Materials for manufacturing high-strength fasteners and methods for manufacturing them.

Abstract

The present invention relates to metallurgy, and more particularly to the manufacture of titanium alloy-based materials with specific mechanical properties for the manufacture of fasteners for use in various industrial sectors, preferably the aerospace industry. The claimed material for the manufacture of high-strength fasteners is manufactured from a titanium alloy containing alloying elements in the form of alpha stabilizing elements, beta stabilizing elements, and neutral strengthening elements, the balance being titanium and unavoidable impurities. The size of the beta subgrains in the structure of the material, which is subjected to solution annealing and aging, does not exceed 15 μm. The material for the manufacture of high-strength fasteners is manufactured in the form of a round bar with a diameter of 40 mm or less or a round wire with a diameter of 18 mm or less, which is subjected to solution annealing and aging. After solution annealing and aging, the material has an ultimate tensile strength of more than 1400 MPa, an elongation of more than 11%, a reduction in area of ​​more than 35%, and a double shear strength of more than 750 MPa. Intermediate blanks for drawing are obtained by melting an ingot of titanium alloy and thermomechanically working this ingot to obtain a forged billet, which is then rolled. Intermediate blanks for drawing can also be obtained by powder metallurgy.

Description

[Technical Field]

[0001] This invention relates to the manufacture of titanium alloy materials with mechanical properties designed for metallurgy, i.e., for the production of fasteners used in various industries, primarily the aerospace industry. [Background technology]

[0002] Titanium-based materials are finding expanding applications in various industries due to their high strength-to-weight ratio and high corrosion resistance. One promising area is the manufacture of fasteners for the aerospace and automotive industries. In modern aerospace engineering, steel fasteners are being replaced with high-strength titanium alloy components to reduce structural weight. For reliable operation of the components, threaded fasteners must possess a range of high-level properties, particularly high values ​​of tensile strength and biface shear strength. Furthermore, titanium alloys have an ultimate strength of σ B 1500 MPa, two-sided shear strength τ sh The mechanical properties of the fastener material must be approximated to those of a steel material with a strength of 900 MPa and an elongation of δ 12%. Strength and ductility are fundamental mechanical properties of metals and alloys, and their combination directly determines the workability and performance characteristics of the fastener material.

[0003] The most cost-effective process for manufacturing male fastener threads is the process of producing threads as a result of plastic deformation of stock using thread rolling tools. The profile of the rolled thread is formed by pressing the tool against the stock material, pushing a portion of the material into the tool's cavity. State-of-the-art equipment and applicable technologies allow thread rolling in the material in the as-thermal state, i.e., after quenching and artificial aging. Furthermore, compressive stress is generated in the internal windings of the thread, significantly increasing the number of cycles before cracking occurs and certainly increasing the overall cycle resistance of the material. However, thread rolling in the as-thermal state is complicated by the high strength of the material, and coupled with its low ductility, the technical capabilities of the process are significantly limited, and the durability of the tools used is reduced. In this regard, a relevant objective is to produce titanium-based materials that combine high strength and ductility in the as-thermal state.

[0004] Known fasteners and methods for producing the same exist for alpha-beta titanium alloys, which include hot rolling, solution treatment, and aging of alpha-beta titanium alloys composed of the following in weight %: 3.9~4.5 Aluminum; 2.2~3.0 Vanadium; 1.2~1.8 Iron; 0.24~0.3 Oxygen; Maximum 0.08 carbon; Maximum 0.05 nitrogen; Maximum 0.3 Other elements (total), Here, the other elements are, in fact, at least one of boron and yttrium, each at a concentration of less than 0.005, and tin, zirconium, molybdenum, chromium, nickel, silicon, copper, niobium, tantalum, manganese, and cobalt, each at a concentration of 0.1 or less, the remainder being titanium and unavoidable impurities, and the titanium alloy is hot-rolled in the alpha-beta region to produce the stock; the produced stock The material is annealed at a temperature of 1200°F (648.9°C) to 1400°F (760°C) for 1 to 2 hours; air-cooled; machined to the specified product size; solution-treated at a temperature of 1500°F (815.6°C) to 1700°F (926.7°C) for 0.5 to 2 hours; cooled at a rate at least equivalent to cooling in air; aged at a temperature of 800°F (426.7°C) to 1000°F (537.8°C) for 4 to 16 hours; and air-cooled (Patent Document 1, IPC C22C 14 / 00, C22F 1 / 18, published April 20, 2016).

