JP6236361B2 - Titanium alloy intermediate forging material, titanium alloy intermediate forging material shape determination method, and titanium alloy β forging material manufacturing method - Google Patents

Description

The present invention relates to a titanium alloy intermediate forging material, a method for determining the shape of a titanium alloy intermediate forging material, and a titanium alloy β forging used for manufacturing a β forging material of an α + β type titanium alloy that is inspected for defects by ultrasonic inspection. about the production how of wood.

  Α + β type titanium alloy, represented by Ti-6Al-4V alloy, has various characteristics such as weldability, superplasticity, and diffusion bondability in addition to light weight, high strength, and high corrosion resistance. Is used a lot. In the α + β type titanium alloy, the dense hexagonal (hcp structure) α phase, which is the main phase, and the β phase of the body-centered cubic (bcc structure) stably coexist at room temperature, and the temperature is higher than the β transformation point (Tβ). It becomes β phase single phase in the region. Forging materials of α + β type titanium alloy, heat forging in a temperature range below Tβ (α + β two-phase region) and forging in this temperature range so as not to reach temperatures above Tβ, and temperatures above Tβ There is a thing by the β forging which heats and forges to a zone (β single phase zone). It is known that the material structure formed is completely different between the α + β forging and the β forging, and the material characteristics are different accordingly.

  The titanium alloy forged material has a needle-like α phase structure according to β forging. Specifically, the organization is formed as follows. First, it becomes a β phase single phase in a temperature range equal to or higher than Tβ, and after the equiaxed β phase (β grains) is flattened by forging, it is cooled to a temperature range lower than Tβ and held in this temperature range. Then, the α phase precipitates in the form of a film along the grain boundaries of β grains, and subsequently the α phase precipitates in the form of needles in the β grains (the white phase shown in FIG. 3 is the α phase). ). In β forging, forging is completed in the β single-phase region, forging continues after the temperature drops outside the β single-phase region (α + β two-phase region), and the temperature drops in the α + β two-phase region. Some start forging after that. Furthermore, the β forging material changes in the form and thickness of the α phase on the grain boundary of the old β grains, and the length and thickness of the acicular α phase in the grains, depending on the forging conditions and the subsequent cooling conditions. May not have a film-like α phase on the grain boundary. On the other hand, the titanium alloy forged material has a granular α structure according to α + β forging (see FIG. 4). In general, forging materials with α + β-type titanium alloy, fracture toughness is better for forged materials with β-forging than forged materials with α + β-forging, and conversely, fatigue strength characteristics are for forged materials with α + β-forging. It is known that this method is superior to the forged material that has been β-forged.

As a technique related to such a titanium alloy forged material, for example, Patent Document 1 contains Al: 5.50 to 6.75%, V: 3.50 to 4.50%, the balance being inevitable impurities and Ti A method of manufacturing a titanium alloy part comprising: In this manufacturing method, the titanium alloy material is isothermally forged at a temperature of 900 ° C. or more and less than the transformation temperature, and the material is deformed while maintaining the strain rate at 5 × 10 ⁻³ / sec or less. It is disclosed that a near net shape molded article having an axis (α + β) structure is obtained, and a necessary machining is performed to obtain a product.

Further, for example, in Patent Document 2, when a material having a circular outer surface shape is squeezed in the axial direction using an open upper and lower molds and forged into a circular material having a circular outer surface shape, the inner diameter is the following (1 A ring tool having a diameter d satisfying the conditions defined in the formula (1) is provided with its axis aligned with the axis of the mold, and in this state, the material being forged is brought into contact with the inner surface of the ring tool, A method for forging a circular material, characterized in that the ring tool is removed and forging is disclosed.
D + 2E ≦ d ≦ D ₁ (1), where D: maximum diameter of the material (mm), E: displacement amount (mm) between the axis of the mold and the axis of the material when the material is charged, D ₁ : The average outer diameter (mm) of the material when the reduction amount is 70% of the total reduction amount.

  Further, for example, Patent Document 3 discloses a β-forged titanium alloy forged material having a polycrystalline structure of old β grains having an average aspect ratio of 2 or more and 10 or less. The boundary has an average angle of 80 ° or less with the line parallel to the forging direction, and the α phase formed on the grain boundary of the old β grain has an average length in the grain boundary direction of 15 μm or less. There is disclosed a titanium alloy forging characterized by the fact.

JP-A-5-25597 JP 2003-19534 A JP 2014-55318 A

  Aircraft engine parts and the like are required to have high fatigue strength characteristics and high reliability, and therefore are inspected for defects by ultrasonic flaw detection. In ultrasonic flaw detection, the ultrasonic wave transmitted (transmitted) from the probe is incident from the surface of the object to be inspected, and the reflected wave reflected by the defect such as a flaw is received by the probe. This is an inspection for determining the presence or absence of internal defects.

  The titanium alloy β-forged material has a problem of achieving both low cycle fatigue strength and ultrasonic flaw detection. Although the low cycle fatigue strength of the titanium alloy β-forged material is improved with an increase in strain applied to the material during β-forging, it is known that the ultrasonic flaw detection property deteriorates as the forging strain increases. When the forged material has a large diameter and thin wall, unevenness of strain in the forged material is likely to occur, and there is a problem that a forging strain is locally increased, resulting in deterioration of ultrasonic flaw detection properties.

  Here, the technique described in Patent Document 1 cannot be applied to forging in the β region, which is the subject of the present application, and the strain distribution cannot be controlled. In the embodiment, the chip is reduced by optimizing the strain rate. However, experimental data for this is not disclosed.

  Further, the forging method described in Patent Document 2 is a method for suppressing uneven thickness caused by misalignment of the shaft core when forging using an open die, and a ring having a predetermined shape is set in the lower die. In this way, uneven thickness at the forging stage is suppressed. However, in the technique described in Patent Document 2, uneven thickness generated in the circular material is suppressed, but this technique does not make the internal strain distribution uniform.

  Moreover, the titanium alloy forged material described in Patent Document 3 achieves both low cycle fatigue strength and ultrasonic flaw detection by reducing the overall β forging strain applied to the forged material. Note that the forging strain is controlled by the amount of reduction within a range of forging strain that is greater than the β forging strain necessary to develop a high low cycle fatigue strength, and on the other hand, does not impair the ultrasonic flaw detection property. However, the technique described in Patent Document 3 has a problem that the range of strain that can achieve both low cycle fatigue strength and ultrasonic flaw detection is narrow, and the degree of freedom of the shape of the β-forged titanium alloy forged material is low.

