JPH07155906A - Method for continuously producing half-solidified metallic material having good workability by electromagnetic stirring method - Google Patents

Abstract

PURPOSE:To obtain a half-solidified metal having good workability by specifying the ratio of the shearing strain speed on the solid-liquid interface to the solidifying speed of molten metal in the inner surface of a cooling mold. CONSTITUTION:The molten Al alloy supplied from the upper part of the cooling mold 4 is stirred with an electromagnetic induction coil 3 under cooling in the mold to cause the solidification to make it into half-solidified metal. The ratio of the shearing strain speed of the solid-liquid interface to the solidifying speed of the molten metal in the inner surface of the cooling mold 4 is made to be >8000. The solidifying speed is adjusted by heat removing speed, vol. and cooling area of the cooling mold and the shearing strain speed on the solid-liquid interface is adjusted by the stirring flow speed by the electromagnetic force. By this method, the growth of solidified shell developed in the cooling mold is prevented and the stable continuous operation can be realized at a high solidified rate and the stable continuous casting of the half-solidified metal having fine and uniform dispersion of the primary crystal grains and good wirkability is facilitated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention proposes a method for continuously producing a semi-solid metal material capable of stably obtaining a solid-liquid mixture (hereinafter referred to as semi-solid metal) having good workability by an electromagnetic stirring method. To do.

[0002]

2. Description of the Related Art As a means for continuously producing a semi-solid metal, it is disclosed in, for example, Japanese Patent Publication No. 56-20944 (apparatus for continuously forming an alloy containing non-dendritic primary crystal solids). As shown in the figure, the molten metal at a constant temperature is introduced between the inner surface of the cylindrical cooling tank and the stirrer rotating at high speed, and cooled with a strong stirring action, and the obtained semi-solidified metal is continuously fed from the bottom. A mechanical stirring method for discharging (hereinafter referred to as a stirrer rotation method) is known. Further, a method using electromagnetic force, that is, an electromagnetic stirring method is widely known as a stirring method for molten metal.

Still another means is, for example, Japanese Patent Laid-Open No.
As disclosed in Japanese Unexamined Patent Publication No. 238645 (method and apparatus for producing semi-solidified metal), a fixed rotor composed of a horizontal axis cylindrical cylinder having heat removal capability and a concave curved surface along the circumference of the cylindrical cylinder of the rotor. Method of supplying semi-solid metal continuously from the lower gap by supplying molten metal to the wall and generating shear strain at the solid-liquid interface by rotating the stirring rotor while cooling and applying discharge force ( Hereinafter, referred to as a single roll method).

In any of these means, the solid phase in the semi-solid metal is stirred violently while cooling the molten metal (generally an alloy), so that the branches of dendrites that are being formed in the melt disappear or are not formed. It is formed by being reduced and converted into a rounded form.

As a method for processing the semi-solid metal thus produced, a thixo-working method in which the obtained semi-solid metal is further cooled and solidified, and then reheated to a half-melting temperature for processing, and For example, there is a rheo processing method that processes the semi-solid metal as it is.

When a semi-solid metal is processed by a thixo-process method or a rheo-process method, its processability depends on the solid phase ratio during processing,
It depends on the size of the primary grains, the morphology of the primary grains and their homogeneity. First, looking at the effect of the solid fraction, if the solid fraction when processing semi-solid metal is too small (the heat content is large), the reduction of the heat load, which is a great advantage of processing semi-solid metal, is impaired. On the contrary, if the solid fraction is too large, problems such as an increase in processing pressure required for processing and deterioration of filling property occur. Further, the smaller the grain size of the primary crystal grains and the more rounded the particles, and the more uniform the dispersion of the primary crystal grains, the better the workability. Therefore, in order to improve the workability of semi-solidified metal and produce a sound processed product, it is important to control not only the solid phase ratio during processing but also the primary crystal grain size, morphology and uniformity.

On the other hand, in any of the above methods, when the heat removal rate of the cooling surface is increased in order to reduce the primary crystal grain size, the solidified shell grows violently. Problems such as reduction of size, coarsening of primary crystal grains, deterioration of quality, and suspension of operation are likely to occur.

As a solution to this problem, for example, Japanese Patent Publication No.
-66958 (Method for producing slurry structure metal composition), the value of ratio of shear rate to solidification rate is 2 x 10 ³ to 8 x.
Although a method of holding in the range of 10 ³ has been proposed and disclosed, inhibition of solidified shell growth, refinement of primary crystal grains, uniformity of grain size and dispersion are still insufficient, and continuous production of semi-solidified metal is difficult. Therefore, the workability was insufficient.

