JP5701720B2 - Mold for continuous casting of ingot made of titanium or titanium alloy and continuous casting apparatus provided with the same - Google Patents

Description

  The present invention relates to a continuous casting apparatus for an ingot made of titanium or a titanium alloy for continuously casting an ingot made of titanium or a titanium alloy, and a mold used therefor.

  An ingot is continuously cast by injecting a metal melted by plasma arc melting or electron beam melting into a bottomless mold and solidifying it and drawing it downward.

  In Patent Document 1, titanium or a titanium alloy is plasma-dissolved in an inert gas atmosphere, and subsequently a thin slab is cast by continuous casting in an inert gas atmosphere, and this is rolled to produce a strip, A method for producing a rolled titanium or titanium alloy material by rolling the strip is disclosed.

  Here, when an ingot made of titanium or a titanium alloy is continuously cast, if there are irregularities or scratches on the surface (cast surface) of the cast ingot, a surface defect occurs in the subsequent rolling process. Therefore, it is necessary to remove irregularities and scratches on the surface of the ingot by rolling before rolling, which causes a cost increase such as a decrease in yield and an increase in work processes. Therefore, it is required to cast an ingot having no irregularities or scratches on the surface.

  As a method for reducing the surface defects of the ingot, Patent Document 2 discloses that after continuous casting in an electron beam melting furnace and drawing, the surface of the ingot is irradiated with an electron beam to remelt the surface layer, and between the rollers. A method for smoothing the surface by feeding is disclosed. Furthermore, as a method for reducing the surface defects of the ingot, in the steelmaking field, there is a method of cooling the surface of the ingot immediately below the mold with spray water. However, in the case of an ingot made of titanium or a titanium alloy, titanium, which is an active metal, is in a high temperature state and absorbs oxygen from water to generate hydrogen.

  Here, the surface defect of the ingot is that the solidified shell grows too close to the wall surface of the mold and is exposed to the molten metal surface, and when the ingot is pulled out from the mold, It is presumed that the solidified shell is torn due to the frictional force acting on the interface with the mold. Therefore, in order to suppress the growth of the solidified shell in the vicinity of the wall surface of the mold, it is necessary to increase the output of the heating device, increase the amount of heat input to the molten metal surface, and remelt the solidified shell. However, in the vicinity of the molten metal surface, the heat extracted from the mold is large, and titanium has a low thermal conductivity. Therefore, there is a possibility that the initial solidified shell cannot be sufficiently dissolved.

  Therefore, it is conceivable that the initial solidified shell is melted by slowly cooling the interface between the mold and the molten metal by lowering the heat conductivity between the mold and the molten metal to reduce the amount of heat removed from the molten metal.

  In Patent Document 3, the initial solidification shell is slowly cooled by changing the thickness and material of the mold, or by changing the flow rate and temperature of the cooling water flowing in the mold. A method for continuous casting of steel to prevent occurrence is disclosed.

Japanese Patent Laid-Open No. 7-118773 JP-A-62-050047 Japanese Patent Laid-Open No. 9-94635

  However, in Patent Document 2, it is necessary to separately install a roller after extracting the ingot and an electron beam generator for surface heating, which causes a problem in equipment cost. In addition, as in Patent Document 3, changing the thickness and material of the mold does not provide a dramatic slow cooling effect, which may cause the mold to melt and deteriorate in quality due to mixing in the molten metal. is there. Furthermore, as in Patent Document 3, the flow rate and temperature of cooling water for cooling the mold may be controlled not only by melting of the mold but also by the complexity of the mold structure, which may reduce maintainability. .

  The objective of this invention is providing the casting_mold | template for continuous casting of the ingot which consists of titanium or a titanium alloy which can cast the ingot with few defects on a surface, and a continuous casting apparatus provided with the same.

The mold for continuous casting of an ingot made of titanium or a titanium alloy in the present invention is used for continuous casting of an ingot made of titanium or a titanium alloy, and a molten metal in which titanium or a titanium alloy is melted is injected into the mold. A bottomless mold, wherein at least a part of the inner peripheral surface of the mold is provided with a slow cooling portion in which the amount of heat removed from the molten metal is smaller than that of the mold at least at a location where the molten metal surface of the molten metal contacts. The slow cooling part is made of a high melting point material having a melting point higher than the temperature of the molten metal surface, and the high melting point material is a high melting point metal having a melting point higher than the temperature of the molten metal surface. It is one of tantalum, molybdenum, niobium, and tungsten .

