Preparation method of high-precision small-caliber titanium steel composite pipe

Abstract

The invention provides a preparation method of a small-caliber titanium-steel composite pipe, which comprises the following steps: firstly, carrying out pipe bending forming on a titanium-steel composite plate by adopting a JCO process, and then carrying out titanium-titanium and steel-steel welding to obtain a titanium-steel composite welded pipe; and then annealing the titanium steel composite welded pipe obtained in the previous step, and then carrying out cold machining and vacuum annealing to obtain the small-caliber titanium steel composite pipe. The cold processing comprises cold rolling and / or cold drawing. According to the preparation method of the small-caliber titanium-steel composite pipe, the technical difficulty of direct compounding is reduced, the welding operation problem of small-caliber pipe titanium on the inner side is avoided, and meanwhile, the appearance precision of a cold-drawn product is higher. According to the method, the bonding strength can be guaranteed, high-precision control is achieved, and continuous and large-scale production capacity can be achieved. By the adoption of the mode, the high-precision titanium steel composite pipe with the diameter smaller than 300 mm can be obtained, and the average economic benefit can reach 0.5 million yuan / ton.

Description

Technical Field

[0001] The present invention belongs to the technical field of small-caliber titanium-steel composite pipe processing, and relates to a preparation method and application of small-caliber titanium-steel composite pipes, in particular to a preparation method of high-precision small-caliber titanium-steel composite pipes. Background Art

[0002] Titanium-steel composite pipes combine the excellent corrosion resistance of titanium materials and the high strength of steel itself, and have great prospects in the field of conveying corrosive media, such as chemical media, seawater conveying pipelines and other fields. Therefore, the market demand is becoming more and more extensive.

[0003] At present, there are mainly two types of titanium-steel composite pipes: seamless composite pipes and welded (seamed) composite pipes. Seamless composite pipes are mostly produced by explosive cladding methods, but the explosive methods have deficiencies such as poor pipe shape control, environmental pollution, and low production efficiency. There are also methods of mechanical cladding, for example, two seamless pipes of titanium and steel are sleeved together in the form of inner titanium and outer steel for pressure expansion jointing. Through expansion, plastic deformation occurs, and after the pressure is released, they are closely fitted due to different springback amounts of the two. However, the titanium-steel composite pipes prepared by this method mainly rely on interference fit, and the interface does not achieve metallurgical bonding. After bearing a certain external force, the titanium and steel are prone to delamination, and the service life is limited. In addition, there are also methods of preparing titanium-steel composite pipes by casting, hot rolling or hot extrusion, but the brittle compound phases at the titanium-steel interface are not easy to control, the process is complex, the technical difficulty is large and it is not easy to control.

[0004] For welded composite pipes, the already-compounded titanium-steel composite plates are welded into pipes. Since the raw materials already have good metallurgical bonding effects, the bonding strength of the products is high and the cost is lower. As is well known, titanium and steel cannot be directly welded. Therefore, when welding titanium-steel composite plates, the method of welding titanium-titanium and steel-steel separately from both sides is often used. Therefore, when the pipe diameter is small and the titanium layer is inside, the inner titanium-titanium welding is not easy to operate, and the preparation of small-caliber pipes cannot be achieved. At present, there is no titanium-steel composite welded pipe with a pipe diameter < 300 mm on the market, and it can only be prepared by other methods such as mechanical bonding or explosive cladding.

[0005] Therefore, how to develop a more suitable preparation method for small-caliber titanium-steel composite pipes to solve the above technical problems existing in the preparation process of existing small-caliber titanium-steel composite pipes has become one of the urgent problems to be solved by many front-line researchers in the industry. Summary of the Invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a preparation method and application of a small-diameter titanium-steel composite pipe, in particular a preparation method of a high-precision small-diameter titanium-steel composite pipe. The novel preparation method of the titanium-steel composite small-diameter pipe provided by the present invention can obtain a high-precision titanium-steel composite pipe with a diameter < 300 mm, which can not only ensure the bonding strength, achieve high-precision control, but also have the ability of continuous and large-scale production. Moreover, the preparation method has simple process, mild conditions, good controllability and strong stability.

