Flow Control During Solidification of AlSi-Alloys by Means of Tailored AC Magnetic Fields

This paper presents an experimental study which in a first stage is focused on obtaining quantitative information about the isothermal flow field exposed to various magnetic field configurations.Melt stirring has been realized by utilizing time-modulated AC magnetic fields in different variants.We consider time-modulated fields or combinations of traveling magnetic fields(TMF)and rotating magnetic fields(RMF).In a second step solidification experiments are carried out to verify the effect of a certain flow field on the solidification process.Our results demonstrate that the melt agitation using modulated magnetic fields offers a considerable potential for a well-aimed modification of casting properties by an effective control of the flow field.     

Columnar-to-Equiaxed Transition During Directional Solidification Under Strong Magnetic Field

Effects of strong magnetic fields on the columnar-to-equiaxed transition(CET)have been investigated experimentally.Experimental results show that the application of a strong magnetic field causes a dendrite fragmentation and then the CET.The thermoelectric magnetic force acting on cells/dendrites and equiaxed grains in the mushy zone has been studied numerically.Numerical results reveal that a torque is created on cells/dendrites and equiaxed grains and the value of the thermoelectric magnetic force increases as the magnetic field intensity increase.This torque breaks cells/dendrites and drives the rotation of equiaxed grains.As a consequence,the CET will occur during directional solidification under a strong magnetic field.This may initiate a new method to induce the CET via an applied strong magnetic field during directional solidification.     

Effect of a High Magnetic Field on the Microstructure During Directionally Solidified Sn-20wt.%Pb Hypoeutectic Alloy

The microstructures of Sn-20wt.%Pb hypoeutectic alloy directionally solidified under a longitudinal magnetic field were investigated.The results show that the application of a high magnetic field has a great influence on the morphology of primary P-Sn phase at a temperature gradient of G_L=52 K/cm.At a certain growth speed,with the increase of magnetic field intensity,the magnetic field causes the primaryβ-Sn phase irregular and to be deformed,further,the magnetic field promotes the columnar to equaixed transition(CET).Further,the thermoelectric magnetic force(TEMF)imposed on the dendrite under a high magnetic field has been calculated and the results show that the numerical magnitude of the TEMF during directional solidification under a 10 Thigh magnetic field is about 10~4N/m~3 and this force should be responsible for the occurrence of the CET in the Sn-Pb alloy.This may act as an experimental proof that the coupling of temperature gradient and high magnetic field will induce the occurrence of the CET in Sn-Pb alloy.Above phenomena may be attributed to the thermoelectric magnetic force(TEMF)in solid.     

Application of MHD Phenomenon on Secondary Refining and Continuous Casting Process

In present work,the application of Magneto Hydrodynamics(MHD)to control the flow of liquid steel during secondary refining and continuous casting has been discussed.A mathematical model was developed to predict the flow field under magnetic field in different metallurgical reactors.As examples,the effect of traveling magnetic filed in RH degasser has been discussed,and the effect of electromagnetic brake(EMBR)on flow field during continuous casting process has also been discussed.The numerical results show that when the EMBR is installed near the nozzle port,the intensity of impinging jet near the narrow face mold wall is reduced,the downward flow becomes weaker,and the lower recirculation zone becomes smaller.The circulation flow rate with traveling magnetic field imposed around the up snorkel in RH degasser is greater than that with magnetic field imposed around the down snorkel if the gas flow rate is less than the saturated value,but they are almost the same if the gas flow rate is greater than the saturated value.     

Fundamental Study on Continuous Casting Process With Swirling Flow by Electromagnetic Force

Swirling flow in a submerged entry nozzle is effective on improving quality of casting block and casting speed in continuous casting of steel.A new method for swirling flow generation in the nozzle has been proposed by the authors,that is a rotating electromagnetic field is set up around a submerged entry nozzle(SEN)to induce swirling flow in it by Lorentz force.In this study,the magnetic field in molten steel in the submerged entry nozzle,the flow and temperature field in the SEN and mold in round,square billet and slab continuous casting process of steel are numerically studied.The model experiment of electromagnetic swirling continuous casting is also conducted with low melting point alloy.The commercial test for slab is undergoing.Results by numerical simulation and experiment show that the swirling flow by the optimum designed electromagnetic swirling generator can not only improve the distribution of flow and temperature in mold but also achieve the same effects generated by the swirling blade process.And,more effects on continuous casting process can be expected after this electromagnetic swirling process is optimized.     

