This paper explained the mechanism of carbon pickup byultra-low-carbon steels during continuous casting and indicated that the major cause of carbon pickup is the contact of the molten steel with the enriched-carbon l...This paper explained the mechanism of carbon pickup byultra-low-carbon steels during continuous casting and indicated that the major cause of carbon pickup is the contact of the molten steel with the enriched-carbon layer of the powder. Forming of the enriched-carbon layer is due to the existing of “carbon core”. Accordingly, the measures to reduce the carbon content and amount of the enriched-carbon layer were investigated. A kind of new powder has been developed and successfully used to minimize the carbon pickup by ultra-low carbon steels during continuous casting.展开更多
An induction levitation melting(ILM) refining process is performed to remove most microsized inclusions in ultra-low carbon steel(UCS). Nanosized, spheroid shaped sulfide precipitates remain dispersed in the UCS. Duri...An induction levitation melting(ILM) refining process is performed to remove most microsized inclusions in ultra-low carbon steel(UCS). Nanosized, spheroid shaped sulfide precipitates remain dispersed in the UCS. During the ILM process, the UCS is molten and is rotated under an upward magnetic field. With the addition of Ti additives, the spinning molten steel under the upward magnetic field ejects particles because of resultant centrifugal, floating, and magnetic forces. Magnetic force plays a key role in removing sub-micrometer-sized particles, composed of porous aluminum titanate enwrapping alumina nuclei. Consequently, sulfide precipitates with sizes less than 50 nm remain dispersed in the steel matrix. These findings open a path to the fabrication of clean steel or steel bearing only a nanosized strengthening phase.展开更多
A mathematical model was established and applied to simulatethe decarburization of RH-MFB process in Pansteel Company. Study of the effects of , , Ar flowrate, evacuation rate and MFB lance blowing parameters on the d...A mathematical model was established and applied to simulatethe decarburization of RH-MFB process in Pansteel Company. Study of the effects of , , Ar flowrate, evacuation rate and MFB lance blowing parameters on the decarburization process was carried out. The results showed that this model could give the quantitative understanding of the process, especially the behavior of MFB lance blowing. This model has realized the optimum process of RH-MFB refining for ultra-low carbonsteels in Pansteel.展开更多
The steel industry is a major source of CO_(2) emissions,and thus,the mitigation of carbon emissions is the most pressing challenge in this sector.In this paper,international environmental governance in the steel indu...The steel industry is a major source of CO_(2) emissions,and thus,the mitigation of carbon emissions is the most pressing challenge in this sector.In this paper,international environmental governance in the steel industry is reviewed,and the current state of development of low-carbon technologies is discussed.Additionally,low-carbon pathways for the steel industry at the current time are proposed,emphasizing prevention and treatment strategies.Furthermore,the prospects of low-carbon technologies are explored from the perspective of transitioning the energy structure to a“carbon-electricity-hydrogen”relationship.Overall,steel enterprises should adopt hydrogen-rich metallurgical technologies that are compatible with current needs and process flows in the short term,based on the carbon substitution with hydrogen(prevention)and the CCU(CO_(2) capture and utilization)concepts(treatment).Additionally,the capture and utilization of CO_(2) for steelmaking,which can assist in achieving short-term emission reduction targets but is not a long-term solution,is discussed.In conclusion,in the long term,the carbon metallurgical process should be gradually supplanted by a hydrogen-electric synergistic approach,thus transforming the energy structure of existing steelmaking processes and attaining near-zero carbon emission steelmaking technology.展开更多
Many researchers have explored the inclusion modification mechanism to improve non-metallic inclusion modifications in steelmaking. In this study, two types of industrial trials on inclusion modifications in liquid st...Many researchers have explored the inclusion modification mechanism to improve non-metallic inclusion modifications in steelmaking. In this study, two types of industrial trials on inclusion modifications in liquid steel were conducted using ultra-low-carbon Al-killed steel with different Mg and Ca contents to verify the effects of Ca and Mg contents on the modification mechanism of Al_2O_3-based inclusions during secondary refining. The results showed that Al_2O_3-based inclusions can be modified into liquid calcium aluminate or a multi-component inclusion with the addition of a suitable amount of Ca. In addition, [Mg] in liquid steel can further reduce CaO in liquid calcium aluminate to drive its evolution into CaO–MgO–Al_2O_3 multi-component inclusions. Thermodynamic analysis confirmed that the reaction between [Mg] and CaO in liquid calcium aluminate occurs when the MgO content of liquid calcium aluminate is less than 3 wt% and the temperature is higher than 1843 K.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 continuous ...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-rolled 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