[0005] However, the tensile strength level of known materials that can be thread-rolled in their as-thermal state is limited to 1370 MPa.

[0006] A method for manufacturing titanium alloy rods is known, which includes manufacturing stocks from ingots and etching hot-rolled rods, vacuum annealing thereof, drawing (drawing process), annealing of the drawn rods, and machining thereof to the final size, and hot-rolling thereof; in this method, the air annealing of the drawn rods is carried out in two stages: first at a temperature of 650-750°C for 15-60 minutes, followed by air cooling to room temperature, and then at a temperature of 180-280°C for 4-12 hours, followed by air cooling to room temperature; furthermore, in a second option, the annealing is carried out first at a temperature of 750-850°C for 15-45 minutes, followed by cooling in a furnace to 500-550°C, followed by air cooling to room temperature, and then at a temperature of 400-500°C for 4-12 hours, followed by air cooling to room temperature (Patent Document 2, IPC C22F 1 / 18, B21C 37 / 04, published November 27, 2007).

[0007] This known method aims at the production of fastener stock made of Vt16 titanium alloy and results in low tensile and double-shear strength because it does not take into account the processing characteristics of other high-strength materials and alloys.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] The present invention aims at the production of a high-strength fastener material made of a titanium alloy having a series of high-level mechanical properties that enable thread rolling while remaining thermally hardened.

Means for Solving the Problems

[0010] The technical result achieved in the embodiments of the present invention is that the strength characteristics of the material are improved while maintaining a high level of ductility.

[0011] According to the present invention, this technical result is achieved in a material for a high-strength fastener made of a titanium alloy containing alloying elements as alpha stabilizing elements (стабилизаторов, stabilizer), beta stabilizing elements, and neutral strengthening elements (нейтральных упрочнителей, neutral strengthener), with the remainder being titanium and inevitable impurities, where the total amount of alloying elements ensuring solution strengthening (твердо-растворное упрочнение, solution strengthening) of the alpha phase of the titanium alloy is defined by the following formula: [Al] eq = [Al] + [O]×10 + [C]×10 + [N]×20 + [Zr] / 6 Here, the concentration of each specific element is in the following range by weight percentage 3.0 to 6.5 aluminum, up to 0.05 nitrogen, 0.05 to 0.3 oxygen up to 0.1 carbon up to 2.0 zirconium and [Al] eq is the aluminum structural equivalent (структурный алюминиевый эквивалент, aluminum structural equivalent), and its value in the alloy is in the range of 5.1 to 9.3, The total amount of elements that ensure solid solution strengthening and increase the volume fraction of the metastable beta phase is defined by the following formula, [Mo] eq =[Mo]+[V] / 1.4+[Cr]×1.67+[Fe]×2.5 Here, the concentration of each specific element is in the following range by weight percentage 4.0 to 6.5 vanadium 4.0 to 6.5 molybdenum 2.0 to 3.5 chromium 0.2 to 1.0 iron and [Mo] eq is the molybdenum structural equivalent (структурный молибденовый эквивалент, molybdenum structural equivalent), and its value in the alloy is in the range of 12.4 to 17.4, Furthermore, it is achieved by the fact that the volume fraction of primary alpha in the structure of the solution-treated and aged material is in the range of 15 to 27%. The plasticity coefficient (коэффициент пластичности, K pm ) of the solution-treated and aged material within the tensile strength range of 1400 to 1500 MPa is defined by the following integral equation, K pm =∫R A dσ в where, R AThis is the reduction of area (relative shrinkage, относительное сужение, reduction of area), %. σ B This is the tensile strength in MPa. 3.7 × 10 3 ~5.0×10 3 It is within the range.

