JP2021079395A - Method of making titanium ingot - Google Patents

Abstract

To provide a method of making a titanium ingot having a good surface quality.SOLUTION: A method of making a titanium ingot comprises a first step of melting a raw material whose main component is titanium, supplying a refined molten metal in a ring-shaped mold, moving a lower part of a semi-ingot comprising a melted portion in an upper part and a solidified portion in the lower part vertically downward by 1-20 mm at an average speed of 100-2000 mm/hour when pulling out the molten metal within the mold while cooling it, and stopping the movement thereof, and a second step of moving the lower part of the semi-ingot vertically upward by 0.05d-0.80d (d: a vertically-downward movement distance in the first step) and stopping the movement thereof, in which the first step and the second step are carried out a plurality of times.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing a titanium ingot, specifically, a method for producing a titanium ingot having a good surface texture.

Since titanium is an active metal that is violently air-oxidized at its melting temperature, it is difficult to melt it in an air atmosphere using a refractory crucible like a steel material. For this reason, in the production of industrial pure titanium ingots or titanium alloy ingots (hereinafter, these are also collectively referred to as "titanium ingots"), water-cooled copper hearth is used and high voltage acceleration is performed under high vacuum. Electron beam melting (EBM) technology that utilizes the impact heat obtained by irradiating the surface of the material to be dissolved with an electron beam, and plasma melting (PAM), which is a melting method using a plasma torch as a non-consumable electrode. : Plasma Arc melting) technology has been put into practical use.

Titanium ingot is a highly reactive metal with a high melting point of titanium of about 1680 ° C. Therefore, a raw material is melted in a chamber using an electron beam or plasma, and the raw material is continuously formed in a mold (hearth) having a water-cooled structure. It is manufactured by being cast in a mold, being cast in a mold, and then being pulled out.

Since a melting method using an electron beam or plasma is used for producing these ingots, the melting rate of the raw material is low, for example, about 800 kg per hour. Therefore, the ingot cooled by the mold is slowly and intermittently drawn out at a speed of about 500 to 1500 mm per hour.

The reason for the intermittent extraction is that a lubricant cannot be used because it is operated in a depressurized chamber, especially in electron beam melting, and solute elements are mixed into the ingot from the lubricant or the like. This is because it is severely restricted, especially as a material for aircraft. Since the titanium ingot is produced by being slowly and intermittently drawn out in this way, defects such as wrinkles are likely to occur on the surface thereof.

Titanium ingots are processed into plates and the like through forging and rolling processes, and are used as parts for aircraft and automobiles. During this processing, if there are defects on the surface of the ingot, cracks will occur. The removal of cracks reduces the yield of the product, resulting in scrap instead of the product. Therefore, it is important to improve the surface quality of the titanium ingot.

Patent Document 1 describes a continuous casting method in which a titanium ingot is continuously cast by injecting a molten metal in which industrial pure titanium or a titanium alloy is melted into a bottomless mold and pulling it downward while solidifying it. It is disclosed.

In this continuous casting method, the molten metal is controlled by controlling at least one of the temperature of the surface of the ingot in the contact region between the mold and the ingot and the heat flux passing from the surface of the ingot to the mold in the contact region. The thickness of the solidified shell in the contact area of the solidified shell is kept within a predetermined range.

In Patent Document 2, a titanium ingot is continuously cast by injecting a molten metal in which industrial pure titanium or a titanium alloy is melted into a bottomless mold having a circular cross section and pulling it downward while solidifying it. A continuous casting apparatus is disclosed.

This continuous casting device is provided above the mold and has a plasma torch that heats the molten metal surface in the mold, and an electromagnetic wave that is provided on the side of the mold and agitates at least the molten metal surface by electromagnetic stirring by an AC current. It has a stirrer. With this electromagnetic agitator, a flow parallel to the wall surface of the mold is generated at least on the surface of the molten metal at the peripheral edge of the surface of the molten metal.

In this continuous casting apparatus, the flow of the molten metal can be controlled by using an electromagnetic agitator, so that the heat from the plasma torch applied to the molten metal surface can be diffused, and in particular, the peripheral portion of the molten metal can be equalized. As a result, the central depth of the molten metal pool can be made shallow, the segregation of components can be reduced, and as a result, an ingot with a good casting surface condition can be obtained.

