JP2018154922A - α+β TYPE TITANIUM ALLOY EXTRUDED SHAPE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an α+β type titanium alloy extruded shape using a Ti-Al-Fe-Mo-based α+β type titanium alloy having higher strength than Ti-Al-C as a raw material, and less in warpage and having fatigue strength and strength ductility balance equivalent to prior art even with having an acicular structure.SOLUTION: There is provided an α+β type titanium alloy extruded shape, containing Al:4.4 to 5.5%, Fe:1.4 to 2.3%, Mo:1.5 to 5.5%, O:over 0% and 0.20% or less, C:over 0% and 0.08% or less, N:over 0% and 0.05% or less, Si:over 0% and 0.1% or less, further selectively one or more kind of Ni:0% or more and less than 0.15%, Cr:0% or more and less than 0.25% and Mn:0% or more and less than 0.25% and the balance Ti with impurities of total amount of 0.4% or less, satisfying a relationship of 1.4%≤[Fe]+[Ni]+[Cr]+[Mn]≤2.3%, and having a metallic structure with an acicular structure and average of old β particle diameter of 300 μm or less.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an α + β type titanium alloy extruded profile.

  Titanium alloys have been used in various fields, such as aircraft aggregates and structural members, civilian products such as golf face club heads and eyeglass frames, and medical applications such as implants, taking advantage of high specific strength and excellent corrosion resistance. ing.

  Among them, α + β type titanium alloys have been widely used mainly in the spacecraft industry because they have a good balance between strength and ductility and excellent fracture toughness. In particular, the α + β type titanium alloy is expected to further improve quality as a shape material such as an aggregate or a seat rail in such an aircraft application.

  Such α + β type titanium alloys have been used for many years mainly in the aircraft field, including Ti-6Al-4V, which is the most used amount. Recently, with the increase in the application ratio of carbon fiber reinforced composite material (CFRP) to the aircraft for further fuel efficiency reduction, the usage rate of titanium alloy has increased, and it may increase further in the future. Expected. This is because aluminum alloys that have been used in the field of aircraft conventionally have different metal contact corrosion due to contact with CFRP, and there is a large difference in thermal expansion coefficient between CFRP and temperature difference between in flight and on the ground (about 100 In contrast to titanium alloy, there is a problem that misalignment, loosening, etc. are likely to occur due to (° C.). It is because it is near.

  The α + β type titanium alloy may be used as a shape material such as an aggregate or a seat rail in such an aircraft application. Some shapes have a complicated cross-sectional shape, and conventionally, they have been manufactured by cutting a forged product having a large cross section or a very thick material. For α + β type titanium alloy, when cutting after forging, by performing strong processing below the β transformation point temperature, the metal structure becomes an equiaxed structure with a high strength / ductility balance, and the required tensile properties, especially High durability was realized.

  However, in recent years, there has been a growing need to reduce the cost of manufacturing parts for aircraft, and by producing a long profile with a cross-sectional shape close to the final product, it is expected to improve yield and productivity, and hot extrusion processing The manufacturing technology of the shape material by has been developed.

  There are methods such as an indirect extrusion method and an isostatic extrusion method for the extrusion process, and the Eugene Sejurune method is one of them. In this method, a round billet produced by forging an ingot is used as a material. As shown in FIG. 1, a material (billet 5) is inserted into the container 1, a hydraulic load is applied to the stem 2, the billet 5 is pushed in the extrusion direction 11 through the dummy block 3, and the die 4 is allowed to pass through various types. By forming into a cross-sectional shape, a long shape 6 can be obtained.

By the way, as described above, the metal structure of the α + β type titanium alloy is subjected to strong processing by forging or the like at a temperature lower than the β transformation point temperature (α + β temperature range) for applications requiring a high strength / ductility balance. The required high tensile strength has been realized by controlling the structure to be equiaxed. On the other hand, when the metal structure is controlled to be an equiaxed structure by extrusion molding, the α + β type titanium alloy has a very high hot deformation resistance in a temperature range lower than the β transformation point temperature (T _β ) by 200 ° C. or more. A large-scale extrusion press that can be added is required, which increases the equipment cost and may make extrusion impossible. Further, even when extrudable, if part of the temperature in the cross section of the profile exceeds the β transformation point temperature due to processing heat generated during extrusion, the equiaxed structure and β transformation temperature in the cross section of the profile The needle-like structure obtained by the above processing is mixed, and a significant mechanical property difference occurs in the cross section. Therefore, in general, extrusion of α + β type titanium alloys can be manufactured with a low extrusion load, and the billet is extruded by heating to a temperature above the β transformation temperature so that surface defects are unlikely to occur. Is controlling.

  However, when the billet is heated to the β transformation point temperature or higher and extruded, the extruded shape has a needle-like structure, and the strength / ductility balance is inferior to that of the equiaxed structure. Furthermore, when the heating temperature of the billet is higher than the β transformation point temperature, the time that is maintained at the β transformation point temperature or longer after extrusion becomes longer, and β grains grow, so that the strength / ductility balance and fatigue strength are inferior. There's a problem. In order to use it in a part closer to the engine, insufficient strength and insufficient fatigue strength due to an increase in inertia weight accompanying an increase in engine speed are serious problems.

  On the other hand, if the billet heating temperature is in the vicinity of the β transformation point temperature or too low than the β transformation point temperature, heat removal due to contact with an extrusion tool such as a container or a die is also affected, and the equiaxed structure is mixed into the surface layer. Further, the surface layer has reduced ductility due to a decrease in temperature, and defects such as cracks and wrinkles may occur during extrusion.

  As a method for improving the fatigue strength of a metal material, a peening process in which metal or nonmetal particles are projected at a high speed is generally known. This is because compressive residual stress is applied to the surface layer of the metal material by the peening process, and fatigue cracks are less likely to occur. However, in a profile having a complex shape, the peening process is not uniform, and the site has a low fatigue strength. Remains. Further, by performing such processing, the processing cost is further increased, so that the manufacturing cost of the shape material is increased.

  In terms of component composition, Al and β-stabilizing elements, which are inexpensive elements that have been conventionally solid-solution-dissolved in α-phase and strengthened at room temperature and high temperature for applications that require high strength, are used. Ti-6Al-4V alloy to which V which is difficult to solidify and segregate is added has been used for many years. However, Ti-6Al-4V has insufficient fatigue strength for the above problems.