Population density function(PDF),which can eliminate the arbitrariness caused by the choice of the number and the size of bins compared to the well-used histograms,was introduced to analyze the amount of inclusions.Th...Population density function(PDF),which can eliminate the arbitrariness caused by the choice of the number and the size of bins compared to the well-used histograms,was introduced to analyze the amount of inclusions.The population evolution of oxide inclusions in forms of PDF in Ti-stabilized ultra-low carbon steels after deoxidation during industrial RH refining and continuous casting processes was analyzed using an automated SEM-EDS system.It was found that after deoxidation till the early stage of casting,the alumina inclusions exhibited a lognormal PDF distribution,and three factors including the existence of a large amount of alumina clusters,the generation of alumina from the reduction of Al-Ti-O inclusions and the reoxidation of molten steel were estimated as the reasons.The shape parameterσwas high after deoxidation and then decreased after Ti treatment,indicating that in a short period after deoxidation,the size of alumina inclusions was widely distributed.After Ti treatment,the distribution of inclusion size was more concentrated.The scale parameter mdecreased with time during the whole refining process,indicating that the proportion of large inclusions decreased during refining.Contrarily,the Al-Ti-O inclusions presented a fractal PDF distribution except at the end of casting with fractal dimension Dof 4.3,and the constant of proportionality C decreased with time during RH refining and increased during casting process.The reoxidation of steel by slag entrapped from ladle was considered as the reason for the lognormal PDF behavior of Al-Ti-O inclusions at the end of casting.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
Through the rapid carbonation test of SFRRC with different fiber volume fractions at ultralow temperature,the influence of ultra-low temperature damage on the carbonation resistance of SFRRC was analyzed,which provide...Through the rapid carbonation test of SFRRC with different fiber volume fractions at ultralow temperature,the influence of ultra-low temperature damage on the carbonation resistance of SFRRC was analyzed,which provides a theoretical basis for the application of SFRRC in ultra-low temperature engineering.The experimental results show that ultra-low temperatures can significantly weaken the carbonization resistance of SFRRC.When the temperature reaches 160℃,the carbonization depth increases by 67.66%compared with the normal state.The proper amount of steel fiber has an evident influence on the carbonation resistance of the material.However,when the addition amount exceeds the optimum content,the carbonation resistance of the material decreases.The grey prediction model established by constructing the original sequence can reasonably predict the carbonation resistance of SFRRC after ultra-low temperatures.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
Two carbonation approaches are considered for studying the effects on the hardening mechanisms of slurries made of 100 wt%electric arc furnace steel slag (EAF) slag or 80 wt%EAF slag incorporating 20 wt% of Portland c...Two carbonation approaches are considered for studying the effects on the hardening mechanisms of slurries made of 100 wt%electric arc furnace steel slag (EAF) slag or 80 wt%EAF slag incorporating 20 wt% of Portland cement,which are applied during the hot-stage pretreatment with simulated gas for raw steel slag or the accelerated carbonation curing of slurry.The mechanical strengths,carbonate products,microstructures and CO_(2) uptakes were quantitatively investigated.Results manifest that accelerated carbonation curing increases the compressive strengths of steel slag slurry,from 17.1 MPa (binder of 80 wt% EAF and 20 wt%cement under standard moisture curing) to 36.0 MPa (binder of 80 wt%EAF and 20 wt%cement under accelerated carbonation curing),with a CO_(2) uptake of 52%.In contrast,hot-stage carbonation applied during the pretreatment of steel slag increases the compressive strengths to 43.7 MPa (binder of 80 wt%carbonated EAF and 20 wt%cement under accelerated carbonation curing),with a CO_(2) uptake of 67%.Hotstage carbonation of steel slag is found for particle agglomeration,minerals remodeling and calcite formed,thus causing an activated steel slag with a dense structure and more active components.Accelerated carbonation curing of steel slag slurry paste results in the newly formed amorphous CaCO_(3),calcite crystalline and silica gels that covered the pores of the matrix,facilitating microstructure densification and strength improvement.Adopting the combinative methods of the hot-stage CO_(2) pretreatment and accelerated carbonation curing creates a promising high-volume steel slag-based binder with high strengths and CO_(2) storage.展开更多
