A method for preparing a carbon-niobium composite ultra-high-strength titanium alloy pipe

Abstract

The present application relates to the technical field of titanium alloy pipe manufacturing, and discloses a preparation method of carbon-niobium composite ultra-high-strength titanium alloy pipe, which comprises the following steps: preparing titanium alloy raw materials containing carbon and niobium elements, melting the titanium alloy raw materials to obtain titanium alloy ingots; performing multi-direction upsetting and drawing forging on the titanium alloy ingots to obtain forged rods, reprocessing the forged rods into titanium alloy round bars and performing annealing treatment; performing high-pressure torsion extrusion treatment on the annealed titanium alloy round bars; and sequentially performing annealing, machining drilling, cold rolling and pickling on the high-pressure torsion extruded bars to obtain titanium alloy pipes. The method can realize synchronous improvement of the strength and toughness of the titanium alloy pipes through the synergistic effect of carbon-niobium composite alloying, multi-direction upsetting and drawing forging and high-pressure torsion extrusion.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy pipe manufacturing technology, and in particular to a method for preparing carbon-niobium composite ultra-high strength titanium alloy pipes. Background Technology

[0002] Titanium alloys, with their low density, high specific strength, and excellent corrosion resistance, are widely used in high-end fields such as aerospace, medical, and chemical industries, with ultra-high-strength titanium alloy pipes being core and critical components. Currently, titanium alloy pipes are mainly produced using traditional smelting, forging, cold rolling, or piercing processes, and compositional strengthening often relies on the addition of single elements, resulting in many insurmountable technical shortcomings.

[0003] In terms of composition design, introducing carbon alone into titanium alloys can refine grains and improve strength through TiC phase pinning at grain boundaries, but it also significantly reduces the alloy's room temperature toughness and plasticity while significantly increasing its resistance to high-temperature deformation, which is detrimental to tube forming and processing. Adding niobium alone can enhance the alloy's strength while retaining toughness and plasticity, but its strengthening effect is limited and cannot meet the performance requirements of ultra-high strength applications. In terms of manufacturing processes, conventional forging and cold rolling processes have insufficient grain refinement capabilities, making it difficult to refine grains to the nanoscale. Uneven precipitation of the second phase and a lack of nucleation sites result in a poor balance between strength and toughness. High-pressure torsional extrusion, as a novel high-plasticity deformation process, can refine grains and promote dynamic recrystallization through triaxial compressive stress and severe shear deformation, effectively improving the material's strength and toughness. However, this process has not yet been rationally applied in the preparation of titanium alloy tubes, and the industry has not yet solved the core problem of the imbalance between strength and toughness in titanium alloy tubes.

[0004] Therefore, there is a need to improve the existing methods for preparing titanium alloy tubing. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method for preparing carbon-niobium composite ultra-high strength titanium alloy pipes. By introducing carbon and niobium elements into the titanium alloy and combining it with high-pressure torsional extrusion technology, ultra-high strength titanium alloy pipes are obtained.

[0006] To achieve the above objectives, embodiments of the present invention provide a method for preparing carbon-niobium composite ultra-high strength titanium alloy tubing, comprising: S1 prepares titanium alloy raw materials containing carbon and niobium, and melts the titanium alloy raw materials into titanium alloy ingots. S2 is used to forge titanium alloy ingots by multi-directional upsetting and drawing to obtain forged bars, which are then processed into titanium alloy round bars and annealed. S3 performs high-pressure torsion extrusion treatment on the annealed titanium alloy round bars; S4 processes high-pressure torsion extrusion of bars into titanium alloy tubes through annealing, machining, drilling, cold rolling, and pickling.

[0007] In some embodiments, in S1, the titanium alloy raw material contains 0.3-0.6% carbon, 1.5-2.0% niobium, 0.03-0.1% oxygen, ≤0.01% nitrogen, and ≤0.008% hydrogen by mass percentage.

[0008] In some implementations, in S1, a vacuum arc furnace is used for smelting, and the smelting is carried out no less than 3 times.

