A medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube and its preparation method

Abstract

The present invention relates to the technical field of TA18 titanium alloy tube preparation, and in particular to a medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube and a preparation method thereof. The present application provides a medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube composed of the following percentage elements: 2.50% to 3.00% Al; 2.80% to 3.10% V; 0.01%‑0.08% Fe; 0.01%‑0.07% Si; 0.01%‑0.003% C; 0‑0.01% N; 0.01%‑0.008% H; 0.01%‑0.08% O; the remainder is Ti. The present application optimizes the element composition and combines boring and rolling treatment methods to not only improve the dimensional accuracy of the tube, but also enhance the bearing capacity of the material. The use of multi-pass rolling treatment adjusts the rolling parameters reasonably, so that the final medium-strength TA18 seamless titanium alloy tube has superior mechanical properties and surface quality.

Description

Technical Field

[0001] The invention relates to the technical field of TA18 titanium alloy tube preparation, and in particular to a medium-strength TA18 seamless titanium alloy small-diameter thick-wall tube and a preparation method thereof. Background Art

[0002] TA18 titanium alloy is a low alloy near-α titanium alloy. Due to its excellent mechanical properties, corrosion resistance, excellent welding performance and cold forming performance, the alloy is applied to the aircraft piping system and the preparation process is becoming more and more mature. TA18 titanium alloy is usually processed into tubes by traditional hot processing technology from rods. During the whole preparation process, due to the microstructure differences, texture differences and uneven mechanical properties at different positions of the rods and tubes, the performance of the tubes will be seriously affected. Therefore, it is necessary to establish the correlation between the microstructure and texture of the alloy and the corresponding mechanical properties.

[0003] In view of the above-mentioned related technologies, the inventors found that the domestic commonly used medium-strength specification process technology is relatively mature, and the production process of small-diameter thick-walled seamless pipes is still insufficient. Small-diameter thick-walled pipes refer to TA18 alloy pipes with a small ratio of outer diameter to wall thickness, and their outer diameter-to-wall thickness ratio D / t is less than 10. Due to geometric reasons, extremely high stress is generated at the positions equivalent to "6 o'clock" and "12 o'clock" on the inner surface of the pipe, and cracks are easily generated during flattening; because its outer diameter-to-wall thickness ratio is small, the diameter reduction per pass during the cold rolling process is large, the metal enters the deformation zone instantaneously, and the actual flow speed of the metal lags behind the pressing speed, and there is no time to complete the longitudinal and radial extension deformation, causing the inner surface to wrinkle and crack. The cracks generated on the outer surface can be removed by polishing, manual scraping and other methods, and the cracks generated on the inner surface cannot be removed by boring because the inner hole is less than ф13mm, so it is difficult to control the inner surface, thereby limiting the mass production of small-diameter thick-walled pipes. Summary of the invention

[0004] In order to improve the defects of the existing TA18 titanium alloy production process, in which cracks are easily generated on the inner surface, resulting in unqualified process performance indicators and low ultrasonic flaw detection pass rate, the present application provides a medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube and a preparation method thereof.

[0005] In the first aspect, the present application provides a medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube, which adopts the following technical solution:

[0006] A medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube is composed of the following percentage elements: 2.20%-3.00% Al; 2.80%-3.10% V; 0.01%-0.08% Fe; 0.01%-0.07% Si; 0.001%-0.003% C; 0-0.01% N; 0.001%-0.008% H; 0.01%-0.08% O; the balance is Ti.

[0007] Through the above technical solution, the present application optimizes the element composition in the medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube. The addition of aluminum can improve the strength of the titanium alloy and improve its oxidation resistance, while the introduction of vanadium helps to improve the strength and toughness of the alloy. Strict restrictions on iron, silicon, carbon, nitrogen, hydrogen and oxygen ensure the stability of the alloy in high temperature and corrosive environments, avoiding embrittlement and performance degradation. In addition, the remaining titanium can maintain the basic properties of the material and enhance the overall durability and wide application of the alloy.

[0008] Furthermore, the medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube has an outer diameter of 19.05 mm, a wall thickness of 3.05 mm, and an inner and outer surface roughness Ra of no more than 1.0 μm.

[0009] Through the above technical solution, this application optimizes the specification parameters of medium-strength TA18 seamless titanium alloy small-diameter thick-walled tubes. This specification design not only ensures the lightweight of the tube, but also meets the requirements for use in high-pressure and high-temperature environments. The requirement that the inner and outer surface roughness Ra is not greater than 1.0μm ensures the high efficiency and fluidity of the tube during fluid transportation, reducing fluid resistance and friction loss. At the same time, the smooth surface also improves the corrosion resistance of the tube and extends its service life.