  As described above, the α + β-type titanium alloy extruded shape having an acicular structure obtained by performing extrusion processing is difficult to control the extrusion temperature. If the extrusion temperature is too high, the tensile properties are deteriorated. If the extrusion temperature is too low, There are problems such as surface defects and high extrusion load, making extrusion impossible. In order to solve these problems, the following prior art is disclosed.

  In Patent Document 1, a Ti-6Al-4V alloy, which is an α + β type titanium alloy, is extruded by heating to an α + β temperature range, and has high strength, high toughness, small dimensional variation in the longitudinal direction of extrusion, and little surface flaws. A method of manufacturing a profile is described.

  In Patent Document 2, an α + β-type titanium alloy is heated to an α + β temperature range or a β single-phase temperature range and subjected to extrusion, followed by a solution treatment in which the α + β type titanium alloy is forcibly cooled after being heated to an α + β temperature range, A method is described in which a two-stage heat treatment for aging treatment is performed to produce a shape having excellent strength and ductility.

  In Patent Document 3, an α + β type titanium alloy billet exhibiting a fine equiaxed α + β structure is extruded at a temperature above the β transformation point temperature, quenched at 5 ° C./second or more, and then annealed to perform extrusion in the α + β region. A method is described for producing an extruded profile having the same strength and ductility as the shaped profile.

Patent Document 4 proposes a method in which the billet is extruded after the surface layer is cooled to the α + β region after the α + β type titanium alloy billet is heated to the β transformation point temperature or higher. In this method, the inside of the billet is heated to the β transformation point temperature or higher at the time of extrusion, so that the hot deformation resistance is small, the extrusion process is possible with a small pushing force, and the obtained shape has a surface layer. It has high strength because it has an equiaxed α + β structure.

  In Patent Document 5, an α + β type titanium alloy billet is heated to an α + β region temperature range calculated by a linear expression including an extrusion ratio to perform an extrusion process. An optional manufacturing method is disclosed.

  Patent Document 6 discloses a method for producing a shape material having excellent fatigue strength by controlling the structure of an α + β type titanium alloy billet by performing extrusion processing at a temperature in an α + β range calculated by a linear expression including an extrusion ratio. Is described.

  On the other hand, Patent Documents 7 to 9 disclose that the component composition not containing V is improved or adjusted, and Patent Documents 7 to 9 include 4.4% or more and less than 5.5% Al, 1.4% or more. Fe containing less than 2.3% Fe, 1.5% or more and less than 5.5% Mo, and as impurities, Si is less than 0.1%, C is less than 0.01%, the remaining titanium and inevitable An α + β type titanium alloy made of impurities is disclosed.

  In Patent Document 7, in order to adjust the Young's modulus of an α + β-type titanium alloy having a tensile strength of 1000 MPa class or higher to a predetermined value, a heat treatment that combines heating in a predetermined temperature range and a predetermined cooling rate corresponding thereto is performed. It is stated that it will be applied.

  Patent Document 8 describes an engine valve made of α + β-type titanium alloy, which is manufactured by roughly forming hot, forming a solution, and cutting after air cooling. In the present invention, a peening process is performed to increase the fatigue strength.

  Patent Document 9 describes that the tensile strength, the elongation, the fatigue strength, the formability, and the drawing of the high-temperature high-speed tensile test are improved by setting the types and amounts of the respective components within a predetermined range.

JP 61-193719 A JP-A 61-284560 JP 63-223155 A Japanese Patent Publication No.5-2405 Japanese Patent No. 2932918 JP 2012-52219 A JP 2007-314834 A JP 2007-1000066 A Japanese Patent Laying-Open No. 2005-320618

  The α + β-type titanium alloy extruded shapes according to Patent Documents 1 to 6 listed in the above prior art are all subjected to forced cooling after extrusion to control the structure, or controlled to a structure other than the needle-shaped structure to balance strength and ductility. Improvements are being made.

Profiles subjected to structure control by forced cooling have a high balance between strength and ductility. This is because the growth during cooling of the side plate α phase and the grain boundary α phase in the needle-like structure is suppressed as the cooling rate increases. However, long materials and shapes with a large cross-sectional area have a problem in that when forced cooling is performed, the overall length and the cooling rate vary between the inside and outside of the shape, resulting in occurrence of sites where the desired structure and material properties cannot be obtained. Furthermore, in the cooling process, stress is generated inside the shape member due to heat shrinkage. For this reason, when the cooling rate difference is remarkably large and the stress is large, the shape deformation such as warpage may occur in the shape material due to plastic deformation, or residual stress may remain after cooling, which is not preferable.

  In the method in which the structure of the shape material is other than the acicular structure, it is necessary to control a part and the entire area of the billet to the α + β temperature range. However, the α + β type titanium alloy has high hot deformation resistance when the processing temperature falls below the β transformation point temperature, and requires a large pressing force. Further, since the processing heat generation amount is large in the α + β temperature range, the processing temperature may exceed the β transformation point temperature due to processing heat generation during extrusion. As a result, there is a problem that a uniform shaped material cannot be obtained and the mechanical properties are not uniform. Furthermore, in the method of heating by providing a temperature gradient within the billet cross section, there is a problem that a stable shape cannot be obtained because the degree of deformation varies due to a slight difference in temperature within the cross section.

  Moreover, in patent document 8 mentioned by prior art, fatigue strength is raised by the peening process. However, as described above, in a shape having a complicated shape, the peening process is not made uniform, and there is a problem that a portion with low fatigue strength remains, which further increases processing costs. Since many products for aircraft parts cut the surface into a desired shape, the surface portion with high fatigue strength may be cut. In addition, secondary processing such as hot correction may be required, but the surface processed portion has low ductility, and cracks may occur.

  Further, Patent Document 9 cited in the above prior art does not mention a shape produced by extrusion, nor does it mention the relationship between the structure and production conditions of the extruded shape and fatigue strength.

  Therefore, the present invention uses a Ti-Al-Fe-Mo type α + β type titanium alloy, which has higher strength than Ti-Al-V, and has a needle-like structure, but has fatigue strength, strength and ductility equivalent to the prior art. An object is to provide an α + β titanium alloy extruded profile having a balance.

  In the present invention, as a mechanical property of an α + β titanium alloy extruded shape, 0.2% proof stress at room temperature is equal to or greater than that of a conventional material of Ti-6Al-4V having an equiaxed structure (such as a very thick material manufactured by rolling). That is, it is 900 MPa or more, and the elongation was set to 10% or more, which is no problem in performing secondary processing such as hot correction. Further, the fatigue strength was set to be equal to or higher than the fatigue strength obtained by subjecting a conventional Ti-6Al-4V material to surface treatment, that is, 550 MPa or more.