The present invention has been made in view of the above problems, and can obtain a titanium alloy β-forged material in which strain distribution generated in the forged material is made uniform and both low cycle fatigue strength and ultrasonic flaw detection properties are achieved. titanium alloy intermediate forging, the shape determining method of a titanium alloy intermediate forging, and, it is an object to provide a manufacturing how titanium alloys β forging.

  The titanium alloy intermediate forging according to the present invention is made of an α + β type titanium alloy, is rotationally symmetric, has a large-diameter thin-walled shape represented by the formulas (1), (2), and (3), and has a radially outer periphery. The titanium alloy intermediate forging material used for the production of titanium alloy β forging material in which the part becomes the product portion, wherein the titanium alloy intermediate forging material has the minimum thickness portion in the central portion and the maximum thickness portion in the outer peripheral portion. 1 exists, satisfies the formula (4), the formula (5), the formula (6), the formula (7), the formula (8), and the shape of the titanium alloy β forging (9) ).

0.1 <b ₁ / A ₁ <0.5 (1)
40 <b ₁ <200 (2)
0.1 <B ₁ / A ₁ <0.9 (3)
1.2 ≦ b ₀ / a ₀ ≦ 4.0 (4)
0.05 <B ₀ / A ₀ ≦ 0.55 (5)
20 ° ≦ θ ≦ 70 ° (6)
_{2A 0/5 ≦ C 0 ··········} (7)
0.5 ≦ c ₀ / b ₀ (8)
0.20 ≦ b ₁ / b ₀ ≦ 0.60 (9)

here,
a ₀ : Minimum thickness (mm) from the bottom of the center of the titanium alloy intermediate forging
b ₀ : Maximum thickness (mm) from the bottom of the outer periphery of the titanium alloy intermediate forging
c ₀ : Thickness (mm) of the outermost peripheral portion of the titanium alloy intermediate forged material
A ₀ : Radius of outer diameter of titanium alloy intermediate forging (mm)
B ₀ : Radius of recess of titanium alloy intermediate forging (mm)
C ₀ : Diameter from the center to the maximum thickness (mm)
A ₁ : Radius of outer diameter of titanium alloy β forged material (mm)
B ₁ : Radius (mm) of inner diameter of titanium alloy β-forged material
b ₁ : Maximum thickness (mm) of the product part of the titanium alloy β-forged material
θ: an angle formed by a tangent at a position (a ₀ + b ₀ ) / 2 from the bottom and a tangent at the bottom of the recess in the inclined portion formed from the center to the outer periphery on the upper surface of the titanium alloy intermediate forging is there.

  According to this configuration, in the large-diameter thin-walled titanium alloy β-forged material manufactured using this titanium alloy intermediate forged material, the strain distribution generated inside is made uniform. As a result, a titanium alloy β-forged material having both low cycle fatigue strength and ultrasonic flaw detection properties can be obtained.

Moreover, it is preferable to use the titanium alloy whose Mo equivalent [Mo] eq represented by Formula (10) is more than 2.7 and less than 15 as the titanium alloy intermediate forging material.
[Mo] eq = [Mo] + [Ta] / 5 + [Nb] /3.6+ [W] /2.5+ [V] /1.5+1.25 [Cr] +1.25 [Ni] +1.7 [ Mn] +1.7 [Co] +2.5 [Fe] (10)
However, [X] in the formula (10) is the content (mass%) of the element X in the titanium alloy.

  According to such a configuration, the obtained titanium alloy β forged material has a reduced α phase volume content, and the influence of the shape of the old β grains becomes stronger, and the ultrasonic flaw detection property is improved.

  The shape determination method of the titanium alloy intermediate forging according to the present invention is characterized in that the shape of the titanium alloy intermediate forging is determined according to the relational expression described above.

  According to such a configuration, the method for determining the shape of the titanium alloy intermediate forged material simply determines the shape of the titanium alloy intermediate forged material to obtain a titanium alloy β forged material that achieves both low cycle fatigue strength and ultrasonic flaw detection. can do.

Method for producing titanium alloy beta forging according to the present invention, the titanium alloy intermediate forged material of the described, when the beta transformation point determined by the alloy components expressed in T _beta, and heated to (T _β + 5 ℃) or higher After holding until the β crystal grain size is in the range of 100 μm or more and less than 800 μm, forging in a temperature range of (T _β −150 ° C.) or higher and immediately cooling to a temperature of (T _β −150 ° C.) or lower. It is characterized by.

  According to such a procedure, the titanium alloy β forging manufacturing method has a large-diameter, thin-walled shape, the strain distribution generated inside is uniform, and the titanium alloy β having both low cycle fatigue strength and ultrasonic flaw detection properties. A forging material can be obtained.

According to the titanium alloy intermediate forging material of the present invention, obtaining a titanium alloy β forging material in which the strain distribution generated in the large-diameter thin-walled forging material is made uniform, and both low cycle fatigue strength and ultrasonic flaw detection properties are achieved. Can do.
According to the titanium alloy intermediate forging material shape determining method of the present invention, the shape of the titanium alloy intermediate forging material can be easily determined.
According to the method for producing a titanium alloy β-forged material of the present invention, a titanium alloy β-forged material in which the strain distribution generated in the large-diameter thin-walled forged material is made uniform and both low cycle fatigue strength and ultrasonic flaw detection properties are achieved. Can be obtained .

It is typical sectional drawing for demonstrating an example of the shape of the titanium alloy beta forging material of this invention. It is typical sectional drawing for demonstrating an example of the shape of the titanium alloy intermediate forging material of this invention. It is an image photograph of the structure of a titanium alloy forging material, and is an example of a β forging material. It is an image photograph of the structure of a titanium alloy forging material, and is an example of an α + β forging material.

Hereinafter, embodiments of the present invention will be described in detail.
<Titanium alloy intermediate forging material>
The titanium alloy intermediate forging material according to the present invention has a uniform distribution of strain generated inside a large-diameter thin-walled forging material, and achieves both low cycle fatigue strength and ultrasonic flaw detection in the manufactured titanium alloy β-forging material. is there. For that purpose, the shape of the material before forging (titanium alloy intermediate forging material) is a butterfly shape, and the intermediate forging material shape is made suitable according to the shape of the titanium alloy β forging material.