Patent Document 3 describes that in the drawing step following the secondary cooling zone of the continuous casting step in the rotary continuous casting of molten metal in which the slab is continuously drawn while rotating, the slab is subjected to a one-stage or multiple-stage reduction device. A method of lightly reducing the pressure at the end of solidification of rotary continuous casting by continuously reducing the pressure between the tip of the liquid phase line crater and the tip of the solid phase line crater is disclosed.

Non-Patent Document 1 discloses a technique for producing a slab having good surface quality by producing a round steel slab by a rotary continuous casting method. It is disclosed that the rotation speed when continuously casting the slab is 30 to 120 rpm. The technique disclosed in Non-Patent Document 1 is cast using the mold disclosed in Patent Document 4.

Patent Document 4 discloses a mold used for rotary casting. This mold has a structure in which the inner wall rotates, the outer side of the inner wall is fixed, and the cooling water flows between the inner wall and the outer side. Semi-continuous casting of industrial pure titanium or titanium alloy has a structure in which a melting furnace, a mold, and a drawing device are installed in a vacuum chamber so that cooling water does not leak from the connection part.

Patent Document 5 describes a refractory metal ingot in which molten metal is supplied into a mold constituting an electron beam melting furnace to form a mold pool, and a cooled solidified ingot near the bottom of the mold pool is drawn while rotating. The manufacturing method is disclosed.

In this manufacturing method, the pull-out distance of the ingot is smaller than the depth of the mold pool, the ingot is moved vertically downward, this movement is temporarily stopped, the ingot is rotated in a horizontal plane, and then the ingot is rotated. By repeating this rotation stop, it is said that a metal ingot with an excellent casting surface can be produced.

Japanese Unexamined Patent Publication No. 2014-133257 Japanese Unexamined Patent Publication No. 2015-157296 Japanese Unexamined Patent Publication No. 9-276993 U.S. Pat. No. 4,019,565 Japanese Unexamined Patent Publication No. 2009-172665

A.I.Gueussler: "Specific Aspect of Rotary Continuous Casting", Iron and Steel Engineer, vol.59 (1982), p.53-59.

The formation of the solidified shell is not determined only by cooling by contact with the mold, but also largely depends on the temperature and flow condition of the molten metal. However, since the continuous casting method disclosed in Patent Document 1 does not consider the temperature and flow of the molten metal at all, it is not possible to produce a titanium ingot having a good surface texture.

The continuous casting apparatus disclosed in Patent Document 2 is based on the idea that the surface texture of the ingot is controlled only by the flow by electromagnetic agitation, but in the actual operation of casting a titanium ingot, it solidifies. The flow of molten metal at the periphery changes depending on the position and thickness of the shell. Therefore, it is not possible to improve the surface texture of the ingot only by controlling the flow of the molten metal by electromagnetic agitation.

The invention disclosed in Patent Document 3 is premised on the use of the technique disclosed in Non-Patent Document 1, and it is assumed that the slab in the rotary continuous casting process is rotating at a speed of about 100 rpm, and titanium. For semi-continuous casting with a slow casting speed such as an ingot, the ingot cannot be rotated at a high speed such as 100 rpm.

In the production of titanium ingots using electron beam melting, melting and casting must be performed in a vacuum chamber, the mold has no oscillation mechanism, and casting is performed without using a lubricant. Then, the liquidus temperature of industrial pure titanium or titanium alloy is high, and it is necessary to raise the temperature of the molten metal injected into the mold. However, if the temperature of the hot water to be injected into the mold is high, the strength of the solidified shell formed in the mold decreases, and if the rotation speed is high, the solidified shell breaks and breakout occurs. Therefore, the technique disclosed in Non-Patent Document 1 cannot be diverted to the production of titanium ingots.

The mold disclosed in Patent Document 4 has a mechanism for rotating the inner wall, and has a structure in which cooling water flows between the inner wall and the outer side. When a mold having such a structure is arranged in a vacuum chamber and operated, cooling water is sucked from the rotating portion of the inner wall of the mold to cause water leakage, and the operation cannot be performed.

In the case of semi-continuous casting of titanium ingots, the pouring flow when pouring the molten metal into the mold affects the pouring flow in the mold and influences the growth of the solidified shell in the mold. If the growth of the solidified shell is non-uniform, not only wrinkles are formed on the surface of the ingot, but also tensile stress and compressive stress act on the solidified shell to cause cracks. Therefore, it is necessary to control the flow of the molten metal in the mold by paying attention to the pouring flow.

