Process method for preparing TC11 high-strength titanium alloy seamless pipe

Abstract

The invention belongs to the technical field of titanium alloy processing, and particularly relates to a process method for preparing a TC11 high-strength titanium alloy seamless pipe, which comprises the following steps of: preparing a TC11 titanium alloy cast ingot by adopting a vacuum consumable electric arc melting process; preparing a TC11 titanium alloy thick-wall pipe blank from the TC11 titanium alloy cast ingot through a vacuum casting method; the TC11 titanium alloy thick-wall pipe blank is subjected to high-temperature solid solution heat treatment, and then a TC11 titanium alloy thin-wall pipe blank close to the target size is prepared through a final forming means; and high-temperature solid solution and low-temperature aging dual heat treatment is conducted on the TC11 titanium alloy thin-wall pipe blank, then aftertreatment is conducted, and preparation of the TC11 high-strength titanium alloy seamless pipe with the target size is completed. The TC11 high-strength titanium alloy seamless pipe is prepared through a low cost and a short process, and the use requirements in the fields of aerospace, weapons and ships, petroleum and natural gas, chemical power, ocean engineering and the like can be met.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy processing, and specifically relates to a process for preparing a TC11 high-strength titanium alloy seamless pipe. Background Art

[0002] High-strength titanium alloy pipes help to achieve structural optimization and weight reduction, adapt to complex working conditions, improve the pressure resistance, corrosion resistance and thermal conductivity of components, and save material costs and improve manufacturing flexibility. These advantages make high-strength titanium alloy pipes have broad application prospects in aerospace, weapons and ships, oil and gas, chemical equipment and heat exchange systems. Among them, TC11 titanium alloy is a (α+β) two-phase titanium alloy with excellent comprehensive performance. Its products can obtain good strength and plasticity matching through thermal deformation and heat treatment in the (α+β) two-phase region. It not only has excellent thermal strength performance below 500°C, but also has high room temperature strength and elongation after fracture. It has become one of the preferred materials for the preparation of high-strength titanium alloy pipes.

[0003] TC11 high-strength titanium alloy has high processing resistance, high yield strength ratio and severe springback, which makes its pipe processing extremely difficult. The current methods for preparing titanium alloy pipes mainly include coil welding process, forged rod perforation hot rolling process and forged rod drilling and extrusion process. The preparation of high-strength titanium alloy pipes by coil welding usually has high requirements for equipment, and it is difficult to control the size of the pipe. The longitudinal welds throughout the pipe are weak areas of the pipe performance, which will greatly reduce the compressive performance of the pipe and seriously weaken the service life of the pipe under complex working conditions. When using the forged rod perforation hot rolling process, the titanium alloy ingot needs to be fired multiple times to prepare the rod. The initial process flow is cumbersome and complicated, and the perforation adopts the oblique rolling perforation process. This process has been widely used only in pure titanium tubes with low strength and good plasticity. For high-strength titanium alloys, oblique rolling perforation with severe deformation characteristics usually leads to severe folding, tearing and other phenomena in the tube preparation process, and the drastic temperature rise during the perforation process will further deteriorate the organizational state of the tube, reduce its processing performance, and bring great difficulties to the subsequent final forming preparation of the tube. The forged rod drilling and extrusion process also requires a complex rod preparation process, and drilling to prepare the tube will greatly reduce the material utilization rate. Usually, the full process yield rate of drilling and extrusion pipe making is less than 15%, resulting in extremely high processing costs and difficult to be accepted by the industry. Therefore, how to prepare TC11 high-strength titanium alloy tubes by simple methods is a technical problem that needs to be solved. Summary of the invention

[0004] In view of the shortcomings of the existing TC11 high-strength titanium alloy pipe preparation technology, the present invention provides a process for preparing TC11 high-strength titanium alloy seamless pipe.

[0005] The present invention is specifically implemented through the following technical solutions.

[0006] The present invention provides a process for preparing seamless tubes of TC11 high-strength titanium alloy, comprising the following steps: Prepare a TC11 titanium alloy ingot by vacuum consumable arc melting process.

[0007] Prepare a thick-walled tube blank of TC11 titanium alloy from the said TC11 titanium alloy ingot by vacuum casting method.

[0008] Perform high-temperature solution heat treatment on the thick-walled tube blank of TC11 titanium alloy, and then prepare a thin-walled tube blank of TC11 titanium alloy with near-target dimensions by final forming means.

[0009] Perform double heat treatment of high-temperature solution and low-temperature aging on the thin-walled tube blank of TC11 titanium alloy, and then perform post-treatment to remove defects such as exposed surface and cracks on the inner and outer surfaces of the tube, thus completing the preparation of seamless tubes of TC11 high-strength titanium alloy with target dimensions.

