Preparation method of ultra-large-diameter titanium alloy seamless pipe

Abstract

The invention relates to the technical field of titanium alloy processing, in particular to a preparation method of an ultra-large-diameter titanium alloy seamless pipe. According to the preparation method, titanium alloy recycled materials with a high adding proportion are used as raw materials for ingot casting burdening, then smelting is carried out, a titanium alloy ingot is obtained, after simple shaping is carried out, backward extrusion on a phase change point is carried out firstly to prepare a hollow blank of a thick-wall pipe blank, and then forward extrusion is carried out to obtain the ultra-large-diameter titanium alloy seamless pipe. And a 680MN extrusion unit or a 500MN extrusion unit is adopted for forward extrusion, so that low-cost preparation of the ultra-large-diameter titanium alloy seamless pipe with the diameter of more than 600mm is realized while efficient utilization of the titanium alloy recycled material is realized. Compared with a preparation method of the ultra-large-diameter titanium alloy seamless pipe in the prior art, the preparation method has the advantages that the material loss rate and the production cost are remarkably reduced, the titanium alloy utilization efficiency and the production efficiency are improved, and the requirements of different fields on the ultra-large-diameter titanium alloy seamless pipe are met.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy processing technology, specifically a method for preparing ultra-large diameter seamless titanium alloy tubes. Background Technology

[0002] Titanium alloys are widely used in marine engineering, military, and chemical industries due to their excellent specific strength, corrosion resistance, and good high-temperature performance. With the development of these fields, especially the continuous increase in the diving depth and displacement of deep-sea equipment, the requirements for the strength, corrosion resistance, and lightweight of key components are also constantly increasing. Therefore, titanium alloys with superior performance are gradually replacing conventional steel materials and becoming the preferred material for ultra-large diameter seamless pipes in marine equipment, such as seawater piping systems for deep-sea submersibles, high-pressure air systems, and high-strength pressure-resistant hulls.

[0003] Ultra-large diameter seamless titanium alloy tubes typically refer to titanium alloy tubes with a diameter exceeding 600 mm and a length exceeding 6000 mm. Their fabrication technology has always been a challenging and hot topic in the field of titanium alloy material processing. Currently, the main fabrication methods for ultra-large diameter seamless titanium alloy tubes include piercing-rolling and forging-machining methods.

[0004] Patent application CN116441311A discloses a continuous casting and rolling method for producing ultra-large diameter TA24 titanium alloy seamless tubes. This method uses an electron beam cold hearth furnace to melt and prepare hollow circular ingots, followed by processes such as skew rolling and rotary rolling to produce ultra-large diameter titanium alloy seamless tubes. While this method enables continuous production of ultra-large diameter titanium alloy seamless tubes, the severe deformation during skew rolling and rotary rolling limits its applicability to tubes made of relatively good-ductility, low-to-medium strength titanium alloys (tensile strength ≥ 750 MPa). It presents significant challenges for producing medium-to-high strength, high-diameter titanium alloy seamless tubes requiring tensile strength ≥ 850 MPa.

[0005] Patent application CN107971706A discloses a method for producing ultra-large diameter seamless titanium alloy tubes. This method involves selecting titanium alloy round ingots and preparing seamless titanium alloy tubes through forging, annealing, nesting drilling, and cold rolling. While this method reduces the piercing, hot rolling, and tube expansion processes in traditional methods, thus improving the yield to some extent, it still requires multiple forging and machining operations, resulting in a long production cycle, significant material loss, and the subsequent cold rolling process for the finished tubes is not suitable for medium-to-high strength titanium alloys, which have high processing difficulty.

[0006] Patent application CN113857786A discloses a method for preparing TC4 titanium alloy tubing. This method uses an extrusion process to prepare the tubing. Before extrusion, the inner hole of the titanium alloy round bar is bored, and after extrusion, a tubing blank is formed. This eliminates the need for re-drilling, improving the yield and reducing material waste. However, this method is mainly suitable for preparing small-diameter titanium alloy tubing, and there are limitations in equipment and processes for preparing ultra-large-diameter seamless titanium alloy tubing.

