JP2001191150A - Vertical continuous casting method of aluminum alloy billet - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To propose a vertical continuous casting method of aluminum alloy billet which can surely prevent cracking defects at the initial stage of casting by a simple method without using complicated equipment. When continuously casting an aluminum alloy into a billet having a required shape, an equivalent plastic strain value (ε) obtained by elasto-plastic deformation analysis in the casting process is equal to or less than a measured breaking strain value (εc) of the aluminum alloy. A vertical continuous casting method of an aluminum alloy billet in which casting conditions such as casting speed (V) are controlled so as to fall within the range of (1). In addition, when continuously casting an aluminum alloy into a billet having a required shape, the equivalent plastic strain value (ε) obtained by elasto-plastic deformation analysis in the casting process is determined by the temperature range in which the solid phase ratio of the alloy is 0.8 or less. Excluded is a vertical continuous casting method of an aluminum alloy billet in which casting conditions are controlled to fall within the range of the measured breaking strain value (εc) or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for vertical continuous casting of an aluminum alloy billet which can reliably avoid cracking defects at the early stage of casting in the vertical continuous casting of aluminum alloy billets.

[0002]

2. Description of the Related Art Generally, as shown in FIG. 11, a billet of an aluminum alloy is vertically continuously cast into a ring-shaped forced cooling mold 1 having an opening at the top and bottom through a spout and a float (not shown). Lower mold 4 for pouring molten alloy M and solidifying ingot C to support the lower end
At the same time as the mold 1 is pulled down. That is, pouring is started in a state where the lower mold 4 is inserted from the lower opening of the mold 1 into the inside thereof, and a predetermined amount of molten metal M is supplied into a space surrounded by the mold 1 and the lower mold 4; When the surface is solidified, the ingot C is pulled down together with the lower mold 4 below the mold 1. Then, the ingot C drawn down from the mold 1 is sprayed downwardly in a conical shape from the nozzle 2 with the cooling water W in the mold 1 on the peripheral surface, and is forcibly cooled to be a billet B. The symbol F in FIG. 11 indicates a solidification interface between the molten metal M and the ingot C.

In the initial stage of the casting,
The lower end of the ingot C pulled down from the mold 1 is quenched by the cooling water W, the temperature of the portion drops sharply, and the temperature gradient along the vertical direction of the ingot C increases, so that the inside of the ingot C Induces thermal stress. At the same time, the temperature gradient between the peripheral surface and the central portion of the ingot C also increases, and a thermal stress similarly occurs. Further, the ingot C is rapidly cooled by contact with the lower mold 4 and similarly generates thermal stress. These thermal stresses, as shown in FIG.
This causes hot cracks 6 at the lower end of the ingot C.
Further, a tensile stress is generated by the crack 6, and a vertical crack is easily generated inside the ingot C. Further, when a gap 8 is formed between the ingot C and the lower mold 4, heat radiation from the ingot C to the lower mold 4 is prevented, and a crack is generated from a remelted portion where the lower end of the ingot C is remelted. There is also. In the steady stage after the initial stage of casting, the molten metal M supplied into the mold 1 is cooled by contact with the mold 1 and has a thickness of about 10 m on its peripheral surface.
A thin solidified layer having a thickness of about m is sequentially formed, and the billet B is elongated in the vertical direction.

[0004] The following methods have been proposed in order to improve the quality of ingots by preventing cracks and the like in the initial stage of casting of the ingots. In other words, there are low-level casting that lowers the level in the mold and casting, and a casting method that reduces the casting speed. However, in these methods, there is a risk that hot water leaks. Furthermore, there is a method of reducing the amount of cooling water, but there is a limit to the adjustment of the cooling rate. Therefore, it is difficult to prevent defects such as cracks in the initial stage of casting by any method depending on the type.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems in the prior art, and uses an aluminum alloy which can reliably prevent cracking defects at an early stage of casting by a simple method without using complicated equipment. An object of the present invention is to propose a vertical continuous casting method for billets.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention has been conceived by comparing the internal strain of a billet with an actually measured breaking strain in an initial stage of vertical continuous casting. . That is, the vertical continuous casting method of the aluminum alloy billet of the present invention, when continuously casting an aluminum alloy into a billet of a required shape, the equivalent plastic strain value (ε) obtained by elastic-plastic deformation analysis in the casting process, The measured fracture strain value (ε
c) The casting condition is controlled so as to fall within the following range. According to this, based on the equivalent plastic strain value (ε) obtained in advance by calculation, this is the measured breaking strain value.
By controlling the casting conditions such as the casting speed and the cooling speed so as to be not more than (εc), it is possible to reliably prevent crack defects at the initial stage. The equivalent plastic strain value
(ε) is the maximum equivalent plastic strain (calculated value) generated in each part of the billet during the solidification process, and the measured breaking strain value (εc) is
4 is a fracture strain (actually measured value) obtained by a high-temperature tensile test in a solid-liquid coexistence region and a solid phase region of the alloy.

