Titanium alloy seamless tube and preparation method thereof

Abstract

The invention discloses a titanium alloy seamless tube and a preparation method thereof. The titanium alloy seamless tube comprises the following chemical components in percentage by mass: 5%-6.5% of Al, 1.5%-3% of Mo, 1.5%-2% of V, 3%-4% of Zr, 2.5%-3.6% of Sn, 0.5%-1.5% of Nb, 0.2%-0.5% of Si, 0.4%-0.6% of B, 0.8%-1.2% of Ce and the balance of Ti and other inevitable impurity elements. The preparation method comprises the working procedures of titanium alloy smelting, pipe blank casting, forging, heat treatment and cold rolling. According to the titanium alloy seamless tube, on the basis of TA15 alloy, components are optimized, the proportion of all the elements is regulated and controlled, and B and Ce elements in a specific proportion are further added; the preparation method is matched with the titanium alloy component, the structure uniformity and the surface quality of the pipe are improved, and the prepared titanium alloy seamless pipe has the excellent performance of high strength and high toughness.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy tube manufacturing technology, specifically relating to a seamless titanium alloy tube and its preparation method. Background Technology

[0002] Titanium and titanium alloys, due to their excellent properties such as low density, high strength, and corrosion resistance, are widely used in aerospace, medical devices, and chemical industries. Among them, seamless titanium alloy tubes, with these performance advantages, have an increasingly large market application and are widely used in industries such as petroleum, gas, thermal power generation, nuclear power, and aerospace. Currently, the traditional manufacturing process of seamless titanium alloy tubes involves forging titanium alloy ingots after multiple meltings into billets through multiple heat treatments. The billets are then hot-rolled, pierced, or drilled and hot-extruded to form tube blanks. These tube blanks then undergo a series of hot rolling, cold rolling, and finishing processes to produce the finished product, with auxiliary processes such as multiple heat treatments, pickling, sandblasting, and machining.

[0003] Existing titanium alloy tube manufacturing processes have several shortcomings. The billets are obtained through multiple forging processes. Traditional titanium alloy forging processes, limited by equipment capacity and forging technology, result in poor uniformity of the forged billet's microstructure and properties, leading to instability in the core and surface properties, failing to meet subsequent processing and usage requirements. Hot rolling and piercing processes, due to their high processing temperatures, result in billets with a predominantly basketweave or Widmanstätten microstructure, exhibiting poor machinability and a tendency to crack during piercing, further hindering subsequent processing and usage. Drilling and hot extrusion for billet preparation are costly and energy-intensive, offering less production flexibility compared to cold extrusion or other processing methods, making surface quality difficult to control, and potentially causing environmental pollution from waste gas and wastewater generated during production.

[0004] Among near-alpha titanium alloys, TA15 alloy is a medium-strength titanium alloy based on the Ti-Al-Zr-Mo-V system. It has good weldability and plasticity, and excellent comprehensive performance. It is mainly used for titanium alloys for aircraft frames. With the development trend of lightweight aircraft, there is room for further improvement in the strength and plasticity of TA15 series titanium alloys.

[0005] Therefore, in order to overcome the above-mentioned technical shortcomings, it is necessary to develop a high-strength titanium alloy and optimize and improve the traditional titanium alloy tube production process technology to quickly, efficiently and cost-effectively produce high-performance, high-strength and high-toughness seamless titanium alloy tubes. Summary of the Invention

[0006] Therefore, in order to overcome the shortcomings of the existing technology, a seamless titanium alloy tube and its preparation method are provided.

[0007] To achieve the above objectives, the following technical solution is adopted: This invention provides a seamless titanium alloy tube, the chemical composition of which, by mass percentage, comprises: Al: 5%~6.5%, Mo: 1.5%~3%, V: 1.5%~2%, Zr: 3%~4%, Sn: 2.5%~3.6%, Nb: 0.5%~1.5%, Si: 0.2%~0.5%, B: 0.4%~0.6%, Ce: 0.8%~1.2%, with the balance being Ti and other unavoidable impurity elements.

[0008] This invention also provides a method for preparing a seamless titanium alloy tube, comprising the following steps: Step S101: Prepare raw materials according to chemical composition, obtain titanium alloy hollow tube blank by melting raw materials and perform surface treatment; Step S102: After uniformly spraying a protective lubricating layer on the inner and outer surfaces of the titanium alloy hollow tube blank processed in step S101, it is heated. The heating process is carried out at a heating rate of 600℃ / h for each heating, and the temperature is first held at 60℃~100℃ below the phase transformation point for 2 hours, and then the temperature is continued to rise to the forging temperature. Step S103: Radial forging of the heated titanium alloy hollow tube blank in step S102; wherein, five-pass radial forging is adopted and the forging temperature gradually decreases in each pass; the last forging is carried out using an arc anvil, the forging reduction per pass is 10%~20%, the mandrel diameter is 4~6mm smaller than the inner diameter of the previous intermediate tube blank, the feed is 100~200mm, and after each forging pass, the blank is rotated 90° and forging is continued until the target specification is reached, and then air-cooled to room temperature; Step S104: The titanium alloy tube obtained in step S103 is subjected to heat treatment and cold rolling processes in sequence to form a seamless titanium alloy tube.