[0010] In the second aspect, the present application provides a method for preparing a medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube, using the following technical solution:

[0011] A method for preparing a medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube comprises the following preparation steps:

[0012] S1. Melting and casting into ingots: taking raw materials according to the formula and die-casting them into electrode blocks, taking multiple electrode blocks and welding them into bundles, and melting them into ingots;

[0013] S2, precision forging treatment: peeling, sampling, flaw detection, cutting off the cap of the ingot surface, upsetting and drawing, and collecting the square billet;

[0014] S3, hot rolling treatment: placing the billet in a heating furnace, heating it up and hot rolling it, and collecting the bar material;

[0015] S4, processing and forming: treating the surface of the bar material, collecting the tube blank, boring it and cold rolling it to prepare the alloy tube blank;

[0016] S5. Quality inspection and flaw detection: After the alloy tube billet is subjected to ultrasonic flaw detection, the qualified product is the medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube.

[0017] Through the above technical scheme, this application optimizes the preparation method of medium-strength TA18 seamless titanium alloy small-diameter thick-walled tubes. First, through the process of melting into ingots, the uniformity and purity of the raw materials are guaranteed, laying a good foundation for subsequent processing. The fine forging step ensures the quality of the ingot by removing surface defects and performing flaw detection, avoiding potential structural weaknesses. The hot rolling treatment not only improves the density of the material, but also improves its mechanical properties. Finally, the quality of the alloy tube billet is strictly controlled by ultrasonic flaw detection to ensure the reliability and safety of the final product. This systematic preparation method can effectively reduce production defects and improve product consistency.

[0018] Furthermore, the upsetting process described in step S2 adopts the following technical solution:

[0019] After the ingot is placed in the first fire at a temperature of 1130-1150℃ for 3-3.5h, it is forged to 220 square meters, and the surface is ground until the cracks are invisible to the naked eye, and then the material is evenly divided;

[0020] After keeping the temperature at the second temperature of 1050-1080℃ for 2.0-2.5h, continue with the three-upsetting and three-drawing process;

[0021] Then keep it at 940-960℃ for the third time for 2-2.5h, and then upset and draw it three times to 290 square.

[0022] Through the above technical scheme, the present application can effectively eliminate the defects inside the ingot by keeping it warm at a specific temperature and performing upsetting and drawing, thereby improving the density and uniformity of the material and thus improving the mechanical properties of the alloy. Heat treatment at a high temperature of 1130-1150°C helps to improve the plasticity of the titanium alloy, enabling it to achieve better forming effects in subsequent processing. The final three-upsetting and three-drawing process further optimizes the organizational structure of the material, giving the finished product better strength and toughness. This sophisticated heat processing process ensures the high performance characteristics of medium-strength TA18 seamless titanium alloy small-diameter thick-walled tubes, while also improving production efficiency and reducing energy consumption.

[0023] Furthermore, the hot rolling process described in step S3 includes the following steps:

[0024] The square billet is placed in a heating furnace, heated to 950-1000°C, kept warm for 2.0-2.5h, and hot-rolled in an 850 hot rolling mill and a continuous rolling mill to prepare a ф130 bar.

[0025] Through the above technical scheme, the present application can effectively improve the microstructure of the material and enhance its strength and ductility by heating the square billet to 950-1000°C and hot rolling. The setting of the holding time ensures uniform heat distribution inside the material and avoids internal stress and deformation caused by temperature gradients. The prepared ф130 bar not only has good processing performance, but also its uniform material requirements lay the foundation for subsequent forming. Precise control during the hot rolling process can effectively reduce material loss and improve production efficiency. This process ensures the performance stability and consistency of the medium-strength TA18 seamless titanium alloy tube.

[0026] Furthermore, the processing and forming described in step S4 includes the following technical solutions:

[0027] S41, surface treatment: the bar material is subjected to surface peeling treatment, cut into ingots according to the process requirements, the ingots after cutting are punched on a lathe, the inner and outer surfaces of the punched ingots are wrapped with a layer of 0.8mm iron sheet, the medium frequency furnace is 900-950℃, the temperature is kept for 2-2.5h, and extrusion is performed to prepare the tube blank;

[0028] S42, blank processing: the outer surface of the blank is peeled, 0.20mm on one side, and the tangible loss is 1.80%~2.50%; then the inner surface of the blank is processed, boring 0.20mm on one side, and the tangible loss is 1.80%~2.50%;

[0029] S43, intermediate rolling: multi-pass rolling processing according to specifications, adjusting rolling parameters: adjusting area reduction, ratio Q of plastic deformation to original thickness, feed amount and rolling speed;

[0030] S44, primary heat treatment: degreasing, pickling and vacuum annealing of the intermediate rolled tube material, controlling the annealing temperature to 700-750℃ for 180-200min, cooling with the furnace, and straightening after annealing;

[0031] S45, boring and rolling treatment: adjusting the single side of the boring hole to 0.20mm, with a tangible loss of 3% to 4%, boring is performed, and the bored tube is rolled and the rolling parameters are adjusted;

[0032] S46, secondary heat treatment: degreasing, pickling and vacuum annealing of the bored and rolled pipes, controlling the annealing temperature to 600-650℃ for 180-200min, cooling with the furnace, and straightening after annealing.

