JP2002167629A - Method for producing high purity titanium ingot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a homogeneous, high purity titanium ingot by using a raw material having an expanded allowable impurity concentration range without adding specified elements thereto. SOLUTION: A sponge titanium cake is produced by a Kroll process. A high purity sponge titanium lump is picked from the central part of the sponge titanium cake and is cut into a plurality of pieces of lump. The concentrations of one impurity selected from contained impurities and contained oxygen are measured for each cut lump. After that, each cut lump is arranged so as to make a gradient in the order of the measured impurity concentrations, and, welding is performed thereto. Provided that the high concentration side of the contained impurities is A, final dissolution is performed under condition that the tip of the final ingot is the part corresponding to A in the case of the impurity elements in which the distribution coefficient (S/L) between solid titanium (S) and liquid titanium (L) is >1. Alternatively, it is performed under condition that the bottom part of the final ingot is the part corresponding to A in the case of the impurity elements in which the distribution coefficient (S/L) is <1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-purity titanium ingot containing a very small amount of impurities from a sponge titanium cake produced by the Kroll method.

[0002]

2. Description of the Related Art In recent years, demand for high-purity titanium has been increasing in various fields such as semiconductor manufacturing and electronic equipment manufacturing. This high-purity titanium is obtained from a high-purity titanium ingot that is produced through a melting step using a sponge titanium cake that is usually made from a raw ore by a crawl method as a raw material.

[0003] As a conventional method for producing titanium for spreading, there is, for example, a production method described in Japanese Patent Publication No. 29722/1992. This is a titanium ingot for wrought material, and the target value of the component concentration is oxygen: 1300 ppm, F
e: 500 ppm. In addition, 15% corresponding to the top part of the secondary dissolution is adjusted so that oxygen is higher by 200 ppm and Fe is lower by 100 ppm than the target values. In practice, the adjustment of the oxygen concentration is made by adding tatatin oxide as an additive to the 15% portion corresponding to the top portion at the time of manufacturing the consumable electrode, thereby increasing the oxygen concentration, and making it equivalent to portions other than the top portion. % Iron iron powder was added as an additive.

[0004] Since the sponge titanium cake has a very large variation in impurity concentration due to the position of the batch, it must be crushed to a fine particle size by a crusher or the like, and unless blended and homogenized, it is used as a dissolving raw material for wrought material. Could not be used. Since the sponge titanium cake as the dissolving material has a high impurity concentration, a sponge titanium cake homogenized by a crushing step and a subsequent blending step is used.

On the other hand, in recent years, specifications required for a high-purity titanium material for semiconductor wiring are, for example, oxygen ≦ 300 pp.
Each element of m, Fe, Ni, Cr, Al, V, Sn, and Mo is extremely low as ≦ 10 ppm. Therefore, the above-mentioned Tokuhei 4-2
As in the production method described in Japanese Patent No. 9722, a method of positively adding oxygen or iron impurities in accordance with a target value to homogenize an ingot must be avoided as much as possible.

As described above, titanium sponge homogenized by the crushing step and the subsequent blending step cannot be used as a high-purity titanium material because of contamination of oxygen and metal impurities. Therefore, for example, Patent No. 286
As described in US Pat. No. 3469, a central part of a sponge titanium cake made in a batch mode is collected,
This is cut to a particle size of 10 to 300 mm with a cutting press,
There has been proposed a method in which a raw material is dissolved without passing through a crushing step and a subsequent blending step. In addition, it is desirable that the inner surface of the reduction container for producing the sponge titanium cake in a batch type is made of pure iron. For example, it is possible to use a reduction container in which the outer surface is made of stainless steel and the inner surface is made of pure iron using a clad material, or a reduction container in which pure iron is buttered (overlay welding) on the inner surface of the stainless steel container.

[0007] The above-mentioned production method is slightly inhomogeneous because the crushing step and the subsequent blending step are not used. It can be used as a dissolving material. However, if the addition of the impurities is avoided in this way, there is a problem that the oxygen concentration is low and the Fe concentration is high at the ingot top portion after the secondary melting, as described in Japanese Patent Publication No. 4-29722. Was.