In the manufactured titanium alloy β forging material,
Β forging strain required to develop fatigue strength characteristics: 0.50 or more Strain required to prevent deterioration of ultrasonic flaw detection property: 2.70 or less (preferably 2.50 or less)
And These values are the criteria obtained as a result of basic experiments.
To prevent false recognition of ultrasonic flaw detection noise and to homogenize characteristics (homogenization of mechanical characteristics and homogenization of ultrasonic flaw detection),
“(Maximum strain amount−minimum strain amount) / maximum strain amount”: 0.70 or less, that is, (ε _max −ε _min ) / ε _max ≦ 0.70
And
In addition, if there is a location with higher noise than the surroundings (corresponding to a location with high distortion) during ultrasonic flaw detection, it may be mistaken for a defect, and overall balance (homogenization) is also required.

This will be specifically described below.
The titanium alloy intermediate forging material of the present invention is made of an α + β type titanium alloy, is rotationally symmetric and has a large-diameter thin-walled shape represented by the formula (1), the formula (2), and the formula (3). Is used for the production of a titanium alloy β-forged material that becomes a product part.
And the titanium alloy intermediate forging material has the minimum thickness portion in the central portion, and there is one maximum thickness portion in the outer peripheral portion, and the equations (4), (5), (6), (7), Formula (8) is satisfied, and the relationship of Formula (9) is established with the shape of the titanium alloy β forged material. These equations are derived by repeating the analysis.

0.1 <b ₁ / A ₁ <0.5 (1)
40 <b ₁ <200 (2)
0.1 <B ₁ / A ₁ <0.9 (3)
1.2 ≦ b ₀ / a ₀ ≦ 4.0 (4)
0.05 <B ₀ / A ₀ ≦ 0.55 (5)
20 ° ≦ θ ≦ 70 ° (6)
_{2A 0/5 ≦ C 0 ··········} (7)
0.5 ≦ c ₀ / b ₀ (8)
0.20 ≦ b ₁ / b ₀ ≦ 0.60 (9)

here,
a ₀ : Minimum thickness (mm) from the bottom of the center of the titanium alloy intermediate forging
b ₀ : Maximum thickness (mm) from the bottom of the outer periphery of the titanium alloy intermediate forging
c ₀ : Thickness (mm) of the outermost peripheral portion of the titanium alloy intermediate forged material
A ₀ : Radius of outer diameter of titanium alloy intermediate forging (mm)
B ₀ : Radius of recess of titanium alloy intermediate forging (mm)
C ₀ : Diameter from the center to the maximum thickness (mm)
A ₁ : Radius of outer diameter of titanium alloy β forged material (mm)
B ₁ : Radius (mm) of inner diameter of titanium alloy β-forged material
b ₁ : Maximum thickness (mm) of the product part of the titanium alloy β-forged material
θ: an angle formed by a tangent at a position (a ₀ + b ₀ ) / 2 from the bottom and a tangent at the bottom of the recess in the inclined portion formed from the center to the outer periphery on the upper surface of the titanium alloy intermediate forging is there.
These parameters can be controlled by various conditions during production, such as wasteland forging in the production of a titanium alloy intermediate forging material and β forging in the production of a titanium alloy β forging material.

  First, equations (1) to (3) relating to the shape of the target titanium alloy β forging will be described with reference to FIG. The titanium alloy β forged material has a shape shown in FIG. The titanium alloy β forged material 10 is rotationally symmetric with respect to a center line L passing through the center portion 18.

[Formula (1): 0.1 <b ₁ / A ₁ <0.5]
Formula (1) defines that the titanium alloy β forged material 10 has a large-diameter thin wall shape.
As shown in FIG. 1, the titanium alloy β forged material 10 includes an outer peripheral portion 13 that is a product portion 11, an inner peripheral portion 14 that is located on one side (inner side) of the outer peripheral portion 13, and the other of the outer peripheral portion 13. It consists of the burr | flash part 12 located in the side (outside). In the titanium alloy β forged material 10, the outer peripheral portion 13 in the radial direction becomes the product portion 11. The radial direction is a direction from the central portion 18 of the titanium alloy β forged material 10 toward the outside. The titanium alloy β-forged material 10 is formed with a concave portion (having a concave portion) in the lower side of the center here by the outer peripheral portion 13 and the inner peripheral portion 14. In addition, in FIG. 1, the thin part of the inner peripheral part 14 is located above the outer peripheral part 13, and the lower side of the center of the titanium alloy β forged material 10 is formed in a concave shape. However, the thin portion of the inner peripheral portion 14 does not necessarily have to be on the upper side of the outer peripheral portion 13, and may be located near or below the thickness center of the outer peripheral portion 13, and further, the inner peripheral portion 14. The thickness of may change in the middle or may have a curve. These are all included in the scope of the present invention. With such a configuration having a thin portion of the inner peripheral portion 14, the yield can be increased.

And the radius of the outer diameter of the titanium alloy β-forged material 10 in A ₁ refers to the length from the central portion 18 of the titanium alloy β-forged material 10 to the outermost end of the product portion 11.
The product portion 11 refers to the outer peripheral portion 13 (main body portion) of the titanium alloy β forged material 10 and is a portion that becomes a product such as an aircraft engine part. Here, the product part 11 is the burr part 12 outside the titanium alloy β forging material 10 from the position where the bottom part (bottom face) 15 is horizontal on the center part 18 side (here, the part having the maximum thickness b ₁ ). (The symbol P is the length of the product part). However, the shape of FIG. 1 is an example, and the product part 11 should just be the outermost end from the innermost end of the site | part actually used as a product. Incidentally, as described later, depending on the shape of the product portion 11, there is a case where the innermost end of the product portion 11 is not a maximum thickness b _1.

Here, the titanium alloy β forged material 10 may have one maximum thickness portion on the outer peripheral portion 13. In Figure 1, all of the product portion 11 (the outer peripheral portion 13) is the maximum thickness b _1, the product portion 11 is maximum thickness portion. However, the thickness of the product part 11 does not need to be constant over the entire length P of the product part, and may be appropriately changed according to a desired product shape. For example, the middle of the region of the length P of the product part 11 may be bound, and the thickness may be different between the outside and the inside (both in the product part 11) sandwiching the constricted part (maximum thickness b _1). May be outside the innermost end of the product part 11).
Further, the titanium alloy β forged material 10 can have the central portion 18 having a minimum thickness. Reference symbol a ₁ is the minimum thickness from the bottom of the center portion 18 of the titanium alloy β forged material 10.
Here, the central portion 18 of the titanium alloy β forged material 10 is a portion that becomes the center of the rotationally symmetric titanium alloy β forged material 10, and in FIG. 1, the center line L intersects with the titanium alloy β forged material 10. It is a part to do. The titanium alloy β forged material 10 is rotationally symmetric with respect to the center line L passing through the center portion 18.

b ₁ / A ₁ is preferably more than 0.2, more preferably more than 0.25. Further, b ₁ / A ₁ is preferably less than 0.4, and more preferably less than 0.35.