[0033] Through the above technical scheme, the present application can extrude poorly shaped materials through surface peeling treatment and medium frequency furnace extrusion molding, with good inner and outer surface quality, and severe deformation in the center of the ingot, which is beneficial to improving the metal structure, ensuring that the internal structure of the tube blank is denser and reducing defects and voids.

[0034] Secondly, the present application not only improves the dimensional accuracy of the pipe but also enhances the bearing capacity of the material through the combination of boring and rolling treatment. The use of multi-pass rolling treatment significantly improves the plasticity and strength of the material through reasonable adjustment of rolling parameters. The combination of primary and secondary heat treatment further optimizes the microstructure of the pipe and ensures its stability under high temperature and high pressure conditions.

[0035] Furthermore, the rolling method used in the intermediate rolling step and the boring and rolling step is a double-rotation double-feed method, and the specific parameters are:

[0036] The double-feed and double-rotation frame reciprocates once for feeding and twice for rotation, with a forward feed of 1.3mm and a rotation angle of a42°, and a rear feed of 0.7mm and a rotation angle of a25°.

[0037] Through the above technical solution, the double-feed and double-rotation solution adopted in this application can effectively control the deformation of the material, making the rolling process more stable and reducing the loss and defects that may occur in the material during the processing. At the same time, the double-rotation design can provide a more uniform pressure distribution during the processing process to ensure the dimensional accuracy and surface quality of the final product. This advanced rolling technology not only improves production efficiency, but also significantly improves the overall performance of medium-strength TA18 seamless titanium alloy tubes to meet the needs of the high-end market.

[0038] Furthermore, the parameters of the intermediate rolling in step S43 are:

[0039] The area reduction ratio is 41% to 52%, the Q value is 0.9 to 1.0, the feed amount is 2 to 3 mm, and the rolling speed is 60 to 70 times / min.

[0040] Furthermore, the parameters of the boring and rolling process and the heavy rolling process described in step S43 are:

[0041] The area reduction rate is 48%-52%, the Q value is 0.9-1.0, the feed amount is 2-3mm, and the rolling speed is 80-100 times / min.

[0042] Through the above technical scheme, the present application further optimizes the Q value and processing deformation, avoiding microstructural defects caused by excessive deformation. The setting of the Q value between 0.9 and 1.0 further optimizes the plastic deformation during the rolling process, making the processing more efficient and uniform. The adjustment of the rolling speed between 80 and 100 times / min not only improves the production efficiency, but also ensures the stability and consistency of the product during the forming process. These fine parameter settings make the final medium-strength TA18 seamless titanium alloy tube have superior mechanical properties and surface quality. The final finished product has uniform wall thickness, no cracks on the inner and outer surfaces of the tube, and the process performance flattening also meets the standards and customer requirements.

[0043] Furthermore, in the boring and rolling process described in step S45, the length of the finishing section is 20-25 cm, the diameter feeding section accounts for 5%-6% of the working section, and the mandrel taper is adjusted to 17.50-12.40 mm.

[0044] Through the above technical scheme, the present application further adjusts the rolling parameters, shortens the feeding section by optimizing the length of the finishing section, increases the length of the working section, and adjusts the taper of the mandrel to reduce the degree of accumulation of metal flow in the diameter reduction section in the later wall reduction section, thereby reducing the probability of crack formation.

[0045] In summary, this application has the following beneficial effects:

[0046] First, this application optimizes the element composition in the medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube. The addition of aluminum can increase the strength of the titanium alloy and improve its oxidation resistance, while the introduction of vanadium helps to improve the strength and toughness of the alloy. Strict restrictions on iron, silicon, carbon, nitrogen, hydrogen and oxygen ensure the stability of the alloy in high temperature and corrosive environments, avoiding embrittlement and performance degradation. In addition, the remaining titanium can maintain the basic properties of the material and enhance the overall durability and wide application of the alloy.

[0047] Second, the present application can extrude poorly shaped materials through surface peeling treatment and medium frequency furnace extrusion molding, with good inner and outer surface quality, and severe deformation of the ingot center, which is beneficial to improving the metal structure, ensuring that the internal structure of the tube blank is denser and reducing defects and voids.

[0048] Secondly, the present application not only improves the dimensional accuracy of the pipe but also enhances the bearing capacity of the material through the combination of boring and rolling treatment. The use of multi-pass rolling treatment significantly improves the plasticity and strength of the material through reasonable adjustment of rolling parameters. The combination of primary and secondary heat treatment further optimizes the microstructure of the pipe and ensures its stability under high temperature and high pressure conditions.

