JP2003340553A - Continuous casting method for magnesium alloy sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a continuous casting method for a magnesium alloy sheet capable of omitting a hot-rolling process and providing the sheet with an excellent mechanical characteristic, the flatness and the like. <P>SOLUTION: The continuous casting method comprises the step of (1) the reducing the thickness of a cast slab containing unsolidified molten metal 2 using a mold 1a whose thickness is reduced gradually in the casting direction, (2) continuous casting method comprises the step of reducing the thickness of the cast slab containing the unsolidified molten metal using a pair of reduction rolls arranged right below the mold, or (3) the continuous casting method comprises the step of casting a plurality of sheets using a mold formed by disposing one or more partition blocks whose thickness is increased in the casting direction in the vicinity of the center part of the thickness inside the mold with intervals over the whole width of the mold. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously casting a magnesium alloy sheet, and more specifically, a sheet as a product by omitting a hot rolling step (hereinafter referred to as "hot rolling step") following the continuous casting step. The present invention relates to a continuous casting method for a magnesium alloy thin plate capable of providing a thin plate which is a material for finish rolling (hereinafter, simply referred to as "raw material for rolling") for obtaining.

[0002]

2. Description of the Related Art Magnesium alloy has a specific gravity of about 2/3 that of aluminum alloy, is the lightest among practical metals, and has a considerable strength, so it is used for aircraft parts, automobile parts, etc. There is.

[0003] A magnesium alloy product sheet is usually obtained by hot rolling a billet, a bloom, a slab or the like obtained by a magnesium alloy ingot or continuous casting, followed by cold rolling (hereinafter referred to as "cold rolling"). Also referred to as “”. Since there is a time interval between the production of the ingot or the slab and the hot rolling (hereinafter, also referred to as “hot rolling”), the temperature of the ingot or the slab falls to around room temperature. Therefore, it is necessary to heat the temperature of the ingot or the slab from around room temperature to the temperature required for hot rolling (about 300 to 400 ° C.), which requires a large amount of energy for heating. Manufacturing cost is high.

If a slab having a thickness capable of cold rolling is directly produced by a single roll method or a twin roll method, the hot rolling step can be omitted. However, even if a thin plate as a material for rolling is obtained by cold rolling the slab produced in this way,
Since it is impossible to increase the reduction ratio, it is difficult to reduce the crystal grain size of the thin plate as a rolling material, which is closely related to the mechanical properties of the product thin plate. for that reason,
The product sheet obtained by using the single roll method or the twin roll method, etc., as is conventionally done, after heating the ingot or slab at room temperature, hot rolling, and then cold rolling. The mechanical properties such as ductility and tensile strength are inferior to the manufactured product sheet.

Further, since the slabs produced by the single roll method or the twin roll method are thin, fluctuations in the amount of hot water supplied during casting,
The thickness of the roll varies greatly depending on the scale attached to the roll and the cooling spots caused by dirt. Even if the thickness of the obtained slab is thin, its effect is large, and even if such a slab is cold-rolled to obtain a thin plate as a material for rolling, and further a product thin plate, the flatness of the product thin plate is Will be reduced.

As described above, in producing a magnesium alloy product thin plate, at present, an ingot or a slab is heated with a great deal of energy to heat up and then hot rolled, or the mechanical properties and There is no choice but to produce a slab having a thickness capable of being cold-rolled by a single roll method or a twin roll method at the expense of flatness.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the prior art, and the object thereof is to omit the hot rolling process and to provide mechanical characteristics. Another object of the present invention is to provide a continuous casting method of a magnesium alloy thin plate having excellent surface properties such as flatness and flatness.

[0008]

In order to solve the above-mentioned problems, the inventors of the present invention conducted continuous casting of magnesium alloy thin plates under various conditions, and conducted repeated studies. As a result, in the continuous casting process, whether the slab is in a high temperature state, and the slab is drawn in the state where unsolidified molten metal exists, or whether it is rolled by using a pair of rolls arranged immediately below the mold. It was also found that a slab having a thickness capable of cold rolling can be obtained by arranging a partition block in the mold and dividing the molten metal. As a result, it is possible to obtain a magnesium alloy thin plate that omits the hot rolling process that is usually performed and that has excellent surface properties such as mechanical properties and flatness.