Low residual-free-oxygen before final de-oxidation was beneficial to improving the cleanness of ultra-low-carbon steel. For ultra-low-carbon steel production, the coordinated control of carbon and oxygen is a precondi...Low residual-free-oxygen before final de-oxidation was beneficial to improving the cleanness of ultra-low-carbon steel. For ultra-low-carbon steel production, the coordinated control of carbon and oxygen is a precondition for achieving low residual oxygen during the Ruhrstahl Heraeus(RH) decarburization process. In this work, we studied the coordinated control of carbon and oxygen for ultra-low-carbon steel during the basic oxygen furnace(BOF) endpoint and RH process using data statistics, multiple linear regressions, and thermodynamics computations. The results showed that the aluminum yield decreased linearly with increasing residual oxygen in liquid steel. When the mass ratio of free oxygen and carbon([O]/[C]) in liquid steel before RH decarburization was maintained between 1.5 and 2.0 and the carbon range was from 0.030wt% to 0.040wt%, the residual oxygen after RH natural decarburization was low and easily controlled. To satisfy the requirement for RH decarburization, the carbon and free oxygen at the BOF endpoint should be controlled to be between 297 × 10-6 and 400 × 10-6 and between 574 × 10-6 and 775 × 10-6, respectively, with a temperature of 1695 to 1715°C and a furnace campaign of 1000 to 5000 heats.展开更多
The burn-on sand is common surface defect encountered in CO2 -cured silicate-bonded sand casting of hydroturbine blade of ultra-low-carbon martensitic stainless steel,its feature,causes and prevention measures are pre...The burn-on sand is common surface defect encountered in CO2 -cured silicate-bonded sand casting of hydroturbine blade of ultra-low-carbon martensitic stainless steel,its feature,causes and prevention measures are presented in this paper.Experiments showed that the burn-on defect is caused by oxidization of chromium in the molten steel at high temperature and can be effectively eliminated by using chromium-corundum coating.展开更多
The decarburization behaviors of ultra low carbon steel in a 210-t RH vacuum degasser were investigated under practical operating conditions.According to the apparent decarburization rate constant (KC) calculated by t...The decarburization behaviors of ultra low carbon steel in a 210-t RH vacuum degasser were investigated under practical operating 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
The microstructure evolution during deformation enhanced transformation of under cooled austenite of a plain low carbon steel has been investigated by means of hot compression simulation experiment under various condi...The microstructure evolution during deformation enhanced transformation of under cooled austenite of a plain low carbon steel has been investigated by means of hot compression simulation experiment under various conditions of strain rate,deforma- tion temperature and strain. The effect of austenite grain size on the strain enhanced ferrite transformation has been studied. The ferrite dynamic recrystallization involved in successive hot deformation has been explored.展开更多
The effects of finishing rolling temperature and coiling temperature on retained austen-ire were studied for hot-rolled transformation induced plasticity (TRIP) steels withdifferent carbon content. The experimental re...The effects of finishing rolling temperature and coiling temperature on retained austen-ire were studied for hot-rolled transformation induced plasticity (TRIP) steels withdifferent carbon content. The experimental results showed that an appropriate volumefraction of retained austenite from 6% to 11% could be obtained according to the dif-ferent carbon content less than 0.20% by controlled finishing rolling and coiling forthe hot-rolled TRIP steels. It can be concluded that carbon content has a significanteffect on the fraction of retained austenite and coiling processing plays stronger roleon retaining austenite than fishing rolling processing.展开更多
文摘This paper explained the mechanism of carbon pickup byultra-low-carbon steels during continuous casting and indicated that the major cause of carbon pickup is the contact of the molten steel with the enriched-carbon layer of the powder. Forming of the enriched-carbon layer is due to the existing of “carbon core”. Accordingly, the measures to reduce the carbon content and amount of the enriched-carbon layer were investigated. A kind of new powder has been developed and successfully used to minimize the carbon pickup by ultra-low carbon steels during continuous casting.