[0007] In summary, the existing technology has the following problems: First, the utilization of recycled titanium alloy materials is insufficient, resulting in high production costs; second, the traditional process route is complex, requiring multiple forging and machining processes, resulting in large material losses and long production cycles; third, the existing process is difficult to meet the low-cost preparation requirements of ultra-large diameter seamless titanium alloy tubes with diameters of 600mm and above; fourth, it is difficult to prepare ultra-large diameter medium-high strength seamless titanium alloy tubes using the existing process; and fifth, the production process consumes a lot of energy, wastes a lot of materials, and has poor economic benefits. Summary of the Invention

[0008] To address the problems of complex manufacturing processes, high costs, long production cycles, and difficulty in achieving low-cost industrial production of ultra-large diameter, high-strength titanium alloy seamless tubes in existing technologies, this invention provides a method for manufacturing ultra-large diameter titanium alloy seamless tubes based on the world's leading ultra-large tonnage extrusion equipment (Zhongtai Qingduan 680MN extrusion press and Hongrun Nuclear Equipment 500MN extrusion press) from relevant domestic processing enterprises. This method uses recycled titanium alloy as raw material, which is then melted to obtain titanium alloy ingots. After simple shaping, it first undergoes reverse extrusion at the phase transformation point to prepare a hollow billet of thick-walled tube blank, followed by forward extrusion to obtain ultra-large diameter titanium alloy seamless tubes. The forward extrusion uses a 680MN or 500MN extrusion press. This method efficiently utilizes recycled titanium alloy, simplifies the process, reduces production costs, and is suitable for manufacturing ultra-large diameter, high-strength titanium alloy seamless tubes with a tensile strength ≥850MPa.

[0009] Based on the above-mentioned technical problems, the present invention adopts the following technical solution: This invention protects a method for preparing ultra-large diameter seamless titanium alloy tubing, comprising the following steps: S1. Using recycled titanium alloy materials, sponge titanium, and related intermediate alloys as raw materials, the proportion of raw materials for titanium alloy ingots is determined.

[0010] S2. Titanium alloy ingots are prepared by single-stage electron beam cold hearth melting (EB melting), single-stage vacuum consumable arc melting (VAR melting), or EB+VAR dual-process, thereby achieving efficient utilization of recycled titanium alloy materials. Single-stage electron beam cold hearth melting (EB melting), single-stage vacuum consumable arc melting (VAR melting), or EB+VAR dual-process are conventional technical means for preparing titanium alloy ingots. Conventional conditions can be applied to this invention, and no restrictions are imposed here.

[0011] S3. After the titanium alloy ingot is prepared, it is simply free-forged and shaped to the required specifications of the extrusion cylinder to obtain the shaped titanium alloy ingot.

[0012] S4. The shaped titanium alloy ingot is subjected to reverse extrusion at the phase transformation point to prepare a hollow billet for thick-walled tube blanks. After the hollow billet is prepared, the inner and outer surfaces of the hollow billet are machined and polished to remove surface cracks and defects.

[0013] S5. The hollow billet is subjected to positive extrusion to produce tubes. Positive extrusion is carried out using a 680MN extrusion press or a 500MN extrusion press. After that, the microstructure and properties of the finished tubes are controlled by heat treatment to obtain ultra-large diameter titanium alloy seamless tubes.

[0014] Preferably, the high proportion of recycled titanium alloy is scrap material generated during the titanium alloy processing with a clearly defined grade and composition conforming to the GB / T3620.1 standard. Its mass percentage accounts for more than 60% of the total raw materials. The remaining components are supplemented by sponge titanium and corresponding intermediate alloys. If the smelting process involves EB smelting, the ingot raw material ratio needs to take into account the burn-off rate of volatile elements (such as Al and Cr) during EB smelting and make corresponding compensation.

[0015] Preferably, the single-stage EB melting process directly uses electron beam cold-bed melting to prepare titanium alloy ingots of the corresponding grade, achieving efficient utilization of recycled titanium alloy materials, and effectively removing high / low density inclusions through the physical mechanism of high-energy electron beam bombardment + cold-bed zone refining; the single-stage VAR melting process directly uses vacuum consumable arc melting to melt titanium alloy ingots of the corresponding grade, wherein the proportion of recycled titanium alloy material added is 100%. Using recycled titanium alloy material as the sole raw material necessitates VAR melting because EB melting causes the loss of volatile elements and an increase in oxygen content. Using recycled titanium alloy material as the sole raw material cannot guarantee the target ingot composition, and the grade of the recycled titanium alloy material must be consistent with the target ingot grade; the EB+VAR dual-stage process first performs electron beam cold-bed melting to prepare a primary titanium alloy ingot, and then performs vacuum consumable arc melting to prepare a secondary titanium alloy ingot, further improving the purity of the titanium alloy ingot and mitigating the component segregation phenomenon. The specific smelting process to be used depends on the different performance requirements of the finished pipes.

