JP7319536B2 - Melting raw material, melting raw material and ingot manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a molten raw material and a method for producing a molten raw material and an ingot.

When melting and casting a titanium alloy, a melting raw material called a master alloy is generally used. A master alloy is a high-concentration alloy used during melting. For example, when Mo and Al are added elements to a titanium alloy, an alloy of Al and Mo (Al--Mo alloy) may be used.

Titanium is a relatively light metal among practical metals and has a small specific gravity. On the other hand, elements such as Mo, Nb, Ru, and Ta, which are added to titanium alloys, have large specific gravities, sink in the direction of gravity when dissolved, and are difficult to dissolve and mix at a uniform concentration.

Also, the above element has a melting point higher than that of Ti. Specifically, the melting points of these elements are over 2000° C., which is higher than the melting point of Ti, 1668° C. Therefore, it is difficult to melt and tends to remain unmelted in the ingot.

In this way, due to the difference in specific gravity and melting point from Ti, the above-mentioned additive elements may remain undissolved. In addition, so-called macro-segregation, which is the occurrence of locally high-concentration portions in the ingot, tends to occur. For this reason, it is common to manufacture a titanium alloy using a mother alloy suitable for the purpose during melting. In this case, in order to make it easier to melt together with metallic titanium, the mother alloy can have a melting point of 2000° C. or less, which is close to that of titanium, and its specific gravity is about the same as that of titanium. In addition, the operability during production, such as mixing or dissolving raw materials, is improved.

For example, Patent Documents 1 to 4 disclose methods of manufacturing titanium alloys using mother alloys.

JP-A-2007-56363 WO2006/047692 JP-A-2-107733 JP-A-10-46269

However, in order to obtain the desired titanium alloy, preparing a master alloy in advance before casting causes an increase in manufacturing costs. Furthermore, even when titanium alloys are melted after preparing a mother alloy, segregation, etc. may occur if convection and stirring are not sufficient during melting due to the high concentration of additive elements in the mother alloy itself. There is As a result, it may not be possible to produce a titanium alloy having a uniform solute concentration.

An object of the present invention is to solve the above problems and to provide a molten raw material and a method for producing a molten raw material and an ingot that can reduce the production cost and suppress the occurrence of macrosegregation in a titanium alloy.

The present invention has been made to solve the above problems, and the gist of the present invention is the following molten raw material, molten raw material, and method for producing an ingot.

(1) A melting raw material used for manufacturing a titanium alloy,
The molten raw material contains an element having a melting point of over 2000°C,
When the total volume of the dissolved raw materials to be added is V and the total surface area is S,
A dissolved raw material, wherein the relationship between the total volume and the total surface area satisfies the following formula (i).
V/S≦100 (μm) (i)

(2) The molten raw material according to (1) above, wherein the element is at least one selected from metal Mo, metal Nb, metal Ru, metal Ta, and C.

(3) A melting material used for manufacturing a titanium alloy,
A melted raw material according to (1) or (2) above and an outer packaging material that wraps the melted raw material,
The melting point of the outer packaging material is 2000 ° C. or less,
melting material.

(4) The outer packaging material is selected from industrial pure titanium, industrial pure aluminum, industrial pure copper, industrial pure zirconium, industrial pure tin, titanium alloys, aluminum alloys, copper alloys, zirconium alloys, and tin alloys. The melting material according to (3) above, which is a foil or a thin plate made of one or more kinds of

(5) (a) The molten raw material described in (1) or (2) above, or the molten raw material described in (3) or (4) above is mixed with a metallic titanium raw material and encapsulated to form a compact or a step of manufacturing raw materials for melting hearth;
(b) melting the compact or melting hearth input raw material produced;
A method for producing a titanium alloy ingot.

According to the present invention, it is possible to obtain a molten raw material and a method for producing a molten raw material and an ingot that can reduce the production cost and suppress the occurrence of macrosegregation in a titanium alloy.

FIG. 1(a) is a diagram showing the results of dissolution simulation of metal Ru when the grain diameter is 45 μm, and FIG. 1(b) is a dissolution simulation of metal Nb when the grain diameter is 45 μm. It is a figure which shows the result of. FIG. 2 is a diagram showing the relationship between V/S and the time required for melting. FIG. 3 is a schematic diagram showing the shape of the compact. 4A and 4B are schematic diagrams showing the manufacturing procedure of the molten raw material. FIG. 4A is a schematic diagram when the molten raw material is added, and FIG. 4B is a schematic diagram when the molten raw material is formed. FIG. 5 is a schematic diagram showing measurement positions of the Ru content in a 1 t titanium ingot.