[0010] Preferably, the number of melting times of the vacuum consumable arc melting is 1 to 3 times. After the final ingot melting is completed, the outer surface of the ingot is peeled and cleaned to remove oxide scale, inclusions, etc. on the ingot surface.

[0011] Preferably, the outer diameter range of the thick-walled tube blank is 80 mm to 600 mm, and the wall thickness range is 10 mm to 100 mm. After the thick-walled tube blank casting is completed, shot peening treatment is performed on the tube blank.

[0012] Preferably, the high-temperature solution heat treatment temperature range of the thick-walled tube blank of TC11 titanium alloy is 950 °C to 1000 °C, and the holding time is 0.5δ + 50 min, where δ is the wall thickness (mm) of the tube blank. The tube blank is air-cooled or forced-air cooled to room temperature and pickling treatment is performed.

[0013] Preferably, the preparation of the thin-walled tube blank of TC11 titanium alloy with near-target dimensions can adopt single final forming means such as radial forging, extrusion or hot rolling, or a combination of the above several final forming means. The deformation temperature of each final forming means is T β ±50 °C, where T β is the phase transformation point of TC11 titanium alloy. After the preparation of the thin-walled tube blank of TC11 titanium alloy with near-target dimensions is completed, the inner diameter of the tube blank is 1 mm to 20 mm smaller than the inner diameter of the target dimensions, and the outer diameter of the tube blank is 1 mm to 20 mm larger than the outer diameter of the target dimensions.

[0014] Preferably, the double heat treatment system of high-temperature solution and low-temperature aging of the thin-walled tube blank of TC11 titanium alloy is: holding at 900 °C to 960 °C, air-cooled or forced-air cooled to room temperature, and then holding at 500 °C to 580 °C for 6 h to 10 h, air-cooled to room temperature, and pickling treatment is performed.

[0015] The tube billet is vertically hoisted in the furnace cavity or placed vertically on the furnace bottom plate during the insulation process in each stage (high temperature solution heat treatment and double heat treatment), and the length of the steel rod or steel pipe supporting the tube billet is not less than the length of the tube billet, and the outer diameter of the steel rod or steel pipe is 1mm~15mm smaller than the inner diameter of the TC11 titanium alloy tube billet. The heat treatment equipment is an electric heating furnace. Post-treatment includes machining, sandblasting and polishing.

[0016] By using the process provided by the present invention, a high-strength TC11 titanium alloy seamless pipe with a room temperature tensile strength greater than or equal to 1030 MPa, a post-fracture elongation greater than or equal to 10%, a pipe outer diameter range of 50-400 mm, and a pipe wall thickness range of 5-20 mm can be obtained.

[0017] Compared with the prior art, the present invention has the following beneficial effects: Compared with the pipe making processes such as forged rod perforation hot rolling and forged rod drilling extrusion, the present invention uses a near-net-shape vacuum casting process to make thick-walled tube blanks, and there is no need to cut off the riser part of the vacuum arc consumable ingot, which greatly improves the yield rate of the tube, significantly reduces the difficulty and manufacturing cost of preparing high-strength titanium alloy thick-walled tube blanks, and significantly optimizes the blank making process of thick-walled tubes. Afterwards, the thick-walled tube blanks are subjected to high-temperature solid solution heat treatment. The high-temperature solid solution heat treatment eliminates defects such as segregation to a certain extent, and further improves the composition uniformity and machinability of the material. TC11 titanium alloy thin-walled tube blanks of near-target size are prepared by final forming means. The subsequent final forming process of the thin-walled tube effectively breaks the coarse grain structure of the thick-walled tube blanks. Combined with the dual heat treatment of high-temperature solid solution and low-temperature aging, the post-processing removes defects such as light and cracks on the inner and outer surfaces of the tube, and obtains a high-strength TC11 titanium alloy seamless tube with excellent strength and plasticity matching. Compared with the traditional coiling and welding process, the seamless pipe prepared by the present invention eliminates the influence of the longitudinal weld on the pressure bearing performance of the pipe, and improves the service and use performance of the pipe.

[0018] In summary, the TC11 high-strength titanium alloy seamless pipe prepared by the present invention through a low-cost and short process can meet the use requirements of high-strength titanium alloy pipes in the fields of aerospace, weapons and ships, oil and gas, chemical power and marine engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the preparation flow chart of TC11 high-strength titanium alloy seamless pipe.

[0020] Figure 2 This is a test report on the mechanical properties of the TC11 high-strength titanium alloy seamless tube prepared in Example 3. DETAILED DESCRIPTION

[0021] In order to enable those skilled in the art to better understand the technical solution of the present invention and implement it, the present invention is further described below in conjunction with specific embodiments and drawings, but the embodiments are not intended to limit the present invention. The experimental methods and detection methods described in the following embodiments are conventional methods unless otherwise specified; the reagents and materials described are all commercially available unless otherwise specified.