[0008]

As described above, in the conventional method for producing high-purity titanium, when the ingot unit is increased, the impurity concentration of the ingot becomes non-uniform due to the dispersion of titanium sponge and macro-segregation. Even within the specification range, if even one kind of element is out of the specification range depending on the position, there is a defect that the entire ingot may not be used as high-purity titanium.

The method of producing a titanium ingot by adjusting the concentration by adding an oxygen source and an iron source in order to make the component concentration of the ingot uniform is required when the spec range of impurities is kept low. Can not be adopted.

[0010] Therefore, in order to produce high-purity titanium having a low impurity concentration by the conventional production method, the impurity concentration must be considerably lower than the upper limit of the specification. The method of collecting a sponge mass has a disadvantage that the yield is significantly reduced.

At present, for the production of high-purity titanium, a method of collecting a melted raw material from the center of a sponge titanium cake by the Kroll method has been carried out. However, recently, the impurity specifications of high-purity titanium have been diversified for each application. The titanium sponge maker selects and uses a lump taken from the central part of the titanium sponge cake as a dissolving raw material within the respective specification ranges. Therefore, depending on the specifications, not all lumps can be used, and only lumps having relatively high purity may be selected and used. For this reason, there is a problem that the high-purity lumps are insufficient, and the lumps that do not slightly satisfy the specifications are too much to be used as a raw material for producing high-purity titanium.

An object of the present invention is to eliminate the above-mentioned disadvantages of the conventional production method, and to obtain a uniform high-purity titanium ingot without adding a specific element. An object of the present invention is to provide a method for producing a high-purity titanium ingot that can ensure uniformity even when the size is increased and further expand the range of impurity concentration that can be used as a raw material for the ingot.

[0013]

Means for Solving the Problems In order to achieve the above object, the present inventors have continued the measurement of the impurity concentration by agglomerating high-purity sponge titanium cake into a plurality of pieces in the course of various experiments and examinations. Of these, it was found that the impurity concentration of each lump varied depending on the element. Therefore, when these agglomerates are used as a dissolving raw material, the solidified segregation can be used to dissolve the raw material in which the agglomerates are arranged and welded, that is, a consumable electrode, so that a gradient can be obtained at a specific impurity concentration. I understood. The present invention has been completed as follows based on this finding.

The agglomerate referred to in the present invention refers to the center of the sponge titanium cake, that is, at least 8% of the height from the top, at least 20% of the height from the bottom, and at least 10% of the diameter from the circumference of the sponge titanium cake. The cut-out central part is cut into a cubic or rectangular parallelepiped shape having a side of about 60 cm by a cutting press or the like, and further cut into a particle size of about 10 to 300 mm and packed in a drum. As for the method of collecting the central portion, it is desirable to cut off at least 10% of the height from the top, 30% or more of the height from the bottom, and 15% or more of the diameter from the circumference of the sponge titanium cake in order to reduce the impurity concentration.

According to the method for producing a high-purity titanium ingot of the present invention, a sponge titanium cake is produced by a crawl method, a high-purity titanium sponge lump is collected from a central portion of the sponge titanium cake, and divided into a plurality of chunks. After measuring the concentration of one or more types of contained impurities for each lump, arranging each mass so as to form a gradient in the order of the measured impurity concentration, melting and casting in that order to produce an ingot, When the high concentration side is A, final dissolution is performed under the following conditions. When the partition coefficient (S / L) between the solid titanium (S) and the liquid titanium (L) is more than 1, the top of the final ingot corresponds to A. When the partition coefficient (S / L) between the solid titanium (S) and the liquid titanium (L) is less than 1, the bottom of the final ingot corresponds to A.

A typical impurity element that poses a problem in a high-purity titanium incot is a partition coefficient (S /
When L) is more than 1, there are O, N, Al, Mo, Nb and the like, and when the distribution coefficient (S / L) is less than 1, Fe, N
i, Cr, As, Sn, C, V, Zr, Sb, Si and the like.

In the above method of manufacturing a high-purity titanium ingot, the method of melting in order is as follows. It is characterized by being dissolved by a method.

