JPH1025527A - Manufacture of high purity titanium material, and multistage melting method of titanium ingot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacture of a high purity titanium material suitable for sputtering target material, etc., from spongy titanium. SOLUTION: A titanium ingot is produced by applying multistage melting to spongy titanium as raw material. At this time, remelting is performed after the surface layer of the titanium ingot obtained in the preceding melting stage is removed. It is preferable to remove the surface layer of the titanium ingot obtained by the preceding melting by a depth of 0.1-20mm, and the high purity titanium material which contains <=400ppm oxygen and <=1ppm of Cu, Mn, and Pb and in which the amount of metallic components having a vapor pressure under melting conditions higher than that of Ti are limited to <=1ppm can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to titanium sponge produced by the crawl method or the Hunter method,
The present invention relates to a method for producing a high-purity titanium material which can be suitably used for applications such as a sputtering target material, and a multi-step melting method for a titanium ingot.

[0002]

2. Description of the Related Art Titanium sponge is obtained by a chlor method of reducing titanium tetrachloride produced by chlorinating a raw ore with metallic magnesium or a Hunter method of reducing with metallic sodium. For example, cylindrical titanium sponge produced by the Kroll method is cooled after removing unreacted magnesium and by-product magnesium chloride in a vacuum separation step after completion of the reduction reaction, and extruded from a reaction vessel in a crushing step. A lot is formed by crushing and mixing to a diameter and stored in a closed drum.

[0003] The production of titanium metal by the Kroll method is carried out in a vacuum or under an atmosphere of an inert gas such as argon and the like, with the outside air being completely shut off. It has been confirmed that the content of impurities such as oxygen and iron becomes higher due to the contact with the atmosphere and the contamination from the contact portion with the reaction vessel as compared with the part.

[0004] Therefore, the titanium sponge of batch size purified by vacuum separation becomes higher in purity from the upper and lower surfaces and the outer peripheral surface toward the center, so that it is used in application fields where high purity is required such as in the electronics field. Has been reported to use titanium sponge collected from this central site as a raw material (Metallurgical Society of
AIME 1988. "Light Metals" 1988. P759-768). It also introduces the use of 4nine5 (99.995%) high-purity titanium material produced from raw materials collected from the center of the crawl titanium sponge as a high-purity titanium material for use in semiconductor devices. [Titanium Association to the 21st Century] (1992)
2. P115 to 123)].

[0005] In addition, LS from sponge titanium by the crawl method is used.
As means for obtaining a titanium material excellent as an element thin film of a wiring material for I, the bottom and top of a cylindrical batch of titanium sponge and the remaining part obtained by cutting a specific part from the circumference toward the center, that is, the sponge titanium in the center part Is dissolved to have an oxygen content of 300 ppm or less, Fe, Ni, Cr, A
A method for producing a high-purity titanium material having a content of each element of l and Si of 10 ppm or less has been proposed (JP-A-7-258765).

[0006] Titanium as an industrial material is produced by melting titanium sponge to produce an ingot, and is processed into a product material through processing steps such as casting and rolling. Therefore, the effect of the melting step on the quality characteristics of the titanium material Is something that cannot be ignored.

As a method for melting titanium or a titanium-based alloy, a consumable electrode type vacuum arc melting method (VAR), a plasma electron beam melting method (PBR), and an electron beam melting method (EB).
R), a non-consumable electrode arc melting method, an electroslag melting method (ESR), etc. are known, and each method has advantages and disadvantages, but the method most widely adopted as a method for dissolving high-purity titanium is a consumable electrode type vacuum arc method. This is a dissolution method (hereinafter abbreviated as VAR).

[0008] This VAR is a consumable electrode obtained by joining briquettes obtained by compression-molding sponge titanium using an electrode welding machine, and is used in a vacuum vessel provided with a water-cooled copper crucible for solidifying molten titanium. This is a method in which a consumable electrode is used as a cathode and an ingot is used as an anode to melt by a DC arc.

