A method for producing small-diameter, thick-walled near-α type titanium alloy tubing and its application

Abstract

This invention provides a method for producing small-diameter, thick-walled near-α-type titanium alloy tubing and its application. This method, through the use of cladding and heated rolling, increases the deformation per rolling pass, reduces the number of rolling passes, and results in a finer microstructure and better mechanical properties in the heated-rolled tubing. Simultaneously, the composite material composed of the cladding layer and silica aerogel effectively prevents the alloy rod from contacting air, avoiding further surface oxidation and reducing the thickness of the oxide layer on the rod surface. Furthermore, the composite material forms a "thermal insulation layer" on the surface of the alloy rod, preventing large temperature differences between the surface and core during heated rolling, thus ensuring better microstructure uniformity and surface quality. In this invention, the cladding process expands the selection of heating furnaces and reduces equipment requirements.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy pipe production technology, specifically relating to a production method and application of small-diameter, thick-walled near-α-type titanium alloy pipe. Background Technology

[0002] Nuclear power, as a highly efficient energy source that combines economic efficiency, safety, and cleanliness, has attracted considerable attention from scholars. Currently, small modular nuclear reactors (SMRs) have become an important development direction in nuclear power technology due to their small size, short construction cycle, fewer application limitations, and ease of assembly and transportation. Among these components, the steam generator, as the core component of a SMR, primarily transfers heat from the primary cooling system to the secondary cooling system. The selection of materials for its heat transfer tubes directly affects the efficiency and reliability of SMRs. In recent years, small-diameter, thick-walled near-α type titanium alloy tubing has been widely used in the piping systems of steam generator heat transfer tubes due to its low density and corrosion resistance.

[0003] The traditional production method for small-diameter, thick-walled near-α type titanium alloy tubes involves multiple cold rolling and annealing passes. This method is characterized by numerous cold rolling passes, small deformation per pass, complex equipment and processes, and long production cycles. Furthermore, the tubes produced are prone to defects such as folds and longitudinal cracks on the inner surface due to their relatively large wall thickness and relatively small inner diameter, which seriously affects product quality.

[0004] In existing research, many scholars have proposed new methods for the preparation of titanium alloy pipes. Patent CN104308461A discloses a titanium alloy and its production method. This method uses a "sloping-bottom furnace heating → sloping rolling piercing → sizing → heated straightening → primary pickling → cold rolling → annealing → heated straightening → secondary pickling" process to prepare a titanium alloy oil pipe with an outer diameter of 60-80 mm. However, this method requires the pickling solution temperature to be controlled between 50 and 70°C. Within this temperature range, the main components of the pickling solution, hydrofluoric acid and nitric acid, volatilize significantly, reducing the concentration of the pickling solution and affecting the pickling effect. Furthermore, the volatilized hydrofluoric acid and nitric acid gases are toxic and pose significant health risks.

[0005] Patent CN 119407483A discloses a method for preparing seamless titanium alloy tubes by hot deformation after introducing an intermediate. This method involves introducing a metal intermediate with lower plasticity and higher strength than the titanium alloy tube blank and then hot-deforming it to obtain the titanium alloy tube. However, this method requires that only axial deformation occur during the hot deformation of the tube blank, without radial deformation. There is no corresponding hot deformation method in actual production, and the patent does not clearly indicate how to achieve this unidirectional ideal deformation. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a method for producing small-diameter, thick-walled near-α-type titanium alloy tubing and its application. The production method has a short preparation cycle, and the resulting near-α-type titanium alloy tubing has a uniform microstructure, no cracks on the inner and outer walls, excellent mechanical properties, and a high yield.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for producing small-diameter, thick-walled near-α-type titanium alloy tubing, comprising the following steps:

[0009] S1: Provides near-α type titanium alloy forged bars;

[0010] S2: After forming a silica aerogel layer on the surface of the titanium alloy forging bar, a coating layer is then formed on the surface of the silica aerogel layer; the bar is then subjected to hot rolling, annealing, drilling, one cold rolling pass, and pickling and degreasing to obtain a small-diameter, thick-walled near-α type titanium alloy tube.

[0011] The coating material is selected from metallic materials with a thermal conductivity of 10~20 W / mK;

[0012] The deformation during the heated rolling process is 65-85%.

[0013] Preferably, the near-α type titanium alloy tube has an outer diameter of 8~50 mm and a wall thickness of 1.6~15 mm; the ratio of wall thickness to outer diameter is 0.2~0.3:1.