[0022] The present invention provides a process for preparing TC11 high-strength titanium alloy seamless pipe, such as Figure 1 As shown, the following steps are included: TC11 titanium alloy ingots were prepared by vacuum consumable arc melting process.

[0023] TC11 titanium alloy thick-walled tube blanks were prepared from TC11 titanium alloy ingots by vacuum casting method.

[0024] The TC11 titanium alloy thick-walled tube was subjected to high-temperature solution heat treatment.

[0025] Then, the TC11 titanium alloy thin-walled tube billet with near-target size is prepared by final forming means.

[0026] The TC11 titanium alloy thin-walled tube was subjected to double heat treatment of high temperature solid solution and low temperature aging.

[0027] After that, post-processing is carried out to complete the preparation of TC11 high-strength titanium alloy seamless pipes of target size.

[0028] It should be noted that, compared with the traditional coil welding process, the seamless pipe prepared by the present invention eliminates the influence of the longitudinal weld on the pressure-bearing performance of the pipe, and improves the service and use performance of the pipe; compared with the pipe making processes such as forged rod perforation hot rolling and forged rod drilling and extrusion, the present invention uses a near-net-shape vacuum casting process to make thick-walled pipe blanks, and at the same time, there is no need to cut off the riser part of the vacuum arc consumable ingot, which greatly improves the yield rate of the pipe, significantly reduces the preparation difficulty and manufacturing cost of high-strength titanium alloy thick-walled pipe blanks, and significantly optimizes the blank making process of thick-walled pipes.

[0029] The high-temperature solution heat treatment of thick-walled tube billets eliminates defects such as segregation to a certain extent, further improving the composition uniformity and machinability of the material. The subsequent final forming process of thin-walled tubes effectively breaks up the coarse grain structure of thick-walled tube billets, and combined with the dual heat treatment of high-temperature solution and low-temperature aging, a high-strength TC11 titanium alloy seamless tube with excellent strength-plasticity matching is obtained.

[0030] Final forming means include radial forging, extrusion or hot rolling. Post-processing includes machining, sandblasting, polishing and other treatments to remove defects such as light and cracks on the inner and outer surfaces of the pipe, and complete the preparation of TC11 high-strength titanium alloy seamless pipes of target size.

[0031] The content of the present invention will be specifically described below through the following examples and comparative examples.

[0032] Example 1: Preparation of high-strength TC11 seamless pipe with an outer diameter of 160 mm and an inner diameter of 150 mm Process flow: ① Prepare a TC11 titanium alloy ingot with a diameter of 480 mm by double vacuum consumable arc melting. Prepare the electrode according to the requirements of GB / T 3620.1-2007 standard. For the first melting of the ingot, a crucible with a diameter of 380 mm is selected. The vacuum degree before melting is ≤ 3.0 Pa, the air leakage rate before melting is ≤ 0.9 Pa / min, the starting arc current is 2.0 kA, the stable arc current in the stable stage is 8.0 A, the stable arc stirring commutation frequency in the stable stage is 20 seconds / time, the maximum allowable vacuum degree is 2.0 Pa, the melting current in the stable stage is 8.0 kA, the arc voltage in the stable stage is 28.0 V. After melting is completed, after cooling for 30 minutes, close the vacuum pump and cool with argon. The argon pressure in the furnace is 2000 Pa. After reaching the cooling time, take out the furnace (the cooling time in the furnace is 180 min); Use the ingot prepared by the first melting as the electrode for the second melting of the ingot. Select a crucible with a diameter of 480 mm. The vacuum degree before melting is ≤ 1.0 Pa, the air leakage rate before melting is ≤ 0.9 Pa / min, the starting arc current is 2.0 kA, the stable arc current in the stable stage is 10.0 A, the stable arc stirring commutation frequency in the stable stage is 20 seconds / time, the maximum allowable vacuum degree is 2.0 Pa, the melting current in the stable stage is 10.0 kA, the arc voltage in the stable stage is 28.0 V. When the remaining electrode is 100 kg, start feeding to the end of melting. After cooling for 30 minutes, close the vacuum pump and cool with argon. The argon pressure in the furnace is 2000 Pa. After reaching the cooling time, take out the furnace (the cooling time in the furnace ≥ 270 min). Then, peel and clean the ingot.