Generally, not only the VAR but also the titanium dissolution is performed not only in the primary dissolution but also in the secondary and tertiary dissolution in order to improve the homogeneity of the composition. In this case, since welding with a joint (stub) for melting in the next stage is necessary, the lower end surface or upper end surface of the ingot is cut and removed by a fixed amount, and then the next stage of melting is performed.

[0010]

As described above, sponge titanium produced by the crawl method becomes an industrial titanium material as a homogeneous ingot through a melting step. However, the bottom, top and outer peripheral surface of the cylindrical sponge titanium are used. However, even if only the high-purity portion of the central portion is dissolved by cutting it off, there is a problem that the purity is impaired by the contamination in the dissolving step.

In particular, in the case of VAR, melting is continued while maintaining a vacuum atmosphere of 10 ^-1 to 10 ^-4 torr, but an increase in the oxygen content in the ingot is considered to be caused by an extremely small amount of leakage in the melting step. Only careful attention has been paid to the management for that purpose. However, even with extremely strict control, the inventors noticed that the oxygen concentration and copper content tended to increase more than the raw material sponge titanium, and as a result of various studies on the cause thereof, the present inventors found that Chloride and the like that cannot be removed at the time of dissolution and remain on the surface layer portion (hereinafter simply referred to as “surface layer” or “surface layer portion”) of the outer surface except for the upper and lower surfaces of the ingot taken out of the water-cooled copper crucible (mold). It has been found that it adheres and easily absorbs moisture in the atmosphere and mixes as oxygen in the ingot in the next stage of dissolution to increase the oxygen concentration. Furthermore, from the standpoint of solidification segregation, they also found that the element having a large equilibrium distribution coefficient and being easily concentrated on the solid phase side, that is, oxygen, is concentrated on the surface layer of the ingot outer peripheral surface as a result. Further, among the components remaining as impurity elements in the sponge titanium, elements having a higher vapor pressure than Ti and a lower melting point, for example, Pb, Mn, Cu, Al, etc., are in contact with the low-temperature portion of the inner wall of the mold. It has been found that the solidification is liable to be solidified, and as a result, the solidification is concentrated on the surface layer on the outer peripheral surface of the ingot.

On the other hand, with respect to the copper content, due to friction when the ingot is taken out of the water-cooled copper crucible, the copper adhered to the surface layer of the ingot is mixed into the ingot at the next melting, and the copper content is higher than that of the raw material sponge titanium. It was found that it would be.

The present invention has been completed on the basis of these findings, and its object is to provide a method of manufacturing a high-purity titanium material which can be suitably used for applications such as a sputtering target material from titanium sponge, and a titanium ingot. To provide a multistage dissolution method.

[0014]

According to the present invention, there is provided a method for producing a high-purity titanium material according to the present invention, in which a sponge is melted in multiple stages to produce a titanium ingot. It is characterized in that the surface layer of the obtained titanium ingot is removed and then redissolved. Further, the method for producing a high-purity titanium material of the present invention is characterized in that the multi-stage melting includes two or more melting steps, and after removing the surface layer portion of the titanium ingot obtained in at least one melting step before re-melting, Redissolving is a structural feature. Further, the multi-stage melting method of the titanium ingot of the present invention is a method of manufacturing a titanium ingot by multi-stage melting of sponge titanium, in which the surface layer portion of the titanium ingot obtained by the previous melting step is removed and then redissolved. This is a structural feature.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail by taking a VAR method as an example. The raw material sponge titanium used in the practice of the present invention is the surface layer portion of the columnar sponge titanium manufactured by the crawl method, that is, the upper surface, the lower surface portion, and the central portion obtained by cutting and removing a certain amount of the circumferential portion. Used. At this time, from the surface layer of the columnar sponge titanium, toward the center, that is, as the cutting removal rate of the upper and lower surfaces and the outer peripheral portion is increased, the impurity element contained in the sponge titanium in the center decreases. The collected amount can be controlled according to the final target purity.
According to the above, sponge titanium sampled from the center in a specific amount is oxygen 450 ppm or less, Cu, Mn, Fe, Ni, C
Each element of r, Al, and Si contained impurities of 10 ppm or less.

The titanium sponge is crushed in a crushing step to an average particle size of about 10 mm, sieved, formed into briquettes by a compression press, and then joined by an electrode welding machine to form consumable electrodes.

