A method for preparing high-toughness titanium alloy pipe and the prepared pipe

Abstract

The application discloses a method for preparing high-strength and high-toughness titanium alloy pipes through precision forging and the prepared pipe. The pipe prepared through the method has small anisotropy and the strength of each direction reaches above 1100 MPa, the elongation rate reaches above 10%, the impact toughness reaches above 25 J / cm2, and the uniformity of the structure and the performance is good.

Description

Technical Field

[0001] This invention relates to a method for producing titanium alloy pipes, specifically to a method for preparing high-strength and high-toughness titanium alloy pipes and the pipes prepared by this method, belonging to the field of titanium alloy material processing technology. Background Technology

[0002] Titanium alloys, due to their low density, high specific strength, good corrosion resistance, low elastic modulus, low thermal conductivity, and high yield strength ratio, have been widely used in aerospace, shipbuilding, chemical, and oil pipeline industries. In the aerospace field, titanium alloys are one of the main structural materials for modern advanced aircraft, primarily used in landing gear components, fuselage skin, frames, beams, heat shields, and shells. The extensive use of advanced titanium alloys is a significant indicator of the advancement of next-generation aircraft, greatly improving structural weight reduction and safety reliability. In the petrochemical industry, titanium alloys have gradually become a key material choice for oil drill pipes and are increasingly being used extensively.

[0003] The mainstream manufacturing methods for titanium alloy tubes are rolling or extrusion, which can meet the manufacturing needs of most medium and low strength titanium alloy tubes. Publication number CN 119114672A discloses a method for manufacturing "high-strength and high-toughness titanium alloy tubes." This method involves obtaining an intermediate billet through multiple upsetting and drawing processes, followed by a single precision forging and drawing at Tβ-(10-20)℃ to prepare a tube blank, and finally extrusion molding to obtain the desired high-strength and high-toughness titanium alloy tube. Publication number CN119406964A discloses a processing method for manufacturing TA15 titanium alloy tubes using skew rolling piercing, with a processing temperature of Tβ-(10-25)℃, and multiple rolling processes to achieve high plasticity. For titanium alloys with strengths above 1000 MPa, the yield rate using rolling and extrusion methods is typically low, and the processing temperature is often above Tβ or 10-25℃ below Tβ. The resulting microstructure at these temperatures is mostly basket webbing or tri-phase, with lower plasticity and fatigue performance than bi-phase or equiaxed microstructures. To obtain titanium alloy tubes with high plasticity and high fatigue performance in bi-phase and equiaxed microstructures, it is necessary to use Tβ-(30-50)℃. However, within this temperature range, the deformation resistance is high, making it difficult to prepare these tubes by rolling and extrusion. Currently, there are few processing methods in China for preparing titanium alloy tubes using precision forging. CN202411992126.1 discloses a processing method for small-diameter titanium alloy tubes, which obtains high-strength small-diameter tubes with good microstructure uniformity through "skew rolling piercing, circumferential rolling, and precision forging." This method essentially controls the microstructure through rolling and improves the yield by finishing the surface through precision forging, resulting in significant anisotropy in the tube material. Summary of the Invention

[0004] To address the technical problems existing in the prior art, the purpose of this invention is to provide a method for preparing high-strength and high-toughness titanium alloy pipes by precision forging, so that the obtained pipes have low anisotropy and strength in all directions of more than 1100 MPa, elongation of more than 10%, impact toughness of more than 25 J / cm2, and good uniformity of microstructure and properties.