[0033] ② Vacuum casting of the ingot to prepare a TC11 titanium alloy thick-walled tube blank with an outer diameter of 220 mm and an inner diameter of 170 mm. The vacuum degree in the furnace in the melting stable stage is ≤ 3.0 Pa, the air leakage rate is ≤ 0.8 Pa / min, the melting current is 16.0 kA, the melting voltage is 45.0 V. 30 minutes after the casting is completed, cool the tube wall with argon by the vacuum pump. The argon pressure in the furnace is 2000 Pa. After reaching the cooling time, take out the tube blank from the furnace (the cooling time in the furnace ≥ 90 min). Then, cut off the gate of the tube blank and shot peening. Recycle the gate and the solidified shell part.

[0034] ③ High-temperature solution heat treatment of the thick-walled tube blank. The solution temperature is 1000 °C, and the holding time is 62.5 min. After solution treatment, air cooling is carried out. During the holding process, an equal-height steel bar with a diameter of 165 mm is used to support the inside of the tube blank. After heat treatment, the tube blank is pickled.

[0035] ④ One-pass radial forging of the thick-walled tube blank. The forging temperature is 980 °C, the mandrel diameter is 145 mm, and the size of the thin-walled tube blank after forging is an outer diameter of 168 mm and an inner diameter of 145 mm.

[0036] ⑤ Double heat treatments of high-temperature solution and low-temperature aging for the thin-walled tube blank, with the solution temperature of 960°C, holding time of 56 min, air cooling, aging temperature of 530°C, holding time of 6 h, air cooling. During the solution and aging processes, a steel bar with a height of 142 mm and equal diameter is used to support the inside of the tube blank. After heat treatment, the tube blank is pickled.

[0037] ⑥ Machine the TC11 titanium alloy thin-walled tube blank to the target dimensions of an outer diameter of 160 mm and an inner diameter of 150 mm.

[0038] Example 2: Preparation of high-strength TC11 seamless tubes with an outer diameter of 160 mm and an inner diameter of 150 mm Process flow: ① Prepare a TC11 titanium alloy ingot with a diameter of 480 mm by twice vacuum consumable arc melting. Prepare the electrode according to the requirements of GB / T 3620.1-2007 standard. For the first melting of the ingot, a crucible with a diameter of 380 mm is selected. Before melting, the vacuum degree ≤ 3.0 Pa, the leakage rate ≤ 0.9 Pa / min, the starting arc current is 5.0 kA, the stable arc current in the stable stage is 8.0 A, the stable arc stirring commutation frequency in the stable stage is 20 seconds / time, the maximum allowable vacuum degree is 2.0 Pa, the melting current in the stable stage is 6.0 kA, the arc voltage in the stable stage is 32.0 V. After melting is completed, after cooling for 30 minutes, close the vacuum pump and cool with argon. The argon pressure in the furnace is 1000 Pa. After reaching the cooling time, take out the furnace (the cooling time in the furnace is 180 min); use the ingot prepared by the first melting as the electrode for the second melting of the ingot. For the second melting of the ingot, a crucible with a diameter of 480 mm is selected. Before melting, the vacuum degree ≤ 1.0 Pa, the leakage rate ≤ 0.9 Pa / min, the starting arc current is 5.0 kA, the stable arc current in the stable stage is 10.0 A, the stable arc stirring commutation frequency in the stable stage is 20 seconds / time, the maximum allowable vacuum degree is 2.0 Pa, the melting current in the stable stage is 12.0 kA, the arc voltage in the stable stage is 34.0 V. When the remaining electrode is 120 kg, start feeding to the end of melting. After cooling for 30 minutes, close the vacuum pump and cool with argon. The argon pressure in the furnace is 3000 Pa. After reaching the cooling time, take out the furnace (the cooling time in the furnace ≥ 270 min). Then, peel and clean the ingot.

[0039] ② Vacuum casting of the ingot to prepare a TC11 titanium alloy thick-walled tube blank with an outer diameter of 220 mm and an inner diameter of 170 mm. During the stable stage of melting, the vacuum degree in the furnace ≤ 3.0 Pa, the leakage rate ≤ 0.8 Pa / min, the melting current is 24.0 kA, the melting voltage is 35.0 V. 30 minutes after the casting is completed, cool the tube wall with argon by the vacuum pump. The argon pressure in the furnace is 3000 Pa. After reaching the cooling time, take out the tube blank from the furnace (the cooling time in the furnace ≥ 90 min). Then, cut off the gate of the tube blank and shot peening. Recover the gate and the solidified shell part.

[0040] ③ Solution heat treatment of thick-walled tube blanks at high temperature, with a solution temperature of 1000 °C, holding for 62.5 min, followed by air cooling after solution. During the holding process, a steel bar of equal height with a diameter of 165 mm is used to support the inside of the tube blank. After heat treatment, the tube blank is pickled.

