-variantε-carbide precipitation from thermodynamics and growing and ripening kinetics.Three distinct variants were identified:Variants 1 and...The modified precipitation theory was employed to directly predict the multi-variantε-carbide precipitation from thermodynamics and growing and ripening kinetics.Three distinct variants were identified:Variants 1 and 2 were the perpendicular plate-likeε-carbides,while the granularε-carbides were Variant 3.The particle sizes of Variants 1 and 2 were usually larger than those of Variant 3.The mean aspect ratios of Variants 1 and 2 were 4.96,4.62 and 4.35 larger than those(1.72,1.63 and 1.56)for the granularε-carbides when coiled at 140,200 and 250℃,respectively.Thermodynamic analysis indicated that Variants 1 and 2 are easier to nucleate than Variant 3.The growing kinetic analysis implied that the relative nucleation time and precipitation time for Variants 1 and 2 were about 8 and 5 orders of magnitude less than those for Variant 3,respectively.The ripening kinetics further displayed that the ripening rate was similar for Variants 1,2 and 3.In addition,the dislocation density has weak influence onε-carbide nucleation.These findings suggest that the precipitation thermodynamic and kinetic models could be extended to second phase precipitation in other materials systems.Besides,nano-scaleε-carbides,fine block size and nano-twins,as well as medium-density dislocations,jointly caused the optimal match between strength and total elongation when coiled at 140℃.展开更多
Direct strip casting(DSC)is one of the cutting-edge technologies for the steel industry in the twenty-first century.Under the background of carbon peak and carbon neutrality,DSC technology has a bright future of appli...Direct strip casting(DSC)is one of the cutting-edge technologies for the steel industry in the twenty-first century.Under the background of carbon peak and carbon neutrality,DSC technology has a bright future of applications as it requires less production time and space with reduced energy consumption.Owing to its sub-rapid cooling rate during solidification and low reduction during hot rolling,DSC process exhibits a series of unique physical metallurgy characteristics.The process characteristics of DSC process and the microstructural evolution during the thermomechanical processing of low-carbon microalloyed steel are reviewed.The effects of hot rolling,cooling,coiling temperatures and microalloying elements on the microstructure and mechanical properties are then discussed.Finally,the future development orientations of DSC technology are suggested to fully utilize its unique features for the enhancement of its competitiveness and for the promotion of carbon neutrality of the steel industry.展开更多
BN–ZrO_(2)ceramics with different additives such as SiC,Al_(2)O_(3) and MgAl_(2)O_(4) were fabricated by hot pressing sintering process to study sintering properties and corrosion resistance by the rotary immersion m...BN–ZrO_(2)ceramics with different additives such as SiC,Al_(2)O_(3) and MgAl_(2)O_(4) were fabricated by hot pressing sintering process to study sintering properties and corrosion resistance by the rotary immersion molten steel test.The results showed that SiC,Al_(2)O_(3) and MgAl_(2)O_(4) can improve the sintering properties of BN–ZrO_(2)ceramics;especially,the introduction of SiC can significantly improve the hardness of the material;thus,the above compounds will help to improve the wear resistance of BN–ZrO_(2)ceramics.The exposed oxide layer is in contact with molten steel and forms liquid phase after BN oxidation and B_(2)O_(3) volatilization,additives can significantly affect the properties of liquid phase,and m-ZrO_(2)grains are sintered and grown by dissolution–precipitation mechanism by liquid phase.Consequently,Al_(2)O_(3) and MgAl_(2)O_(4) are more conducive to the formation of working layer with solid skeleton,which determines the corrosion resistance of BN–ZrO_(2)ceramics.展开更多
基金supports from National Natural Science Foundation of China(Nos.52304361 and 52130408)Natural Science Foundation of Hunan Province(2023JJ40737)are great acknowledged.