[0009]

In view of the above-mentioned circumstances, in order to enable the continuous production of semi-solidified metal and further improve the workability, means for preventing the growth of the solidified shell and semi-solidified semi-solidified steel to be produced. It is important to find a means for further reducing the primary crystal grain size of metal and uniformly dispersing the primary crystal grains. On the other hand, the electromagnetic stirring method and the continuous casting method connected thereto are particularly excellent as a manufacturing process of a material for thixo working, and it is very significant to realize uniform miniaturization and uniform dispersion of primary crystal grains by this method. is there.

Therefore, an object of the present invention is to propose a stable continuous production method of a semi-solidified metal material in which primary crystal grains are fine and uniformly dispersed by an electromagnetic stirring method and good workability can be obtained. .

[0011]

SUMMARY OF THE INVENTION The inventors of the present invention are concerned with a method of refining primary crystal grains of a semi-solidified metal and a uniform dispersion method in the production of a semi-solidified metal in which a molten metal is cooled while being stirred by electromagnetic force in a cooling mold. As a result of further research, the solidified shell grows in the mold, so the amount of heat removed in the mold is distributed to the growth of the solidified shell, and the solidified shell becomes a thermal resistance. There is a limit to the miniaturization of primary grains by increasing the speed, and in order to increase the solidification speed in the mold and continuously produce semi-solidified metal, the method of inhibiting and controlling the growth of the solidified shell in the mold The present invention has been accomplished by discovering that the development of the above is important and the development of a method for uniformly dispersing primary crystal grains in a semi-solid metal is important.

That is, the gist of the present invention is as follows. The molten metal supplied from above the cylindrical cooling mold is stirred by electromagnetic force under cooling to obtain a solid-liquid mixed phase slurry in which fine non-dendritic primary crystals of particles are suspended, By increasing the ratio of the solid-liquid interface shear strain rate to the melt solidification rate on the inner surface of the mold to more than 8,000, the growth of the solidified shell in the cooling mold is prevented, the decrease of the heat removal rate is prevented, and the high solidification rate. Is maintained and the coarsening of primary crystal grains is prevented, which is a continuous manufacturing method of a semi-solid metal material having good workability by an electromagnetic stirring method.

In the item, the ratio of the solid-liquid interface shear strain rate to the melt solidification rate on the inner surface of the cooling mold is 80
The value over 00 is due to the heat removal rate of the cooling mold, the adjustment of the solidification rate by the volume and the cooling area, and the adjustment of the shear strain rate of the solid-liquid interface by the stirring flow rate by the electromagnetic force.

Alternatively, the semi-solidified metal produced according to the item (1) is discharged through a sliding nozzle for discharging speed control or a stopper for discharging speed control, which is arranged at the lower end of the cooling mold.

Alternatively, the semi-solidified metal produced according to the item (1) is continuously cast by a rapid cooling continuous casting mold continuously arranged at the lower end of the cooling mold. Here, semi-solidified metal is advantageous as a raw material for processing such as for rheo processing, which is processed as it is, after making into a single ingot or continuous cast strand, for thixo processing to be reheated to a semi-molten state for processing, forging, etc. It is applicable, and the semi-solid metal and the cast material for these processes are collectively referred to as the semi-solid metal material.

[0016]

The operation of the present invention will be described below based on experimental examples. 1, 2 and 3 are used to produce semi-solidified metal, which is subjected to rho-processing and thixo-processing by die casting, stable operating conditions, and the obtained primary-solidified grain size of the semi-solidified metal and dispersion of primary-grains. The situation and its processability were examined.

Here, FIG. 1 is an explanatory view of a semi-solidifying metal manufacturing apparatus by a magnetic stirring method equipped with a continuous casting machine. In the figure, 2 is a dipping nozzle, 3 is an electromagnetic induction coil, and 4 is a heat removal rate. Control cooling mold, 5 rapid cooling continuous casting mold, 6 cooling water spray, 7 slab drawing roll,
12 is a thermocouple, 13 is a semi-solid metal, and 14 is a slab.

FIG. 2 is an explanatory view of a semi-solidified metal manufacturing apparatus by a magnetic stirring method provided with a sliding nozzle for controlling a discharging speed. In the figure, 2 is a dipping nozzle, 3 is an electromagnetic induction coil, and 4 is heat removal. Cooling mold for speed control, 8
Is a discharge nozzle having a heat insulation mechanism by a heater, 9 is a sliding nozzle for controlling the discharge speed, 10 is a motor for controlling the sliding nozzle, 12 is a thermocouple, and 13 is a semi-solidified metal.

FIG. 3 is an explanatory view of an apparatus for producing semi-solidified metal by an electromagnetic stirring method equipped with a discharge control stopper. In the figure, 1 is a tundish, 3 is an electromagnetic induction coil, and 4 is a heat removal rate control. Is a cooling mold, 8 is a discharge nozzle equipped with a heat insulating mechanism by a heater, 11 is a stopper, 12 is a thermocouple, and 13 is a semi-solidified metal.

