JP2012011464A - Nozzle for continuous casting, continuous casting method, and cast material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nozzle for continuous casting, which is configured so that molten metal hardly flows into a gap formed between the nozzle and a movable mold, and thus is perfect for providing a cast material excellent in surface quality.SOLUTION: The nozzle 1 for continuous casting for supplying a molten metal 10 of pure magnesium or magnesium alloy to the movable mold 20 for continuous casting includes: a nozzle body 2, and a coating layer 3 provided in a top end area extending from the top end surface of the nozzle body 2 to the outer periphery thereof on the movable mold 20 side. The coating layer 3 contains at least one substance selected from nitride, carbide and carbon as a main component. Thus, the wettability of the coating layer 3 to the molten metal 10 becomes lower than the wettability of the nozzle body 2 to the molten metal 10. The formation of the coating layer 3 with low wettability to the molten metal 10 can eliminate local turbulence of molten metal flow in the gap between the nozzle 1 and the movable mold 20, and solidification of the molten metal 10 therein can be thus prevented.

Description

  The present invention relates to a continuous casting nozzle suitable for use in continuous casting using a movable mold, a method for producing a cast material using the continuous casting nozzle, and a cast material obtained by the casting method. is there. In particular, the present invention relates to a continuous casting nozzle suitable for producing a cast material of pure magnesium or magnesium alloy.

  Conventionally, continuous casting is known in which a molten metal is supplied to a movable mold such as a roll or a belt, and the molten metal is cooled and solidified by contacting the molten mold to continuously produce a cast material. The molten metal is supplied to the movable mold through a nozzle. Examples of the casting nozzle include those described in Patent Documents 1 and 2. Patent Document 1 discloses a nozzle in which the tip of the nozzle has a three-layer structure of a good heat conduction layer, a low heat conduction layer, and a high strength elastic layer in order to reduce variations in the temperature of the molten metal in the width direction of the material during casting. Is disclosed. Patent Document 2 discloses a nozzle suitable for use when continuously casting pure magnesium or a magnesium alloy. Since magnesium is an active metal, in order to prevent the reaction between the molten magnesium and the nozzle forming material, when the nozzle body is made of an oxide material, the surface that comes into contact with the molten metal is made of a low oxygen material. A nozzle provided with a layer is described.

JP 2006-015361 A JP 2006-263784 A

  However, when the molten metal is supplied from the nozzle to the movable mold, a gap is formed between the nozzle and the movable mold at this supply location. This gap can be formed in an area surrounded by an extension line extending in the axial direction of the nozzle from the inner peripheral edge of the nozzle tip and the movable mold. The molten metal slightly flowing into the gap is cooled by the movable mold and solidifies in the gap, thereby locally disturbing the molten metal flow and causing the surface properties of the cast material to deteriorate. In addition, the molten metal that has become a solidified product is considered to be attached to a movable mold (for example, a roll) and cause a surface defect of the cast material.

  The present invention has been made in view of the above circumstances, and one of its purposes is optimal for obtaining a casting material in which the molten metal does not easily flow into the gap formed between the nozzle and the movable mold and has excellent surface quality. The object is to provide a nozzle for continuous casting. Another object of the present invention is to provide a casting material casting method using the continuous casting nozzle and a casting material obtained by the casting method.

  In the present invention, a layer made of a material having low wettability with respect to the molten metal is provided at the tip of the movable nozzle side of the casting nozzle so that the molten metal does not easily flow into the gap formed between the casting nozzle and the movable mold. The above objective is achieved.

  The present invention relates to a continuous casting nozzle that supplies a pure magnesium or magnesium alloy melt to a movable mold for continuous casting. The nozzle of the present invention comprises a nozzle body and a coating layer provided at least in a tip region from the tip surface on the movable mold side to the outer peripheral surface of the surface of the nozzle body, and the coating layer is formed of a nitride or a carbide. And at least one selected from carbon as a main component. Here, the main component of a coating layer is a component which occupies 60 mass% or more among coating layers.