  According to the above configuration, at least a part of the inner peripheral surface of the mold is provided with the slow cooling portion at least at a location where the molten metal surface contacts, so that the amount of heat removed from the molten metal that contacts the slow cooling portion can be reduced. It becomes smaller than the amount of heat removed from the molten metal in contact with. Then, since the cooling rate of the solidified shell that comes into contact with the slow cooling portion becomes slow, the growth of the solidified shell at the portion where the slow cooling portion is provided is suppressed. This suppresses the occurrence of defects on the surface of the ingot due to the growth of the solidified shell in the vicinity of the wall surface of the mold. Therefore, the ingot with few defects on the surface can be cast.

Moreover , since the slow cooling part consists of a high melting-point material whose melting | fusing point is higher than the temperature of the molten metal surface, a slow cooling part can be made hard to melt.

Moreover , since the high melting point metal has a slow diffusion in titanium and does not easily react with titanium, the activity of the titanium surface can be suppressed. In the mold for continuous casting of an ingot made of titanium or a titanium alloy in the present invention, the high melting point material may be either tantalum or niobium.

  An ingot continuous casting apparatus made of titanium or a titanium alloy according to the present invention includes the above mold, a molten metal injection apparatus for injecting the molten metal into the mold, and an ingot in which the molten metal has solidified in the mold. And a drawing device that pulls out below the mold.

  According to the above configuration, since the solidified shell is prevented from growing at the location where the slow cooling portion on the inner peripheral surface of the mold is provided, an ingot having few defects on the surface can be continuously cast. .

  In the continuous casting apparatus for ingots made of titanium or titanium alloy according to the present invention, at least the periphery of the mold is in an inert gas atmosphere, and the molten metal surface injected into the mold is plasma arced. You may further have a plasma arc heating apparatus heated with. According to said structure, since the stable heat input with a plasma arc can be given to the molten metal surface, the amount of heat removal from the slow cooling part of the internal peripheral surface of a casting_mold | template can be kept constant. Thereby, it is possible to suppress the growth of the solidified shell and stably and continuously cast an ingot having few defects on the surface.

  According to the mold for continuous casting of an ingot made of titanium or a titanium alloy of the present invention and the continuous casting apparatus equipped with the same, at least a part of the inner peripheral surface of the mold is loosened at least at a location where the molten metal surface contacts. By providing the cooling part, the cooling rate of the solidified shell that contacts the slow cooling part is moderated, so that the growth of the solidified shell at the place where the slow cooling part is provided is suppressed. This suppresses the occurrence of defects on the surface of the ingot due to the growth of the solidified shell in the vicinity of the wall surface of the mold, so that an ingot having few defects on the surface can be cast.

It is a perspective view which shows a continuous casting apparatus. It is sectional drawing which shows a continuous casting apparatus. It is explanatory drawing showing the generation | occurrence | production mechanism of a surface defect. It is explanatory drawing showing the generation | occurrence | production mechanism of a surface defect. It is a perspective view which shows a continuous casting apparatus.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
(Construction of continuous casting equipment)
A mold (mold) 2 for continuous casting of an ingot made of titanium or a titanium alloy according to the present embodiment is provided in a continuous casting apparatus (continuous casting apparatus) 1 of an ingot made of titanium or a titanium alloy. As shown in FIG. 1 which is a perspective view and FIG. 2 which is a cross-sectional view, the continuous casting apparatus 1 includes a mold 2, a cold hearth (a molten metal injection apparatus) 3, a raw material charging apparatus 4, and a plasma torch 5. And a starting block (drawing device) 6 and a plasma torch (plasma arc heating device) 7. The continuous casting apparatus 1 is surrounded by an inert gas atmosphere made of argon gas, helium gas, or the like.

  The raw material input device 4 inputs the raw material of titanium or titanium alloy such as sponge titanium and scrap into the cold hearth 3. The plasma torch 5 is provided above the cold hearth 3 and generates a plasma arc to melt the raw material in the cold hearth 3. The cold hearth 3 injects the molten metal 12 in which the raw material is melted into the mold 2 from the pouring part 3a. The casting mold 2 is made of copper and has a bottomless rectangular cross section, and is cooled by water circulating inside the four walls. The starting block 6 is moved up and down by a drive unit (not shown) and can close the lower opening of the mold 2. The plasma torch 7 is provided above the mold 2 and heats the surface of the molten metal 12 injected into the mold 2 with a plasma arc.