In this experiment, the primary crystal grain size of the semi-solidified metal, the primary crystal grain size and the uniformity of dispersion were determined by the solidification rate of the molten metal and the shear strain rate at the solid-liquid interface (cooling mold 4).
(Including the shear strain rate of the solid-liquid interface on the inner surface). The solidification rate is the rate of solid phase increase in the cooling mold 4, and depends on the unit molten metal amount and the heat removal amount per unit time. Therefore, the heat removal rate of the cooling mold 4, the cooling area of the cooling mold 4, and the void volume. Controlled by. The cooling area and the void volume are for the portion below the molten metal surface of the supplied molten metal.

The solid fraction of each semi-solid metal produced is controlled by the discharge rate (casting rate), and the solid fraction is based on the temperature measured by the thermocouple 12 grounded below the cooling mold 4. Determined from the state diagram.

The solidification rate was calculated by the following equation (1) from the solid phase rate determined as described above and the residence time in the cooling mold 4. Solidification rate (s ^-1 ) = dfs / dt ---- (1) where dfs: solid phase ratio of semi-solidified metal at outlet of cooling mold dt: void volume of cooling mold (m ³ ) / discharge rate (m ³ /
s)

On the other hand, the shear strain rate of the solid-liquid interface (shear strain rate of the solid-liquid interface on the inner surface of the cooling mold 4 or the solidified shell surface generated) can be calculated by performing a flow analysis in a double cylinder in electromagnetic stirring. Possible, but
Since this is a complicated solution, there is no big difference from this exact solution, and the calculation is performed by the following simple formula (2). Ω in equation (2)
_M is the average angular velocity of the molten metal stirring flow and was calculated by the following equation (3). According to these equations (2) and (3), the cooling mold 4
The shear strain rate γ of the inner surface or the solid-liquid interface can be controlled by the angular velocity Ω _C of the rotating magnetic field by the electromagnetic induction coil 3, the magnetic flux density B _O during idle operation, the radius of the cooling mold 4 and the solid-liquid interface radius r _2. it can. Although the value of α differs depending on the alloy to be used, the solid fraction, the frequency applied to the electromagnetic induction coil 3, etc., the following formula (4) is used based on the result of measuring the stirring flow velocity in advance by a molten metal stirring experiment. Calculated.

[0024]

[Equation 1] Equations (2), (3) and (4) are flow equations and are derived as a steady laminar flow in a concentric double cylinder.

For the solidified shell thickness grown in the cooling mold 4, when the molten metal is extracted during operation and the molten metal does not remain solidified in the cooling mold 4, the solidified shell thickness is directly measured, and the molten metal remains solidified. Was measured from the occurrence of negative segregation. In some experiments, the cooling mold 4
One or two kinds of tracer components were charged therein, their positions were confirmed by analysis of the stepped sample, and the solidified shell thickness during operation (when the tracer was charged) was measured.

FIG. 4 is a graph in which the presence or absence of solidified shell growth determined from the solidified shell thickness thus measured is plotted in a matrix of the solidification rate and the shear strain rate at the solid-liquid interface. From this figure, in order to prevent solidified shell growth in the cooling mold 4, it is necessary to increase the shear strain rate at the solid-liquid interface when the solidification rate is increased,
The boundary line with and without the growth of the solidified shell can be expressed by the following equation (4). γ = 8100 × dfs / dt ---- (4) where γ: Shear strain rate of solid-liquid interface (s ^-1 ) dfs / dt: Solidification rate (s ^-1 )

When the shear strain rate on the inner surface of the cooling mold 4 is larger than the boundary value determined by the equation (4), naturally, the solidified shell does not grow on the inner surface of the cooling mold 4. However, in actual operation, in order to realize stable continuous operation without growing the solidified shell when operating conditions such as heat removal rate and discharge rate change,
It is preferable to set the shear strain rate of the inner surface of the cooling mold 4 as large as possible than the value calculated by the expression (4).

Next, the primary crystal grain size, its dispersion state, workability and the like will be described below. FIG. 5 is a graph showing the effect of the solidification rate on the average crystal grain size observed for the cast piece cast by the apparatus of FIG. 1. From this figure, the average crystal grain size of the cast piece (this crystal grain size is the primary crystal grain Depends on diameter)
Has a smaller diameter as the solidification rate increases.

[0029] FIGS. 6 (a) and (b) is a metal structure photograph of the Al alloy in the case of the case of the 1000 s ^-1 shear strain rate of the solid-liquid interface is respectively 200 s ^-1 (cast in the apparatus of FIG. 1) From these photographs, in Fig. 6 (a) where the shear strain rate at the solid-liquid interface is small, while the crystal grains are coalesced, the stirring strain is enhanced to increase the shear strain rate at the solid-liquid interface.
In (b), the primary crystal grains are uniformly dispersed. It is presumed that this is because the higher the shear strain rate at the solid-liquid interface, the more intense the stirring and the more uniform the cooling rate.