The present invention was made on the basis of the above findings, and its gist resides in the continuous casting method for magnesium alloy thin plates described in (1) to (3) below.

(1) A continuous casting method in which the thickness of a slab containing unsolidified molten metal is reduced by using a mold in which the thickness of the mold is gradually reduced in the casting direction. A continuous casting method for a magnesium alloy thin plate, wherein the solid fraction of the thickness center of the slab is less than 1.

(2) A continuous casting method for reducing the thickness of a cast piece containing unsolidified molten metal by using a pair of reduction rolls installed just below the mold, and a roll shaft of the reduction roll pair. A continuous casting method for a magnesium alloy thin plate, wherein a solid phase ratio of a thickness center portion of a cast slab after reduction in a line connecting cores is less than 1.

(3) One or more partition blocks, whose thickness gradually increases in the casting direction, are provided in the vicinity of the center of the thickness in the mold and are arranged over the entire width of the mold. The top end of the partition block is placed in the molten metal. A continuous casting method of a magnesium alloy thin plate in which a plurality of thin plates are obtained by using a mold positioned below the partition block near the lower end of the mold.

The term "magnesium alloy" as used herein includes not only magnesium alloys prepared by adding alloy elements such as aluminum and zinc to magnesium, but also pure metals such as pure magnesium. The "magnesium alloy thin plate" is a thin plate as a rolling material (finish rolling material) for obtaining a magnesium alloy product thin plate, as described above.

The above-mentioned "thickness of the mold" means the thickness direction of the cast piece (that is, the cast piece obtained by this mold) among the inner dimensions (dimension of the molten metal containing portion) that define the shape of the mold. Is the length (distance) in the direction corresponding to. Hereinafter, it is also simply referred to as “mold thickness”.

The term "solid fraction in the central portion of the thickness of the slab" means the proportion of solid phase in the unit volume of the central portion. For example, it can be determined from the content determined from the calculation of solute redistribution during solidification, and the relationship between the content determined from thermodynamic calculation and the solid fraction.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION A continuous casting method for a magnesium alloy sheet according to the present invention (the continuous casting method described in (1), (2) or (3) above) will be specifically described below with reference to the drawings. explain.

FIG. 1 is a schematic diagram for explaining the continuous casting method of the present invention, which is a vertical cross-sectional view of an example of the mold used in carrying out the continuous casting method described in (1) above. is there.

As shown in FIG. 1, the mold 1a used in this continuous casting method is a mold whose thickness gradually decreases in the casting direction, that is, the thickness of the lower end of the mold 1a corresponding to the thickness of the cast piece. Is a mold that is narrower than the upper end of the mold 1a. The portion (starting point) where the thickness of the mold 1a starts to gradually decrease does not necessarily have to be the upper end portion of the mold 1a. In this example, the starting point is a portion that is lowered from the upper end of the mold by about ⅔ of the length of the mold, and the mold thickness gradually decreases from there to the lower end of the mold.

A molten magnesium alloy 2 is supplied from a dipping nozzle 3 into the continuous casting mold 1a, and a solidified shell 7 is formed near the wall surface of the mold 1a. In this example, a heater 4 for heating the mold is provided over the entire circumference in the mold 1a where the thickness of the mold 1a starts to gradually decrease and in the vicinity of the lower end of the mold 1a.
Is installed, and a thermocouple 5 for temperature control is installed. In addition, a lubricating oil supply hole 6 for supplying lubricating oil is provided in a portion where the thickness of the mold 1a is gradually decreasing. The boundary line between the molten metal 2 and the solidified shell 7 indicates the interface with a solid phase ratio of 1.

Using the continuous casting mold 1a configured as described above, the slab is pulled out downward (in the direction shown by the white arrow in the figure) in the state where the slab has a high temperature and the unsolidified molten metal exists. By reducing the thickness of the slab, that is, by subjecting the slab to drawing, it is possible to obtain a slab having a thickness that enables cold rolling.