  Moreover, the continuous casting apparatus 1 has the flux injection apparatus which is not shown in figure. The flux feeding device feeds the solid phase flux 9 to the molten metal 12 in the mold 2. The flux 9 melted on the surface of the molten metal 12 enters between the mold 2 and the molten metal 12 and exhibits a lubricating effect of reducing the frictional resistance between the mold 2 and the solidified shell 13, and the mold 2 and the molten metal 12. The effect of slowly cooling the interface with is exhibited.

  A mild cooling plate (slow cooling part) 8 a is attached to the inner side surface of the wall part that forms the long side of the mold 2. The slow cooling plate 8a is provided over the entire length of the inner side surface of the wall portion forming the long side of the mold 2 in the long side direction of the mold 2, and the molten metal 12 is used in the vertical direction of the mold 2. It is provided between the upper end of the mold 2 and the upper end of the lower end with the sandwich. Further, a slow cooling plate (slow cooling portion) 8b is attached to the inner side surface of the wall portion forming the short side of the mold 2 respectively. The slow cooling plate 8b is provided over the entire length of the inner surface of the wall portion forming the short side of the mold 2 in the short side direction of the mold 2, and the molten metal 12 is used in the vertical direction of the mold 2. It is provided between the upper end of the mold 2 and the upper end of the lower end with the sandwich. Thus, the entire circumference of the molten metal 12 is surrounded by the slow cooling plate 8a and the slow cooling plate 8b.

  The slow cooling plate 8a may be provided on a part of the inner side surface of the wall portion forming the long side of the mold 2 as long as it is at least a location where the molten metal surface of the molten metal 12 contacts. Similarly, the slow cooling plate 8b may be provided on a part of the inner side surface of the wall portion that forms the short side of the mold 2 as long as it is a place where at least the surface of the molten metal 12 contacts. Alternatively, the slow cooling plate 8 a may be provided on the entire inner surface of the wall portion that forms the long side of the mold 2. Similarly, the slow cooling plate 8b may be provided on the entire inner surface of the wall portion forming the short side of the mold 2.

  In the above configuration, the molten metal 12 injected into the mold 2 is solidified from the contact surface with the water-cooled mold 2. Then, the starting block 6 that has closed the lower opening of the mold 2 is pulled downward at a predetermined speed, whereby the slab 11 in which the molten metal 12 has solidified is continuously cast while being pulled downward.

  In electron beam melting in a vacuum atmosphere, the energy density of the electron beam itself is high, and the metal element having a low melting point and a high vapor pressure evaporates. Therefore, it is difficult to manufacture a titanium alloy in terms of component control. In the plasma arc melting in an inert gas atmosphere, not only pure titanium but also a titanium alloy can be cast. In addition, in the electron beam melting in a vacuum atmosphere, the flux 9 is scattered, so it is difficult to put the flux 9 into the molten metal 12 in the mold 2. However, in the plasma arc melting in an inert gas atmosphere, the flux 9 is changed. Preferably, it can be put into the molten metal 12 in the mold 2.

(Surface defect generation mechanism)
By the way, when the slab 11 made of titanium or a titanium alloy is continuously cast, if there are irregularities or scratches on the surface of the slab 11, a surface defect occurs in the next rolling process. Therefore, it is necessary to remove irregularities and scratches on the surface of the slab 11 by cutting or the like before rolling, which causes a cost increase such as a decrease in yield and an increase in work processes. Therefore, it is required to cast the slab 11 having no irregularities or scratches on the surface.

  Here, it is presumed that some of the defects generated on the surface of the slab 11 are caused by the fact that the solidified shell grows too much in the vicinity of the wall surface of the mold 2 and is exposed to the molten metal surface, and the molten metal is generated. The mechanism will be described with reference to FIG. First, as shown in FIG. 3A, the solidified shell 13 grows in the vicinity of the wall surface of the mold 2. Next, as shown in FIG. 3B, the solidified shell 13 is lowered by drawing in a state where the molten metal 12 is not supplied near the wall surface of the mold 2. Then, as shown in FIG. 3C, the molten metal 12 flows onto the solidified shell 13 because the upper end of the solidified shell 13 is lower than the liquid level of the molten metal 12. Then, as shown in FIG. 3 (d), the molten metal 12 that has flowed onto the solidified shell 13 is solidified to become the solidified shell 13, so that a surface defect occurs in the solidified shell 13, which is a surface defect of the slab 11. Become.

  Further, it is estimated that some of the defects generated on the surface of the slab 11 are caused by the rupture of the solidified shell 13. The mechanism will be described with reference to FIG. The solidified shell 13 grown in the vicinity of the wall surface of the mold 2 is lowered by drawing. At this time, the solidified shell 13 is ruptured by the frictional force acting on the interface between the grown solidified shell 13 and the mold 2, and this rupture becomes a surface defect of the slab 11.