基金supported partly by the National Natural Science Foundation of China (No. 51472170)the Major State Basic Research Development Program of China (No. 2011CB932700)
文摘An induction levitation melting(ILM) refining process is performed to remove most microsized inclusions in ultra-low carbon steel(UCS). Nanosized, spheroid shaped sulfide precipitates remain dispersed in the UCS. During the ILM process, the UCS is molten and is rotated under an upward magnetic field. With the addition of Ti additives, the spinning molten steel under the upward magnetic field ejects particles because of resultant centrifugal, floating, and magnetic forces. Magnetic force plays a key role in removing sub-micrometer-sized particles, composed of porous aluminum titanate enwrapping alumina nuclei. Consequently, sulfide precipitates with sizes less than 50 nm remain dispersed in the steel matrix. These findings open a path to the fabrication of clean steel or steel bearing only a nanosized strengthening phase.
文摘A mathematical model was established and applied to simulatethe decarburization of RH-MFB process in Pansteel Company. Study of the effects of , , Ar flowrate, evacuation rate and MFB lance blowing parameters on the decarburization process was carried out. The results showed that this model could give the quantitative understanding of the process, especially the behavior of MFB lance blowing. This model has realized the optimum process of RH-MFB refining for ultra-low carbonsteels in Pansteel.
文摘The steel industry is a major source of CO_(2) emissions,and thus,the mitigation of carbon emissions is the most pressing challenge in this sector.In this paper,international environmental governance in the steel industry is reviewed,and the current state of development of low-carbon technologies is discussed.Additionally,low-carbon pathways for the steel industry at the current time are proposed,emphasizing prevention and treatment strategies.Furthermore,the prospects of low-carbon technologies are explored from the perspective of transitioning the energy structure to a“carbon-electricity-hydrogen”relationship.Overall,steel enterprises should adopt hydrogen-rich metallurgical technologies that are compatible with current needs and process flows in the short term,based on the carbon substitution with hydrogen(prevention)and the CCU(CO_(2) capture and utilization)concepts(treatment).Additionally,the capture and utilization of CO_(2) for steelmaking,which can assist in achieving short-term emission reduction targets but is not a long-term solution,is discussed.In conclusion,in the long term,the carbon metallurgical process should be gradually supplanted by a hydrogen-electric synergistic approach,thus transforming the energy structure of existing steelmaking processes and attaining near-zero carbon emission steelmaking technology.