[0041] ④ Radial forging of thick-walled tube blanks in one heat, with a forging temperature of 980 °C and a mandrel diameter of 145 mm. The dimensions of the thin-walled tube blank after forging are an outer diameter of 168 mm and an inner diameter of 145 mm.

[0042] ⑤ Solution heat treatment and low-temperature aging heat treatment of thin-walled tube blanks. The solution temperature is 960 °C, the holding time is 56 min, followed by air cooling. The aging temperature is 530 °C, the holding time is 6 h, followed by air cooling. During the solution and aging processes, a steel bar of equal height with a diameter of 142 mm is used to support the inside of the tube blank. After heat treatment, the tube blank is pickled.

[0043] ⑥ Machining the TC11 titanium alloy thin-walled tube blank to the target dimensions of an outer diameter of 160 mm and an inner diameter of 150 mm.

[0044] Example 3: Preparation of high-strength TC11 seamless tubes with an outer diameter of 204 mm and an inner diameter of 168 mm Process flow: ① The TC11 titanium alloy ingot with a diameter of 560 mm was prepared by triple vacuum consumable arc melting. The electrodes were prepared according to the requirements of GB / T 3620.1-2007 standard. For the first melting of the ingot, a crucible with a diameter of 380 mm was selected. Before melting, the vacuum degree ≤ 3.0 Pa, the air leakage rate ≤ 0.9 Pa / min, the starting arc current 2.0 kA, the stable arc current in the stable stage 3.0 A, the stable arc stirring commutation frequency in the stable stage 20 s / time, the maximum allowable vacuum degree 2.0 Pa, the melting current in the stable stage 8.0 kA, the arc voltage in the stable stage 32.0 V. After melting, after cooling for 30 minutes, the vacuum pump was closed and argon was filled for cooling. The argon pressure in the furnace was 1000 Pa. After reaching the cooling time, the ingot was taken out of the furnace (the cooling time in the furnace was 180 min); the ingot prepared by the first melting was used as the electrode for the second melting of the ingot. For the second melting of the ingot, a crucible with a diameter of 480 mm was selected. Before melting, the vacuum degree ≤ 1.0 Pa, the air leakage rate ≤ 0.9 Pa / min, the starting arc current 5.0 kA, the stable arc current in the stable stage 10.0 A, the stable arc stirring commutation frequency in the stable stage 20 s / time, the maximum allowable vacuum degree 2.0 Pa, the melting current in the stable stage 12.0 kA, the arc voltage in the stable stage 34.0 V. After melting, after cooling for 30 minutes, the vacuum pump was closed and argon was filled for cooling. The argon pressure in the furnace was 3000 Pa. After reaching the cooling time, the ingot was taken out of the furnace (the cooling time in the furnace ≥ 270 min); the ingot prepared by the second melting was used as the electrode for the third melting of the ingot. For the third melting of the ingot, a crucible with a diameter of 560 mm was selected. Before melting, the vacuum degree ≤ 1.0 Pa, the air leakage rate ≤ 0.9 Pa / min, the starting arc current 5.0 kA, the stable arc current in the stable stage 10.0 A, the stable arc stirring commutation frequency in the stable stage 20 s / time, the maximum allowable vacuum degree 2.0 Pa, the melting current in the stable stage 13.0 kA, the arc voltage in the stable stage 34.0 V. When the remaining electrode was 140 kg, feeding was started until melting was completed. After cooling for 30 minutes, the vacuum pump was closed and argon was filled for cooling. The argon pressure in the furnace was 3000 Pa. After reaching the cooling time, the ingot was taken out of the furnace (the cooling time in the furnace was 300 min). After that, the ingot was peeled and cleaned.

[0045] ② The TC11 titanium alloy thick-walled tube blank with an outer diameter of 312 mm and an inner diameter of 168 mm was prepared by vacuum casting of the ingot. During the stable melting stage, the vacuum degree in the furnace ≤ 3.0 Pa, the air leakage rate ≤ 0.8 Pa / min, the melting current 24.0 kA, the melting voltage 45.0 V. 30 minutes after the casting was completed, the tube wall was flushed with argon by the vacuum pump for cooling. The argon pressure in the furnace was 2000 Pa. After reaching the cooling time, the tube blank was taken out of the furnace (the cooling time in the furnace was 120 min). After that, the gate of the tube blank was cut off and shot peened, and the gate and the ingot shell part were recycled.

[0046] ③ Solution heat treatment of thick-walled tube blanks at high temperature, with a solution temperature of 1000 °C, holding for 86 min, followed by air cooling after solution. During the holding process, a steel bar with a diameter of 162 mm and equal height is used to support the inside of the tube blank. After heat treatment, the tube blank is pickled.

