JP2022076856A - Ingot of pure titanium or titanium alloy - Google Patents

Abstract

To provide an ingot of pure titanium or titanium alloy that is less in segregation and high in productivity.SOLUTION: A columnar ingot of pure titanium or titanium alloy comprises, provided that a radius of the ingot is R, a radial distance from a central axis of the ingot is r, an axial distance from an upper end of the ingot is L (mm), and an acute angle defined between a growth direction of a columnar structure formed outer than the central axis of the ingot in a longitudinal section passing the central axis of the ingot and the central axis of the ingot is θ(deg), a maximum value of θ at 3/8×R≤r≤5/8×R and L≤600 mm is 70° or greater and a minimum value of θ at 3/8×R≤r≤5/8×R and 200 mm≤L≤600 mm is 50° or smaller.SELECTED DRAWING: Figure 3

Description

The present invention relates to ingots of pure titanium or titanium alloys.

Since titanium is active to oxygen, a vacuum arc remelting method (VAR) or the like, which is not easily affected by oxygen, is used for melting and casting pure titanium or a titanium alloy. Pure titanium or titanium alloys contain solute elements such as alloying elements and inclusions. In the solidification process of the ingot, macrosegregation of solute elements may occur, which may cause bias in the components of the ingot. Therefore, the concentration of solute elements may increase at the top of the ingot. It is necessary to cut off the portion where the solute element concentration exceeds the predetermined concentration, but this leads to a decrease in yield. Therefore, a technique for suppressing the generation of segregation has been proposed.

Patent Document 1 discloses a method for melting a titanium ingot in which the arc gap, which is the distance from the lower end of the consumable electrode to the surface of the molten metal, is changed depending on the type of the titanium ingot to be melted. By selecting different arc gaps depending on the type of metal to be melted, segregation of alloy components can be efficiently avoided.

Patent Document 2 discloses a metal vacuum arc melting method in which a melting operation is performed while helium gas is allowed to flow in the space between the ingot melted in the mold and the mold. By flowing helium gas through the space between the ingot and the mold, an alloy ingot with less component segregation can be melted.

In Patent Document 3, the maximum value θ of the acute angle formed between the growth direction of the columnar crystal structure formed inside the ingot and outside the center of the ingot and the central axis of the ingot is equal to or less than the threshold value θ _cr . The ingot is disclosed. By manufacturing the ingot so that the maximum value θ of the acute angle is equal to or less than the threshold value θ _cr , it is possible to obtain an ingot with less bias of the alloy component.

Japanese Unexamined Patent Publication No. 2010-116581 Japanese Unexamined Patent Publication No. 2010-116589 Japanese Unexamined Patent Publication No. 2019-12980

It is desirable that the ingots of pure titanium or titanium alloy are ingots with high productivity in addition to low segregation. As a method for increasing productivity, it is conceivable to increase the melting rate of pure titanium or a titanium alloy during the production of ingots. However, it is known that the faster the melting rate, the more segregation tends to occur at the top of the ingot.

An object of the present invention is to provide an ingot of pure titanium or a titanium alloy with low segregation and high productivity.

The ingot of pure titanium or a titanium alloy of the present invention is a columnar ingot made of pure titanium or a titanium alloy, in which the radius of the ingot is R, the radial distance from the central axis of the ingot is r, and the casting is performed. The axial distance from the top of the ingot is L (mm), and the sharp angle between the growth direction of the columnar structure formed outside the central axis of the ingot and the central axis of the ingot in the vertical cross section passing through the central axis of the ingot. When it is set to θ (deg)
The maximum value of θ at 3/8 × R ≦ r ≦ 5/8 × R and L ≦ 600 mm is 70 ° or more.
And,
The minimum value of θ in 3/8 × R ≦ r ≦ 5/8 × R and 200 mm ≦ L ≦ 600 mm is 50 ° or less.

According to the present invention, it is possible to provide an ingot of pure titanium or a titanium alloy having low segregation and high productivity.