Further, as a result of observing the metallographic structure of the sample in which the semi-solidified metal discharged by the apparatus of FIGS. 2 and 3 was rapidly solidified between the copper plates, the larger the solidification rate, the finer the primary crystal grains and the solid-liquid interface. It was confirmed that the higher the shear strain rate, the more uniform the primary crystal grain size and the more uniform dispersion.

In Table 1, the results of the continuous casting of the Al alloy slab using the apparatus of FIG. 1 and the produced Al alloy slab were reheated to a semi-molten state (solid phase ratio: 0.30 to 0.35),
Table 2 and Table showing the relationship between the filling defect rate (n = 50) of the processed product and the average crystal grain size of the slab, the solidification rate, the shear strain rate of the solid-liquid interface, etc. In Fig. 3, the results of continuous discharge of semi-solidified metal of the Al alloy and cast iron by the apparatus of Fig. 2 and the case where the discharged semi-solidified metal of Al alloy and cast iron were rheo-processed by a die casting machine (Table 2 ), And a semi-solid metal are received in a mold and solidified, and then a semi-molten state (solid phase ratio:
Refilling rate (n = 50) of each processed product when reheated to 0.30 to 0.35) and subjected to thixo-processing with a die casting machine (Table 3), primary crystal grain size of semi-solidified metal, solidification rate and solid-liquid Shows the relationship with the shear strain rate of the interface,

Tables 4 and 5 show the results of continuous discharge of semi-solidified metal of the Al alloy and cast iron by the apparatus of FIG. 3 and the discharged semi-solidified metal of Al alloy and cast iron in the same manner as described above. Filling failure rate (n = 50) of each processed product when rheo-processed (Table 4) and thixo-processed (Table 5) by a casting machine, primary crystal grain size of semi-solidified metal, solidification rate and shear of solid-liquid interface It shows the relationship with the strain rate.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

[Table 3]

[0036]

[Table 4]

[0037]

[Table 5]

In any case, these are the cooling molds 4.
When the shear strain rate on the inner surface is equal to or less than the value of the expression (4), that is, when the ratio of the shear strain rate on the inner surface of the cooling mold 4 to the solidification rate is 8100 or less, a solidified shell is generated on the inner surface of the cooling mold 4, The heat removal rate (solidification rate) decreases with the growth of the solidified shell that is produced, and the growth of the solidified shell is stopped when the ratio of the shear strain rate to the solidification rate reaches the above value. Therefore, even in such a case, if the growth of the solidified shell is prepared, the solidification rate can be increased by increasing the shear strain rate, and the primary crystal grain size can be reduced. However, if the solidified shell formed on the inner surface of the cooling mold 4 grows too much, continuous casting or continuous discharge cannot be performed.

On the other hand, when the ratio of the shear strain rate of the inner surface of the cooling mold 4 to the solidification rate, which is a condition in which the solidified shell does not grow, is larger than 8100, continuous casting or continuous discharge is possible without trouble, and the crystal grains depending on the solidification rate. The smaller the diameter or the primary crystal grain size and the higher the shear strain rate at the solid-liquid interface, the smaller the filling failure rate in die casting and the better the workability.

As described above, according to the present invention, in a method for producing a semi-solid metal in which a molten metal is stirred in a cooling mold under cooling by electromagnetic force, the ratio of the solidification rate to the shear strain rate at the solid-liquid interface is optimized. This prevents the solidified shell from growing in the cooling mold and enables stable continuous operation. As a result, it becomes possible to increase the solidification rate of the molten metal and facilitate the refining of the primary crystal grains. Also,
By increasing the shear strain rate at the solid-liquid interface in combination with the increase in solidification rate, the particle size and dispersion of fine primary crystal grains can be made uniform, and semi-processable as a material for thixo-processing, rheo-processing, and other forging. A solidified metal material can be stably and continuously produced.

[0041]

【Example】

Example 1 The AC4C (Al alloy) molten metal supplied from above the cooling mold 4 of the semi-solidified metal manufacturing apparatus using the electromagnetic stirring method equipped with the continuous casting machine shown in FIG. On the contrary, in the mold, while being cooled, it is electromagnetically stirred by the electromagnetic induction coil 3 to cause solidification to form a semi-solidified metal, and then a rapid cooling continuous mold 5 is used to form a solidified shell on the surface and shape it, and then a cooling water spray is formed. The slab was cooled by 6 to form a slab 14 and each slab was drawn by a drawing roll 7.

In the above, the solidification rate is controlled by the heat removal rate of the cooling mold 4, the cooling area and the volume, and is determined from the measured temperature of the thermocouple 12 installed at the lower end of the cooling mold 4 and the state diagram of the alloy. The solid phase ratio and the residence time in the cooling mold 4 were used to calculate by the above formula (1). The solid fraction was adjusted by the casting speed.