文摘A novel droplet solidification technique was developed to emulate sub-rapid solidification and facilitate the formation of deposited films during the strip casting of silicon steels(w(Si):2.5 and 3.5 wt.%).With the increasing number of droplet ejection experiments,the peak heat fluxes between droplet and substrate decreased firstly(1rd–5th ejection),then increased(5th–7th ejection),and finally decreased again(>7th ejection).In the first five experiments,the interfacial thermal resistance between the droplet and the substrate improved with increasing film thickness.However,at the onset of the 6th droplet ejection experiment,the deposited film initiated its melting process due to the accumulated thermal resistance,which has the potential to eradicate the cavity or air space existing between the droplet and the substrate.Consequently,the interfacial contact condition was improved gradually with the increasing melting area from 5th to 7th droplet ejection experiments,leading to an increase in heat fluxes.Increased SiO_(2) content in deposited films for 3.5 wt.%Si steel led to lower peak heat fluxes than for 2.5 wt.%Si steel.The solidification structure of the 2.5 wt.%Si steel droplet sample comprised a fine grain zone at the base,a columnar grain zone in the center,and an equiaxed grain zone at the top.However,the solidification structure of the 3.5 wt.%Si steel droplet only contained columnar grains and equiaxed grains,with a larger average grain size due to the lower interfacial heat flux.
基金The financial support for this work from the National Natural Science Foundation of China(52274342,52130408)the Hunan Scientific Technology Projects(Grant No.2020WK2003)+1 种基金the Natural Science Foundation of Hunan Province(2021JJ40731)the Postgraduate Scientific Research Innovation Project of Hunan Province(CX20220099)is gratefully acknowledged.
文摘Typical Q235 low-carbon steel samples with different hydrogen contents(0.0004,0.0008,and 0.0013 wt.%)were prepared by adjusting the environment humidity and moisture.The effects of hydrogen on interfacial heat transfer,contact behavior,and microstructure evolution were investigated using a novel droplet solidification technique.The results revealed that when the hydrogen content increases from 0.0004 to 0.0013 wt.%,the maximum heat flux between the molten steel and cooling substrate decreases from 8.01 to 6.19 MW/m^(2),and the total heat removed in the initial 2 s reduces from 10.30 to 8.27 MJ/m^(2).Moreover,the final contact angle between the molten steel and substrate increases from 103.741°to 113.697°,and the number of pores on the droplet bottom surface increases significantly from 21 to 210 with the increase in hydrogen.The surface roughness of the droplet bottom surface increases from 20.902 to 49.181 pm.In addition,the average grain size of the droplet increases from 14.778 to 33.548 pm with the increase in the hydrogen content.The interfacial contact condition becomes worse due to the escape of hydrogen from the steel matrix during the cooling process,which leads to the reduction in the interfacial heat transfer and the increase in the grain size.
文摘Microstructure evolution, dynamic recrystallization, high temperature oxidation and hot ductility of 1.4 % Si non-oriented electrical steel sheets were investigated to reduce edge cracking. The causes of cracking were found to be coarse as-cast microstructure, grain boundary oxidation in reheating furnace, lack of dynamic recrystallization during hot rolling and increase of temperature, resulting in reduced hot ductility in strip edge region. Countermeas- ures against the edge crack are proposed accordingly. Lowering reheating temperature and reducing holding time re- duced oxidation and decarburization. Hot charging temperature was increased to decrease reheating temperature. And using an edger can refine microstructure in strip edge region. Finally, edge heater can be added to increase edge re- gion formability by inducing dynamic reerystallization and ductility by increasing temperature.
基金The National Natural Science Foundation of China(Nos.52130408 and 52204356)the Natural Science Foundation of Hunan Province,China(2023JJ40762)the National Key Research and Development Program of China(No.2021YFB3702401)are greatly acknowledged.
