JP2013252550A - Method of manufacturing titanium ingot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a titanium ingot in which rotation of generation of arc is promoted to efficiently dissolve a consumable electrode, thereby preventing a casting surface defect of a casting.SOLUTION: In a method of manufacturing a titanium ingot in which arc melting treatment that dissolves a consumable electrode 3 by generating arc between the consumable electrode 3 containing titanium and a mold 2 is performed twice to manufacture a titanium ingot; a raw material containing Cl is supplied by a side charge at the arc melting treatment of a first time so that at least 0.02 mass% of Cl may remain in a first ingot after the arc melting treatment of the first time.

Description

  The present invention relates to a titanium ingot manufacturing method for manufacturing a titanium ingot, for example, by melting a consumable electrode composed of pure titanium or a titanium alloy, and in particular, manufacturing a titanium ingot having excellent surface properties of a casting surface. On how to do.

Conventionally, in order to manufacture a titanium ingot, first, a sponge titanium as a raw material of titanium is pressed to produce a compact material, and a plurality of compact materials are connected to form a consumable electrode. Then, this consumable electrode is set in a melting furnace (in the mold), an arc is generated between the consumable electrode and the mold, and the consumable electrode is melted and cooled to manufacture a titanium ingot. Yes.
The production of this titanium ingot mainly uses a vacuum arc melting device [VAR (Vacuum Arc Remelting)] that melts consumable electrodes in a vacuum atmosphere or in an inert gas atmosphere. ) Are shown in Patent Literature 1 to Patent Literature 4.

In Patent Document 1, in a metal ingot melting method using an electron beam melting furnace, a mixture of an ingot (oxide ingot) obtained by firing an oxide and a granular metal material is used as a melting material. ing.
In Patent Document 2, a TiAl alloy ingot having a diameter of 200 mm or more is manufactured by casting a molten metal obtained by melting Ti and Al as melting raw materials by high-frequency induction melting in a ceramic crucible in a mold.

  Patent Document 3 discloses a technique of a metal ingot melting apparatus, which includes a vacuum chamber, a metal raw material supply means, an electron beam irradiation means for melting the metal raw material, and a molten metal. In a hearth-type electron beam melting furnace having a melting hearth to be held, a mold for pouring the molten metal, and a drawing means for ingots formed in the mold, It is characterized by providing a plurality.

  In Patent Document 4, a titanium ingot is manufactured while stirring the molten pool by rotating the arc at a rotation speed of 4.0 to 20.0 sec / rotation.

JP 2011-127148 A JP 2011-036877 A JP 2010-247202 A JP 2010-037651 A

  Although the titanium ingot can be manufactured by using the vacuum arc melting apparatus (vacuum arc melting method) shown in Patent Document 1 to Patent Document 4, the surface of the ingot is rough in the manufacturing process of the titanium ingot. There is a problem that (casting surface failure) occurs and the yield is lowered due to this casting surface failure. The term “yield” as used herein refers to the ratio between the input raw material and the clean ingot after removing defects such as irregularities and voids from the ingot surface.

The defective casting surface that occurs on the surface of the ingot is that when the consumable electrode is melted, the molten metal adheres to the inner wall of the mold (crucible) by splashing and becomes an undissolved deposit (splash undissolved part). It is considered that the splash undissolved part remains without being re-dissolved.
Therefore, in order to solve the defective casting surface, the arc generated between the consumable electrode and the molten metal is rotated so as to move in the mold (the inner wall of the pot) where the arc is stable, and the melt of the splash unmelted portion is melted by the arc heat. It can be promoted. However, the arc behavior is complicated by various factors such as stirrer agitation, natural magnetic field, and device characteristics, and it is difficult to achieve stable arc rotation. The reality is difficult.

Therefore, in view of the above problems, the present invention provides a method for manufacturing a titanium ingot capable of preventing casting surface defects by promoting the rotation of arc generation and efficiently dissolving a consumable electrode. Objective.

In order to achieve the above object, the present invention has taken the following measures.
That is, the technical means for solving the problem in the present invention is that a titanium ingot is formed by performing an arc melting process twice to melt an arc by generating an arc between a consumable electrode containing titanium and a mold. In the method for producing a titanium ingot for producing a raw material containing Cl during the first arc melting treatment, 0.02% by mass or more of Cl remains in the primary ingot after the first arc melting treatment. Supplying by side charge.