It is a schematic diagram which shows the manufacturing apparatus of an ingot. It is a figure which shows the relationship between the dissolution current, the dissolution rate, and the dissolution time. It is a schematic diagram which shows the time-dependent change in the mold at the time of manufacturing an ingot in order. It is a schematic diagram of the cross-sectional structure form of an ingot. It is a vertical sectional view of an ingot. It is a figure which shows the example of the relationship between the dissolution current and the dissolution time. It is a figure which shows the example of the relationship between the dissolution rate and the dissolution time. It is a figure which shows the relationship between the dissolution current, the dissolution rate, and the dissolution time of Examples 1 and 2 and Comparative Examples 1 and 2. It is a figure for demonstrating the position to measure the acute angle θ formed by the growth direction of a columnar structure and the central axis O of an ingot in the vertical cross section of an ingot. It is a figure which shows the segregation degree in the radial direction of iron of Examples 1 and 2 and Comparative Examples 1 and 2. It is a figure which shows the result of the comparative example 1. FIG. It is a figure which shows the result of the comparative example 2. It is a figure which shows the result of Example 1. FIG. It is a figure which shows the result of Example 2. FIG.

Hereinafter, preferred embodiments of the present invention will be described.

The ingot according to the present embodiment is a columnar pure titanium ingot or a titanium alloy ingot. Examples of pure titanium and titanium alloys include pure titanium and titanium alloys specified in JIS H4600 (2012).

A "pure titanium ingot" is an ingot produced by melting and casting pure titanium. In the present invention, the "pure titanium ingot" may be referred to as a "pure titanium ingot" or a "pure titanium ingot". The "pure titanium ingot" may contain inclusions and the like produced during melting or casting of pure titanium.

The "titanium alloy ingot" is an ingot produced by melting and casting a titanium alloy. In the present invention, the "titanium alloy ingot" may be referred to as a "titanium alloy ingot" or an "alloy made of a titanium alloy". The "titanium alloy ingot" may contain inclusions and the like generated during melting or casting of the titanium alloy.

FIG. 1 shows an example of an apparatus for manufacturing an ingot according to the present embodiment. FIG. 1 shows a vacuum arc melting furnace 1 that manufactures ingots by a vacuum arc melting method.

The vacuum arc remelting furnace 1 has a mold 2, an electrode support 3, and a controller 4. The electrode support 3 is arranged in the mold 2 so as to be able to move up and down. A consumable electrode 10, which is a raw material for ingots, is attached to the lower part of the electrode support 3. By applying a predetermined voltage between the mold 2 and the consumable electrode 10, an arc discharge is generated between the mold 2 and the consumable electrode 10. By the arc discharge, the consumable electrode 10 is melted and dropped. A molten metal pool 5 in which droplets are collected is formed in the mold 2. Further, the molten metal is cooled by the mold 2 to form a solidified shell 6. The "molten metal" here is a melted consumable electrode. The raising and lowering of the electrode support 3 and the amount of heat input to the molten metal surface of the molten metal pool 5 are controlled by the controller 4.

FIG. 2A shows an example of the dissolution current and the dissolution rate when producing an ingot. FIG. 2B shows the changes with time in the mold 2 in order. The "dissolution current" is a current flowing through the mold 2 and the consumable electrode 10 shown in FIG. The "dissolution rate" is the rate at which the consumable electrode 10 dissolves. The dissolution rate is calculated, for example, based on the weight of the consumable electrode 10 and the dissolution time. The larger the melting current, the larger the amount of discharge due to the arc discharge, and the faster the melting rate.

During the production of the ingot, as shown in FIGS. 2A and 2B, it is roughly divided into three, a melting initial stage, a stationary phase, and a hot top phase. After the start of melting of the consumable electrode 10, as shown in FIG. 2A, the melting current increases and reaches a predetermined current value (initial stage of melting). As the dissolution current increases, the dissolution rate increases and reaches a predetermined rate (initial stage of dissolution). After that, the dissolution current and dissolution rate become almost constant (stationary phase). Then, the dissolution current drops, drops to a predetermined low current, and then the predetermined low current is maintained (hot top period). As the dissolution current decreases, the dissolution rate decreases, and finally the dissolution rate becomes zero (hot top period).