[0014] Preferably, the thickness of the silica aerogel layer is 1~3 μm.

[0015] Preferably, the thickness of the coating layer is 0.5~1 mm.

[0016] Preferably, the material of the coating layer is selected from copper and / or stainless steel.

[0017] Preferably, the temperature of the heated rolling is 880~950℃, and the deformation is 65~85%.

[0018] Preferably, the annealing temperature is 680~750℃ and the time is 1.5~3 h.

[0019] Preferably, the roughness of the tube blank obtained after drilling is 0.1~0.5 μm.

[0020] Preferably, the rolling Q value of the cold rolling is 1 to 1.9, and the deformation amount of the cold rolling is 0.4 to 0.65.

[0021] Preferably, the near-α type titanium alloy forged bar is obtained by melting and forging titanium alloy electrodes;

[0022] The titanium alloy electrode, by weight, consists of Al 2.0~3.5%, Zr 2.0~2.5%, impurities: iron not more than 0.2%, silicon not more than 0.1%, carbon not more than 0.1%, nitrogen not more than 0.03%, hydrogen not more than 0.002%, oxygen not more than 0.1%, and other impurities not exceeding 0.3%; the balance is titanium.

[0023] Secondly, the present invention provides an application of the above-mentioned small-diameter, thick-walled near-α-type titanium alloy tube in the heat transfer pipe system of a steam generator for a modular nuclear reactor.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] This invention, by employing cladding and heated rolling, increases the deformation per rolling pass, reduces the number of rolling passes, and results in a finer microstructure and better mechanical properties in the heated rolled tubing. Simultaneously, the composite material, consisting of the cladding layer and silica aerogel, effectively prevents the alloy bar from contacting air, avoiding further surface oxidation and reducing the thickness of the oxide layer on the bar surface. Furthermore, the composite material forms a "thermal insulation layer" on the surface of the alloy bar, preventing large temperature differences between the bar surface and core during heated rolling, thus ensuring better microstructure uniformity and surface quality. In this invention, the cladding of the alloy bar expands the selection of heating furnaces and reduces equipment requirements. In summary, this invention, without adding more production equipment, introduces cladding strip warm rolling, increases the deformation per pass, reduces the number of rolling passes, and only requires one cold rolling pass, shortening the original multi-pass cold rolling process. This facilitates continuous batch production of pipes, resulting in pipes with uniform structure, fine grains, and no defects such as cracks on the inner and outer surfaces. It also results in high production efficiency and excellent forming quality. Attached Figure Description

[0026] Figure 1 This is a cold-state microstructure image of the finished pipe obtained after pickling and degreasing in Example 1;

[0027] Figure 2 This is the BC diagram of the finished pipe material from Example 1;

[0028] Figure 3 This is the IPF+GB diagram of the finished pipe material from Example 1;

[0029] Figure 4 This is a diagram showing the external surface defects of the finished pipe from Example 1.

[0030] Figure 5 This is a diagram showing the inner surface defects of the finished pipe from Example 1. Detailed Implementation

[0031] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] Given the low thermal conductivity and susceptibility to oxidation of titanium alloys, titanium alloy tube blanks are mostly heat-treated using vertical / horizontal vacuum furnaces. Compared to inclined-bottom furnaces, walking beam furnaces, and roller furnaces, vacuum furnaces can effectively prevent oxidation of the titanium alloy tube blank surface. However, the addition of components such as vacuum pumps, highly sealed cavities, and vacuum gauges to the furnace equipment increases both equipment procurement and maintenance costs. Traditional methods for producing titanium alloy tubes typically require multiple passes of cold rolling and annealing, resulting in longer production cycles and higher production costs.

[0033] To address the aforementioned technical issues, this invention provides a low-cost, short-cycle, simple-equipment-use production method for small-diameter, thick-walled near-α-type titanium alloy tubes with excellent surface quality. This method optimizes the traditional multi-pass cold rolling + annealing tube rolling process. Furthermore, the near-α-type titanium alloy tubes prepared by this invention exhibit uniform microstructure, crack-free inner and outer walls, excellent mechanical properties, and high yield, providing technical support for the preparation and application of near-α-type titanium alloy tubes in my country. In this invention, the small diameter refers to the outer diameter of the titanium alloy tube being in the range of 8 to 50 mm, such as 8 mm, 10 mm, 20 mm, 30 mm, 40 mm, or 50 mm; the thick wall refers to the wall thickness of the titanium alloy tube being in the range of 1.6 to 15 mm, such as 1.6 mm, 3 mm, 5 mm, 8 mm, 10 mm, 12 mm, or 15 mm; and the ratio of wall thickness to outer diameter is 0.2 to 0.3:1, such as 0.2:1, 0.21:1, 0.22:1, 0.23:1, 0.24:1, 0.25:1, 0.26:1, 0.27:1, 0.28:1, 0.29:1, or 0.3:1, etc., which can be determined according to the product requirements.