By the way, in actual operation, when the molten metal in the hearth is poured into the mold, the molten metal is often poured from one place so as to be along the inner wall of the mold. When poured from one place, the flow of molten metal in the mold becomes non-uniform, the growth of the solidified shell also becomes non-uniform in the circumferential direction of the mold, the thickness differs, and the shape of the molten pool also becomes non-uniform. The surrounding molten pool that is poured into the mold becomes deeper, which delays solidification.

When the difference in the thickness of the solidified shell becomes large, the tensile stress and the compressive stress acting on the solidified shell are different, and defects such as cracks and wrinkles on the surface occur. In order to suppress such defects, it is necessary to make the growth of the solidified shell forming the surface of the ingot uniform and the depth of the molten pool uniform.

To do this, the shape of the molten pool formed in the mold may be cast so as to be rotationally symmetric with respect to the line passing through the center of the mold thickness. Since the molten metal from the hearth is supplied from one place of the mold along the wall surface, the molten pool is not rotationally symmetric, the molten pool at the supply position is the deepest, and the pool at the position symmetrical with the supply position is shallow. Become.

However, it is practically difficult to change the position of injecting the molten metal from the hearth into the mold with time because the equipment cost increases.

As disclosed in Patent Document 5, if the ingot during casting is rotated, the molten pool depth becomes rotationally symmetric even if the pouring position is the same, and a uniform solidified shell can be obtained. We focused on the fact that it can be formed and that tensile stress and compressive stress are not locally applied.

However, in the invention disclosed in Patent Document 5, the ingot is moved vertically downward, the movement is temporarily stopped, the ingot is rotated in one direction in the horizontal plane, and then this rotation is stopped. The coagulation shell formed by the coagulation structure tilted in the direction (rotational direction) coagulates and contracts. Therefore, thermal stress may be generated in that direction to form wrinkles on the surface of the ingot, and it is not possible to produce a titanium ingot having excellent surface quality.

The present invention has been made in view of this problem of the prior art, and an object of the present invention is to provide a method for producing a titanium ingot having a good surface texture.

As a result of diligent studies to solve the above problems, the present inventors have obtained the following findings.
At the time of casting, the lower part of the semi-ingot having the molten part in the upper part and the solidifying part (solidification shell) in the lower part is moved vertically downward, and then the lower part of the semi-ingot is moved vertically upward to perform uniform solidification. A shell can be formed. This raises the solidified shell against the static pressure acting on the solidified shell, so a pressure higher than the static pressure acts on the solidified shell, especially the thin solidified shell near the bottom of the molten metal. .. Then, since the solidified shell is pressed against the inner wall of the mold, it is considered that the deformation of the solidified shell is eliminated and an ingot having a good surface texture is obtained. Therefore, tensile stress and compressive stress are not locally applied, and it is easy to obtain a titanium ingot having excellent surface quality.

As a more preferable method, the present inventors move the lower part of the semi-ingot vertically downward, and then rotate the lower part of the semi-ingot about the axis of the mold in the forward direction in one direction and further in the reverse direction. After that, he found a way to move the lower part of the semi-ingot vertically upward. It has been found that this method can increase the strength of the solidified shell and suppress cracking. This is because when the lower part of the semi-ingot is moved vertically upward, the solidified shell grown in the previous process (pulling-forward rotation-reverse rotation) is pushed up and integrated with the solidified shell grown after that, apparently hot water. The thickness of the solidified shell formed below the surface can be increased. It is considered that this is because the strength of the solidified shell can be increased.

The present invention has been completed based on the above findings, and the gist thereof is as listed below.

(1) The molten metal obtained by irradiating a raw material whose main component is titanium with an electron beam is supplied to Haas, and a part of the molten metal is cooled and solidified to be separated, while the remaining molten metal is ring-shaped. This is a method for producing a titanium ingot made of industrial pure titanium or a titanium alloy by supplying the molten metal in the mold and drawing it vertically downward while cooling the molten metal in the mold.
The first step of moving the lower part of a semi-ingot having a molten part at the upper part and a solidifying part at the lower part vertically downward by 1 to 20 mm at an average speed of 100 to 2000 mm / hour and stopping the movement.
A second step of moving the lower part of the semi-ingot vertically upward by 0.05 d to 0.80 d (however, d: a moving distance vertically downward in the first step) and stopping the movement is provided. ,
A method for producing a titanium ingot, wherein the first step and the second step are performed a plurality of times.

(2) After the first step and before the second step,
A third step in which the lower part of the semi-ingot is rotated forward in one direction around the axis of the mold and the rotation is stopped, and the lower part of the semi-ingot is rotated around the axis of the mold in one direction. Titanium casting according to (1) above, wherein the fourth step of rotating in the reverse direction at a rotation angle of 0.05θ to 0.80θ (however, θ: the rotation angle of the forward rotation) and stopping the rotation is carried out. How to make a lump.

