JP2004306116A - Continuous casting method and machine for microstructural refinement by electromagnetic vibration - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a continuous casting method and machine for microstructural refinement by electromagnetic vibration. <P>SOLUTION: In the invented continuous casting method, a metallic material is continuously cast with its metallographic structure being refined by electromagnetic vibration. The metallic material is put into a mold and is refined by applying an AC electric field and a DC magnetic field to a solid-liquid coexisting layer melted in a heating furnace around the mold. In a process of continuously drawing the metallic material cooled and solidified in a chiller, the thickness of the solid-liquid coexisting layer is controlled by adjusting the drawing speed of the solidified metallic material, the cooling conditions of the chiller and the heating conditions of the heating furnace around the mold. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for miniaturizing a metal structure by electromagnetic vibration and continuously casting the metal structure, and more particularly, to controlling the thickness of a solid-liquid coexistence layer in a step of miniaturizing a metal structure by electromagnetic vibration. The present invention relates to a method for continuously producing a finely divided casting continuously and efficiently, and a continuous casting apparatus for the method. INDUSTRIAL APPLICABILITY The present invention is useful as providing a new continuous casting technique that enables continuous casting of a metal material whose structure is refined by electromagnetic vibration and another material having electrical conductivity.
[0002]
[Prior art]
The conventional method of miniaturizing the metal structure and continuously casting is to apply an electromagnetic force to the metal passing through the water-cooled mold in the vertical plane or the horizontal plane or the spiral plane by the electromagnetic coil arranged around it, This has been done by agitating the solidifying metal. For this reason, the structure is not columnar but equiaxed, but its size is limited to several mm to several cm. Further, when the solid fraction during stirring becomes 30% or more, there is a problem that stirring becomes impossible due to an increase in viscosity. To illustrate some of these specific examples, as a continuous casting method of molten metal, for example, a water-cooled mold is provided with a constant period of vibration in the vertical direction and an electromagnetic coil arranged around the mold. In a method of continuously casting a molten metal by applying an electromagnetic force in a vertical plane, a continuous casting method has been proposed in which an oxide is uniformly dispersed in the molten metal to achieve a finer metal structure (Patent) Reference 1). In addition, as a method for producing a surface-modified aluminum plate, for example, in order to reduce the compound secondary phase or crystal grains using rapid solidification on the surface of the aluminum plate, A method for manufacturing an aluminum plate, comprising irradiating a beam having a predetermined energy density to melt the surface of the continuous aluminum ingot, then cooling at a predetermined cooling rate, and then performing hot rolling. (See Patent Document 2).
[0003]
[Patent Document 1]
JP-A-8-155613 [Patent Document 2]
Japanese Patent Publication No. 7-45702
[Problems to be solved by the invention]
Under such circumstances, the present inventors have eagerly aimed at developing a method and an apparatus for continuously and efficiently casting a fine metal structure by electromagnetic vibration and continuously and efficiently in view of the related art. As a result of repeated studies, they have found that in the step of refining the metal structure by electromagnetic vibration, the intended purpose can be achieved by controlling the thickness of the solid-liquid coexisting layer, and have completed the present invention.
An object of the present invention is to provide a continuous casting method and a device therefor for refining a metal structure by electromagnetic vibration.
It is another object of the present invention to provide a continuous casting apparatus suitable for the continuous casting, including a mold, a heating furnace, a cooling chill, a casting pulling means, and the like.
[0005]
[Means for Solving the Problems]
The present invention for solving the above-mentioned problems includes the following technical means.
(1) A method in which a metal structure is refined by electromagnetic vibration to perform continuous casting, in which a metal material is charged into a mold, and an AC electric field and a DC magnetic field are applied to a solid-liquid coexisting layer melted by a heating furnace around the mold. In the step of continuously pulling out the metal material cooled and solidified by the cooling chill from the mold outlet, the thickness of the solid-liquid coexistence layer is adjusted by the pulling speed of the solidified metal material, cooling conditions by the cooling chill. A continuous casting method characterized by controlling heating conditions of a heating furnace around a mold.
(2) The continuous casting method according to (1), wherein the metal material cooled and solidified is pulled out while controlling the position of the solid-liquid interface.
(3) The continuity according to (1), wherein the position of the electrode or the position of the solid-liquid interface is set so that the current flows through the electrode provided around the mold around the solid-liquid coexisting layer. Casting method.
(4) A continuous casting apparatus for refining a metal structure by electromagnetic vibration, which is positioned around a mold for charging a metal material and melting the charged metal to form a solid-liquid coexistence layer. Heating furnace, electrode and magnetic field forming means for applying an AC electric field and a DC magnetic field to the molten metal, cooling chill for solidifying the molten metal material, means for continuously pulling out the solidified metal material, Means for controlling the pulling speed of the metal material, cooling conditions by the cooling chill and heating conditions of the heating furnace around the mold, as components, the thickness of the solid-liquid coexistence layer, the pulling speed, the cooling chill and the heating furnace. A continuous casting apparatus characterized by being controlled by controlling.