[0034] In this invention, the method for producing the small-diameter, thick-walled near-α-type titanium alloy tube includes the following steps:

[0035] S1: Provides near-α type titanium alloy forged bars;

[0036] S2: After forming a silica aerogel layer on the surface of the titanium alloy forging bar, a coating layer is then formed on the surface of the silica aerogel layer; the bar is then subjected to hot rolling, annealing, drilling, one cold rolling pass, and pickling to remove oil, in sequence, to obtain a small-diameter, thick-walled near-α type titanium alloy tube.

[0037] Specifically, in some embodiments of the present invention, the main steps of the above-mentioned production method include, in sequence: smelting → forging → cladding strip warm rolling → annealing → drilling to prepare tube blanks → cold rolling → pickling and degreasing. The cladding strip warm rolling refers to performing the cladding as described in step S2 above, followed by strip warm rolling.

[0038] The following explanations and descriptions are provided to better understand the technical solution of the present invention.

[0039] In this invention, the smelting process specifically involves using a vacuum arc remelting furnace to smelt near-α type titanium alloy electrodes to obtain near-α type titanium alloy ingots. The composition of the titanium alloy electrodes is as follows (by weight): Al 2.0~3.5%; Zr 2.0~2.5%; impurity element control requirements: iron not more than 0.2%, silicon not more than 0.1%, carbon not more than 0.1%, nitrogen not more than 0.03%, hydrogen not more than 0.002%, oxygen not more than 0.1%, and other impurities not exceeding 0.3% in total; balance titanium.

[0040] The aforementioned Al 2.0~2.5% can be 2.0%, 2.1%, 2.2%, 2.3%, 2.4% or 2.5%, etc.

[0041] The Zr content of 2.0~2.5% mentioned above can be 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, or 2.5%, etc.

[0042] In this invention, the forging process involves blanking and forging a smelted near-α type titanium alloy to obtain a near-α type titanium alloy forging bar.

[0043] In this invention, the hot rolling of the coated strip is a key technical means, specifically including the following steps:

[0044] A 1-3 mm thick layer of silica aerogel is uniformly coated onto the surface of the titanium alloy forging bar as a lubricant. Then, a 0.5-1 mm thick cladding material is used to completely coat the titanium alloy forging bar, with the cladding joints welded together. The cladding material is a ductile metal, preferably with a thermal conductivity slightly lower than that of the rolling alloy. For example, a metal with a thermal conductivity of 10-20 W / mK can be used, specifically copper and / or stainless steel. After cladding, the rolling process is appropriately allocated, and the titanium alloy bar is subjected to heated rolling. The rolling deformation during the heated rolling process is 65-85%, and the temperature is controlled within the α+β two-phase region of the titanium alloy. In this temperature range, the alloy bar will undergo dynamic recrystallization, which can eliminate work hardening, refine the grains, and improve the toughness of the alloy bar. Preferably, the temperature is 50-100℃ at the β transformation temperature, specifically 880-950℃, such as 880℃, 890℃, 900℃, 910℃, 920℃, 930℃, 940℃, or 950℃.

[0045] The aforementioned 1~3 mm can be 1 mm, 1.2 mm, 1.5 mm, 1.8 mm, 2 mm, 2.2 mm, 2.5 mm, 2.8 mm or 3 mm, etc.

[0046] The aforementioned 0.5~1 mm can be 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, or 1 mm, etc.

[0047] The aforementioned deformation amount is 65-85%, and can be 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, or 80%, etc.