In order to solve this problem, the gist of the present invention is as follows.
[1]
In mass%, Al: 4.4 to 5.5%, Fe: 1.4 to 2.3%, Mo: 1.5 to 5.5%, O: more than 0% and 0.20% or less, C: More than 0% and 0.08% or less, N: more than 0% and 0.05% or less, Si: more than 0% and 0.1% or less, more selectively, Ni: 0% or more and less than 0.15%, One or more of Cr: 0% or more and less than 0.25% and Mn: 0% or more and less than 0.25%, with the balance being Ti and a total amount of impurities of 0.4% or less. Α + β satisfying the relationship of 4% ≦ [Fe] + [Ni] + [Cr] + [Mn] ≦ 2.3%, the metal structure is a needle-like structure, and the average of the old β particle diameter is 300 μm or less. Type titanium alloy extruded shape. Here, [Fe], [Ni], [Cr] and [Mn] indicate mass% of each component.
[2]
The α + β-type titanium alloy extruded profile according to [1], wherein the average of the old β grain size is 250 μm or less.
[3]
The α + β-type titanium alloy extruded profile according to [1] or [2], wherein the average maximum width of the grain boundary α phase is 5 μm or less.
[4]
An average particle diameter d ₁ (m) of an old β grain having a cross section perpendicular to the extruding direction of the extruded profile, and an extruding shape that is parallel to the one cross section and separated from the one cross section by a distance L (m) in the extruding direction. Any of [1] to [3], wherein the value of the following formula (1) calculated by the average particle diameter d ₂ (m) of the old β grains of another cross section of the material is 25 or less The α + β type titanium alloy extruded shape according to any one of the above.
| (D ₁ −d ₂ ) / L | × 10 ⁶ (1)

  According to the present invention, with respect to an α + β type titanium alloy profile having a specific composition, the 0.2% proof stress is 900 MPa or more because the metal structure is an acicular structure and the average of the old β grain size is 300 μm or less. , An extruded shape having an elongation of 10% or more. Furthermore, it can be set as the extrusion shape material which has the characteristic that 0.2% yield strength is 550 Mpa or more.

  Since the α + β type titanium alloy extruded profile of the present invention has excellent strength and fatigue strength and can be mass-produced, it can be used for structural members for aircraft, automobiles and motorcycles at low cost. Can be manufactured. According to the present invention, industrial applications are expanded, and it is possible to obtain an effect such as improvement in fuel consumption of an aircraft or an automobile due to its light weight and high strength characteristics.

It is a schematic diagram of the extrusion press machine in the Eugene Sejurune method. It is a microscope picture which shows the acicular structure of (alpha) + (beta) type | mold titanium alloy extruded shape material. (A)-(d) is a graph which shows the heat history which illustrated the manufacturing method of the (alpha) + (beta) type | mold titanium alloy extrusion shape material of this invention, all. It is a schematic diagram of the cross-sectional shape of the extrusion profile manufactured in the Example. It is explanatory drawing of the "warp" of the extrusion shape member measured in the Example.

  The α + β type titanium alloy targeted by the present invention is composed of an α phase having an HCP structure and a β phase having a BCC structure below the β transformation point temperature, and the α phase is transformed into the β phase above the β transformation point temperature. It consists only of β phase. The acicular structure is a form generated after processing at a temperature equal to or higher than the β transformation point, and the form of the structure is shown in FIG. A grain boundary α phase is formed at the boundary of the old β grains which were one grain at a temperature equal to or higher than the β transformation temperature. That is, a grain boundary α phase is formed during cooling at the grain boundaries of β grains (old β grains) that existed at a temperature equal to or higher than the β transformation temperature. In the present invention, the region surrounded by the grain boundary α phase, which is the grain boundary of β grains (old β grains) that existed at the β transformation temperature or higher, is called “old β grains”. A structure in which α phases and β phases called a plurality of colonies are arranged in layers is formed in the old β grains. Hereinafter, the α phase in the colony is referred to as a side plate α phase, and the β phase is referred to as a side plate β phase.

  In addition, metals generally shrink due to heat shrinkage during cooling, resulting in a decrease in volume. When there is a difference in the cooling rate depending on the part, the amount of heat shrinkage varies at a certain time during cooling, so that stress is generated inside the shape member. When the cooling rate of the profile is slow, such as air cooling or furnace cooling, such stress only gives elastic deformation to the profile. However, in the prior art, a high strength / ductility balance is obtained by controlling the structure and composition by forced cooling immediately after extrusion or by solution treatment (forced cooling from a high temperature range) in heat treatment after extrusion. In these forced coolings, since the difference in cooling rate is large, significant stress is generated and plastic deformation such as warpage is given to the profile. Further, even if a shape defect does not occur at the time of cooling, a residual stress is generated inside the shape member, and a shape defect such as a warp is given during processing or cutting of the shape member.

  Therefore, the present inventors examined the relationship between the tensile properties of the profile and the acicular structure by subjecting the α + β type titanium alloy having a specific composition to hot extrusion under various heating conditions. As a result, Ti-6Al-4V having an equiaxed structure can be obtained by forming the metal structure to be an acicular structure and making the average of the old β grain size 300 μm or less without using forced cooling that causes shape defects. It has been found that an α + β-type titanium alloy extruded shape having a 0.2% proof stress and fatigue strength equal to or higher and having a practically satisfactory ductility can be obtained.

  In the present invention, the significance of determining the component composition will be described. The percentages of the following component compositions are all mass%.

  The present invention is directed to a titanium alloy mainly containing Al, Fe, and Mo, that is, Ti-5Al-2Fe-3Mo. Hereinafter, the reason for limitation of each component is demonstrated.

Al: 4.4 to 5.5%
Al is an α stabilizing element and is an element added to increase the fraction of the α phase. If the content is less than 4.4%, the fraction of the α phase, which is higher in strength than the β phase, becomes too small to obtain sufficient strength, and excellent 0.2% proof stress cannot be obtained. On the other hand, if the content exceeds 5.5%, the stacking fault energy is increased, and the hot and room temperature ductility deteriorates in order to suppress twin deformation, and Ti ₃ Al precipitates toughness. Deteriorates and processability decreases. Furthermore, if the content exceeds 5.5%, a smooth local slip is induced, so that cracks are likely to occur at the location where the local slip occurs, and the fatigue characteristics are degraded. Therefore, the lower limit of the Al content is 4.4% and the upper limit is 5.5%.