(5) The apparatus according to (4), wherein the heating furnace is provided around the mold.
(6) The apparatus according to (4), wherein the cooling chill is provided at a mold outlet.
(7) The apparatus according to (4), further including a thermocouple for monitoring a temperature near the electrode.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the present invention will be described in more detail.
One example of the apparatus of the present invention is schematically shown in FIGS. The apparatus of the present invention is divided according to the state of the injection material, and FIG. 1 shows a case where a liquid material such as a molten metal is injected, and FIG. 2 shows a case where a solid material such as a lump or a powder is injected. As shown in FIG. 1, an AC current and a DC magnetic field are simultaneously applied to a solution (Melt) injected into a mold by continuous solution injection (Continuous Melt Input), so that the casting during solidification can be formed. Electromagnetic vibration is generated to continuously refine the metal structure. A DC magnetic field is applied by a magnet installed outside the mold, and an AC current is directly supplied to the solution (AC / DC Power Supply) from a power supply by an electrode fixed to the mold wall.
[0007]
In the present invention, when a liquid material is used as the injection material, the heating furnace can be omitted from the apparatus of the present invention in some cases. Further, regardless of the state of the injection material (solid or liquid), the cooling chill can be removed as necessary. In these cases, the control of the thickness of the solid-liquid coexisting layer becomes strict, but the control can be performed only by the temperature and the pulling speed of the injection material.
[0008]
The product (Refined Solid) having a fine structure is pulled out by an appropriate device, for example, a stepping motor while controlling the position of the solid-liquid interface at an appropriate speed. In the present invention, in order to more accurately control the temperature of the molten metal, that is, the solid-liquid interface, a water-cooled chill having a water supply inlet (Water Inlet) and an outlet (Water Outlet) at the mold outlet is provided. ), And a heating furnace (Furnace) is set around the mold, and the temperature near the electrodes is monitored with a thermocouple. FIG. 2 shows a case where a solid is used as an injection material. In this case, the solid is directly injected into the mold by continuous solid injection, and is melted by a heating furnace installed around the mold in the mold, and is brought into a molten (Semi-Solid) state. Become. Subsequent processes are the same as those for the liquid material in FIG.
[0009]
The present invention is applied to a metal material, but the metal material as used herein is defined as including a metal, an alloy, and another material having electric conductivity, and is not limited to a metal in a narrow sense. Materials having all kinds of electrical conductivity equivalent or similar to metals are also applicable. The apparatus of the present invention is a continuous casting apparatus for refining a metal structure by electromagnetic vibration, and is used for forming a mold (Mold) for charging a metal material, melting the charged metal, and forming a solid-liquid coexistence layer. A heating furnace (Furnace) located around the mold, an electrode for applying an AC electric field and a DC magnetic field to the molten metal (AC / DC Power Supply), and a magnetic field forming means (Magnet), for solidifying the molten metal material Water-cooled chill, means for continuously pulling out the solidified metal material (Stepping Motor), the pulling speed of the solidified metal material, cooling conditions by the cooling chill, and heating conditions of the heating furnace around the mold. Means for controlling the thickness of the solid-liquid coexisting layer, , A cooling chill and a heating furnace.
[0010]
The specific configuration of each of the above means is not particularly limited, and can be arbitrarily designed, and can be appropriately replaced by a similar means having a similar function. A heating furnace (Furnace) for heating the injected liquid material is installed at an injection port (Tundish) for injecting the liquid material. In the solid-liquid coexistence layer, an AC electric field and a DC magnetic field are applied to the molten material by an electrode and a magnet installed in the middle stage of the mold. Thereby, the structure is refined by the generated cavity. In this case, the thinner the solid-liquid coexisting layer, the higher the current density can be obtained.On the other hand, the thicker the solid-liquid coexisting layer, the higher the probability of current flowing through the solid layer. It is important to control.
[0011]
In the present invention, the thickness of the solid-liquid coexisting layer is controlled by controlling the pulling speed of the casting, the cooling condition of the cooling chill, and the heating condition of the heating furnace around the mold. By adjusting these, the thickness of the solid-liquid coexisting layer is controlled, thereby enabling continuous and efficient continuous casting. The cooling chill is installed near the exit of the mold. The position of the electrode installed in the middle stage of the mold is set to a suitable position in relation to the solid-liquid interface. Examples of the heating furnace include an electric furnace using a metal and ceramic heater, an electric resistance heating furnace, a carbon heater, a ceramic heater, an optical heater, and the like. Examples of the magnet include a superconducting magnet. However, the present invention is not limited to these, and any similar means can be used. The mold is preferably, for example, a mold made of silicon nitride.