[0016] Preferably, simple shaping involves surface treatment and dimensional adjustment of the titanium alloy ingot to meet the specifications of the extrusion cylinder, without the need for riser removal or complex forging and machining processes.

[0017] Preferably, reverse extrusion billet forming involves reverse extrusion and punching at the phase transformation temperature of the titanium alloy ingot to obtain an initial thick-walled tube blank. The reverse extrusion temperature range is... T β +(50~100)℃, where, T β The phase transformation temperature of titanium alloy is used; the punching and blanking end of the thick-walled tube blank is the riser end of the titanium alloy ingot, that is, the punching and blanking part includes the ingot riser, which further improves the utilization rate of raw materials; an anti-oxidation coating is uniformly applied to the surface of the shaped titanium alloy ingot; the shaped titanium alloy ingot is first heated to the reverse extrusion temperature and held for 8h~12h to fully homogenize the microstructure of the shaped titanium alloy ingot; after heating, a high-temperature lubricant is applied to the surface, and then it is placed in the extrusion cylinder for reverse extrusion and punching and blanking. The inner diameter of the extrusion cylinder used for reverse extrusion is 1000mm~1800mm, the extrusion speed is 5mm / s~20mm / s, and the diameter of the extrusion needle is consistent with the inner diameter of the finished ultra-large diameter titanium alloy seamless tube. During the reverse extrusion process, the mold temperature is maintained at 400℃~450℃ to prevent cracking caused by excessive cooling. After the reverse extrusion and punching are completed, a hollow blank is obtained. The outer diameter of the hollow blank is 1000~1800mm, and the wall thickness is 100~500mm.

[0018] Preferably, forward extrusion tube making is based on reverse extrusion billet making, and then uses a forward extrusion process to process the hollow billet into the final required ultra-large diameter seamless titanium alloy tube; the forward extrusion temperature range is... T β ±100℃, among which, T β The phase transformation temperature of titanium alloy is used as the reference temperature. The hollow billet is heated to the positive extrusion temperature and held for 5-10 hours. Before heating, the inner and outer surfaces of the hollow billet are uniformly coated with an anti-oxidation coating. After heating, the inner and outer surfaces are coated with a high-temperature lubricant. Then, the hollow billet is placed in a 50,000t or 68,000t vertical extrusion press for positive extrusion. The extrusion speed is 5mm / s to 20mm / s. The diameter of the extrusion needle is consistent with the inner diameter of the ultra-large diameter titanium alloy seamless tube. During the positive extrusion process, the die temperature is maintained at 420-470℃. After positive extrusion, the outer diameter of the ultra-large diameter titanium alloy seamless tube is 600mm-1200mm, and the wall thickness is 30mm-200mm.

[0019] Preferably, the finished ultra-large diameter titanium alloy seamless tubes are subjected to heat treatment to regulate their microstructure and mechanical properties. The heat treatment process is either single annealing or a solution + aging dual heat treatment process. The specific heat treatment process is selected and formulated according to the alloy grade and performance requirements.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention provides a novel method for preparing ultra-large diameter seamless titanium alloy tubes. The method involves sequentially batching, melting, and shaping, followed by reverse extrusion at the phase transformation point to prepare a hollow billet for a thick-walled tube. Then, a 50,000-ton or 68,000-ton vertical extrusion press is used for forward extrusion to produce the tube. Compared to existing methods, this invention provides, for the first time, the preparation of ultra-large diameter seamless titanium alloy tubes through both forward and reverse extrusion. Compared to existing technologies, the method of this invention offers the following advantages: The titanium alloy ingots for ultra-large diameter seamless titanium alloy pipes use recycled titanium alloy materials with a high addition ratio as raw materials, achieving efficient utilization of recycled titanium alloy materials and reducing material costs by more than 40%.

[0021] After the titanium alloy ingot is prepared, it is simply shaped to the required specifications of the extrusion cylinder. Then, the hollow thick-walled tube blank is produced by the low material loss reverse extrusion process at the phase transformation point, and then the tube is produced by forward extrusion. This process avoids the problems of high material loss and long processing cycle caused by multiple forging and machining hole making processes in traditional processes. The material utilization rate is increased by more than 30%, and the production cycle is shortened by more than 50%.