Further, in the above-mentioned method for producing a high-purity titanium ingot, the method of forming a gradient in the order of impurity concentration is as follows: When the end corresponding to the bottom is set to 1, when the position of {impurity concentration / (average value of impurity concentration)} for each lump is plotted, the absolute value of the slope of the linear approximation line is 0.1 or more. It is characterized in that the number of lumps is 10 or more.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the present invention makes use of the variety of the impurity concentration of each lump, the lump whose impurity concentration is not much lower than the upper limit of the specification, and furthermore, the impurity concentration of some lump is lower than the upper limit of the specification. When the solidifying segregation, that is, the solidifying of titanium as a solvent, is also performed using the oversized lump, the impurity element as a solute causes a certain partition coefficient (S / S) between solid titanium (S) and liquid titanium (L). Using the phenomenon distributed in L), the individual lumps are arranged so that the impurity concentration has a gradient.

At this time, the arrangement of the respective lumps is based on the distribution coefficient (S / L) between the solid titanium (S) and the liquid titanium (L).
Is more than one impurity element, and the distribution coefficient (S / L) is 1
It was reversed for the case of less than the impurity element. For example, impurity elements such as oxygen having a distribution coefficient (S / L) of more than 1 are dissolved in the final dissolution so that the top of the final ingot corresponds to the high concentration side. In addition, the distribution coefficient (S /
Conversely, the impurity element having L) of less than 1 is dissolved.

The titanium ingot, which has been finally melted as described above, is used as a billet, and all impurity concentrations whose specifications are set in a direction corresponding to the height direction of the ingot are measured. The concentration could be within the specification range, and the impurity concentration was uniform.

The sponge titanium cake produced by the crawl method used in the present invention is not limited in batch size, as long as a desired high-purity titanium sponge lump is obtained at the center of the sponge titanium cake. There is no limitation on the method of collecting the high-purity titanium sponge mass or the size of the mass. In order to obtain many combinations of impurity concentrations, it is desirable to collect a high-purity titanium sponge mass from as many sponge titanium cakes as possible.

The collected high-purity titanium sponge mass is divided into a plurality of masses, but the method of mass formation is not limited. However, 1
The weight per agglomerate is preferably in the range of 1 to 10% of the ingot weight. The reason is that if the concentration is less than 1%, the effect of making the impurity concentration of the ingot uniform does not become large, and the measurement of the impurity concentration increases, and it takes much time. If it exceeds 10%, the effect of making the impurity concentration of the ingot uniform is obtained. This is because it becomes smaller. The most desirable range is 2 to 6%. Also, it is not necessary to keep the weight per lump constant. And for the VAR compact press and the measurement of impurity concentration, assuming contamination prevention measures,
After pulverization, a step of further crushing may be added.

[0024] The present invention is a method for obtaining a homogeneous ingot by utilizing the variation in the impurity concentration of each lump,
If the number of lumps is too small, it may be difficult to form an appropriate gradient of the impurity concentration. Therefore, the number of used lumps must be at least 10 or more, and more preferably 20 or more.

Each of the lumps produced as described above is individually measured for the impurity concentration, but the measuring method is not limited. However, it is desirable to measure by the same method as that of the final product. For example, if the impurity concentration of a lump is measured using a measuring device of high frequency plasma emission spectroscopy (ICP), the impurity concentration of the final product is also measured using the same measuring device.

The lumps for which the measurement of the impurity concentration has been completed are arranged and welded so as to have a gradient in the order of the impurity concentration. Here, arranging means determining the order in which each mass is dissolved, and providing a gradient in the impurity concentration involves regressing the relationship between the impurity concentration of each mass and the order in which the mass is arranged in a straight line. This is because a straight line is inclined when the calculation is performed. In addition, the order of dissolving each mass can be determined by any of the following three methods.

A first method which is effective when many types of lumps having different combinations of impurity concentrations are stocked, first focuses on only the most important one impurity so as to fall within the scope of the present invention. Arrange in order of concentration. Next, the arrangement of other impurities is checked. If the arrangement does not fall within the scope of the present invention, be careful not to deviate from the scope of the present invention the arrangement of the impurities initially focused on the other impurities that are stored separately from the lumps to be used. Work to replace with lump,
The process is repeated by trial and error so that other impurities are arranged within the scope of the present invention.