  According to the configuration of the present invention, when the molten magnesium or magnesium alloy is supplied to the movable mold through the nozzle, the molten metal is repelled in the nozzle tip region, so that a gap is formed between the nozzle and the movable mold. It is possible to make the molten metal difficult to flow into. As a result, in the gap formed between the nozzle and the movable mold, the molten metal flow is not locally disturbed, the molten metal can be prevented from solidifying, and a cast material excellent in surface quality can be obtained.

  Here, among nitrides, carbides, and carbon, nitrides in particular are easy to play the molten metal without getting wet or reacting with the molten metal, and are excellent in chemical stability. In addition, since nitride is a low oxygen material that does not substantially contain oxygen, it is less likely to be eroded by reaction with pure magnesium or a molten magnesium alloy. Furthermore, since nitride has high thermal conductivity and low thermal expansion, expansion and contraction due to thermal conduction from the molten metal is small, and the coating layer is difficult to peel off from the nozzle body and is not easily damaged.

  As one form of the continuous casting nozzle of the present invention, the coating layer preferably contains alumina as a component other than the main component.

  As an element that determines the wettability of the coating layer to the molten metal, the denseness of the coating layer can also be cited as an important factor. On the other hand, if the density is too low, the durability of the layer is lowered and the layer is peeled off or damaged. Alumina has the effect of improving the density of the coating layer.

  As one form of the nozzle for continuous casting of the present invention, the relative density of the coating layer is preferably 30% or more and 95% or less, and more preferably 40% or more and 85% or less.

  The denser the coating layer, the more the molten metal can be repelled, so that the molten metal can be prevented from flowing into the gap formed between the nozzle and the movable mold, and the durability of the coating layer is good. Moreover, when the density of a coating layer is below the said upper limit, the heat conductivity of a coating layer can be lowered | hung, the heat removal from a nozzle member to a casting roll can be lowered | hung, and it is suitable for the stable casting. Here, the relative density refers to a value obtained by (density of coating layer) / (theoretical density of main component × component ratio + theoretical density of subcomponent × component ratio) × 100 (%). The density of the coating layer is a value measured by, for example, bulk density measurement or Archimedes method.

  As one form of the nozzle for continuous casting of the present invention, the coating layer has a thickness of 200 μm or more.

  If the coating layer provided in the tip region of the nozzle body is too thin, it may be peeled off or broken by the progress of the molten metal, and is preferably 200 μm or more. More preferably, it is 300 μm or more. However, if the coating layer is too thick, the adhesion between the coating layer and the nozzle body is reduced, and the coating layer may be peeled off from the nozzle body. Therefore, the thickness is preferably 1000 μm or less, and preferably 500 μm or less. More preferred.

  As one form of the nozzle for continuous casting of the present invention, the coating layer may be a layer formed by fixing powder to the surface of the tip region of the nozzle body by heat treatment.

  As a method for forming the coating layer, for example, a slurry is prepared by mixing a predetermined amount of a solvent or a binder with powder (that is, a main component powder) as a raw material of the coating layer, and the surface of the tip region of the nozzle body And a method of applying the slurry to heat treatment. Application | coating may be performed with a brush and may be performed by spraying with an air spray. Also, by applying heat treatment to the applied slurry, the powders are fired or sintered to form a high-strength and high-hardness coating layer in close contact with the surface of the tip region of the nozzle body. The powder preferably has an average particle diameter such that the surface roughness Ra of the coating layer after heat treatment is 10 μm or less. The method of fixing the powder is preferable because a coating layer that is strong and has low wettability can be obtained, and the density adjustment described above can be easily performed. Such a material is suitably used as a coating layer even if the strength is insufficient for use in the nozzle body. In addition, powder fixation is excellent in productivity.

  In addition, other methods for forming the coating layer include a method of forming by a CVD method or a PVD method. However, a commercially available release agent (spray) diluted with an organic solvent or the like to 20% or less and using an organic binder has a low density and a low adhesion strength, so it has poor durability, and is the target effect of the present application. Is not preferable.

  On the other hand, the continuous casting method of the present invention is characterized in that twin roll casting is performed using the continuous casting nozzle of the present invention and a twin roll type movable mold.