The consumable electrode is placed in a melting furnace equipped with a water-cooled copper crucible containing a starting material at the bottom, and the inside of the furnace is 10 ^-1.
While maintaining the degree of vacuum at 〜１０10 ⁻⁴ torr, melting is performed by a DC arc using the consumable electrode as a cathode and an ingot as an anode, or using the consumable electrode as an anode and an ingot as a cathode.

Although the dissolution treatment is performed in multiple stages, the present invention provides a method for re-dissolving the ingot obtained in the previous dissolution after the dissolution in a stage prior to the final dissolution, in other words, in the process of re-dissolving the ingot obtained in the previous dissolution. In the case of the first dissolution, in the case of the tertiary dissolution, after the first or second dissolution, either after the first dissolution or after the second dissolution, the lower end surface (bottom) of the ingot taken out of the water-cooled copper crucible, In addition to cutting or removing the upper end face (crown), after removing the surface layer portion of the circumferential portion, the final stage of melting is performed to produce a high-purity titanium material. It is desirable to remove the surface layer portion by a depth (thickness to be removed) from the outer periphery toward the center of 0.1 to 20 mm, preferably 0.5 to 15 mm, and more preferably 2 to 10 mm. Although removal of 20 mm or more cannot be prevented, it is not preferable in consideration of the effect and economy. The removal means of the surface layer is generally mechanically cut and removed, but it may be appropriately performed by chemical treatment with a mixed aqueous solution of hydrofluoric acid and nitric acid, or a combination of the chemical treatment and mechanical cutting. Selected. By dissolving the ingot with the surface layer removed in this way as a consumable electrode for final dissolution, the impurity content of oxygen is 400 ppm or less, Fe, Ni, and Cr are 10 ppm or less, respectively, and Cu, Mn, Pb, and Al are It is possible to produce a high-purity titanium material having a metal component having a vapor pressure of 1 ppm or less and a vapor pressure higher than that of Ti under the dissolution condition of 1 ppm or less.

Although the present invention is suitable for the VAR method as described above, the above-mentioned dissolution, that is, the former dissolution is carried out by EBR or another dissolution method, and the final dissolution (re-dissolution) is carried out by the VAR method. Dissolution (prior dissolution) of
Even when the final dissolution (redissolution) is carried out by EBR or another dissolution method, it can be suitably applied. As described above, by removing the surface layer of the ingot by a desired thickness when forming the consumable electrode before re-melting, a high-purity titanium material can be obtained.

The combination of the method for removing the surface layer of the titanium ingot and the method for dissolving the titanium ingot in the present invention is exemplified as follows by secondary dissolution and tertiary dissolution. Table 1 shows the case of secondary dissolution,
Table 2 shows the case of the tertiary dissolution. In the case of the fourth or higher dissolution, the combination can be appropriately selected within a range that can be easily developed from this combination.

[0021]

[Table 1]

[0022]

[Table 2]

As described above, various processes other than the above can be used for the combination of the dissolving method of VAR, EBR, PBR and the like, and various processes can be performed. , And cost.

[0024]

Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples.

Example 1 High-purity sponge titanium obtained by cutting and removing the upper, lower and outer peripheral parts of sponge titanium purified by the Kroll method is pulverized in a crushing step, sieved, and sieved to obtain sponge titanium particles having an average particle diameter of 10 mm. I got The components of the titanium sponge were analyzed, and the results are shown in Table 3. Next, the sponge titanium particles were compression-molded into a briquette by a compression press machine, joined together by an electrode welding machine, and further welded with a stub to prepare a primary consumable electrode for VAR melting. By setting this primary consumable electrode to the cathode of a consumable electrode type vacuum arc melting furnace, and performing VAR melting by maintaining the degree of vacuum in the furnace at 10 ^-1 to 10 ^-4 torr using a water-cooled copper crucible as an anode, A primary ingot having an outer diameter of about 460 mm and a weight of about 2 tons was manufactured.