[0005] To achieve the above objectives, one of the technical solutions adopted by the present invention is as follows: A method for preparing a high-strength and high-toughness titanium alloy tube, characterized by the following main steps: Step 1): This step is completed in 1-2 heats. First, the ingot is upset and forged at 1100℃-1150℃. In this step, the upsetting deformation in each heat is controlled at 25%-40%. After forging, the ingot is air-cooled or the hot material is returned to the furnace. Step 2): This step is completed in 2-4 heats. The billet that has completed Step 1 is heated at a temperature of 50°C below the β transformation temperature to 100°C above the β transformation temperature for a period of time. After being taken out of the furnace, it is upset or drawn into a square billet. In this step, the upsetting deformation is controlled at 25%-40% and the drawing deformation is controlled at 30%-40% per heat. After forging, it is air-cooled. Step 3): This step is completed in 2-5 heats. The billet from Step 2 is heated and held at 80℃-120℃ below the β transformation temperature for a period of time. After being taken out of the furnace, it is upsetting and drawing forging to form a slab (the thickness direction of the slab is marked as S, the width direction as T, and the length direction as L). The upsetting deformation is controlled at 25%-40% and the drawing deformation is controlled at 30%-40% per heat in this step. After forging, it is air-cooled or hot material is returned to the furnace. Step 4): The slab completed in Step 3 is sawn along the T direction to obtain a square billet of equal diameter with equal length in the S direction and the T direction; Step 5): Heat the billet from Step 4 at 30℃-60℃ below the β transformation temperature and hold it for a period of time. After taking it out of the furnace, elongate and roll it into a round bar, octagonal or hexagonal bar billet along the L direction. Step 6): The prepared round bar, octagonal or hexagonal bar blank is machine-bored to obtain a tube blank; Step 7): This step is completed in 1-3 heats. The round bar, octagonal or hexagonal bar billet billet completed in step 6 is heated and held at 30℃-70℃ below the β transformation temperature for a period of time. After being taken out of the furnace, it is forged along the L phase to the finished pipe using a precision forging machine. The wall reduction per pass in this step shall not exceed 10mm, and the precision forging passes per heat shall not exceed 5 passes. After forging, it is air-cooled. Step 8): Perform conventional heat treatment and finishing on the finished pipe after precision forging to finally obtain the target finished product.

[0006] Furthermore, the heating and holding time in steps 1) and 2) above are calculated as [(0.6-0.9) × minimum cross-sectional dimension of billet] min, and the heating and holding time in step 3) is calculated as [(1.2-1.5) × minimum cross-sectional dimension of billet] min.

[0007] Furthermore, the reversing upsetting process in step 3) above consists of two upsetting and two drawing operations. Specifically: in the first upsetting operation, the roughing is performed along the L direction, followed by four passes along the T direction for elongation, at which point the T direction becomes the axial direction of the billet; in the second upsetting operation, the roughing is performed along the T direction, followed by six passes along the L direction for elongation, at which point the L direction becomes the axial direction of the billet. After the reversing upsetting is completed, elongation is performed along the T direction. The reversing upsetting process in step 3), with elongation along the T direction to obtain the slab, lays the foundation for the uniformity of the subsequent pipe material.

[0008] Furthermore, in step 6) above, the inner diameter of the tube blank should not be greater than 1 / 3 of the outer diameter of the round, octagonal or hexagonal bar blank when step (5) is completed, so as to ensure the uniformity of the deformation structure of the subsequent precision forging.

[0009] Furthermore, in step 7) above, the heating and holding time is (0.6-0.9)*(D1-D0) / 2 min, where D1 is the outer diameter of the tube blank in step 6) and D0 is the inner diameter of the tube blank; the diameter and wall reduction amount of each forging is 3-9 mm.

[0010] The second technical solution adopted in this invention is to provide a pipe prepared according to the above-mentioned method for preparing high-strength and high-toughness titanium alloy pipes.

[0011] This invention is applicable to the processing of high-strength and high-toughness medium-thickness titanium alloy tubes with a wall thickness of 20-50mm, an inner diameter of Φ60-Φ120mm, and a length of 2000-4000mm in the two-phase region. It can be applied to alloys such as TC18, Ti55531, TB17, and TC17.