The shear strain rate at the solid-liquid interface is controlled by the equation (3) according to the current and frequency applied to the electromagnetic induction coil 3 by controlling the average angular velocity Ω _M of the molten metal stirring flow in the cooling mold 4 and the above (2). Calculated by the formula. Note that (2),
In the equation (3), the magnetic flux density B _O in the electromagnetic induction coil 3 during idling was formulated as a function of the measured value in the coil and the current and frequency applied to the coil at that time and used. Further, the magnetic efficiency α was determined by the equation (4) using the circumferential flow velocity of the molten metal in the ½ radius portion of the cooling mold 4 which was previously measured in the molten metal stirring experiment. The thickness of the solidified shell in the cooling mold 4 is determined by measuring the thickness of the solidified shell remaining by extracting the molten metal downward during the operation and the position of the tracer component added during the operation to determine whether the solidified shell has grown. investigated.

A graph in which the presence or absence of solidified shell growth determined from the solidified shell thickness thus measured is arranged in a matrix of the solidification rate and the shear strain rate at the solid-liquid interface is shown in FIG. The boundary condition with and without the solidified shell growth on the inner surface can be expressed by the above equation (4). Therefore, in order to prevent the growth of the solidified shell on the inner surface of the cooling mold 4 and to obtain a semi-solidified metal having good workability, shearing on the inner surface of the cooling mold 4 is performed at a high solidification rate necessary for refining the solidified structure. It is important that the strain rate be equal to or higher than the value satisfying the equation (4). When the shear strain rate on the inner surface of the cooling mold 4 is higher than the boundary condition of the equation (4), stable operation can be achieved without the solidified shell growing even if the operating conditions such as the heat removal rate and the casting rate change. Therefore, the shear strain rate on the inner surface of the cooling mold 4 is preferably as high as possible. The ratio of the shear strain rate at the solid-liquid interface on the inner surface of the cooling mold 4 to the solidification rate was 8100.
When the value is slightly smaller, the solidified shell slightly grows on the inner surface of the cooling mold 4 until the above value reaches 8100, but the solidified shell grown on the inner surface of the cooling mold 4 is pulled out downward and continuous casting is possible. Also in this case, the solidification rate can be increased by increasing the shear strain rate at the solid-liquid interface to enable continuous casting, and the workability as a material for the processing is improved.

FIG. 5 is a graph showing the relationship between the average crystal grain size and the solidification rate of the slab thus produced.
As is clear from this figure, the larger the solidification rate, the finer the crystal grains depending on the primary crystal grains of the semi-solidified metal.

6 (a) and 6 (b) are photographs of the metallographic structures of the slabs when the solidification rate is 0.02 and the shear strain rate at the solid-liquid interface is small (a) and large (b). . From these metallographic photographs, it is shown that increasing the shear strain rate at the solid-liquid interface results in more uniform crystal grain size and dispersed state. The shear strain rate at the interface is preferably high.

As described above, in order to stabilize the operation and homogenize the metal structure of the slab, it is advantageous to strengthen the stirring force in the cooling mold 4 and maximize the shear strain rate.

Next, as a result of the continuous casting as described above, and the produced slabs are reheated to a semi-molten state having a solid fraction of 0.30 to 0.35 and thixo-processed by a die casting machine. The relationship between the filling failure rate (n = 50) of the product, the average crystal grain size of the slab, the solidification rate, and the shear strain rate of the inner surface of the cooling mold 4 is shown in Table 1 above. If the ratio of shear strain rate to solidification rate is less than 8000, continuous casting is difficult. When the above value is 8000 or more and less than 8100, the solidified shell grows until the ratio of the shear strain rate at the solid-liquid interface of the molten metal to the solidification rate generated on the inner surface of the cooling mold 4 becomes 8100, but continuous casting is performed. In this case, the solidification rate can be increased by increasing the shear strain rate at the solid-liquid interface, and as shown in Table 1, the workability is improved. Furthermore, the above value that allows continuous casting is 80
In the case of more than 00, the filling failure occurrence rate in thixoprocessing can be improved by making the average grain size finer by increasing the solidification rate and increasing the shear strain rate at the solid-liquid interface to make the grain size uniform. I understand. The defective filling rate of processed products was determined by visual inspection and density measurement.

Example 2 The semi-solid metal producing apparatus by the electromagnetic stirring method equipped with the sliding nozzle for controlling the discharge rate shown in FIG. 2 was used.
For AC4C (Al alloy) and cast iron, changing various conditions,
Sliding nozzle 9 so that the discharge solid phase ratio becomes 0.3
The discharge rate was controlled by controlling the opening of the semi-solid metal and the continuous discharge of semi-solidified metal was tried.

As a result, the growth of the solidified shell in the cooling mold 4 can be prevented by setting the shear strain rate of the inner surface of the cooling mold 4 to be equal to or more than the value of the above equation (4) with respect to the solidification rate. It could be confirmed by the same investigation method as in 1.