[0048] It should be noted that the temperature control of the above-mentioned heated rolling is carried out in the α+β two-phase region of the titanium alloy. In this temperature range, the alloy bar will undergo dynamic recrystallization, which can eliminate work hardening, refine the grains, and improve the toughness of the alloy bar. At the same time, since titanium alloy has low thermal conductivity, the present invention uses heated rolling process instead of cold rolling process, which can increase the deformation per rolling pass and reduce the number of rolling passes. Moreover, the microstructure of the heated rolled tube is fully refined, and the mechanical properties are better. However, during heated rolling, there is a temperature gradient between the surface and core of the alloy bar. The large temperature difference will aggravate the uneven metal flow, and the large tensile stress on the surface will make the bar surface prone to cracking during deformation. The present invention uses a multilayer material composed of a coating layer and silica aerogel. On the one hand, it can effectively block the alloy bar from contacting the air, avoid further surface oxidation, and reduce the thickness of the oxide layer on the bar surface. On the other hand, it can form a "thermal insulation layer" on the surface of the alloy bar, avoiding a large temperature difference between the bar surface and core during heated rolling, thereby ensuring the surface quality of the bar. After coating, the bar stock is not sensitive to the choice of heating furnace and can be heated using a non-vacuum heating furnace.

[0049] In this invention, the annealing process serves to further eliminate the internal stress caused by thermal deformation. The annealing temperature is between 680 and 750°C, such as 680°C, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C, or 750°C; the holding time is 1.5 to 3 hours, such as 1.5 hours, 2.0 hours, 2.5 hours, or 3.0 hours; and the cooling method is air cooling or furnace cooling.

[0050] In this invention, the drilling is mainly used for preparing the tube blank. Specifically, this invention uses machining to remove the cladding material on the surface of the titanium alloy bar and then performs drilling to prepare the titanium alloy tube blank. The titanium alloy tube blank prepared by this invention has smooth inner and outer surfaces with no machining marks remaining, and a roughness of 0.1~0.5 μm, such as 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, or 0.5 μm, etc.

[0051] It should be noted that in this invention, the roughness described above has been screened and optimized. If it is greater than 0.5 μm, it will prevent the subsequent cold rolling process from yielding cold-rolled tubes with good internal and external surface quality, and defects such as cracks and fissures will easily appear on the inner and outer walls of the tubes, thus reducing the tube yield. Conversely, if it is less than 0.1 μm, although the quality can be improved, the cost will increase significantly.

[0052] In this invention, the cold rolling is a single-pass rolling process, which significantly reduces the number of rolling passes compared to conventional methods. In some embodiments of this invention, the cold rolling is performed using a two-roll Pilger tube mill to roll the titanium alloy tube blank.

[0053] As a preferred embodiment, the rolling Q value of the cold rolling process is controlled between 1 and 1.9, such as 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or 1.9; the deformation is controlled between 40% and 65%, such as 40%, 45%, 50%, 55%, 60%, or 65%. Under these process conditions, the pipe is more likely to obtain radial texture, and the corresponding pipe flattening and flaring performance is also superior.

[0054] It should be noted that if the deformation is less than 0.4, the cold rolling process will fail to achieve the target size in one pass; if the deformation is greater than 0.65, the excessive deformation will cause the pipe to crack during the rolling process.

[0055] If the rolling Q value is less than 1, the tube's microstructure will tend towards a circumferential texture; conversely, if the Q value is greater than 1, the tube's microstructure will tend towards a radial texture. Existing research shows that tubes with radial texture have superior strength, plasticity, flattening performance, and flaring performance. However, due to the size limitations of small-diameter, thick-walled tubes, an excessively large Q value will result in wall reduction far exceeding diameter reduction, making it difficult to achieve this change through a single cold rolling pass.

[0056] Therefore, in order to achieve the results described in this invention, the parameter range given in this patent should be preferred.

[0057] In this invention, rolling oil is used for cooling and lubrication during cold rolling, so the cold-rolled billet needs to be pickled to remove oil. This pickling is a conventional technique in the art. In some embodiments of this invention, the pickling solution mainly consists of hydrofluoric acid, nitric acid, and water, with a volume ratio of (2~10):(20~25):(65~78). Those skilled in the art can adjust the above ratio as needed. Hydrofluoric acid can corrode and remove oxide scale, and nitric acid can alleviate hydrogen absorption by the titanium alloy during the pickling process.

[0058] In summary, the near-α type titanium alloy tubes prepared according to the above-mentioned production method provided by the present invention can, while meeting the requirements of small diameter and thick wall, have the characteristics of uniform structure, no cracks in the inner and outer walls, excellent mechanical properties, and high yield.