[0007] The present invention provides a preparation method of a small-diameter titanium-steel composite pipe, comprising the following steps:

[0008] 1) The titanium-steel composite plate is formed into a bent pipe by the JCO process, and then welded between titanium-titanium and steel-steel to obtain a titanium-steel composite welded pipe;

[0009] 2) The titanium-steel composite welded pipe obtained in the above step is annealed, and then a small-diameter titanium-steel composite pipe is obtained after cold working and vacuum annealing;

[0010] The cold working includes cold rolling and / or cold drawing.

[0011] Preferably, the titanium-steel composite welded pipe includes a titanium-steel composite welded pipe with steel on the outside and titanium on the inside or a titanium-steel composite welded pipe with titanium on the outside and steel on the inside;

[0012] The outer diameter of the titanium-steel composite welded pipe is less than or equal to 600 mm.

[0013] Preferably, the interface temperature of the welding is less than or equal to 800 °C;

[0014] After the welding, it further includes the steps of weld treatment and roundness correction.

[0015] Preferably, the annealing temperature is 550-800 °C;

[0016] The annealing time is 60-240 min.

[0017] Preferably, when the wall thickness of the titanium-steel composite welded pipe is less than or equal to 20 mm, the annealing time is less than or equal to 180 min;

[0018] The annealing method includes annealing under a protective atmosphere or vacuum annealing.

[0019] Preferably, the cold working includes single-pass or multi-pass cold working;

[0020] When the cold working is multi-pass cold working, vacuum annealing is carried out after each pass of cold working.

[0021] Preferably, the cumulative deformation amount of the cold working ≤ 75%;

[0022] The deformation amount per pass of the cold working is ≤ 50%;

[0023] The wall thickness reduction per pass of the cold working is ≤ 2 mm.

[0024] Preferably, the temperature of the vacuum annealing is (800 - 8S) °C; where S is the wall thickness in mm;

[0025] The time of the vacuum annealing is (20 × S) min; where S is the wall thickness in mm.

[0026] Preferably, the outer diameter of the small-diameter titanium-steel composite pipe is less than or equal to 300 mm;

[0027] The wall thickness of the small-diameter titanium-steel composite pipe is 0.5 - 10 mm.

[0028] The present invention also provides an application of the preparation method described in any one of the above technical solutions in the preparation of small-diameter titanium-steel composite pipes;

[0029] The outer diameter of the small-diameter titanium-steel composite pipe is less than or equal to 300 mm.

[0030] The present invention provides a preparation method of a small-diameter titanium-steel composite pipe, including the following steps: First, the titanium-steel composite plate is formed into a bent pipe by the JCO process, and then after titanium-titanium and steel-steel welding, a titanium-steel composite welded pipe is obtained; then the titanium-steel composite welded pipe obtained in the above step is annealed, and then after cold working and vacuum annealing, a small-diameter titanium-steel composite pipe is obtained; the cold working includes cold rolling and / or cold drawing. Compared with the prior art, the present invention creatively designs a preparation method of a small-diameter titanium-steel composite pipe with specific steps, adopting the process route of titanium-steel composite plate raw material → bent pipe forming → titanium and steel welding respectively → weld treatment → roundness correction → annealing → cold working (cold rolling or cold drawing) → annealing → straightening → flaw detection → offline, that is, first preparing a titanium-steel composite welded pipe, and then using this as the raw material to realize diameter reduction through cold rolling or cold drawing, and finally obtaining a high-precision small-diameter titanium-steel composite pipe. The whole process reduces the technical difficulty of direct composite, avoids the welding operation problem of titanium on the inner side of small-diameter pipes, and at the same time, the shape accuracy of the product after cold drawing is higher.

[0031] The preparation method of the small-diameter titanium-steel composite pipe provided by the present invention can not only ensure the bonding strength, realize high-precision control, but also have the ability of continuous and large-scale production, and moreover, the process is simple, the conditions are mild, the controllability is good, and the stability is strong. By this method, high-precision titanium-steel composite pipes with a diameter < 300 mm can be obtained, and the average economic benefit can reach 0.5 ten thousand yuan per ton.

[0032] The preparation method provided by the present invention can be popularized and applied in the production of titanium-steel composite pipes, producing high-precision small-diameter titanium-steel composite pipes, and has good prospects for popularization and application. Detailed Embodiments

[0033] To further understand the present invention, the preferred embodiments of the present invention will be described below in conjunction with embodiments. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention, rather than limiting the claims of the invention.