[0009] In some embodiments, in step S102, "continuing to heat to the forging temperature" includes: holding at a temperature of 30°C below the phase transformation point to 200°C above the phase transformation point for 1 hour, and then removing from the furnace for subsequent radial forging.

[0010] In some embodiments, in step S101, the raw materials are sponge titanium, baked TiO2 powder, vanadium aluminum alloy, aluminum molybdenum, sponge zirconium, intermediate alloy containing tin and niobium, and cerium hexaboride. The chemical composition, by mass percentage, includes: Al: 5%~6.5%, Mo: 1.5%~3%, V: 1.5%~2%, Zr: 3%~4%, Sn: 2.5%~3.6%, Nb: 0.5%~1.5%, Si: 0.2%~0.5%, B: 0.4%~0.6%, Ce: 0.8%~1.2%, with the balance being Ti and other unavoidable impurity elements; The smelting process involves a primary smelting using a vacuum electron beam cold hearth furnace or a vacuum plasma cold hearth furnace to obtain a primary ingot, followed by a secondary smelting using a vacuum plasma cold hearth furnace. The molten titanium alloy from the secondary smelting is then cast into a hollow titanium alloy tube blank.

[0011] In some embodiments, in step S101, the surface treatment involves grinding the outer surface of the titanium alloy hollow tube blank and boring the inner hole until there are no defects on both the inner and outer surfaces, resulting in a titanium alloy hollow tube blank with both the inner and outer surfaces in a bright white state.

[0012] In some embodiments, in step S102, the protective lubricating layer is a glass protective lubricant.

[0013] In some embodiments, during step S103, during the first radial forging, the mandrel diameter is 6-10 mm smaller than the inner diameter of the tube blank, the radial indentation per hammer is 15-25 mm, the axial feed speed is 2.5-3 m / min, the tube blank rotation speed is 25-40 r / min, the hammering speed is 1500-2000 times / min, and the overall deformation is 40%-60%. During the second and third radial forgings, the mandrel diameter is 10-15 mm smaller than the inner diameter of the intermediate tube blank obtained in the previous forging, the radial indentation per hammer is 20-30 mm, and the axial feed speed is 2.5-3 m / min. The billet rotation speed is 25~40 r / min, the hammering speed is 2000~2500 times / min, and the overall deformation is 60%~70%. In the fourth radial forging, the mandrel diameter is 6~8 mm smaller than the inner diameter of the intermediate billet obtained in the previous step, the radial indentation per hammer is 10~15 mm, the axial feed speed is 2.5~3 m / min, the billet rotation speed is 25~40 r / min, the hammering speed is 1500~2000 times / min, and the overall deformation is 30%~40%. The final forging temperature for each radial forging is guaranteed to be 100~120℃ higher than the phase transformation point. In some embodiments, in step S103, the arc-shaped anvil includes an upper anvil and a lower anvil arranged symmetrically. The upper anvil and the lower anvil include a main body with an arc-shaped groove. Each side of the arc-shaped groove has a straight inclined surface, and the straight inclined surfaces are connected by a horizontal segment. The radius R of the arc-shaped groove is the outer diameter of the forged pipe + (30 mm ~ 60 mm), the angle φ between the tangents at the connection point of the straight inclined surface and the arc-shaped groove is 15-25°, and the length and width of the main body are 150~300 mm and 150~300 mm, respectively.

[0014] In some embodiments, in step S104, the heat treatment adopts a two-stage heat treatment method of heat treatment and aging treatment. The heat treatment involves holding at 30°C below the phase change point for 2 hours, then air cooling to room temperature, and then reheating to 600°C and holding for 6 hours before air cooling to room temperature.

[0015] In some embodiments, in step S104, the cold rolling process involves multiple passes of cold rolling, degreasing, removal of internal and external surface defects, pickling, annealing, straightening, pickling, and flaw detection for the titanium alloy tube.