According to another vertical continuous casting method of an aluminum alloy billet of the present invention, when an aluminum alloy is continuously cast into a billet having a required shape, an equivalent plastic strain value obtained by elasto-plastic deformation analysis in the casting process.
(ε) is the measured breaking strain value (εc) of the aluminum alloy except for a temperature range corresponding to a solid fraction of 0.8 or less of the alloy.
It is characterized in that casting conditions are controlled so as to fall within the following range.

According to this, in the cooling temperature range, in the temperature range where the solid fraction is 0.8 or less, the equivalent plastic strain value (ε) exceeds the measured breaking strain value (εc), and fine cracks due to deformation are generated. Even if it occurs, the residual molten metal penetrates into the crack and the crack can be healed. Therefore, the temperature range corresponding to the solid fraction of 0.8 or less is an exception, and in other temperature ranges, the equivalent plastic strain value (ε) is, as a rule, within the range of the measured breaking strain value (εc) or less. To control the casting conditions. This makes it possible to reliably and precisely prevent cracking defects in the initial stage of vertical continuous casting of an aluminum alloy billet.

In the continuous casting, the product of the casting speed (V) and the number of bios (Bi), which are the casting conditions, is used as a cooling parameter, and the cooling parameter value is set to 0.0055 m / s or less. Includes the method of vertical continuous casting of aluminum alloy billets. The Biot number (Bi) is an index indicating the resistance to heat flow in a solid and a fluid, and indicates the surface of the billet and the primary cooling medium, the secondary cooling medium, and / or the tertiary cooling medium. Is the value (h × R / κ) obtained by dividing the product of the overall heat transfer coefficient (h) and the radius (R) of the billet by the thermal conductivity (κ) of the aluminum alloy. As described above, by appropriately selecting the cooling parameter, vertical continuous casting can be reliably performed while maintaining the equivalent plastic strain value (ε) within the range of the measured breaking strain value (εc) or less. Can be cast reliably without any aluminum alloy billets.

As a specific embodiment of the present invention, in particular, a primary cooling medium composed of a cylindrical shaped forced cooling mold for pouring a molten aluminum alloy during the continuous casting, Using the arranged ring-shaped wiper,
From the nozzle at the lower end of the inner peripheral surface of the primary cooling medium, a secondary cooling medium that cools the peripheral surface of the billet is jetted, and the secondary cooling medium is below the secondary cooling medium by the wiper. And a method of vertically casting an aluminum alloy billet, wherein a third cooling medium is sprayed on the peripheral surface of the billet hanging down from the primary cooling medium and the wiper. According to this multi-stage cooling casting method, the equivalent plastic strain inside the billet can be alleviated, so even when casting at a casting speed where cracks occur without a wiper or when casting a large diameter billet, aluminum alloy is used. Crack defects at the initial stage of the vertical continuous casting of the billet can be reliably prevented.

In addition, the billet has a diameter of 300 mm.
In the above case, the vertical dimension (L) of the secondary cooling zone should be 4
A vertical continuous casting method of an aluminum alloy billet having a diameter of 5 mm or less is included. According to this, since the equivalent plastic strain value (ε) of each part of the billet can be easily made smaller than the measured breaking strain value (εc), it is possible to reliably prevent the billet from cracking. In addition, the vertical dimension (L) of the secondary cooling zone means that the secondary cooling medium ejected from the lower end of the mold is from the upper end position hitting the billet surface to the lower end of the wiper (the upper end of the horizontal piece in the wiper). Refers to the distance.