[0012] The size of the beta subgrain in the structure of the solution-treated and aged material does not exceed 15 μm. The material for high-strength fasteners is manufactured in the form of a round bar with a diameter of 40 mm or less, after solution treatment and aging. The material for high-strength fasteners is also manufactured in the form of a round wire with a diameter of 18 mm or less, after solution treatment and aging. The solution-treated and aged high-strength fastener material has a tensile strength exceeding 1400 MPa, an elongation exceeding 11%, and a cross-sectional reduction rate exceeding 35%. The solution-treated and aged high-strength fastener material has a two-sided shear strength exceeding 750 MPa.

[0013] This technical achievement also relates to a method for manufacturing a high-strength fastener material, comprising the production of an intermediate drawn stock of a titanium alloy, the production of a cold drawn stock, and its final heat treatment, wherein the intermediate drawn stock is produced from a titanium alloy containing alloying elements as alpha-stabilizing elements, beta-stabilizing elements, and neutral strengthening elements, with the remainder being titanium and unavoidable impurities, and furthermore, the total amount of alloying elements that guarantee solid solution strengthening of the alpha phase of the titanium alloy is defined by the following formula: [Al] eq =[Al]+[O]×10+[C]×10+[N]×20+[Zr] / 6 Here, the concentration of each specific element is within the following range in weight percent: 3.0~6.5 Aluminum, Maximum 0.05 nitrogen, 0.05~0.3 Oxygen Maximum 0.1 carbon Maximum 2.0 Zirconium [Al] eqThis is the structural equivalent of aluminum, and its value in this alloy is in the range of 5.1 to 9.3. The total amount of elements that guarantee solid solution strengthening and increase the volume fraction of the metastable beta phase is defined by the following formula: [Mo] eq =[Mo]+[V] / 1.4+[Cr]×1.67+[Fe]×2.5 Here, the concentration of each specific element is within the following range in weight percent: 4.0~6.5 Vanadium 4.0~6.5 Molybdenum 2.0~3.5 Chromium 0.2~1.0 Iron And [Mo] eq This is the molybdenum structural equivalent, and its value in this alloy is in the range of 12.4 to 17.4. Prior to drawing, the intermediate stock is annealed at a temperature of (BTT-20)°C to (BTT-50)°C (where BTT is the beta transformation temperature), then cooled to room temperature at an arithmetic mean rate of at least 15°C / min, and cold drawn stock is produced by drawing at a draw ratio of 1.8 to 5. Furthermore, the final heat treatment of the cold drawn stock is carried out under the following conditions: solution treatment after metal heating to a temperature of (BTT-50)°C to (BTT-80)°C and holding for 1 to 8 hours, followed by cooling at an arithmetic mean rate of at least 10°C / min to a temperature below the subsequent aging temperature, aging at a metal heating temperature of 400 to 530°C for at least 8 hours, followed by cooling to room temperature. This is the method for producing high-strength fastener material. Intermediate drawn stock is produced by melting titanium alloy ingots, thermomechanically treating the ingots to produce forged billets, and then rolling them. Intermediate drawn stock is produced by powder metallurgy. [Brief explanation of the drawing]

[0014] [Figure 1] This shows the material's microstructure in the longitudinal direction at a magnification of 4000x. [Modes for carrying out the invention]

[0015] To manufacture this material, titanium alloys containing alpha-stabilizing elements (aluminum, oxygen, nitrogen, carbon), beta-stabilizing elements (vanadium, molybdenum, chromium, iron), and neutral-strengthening elements (zirconium) are used. The principle of manufacturing this material is based on the various effects of specific groups of alloying elements on titanium. Elements equivalent to aluminum (alpha-stabilizing elements and neutral-strengthening elements) strengthen the titanium alloy mainly as a result of solid solution strengthening, while elements equivalent to molybdenum (beta-stabilizing elements) ensure precipitation hardening of the alloy during aging, both as a result of solid solution strengthening and as a result of an increase in the amount of metastable beta phase. Structural equivalents disclosed herein [Al] eq and [Mo] eq This, along with the designed processing conditions, is a standard that regulates the manufacturing process of high-quality fastener materials.