[Formula (2): 40 <b ₁ <200]
Formula (2) defines the thickness range of the assumed titanium alloy β forged material 10.
b ₁ is preferably more than 60 mm, more preferably more than 80 mm. In addition, b ₁ is preferably less than 170 mm, more preferably less than 150 mm.

[Formula (3): 0.1 <B ₁ / A ₁ <0.9]
Formula (3) defines the ratio of the outer peripheral portion 13 and the inner peripheral portion 14 of the titanium alloy β forged material 10.
Here, the outer peripheral portion 13 of the titanium alloy β forged material 10 is a predetermined region outside the titanium alloy β forged material 10. Further, the inner peripheral portion 14 of the titanium alloy β-forged material 10 is a predetermined region inside (center portion side) of the titanium alloy β-forged material, and is a region closer to the central portion 18 than the outer peripheral portion 13 (product portion 11). It is.
Further, the radius of the inner diameter of the titanium alloy β forged material 10 in B ₁ refers to the length from the central portion 18 of the titanium alloy β forged material 10 to the innermost end of the product portion 11 as shown in FIG. Here, the innermost end of the product portion 11 refers to a position where the bottom portion (bottom surface) 15 is horizontal on the central portion 18 side of the product portion 11 (here, a portion having the maximum thickness b ₁ ). However, as described above, the innermost end of the product portion 11 may not have the maximum thickness b _1. Even in this case, the innermost end of the part actually used as the product is the radius of the inner diameter of the titanium alloy β forged material 10. This should be the standard. The product portion 11 is located outside the innermost end of the product portion 11.
B ₁ / A ₁ is preferably more than 0.2, more preferably more than 0.25. Further, B ₁ / A ₁ is preferably less than 0.8, and more preferably less than 0.75.

  Next, equations (4) to (8) relating to the shape of the titanium alloy intermediate forged material will be described with reference to FIG. The titanium alloy intermediate forging material has a shape shown in FIG. The titanium alloy intermediate forged material 100 is rotationally symmetric with respect to a center line L passing through the center portion 28.

[Formula (4): 1.2 ≦ b ₀ / a ₀ ≦ 4.0]
When b ₀ / a ₀ is less than 1.2, strain concentration occurs in the inner peripheral portion 14 of the titanium alloy β forged material 10. On the other hand, when b ₀ / a ₀ exceeds 4.0, strain concentration occurs in the outer peripheral portion 13 of the titanium alloy β forged material 10. Therefore, the titanium alloy intermediate forged material 100 satisfies “1.2 ≦ b ₀ / a ₀ ≦ 4.0” as the formula (4).
Here, the bottom portion 25 of the titanium alloy intermediate forged material 100 at a ₀ and b ₀ is the bottom surface of the titanium alloy intermediate forged material 100, and is a portion where the bottom surface of the titanium alloy intermediate forged material 100 is horizontal. The bottom portion 25 does not include a convex portion 40 on the bottom surface described later.
Further, the outer peripheral portion 23 of the titanium alloy intermediate forged material 100 refers to a portion outside the position perpendicular to a contact point between a tangent line 51 and a tangent line 52 described later.

Here, the titanium alloy intermediate forged material 100 is assumed to have one maximum thickness portion on the outer peripheral portion 23. (Length in the radial direction) area of maximum thickness b ₀ may be appropriately adjusted according to the shape of the titanium alloy β forging material 10 to be manufactured. Further, the titanium alloy intermediate forging material 100 has the central portion 28 having a minimum thickness.
b ₀ / a ₀ means that strain concentration occurs on the inner peripheral side of the product portion 11 (position close to the inner peripheral portion 14) due to concentration of strain on the inner peripheral portion 14 of the titanium alloy β-forged material 10. From a viewpoint of suppressing, Preferably it is 1.5 or more, More preferably, it is 1.65 or more. Further, b ₀ / a ₀ is preferably 3.5 or less, and more preferably 2.8 or less, from the viewpoint of suppressing the concentration of strain on the outer peripheral portion 13 of the titanium alloy β-forged material 10.

[Formula (5): 0.05 <B ₀ / A ₀ ≦ 0.55]
When B ₀ / A ₀ is 0.05 or less, the tendency for strain to concentrate at the center of the titanium alloy β-forged material 10 becomes stronger. The central portion of the titanium alloy β forged material 10 is a portion including the inner peripheral portion 14 and the inner peripheral portion 14 of the product portion 11. On the other hand, if B ₀ / A ₀ exceeds 0.55, the load during forging of the titanium alloy intermediate forged material 100 becomes high. Therefore, the titanium alloy intermediate forging material 100 is set to “0.05 <B ₀ / A ₀ ≦ 0.55” as the formula (5).
Here, the concave portion 30 of the titanium alloy intermediate forged material 100 in B ₀ is a concave portion formed on the upper surface of the central portion 28 of the titanium alloy intermediate forged material 100. That is, the titanium alloy intermediate forged material 100 has a recess 30 at the center thereof. The center of the titanium alloy intermediate forged material 100 is a portion in the vicinity of the center portion 28 including the center portion 28. Here, it is a region inside the radius B ₀ with the center line L as the center. And the radius of the recessed part 30 of the titanium alloy intermediate forged material 100 means the length from the center part 28 to the position perpendicular to the contact point of the tangent line 51 and the tangent line 52 described later.
In addition, the radius of the outer diameter of the titanium alloy intermediate forged material 100 at A ₀ refers to the length from the center portion 28 of the titanium alloy intermediate forged material 100 to the outermost peripheral portion of the titanium alloy intermediate forged material 100.
B ₀ / A ₀ is preferably more than 0.16 from the viewpoint of suppressing the concentration of strain in the central portion of the titanium alloy β forged material 10. Further, B ₀ / A ₀ is preferably 0.5 or less, more preferably 0.45 or less, from the viewpoint of reducing the load during forging of the titanium alloy intermediate forged material 100.