[0012] The main innovations and principles of this invention are as follows: This invention primarily addresses the problem of high anisotropy. To solve this problem, this application controls anisotropy from two aspects: First, it reduces texture formation by employing low-temperature forging in the two-phase region. Specifically, during the tube blanking stage, forging is performed in the range of 80-120°C below the β transformation temperature. At this temperature, the α phase can effectively form a "pinning effect" in the β phase, hindering the movement of the β phase during plastic deformation, thereby inhibiting grain coarsening and microtexture formation. In the subsequent tube manufacturing process, forging is performed at 30-70°C below the β transformation temperature. By controlling parameters such as the amount of fine forging deformation and temperature, the coupling of α phase precipitation and dynamic recrystallization of the β phase can be achieved, enabling the control of α phase content and β phase size and morphology, resulting in a high-strength and tough bimodal structure or equiaxed structure. Second, the anisotropy is reduced by interchanging the T-axis and L-axis during the forming process and simultaneously controlling the forging ratio of the T-axis to the L-axis. In the tube blank forming stage, after axial upsetting and side upsetting, a slab blank with a greater deformation in the T direction than in the L direction is prepared by drawing along the T direction. This ensures that the deformation of the blank along the T direction is greater than that in the L direction. During precision forging, the blank undergoes the same amount of deformation along the L direction as in the T direction, thus achieving equivalent deformation in the L and T directions. This ensures that the deformation of the tube material remains consistent in all directions, effectively improving the anisotropy problem. The key to achieving the above objective lies in the innovative approach of this invention, which proposes to first forge a slab blank along the T direction and then saw it into a square blank of equal diameter along the T direction, thereby changing the deformation direction. Compared to the traditional method of preparing tube blanks by drawing along only one direction, this invention is feasible and innovative.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. Due to their high strength and high toughness, high-strength titanium alloys are prone to overheating and have a narrow processing window, making it difficult to obtain a two-phase microstructure through rolling or other methods. Rolling and extrusion methods typically have low yields and often require processing temperatures above Tβ or 10-25°C below Tβ. The microstructures obtained at these temperatures are mostly basket webbing or tri-phase structures, which have lower strength, plasticity, and fatigue properties than bi-phase or equiaxed structures. Extrusion and rolling are difficult to complete at lower temperatures. The processing method in this invention allows for forging at temperatures 30-70°C below Tβ. By controlling parameters such as precision forging deformation and temperature, the content and morphology of the primary α-phase can be adjusted, whereas it is difficult to achieve microstructure control in rolled or extruded tubing. 2. In most existing technologies, the billet is directly drawn along the axial direction to form a bar, and then rolled into a tube by boring or piercing. However, in this invention, after reverse upsetting, the billet is first drawn and forged to form a slab to ensure sufficient deformation in the T direction. Then, it is sawn to obtain a square billet of equal diameter with equal length in the S and T directions, drawn and rolled to form a bar, and then precision forged and drawn along the L direction to ensure that the deformation in the L and T directions is consistent, thereby effectively improving the anisotropy problem.

[0014] This invention achieves a wider processing temperature range compared to traditional rolling or extrusion processes through the synergistic effects of low-temperature forging and precision forging of the tube structure. This results in a better match between strength, plasticity, and toughness, with less anisotropy and better uniformity of the tube structure. Attached Figure Description

[0015] Figure 1 This is a high-magnification micrograph of the TC18 titanium alloy Φ160 / Φ70×L mm tube prepared in Example 1 of the present invention; Figure 2 This is a high-magnification micrograph of the Ti55531 titanium alloy Φ120 / Φ80×L mm tube prepared in Example 2 of the present invention; Figure 3 High-magnification photograph of TC18 alloy Φ140 / Φ70×2500 mm pipe prepared for comparative purposes. Detailed Implementation

[0016] The present invention will now be further described with reference to specific embodiments. Any parts not detailed below are based on existing techniques in the art.

[0017] Example 1 (Preparation method of TC18 titanium alloy Φ120 (outer diameter) / Φ70 (inner diameter) × L mm pipe) The TC18 titanium alloy ingot with a diameter of 680mm was selected, and the β transformation temperature of the ingot was 845℃.