Study on the Grain Refinement of an Al-Zn-Mg-Cu Alloy Prepared by LFEC Process

Low frequency electromagnetic casting(LFEC)process has been developed for years with the application of an induction coil outside the conventional direct chill(DC)casting mould.It has been demonstrated that the LFEC process has a significant grain refining effect on aluminium alloys.However,how it refines the microstructure is still not clearly understood.In the present work,the temperature measurement were carried out to study the temperature field during casting and to understand the mechanism of the grain refining effect of the LFEC process.The results showed that in contrast to the conventional DC casting process,during the LFEC process,the liquid melt flowing from the launder into the mould is cooled with very high cooling rate directly to 3-6℃below the liquidus and the temperature field of the entire melt in the mould and the hot top is quite uniform,which results in enhanced heterogeneous nucleation and improved survival rate of the nuclei.This is believed to be the main reason why the LFEC process can significantly refine the grain size of aluminium alloys.     

Numerical Analysis of Fluctuation Behavior of Steel/Slag Interface in Continuous Casting Mold with Static Magnetic Field

Utilizing ANSYS CFX commercial software and volume fraction of fluid （VOF） model, fluctuation behav- ior of steel/slag interface was numerically simulated in continuous casting mold with static magnetic field, and the influence of metal jet characteristics on the behavior of steel/slag interface was investigated. The results indicated that the behavior of steel/slag interface is similar at different process parameters, which is closely related to the characteristic of the flow field. The steel/slag interface has an obvious trough characteristic, which can be divided in- to three zones： frontal valley zone, back valley zone and horizontal zone~ as the magnetic flux density increases, the fluctuation of liquid level increases firstly and then decreases, and a reasonable magnetic flux density can make steel/ slag interface obtain a relatively flat interface, which can prevent slag from being entrapped into liquid steel. For a thin slab continuous casting process, when the casting speed is 4 m/min, a reasonable magnetic flux density is about 0.5 T, and the interfacial fluctuation is weaker. No matter the position of magnetic field is horizontal or vertical, for different operating parameters, there is a corresponding reasonable magnetic field position where the steel/slag inter- face fluctuation can be properly controlled and slag entrapment can be prevented.     

Effects of High Magnetic Field on Microstructure and Properties of Low Aspect Ratio Bi₂Sr₂CaCu₂O_x/AgMg Wire

Here,we report the effect of an 8 T magnetic field on the microstructure and properties of a reetangular Bi₂Sr2CaCu20x/AgMg（Bi2212/AgMg）conductor with low aspect ratio.The magnetic field was applied during split melt process with the field direction perpendicular and parallel to the wide surface of the conductors.After heat treatment,the conductors were electrically characterized using four-point critical current measurements as a function of magnetic field and magnetic field orientation relative to the conductor.The superconducting transition and magnetization hysteresis were measured using a SQUID magnetometer.The microstructure was characterized using scanning electron microscopy.It was found that the presence of magnetic field during split melt processing enhances the electrical transport and magnetic behavior.The magnetic field increases the Bi2212 grains alignment and long range texture within filaments and bridges between filaments by textured growth of Bi2212 phase.     

Influence of the Earth Magnetic Field on Electrically Induced Flows

The present paper aims at numerical simulation of the intriguing experimental observations made by Bojarevics on the appearance of swirl in flows in an electrically induced flow.Although controlled by poloidal force,the flow rotates due to the presence of the earth magnetic field.The bulk flow rotates almost as a whole which indicates that the swirl is generated through a mechanism of"poloidal suppression".     