In the mold 2, as shown in FIG. 2B, the size of the molten metal pool 5 gradually increases at the initial stage of melting and reaches a predetermined size. As the molten metal pool 5 becomes larger, the molten metal pool 5 becomes deeper. During the steady phase, the molten pool 5 is maintained at a substantially constant size. The depth of the molten metal pool 5 is also maintained almost constant. After that, in the hot top period, the molten metal pool 5 becomes smaller. As the molten metal pool 5 becomes smaller, the molten metal pool 5 becomes shallower. An ingot is obtained by solidifying all the molten metal in the mold 2. The ingot is, for example, a columnar ingot having a diameter of 700 mm or more and 1200 mm or less and an axial length of 1000 mm or more and 3000 mm or less.

From FIGS. 2A and 2B, it can be seen that the faster the melting rate, the deeper the molten metal pool 5. The length and ratio of each of the initial melting phase, the stationary phase, and the hot top phase can be changed and are not limited to the length and ratio shown in FIG. 2B.

[Structural morphology of ingots]
FIG. 3 shows a schematic diagram of the structure of the ingot. FIG. 3 shows a vertical cross section of the columnar ingot passing through the central axis O. The figure shown in FIG. 3 is a figure described in Hayakawa, H., et al., ISIJ Int., Vol.31, No.8, pp.775-784 (1991).

During casting, the portion in contact with the bottom surface and the side surface of the mold becomes a quenching equiaxed grain structure CH called a chill layer by quenching with the mold. The portion along the axial direction near the center of the ingot has an equiaxed grain structure EA. The other part of the ingot has a columnar crystal structure CO.

The portion indicated by the alternate long and short dash line in the columnar crystal structure CO is the portion that was the interface (solidification interface) between the molten metal pool 5 and the solidification shell 6 during casting (see FIG. 2A). In FIG. 3, the normal direction of the solidification interface indicated by the arrow is the solidification direction of the columnar crystal structure CO formed outside the center of the ingot, and the columnar crystals formed outside the center of the ingot. This is the growth direction of organizational CO. The acute angle formed by the growth direction of the columnar crystal structure CO and the central axis O of the ingot is θ [degree]. The growth direction of the columnar structure can be visually recognized by, for example, corroding the vertical cross section of the ingot with an acid or the like.

During casting, θ is large in the portion solidified when the molten metal pool 5 is deep. Therefore, in the vertical cross section of the ingot, the portion where a large θ exists is considered to be the portion solidified when the molten metal pool 5 is deep. On the other hand, θ is small in the portion solidified when the molten metal pool 5 is shallow. Therefore, in the vertical cross section of the ingot, the portion where a small θ exists is considered to be a portion solidified when the molten metal pool 5 is shallow. Here, from FIGS. 2A and 2B, it can be seen that the faster the melting rate, the deeper the molten metal pool. Therefore, in the longitudinal section of the ingot, the portion where a large θ exists is considered to be the portion solidified when the melting rate is high. In the longitudinal section of the ingot, the portion where a small θ exists is considered to be the portion solidified when the melting rate is slow.

[Ingot according to this embodiment]
In the vertical cross section of the ingot I according to the present embodiment, the radius of the ingot I is R, the radial distance from the central axis O of the ingot I is r, and the axial distance from the upper end of the ingot I. L (mm), the acute angle formed by the growth direction of the columnar structure formed outside the central axis O of the ingot I and the central axis O of the ingot I in the longitudinal cross section passing through the central axis O of the ingot I is θ. When (deg) is set, as shown in FIG. 4, as shown in FIG.
(1) The maximum value of θ in the region X ₁ of 3/8 × R ≦ r ≦ 5/8 × R and L ≦ 600 mm is 70 ° or more.
And,
(2) The minimum value of θ in the region X ₂ of 3/8 × R ≦ r ≦ 5/8 × R and 200 mm ≦ L ≦ 600 mm is 50 ° or less.
It is a columnar pure titanium ingot or a titanium alloy ingot.
In FIG. 4, the “region X ₁ ” is colored and the “region X ₂ ” is hatched. “Region X ₁ ” and “Region X ₂ ” are portions near the upper end of the ingot I.
The "upper end of the ingot" is one end of the ingot I in the axial direction and the other end that is not in contact with the bottom surface and the side surface of the mold during casting. The other end of the ingot I, which was in contact with the bottom surface of the mold during casting, is the "lower end of the ingot".

