查看更多>>摘要：Refill friction stir spot welding(RFSSW)provides a novel method to join similar and/or dissimilar metallic materials without a key-hole in the center of the joint.Having the key-hole free characterization,the similar/dissimilar RFSSW joint exhibits remarkable and endurable characteristics,including high shear strength,long fatigue life,and strong corrosion resistance.In the meanwhile,as the key-hole free joint has different microstructures compared with conventional friction stir spot welding,thus the RFSSW joint shall possess different shear and fatigue fracture mechanisms,which needs further investigation.To explore the underlying failure mechanism,the similar/dissimilar metallic material joining parameters and pre-treatment,mechanical properties,as well as fracture mechanisms under this novel technology will be discussed.In details,the welding tool design,welding parameters setting,and the influence of processing on the lap shear and fatigue properties,as well as the corrosion resistance will be mainly discussed.Moreover,the roadmap of RFFSW is also discussed.
查看更多>>摘要：Due to the instability of FeO at temperatures below 843 K,the fluidization reduction pathway of iron ore powder changes with the reduction temperature.Thus,the effect of temperature and reaction pathway interaction on the kinetics of fluidization reduction of iron ore powder under low-temperature conditions ranging from 783 to 903 K was investigated to describe the fluidization reduction rate of iron ore powder from three aspects:microstructure change,reaction limiting link,and apparent activation energy of the reaction,exploring their internal correlation.The experimental results revealed that in a temperature range of 783-813 K,the formation of a dense iron layer hindered the internal diffusion of reducing gas,resulting in relatively high gas diffusion resistance.In addition,due to the differences in limiting links and reaction pathways in the intermediate stage of reduction,the apparent activation energy of the reaction varied.The apparent activation energy of the reaction ranged from 23.36 to 89.13 kJ/mol at temperature ranging from 783 to 813 K,while it ranged from 14.30 to 68.34 kJ/mol at temperature ranging from 873 to 903 K.
查看更多>>摘要：The inhomogeneous sinter properties in super-high bed sintering have been reported in our previous research.To inves-tigate the reasons for the inhomogeneous phenomena,detailed sampling and analysis of mixed material bed and sintered bed in super-high bed sintering plant were executed.The results indicated that the higher porosity and thinner dendrite of silico-ferrite of calcium and aluminum in the upper layer as well as dense structure and higher secondary hematite content in the lower layer led to the heterogeneities of mechanical strength and reduction properties exceeding 20％and 10％,respectively.From the bed top downward,the basicity of mixed material decreased from 2.13 to 1.68 because the average particle size increased from 2.65 to 4.56 mm.Fluxes and fuels gathered in finer particles(-3 mm)of mixed material,and the-3 mm particles of mixed material generated more liquid phase than+3 mm ones.The heat input of super-high sintering bed was inhomogeneous due to the heat accumulation effect and unreasonable fuel distribution.The inhomo-geneous sintering heat condition in sintering bed resulted in the different quantities and properties of liquid phase.The inhomogeneous quantities and properties of liquid phase that were influenced by inhomogeneous distribution of chemical composition,particle size,and heat input led to inhomogeneous mineralizing results.Homogeneous mineralizing condition is the key for homogeneous super-high bed sintering.
查看更多>>摘要：With increasingly stringent environmental protection policies,cost-effective and value-added treatment of massive lead-zinc waste rock(LZWR)generated from the preconcentration process has attracted substantial attention.A type of dolomitic LZWR with 18 wt.％MgO,27 wt.％CaO,0.29 wt.％Zn and 1.43 wt.％S was used as a replacement flux in the iron ore sintering process.Traditional sinter pot tests were carried out based on an industrial ore blend.The results show that replacing 0％-60％of dolomite with LZWR does not adversely affect the sintering productivity,fuel consumption rate,and the quality of the sinter products,while the Zn and S elements contained in LZWR can be effectively removed with the residual Zn and S contents of the resultant sinter products being less than 0.02 and 0.055 wt.％,respectively.However,substituting LZWR for dolomite as a flux inevitably increases the SO2 concentration in the sintering flue gas due to its high sulfur content.Considering the processing capacity of the sintering flue gas desulfurization system,the replacement ratio of dolomite can reach 40％,equal to LZWR consumption of 24.3 kg per ton of sinter.The SO2 in sintering flue gas can be recovered to produce(NH4)2SO4 or H2SO4,while the volatilized Zn collected into the zinc-containing dust can be subsequently recycled by the rotary hearth furnace process.Therefore,it is technologically and economically feasible to use the LZWR as a replacement flux in the iron ore sintering process,providing a new way for the safe,large-scale and low-cost treatment of LZWR.