[0059] Based on this, the present invention also provides an application of the above-mentioned small-diameter thick-walled near-α type titanium alloy tube in the heat transfer pipe pipeline of a steam generator for a modular nuclear reactor.

[0060] To further illustrate the present invention, the following embodiments provide a detailed description. The experimental materials used in the following embodiments of the present invention are all commercially available products.

[0061] Example 1

[0062] First, the titanium alloy raw materials are uniformly mixed and pressed into electrodes. The electrodes are then melted three times in a vacuum arc remelting furnace to obtain alloy ingots. The titanium alloy raw material composition is: Al 2.0%; Zr 2.5%; impurity element control requirements: iron 0.1%, silicon 0.05%, carbon 0.01%, nitrogen 0.005%, hydrogen 0.001%, oxygen 0.06%, other impurities not exceeding 0.3%; balance titanium. After the titanium alloy ingot is removed from the furnace, it is roughened and forged to obtain a near-α type titanium alloy forged bar with a size of Φ36 mm. A 1.0 mm thick layer of silica aerogel is uniformly coated on the surface of the titanium alloy forged bar as a lubricant. Then, a 0.5 mm thick stainless steel foil is used as a cladding material to completely clad the titanium alloy forged bar, and the cladding joint is welded together. After cladding, the rolling process is rationally allocated, and the titanium alloy bar is subjected to heated rolling with a rolling deformation of 78%, resulting in a rolled alloy size of Φ17 mm. The rolling temperature was controlled at 850℃. After rolling, the titanium alloy billet was annealed at 700℃ for 2 hours, and then cooled by furnace cooling. After annealing, the titanium alloy billet was machined to remove the surface coating and drill holes, resulting in smooth inner and outer surfaces without machining marks and a surface roughness Ra=0.5 μm. The prepared titanium alloy tube billet with dimensions of Φ15×4mm was cold rolled using a two-roll Pilger tube mill. The rolling Q value was 1.5, and the deformation was controlled at 0.636. After cold rolling, it was pickled and degreased, finally yielding a titanium alloy tube with dimensions of Φ10×2 mm (wall thickness to outer diameter ratio = 0.2).

[0063] Figure 1 This is a cold-state microstructure image of the finished pipe after pickling and degreasing. Figure 2 This is the BC diagram of the finished pipe material from Example 1; Figure 3 This is the IPF+GB diagram of the finished pipe from Example 1. (From...) Figures 1-3 It can be seen that the cold-rolled microstructure is elongated along the rolling direction, with an average grain size of approximately 5.8 μm, and the microstructure is uniform, with no abnormally large grains observed. Visual inspection of the inner and outer surfaces revealed that the inner and outer surfaces of the rolled tube were smooth, without defects such as folds, large cracks, fissures, or burrs. Figure 4 This is a diagram showing the external surface defects of the finished pipe from Example 1. Figure 5 This is an image of the inner surface defects of the finished pipe from Example 1 under a 50x optical microscope. Figure 4 and Figure 5 It can be seen that, when the inner and outer surfaces of the finished pipe are observed under a high-magnification electron microscope, the depth of the small defects is less than 7 μm, and the surface quality is good.

[0064] Example 2

[0065] First, the titanium alloy raw materials are uniformly mixed and pressed into electrodes. The electrodes are then melted three times in a vacuum arc remelting furnace to obtain alloy ingots. The titanium alloy raw material composition is: Al 3.5%; Zr 2.0%; impurity element control requirements: iron 0.05%, silicon 0.001%, carbon 0.01%, nitrogen 0.0015%, hydrogen 0.001%, oxygen 0.05%, other impurities not exceeding 0.3%; balance titanium. After the titanium alloy ingots are removed from the furnace, they are roughened and forged to obtain near-α type titanium alloy forged bars with a size of Φ75 mm. A 1.5 mm thick layer of silica aerogel is uniformly coated on the surface of the titanium alloy forged bar as a lubricant. Then, a 0.5 mm thick Cu foil is used as a cladding material to completely clad the titanium alloy forged bar, and the cladding joints are welded together. After cladding, the rolling process is rationally allocated, and the titanium alloy bar is subjected to heated rolling with a rolling deformation of 80%, resulting in a final alloy size of Φ34 mm. The rolling temperature was controlled at 880℃. After rolling, the titanium alloy billet was annealed at 720℃ for 2 hours, and the cooling method was furnace cooling. After annealing, the titanium alloy billet was machined to remove the cladding layer on the surface of the titanium alloy bar and drilled holes, so that the inner and outer surfaces of the billet were smooth and free of machining marks, with a roughness Ra=0.5 μm. The prepared titanium alloy tube billet had a size of Φ32×7.5mm and was cold rolled using a two-roll Pilger tube rolling mill. The rolling Q value was 1.52, and the deformation was controlled at 0.46. After cold rolling, it was pickled and degreased, finally obtaining a titanium alloy tube with a size of Φ25×5 mm (referring to an outer diameter of 25 mm and a wall thickness of 5 mm) (the ratio of wall thickness to outer diameter = 0.2).