[0012]

Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a general vertical continuous casting method of an aluminum alloy billet. As shown in the figure, a pouring cylinder 10 erected inside a forced cooling mold (primary cooling medium) 1 having a substantially cylindrical shape and a rectangular vertical cross section and a hollow structure, and a float guided by the pouring cylinder 10. The molten metal M of the aluminum alloy is cast via the shared flow plate 12. At the lower end of the inner peripheral surface of the mold 1, a slit-shaped nozzle 2 is formed obliquely downward and the peripheral surface of the ingot C is cooled by cooling water W (secondary cooling medium) sprayed from the nozzle. The molten metal M is cooled by the mold 1 and the cooling water W,
Through the solidification interface F, the ingot C is formed. The ingot C is lowered below the mold 1 by lowering the lower mold 4 previously inserted into the mold 1 together with the elevating shaft 5 to form a billet B.

FIG. 2 shows a state in which a wiper 3 having a ring shape and a substantially L-shaped cross section in a plan view is disposed below the mold 1, and a drain hole 3a for cooling water W is formed outside the wiper 3. ing. By using the wiper 3, the cooling water W as the secondary cooling medium is discharged to the outside, the cooling speed by the cooling water W is adjusted, and the lower surface of the cooling water W By spraying a (tertiary cooling medium), it is possible to perform multi-stage cooling casting for controlling the cooling rate of the ingot C. Therefore, distortion due to thermal stress in the ingot C can be reduced, and crack defects in the initial casting stage of the billet B can be reliably prevented. Symbol L in FIG.
Indicates the vertical dimension of the secondary cooling zone. Note that the secondary and tertiary cooling media are not limited to the above-described embodiment, and other media that can obtain appropriate cooling parameters and combinations thereof may be selected.

In the present invention, it is assumed that the casting apparatus shown in FIGS. 1 and 2 is used, and the equivalent plastic strain inside the billet B is analyzed by performing the heat of solidification and the thermal deformation stress analysis on the billet B to be cast. Calculate (ε). And
As a result of examining the transition of the distribution of the equivalent plastic strain (ε) inside the billet B, as will be described later, the crack defect of the billet B in the initial stage of casting is caused by the casting tip (lower end).
Found to occur from the center. The equivalent plastic strain value (ε) is the maximum equivalent plastic strain (calculated value) generated in each part of the billet B during the solidification process.

Based on the knowledge, the casting speed was changed, and the equivalent plastic strain (ε) corresponding to the distance from the tip and the breaking strain of the billet B having the alloy composition were determined at each part of the casting tip of the billet B. The measured value of (εc) was compared. As a result, it has been found that, in principle, when the equivalent plastic strain (ε) obtained in advance by analysis is smaller than the measured breaking strain (εc), no crack defect occurs. The measured breaking strain value
(εc) is a breaking strain (actually measured value) obtained by a tensile test in a temperature range from 400 ° C. to a total solid-liquid coexistence region. Further, in the range where the solid phase ratio is low in the aluminum alloy, that is, in the range where the solid phase ratio is 0.8 or less, since the molten metal M remains to some extent, the equivalent plastic strain (ε) is larger than the measured breaking strain (εc). However, it was also found that cracking hardly occurred. This is because the remaining molten metal M penetrates into fine cracks generated by thermal deformation, thereby repairing the cracks.

The above-mentioned appropriate range is set so that the cooling parameter, which is the product of the casting speed (V) of the aluminum alloy and the bio number (Bi), which is the casting condition, is 0.0055 m / s or less. It is determined by controlling the conditions.
The Biot number (Bi) is an index indicating the resistance to heat flow in a solid and a fluid, and indicates the surface of the billet and the primary cooling medium.
Overall heat transfer coefficient between (mold 1), secondary cooling medium (cooling water W), and / or tertiary cooling medium (air a)
This is a value (h × R / κ) obtained by dividing the product of (h) and the radius (R) of the billet by the thermal conductivity (κ) of the alloy. Therefore, in order to obtain the overall heat transfer coefficient (h) in which the cooling parameter is 0.0055 m / s or less, the type of the primary cooling medium, the secondary cooling medium, and / or the tertiary cooling medium, By selecting and calculating a combination of flow rates in advance, it is possible to easily set appropriate billet casting conditions.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described. First, a solidification heat analysis was performed on a billet B of 6000 series aluminum alloy having a diameter of 325 mm obtained by the vertical continuous casting apparatus shown in FIG. The internal equivalent plastic strain (ε) was calculated by thermal deformation stress analysis.