查看更多>>摘要：Based on a thermodynamic study of 5 wt.％Si high-silicon austenitic stainless steel(SS-5Si)smelting using CaF2-CaO-Al2O3-MgO-SiO2 slag to obtain a low oxygen content of less than 10 x 10-4 wt.％,a kinetic mass transfer model for deep deoxidation was established through laboratory studies,and the effects of slag components and temperature on deoxidation during the slag-steel reaction process of SS-5Si were systematically studied.The experimental data verified the accuracy of the model predictions.The results showed that the final oxygen content in the steel at 1873 K was mainly controlled by the oxygen content derived from the activity of SiO2 regulated by the[Si]-[O]equilibrium reaction in the slag system;in particular,when the slag basicity R(R=w(CaO)/w(SiO2),where w(CaO)and w(SiO2)are the contents of CaO and SiO2 in the slag,respectively)is 3,the A12O3 content in the slag needs to be less than 2.7％.The mass transfer rate equation for the kinetics of the deoxidation reaction revealed that the mass transfer of oxygen in the liquid metal is the rate-controlling step under different slag conditions at 1873 K,and the oxygen transfer coefficient kom increases with increasing the slag basicity from 4.0 × 10-6 m s-1(R=1)to 4.3 × 10-5 m s-1(R=3).kOm values at R=2 and R=3 are almost the same,indicating that high slag basicity has little effect.The integral of the mass transfer rate equation for the deoxidation reaction of SS-5Si under different slag conditions is obtained.The total oxygen content of the molten steel decreases with increasing basicity from an initial content of 22 × 10-4 to 3.2 × 10-4 wt.％(R=3),consistent with the change in kO,m with slag basicity.At R=2,the slag-steel reaction takes 15 min to reach equilibrium(w[O]=5.5 × 10-4 wt.％),whereas at R=3,the slag-steel reaction takes 30 min to reach equilibrium(w[O]=3.2 × 10-4 wt.％).Considering the depth of deoxidation and reaction time of SS-5Si smelting,it is recommended the slag basicity be controlled at approximately 2.Similarly,the effect of temperature on the deep deoxidation of SS-5Si was studied.
查看更多>>摘要：The influence of Al content(0.0053,0.0171,and 0.0578 wt.％)on the modification behavior of non-metallic inclusions in 20CrMoVTiB steel treated with rare earth elements was studied through high-temperature experiments and thermodynamic simulation.The results showed that the modification products varied with the Al content in steel under 0.01 wt.％of Ce addition.The formation sequence of typical rare earth inclusions in steel with the increase in Al content was Ce2O3 →CeAlO3 → CeAl11O18,and the final stable products were highly Al content dependent.When the Al content was 0.0053 wt.％,the stable phase in steel was Ce2O3;while the[Al]reached 0.0171 wt.％,the stable phase became CeAlO3.As the Al content reached 0.0578 wt.％,CeAl11O18 became the stable phase.As a result,increasing the Al content could inhibit the precipitation of Ce2O3 inclusions in steel while promote the formation of CeAlO3 and CeAl11O18 inclusions.In addition,both Ca treatment and Ce treatment could effectively refine the size of inclusions in steel by changing their types.However,the feeding amount of Ca wire into molten steel should be appropriately reduced under the condition of adding Ce simultaneously,which is expected to be beneficial for an improved Ce treatment effect.
查看更多>>摘要：The effect of nano-carbon black content(0,8 and 12 wt.％)on the wettability of molten steel on A12O3-C substrates was investigated by the sessile drop wetting method at 1500 ℃ under argon atmosphere.At the beginning of the wetting experiment,the contact angle decreased with the increase in nano-carbon black content.As the wetting experiment progressed,FeAl2O4 layer and sheet A12O3 layer were found at the interface between the molten steel and the A12O3-C substrates with 0 and 8 wt.％nano-carbon black content,and the contact angle deceased with time.When the content of nano-carbon black was 12 wt.％,a large number of nano-Al2O3 whiskers were observed,which made the contact angle between the molten steel and A12O3-C substrate become large.Based on the scanning electron microscope and energy dispersive spectrometry results,the formation mechanism of FeAl2O4 layer and A12O3 layer and the interfacial reaction mechanism were proposed.