[0009] In some embodiments, in S2, the multi-directional upsetting forging includes at least two heat passes, wherein, First heating temperature T β - (15~20)℃, the billet is tilted 55-65° relative to the vertical direction and then upset once, with a deformation of 40-50%, followed by drawing, with a height-to-diameter ratio of 1.5-2.5; The second heating is brought to T. β - (60~80)℃, after axial upsetting of the billet, rotate it 90° and then radially elongate it, with a deformation of 30-50%, repeat 2-3 times to form a square billet.

[0010] In some embodiments, in S2, the diameter of the titanium alloy round bar is 20-60 mm and the length is 150-300 mm.

[0011] In some embodiments, in S2, the annealing temperature is 250–380°C below the β-phase transformation temperature of the titanium alloy, and the annealing time is 1–2 hours.

[0012] In some embodiments, in S3, before high-pressure torsional extrusion, a lubricant is uniformly applied to the surface of the extruded billet and the die. The extrusion pressure is 1 to 3 GPa, the extrusion temperature is 200 to 350°C, the extrusion speed is 0.6 to 1.0 mm / s, the rotation speed of the die extrusion cylinder is 10 to 20 rpm, and the number of extrusion revolutions is 6 to 10.

[0013] In some embodiments, in S3, after high-pressure torsional extrusion, the diameter of the titanium alloy round bar is 15-50 mm, and the extrusion ratio is 1.5-2.5.

[0014] In some embodiments, in S4, the annealing temperature is 400–500°C and the annealing time is 0.5–1 h.

[0015] In some implementations, the base composition of the titanium alloy is TC4, TC6, or TC11.

[0016] The present invention has at least the following beneficial technical effects: This invention achieves a simultaneous improvement in the strength and toughness of titanium alloy tubes through the synergistic effect of carbon-niobium composite alloying, multi-directional upsetting and forging, and high-pressure torsional extrusion. After the addition of carbon and niobium, carbon precipitates at grain boundaries to strengthen the alloy, while niobium, while increasing strength, avoids a significant decrease in toughness and plasticity, thus solving the problem of strength-toughness imbalance in single-element strengthening. Multi-directional upsetting and forging homogenizes the microstructure, breaks up coarse grains, and completes the initial refinement of the billet microstructure, improving the uniformity of subsequent deformation. High-pressure torsional extrusion refines the grains to the nanoscale through intense shear deformation, significantly increasing the nucleation sites for the second phase and inducing the precipitation of the second phase, further strengthening the alloy, ultimately obtaining titanium alloy tubes with ultra-high strength and a high-toughness-plasticity balance. 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 embodiments can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of an embodiment of the method for preparing carbon-niobium composite ultra-high strength titanium alloy tubing provided by the present invention; Figure 2 This is a schematic diagram of the torsion extrusion molding process provided by 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] The terms "comprising" and "having," and any variations thereof, used in the specification, claims, and accompanying drawings of this invention are intended to cover non-exclusive inclusion; the terms "first," "second," etc., used in the specification, claims, and accompanying drawings are used to distinguish different objects, not to describe a particular order. "A plurality of" means two or more, unless otherwise explicitly specified.

[0021] Furthermore, the reference to "embodiment" herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0022] like Figure 1The present invention illustrates a method for preparing a carbon-niobium composite ultra-high strength titanium alloy tube, comprising: S1 prepares titanium alloy raw materials containing carbon and niobium, and melts the titanium alloy raw materials into titanium alloy ingots. S2 is used to forge titanium alloy ingots by multi-directional upsetting and drawing to obtain forged bars, which are then processed into titanium alloy round bars and annealed. S3 performs high-pressure torsion extrusion treatment on the annealed titanium alloy round bars; S4 processes high-pressure torsion extrusion of bars into titanium alloy tubes through annealing, machining, drilling, cold rolling, and pickling.

[0023] Furthermore, in S1, the titanium alloy raw material contains 0.3–0.6% carbon, 1.5–2.0% niobium, 0.03–0.1% oxygen, ≤0.01% nitrogen, and ≤0.008% hydrogen by mass percentage. By precisely controlling the ratio of carbon and niobium, a stable TiC phase can be formed at the grain boundaries to achieve grain boundary pinning and refinement. At the same time, niobium synergistically regulates the alloy microstructure, improving strength while avoiding deterioration of toughness and plasticity. Strictly controlling the content of oxygen, nitrogen, and hydrogen impurities can reduce the alloy's brittleness tendency and improve the microstructure stability and mechanical property uniformity of the pipe.