The present inventors have made various studies in order to obtain a molten raw material and a method for producing an ingot that can reduce the production cost and suppress the occurrence of macrosegregation. As a result, the following findings (a) to (d) were obtained.

(a) Using the aforementioned master alloy of elements such as Mo, Nb, Ru, and Ta lowers the melting point to 2000° C. or less compared to adding pure metals. For this reason, unmelted portions are less likely to occur in the ingot, and the occurrence of macro segregation is suppressed.

(b) On the other hand, macro segregation may occur even when a master alloy is used. When using the master alloy, the master alloy is pulverized or cut into lumps of several millimeters and mixed with metallic titanium raw materials such as sponge titanium and titanium scrap. At this time, if the bulk density of the metal titanium raw material and the bulk density of the crushed or cut master alloy are significantly different, uniform dissolution is not achieved due to uneven distribution during mixing and sedimentation during dissolution, and macrosegregation tends to occur. Become.

Furthermore, titanium is an element that is highly oxidized at high temperatures. Therefore, when casting a titanium alloy, from the viewpoint of suppressing oxidation, a vacuum arc melting method (also referred to as "VAR: Vacuum Arc Remelting") or a plasma arc melting method (also referred to as "PAM: Plasma Arc Melting") is used. ), or a melting method such as an electron beam melting method (also referred to as “EBR: Electron Beam Remelting”). In the case of a titanium alloy, when the heating temperature during melting is low, the temperature is about 2000°C. As a result, the range in which the raw material can be dissolved is narrowed, and undissolved material is more likely to be left undissolved.

(c) Therefore, it is desirable to be able to produce a titanium alloy in which the occurrence of macro-segregation is suppressed by using pure metal or the like without using a master alloy. Here, the present inventors investigated the dissolution mechanism in the case of using a pure metal or the like as a dissolution raw material without using a master alloy, based on a binary system equilibrium diagram of Ti and a pure metal element.

Considering the binary phase diagram, the above-described elements such as Mo, Nb, Ru and Ta tend to gradually decrease in melting point as the Ti concentration increases. For example, in the case of Ru, the melting point decreases until the Ti concentration reaches about 15% by mass. After that, in the Ti concentration range where TiRu is formed, the melting point once rises and exceeds 2000°C, but when the Ti concentration exceeds about 33% by mass, the melting point drops again to 2000°C or less. Furthermore, when the Ti concentration is about 70% by mass, the melting point drops to about 1550°C.

(d) Since the heating temperature in the melting method described above is about 2000°C, the Ti concentration is increased in a short time with respect to the melting raw material of the pure metal element existing in the solid phase state, and the melting point becomes 2000°C or less. It is desirable to control the composition within the range. As a result, it is possible to suppress the occurrence of unmelted residue and macro segregation, which may occur in the raw material for melting pure metal elements. Therefore, during melting, the pure metal element is surrounded by the molten Ti in a short time and the composition range of the pure metal element is such that the melting point becomes 2000° C. or lower in an early stage. It is effective to control the dissolved raw materials.

The present invention has been made based on the above findings. Each requirement of the present invention will be described in detail below.

1. Melting Raw Material The melting raw material according to the present invention is a melting raw material used for producing a titanium alloy (titanium ingot). Also, the raw material to be melted contains an element having a melting point of over 2000°C. This element is not particularly limited as long as the melting point is higher than 2000° C., but for example, it is one or more selected from metal Mo, metal Nb, metal Ru, metal Ta, and C (graphite, diamond, etc.). preferable.

Here, metal Mo refers to pure Mo used for industrial purposes, and the Mo content is usually 99% or more. Similarly, metal Nb, metal Ru, and metal Ta refer to pure Nb, pure Ru, and pure Ta for industrial use, and the content of each of the above elements is usually 99% or more.