[0022] This invention, based on ultra-large tonnage extrusion equipment (Zhongtai Qingduan 680MN extrusion press and Hongrun Nuclear Equipment 500MN extrusion press), adopts an integrated process flow design, breaking through the limitations of existing processing technologies. It significantly reduces energy consumption and material waste during production, achieving low-cost manufacturing of ultra-large diameter, high-strength titanium alloy seamless tubes with diameters exceeding 600mm. Compared with traditional processes, the overall cost is reduced by more than 40%, demonstrating good economic benefits and practical value, effectively meeting the demand for ultra-large diameter titanium alloy seamless tubes in marine engineering, military, and chemical industries.

[0023] Based on ultra-large tonnage extrusion equipment, this invention also realizes the preparation of ultra-large diameter medium-high strength titanium alloy seamless tubes. Studies have shown that the tensile strength of ultra-large diameter titanium alloy seamless tubes obtained by the method of this invention is ≥850MPa. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating the efficient and low-cost preparation process of the ultra-large diameter seamless titanium alloy tube of this invention.

[0025] Figure 2The reverse-extruded tube blank prepared in Example 1 and Φ 内径 740mm×Φ 外径 A real picture of a 560mm×6500mm ultra-large diameter TC4 titanium alloy seamless pipe.

[0026] Figure 3 The reverse-extruded tube blank prepared in Example 2 and Φ 内径 740mm×Φ 外径 A physical image of a 560mm×6500mm ultra-large diameter Ti52 titanium alloy seamless tube.

[0027] Figure 4 The reverse-extruded tube blank and Φ prepared in Example 3 内径 980mm×Φ 外径 A real picture of an 850mm×6000mm ultra-large diameter Ti52 titanium alloy seamless tube. Detailed Implementation

[0028] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] Considering that existing technologies can only produce ultra-large diameter seamless titanium alloy tubes using piercing-rolling or forging-machining methods, and that existing extrusion molding methods can only produce small diameter titanium alloy tubes, this invention proposes for the first time a technical solution to produce ultra-large diameter seamless titanium alloy tubes directly from a simply shaped ingot using a forward and reverse extrusion molding method. Based on the world's leading ultra-large tonnage extrusion equipment from relevant domestic processing enterprises (Zhongtai Qingduan 680MN extrusion press and Hongrun Nuclear Equipment 500MN extrusion press), reverse extrusion is first performed at the phase transformation point to prepare a hollow billet of thick-walled tube blank, followed by forward extrusion to obtain ultra-large diameter seamless titanium alloy tubes. This solves the technical defects of existing piercing-rolling or forging-machining methods, and simultaneously realizes the application of extrusion molding in the preparation of ultra-large diameter seamless titanium alloy tubes.

[0030] Furthermore, the preparation method of this invention also achieves efficient utilization of recycled titanium alloy materials, with the recycled titanium alloy materials accounting for more than 60% of the total raw materials by mass, and even the recycled titanium alloy materials can be used entirely as raw materials; the preparation of ultra-large diameter seamless titanium alloy tubes of this invention only requires forward and reverse extrusion, and the integrated process flow design overcomes the material loss problem caused by multiple forging and machining hole making, and also reduces energy consumption in the production process; it can be seen that the preparation method of this invention achieves the purpose of cost reduction and efficiency improvement.

[0031] Finally, this invention achieves low-cost preparation of ultra-large diameter titanium alloy seamless tubes with a diameter of 600 mm or more through a simple process. At the same time, the obtained ultra-large diameter medium-high strength titanium alloy seamless tubes have a tensile strength of ≥850 MPa, which is superior to the existing ultra-large diameter titanium alloy seamless tubes.

[0032] The technical solution of the present invention will be further studied using the following embodiments. The specific research methods and results are shown below: Example 1 Φ 内径 740mm×Φ 外径 A low-cost manufacturing method for 560mm ultra-large diameter TC4 titanium alloy seamless tubing includes the following steps: S1. Ingot Batching: Using 100% recycled material as raw material, select recycled TC4 titanium alloy bars and plates as processing scraps, totaling 5t. The recycled material is first pickled and then alkaline washed to remove surface oil, oxide layer and other impurities.