[0018] Step 1: Heat the TC18 ingot to 1150℃ and hold for 480 minutes. After heating, perform one upsetting and one drawing forging to form a □670mm square billet with an upsetting deformation of 40%. After forging, air cool to obtain billet one. Step 2: After holding the billet at 810℃ for 510 minutes, perform one upsetting and one drawing forging to form a □670mm square billet. The upsetting deformation is 30-35% and the drawing deformation is 30%-40%. After forging, return the billet to the furnace and hold it at 930℃ for 360 minutes. Then, perform one upsetting and one drawing forging to form a □670mm square billet. After forging, air cool it. Repeat this step twice to obtain billet two. The size of billet two after forging is □670mm. Step 3: Hold billet two at 745℃ with a heating coefficient of 1.2-1.3 min / mm, and prepare a square billet of □670mm by one shaft upsetting and side upsetting and shaft upsetting. Finally, draw it in three heats along the T direction to obtain 230 (S) × 1400 (T) × L mm. Control the total forging ratio of T-direction drawing to be about 3.0. After each heat, air cooling or hot material remelting is used to obtain billet three. Step 4: Cut billet three along the T direction to a size similar to that of the S direction to obtain a square billet four with a diameter of □230×L mm; Step 5: Hold the square billet four at 810℃ for 180 minutes, then elongate and roll it along the L direction to form a round billet five with a diameter of Φ220×L mm; Step 6: Drill a Φ67mm inner hole along the shaft core using a boring machine to obtain billet 6; Step 7: After holding the billet at 810℃ for 60 minutes, remove it from the furnace for precision forging. During precision forging, select a mandrel with a diameter of Φ65 (Φ60) mm (the mandrel needs to have a certain taper to facilitate extraction, with one end having a diameter of Φ65 mm and the other end having a diameter of Φ60 mm, and a length of 4000 mm) and place it in the inner hole of the billet. Precision forging is carried out along the L direction, and it is forged in 4 passes to produce a finished Φ123 / Φ65×L (L is about 2700 mm) pipe. The reduction in pipe wall thickness in each pass is no more than 9 mm. After forging, the pipe is air-cooled. Step 8: After the finished pipe is subjected to conventional heat treatment according to the following process: 830℃ / 60min, furnace cooling to 740℃ / 3h, air cooling +600℃ / 4h, and air cooling, it is then precision machined to Φ120 / Φ70×Lmm pipe.

[0019] The mechanical properties and high-magnification microstructure of the TC18 titanium alloy Φ120 (outer diameter) / Φ70 (inner diameter) × L mm tube prepared in Example 1 are shown in Table 1 and 2, respectively. Figure 1 .

[0020] The TC18 titanium alloy tubing obtained through the above steps exhibits a uniform low-magnification microstructure and a two-phase processed microstructure under high-magnification. The tubing has a transverse and longitudinal strength ≥1130 MPa, elongation ≥10%, and impact toughness ≥30 J / cm². 2 .

[0021] Example 2 (Preparation method of Ti55531 alloy Φ160 (outer diameter) / Φ85 (inner diameter) × L mm pipe)

[0022] The Ti55531 titanium alloy ingot with a diameter of 780mm was selected, and the β transformation temperature of the ingot was 840℃.

[0023] Step 1: Heat the Ti55531 ingot to 1150℃ and hold for 480 minutes. After heating, perform 2 upsetting and 2 drawing forging to form a 570mm square billet. The upsetting deformation is 35-40%. After forging, air cool to obtain billet one. Step 2: After holding the billet at 800℃ for 480 minutes, perform one upsetting and one drawing forging to form a □570mm square billet. The upsetting deformation is 25-35%. After forging, return the billet to the furnace and hold it at 920℃ for 390 minutes. Then, perform one upsetting and one drawing forging to form a □570mm square billet. After forging, air cool the billet to obtain billet two. Step 3: After holding the second billet at 800℃ for 480 minutes, it is forged into a □570mm square billet by one upsetting and one drawing. The upsetting deformation is 25-35% and the drawing deformation is 30%-40%. After forging, it is returned to the furnace and held at 870℃ for 390 minutes. After taking it out of the furnace, it is forged into a □570mm square billet by one upsetting and one drawing. After forging, it is air-cooled to obtain the third billet. Step 4: Hold billet 3 at 760℃ with a heating coefficient of 1.3-1.5 min / mm, and prepare a square billet of □570mm by one shaft upsetting and side upsetting shaft upsetting. Finally, draw it in the T direction for 3 times to obtain 250 (S) × 1150 (T) × L mm. Control the total forging ratio of T direction drawing to about 2.0. After each forging, air cooling or hot material remelting is used to obtain billet 4. Step 5: Cut billet four along the T direction to a size similar to that of the S direction to obtain a square billet five with a diameter of □250×L mm; Step 6: Hold the square billet five at 790℃ for 180 minutes, then elongate and roll it along the L direction to form a round billet six with a diameter of Φ230×L mm; Step 7: Drill an 82mm inner hole along the shaft core using a boring machine to obtain tube blank 7; Step 8: After holding the tube blank seven at 795℃ for 120 minutes, remove it from the furnace for precision forging. During precision forging, select a mandrel with a diameter of Φ80 (Φ75) mm (one end of the mandrel has a diameter of Φ80 mm, the other end has a diameter of Φ75 mm, and the length is 4000 mm) and place it in the inner hole of the blank seven. The precision forging is carried out in 5 passes to form a blank eight with a diameter of Φ160 / Φ80×L mm. The reduction in tube wall thickness in each pass is no more than 9 mm. After forging, the tube is air-cooled. Step 9: After holding the billet at 795℃ for 60 minutes, remove it from the furnace for precision forging. During precision forging, a mandrel with a diameter of Φ80 (Φ75) mm is placed in the inner hole of the billet. The precision forging is carried out in 3 passes along the L direction to achieve a finished size of Φ123 / Φ80×Lmm. The reduction in pipe wall thickness in each pass is no more than 7mm. After forging, the pipe is air-cooled. Step 10: Air-cool the finished pipe at 800℃ for 60 minutes, then rough-machine it to Φ121 / Φ84×L mm. After rough machining, air-cool it at 600℃ for 8 hours, and finally finish it with conventional finishing to Φ160 / Φ85×L mm pipe.