[Formula (6): 20 ° ≦ θ ≦ 70 °]
When θ is less than 20 °, strain tends to concentrate on the inner peripheral portion 14 of the titanium alloy β-forged material 10. On the other hand, when θ exceeds 70 °, the load at the time of forging of the titanium alloy intermediate forged material 100 is increased, and strain is easily concentrated on the outer peripheral portion 13 of the titanium alloy β forged material 10. Therefore, the titanium alloy intermediate forged material 100 is set to “20 ° ≦ θ ≦ 70 °” as the equation (6).
Here, θ is the smaller one of the angles formed by the tangent line 51 and the tangent line 52.
The tangent line 51 is a tangent line at a position of (a ₀ + b ₀ ) / 2 from the bottom part 25 in the inclined part formed from the center part 28 to the outer peripheral part 23 on the upper surface of the titanium alloy intermediate forging material 100. That is, the tangent line 51 is a line drawn along the slope on the inner side of the upper surface of the titanium alloy intermediate forged material 100 (the slope formed continuously with the recess 30). Further, the tangent line 52 is a tangent line of the bottom surface of the concave portion 30 orthogonal to the center line L. That is, the tangent line 52 is a line drawn along the bottom surface of the recess 30 so as to be orthogonal to the center line L.
θ is a viewpoint that suppresses the occurrence of strain concentration on the inner peripheral side (position close to the inner peripheral portion 14) of the product portion 11 due to the concentration of strain on the inner peripheral portion 14 of the titanium alloy β forged material 10. Therefore, it is preferably 30 ° or more, and more preferably 40 ° or more. Further, θ is preferably 65 ° or less from the viewpoint of reducing the load during forging of the titanium alloy intermediate forging material 100 and suppressing the concentration of strain on the outer peripheral portion 13 of the titanium alloy β forging material 10.

Expression _{(7): 2A 0/5} ≦ C 0]
The maximum thickness portion from the bottom portion 25 of the titanium alloy intermediate forged material 100 is located at a position 2/5 of the radius of the titanium alloy intermediate forged material 100 or outside the position of 2/5. When the maximum thickness part from the bottom part 25 exists inside the position of 2/5, the strain tends to concentrate on the inner peripheral part 14 of the titanium alloy β-forged material 10. Therefore, the titanium alloy intermediate forged material 100, and _{"2A 0/5} ≦ _C 0" as an expression (7).
Here, the center portion 28 of the titanium alloy intermediate forged material 100 at a ₀ and C ₀ is a portion that becomes the center of the rotationally symmetric titanium alloy intermediate forged material 100. In FIG. This is a portion where the intermediate forging material 100 intersects. The titanium alloy intermediate forged material 100 is rotationally symmetric with respect to the center line L passing through the center portion 28.

[Formula (8): 0.5 ≦ c ₀ / b ₀ ]
When c ₀ / b ₀ is less than 0.5, for example, the region having the maximum thickness b ₀ outside C ₀ is reduced, and the distortion of the outer peripheral portion 13 of the titanium alloy β-forged material 10 may be reduced. Therefore, the titanium alloy intermediate forged material 100 is set to “0.5 ≦ c ₀ / b ₀ ” as the equation (8).
Here, the outermost peripheral portion of the titanium alloy intermediate forged material 100 at c ₀ refers to a portion where the outermost side surface of the titanium alloy intermediate forged material 100 is vertical.

  Next, equation (9) relating to the relationship between the shape of the titanium alloy intermediate forging material and the shape of the titanium alloy β forging material will be described with reference to FIGS.

[Formula (9): 0.20 ≦ b ₁ / b ₀ ≦ 0.60]
When b ₁ / b ₀ is less than 0.20, the distortion of the outer peripheral portion 13 of the titanium alloy β forged material 10 becomes too large. On the other hand, if b ₁ / b ₀ exceeds 0.60, a predetermined strain cannot be applied to the outer peripheral portion 13 of the titanium alloy β-forged material 10. Therefore, the titanium alloy intermediate forged material 100 satisfies “0.20 ≦ b ₁ / b ₀ ≦ 0.60” as the equation (9).
b ₁ / b ₀ is preferably 0.30 or more, more preferably 0.35 or more, from the viewpoint of suppressing the distortion of the outer peripheral portion 13 of the titanium alloy β forged material 10. Further, b ₁ / b ₀ is preferably 0.50 or less from the viewpoint of easily applying a predetermined strain to the outer peripheral portion 13 of the titanium alloy β forged material 10.

[Others]
As shown in FIG. 2, the titanium alloy intermediate forging material 100 has a convex portion on the bottom surface of the titanium alloy intermediate forging material 100 in order to facilitate positioning when the titanium alloy intermediate forging material 100 is installed in the lower mold during forging. 40 is preferably provided.
Moreover, titanium alloy intermediate forged material 100, to facilitate positioning, it is preferable that the d ₀ in FIG. 2 or more 10 mm. d ₀ is a portion from the bottom 25 of the titanium alloy intermediate forged material 100 to the outermost side surface of the titanium alloy intermediate forged material 100 becoming vertical. The upper limit of d ₀ is can be increased to b _0, to ensure the uniformity of the forging deformation, preferably (2/3) b ₀ or less.

(Titanium alloy: Mo equivalent 2.7 and less than 15)
The titanium alloy forming the titanium alloy β forging according to the present invention can be applied as long as it is an α + β type titanium alloy, but the Mo equivalent [Mo] eq represented by the following formula (10) is 2.7. The composition is preferably more than 15 and less than 15. This is because in the titanium alloy, as the Mo equivalent increases, the volume content of the α phase decreases and the influence of the shape of the old β grains becomes stronger, and the influence of forging strain on ultrasonic flaw detection becomes stronger. The Mo equivalent of the titanium alloy is more preferably 4.5 or more, and even more preferably 6.5 or more, from the viewpoint of strengthening the influence of forging strain on ultrasonic flaw detection. On the other hand, the titanium alloy is preferably less than 15 because the alloy element is easily segregated and the structure may vary as the Mo equivalent [Mo] eq increases. The Mo equivalent of the titanium alloy is more preferably 12 or less, and even more preferably 10.5 or less, from the viewpoint of further reducing the possibility that the structure varies.

