查看更多>>摘要：Enhancing the ductility and toughness of advanced high-strength steels is essential for the wide range of promising applications.The retained austenite(RA)is a key phase due to the austenite-to-martensite transformation and its trans-formation-induced plasticity effect.It is commonly accepted that slow RA-to-martensite transformation is beneficial to ductility;therefore,the RA fraction and stability should be carefully controlled.The RA stability is related to its mor-phology,size,carbon content,neighboring phase and orientation.Importantly,these factors are cross-influenced.It is noteworthy that the influence of RA on ductility and fracture toughness is not consistent because of their difference in stress state.There is no clear relationship between fracture toughness and tensile properties.Thus,it is important to understand the role of RA in toughness.The toughness is enhanced during the RA-to-martensite transformation,while the fracture toughness is decreased due to the formation of fresh and brittle martensite.As a result,the findings regarding to the effect of RA on fracture toughness are conflicting.Further investigations should be conducted in order to fully understand the effects of RA on ductility and fracture toughness,which can optimize the combination of ductility and toughness in AHSSs.
查看更多>>摘要：The iron oxide(FeO)content had a significant impact on both the metallurgical properties of sintered ores and the economic indicators of the sintering process.Precisely predicting FeO content possessed substantial potential for enhancing the quality of sintered ore and optimizing the sintering process.A multi-model integrated prediction framework for FeO content during the iron ore sintering process was presented.By applying the affinity propagation clustering algorithm,different working conditions were efficiently classified and the support vector machine algorithm was utilized to identify these conditions.Comparison of several models under different working conditions was carried out.The regression prediction model char-acterized by high precision and robust stability was selected.The model was integrated into the comprehensive multi-model framework.The precision,reliability and credibility of the model were validated through actual production data,yielding an impressive accuracy of 94.57%and a minimal absolute error of 0.13 in FeO content prediction.The real-time prediction of FeO content provided excellent guidance for on-site sinter production.
查看更多>>摘要：In order to achieve ultra-low emissions of SO2 and NOx,the oxygen blast furnace with sintering flue gas injection is presented as a promising novel process.The CO2 emission was examined,and a cost analysis of the process was conducted.The results show that in the cases when the top gas is not circulated(Cases 1-3),and the volume of injected sintering flue gas per ton of hot metal is below about 1250 m3,the total CO2 emissions decrease first and then increase as the oxygen content of the blast increases.When the volume of injected sintering flue gas per ton of hot metal exceeds approximately 1250 m3,the total CO2 emissions gradually decrease.When the recirculating top gas and the vacuum pressure swing adsorption are considered,the benefits of recovered gas can make the ironmaking cost close to or even lower than that of the ordinary blast furnace.Furthermore,the implementation of this approach leads to a substantial reduction in total CO2 emissions,with reductions of 69.13%(Case 4),70.60%(Case 5),and 71.07%(Case 6),respectively.By integrating previous research and current findings,the reasonable oxygen blast furnace with sintering flue gas injection can not only realize desulfurization and denitrification,but also achieve the goal of reducing CO2 emissions and iron-making cost.
查看更多>>摘要：Developing deNOx catalysts with lower activity temperatures range significantly reduces NH3 selective catalytic reduction(SCR)operating costs for low-temperature industrial flue gases.Herein,a novel FeVO4/CeO2 catalyst with great low-temperature NH3-SCR and nitrogen selectivity was synthesized using a dipping method.Characterization techniques such as X-ray diffraction,Raman spectroscopy,specific surface and porosity analysis,H2 temperature-programmed reduction,NH3 temperature-programmed desorption,X-ray photoelectron spectroscopy,and the in situ diffused reflectance infrared Fourier transform spectroscopy were used to investigate the catalytic mechanism.An appropriate addition for FeVO4 in the catalyst was 5 wt.％from the results,and the active substance content reached the maximum dispersal capacity of the carrier.The NOx conversion exceeded 90％,and the nitrogen selectivity was more than 98％over this catalyst at 200-350℃.The activity was kept at 88％after 7.5 h of reaction at 200℃ for 7.5 h in 35 mg m-3 SO2 gas.The remarkable deNOx activity,nitrogen selectivity,and sulphur resistance performances are attributed to the low redox temperature,the abundance of medium-strong acid and strong acid sites,the sufficient adsorbed oxygen,and the superior Fe2+content on the surface.The Langmuir-Hinshelwood mechanism was observed on the FeVO4/CeO2 catalyst in the NH3 selective catalytic reduction of NOx.
查看更多>>摘要：Ferrotitanium slag(FS)is a waste slag produced during the smelting of ferrotitanium alloys by thermite reduction.Its alumina content is high and can be used as alumina raw material.Iron runner castables containing different amounts of FS were prepared and characterized.The results show that the introduction of FS is beneficial to the sintering of the castables sample.When the FS concentration is 11.2 wt.%,the aggregate and matrix of the castables sample have a good combination,and the mechanical strength of the Al2O3-SiC-C castable reaches a maximum at room temperature.How-ever,excessive introduction of FS generates a large amount of anorthite phase,which reduces the mechanical strength of the Al2O3-SiC-C castable at room temperature.In addition,the high-melting phase CaTiO3 is formed in FS,which has good mechanical properties.Meanwhile,the cracks of FS are reduced,and the combination between phases is closer,thus significantly improving the hot modulus of rupture of the castable.When the FS concentration is not above 33.6 wt.%,the castables show good slag resistance.The TiO2 in FS is transformed into TiC by carbothermal reaction,which is enriched at the boundary and prevents further reaction of the slag.