  When continuous casting is performed by the twin roll method, the position of the mold surface (the surface of the mold in contact with the molten metal) can be easily held constant. In addition, since the surface in contact with the molten metal appears continuously as the roll rotates, the release agent is applied and the deposits are removed before the surface used for casting comes into contact with the molten metal again. The equipment for performing such operations as application and removal can be simplified. Needless to say, the continuous casting nozzle of the present invention can also be used for continuous casting other than twin roll casting.

  As one form of the continuous casting method of the present invention, when the thickness of the meniscus portion of the molten metal formed in the gap between the continuous casting nozzle and the twin-roll movable mold is D1, and the distance between the rolls is D2, D1 < It is preferable to perform twin-roll casting with the continuous casting nozzle facing a twin-roll movable mold so that 1.4 × D2.

  It is preferable to keep the continuous casting nozzle as close to the movable mold as possible. When the gap between the continuous casting nozzle and the movable mold becomes large, the molten metal leaks into the gap, and if the molten metal that has become a solidified product due to the leakage adheres to the movable mold, it may cause surface defects in the cast material. Because it becomes. However, when the continuous casting nozzle and the movable mold come into contact with each other, the continuous casting nozzle is cooled, so that the molten metal in the nozzle is also cooled, and the molten metal may solidify before contacting the movable mold. is there. On the other hand, if the continuous casting nozzle faces the movable mold so that D1 <1.4 × D2, it is possible to effectively suppress the occurrence of the above problem and improve the quality. In this case, a good casting state can be obtained. The configuration of the present application can be used most effectively under such conditions.

  The cast material of the present invention is obtained by the above continuous casting method of the present invention.

  The cast material obtained by the continuous casting method of the present invention has a uniform surface shape.

  In the present invention, pure magnesium means that 99.0% by mass or more of the Mg component is contained by mass without intentionally adding other elements, and the magnesium alloy means that the additive element and the balance are Mg. And impurities. Examples of additive elements include Al, Zn, Mn, Si, Cu, Ag, Y, Zr, Ca, Sr, Sn, Li, Ce, Be, Ni, Au, and rare earth elements (excluding Y and Ce). Among the element group, at least one kind of element can be mentioned. Such additive elements are preferably contained in the magnesium alloy in an amount of 7.3% by mass or more. Examples of the magnesium alloy containing the additive element include AZ, AS, AM, and ZK in the ASTM symbol. In particular, a magnesium alloy containing 7.3 to 12% by mass of Al, and a magnesium alloy containing 0.1% by mass in total of at least one of Y, Ce, Ca, and rare earth elements has high strength and excellent corrosion resistance. Therefore, it is preferable. In addition, the continuous casting nozzle of the present invention can also be used for continuous casting of a composite material composed of a magnesium alloy and a carbide, and a composite material composed of a magnesium alloy and an oxide.

  The continuous casting nozzle of the present invention can prevent the molten metal from flowing into the gap formed between the nozzle and the movable mold by providing a coating layer made of a material having low wettability to the molten metal at the tip of the nozzle body. Moreover, the casting material which is excellent in surface quality can be obtained by performing casting using this nozzle for continuous casting.

It is a schematic block diagram which shows a mode that the continuous casting by the twin roll method is performed using the nozzle for continuous casting of Embodiment 1. FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

<Embodiment 1>
[overall structure]
A nozzle (continuous casting nozzle) 1 according to the present invention will be described with reference to FIG. The nozzle 1 is used as a molten metal transport path for supplying a pure magnesium melt or a magnesium alloy melt 10 melted in a melting furnace (not shown) to the movable mold 20 via a sump 30 or the like. It is a member. The nozzle 1 is particularly used for continuous casting (a twin roll method) using a movable mold 20 composed of a pair of rolls 21.