(3) The rotation speed of the forward rotation or the reverse rotation is 1 to 120 times / hour.
The method for producing a titanium ingot according to (2).

According to the present invention, a titanium ingot having good surface quality can be produced.

FIG. 1 is a perspective view schematically showing an example of a titanium alloy ingot manufacturing apparatus used in the present invention. FIG. 2 is a perspective view showing an example of each step in the method for manufacturing a titanium ingot according to the present embodiment, in which (a) is a drawing step, (b) is a pushing step, (c) is a pulling step, and (d). ) Indicates the pushing process. FIG. 3 is a perspective view showing an example of each step in the method for manufacturing a titanium ingot according to the present embodiment, in which (a) is a drawing step, (b) is a forward rotation step, and (c) is a reverse rotation step. (D) shows a pushing step, and (e) shows a pulling step.

The present invention will be described. In the following description, "%" regarding the chemical composition means "mass%" unless otherwise specified. Further, in the following description, the case of manufacturing a titanium alloy ingot will be taken as an example, but the situation is the same even in the case of manufacturing an industrial pure titanium ingot.

1. 1. Manufacturing Equipment FIG. 1 is a perspective view schematically showing an example of manufacturing equipment 1 of the titanium alloy ingot 0 used in the present invention.

The manufacturing apparatus 1 includes a raw material supply means 2, an electron beam irradiation means (hereinafter, simply referred to as “irradiation means”) 3, hearths 4 and 5, and a mold 6.

The raw material supply means 2 supplies a titanium raw material 7 whose main component is titanium. The raw material 7 is preferably titanium briquette, but titanium scrap or the like may be mixed. The titanium briquette is formed by pressing a titanium raw material such as titanium sponge and molding it into a specific shape.

The melting raw material 7 is melted by an electron beam while being continuously supplied above the melting hearth 4, which will be described later, and the molten metal is supplied to the melting hearth 4 to stably maintain the temperature of the molten metal supplied to the melting hearth 4. As a result, the temperature of the molten metal supplied to the refining hearth 5 can be kept stable. The chemical component of the raw material 7 may be any titanium as the main component, and may be an industrial pure titanium or a titanium alloy containing an alloy element such as aluminum.

Further, the raw material supply means 2 preferably supplies the raw material 7 at a supply rate corresponding to the dissolution rate of the raw material 7 by the irradiation means 3.

The irradiation means 3 dissolves the raw material 7 by irradiating the supplied raw material 7 with an electron beam. Further, it is desirable to provide an irradiation means 9 for adjusting the temperature of the molten metal by irradiating the surface of the molten metal flowing through the molten hearth 4 and the refining hearth 5, which will be described later, while scanning an electron beam.

The manufacturing apparatus 1 has two irradiation means 3 for dissolving the raw material 7, two irradiation means 9 for the dissolution hearth 4, and two irradiation means 9 for the refining hearth 5. The number of means 3 and 9 installed is not limited to this form, and may be appropriately determined in consideration of the capacity required for the manufacturing apparatus 1 and the like.

It is desirable that the raw material supply means 2 continuously supplies the raw material 7 and the irradiation means 3 continuously dissolves the supplied raw material 7.

In the manufacturing apparatus 1, the melted hearth 4 accommodates the molten metal of the raw material that is melted and flows down, and the refining hearth 5 cools and solidifies a part of the molten metal flowing in from the melted hearth 4, and puts a solid skull on the bottom 5a. The remaining molten metal is poured while forming and separating.

The melting hearth 4 has a function of irradiating the raw material 7 with an electron beam to form a melting pool of the melted raw material and supplying the raw material 7 to the refining hearth 5. The refining hearth 5 has a function of receiving the molten metal from the molten hearth 4, temporarily storing it, irradiating it with an electron beam, and supplying the molten metal to the mold 6. The melted hearth 4 and the refined hearth 5 are connected via the runner 8 so that the flow direction of the refined hearth 5 is substantially perpendicular to the direction of the flow from the runner 8.

In the melting hearth 4, when the raw material 7 irradiated with the electron beam is melted and the inside of the melting hearth 4 is filled, the molten metal is poured into the refining hearth 5 through the supply port to the refining hearth 5.