“The maximum value of θ in the region X ₁ is 70 ° or more” means that a large θ exists in the region X ₁ . As described above, the portion where a large θ exists is considered to be the portion solidified when the dissolution rate is high. From FIG. 2B, the dissolution rate is high in the steady phase. Then, "the maximum value of θ in the region X ₁ is 70 ° or more" means that the region X ₁ has a solidified portion in the stationary phase and the dissolution rate in the stationary phase is high. The faster the dissolution rate, the shorter the production time, and the higher the productivity. Therefore, the ingot I according to the present embodiment is a highly productive ingot.

Here, in the existing production method in which the dissolution rate in the stationary phase is high, the dissolution rate is rapidly reduced in a short time after the stationary phase. Therefore, the hot top period is short. From the findings of the present inventors, when the ingot is manufactured by an existing manufacturing method having a high melting rate, the concentration of solute elements changes significantly in the radial direction of the ingot, so that segregation increases at the top of the ingot. I understood. The "ingot top portion" is near the upper end of the ingot, and is, for example, a range within about 200 mm in the axial direction from the upper end of the ingot.

The ingot I according to the present embodiment has "the maximum value of θ in the region X ₁ is 70 ° or more" and "the minimum value of θ in the region X ₂ is 50 ° or less".
“The minimum value of θ in the region X ₂ is 50 ° or less” means that a relatively small θ exists in the region X ₂ . As described above, the portion where the small θ is present is considered to be the portion solidified when the dissolution rate is slow. This region X ₂ exists 200 mm or more and 600 mm or less from the upper end of the ingot I (see FIG. 4). Since it is considered that a solidified portion exists in the region X ₁ 600 mm or less from the upper end of the ingot I in the stationary phase, the existence of a relatively small θ in the region X ₂ means that the melting rate is relatively fast. It is thought to mean that it has decreased. In addition, it is considered that the hot-top period in which the dissolution rate decreases is long, and the dissolution rate gradually decreases over time in the hot-top period. Therefore, even if the melting rate in the steady phase is high, it is considered that the segregation of the top portion of the ingot is small because the concentration of solute elements is suppressed from changing in the radial direction of the ingot during the hot top phase.

From the above, the ingot I according to the present embodiment has "the maximum value of θ in the region X ₁ is 70 ° or more" and "the minimum value of θ in the region X ₂ is 50 ° or less". As a result, the ingot has high productivity and less segregation.

In the region X ₁ , if the maximum value of θ is 70 ° or more, θ other than the maximum value may be less than 70 °. Only one θ of 70 ° or more may be present in the region X ₁ , and two or more θ of 70 ° or more may be present. The upper limit of the maximum value of θ in the region X ₁ is not particularly limited.

In the region X ₂ , if the minimum value of θ is 50 ° or less, θ other than the minimum value may exceed 50 °. Only one θ of 50 ° or less may be present in the region X ₂ , and two or more θ of 50 ° or less may be present. The lower limit of the minimum value of θ in the region X ₂ is not particularly limited.

In the ingot I according to the present embodiment, in addition to the above (1) and (2), the maximum value of θ in (3) 3/8 × R ≦ r ≦ 5/8 × R and 300 mm ≦ L ≦ 600 mm is 70. It may be greater than or equal to °. In this case, it is considered that there is a solidified portion in the steady-state period in which the dissolution rate is high in the region of 300 mm ≦ L ≦ 600 mm.