Fe: 1.4 to 2.3%
Fe is a β-stabilizing element and, when added, has the effect of lowering the β transformation point temperature. Moreover, since it has the effect | action which improves a 0.2% yield strength, 1.4% or more of Fe is added. On the other hand, if the content exceeds 2.3%, segregation during solidification becomes remarkable, and the influence cannot be eliminated in subsequent manufacturing processes such as processing and heat treatment. Furthermore, the elongation deteriorates and the workability is reduced. Therefore, the upper limit of the Fe content is set to 2.3%.

Mo: 1.5 to 5.5%
Mo is a β-stabilizing element and can lower the β transformation point temperature of the titanium alloy in the same manner as Fe. Moreover, by adding 1.5% or more, 0.2% yield strength, ductility and fatigue strength are improved, and hot workability is improved. On the other hand, when the addition amount exceeds 5.5%, a problem of solidification segregation occurs as in the case of Fe. Therefore, the upper limit of the Mo content is set to 5.5% as an addition amount that does not cause solid segregation in a large ingot.

Further, by mass%, Ni: 0% to less than 0.15%, Cr: 0% to less than 0.25%, Mn: 0% to less than 0.25% The α + β type titanium alloy extruded profile is further added as an optional additive element in mass%, Ni: 0% to less than 0.15%, Cr: 0% to less than 0.25%, Mn: 0% to 0% to 0 One or two or more of less than 25% may be contained. In these, a part of Fe is replaced with an inexpensive element that functions in the same manner as Fe.

Here, the upper limit of the addition amount of Ni, Cr, and Mn is less than 0.15%, less than 0.25%, and less than 0.25%, respectively. This is because an intermetallic compound (Ti ₂ Ni, TiCr ₂ , TiMn) which is an equilibrium phase is generated, and fatigue strength and room temperature ductility deteriorate. The total amount of Ni, Cr, Mn, and Fe needs to be 1.4% or more and 2.3% or less. This is because if it is less than 1.4%, the room temperature tensile strength becomes small, and if it exceeds 2.3%, the room temperature ductility is lowered.

O: more than 0% to 0.20% or less, C: more than 0% to 0.08% or less, N: more than 0% to 0.05% or less, Si: more than 0% to 0.1% or less O, C, N, Si Is an α-stabilizing element which, when added, increases the α-phase fraction and improves the 0.2% yield strength. However, when the content of each element is increased, ductility is lowered and workability is lowered. Therefore, O: more than 0% and 0.20% or less, C: more than 0% and 0.08% or less, N: more than 0% and 0.05% or less, and Si: more than 0% and 0.1% or less.

Balance: Ti and impurities with a total amount of 0.4% or less The balance is Ti and impurities. Illustrative examples of the impurity element include Cl, Na, Mg mixed in the titanium refining process, and impurities such as Zr, Sn, Cu, Mo, Nb, Ta mixed from scrap. When the content of any impurity is increased, Ti and a compound are generated and toughness is lowered, and as a result, workability is lowered. In addition, when the total content of impurities is excessive, ductility is lowered and workability is deteriorated. Therefore, the total of other elements must be controlled to 0.4% or less so as not to hinder the effects of the present invention.

  Next, the significance of limiting the old β particle size in the present invention will be described. In acicular tissue, some dislocations easily propagate through the α / β phase boundary, so the deposition distance of some dislocations is given by half the colony size. Also, the colony size decreases as the old β particle size decreases. Therefore, as the old β grain size decreases, the stress field due to the accumulation of dislocations at the colony boundary decreases, and the 0.2% proof stress tends to increase due to the strengthening of the microstructure. In other words, when the old β grain size is increased, the stress concentration generated at the colony boundary is increased due to an increase in the dislocation deposition distance, so that the 0.2% yield strength is reduced. Furthermore, as the old β grain size becomes smaller, the colony size becomes smaller, and the number of dislocations deposited at the old β grain boundary and the colony boundary decreases, so the stress concentration at the old β grain boundary and the colony boundary is relaxed and elongation increases. To rise. Therefore, in the present invention, the upper limit is set to 300 μm, which is the average of the old β grain size, in which the 0.2% proof stress is 900 MPa or more, the fatigue strength is 550 MPa or more, and the elongation is 10%. Preferably, the average of the old β particle size is 250 μm or less. On the other hand, the lower limit is not necessarily limited, but is preferably 50 μm or more. In order to make it finer, it is necessary to lower the extrusion temperature or to perform strong processing during extrusion, and the deformation resistance becomes large, so the burden on the apparatus is large, so the above lower limit is preferable.

  In an acicular structure, the ductility decreases as the average maximum width of the grain boundary α-phase increases. The grain boundary α phase is generated in the old β grain boundary where dislocations are likely to accumulate during processing. Therefore, voids during processing are also likely to be generated at the grain boundary α-phase interface, but when the average maximum width of the grain boundary α-phase is increased, the voids are likely to progress along the grain boundary α. Therefore, in the present invention, it is preferable that 5 μm, which is the maximum grain boundary α width obtained by normal cooling, be the upper limit of the average maximum width of the grain boundary α. On the other hand, the lower limit is not necessarily limited, but 0.5 μm or more is preferable in order to suppress the occurrence of warpage of the extruded profile. In order to reduce the temperature further, forced cooling such as water cooling or fan air cooling is required.In order to increase the temperature difference inside the profile, shape defects caused by internal stress and residual stress after air cooling are generated. The above lower limit is preferable because it causes.

  A method for measuring the average maximum width of the grain boundary α phase will be described. In the cross section of the extruded shape shown in FIG. 4, five old β grains confirmed at a structure observation position by a microscope are arbitrarily selected, and the maximum width of each grain boundary α phase is measured. When selecting old β grains, avoid selecting adjacent old β grains. The average value of the five maximum widths is defined as the average maximum width of the grain boundary α phase.