[0024] The mechanical properties and high-magnification microstructure of the Ti55531 alloy Φ160 (outer diameter) / Φ85 (inner diameter) × L mm tube prepared in Example 2 are shown in Table 1 and Table 2, respectively. Figure 2 .

[0025] The Ti55531 titanium alloy tubing obtained through the above steps exhibits a uniform low-magnification microstructure and a two-phase processed microstructure under high-magnification. The tubing demonstrates a strength ≥1250 MPa, elongation ≥10%, and impact toughness ≥25 J / cm² in all directions. 2 .

[0026] Comparative Example (Preparation Method of TC18 Titanium Alloy Φ140 (Outer Diameter) / Φ70 (Inner Diameter) × L mm Pipe) The TC18 titanium alloy ingot with a diameter of 680mm was selected, and the β transformation temperature of the ingot was 845℃.

[0027] Step 1: Heat the TC18 ingot to 1150℃ and hold for 480 minutes. After heating, perform one upsetting and one drawing forging to form a □670mm square billet with an upsetting deformation of 40%. After forging, air cool to obtain billet one. Step 2: After holding the billet at 810℃ for 510 minutes, perform one upsetting and one drawing forging to form a □670mm square billet. The upsetting deformation is 30-35% and the drawing deformation is 30%-40%. After forging, return the billet to the furnace and hold it at 930℃ for 360 minutes. Then, perform one upsetting and one drawing forging to form a □670mm square billet. After forging, air cool it. Repeat this step twice to obtain billet two. The size of billet two after forging is □670mm. Step 3: Hold billet 2 at 810℃ for 510 minutes, and then prepare a square billet with a diameter of 670mm by two upsetting and two drawing processes. Finally, draw and roll the billet to a diameter of 230×L mm by five heating processes to obtain round billet 3. Step 4: Drill a Φ67mm inner hole along the shaft core using a boring machine to obtain billet four; Step 5: After holding the billet at 810℃ for 60 minutes, remove it from the furnace for precision forging. During precision forging, select a mandrel with a diameter of Φ65 (Φ60) mm (the mandrel needs to have a certain taper to facilitate extraction, with one end having a diameter of Φ65 mm and the other end having a diameter of Φ60 mm, and a length of 4000 mm) and place it in the inner hole of the billet. Precision forging is carried out along the L direction, and it is forged in 4 passes to produce a finished Φ143 / Φ65×L (L is about 2200 mm) pipe. The reduction in pipe wall thickness in each pass is no more than 10 mm. After forging, the pipe is air-cooled. Step 6: After the finished pipe is subjected to conventional heat treatment according to the following process: 830℃ / 60min, furnace cooling to 740℃ / 3h, air cooling +600℃ / 4h, and air cooling, it is then precision machined to Φ140 / Φ70×Lmm pipe.