[0049] Third, the double-feed and double-rotation solution adopted in this application can effectively control the deformation of the material, making the rolling process more stable and reducing the loss and defects that may occur in the material during processing. At the same time, the double-rotation design can provide a more uniform pressure distribution during the processing process, ensuring the dimensional accuracy and surface quality of the final product. This advanced rolling technology not only improves production efficiency, but also significantly improves the overall performance of medium-strength TA18 seamless titanium alloy tubes to meet the needs of the high-end market.

[0050] Fourth, this application further optimizes the Q value and processing deformation, avoiding microstructural defects caused by excessive deformation. The setting of the Q value between 0.9 and 1.0 further optimizes the plastic deformation during the rolling process, making the processing more efficient and uniform. The adjustment of the rolling speed between 80 and 100 times / min not only improves production efficiency, but also ensures the stability and consistency of the product during the forming process. These fine parameter settings make the final medium-strength TA18 seamless titanium alloy tube have superior mechanical properties and surface quality. The final finished product has uniform wall thickness, no cracks on the inner and outer surfaces of the tube, and the process performance flattening also meets the standards and customer requirements. DETAILED DESCRIPTION

[0051] The present application is further described in detail below with reference to the embodiments.

[0052] In the examples of the present application, the raw materials and instruments used are as follows, but not limited thereto. Raw materials not otherwise specified are of analytical grade.

[0053] Example 1

[0054] A medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube is composed of the following percentage elements: 2.50% Al; 2.80% V; 0.08% Fe; 0.07% Si; 0.001% C; 0.01% N; 0.003% H; 0.02% O; and the balance is Ti.

[0055] A method for preparing a medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube comprises the following preparation steps:

[0056] S1. Melting into ingots: Take 0A-grade sponge titanium with a particle size of 8 to 20 mm according to the formula, mix the alloy package with a mass fraction of 55% V and a mass fraction of 45% Al, and the aluminum beans with a purity of 99.90% evenly, press them into electrode blocks with a 6300t powder press, weld several electrode blocks into a bundle of rods by argon arc welding technology, melt them into ingots three times by vacuum consumable furnace arc method, and pass the uniform small-particle sponge titanium through the vacuum consumable furnace three times to make the ingot composition uniform, and then melt them into ingots;

[0057] S2, precision forging treatment: the surface of the ingot is peeled, sampled, flaw detected, and the cap is cut off to obtain an ingot with an outer diameter of ф680mm. The ingot is subjected to upsetting and squeegee treatment. After the ingot is placed in the first fire at a temperature of 1130℃ for 3 hours of heat preservation, the ingot is forged to 220 square meters, and the surface is ground until cracks cannot be seen by the naked eye, and then the material is evenly divided; after being kept in the second fire at 1050℃ for 2.0 hours, it is continued to be upset and drawn three times; after being kept in the third fire at 940℃ for 2 hours, it is upset and drawn three times again to obtain a ф290mm square billet;

[0058] S3, hot rolling treatment: the billet is placed in a heating furnace, heated to 980°C and kept at this temperature for 2 hours, and hot rolled by a 850 hot rolling mill and a continuous rolling mill group 1 to obtain a bar of ф130 mm;

[0059] S41, surface treatment: the bar material is subjected to surface peeling treatment, cut into 50cm ingots according to the process requirements, the ingots after cutting are punched on a lathe, the hole diameter is Φ20mm±0.20, the inner and outer surfaces of the punched ingots are wrapped with a layer of 0.8mm iron sheet, the medium frequency furnace is heated at 900℃, kept warm for 2h, and extruded into 45mm×8mm tube blanks on a 2500t horizontal extruder;

[0060] S42, blank processing: the outer surface of the blank is peeled, 0.20mm on one side, and the tangible loss is 1.80%; then the inner surface of the blank is processed, boring 0.20mm on one side, and the tangible loss is 1.80%;

[0061] S43, intermediate rolling: rolling through the ring hole type LG45 to a specification of Ø27.00×4.40, controlling the surface reduction rate to 41%, the Q value to 0.9, the feed amount to 2 mm, and the rolling speed to 60 times / min;

[0062] S44, primary heat treatment: degreasing, pickling and vacuum annealing of the intermediate rolled tube material, controlling the annealing temperature to 700℃ for 180min, cooling with the furnace, and straightening after annealing;

[0063] S45, boring and rolling treatment: adjust the boring single side 0.20mm, tangible loss 3%, boring, rolling the bored tube and adjusting the rolling parameters, double feeding double rotary frame back and forth once feeding and rotating twice each, front feeding amount 1.3mm, rotation angle a42°, rear feeding 0.7mm, rotation angle a25°, at the same time adjust the finishing section length to 20cm, the feeding section accounts for 5% of the working section, and adjust the mandrel taper to 17.50mm;

[0064] S46, secondary heat treatment: degreasing, pickling and vacuum annealing of the bored and rolled pipes, controlling the annealing temperature to 600℃ for 180min, cooling with the furnace, and straightening after annealing.