The molten metal from the supply port of the melting hearth 4 flows toward the wall surface of the refining hearth 5, collides with this wall surface, and the direction of the flow changes. The molten metal whose flow direction has changed flows toward the outlet 5b of the refining hearth 5, that is, the supply port to the mold 6.

The manufacturing apparatus 1 has a melting hearth 4 and a refining hearth 5, but the present invention is not limited to this form, and one hearth in which the melting hearth and the refining hearth are integrated can also be used.

The mold 6 cools the molten metal supplied from the refining hearth 5 to make an ingot 0. An irradiation means for irradiating the supplied molten metal with an electron beam may be provided above the mold 6. As a result, the molten metal supplied to the mold 6 can be agitated by the electron beam from the irradiation means.

Further, the bottom portion of the ingot 0 is fixed to a dummy block (not shown) formed on the support base 13. The support base 13 is connected to the movement control device (not shown) via the shaft 14. The movement control device includes a mechanism for controlling the vertical movement of the support base 13, and further includes a mechanism for controlling the rotation (forward rotation, reverse rotation) of the shaft 14 around the axis.

2. Manufacturing Method As shown in FIG. 2, in the method for manufacturing a titanium ingot according to the present embodiment, the molten metal in the mold 6 is cooled, and a semi-ingot having a molten portion at the upper part and a solidified portion at the lower part (not shown). (Omitted), and the lower part thereof is pulled out vertically downward to continuously produce titanium ingot 0. As shown in FIG. 2A, by moving the support base 13 vertically downward, the titanium ingot 0 is moved vertically downward by a predetermined distance (d), and the lower part of the semi-ingot (not shown) is vertically moved. Move it downward and stop the movement (pulling process). Subsequently, as shown in FIG. 2B, by moving the support base 13 vertically upward, the titanium ingot 0 is moved vertically upward by a predetermined distance (0.05d to 0.80d), and the semi-casting is performed. The lower part of the mass (not shown) is moved vertically upward and the movement is stopped (pushing step). Do this work multiple times. That is, as shown in FIG. 2 (c), the drawing step is carried out by moving the support base 13 vertically downward, and then, as shown in FIG. 2 (d), the support base 13 is moved vertically upward. By moving, the pushing process is carried out.

As a result, the solidified shell is raised against the static pressure acting on the solidified shell, so that a pressure larger than the static pressure acts on the solidified shell, especially the thin solidified shell near the bottom of the molten metal. Since the solidified shell is pressed against the inner wall of the mold, the deformation of the solidified shell is eliminated, and a titanium ingot having good surface quality can be produced, which is an ingot having good surface texture.

As shown in FIG. 3A, in the method for producing a titanium ingot according to another embodiment, the titanium ingot 0 is moved vertically downward by a predetermined distance (d) by moving the support base 13 vertically downward. By moving, the lower part of the semi-ingot (not shown) is moved vertically downward, and the movement is stopped (drawing step). Subsequently, as shown in FIG. 3B, by rotating the support base 13 in one direction around the axis of the shaft 14, the lower portion of the semi-ingot is rotated around the axis of the mold at a predetermined rotation angle (θ). Rotates in one direction (the direction of the arrow in FIG. 3B is defined as forward rotation) and stops the rotation (forward rotation step). Next, as shown in FIG. 3 (c), by rotating the support base 13 around the axis of the shaft 14 in the direction opposite to that of FIG. 3 (b), the lower part of the semi-ingot is moved around the axis of the mold. Reverse rotation (the direction of the arrow in FIG. 3C is reverse rotation) at a predetermined rotation angle (0.05θ to 0.80θ) in the direction opposite to the one direction, and stop the rotation (reverse rotation). Process). Next, as shown in FIG. 3D, by moving the support base 13 vertically upward, the titanium ingot 0 is moved vertically upward by a predetermined distance (0.05d to 0.80d), and the semi-casting is performed. The lower part of the mass (not shown) is moved vertically upward and the movement is stopped (pushing step). Do this work multiple times. That is, subsequently, as shown in FIG. 3 (e), the drawing step is carried out by moving the support base 13 vertically downward, and then the forward rotation step, the reverse rotation step, and the pushing step are carried out.

Hereinafter, specific conditions of the drawing step, the forward rotation step, the reverse rotation step, and the pushing step in the titanium ingot manufacturing method according to this embodiment and other embodiments will be described.