[0066] Example 3

[0067] First, the titanium alloy raw materials are uniformly mixed and pressed into electrodes. The electrodes are then melted three times in a vacuum arc remelting furnace to obtain alloy ingots. The titanium alloy raw material composition is: Al 3.0%; Zr 2.2%; impurity element control requirements: iron 0.1%, silicon 0.035%, carbon 0.01%, nitrogen 0.005%, hydrogen 0.001%, oxygen 0.06%, other impurities not exceeding 0.3%; balance titanium. After the titanium alloy ingot is removed from the furnace, it is roughened and forged to obtain a near-α type titanium alloy forged bar with a size of Φ36 mm. A 1.5 mm thick layer of silica aerogel is uniformly coated on the surface of the titanium alloy forged bar as a lubricant. Then, a 0.5 mm thick Cu foil is used as a cladding material to completely clad the titanium alloy forged bar, and the cladding joint is welded together. After cladding, the rolling process is rationally allocated, and the titanium alloy bar is subjected to heated rolling with a rolling deformation of 78%, resulting in a rolled alloy size of Φ24 mm. The rolling temperature was controlled at 870℃. After rolling, the titanium alloy billet was annealed at 700℃ for 2 hours, and then cooled by furnace cooling. After annealing, the titanium alloy billet was machined to remove the surface coating and drill holes, resulting in smooth inner and outer surfaces without machining marks and a surface roughness Ra=0.5 μm. The prepared titanium alloy tube billet with dimensions of Φ22×5 mm was cold rolled using a two-roll Pilger tube mill. The rolling Q value was 1.32, and the deformation was controlled at 0.44. After cold rolling, it was pickled and degreased, finally yielding a titanium alloy tube with dimensions of Φ17×3.5 mm (wall thickness to outer diameter ratio = 0.21).

[0068] Comparative Example 1

[0069] First, the titanium alloy raw materials are uniformly mixed and pressed into electrodes. The electrodes are then melted three times in a vacuum arc remelting furnace to obtain alloy ingots. The titanium alloy raw material composition is: Al 2.0%; Zr 2.5%; impurity element control requirements: iron 0.1%, silicon 0.05%, carbon 0.01%, nitrogen 0.005%, hydrogen 0.001%, oxygen 0.06%, other impurities not exceeding 0.3%; balance titanium. After the titanium alloy ingot is removed from the furnace, it is roughened and forged to obtain a near-α type titanium alloy forged bar with a size of Φ36 mm. A 1.0 mm thick layer of silica aerogel is uniformly coated on the surface of the titanium alloy forged bar as a lubricant. Then, a 0.5 mm thick low-carbon steel foil is used as a cladding material to completely clad the titanium alloy forged bar, and the cladding interface is welded together. After cladding, the rolling process is rationally allocated, and the titanium alloy bar is subjected to heated rolling with a rolling deformation of 78%, resulting in a rolled alloy size of Φ17 mm. The rolling temperature was controlled at 850℃. After rolling, the titanium alloy billet was annealed at 700℃ for 2 hours, and then cooled by furnace cooling. After annealing, the titanium alloy billet was machined to remove the surface coating and drill holes, resulting in smooth inner and outer surfaces without machining marks and a surface roughness Ra=0.5 μm. The prepared titanium alloy tube blank had a size of Φ14×3mm. It was cold rolled using a two-roll Pilger tube mill. The rolling Q value was 1.2, and the deformation was controlled at 0.5. After cold rolling, it was pickled and degreased, finally obtaining a titanium alloy tube with a size of Φ10×2mm (wall thickness to outer diameter ratio = 0.2).