[0065] S5. Quality inspection and flaw detection: After the alloy tube billet is subjected to ultrasonic flaw detection, when the amplitude of the defect reflection wave is below 30% of the ultrasonic alarm gate, the medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube is a qualified product.

[0066] Example 2

[0067] A medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube is composed of the following percentage elements: 2.75% Al; 2.95% V; 0.05% Fe; 0.04% Si; 0.002% C; 0.01% N; 0.005% H; 0.01% O; and the balance is Ti.

[0068] A method for preparing a medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube comprises the following preparation steps:

[0069] S1. Melting into ingots: Take 0A-grade sponge titanium with a particle size of 8 to 20 mm according to the formula, mix the alloy package with a mass fraction of 55% V and a mass fraction of 45% Al, and the aluminum beans with a purity of 99.90% evenly, press them into electrode blocks with a 6300t powder press, weld several electrode blocks into a bundle of rods by argon arc welding technology, melt them into ingots three times by vacuum consumable furnace arc method, and pass the uniform small-particle sponge titanium through the vacuum consumable furnace three times to make the ingot composition uniform, and then melt them into ingots;

[0070] S2, precision forging treatment: the surface of the ingot is peeled, sampled, flaw detected, and the cap is cut off to obtain an ingot with an outer diameter of ф680mm. The ingot is subjected to upsetting and squeegee treatment. After the ingot is placed in the first fire at a temperature of 11340℃ for 3.2 hours of heat preservation, the ingot is forged to 220 square meters, and the surface is ground until cracks cannot be seen by the naked eye, and then the material is evenly divided; after being kept in the second fire at 1075℃ for 2.3 hours, it is continued to be upset and drawn three times; after being kept in the third fire at 950℃ for 2.3 hours, it is upset and drawn three times again to obtain a ф290mm square billet;

[0071] S3, hot rolling treatment: the billet is placed in a heating furnace, heated to 980°C and kept at this temperature for 2.3 hours, and hot rolled by a 850 hot rolling mill and a continuous rolling mill group 1 to obtain a bar of ф130 mm;

[0072] S41, surface treatment: the bar material is subjected to surface peeling treatment, cut into 50cm ingots according to the process requirements, the ingots after cutting are punched on a lathe, the hole diameter is Φ20mm±0.20, the inner and outer surfaces of the punched ingots are wrapped with a layer of 0.8mm iron sheet, the medium frequency furnace is 925℃, the temperature is kept for 2.3h, and extruded into 45mm×8mm tube blanks on a 2500t horizontal extruder;

[0073] S42, blank processing: the outer surface of the blank is peeled, 0.20mm on one side, and the tangible loss is 1.80%~2.50%; then the inner surface of the blank is processed, boring 0.20mm on one side, and the tangible loss is 2.10%;

[0074] S43, intermediate rolling: rolling through the ring hole type LG45 to a specification of Ø27.00×4.40, controlling the surface reduction rate to 45%, the Q value to 0.9, the feed amount to 2 mm, and the rolling speed to 65 times / min;

[0075] S44, primary heat treatment: degreasing, pickling and vacuum annealing of the intermediate rolled tube material, controlling the annealing temperature to 725℃ for 190min, cooling with the furnace, and straightening after annealing;

[0076] S45, boring and rolling treatment: adjust the boring single side 0.20mm, tangible loss 3%, boring, rolling the bored tube and adjusting the rolling parameters, double feeding double rotary frame back and forth once feeding and rotating twice each, front feeding amount 1.3mm, rotation angle a42°, rear feeding 0.7mm, rotation angle a25°, at the same time adjust the finishing section length to 23cm, the feeding diameter section accounts for 5% of the working section, and adjust the mandrel taper to 17.50mm;

[0077] S46, secondary heat treatment: degreasing, pickling and vacuum annealing of the bored and rolled pipes, controlling the annealing temperature to 625℃ for 190min, cooling with the furnace, and straightening after annealing.

[0078] S5. Quality inspection and flaw detection: After the alloy tube billet is subjected to ultrasonic flaw detection, when the amplitude of the defect reflection wave is below 30% of the ultrasonic alarm gate, the medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube is a qualified product.

[0079] Example 3

[0080] A medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube is composed of the following percentage elements: 3.00% Al; 3.10% V; 0.08% Fe; 0.07% Si; 0.003% C; 0.01% N; 0.008% H; 0.08% O; and the balance is Ti.