[0016] Aluminum structural equivalent [Al] eq This allows for the evaluation of the degree of alpha phase stabilization, which is simultaneously influenced by alpha-stabilizing elements present in the alloy: aluminum, oxygen, carbon, nitrogen, and zirconium. The set value for the total amount of alloying elements [Al] guarantees solid solution strengthening of titanium alloys. eq These ranges from 5.1 to 9.3. This allows us to obtain the required amount of alpha phase within the specified range of the titanium alloy's chemical composition, taking into account the processing temperature and rate parameters.

[0017] The concentration values ​​of each element are defined based on the following principles: Aluminum increases the strength-to-weight ratio of the alloy and improves the strength and elastic modulus of titanium. If the aluminum concentration in the alloy is less than 3.0%, the required strength is not achieved, and the probability of ω phase formation, which reduces plastic behavior, also increases. On the other hand, if the aluminum concentration in the alloy exceeds 6.5%, it leads to a decrease in the working ductility of the alloy and the possibility of formation of Ti3Al particles, which can cause material embrittlement. The presence of oxygen in the range of 0.05 to 0.3% improves strength without degrading plasticity. The presence of nitrogen in the alloy at a concentration not exceeding 0.05% and carbon at a concentration not exceeding 0.1% does not significantly affect the decrease in plasticity at room temperature. To increase the strength of the alpha phase, the alloy is further alloyed with zirconium at a concentration not exceeding 2.0%, thereby improving the strength of the alloy without substantially reducing the plasticity and crack resistance of the alloy.

[0018] 12.4 to 17.4 molybdenum equivalents [Mo] eq Adding vanadium, molybdenum, chromium, and iron concentrations corresponding to these amounts to the alloy can reduce the critical cooling rate, ensuring the maintenance of the metastable beta phase during air cooling of sections 40 mm or less and longer, and guaranteeing the formation of a large amount of metastable beta phase necessary to obtain high strength after aging and improved work ductility during cold working.

[0019] Furthermore, the concentrations of each element are further defined among the beta-stabilizing elements. Vanadium, with its high solubility in the range of 4.0–6.5% in titanium, enhances thermosetting properties and ensures stabilization of the beta phase and strengthening of the alpha phase. Alloying with molybdenum in the range of 4.0–6.5% effectively improves strength at room temperature and high temperatures, and also improves the thermal stability of alloys containing chromium and iron. The chromium concentration set in the range of 2.0–3.5% is due to the element's ability to act as a strong beta-stabilizing element and significantly strengthen titanium alloys. Alloying with chromium exceeding 3.5% may lead to the formation of the intermetallic phase TiCr2, which causes embrittlement of the alloy. Adding iron in the range of 0.2–1.0% improves the workability during hot working of the alloy and can prevent deformation defects. Iron concentrations exceeding 1.0% increase chemical heterogeneity between the melting and solidification of the alloy, resulting in structural heterogeneity and, consequently, mechanical heterogeneity. The increased plasticity of the material in the as-thermal state guarantees a combination of numerous subboundaries and grain boundary dislocations at boundary / subboundary points, with beta subgrain sizes of 15 μm or less, as well as long interphase boundaries guaranteed by primary alpha particles at a volume fraction of 15-27%.

[0020] The ability of thermosetting materials to thread roll without fracture at tensile strengths exceeding 1400 MPa is characterized by the following experimentally established mathematical relationship: K pm =∫R A dσ в In the formula, K pm This is the plasticity ratio of the thermosetting material, and is 3.7 × 10⁻⁶. 3 ~5.0×10 3 This corresponds to, R A This is the cross-sectional reduction rate, in %, σ B This represents a tensile strength in the range of 1400-1500 MPa.

[0021] The properties of the proposed method for manufacturing high-strength fastener materials are based on the following:

[0022] To manufacture the above material, the intermediate drawn stock is produced from titanium and titanium alloys, with the remainder consisting of alpha-stabilizing elements, beta-stabilizing elements, and neutral strengthening elements, with the remainder being titanium and unavoidable impurities.