[0012]
Next, the mechanism of the present invention will be described with reference to FIGS. By simultaneously applying an AC electric field (frequency “f”, current density “J”) and a DC magnetic field (magnetic flux density “B”) to the molten metal, a force oscillating in the liquid at the same frequency as the AC current (F = J × B) occurs, and all particles of the liquid vibrate. The pressure “P = BJ (V / A) Sin (2πft)” is generated by this vibration force. Here, “V” and “A” are the volume of the solid-liquid coexisting layer and the cross-sectional area in the direction perpendicular to the force direction, respectively. At the solid-liquid interface, the oscillating force is repeated as a movement of a compression force and an expansion force. A cavity can be created when the oscillating force, which appears as an expansion force, has the strength to pull the liquid away from the solid.
[0013]
The generated cavity is contracted under the influence of the compressive force acting in the next half cycle, and releases a part of the gas absorbed from the surroundings during the expansion to the surroundings. However, the cavity under compression may not be completely extinguished because the diffusion area is smaller than that of the cavity under expansion and all the gas cannot be released. Due to the repetition of such a phenomenon, the cavity grown to a certain size is destroyed by the balance between the internal and external pressures, and may impact the solid interface by impacting the solid interface. Further, a force consisting of an alternating current and an induced magnetic field generated by the alternating current is generated, which results in stirring of the solution and homogenization of the tissue.
[0014]
3 and 4, the thickness of the solid-liquid coexistence layer (Liquid-Solid Zone) of the metal material injected into the mold (Mold) is an important factor in terms of performing continuous casting and its efficiency, and The installation position of the electrode (Electrode) is extremely important for accurately controlling the liquidus temperature (Liquidus Temp.). The solid-liquid coexisting layer is cooled by a cooling chill near the exit of the mold, forms a solid-liquid interface at its solidus temperature (Solidus Temp.), And forms a fine solid (Refined Solid). When the electrode is located at a position close to the solid-liquid interface, the current (AC Current) flows through the solid layer having high electrical conductivity. It is important to set the position such that it flows through the electrode in the solid-liquid coexistence layer at the center. When a solid material is injected into the mold, the solid material is eroded by the solid-liquid coexistence layer and melts.
[0015]
As described above, the location of the electrode is important, but of course the temperature is not controlled by the location of the electrode, but the temperature near the location of the electrode is controlled by the heating furnace, cooling chill and pulling speed. It is extremely important to control the temperature so that the liquidus temperature (Liquidus Temp.) Of the metal material is adjusted. The liquidus temperature (Liquidus Temp.) And the solidus temperature (Solidus Temp.) Change depending on the components of the metal material and the composition thereof (when the pressure is considered constant). Can be confirmed in the state diagram. Therefore, as described above, it is important to control the thickness of the solid-liquid coexisting layer by controlling the metal material to be injected to an appropriate temperature by controlling the pulling speed, the cooling chill, and the heating furnace. .
[0016]
In the case of a liquid injection material, since the electric conductivity of a solid is generally higher than that of a molten state in the case of a metal, current flows mainly through a solid-liquid coexistence layer through an electrode provided on a mold wall, and the solidified casting is formed. The object is miniaturized (FIG. 3).
In addition, in the case of a solid injection material, in addition to the above effects, the injected solid is eroded by a cavitation phenomenon caused by electromagnetic vibration, and has an effect of assisting dissolution (FIG. 4). In the present invention, as conditions for refining the metal structure, for example, the electromagnetic pressure (P) in the liquid is preferably 10 ⁵ Pa or more, and the current density range is 0.1 × 10 5 ⁶ is a -7 × ¹⁰ 6 a / m2, the range of the magnetic flux density is 0.1-15T, range of frequency is 10 Hz-5 kHz. When the pressure is constant, the liquidus temperature and the solidus temperature change depending on the components of the metal material and the composition thereof. The above pulling speed, cooling chill and heating furnace conditions are controlled so as to reach the temperature.
[0017]
【Example】
Next, a preferred embodiment of the present invention will be described.