[0081] A method for preparing a medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube comprises the following preparation steps:

[0082] S1. Melting into ingots: Take 0A-grade sponge titanium with a particle size of 8 to 20 mm according to the formula, mix the alloy package with a mass fraction of 55% V and a mass fraction of 45% Al, and the aluminum beans with a purity of 99.90% evenly, press them into electrode blocks with a 6300t powder press, weld several electrode blocks into a bundle of rods by argon arc welding technology, melt them into ingots three times by vacuum consumable furnace arc method, and pass the uniform small-particle sponge titanium through the vacuum consumable furnace three times to make the ingot composition uniform, and then melt them into ingots;

[0083] S2, precision forging treatment: the surface of the ingot is peeled, sampled, flaw detected, and the cap is cut off to obtain an ingot with an outer diameter of ф680mm. The ingot is subjected to upsetting and squeegee treatment. After the ingot is placed in the first fire at a temperature of 1150℃ for 3.5 hours of heat preservation, the ingot is forged to 220 square meters, and the surface is ground until cracks cannot be seen by the naked eye, and then the material is evenly divided; after being kept in the second fire at 1080℃ for 2.5 hours, it is continued to be upset and drawn three times; after being kept in the third fire at 960℃ for 2.5 hours, it is upset and drawn three times again to obtain a ф290mm square billet;

[0084] S3, hot rolling treatment: the billet is placed in a heating furnace, heated to 980°C and kept at this temperature for 2.5 hours, and hot rolled by a 850 hot rolling mill and a continuous rolling mill group 1 to obtain a bar of ф130 mm;

[0085] S41, surface treatment: the bar material is subjected to surface peeling treatment, cut into 50cm ingots according to the process requirements, the ingots after cutting are punched on a lathe, the hole diameter is Φ20mm±0.20, the inner and outer surfaces of the punched ingots are wrapped with a layer of 0.8mm iron sheet, the medium frequency furnace is heated to 950℃, kept warm for 2.5h, and extruded into 45mm×8mm tube blanks on a 2500t horizontal extruder;

[0086] S42, blank processing: the outer surface of the blank is peeled, 0.20mm on one side, and the tangible loss is 2.50%; then the inner surface of the blank is processed, boring 0.20mm on one side, and the tangible loss is 2.50%;

[0087] S43, intermediate rolling: rolling through the ring hole type LG45 to a specification of Ø27.00×4.40, controlling the area reduction rate to 52%, the Q value to 1.0, the feed amount to 3 mm, and the rolling speed to 70 times / min;

[0088] S44, primary heat treatment: degreasing, pickling and vacuum annealing of the intermediate rolled tube material, controlling the annealing temperature to 750℃ for 200min, cooling with the furnace, and straightening after annealing;

[0089] S45, boring and rolling treatment: adjust the boring single side 0.20mm, tangible loss 4%, boring, rolling the bored tube and adjusting the rolling parameters, double feeding double rotary frame back and forth once feeding and rotating twice each, front feeding amount 1.3mm, rotation angle a42°, rear feeding 0.7mm, rotation angle a25°, at the same time adjust the finishing section length to 25cm, the feeding section accounts for 6% of the working section, and adjust the mandrel taper to 12.40mm;

[0090] S46, secondary heat treatment: degreasing, pickling and vacuum annealing of the bored and rolled pipes, controlling the annealing temperature to 650℃ for 200min, cooling with the furnace, and straightening after annealing.

[0091] S5. Quality inspection and flaw detection: After the alloy tube billet is subjected to ultrasonic flaw detection, when the amplitude of the defect reflection wave is below 30% of the ultrasonic alarm gate, the medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube is a qualified product.

[0092] Example 4

[0093] A medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube is composed of the following percentage elements: 2.2% Al; 2.90% V; 0.03% Fe; 0.02% Si; 0.003% C; 0.01% N; 0.006% H; 0.05% O; the balance is Ti.

[0094] A method for preparing a medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube comprises the following preparation steps:

[0095] S1. Melting into ingots: Take 0A-grade sponge titanium with a particle size of 8 to 20 mm according to the formula, mix the alloy package with a mass fraction of 55% V and a mass fraction of 45% Al, and the aluminum beans with a purity of 99.90% evenly, press them into electrode blocks with a 6300t powder press, weld several electrode blocks into a bundle of rods by argon arc welding technology, melt them into ingots three times by vacuum consumable furnace arc method, and pass the uniform small-particle sponge titanium through the vacuum consumable furnace three times to make the ingot composition uniform, and then melt them into ingots;

[0096] S2, precision forging treatment: the surface of the ingot is peeled, sampled, flaw detected, and the cap is cut off to obtain an ingot with an outer diameter of ф680mm. The ingot is subjected to upsetting and squeegee treatment. After the ingot is placed in the first fire at a temperature of 11340℃ for 3.2 hours of heat preservation, the ingot is forged to 220 square meters, and the surface is ground until cracks cannot be seen by the naked eye, and then the material is evenly divided; after being kept in the second fire at 1075℃ for 2.3 hours, it is continued to be upset and drawn three times; after being kept in the third fire at 950℃ for 2.3 hours, it is upset and drawn three times again to obtain a ф290mm square billet;