[0047] ④ Hot extrusion forming of thick-walled tube blanks in one pass. The inner diameter of the extrusion cylinder is 320 mm, the diameter of the extrusion needle is 160 mm, the diameter of the extrusion die is 210 mm, the extrusion temperature is 960 °C, and the extrusion speed is 40 mm / s. Before extrusion, the thick-walled tube blank is treated with a double jacket of steel on the inside and copper on the outside. The thickness of the steel skin is 1 mm, and the thickness of the copper skin is 1.5 mm. After extrusion, the thin-walled tube blank is pickled to remove the jacket. The dimensions of the thin-walled tube blank are an outer diameter of 210 mm and an inner diameter of 160 mm.

[0048] ⑤ Solution heat treatment and low-temperature aging heat treatment of thin-walled tube blanks. The solution temperature is 930 °C, the holding time is 60 min, followed by air cooling. The aging temperature is 550 °C, the holding time is 6 h, and then air cooling. During the solution and aging processes, a steel bar with a diameter of 176 mm and equal height is used to support the inside of the tube blank. After heat treatment, the tube blank is pickled.

[0049] ⑥ Machine the TC11 titanium alloy thin-walled tube blank to the target dimensions of an outer diameter of 204 mm and an inner diameter of 168 mm.

[0050] Example 4: Preparation of high-strength TC11 seamless tubes with an outer diameter of 204 mm and an inner diameter of 168 mm Process flow: ①The TC11 titanium alloy ingot with a diameter of 560 mm was prepared by triple vacuum consumable arc melting. The electrodes were prepared according to the requirements of the standard GB / T 3620.1-2007. For the first melting of the ingot, a crucible with a diameter of 380 mm was selected. Before melting, the vacuum degree ≤ 3.0 Pa, the leakage rate ≤ 0.9 Pa / min, the starting arc current 5.0 kA, the stable arc current in the stable stage 8.0 A, the stable arc stirring commutation frequency in the stable stage 20 seconds / time, the maximum allowable vacuum degree 2.0 Pa, the melting current in the stable stage 6.0 kA, the arc voltage in the stable stage 28.0 V. After melting, after cooling for 30 minutes, the vacuum pump was turned off and argon was filled for cooling. The argon pressure in the furnace was 2000 Pa. After reaching the cooling time, the ingot was taken out of the furnace (the cooling time in the furnace was 180 min); the ingot prepared by the first melting was used as the electrode for the second melting of the ingot. A crucible with a diameter of 480 mm was selected. Before melting, the vacuum degree ≤ 1.0 Pa, the leakage rate ≤ 0.9 Pa / min, the starting arc current 2.0 kA, the stable arc current in the stable stage 10.0 A, the stable arc stirring commutation frequency in the stable stage 20 seconds / time, the maximum allowable vacuum degree 2.0 Pa, the melting current in the stable stage 10.0 kA, the arc voltage in the stable stage 28.0 V. After melting, after cooling for 30 minutes, the vacuum pump was turned off and argon was filled for cooling. The argon pressure in the furnace was 2000 Pa. After reaching the cooling time, the ingot was taken out of the furnace (the cooling time in the furnace ≥ 270 min); the ingot prepared by the second melting was used as the electrode for the third melting of the ingot. A crucible with a diameter of 560 mm was selected. Before melting, the vacuum degree ≤ 1.0 Pa, the leakage rate ≤ 0.9 Pa / min, the starting arc current 2.0 kA, the stable arc current in the stable stage 10.0 A, the stable arc stirring commutation frequency in the stable stage 20 seconds / time, the maximum allowable vacuum degree 2.0 Pa, the melting current in the stable stage 16.0 kA, the arc voltage in the stable stage 28.0 V. When the remaining electrode was 120 kg, feeding was started until melting was completed. After cooling for 30 minutes, the vacuum pump was turned off and argon was filled for cooling. The argon pressure in the furnace was 2000 Pa. After reaching the cooling time, the ingot was taken out of the furnace (the cooling time in the furnace was 300 min). After that, the ingot was peeled and cleaned.

[0051] ②The ingot prepared in ① was vacuum cast to prepare a TC11 titanium alloy thick-walled tube blank with an outer diameter of 312 mm and an inner diameter of 168 mm. During the stable melting stage, the vacuum degree in the furnace ≤ 3.0 Pa, the leakage rate ≤ 0.8 Pa / min, the melting current 16.0 kA, the melting voltage 35.0 V. 30 minutes after the casting ended, the tube wall was flushed with argon by the vacuum pump for cooling. The argon pressure in the furnace was 3000 Pa. After reaching the cooling time, the tube blank was taken out of the furnace (the cooling time in the furnace was 120 min). After that, the gate of the tube blank was cut off and shot peened, and the gate and the solidified shell part were recycled.