[0016] The present invention has the following beneficial technical effects: The titanium alloy seamless tube of this invention optimizes the composition and controls the proportion of each element based on TA15 alloy, and adds a specific proportion of B and Ce elements to improve strength and toughness. The preparation method of the titanium alloy seamless tube of this invention is adapted to the titanium alloy composition and has an integrated process of melting and casting hollow tube blank, protective heating, five-stage sub-gradient radial forging, two-stage heat treatment and cold rolling finishing. Furthermore, by controlling the temperature heating, gradient forging, customized arc anvil forging and heat treatment, the uniformity of the tube structure and surface quality are improved, and the prepared titanium alloy seamless tube has excellent properties of high strength and high toughness. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart illustrating a method for preparing a seamless titanium alloy tube according to an embodiment of the present invention; Figure 2 This is a front view of an arc-shaped anvil according to an embodiment of the present invention; Figure 3 This is a side view of an arc-shaped anvil according to an embodiment of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0020] It should be understood that the embodiments of the invention shown in the exemplary embodiments are merely illustrative. Although only a few embodiments have been described in detail in this invention, those skilled in the art will readily recognize that various modifications are possible without substantially departing from the teachings of the invention. Accordingly, all such modifications should be included within the scope of the invention. Other substitutions, modifications, variations, and deletions can be made to the design, operating conditions, and parameters of the following exemplary embodiments without departing from the spirit of the invention.

[0021] This invention optimizes and adjusts the composition of TA15 alloy. The main process flow includes: titanium alloy smelting, casting of tube blanks, radial forging, cold rolling, annealing, and machining. Specifically, it relates to a method for producing seamless titanium alloy tubes from a high-strength titanium alloy with optimized composition through smelting, casting, multiple radial forgings, and cold rolling processes.

[0022] Based on the above objectives, a first aspect of the embodiments of the present invention provides a seamless titanium alloy tube, wherein the chemical composition of the seamless titanium alloy tube, by mass percentage, comprises: Al: 5%~6.5%, Mo: 1.5%~3%, V: 1.5%~2%, Zr: 3%~4%, Sn: 2.5%~3.6%, Nb: 0.5%~1.5%, Si: 0.2%~0.5%, B: 0.4%~0.6%, Ce: 0.8%~1.2%, with the balance being Ti and other unavoidable impurity elements.

[0023] A second aspect of the present invention provides a method for preparing seamless titanium alloy tubes.

[0024] Figure 1 The method for preparing a seamless titanium alloy tube shown includes the following steps: Step S101: Prepare raw materials according to chemical composition, obtain titanium alloy hollow tube blank by melting raw materials and perform surface treatment; Step S102: After uniformly spraying a protective lubricating layer on the inner and outer surfaces of the titanium alloy hollow tube blank processed in step S101, it is heated. The heating process is carried out at a heating rate of 600℃ / h for each heating, and the temperature is first held at 60℃~100℃ below the phase transformation point for 2 hours, and then the temperature is continued to rise to the forging temperature. Step S103: Radial forging of the heated titanium alloy hollow tube blank in step S102; wherein, five-pass radial forging is adopted and the forging temperature gradually decreases in each pass; the last forging is carried out using an arc anvil, the forging reduction per pass is 10%~20%, the mandrel diameter is 4~6mm smaller than the inner diameter of the previous intermediate tube blank, the feed is 100~200mm, and after each forging pass, the blank is rotated 90° and forging is continued until the target specification is reached, and then air-cooled to room temperature; Step S104: The titanium alloy tube obtained in step S103 is subjected to heat treatment and cold rolling processes in sequence to form a seamless titanium alloy tube.

[0025] In one optional embodiment, in step S102, "continuing to heat to the forging temperature" includes: holding at a temperature of 30°C below the phase transformation point to 200°C above the phase transformation point for 1 hour, and then removing from the furnace for subsequent radial forging.

[0026] In one alternative embodiment, in step S101, the raw materials are sponge titanium, baked TiO2 powder, vanadium aluminum alloy, aluminum molybdenum, sponge zirconium, intermediate alloy containing tin and niobium, and cerium hexaboride. The chemical composition, by mass percentage, includes: Al: 5%~6.5%, Mo: 1.5%~3%, V: 1.5%~2%, Zr: 3%~4%, Sn: 2.5%~3.6%, Nb: 0.5%~1.5%, Si: 0.2%~0.5%, B: 0.4%~0.6%, Ce: 0.8%~1.2%, with the balance being Ti and other unavoidable impurity elements; The smelting process involves a primary smelting using a vacuum electron beam cold hearth furnace or a vacuum plasma cold hearth furnace to obtain a primary ingot, followed by a secondary smelting using a vacuum plasma cold hearth furnace. The molten titanium alloy from the secondary smelting is then cast into a hollow titanium alloy tube blank.

[0027] In one optional embodiment, in step S101, the surface treatment involves grinding the outer surface of the titanium alloy hollow tube blank and boring the inner hole until there are no defects on both the inner and outer surfaces, resulting in a titanium alloy hollow tube blank with both the inner and outer surfaces in a bright white state.