文摘Sub-rapid solidification has the potential to enhance the columnar structure and the magnetic property of electrical steels.However,research on the hot deformation behavior of sub-rapid solidified non-oriented electrical steel,particularly at varying strain rates,has yet to be fully understood.The effect of thermal compression on the microstructure and mechanical properties of 3.15 wt.%Si non-oriented electrical steel strips produced through a strip casting simulator was systematically investigated.The findings reveal that increasing the deformation temperature enhances grain recrystallization,while the peak stress decreases with higher temperature.Furthermore,a lower strain rate favors dynamic recrystallization and reduces thermal stress.It can be seen that sub-rapid solidification can effectively reduce the thermal activation energy of non-oriented electrical steel,and the thermal activation energy is calculated to be 204.411 kJ/mol.In addition,the kinetic models for the dynamic recrystallization volume fraction of the studied 3.15 wt.%Si non-oriented electrical steel were established.
基金supported by the National Natural Science Foundation of China(No.52293395)National Key R&D Program of China(No.2021YFB3702403).
文摘The modified precipitation theory was employed to directly predict the multi-variantε-carbide precipitation from thermodynamics and growing and ripening kinetics.Three distinct variants were identified:Variants 1 and 2 were the perpendicular plate-likeε-carbides,while the granularε-carbides were Variant 3.The particle sizes of Variants 1 and 2 were usually larger than those of Variant 3.The mean aspect ratios of Variants 1 and 2 were 4.96,4.62 and 4.35 larger than those(1.72,1.63 and 1.56)for the granularε-carbides when coiled at 140,200 and 250℃,respectively.Thermodynamic analysis indicated that Variants 1 and 2 are easier to nucleate than Variant 3.The growing kinetic analysis implied that the relative nucleation time and precipitation time for Variants 1 and 2 were about 8 and 5 orders of magnitude less than those for Variant 3,respectively.The ripening kinetics further displayed that the ripening rate was similar for Variants 1,2 and 3.In addition,the dislocation density has weak influence onε-carbide nucleation.These findings suggest that the precipitation thermodynamic and kinetic models could be extended to second phase precipitation in other materials systems.Besides,nano-scaleε-carbides,fine block size and nano-twins,as well as medium-density dislocations,jointly caused the optimal match between strength and total elongation when coiled at 140℃.
文摘Direct strip casting(DSC)is one of the cutting-edge technologies for the steel industry in the twenty-first century.Under the background of carbon peak and carbon neutrality,DSC technology has a bright future of applications as it requires less production time and space with reduced energy consumption.Owing to its sub-rapid cooling rate during solidification and low reduction during hot rolling,DSC process exhibits a series of unique physical metallurgy characteristics.The process characteristics of DSC process and the microstructural evolution during the thermomechanical processing of low-carbon microalloyed steel are reviewed.The effects of hot rolling,cooling,coiling temperatures and microalloying elements on the microstructure and mechanical properties are then discussed.Finally,the future development orientations of DSC technology are suggested to fully utilize its unique features for the enhancement of its competitiveness and for the promotion of carbon neutrality of the steel industry.
基金The authors gratefully acknowledge the support of National Natural Science Foundation of China(51932008 and 51772277)Central China Thousand Talents Project(204200510011).
文摘BN–ZrO_(2)ceramics with different additives such as SiC,Al_(2)O_(3) and MgAl_(2)O_(4) were fabricated by hot pressing sintering process to study sintering properties and corrosion resistance by the rotary immersion molten steel test.The results showed that SiC,Al_(2)O_(3) and MgAl_(2)O_(4) can improve the sintering properties of BN–ZrO_(2)ceramics;especially,the introduction of SiC can significantly improve the hardness of the material;thus,the above compounds will help to improve the wear resistance of BN–ZrO_(2)ceramics.The exposed oxide layer is in contact with molten steel and forms liquid phase after BN oxidation and B_(2)O_(3) volatilization,additives can significantly affect the properties of liquid phase,and m-ZrO_(2)grains are sintered and grown by dissolution–precipitation mechanism by liquid phase.Consequently,Al_(2)O_(3) and MgAl_(2)O_(4) are more conducive to the formation of working layer with solid skeleton,which determines the corrosion resistance of BN–ZrO_(2)ceramics.