The heat of solidification analysis was an axially symmetric model which was assumed to be geometrically and thermally symmetrical with respect to 600 mm from the casting tip of the billet B. The analysis area includes the metal of the billet B (the molten metal M + the ingot C), the mold 1, and the lower mold 4, and is 165 mm in the radial direction of the billet B.
It was set to 675 mm in the axial direction, and equally divided at 5 mm intervals in both directions. Further, as an analysis method, an unsteady heat conduction analysis in a solidification process of the ingot C was performed by a direct difference outer node method. The latent heat of solidification of the alloy was measured using a differential scanning calorimeter (DSC) in a range from room temperature to 720 ° C. The thermal conductivity was measured at room temperature using the laser flash method.
The test was performed at 300 ° C. and 600 ° C. Table 1 shows the physical property values of the billet B, the mold 1, and the lower mold 4 used in the solidification analysis.

The solid fraction was calculated from the relationship between the solid fraction and the temperature by the method proposed by the inventors. This was measured by using an adiabatic specific heat measurement device (manufactured by Vacuum Riko Co., Ltd.) from room temperature to 97
In this method, the specific heat up to 3 K is continuously measured, and the solid fraction is determined from the specific heat-temperature curve in the measured solid-liquid coexistence region. In this case, the solid fraction (fs) at a certain temperature is obtained by dividing the amount of heat absorbed (Si) when passing through that temperature by the total absorbed heat (Sto).
tal). FIG. 3 shows an example of the relationship between the solid fraction and the temperature of an aluminum alloy calculated from the specific heat-temperature curve. That is, the amount of heat indicated by hatching in FIG.
(Si) and total absorbed heat (Stotal), and (Note) in FIG.
The calculation formulas (* ¹ , * ² ) are shown in parentheses.

[0020]

[Table 1]

Next, a thermal deformation stress analysis was performed. The objects of this are also a metal (melt M + ingot C), a mold 1, and a lower mold 4, but the mold 1 and the lower mold 4 are assumed to be rigid bodies and do not consider thermal deformation. The analysis target was a casting length of 300 mm from the casting tip of the billet B, assumed to be geometrically and mechanically axisymmetric, and a two-dimensional axisymmetric elasto-plastic model was used. The analysis code is a finite element method general-purpose analysis program “A
NSYS Ver 5.4 ", the metal region was a two-dimensional structural solid (PLANE42) as an element, and the mold 1 and the lower mold 4 were two-dimensional points (CONTACT 12).

FIG. 4 shows the distribution of equivalent plastic strain (ε) inside billet B calculated by elasto-plastic analysis based on each of the above analyses.
Shown in As shown in FIG.
In the range up to mm, the equivalent plastic strain (ε) is maximum near the surface layer (peripheral surface) of the billet B1. FIG.
As shown in (B) and (C), the largest part of the equivalent plastic strain (ε) is caused by the solidification shrinkage of the molten metal M with the increase in the casting length.
The billet moves to the center of the billets B2 and B3. In particular, when the casting length is 200 mm, 40 mm from the casting tip
The value of the equivalent plastic strain (ε) became the maximum at the position of the center of 70 mm.

This is because the quenching of the cooling water W from the mold 1 increases the temperature between the surface layer and the center of the billet B, so that the difference in rigidity between the surface layer and the center also increases. This is because a large tensile strain was generated in the center as a result of the solidification shrinkage being inhibited in the surface layer. Further, as shown in FIGS. 4B and 4C, billets B2 and
Regardless of the casting length of B3, the maximum part of the equivalent plastic strain (ε) is generated within a range of about 40 to 70 mm from the casting tip. Thereby, the crack of billet B is
It can be seen that there is a high danger generated from the center of the casting tip.

Next, as shown in FIG.
Casting speed using the casting device and the aluminum alloy
(V) was set to 42 mm / min, the calculated value of the equivalent plastic strain (ε) at each position 30 to 120 mm from the casting tip in the center of the billet B, and the breaking strain (εc) of the billet B obtained by the tensile test Are shown in a graph of the temperature history at the time of casting. As shown in this graph, the equivalent plastic strain (ε) calculated in the above analysis was smaller than the breaking strain (εc) at each position. Therefore, it can be predicted that the billet B cast at the above casting speed does not crack.