[0028] In one alternative embodiment, in step S102, the protective lubricating layer is a glass protective lubricant.

[0029] Specifically, the surface-treated titanium alloy tube blank is fed into an electric resistance furnace for heating. Before heating, an environmentally friendly glass protective lubricant is uniformly sprayed onto the inner and outer surfaces of the titanium alloy, which can play a role in protection, lubrication, and heat insulation, and helps to improve the surface quality of the tube during the forging process.

[0030] In one optional embodiment, in step S103, during the first radial forging, the mandrel diameter is 6-10 mm smaller than the inner diameter of the tube blank, the radial indentation per hammer is 15-25 mm, the axial feed speed is 2.5-3 m / min, the tube blank rotation speed is 25-40 r / min, the hammering speed is 1500-2000 times / min, and the overall deformation is 40%-60%. During the second and third radial forgings, the mandrel diameter is 10-15 mm smaller than the inner diameter of the intermediate tube blank obtained in the previous forging, the radial indentation per hammer is 20-30 mm, and the axial feed speed is 2.5-3 m / min. The billet rotation speed is 25~40 r / min, the hammering speed is 2000~2500 times / min, and the overall deformation is 60%~70%; during the fourth radial forging, the mandrel diameter is 6~8 mm smaller than the inner diameter of the intermediate billet obtained in the previous step, the radial pressing amount per hammer is 10~15 mm, the axial feeding speed is 2.5~3 m / min, the billet rotation speed is 25~40 r / min, the hammering speed is 1500~2000 times / min, and the overall deformation is 30%~40%; in particular, the final forging temperature of each radial forging is guaranteed to be 100~120℃ higher than the phase transformation point.

[0031] Specifically, radial forging consists of four symmetrically distributed planar hammers, an intermediate mandrel, and a clamping device. The clamping device can simultaneously rotate and feed the tube blank. The intermediate mandrel is clamped by a specific clamping device, which enables the rotation and feeding of the tube during the forging process.

[0032] In one optional embodiment, in step S103, the arc-shaped anvil includes an upper anvil and a lower anvil arranged symmetrically. The upper anvil and the lower anvil each include a main body with an arc-shaped groove. Each side of the arc-shaped groove has a straight inclined surface, and the straight inclined surfaces are connected by a horizontal segment. The radius R of the arc-shaped groove is the outer diameter of the forged pipe + (30 mm ~ 60 mm), the angle φ between the tangents at the connection point of the straight inclined surface and the arc-shaped groove is 15-25°, and the length and width of the main body are 150~300 mm and 150~300 mm, respectively.

[0033] Specifically, after the fourth radial forging, a fifth forging is performed using a specially designed arc-shaped anvil. The upper and lower anvils have the same shape. Taking the structure of the lower anvil as an example, the structure of the lower anvil is as follows: Figure 2 and 3As shown, the lower anvil comprises a main body with an arc-shaped groove. Each side of the arc-shaped groove has a straight inclined surface, which connects to a horizontal section. The key dimensions involved are the arc radius R and the angle φ between the tangent of the straight inclined surface and the arc connection point. The main body of the lower anvil is rectangular, with a length a and a width b. Specifically, the arc radius R is the outer diameter of the forged pipe + (30~60) mm, the angle φ between the straight section and the tangent of the arc connection point is 15-25°, the length a is 150~300 mm, and the width b is 150~300 mm. The upper and lower anvils are arranged symmetrically, with the arc-shaped grooves aligned. The central mandrel is held by a specific clamping device, enabling the rotation and feeding of the pipe during forging. During forging, the reduction per pass is 10%~20%, the mandrel diameter is 4~6mm smaller than the inner diameter of the intermediate tube blank obtained in the previous pass, and the feed rate is 100~200mm. After each forging pass is completed, the billet is rotated 90° before the next forging pass is performed. This process is repeated until the target specification is reached, and then the billet is air-cooled to room temperature.

[0034] In one optional embodiment, in step S104, the heat treatment adopts a two-stage heat treatment method of heat treatment and aging treatment. The heat treatment involves holding the temperature at 30°C below the phase change point for 2 hours, then air cooling to room temperature, and then reheating to 600°C and holding for 6 hours before air cooling to room temperature.

[0035] In one optional embodiment, in step S104, the cold rolling process involves multiple passes of cold rolling, degreasing, removal of internal and external surface defects, pickling, annealing, straightening, pickling, and flaw detection for the titanium alloy tube.

[0036] The glass protective lubricant is an environmentally friendly glass protective lubricant commonly used in this field.

[0037] The present invention will be further illustrated by the following examples.

[0038] Example 1 This embodiment discloses a high-strength titanium alloy seamless tube and its preparation method.