[0070] Compared with Example 1, Comparative Example 1 differs in the following aspects:

[0071] (1) Differences exist in the types of cladding materials. The thermal conductivity of the forged bar to be clad was measured to be 14 W / mK, while the thermal conductivity of the low-carbon steel in the comparative example was approximately 54 W / mK, and the thermal conductivity of the stainless steel foil used in Example 1 was approximately 12 W / mK. In Example 1, the thermal conductivity of the stainless steel foil was close to and slightly lower than that of the forged bar to be clad. During the cladding strip rolling process, the stainless steel foil formed a "thermal insulation layer" on the surface of the forged bar, avoiding a large temperature difference between the bar surface and the core, resulting in good uniformity of the bar structure. In Comparative Example 1, the thermal conductivity of the low-carbon steel foil was higher than that of the forged bar to be clad. During the strip rolling process, a temperature gradient was generated between the bar surface and the core due to the difference in thermal conductivity, resulting in a large difference between the outer surface structure and the core structure of the bar after the cladding strip rolling annealing, leading to poor uniformity of the tube structure.

[0072] (2) The dimensions of the tube blanks differ after mechanical processing such as drilling. The metal removal amount in Comparative Example 1 is greater, resulting in a lower tube yield in Comparative Example 1 compared to Example 1. To ensure the uniformity of the finished tube structure, the metal removal amount on the outer surface of the tube in Comparative Example 1 needs to be increased, resulting in a slightly smaller tube size after drilling compared to Example 1, which is Φ14×3 mm. In the drilling process, the metal removal amount of the bar in Example 1 is approximately 44.6% during mechanical processing; the metal removal amount of the bar in Comparative Example 1 is approximately 54.3%, indicating a higher tube yield in Example 1.

[0073] (3) The cold rolling process parameters changed in one pass. Because the billet size of Comparative Example 1 and Example 1 was different after drilling, the process parameters of the last rolling pass were also adjusted accordingly. In order to obtain a pipe with a target size of Φ10×2 mm, the Q value in Comparative Example 1 was 1.2, and the deformation was controlled at 0.5.

[0074] In summary, compared with Example 1, the selection of the coating material in Comparative Example 1 was unreasonable, resulting in a decrease in the yield of pipes.

[0075] Comparative Example 2

[0076] First, the titanium alloy raw materials are uniformly mixed and pressed into electrodes. The electrodes are then melted three times in a vacuum arc remelting furnace to obtain alloy ingots. The titanium alloy raw material composition is: Al 3.5%; Zr 2.0%; elemental control requirements: iron 0.05%, silicon 0.001%, carbon 0.01%, nitrogen 0.0015%, hydrogen 0.001%, oxygen 0.05%, other impurities not exceeding 0.3%; balance titanium. After the titanium alloy ingots are removed from the furnace, they are roughened and forged to obtain near-α type titanium alloy forged bars with a diameter of Φ75 mm. No lubricant is applied to the surface of the titanium alloy forged bars; instead, a 0.5 mm thick Cu foil is used as the cladding material to directly clad the entire titanium alloy forged bar, and the cladding joints are welded together. After cladding, the rolling process is rationally allocated, and the titanium alloy bar is subjected to heated rolling at a temperature controlled at 880℃, with a rolling deformation of 80%, resulting in a final alloy size of Φ34 mm.

[0077] Because no lubricant was applied to Comparative Example 2, the coating layer cracked during the rolling process, making it impossible to proceed with subsequent processing steps.

[0078] Comparative Example 3

[0079] First, the titanium alloy raw materials are uniformly mixed and pressed into electrodes. The electrodes are then melted three times in a vacuum arc remelting furnace to obtain alloy ingots. The titanium alloy raw material composition is: Al 3.0%; Zr 2.2%; impurity element control requirements: iron 0.1%, silicon 0.035%, carbon 0.01%, nitrogen 0.005%, hydrogen 0.001%, oxygen 0.06%, other impurities not exceeding 0.3%; balance titanium. After the titanium alloy ingot is removed from the furnace, it is roughened and forged to obtain a near-α type titanium alloy forged bar with a size of Φ36 mm. A 1.5 mm thick layer of silica aerogel is uniformly coated on the surface of the titanium alloy forged bar as a lubricant. Then, a 0.5 mm thick Cu foil is used as a cladding material to completely clad the titanium alloy forged bar, and the cladding joint is welded together. After cladding, the rolling process is rationally allocated, and the titanium alloy bar is subjected to heated rolling with a rolling deformation of 78%, resulting in a rolled alloy size of Φ24 mm. The rolling temperature was controlled at 870℃. After rolling, the titanium alloy billet was annealed at 700℃ for 2 hours, and then cooled by furnace cooling. After annealing, the titanium alloy billet was machined to remove the cladding layer on the surface of the titanium alloy bar and drilled holes, resulting in smooth inner and outer surfaces of the billet with no machining marks and a surface roughness Ra=0.5 μm. The prepared titanium alloy tube billet had a size of Φ20×5 mm and was cold rolled using a two-roll Pilger tube mill. The rolling Q value was 2, and the deformation was controlled at 0.37. After cold rolling, it was pickled and degreased, finally obtaining a titanium alloy tube with a size of Φ17×3.5 mm (wall thickness to outer diameter ratio = 0.21).