At this time, the solid phase ratio (hereinafter referred to as "central solid phase ratio") at the center of the thickness of the cast piece at the mold outlet (that is, the opening provided at the lower end of the mold 1a) is less than 1. To do. If the slab contains unsolidified molten metal at the part where the thickness of the slab is reduced by drawing, the slab can be drawn out without any problem, and a slab with a thickness capable of cold rolling can be obtained. Is.

FIG. 2 is a schematic view for explaining the continuous casting method of the present invention, and is a longitudinal cross-sectional view of an example of the mold used when the continuous casting method described in (2) above is carried out. Is.

As shown in FIG. 2, the mold 1b used in this continuous casting method has a constant thickness from the upper end to the lower end thereof, and a pair of reduction rolls 8 is provided just below the mold 1b. is set up. Further, in this example, a heat retaining cover 9 for retaining the temperature of the slab is attached between the lower end of the mold 1b and the pair of reduction rolls 8. Incidentally, "just below the mold 1b"
Means just below the template 1b or slightly below it.
For example, a gap is generated between the pressing roll pair 8 due to a restriction on the equipment when the rolling roll pair 8 is installed, and the heat insulating cover 9 as illustrated.
Since it may be attached, such a case is also included in “directly below”.

A molten magnesium alloy 2 is supplied from a dipping nozzle 3 into the continuous casting mold 1b thus constructed, and a solidified shell 7 is formed near the wall surface of the mold 1b. Then, a rolling roll pair 8 in which a slab in a high temperature state containing unsolidified molten metal coming out of the mold 1b is installed immediately below the mold 1b.
By rolling. This reduces the thickness of the slab,
After that, the slab can be obtained by pulling the slab downward (in the direction indicated by the white arrow in the figure) to a thickness that allows cold rolling. Instead of the reduction by the reduction roll pair 8, the thickness of the cast piece may be reduced by forging pressure using a reduction jig so that the thickness can be cold rolled.

During rolling with the rolling roll pair 8, the center solid of the cast slab after rolling at the height level represented by the line connecting the roll axes of the rolling roll pair 8, that is, the imaginary line. The phase ratio is less than 1. As in the case of the continuous casting method described in (1) above, if unsmelted molten metal is contained in the slab at a site where the thickness of the slab decreases due to the reduction, an excessive load is applied to the reduction roll pair 8. This is because the slab can be pulled out without causing any damage and a slab with a thickness that enables cold rolling can be obtained.

FIG. 3 is a schematic view for explaining the continuous casting method of the present invention as well, and is a vertical cross-sectional view of an example of a mold used for carrying out the continuous casting method described in (3) above. Is.

As shown in FIG. 3, the mold 1c used in this continuous casting method has a partition block 10 in which the thickness gradually increases in the casting direction, in the vicinity of the center of the mold thickness in the mold 1c. . The partition block 10 is arranged over the entire width of the mold 1c, its upper end is located in the molten metal 2 and its lower part is located near the lower end of the mold 1c. Further, in this example, in order to prevent skinning of the surface of the molten metal in the mold 1c, a heater 11 is installed on the entire circumference in the vicinity of the meniscus in the mold 1c, and a thermocouple 12 for temperature control is installed.

There is no particular restriction on the shape of the partition block, and the thickness of the lower end portion is appropriately adjusted so that a slab having a thickness capable of cold rolling can be obtained. Further, although the partition block 10 is one in the example shown in FIG. 3, it may be two or more. In that case, the plurality of partition blocks are arranged at intervals in the vicinity of the center of the mold thickness so that a slab having a thickness capable of cold rolling can be obtained. In addition,
The range of "the vicinity of the central portion" varies depending on the number of partition blocks installed. When the number of installed partition blocks is 1, the range is narrow and becomes substantially the center of the mold thickness, but it increases as the number of installed blocks increases. When the number of molds is two, it means a range corresponding to the central part of the mold thickness divided into three equal parts.