[0039] The chemical composition of the high-strength titanium alloy (by element mass percentage) is as follows: Al: 5.20%, Mo: 1.58%, V: 1.56%, Zr: 3.12%, Sn: 2.67%, Nb: 0.56%, Si: 0.22%, B: 0.41%, Ce: 0.83%; the balance is Ti and other unavoidable impurity elements.

[0040] The specific preparation method is as follows: (1) Smelting: The raw materials are prepared according to the above chemical composition. The raw materials are sponge titanium, baked TiO2 powder, vanadium aluminum alloy, aluminum molybdenum, sponge zirconium, intermediate alloy containing tin and niobium and cerium hexaboride (CeB6). The raw materials are weighed and proportioned according to the chemical composition of the finished titanium alloy. The first smelting is carried out in a vacuum electron beam cold hearth furnace or a vacuum plasma cold hearth furnace to obtain a first ingot. Then, the second smelting is carried out in a vacuum plasma cold hearth furnace. The titanium alloy liquid smelted in the second smelting is cast into shape to obtain a titanium alloy hollow tube blank.

[0041] (2) Surface treatment: The titanium alloy hollow tube blank obtained by secondary melting and casting is polished on the outer surface and the inner hole is bored until there are no defects on the inner and outer surfaces, resulting in a titanium alloy tube blank with a bright white appearance on both the inner and outer surfaces.

[0042] (3) Billet heating: The surface-treated titanium alloy billet is sent into the resistance furnace for heating. Before heating, an environmentally friendly glass protective lubricant is uniformly sprayed on the inner and outer surfaces of the titanium alloy to provide protection, lubrication and heat insulation, which helps to improve the surface quality of the pipe during the forging process. The heating rate is 600℃ / h for each heating cycle. First, the temperature is held at 6℃ below the phase transformation point for 2 hours, and then the temperature is raised to the forging temperature, that is, held at 20℃ above the phase transformation point for 1 hour. Then, the billet is taken out of the furnace for radial forging.

[0043] (4) Radial forging: The forging process consists of four symmetrically distributed planar hammers, an intermediate mandrel, and a clamping device. The clamping device can simultaneously rotate and feed the tube blank. The forging process includes five radial forging passes, with the forging temperature gradually decreasing in each pass. In the first radial forging pass, the mandrel diameter is 6 mm smaller than the inner diameter of the tube blank, the radial indentation per hammer is 15 mm, the axial feed rate is 2.5 m / min, the tube blank rotation speed is 25 r / min, the hammering speed is 1600 times / min, and the overall deformation is 40%. In the second and third radial forging passes, the mandrel diameter is 10 mm smaller than the inner diameter of the intermediate tube blank obtained in the previous pass, the radial indentation per hammer is 20 mm, the axial feed rate is 2.5 m / min, the tube blank rotation speed is 30 r / min, the hammering speed is 2000 times / min, and the overall deformation is 60%. During the fourth radial forging, the mandrel diameter was 6 mm smaller than the inner diameter of the intermediate tube blank obtained in the previous forging. The radial pressing amount per hammer was 10 mm, the axial feed speed was 2.5 m / min, the tube blank rotation speed was 25 r / min, the hammering speed was 1500 times / min, and the overall deformation was 30%. The final forging temperature of each radial forging was ensured to be 100~120℃ higher than the phase transformation point.

[0044] After the fourth radial forging, a fifth forging is performed using upper and lower anvils of a specific design: the design of the upper and lower anvils is shown in the attached figure. Figure 1 and 2As shown, the bottom of the anvil is composed of an arc. Above the arc, on both the left and right sides, there are straight segments connecting to the arc, followed by horizontal straight segments connecting to the arc. The key dimensions involved are the arc radius R, the angle φ between the tangents of the straight segments and the arc connection point, and the length a and width b of the upper and lower anvils. Specifically, the arc radius R is the outer diameter of the forged pipe + 30mm, the angle φ between the straight segments and the arc connection point is 15°, and the length and width of the upper and lower anvils are both 150mm. The same arc-shaped anvils are arranged symmetrically, and the mandrel in the middle is held by a clamping device to achieve the rotation and feeding of the pipe during forging. During forging, the reduction per pass is 10%~20%, the mandrel diameter is 4mm smaller than the inner diameter of the intermediate billet obtained in the previous pass, and the feed is 100mm. After each forging pass, the billet is rotated 90° before the next forging pass, and this process is repeated until the target specification is reached. Then, it is air-cooled to room temperature.

[0045] (5) Heat treatment: Two-stage heat treatment is adopted, namely heat treatment and aging. The specific heat treatment process is to keep it at 30°C below the phase change point for 2 hours, then air cool it to room temperature, and then reheat it to 600°C and keep it at 6 hours, then air cool it to room temperature.