[Mo] eq = [Mo] + [Ta] / 5 + [Nb] /3.6+ [W] /2.5+ [V] /1.5+1.25 [Cr] +1.25 [Ni] +1.7 [ Mn] +1.7 [Co] +2.5 [Fe] (10)
However, [X] in the formula (10) is the content (mass%) of the element X (X: Mo, Ta, Nb, W, V, Cr, Ni, Mn, Co, Fe) in the titanium alloy. And

  Specific examples of such a titanium alloy include titanium alloys specified by AMS4981 and AMS4995. Titanium alloys (Ti-6Al-2Sn-4Zr-6Mo alloy, Ti-6246 alloy) specified by AMS4981 are Al: 5.50-6.50 mass%, Sn: 1.75-2.25 mass%, Zr: 3.50 to 4.50% by mass, Mo: 5.50 to 6.50% by mass, the balance being Ti and inevitable impurities, and the Mo equivalent calculated from the average value of each element is 6 .0. The inevitable impurities generally include N: 0.04 mass%, C: 0.08 mass%, H: 0.015 mass%, Fe: 0.15 mass%, and O: 0.15 mass%. To do.

  Titanium alloy (Ti-5Al-2Sn-2Zr-4Cr-4Mo alloy, Ti-17 alloy) specified by AMS4995 is Al: 4.5 to 5.5 mass%, Sn: 1.5 to 2.5 mass %, Zr: 1.5 to 2.5% by mass, Cr: 3.5 to 4.5% by mass, Mo: 3.5 to 4.5% by mass, O: 0.08 to 0.12% by mass The balance is Ti and inevitable impurities, and the Mo equivalent calculated from the average value of each element is 9.5. The inevitable impurities generally include Fe: 0.03% by mass, C: 0.05% by mass, N: 0.04% by mass, and H: 0.0125% by mass.

<Titanium alloy intermediate forging shape determination method>
The method for determining the shape of the titanium alloy intermediate forged material according to the present invention determines the shape of the titanium alloy intermediate forged material described above in accordance with the relational expressions (1) to (9).
That is, the thickness, the inner diameter, and the outer diameter are determined so as to satisfy the expressions (1) to (3) with respect to the assumed shape of the titanium alloy β forged material. And based on it, about thickness of a titanium alloy intermediate forging material, thickness, an internal diameter, an outer diameter, the shape of a recessed part, etc. are determined so that Formula (4)-(8) may be satisfied. Furthermore, Formula (9) regarding the relationship between the shape of the titanium alloy intermediate forging material and the shape of the titanium alloy β forging material is determined.
Further, as described above, the titanium alloy intermediate forging material may be a titanium alloy having a Mo equivalent [Mo] eq represented by the formula (10) of more than 2.7 and less than 15.

<Method for producing titanium alloy β-forged material>
The titanium alloy β forged material according to the present invention is formed by forging an ingot made of a titanium alloy having a desired composition into a billet by a known method (referred to as a billet forging step), and performing machining as necessary, and then α + β two Wasteland forging is performed in the phase area to obtain a titanium alloy intermediate forging material. Thereafter, β forging is performed to produce a desired product shape. The billet forging step is performed, for example, in the order of β forging → α + β forging → β heat treatment → stress relief annealing → α + β forging → annealing. α + β forging is heated to a temperature range about 10 to 200 ° C. lower than the β transformation point (appropriately expressed as T _β ), and β forging is heated to a temperature range about 10 to 150 ° C. higher than T _β. Forging is performed at a ratio (area ratio after forging of the cross section perpendicular to the forging direction to before forging, for example, 1.5), and cooled to room temperature. Whether the forging in the billet forging process is α + β forging or β forging may be set according to the characteristics required for the product, and the number of forgings may be determined according to the desired billet diameter and the like. Further, the two annealings may be performed as necessary. For example, the second annealing is performed to facilitate subsequent machining. Furthermore, by machining the titanium alloy billet, the surface oxide film, wrinkles and burrs can be removed, and the surface roughness can be adjusted, and then forging (forging for rough ground and titanium alloy β in the production of titanium alloy intermediate forgings) (Β forging in the production of forgings) is easy to perform. And in order to manufacture the titanium alloy β forged material according to the present invention, the titanium alloy intermediate forged material is β forged by the following method.

Method for producing titanium alloy beta forging according to the present invention, the titanium alloy intermediate forging, when the beta transformation point determined by the alloy components expressed in T _beta, and heated to (T _β + 5 ℃) above, After holding until the β crystal grain size (average grain size) is in the range of 100 μm or more and less than 800 μm, forging is performed in a temperature range of (T _β −150 ° C.) or more, and immediately below (T _β −150 ° C.). It is the method of cooling to.

(Heating temperature before forging: ( _Tβ + 5 ° C) or more)
The heating before forging is performed in order to heat the titanium alloy intermediate forging material to the β single-phase region to form the β-phase single phase before forging, as in general β forging. The β single-phase region is a temperature region above the β transformation point (T _β ), and T _β is the lowest temperature at which the entire titanium alloy billet (100%) becomes the β phase, and the titanium alloy intermediate forging material (titanium alloy) It varies depending on the composition of the titanium alloy forming the (β-forged material). For example, the T _beta titanium alloy as defined in AMS4981 (Ti-6246 alloy) is about 960 ° C., the T _beta titanium alloy as defined in AMS4995 (Ti-17 alloy) is about 890 ° C.. In the present invention, the titanium alloy intermediate forged material is surely made into a β-phase single phase up to the deep part, and forging is completed in a temperature range of (T _β −150 ° C.) or higher. In the present invention, the heating temperature before forging is set to (T _β + 5 ° C.) or more in order to ensure that the titanium alloy intermediate forged material is a β-phase single phase to the deep part. On the other hand, as the titanium alloy intermediate forging material becomes higher in the β single-phase region, the growth rate of the β-phase crystal grains becomes faster, so it becomes difficult to control the crystal grain size, and when it exceeds (T _β + 150 ° C) Since a thick oxide scale is easily formed on the surface and needs to be removed after forging, the heating temperature is preferably (T _β + 150 ° C.) or less (more preferably T _β + 100 ° C.). Further, when the heating temperature before forging is too high, higher temperature during forging completion is cooled after forging (T _beta -150 ° C.) or higher temperatures outside _((T β -150 ℃) below) By the time, β crystal grains (non-flat grains) may grow excessively.

After heating the titanium alloy intermediate forging material to reach the β single phase region, the titanium alloy intermediate forging material is held for a certain period of time before forging starts, and the β crystal grains are appropriately sized, specifically in the range of 100 μm or more and less than 800 μm in diameter. Grow. The holding time varies depending on the holding temperature of the titanium alloy intermediate forging material, but may be held, for example, at 1000 ° C. for about 60 to 480 minutes. Once the desired β crystal grain structure is formed, the temperature of the titanium alloy intermediate forging may drop below (T _β + 5 ° C.) before forging, but as described later, forging is completed. until it sets so as to be able to hold the temperature range of not lower than (T β -150 _℃).