By the way, the average particle size of the old β grains of the extruded profile is usually not uniform in the extrusion direction of the extruded profile. The reason is in the extrusion process. When extruding, the tip part which is the top of the billet 5 which first contacts the extrusion mold is removed by contact with the die 4 and the temperature tends to decrease. On the other hand, the rear end portion of the extrusion removes heat to contact the dummy block 3, and the heat removal amount is large because the contact time with the container 1 is longer than that of the front end portion. Since the degree of heat removal differs between the front end portion and the rear end portion, the extrusion temperature is not uniform at the front end portion and the rear end portion, and appears as a difference in the average particle diameter of the old β grains.
The difference in the average particle size of the old β grains appears as it is as the difference in the strength of each part. Therefore, in order to obtain an extruded shape having uniform mechanical strength in the extrusion direction, the value calculated by the following equation (1) is preferably 25 or less. In the formula (1), the difference between the average particle diameter d ₁ (m) of the old β grains in one cross section and the average particle diameter d ₂ (m) of the old β grains in another cross section is divided by L (m). The absolute value. A more preferable value of the formula (1) is 15 or less, more preferably 10 or less.
| (D ₁ −d ₂ ) / L | × 10 ⁶ (1)
d ₁ : average particle diameter (m) of old β grains having one cross section perpendicular to the extrusion direction of the extruded profile
d ₂ : Average particle diameter (m) of the old β grains in another cross section of the extruded profile that is a distance L (m) away from one cross section in the extrusion direction
L: Distance in the extrusion direction between one cross section and another cross section (m)
The distance L is preferably 0.3 m or more, and more preferably 1 m or more. Therefore, the length of the extruded profile is preferably 2 m or longer, more preferably 3 m or longer, which is longer than L.

Next, the manufacturing method of the α + β type titanium alloy extruded profile of the present invention will be described with reference to FIG. In FIG. 3, (a) is a production method for obtaining a needle-like structure by performing hot extrusion in a temperature range equal to or higher than the β transformation point temperature (T _β ), and (b) is equal to or higher than the β transformation point temperature (T _β ). After producing the needle-like structure by performing hot extrusion in the temperature range of (c), after performing extrusion in the temperature range lower than the β transformation point temperature (T _β ), (c) A production method in which a β single-phase region heat treatment is carried out to obtain an acicular structure, (d) is obtained by performing _β extrusion in a temperature range lower than the β transformation temperature (T _β ) and then obtaining a needle-like structure. This is a manufacturing method in which phase region heat treatment is performed and strain relief annealing is performed. These are merely examples, and the α + β-type titanium alloy extruded profile of the present invention is not limited to those obtained by these production methods.

In a production method in which the extrusion temperature is set to the β transformation point temperature or higher and the β single-phase region heat treatment is not performed after the extrusion as shown in FIGS. 3 (a) and 3 (b), the titanium alloy billet is heated to the β transformation point temperature or higher. When hot extrusion is performed, it is necessary that the temperature of the billet surface, including the center and the center, be soaked to a predetermined temperature equal to or higher than the β transformation point temperature.
First, the manufacturing method shown in FIG. 3A in which annealing is not performed after extrusion will be described.
Titanium has a low thermal conductivity, so in order to soak the titanium alloy billet to a predetermined temperature, the heating rate during heating is slowed down or the furnace is kept in the furnace for a long time to include the billet center. To reach the target temperature. In this way, if the target temperature is reached to the center of the billet, the billet surface becomes higher than the β transformation point temperature earlier than the center, so the staying time after reaching the β transformation point temperature or longer is longer. Become. As a result, the growth of β grains is promoted on the billet surface, and the β grain size before extrusion increases. When the β grains before extrusion are coarsened, the number of recrystallized nucleation sites of the beta grains after extrusion is small, so the beta grains after extrusion are also coarsened, and the average of the old β grain size exceeds 300 μm, 0.2 % Yield strength decreases.

  Therefore, preheating is performed so that the billet is soaked at a predetermined temperature equal to or lower than the β transformation point temperature, and then rapid heating is performed to bring the entire billet to a predetermined temperature equal to or higher than the β transformation point temperature. The idea was to create a hot extrusion process with a shorter temperature holding time. In the preheating, the billet is soaked at a temperature equal to or lower than the β transformation point temperature, so that no coarsening of β grains occurs. Since preheating is performed, it is possible to perform rapid heating thereafter, and when the billet center reaches a predetermined temperature equal to or higher than the β transformation point temperature, the holding time equal to or higher than the β transformation point temperature on the billet surface is set to a short time. It becomes possible to do. As a result, including the surface of the billet, β grain coarsening before extrusion can be prevented, and β grain coarsening after extrusion can be prevented, and the average of the old β grain size can be made 300 μm or less. did.

In preheating, the temperature of the billet surface and the center _{(T β -500) ~ (T} β -80) ℃, the temperature difference between the surface and the center performs preheating so that the 50 ° C. or less.

  The billet surface temperature may be measured with a radiation thermometer. On the other hand, the temperature measurement of the billet center is performed by drilling the center position of the circle at the bottom of the billet prior to heating, drilling to the center of the billet, and inserting a thermocouple protected by an insulating tube. It is good to do by.

If the billet temperature after pre-heating is too low, it is necessary to increase the holding time after rapid heating in order to make the billet center more than the predetermined β transformation point temperature when performing rapid heating thereafter. As a result, the retention time of the billet surface above the β transformation point temperature increases, and the β grains become coarse. In the present invention, by setting the preheat temperature limit (T _β -500) ℃, shorten the retention time after the rapid heating, and can be the average of the old beta particle size after extrusion and 300μm or less became.

Titanium tends to oxidize when heated in the atmosphere, and when heated above a certain temperature, forms a hardened layer called α-case on the surface, and the thickness increases as the heating temperature increases. Since the α case is hard and has poor ductility, it becomes the starting point of cracks during extrusion, and cracks occur in the extruded product. Further, since the die is worn significantly by the polishing action of the hardened surface layer, the cross-sectional dimension varies greatly in the longitudinal direction of the extruded material. So, the upper limit of α formation of the case is not significantly _(T β -80) ℃ the billet preheat temperature.

  Titanium has poor heat conductivity, and if the rapid heating is performed from the billet surface in a state where the billet is not sufficiently soaked after preheating, the entire billet is not heated uniformly. Therefore, the time from when a part of the billet reaches the β transformation point temperature during rapid heating until the whole billet reaches the β transformation point temperature is short, and the old β particle size after extrusion is within the cross section of the old β particle size. The upper limit of the temperature difference between the billet surface and the center during preheating was set to 50 ° C. so that the average upper limit of 300 μm was not exceeded. In actual operation, the temperature difference is preferably 20 ° C. or less.

After preheated billet, heated to _{T β ~ (T β +200)} ℃ at 1.0 ° C. / s or higher when energized heating or induction heating of the heating rate, then performing the extrusion.