[0046] (6) Cold rolling: The tube obtained above is subjected to multiple passes of cold rolling, degreasing, removal of internal and external surface defects, pickling, annealing, straightening, pickling, and flaw detection to obtain the finished titanium alloy seamless tube.

[0047] Example 2 This embodiment discloses a high-strength titanium alloy seamless tube and its preparation method.

[0048] The chemical composition of the high-strength titanium alloy (by element mass percentage) is as follows: Al: 6.45%, Mo: 2.84%, V: 1.89%, Zr: 3.84%, Sn: 3.55%, Nb: 1.46%, Si: 0.45%, B: 0.56%, Ce: 1.19%; the balance is Ti and other unavoidable impurity elements.

[0049] The specific preparation method is as follows: (1) Smelting: The raw materials are prepared according to the above chemical composition. The raw materials are sponge titanium, baked TiO2 powder, vanadium aluminum alloy, aluminum molybdenum, sponge zirconium, intermediate alloy containing tin and niobium and cerium hexaboride (CeB6). The raw materials are weighed and proportioned according to the chemical composition of the finished titanium alloy. The first smelting is carried out in a vacuum electron beam cold hearth furnace or a vacuum plasma cold hearth furnace to obtain a first ingot. Then, the second smelting is carried out in a vacuum plasma cold hearth furnace. The titanium alloy liquid smelted in the second smelting is cast into shape to obtain a titanium alloy hollow tube blank.

[0050] (2) Surface treatment: The titanium alloy hollow tube blank obtained by secondary melting and casting is polished on the outer surface and the inner hole is bored until there are no defects on the inner and outer surfaces, resulting in a titanium alloy tube blank with a bright white appearance on both the inner and outer surfaces.

[0051] (3) Tube blank heating: The surface-treated titanium alloy tube blank is sent into the resistance furnace for heating. Before heating, an environmentally friendly glass protective lubricant is uniformly sprayed on the inner and outer surfaces of the titanium alloy to provide protection, lubrication and heat insulation, which helps to improve the surface quality of the tube during the forging process. The heating rate is 600℃ / h for each heating. First, the temperature is held at 100℃ below the phase transformation point for 2 hours, and then the temperature is raised to the forging temperature, that is, at 30℃ below the phase transformation point to 200℃ above the phase transformation point for 1 hour. Then, the tube blank is taken out of the furnace for radial forging.

[0052] (4) Radial forging: The forging process consists of four symmetrically distributed planar hammers, an intermediate mandrel, and a clamping device. The clamping device can simultaneously rotate and feed the tube blank. The forging process includes five radial forging passes, with the forging temperature gradually decreasing in each pass. In the first radial forging pass, the mandrel diameter is 10 mm smaller than the inner diameter of the tube blank, the radial indentation per hammer is 25 mm, the axial feed rate is 3 m / min, the tube blank rotation speed is 40 r / min, the hammering speed is 2000 times / min, and the overall deformation is 60%. In the second and third radial forging passes, the mandrel diameter is 15 mm smaller than the inner diameter of the intermediate tube blank obtained in the previous pass, the radial indentation per hammer is 30 mm, the axial feed rate is 3 m / min, the tube blank rotation speed is 40 r / min, the hammering speed is 2500 times / min, and the overall deformation is 65%. During the fourth radial forging, the mandrel diameter was 8 mm smaller than the inner diameter of the intermediate tube blank obtained in the previous forging. The radial pressing amount per hammer was 15 mm, the axial feeding speed was 3 m / min, the tube blank rotation speed was 40 r / min, the hammering speed was 2000 times / min, and the overall deformation was 40%. The final forging temperature of each radial forging was ensured to be 100~120℃ higher than the phase transformation point.

[0053] After the fourth radial forging, a fifth forging is performed using upper and lower anvils of a specific design: the design of the upper and lower anvils is shown in the attached figure. Figure 1 and 2As shown, the bottom of the anvil is composed of an arc. Above the arc, on both the left and right sides, there are straight segments connecting to the arc, followed by horizontal straight segments connecting to the arc. The key dimensions involved are the arc radius R, the angle φ between the tangents of the straight segments and the arc connection point, and the length a and width b of the upper and lower anvils. Specifically, the arc radius R is the outer diameter of the forged pipe + 60mm, the angle φ between the straight segments and the arc connection point is 20°, and the length and width of the upper and lower anvils are 300mm and 300mm respectively. Identical arc-shaped anvils are arranged symmetrically, and the mandrel in the middle is held by a specific clamping device, enabling the rotation and feeding of the pipe during forging. During forging, the reduction per pass is 20%, the mandrel diameter is 6mm smaller than the inner diameter of the intermediate billet obtained in the previous pass, and the feed is 200mm. After each forging pass, the billet is rotated 90° before the next forging pass, repeating this process until the target specification is reached, and then air-cooled to room temperature.