  The nozzle 1 includes a cylindrical nozzle body 2, and the inner peripheral side thereof serves as a transport path for the molten metal 10. In the nozzle 1, one end side having an opening is used as a pouring port 4 for supplying the molten metal 10 to the movable mold 20. The pouring port 4 has a rectangular shape corresponding to the cross section of the casting material 100 such that the major diameter of the pouring port 4 (the width of the casting material 100) >> the short diameter of the pouring port 4 (the thickness of the casting material 100). . The major axis and minor axis of the pouring gate 4 are appropriately changed according to the desired width and thickness of the cast material 100. In addition, for example, the width of the cast material 100 can be changed by arranging weirs on both sides of the pouring gate 4. The other end of the nozzle 1 is fixed to a hot water reservoir 30 for temporarily storing a molten metal 10 from a melting furnace (not shown). A transfer tub 31 is connected to the basin 30, and the molten metal 10 from the melting furnace is supplied to the basin 30 via the transfer basin 31. The molten metal 10 is transported from the sump 30 to the nozzle 1 and supplied from the nozzle 1 to the roll 21. Each of the rolls 21 is a cylindrical body, is opposed to each other with a predetermined interval, and rotates in opposite directions as indicated by arrows in FIG. The interval between the rolls 21 is appropriately selected according to the desired thickness of the cast material 100, but is preferably the same as or slightly narrower than the short diameter of the pouring port 4 of the nozzle 1. A water channel 22 is provided inside the roll 21 so that water is circulated as needed, and the surface of the roll 21 is cooled by this water. That is, the roll 21 has a water cooling structure.

  As shown in the figure, when the thickness (maximum thickness) of the meniscus portion formed in the gap between the nozzle 1 and the roll 21 is D1 and the distance D2 between the rolls 21 is D1 <1.4. It is preferable that the nozzle 1 faces the roll 21 so that × D2. By doing so, the distance d between the nozzle 1 and the roll 21 can be set to an appropriate value regardless of the sizes of the nozzle 1 and the roll 21. These D1 and D2 can be confirmed by once interrupting the casting.

  Casting material 100 can be obtained by casting using nozzle 1 and roll 21. The molten metal 10 is transported through the nozzle 1 and supplied between the rolls 21 from the pouring port 4 at the tip of the nozzle 1. The supplied molten metal 10 is rapidly cooled and solidified by coming into contact with the rotating roll 21, and is discharged as a cast material 100 from between the rolls 21. Thus, the continuous casting material 100 is obtained by continuously supplying the molten metal 10 between the rolls 21. In this example, a plate-shaped cast material 100 is manufactured.

[nozzle]
The nozzle body 2 constituting the nozzle 1 can be formed of, for example, a carbon-based material, a low oxygen material such as molybdenum, tungsten, tantalum, or SUS. Since the carbon-based material is excellent in thermal conductivity, variations in the temperature of the molten metal 10 can be suppressed in the transverse width direction of the nozzle 1. In addition, since it has lower oxygenity than oxide materials such as alumina and silica, when pure magnesium or magnesium alloy is continuously cast, it can reduce the bonding of magnesium to oxygen and lower the surface quality. Is preferable.

  The feature of the nozzle 1 is that a coating layer 3 mainly composed of a material having lower wettability with respect to the molten metal 10 than the nozzle body 2 is provided in the tip region of the nozzle body 2. As materials having low wettability with respect to the molten metal 10, nitrides such as AlN, BN and SiN, carbides such as SiC and TaC, or C can be used. Here, the main component is a component whose content in the coating layer 3 is 20% by mass or more.

  Moreover, the coating layer 3 may contain alumina as a component other than the main component. By making the coating layer 3 contain alumina, the coating layer 3 can be made dense. The content of alumina in the coating layer 3 is preferably 2 to 10% by mass with respect to the main component of the coating layer 3 (that is, alumina is 2 to 10 when the main component is 100% by mass%).

  The coating layer 3 is formed by fixing the powder as a raw material of the coating layer 3 to the surface of the tip region of the nozzle body 2 by heat treatment. For example, when forming the coating layer 3 containing BN as a main component and alumina as a component other than the main component, first, a slurry containing BN powder and alumina powder is prepared. Next, the slurry is applied to the surface of the tip region of the nozzle body 2 and subjected to heat treatment. The average particle size of the BN powder is preferably 5 μm or less, and the average particle size of the alumina powder is preferably 1 μm or less. By doing so, the surface of the coating layer 3 can be made smooth.

  On the other hand, the tip region of the nozzle body 2 on which the coating layer 3 is provided refers to the tip surface between the inner periphery and the outer periphery of the nozzle body 2 on the movable mold 20 side of the nozzle body 2 and the nozzle continuously from the tip surface. It is a region extending over the outer peripheral surface of the main body 2 and indicates a portion other than the molten metal contact surface in the nozzle. Here, the coating layer 3 is not provided on the inner peripheral surface of the nozzle body 2.