[0034] For all raw materials of the present invention, there are no special restrictions on their sources, and they can be purchased on the market or prepared by conventional methods well-known to those skilled in the art.

[0035] For all raw materials of the present invention, there are no special restrictions on their purity. The present invention preferably adopts industrial purity or the conventional purity requirements in the field of titanium-steel composite pipe preparation.

[0036] For all raw materials of the present invention, their grades and abbreviations are all conventional grades and abbreviations in the art. Each grade and abbreviation is clear and definite in the field of its related uses. Those skilled in the art can obtain them from the market or prepare them by conventional methods according to the grade, abbreviation, and corresponding uses.

[0037] For the processes used in the present invention, their abbreviations are all conventional abbreviations in the art. The specific steps and conventional parameters of each abbreviation are clear and definite in their related fields. Those skilled in the art can implement them by conventional methods according to the abbreviations.

[0038] The present invention provides a method for preparing a small-diameter titanium-steel composite pipe, comprising the following steps:

[0039] 1) The titanium-steel composite plate is formed into a bent pipe by the JCO process, and then after titanium-titanium and steel-steel welding, a titanium-steel composite welded pipe is obtained;

[0040] 2) The titanium-steel composite welded pipe obtained in the above step is annealed, and then after cold working and vacuum annealing, a small-diameter titanium-steel composite pipe is obtained;

[0041] The cold working includes cold rolling and / or cold drawing.

[0042] The present invention first forms the titanium-steel composite plate into a bent pipe by the JCO process, and then after titanium-titanium and steel-steel welding, a titanium-steel composite welded pipe is obtained.

[0043] In the present invention, the titanium-steel composite welded pipe preferably includes a titanium-steel composite welded pipe with steel on the outside and titanium on the inside or a titanium-steel composite welded pipe with titanium on the outside and steel on the inside.

[0044] In the present invention, the outer diameter of the titanium-steel composite welded pipe is preferably less than or equal to 600 mm, more preferably less than or equal to 500 mm, and even more preferably less than or equal to 300 mm.

[0045] In the present invention, the interface temperature of the welding is preferably less than or equal to 800 °C, more preferably less than or equal to 750 °C, and still more preferably less than or equal to 700 °C.

[0046] In the present invention, after the welding, it preferably further includes the steps of weld treatment and roundness correction.

[0047] In the present invention, the titanium-steel composite welded pipe obtained from the above steps is continuously annealed, and then after cold working and re-continuous annealing, a small-diameter titanium-steel composite pipe is obtained.

[0048] In the present invention, the cold working includes cold rolling and / or cold drawing, and can be cold rolling or cold drawing.

[0049] In the present invention, the annealing temperature is preferably less than or equal to 800 °C, more preferably less than or equal to 750 °C, and still more preferably less than or equal to 700 °C. Specifically, it can be 550 - 800 °C, or 600 - 750 °C, or 650 - 700 °C.

[0050] In the present invention, the annealing time is preferably 60 - 240 min, more preferably 90 - 210 min, and still more preferably 120 - 180 min.

[0051] In the present invention, when the wall thickness of the titanium-steel composite welded pipe is preferably less than or equal to 20 mm, the annealing time is preferably less than or equal to 180 min, more preferably less than or equal to 150 min, and still more preferably less than or equal to 120 min.

[0052] In the present invention, the annealing method preferably includes annealing under a protective atmosphere or vacuum annealing, and more preferably vacuum annealing.

[0053] In the present invention, the cold working preferably includes single-pass or multi-pass cold working;

[0054] In the present invention, when the cold working is preferably multi-pass cold working, annealing under a protective atmosphere or vacuum annealing is performed after each pass of cold working.

[0055] In the present invention, the cumulative deformation amount of the cold working is preferably ≤ 75%, more preferably ≤ 70%, and still more preferably ≤ 65%.

[0056] In the present invention, the deformation amount of each pass of the cold working is preferably ≤ 50%, more preferably ≤ 45%, and still more preferably ≤ 40%.

[0057] In the present invention, the wall thickness reduction amount of each pass of the cold working is preferably ≤ 2 mm, more preferably ≤ 1.8 mm, and still more preferably ≤ 1.6 mm.

[0058] In the present invention, the temperature of the vacuum annealing is preferably (800 - 8S) °C; where S is the wall thickness, in mm.