[0054] (5) Heat treatment: Two-stage heat treatment is adopted, namely heat treatment and aging. The specific heat treatment process is to keep it at 30°C below the phase change point for 2 hours, then air cool it to room temperature, and then reheat it to 600°C and keep it at 6 hours, then air cool it to room temperature.

[0055] (6) Cold rolling: The tube obtained above is subjected to multiple passes of cold rolling, degreasing, removal of internal and external surface defects, pickling, annealing, straightening, pickling, and flaw detection to obtain the finished titanium alloy seamless tube.

[0056] Comparative Example 1 The chemical composition of the titanium alloy (by element mass percentage) is as follows: Al: 6.50%, Mo: 2.00%, V: 2.00%, Zr: 2.00%, Sn: 0.20%, Nb: 0.20%, Si: 0.10%, with the balance being Ti and other unavoidable impurity elements.

[0057] The specific preparation method is as follows: (1) Smelting: The raw materials are prepared according to the above chemical composition. The raw materials are conventional raw materials such as sponge titanium, vanadium aluminum alloy, aluminum molybdenum alloy, and sponge zirconium. The titanium alloy ingot is obtained by three smeltings in a vacuum consumable electric arc furnace.

[0058] (2) Forging: The ingot is forged into a billet by 2-3 hot forging and 3-4 free forging at 900℃~1150℃. Ordinary flat anvil is used for forging, and no custom arc anvil is used. After forging, it is air-cooled to room temperature.

[0059] (3) Tube blank preparation: The bar billet is prepared by hot rolling and piercing process. The piercing heating temperature is 1080℃. After piercing, the tube blank is pickled to remove the oxide scale and obtain titanium alloy tube blank.

[0060] (4) Heat treatment of tube blank: The tube blank is sent into a gas furnace for heating. The heating rate is not precisely controlled. A single-stage heat treatment method is adopted. After holding at 900℃~1050℃ for 2 hours, the tube blank is cooled to room temperature in the furnace. There is no aging treatment step.

[0061] (5) Cold rolling and finishing: The tubes obtained above are subjected to multiple cold rolling processes, and then simply sandblasted, pickled, annealed, straightened and tested for flaws to obtain finished titanium alloy seamless tubes.

[0062] The properties of the TA15 titanium alloy seamless tubes of Examples 1-2 and Comparative Examples are shown in Table 1 below.

[0063] In Examples 1-2 and the comparative examples, test samples were prepared from finished seamless tubes of the same specifications. The tensile test samples were taken from the transverse side of the tube.

[0064] Among them, R m Tensile strength refers to the maximum stress per unit area that the specimen can withstand before it breaks. A represents elongation.

[0065] Table 1. Performance of Titanium Alloy Seamless Tubes

[0066] As can be seen from the results in Table 1, R in Examples 1-2 m Both A and B are higher than those of Comparative Example 1, indicating that the preparation method of the present invention has successfully obtained a seamless titanium alloy tube with both high strength and high toughness.

[0067] The above are exemplary embodiments disclosed in this invention. However, it should be noted that various changes and modifications can be made without departing from the scope of the embodiments of this invention as defined by the claims. Although the elements disclosed in the embodiments of this invention may be described or claimed individually, they may be understood as multiple unless explicitly limited to a singular number.

[0068] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of different aspects of the invention exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A seamless titanium alloy tube, characterized in that, The chemical composition of the titanium alloy seamless tube, by mass percentage, includes: Al: 5%~6.5%, Mo: 1.5%~3%, V: 1.5%~2%, Zr: 3%~4%, Sn: 2.5%~3.6%, Nb: 0.5%~1.5%, Si: 0.2%~0.5%, B: 0.4%~0.6%, Ce: 0.8%~1.2%, with the balance being Ti and other unavoidable impurity elements.

2. A method for preparing a seamless titanium alloy tube, characterized in that, Includes the following steps: Step S101: Prepare raw materials according to chemical composition, obtain titanium alloy hollow tube blank by melting raw materials and perform surface treatment; Step S102: After uniformly spraying a protective lubricating layer on the inner and outer surfaces of the titanium alloy hollow tube blank processed in step S101, it is heated. The heating process is carried out at a heating rate of 600℃ / h for each heating, and the temperature is first held at 60℃~100℃ below the phase transformation point for 2 hours, and then the temperature is continued to rise to the forging temperature. Step S103: Radial forging of the heated titanium alloy hollow tube blank in step S102; wherein, five-pass radial forging is adopted and the forging temperature gradually decreases in each pass; the last forging is carried out using an arc anvil, the forging reduction per pass is 10%~20%, the mandrel diameter is 4~6mm smaller than the inner diameter of the previous intermediate tube blank, the feed is 100~200mm, and after each forging pass, the blank is rotated 90° and forging is continued until the target specification is reached, and then air-cooled to room temperature; Step S104: The titanium alloy tube obtained in step S103 is subjected to heat treatment and cold rolling processes in sequence to form a seamless titanium alloy tube.