Further, as a result of attempting continuous discharge as described above,
Also, the discharged semi-solidified metal is received in a container made of kao wool, which has a very low thermal conductivity, transferred to a die-casting machine, and then the filling failure rate (n = 50) of the processed product rheo-processed by the die-casting machine. Average primary crystal grain size of semi-solid metal,
Table 2 shows the relationship between the solidification rate and the shear strain rate of the inner surface of the cooling mold 4. On the other hand, each discharged semi-solidified metal is once received in a mold, cooled and solidified, then re-heated to a semi-molten state with a solid fraction of 0.30 to 0.35, and thixotropic processed by a die casting machine. Table 3 shows the relationship among the ratio (n = 50), the average primary crystal grain size of the semi-solidified metal, the solidification rate, and the shear strain rate on the inner surface of the cooling mold 4.

From Table 2, when the ratio of the shear strain rate on the inner surface of the cooling mold 4 to the solidification rate is slightly smaller than 8100, the shear strain rate on the solid-liquid interface between the solidified shell and the molten metal formed on the inner surface of the cooling mold 4 is solidified. The solidified shell grows until the ratio to speed value reaches 8100, but its thickness is thin and continuous discharge is possible. In this case, as shown in Table 2, if the shear strain rate at the solid-liquid interface is increased and the solidification rate is increased, the workability is improved. It is considered that the reason is that when the solidification rate and the shear strain rate are high, the primary crystal grains are reduced in size and uniformly dispersed. When the ratio of the shear strain rate on the inner surface of the cooling mold 4 to the solidification rate is very small, the solidified shell growing on the inner surface of the cooling mold 4 becomes extremely thick, which makes discharge difficult. On the other hand, Tables 2 and 3
As is clear from the above, in the case where the above-mentioned value capable of continuous discharge exceeds 8000, both in the case of rheo processing and thixo processing,
It can be seen that by increasing the solidification rate to refine the primary crystal grains of the discharged semi-solidified metal and increasing the shear strain rate at the solid-liquid interface, the filling failure rate is reduced and the workability is good.

Example 3 AC4C (Al was used by using a semi-solidified metal production apparatus by the electromagnetic stirring method equipped with the stopper for discharging rate control shown in FIG. 3 above.
Alloy) and cast iron, various conditions were changed, and the discharge rate was controlled by the opening degree of the stopper 11 so that the discharge solid phase ratio was 0.3, and the continuous discharge of semi-solidified metal was tried.

As a result, it is possible to prevent the growth of the solidified shell in the cooling mold 4 by setting the shear strain rate on the inner surface of the cooling mold 4 to be equal to or more than the value of the equation (4) in relation to the solidification rate. It could be confirmed by the same investigation method as in 1.

As a result of attempting continuous discharge as described above,
And the discharged semi-solid metal was subjected to rheo-processing and thixo-processing by a die casting machine in the same manner as in Example 2, the filling failure rate (n = 50), the average primary crystal grain size of the semi-solid metal, and the solidification rate. And the relationship with the shear strain rate of the solid-liquid interface on the inner surface of the cooling mold 4 described above (Table 4 (Rheo processing))
And 5 (thixo processed).

From Table 4, when the ratio of the shear strain rate on the inner surface of the cooling mold 4 to the solidification rate is slightly smaller than 8100, the solidification of the shear strain rate on the solid-liquid interface between the solidified shell and the molten metal formed on the inner surface of the cooling mold 4 is solidified. The solidified shell grows until the ratio to speed value reaches 8100, but its thickness is thin and continuous discharge is possible. In this case, as shown in Table 4, the workability is improved by increasing the shear strain rate at the solid-liquid interface and increasing the solidification rate. It is considered that the reason is that when the solidification rate and the shear strain rate are high, the primary crystal grains are reduced in size and uniformly dispersed. When the ratio of the shear strain rate on the inner surface of the cooling mold 4 to the solidification rate is very small, the solidified shell growing on the inner surface of the cooling mold 4 becomes extremely thick, which makes discharge difficult. On the other hand, as is clear from Tables 4 and 5, the above value that allows continuous emission is 8000.
In the case of exceeding, both in the case of rheo processing and thixo processing, the solidification rate is increased to refine the primary crystal grains of the discharged semi-solidified metal, and the failure rate of filling is reduced by increasing the shear strain rate of the solid-liquid interface. It can be seen that the workability is better.