查看更多>>摘要：Free water available in calcium aluminate cement(CAC)-bonded castables is crucial for the hydration of CAC and the conversion of hydration products in the curing and drying processes,as both the hydration and conversion reactions are dissolution-precipitation reactions.To elucidate the effect of different levels of free water loss upon the hydration of CAC,the conversion of hydration products and the mechanical strength of the CAC-bonded castables,the CAC-bonded casta-bles were subjected to sealed and unsealed curing conditions at 50℃ and drying at 110℃.The results demonstrate that the fast removal of free water during unsealed curing would hinder the conversion from 2CaO·Al2O3·8H2O to 3CaO·Al2O3·6H2O and consequently prevent the deterioration of strength.As a comparison,although sealed-cured samples have less water loss and high degree of hydration of CAC,they still show lower strength than the unsealed samples after curing.The following drying process further accelerates the hydration of residual calcium aluminate clinkers for both the sealed and unsealed samples,but still does not favor the conversion from 2CaO·Al2O3·8H2O to 3CaO·Al2O3·6H2O in the unsealed-cured samples.
查看更多>>摘要：Aiming at the paddle tilt angle of the spray-blowing agitation composite process,the four-blade stirring and blowing composite desulfurization agitator was chosen as the research object,and the computational fluid dynamics numerical simulation was used to investigate the changes in flow field velocity,turbulent kinetic energy magnitude,and distribution caused by the blade tilt angle.Furthermore,the impact of blade tilt angle on the flow fragmentation behavior of individual bubbles and the coalescence process of multiple bubbles at different positions was studied.Under the same stirring and blowing process parameters,with the increase in the blade tilt angle of the agitator,the velocity of the flow field and the average turbulent kinetic energy inside the agitator decreased,and the bubble fragmentation speed decreased while the merging speed accelerated.The turbulent kinetic energy at the agitator bottom was greater when the blade tilt angle was 3.2°compared to when it was 13.2°,while the turbulent kinetic energy at the agitator upper part was relatively smaller.The results for single bubbles represented the state and trajectory of the bubble fragmentation process,and the results for multiple bubbles illustrated the state and trajectory of the bubble aggregation process.
查看更多>>摘要：To optimize the comprehensive utilization of vanadium titanomagnetite by direct reduction-smelting processes,it is essential to acquire titanium slag with a higher TiO2 content of 45-60 wt.%.A thermodynamic model was developed based on the ion and molecule coexistence theory,specifically targeting the CaO-SiO2-Al2O3-MgO-TiO2-V2O3-FeO slag system.The impact of slag composition on the smelting of vanadium titanomagnetite was assessed,and the thermodynamic model was utilized to identify the optimal high-titanium slag.The results revealed that increasing the basicity,MgO content,and FeO content within the slag effectively suppressed the reduction of titanium and silicon oxides.Furthermore,the calculated activity coefficient of TiO2 decreased with higher basicity,MgO,and FeO levels.While an increase in basicity significantly enhanced the reduction of vanadium oxides,the effects of MgO and FeO contents on vanadium oxide reduction were comparatively less significant.Notably,higher basicity and FeO content promoted the formation of calcium titanates,whereas an elevated MgO content favored the formation of magnesium titanates.The smelting results indicated that a lower V2O3 content and higher TiO2 activity corresponded to a smaller titanium mass fraction in the iron alloy,while the opposite trend was observed for vanadium.
查看更多>>摘要：A three-dimensional mathematical model coupling electromagnetic,flow,heat transfer,and solidification has been developed to investigate the effect of eccentric mold electromagnetic stirring(EM-EMS)on the flow and heat transfer of molten steel in round blooms with different cross sections.The uneven distribution of the flow field caused by EM-EMS was improved by changing the straight submerged entry nozzle(SEN)to a four-port SEN.The symmetry index was determined by the velocity distributions on the left and right sides of the center cross section of mold electromagnetic stirring(M-EMS),which quantitatively evaluated the symmetry of EM-EMS on the flow field.In the presence of EM-EMS,the maximum temperature difference of φ500 mm and φ650 mm round blooms between the inner and outer curves amounted to 63 and 26 K,respectively.The maximum distinction between the solidified shells in the inner and outer curves was 11.5 and 5.3 mm,respectively.After using the four-port SEN,the temperature and the shell distribution on the inner and outer curves for the φ500 mm round bloom were almost the same.The symmetry indices of φ500 mm and φ650 mm round blooms were increased from 0.55 and 0.70 to 0.77 and 0.87,respectively.The four-port SEN can be used to mitigate the negative impact of EM-EMS on the steel flow field.
查看更多>>摘要：The external residence time distribution(RTD)curve is extensively used to characterise fluid flow within the single-strand continuous casting tundish.Dead volume fraction determination typically relies on the external RTD curve to reveal macroscopic fluid flow behaviour.Based on the external RTD to effectively assess dead volume fractions and other fluid characteristics under conditions of internal non-uniform flow,an internal RTD was introduced.In a smooth pipe under laminar flow conditions,the dead region occupies 25%of the total volume,which is defined as the space between the pipe wall and a radius of 0.866 R0(where R0 is the radius of pipe).Under turbulent flow conditions,the dead region only occupies 0.38%of the reactor's internal volume,spanning from the pipe wall to a radius of 0.00189 R0.The results obtained using the external RTD method are consistent with the theoretical analysis.Experimental trials involving water were conducted to examine the flow of molten steel within a five-strand tundish.Subsequently,an analysis approach employing internal RTD was employed to evaluate fluid mixing within a multi-flow continuous casting tundish.Using the internal RTD method,the analysis revealed that the whole dead zone volume fraction of the intermediate package decreased from 26.9%to 18.9%after the addition of the flow control device.The dead volume fraction can be accurately depicted by utilising the internal mean RTD function.The association between the internal RTD function and the external average RTD can be effectively employed to scrutinise the response curve of the tracer within a system exhibiting uneven flow distribution.
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