The lower end surface (bottom) of the primary ingot is cut smoothly so as not to hinder the welding of the stub, the projection on the upper end surface (crown) is cut off, and the side surface (surface layer) of the ingot is thickened. 2.5mm (5.
0 mm) After cutting and removing, a stub was welded to form a secondary consumable electrode. Next, a secondary dissolution (final dissolution) using a VAR was performed under the same conditions as in the primary dissolution except that the outer diameter of the water-cooled copper crucible was made larger than that in the primary dissolution, and the outer diameter was about 550 mm, and the weight was About 2 tons of secondary ingots were produced. The component analysis of the obtained secondary ingot was performed, and the results are shown in Table 3.

Example 2 Primary and secondary melting were carried out under the same conditions as in Example 1, and the surface layer of the obtained secondary ingot was cut and removed under the same conditions as in Example 1, followed by secondary melting. A tertiary dissolution by VAR was performed under the same conditions to produce a tertiary ingot. The components of the resulting tertiary ingot were analyzed, and the results are shown in Table 3.

Example 3 A primary ingot was manufactured by VAR under the same conditions as in Example 1 and the surface layer of the ingot was cut and removed under the same conditions as in Example 1, and then the degree of vacuum in the furnace was set to 10 ⁻³ to 10 ^−3. EBR melting was performed in an EB melting furnace maintained at ^-5 torr to produce a secondary ingot. The components of the resulting secondary ingot were analyzed, and the results are shown in Table 3.

Comparative Example 1 A secondary ingot was manufactured under the same conditions as in Example 1 except that the surface layer of the primary ingot was not cut off. The components of the resulting secondary ingot were analyzed, and the results are shown in Table 3.

[0030]

[Table 3]

From the results shown in Table 1, according to the present invention, oxygen, C
The content of impurities such as u, Mn, and Pb can be equal to or less than that of the raw titanium sponge. Further, the content of impurities such as Fe and Ni is about 1 ppm lower than that of the raw material titanium sponge, and it is possible to produce a titanium material having higher purity than the conventional method.

[0032]

According to the titanium material (titanium ingot) produced by the method of the present invention, the concentration of impurities contained in the raw titanium sponge, in particular, the VAR method is used in spite of using the conventionally known VAR melting method. Contrary to the belief that the oxygen content increases, it can be reduced to titanium sponge or less. Further, among impurity elements such as Cu, Mn, and Pb, elements having a vapor pressure higher than that of Ti under melting conditions and a low melting point can be reduced from the content of the raw material sponge titanium, and Fe, Ni It has also been confirmed that heavy metal elements such as. Therefore, the high-purity titanium material produced according to the present invention can be obtained as a titanium material of 4 nines (99.995%) or more, which can sufficiently cope with applications such as semiconductor devices.

Claims (6)

[Claims] 1. A method for producing a titanium ingot by dissolving titanium sponge in multiple stages, comprising removing the surface layer of the titanium ingot obtained in the previous melting step and then redissolving it. Manufacturing method. 2. The method according to claim 1, wherein the multi-stage melting comprises two or more melting steps, and the surface layer portion of the titanium ingot obtained in at least one melting step before the re-melting is removed and then redissolved. Manufacturing method of high purity titanium material. 3. The method for producing a high-purity titanium material according to claim 1, wherein the surface layer portion of the titanium ingot obtained in the previous melting step is removed at a depth of 0.1 to 20 mm and then redissolved. 4. The content of impurities in the titanium ingot after the final melting is 400 ppm or less oxygen, 10 ppm or less each of Fe, Ni, and Cr, and 1 ppm each of Cu, Mn, and Pb.
The metal component having a vapor pressure of not more than 1 ppm or less than Ti under the dissolution condition is 1 ppm or less.
The method for producing a high-purity titanium material according to the above item. 5. The method according to claim 1, wherein the multi-stage melting is a consumable electrode type vacuum arc melting, a non-consumable electrode type vacuum arc melting, an electron beam melting or a plasma arc melting and a combination thereof. Production method of high purity titanium material. 6. A method for producing a titanium ingot by melting titanium sponge in multiple stages, wherein the surface layer portion of the titanium ingot obtained in the previous melting step is removed and then redissolved. Multi-stage dissolution method.