[0059] In the present invention, the time of the vacuum annealing is preferably (20×S) min, where S is the wall thickness in the unit of mm.

[0060] In the present invention, the outer diameter of the small-caliber titanium-steel composite pipe is preferably less than or equal to 300 mm, more preferably less than or equal to 250 mm, and even more preferably less than or equal to 200 mm. Specifically, there is no special requirement for the outer diameter of the small-caliber titanium-steel composite pipe, which depends on the equipment boundary conditions.

[0061] In the present invention, the wall thickness of the small-caliber titanium-steel composite pipe is preferably 0.5 - 10 mm, more preferably 1 - 9 mm, even more preferably 3 - 7 mm, and even more preferably 4 - 6 mm. Specifically, there is no special requirement for the wall thickness. The above cold working and annealing can be repeated. For example, when the total deformation amount is greater than 75%, cold working can be carried out again after annealing and then annealed until the target specifications are obtained.

[0062] The present invention provides an application of the preparation method according to any one of the above technical solutions in the preparation of small-caliber titanium-steel composite pipes.

[0063] The outer diameter of the small-caliber titanium-steel composite pipe is less than or equal to 300 mm.

[0064] In order to complete and refine the overall technical solution of the present invention, better ensure the structure and performance of the small-caliber titanium-steel composite pipe, and further improve the efficiency and stability in the preparation process of the small-caliber titanium-steel composite pipe, the preparation method of the above high-precision small-caliber titanium-steel composite pipe may specifically include the following:

[0065] The process scheme adopted in the present invention is: titanium-steel composite plate raw material → pipe bending forming → welding of titanium and steel respectively → weld treatment → roundness correction → annealing → cold working (cold rolling or cold drawing) → annealing → straightening → flaw detection → off-line. That is, first prepare the titanium-steel composite welded pipe, and then use this as the raw material to realize the diameter change through cold rolling or cold drawing, and finally obtain the high-precision small-caliber titanium-steel composite pipe.

[0066] Specifically, it is preferred to use the titanium-steel composite plate produced by the rolling method. Because the thickness and the control precision of the thickness difference of the titanium-steel composite plate prepared by the rolling method are higher, the interface bonding consistency is good, which can avoid local disturbances during subsequent welding and cold drawing. At the same time, for the titanium-steel composite plate prepared by the rolling method, the plastic deformation of the two metals is carried out synchronously above the recrystallization temperature, with small internal stress and better forming performance.

[0067] Specifically, it is preferred to use the JCO process as the pipe bending forming process for the titanium-steel composite plate. JCO is progressive pressure forming, which makes the deformation of the composite plate more uniform during the forming process, with small residual stress, and can avoid the interface from shearing and rubbing.

[0068] Specifically, after the bent pipe is formed, titanium-titanium and steel-steel welding are respectively carried out on the open "O"-shaped pipe blank from the titanium and steel sides. During welding, the mutual dissolution of titanium and steel should be prevented. At the same time, it is necessary to pay attention that the heat input should not be too high, and the interface temperature should be controlled below 800 °C. Otherwise, titanium and steel will diffuse to form brittle compounds, reducing the interface bonding strength.

[0069] Specifically, grind the weld bead buildup and burrs.

[0070] Specifically, round the titanium-steel composite welded pipe.

[0071] Specifically, anneal the obtained titanium-steel composite welded pipe at a temperature below 800 °C. The annealing time is related to the thickness. When the wall thickness is less than 20 mm, the annealing time should not exceed 180 min.

[0072] Specifically, cold process the welded pipe on cold rolling or cold drawing equipment. Before cold processing, the surface oxide scale needs to be removed and then lubricant is applied. According to the finished product size requirements, single or multi-pass cold rolling can be carried out and the composite pipe after each cold rolling is subjected to vacuum annealing. Among them, the deformation amount per pass is controlled ≤50%, the wall thickness reduction is ≤2 mm, and the cumulative deformation amount is ≤75%.

[0073] The vacuum annealing temperature and time are related to the wall thickness. The specific temperature is (800 - 8 × wall thickness) °C, and the time is 20 min × wall thickness mm. The vacuum annealing temperature and time vary with the wall thickness. When the wall thickness is large, the annealing temperature is low and the time is long; when the wall thickness is small, the annealing time is short and the annealing temperature is relatively high.