[0023] The design chemical composition of the ingot is determined based on the relationship between the total amount of alloying elements that guarantee solid solution strengthening of the titanium alloy alpha phase, and is defined by the following formula: [Al] eq =[Al]+[O]×10+[C]×10+[N]×20+[Zr] / 6 Here, the concentration of each specific element is within the following range in weight percent: 3.0~6.5 Aluminum, Maximum 0.05 nitrogen, 0.05~0.3 Oxygen Maximum 0.1 carbon Maximum 2.0 Zirconium [Al] eq This is the structural equivalent of aluminum, and its value in this alloy is in the range of 5.1 to 9.3. The total amount of elements that guarantee solid solution strengthening and increase the volume fraction of the metastable beta phase is defined by the following formula: [Mo] eq =[Mo]+[V] / 1.4+[Cr]×1.67+[Fe]×2.5 Here, the concentration of each specific element is within the following range in weight percent: 4.0~6.5 Vanadium 4.0~6.5 Molybdenum 2.0~3.5 Chromium 0.2~1.0 Iron And [Mo] eq This is the molybdenum structural equivalent, and its value in alloys ranges from 12.4 to 17.4.

[0024] One optional method for producing intermediate stock is thermomechanical treatment by melting the ingot and converting it into a forged stock (billet) at temperatures in the beta and / or alpha-beta phase region. It is advisable to machine the forged billet to remove gas-saturated layers and surface deformation defects. The billet is then rolled to produce intermediate stock in the form of a rolled bar. Other optional methods for producing intermediate stock include powder metallurgy.

[0025] The maximum diameter of a manufactured drawn stock can only be limited by the capacity of the drawing equipment used for cold working, because increasing the diameter of the workpiece while maintaining the same degree of deformation significantly increases the load on the deforming tool and the specific drawing force.

[0026] Furthermore, as the diameter of the intermediate drawn stock increases, deformation non-uniformity in the outer and central stock layers accumulates during subsequent drawing, leading to increased cross-sectional deformation non-uniformity and, consequently, structural non-uniformity in the final product.

[0027] Prior to drawing, the intermediate stock undergoes annealing, including vacuum annealing at temperatures of (BTT-20)°C to (BTT-50)°C, and is subsequently cooled at an arithmetic mean rate of at least 15°C / min. Heating an intermediate stock with a specific chemical composition in the temperature range of (BTT-20)°C to (BTT-50)°C yields a structure containing a metastable matrix beta phase with a primary alpha proportion in the range of 6–17%. During the plastic cold deformation process, the primary alpha phase hinders dislocation movement by reducing their distances to the distance between alpha phase particles. The 6–17% proportion of primary alpha phase required for stress redistribution and homogenization before subsequent drawing contributes to the effective accumulation of dislocations during further cold deformation, determining the subsequent return, polygonization, and recrystallization processes. Cooling at an arithmetic mean rate of 15°C / min or higher from the annealing temperature allows for the maintenance of the metastable beta phase without fracture, as well as the maintenance of an established amount of primary alpha phase. Furthermore, the specified rate helps to avoid the formation of a secondary alpha phase, whose presence significantly increases the strengthening rate and prevents high draw rates from being obtained in subsequent stages of the plastic deformation process.

[0028] Drawing of the intermediate stock is performed at room temperature with a draw factor ranging from 1.8 to 5. During the drawing process, the dislocation density increases significantly in the beta phase, as well as at the interphase boundaries and in the alpha phase. A quantity of 6–17% primary alpha particles allows for an optimal distribution of dislocations along the flow lines, thus resulting in their uniform distribution within the material volume. When the draw factor exceeds 1.8, a cellular structure is formed and stabilized in the material, ensuring the size and number of beta subgrains required during solution treatment. At draw factors less than 1.8, fewer specific portions of cells are converted into beta subgrains, and even with an extended temperature range, the stability of the cellular structure during subsequent solution treatment is not guaranteed, leading to an increase in beta subgrain size and failing to guarantee the mechanical properties after the final heat treatment. The maximum draw factor is characterized by the extreme fragility of the material before fracture, which depends heavily on the drawing parameters and the structure of the starting stock. After drawing, the material in the form of a wire or rod is subjected to a thermal curing process consisting of solution treatment and subsequent artificial aging.