The molten magnesium alloy 2 is supplied from the dipping nozzle 3 into the continuous casting mold 1c thus constructed, and the solidified shell 7 is formed near the wall surface of the mold 1c. At this time, the starting point of the formation of the solidified shell 7 near the wall surface of the mold 1c is the partition block 10 installed in the mold 1c.
The molten metal 2 is heated by the heater 11 installed in the mold 1c so that the height level is almost the same as the starting point of the formation of the solidified shell 7 in the vicinity of the surface. Then, when the cast piece is pulled out downward (in the direction shown by the white arrow in the figure), the molten metal is divided by the partition block 10 arranged in the mold 1c, so that the two cast pieces are drawn as shown in the figure. Pieces are obtained, and the thickness of each cast piece is such that cold rolling is possible.

By using this mold, a plurality of raw materials for rolling can be obtained at the same time with one mold, and a slab having a thickness capable of cold rolling can be efficiently manufactured.

The slabs obtained by the continuous casting method described in (1), (2) or (3) above all have a thickness that allows cold rolling, so the next hot rolling step is omitted. It is possible to achieve energy saving. Moreover, in the continuous casting method described in (1) or (2), a high reduction ratio is secured by drawing a slab having a high temperature and having a thickness, or by rolling with a pair of reduction rolls arranged immediately below the mold. It is possible to make the crystal grains finer. Further, since there is no decrease in flatness as in the case of cold rolling a slab manufactured by the conventional single roll method or twin roll method, a magnesium alloy thin plate excellent in mechanical properties and surface properties can be obtained. . The slab obtained by the continuous casting method described in (3) has excellent surface properties such as flatness and the degree of drawing is lower than that in the continuous casting method described in (1). However, since the thickness of the partition block is gradually increased in the casting direction, the partition block is subjected to the drawing process, and the mechanical characteristics are secured. Hereinafter, the effects of the present invention will be specifically described with reference to Examples.

[0032]

EXAMPLES Example 1 A magnesium alloy thin plate was produced by the continuous casting method of the present invention (the method described in (1) above) using the mold having the structure shown in FIG. The experimental conditions were the following ah. The applied voltage of the heater 4 for heating the mold was controlled so that the temperature of the thermocouple 5 was 100 to 400 ° C.

A. Magnesium alloy: Mg-3% Al-1% Zn (melting point 632
C.) b. Pouring temperature: 750 ° C c. Mold material: SUS430 d. Mold size (inner size): width 700 mm x length 200 mm The mold thickness gradually decreases from the upper end of the mold to the lower end 150 mm below the upper end, and the thickness of the upper end is 100 m
m, the thickness of the lower end is 20 mm e. Extraction speed: 0.5m / min f. Mold vibration condition: Vibration frequency 2.5Hz, sine wave vibration of stroke 3mm g. Heater specifications: 1000W, 200V h. Lubricating Oil: Molybdenum Disulfide For comparison, the above-mentioned magnesium alloy slab was manufactured by the conventional continuous casting method using the mold shown in FIG. This mold 1d has a width of 700 mm and a length of 200 mm, and has a constant thickness (100 mm) from its upper end to its lower end,
Molten magnesium alloy 2 is immersed in this mold 1d Nozzle 3
When it is supplied through the mold, the solidified shell 7 is formed in the vicinity of the wall surface of the mold 1d, and the solidified shell 7 is formed downward (in the direction indicated by the white arrow in the figure).
By pulling out to, a slab having a thickness corresponding to the thickness of the lower end of the mold 1d can be obtained.

As a result of the above casting experiment, a magnesium alloy thin plate (rolling material) having a thickness capable of omitting hot rolling was obtained by the continuous casting method of the present invention. Moreover, this magnesium alloy thin plate was homogeneous without segregation (concentration) of alloy components in the casting direction. On the other hand, since the slab obtained by the conventional continuous casting method is thick, it was necessary to go through the same hot rolling step as usual. Example 2 Using a mold having the configuration shown in FIG.
A magnesium alloy thin plate was manufactured by the continuous casting method of the present invention (the method described in (2) above). The experimental conditions were the following ah.