Example (1) Experiment of miniaturization of metal material using this apparatus For the purpose of the experiment, a continuous casting apparatus capable of applying electromagnetic vibration during solidification was designed and manufactured, and was installed at the center of a superconducting magnet. In this apparatus, graphite electrodes having a diameter of 7 mm are penetrated on both sides of a silicon nitride mold having an outer shape and an inner diameter of 50 mm and 40 mm, respectively, so that a current can be directly passed through the casting. An Al-7 wt% Si alloy was heated and melted in a mold to 617 ° C. by a heating furnace attached around the mold. In a magnetic field having a magnetic flux density of 10 T, an electric field having a current density of 1.4 × 10 ⁶ A / m ² and a frequency of 200 Hz was applied to generate electromagnetic vibration, and an attempt was made to make the structure finer. FIG. 5 shows a microstructure without vibration, and FIG. 6 shows a microstructure refined by electromagnetic vibration. From these results, miniaturization of the metal structure was confirmed, and the miniaturization function of the present apparatus and its effectiveness were confirmed.
[0018]
(2) Examination of Current Density, Magnetic Flux Density, and Frequency Range Next, an experiment was conducted to study suitable current density, magnetic flux density, and frequency range.
Using the above devices and materials, suitable conditions of current density, magnetic flux density and frequency range were examined. The thinner the solid-liquid coexistence layer, the higher the current density was obtained, which led to an improvement in the efficiency of the miniaturization effect by electromagnetic vibration. However, the higher the solid phase ratio, the higher the probability that the current flows through the connected solid, so the efficiency of the electromagnetic vibration was reduced. Therefore, it was found that it is important to appropriately control the thickness of the solid-liquid coexisting layer. The thickness of the solid-liquid coexisting layer was controlled by the pulling speed, the cooling chill, and the heating furnace around the mold. As a result, the following matters were found.
In order to obtain a suitable miniaturization effect, the electromagnetic pressure (P) in the liquid needs to be 10 ⁵ Pa or more. However, depending on the amount of gas contained in the molten metal, a certain refinement effect can be obtained even at a lower electromagnetic pressure. The range of the current density was 0.1 × 10 ⁶ -7 × 10 ⁶ A / m ² , and the range of the magnetic flux density was 0.5 to 15T. The optimum frequency range was 10 Hz-5 kHz.
[0019]
【The invention's effect】
As described in detail above, the present invention relates to a continuous casting method and a device therefor for microstructure refinement by electromagnetic vibration. According to the present invention, 1) a continuously and efficiently refined cast product is obtained. It can be manufactured 2) It can provide a new continuous casting technique for microstructural refinement by electromagnetic vibration 3) It can provide a continuous casting device for continuously miniaturizing the casting during solidification 4) From the electrode This has the effect of reducing the loss of current and enabling efficient continuous casting with energy saving.
[Brief description of the drawings]
FIG. 1 shows an example of a continuous casting apparatus of the present invention.
FIG. 2 shows an example of the continuous casting apparatus of the present invention.
FIG. 3 is a diagram illustrating a mechanism of microstructuring by electromagnetic vibration (in the case of liquid material injection).
FIG. 4 is a diagram showing a mechanism of microstructuring by electromagnetic vibration (in the case of solid material injection).
FIG. 5 shows the microstructure of an unrefined casting.
FIG. 6 shows the microstructure of a refined casting.

Claims (7)

A method of continuous casting by refining the metal structure by electromagnetic vibration, in which a metal material is put into a mold, and an AC electric field and a DC magnetic field are applied to a solid-liquid coexisting layer melted by a heating furnace around the mold to form the metal material. In the step of continuously pulling out the metal material cooled and solidified by the cooling chill from the mold outlet, the thickness of the solid-liquid coexistence layer is adjusted by the pulling speed of the solidified metal material, the cooling conditions by the cooling chill, and the surroundings of the mold. A continuous casting method characterized by controlling the heating conditions of the heating furnace. The continuous casting method according to claim 1, wherein the metal material cooled and solidified is pulled out while controlling the position of the solid-liquid interface. 2. The continuous casting method according to claim 1, wherein the position of the electrode or the position of the solid-liquid interface is set such that a current flows through the solid-liquid coexisting layer through an electrode provided around the mold. 3. A continuous casting apparatus for refining the metal structure by electromagnetic vibration, a mold for charging a metal material, a heating furnace positioned around the mold to melt the charged metal and form a solid-liquid coexistence layer, An electrode and a magnetic field forming means for applying an AC electric field and a DC magnetic field to the molten metal, a cooling chill for solidifying the molten metal material, a means for continuously pulling out the solidified metal material, Means for controlling the pulling speed, cooling conditions by the cooling chill, and heating conditions of the heating furnace around the mold, as components, controlling the thickness of the solid-liquid coexistence layer, the pulling speed, the cooling chill, and the heating furnace. A continuous casting apparatus characterized in that the apparatus is controlled by: The apparatus according to claim 4, wherein the heating furnace is provided around the mold. The apparatus according to claim 4, wherein a cooling chill is provided at the mold outlet. 5. The device according to claim 4, comprising a thermocouple for monitoring the temperature near the electrode.

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