The older β particle size increases as the billet temperature after rapid heating increases. This is because the β grains processed during extrusion recrystallize while being held above the β transformation point temperature after extrusion, but as the billet temperature before extrusion rises, it rises above the β transformation point temperature after extrusion. This is because the time that is held in the crystal increases and the grain growth time after recrystallization becomes longer. It has been found that when the billet temperature after rapid heating exceeds (T _β +200) ° C., the average β grain size of the profile exceeds 300 μm, the 0.2% proof stress is 900 MPa, and the fatigue strength is less than 550 MPa.
Titanium easily oxidizes when heated in the atmosphere, and when heated above a certain temperature, forms a hardened layer called α-case on the surface, and the thickness increases as the heating temperature increases. Since the α case is hard and has poor ductility, it becomes the starting point of cracks during extrusion, and cracks occur in the extruded product. Further, since the die is worn significantly by the polishing action of the hardened surface layer, the cross-sectional dimension varies greatly in the longitudinal direction of the extruded material. Therefore, the upper limit of the billet rapid heating temperature was set to an average of the old β particle diameter of 300 μm or less and the formation of α case was not significant (T _β +200) ° C.
On the other hand, when the temperature after the rapid heating is in the vicinity of the β transformation point temperature (T _β ), the shape material surface layer portion has a processing temperature lowered to T _β or less due to heat removal when contacting the die during extrusion, etc. Has an axial structure. As the die temperature increases with the progress of extrusion, the processing temperature of the shape material layer also rises, and in order to produce a shape material having a needle-like structure stably, although it has a needle-like structure in the stationary part, The temperature after rapid heating is preferably (T _β +50) ° C. or higher.

  If the heating rate at the time of rapid heating of the billet before extrusion is slow, the billet surface is held for a longer time than the β transformation point temperature, the old β particle size before extrusion becomes coarse, β particle size increases. Therefore, the lower limit of the heating rate was set to 1.0 ° C./s at which the growth of β grains on the billet surface before extrusion was suppressed and the average of the old β particle diameter after extrusion was 300 μm or less.

  Since titanium has poor thermal conductivity, it is preferable to provide a predetermined holding time after rapid heating in order to heat the entire billet evenly when rapid heating is performed by energization heating or induction heating. In order for the entire billet to be heated to a temperature equal to or higher than the β transformation temperature, it is desirable to hold it for 20 seconds or more after rapid heating. On the other hand, if the holding time after rapid heating is too long, the β grains are coarsened during the holding time, and the β grains after extrusion are also coarsened. In the present invention, by setting the holding time after rapid heating to 20 minutes or less, the average of the old β particle diameter of the profile can be set to 300 μm or less.

  After performing the extrusion process, it is preferable to cool to room temperature at a cooling rate of less than 5 ° C./second. The cooling rate here refers to a cooling rate up to 500 ° C. When forced cooling at 5 ° C./second or more is performed after extrusion, the cooling rate becomes non-uniform, stress due to the temperature difference inside the shape is generated inside the shape, and plastic deformation such as warping and bending occurs. Even if plastic deformation does not occur, residual stress is generated inside the shape after cooling to room temperature, giving shape defects such as warpage during processing or cutting of the shape. Therefore, it is preferable to cool after extrusion processing at a cooling rate of less than 5 ° C./second. On the other hand, if the cooling rate is slow, the grain boundary α phase grows during cooling and the ductility decreases. Therefore, the cooling rate after extrusion is allowed to cool at 0.5 ° C./second or more. In actual operation, cooling (about 1 ° C./second) is preferable.

Although the above is description of the manufacturing method shown to Fig.3 (a), in addition to it, like the manufacturing method shown in FIG.3 (b), after standing_to_cool, (T ( _beta ) -500)-(T ( _beta ) -200). ) Strain removal annealing may be performed at ° C.

  Even if it is allowed to cool after extrusion, an internal stress is generated during cooling due to a temperature difference inside the profile. Therefore, in the present invention, the bending generated at the time of cutting or the like can be reduced by removing the internal strain from the shape material after cooling and performing annealing for a time sufficient to reduce the internal stress.

On the other hand, as the annealing temperature rises, the width of the α phase (side plate α phase) in the colony increases and the deposition distance of some dislocations increases, so the 0.2% proof stress and strength decrease. Therefore, the width of the side plate α phase starts increasing _(T β -200) ℃ was made the upper limit of the annealing temperature.

Unlike the manufacturing method shown in FIGS. 3 (a) and 3 (b), as shown in FIGS. 3 (c) and 3 (d), the present invention can be manufactured by extrusion at a temperature lower than the β transformation point temperature.
In the manufacturing method shown in FIGS. 3C and 3D, since the extrusion process is performed in a temperature range lower than the β transformation point temperature (T _β ), the structure after the extrusion process is an equiaxed structure. Therefore, in order to make the equiaxed tissue portion into a needle-like structure, β single-phase region heat treatment is next performed. The conditions for the β single-phase region heat treatment are described in detail below.

A manufacturing method shown in FIG. 3C in which annealing is not performed after the β single-phase region heat treatment will be described.
The α + β titanium alloy usually has a complicated cross-sectional shape of the hot-extruded shape, and when the processing rate of extrusion is high, the processing heat generation becomes large and the heat generation can be used, so the structure tends to become a needle-like structure. When the cross-sectional shape is simple or the processing rate of extrusion is low, the heat taken away by contact with the die or container exceeds the calorific value of the processing. Is difficult.

Therefore, after the extrusion process, the whole is transformed into the β phase by heating to a temperature _{equal to} or higher than the β transformation temperature Tβ, and a needle-like structure can be obtained after cooling. Therefore, after the extrusion process, β single-phase region heat treatment with T _β as the lower limit temperature is performed.

However, as the β single-phase region heat treatment temperature increases, the diffusion rate of atoms increases and the growth rate of β grains increases, and the time required for cooling to the β transformation temperature or less increases. Grain growth is promoted. As a result, if the β single-phase region heat treatment is too high, the β grain size (old β grain size) grows beyond 300 μm, the dislocation deposition distance increases, and the stress concentration generated at the colony boundary increases, 0.2% yield strength is greatly reduced. Therefore, the upper limit temperature of the β single-phase region heat treatment was set to (T _β +200) ° C. where the growth rate of β grains was not significant and the cooling time to the β transformation point temperature or less was short.