A. Magnesium alloy: Mg-3% Al-1% Zn (melting point 632
C.) b. Pouring temperature: 750 ° C c. Mold material: SUS430 d. Mold size (inner size): width 700 mm x length 200 mm x thickness 100 m
me. Extraction speed: 0.5m / min f. Mold vibration condition: Vibration frequency 2.5Hz, sine wave vibration of stroke 3mm g. External shape of the pressing roll: 200 mm h. Thickness of cast slab after reduction: 20 mm As a result of the above-mentioned casting experiment, as in the case of Example 1, the thickness was such that hot rolling could be omitted, and segregation of alloy components (concentration) in the casting direction was performed. ) -Free, homogeneous magnesium alloy sheet was obtained. Example 3 A magnesium alloy thin plate was produced by the continuous casting method of the present invention (method described in (3) above) using the mold having the partition block shown in FIG. The experimental conditions were the following a to i.

A. Magnesium alloy: Mg-3% Al-1% Zn (melting point 632
C.) b. Pouring temperature: 750 ° C c. Mold material: SUS430 d. Mold size (inner size): width 400mm x length 200mm, the thickness of the upper end is 20mm, the position of the upper tip of the partition block is 50mm below the upper end of the mold, and the lower end of each divided by it The thickness of the part is 5 mm e. Extraction speed: 0.5m / min f. Mold vibration condition: Vibration frequency 2.5Hz, sine wave vibration of stroke 3mm g. Heater capacity: 200V, 1000W h. Heater position: 100mm downward from the top of the mold
Position (below meniscus) i. Heater temperature: 650 ° C. As a result of the above casting experiment, it was possible to obtain a magnesium alloy thin plate having a thickness capable of omitting hot rolling.

[0037]

EFFECTS OF THE INVENTION According to the continuous casting method of the present invention, it is possible to manufacture a magnesium alloy thin plate which can omit the hot rolling step and has excellent mechanical properties and surface properties such as flatness.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of an example of a mold used in carrying out a continuous casting method of the present invention in a mold thickness direction.

FIG. 2 is a vertical cross-sectional view in the mold thickness direction of another example of the mold used when carrying out the continuous casting method of the present invention.

FIG. 3 is a vertical cross-sectional view of a mold used in carrying out the continuous casting method of the present invention in a mold thickness direction of yet another example.

FIG. 4 is a vertical cross-sectional view of an example of a mold used in carrying out a conventional continuous casting method in the mold thickness direction.

[Explanation of symbols]

1a, 1b, 1c, 1d: Continuous casting mold 2: Molten metal 3: Immersion nozzle 4: heater 5: Thermocouple 6: Lubricating oil supply hole 7: Solidified shell 8: Rolling roll pair 9: Thermal insulation cover 10: Partition block 11: heater 12: Thermocouple

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B22D 11/20 B22D 11/20 C (72) Inventor Toshihiko Murakami 4-5 Kitahama, Chuo-ku, Osaka-shi, Osaka No. 33 Sumitomo Metal Industries, Ltd.

Claims (3)

[Claims] 1. A continuous casting method for reducing the thickness of a slab containing an unsolidified molten metal by using a mold in which the thickness of the mold is gradually reduced in a casting direction, the casting after the thickness is reduced at a mold outlet. A continuous casting method for a magnesium alloy thin plate, characterized in that the solid phase ratio of the thickness center portion of the piece is less than 1. 2. A continuous casting method for reducing the thickness of a cast slab containing unsolidified molten metal by using a pair of reduction rolls installed directly below a mold, the roll axis of the pair of reduction rolls. A continuous casting method for a magnesium alloy thin plate, characterized in that the solid phase ratio of the thickness center portion of the cast slab on the line connecting the two is less than 1. 3. One or more partition blocks having a thickness gradually increasing in the casting direction are provided over the entire width of the mold at intervals in the vicinity of the center of the thickness in the mold, and the upper end of the partition block is located in the molten metal. Then, a lower part of the partition block is positioned near the lower end of the mold, and a plurality of thin plates are obtained by using the mold.