[0029] The solution treatment is carried out under the following conditions: heating of the material to a temperature of (BTT-50)°C to (BTT-80)°C, holding at the specified temperature for 1 to 8 hours, and then cooling to a temperature below the aging temperature at an arithmetic mean rate of 10°C / min or more.

[0030] The above specified conditions are intended to obtain the necessary parameters for the alpha and beta phases. During this heat treatment, as a result of transformation and dislocation redistribution, a structure is obtained in which the volume fraction of the primary alpha phase increases to 15-27%, and beta subgrains with a size not exceeding 15 μm are present in this structure.

[0031] Heating the material beyond the specified temperature range significantly increases the size of the beta particles, decreases the volume fraction of the alpha phase, and ultimately reduces the ductility of the material in its final state. Since the volume fraction of the alpha phase increases while the material is heated to temperatures below (BTT-80)°C, it becomes difficult to achieve a strength exceeding 1450 MPa after aging. The minimum holding time during heating to the solution treatment temperature is 1 hour because this time allows sufficient time for the cellular structure to convert to a subgrain structure; holding the material for more than 8 hours increases the subgrain size, thus reducing ductility. An arithmetic mean cooling rate of 10°C / min is the minimum rate that ensures the metastable beta phase is not destroyed during the solution treatment, the primary alpha phase portion is maintained, and therefore the formation of the secondary alpha phase is suppressed.

[0032] After solution treatment, the material undergoes artificial aging at a temperature of 400-530°C for at least 8 hours.

[0033] By artificially aging the material at temperatures of 400-530°C, the tensile strength can be varied within a range of 1400 MPa, taking into account the solution treatment temperature range. Furthermore, in combination with solution treatment, it is possible to create structures with improved plasticity and guarantee a material elongation of at least 11%. The aging temperature range is determined by obtaining the required strength of the material, which will later determine the strength of the manufactured fastener (i.e., it is possible to obtain this strength). The selection of the aging temperature range is determined by the degree of stability of the alpha phase that decomposes during aging, and the dispersion of the precipitated secondary alpha phase, which also predetermines the acquisition of high material strength values. An aging time of at least 8 hours ensures that the beta phase is completely decomposed and the material reaches equilibrium.

[0034] The industrial applicability of the present invention will be demonstrated by specific examples. [Examples]

[0035] To produce material for fasteners in the form of wires with a diameter of 8.05 mm, an ingot having the chemical composition shown in Table 1 was melted. The alloy beta transformation temperature (BTT), measured by metallographic methods, was equal to 838°C.

[0036] [Table 1]

[0037] The molten ingot was transformed at temperatures in the beta and alpha-beta phase regions. The stock was subjected to the final transformation to produce forged billets for rolling and subsequent machining. The machined billets were rolled to produce a rolled intermediate stock with a diameter of 13.3 mm, where the deformation temperature ended in the beta region. As a result, a recrystallized equiaxed beta particle structure was obtained. The intermediate stock with a diameter of 7.9 mm was annealed in a vacuum furnace at a temperature of 802°C (BTT-36)°C at a rate of 15°C / min. The above The material was cooled to room temperature at an arithmetic mean rate. Auxiliary operations were performed to produce a stock with a diameter of 12.3 mm to remove surface defects and the gas-saturated layer. The 12.3 mm diameter stock was drawn to a diameter of 8.6 mm at room temperature. Surface defects and the gas-saturated layer were then removed by polishing, grinding, and pickling, during which the stock diameter was reduced to 8.05 mm. The wire material was then thermocured under the following conditions: solution treatment with heating to 768°C (BTT-70)° and holding for 4 hours, air-cooled to room temperature at an arithmetic mean rate of at least 10°C / min; artificial aging with holding at 500°C for 8 hours, and air-cooled. The results of mechanical testing of the 8.05 mm diameter wire material in the as-thermally cured state are shown in Table 2. The longitudinal microstructure of the material at a magnification of 4000x is shown in Figure 1.