[0080] Compared to Example 3, Comparative Example 3 changed the billet size for the final cold rolling pass, resulting in changes to the final cold rolling parameters. The Q value was set to 2, exceeding the upper limit (1~1.9), and the deformation was set to 0.37, exceeding the lower limit (0.4~0.65). The change in billet size led to a 7% increase in the amount of metal removed during drilling and internal / external surface treatment, resulting in a decrease in the tube yield. Furthermore, significant cracks appeared on the inner surface of the rolled tube, indicating a poorer surface quality compared to Example 3.

[0081] Performance testing

[0082] Performance testing included room temperature tensile tests and 350°C high-temperature tensile tests. The room temperature tensile test was performed according to GB / T 228.1, and the high-temperature tensile test was performed according to GB / T 228.2. 5% of the pipes obtained in Example 1 were randomly selected from each batch, but no fewer than two pipes were allowed. One tensile specimen was taken from each end of each pipe. The experimental results are shown in Table 1 (room temperature tensile test) and Table 2 (high-temperature tensile test):

[0083] Table 1

[0084]

[0085] Table 2

[0086]

[0087] It can be seen that the cold rolling yield of small-diameter, thick-walled near-α type titanium alloy tubes prepared according to this method is controlled at 100%.

[0088] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method of producing a small-diameter, thick-walled, near-alpha titanium alloy tube, characterized by, The method comprises the following steps: S1: providing a near-alpha titanium alloy forging bar; S2: forming a silica aerogel layer on the surface of the titanium alloy forging bar, and then forming a cladding layer on the surface of the silica aerogel layer; sequentially performing warm rolling, annealing, drilling, one-pass cold rolling, and acid pickling to remove oil to obtain a small-diameter thick-wall near-alpha titanium alloy pipe; the cladding layer material on the surface of the titanium alloy bar is removed by mechanical processing before drilling; The material of the cladding layer is selected from a metal material with a thermal conductivity of 10-20 W / mK; The temperature of the warm rolling is 880-950℃, and the deformation is 65-85%; The roughness of the pipe blank obtained after drilling is 0.1-0.5 μm; The rolling Q value of the cold rolling is 1-1.9, and the deformation of the cold rolling is 0.4-0.

65.

2. The production method according to claim 1, characterized by, The outer diameter of the near-alpha titanium alloy pipe is 8-50 mm, the wall thickness is 1.6-15 mm, and the ratio of the wall thickness to the outer diameter is 0.2-0.3:

1.

3. The production method according to claim 1 or 2, characterized by, The thickness of the silica aerogel layer is 1-3 μm.

4. The production method according to claim 1, characterized by, The thickness of the cladding layer is 0.5-1 mm; The material of the cladding layer is selected from copper and / or stainless steel.

5. The production method according to claim 1, characterized by, The annealing temperature is 680-750℃, and the time is 1.5-3 h.

6. The production method according to claim 1, characterized by, The near-alpha titanium alloy forging bar is obtained by melting and forging a titanium alloy electrode; The titanium alloy electrode comprises, by weight, Al 2.0-3.5%, Zr 2.0-2.5%, iron ≤0.2%, silicon ≤0.1%, carbon ≤0.1%, nitrogen ≤0.03%, hydrogen ≤0.002%, oxygen ≤0.1%, other impurities ≤0.3%, and the balance of titanium.

7. Application of the small-diameter thick-wall near-alpha titanium alloy pipe prepared by the production method of any one of claims 1-6 in a steam generator heat transfer pipe circuit of a modular nuclear reactor.

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