查看更多>>摘要：Magnesia-calcia refractories are widely used in the production process of clean steel due to their excellent high-tem-perature stability,slag resistance and ability to purify molten steel.However,there are still problems such as difficult sintering and easy hydration.Magnesia-calcia materials with various calcium oxide contents were prepared by using induction sintering,and the sintering property combined with the hydration resistance of the materials was investigated.The experimental results showed that the magnesia-calcia materials prepared under induction field had higher density,microhardness and hydration resistance.In particular,the relative density of induction sintered magnesia-calcia materials with 50 mol％CaO was greater than 98％,and the average grain size of CaO was 4.56 μm,which was much larger than that of traditional sintered materials.In order to clarify the densification and microstructure evolution mechanism of the magnesia-calcia materials,the changes in temperature and magnetic field throughout the sintering process were analyzed by using finite element simulation.The results showed that the larger heating rate and higher sintering temperature under the induction sintering mode were beneficial to the rapid densification.In addition,the hot spots generated within the material due to the difference in high-temperature electric conductivity between MgO and CaO were the critical factor to realize selective sintering in MgO-CaO system,which provides a novel pathway to solve the problem of difficult sintering and control the microstructure of high-temperature composite material used in the field of high-purity steel smelting.
查看更多>>摘要：The evolution of Ce-containing inclusions and its correlation with the reoxidation of liquid steel during protective atmosphere electroslag remelting(ESR)of heat-resistant steel were studied.The reoxidation of liquid steel took place during the ESR,resulting in the oxygen pickup from 0.0014 to 0.0053 wt.％.The inclusions in the consumable electrode,liquid metal pool and remelted ingot are Ce2O2S and Ce2O3 inclusions invariably.The inclusions in the remelted ingot are originated from three ways:(Ⅰ)the original inclusions from the electrode;(Ⅱ)the newly formed Ce2O2S and Ce2O3 inclusions in the liquid metal pool by reoxidation remaining still in remelted ingot;(Ⅲ)the newly generated Ce2O2S and Ce2O3 inclusions during cooling and solidification of liquid steel.The relative proportions of Ce2O3 inclusions in liquid metal pool and remelted ingot are 41％and 76.5％,respectively.The inclusions ranging from 2 to 5 μm in the remelted ingot take up 55％,followed by the inclusions smaller than 2 μm(43％of total inclusions).The number proportion of the Ce2O3 inclusions in the liquid metal pool which were removed by floating up into slag is 1.96 x 10-5％.
查看更多>>摘要：The effect of TiO2 absorption into two different CaO-BaO-SiO2-Al2O3-based mold slags from the steel plant on the viscosity,melting performance and microstructure of slags was investigated through the measurement of the viscosity-temperature relationship,melting temperature and Raman spectroscopy.The parameter of the number of non-bridging oxygen per tetrahedrally-coordinated atom(NBO/T)was also calculated to explain the microstructure variation of molten slags with different TiO2 absorption.The variation of the actual slag consumption and the depth of the liquid slag in mold was explained through the comparison of the viscosity and the melting temperature of two different slags.The viscosity of mold slags(basicity=0.6)decreased from 1.1 to 0.68 Pa s with the increase in the TiO2 absorption from 0 to 10％,while that of slags(basicity=0.7)decreased from 0.76 to 0.56 Pa s with the TiO2 absorption from 0 to 6％.The activation energy of both two groups of slags had the tendency to decrease with the increasing TiO2 absorption.The network structure of both two groups of slags measured by the Raman spectra showed that the fraction of complex structure units(Q1,Q2,Q3 and Al-O-Al)decreased and simple structure units(Al-O-and Q0)increased with the increase in TiO2 absorption.NBO/T also increased with the increase in the TiO2 absorption,indicating that the absorption of TiO2 into slags resulted in the destruction of silicate/aluminate structure.Hence,the absorption of TiO2 into the current CaO-BaO-SiO2-Al2O3 mold slags decreased the degree of polymerization of these slags and then led to the decrease of viscosity.
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