[0074] Specifically, perform ultrasonic flaw detection on the obtained finished pipe.

[0075] The above content of the present invention provides a preparation method and application of a high-precision small-diameter titanium-steel composite pipe. The present invention adopts the process route of titanium-steel composite plate raw material → bent pipe forming → titanium and steel welding separately → weld treatment → rounding → annealing → cold processing (cold rolling or cold drawing) → annealing → straightening → flaw detection → offline, that is, first prepare the titanium-steel composite welded pipe, and then use this as the raw material to realize diameter reduction through cold rolling or cold drawing, and finally obtain a high-precision small-diameter titanium-steel composite pipe. The whole process reduces the technical difficulty of direct composite, avoids the welding operation problem of titanium on the inner side of small-diameter pipes, and at the same time the shape accuracy of the product is higher after cold drawing.

[0076] The preparation method of the small-diameter titanium-steel composite pipe provided by the present invention can not only ensure the bonding strength, achieve high-precision control, but also have the ability of continuous and large-scale production. Moreover, the process is simple, the conditions are mild, the controllability is good, and the stability is strong. By using this method, a high-precision titanium-steel composite pipe with a diameter < 300 mm can be obtained, and the average economic benefit can reach 0.5 ten thousand yuan per ton.

[0077] The preparation method provided by the present invention can be popularized and applied in the production of titanium-steel composite pipes, and high-precision small-caliber titanium-steel composite pipes can be produced, having good prospects for popularization and application.

[0078] To further illustrate the present invention, the following describes in detail a preparation method and application of a small-caliber titanium-steel composite pipe provided by the present invention in combination with embodiments. However, it should be understood that these embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation processes are given, only to further illustrate the features and advantages of the present invention, rather than a limitation on the claims of the present invention. The protection scope of the present invention is not limited to the following embodiments.

[0079] Example 1

[0080] In this example, a titanium-steel composite pipe with a specification of Φ200×6mm (i.e., an outer diameter of 200mm and a wall thickness of 6mm) is prepared using a titanium-steel composite plate with a thickness of (8+2)mm (i.e., a steel plate thickness of 8mm and a titanium plate thickness of 2mm).

[0081] The titanium-steel composite plate with a thickness of (8+2)mm produced by the rolling method is bent into a Ф300mm pipe (steel on the outside, titanium on the inside) by the JCO pipe-making process, and welding is completed from the steel side and the titanium side respectively. The weld bead buildup is ground, and the pipe is made round. Then, annealing is carried out at 800°C for 180 min. After pickling to remove the oxide scale, cold rolling is carried out, a total of two passes, from Ф300×10 to Ф260×8mm. According to calculations, vacuum annealing is carried out at 736°C for 160 min, and then processed to Ф200×6mm. After recalculation, the annealing process is 752°C annealing for 120 min. After straightening and flaw detection, the finished product is obtained.

[0082] The interface shear strength of the titanium-steel composite pipe with a specification of Φ200×6mm prepared in this example can reach 210 MPa.

[0083] Example 2

[0084] In this example, a titanium-steel composite pipe with a specification of Φ259×5.5mm (i.e., an outer diameter of 259mm and a wall thickness of 5.5mm) is prepared using a titanium-steel composite plate with a thickness of (6+1.2)mm (i.e., a steel plate thickness of 6mm and a titanium plate thickness of 1.2mm).

[0085] The titanium-steel composite plate with a thickness of (6+1.2)mm produced by the rolling method is bent into a Ф320mm pipe (steel on the outside, titanium on the inside) by the JCO pipe-making process, and welding is completed from the steel side and the titanium side respectively. The weld bead buildup is ground, and the pipe is made round. Then, annealing is carried out at 750°C for 150 min. After pickling to remove the oxide scale, cold rolling is carried out in one pass, from Ф320×7.2 to Ф259×5.5mm. According to calculations, vacuum annealing is carried out at 756°C for 110 min, and then after straightening and flaw detection, the finished product is obtained.

[0086] The interfacial shear strength of the titanium-steel composite pipe with a specification of Φ259×5.5mm prepared in this example can reach 198 MPa.