[0097] S3, hot rolling treatment: the billet is placed in a heating furnace, heated to 980°C and kept at this temperature for 2.3 hours, and hot rolled by a 850 hot rolling mill and a continuous rolling mill group 1 to obtain a bar of ф130 mm;

[0098] S41, surface treatment: the bar material is subjected to surface peeling treatment, cut into 50cm ingots according to the process requirements, the ingots after cutting are punched on a lathe, the hole diameter is Φ20mm±0.20, the inner and outer surfaces of the punched ingots are wrapped with a layer of 0.8mm iron sheet, the medium frequency furnace is 925℃, the temperature is kept for 2.3h, and extruded into 45mm×8mm tube blanks on a 2500t horizontal extruder;

[0099] S42, blank processing: the outer surface of the blank is peeled, 0.20mm on one side, and the tangible loss is 1.80%~2.50%; then the inner surface of the blank is processed, boring 0.20mm on one side, and the tangible loss is 2.10%;

[0100] S43, intermediate rolling: rolling through the ring hole type LG45 to a specification of Ø27.00×4.40, controlling the surface reduction rate to 45%, the Q value to 0.9, the feed amount to 2 mm, and the rolling speed to 65 times / min;

[0101] S44, primary heat treatment: degreasing, pickling and vacuum annealing of the intermediate rolled tube material, controlling the annealing temperature to 725℃ for 190min, cooling with the furnace, and straightening after annealing;

[0102] S45, boring and rolling treatment: adjust the boring single side 0.20mm, tangible loss 3%, boring, rolling the bored tube and adjusting the rolling parameters, double feeding double rotary frame back and forth once feeding and rotating twice each, front feeding amount 1.3mm, rotation angle a42°, rear feeding 0.7mm, rotation angle a25°, at the same time adjust the finishing section length to 23cm, the feeding section accounts for 6% of the working section, and adjust the mandrel taper to 17.50mm;

[0103] S46, secondary heat treatment: degreasing, pickling and vacuum annealing of the bored and rolled pipes, controlling the annealing temperature to 625℃ for 190min, cooling with the furnace, and straightening after annealing.

[0104] S5. Quality inspection and flaw detection: After the alloy tube billet is subjected to ultrasonic flaw detection, when the amplitude of the defect reflection wave is below 30% of the ultrasonic alarm gate, the medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube is a qualified product.

[0105] Performance Testing

[0106] The medium-strength TA18 seamless titanium alloy small-diameter thick-walled tubes prepared in Examples 1-4 were subjected to performance tests:

[0107] The testing standard is based on GB / T228.1-2010 to test tensile strength, non-proportional extension strength and elongation;

[0108] The flattening value and inner diameter expansion value are tested according to GB / T246-2007 and GB / T242-2007.

[0109] The results are shown in Table 1 below:

[0110] Table 1 Performance test table

[0111]

[0112] From the above examples 1-4, combined with the test results in Table 1, it can be found that:

[0113] Combined with the test results of Examples 1-4, it is shown that the technical solution of this application not only improves the dimensional accuracy of the pipe but also enhances the bearing capacity of the material by optimizing the element composition in the medium-strength TA18 seamless titanium alloy small-diameter thick-walled pipe and combining boring and rolling treatment methods. The use of multi-pass rolling treatment significantly improves the plasticity and strength of the material through reasonable adjustment of rolling parameters. The combination of primary and secondary heat treatment further optimizes the microstructure of the pipe and ensures its stability under high temperature and high pressure conditions.

[0114] At the same time, the double-feed and double-rotation solution adopted in this application can effectively control the deformation of the material, making the rolling process more stable and reducing the loss and defects that may occur in the material during processing. And by further optimizing the Q value and processing deformation, microstructural defects caused by excessive deformation are avoided. The final medium-strength TA18 seamless titanium alloy tube has excellent mechanical properties and surface quality, the final finished product has uniform wall thickness, no cracks on the inner and outer surfaces of the tube, and the process performance flattening also meets the standards and customer requirements.

[0115] The present invention has been described in detail above in conjunction with specific implementations and exemplary examples, but these descriptions cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, a variety of equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the attached claims.

[0116] All publications, patent applications, patents and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings conventionally understood by those skilled in the art. In the event of a conflict, the definition in this specification shall prevail.

[0117] When this specification uses the prefix "well-known to those skilled in the art", "prior art" or similar terms to introduce materials, substances, methods, steps, devices or components, etc., the objects introduced by the prefix cover those commonly used in the art when this application is filed, but also include those that are not commonly used at present but will become recognized in the art as being suitable for similar purposes.

[0118] In the context of the present specification, any matters or items not mentioned are directly applicable to those known in the art without any changes except those explicitly stated.