[0024] Furthermore, in S1, a vacuum arc remelting furnace is used for melting, and the melting process is repeated at least three times. Multiple meltings in a vacuum arc remelting furnace effectively remove gaseous impurities and inclusions from the alloy, improve the uniformity of the ingot composition, prevent compositional segregation, and provide a uniformly structured billet for subsequent forging and plastic deformation, ensuring stable pipe performance.

[0025] Furthermore, in S2, the multi-directional upsetting forging includes at least two heating stages, wherein the first heating stage is heated to a temperature T. β - (15~20)℃, place the billet at an angle of 55-65° relative to the vertical direction for one oblique upsetting, with a deformation of 40-50%, followed by elongation, with a height-to-diameter ratio of 1.5-2.5; reheat to T in the second firing. β At - (60~80)℃, the billet is axially upset, then rotated 90° and radially drawn, with a deformation of 30-50%. This process is repeated 2-3 times to form a square billet. Multi-fire, multi-directional upsetting and drawing forging can completely break down the coarse grains in the cast state, achieve homogenization and preliminary refinement of the billet structure, eliminate anisotropy, and improve the plastic deformation capacity of the billet, laying the microstructure foundation for subsequent high-pressure torsional extrusion nanocrystal refinement.

[0026] Furthermore, in S2, the diameter of the titanium alloy round bar is 20–60 mm, and the length is 150–300 mm. Machining the forged bar into a round bar of suitable size can match the processing requirements of high-pressure torsional extrusion equipment, ensuring uniform stress and sufficient deformation during extrusion, and avoiding uneven deformation or cracking caused by improper billet dimensions.

[0027] Furthermore, in S2, the annealing temperature is 250–380°C below the β-phase transformation temperature of the titanium alloy, and the annealing time is 1–2 hours. Annealing below the β-phase transformation temperature can eliminate residual stress from forging and machining, soften the billet, improve plasticity, and retain a suitable microstructure, facilitating subsequent high-pressure torsional extrusion.

[0028] like Figure 2 As shown, the device consists of a fixed punch (upper part) and a rotating die extrusion cylinder (lower part): the billet is placed inside the punch extrusion cylinder, and the punch applies high axial pressure vertically downwards, causing the billet to enter the conical deformation zone. Because the outlet diameter of the extrusion cylinder is smaller than the inlet diameter, and the billet extrusion process is hindered in the conical zone, the material entering the conical zone first undergoes diameter expansion, filling the conical zone. The billet in this zone is under triaxial compressive stress. The die extrusion cylinder rotates uniformly around its axis, applying circumferential shear force to the billet. The axial pressure and circumferential shear force are coupled to form a high-pressure torsional extrusion composite deformation, causing the billet to undergo severe large plastic deformation, achieving nanoscale grain refinement and uniform precipitation of the second phase. By controlling the rotation speed and the number of rotations, the total amount of shear deformation can be precisely controlled to meet the refinement requirements of large plastic deformation of titanium alloys. In the diagram, the punch angle α (120°~145°) and the die angle β (100°~110°) are shown. The punch angle can evenly distribute the axial high pressure, avoiding stress concentration and cracking at the top of the billet, and ensuring that the billet is fully filled in the two conical regions. At the same time, it can stably constrain the axial position of the billet when the punch is fixed, preventing axial movement of the billet when the die rotates, and ensuring uniform deformation. The die angle β and the punch angle form a gradually changing composite deformation cavity. When the die rotates, the conical surface can drive the billet to produce continuous shear deformation across the entire cross section, avoiding shear dead angles. At the same time, it guides the billet to flow plastically in an orderly manner along the conical surface, precisely controlling the amount of extrusion deformation and ensuring grain refinement.

[0029] Furthermore, in S3, before high-pressure torsional extrusion, lubricant is uniformly applied to the surfaces of the extruded billet and the die. The extrusion pressure is 1–3 GPa, the extrusion temperature is 200–350℃, the extrusion speed is 0.6–1.0 mm / s, the die extrusion cylinder rotation speed is 10–20 rpm, and the number of extrusion revolutions is 6–10. Applying lubricant before extrusion reduces the frictional resistance between the billet and the die, preventing surface scratches. By using a fixed punch and a rotating die, the billet can withstand stable triaxial compressive stress and shear deformation, ensuring uniform grain refinement.

