EXPERIMENTAL RESEARCH AND NUMERICAL SIMULATION OF MOLD TEMPERATURE FIELD IN CONTINUOUS CASTING OF STEEL

Mold is the heart of the continuous casting machine. Heat transfer and solidification in a water- cooled mold are the most important factors during the continuous casting of steel. For studying the temperature distribution of a mold wall, a simulated apparatus of mold was designed and experiments were performed by it. The measured results indicated that the mold wall temperature approaches the temperature of cooling-water. An equivalent thermal-conductivity coefficient was proposed and deduced on the basis of the conclusion of the experiments. This coefficient was applied to solve the heat transfer between the melt and cooling water, and to characterize the heat transfer capacity of the mold. By this equivalent thermal-conductivity coefficient, it is very easy and convenient to numerically simulate the solidification process of continuous casting. And the calculation results are in agreement with the experiments. The effects of custing speed and water flow rate on the mold temperature field were also discussed.

Research on horizontal electromagnetic continuous casting of copper tube blanks

The effect of commercial frequency electromagnetic field on the solidification structure and mechanical propertiesof copper hollow blanks prepared by horizontal continuous casting method was investigated. The results show thatwhen the electromagnetic field is imposed, columnar grains are evidently refined and fine equiaxed grains areobtained in the inner side of the cross-section. Moreover, with the increase of input current, the equiaxed grain regionwidens and the grains distribute more uniformly in the circumferential direction. Meanwhile, the mechanical properties areremarkably improved by the application of electromagnetic field. When the input current is 140 A, the tensile strengthincreases 15% and the elongation increases 10%. However, the electromagnetic field has no effect on the distribution ofmicroelements.

Effects of yttrium on microstructure and mechanical properties of Mg-Zn-Cu-Zr alloys

The effects of yttrium addition on microstructure and mechanical properties of as-cast Mg-6Zn-3Cu-0.6Zr-xY(x=0,0.5, 1.0,1.5 and 2.0,mass fraction,%)(ZCK630+xY for short in this study)alloys were investigated by means of OM,XRD and SEM. The results show that the average grain size of Mg-Zn-Cu-Zr magnesium alloy is effectively reduced(from 57μm to 39μm)by Y addition.The analysis of XRD indicates the existence of I-phase(Mg3Zn6Y)and W-phase(Mg3Zn3Y2)in ZCK630 alloys with Y addition.The ultimate tensile strength of ZCK630 alloys is significantly deteriorated with increasing Y addition,which is possibly related to the continuous networks of intergranular phases and the increase of W-phase.

Flow of Steel in Mold Region During Continuous Casting

The particle image velocimetry （PIV） technique was used to study the fluid flow phenomena that occurred during continuous casting, using a water model with dimensions of 1 840mm× 280 mm. Two types of solidified shells, i. e. , the smooth type and the coarse type, were used to characterize the dendrite in order to simulate different liquid-solid interfacial conditions. The influence of the nozzle angle and the immersion depth of nozzle, as well as the casting speed on the flow behavior was investigated quantitatively. The results were as follows： （1） There are two large recirculations above and below the fluid jet in the mold, respectively, under the smooth interface condition. However, in the case of the dendrite solidified shell, it was found that the flow velocity of the fluid decreased and more smaller vortices appeared in the upper region of the mold. （2） The angle and the immersion depth of nozzle are two important factors affecting the flow pattern, and they are also capable of bringing about the change in the flow direction. （3） The higher the casting speed, the higher are the jet stream and the impacting point on the narrow face. However, the high casting speed causes serious fluctuation of the meniscus, and correspondingly leads to various defects.

Microstructure and corrosion property of AZ61 magnesium alloy by electromagnetic stirring

The influence of permanent-magnet-driven stirring during solidification on the microstructure and corrosion property of AZ61 magnesium alloy was investigated. The corrosion behaviour of AZ61 was studied in 3.5mol/L NaCl by measuring electrochemical polarization. The results show that the permanent-magnet stirring refines the microstructure of AZ61 magnesium alloy, which improves the precipitation amount and distribution uniformity of β phase and decreases the content of hydrogen, but it has less influence on the distribution uniformity of Zn. The change of precipitation amount of β phase influences the corrosive nature of the matrix, and it has no direct proportion with the corrosion resistance of the matrix.

MEASUREMENT AND ANALYSIS OF MAGNETIC FIELDS OF ELECTROMAGNETIC CASTING ALUMINUM ALLOYS

Results of magnetic field investigation in a Kaiser type caster show that magnetic induction decays rapidly on moving inward from the outer surface and is almost doubled near corner.In the presence of screenings magnetic field strength is attenuated near periphery,but it isn't influenced within the interior.The resultant electromagnetic pressure balances with static head of liquid column,i.e,the upper magnetic induction is smaller than the lower's.However»the maximum pressure moves downward about 1 cm from half height of inductor.

Control of deflection deformation of plate-shape castings in solidification

The deformation mechanism during the solidification was analyzed based on the experimental results of the castings. An approximate quadratic differential equation and its discrete model of calculation deflection were proposed. The model indicates that the key factors leading to the deflection deformation are the thermal bending moment M and the flexural rigidity EJ. The smaller the former and the larger the latter is, the smaller the deflection deformation will be. The experiments are carried out at various technical conditions, and their results appear good agreement with calculation ones. A method was proposed to predict and control the casting deformation.

Technical parameters in electromagnetic continuous casting of aluminum alloy

The temperature field of aluminum ingot during electromagnetic continuous casting was calculated by the numerical method, and the effects of cooling water strength, position of the cooling water holes and pouring temperature as well as induction heat on casting speed, were studied. The results show that among the technical parameters the distance from the position of the cooling water holes to the bottom of the mold is the most important factor, whose change from 20 mm to 15 mm and from 15 mm to 10 mm causes the setting rate increasing respectively by 0.14 mm/s and 0.3 mm/s.The calculated results also agree with the experiment well. The simulation program can be used to determine technical parameters of electromagnetic casting of aluminum ingot effectively.

Mathematical modeling of electromagnetic dimensionless number for electromagnetic casting of metals and its application

In order to estimate the feasibility of electromagnetic casting (EMC) for different metals, a mathematical model named the electromagnetic dimensionless number (EMDN) was presented, and its validity was proved by the experiments of aluminum and Sn-3%Pb alloy. From the experiment and the analysis of EMDN it can be concluded that the EMC of steel can be attained only when the magnetic flux density is larger than 0.09T, while that required for aluminum is only 0.04T. The mathematical expression of the electromagnetic dimensionless number was given out.

Microstructures of electromagnetic casting and direct chill casting LY12 aluminum alloys

LY12 aluminum alloys made by electromagnetic casting (EMC) and direct chill casting (DCC), were analyzed by optical microscope, differential scanning calorimetry, transmission electron microscope and X ray diffraction. It is found that the surface and subsurface quality of the ingot is improved largely due to the absence of an ingot mold, which is impossible to achieve with conventional DCC. It is also found that the intense forced convection can promote the fast superheat evacuation and break the dendrite arms, leading to the grain multiplication and the appearance of a fine equiaxed grains over the whole cross section. As a result, the hardness of EMC specimens increases one time than that from DCC in the as cast state. Even though after the solid solution treatment and the artificial aging, the DCC ingot still can not get the same hardness as EMC ones.