[0087] Comparative Example 1

[0088] In this example, a titanium-steel composite pipe with a specification of Φ259×5.5mm (i.e., an outer diameter of 259mm and a wall thickness of 5.5mm) was prepared using a titanium-steel composite plate with a thickness of (6 + 1.2)mm (i.e., a steel plate thickness of 6mm and a titanium plate thickness of 1.2mm). The JCO pipe-making process was used to bend the (6 + 1.2)mm thick titanium-steel composite plate produced by the rolling method into a Ф320mm pipe (steel on the outside, titanium on the inside), and single-sided welding and double-sided forming were carried out from the steel side. The weld bead buildup was ground, made round, and then annealed at 750°C for 150 minutes. Cracks appeared at the weld after annealing.

[0089] Comparative Example 2

[0090] In this example, a titanium-steel composite pipe with a specification of Φ160×5mm (i.e., an outer diameter of 160mm and a wall thickness of 5mm) was prepared using a titanium-steel composite plate with a thickness of (8 + 2)mm (i.e., a steel plate thickness of 8mm and a titanium plate thickness of 2mm). The JCO pipe-making process was used to bend the (8 + 2)mm thick titanium-steel composite plate produced by the rolling method into a Ф350mm pipe (steel on the outside, titanium on the inside), and welding was completed separately from the steel side and the titanium side. The weld bead buildup was ground, made round, and then annealed at 800°C for 180 minutes. It was rolled from Ф350×10 to Ф260×7mm in one pass, with excessive deformation, and delamination occurred at the titanium-steel interface during the rolling process.

[0091] The above has introduced in detail a preparation method of a high-precision small-diameter titanium-steel composite pipe provided by the present invention. Specific examples are used herein to elaborate on the principle and implementation manner of the present invention. The description of the above examples is only used to help understand the method and its core idea of the present invention, including the best mode, and also enables any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention. The protection scope of this invention patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements that are not different from the literal description of the claims, or if they include equivalent structural elements that have no substantial difference from the literal description of the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A method for preparing a small-diameter titanium-steel composite pipe, characterized in that, It includes the following steps: 1) The titanium-steel composite plate is formed into a bent pipe by the JCO process, and then after titanium-titanium and steel-steel welding, a titanium-steel composite welded pipe is obtained; 2) The titanium-steel composite welded pipe obtained in the above step is annealed, and then after cold working and annealing, a small-diameter titanium-steel composite pipe is obtained; The cold working includes cold rolling and / or cold drawing.

2. The preparation method according to claim 1, characterized in that, The titanium-steel composite welded pipe includes a titanium-steel composite welded pipe with steel on the outside and titanium on the inside or a titanium-steel composite welded pipe with titanium on the outside and steel on the inside; The outer diameter of the titanium-steel composite welded pipe is less than or equal to 600 mm.

3. The preparation method according to claim 1, characterized in that, The interface temperature of the welding is less than or equal to 800 °C; After the welding, it also includes the steps of weld treatment and roundness correction.

4. The preparation method according to claim 1, wherein The temperature of the annealing is 550-800 °C; The time of the annealing is 60-240 min.

5. The preparation method according to claim 1, characterized in that, When the wall thickness of the titanium-steel composite welded pipe is less than or equal to 20 mm, the annealing time is less than or equal to 180 min; The annealing method includes annealing under a protective atmosphere or vacuum annealing.

6. The preparation method according to claim 1, characterized in that, The cold working includes single-pass or multi-pass cold working; When the cold working is multi-pass cold working, vacuum annealing is carried out after each pass of cold working.

7. The preparation method according to claim 6, characterized in that, The cumulative deformation amount of the cold working is ≤75%; The deformation amount of each pass of the cold working is ≤50%; The wall thickness reduction amount of each pass of the cold working is ≤2 mm.

8. The preparation method according to claim 6, characterized in that, The temperature of the vacuum annealing is (800 - 8S) °C; where S is the wall thickness in mm; The time of the vacuum annealing is (20×S) min; where S is the wall thickness in mm.

9. The preparation method according to claim 1, characterized in that The outer diameter of the small-diameter titanium-steel composite pipe is less than or equal to 300 mm; The wall thickness of the small-diameter titanium-steel composite pipe is 0.5 - 10 mm.

10. Application of the preparation method according to any one of claims 1 to 9 in the preparation of small-diameter titanium-steel composite pipes; The outer diameter of the small-diameter titanium-steel composite pipe is less than or equal to 300 mm.