A second method which is effective when a large number of types of lumps having different combinations of impurity concentrations are used is to focus on only one of the most important impurities and to fall within the scope of the present invention. Arrange in order of concentration. Next, the arrangement of other impurities is checked. If the arrangement is not within the scope of the present invention, the work of replacing the front and rear of the lumps is repeated by trial and error while paying attention so that the arrangement of the impurities initially focused does not deviate from the scope of the present invention. This is done so that the arrangement of other impurities is also within the scope of the present invention.

An effective third method when usable masses are predetermined is that when the distribution coefficients of two kinds of impurities a and b are more than 1 and less than 1, respectively, for example,
Arrange in the following manner. Let A be the value obtained by dividing the impurity a of each mass by the average impurity concentration of all the masses, and let B be the value obtained by dividing the impurity b of each mass by the average impurity concentration of all the masses. Assuming that the standard deviation of A is ST (A) and the standard deviation of B is ST (B), A ^{ST (B)} / B ^{ST (A)}
In order. If the distribution coefficients of the two types of impurities a and b are both more than 1 or less than 1, A ^{ST (B)}
× B Arrange in the order of ^{ST (A)} .

The gradient has no upper limit.
The reason is that the impurity concentration of the raw material used in the production of high-purity titanium ingots is naturally limited to a range determined by the lower limit concentration obtained by the Kroll method and the upper limit concentration of the spec or a concentration slightly higher than this. This is because the upper limit of the gradient is set. When the relationship between the dimensionless density C divided by the average density and the dimensionless number P divided by the total length in which the positions are arranged in the arrangement direction is linearly regression-calculated, the gradient C / P is absolutely lower. It is desirable that the value be 0.1 or more. Because, when the gradient C / P is less than 0.1, macrosegregation due to final dissolution acts to make the ingot non-uniform, and the effect of correcting abnormalities in impurity concentration due to macrosegregation due to final dissolution cannot be sufficiently obtained. Because. When the dissolution is performed twice or more in the case of VAR, the gradient C / P is desirably 0.2 or more.

In the method according to the third aspect, the absolute value of the slope of the linear approximation line is 0.1 or more when the impurity is a nonmetallic element such as oxygen or nitrogen, and the impurity is iron or nickel. In the case of the metal element, it is more preferably 0.3 or more.

It is desirable that all the impurity elements can be arranged so as to have a gradient. But,
There is a limit to the diversity of the impurity concentration, and the arrangement may be substantially difficult. In such a case, an element having a high impurity concentration or an element having a distribution coefficient (S / L) far apart from 1 is selected as a main element. For example, two elements of iron and oxygen are selected as main elements. What is necessary is to make the gradient only in the main element.

In the case of dissolving two or more times, the dissolving direction may be the same depending on the impurity concentration difference of the obtained raw material and the conditions of each dissolution such as the rate of increase of the ingot cross-sectional area. , And may be reversed. In a general vacuum arc melting method, it is more desirable to reverse the melting direction. This is because, even when the impurity concentration difference of the obtained raw material is small, the ingot can be made more uniform in the final second melting by increasing the concentration difference once in the first melting.

In the practice of the present invention, there is no limitation on the method of melting the titanium ingot, but melting by the vacuum arc melting method is most desirable in that the effect of macro-segregation can be more greatly utilized. If the raw material is supplied on the water-cooled copper hearth according to the order of the present invention, an electron beam melting method may be used.

[0035]

EXAMPLE A sponge titanium cake of about 7 tons was produced by the Kroll method. 10% height from the top, 20% height from the bottom and 12% of the diameter from the circumference of the titanium sponge cake
A high-purity titanium sponge mass was collected from the central portion where the was cut off. This high-purity titanium sponge mass was divided into 150 kg portions. Then, each concentration of iron (partition coefficient was less than 1) and oxygen (partition coefficient was more than 1) was measured for each agglomerate. These lumps are further pressed by a hydraulic press to a diameter of 470 mm.
Halved into 60 compact briquettes weighing 75 kg.