(Forging _temperature: (T β -150 ℃) or higher)
By performing the forging temperature at (T _β −150 ° C.) or more, the α phase is prevented from precipitating on the grain boundaries and in the grains before forging, and the fracture toughness is hardly lowered.
When the forging temperature is less than (T _β −150 ° C.), the α phase starts to precipitate on the grain boundaries and in the grains of the β crystal grains. If these α phases are formed before forging is completed, the fracture toughness may deteriorate. Therefore, (more specifically, the temperature at the completion of the forging of titanium alloy intermediate forging) forging temperature, and (T _beta -150 ° C.) or higher. The forging temperature is preferably (T _β −100 ° C.) or more from the viewpoint of making it difficult to precipitate the α phase on the grain boundaries and in the grains of the β crystal grains. At this time, the mold used for forging is preferably heated to 400 ° C. or higher, and more preferably heated to a forging temperature (temperature of the titanium alloy intermediate forging material). By using such a heated die, the surface of the forged titanium alloy intermediate forging material is not cooled too quickly with respect to the inside, and the vicinity of the surface is also maintained at T _β −150 ° C. or higher. Forging can be completed. Note that it is the product part of the titanium alloy β-forged material that needs to be maintained in a temperature range of not less than (T _β −150 ° C.) until the forging is completed, and the surplus of the surface layer and the like removed after forging (after cooling) The temperature in the meat (other than the product part) is not limited to this.

As long as the processing rate (reduction rate) in forging is a condition that satisfies the configuration of the present invention, forging can be performed under the same conditions as in general finish forging. For example, in order to make β crystal grains into flat grains having an aspect ratio of more than 3, for example, forging a cylindrical billet with a mold having a flat surface, a reduction ratio of 45% or more, preferably 55% or more, Or it is preferable to add the process equivalent to it. Moreover, it is preferable that the moving speed of the mold with respect to the titanium alloy billet is 10 ⁻³ to 10 (1 / s).

Growth of non-flat β crystal grains outside the β single-phase region (α + β two-phase region) by cooling the forged titanium alloy intermediate forged material to less than (T _β -150 ° C) immediately after the holding time has elapsed. And the precipitation of a thick and continuous α phase at the grain boundaries of the old β grains is prevented, thereby preventing the fatigue strength of the obtained titanium alloy β forging from deteriorating. Therefore, the cooling rate after holding is preferably 10 ° C./min or more, more preferably 50 ° C./min or more. On the other hand, the upper limit of the cooling rate is not particularly defined, but 500 ° C./min or less is practical, and is preferable because the acicular α phase in the grains is lengthened to improve fracture toughness. The cooling method may be a known method such as air cooling, air blowing, water cooling, hot water cooling, or oil cooling.

  The obtained titanium alloy β forged material is subjected to a tempering heat treatment by a solution treatment and an aging treatment by a known method, if necessary, and further machined to remove an oxide film and surplus, An ultrasonic flaw inspection is conducted. Specifically, it is preferable to perform ultrasonic flaw detection after removing a thickness of 1 mm or more from the surface and smoothing the surface to a surface roughness of 6.3S or more. Thereafter, the titanium alloy β forged material is machined again as necessary to become a product such as an engine part. These processes may be performed by a known method.

<Titanium alloy β forging material>
The titanium alloy β forged material of the present invention is manufactured by the above-described method for manufacturing a titanium alloy β forged material. That is, the titanium alloy β forging material is made of an α + β type titanium alloy, and as shown in FIG. 1, is a rotationally symmetric and large-diameter thin-walled shape represented by the formulas (1) to (3), and has a radially outer peripheral portion. Becomes the forging material that becomes the product part.
The titanium alloy β forged material can be used, for example, for aircraft engine parts. Examples of aircraft engine parts include rotating parts of aircraft engines.
The titanium alloy β-forged material has a large-diameter and thin-walled shape, and has a uniform strain distribution generated inside. As a result, a titanium alloy β-forged material having both low cycle fatigue strength and ultrasonic flaw detection properties is obtained.

<Ultrasonic flaw detection method>
The ultrasonic flaw detection inspection for the titanium alloy β forged material according to the present invention can be performed by a known method, and the probe is selected from a probe having a diameter of 5 to 30 mm, and the ultrasonic wave (transmitted wave) is A frequency range of 1-20 MHz is used. The probe diameter is preferably 10 mm or more, and the ultrasonic frequency is preferably 15 MHz or less. Moreover, it is preferable to perform inspection by a water immersion flaw detection method having high defect detection resolution. The titanium alloy β forged material according to the present invention can be subjected to an ultrasonic flaw detection inspection in which flaw detection is performed in a direction including a direction parallel to the direction in which the amount of reduction in the forging is the largest. The direction of ultrasonic flaw detection inspection refers to the traveling direction of the transmission wave (the direction in which the inside of the titanium alloy β-forged material is transmitted). Titanium alloy β-forged materials tend to have the most noise in the direction of the largest forging reduction amount, but the titanium alloy β-forged materials according to the present invention have sufficiently low noise and high-precision inspection even if flaw detection is performed in such directions. It can be performed. In addition, since the titanium alloy β-forged material is often the smallest (thin) in this direction, it can be inspected to the deep part with high accuracy, and the surface perpendicular to this direction for scanning the probe can be obtained. Since the area is often large, it is easy to inspect. Moreover, it is preferable to inspect for a total of two or more times by flaw detection in one direction or further changing the direction according to the shape of the titanium alloy β forged material (product). Further, depending on the thickness of the titanium alloy β forged material (the length in the traveling direction of the transmission wave), the transmission wave may be incident from the opposite direction.
Since the ultrasonic flaw detection method is sufficiently noise-free even if flaw detection is performed in the forging direction, which results in relatively high noise, the surface of the titanium alloy β forged material can be scanned with a probe, and inspection can be performed. It becomes easy and a highly accurate inspection can be performed.

  As mentioned above, although embodiment of this invention was described, this invention is applied also to the forging material by which the outer periphery of the titanium alloy beta forging material of the thin-walled large diameter shape of rotational symmetry is equipped with the blade | wing shape site | part. be able to.

  As mentioned above, although the form for implementing this invention has been described, the Example which confirmed the effect of this invention is demonstrated concretely compared with the comparative example which does not satisfy | fill the requirements of this invention below. It should be noted that the present invention is not limited by this embodiment, and can be implemented with modifications within the scope shown in the claims, all of which are included in the technical scope of the present invention.