[0038] [Table 2]

[0039] Thus, the claimed material for high-strength fasteners features improved levels of workability and performance characteristics obtained by optimizing the chemical composition and concentration of alloying elements in the titanium alloy, as well as optimizing transformation and heat treatment process conditions to ensure a specific microstructure is obtained.

Claims

1. A method for manufacturing a high-strength fastener material, comprising the manufacture of an intermediate drawn stock of a titanium alloy, the manufacture of a cold drawn stock, and the final heat treatment thereof, characterized in that the intermediate drawn stock is manufactured from a titanium alloy containing alloying elements as an alpha-stabilizing element, a beta-stabilizing element, and a neutral strengthening element, with the remainder being titanium and unavoidable impurities, wherein the total amount of the alpha-stabilizing element and the neutral strengthening element, which are alloying elements that guarantee solid solution strengthening of the alpha phase of the titanium alloy, is defined by the following formula: [Al] ｅｑ =[Al]+[O]×10+[C]×10+[N]×20+[Zr] / 6 Here, the concentration of each specific element is within the following range in weight percent: 3.0-6.5 Aluminum, Maximum 0.05 nitrogen, 0.05–0.3 oxygen Maximum 0.1 carbon Maximum 2.0 Zirconium [Al] ｅｑ This is the structural equivalent of aluminum, and its value in the aforementioned alloy is in the range of 5.1 to 9.

3. The total amount of the beta-stabilizing elements, which guarantee solid solution strengthening and increase the volume fraction of the metastable beta phase, is defined by the following formula: [Mo] ｅｑ =[Mo]+[V] / 1.4+[Cr]×1.67+[Fe]×2.5 Here, the concentration of each specific element is within the following range in weight percent: 4.0–6.5 Vanadium 4.0-6.5 molybdenum 2.0-3.5 chromium 0.2-1.0 iron And [Mo] ｅｑ This is the molybdenum structural equivalent, and its value in the aforementioned alloy is in the range of 12.4 to 17.

4. A method for producing a high-strength fastener material, wherein, prior to drawing, the intermediate drawn stock is annealed at a temperature of (BTT-20)°C to (BTT-50)°C (where BTT is the beta transformation temperature), cooled to room temperature at an arithmetic mean rate of at least 15°C / min, a cold drawn stock is produced by drawing at a draw ratio of 1.8 to 5, and the final heat treatment of the cold drawn stock is carried out under the following conditions: solution treatment after metal heating to a temperature of (BTT-50)°C to (BTT-80)°C and holding for 1 to 8 hours, followed by cooling to a temperature below the subsequent aging temperature at an arithmetic mean rate of 10°C / min or more, aging at a metal heating temperature of 400 to 530°C for at least 8 hours, followed by cooling to room temperature.

2. A method for producing a high-strength fastener material according to claim 1, characterized by melting a titanium alloy ingot, thermomechanically treating the ingot to produce a forged billet, and then rolling it to produce the intermediate drawn stock.

3. A method for producing a high-strength fastener material according to claim 1, characterized in that the intermediate drawn stock is produced by powder metallurgy.

4. A method for producing a high-strength fastener material according to claim 1, characterized in that the obtained high-strength fastener material is in the form of a round bar having a diameter of 40 mm or less.

5. A method for producing a high-strength fastener material according to claim 1, characterized in that the obtained high-strength fastener material is in the form of a round wire having a diameter of 18 mm or less.

6. The method for producing a high-strength fastener material according to claim 1, characterized in that the obtained high-strength fastener material has a structure in which the volume fraction of the primary alpha phase is 15 to 27%.

7. The method for producing a high-strength fastener material according to Claim 1, characterized in that the obtained high-strength fastener material has a structure in which the size of the beta subgrains does not exceed 15 μm.

8. The method for producing a high-strength fastener material according to Claim 1, characterized in that the obtained high-strength fastener material has a tensile strength of more than 1400 MPa.

9. The method for producing a high-strength fastener material according to Claim 1, characterized in that the obtained high-strength fastener material has an elongation of more than 11% and a cross-sectional reduction rate of more than 35%.

10. The method for producing a high-strength fastener material according to claim 1, characterized in that the obtained high-strength fastener material has a biface shear strength of 750 MPa or more.

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