[0057]

INDUSTRIAL APPLICABILITY The present invention relates to a method for producing a semi-solid metal in which a molten metal is electromagnetically stirred under cooling in a cooling mold to form a solid-liquid mixed phase slurry in which fine non-dendritic primary crystal grains are suspended. The value of the ratio of the solidification rate to the shear strain rate of the solid-liquid interface on the inner surface of the cooling mold is set to more than 8000, and according to the present invention, the growth of the solidified shell generated in the cooling mold is prevented, and the stability is stabilized. Continuous operation and high solidification rate can be realized, and as a result, stable continuous discharge and continuous casting of semi-solidified metal with good workability in which primary crystal grains are finely divided and uniformly dispersed are facilitated. The semi-solidified metal material produced in this way is a material for rheo-processing, thixo-processing and casting, which realizes the near net shape process advantageously, greatly reducing the processing energy and a new material using semi-solidified metal. Increase the potential for development.

[Brief description of drawings]

FIG. 1 is an explanatory view of an apparatus for producing semi-solid metal by an electromagnetic stirring method equipped with a continuous casting machine.

FIG. 2 is an explanatory view of a semi-solidified metal production apparatus by a magnetic stirring method provided with a sliding nozzle for controlling a discharge rate.

FIG. 3 is an explanatory view of a semi-solidified metal manufacturing apparatus by a magnetic stirring method provided with a stopper for controlling a discharging speed.

FIG. 4 is a graph in which a solidification rate and a shear strain rate at a solid-liquid interface are plotted in a matrix with and without solidified shell growth.

FIG. 5 is a graph showing the effect of the solidification rate on the average crystal grain size of a cast slab.

FIG. 6 (a) shows a shear strain rate of 200 at the solid-liquid interface.
It is a metallographic photograph of the slab in the case of s ^-1 . (B) is a metallographic photograph of a slab when the shear strain rate at the solid-liquid interface is 1000 s ⁻¹ .

[Explanation of symbols]

 1 Tundish 2 Immersion Nozzle 3 Electromagnetic Induction Coil 4 Cooling Mold 5 Quenching Continuous Casting Mold 6 Cooling Water Spray 7 Cooling Water Spray 7 Drawing Roll 8 Discharge Port 9 Sliding Nozzle 10 Sliding Nozzle Control Motor 11 Stopper 12 Thermocouple 13 Semi-solid Metal 14 Cast Piece

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[Procedure amendment]

[Submission date] December 16, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0023

[Correction method] Change

[Correction content]

On the other hand, the shear strain rate of the solid-liquid interface (shear strain rate of the solid-liquid interface on the inner surface of the cooling mold 4 or the solidified shell surface generated) can be calculated by performing a flow analysis in a double cylinder in electromagnetic stirring. Although it is possible, since it is a complicated solution, it is calculated by the following simple formula (2), which is not much different from this exact solution. Ω _{M in the} equation (2) is an average angular velocity of the molten metal stirring flow and is calculated by the following equation (3). According to these equations (2) and (3), the shear strain rate γ of the inner surface of the cooling mold 4 or the solid-liquid interface is the angular velocity Ω _C of the rotating magnetic field by the electromagnetic induction coil 3, the magnetic flux density B _O during idle operation, and the cooling mold 4 Radius or solid-liquid interface radius r
It can be controlled by ₂ etc. Although the value of α differs depending on the alloy to be used, the solid fraction, the frequency applied to the electromagnetic induction coil 3, etc., the following formula (4) is used based on the result of measuring the stirring flow velocity in advance by a molten metal stirring experiment. Calculated.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction content]

FIG. 4 is a graph in which the presence or absence of solidified shell growth determined from the solidified shell thickness thus measured is plotted in a matrix of the solidification rate and the shear strain rate at the solid-liquid interface. From this figure, in order to prevent solidified shell growth in the cooling mold 4, it is necessary to increase the shear strain rate at the solid-liquid interface when the solidification rate is increased,
The boundary line with and without the growth of the solidified shell can be expressed by the following equation (5). γ = 8100 × dfs / dt ---- (5) where γ: Shear strain rate of solid-liquid interface (s ^-1 ) dfs / dt: Solidification rate (s ^-1 )

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0027

[Correction method] Change

[Correction content]

When the shear strain rate on the inner surface of the cooling mold 4 is larger than the boundary value determined by the equation (5), the solidified shell naturally does not grow on the inner surface of the cooling mold 4. However, in actual operation, in order to realize stable continuous operation without growing the solidified shell when operating conditions such as heat removal rate and discharge rate change,
It is preferable to set the shear strain rate of the inner surface of the cooling mold 4 as large as possible than the value calculated by the equation (5).