[0030] Furthermore, in S3, after high-pressure torsional extrusion, the diameter of the titanium alloy round bar is 15–50 mm, and the extrusion ratio is 1.5–2.5. By optimizing parameters such as extrusion pressure, temperature, speed, rotation speed, and number of revolutions, the amount and rate of shear deformation can be precisely controlled, the grains can be refined to the nanoscale, and the uniform precipitation of the second phase can be induced, thereby maximizing the improvement of the alloy's strength and toughness.

[0031] Furthermore, in S4, the annealing temperature is 400–500℃, and the annealing time is 0.5–1 hour. Low-temperature short-time annealing can eliminate torsional and processing residual stresses, and stabilize the microstructure and properties.

[0032] Furthermore, the basic composition of titanium alloys is TC4, TC6, or TC11.

[0033] Based on the above methods, the present invention adds carbon and niobium elements to the composition. Through grain boundary precipitation, these elements act as pinning agents, improving the alloy strength. Niobium, while maintaining strength, reduces the decrease in toughness and plasticity. Multi-directional upsetting is employed to homogenize the microstructure, break up large grains, and refine the billet microstructure. A high-pressure torsional extrusion process is used to refine the grains to the nanoscale through large shear deformation, providing sufficient nucleation sites for the precipitation of the second phase. Simultaneously, the large deformation induces the precipitation of the second phase, improving the alloy strength.

[0034] The present invention will be further explained and described below with reference to specific embodiments.

[0035] Example 1 Add 0.3% C and 2.0% Nb to the TC4 ingot, and control the gas composition to 0.03% O, 0.008% N, and 0.005% H.

[0036] Titanium alloy is melted three times in a vacuum arc remelting furnace to form titanium alloy ingots.

[0037] The forging billet is heated to 983℃, then tilted at a 55° angle to the vertical direction for oblique upsetting with a deformation of 40%, followed by elongation to a height-to-diameter ratio of 1.5. It is then heated a second time to 918℃, upset, rotated 90°, and then radially elongated with a deformation of 50%. This process is repeated twice to form a square billet.

[0038] The forged bar is processed into a round bar with a diameter of 20mm and a length of 300mm, and then annealed at 720℃ for 2 hours.

[0039] High-Pressure Torsional Extrusion (HPTE) Treatment: Lubricant is evenly applied to the surface of the extrusion blank and the die before extrusion. Extrusion pressure: 1 GPa, extrusion temperature: 200℃, extrusion speed: 1.0 mm / s, the punch remains stationary, the die extrusion cylinder rotates at 10 rpm for 10 revolutions, forming a small round bar with a diameter of 15 mm.

[0040] After being twisted and extruded, the round bars are annealed at 400℃ for 1 hour, and then machined, drilled, and pickled to form titanium alloy pipes.

[0041] Example 2 Add 0.6% C and 1.5% Nb to the TC4 ingot, and control the gas composition to 0.1% O, 0.01% N, and 0.007% H.

[0042] Titanium alloy is melted three times in a vacuum arc remelting furnace to form titanium alloy ingots.

[0043] The forging billet is heated to 978℃, then tilted at a 65° angle to the vertical direction for oblique upsetting with a deformation of 50%, followed by elongation to a height-to-diameter ratio of 2.5. It is then heated a second time to 940℃, upset, rotated 90°, and then radially elongated with a deformation of 30%. This process is repeated three times to form a square billet.

[0044] The forged bar is processed into a round bar with a diameter of 60 mm and a length of 150 mm, and then annealed at 720℃ for 2 hours.

[0045] High-Pressure Torsional Extrusion (HPTE) Treatment: Lubricant is evenly applied to the surface of the extrusion blank and the die before extrusion. Extrusion pressure: 3 GPa, extrusion temperature: 350℃, extrusion speed: 0.6 mm / s, the punch remains stationary, the die extrusion cylinder rotates at 20 rpm for 6 revolutions, forming a small round bar with a diameter of 50 mm.

[0046] After being twisted and extruded, the round bars are annealed at 500℃ for 0.5 hours, and then machined, drilled, and pickled to form titanium alloy pipes.

[0047] Comparative Example 1 The TC4 ingot was melted twice and then freely forged into a Φ220mm forging bar.