2. Ratio of Total Volume to Total Surface Area of Melting Raw Materials The present inventors verified the time required for melting metal Ru, metal Nb, and metal Mo when the shape of the melting raw materials was granular powder. Verification was performed using simulation. In the simulation, a model was assumed in which the metal element was surrounded by molten Ti with a predetermined thickness, and the time required for the melting raw material to reach a 100% liquid phase was set as the time required for melting. Thermo-Calc2019a, DICTRA module was used for the simulation of the raw material to be dissolved.

(a) and (b) of FIG. 1 show simulation results until the melting raw materials of metal Ru and metal Nb are melted when the diameter is 45 μm. From (a) and (b) of FIG. 1, it can be seen that metal Ru and metal Nb are dissolved within about 0.3 s. Similarly, the time required for complete dissolution of metallic Ru and metallic Nb was about 30 seconds for metallic Ru and about 73 seconds for metallic Nb when the grain diameter was 1 mm in the simulation. Further, when the particle diameter is 4 mm, it takes about 3.5 minutes for metal Ru and about 29 minutes for metal Nb. The results of each simulation performed are summarized in FIG.

Further, a vacuum arc melting test was actually conducted using Ru as the melting raw material, using granular powder as the melting raw material. In the vacuum arc melting test, when the time required for melting exceeds 60 seconds and V/S (see simulation results in FIG. 2), the added melting raw material remains unmelted or significant macrosegregation occurs. A study was conducted with reference to the results of the vacuum arc melting test and the simulation results. According to this study, if the time required for melting is 60 seconds or less, it is considered that the unmelted raw material and macrosegregation described above do not occur.

As described above, Ti, whose melting point is 1668°C, melts before the solid phase of the metal element whose melting point exceeds 2000°C. After the molten Ti covers the solid phase of the metal element, the Ti concentration in the solid phase of the metal element increases due to interdiffusion. As a result, it is considered that the metal element melts while changing to a composition with a melting point of 2000° C. or less. Therefore, it is considered that the larger the total surface area S in contact with the molten Ti and the smaller the total volume V, the shorter the melting time of the raw material for melting the metal element.

Therefore, in the raw material to be dissolved according to the present invention, the relationship between the total volume and the total surface area satisfies the following formula (i), where V is the total volume of the raw material to be added, and S is the total surface area. The above V and S are the sum of the volume and area of the total amount of the raw material to be dissolved, and are referred to as total volume and total surface area.
V/S≦100 (μm) (i)

If the left-hand side value of the above formula (i) exceeds 100 (μm), it becomes difficult for molten Ti to cover the periphery of the element whose melting point exceeds 2000° C. in a short period of time. Then, the Ti concentration in the solid phase of the element does not increase, and the dissolution is not sufficiently achieved. As a result, diffusion of elements does not occur, and undissolved or macrosegregation occurs. Therefore, the left side value of the above formula (i) is set to 100 (μm) or less.

It is desirable to shorten the time required for melting and promote the diffusion of the above elements. Therefore, based on the study results, it is preferable to set the left side value of the formula (i) to 30 (μm) or less so that the time required for melting is shortened to 5 seconds or less. In addition, it is more preferable to set the left side value of the formula (i) to 13 (μm) or less so that the time required for melting is further shortened to 1 s or less. For the reason described above, the smaller the left side value of formula (i), the better.

The shape of the raw material to be dissolved is not particularly limited as long as it satisfies the above formula (i). The shape may be, for example, a granular powder, a thin wire shape, or a foil shape. In addition, in the case of a granular powder, V/S is 100 (μm) when the particle diameter is about 600 (μm). Also, when the shape is a thin wire with a length of about 10 mm, V/S is 100 (μm) when the diameter of the thin wire is 405 (μm). Furthermore, when the shape is a 10 mm square foil, the V/S is 100 (μm) when the thickness is about 205 (μm).

The S of V/S may be obtained by measuring the BET surface area (specific surface area per mass) by a gas adsorption method. As the measurement conditions at this time, the sample (powder, grain, foil, lump) is put into the measuring device, vacuum heating degassing is performed at 200 ° C. for 2 hours, and then liquid nitrogen is used at a temperature of 77 K. Adsorb _N2 , create a BET plot, and measure. The sample is adjusted to a size of 8 mm or less so that it can pass through a φ8 mm sample introduction tube and fit in a φ25 mm measuring chamber. In the present invention, ASAP2010 manufactured by Shimadzu Corporation is used as a measuring device. This is an effective measurement method for small particles such as powders and grains.