Further, as shown in FIG. 5 (B), under the same conditions as above and at a casting speed (V) of 50 mm / min, the calculated value of the equivalent plastic strain (ε) at the same position of the billet B as described above was obtained. The change in breaking strain (εc) was plotted as a graph. As shown in the graph of FIG.
Equivalent plastic strain (ε) at the position of
° C, at 614 ° C, it became larger than the breaking strain (εc), but at other temperatures and other positions, the equivalent plastic strain
(ε) were all smaller than the breaking strain (εc). By the way, cracks should be originally generated at the 50 and 100 mm positions where the equivalent plastic strain (ε) is larger than the breaking strain (εc). However, in actual casting, the casting speed is 50 m
No crack was observed in the billet B obtained at m / min.

The temperature range in which the above-mentioned equivalent plastic strain (ε) became larger than the breaking strain (εc) occurred when the solid fraction was 0.8.
(Specifically, 612 ° C. to 620 ° C.). For this reason, even if fine cracks occur in the billet B due to deformation, the solid fraction is low in the above-mentioned temperature range, and the remaining molten metal M exists to some extent, so that the molten metal M enters the cracks. The crack has been repaired. In other words, in the temperature range where the solid fraction is 0.8 or less, even if the equivalent plastic strain (ε) becomes larger than the breaking strain (εc), the crack can be repaired. However, in the temperature range below this, it is possible to reliably prevent the crack defect of the billet B by selecting the casting speed and the like so that, in principle, the equivalent plastic strain (ε) becomes smaller than the breaking strain (εc). It becomes possible.

Further, as shown in FIG. 6, under the same conditions as above and at a casting speed (V) of 55 mm / min, the calculated value of the equivalent plastic strain (ε) at the same position of the billet B as
The change in breaking strain (εc) of billet B was plotted as a graph. As shown in the graph of FIG.
The equivalent plastic strain (ε) at the position of 0,100 mm was larger than the breaking strain (εc) at 615 ° C., 614 ° C., 594 ° C., and 613 ° C., respectively, but was significant at other temperatures and other positions. All plastic strains (ε)
It was smaller than c).

Now, the equivalent plastic strain is larger than the breaking strain (εc).
At the temperatures at the above-mentioned 30, 50, and 100 mm positions where (ε) has increased, since the solid fraction is 0.8 or less, it can be predicted that cracks originally occurring can be cured. On the other hand, 7
In the temperature range where the equivalent plastic strain (ε) at the position of 0 mm becomes larger than the breaking strain (εc), the corresponding solid phase ratio is as high as 0.88, so that it can be predicted that the crack cannot be cured. Then, in actual casting, a crack defect was observed in the vicinity of the above position of the billet B obtained at a casting speed of 55 mm / min, confirming the accuracy of the prediction. Further, as a result of observing the fracture surface of the billet B having cracks, it was found that the cracks occurred in the solid-liquid coexistence region, which was as predicted above.

FIG. 7 is a graph showing a case where a cooling parameter, which is a product of a casting speed (V) and a bio number (Bi), which is a casting condition, is changed when the casting apparatus of FIG. 1 and the aluminum alloy are used. 7 is a graph showing a change in the ratio (ε / εc) between the equivalent plastic strain (ε) and the measured breaking strain (εc) at the center of the billet B. The Biot number (Bi) is an index indicating resistance to heat flow in a solid and a fluid, and is a value between the billet surface and the primary cooling medium, the secondary cooling medium, and / or the tertiary cooling medium. Heat transfer coefficient (h) and billet radius in the field
(R) divided by the thermal conductivity (κ) of the alloy (h ×
R / κ).

As shown in the graph of FIG. 7, as the cooling parameter (V × Bi) increases, the ratio (ε / εc) also increases. And a cooling parameter with a ratio (ε / εc) of 1
(V × Bi) is 0.0055 m shown by a broken line in the above graph.
/ S. Therefore, the parameter (V × Bi) is set to 0.
By controlling the conditions such as the casting speed so as to be 0055 m / s or less, it is possible to reliably prevent the crack defect of the billet B of the aluminum alloy in the vertical continuous casting method. In addition, using the casting apparatus of FIG. 1 and the aluminum alloy, including the respective graphs shown in FIGS. 5 (A), (B) and FIG. 6, the casting speed (V) and the cooling parameter (V × Bi) were changed. Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 2.
The results in Table 2 also support the relationship between the casting speed (V) and the crack described above, and the relationship between the cooling parameter (V × Bi) and the crack described above.