[effect]
By providing the coating layer 3 having low wettability to the molten metal 10 in the tip region of the nozzle body 2, the molten metal 10 is repelled by the coating layer 3, so that the molten metal is formed in a gap formed between the nozzle 1 and the movable mold 20. 10 can hardly flow. Moreover, since the coating layer 3 has a low oxygen property, it is difficult to be eroded by reaction with the molten magnesium 10 of pure magnesium or magnesium alloy. Accordingly, when the molten magnesium 10 of pure magnesium or magnesium alloy is supplied to the movable mold 20 via the nozzle 1, local disturbance of the molten metal flow is prevented and the molten metal 10 is solidified before being injected between the rolls 21. This can be prevented, and the cast material 100 having excellent surface quality can be obtained.

<Test Example 1>
In this test example, the effect of the presence or absence of the coating layer and the thickness of the coating layer on the cast material made of the magnesium alloy was examined.

[Sample 1]
First, the nozzle main body 2 which processed carbon was prepared. The nozzle body 2 had a tip thickness of 1 mm and a width of 300 mm.

  Next, the coating layer 3 was formed in the tip region of the nozzle body 2 on the movable mold 20 side, and the nozzle 1 was completed. The coating layer 3 is made of aluminum nitride powder containing 10% by mass of alumina powder having an average particle size of 0.3 μm with respect to the aluminum nitride powder, and the slurry is formed in the tip region of the nozzle body 2. After applying by spraying, it was formed by heat treatment at a temperature of 800 ° C. The surface roughness Ra (arithmetic mean roughness) of the coating layer 3 after the heat treatment was 5 μm, the thickness of the coating layer 3 was 300 μm, and the relative density of aluminum nitride was 65%. The measuring method of the surface roughness Ra was measured according to the method prescribed in JIS B 0601. Specifically, it is an average value of values measured at 5 points at a measurement length of 3 mm.

  The nozzle 1 having the coating layer 3 was disposed such that the distance d between the tip of the nozzle 1 disposed on the movable mold 20 side and the movable mold 20 was 50 μm. And the molten metal 10 of the magnesium alloy equivalent to AZ91 was supplied to the movable mold 20 from the nozzle 1, and the plate-shaped casting material 100 of thickness 5mm x width 300mm was manufactured. At this time, the thickness D1 of the meniscus portion was 1.2 times the distance D2 between the rolls 21. In producing the cast material 100, a defective rate is obtained when the magnesium alloy melt 10 of 0.5 t / lot is used. The defect rate means that a spot (a spot with a dent, a crack, or the like) where the surface properties of the manufactured cast material 100 are deteriorated due to the leakage of molten metal between the nozzle 1 and the roll 21 is visually observed. The ratio of the length of the cast material that was determined to be defective with respect to the length of the cast material when the total amount of the molten metal was confirmed was calculated. The defect rate and the configuration of the nozzle 1 are shown in Table 1.

[Samples 2 and 3]
Samples 2 and 3 measured by changing the thickness of the coating layer 3 differ from the sample 1 only in the thickness of the coating layer 3, and other dimensions other than the dimensions of the nozzle body 2 formed of carbon and the thickness of the coating layer 3. The casting method and the defect rate calculation method are the same as those of Sample 1.

[Sample 4]
The sample 4 is different from the sample 1 in that the coating layer 3 is made only of AlN, the thickness of the coating layer 3 is 5 μm, and the relative density is 29%. Except for these points, it is the same as Sample 1.

[Sample 5]
The sample 5 is the same as the sample 1 except that the coating layer 3 is not provided in the tip region of the nozzle body 2, and the rest is the same as the sample 1.