The Cl content ratio, which is the ratio of the Cl content contained in the raw material supplied by the side charge and the Cl content contained in the consumable electrode, is preferably 0.73 or more.
It is preferable to supply a sponge titanium containing the amount of Cl calculated by the following formula by side charge as the raw material for supplying Cl.

The raw material supplied by the side charge preferably contains one or more of LiCl, NaCl, and MgCl ₂ .
Another technical means of the present invention is a titanium casting for producing a titanium ingot by performing an arc melting process for generating an arc between a consumable electrode containing titanium and a mold and melting the consumable electrode a plurality of times. In the lump manufacturing method, one or more of LiCl, NaCl, and MgCl ₂ are applied to the surface of the consumable electrode in the final arc melting process, and the final arc melting process is performed. And

  According to the present invention, during the arc melting process, the rotation of arc generation is promoted, the consumable electrode can be efficiently melted, and casting surface defects can be prevented.

It is the figure which showed the procedure of the manufacturing method of a titanium ingot. It is a top view for demonstrating rotation of the arc in a casting_mold | template. It is a related figure of Cl amount of a primary ingot, and a yield. FIG. 6 is a relationship diagram between the content ratio of the amount of Cl contained in the charge raw material and the amount of Cl contained in the primary consumable electrode and the yield. It is a relationship diagram between the yield and the number of charges when MgCl ₂ is applied to the surface of the consumable electrode.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The titanium ingot is manufactured by melting a raw material composed of sponge titanium or the like in a mold (in a crucible) using a vacuum arc melting apparatus and cooling the molten metal.
FIG. 1 shows the procedure of a method for producing a titanium ingot.
First, a vacuum arc melting apparatus will be described with reference to FIG.

The vacuum arc melting apparatus 1 is a VAR apparatus (Vacuum) that melts a consumable electrode set in a mold 2 by arc discharge while the mold 2 is in a vacuum atmosphere or an inert gas atmosphere.
Arc remelting apparatus), which includes a mold 2, an electrode support 4 to which a consumable electrode 3 set in the mold 2 is attached, and a supply device 5 for supplying the raw material into the mold 2.
The mold 2 is provided with a cooling device (not shown) for cooling the mold 2, and arc discharge (sometimes simply referred to as an arc) generated between the consumable electrode 3 and the mold 2 is caused by the mold 2. An arc induction device (not shown) for rotating the arc by a magnetic field is provided so as to reach the entire inner wall. In addition, an opening 6 is provided in the upper part of the mold 2 to discharge the evacuated exhaust to the outside or supply an inert gas into the mold 2.

The electrode support 4 is movable up and down, and a predetermined voltage is applied between the electrode support 4 (consumable electrode 3) and the mold 2. The supply device 5 supplies, for example, a raw material 7 such as sponge titanium or recycled scrap (also referred to as a charge raw material 7 or simply a raw material 7) into the mold 2, and includes a hopper 8 for storing the raw material 7, and a hopper A conveyance chute 9 for supplying the raw material 7 in the mold 8 to the mold 2 is provided. The additional charging of the charge material 7 into the mold 2 by the supply device 5 is called “side charge”.

In such a vacuum arc melting apparatus 1, the consumable electrode 3 is attached to the electrode support 4 and a voltage is applied between the electrode support 4 and the mold 2, whereby an arc is generated between the consumable electrode 3 and the mold 2. An arc melting process (referred to as VAR melting) is performed in which discharge is generated and the consumable electrode 3 is melted by an arc.
In the VAR melting, as shown in FIG. 2, the arc is rotated around the consumable electrode 3 by an arc induction device. Further, during VAR melting, the raw material 7 supplied from the consumable electrode 3 and the hopper 8 is melted while the inside of the mold 2 is in a vacuum state or an inert gas atmosphere and side charging is performed, and the melted molten metal is cast into the mold. A titanium ingot is produced by cooling with the cooling device 2.

Now, in this invention, a titanium ingot is manufactured by performing VAR melt | dissolution by the vacuum arc melting apparatus 1 in multiple times. In this embodiment, the VAR melting is performed twice, and the second VAR melting corresponds to the “final round” in the casting by a plurality of times.
As shown in FIG. 1, first, in the first VAR melting (one before the final round), the charge raw material 7 is melted while performing side charging to supply the mold 2 in an inert gas atmosphere. In the second VAR melting (final round), first, the primary ingot 10 manufactured by the first VAR melting is set in the mold 2 as a consumable electrode 3, and the mold 2 is placed in a vacuum atmosphere to perform side charge. Dissolve without performing. In the second VAR melting, side charge is not performed, but the same vacuum arc melting apparatus 1 is used for the first VAR melting and the second VAR melting.