基金financially supported by the Fundamental Research Funds for the Central Universities (No. FRF-TP-16-079A1)the National Science Foundation for Young Scientists of China (No. 51704021)+1 种基金the Joint Funds of National Natural Science Foundation of China (No. U1560203)supported by Beijing Key Laboratory of Special Melting and Preparation of High-end Metal Materials
文摘Many researchers have explored the inclusion modification mechanism to improve non-metallic inclusion modifications in steelmaking. In this study, two types of industrial trials on inclusion modifications in liquid steel were conducted using ultra-low-carbon Al-killed steel with different Mg and Ca contents to verify the effects of Ca and Mg contents on the modification mechanism of Al_2O_3-based inclusions during secondary refining. The results showed that Al_2O_3-based inclusions can be modified into liquid calcium aluminate or a multi-component inclusion with the addition of a suitable amount of Ca. In addition, [Mg] in liquid steel can further reduce CaO in liquid calcium aluminate to drive its evolution into CaO–MgO–Al_2O_3 multi-component inclusions. Thermodynamic analysis confirmed that the reaction between [Mg] and CaO in liquid calcium aluminate occurs when the MgO content of liquid calcium aluminate is less than 3 wt% and the temperature is higher than 1843 K.
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-rolled 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.
基金Item Sponsored by National Natural Science Foundation of China(51274034,51334002,51404019)Independent Research and Development Program from State Key Laboratory of Advanced Metallurgy of China
文摘Population density function(PDF),which can eliminate the arbitrariness caused by the choice of the number and the size of bins compared to the well-used histograms,was introduced to analyze the amount of inclusions.The population evolution of oxide inclusions in forms of PDF in Ti-stabilized ultra-low carbon steels after deoxidation during industrial RH refining and continuous casting processes was analyzed using an automated SEM-EDS system.It was found that after deoxidation till the early stage of casting,the alumina inclusions exhibited a lognormal PDF distribution,and three factors including the existence of a large amount of alumina clusters,the generation of alumina from the reduction of Al-Ti-O inclusions and the reoxidation of molten steel were estimated as the reasons.The shape parameterσwas high after deoxidation and then decreased after Ti treatment,indicating that in a short period after deoxidation,the size of alumina inclusions was widely distributed.After Ti treatment,the distribution of inclusion size was more concentrated.The scale parameter mdecreased with time during the whole refining process,indicating that the proportion of large inclusions decreased during refining.Contrarily,the Al-Ti-O inclusions presented a fractal PDF distribution except at the end of casting with fractal dimension Dof 4.3,and the constant of proportionality C decreased with time during RH refining and increased during casting process.The reoxidation of steel by slag entrapped from ladle was considered as the reason for the lognormal PDF behavior of Al-Ti-O inclusions at the end of casting.
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.
基金the Natural Science Foundation of Hubei Province of China(No.2020CFB860)。
文摘Through the rapid carbonation test of SFRRC with different fiber volume fractions at ultralow temperature,the influence of ultra-low temperature damage on the carbonation resistance of SFRRC was analyzed,which provides a theoretical basis for the application of SFRRC in ultra-low temperature engineering.The experimental results show that ultra-low temperatures can significantly weaken the carbonization resistance of SFRRC.When the temperature reaches 160℃,the carbonization depth increases by 67.66%compared with the normal state.The proper amount of steel fiber has an evident influence on the carbonation resistance of the material.However,when the addition amount exceeds the optimum content,the carbonation resistance of the material decreases.The grey prediction model established by constructing the original sequence can reasonably predict the carbonation resistance of SFRRC after ultra-low temperatures.