[result]

  By comparing the samples 1 to 4 using the nozzle 1 with the coating layer 3 and the sample 5 using the nozzle without the coating layer 3, it can be seen that the defective rate can be reduced by providing the coating layer 3. This is because the molten metal 10 is repelled by the coating layer 3 by providing the coating layer 3 having low wettability with respect to the molten metal 10 at the tip region of the nozzle 1, so that it can be formed between the nozzle 1 and the movable mold 20. It is considered that the molten metal 10 is difficult to flow into the gap. Therefore, in the gap formed between the nozzle 1 and the movable mold 20, the molten metal flow is not locally disturbed, the molten metal 10 can be prevented from solidifying, and the cast material 100 having excellent surface quality can be obtained. it can.

  Moreover, it became clear by comparing the samples 1-4 that the defective rate can be drastically reduced by setting the thickness of the coating layer 3 in the range of 200-1000 μm.

<Test Example 2>
The effect of the difference in D1 indicating the positional relationship between the nozzle 1 and the roll 21 on the cast material was examined.

[Sample 6]
Sample 6 is the same as Sample 2 except that the main component of the coating layer 3 is SiC, the thickness of the coating layer 3 is 200 μm, and the relative density is 70%.

[Sample 7]
The sample 7 is the same as the sample 6 except that the main component of the coating layer 3 is BN and the relative density is 95%.

[Sample 8]
The sample 8 is the same as the sample 6 except that the nozzle body 2 made of molybdenum is used, and that D1 = 1.3 × D2 is used.

[Sample 9]
Sample 9 is that the nozzle body 2 made of alumina is used, the main component of the coating layer 3 is BN, the relative density of the coating layer 3 is 80%, and the point that D1 = 1.5 × D2 Different from 6. Other than that is the same as Sample 6.

[Sample 10]
The sample 10 is different from the sample 6 in that D1 = 1.5 × D2. Other than that is the same as Sample 6.

[result]

  By comparing samples 6 to 10, it was found that the defect rate of the cast material can be reduced by setting D1 <1.4 × D2. This is because when the distance between the nozzle 1 and the roll 21 is too large, the molten metal leaks into the gap between the two, and the leaked molten metal solidifies and adheres to the nozzle 1, and good cooling conditions cannot be obtained. Inferred to be the cause.

  The above-described embodiments can be appropriately changed without departing from the gist of the present invention, and the scope of the present invention is not limited to the above-described configuration.

  The nozzle for continuous casting of the present invention can be suitably used as a molten metal transport member for supplying molten metal from a melting furnace or the like to a movable mold when performing continuous casting of pure magnesium or a magnesium alloy. In addition, the continuous casting method of the present invention is optimal for obtaining a cast material having excellent surface properties. Furthermore, the cast material obtained by this continuous casting method can be used as a secondary processing material such as rolling.

1 Nozzle (continuous casting nozzle)
2 Nozzle body 3 Coating layer 4 Pouring port 10 Molten metal 100 Cast material 20 Movable mold 21 Roll 22 Water channel 30 Reservoir 31 Transfer rod

Claims (8)

A continuous casting nozzle for supplying a pure magnesium or magnesium alloy melt to a movable mold for continuous casting,
A nozzle body;
Of the surface of the nozzle body, comprising at least a coating layer provided in the tip region extending from the tip surface on the movable mold side to the outer peripheral surface,
The continuous casting nozzle, wherein the coating layer contains at least one selected from nitride, carbide, and carbon as a main component.   The nozzle for continuous casting according to claim 1, wherein the coating layer contains alumina as a component other than the main component.   The continuous casting nozzle according to claim 1, wherein a relative density of the coating layer is 30% or more and 95% or less.   The thickness of the said coating layer is 200 micrometers or more, The nozzle for continuous casting as described in any one of Claims 1-3 characterized by the above-mentioned.   5. The continuous casting according to claim 1, wherein the coating layer is a layer formed by adhering powder to a surface of a tip region of the nozzle body by heat treatment. nozzle.   6. A continuous casting method, wherein twin roll casting is performed using the continuous casting nozzle according to any one of claims 1 to 5 and a twin roll type movable mold. When the thickness of the meniscus portion of the molten metal formed in the gap between the continuous casting nozzle and the twin-roll movable mold is D1, and the distance between the rolls is D2,
The continuous casting method according to claim 6, wherein twin roll casting is performed with the continuous casting nozzle facing a twin roll movable mold so that D 1 <1.4 × D 2.   A cast material obtained by the continuous casting method according to claim 6 or 7.

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