In order to prevent the β grain size (old β grain size) of the needle-like structure portion from being coarsely changed, the heating time of the β single-phase region heat treatment is also important. As the β single-phase region heat treatment time increases, the β particle size (old β particle size) increases. This is because if the holding temperature equal to or higher than the β transformation point temperature is long, the interfacial energy of the β grains is lowered, and the β grains start to coalesce. Titanium easily oxidizes when heated in the atmosphere, and when heated above a certain temperature, forms a hardened layer called α-case on the surface, and the thickness increases as the heating temperature increases. Since the α case is hard and has poor ductility, it becomes the starting point of cracks and causes cracks in the product. Therefore, the average of the beta grain size (formerly beta particle size) becomes 300μm or less, and α formed of the case is not significantly, by T _beta ° C. hold profile 1000 seconds or more (beta single phase region annealing temperature) All of the equiaxed tissue parts can be made into a needle-like structure without coarsely changing the old β particle diameter of the needle-like tissue part. On the other hand, the lower limit of the β single-phase region heat treatment time depends on the thickness of the profile, but considering the heat transfer time to the center of the profile, the whole is heated to the β transformation temperature or higher for 10 seconds. The degree is preferred.

Also in the case where the β single-phase region heat treatment is performed in this way, it is necessary that the billet surface and the center are uniformized to a predetermined temperature equal to or higher than the β transformation point temperature. Therefore, in the manufacturing method shown in FIGS. 3 (a) and 3 (b), β single-phase region heat treatment is performed to heat to the β transformation point temperature or higher, similarly to the case of heating to the β transformation point temperature or higher before hot extrusion. In some cases, the billet is soaked at a predetermined temperature not higher than the β transformation temperature (surface and center temperature (T _β −500) to (T _β −80) ° C., temperature difference between the surface and the center 50 ° C. or less). Preheating, followed by rapid heating (temperature increase rate of 1.0 ° C / s or more) to bring the entire billet to a predetermined temperature above the β transformation point temperature, and shorten the temperature holding time above the β transformation point temperature. Then, β single-phase region heat treatment is performed. Thereby, it becomes possible to make the average of the old β grain size 300 μm or less.

  And after performing beta single phase region heat treatment, it is preferable to cool to room temperature at a cooling rate of less than 5 ° C./second. As a result, plastic deformation such as warping and bending is prevented, and residual stress does not occur inside the profile.

Although the above is description of the manufacturing method shown in FIG.3 (c), in addition to it, like the manufacturing method shown in FIG.3 (d), after standing_to_cool, (T ( _beta ) -500)-(T ( _beta ) -200). ) Strain relief annealing may be performed at ° C. Thereby, the distortion which generate | occur | produced inside can be removed and the curvature which generate | occur | produces at the time of secondary processes, such as cutting, can be suppressed.

  As described above, the α + β type titanium alloy extruded shape of the present invention is not obtained only by these production methods. For example, in the manufacturing method shown in FIGS. 3C and 3D, the extrusion process may be performed at the β transformation temperature or higher. Further, the diffusion annealing may be continuously performed during cooling after the extrusion process or during cooling after the β single-phase region heat treatment.

  In order to reduce the value of the expression (1) to 25 or less in the extruded shape, the container 1, the stem 2, the dummy block 3, the die contacted with the billet 5 in consideration of heat removal at the front end and the rear end. The amount of heat removal is calculated from the temperature, contact time, and heat capacity of No. 4, and heating that compensates in advance for the temperature that decreases due to the amount of heat removal is performed at the front end and rear end, and a temperature gradient is applied to both.

  Obtained by hot forging a Ti-5Al-2Fe-3Mo ingot having a composition shown in Table 1 with a diameter of 700 mm and a weight of 5 tons obtained by melting twice in a vacuum arc to an area reduction rate of 60% in the α + β temperature region. The surface oxidized layer of the billet was cut to obtain an extrusion billet.

  For the manufacturing methods (a) and (b), the billet was preheated to 700 ° C. in an Ar gas atmosphere (temperature difference between the surface and the center was 5 ° C.) and then increased at a rate of temperature increase of 1.3 ° C./s. After heating and extruding into a convex cross-sectional shape under the production conditions shown in Table 2, it was allowed to cool to room temperature. Regarding the manufacturing method (b), the hot stamped material was then subjected to strain relief annealing under the conditions shown in Table 2. For the production methods (c) and (d), the extruded shape extruded at the extrusion temperature shown in Table 2 was preliminarily heated to 700 ° C. in an Ar gas atmosphere (the temperature difference between the surface and the center was 5 ° C.) by induction heating. After heating, the temperature was raised at a rate of temperature rise of 1.3 ° C./s, and the β single-phase region heat treatment shown in Table 3 was performed. Regarding the production method (d), the hot-pressed material was then subjected to strain relief annealing under the conditions shown in Table 2. In the case of (a) and (b), “with” induction heating in Table 2 means that induction heating was performed in preheating before extrusion, and in the cases of (c) and (d) This means that induction heating was performed in the preheating before the β single phase region heat treatment. In addition, extrusion temperature is the temperature measured in the position of 110 mm from the most advanced billet.

<Tensile test>
An ASTM E8 half-size tensile test piece (parallel portion φ6.35 mm, gauge length 25 mm) was obtained from the position shown in FIG. 4 of the hot stamped material. 0.2% proof stress, tensile strength, and elongation at break were measured by a tensile test.

<Tissue observation test>
A structure observation test piece was collected from the same position as the position where the tensile test piece was collected, and the L section was subjected to structure observation using an optical microscope observation photograph. For the old β particle size, the equivalent circle diameter was measured by a cutting method, and the average of 3 mm × 6 mm (minimum number of particles: about 200) was obtained.
Regarding the average maximum width of the grain boundary α phase, as described above, in the cross section of the extruded shape shown in FIG. 4, arbitrarily select five old β grains confirmed at the structure observation position by the optical microscope, The maximum width of the grain boundary α phase is measured. When selecting old β grains, avoid selecting adjacent old β grains. Then, the average value of the five maximum widths was determined as the average maximum width of the grain boundary α phase.

<Tissue distribution>
The equiaxed tissue part and the acicular tissue part can be determined by macro-structure observation. The macro structure is divided into two regions: a region with a strong metallic luster and a region with a low gloss that appears white. In any region, the light is reflected by the unevenness of the surface caused by the macro etching, resulting in a metallic luster. However, in the region containing fine equiaxed α-grains, the unevenness generated on the surface is finer than the region of the needle-like tissue, and light is irregularly reflected. Therefore, the equiaxed tissue region appears white compared to the acicular tissue region. Regarding the tissue distribution, a cross section (including the end face of the most advanced portion) obtained by dividing a shape member having a total length of 4000 mm every 200 mm was examined.

<Fatigue test>
Fatigue strength was measured using a round bar test piece, a stress ratio R = σmin / σmax = −1 (σmin is a compressive stress, σmax is a tensile stress), a rotational speed of 3600 rpm, a room temperature, and a rotating bending fatigue test. The maximum value of strength σmax that did not break at 1.0 × 10 ⁷ times was defined as fatigue strength.