In the second VAR melting (final round), if the arc does not reach the inner wall of the mold 2 sufficiently, the undissolved portion of the splash adhering to the inner wall of the mold 2 cannot be melted by the arc. On the surface of the ingot after VAR melting, there are defects such as irregularities and voids, resulting in a defective casting surface, and ultimately the yield of the titanium ingot is lowered.
Therefore, the inventors have verified from various angles how the arc sufficiently reaches the mold 2 in the second VAR melting (final round) and melts the splash undissolved portion with arc heat.

  As a result, when the amount of Cl contained in the consumable electrode 3 used during the second VAR melting (final round) is large, the arc stabilizes the inner wall of the mold 2 during the VAR melting as shown in FIG. It was found that the arc efficiently rotates along the inner wall of the mold 2 while passing, and the splash unmelted portion can be melted by the arc heat. That is, if Cl is contained in the consumable electrode 3 in the second VAR melting (final round) and the primary ingot 10 in the first VAR melting (one before the final round), the rotation of the arc is improved. I found a trend.

  The inventors conducted further verification and investigated the Cl content in the primary ingot 10. Specifically, if the rotation of the arc is improved during casting, it is considered that the splash unmelted portion is reduced and the yield of the titanium ingot can be improved. And the yield of the titanium ingot when the second VAR melting was performed using the primary ingot 10 as the consumable electrode 3 was summarized.

FIG. 3 summarizes the relationship between the amount of Cl in the primary ingot (the amount of residual Cl) and the yield.
As shown in FIG. 3, when the Cl amount (residual Cl amount) of the primary ingot is less than 0.02 mass%, the yield may be as high as 98%, but the yield varies. There is 91% when the yield is low. On the other hand, when the amount of Cl in the primary ingot is 0.02% by mass or more, the yield can be 98% or more, and the high yield can be reliably maintained. Further, it was found that when the Cl amount of the primary ingot is 0.02% by mass or more, a high yield close to 100% can be achieved.

Therefore, in the present invention, the first time so that Cl remains 0.02 mass% or more in the primary ingot 10 one time before the last time, that is, after the first VAR melting (arc melting treatment). The raw material 7 containing Cl was supplied at the time of VAR dissolution.
Specifically, first, titanium sponge containing Cl and recycled scrap are put into the hopper 8 before the first VAR melting. At the time of the first VAR melting, the inside of the mold 2 is made an inert gas atmosphere, and sponge titanium containing chlorine and recycled scrap (charge raw material 7) are supplied from the hopper 8 into the mold 2 by side charge. Arc discharge is performed while melting the charge raw material 7 and the consumable electrode 3 so that 0.02 mass% or more of Cl remains in the primary ingot 10.

Here, when supplying sponge titanium containing Cl into the mold 2, it is conceivable that the mold 2 is in a vacuum state. However, when VAR melting is performed in a vacuum state, Cl remains in the primary ingot. In the present invention, therefore, Cl is supplied in an inert atmosphere rather than in a vacuum state in the mold 2.
The yield can be improved by setting the Cl concentration of the primary ingot to 0.02% by mass or more. However, if the Cl concentration of the primary ingot exceeds 0.10% by mass, a large amount of Cl May remain as impurities in the product or the mechanical properties may deteriorate. Further, if side charging with a Cl concentration of the primary ingot exceeding 0.10 mass%, the piping of the exhaust system of the vacuum arc melting apparatus 1 is easily corroded, the frequency of maintenance increases, and the equipment life May decrease. For this reason, the Cl concentration of the primary ingot is preferably 0.02 mass% or more and 0.10 mass% or less.

  The Cl concentration (residual Cl amount) A of the primary ingot can be obtained by Expressions (1) and (2).

As shown in equation (1), first-order relationship ingot volume V, primary ingot weight W of the ingot, the density of the primary ingot (density [rho ₁ of pure _titanium, the density of titanium sponge [rho ₂ ). Further, as shown in the formula (2), the Cl concentration (residual Cl concentration) A of the primary ingot is blended with the ratio x of undissolved sponge titanium remaining in the primary ingot and the sponge titanium of the charge raw material 7. It is represented by the blended value of the amount of Cl (the amount of Cl in the charge material) B. Therefore, in the first VAR melting, the ingot volume V of the primary ingot, the mass W of the primary ingot, the density ρ _{1 of} pure titanium, the density ρ _{2 of} sponge titanium, and the Cl amount of the charge raw material By applying B to the equations (1) and (2), the Cl concentration (residual Cl concentration) A of the primary ingot can be calculated.