In the ingot I according to the present embodiment, in addition to the above (1) and (2), (4) the minimum value of θ in (4) 3/8 × R ≦ r ≦ 5/8 × R and 200 mm ≦ L ≦ 300 mm is 50. It may be less than or equal to °. In this case, the region within at least 300 mm from the upper end of the ingot is considered to be the portion solidified during the hot top period in which the melting rate is decreasing. Therefore, it can be considered that the hot-top period was long and the dissolution rate was surely gradually decreased over time. It is considered that this surely suppressed the generation of segregation.
The ingot I according to the present embodiment may be an ingot satisfying the above (3) and (4) in addition to the above (1) and (2).

In the ingot I according to the present embodiment, in addition to the above (1) and (2), (5) the minimum value of θ in (5) 3/8 × R ≦ r ≦ 5/8 × R and 200 mm ≦ L ≦ 300 mm is 40. It may be ° or more and 50 ° or less. In this case, in addition to the effect of (4) above, it is considered that the dissolution rate gradually decreased over time in the hot top period. It is considered that this surely suppressed the generation of segregation.
The ingot according to the present embodiment may be an ingot satisfying the above (3) and (5) in addition to the above (1) and (2).

The ingot I according to the present embodiment does not have to satisfy the above (3) to (5) as long as it satisfies the above (1) and (2). The ingot according to the present embodiment may satisfy only one or two of the above (3) to (5) as long as the above (1) and (2) are satisfied.

Next, an example of the dissolution current and the dissolution rate when producing the ingot according to the present embodiment will be described.

FIG. 5 shows the relationship between the dissolution current and the dissolution time. FIG. 6 shows the relationship between the dissolution rate and the dissolution time. Example 1 shown in FIGS. 5 and 6 is an example of an existing manufacturing method in which the dissolution rate in the stationary phase is high. This example shown in FIGS. 5 and 6 is an example of an ingot manufacturing method according to the present embodiment.

In Example 1, as shown in FIG. 5, the dissolution current in the steady state is large. In Example 1, as shown in FIG. 6, the dissolution rate in the stationary phase is high. Therefore, productivity is high. In Example 1, as shown in FIG. 5, the steady-state period is relatively long, and in the hot-top period, the dissolution current drops rapidly in a short time. In Example 1, as shown in FIG. 6, the dissolution rate rapidly decreases in a short time in the hot top phase (see FIG. 6). When an ingot is manufactured under these conditions, segregation tends to increase at the top of the ingot. Therefore, the ingot produced under the condition of Example 1 is an ingot having high productivity but a large segregation.

In this example, as shown in FIG. 5, the dissolution current is increased to a current value equivalent to the dissolution current in the steady phase of Example 1. As a result, as shown in FIG. 6, the dissolution rate increases to a rate equivalent to the dissolution rate in the stationary phase of Example 1. Then, as shown in FIG. 5, the dissolution current is reduced earlier than in Example 1. Further, the dissolution current is gradually reduced to a predetermined current value over time from Example 1. As a result, as shown in FIG. 6, the dissolution rate decreases earlier than in Example 1. The dissolution rate gradually decreases over time from Example 1 and finally reaches zero.

The stationary phase of this example is shorter than the stationary phase of Example 1, but the hot top phase of this example is longer than the hot top phase of Example 1. The dissolution rate of this example is gradually lower than that of Example 1 over time.

When the ingot is produced under the above-mentioned conditions, the melting rate in the steady state is the same as the melting rate of Example 1, so that the productivity is high as in Example 1. In addition, the dissolution rate decreases earlier than in Example 1. The dissolution rate gradually decreases over time from the dissolution rate of Example 1. Therefore, segregation is unlikely to occur at the top of the ingot. As a result, the ingot produced under the conditions of this example becomes an ingot having low segregation and high productivity.

In FIGS. 5 and 6, the initial dissolution time of Example 1 and the initial dissolution time of this example are almost the same, but the initial dissolution time of Example 1 and the initial dissolution time of this example are different. May be.

Next, an experiment conducted to obtain the above findings will be described.