[0031]

[Table 2]

Using a casting apparatus having the wiper 3 shown in FIG. 2 and the same aluminum alloy as above, the vertical dimension L of the secondary cooling zone (the cooling water W as a secondary cooling medium ejected from the lower end of the mold 1) (A distance from the upper end position of the wiper 3 to the upper end of the horizontal piece of the wiper B) and the cooling parameter (V × Bi) were changed to perform a multi-stage cooling casting method. FIGS. 8 to 10 show that in the casting method, 20 to 140 from the casting tip at the center of the billet B.
The graph shows the calculated value of the equivalent plastic strain (ε) at each position of mm and the temperature history at the time of casting of the breaking strain (εc) of the actually cast billet B.

As shown in the graph of FIG.
Even at 5 mm / min, in the slow cooling continuous casting method in which the vertical dimension L of the secondary cooling zone is 30 mm, the equivalent plastic strain (ε) becomes smaller than the breaking strain (εc) at each position, and the cooling parameter 0.0005m / s at 0.0051m / s
s. The billet B actually cast under the same conditions as above did not crack. That is, if the vertical dimension L (wipe-off position) of the secondary cooling zone is 30 mm, rapid cooling by the cooling water W from the mold 1 is alleviated, and the equivalent plastic strain (ε) at the center of the billet B is reduced by the breaking strain. Since it was much smaller than (εc), it did not break.

On the other hand, as shown in the graph of FIG. 9, the casting speed is 55 mm / min, and the vertical dimension L of the secondary cooling zone is 45 mm.
mm, the cooling parameter (V
× Bi) becomes 0.0054 m / s, and the equivalent plastic strain (ε)
All became smaller than the breaking strain (εc) at each position of 30 mm to 140 mm from the casting tip. Moreover, the billet B actually cast under the same conditions as above did not crack. This is because when the vertical dimension L of the wiper 3 is 45 mm, the quenching by the cooling water W is considerably suppressed, so that even if the equivalent plastic strain (ε) at the center of the billet B becomes larger than the breaking strain (εc), it does not crack. It is.

Further, as shown in the graph of FIG. 10, the casting speed was 55 mm / min, and the vertical dimension L of the secondary cooling zone was 5 mm.
In the continuous casting method with a low cooling of 0 mm, the cooling parameter
(V × Bi) becomes 0.0061 m / s and the equivalent plastic strain
(ε) became larger than the breaking strain (εc) at 120 mm and 140 mm from the casting tip. Further, the billet B actually cast under the same conditions as above had cracks. This is because when the vertical dimension L is 50 mm, the quenching by the cooling water W is not so much eased, so that the equivalent plastic strain (ε) at the center of the billet B becomes larger than the breaking strain (εc), and the billet B is broken. As described above, even in the billet B cast at the same casting speed of 55 mm / min as in the case of the graph of FIG. 6, the billet B is controlled by controlling the cooling parameter by adjusting the longitudinal dimension L of the secondary cooling zone. It can be seen that cracks can be prevented from occurring. The longitudinal dimension L of the secondary cooling zone for preventing cracking depends on the size of the billet B, but when using the cooling water W as the secondary cooling medium for the billet B having a diameter of 300 mm or more, 45 mm It is desirable to make the following.

It should be noted that the vertical continuous casting method of the present invention can be applied to the case where an aluminum alloy other than the above alloys, such as 6000 series or 7000 series, is applied by actually measuring the strain at break in a high temperature tensile test. . If the cooling parameter value is set within the range of 0.0055 m / s or less, the casting speed (V) constituting the cooling parameter value can be appropriately changed after the start of casting. For example, even when the diameter of the billet B, the casting speed (V), the amount of cooling water, or the like is changed, casting cracks can be prevented by setting the cooling parameter within the above range.

[0037]

As described above, according to the vertical continuous casting method of the present invention, the equivalent plastic strain value (ε) obtained in advance by the calculation based on the measured breaking strain value (εc) is used. By controlling the casting conditions such as the casting speed and the cooling speed within a range not exceeding the value (εc), it is possible to reliably prevent the billet crack defect in the initial stage, which is the main cause of the crack. Therefore, not only existing aluminum alloys but also developed aluminum alloys for various applications can be efficiently subjected to vertical continuous casting as crack-free billets.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a vertical continuous casting method of the present invention.