  In the first VAR melting described above, the Cl concentration of the primary ingot is obtained by using the equations (1) and (2), and the obtained Cl concentration of the primary ingot is 0.02% by mass. As described above, side charging is performed, but the amount of Cl contained in the charge raw material 7 and the consumable electrode 3A (referred to as the primary consumable electrode) set in the vacuum arc melting apparatus 1 (mold 2) are included. The first VAR dissolution may be performed based on the Cl content ratio with respect to the Cl amount.

Specifically, the Cl content ratio obtained by dividing the Cl content contained in the charge raw material 7 by the Cl content contained in the primary consumable electrode [Cl content ratio = Cl content contained in the charge raw material ÷ primary consumable electrode The value of Cl content to be contained is set to 0.73 or more.
FIG. 4 summarizes the relationship between the content ratio between the amount of Cl contained in the charge material (charge material Cl amount) and the amount of Cl contained in the primary consumable electrode (electrode content Cl amount) and the yield. is there.
As shown in FIG. 4, when the Cl content ratio is less than 0.73%, there is a large variation even though some high yields are observed. On the other hand, when the Cl content ratio is 0.73% or more, the yield can be stabilized at a high yield around 98%.

  For example, among the titanium sponges used for the charge raw material 7 and the primary consumable electrode 3, the sponge titanium containing a high concentration of Cl is used as the charge raw material 7 in the first VAR melting and contains a relatively low concentration of Cl. Sponge titanium is used as the primary consumable electrode 3A in the first VAR dissolution. In addition, the relationship between the primary consumable electrode 3A used for the first VAR melting and the charge raw material 7, that is, the blending amount of the primary consumable electrode 3A and the charge raw material 7 so that the Cl content ratio is 0.73 or more. 1st VAR dissolution is performed.

If the Cl content ratio exceeds 10, as described above, a large amount of Cl remains as an impurity in the product, the mechanical properties deteriorate, the maintenance of the vacuum arc melting apparatus 1 increases, Equipment life may be reduced. Therefore, the Cl content ratio is preferably 0.73 or more and 10 or less.
Now, the amount of Cl contained in the sponge titanium is 0.02% by mass to 0.1% by mass, and the recycled scrap does not contain Cl. Therefore, the amount of Cl obtained by the formula (3) is included. Sponge titanium is preferably used as the Cl supply source from the side charge.

Here, the content ratio of sponge titanium in the charge raw material 7 is the ratio of sponge titanium to the charge raw material 7 and can be determined by the amount of sponge titanium (mass%) ÷ the amount of charge raw material (mass%). .
For example, when the content ratio of sponge titanium is 100% (all charge raw materials are sponge titanium), sponge titanium having a Cl content of 0.02% by mass may be used as the Cl supply source. Further, when the content ratio of sponge titanium is 40% (for example, 60% of recycled scrap is 40% of charge raw material 7 and 40% of sponge titanium), sponge titanium having a Cl content of 0.05 mass% is a Cl supply source. May be used.

As described above, in this embodiment, sponge titanium containing Cl is used as the supply source of Cl, but the supply source of Cl is not limited to sponge titanium containing Cl. For example, a raw material 7 containing one or more of LiCl, NaCl, and MgCl ₂ may be used as a Cl supply source.
As described above, according to the present invention, the raw material 7 such as titanium sponge containing Cl is supplied by side charge at the time of VAR melting (at the time of the first VAR melting) one time before the final round. The primary ingot 10 after the second VAR melting contains 0.02% by mass or more of Cl. In particular, since Cl is supplied by the side charge method, the raw material 7 containing Cl dissolves while being located outside the ingot, and therefore, Cl tends to exist on the surface side of the primary ingot 10.

  In addition, since the primary ingot 10 containing Cl is used as the consumable electrode 3 during the final VAR melting (second VAR melting), the action of Cl contained in the consumable electrode 3 (primary ingot 10) The arc discharge during the second VAR melting will pass through the inner wall of the mold 2 stably. That is, as shown in FIG. 2, in the second VAR melting, the arc efficiently rotates the inner wall of the mold 2 and melts the splash unmelted portion of the inner wall of the mold 2. It is possible to prevent a casting surface defect of a certain ingot.