(Manufacturing of ingots)
Using the apparatus shown in FIG. 1, a titanium alloy ingot was produced by a vacuum arc remelting method (VAR). The molten metal component is a 64 alloy (Ti-6Al-4V). The ingot is a columnar ingot having a diameter of 820 mm. The inner diameter of the mold was 840 mm.

FIG. 7 shows the dissolution current and the dissolution time.
In Comparative Example 1, the dissolution rate in the steady phase is high. In addition, the dissolution rate is rapidly decreasing in a short time.
In Comparative Example 2, the dissolution rate in the steady phase is slow. The stationary phase is long and the dissolution time is long.
In Example 1 and Example 2, the dissolution rate in the stationary phase is as high as that in Comparative Example 1. In Example 1 and Example 2, the dissolution rate is lower than that of Comparative Example 1. The dissolution rate gradually decreases over time as compared with Comparative Example 1.

(Evaluation 1)
The segregation of the ingot was evaluated from the degree of segregation of iron (Fe) in which macrosegregation (positive segregation) is likely to appear remarkably. The iron (Fe) content of the titanium alloy is very small, but the concentration range where quality is required is narrow. The degree of segregation of iron (Fe) was determined by the following method.
In the range of 600 mm axially from the upper end of the ingot, including the top of the ingot where segregation is likely to occur, at a predetermined pitch in the axial direction from the upper end of the ingot, the center of the ingot (the axial center of the ingot) and the surface layer of the ingot. The iron concentration was measured in. The "concentration difference between the center of the ingot and the surface layer of the ingot" with respect to the "concentration of iron in the center of the ingot" was defined as the degree of segregation.
If the degree of segregation of iron is less than 40%, the quality criteria are met. If the degree of segregation of iron is 40% or more, the quality standard is not satisfied. Regions with an iron segregation degree of 40% or more are truncated.

(Evaluation 2)
Productivity was evaluated by the ratio of "melting time" (of each example) to "total melting time when 6 ton ingots were melted under the production conditions of Comparative Example 1". When the ratio is less than 1.2, it is judged that the productivity is high, and when the ratio is 1.2 or more, it is judged that the productivity is low.

(Evaluation 3)
After the vertical cross section passing through the central axis O of the ingot is corroded by acid, in the cross section, the growth direction of the columnar structure formed outside the central axis O of the ingot I and the central axis O of the ingot I The acute angle formed was measured by θ (deg). θ is measured in the range of 600 mm in the axial direction from the upper end of the ingot at a pitch of 50 mm in the axial direction from the upper end of the ingot, and on the line where the radial distance r from the central axis of the ingot is 150 mm, 200 mm, 250 mm, and 300 mm. It went (see FIG. 8).

Table 1 below shows the manufacturing conditions of the ingot and the results of evaluations 1 and 2. FIG. 9 shows the result of evaluation 1.

The "final low current holding time" in the "ratio of the final low current holding time" in Table 1 is the low current holding time after the dissolution current is lowered after the steady phase and the predetermined low current is reached. be. The "ratio of the final low current holding time" in Table 1 is based on the final low current holding time of Comparative Example 1 and is the "final (of each example)" with respect to the "final low current holding time of Comparative Example 1". Low current holding time "ratio.

From Table 1 and FIG. 9, the following was found.

The ingot of Comparative Example 1 was an ingot having high productivity but low quality. In Comparative Example 1, as shown in FIG. 9, the radial segregation degree of iron exceeded 40% at the top portion of the ingot. Since it is necessary to cut off the portion where the segregation degree exceeds 40%, the yield is low in Comparative Example 1.

As shown in Table 1, the ingots of Comparative Example 2 were ingots of high quality but low productivity. In Comparative Example 2, as shown in FIG. 9, the radial segregation degree of iron was less than 30% at the top portion of the ingot.

As shown in Table 1, the ingots of Examples 1 and 2 were high quality and highly productive ingots. In Examples 1 and 2, as shown in FIG. 9, the radial segregation degree of iron was less than 35% at the ingot top portion. Compared with Comparative Example 1, the segregation degree of the ingot top portion was improved by about 10 to 20%.