Further, the above V may be obtained by measuring the specific volume (reciprocal of density) by a gas replacement method in accordance with JIS R 1620:1995. In the gas replacement method, the sample is placed in the sample chamber (volume VCELL), and after the constant pressure P1 is set with He gas, the valve between the expansion chamber (volume VEXP) is opened and the sample chamber and the expansion chamber are connected. , the gas in the system expands to the pressure P2, so the measured pressures P1 and P2 are used to calculate the volume of the sample. As a specific device, Ultra Pycnometer Model 1000 manufactured by QUANTACHROME INSTRUMENTS can be used.

If the particle diameter exceeds 8 mm, the sample is too large to measure the BET surface area by the gas adsorption method. Therefore, when the raw material to be dissolved is powder, V/S may be calculated using a particle size distribution analyzer. Specifically, the V/S can be determined by calculating the radius of the particles by approximating them to a spherical shape using a particle size distribution analyzer.

As a measuring device, for example, a laser micron sizer LMS-3000 laser diffraction/scattering particle size distribution analyzer manufactured by Seishin Enterprise Co., Ltd. may be used. Further, the measurement conditions may be a shape factor of 1.00 (set as a sphere) and a solvent refractive index of 1.33 (using water as a dispersion medium). As a result, the specific surface area S/V per unit volume is measured, and the reciprocal thereof is calculated to obtain V/S.

3. Melting material Wrapping the above-described melting material in a material such as foil facilitates the operation when adding the melting material. In the present invention, the melted raw material wrapped in a material such as foil is called a melted raw material. The molten material is used to produce titanium alloy ingots. Further, the molten raw material includes the above-described molten raw material and an outer packaging material that wraps the molten raw material.

The melting point of the outer wrapping material is 2000° C. or lower. The material of the outer wrapping material is not particularly limited as long as it can wrap the raw material to be dissolved. For example, the outer wrapping material is one selected from industrial pure titanium, industrial pure aluminum, industrial pure copper, industrial pure zirconium, industrial pure tin, titanium alloys, aluminum alloys, copper alloys, zirconium alloys, and tin alloys. It is preferably a foil or thin plate made of the above.

Here, industrially pure titanium is a titanium material exemplified by JIS Classes 1 to 4 or ASTM/ASME Grades 1 to 4. Impurity elements of these industrially pure titanium include C, H, O, N, Fe, and the like. For example, the contents of these elements are C: 0.08% or less, H: 0.015% or less, O: 0.40% or less, N: 0.05% or less, and Fe: 0.50% or less. be. In industrially pure titanium of JIS 1 to 4 or ASTM/ASME Grades 1 to 4, it is preferable to use JIS 1 or ASTM/ASME Grade 1, which has a low impurity content, as the outer wrapping material.

Industrial pure aluminum has an Al content of 99% or more and is usually called 1000 series aluminum. Similarly, industrial pure copper has a Cu content of 99% or more. Technically pure zirconium has a Zr content of 99% or more. Industrial pure tin has a Sn content of 99% or more. Titanium alloys, aluminum alloys, copper alloys, zirconium alloys, and tin alloys may be general alloy types.

4. Production method Adjustment is made so that the raw material to be dissolved satisfies the formula (i). As described above, the shape and the like are not particularly limited as long as the above formula (i) is satisfied. A preferred method for producing a titanium alloy ingot using the above melting raw material and melting raw material will be described.

A method for producing a titanium alloy ingot according to the present invention comprises:
(a) a step of mixing the molten raw material or molten raw material with a metallic titanium raw material and encapsulating it to produce a compact or raw material for melting hearth input;
(b) melting the compact or melting hearth input material produced;
have

The above manufacturing method will be specifically described below. In addition, the case where the raw material to be dissolved is granular powder will be described as an example.

Titanium alloy melting methods include a vacuum arc melting method, a plasma arc melting method, an electron beam melting method, and the like. When the electron beam melting method or the plasma arc melting method is used, the melting raw material or the melting raw material and the metal titanium raw material are put into a melting hearth and melted. When a melting hearth is used, unlike the case of manufacturing a compact, the melting raw material and the titanium raw material are simply mixed in the melting hearth, and compression by a press, which will be described later, need not be performed. Then, in the melting step, the mixture of the melting raw material and the titanium raw material charged into the hearth (also referred to simply as "the raw material for melting hearth charging") is melted. In the following explanation, the vacuum arc melting method, which is a typical melting method, will be taken as an example.