[0033] S2. Single VAR melting to prepare TC4 titanium alloy ingots: The cleaned recycled material is welded, bound, and fixed to prepare a melting electrode, which is then subjected to VAR melting; the VAR melting is carried out under a vacuum of 1×10⁻⁶. -2 ~5×10 -2 The melting process was carried out under a pressure of Pa, with the arc current set at 8000~12000A and the melting speed controlled at 200~300kg / h. Through VAR melting, the uniformity and purity of the alloy were improved, and TC4 titanium alloy ingots for pipe extrusion were obtained.

[0034] S3. Simple shaping of ingots: The TC4 titanium alloy ingots are simply shaped to meet the specifications of the extrusion cylinder. The shaping process includes surface cleaning and simple free forging to the required size, resulting in a shaped TC4 titanium alloy ingot with dimensions of Φ956×1870mm.

[0035] S4. Reverse Extrusion Blanking at Phase Transformation Point: A uniform anti-oxidation coating is applied to the surface of the shaped TC4 titanium alloy ingot. The ingot is then heated to 1080℃ and held for 11 hours to ensure a fully homogenized microstructure. After heating, a high-temperature lubricant is applied to the surface, and the ingot is then placed in an extrusion cylinder for reverse extrusion and punching. The extrusion cylinder has an outer diameter of 1300mm, and a 7000t vertical extrusion press is used. The extrusion speed is controlled at 15mm / s, and the extrusion needle diameter is 560mm. During reverse extrusion, the die temperature is maintained at 400℃~450℃ to prevent cracking due to rapid cooling. After reverse extrusion and punching, a hollow blank is obtained with dimensions Φ. 外径 1270×Φ 内径The blank is 566×1300mm. After that, the hollow blank is simply machined and polished to remove oxide scale and surface cracks.

[0036] S5. Positive Extrusion Tube Making, Heat Treatment, and Residual Heat Straightening: The hollow billet is reheated to 1050℃ and held for 5-10 hours. Before heating, an anti-oxidation coating is uniformly applied to the inner and outer surfaces of the hollow billet. After heating, a high-temperature lubricant is applied to the inner and outer surfaces. Then, the hollow billet is placed in an extrusion cylinder for positive extrusion. The specifications of the extrusion cylinder for positive extrusion are the same as those for reverse extrusion. A 50,000t vertical extrusion press is used for positive extrusion, with the extrusion speed controlled at 10mm / s and the extrusion needle diameter at 560mm. During positive extrusion, the die temperature is maintained at 420℃-470℃. After positive extrusion, ultra-large diameter seamless titanium alloy tubes are obtained, with a dimension of Φ. 外径 740×Φ 内径 560×6500mm, see actual product image. Figure 2 .

[0037] The ultra-large diameter seamless titanium alloy tubes obtained by extrusion were subjected to annealing heat treatment under the following conditions: heating temperature 800℃, holding time 2h, followed by air cooling. After heat treatment, the ultra-large diameter seamless titanium alloy tubes were straightened using residual heat. The mechanical properties of the annealed ultra-large diameter seamless titanium alloy tubes are shown in Table 1, with tensile strengths ranging from 885MPa to 895MPa. (Tables 1-3 are omitted as they are not directly related to the main text.) R m For tensile strength, R p0.2 This represents the stress value corresponding to a material exhibiting 0.2% plastic strain during tensile testing. A Elongation at break, a KV V-notch impact energy absorption is used to measure a material's ability to absorb plastic deformation work and fracture work.

[0038] Table 1. Performance of ultra-large diameter TC4 titanium alloy seamless tubes after annealing in Example 1 The above-described process enables the low-cost fabrication of ultra-large diameter TC4 titanium alloy seamless tubing with a diameter of 740mm. Throughout the fabrication process, material utilization exceeds 85%, and compared to traditional processes, the production cycle is shortened by more than 50%, and production costs are reduced by more than 50%.

[0039] Example 2 Φ 外径 740×Φ 内径 A low-cost preparation method for 560mm ultra-large diameter Ti52 titanium alloy seamless tubing includes the following steps: S1, Ti52 titanium alloy ingot batching with 63wt% recycled material: The target composition of the Ti52 titanium alloy ingot is set as Ti-5.7Al-2.5V-1.0Zr-1.5Mo-1.5Cr-0.50Fe. Considering the volatilization characteristics of the EB furnace, the batching composition of the 5t ingot is set as: Ti-6.7Al-2.5V-1.0Zr-1.5Mo-2Cr-0.50Fe. The raw material ratio of the Ti52 titanium alloy ingot is completed by using recycled materials from the processing of TA15 titanium alloy and TC6 titanium alloy plates and bars as the main raw materials, combined with electrode blocks pressed from sponge titanium and related intermediate alloys. The recycled materials are first pickled and then alkaline washed to remove surface oil, oxide layer and other impurities.