Next, with reference to FIGS. 10 to 13, the acute angle θ formed by the growth direction of the columnar structure and the central axis O of the ingot I will be examined. In the following, the "axial distance L from the upper end of the ingot" may be referred to as "distance from the upper end of the ingot", "distance L from the upper end of the ingot", or "L".

Here, the measurement of θ is performed on both sides of the central axis 0, as shown in FIG. For example, θ is measured at the position of r = 150 mm on the right side of the figure and the position of r = 150 mm on the left side of the figure with respect to the central axis 0. Each figure shown in FIGS. 10 to 13 may have two plots in the vertical direction or one plot in the vertical direction. When there are two plots in the vertical direction, the two plots are θ measured on the right side of the figure and θ measured on the left side of the figure with respect to the central axis 0 of the ingot, respectively. When there is one plot in the vertical direction, θ measured on the right side of the figure and θ measured on the left side of the figure are the same with respect to the central axis 0 of the ingot, and one plot is obtained by overlapping these plots. It looks like.

In Comparative Example 1, as shown in FIG. 10, a large θ of 70 ° or more was present in a region where the distance L from the upper end of the ingot was 100 mm or more and 600 mm or less. In Comparative Example 1, since the dissolution rate in the steady phase is high, it is considered that a large θ of 70 ° or more existed.
In Comparative Example 1, a small θ of 40 ° or less exists only in the region where the distance L from the upper end of the ingot is 100 mm or less. All θ in this region are 40 ° or less. The degree of segregation in this region was high (see FIG. 9). This region is considered to be the part that solidified when the dissolution rate was rapidly reduced. Ingots having such a structure were ingots having high productivity but low quality.

In Comparative Example 2, as shown in FIG. 11, in the region where the distance L from the upper end of the ingot is within 600 mm, all θ are less than 70 °. In the region where the distance L from the upper end of the ingot is within 500 mm, there is a relatively small θ of 50 ° or less. In Comparative Example 2, it is considered that θ was small because the dissolution rate was slow. Ingots having such a structure were ingots having low productivity but high quality.

In Example 1, as shown in FIG. 12, a large θ of 70 ° or more was present in a region where the distance L from the upper end of the ingot was within 600 mm. It is considered that this is because the dissolution rate in the steady phase was high (see FIG. 7). In particular, there was a θ of 70 ° or more in the region where the distance L from the upper end of the ingot was 300 mm or more and 600 mm or less.
In addition, in Example 1, as shown in FIG. 12, a relatively small θ of 50 ° or less was present in a region where the distance L from the upper end of the ingot was 200 mm or more and 600 mm or less. It is considered that this is because the dissolution rate began to decrease at an early stage (see FIG. 7).
Further, as shown in FIG. 12, θ gradually decreases in a region where the distance L from the upper end of the ingot is within 300 mm. For example, in a region where the distance L from the upper end of the ingot is 200 mm or more and 300 mm or less, the minimum value of θ is 50 ° or less, but the minimum value of θ is 40 ° or more. In the region where the distance L from the upper end of the ingot is 100 mm or more and 200 mm or less, the maximum value of θ is 50 ° or more. It is considered that this is because the dissolution rate gradually decreased over time (see FIG. 7).
The ingot having such a structure was an ingot having high quality and high productivity.

In Example 2, the same tendency as in Example 1 was observed. In the region where the distance L from the upper end of the ingot was within 600 mm, there was a large θ of 70 ° or more. A relatively small θ of 50 ° or less was present in a region where the distance L from the upper end of the ingot was 200 mm or more and 600 mm or less. In the region where the distance L from the upper end of the ingot was within 300 mm, θ gradually decreased. The ingot having the structure of Example 2 was also an ingot having high quality and high productivity.

From the above, the maximum value of θ existing in the region where the distance L from the upper end of the ingot is 600 mm or less is 70 ° or more, and θ exists in the region where the distance L from the upper end of the ingot is 200 mm or more and 600 mm or less. It was found that the ingot having a minimum value of 50 ° or less was an ingot having high quality and high productivity.