(First step) Pulling step In this step, the ingot is pulled out intermittently, so it is evaluated by the average pulling speed, and the average pulling speed is the sum of the pulling time and the stopped time. It is calculated by dividing the value. The average withdrawal speed is preferably 100 to 2000 mm / hour. If the average drawing speed is less than 100 mm / hour, the temperature of the molten metal in the mold may drop during drawing and the molten metal may solidify. To prevent this, when the molten metal surface is irradiated with an electron beam or plasma, titanium evaporates in the case of pure titanium, and in the case of titanium alloy, alloy components such as aluminum evaporate in addition to titanium, and the evaporation thereof. Since the amount is large, a large amount of vapor deposition may adhere to the vacuum chamber, causing operational troubles. If the average drawing speed exceeds 2000 mm / hour, the solidification shell formed just below the surface of the molten metal in the mold will not grow sufficiently, and breakout may occur when the ingot is pulled out. Therefore, it is desirable that the average drawing speed is 100 to 2000 mm / hour.

It is desirable that the distance (d) at one time when the ingot is pulled out intermittently is 1 to 20 mm. If the drawing pitch is less than 1 mm, the casting time of the ingot becomes long, so that the temperature of the molten metal surface in the mold is lowered and solidification of the molten metal surface is likely to occur. When the molten metal surface is irradiated with an electron beam or plasma to suppress this, the amount of evaporation of titanium and alloy components increases. Further, a large amount of evaporated titanium adheres to the inner wall of the vacuum chamber, and when it falls into the mold, there arises a problem that the molten metal component changes significantly. Further, if the drawing pitch exceeds 20 mm, the solidified shell formed under the surface of the molten metal in the mold cannot grow in time, and the molten metal above the solidified shell wraps around between the solidified shell and the inner wall of the mold during the drawing. It may cause a breakout. For this reason, the pull-out pitch is preferably 1 to 20 mm.

(Third Step) Forward Rotation Step After the step (1) above, a forward rotation step may be carried out. This step is a step of rotating the lower part of the semi-ingot obtained in the first step in the forward direction around the axis of the mold in one direction and stopping the rotation. By this step, the depth of the molten pool is made rotationally symmetric, and it becomes easy to form a uniform solidified shell.

The rotation speed of the ingot is preferably 1 to 120 times / hour. At one revolution or more per hour, the shape of the molten pool becomes uniform, the stress applied to the solidified shell in the mold is weakened, and the surface texture of the ingot is further improved. Further, when the rotation speed is 120 rpm or less, the frictional force between the mold and the solidified shell is suppressed, and the strength of the solidified shell against the frictional force is sufficiently secured, so that the risk of breaking of the solidified shell can be reduced. Therefore, the rotation speed is preferably 1 to 120 rotations per hour.

(Fourth Step) Reverse Rotation Step After the first step, the third step may be carried out, and then the reverse rotation step may be further carried out. In this step, the lower part of the semi-ingot obtained in the third step is around the axis of the mold, and in the direction opposite to the forward rotation of the third step, 0.05θ to 0.80θ (however, θ). : It is a process of rotating in the reverse direction at a rotation angle of forward rotation) and stopping the rotation. By adding this step to the third step, the rotational symmetry of the molten pool depth is enhanced, and as a result, wrinkles on the ingot surface are significantly reduced.

The rotation angle of the reverse rotation is preferably 0.05θ to 0.80θ, where θ is the rotation angle of the forward rotation. When the rotation angle of the reverse rotation is 0.05θ or more, the inclination of the solidified structure of the solidified shell can be reduced and the effect of reducing the wrinkles on the ingot surface can be increased. On the other hand, when the rotation angle of the reverse rotation is 0.80θ or less, the time required for the reverse rotation is slightly longer, but the effect of reducing wrinkles on the surface of the ingot can be fully enjoyed.

The rotation speed of the ingot is preferably 1 to 120 times / hour. At 1 rpm or more, the shape of the molten pool can be made rotationally symmetric with respect to the center line of the mold, the stress applied to the solidification shell in the mold becomes slight, and the deformation of the ingot surface can be suppressed. The surface texture becomes good. Further, when the rotation speed is 120 rpm or less, the frictional force between the mold and the solidified shell is suppressed, and the strength of the solidified shell against the frictional force is sufficiently secured, so that the risk of breaking of the solidified shell can be reduced. Therefore, the rotation speed is preferably 1 to 120 rotations per hour.