[0040] S2, EB+VAR dual process for preparing Ti52 titanium alloy ingots: The proportioned raw materials are uniformly placed in the hopper and subjected to EB melting, electron beam melting at a vacuum degree of 2×10 -3 The melting process was carried out in an environment of Pa, with the electron beam power set at 1000 kW and the melting rate controlled at 350 kg / h. After electron beam melting, a primary EB ingot was obtained. The primary EB ingot was then subjected to VAR remelting at a vacuum degree of 1 × 10⁻⁶. -2 ~5×10 -2 The melting process was carried out under the following conditions: the arc current was set to 10000A, the melting speed was controlled at 300~350kg / h, and the uniformity and purity of the alloy were further improved by VAR remelting to obtain Ti52 titanium alloy ingots. The dual melting process ensured that the oxygen content in the Ti52 titanium alloy ingots was controlled below 0.12%, the nitrogen content was controlled below 0.05%, and the hydrogen content was controlled below 0.0015%.

[0041] S3. Simple shaping of ingots: The Ti52 titanium alloy ingots are simply shaped to meet the specifications of the extrusion cylinder. The shaping process includes surface cleaning and simple free forging to the required size, resulting in a shaped Ti52 titanium alloy ingot with dimensions of Φ956×1870mm.

[0042] S4. Reverse Extrusion Billet Forming at Phase Transformation Point: A uniform anti-oxidation coating is applied to the surface of the shaped Ti52 titanium alloy ingot. The ingot is then heated to 1080℃ and held for 10 hours to ensure a fully homogenized microstructure. After heating, a high-temperature lubricant is applied to the surface, and the ingot is then placed in an extrusion cylinder for reverse extrusion and punching. The extrusion cylinder has an outer diameter of 1300mm, and a 7000t vertical extrusion press is used. The extrusion speed is controlled at 20mm / s, and the extrusion needle diameter is 560mm. During reverse extrusion, the die temperature is maintained at 400℃~450℃ to prevent cracking due to rapid cooling. After reverse extrusion and punching, a hollow billet is obtained with dimensions Φ. 外径 1270×Φ 内径 The blank is 566×1300mm. After that, the hollow blank is simply machined and polished to remove oxide scale and surface cracks.

[0043] S5. Positive Extrusion Tube Making, Heat Treatment, and Residual Heat Straightening: The hollow billet is reheated to 1050℃ and held for 5-10 hours. Before heating, an anti-oxidation coating is uniformly applied to the inner and outer surfaces of the hollow billet. After heating, a high-temperature lubricant is applied to the inner and outer surfaces. Then, the hollow billet is placed in an extrusion cylinder for positive extrusion. The specifications of the extrusion cylinder for positive extrusion are the same as those for reverse extrusion. A 50,000t vertical extrusion press is used for positive extrusion, with the extrusion speed controlled at 15mm / s and the extrusion needle diameter at 560mm. During positive extrusion, the die temperature is maintained at 420℃-470℃. After positive extrusion, ultra-large diameter seamless titanium alloy tubes are obtained, with a dimension of Φ. 外径 740×Φ 内径 560×6500mm, see actual product image. Figure 3 .

[0044] The ultra-large diameter seamless titanium alloy tubes obtained by extrusion were subjected to annealing heat treatment under the following conditions: heating temperature 800℃, holding time 3h, followed by air cooling. After heat treatment, the ultra-large diameter seamless titanium alloy tubes were straightened using residual heat. The mechanical properties of the ultra-large diameter seamless titanium alloy tubes after annealing are shown in Table 2.

[0045] Table 2. Performance of Ultra-Large Diameter Ti52 Titanium Alloy Seamless Tubes after Annealing (Example 2) The above-described process enables the low-cost fabrication of ultra-large diameter Ti52 high-strength titanium alloy seamless tubes with a diameter of 740mm. Throughout the fabrication process, material utilization exceeds 85%, and compared to traditional processes, the production cycle is shortened by more than 40%, and production costs are reduced by more than 40%.