[0052] ③ Solution heat treatment of thick-walled tube blanks at high temperature, solution temperature 1000°C, holding time 86 min, air cooling after solution, during the holding process, steel bars with equal height and a diameter of 162 mm are used to support the inside of the tube blank, and the tube blank is pickled after heat treatment.

[0053] ④ Hot extrusion forming of thick-walled tube blanks in one pass, inner diameter of the extrusion cylinder 320 mm, diameter of the extrusion needle 160 mm, diameter of the extrusion die 210 mm, extrusion temperature 960°C, extrusion speed 40 mm / s. Before extrusion, the thick-walled tube blank is treated with a double jacket of steel on the inside and copper on the outside, thickness of the steel skin 1 mm, thickness of the copper skin 1.5 mm. After extrusion, the thin-walled tube blank is pickled to remove the jacket, and the dimensions of the thin-walled tube blank are outer diameter 210 mm and inner diameter 160 mm.

[0054] ⑤ Solution heat treatment and low-temperature aging heat treatment of thin-walled tube blanks, solution temperature 930°C, holding time 60 min, air cooling, aging temperature 550°C, holding time 6 h, air cooling. During solution and aging, steel bars with equal height and a diameter of 176 mm are used to support the inside of the tube blank, and the tube blank is pickled after heat treatment.

[0055] ⑥ Machine the TC11 titanium alloy thin-walled tube blank to the target dimensions of outer diameter 204 mm and inner diameter 168 mm.

[0056] The room-temperature tensile strength range of the TC11 high-strength titanium alloy seamless tube prepared in Example 3 of the present invention is 1128~1151 MPa, and the elongation after fracture range is 12.5%~14.0%. For details, see Appendix Figure 2 Among them, Sample No. 1 and Sample No. 2 are samples at two positions in the materials prepared in Example 3.

[0057] Comparative Example 1 Preparation of TC11 titanium alloy tubes by forging bar piercing and hot rolling process The invention patent CN103540796A discloses a TC11 titanium alloy rolled tube and its preparation method. In Example 2 thereof, a TC11 titanium alloy tube blank with an outer diameter of 300 mm and an inner diameter of 250 mm was first obtained by skew rolling piercing of a forging bar, and then finished tubes with an outer diameter of 219 mm and an inner diameter of 183 mm were prepared by a four-pass hot rolling and heat treatment process. Among them, the online heating temperature in the first pass of hot rolling was 1200 °C, the rolling deformation was 45%, and the rolled tube blank was air-cooled and then subjected to oxidation annealing at 900 °C for 3 hours. After oxidation annealing, the tube blank was subjected to alkali washing, water washing, inspection and defect scraping; the online heating temperature in the second pass was 1200 °C, the rolling deformation was 40%, and the rolled tube blank was air-cooled and then subjected to oxidation annealing at 800 °C for 3 hours. After oxidation annealing, the tube blank was subjected to alkali washing, water washing, inspection and defect scraping; the online heating temperature in the third pass was 1100 °C, the rolling deformation was 35%, and the rolled tube blank was air-cooled and then subjected to oxidation annealing at 800 °C for 2.5 hours. After oxidation annealing, the tube blank was subjected to alkali washing, water washing, inspection and defect scraping; the online heating temperature in the fourth pass was 900 °C, the rolling deformation was 30%, and the finished product after air cooling was subjected to annealing heat treatment under two systems. The first finished product annealing system was 650 °C for 2 hours, air-cooled, and after annealing, the finished product was subjected to alkali washing and water washing. The second finished product annealing system was vacuum annealing at 750 °C for 2 hours, furnace cooling, and after annealing, the finished product was subjected to pickling and water washing. The measured room temperature tensile strength of the finished tube after heat treatment under the first system was 1000 MPa, and the elongation after fracture was 10%. The measured room temperature tensile strength of the finished tube after heat treatment under the second system was 980 MPa, and the elongation after fracture was 12%.

[0058] It can be seen by comparison that the mechanical properties of the TC11 titanium alloy tubes prepared by the forging bar piercing and hot rolling process are significantly lower than those of the TC11 titanium alloy tubes prepared by the present invention. Moreover, skew rolling piercing with severe deformation characteristics usually causes serious folding, tearing and other phenomena during the preparation of the tube blank. At the same time, the severe temperature rise during the piercing process will further deteriorate the microstructure state of the tube blank and reduce its processing performance. Therefore, this method has great difficulties, and its implementation effect is far lower than the tube preparation method adopted by the present invention.