(Slow cooling)
In the present embodiment, as shown in FIGS. 1 and 2, in order to suppress the occurrence of defects on the surface of the slab 11, a slow cooling plate 8 a is provided on the inner surface of the wall portion that forms the long side of the mold 2. A slow cooling plate 8b is provided on the inner side surface of the wall portion forming the short side of each. The slow cooling plate 8a and the slow cooling plate 8b are made of a high melting point metal having a melting point higher than the temperature of the molten metal 12 surface. Here, when the temperature of the molten metal 12 is made of pure titanium, the temperature of the molten metal 12 is higher than 1680 ° C., which is the melting point of titanium, and is estimated to be even higher at the portion heated by the plasma torch 7. The Therefore, tantalum (Ta), molybdenum (Mo), niobium (Nb), and tungsten (W) can be cited as high melting point metals having a melting point higher than the temperature of the molten metal 12. Of these, tantalum (Ta) and niobium (Nb) are particularly preferable. Since these refractory metals have a large melting point difference from that of titanium, they hardly react with titanium. Moreover, it is suitable because it has high corrosion resistance in a vacuum or an inert gas environment.

  Since the mild cooling plates 8a and 8b have a lower thermal conductivity than copper, the amount of heat removed from the molten metal 12 is smaller than that of the copper mold 2. Therefore, by providing the slow cooling plates 8a and 8b at locations where the molten metal surface of the molten metal 12 is in contact with the entire circumference of the inner peripheral surface of the mold 2, the amount of heat removed from the molten metal 12 in contact with the slow cooling plates 8a and 8b is The amount of heat removed from the molten metal 12 in contact with the mold 2 is smaller. Then, the cooling rate of the solidified shell 13 in contact with the slow cooling plates 8a and 8b becomes slow, so that the solidified shell 13 is prevented from growing at the place where the slow cooling plates 8a and 8b are provided. As a result, the occurrence of defects on the surface of the slab 11 due to the growth of the solidified shell 13 in the vicinity of the wall surface of the mold 2 is suppressed.

  Further, since the slow cooling plates 8a, 8b are made of a high melting point metal having a melting point higher than the temperature of the molten metal 12, the slow cooling plates 8a, 8b are not easily melted. In addition, the high melting point metal has a slow diffusion in titanium and hardly reacts with titanium, so that the activity on the titanium surface is suppressed.

  In addition, the flux 9 introduced into the molten metal 12 in the mold 2 from a flux charging device (not shown) has a thermal conductivity between the mold 2 and the molten metal 12 in addition to the effect of lubricating the mold 2 and the solidified shell 13. The effect of slowly cooling the interface between the mold 2 and the molten metal 12 is exhibited. Since the slow cooling effect further suppresses the growth of the solidified shell 13, it is preferable to use the flux 9 in combination.

(effect)
As described above, according to the mold 2 and the continuous casting apparatus 1 according to the present embodiment, at least a part of the inner peripheral surface of the mold 2 is at the location where the molten metal surface of the molten metal 12 contacts at least. By providing 8b, the amount of heat removed from the molten metal 12 in contact with the slow cooling plates 8a and 8b is smaller than the amount of heat removed from the molten metal 12 in contact with the mold 2. Then, the cooling rate of the solidified shell 13 in contact with the slow cooling plates 8a and 8b becomes slow, so that the solidified shell 13 is prevented from growing at the place where the slow cooling plates 8a and 8b are provided. As a result, the occurrence of defects on the surface of the slab 11 due to the growth of the solidified shell 13 in the vicinity of the wall surface of the mold 2 is suppressed. Therefore, the slab 11 with few defects on the surface can be cast.

  Further, since the slow cooling plates 8a and 8b are made of a high melting point metal having a melting point higher than the temperature of the molten metal 12, the slow cooling plates 8a and 8b can be made difficult to melt. Moreover, since the high melting point metal has a slow diffusion in titanium and does not easily react with titanium, the activity of the titanium surface can be suppressed.

  In addition to the lubrication effect between the mold 2 and the solidified shell 13, the flux 9 has an effect of slowly cooling the interface between the mold 2 and the molten metal 12 by lowering the thermal conductivity between the mold 2 and the molten metal 12. There is. According to the continuous casting apparatus 1 according to the present embodiment, it is possible to further suppress the growth of the solidified shell 13 by using the flux 9 in combination in the plasma arc melting in an inert gas atmosphere.