In the case of the vacuum arc melting method, the raw material to be melted and the raw material of metallic titanium are mixed and compressed by press molding to produce a compact having a shape as shown in FIG. Here, the metallic titanium raw material refers to a raw material that serves as a supply source of titanium, such as sponge titanium and titanium scrap.

When manufacturing the compact, the melted raw material may be wrapped in a material such as foil and put into the melted raw material. This is because when the melted raw material is used, the operation of charging the melted raw material becomes easy even if the grains are very fine.

For example, a coil of foil or thin plate is continuously unrolled and rolled into a V-shaped or U-shaped curved shape, and then the raw material is melted into the curved part of the coil of foil or thin plate. (See Fig. 4(a)), after which a coil of foil or sheet is folded to enclose the molten raw material (See Fig. 4(b), (c)). If necessary, the edges of the foil or thin plate may be sealed by seam welding or the like when wrapping the raw material to be melted.

A plurality of the above compacts are manufactured, and the compacts are welded together in a vacuum to form a titanium consumable electrode. Vacuum arc melting is performed using the obtained titanium consumable electrode. Usually, in vacuum arc melting, from the viewpoint of homogenizing the concentration of additive elements, when melting a titanium alloy, the consumable electrode is turned upside down and the melting is performed multiple times. Many are double melts. Thus, in the production method according to the present invention, a titanium alloy ingot can be produced without using a master alloy.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples.

V/S was varied to produce melted raw materials. Metal Ru (purity 99.95%) powder was used as the melting raw material. This melted raw material was wrapped in a foil (JIS Class 1) made of industrial pure titanium to obtain a melted raw material. The melted raw material and the titanium metal raw material thus obtained were mixed and compression-molded by a press to produce a compact.

Vacuum arc melting was performed using the compact as a titanium consumable electrode. In the vacuum arc melting, melting was performed twice. In the second dissolution, dissolution was performed by turning the consumable electrode upside down from that in the first dissolution. Through the above steps, a 7 kg titanium alloy ingot having a diameter of 140 mm and a length of 80 mm was produced (see Test Nos. 1 to 5).

In addition, a lump of Ru metal with a size of 3 to 5 mm is used, mixed with a metal titanium raw material, a compact is produced, and the above-mentioned melting is performed to produce a 7 kg titanium alloy ingot with the same shape as the above. (see Test No. 6). Further, a Ti-30%Ru master alloy with a thickness of 3 to 5 mm was similarly mixed with the metallic titanium raw material to produce a compact. Subsequently, by performing the above melting, a 7 kg titanium alloy ingot having the same shape as above was produced (see Test No. 7). In addition, test No. In Examples 1 to 7, the target chemical composition was Ti-0.03% by mass Ru.

Table 1 shows the V/S in each example, the chemical composition of the entire titanium alloy ingot obtained, the Ru content (%) at each position, the average Ru content at each position, and the macro segregation evaluation. rice field.

(About measurement of V/S)
Test no. In any of 1 to 7, the dissolved raw material S measures the BET surface area (specific surface area) by the gas adsorption method, and V measures the specific volume (the reciprocal of the density) by the gas replacement method. Calculated. In the gas adsorption method, Shimadzu ASAP2010 was used as a measuring device. Then, the sample was loaded into the measurement device and subjected to vacuum heating degassing at 200 ° C. for 2 hours, after which N ₂ was adsorbed at a temperature of 77 K using liquid nitrogen, and a BET plot was created and measured. . In addition, in the gas replacement method, an Ultra Pycnometer Model 1000 manufactured by QUANTACHROME INSTRUMENTS was used as a measuring apparatus according to JIS R1620.

(Macro segregation evaluation)
In the obtained titanium alloy ingot, the Ru content was measured at each position of the top, middle and bottom. The Ru content was measured using an analysis method of ICP emission spectrometry. The measurement procedure is TIS standard TIS No. of the Japan Titanium Society. 9632, using ICP emission spectroscopy.