<Warpage>
As shown in FIG. 5, the warp was defined as a warp in the center of the shape with respect to a straight line connecting both ends of the shape extrusion longitudinal direction. The actual measurement was performed by attaching a string to point A (FIG. 4) at both ends of the profile.

  Those underlined in Table 2 are outside the scope of the present invention, and in Table 2, the pattern of the manufacturing method indicates any one of (a) to (d) in FIG. Measurement was performed at the position A shown in FIG. The preferable range was 0.2% proof stress of 900 MPa or more, elongation of 10% or more, fatigue strength of 550 MPa or more, and warpage of 9 mm (2.25 mm per 1000 mm) or less.

Test No. 12 of the comparative example, since the billet temperature after induction heating exceeds (T _β +200) ℃, Test No. 13 of the comparative example, the temperature of the beta single phase region heat treatment the (T _β +200) ℃ In both cases, β grains grew while being held at a temperature _{equal to} or higher than T _β after extrusion. As a result, the recrystallization nucleation sites after extrusion decreased, the average of the old β grain size exceeded 300 μm, the 0.2% proof stress was 900 MPa, and the fatigue strength was less than 550 MPa.

  In the test number 14 of the comparative example, since the billet was heated without rapid heating, β grains were coarsened before extrusion, and there were few recrystallization nucleation sites after extrusion. The average also exceeded 300 μm. For this reason, the 0.2% proof stress was 900 MPa and the fatigue strength was less than 550 MPa.

  Test numbers 15 and 16 of the comparative examples are hot stamping materials manufactured with a conventional Ti-6Al-4V alloy. In both cases, the 0.2% proof stress was 900 MPa, and the fatigue strength was less than 550 MPa.

  Test No. 11 of the present invention was produced by extruding at a temperature equal to or higher than the β transformation temperature and then forced cooling by water cooling. Compared to Test Nos. 1 to 4 of the present invention, although the old β grain size is small, the average maximum width of the grain boundary α phase is small, and therefore, it has the tensile characteristics of the present invention. However, since the cooling rate after the β single-phase region heat treatment is higher than that of other present inventions, the warping of the shape is large, and post-treatment such as correction is required for actual use.

  In Test No. 17, the cooling rate after extrusion was slow, and the average maximum width of the grain boundary α phase exceeded 5 μm, so the 0.2% proof stress was less than 900 MPa and the elongation was also less than 10%.

  On the other hand, Test Nos. 1 to 11, which are examples of the present invention, had good characteristics with 0.2% proof stress of 900 MPa or more, fatigue strength of 550 MPa or more, and elongation exceeding 10% in any alloy components. .

Next, in the extruded shape, an attempt was made to reduce the difference in the size of the old β grains in the extrusion direction and to make the mechanical properties uniform in the extrusion direction.
The production conditions and the results are shown in Table 3. In Test Nos. 18 to 23, a temperature gradient was given at the front and rear ends of the billet during billet heating before extrusion while observing the manufacturing methods a to d, and heat removal due to a die or the like was compensated. These are described as “Yes” in the temperature gradient of the billet tip and tail. On the other hand, Test Nos. 24 and 25 did not perform heat compensation for the extracted heat, although the manufacturing method a was observed. These are described as “none” temperature gradient at the tip and rear ends of the billet.
The average measurement of the old β grain size at the front end and the rear end, and the collection of test pieces for measuring the yield strength and elongation at the front end and the rear end were performed at a position of 300 mm from the front and rear ends.

In Test Nos. 18 to 23, as shown in Table 3, in order to compensate for the temperature drop due to heat removal, a gradient was given to the extrusion heating temperature of the front end portion and the rear end portion. And the average difference in the old β grain size at the rear end could be reduced. As a result, it was possible to homogenize the mechanical properties of the extruded shape in the extrusion direction. On the other hand, in Test Nos. 23 and 24, although both the yield strength and elongation at each part exceeded the preferred values, the average difference in the old β grain size in the extrusion direction was large, and a difference in mechanical properties appeared.
In Test Nos. 1 to 17, a gradient is not given to the extrusion heating temperature at the front end and the rear end.

  According to the present invention, by controlling the metal structure of the profile to an acicular structure with an old β particle size of 300 μm or less, it has tensile properties that are not problematic in practice, and compared to when forced cooling is performed. Thus, a shape having a good shape can be obtained. Therefore, the cooling device and the shape correction cost can be reduced, which is particularly useful in the industry. In addition, the α + β type titanium alloy extruded shape of the present invention has little residual stress and no variation in structure, so that it is less bent during machining and has good fatigue strength, so it is useful for applications such as aircraft. .

1 Container 2 Stem 3 Dummy block 4 Die 5 Billet 6 Profile 11 Extrusion direction

Claims (4)

  In mass%, Al: 4.4 to 5.5%, Fe: 1.4 to 2.3%, Mo: 1.5 to 5.5%, O: more than 0% and 0.20% or less, C: More than 0% and 0.08% or less, N: more than 0% and 0.05% or less, Si: more than 0% and 0.1% or less, more selectively, Ni: 0% or more and less than 0.15%, One or more of Cr: 0% or more and less than 0.25% and Mn: 0% or more and less than 0.25%, with the balance being Ti and a total amount of impurities of 0.4% or less. Α + β satisfying the relationship of 4% ≦ [Fe] + [Ni] + [Cr] + [Mn] ≦ 2.3%, the metal structure is a needle-like structure, and the average of the old β particle diameter is 300 μm or less. Type titanium alloy extruded shape. Here, [Fe], [Ni], [Cr] and [Mn] indicate mass% of each component.   The α + β type titanium alloy extruded profile according to claim 1, wherein the average of the old β grain size is 250 µm or less.   The α + β-type titanium alloy extruded profile according to claim 1 or 2, wherein the average maximum width of the grain boundary α phase is 5 µm or less. An average particle diameter d ₁ (m) of an old β grain having a cross section perpendicular to the extruding direction of the extruded profile, and an extruding shape that is parallel to the one cross section and separated from the one cross section by a distance L (m) in the extruding direction. The value of the following formula (1) calculated by the average particle diameter d ₂ (m) of the old β grains in another cross section of the material is 25 or less, any one of claims 1 to 3 The α + β type titanium alloy extruded shape according to any one of the above items.
| (D ₁ −d ₂ ) / L | × 10 ⁶ (1)