[0046] The prepared ultra-large diameter Ti52 high-strength titanium alloy seamless pipe has a tensile strength of over 940MPa, a yield strength of over 868MPa, and an elongation of over 10%, fully meeting the requirements for use in marine engineering, military, chemical and other fields.

[0047] Example 3 Φ 外径 980×Φ 内径 A low-cost preparation method for 850mm ultra-large diameter Ti52 titanium alloy seamless tubing includes the following steps: S1. Ti52 titanium alloy ingot batching with 69% recycled material: The target composition of the Ti52 titanium alloy ingot is set as Ti-5.7Al-2.5V-1.0Zr-1.5Mo-1.5Cr-0.50Fe. Considering the volatilization characteristics of the EB furnace, the batching composition of the 6.6t ingot is set as: Ti-6.7Al-2.5V-1.0Zr-1.5Mo-2Cr-0.50Fe. The raw material ratio of the Ti52 titanium alloy ingot is completed by using recycled materials from the processing of TA15 titanium alloy and TC6 titanium alloy plates and bars as the main raw materials, combined with electrode blocks pressed from sponge titanium and related intermediate alloys. The recycled materials are first pickled and then alkaline washed to remove surface oil, oxide layer and other impurities.

[0048] S2. Single-pass EB melting process for preparing Ti52 titanium alloy ingots: The proportioned raw materials are evenly placed in the hopper and EB melting is performed. Electron beam melting is carried out under a vacuum of 2×10⁻⁶. -3 The process was carried out in an environment of Pa, with the electron beam power set at 1000kW and the melting speed controlled at 400kg / h. After the electron beam melting was completed, Ti52 titanium alloy ingots for pipe extrusion were obtained.

[0049] S3. Simple shaping of ingots: The Ti52 titanium alloy ingots are simply shaped to meet the specifications of the extrusion cylinder. The shaping process includes surface cleaning and simple free forging to the required size, resulting in a shaped Ti52 titanium alloy ingot with dimensions of Φ1334×952mm.

[0050] S4. Reverse Extrusion at Phase Transformation Point: A uniform anti-oxidation coating is applied to the surface of the shaped Ti52 titanium alloy ingot. The ingot is then heated to 1080℃ and held for 10 hours to ensure a fully homogenized microstructure. After heating, a high-temperature lubricant is applied to the surface, and the ingot is then placed in an extrusion cylinder for reverse extrusion and punching. The extrusion cylinder has an outer diameter of 1400mm, and a 10000t vertical extrusion press is used. The extrusion speed is controlled at 5mm / s, and the extrusion needle diameter is 850mm. During reverse extrusion, the die temperature is maintained at 400℃~450℃ to prevent cracking due to rapid cooling. After reverse extrusion and punching, a hollow billet is obtained with dimensions Φ. 外径 1365×Φ 内径 The blank is 838×1300mm. After that, the hollow blank is simply machined and polished to remove oxide scale and surface cracks.

[0051] S5. Positive Extrusion Tube Making, Heat Treatment, and Residual Heat Straightening: The hollow billet is reheated to 1050℃ and held for 5 hours. Before heating, an anti-oxidation coating is uniformly applied to the inner and outer surfaces of the hollow billet. After heating, a high-temperature lubricant is applied to the inner and outer surfaces. Then, the hollow billet is placed in an extrusion cylinder for positive extrusion. The specifications of the extrusion cylinder for positive extrusion are the same as those for reverse extrusion. A 68000t vertical extrusion press is used for positive extrusion, with the extrusion speed controlled at 10mm / s and the extrusion needle diameter at 850mm. During positive extrusion, the die temperature is maintained at 420℃~470℃. After positive extrusion, ultra-large diameter seamless titanium alloy tubes are obtained, with a dimension of Φ. 外径 980×Φ 内径 850×6000mm, see actual product image. Figure 4 .

[0052] The ultra-large diameter seamless titanium alloy tubes obtained by extrusion were subjected to annealing heat treatment under the following conditions: heating temperature 800℃, holding time 3h, followed by air cooling. After heat treatment, the ultra-large diameter seamless titanium alloy tubes were straightened using residual heat. The mechanical properties of the ultra-large diameter seamless titanium alloy tubes after annealing are shown in Table 3.