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0035

[Correction method] Change

[Correction content]

[0035]

[Table 3]

[Procedure Amendment 5]

[Document name to be amended] Statement

[Name of item to be corrected] 0037

[Correction method] Change

[Correction content]

[0037]

[Table 5]

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0038

[Correction method] Change

[Correction content]

In any case, these are the cooling molds 4.
When the shear strain rate on the inner surface is less than or equal to the value of the expression (5), that is, when the value of the ratio of the shear strain rate on the inner surface of the cooling mold 4 to the solidification rate is 8100 or less, a solidified shell is generated on the inner surface of the cooling mold 4, The heat removal rate (solidification rate) decreases with the growth of the solidified shell that is produced, and the growth of the solidified shell is stopped when the ratio of the shear strain rate to the solidification rate reaches the above value. Therefore, even in such a case, if the growth of the solidified shell is prepared, the solidification rate can be increased by increasing the shear strain rate, and the primary crystal grain size can be reduced. However, if the solidified shell formed on the inner surface of the cooling mold 4 grows too much, continuous casting or continuous discharge cannot be performed.

[Procedure Amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0044

[Correction method] Change

[Correction content]

A graph in which the presence or absence of solidified shell growth determined from the solidified shell thickness thus measured is arranged in a matrix of the solidification rate and the shear strain rate at the solid-liquid interface is shown in FIG. The boundary condition with and without the solidified shell growth on the inner surface can be expressed by the above equation (5). Therefore, in order to prevent the growth of the solidified shell on the inner surface of the cooling mold 4 and to obtain a semi-solidified metal having good workability, shearing on the inner surface of the cooling mold 4 is performed at a high solidification rate necessary for refining the solidified structure. It is important that the strain rate be equal to or higher than the value satisfying the expression (5). When the shear strain rate on the inner surface of the cooling mold 4 is higher than the boundary condition of the equation (5), stable operation can be achieved without causing the solidified shell to grow even if the operating conditions such as the heat removal rate and the casting rate change. Therefore, the shear strain rate on the inner surface of the cooling mold 4 is preferably as high as possible. The ratio of the shear strain rate at the solid-liquid interface on the inner surface of the cooling mold 4 to the solidification rate was 8100.
When the value is slightly smaller, the solidified shell slightly grows on the inner surface of the cooling mold 4 until the above value becomes 8100, but the solidified shell grown on the inner surface of the cooling mold 4 is pulled out downward and continuous casting is possible. Also in this case, the solidification rate can be increased by increasing the shear strain rate at the solid-liquid interface to enable continuous casting, and the workability as a material for the processing is improved.

[Procedure Amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0050

[Correction method] Change

[Correction content]

As a result, it is possible to prevent the growth of the solidified shell in the cooling mold 4 by setting the shear strain rate on the inner surface of the cooling mold 4 to be equal to or more than the value of the equation (5) in relation to the solidification rate. It could be confirmed by the same investigation method as in 1.

[Procedure Amendment 9]

[Document name to be amended] Statement

[Correction target item name] 0054

[Correction method] Change

[Correction content]

As a result, it is possible to prevent the growth of the solidified shell in the cooling mold 4 by setting the shear strain rate of the inner surface of the cooling mold 4 to be equal to or more than the value of the equation (5) in relation to the solidification rate. It could be confirmed by the same investigation method as in 1.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroyoshi Takahashi, 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Stock Company Rheotec (72) Akihiko Namba 1, Kawasaki-cho, Chuo-ku, Chiba Stock Company In rheotech

Claims (5)

[Claims] 1. A semi-solid metal which is a solid-liquid mixed phase slurry in which a non-dendritic primary crystal having fine particles is suspended by stirring a molten metal supplied from above a cylindrical cooling mold by electromagnetic force under cooling. In the manufacturing method, the ratio of the solid-liquid interface shear strain rate to the melt solidification rate on the inner surface of the cooling mold is set to more than 8000 to prevent the solidified shell from growing in the cooling mold and prevent the heat removal rate from decreasing. A continuous production method of a semi-solid metal material having good workability by an electromagnetic stirring method, which is characterized by maintaining a high solidification rate and preventing coarsening of primary crystal grains. 2. A value of more than 8000 of the ratio of the solid-liquid interface shear strain rate to the melt solidification rate on the inner surface of the cooling mold is adjusted by the heat removal rate of the cooling mold, the volume and the cooling area and the electromagnetic force. The method for continuously producing a semi-solid metal material having good workability by the electromagnetic stirring method according to claim 1, which is based on the adjustment of the shear strain rate at the solid-liquid interface by the stirring flow rate. 3. A semi-solid metal produced according to claim 1 or 2 is discharged through a sliding nozzle for discharging speed control arranged at a lower end of a cooling mold, which has good workability by an electromagnetic stirring method. Continuous manufacturing method for simple semi-solid metal materials. 4. The semi-solid metal produced according to claim 1 or 2 is discharged through a stopper for discharging speed control arranged at a lower end of a cooling mold, which has good workability by an electromagnetic stirring method. Continuous production method of semi-solid metal materials. 5. A semi-solid metal having good workability by an electromagnetic stirring method, characterized in that the semi-solidified metal produced according to claim 1 or 2 is continuously cast by a rapid cooling continuous casting mold provided at a lower end of a cooling mold. Continuous production method of solidified metal material.