Here, the top refers to the area up to 10 mm from the solidified surface formed in the second melting in an 80 mm long ingot, the middle refers to the central position of the ingot, and the bottom refers to , refers to the area up to 10 mm from the solidification surface of the first melting.

Evaluation of macro segregation was performed as follows. Specifically, the Ru content at each of the top, bottom, and middle positions was measured, and the average Ru content at each position was calculated. The measured content at each position and the average at each position were substituted into the following formula (1) to calculate the following segregation evaluation value (%).

Segregation evaluation value (%)
= (maximum value of X content - minimum value of X content)/average of X content at each position x 100 (1)
Here, X is an element selected from Ru, Nb and Mo. Further, the maximum value of the content of X means the maximum content among the contents of X measured at each position. The minimum value of the content of X means the minimum content among the X contents measured at each position.

When the segregation evaluation value is within 10%, the macro segregation is extremely small, indicating that the material is very good and indicated by ⊚. When the segregation evaluation value was more than 10% and 30% or less, the macrosegregation was small and the material was good, and was indicated by ◯.

Furthermore, when the segregation evaluation value is more than 30 and not more than 50%, although macrosegregation occurs to some extent, the case where there is no problem as a material is indicated by Δ. In addition, when the segregation evaluation value is over 50%, macro segregation occurs, which is indicated by x as an unfavorable material. Table 1 shows the results.

Test no. 1 to 3 satisfy the definition of the present invention. Moreover, No. 1 using the master alloy which is a conventional example. It was possible to obtain a titanium alloy in which the occurrence of macrosegregation was suppressed in the same manner as in No. 7 or more. Also, test no. In Nos. 4 and 5, the segregation evaluation values were higher than those of the other invention examples, and macrosegregation occurred slightly, but there was no problem as a material. On the other hand, Test No. No. 6 did not satisfy the requirements of the present invention, and macrosegregation occurred.

A 1-ton titanium alloy ingot was produced by the same procedure as in Example 1. The total number of compacts used at this time was 36 pieces. The resulting columnar titanium alloy ingot was divided into quarters with equal intervals between the top and bottom in the longitudinal direction of the ingot as shown in FIG. At each position of the six surfaces including the top surface, the bottom surface, and the four surfaces exposed by division, the edge, the 1/4 part from the edge, and the center of the diameter. The Ru content was measured by collecting samples for analysis from a total of 20 points, 1/4 part from the edge, 3/4 part in addition to the central part of the diameter, and 3/4 part and the opposite edge. The target Ru content was 0.03% by mass. Table 2 shows the results.

As a result of analyzing the Ru content at 20 points from the table below, it was 0.030 to 0.034% by mass, and the segregation evaluation value calculated from the content at each measurement point was also good at 12.5%.

V/S was varied to produce melted raw materials. Metallic Nb (purity 99.9%) powder was used as the raw material to be melted. This melted raw material was wrapped in a foil (JIS Class 1) made of industrial pure titanium to obtain a melted raw material. The melted raw material and the titanium metal raw material thus obtained were mixed and compression-molded by a press to produce a compact. Vacuum arc melting was performed using the compact as a titanium consumable electrode. In the vacuum arc melting, melting was performed twice. In the second dissolution, dissolution was performed by turning the consumable electrode upside down from that in the first dissolution. Through the above steps, a 7 kg titanium alloy ingot having a diameter of 140 mm and a length of 80 mm was produced (see Test Nos. 8 to 10).

In addition, a 7-kg titanium alloy ingot having the same shape as the above was produced by mixing metal Nb in the form of lumps with a size of 3 to 5 mm with a metallic titanium raw material to produce a compact and performing the above-described melting. (see Test No. 11). Further, a Ti-50%Nb master alloy with a thickness of 3 to 5 mm was similarly mixed with the metallic titanium raw material to produce a compact. Subsequently, by performing the above-described melting, a 7 kg titanium alloy ingot having the same shape as above was produced (see Test No. 12). In addition, test No. In Examples 8 to 12, the chemical composition was Ti-0.5 mass % Nb.

In the same manner as in Example 1, the V/S in each example, the chemical composition and content of the entire titanium alloy ingot obtained, the Nb content (%) at each position, and the Nb content at each position , and segregation evaluation values were examined. The segregation evaluation value was calculated by the following procedure. Specifically, based on the Nb content at each position, the maximum and minimum values of the Nb content and the average of the Nb content at each position were calculated. Subsequently, the same procedure as in Example 1 was used to calculate the segregation evaluation value. Table 3 shows the results.