In the embodiment described above, Cl is 0.0 in the primary ingot 10 after the first VAR melting.
Cl was supplied during the first VAR melting so that 2% by mass or more remained, and the primary ingot 10 containing the Cl was used as the consumable electrode 3 used for the second VAR melting. The VAR dissolution may be performed without intentionally supplying Cl, and Cl may be applied to the surface of the consumable electrode 3 used for the second VAR dissolution.

Specifically, in the first VAR melting, the consumable electrode 3 is melted while side-charging sponge titanium and recycled scrap. In this case, the sponge titanium may be anything different from the embodiment described above. That is, the titanium sponge used for the first VAR dissolution may contain no Cl or a trace amount of Cl.
Next, when the first VAR melting is completed, the primary ingot 10 manufactured by the VAR melting is used as the consumable electrode 3 in the second VAR melting, and LiCl, NaCl is formed on the surface of the consumable electrode 3. One or more of MgCl ₂ are applied. Then, the consumable electrode 3 coated with Cl is set in the mold 2, and the second VAR dissolution is performed while the mold 2 is in a vacuum state.

FIG. 5 shows the relationship between the yield and the number of charges when MgCl ₂ is applied to the surface of the consumable electrode used for the _second VAR melting and VAR melting is performed.
As shown in FIG. 5, when the second VAR dissolution was performed without applying MgCl ₂ to the surface of the consumable electrode 3, the yield was less than 93 to 99%, and the variation was large. In particular, 98% with respect to the total number of charges. The number of yield charges was 30% or less. On the other hand, when the second VAR dissolution is performed by applying MgCl ₂ on the surface of the consumable electrode 3 and the yield is 98% or more, the charge is the most, and the MgCl ₂ is not applied on the surface of the consumable electrode 3 Compared with, the yield was greatly improved. The same effect can be obtained by applying LiCl and NaCl other than MgCl _{2 to} the surface of the consumable electrode 3 used for the second VAR dissolution.

  As described above, in the titanium ingot manufacturing method for manufacturing a titanium ingot by performing an arc melting process for melting the consumable electrode by generating an arc between the consumable electrode containing titanium and the mold. A predetermined amount of Cl is made to exist by applying Cl to the surface of the consumable electrode in the final VAR melting (second arc melting treatment). Therefore, in the final VAR melting, rotation of arc generation is promoted, so that it is possible to prevent casting surface defects after casting.

  In the embodiment disclosed herein, matters not explicitly disclosed, for example, operating conditions, various parameters, dimensions, weights, volumes, etc. of the components do not deviate from the range normally practiced by those skilled in the art. However, matters that can be easily assumed by those skilled in the art are employed.

DESCRIPTION OF SYMBOLS 1 Vacuum arc melting apparatus 2 Mold 3 Consumable electrode 4 Electrode support body 5 Supply apparatus 6 Opening 7 Raw material (charge raw material)
8 Hopper 9 Transport chute 10 Charge material

Claims (5)

In a titanium ingot manufacturing method for manufacturing a titanium ingot by performing an arc melting process of generating an arc between a consumable electrode containing titanium and a mold to melt the consumable electrode,
Titanium characterized by supplying a raw material containing Cl by side charge during the first arc melting treatment so that 0.02 mass% or more of Cl remains in the primary ingot after the first arc melting treatment. Ingot manufacturing method.   2. The titanium according to claim 1, wherein a Cl content ratio that is a ratio of a Cl content contained in a raw material supplied by the side charge and a Cl content contained in a consumable electrode is 0.73 or more. Ingot manufacturing method. 3. The method for producing a titanium ingot according to claim 2, wherein sponge titanium containing a Cl amount obtained by the following formula is supplied by side charge as the raw material for supplying Cl.
The raw material supplied by the side-charged, LiCl, NaCl, method of producing the titanium ingot according to any one of claims 1 to 3, characterized in that it contains one or two or more of MgCl ₂ . In the titanium ingot manufacturing method of manufacturing a titanium ingot by performing an arc melting process for generating an arc between a consumable electrode containing titanium and a mold and melting the consumable electrode a plurality of times,
A titanium ingot characterized in that one or more of LiCl, NaCl, and MgCl ₂ are applied to the surface of the consumable electrode in the final arc melting treatment, and the final arc melting treatment is performed. Production method.