[0059] Comparative Example 2 Preparation of TC11 titanium alloy tubes by forging bar drilling and extrusion process The invention patent CN104232993A discloses a high-performance TC11 tube and its preparation method. This method first uses grade 1 sponge titanium-related master alloys to prepare a TC11 titanium alloy ingot through two times of vacuum consumable melting. The ingot is forged into a black bar blank through 6 forging passes, and then an extrusion ingot blank is prepared through machining and surface grinding. The ingot blank is extruded into a tube blank after drilling, sheathing, and heating, and then through hot straightening, surface treatment, and heat treatment. Finally, the finished TC11 tube is prepared through internal boring and external turning by machining. The size of the finished tube is 115 mm in outer diameter and 65 mm in inner diameter. The performance test results of the tube show that its room-temperature tensile strength is 1105 MPa and the elongation after fracture is 18.5%.

[0060] By comparison, it can be seen that the mechanical properties of the TC11 titanium alloy tube prepared by the forging bar drilling and extrusion process are basically equivalent to those of the TC11 titanium alloy tube prepared by the present invention. However, the forging bar drilling and extrusion process requires a complex bar preparation process, and drilling to prepare the tube blank will significantly reduce the material utilization rate and greatly increase the processing cost of the tube. Therefore, the tube preparation method provided by the present invention has obvious advantages of short process flow and low cost.

[0061] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and its equivalent technologies, these changes and modifications are also intended to be included.

Claims

1. A process for preparing TC11 high-strength titanium alloy seamless pipe, characterized in that: The following steps are involved: The TC11 titanium alloy ingot was prepared by vacuum consumable arc melting process; The TC11 titanium alloy ingot is cast by vacuum casting to prepare a TC11 titanium alloy thick-walled tube blank; The TC11 titanium alloy thick-walled tube blank is subjected to high-temperature solution heat treatment, and then a TC11 titanium alloy thin-walled tube blank having a near-target size is prepared by final forming means; The TC11 titanium alloy thin-walled tube blank is subjected to a dual heat treatment of high-temperature solid solution and low-temperature aging, and then subjected to a post-treatment to complete the preparation of a TC11 high-strength titanium alloy seamless tube of a target size.

2. The process for preparing TC11 high-strength titanium alloy seamless pipe according to claim 1, characterized in that: The outer diameter of the TC11 titanium alloy thick-walled tube billet is 80mm~600mm, and the wall thickness is 10mm~100mm. After the thick-walled tube billet is cast, the tube billet is shot peened.

3. The process for preparing TC11 high-strength titanium alloy seamless pipe according to claim 1, characterized in that: The high temperature solution heat treatment temperature is 950℃~1000℃, and the holding time is 0.5δ+50min, where δ is the wall thickness of the tube billet in mm. The tube billet is air-cooled or air-cooled to room temperature and pickled.

4. The process for preparing TC11 high-strength titanium alloy seamless pipe according to claim 1, characterized in that: The final forming means is one or a combination of radial forging, extrusion and hot rolling.

5. The process for preparing TC11 high-strength titanium alloy seamless pipe according to claim 1, characterized in that: The deformation temperature of the final forming means is T β ±50℃, where T β It is the phase transition point of TC11 titanium alloy.

6. The process for preparing TC11 high-strength titanium alloy seamless pipe according to claim 1, characterized in that: After the preparation of TC11 titanium alloy thin-walled tube billets close to the target size is completed, the inner diameter of the tube billet is 1mm~20mm smaller than the inner diameter of the target size, and the outer diameter of the tube billet is 1mm~20mm larger than the outer diameter of the target size.

7. The process for preparing TC11 high-strength titanium alloy seamless pipe according to claim 1, characterized in that: The double heat treatment system of high temperature solution and low temperature aging is: keep warm at 900℃~960℃, air cool or wind cool to room temperature, then keep warm at 500℃~580℃ for 6h~10h, air cool to room temperature, and pickling.

8. The process for preparing TC11 high-strength titanium alloy seamless pipe according to claim 1, characterized in that: During the high-temperature solution heat treatment and double heat treatment insulation process, the tube billet is vertically hoisted in the furnace cavity or placed vertically on the furnace bottom plate, and the tube billet is supported by steel rods or steel pipes. The length of the steel rods or steel pipes is not less than the length of the tube billet, and the outer diameter of the steel rods or steel pipes is 1mm~15mm smaller than the inner diameter of the tube billet.

9. The process for preparing TC11 high-strength titanium alloy seamless pipe according to claim 1, characterized in that: Post-processing includes machining, sandblasting and polishing.

10. The process for preparing TC11 high-strength titanium alloy seamless pipe according to claim 1, characterized in that: The vacuum consumable arc melting process is performed 1 to 3 times. After the final ingot melting is completed, the outer surface of the ingot is cleaned and peeled to remove the oxide scale and inclusions on the surface of the ingot.

Images