Effect of 31.2T Magnetic Field on Microstructure and Performance of an Ag-45.8wt%Ni Alloy

Ag/Ni Multilayers were prefabricated by Accumulative Roll-Bonding(ARB),with an average layer thickness ranging 20-100 nm.The Ag-45.8wt%Ni alloys were annealed under 31.2T high magnetic field to study its effect on microstructure and performance.31.2T high magnetic field significantly suppressed the coarsening of layer structure during annealing,the magnetic field parallel to the layer has a larger suppression effect.As the annealing temperature increased,the resistivity of Ag/Ni multilayers increased,and the hardness decreased.The case of perpendicular high magnetic field has the largest resistivity and the largest hardness,compared with die other two cases.The hysteresis loops shows that Ag-Ni has a hard ferromagnetic property.The case of parallel magnetic field has the largest coercivity about90Gs.     

Experimental Modelling of the Impact of a DC Magnetic Field on the Melt Flow in a Continuous Casting Mould

This paper describes experimental investigations of flow structures and related transport processes in the continuous casting mould under the influence of an external DC magnetic field at laboratory scale.Experimental results will be presented here which have been obtained using a physical model(mini-LIMMCAST)operating with the low melting point alloy GaInSn.According to the concept of the electromagnetic brake the impact of a DC magnetic field on the outlet flow from the Submerged Entry Nozzle(SEN)has been studied up to Hartmann numbers of about 400.The Ultrasound-Doppler-Velocimetry(UDV)was applied for measurements of the flow pattern in the mould.Local conductivity anemometers were used to measure the turbulent quantities of the flow.The effect of the magnetic field on the flow structure turned out to be manifold and rather complex.The magnetic field causes a deflection of the jet,at which the respective exit angle from the nozzle ports becomes more flat.Thus,both the penetration depth of the discharging flow into the lower part of the mould and the impinging velocity of the jet onto the side wall are reduced.A significant return flow occurs in the adjacent regions of the jet.Specific vortices are formed with axes being aligned with the magnetic field direction.Such vortical structures are typical for quasi-two-dimensional magneto-hydrodynamic(MHD)flows.The flow measurements do not manifest a general braking effect which would be expected as an overall damping of the flow velocity and the related fluctuations all-over the mould volume.Variations of the wall conductivity showed a striking impact on the resulting flow structures.     

Modeling of Electromagnetic,Temperature,and Velocity Fields During Solidification in an Electromagnetically Stirred Melt

This paper describes a comprehensive model for predicting the evolution of the velocity and temperature fields in electromagnetically-driven flows during solidification.The electromagnetic field was formulated using the mutual inductance method,which accounts for the metal,chill blocks,and magnetic shields.The model solves the heat transfer equation throughout the system,as well as the fluid flow equations in the liquid and mushy regions.A two-zone model for the mushy region that accounts for dampening of momentum by the turbulent field has been developed.The turbulence in the molten region was determined using the k-s model.Calculations were performed for unidirectional solidification in a bottom chill mold placed in a stationary magnetic field.Computed results show that the flow field at the beginning of solidification shows typical four recirculating loops,and later evolves to two recirculating loops as solidification progresses.The magnitude of the velocity in the bulk liquid was found to decrease as solidification progresses.     

Numerical Simulation of Electromagnetic Stirring in Secondary Cooling Zone of CSP Casting

A there-dimensional unsteady coupled mathematical model has been used to analyze the turbulent flow,temperature fields,magnetic field and macroscopic solidification of molten steel in compact strip production(CSP)thin slab continuous casting with electromagnetic stirring(EMS)on secondary cooling zone,in which induced current caused both by flow movement and external magnetic field and end effect of stirrer has been considered.Lorenz force and Joule heat contributed by induction current also have been considered.EMS in secondary cooling zone results in the obverse flow changes in molten steel flow pattern,and leads to horizontal recirculation flow within stirrer zone.Degree of superheat is reduced or eliminated rapidly when molten steel is stirred by EMS.The process of EMS makes the temperature in molten steel homogeneous.After a relatively shot period of time when using EMS,the flow pattern and temperature field will reach to a new"quasi-static-state".Molten steel could be uniformly stirred by a one-sided stirrer concerned.     