(Second Step) Pushing Step In this step, the lower part of the semi-ingot obtained in the first step is moved vertically downward from 0.05d to 0.80d (however, d: in the first step). Distance) This is a process of moving vertically upward and stopping the movement. By this step, the solidified shell grown in the previous step is pushed up and integrated with the solidified shell grown after that, and the thickness of the solidified shell formed below the surface of the molten metal can be increased. This makes it possible to increase the strength of the solidified shell. In addition, since this step raises the solidified shell against the static pressure acting on the solidified shell, a pressure larger than the static pressure acts on the solidified shell, especially the thin solidified shell near the bottom of the molten metal. It will be. Then, since the solidified shell is pressed against the inner wall of the mold, the deformation of the solidified shell is eliminated, and an ingot having a good surface texture is obtained.

The moving distance of the lower part of the semi-ingot to the vertical direction is in the range of 0.05d to 0.80d, where d is the moving distance of the lower part of the semi-ingot in the first step. When this moving distance is less than 0.05d, there is a problem that the amount of increase in the thickness of the solidified shell is small and the deformation of the solidified shell cannot be sufficiently eliminated. On the other hand, if this moving distance exceeds 0.80d, the effect of eliminating the deformation of the solidified shell is saturated, and the operating time is required for the time required for ascending, resulting in a problem that the operating efficiency is lowered. There is.

In this step, the ingot is pushed in intermittently, so it is evaluated by the average pushing speed, and the average pushing speed is calculated by dividing the pushing length by the total of the pushing time and the stopped time. .. The average pull-out speed is also obtained by the same method as the average push-in speed, and the average push-in speed / pull-out speed is preferably 0.2 to 0.7. When the average pushing speed / pulling speed is 0.2 or more, the pushing does not take a long time and the risk of solidification of the molten metal surface is eliminated. When the average pushing speed / drawing speed is 0.7 or less, the waviness of the molten metal surface in the mold is suppressed, the solidification just below the molten metal surface becomes uniform, and the thermal stress becomes uniform, so that the surface of the ingot Can prevent cracking. Therefore, it is desirable that the average pushing speed / pulling speed is 0.2 to 0.7.

3. 3. Titanium ingots The chemical components of titanium ingots that can be produced by the production method according to this embodiment are listed below.

In the case of titanium alloy, Al: 4.1 to 7.5%, Fe: 0.1 to 2.1%, V: 2.8 to 5.0%, O: 0.03 to 0.5%, N : 0.005 to 0.2%, C: 0.005 to 0.2%, the balance Ti and impurities are exemplified.

Al is an α-stabilizing element and has the effect of improving Young's modulus and reducing the density. When the content is 4.1% or more, the strength can be ensured, the density can be sufficiently reduced, and the weight can be reduced. Further, when the content is 7.5% or less, _{the formation of Ti 3} Al is suppressed and embrittlement can be prevented. Therefore, the Al content was set to 4.1 to 7.5%.

Fe is a β-stabilizing element, and its strength increases according to the amount of addition, and the fatigue strength improves. When the content is 0.1% or more, the increase in strength is large and the effect is recognized. Further, when the content is 2.1% or less, the segregation at the time of solidification is not remarkable, and the segregation can be eliminated in the processing heat treatment step. Therefore, the Fe content was set to 0.1 to 2.1%.

V is a β-stabilizing element and improves cold workability. When the content is 2.8% or more, the effect of improving cold workability is exhibited. Further, since V is a relatively expensive element, it is economically desirable to limit it to 5.0% or less. Therefore, the V content was set to 2.8 to 5.0%.

O, N, and C are α-stabilizing elements, and the amounts contained as impurities are 0.03 to 0.5% for O, 0.005 to 0.2% for N, and 0.005 to C for C. It is 0.2%. There is a tendency to improve the strength by increasing the content of these elements, but if the above upper limit is exceeded, the ductility of the product will decrease. On the other hand, even if the content is lowered so as to be less than the above lower limit value, the ductility is not improved and the manufacturing cost is increased. Therefore, O was 0.03 to 0.5%, N was 0.005 to 0.2%, and C was 0.005 to 0.2%.

In the case of industrial pure titanium, O: 0.15% or less, Fe: 0.20% or less, N: 0.03% or less, C: 0.08% or less, H: 0.013% or less, and the balance Those that are Ti are exemplified. If it exceeds the above range, the ductility of the product will decrease. Therefore, the components of each element are within the above range.