(Modification)
The slow cooling plates 8a and 8b may be made of titanium or a titanium alloy. When casting the slab 11 made of pure titanium, the slow cooling plates 8a and 8b are made of pure titanium. When casting the slab 11 made of titanium alloy, the slow cooling plates 8a and 8b are made of the same kind of titanium. By using an alloy, even if the slow cooling plates 8a and 8b are melted, the surface quality of the slab 11 is not deteriorated.

[Second Embodiment]
(Slow cooling)
Next, a continuous casting apparatus 201 according to the second embodiment of the present invention will be described. In addition, about the same component as the component mentioned above, the same reference number is attached | subjected and the description is abbreviate | omitted. The continuous casting apparatus 201 of the present embodiment is different from the continuous casting apparatus 1 of the first embodiment in that a sprayed film (slow cooling part) 8c is formed on the inner surface of the mold 2 as shown in FIG. It is.

  The sprayed film 8c is a sprayed film made of a high melting point metal having a melting point higher than the temperature of the molten metal surface of the molten metal 12, or ceramics, which is a generic term for inorganic materials such as oxides and carbides. The sprayed film 8 c is formed on the entire inner surface of the mold 2. Note that the sprayed film 8 c may be provided on a part of the inner surface of the mold 2 as long as it is a place where at least the surface of the molten metal 12 contacts. The sprayed film 8c may be a sprayed film made of titanium or a titanium alloy. In addition, in titanium alloys for aircraft, the inclusion of tungsten carbide, which is the starting point of fatigue fracture, is limited. However, when casting titanium or titanium alloys other than for aircraft, tungsten carbide is used for the sprayed film 8c. May be.

  Even in the configuration as described above, the same effects as those of the first embodiment can be obtained.

(Modification of this embodiment)
The embodiment of the present invention has been described above, but only specific examples are illustrated, and the present invention is not particularly limited, and the specific configuration and the like can be appropriately changed in design. Further, the actions and effects described in the embodiments of the invention only list the most preferable actions and effects resulting from the present invention, and the actions and effects according to the present invention are described in the embodiments of the present invention. It is not limited to what was done.

  For example, it is not limited to the configuration in which the rectangular slab 11 is continuously cast, but may be a configuration in which an ingot having a circular cross section is continuously cast.

  Further, the slow cooling plates 8a and 8b may be made of ceramics having a melting point higher than the temperature of the molten metal 12 surface.

  Moreover, it is not limited to the structure which heats the hot_water | molten_metal surface of the molten metal 12 with the plasma arc from the plasma torch 7, Even if it is the structure which heats the hot_water | molten_metal surface of the molten metal 12 by an electron beam, a non-consumable electrode type arc, and high frequency induction heating. Good.

1,201 Continuous casting equipment 2 Mold 3 Cold hearth (molten pouring equipment)
3a Pouring section 4 Raw material charging device 5 Plasma torch 6 Starting block (drawing device)
7 Plasma torch (plasma arc heating device)
8a, 8b Slow cooling plate 8c Sprayed film 9 Flux 11 Slab 12 Molten metal 13 Solidified shell

Claims (4)

A bottomless mold that is used for continuous casting of an ingot made of titanium or a titanium alloy and into which a molten metal obtained by melting titanium or a titanium alloy is poured,
In at least a part of the inner peripheral surface of the mold, at least at a location where the molten metal surface of the molten metal comes into contact, a slow cooling part in which the amount of heat removed from the molten metal is smaller than that of the mold is provided ,
The slow cooling part is made of a high melting point material having a melting point higher than the temperature of the molten metal surface,
A continuous ingot made of titanium or a titanium alloy , wherein the high-melting-point material is any one of tantalum, molybdenum, niobium, and tungsten, which is a high-melting-point metal having a melting point higher than the temperature of the molten metal surface. Casting mold.   The mold for continuous casting of an ingot made of titanium or a titanium alloy according to claim 1, wherein the high melting point material is either tantalum or niobium. The mold according to claim 1 or 2 ,
A molten metal injection device for injecting the molten metal into the mold,
A drawing device for drawing the ingot in which the molten metal has solidified in the mold, below the mold;
An ingot continuous casting apparatus made of titanium or a titanium alloy. At least around the mold is an inert gas atmosphere,
4. The continuous casting apparatus for an ingot made of titanium or a titanium alloy according to claim 3 , further comprising a plasma arc heating device for heating the molten metal surface injected into the mold by a plasma arc.

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