Claims

1. A medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube, characterized in that: It is composed of the following percentage elements: Al 2.20%～3.00%； V 2.80%～3.10%； Fe 0.01%-0.08%; Si 0.01%-0.07%; C 0.001%-0.003%； N 0-0.01%； H 0.001%-0.008%； O 0.01%-0.08%； The remainder is Ti; The method for preparing a medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube is characterized in that it comprises the following preparation steps: S1. Melting and casting into ingots: taking raw materials according to the formula and die-casting them into electrode blocks, taking multiple electrode blocks and welding them into bundles, and melting them into ingots; S2, precision forging treatment: peeling, sampling, flaw detection, cutting off the cap of the ingot surface, upsetting and drawing, and collecting the square billet; S3, hot rolling treatment: placing the billet in a heating furnace, heating it up and hot rolling it, and collecting the bar material; S4, processing and forming: treating the surface of the bar material, collecting the tube blank, boring it and cold rolling it to prepare the alloy tube blank; S5. Quality inspection and flaw detection: After the alloy tube billet is subjected to ultrasonic flaw detection, the qualified product is the medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube; The processing and forming described in step S4 includes the following technical solutions: S41, surface treatment: the bar material is subjected to surface peeling treatment, cut into ingots according to the process requirements, the ingots after cutting are punched on a lathe, the inner and outer surfaces of the punched ingots are wrapped with a layer of 0.8mm iron sheet, the medium frequency furnace is 900-950℃, the temperature is kept for 2-2.5h, and extrusion is performed to prepare the tube blank; S42, blank processing: the outer surface of the blank is peeled, 0.20mm on one side, and the tangible loss is 1.80%~2.50%; then the inner surface of the blank is processed, boring 0.20mm on one side, and the tangible loss is 1.80%~2.50%; S43, intermediate rolling: multi-pass rolling processing according to specifications, adjusting rolling parameters: adjusting area reduction, ratio Q of plastic deformation to original thickness, feed amount and rolling speed; S44, primary heat treatment: degreasing, pickling and vacuum annealing of the intermediate rolled tube material, controlling the annealing temperature to 700-750℃ for 180-200min, cooling with the furnace, and straightening after annealing; S45, boring and rolling treatment: adjusting the single side of the boring hole to 0.20mm, with a tangible loss of 3% to 4%, boring is performed, and the bored tube blank is rolled and the rolling parameters are adjusted; S46, secondary heat treatment: degreasing, pickling and vacuum annealing of the bored and rolled pipes, controlling the annealing temperature to 600-650℃ for 180-200min, cooling with the furnace, and straightening after annealing; The rolling method used in the intermediate rolling step and the boring and rolling step is a double-rotation double-feed method, and the specific parameters are: The double-feed and double-rotation frame reciprocates once for feeding and twice for rotation, with a forward feed of 1.3mm and a rotation angle of a42°, and a rear feed of 0.7mm and a rotation angle of a25°.

2. A medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube according to claim 1, characterized in that: The medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube has an outer diameter of 19.05 mm, a wall thickness of 3.05 mm, and an inner and outer surface roughness Ra of no more than 1.0 μm.

3. A medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube according to claim 1, characterized in that: The upsetting process described in step S2 adopts the following technical scheme: After the ingot is placed in the first fire at a temperature of 1130-1150°C for 3-3.5 hours of heat preservation, it is forged to 220 square meters, and the surface is ground until the cracks are invisible to the naked eye, and then the material is evenly divided; After keeping the temperature at the second temperature of 1050-1080℃ for 2.0-2.5h, continue with the three-upsetting and three-drawing process; Then keep it at 940-960℃ for 2-2.5h, and then upset and draw it three times to 290 square.

4. The medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube according to claim 1, characterized in that: The hot rolling process described in step S3 comprises the following steps: The square billet is placed in a heating furnace, heated to 950-1000°C, kept warm for 2.0-2.5h, and hot-rolled in an 850 hot rolling mill and a continuous rolling mill to prepare a ф130 bar.

5. The medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube according to claim 1, characterized in that: The parameters of the intermediate rolling described in step S43 are: The area reduction ratio is 41% to 52%, the Q value is 0.9 to 1.0, the feed amount is 2 to 3 mm, and the rolling speed is 60 to 70 times / min.

6. The medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube according to claim 1, characterized in that: The parameters of the boring and rolling process and the heavy rolling process described in step S43 are: The area reduction rate is 48%-52%, the Q value is 0.9-1.0, the feed amount is 2-3mm, and the rolling speed is 80-100 times / min.

7. The medium-strength TA18 seamless titanium alloy small-diameter thick-walled tube according to claim 1, characterized in that: In the boring and rolling process described in step S45, the length of the finishing section is 20-25 cm, the diameter feeding section accounts for 5%-6% of the working section, and the mandrel taper is adjusted to 17.50-12.40 mm.

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