The influence of the shape of the titanium alloy intermediate forging material on the strain distribution generated in the titanium alloy forging material was investigated by FEM (Finite Element Method) analysis.
Here, as the titanium alloy material, Ti-6246 alloy defined by AMS4981: it was FEM analysis using the physical property values of (T β 960 _℃).

In the analysis, the temperature distribution in the titanium alloy intermediate forging was made constant at a predetermined temperature, then taken out of the furnace, installed in the lower die, and then forged.
As a result of the analysis, strain distribution was output, and the maximum and minimum values in the product part were extracted. Here, the amount of strain is evaluated as a product part 10 mm inside from the outer peripheral surface of the forged material and the surface in contact with the mold, and the strain amount is in the range of 0.50 to 2.70 and the strain uniformity is “ A shape condition in which “(maximum strain−maximum strain) / maximum strain” was within 0.70 was determined to be acceptable.
The results are shown in Table 1. The analysis conditions are as follows.

[Analysis conditions]
Heating temperature before forging: 990 ° C (T _β + 30 ° C)
Forging temperature: 930 ℃ or higher _((T β -150 ℃) or higher)
Cooling temperature: Immediately after forging, cooling to 800 ° C or lower Mold temperature: 650 ° C
Atmospheric temperature: 20 ° C
Forging speed: 10mm / sec
Mold method: Semi-closed die

  As shown in Table 1, it can be seen that the specimens 1 to 9 satisfying the predetermined shape conditions have an appropriate strain distribution, and have both low cycle fatigue strength and ultrasonic flaw detection. On the other hand, since the test bodies 10 to 15 do not satisfy the prescribed shape conditions, the strain distribution is poor. Specifically, it is as follows.

In the test body 10, the formulas (4), (5), (6), and (7) are outside the specified range, and the strain uniformity is poor.
In the test body 11, formulas (7) and (9) are outside the specified range, the minimum strain is small, and the strain uniformity is poor.
In the test body 12, the formula (9) is below the lower limit, exceeds the upper limit of the formula (6), the maximum strain exceeds the upper limit, and the strain uniformity is poor.
As for the test body 13, Formula (4) is less than a minimum, and the uniformity of distortion is bad.
In the test bodies 14 and 15, Equation (9) exceeds the upper limit, the minimum strain is small, and the strain uniformity is poor.

  The present invention has been described in detail with reference to the embodiments and examples. However, the gist of the present invention is not limited to the above-described contents, and the scope of right is widely interpreted based on the description of the claims. Must. Needless to say, the contents of the present invention can be widely modified and changed based on the above description.

DESCRIPTION OF SYMBOLS 10 Titanium alloy beta forging material 11 Product part 12 Burr part 13 Titanium alloy beta forging material outer peripheral part 14 Titanium alloy beta forging inner part 15 Titanium alloy beta forging bottom part 18 Titanium alloy beta forging center part 23 Titanium Peripheral portion of alloy intermediate forging material 25 Bottom portion of titanium alloy intermediate forging material 28 Center portion of titanium alloy intermediate forging material 30 Recessed portion of titanium alloy intermediate forging material 40 Convex portion 51 Tangent line 52 Tangent line 100 Titanium alloy intermediate forged material L Center line

Claims (4)

Titanium alloy β-forged material made of α + β-type titanium alloy, which is rotationally symmetric and has a large-diameter, thin-walled shape represented by formula (1), formula (2), and formula (3), and the outer peripheral portion in the radial direction is the product Titanium alloy intermediate forging material used for the production of
The titanium alloy intermediate forging material has a minimum thickness portion at the center and one maximum thickness portion on the outer peripheral portion. Formula (4), Formula (5), Formula (6), Formula (7), Formula (8) is satisfied, and
A titanium alloy intermediate forging material having a relationship of the formula (9) with the shape of the titanium alloy β forging material.
0.1 <b ₁ / A ₁ <0.5 (1)
40 <b ₁ <200 (2)
0.1 <B ₁ / A ₁ <0.9 (3)
1.2 ≦ b ₀ / a ₀ ≦ 4.0 (4)
0.05 <B ₀ / A ₀ ≦ 0.55 (5)
20 ° ≦ θ ≦ 70 ° (6)
_{2A 0/5 ≦ C 0 ··········} (7)
0.5 ≦ c ₀ / b ₀ (8)
0.20 ≦ b ₁ / b ₀ ≦ 0.60 (9)
here,
a ₀ : Minimum thickness (mm) from the bottom of the center of the titanium alloy intermediate forging
b ₀ : Maximum thickness (mm) from the bottom of the outer periphery of the titanium alloy intermediate forging
c ₀ : Thickness (mm) of the outermost peripheral portion of the titanium alloy intermediate forged material
A ₀ : Radius of outer diameter of titanium alloy intermediate forging (mm)
B ₀ : Radius of recess of titanium alloy intermediate forging (mm)
C ₀ : Diameter from the center to the maximum thickness (mm)
A ₁ : Radius of outer diameter of titanium alloy β forged material (mm)
B ₁ : Radius (mm) of inner diameter of titanium alloy β-forged material
b ₁ : Maximum thickness (mm) of the product part of the titanium alloy β-forged material
θ: an angle formed by a tangent at a position (a ₀ + b ₀ ) / 2 from the bottom and a tangent at the bottom of the recess in the inclined portion formed from the center to the outer periphery on the upper surface of the titanium alloy intermediate forging is there. The titanium alloy intermediate forging material according to claim 1, wherein a titanium alloy having a Mo equivalent [Mo] eq represented by the formula (10) of more than 2.7 and less than 15 is used.

[Mo] eq = [Mo] + [Ta] / 5 + [Nb] /3.6+ [W] /2.5+ [V] /1.5+
1.25 [Cr] +1.25 [Ni] +1.7 [Mn] +1.7 [Co] +2.5 [Fe] (10)
However, [X] in the formula (10) is the content (mass%) of the element X in the titanium alloy.   The shape determination method of the titanium alloy intermediate forging material characterized by determining the shape of the titanium alloy intermediate forging material according to the relational expression according to claim 1. The titanium alloy intermediate forging material according to claim 1 or 2 is heated to (T _β + 5 ° C) or higher when a β transformation point determined by the alloy component is expressed by T _β , and a β crystal grain size is 100 μm. The titanium alloy β is characterized in that after being held to a range of less than 800 μm, forging in a temperature range of (T _β −150 ° C.) or higher and immediately cooled to a temperature of less than (T _β −150 ° C.) A method for producing forgings.