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Funded by the National Key Research and Development Program of China-Intergovernmental International Cooperation in Scientific and Technological Innovation MOST,China (No.2018YFE0107300)。
文摘Two carbonation approaches are considered for studying the effects on the hardening mechanisms of slurries made of 100 wt%electric arc furnace steel slag (EAF) slag or 80 wt%EAF slag incorporating 20 wt% of Portland cement,which are applied during the hot-stage pretreatment with simulated gas for raw steel slag or the accelerated carbonation curing of slurry.The mechanical strengths,carbonate products,microstructures and CO_(2) uptakes were quantitatively investigated.Results manifest that accelerated carbonation curing increases the compressive strengths of steel slag slurry,from 17.1 MPa (binder of 80 wt% EAF and 20 wt%cement under standard moisture curing) to 36.0 MPa (binder of 80 wt%EAF and 20 wt%cement under accelerated carbonation curing),with a CO_(2) uptake of 52%.In contrast,hot-stage carbonation applied during the pretreatment of steel slag increases the compressive strengths to 43.7 MPa (binder of 80 wt%carbonated EAF and 20 wt%cement under accelerated carbonation curing),with a CO_(2) uptake of 67%.Hotstage carbonation of steel slag is found for particle agglomeration,minerals remodeling and calcite formed,thus causing an activated steel slag with a dense structure and more active components.Accelerated carbonation curing of steel slag slurry paste results in the newly formed amorphous CaCO_(3),calcite crystalline and silica gels that covered the pores of the matrix,facilitating microstructure densification and strength improvement.Adopting the combinative methods of the hot-stage CO_(2) pretreatment and accelerated carbonation curing creates a promising high-volume steel slag-based binder with high strengths and CO_(2) storage.
基金financially supported by the State Key Laboratory of Advanced Metallurgy Foundation in China (No. KF13-09)the National Natural Science Foundation of China (No. 51404018)+1 种基金the Fundamental Research Funds for the Central Universities (No. FRF-TP-14-125A2)the Doctoral Fund of the Ministry of Education of China (No. 20130006110023)
文摘Low residual-free-oxygen before final de-oxidation was beneficial to improving the cleanness of ultra-low-carbon steel. For ultra-low-carbon steel production, the coordinated control of carbon and oxygen is a precondition for achieving low residual oxygen during the Ruhrstahl Heraeus(RH) decarburization process. In this work, we studied the coordinated control of carbon and oxygen for ultra-low-carbon steel during the basic oxygen furnace(BOF) endpoint and RH process using data statistics, multiple linear regressions, and thermodynamics computations. The results showed that the aluminum yield decreased linearly with increasing residual oxygen in liquid steel. When the mass ratio of free oxygen and carbon([O]/[C]) in liquid steel before RH decarburization was maintained between 1.5 and 2.0 and the carbon range was from 0.030wt% to 0.040wt%, the residual oxygen after RH natural decarburization was low and easily controlled. To satisfy the requirement for RH decarburization, the carbon and free oxygen at the BOF endpoint should be controlled to be between 297 × 10-6 and 400 × 10-6 and between 574 × 10-6 and 775 × 10-6, respectively, with a temperature of 1695 to 1715°C and a furnace campaign of 1000 to 5000 heats.
文摘The burn-on sand is common surface defect encountered in CO2 -cured silicate-bonded sand casting of hydroturbine blade of ultra-low-carbon martensitic stainless steel,its feature,causes and prevention measures are presented in this paper.Experiments showed that the burn-on defect is caused by oxidization of chromium in the molten steel at high temperature and can be effectively eliminated by using chromium-corundum coating.
文摘The decarburization behaviors of ultra low carbon steel in a 210-t RH vacuum degasser were investigated under practical operating 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.
基金Acknowledgements-Financial support of National Science and Technology Ministry to the research projectfundamental research of
文摘The microstructure evolution during deformation enhanced transformation of under cooled austenite of a plain low carbon steel has been investigated by means of hot compression simulation experiment under various conditions of strain rate,deforma- tion temperature and strain. The effect of austenite grain size on the strain enhanced ferrite transformation has been studied. The ferrite dynamic recrystallization involved in successive hot deformation has been explored.
文摘The effects of finishing rolling temperature and coiling temperature on retained austen-ire were studied for hot-rolled transformation induced plasticity (TRIP) steels withdifferent carbon content. The experimental results showed that an appropriate volumefraction of retained austenite from 6% to 11% could be obtained according to the dif-ferent carbon content less than 0.20% by controlled finishing rolling and coiling forthe hot-rolled TRIP steels. It can be concluded that carbon content has a significanteffect on the fraction of retained austenite and coiling processing plays stronger roleon retaining austenite than fishing rolling processing.