Development of Test Method for Measuring Sintering Temperature of Mould Fluxes

 Excessive sintering of mould fluxes can readily cause defects and sticker breakouts in continuously cast strands. Studying the sintering property is important to minimize problems related to sintering arising from the use of mould fluxes in continuous casting. An effective method of measuring the apparent sintering temperature has been developed in this study. The method is based on monitoring the formation of cavities caused by melting of samples. For monitoring, the differential pressure of an inert gas flow was measured through a set volume of sample (mould flux A) held in a furnace tube. The apparent sintering temperature was defined in this test to determine sintering process. The sintering properties of fluxes with various contents of carbon black were examined along with identification of mineralogical phases and the nature of the sinter for samples of mould flux A held for one hour at different temperatures. The experimental results indicated that the apparent sintering temperature (AST) was a useful parameter to assess the threat of problems related to sinter.     

Preparing High Silicon Steel by Sintering Fe-6.5%Si Powder Compacts in Static Magnetic Field

In this research,sintering Fe-6.5wt%Si Compact specimen in static magnetic field is proposed for preparing high silicon steel.It is found that the densifications of the compacts are affected remarkably by superimposing magnetic field.The density of the compacts can be increased when the MFD is higher than 0.2 T.The highest relative density of the samples is 97.2%.The magnetic property of silicon steel could be improved when superimpose static magnetic field in sintering process,the permeability of the compact are two times of that without magnetic field,and the magnetic property parallel to the direction of the magnetic field was evidently higher than that in perpendicular direction.     

Large Magnetostriction of Fe-Ga Alloys by Solidification With a Static Magnetic Field

A simple but effective process to fabricate the bulk and practical Fe-Ga alloys at low fields is proposed just by applying a static magnetic field to their solidification process.We have introduced a static 1-T magnetic field to solidify the Fe-17%Ga alloys.The results indicate that the magnetostriction of a polycrystalline textured Fe-17%Ga alloy is increased about threefold by solidifying with a 1-T magnetic field compared to that without a magnetic field.This large magnetostiction could be attributed to the increasing volume fraction and the strong texture of the disordered a-Fe phases.The systematic analysis shows that they are originated from the undercooling and orientation effects induced by the imposed magnetic field during the solidification process.     

Effect of Magnetic Field on Synthesis of Nano-FeOOH by Low-Temperature Neutralization Method

Using XRD,TEM and VSM methods,the phase,morphology and magnetic property of iron hydroxide oxide(FeOOH)which has been prepared by low-temperature neutralization reaction under different magnetic fields were analyzed.It can be found that the magnetic field had a great influence on the product.Acicular goethite(α-FeOOH)was synthetized without magnetic field.When the magnetic flux density was increased to 0.1T,γ-FeOOH was obtained.If the magnetic field intensity was raised to 0.5T,the product was all composed ofσ-FeOOH.Moreover,the crystallization of FeOOH was greatly influenced by magnetic field as well.Thermodynamic calculation results show that the magnetic free energy of chemical reaction reached to more than hundreds KJ/mol when the magnetic field is applied.It meaned that the application of magnetic field was conducived to producing the products with higher susceptibility.Even under the low magnetic field,due to the stability of the reaction products was broken by the magnetic field,the magnetic free energy was also effective.     

Microstructure Evolution of Cu-6%Ag Alloys by Modified Unidirectional Solidification Under a Horizontal Static Magnetic Field

The microstructure evolution of Cu dendrites in Cu-6%Ag alloys by modified unidirectional solidification under a static magnetic field has been investigated experimentally and quantitatively.The results show that the proeutectic Cu dendrites are finer when they are closer to the water-cooling copper mould and the unidirectional effect is more obvious,which is attributed to the higher solidification velocity.The quantitative analysis of the microstructure indicates that with increasing external magnetic flux density,the primary arms of the proeutectic Cu dendrites are refined and along a given direction.The analysis indicates that it is both the thermoelectromagnetic convection effect by the external magnetic field and the branch effect of the dendrites.     

Application of the DHCR technology in Ningbo Steel

This paper presented the application of the direct hot charge rolling (DHCR) technology in Ningbo Steel.Five aspects have been systematically addressed and analyzed,which include sales order,production schedule programming,steelmaking,continuous casting and hot-rolling.The average DHCR product rate has reached 55% and the average slab charging temperature 699℃.As a result,the production cost,the energy consumption and the CO2emission have been significantly reduced.It is concluded that a breakthrough in application of the DHCR technology has been achieved at Ningbo Steel.