[0028] The mechanical properties and high-magnification microstructure of the TC18 Φ140 (outer diameter) / Φ70 (inner diameter) × L mm pipes prepared in the comparative example are shown in Table 1 and Table 2, respectively. Figure 3 .

[0029] Table 1 Mechanical properties of bars from the examples 。

Claims

1. A method for preparing a high-strength and high-toughness titanium alloy pipe, characterized in that, This can be achieved through the following main steps: Step 1): This step is completed in 1-2 heats. First, heat the ingot to 1100℃-1150℃ and hold it for upsetting and drawing. In this step, the upsetting deformation in each heat is controlled to be 25%-40%. After forging, air cool or hot material is returned to the furnace. Step 2): This step is completed in 2-4 heats. The billet that has completed Step 1 is heated and held at a temperature of 50°C below the β transformation temperature to 100°C above the β transformation temperature. After being taken out of the furnace, it is upset or drawn and forged into a square billet. In this step, the upsetting deformation is controlled at 25%-40% and the drawing deformation is controlled at 30%-40% per heat. After forging, it is air-cooled. Step 3): This step is completed in 2-5 heats. The billet from Step 2 is heated and held at 80℃-120℃ below the β transformation temperature. After being taken out of the furnace, it is upsetting and forging to a slab. The thickness direction of the slab is marked as S, the width direction as T, and the length direction as L. The upsetting deformation is controlled at 25%-40% and the elongation deformation is controlled at 30%-40% per heat. After forging, it is air-cooled or hot material is returned to the furnace. Step 4): The slab completed in Step 3 is sawn along the T direction to obtain a square billet of equal diameter with equal length in the S direction and the T direction; Step 5): Heat and hold the square billet from Step 4 at 30℃-60℃ below the β transformation temperature. After being taken out of the furnace, elongate and roll it into a round bar, octagonal or hexagonal bar billet along the L direction. Step 6): The prepared round bar, octagonal or hexagonal bar blank is machine-bored to obtain a tube blank; Step 7): This step is completed in 1-3 heats. The round bar, octagonal or hexagonal bar billet billet completed in step 6 is heated and held at 30℃-70℃ below the β transformation temperature. After being taken out of the furnace, it is forged along the L direction to the finished pipe using a precision forging machine. The wall reduction per pass in this step shall not exceed 10mm, and the precision forging passes per heat shall not exceed 5 passes. After forging, it is air-cooled. Step 8): Perform conventional heat treatment and finishing on the finished pipe after precision forging to finally obtain the target finished product.

2. The method for preparing a high-strength and high-toughness titanium alloy tube according to claim 1, characterized in that, In steps 1) and 2) above, the heating and holding time is calculated as [(0.6-0.9) × minimum cross-sectional dimension of billet] min, and in step 3) the heating and holding time is calculated as [(1.2-1.5) × minimum cross-sectional dimension of billet] min.

3. The method for preparing a high-strength and high-toughness titanium alloy tube according to claim 2, characterized in that, The reversing upsetting and drawing in step 3) above is two upsetting and two drawing, specifically: during the first upsetting and drawing, the upsetting is carried out along the L direction, and then the lengthening is carried out by flipping along the T direction for 4 passes. At this time, the T direction becomes the axial direction of the billet; during the second upsetting and drawing, the upsetting is carried out along the T direction, and then the lengthening is carried out by flipping along the L direction for 6 passes. At this time, the L direction becomes the axial direction of the billet.

4. The method for preparing a high-strength and high-toughness titanium alloy tube according to claim 3, characterized in that, In step 6) above, the inner diameter of the tube blank should not be greater than 1 / 3 of the outer diameter of the round, octagonal or hexagonal bar blank when step (5) is completed.

5. The method for preparing a high-strength and high-toughness titanium alloy tube according to claim 3, characterized in that, In step 7) above, the heating and holding time is (0.6-0.9)*(D1-D0) / 2 min, where D1 is the outer diameter of the tube blank in step 6) and D0 is the inner diameter of the tube blank; the diameter and wall reduction of each forging is 3-9 mm.

6. The pipe prepared by the method for preparing a high-strength and high-toughness titanium alloy pipe according to claim 1, 2, 3, 4 or 5.

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