[0053] Table 3. Performance of Ultra-Large Diameter Ti52 Titanium Alloy Seamless Tubes after Annealing (Example 3) The above-described process enables the low-cost fabrication of ultra-large diameter Ti52 high-strength titanium alloy seamless tubes with a diameter of 980mm. Throughout the fabrication process, material utilization exceeds 85%, and compared to traditional processes, the production cycle is shortened by more than 50%, and production costs are reduced by more than 50%.

[0054] The prepared ultra-large diameter Ti52 high-strength titanium alloy seamless pipe has a tensile strength of over 950MPa, a yield strength of over 875MPa, and an elongation of over 10%, fully meeting the requirements for use in marine engineering, military, chemical and other fields.

[0055] It should be noted that Examples 1, 2, and 3 are all low-cost methods for preparing ultra-large diameter seamless titanium alloy tubes.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method of producing a super-large diameter titanium alloy seamless pipe, characterized by, It comprises the following steps: Titanium alloy scrap, titanium sponge and intermediate alloy are used as raw materials to prepare titanium alloy ingot; Titanium alloy ingot is prepared by melting; The titanium alloy ingot is shaped by free forging to the required specification of the extrusion cylinder to obtain a shaped titanium alloy ingot; The shaped titanium alloy ingot is subjected to reverse extrusion at the phase transition point to prepare a hollow blank for thick-walled pipe blank; The hollow blank is subjected to positive extrusion pipe preparation using a 50000t vertical extruder or a 68000t vertical extruder to obtain a super-large diameter titanium alloy seamless pipe.

2. The method of producing an ultra-large diameter titanium alloy seamless pipe according to claim 1, characterized by, Titanium alloy scrap is a clear grade, component conforming to GB / T3620.1 standard scrap produced during titanium alloy processing, and its mass percentage accounts for more than 60% of the total amount of raw materials.

3. The method of producing an ultra-large diameter titanium alloy seamless pipe according to claim 1, characterized by, The temperature range for backward extrusion is T β + (50-100) °C, wherein, T β is the phase transition temperature of the titanium alloy.

4. The method of producing an ultra-large diameter titanium alloy seamless pipe according to claim 3, characterized by, The operation of reverse extrusion is as follows: the surface of the shaped titanium alloy ingot is uniformly coated with an anti-oxidation coating, the shaped titanium alloy ingot is heated to the reverse extrusion temperature and kept for 8h~12h, then the surface is coated with a high-temperature lubricant, and then the shaped titanium alloy ingot is put into the extrusion cylinder for reverse extrusion and punching and blanking, the inner diameter of the extrusion cylinder is 1000mm~1800mm, the extrusion speed is 5mm / s~20mm / s, the diameter of the extrusion needle is consistent with the inner diameter of the finished super-large diameter titanium alloy seamless pipe, and a hollow blank is obtained.

5. The method of producing an ultra-large diameter titanium alloy seamless pipe according to claim 4, characterized by, The outer diameter of the hollow blank is 1000~1800mm, and the wall thickness is 100~500mm.

6. The method of producing an ultra-large diameter titanium alloy seamless pipe according to claim 1, characterized by, The positive extrusion temperature range is T β ± 100 °C, wherein, T β is the phase transition temperature of the titanium alloy.

7. The method of producing an ultra-large diameter titanium alloy seamless pipe according to claim 6, characterized by, The operation of positive extrusion is as follows: the inner and outer surfaces of the hollow blank are uniformly coated with an anti-oxidation coating, the hollow blank is heated to the positive extrusion temperature and kept for 5h~10h, then the inner and outer surfaces are coated with a high-temperature lubricant, and then the hollow blank is put into a 50000t vertical extruder or a 68000t vertical extruder for positive extrusion, the extrusion speed is 5mm / s~20mm / s, the diameter of the extrusion needle is consistent with the inner diameter of the finished super-large diameter titanium alloy seamless pipe, and a super-large diameter titanium alloy seamless pipe is obtained.

8. The method of producing an ultra-large diameter titanium alloy seamless pipe according to claim 7, characterized by, The outer diameter of the super-large diameter titanium alloy seamless pipe is 600mm~1200mm, and the wall thickness is 30mm~200mm.

9. The method of producing an ultra-large diameter titanium alloy seamless pipe according to claim 1, wherein Single electron beam cold bed melting process, single vacuum consumable arc melting process or electron beam cold bed melting + vacuum consumable arc melting double process are used for melting.

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