Test no. 8-9 satisfy the definition of the present invention. For this reason, No. 1 using the master alloy, which is a conventional example, It was possible to obtain a titanium alloy in which the occurrence of macrosegregation was suppressed in the same manner as in No. 12 or more. Also, test no. In No. 10, the segregation evaluation value was higher than those of the other invention examples, and macrosegregation was slightly generated, but there was no problem as a material. On the other hand, Test No. No. 11 did not satisfy the requirements of the present invention and macrosegregation occurred.

V/S was varied to produce melted raw materials. Metallic Mo (purity 99.8%) powder was used as the raw material to be dissolved. This melted raw material was wrapped in a foil (JIS Class 1) made of industrial pure titanium to obtain a melted raw material. The melted raw material and the titanium metal raw material thus obtained were mixed and compression-molded by a press to produce a compact. Vacuum arc melting was performed using the compact as a titanium consumable electrode. In the vacuum arc melting, melting was performed twice. In the second dissolution, dissolution was performed by turning the consumable electrode upside down from that in the first dissolution. Through the above steps, a 7 kg titanium alloy ingot having a diameter of 140 mm and a length of 80 mm was produced (see Test Nos. 13 to 15).

In addition, a 7-kg titanium alloy ingot having the same shape as the above is manufactured by using lump-like metal Mo with a size of 3 to 5 mm, mixing it with a metal titanium raw material, producing a compact, and performing the above-described melting. (see Test No. 16). Further, a Ti-50%Mo master alloy with a thickness of 3 to 5 mm was similarly mixed with the metal titanium raw material to produce a compact. Subsequently, by performing the above melting, a 7 kg titanium alloy ingot having the same shape as above was produced (see Test No. 17). In addition, test No. In Examples 13 to 17, the chemical composition was Ti-0.3 mass % Mo.

In the same procedure as in Example 1, the V/S in each example, the average Mo content in the entire titanium alloy ingot obtained, the Mo content (%) at each position, the Mo content at each position Mean and segregation ratings were examined. The segregation evaluation value was calculated by the following procedure. Specifically, based on the Mo content at each position, the maximum and minimum values of the Mo content and the average of the Mo content at each position were calculated. Subsequently, the same procedure as in Example 1 was used to calculate the segregation evaluation value. Table 4 shows the results.

Test no. 13-14 satisfy the definition of the present invention. For this reason, No. 1 using the master alloy, which is a conventional example, It was possible to obtain a titanium alloy in which the occurrence of macrosegregation was suppressed in the same manner as in No. 17 or more. Also, test no. In No. 15, the segregation evaluation value was higher than those of the other invention examples, and macrosegregation was slightly generated, but there was no problem as a material. On the other hand, Test No. No. 16 did not satisfy the requirements of the present invention and macrosegregation occurred.

Claims (5)

A melting raw material used in the production of a titanium alloy,
The molten raw material contains an element having a melting point of over 2000°C,
When the total volume of the dissolved raw materials to be added is V and the total surface area is S,
A dissolved raw material, wherein the relationship between the total volume and the total surface area satisfies the following formula (i).
15.4≦ V/S≦100 (μm) (i) 2. The raw material for melting according to claim 1, wherein said element is one or more selected from metal Mo, metal Nb, metal Ru, metal Ta and C. A melting material used in the manufacture of a titanium alloy,
A melted raw material according to claim 1 or 2, and an outer packaging material that wraps the melted raw material,
The melting point of the outer packaging material is 2000 ° C. or less,
melting material. The outer wrapping material is one or more selected from industrial pure titanium, industrial pure aluminum, industrial pure copper, industrial pure zirconium, industrial pure tin, titanium alloys, aluminum alloys, copper alloys, zirconium alloys, and tin alloys. 4. The melting material according to claim 3, which is a foil or sheet consisting of: (a) A step of mixing the raw material for melting according to claim 1 or 2 or the raw material for melting according to claim 3 or 4 with a metallic titanium raw material and encapsulating it to produce a compact or a raw material for melting hearth charging. and,
(b) melting the compact or melting hearth input raw material produced;
A method for producing a titanium alloy ingot.

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