FIG. 2 is a schematic sectional view showing a vertical continuous casting method of a different form.

FIG. 3 is a graph showing a specific heat-temperature curve of a certain aluminum alloy.

FIGS. 4A to 4C are schematic cross-sectional views showing distribution of equivalent plastic strain inside a billet for each casting length.

5 (A) and 5 (B) show the temperature at the time of casting of the equivalent plastic strain and the measured breaking strain at each position in the center of the billet when the casting speed was changed using the casting apparatus of FIG. Graph showing history.

FIG. 6 is a graph showing the temperature history during casting of the equivalent plastic strain and the measured breaking strain at each position of the billet center at a casting speed different from that of FIG. 5;

FIG. 7 is a graph showing a relationship between a cooling parameter and a ratio of equivalent plastic strain and measured breaking strain.

8 is a graph showing the temperature history after casting of the equivalent plastic strain and the measured breaking strain at each position in the center of the billet when the casting device of FIG. 2 is used and the vertical dimension of the secondary cooling zone is specified. .

9 shows a case where the equivalent plastic strain and the measured breaking strain at each position of the billet center portion after casting are obtained when the casting device of FIG. 2 is used and the vertical dimension of the secondary cooling zone is increased with respect to FIG. 4 is a graph showing a temperature history.

FIG. 10 shows the relationship between the equivalent plastic strain and the measured breaking strain at each position of the billet center when the casting apparatus of FIG. 2 is used and the vertical dimension of the secondary cooling zone is increased with respect to FIGS. 4 is a graph showing a temperature history after casting.

FIG. 11 is a schematic sectional view showing a conventional vertical continuous casting method.

[Explanation of symbols]

 1 ... forced cooling mold (primary cooling medium) 2 ... nozzle 3 ... wiper B, B1, B2, B3 ... billet W ... …… Cooling water (secondary cooling medium) a ……………… Air (third cooling medium) L ………………………… Vertical dimension of secondary cooling zone

Claims (5)

[Claims] When an aluminum alloy is continuously cast into a billet having a required shape, an equivalent plastic strain value (ε) obtained by elasto-plastic deformation analysis in the casting process is measured by a measured fracture strain value (εc) of the aluminum alloy. A vertical continuous casting method for an aluminum alloy billet, wherein casting conditions are controlled to fall within the following range. 2. An equivalent plastic strain value (ε) obtained by elasto-plastic deformation analysis in the casting process when continuously casting an aluminum alloy into a billet having a required shape is reduced to a solid fraction of 0.8 or less of the alloy. A method for vertically casting an aluminum alloy billet, wherein the casting conditions are controlled so as to fall within a range of not more than a measured breaking strain value (εc) of the aluminum alloy except for a corresponding temperature range. 3. The continuous casting, wherein the product of the casting speed (V) and the number of bios (Bi), which are the casting conditions, is used as a cooling parameter, and the cooling parameter value is set to 0.0055 m / s or less. The vertical continuous casting method of an aluminum alloy billet according to claim 1 or 2, wherein: The above bio number
(Bi) is an index indicating the resistance to heat flow in solids and fluids, and is the product of the overall heat transfer coefficient (h) between the billet surface and the cooling medium and the radius (R) of the billet, It is a value (h × R / κ) divided by the thermal conductivity (κ) of the alloy. 4. A continuous cooling medium comprising a cylindrical forced cooling mold for pouring molten aluminum alloy and a ring-shaped wiper disposed below the medium during the continuous casting. From the nozzle at the lower end of the inner peripheral surface of the primary cooling medium, a secondary cooling medium for cooling the peripheral surface of the billet is jetted, and the secondary cooling is performed by the wiper below the secondary cooling medium. The medium according to any one of claims 1 to 3, wherein the medium is discharged to the outside, and a tertiary cooling medium is sprayed on a peripheral surface of the billet hanging downward from the primary cooling medium and the wiper. Vertical continuous casting method for aluminum alloy billet. 5. The aluminum alloy billet according to claim 4, wherein when the billet has a diameter of 300 mm or more, the vertical dimension (L) of the secondary cooling zone is 45 mm or less. Continuous casting method.