In order to confirm the effect of the continuous casting method of the slab of the present invention, the following tests were carried out and the results were evaluated.
(1) Melting and Casting Conditions In order to confirm the effect of the present invention, the following tests were carried out using the manufacturing apparatus 1 shown in FIG. 1 (the mold 6 has an annular shape), and the results were evaluated.
(1-1) Molten component: Ti-6.4% Al-4.2% V
(1-2) Molten temperature: 1700 ° C (melt temperature in refining hearth 5)
(1-3) Inner diameter of mold 6: 650 mm
(1-4) Dissolved amount: 8000 kg
(1-5) Dissolution rate: 800 kg / hour (1-6) Irradiation method: Electron beam (1-7) Hearth: The following two types (melting hearth 4 and refining hearth 5)
(I) Melting hearth 4
The melting hearth 4 is a hearth for melting the raw material 7 with an electron beam, storing the molten metal, and supplying it to the refining hearth 5. The dimensions are width 500 mm × length 1500 mm × depth 100 mm.
(Ii) Refining Hearth 5
The refining hearth 5 is a hearth for temporarily storing the molten metal from the melted hearth 4 and supplying it to the mold 6. The dimensions are width 500 mm × length 1000 mm × depth 150 mm.
(1-8) Connection angle of melting hearth 4 and refining hearth 5: right angle (1-9) melting raw material 7: briquette (1-10) melting raw material 7 having a diameter of 100 mm and a length of 200 mm, which is a mixture of sponge titanium and alloy components. Dissolution method: The dissolution raw material 7 is continuously supplied according to the dissolution rate, or the dissolution raw material 7 is added in batches into the dissolution hearth 4 in 8 batches of 1000 kg each.
(1-11) Electron beam irradiation means: Two irradiation means 3 for dissolution of raw material 7, two irradiation means 9 for dissolution hearth 4, two irradiation means 9 for refining hearth 5, and irradiation means for mold 6 (1-11) A total of 7 units (not shown) were prepared.
(1-12) Movement control device (not shown)
The movement control device includes a mechanism for controlling the vertical movement of the support base 13, and further includes a mechanism (servo motor) for controlling the rotation (forward rotation, reverse rotation) of the shaft 14 around the axis. The movement and rotation are performed via a dummy block (not shown) formed on the support base 13.

(2) Evaluation The drawing conditions, rotation conditions, and pushing conditions of the ingot are changed in various ways, and each process is continuously performed from the start to the end of casting to perform semi-continuous casting to obtain the surface texture of the ingot. We examined the improvement.

Wrinkles peculiar to semi-continuous casting are formed on the surface of the ingot. In order to evaluate the effect of reducing the wrinkles, a sample of a vertical cross section was taken from the surface layer of the ingot, and the difference in surface unevenness was dimensionally measured. As for the difference in surface unevenness, 2.0 mm or less was passed, and more than 2.0 mm was rejected. If it is 1.5 mm or less even in the pass, wrinkles are not conspicuous and it is more preferable. According to the present invention, it has been found that this value is small and the unevenness generated on the surface is small.

The presence or absence of surface cracks in the ingot was evaluated by visually observing the surface of the ingot. It was found that the present invention can suppress surface cracking.

It was also found that breakout can be suppressed by appropriately determining the drawing conditions, pushing conditions, and rotation conditions of the ingot.

As shown in Table 1, in the example of the present invention, it is possible to produce an ingot having good surface quality.

Claims (3)

The molten metal obtained by irradiating a raw material whose main component is titanium with an electron beam is supplied to Haas, and a part of the molten metal is cooled and solidified to be separated, while the remaining molten metal is used as a ring-shaped mold. It is a method for producing a titanium ingot made of industrial pure titanium or a titanium alloy by supplying and drawing the molten metal in the mold vertically downward while cooling it.
The first step of moving the lower part of a semi-ingot having a molten part at the upper part and a solidifying part at the lower part vertically downward by 1 to 20 mm at an average speed of 100 to 2000 mm / hour, and stopping the movement.
A second step of moving the lower part of the semi-ingot vertically upward by 0.05 d to 0.80 d (however, d: a moving distance vertically downward in the first step) and stopping the movement is provided. ,
A method for producing a titanium ingot, wherein the first step and the second step are performed a plurality of times. After the first step and before the second step,
A third step in which the lower part of the semi-ingot is rotated forward in one direction around the axis of the mold and the rotation is stopped, and the lower part of the semi-ingot is rotated around the axis of the mold in one direction. The titanium according to claim 1, wherein a fourth step of rotating in the reverse direction at a rotation angle of 0.05θ to 0.80θ (however, θ: the rotation angle of the forward rotation) and stopping the rotation is carried out. Ingot manufacturing method. The rotation speed of the forward rotation or the reverse rotation is 1 to 120 times / hour.
The method for producing a titanium ingot according to claim 2.

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