[0048] TC4 forged bars are punctured and extruded to form titanium alloy tube blanks.

[0049] Titanium alloy tube blanks are straightened, machined, pickled, and inspected to produce titanium alloy tube products.

[0050] The grain size of the titanium alloy tube was analyzed by metallographic method, and the tensile properties of the tube were measured by universal testing machine.

[0051] Table 1 Grain size and tensile properties of TC4 titanium alloy tubing

[0052] 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. The functions, steps, and / or actions of the methods according to the disclosed embodiments described herein do not need to be performed in any particular order. Furthermore, 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.

[0053] It should be understood that, as used herein, unless the context clearly supports an exception. It should also be understood that, as used herein, "and / or" means any and all possible combinations of one or more of the associated listed items.

[0054] The embodiment numbers disclosed in the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0055] 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 method for preparing a carbon-niobium composite ultra-high strength titanium alloy pipe, characterized in that, include: S1 prepares titanium alloy raw materials containing carbon and niobium, and melts the titanium alloy raw materials to make titanium alloy ingots; S2 is used to forge a titanium alloy ingot by multi-directional upsetting and drawing to obtain a forged bar, and the forged bar is further processed into a titanium alloy round bar and then annealed. S3 performs high-pressure torsion extrusion treatment on the annealed titanium alloy round bars; S4 processes high-pressure torsion extrusion of bars into titanium alloy tubes through annealing, machining, drilling, cold rolling, and pickling.

2. The method for preparing carbon-niobium composite ultra-high strength titanium alloy tubing according to claim 1, characterized in that, In S1, the titanium alloy raw material contains 0.3-0.6% carbon, 1.5-2.0% niobium, 0.03-0.1% oxygen, ≤0.01% nitrogen, and ≤0.008% hydrogen by mass percentage.

3. The method for preparing carbon-niobium composite ultra-high strength titanium alloy tubing according to claim 1, characterized in that, In S1, a vacuum arc furnace is used for smelting, and the smelting is carried out no less than 3 times.

4. The method for preparing carbon-niobium composite ultra-high strength titanium alloy tubing according to claim 1, characterized in that, In S2, multi-directional upsetting forging includes at least two heat treatments, wherein, First heating temperature T β - (15~20)℃, the billet is tilted 55-65° relative to the vertical direction and then upset once, with a deformation of 40-50%, followed by drawing, with a height-to-diameter ratio of 1.5-2.5; The second heating is brought to T. β - (60~80)℃, after axial upsetting of the billet, rotate it 90° and then radially elongate it, with a deformation of 30-50%, repeat 2-3 times to form a square billet.

5. The method for preparing carbon-niobium composite ultra-high strength titanium alloy tubing according to claim 1, characterized in that, In S2, the diameter of the titanium alloy round bar is 20-60 mm and the length is 150-300 mm.

6. The method for preparing carbon-niobium composite ultra-high strength titanium alloy tubing according to claim 1, characterized in that, In S2, the annealing temperature is 250–380°C below the β-phase transformation temperature of the titanium alloy, and the annealing time is 1–2 hours.

7. The method for preparing carbon-niobium composite ultra-high strength titanium alloy tubing according to claim 1, characterized in that, In S3, before high-pressure torsional extrusion, lubricant is evenly applied to the surface of the extruded billet and the die. The extrusion pressure is 1-3 GPa, the extrusion temperature is 200-350℃, the extrusion speed is 0.6-1.0 mm / s, the rotation speed of the die extrusion cylinder is 10-20 rpm, and the number of extrusion revolutions is 6-10 revolutions.

8. The method for preparing carbon-niobium composite ultra-high strength titanium alloy tubing according to claim 1, characterized in that, In S3, after high-pressure torsional extrusion, the diameter of the titanium alloy round bar is 15-50 mm, and the extrusion ratio is 1.5-2.

5.

9. The method for preparing carbon-niobium composite ultra-high strength titanium alloy tubing according to claim 1, characterized in that, In S4, the annealing temperature is 400–500℃ and the annealing time is 0.5–1h.

10. The method for preparing carbon-niobium composite ultra-high strength titanium alloy tubing according to claim 1, characterized in that, The basic composition of the titanium alloy raw material is TC4, TC6 or TC11.

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