Here, in this experiment, in an ingot having a diameter of 820 mm, θ is measured on lines with radial distances r from the central axis O of the ingot of 150 mm, 200 mm, 250 mm, and 300 mm (see FIG. 8). ). When θ is measured on these lines, the maximum value of θ existing in the region where the distance L from the upper end of the ingot is within 600 mm is 70 ° or more, and the distance L from the upper end of the ingot is 200 mm or more and 600 mm. The ingot having a minimum value of θ existing in the region within 50 ° or less was an ingot having high quality and high productivity.
From this, it is considered that an ingot having a θ above satisfying the above in a range where the radial distance r from the central axis O of the ingot is 150 mm or more and 300 mm or less is a high quality and highly productive ingot. Be done.
Then, θ in the range of 3/8 × R ≦ r ≦ 5/8 × R (R is the radius of the ingot) in which the radial distance r from the central axis O of the ingot is within the range of 150 mm or more and 300 mm or less. Is also considered to be an ingot having high quality and high productivity.

From the above, in the vertical cross section passing through the central axis O, the radius of the ingot is R, the radial distance from the central axis of the ingot is r, the axial distance from the upper end of the ingot is L (mm), and the center of the ingot. When the sharp angle between the growth direction of the columnar structure formed outside the central axis O of the ingot and the central axis of the ingot in the vertical cross section passing through the axis is θ (deg).
(1) The maximum value of θ in the region X ₁ of 3/8 × R ≦ r ≦ 5/8 × R and L ≦ 600 mm is 70 ° or more.
And,
(2) When the minimum value of θ in the region X ₂ of 3/8 × R ≦ r ≦ 5/8 × R and 200 mm ≦ L ≦ 600 mm is 50 ° or less.
It was found that the ingot has high quality and high productivity.

In the above experiment, a titanium alloy ingot was used, but the same result as above can be obtained with a pure titanium ingot.

Although the embodiments of the present invention have been described above with reference to the drawings, it should be considered that the specific configuration is not limited to these embodiments. The scope of the present invention is shown by the scope of claims rather than the above description, and includes all modifications within the meaning and scope equivalent to the scope of claims.

For example, in the above-described embodiment, the method of producing the ingot by the vacuum arc melting method has been described, but the method of producing the ingot is not limited to the above-mentioned method. Further, the ingot production conditions (dissolution current, dissolution rate, etc.) are not limited to the above-mentioned embodiments and experimental conditions.

1 Vacuum arc remelting furnace 2 Mold 3 Electrode support 4 Controller 5 Molten pool 6 Solidification shell 10 Consumable electrode I Ingot O Central axis of ingot

Claims (4)

A columnar ingot made of pure titanium or a titanium alloy.
The radius of the ingot is R, the radial distance from the ingot central axis is r, the axial distance from the ingot upper end is L (mm), and the vertical cross section passing through the ingot central axis is from the ingot central axis. When the sharp angle between the growth direction of the columnar structure formed on the outside and the central axis of the ingot is θ (deg),
The maximum value of θ at 3/8 × R ≦ r ≦ 5/8 × R and L ≦ 600 mm is 70 ° or more.
And,
An ingot of pure titanium or a titanium alloy, characterized in that the minimum value of θ in 3/8 × R ≦ r ≦ 5/8 × R and 200 mm ≦ L ≦ 600 mm is 50 ° or less. The ingot of pure titanium or a titanium alloy according to claim 1, wherein the maximum value of θ in 3/8 × R ≦ r ≦ 5/8 × R and 300 mm ≦ L ≦ 600 mm is 70 ° or more. The casting of pure titanium or a titanium alloy according to claim 1 or 2, wherein the minimum value of θ in 3/8 × R ≦ r ≦ 5/8 × R and 200 mm ≦ L ≦ 300 mm is 50 ° or less. mass. The pure titanium or titanium alloy according to claim 3, wherein the minimum value of θ in 3/8 × R ≦ r ≦ 5/8 × R and 200 mm ≦ L ≦ 300 mm is 40 ° or more and 50 ° or less. Ingot.

Images