3. The method for preparing a seamless titanium alloy tube according to claim 2, characterized in that, In step S102, "continue heating to the forging temperature" includes: holding the temperature for 1 hour at a temperature 30°C below the phase transformation point to 200°C above the phase transformation point, and then removing the product from the furnace for subsequent radial forging.

4. The method for preparing a seamless titanium alloy tube according to claim 2, characterized in that, In step S101, the raw materials are sponge titanium, baked TiO2 powder, vanadium aluminum alloy, aluminum molybdenum, sponge zirconium, intermediate alloy containing tin and niobium, and cerium hexaboride. The chemical composition, by mass percentage, includes: Al: 5%~6.5%, Mo: 1.5%~3%, V: 1.5%~2%, Zr: 3%~4%, Sn: 2.5%~3.6%, Nb: 0.5%~1.5%, Si: 0.2%~0.5%, B: 0.4%~0.6%, Ce: 0.8%~1.2%, with the balance being Ti and other unavoidable impurity elements; The smelting process involves a primary smelting using a vacuum electron beam cold hearth furnace or a vacuum plasma cold hearth furnace to obtain a primary ingot, followed by a secondary smelting using a vacuum plasma cold hearth furnace. The molten titanium alloy from the secondary smelting is then cast into a hollow titanium alloy tube blank.

5. The method for preparing a seamless titanium alloy tube according to claim 2, characterized in that, In step S101, the surface treatment involves grinding the outer surface of the titanium alloy hollow tube blank and boring the inner hole until there are no defects on the inner and outer surfaces, resulting in a titanium alloy hollow tube blank with a bright white appearance on both the inner and outer surfaces.

6. The method for preparing a seamless titanium alloy tube according to claim 2, characterized in that, In step S102, the protective lubricating layer is a glass protective lubricant.

7. The method for preparing a seamless titanium alloy tube according to claim 2, characterized in that, In step S103, during the first radial forging, the mandrel diameter is 6-10 mm smaller than the inner diameter of the tube blank, the radial indentation per hammer is 15-25 mm, the axial feed speed is 2.5-3 m / min, the tube blank rotation speed is 25-40 r / min, the hammering speed is 1500-2000 times / min, and the overall deformation is 40%-60%. During the second and third radial forgings, the mandrel diameter is 10-15 mm smaller than the inner diameter of the intermediate tube blank obtained in the previous forging, the radial indentation per hammer is 20-30 mm, the axial feed speed is 2.5-3 m / min, and the tube blank rotation speed is 25-40 r / min. The hammering speed is 25~40 r / min, the hammering speed is 2000~2500 times / min, and the overall deformation is 60%~70%; during the fourth radial forging, the mandrel diameter is 6~8 mm smaller than the inner diameter of the intermediate tube blank obtained in the previous one, the radial pressing amount per hammer is 10~15 mm, the axial feeding speed is 2.5~3 m / min, the tube blank rotation speed is 25~40 r / min, the hammering speed is 1500~2000 times / min, and the overall deformation is 30%~40%; among them, the final forging temperature of each radial forging is guaranteed to be 100~120℃ higher than the phase transformation point.

8. The method for preparing a seamless titanium alloy tube according to claim 2, characterized in that, In step S103, the arc-shaped anvil includes an upper anvil and a lower anvil arranged symmetrically. The upper anvil and the lower anvil each include a main body with an arc-shaped groove. Each side of the arc-shaped groove has a straight inclined surface, and the straight inclined surfaces are connected by a horizontal section. The radius R of the arc-shaped groove is the outer diameter of the forged pipe + (30mm ~ 60mm), the angle φ between the tangents at the connection point of the straight inclined surface and the arc-shaped groove is 15-25°, and the length and width of the main body are 150~300mm.

9. The method for preparing a seamless titanium alloy tube according to claim 2, characterized in that, In step S104, the heat treatment adopts a two-stage heat treatment method of heat treatment and aging treatment. The heat treatment involves holding at 30°C below the phase change point for 2 hours, then air cooling to room temperature, and then reheating to 600°C and holding for 6 hours, followed by air cooling to room temperature.

10. The method for preparing a seamless titanium alloy tube according to claim 2, characterized in that, In step S104, the cold rolling process involves multiple passes of cold rolling, degreasing, removal of internal and external surface defects, pickling, annealing, straightening, pickling, and flaw detection for the titanium alloy tube.

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