According to the practice of the present invention, 30 of the 60 compact briquettes in the above-mentioned 60 compact briquettes have a lump number 31 in Table 1.
As shown in Tables 60 to 60, the iron and oxygen concentrations were randomly arranged so as to have a gradient in the order, and were welded by plasma arc welding. The diameter was 470 mm, the number of steps was 30, and the weight was 4500.
kg of consumable electrode was produced. The results of the above example are shown in the graph of FIG. From this graph, it can be seen that the compact briquettes are arranged with a gradient in the order of the iron and oxygen concentrations of the impurities.

The other half of the compact briquette, 30
As shown in the lump numbers 1 to 30 as comparative examples in Table 1, the pieces were randomly arranged regardless of the magnitude of the measured iron and oxygen concentrations, and were welded by plasma arc welding to obtain a diameter of 470.
A consumable electrode having a thickness of 4,500 kg was prepared. The results of the comparative example are shown in the graph of FIG. From this graph, it can be seen that the compact briquettes are randomly arranged irrespective of the magnitude of the iron and oxygen concentrations of the impurities.

The above-mentioned consumable electrode is formed by a vacuum arc melting method.
As shown in Table 1, the comparative example was primarily melted in the direction of the stage number 1 and the example of the present invention was primarily melted in the direction of the agglomeration number 34 to prepare a primary ingot having a diameter of 560 mm and a weight of 4500 kg. Subsequently, the primary ingot was inverted and the comparative example was secondarily melted in the direction of the stage number 30 and the example of the present invention was secondarily melted in the direction of the lumps number 38. Each of the secondary ingots was 740 mm in diameter and 4500 kg in weight. An ingot was made.

The obtained secondary ingot was processed into a billet having a diameter of 155 mm by hot forging. Then, the concentrations of iron and oxygen were measured at one-fifth positions of the billet length. Table 2 shows the results.

[0040]

[Table 1]

[0041]

[Table 2]

From the test results in Table 2 above, regardless of the magnitude of the measured iron and oxygen concentrations, in the case of the comparative example in which compact briquettes were randomly arranged, the impurity concentration varied greatly depending on the position of the ingot. The top part exceeds the specifications, and it can be seen that the product yield is poor when used as a high-purity titanium ingot.
On the other hand, according to the embodiment of the present invention, the impurity concentration from the top to the bottom is in a uniform low range within the specification, and it can be seen that the entire ingot can be used as a high-purity titanium ingot.

[0043]

According to the present invention, a homogeneous high-purity titanium ingot can be produced without adding a specific element and using a raw material whose usable impurity concentration range is expanded.

[Brief description of the drawings]

FIG. 1 is a graph showing a linear approximation of iron and oxygen based on the data of Comparative Example in Table 1.

FIG. 2 is a graph showing a linear approximation of iron and oxygen based on the data of the example of the present invention in Table 1.

Claims (3)

[Claims] 1. A sponge titanium cake is produced by the Kroll method, a high-purity titanium sponge mass is collected from a central portion of the sponge titanium cake, and divided into a plurality of masses.
After measuring the concentration of contained impurities of more than one kind, arrange each lumps so that a gradient can be created in the order of the measured impurity concentration, and melt and cast in that order to produce an ingot. A is a method for producing a high-purity titanium ingot, wherein the final dissolution is performed under the following conditions. When the partition coefficient (S / L) between the solid titanium (S) and the liquid titanium (L) is more than 1, the top of the final ingot corresponds to A. When the partition coefficient (S / L) between the solid titanium (S) and the liquid titanium (L) is less than 1, the bottom of the final ingot corresponds to A. 2. A method of melting in order, wherein each mass is arranged and welded in the above order to produce a rod-shaped melting raw material and then melted by an electron beam melting method or a vacuum arc melting method. Item 4. The method for producing a high-purity titanium ingot according to Item 1. 3. A method of forming a gradient in the order of impurity concentration, in which, at both ends of each of the sequentially arranged lumps, the position of the end corresponding to the top of the final ingot is set to 0, and the end corresponding to the bottom is set to 1. When plotting the position of {impurity concentration / (average impurity concentration)} for each lump, the absolute value of the slope of the linear approximation line is 0.1 or more, and the number of lumps is 10 or more. The method for producing a high-purity titanium ingot according to claim 1, wherein: