Method for integrated rolling of titanium alloy pipe and bar

Abstract

The application discloses a titanium alloy pipe and bar integrated composite rolling method in the technical field of titanium alloy plastic working. The method takes a forged titanium alloy round bar, punches a hole on the end face of the round bar, adopts a wire cutting to cut around the outside of the hole, takes out a cylindrical core material completely, forms an outer layer tubular blank and an inner layer solid core bar, carries out regular treatment on the outer surface of the solid core bar, coats a metal isolation layer, assembles the tubular blank, welds and seals two ends, forms an integrated composite blank, heats and keeps warm the composite blank, reduces the diameter through multi-pass rolling, cuts off the head and tail after rolling into a finished product, and dissolves and removes the metal isolation layer, so that the outer layer titanium alloy pipe blank and the inner layer titanium alloy solid core bar are separated, the pipe blank is cold-rolled to prepare a seamless titanium pipe, and the solid core bar is drawn to prepare a titanium alloy bar wire. The single titanium alloy blank can synchronously output the seamless pipe blank and the solid core blank, the overall material yield can reach 94%~97%, and titanium alloy raw material consumption and production cost are greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy processing technology, and in particular to a method for integrated composite rolling of titanium alloy tubes and bars. Background Technology

[0002] Titanium alloy tubes and bars possess outstanding advantages such as high specific strength and excellent corrosion resistance, making them widely used in key components of high-end equipment such as aviation, low-altitude aircraft, and nuclear reactor heat exchange pipelines. Currently, the industry generally employs independent production models for titanium alloy tubes and bars: seamless titanium alloy tubes are typically produced by forging combined with machining to prepare tube blanks or extrusion forming, followed by cold rolling to form finished tubes; titanium alloy bars are produced using forging or rolling processes. The process routes for these two types of products are separate, requiring independent production lines and tooling.

[0003] However, existing titanium alloy tube blank preparation processes, whether using extrusion or forging combined with machining, generate a large amount of titanium alloy waste. Taking forging combined with machining as an example, deep hole drilling and boring are required to obtain the inner hole of the tube blank. The removed core material is often processed into fragments that are difficult to recycle, resulting in significant titanium alloy raw material loss. Chinese patent application CN101121184A discloses a method for manufacturing titanium-based composite tubes and rods. This method uses copper or aluminum metal tubes and rods as cores, coats the cores with a layer of titanium, and uses extrusion, drawing, and other processes to tightly bond the cores to the titanium tubes, followed by rolling to produce titanium-based composite materials. However, in this method, the cores and titanium layers are tightly bonded as a composite material, and the core rods and tubes are not separated by demolding. The product is a titanium-based composite material, which cannot achieve the simultaneous production of titanium alloy tubes and titanium alloy rods.

[0004] Given the high cost of titanium alloy raw materials and the significant material loss during processing, improving the utilization rate of titanium alloy materials and shortening the processing flow of titanium alloy tubes and bars have become urgent technical challenges in this field. However, existing publicly available technologies mostly focus on the forming processes of single tubes or bars, and no reports have been found on technologies for the integrated composite forming of titanium alloy tubes and bars. Summary of the Invention

[0005] To overcome the above-mentioned shortcomings of existing titanium alloy tube and bar manufacturing technologies, the technical problem to be solved by the present invention is to provide an integrated composite rolling method for titanium alloy tubes and bars with high yield and capable of simultaneously producing seamless tube blanks and solid bar blanks from a single titanium alloy billet.

[0006] The technical solution adopted by this invention to solve its technical problem is: A method for integrated composite rolling of titanium alloy tubes and bars includes the following steps: S1. Take a forged titanium alloy round bar, drill a hole on the end face of the round bar, and then use wire cutting to cut around the outside of the hole to completely remove the central cylindrical core material, forming an outer tubular blank and an inner solid core bar. S2. After the outer surface of the solid mandrel is regularized, a metal isolation layer is applied. S3. The mandrel covered with the metal isolation layer is assembled into the tubular blank, and the two ends are welded and sealed to form an integrated composite blank of outer titanium tube-metal isolation layer-inner titanium core. S4. Heat and hold the composite billet at the specified temperature, then perform multi-pass rolling to reduce the diameter. S5. After rolling into a finished product, the head and tail are cut off, and the metal isolation layer is dissolved and removed to achieve separation of the outer titanium alloy tube blank and the inner titanium alloy solid mandrel. S6. The separated tube blanks are cold-rolled to prepare seamless titanium tubes, and solid mandrels are drawn to prepare titanium alloy rods and wires.

[0007] Furthermore, in step S1, the diameter of the forged titanium alloy round bar is φ100~220mm and the length is 600~800mm; a high-speed EDM drilling machine is used to drill holes on the end face of the round bar, and the hole diameter is controlled to be below 3mm.

[0008] Furthermore, at the location where the hole is drilled on the end face of the round bar, according to formula R... 孔 =0.5×(d) t / D t ×D0-3) is determined, where D0 is the outer diameter of the round bar, D t d represents the predetermined outer diameter of the titanium alloy tube blank obtained in step S5. t R is the predetermined inner diameter of the titanium alloy tube blank obtained in step S5. 孔 This is the distance from the center of the hole to the center of the end face of the round bar.

[0009] Furthermore, in step S2, 3mm is first removed from the outer surface of the solid mandrel by wire cutting, and then a metal isolation layer with a thickness not exceeding 3mm is coated.

[0010] Furthermore, the metal isolation layer consists of a 1mm thin copper sheet and a 1mm iron sheet, each coated with a graphite-type boron nitride coating, sequentially covering the outer surface of the solid mandrel.

[0011] Furthermore, in step S3, the tubular blank is pre-cooled with liquid nitrogen before assembly, and the composite blank is placed in an oven to dry after assembly.

[0012] Furthermore, in step S4, the heating and heat preservation process involves feeding the composite billet into a trolley heating furnace and heat preservation at 40-80°C below the phase transformation point of the titanium alloy for 90-120 minutes.

[0013] Furthermore, in step S4, the multi-pass rolling adopts a heavy-duty reinforced transverse periodic rolling mill or a high-speed continuous rolling mill, and the single-pass section shrinkage rate is controlled at 15%~22%.

[0014] Furthermore, in step S5, the dissolution and removal of the metal isolation layer is carried out by electrochemical corrosion: the rolled billet is immersed in a dilute sulfuric acid washing solution prepared by deionized water and 98% concentrated sulfuric acid at a volume ratio of 10:1, the billet is connected to the anode, and the tank voltage is controlled at 5.0~20.0V to dissolve the metal isolation layer.

[0015] Furthermore, if the titanium alloy tube blank and the solid rod still do not separate after electrochemical corrosion, physical separation is achieved by cooling with liquid nitrogen and then hydraulically ejecting the mandrel.

[0016] The beneficial effects of this invention are: 1. Significantly improved yield: This invention uses wire cutting to completely remove the central core material and reuse it as a solid billet. There are only minor machining losses caused by wire cutting and losses from cutting off the head and tail after rolling. The overall yield can reach 94%~97%, which is more than 20 percentage points higher than the traditional deep hole drilling billet making process, and significantly reduces the consumption of high-value titanium alloy raw materials. 2. Dual production from a single billet, improving production efficiency: A single titanium alloy round bar can simultaneously produce seamless tube billets and solid bar billets through one heating and multiple rolling passes. The two processes of tube processing and bar processing are combined, and one rolling production line can simultaneously supply both cold-rolled seamless tube and wire drawing processes, shortening the processing flow and reducing production costs. 3. Reliable isolation layer process: The metal isolation layer plays a role in high-temperature lubrication and anti-diffusion isolation during the rolling process, avoiding metallurgical adhesion between the inner wall of the titanium tube and the titanium core rod. After rolling, the outer titanium alloy tube blank and the inner titanium alloy solid core rod can be separated without damage by dissolving and removing the metal isolation layer, resulting in excellent product surface quality. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the drilling positions of the forged titanium alloy round bar of the present invention; Figure 2 This is a cross-sectional view of the finished tube blank obtained by the present invention; Figure 3 This is a schematic diagram of the assembly of the tubular blank and the solid mandrel of the present invention.

[0018] The markings in the figure are: 1-tubular billet, 2-solid mandrel, 3-metal isolation layer, 4-forged titanium alloy round bar, 5-titanium alloy tubular billet. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] The overall process of the integrated composite rolling method for titanium alloy tubes and bars of the present invention is as follows: S1. Take a forged titanium alloy round bar 4, drill a hole on the end face of the round bar, and then use wire cutting to cut around the outside of the hole to completely remove the central cylindrical core material, forming the outer tubular blank 1 and the inner solid core bar 2. S2. After the outer surface of the solid core rod 2 is regularized, a metal isolation layer 3 is applied. S3. The solid core rod 2 covered with the metal isolation layer 3 is assembled into the tubular blank 1, and the two ends are welded and sealed to form an integrated composite blank of outer titanium tube-metal isolation layer-inner titanium core. S4. Heat and hold the composite billet at the specified temperature, then perform multi-pass rolling to reduce the diameter. S5. After rolling into a finished product, the head and tail are cut off, and the metal isolation layer is dissolved and removed to achieve the separation of the outer titanium alloy tube blank 5 and the inner titanium alloy solid mandrel. S6. The separated titanium alloy tube blank 5 is cold rolled to prepare seamless titanium tube, and the solid mandrel is drawn to prepare titanium alloy rod and wire.

[0021] Regarding step S1: as follows Figure 1 As shown, the diameter of the forged titanium alloy round bar 4 used in this invention is preferably φ100~220mm, and the length is 600~800mm. The basis for this preference is that if the diameter of the round bar is too small (less than 100mm), the resulting solid mandrel is too thin, the tubular billet wall is too thin, resulting in poor economic efficiency and easy instability of the tube wall during rolling; if the diameter is too large (greater than 220mm), the wire cutting processing cycle is long, the equipment load is high, and it exceeds the billet specification range of conventional rolling mills. If the length of the round bar is too short, it will lead to an increased proportion of the head and tail sections removed after rolling, resulting in a decreased yield; if the length is too long, it will be limited by the furnace chamber and rolling mill layout. Therefore, this invention preferably uses a diameter of φ100~220mm and a length of 600~800mm for the forged titanium alloy round bar 4, which can balance yield, processing efficiency, and equipment adaptability.

[0022] In step S1, a high-speed EDM drilling machine is used to drill a hole on the end face of the round bar, with the hole diameter controlled to be less than 3mm. This hole is only for wire EDM threading; a larger hole diameter results in greater material loss and affects the subsequent mandrel preparation. Controlling the hole diameter to less than 3mm satisfies the threading requirements of medium-speed wire EDM while minimizing machining losses. After drilling, a medium-speed wire EDM is used to make a circumferential cut along the outer side of the hole along the axial direction. The cut width is approximately 0.3mm, resulting in minimal material loss and allowing the complete removal of the central cylindrical core material.

[0023] The location of the drilled hole is related to the wall thickness requirements of the finished tube blank. For example... Figure 1 , Figure 2As shown, since the rolling process can be considered as uniform deformation along the radial direction, the predetermined outer diameter D of the titanium alloy tube blank 5 obtained in step S5 can be used as a reference. t With the predetermined inner diameter d t The dimensions of the tubular blank 1 obtained by reverse wire cutting, i.e., the location of the holes, are determined according to formula R. 孔 =0.5×(dt / Dt×D0-3)determines the value, where D0 is the outer diameter of the round bar, and R 孔 This is the distance from the center of the hole to the center of the end face of the round bar. Determining the hole position according to this formula can match the inner and outer diameters of the separated titanium alloy tube blank 5 with the predetermined dimensions, reducing the amount of internal boring work required to achieve the predetermined dimensions.

[0024] Regarding step S2: First, 3mm is removed from the outer surface of the solid mandrel 2 using wire cutting. This is to remove the surface alteration layer and micro-irregularities formed by wire cutting, as well as the holes remaining on the mandrel from electrical discharge machining, ensuring the surface quality of the mandrel. After removing 3mm, a metal isolation layer 3 with a thickness not exceeding 3mm is applied. This ensures that the outer diameter of the solid mandrel 2 after being covered with the metal isolation layer 3 matches the inner diameter of the tubular billet 1, guaranteeing assembly accuracy. The preferred thickness of the metal isolation layer 3 is based on the fact that if the isolation layer is too thick (exceeding 3mm), the rolling reduction is difficult to effectively transfer to the titanium alloy body, resulting in inconsistent deformation between the inner and outer layers. Therefore, controlling the thickness of the metal isolation layer 3 to within 3mm balances the isolation effect with the coordination of rolling deformation.

[0025] Furthermore, the metal isolation layer 3 consists of a 1mm thin copper sheet and a 1mm iron sheet, each coated with a graphite-type boron nitride coating, sequentially covering the outer surface of the solid mandrel 2. The thin copper sheet has good ductility, allowing it to adhere tightly to the mandrel surface; the iron sheet has high rigidity, protecting the copper sheet from damage during assembly and the initial stages of rolling; the graphite-type boron nitride coating provides lubrication and prevents diffusion during high-temperature rolling. The copper / iron sheet and the graphite-type boron nitride coating form a double isolation layer, preventing metallurgical adhesion between the inner wall of the titanium tube and the titanium mandrel.

[0026] Regarding step S3: Before assembly, the tubular blank 1 is pre-cooled with liquid nitrogen. The dimensional changes of the tubular blank 1 at low temperature are used to adjust the assembly gap between it and the solid mandrel 2, facilitating the smooth insertion of the solid mandrel 2 covered with the metal isolation layer 3. After the composite blank returns to room temperature, a tight fit is achieved, forming an interference fit. After assembly, the composite blank is placed in an oven to dry, removing the moisture condensed on the surface during pre-cooling and preventing moisture from affecting the quality of subsequent welding and sealing. After welding and sealing at both ends, an integrated composite blank of "outer titanium tube - metal isolation layer - inner titanium core" is formed, as shown below. Figure 3 As shown, welding seals can prevent oxidizing atmospheres from entering the composite billet during heating and rolling processes and contaminating the bonding interface.

[0027] Regarding step S4: The heating and holding process involves feeding the composite billet into a trolley heating furnace and holding it at 40-80°C below the phase transformation point of the titanium alloy for 90-120 minutes. The optimal heating temperature is determined by the following: if the heating temperature is higher than the phase transformation point or too close to it (below 40°C), the titanium alloy grains tend to coarsen, and the microstructure deteriorates; if the heating temperature is too low (above 80°C below the phase transformation point), the deformation resistance is high, and cracking is likely during rolling. The optimal holding time is determined by the following: if the holding time is too short (less than 90 minutes), the temperature inside and outside the composite billet will be uneven, leading to inconsistent deformation during rolling; if the holding time is too long (more than 120 minutes), the grains will grow larger, resulting in low production efficiency and high energy consumption. Therefore, the preferred heating and holding time is 40-80°C below the phase transformation point of the titanium alloy for 90-120 minutes, which balances microstructure and rollability while ensuring uniform temperature inside and outside the billet.

[0028] In step S4, multi-pass rolling employs a heavy-duty reinforced tandem periodic mill or a high-speed continuous rolling mill, with the single-pass section reduction rate controlled between 15% and 22%. The optimal single-pass section reduction rate is based on the following criteria: if the reduction rate is too small (below 15%), the number of rolling passes increases, deformation penetration is insufficient, and production efficiency is low; if the reduction rate is too large (above 22%), the composite billet is prone to cracking and surface defects, and the mill load is excessive. Controlling the single-pass section reduction rate between 15% and 22% ensures that deformation penetrates to the core, allowing the tubular billet 1 and the solid mandrel 2 to reduce diameter in a coordinated manner.

[0029] Regarding step S5: After rolling, the ends are removed, i.e., the welded areas at both ends are removed, and the material can be cut into sections according to length. The dissolution and removal of the metal isolation layer 3 is carried out by electrochemical corrosion: the rolled billet is immersed in a dilute sulfuric acid washing solution prepared by deionized water and 98% concentrated sulfuric acid at a volume ratio of 10:1. The billet is connected to the anode, and the cathode is connected to the solution or dissolution tank. The tank voltage is controlled at 5.0~20.0V. The principle is that titanium alloy is easily passivated in dilute sulfuric acid and has good corrosion resistance, while copper and iron dissolve rapidly under anodic polarization conditions, thereby achieving selective dissolution of the metal isolation layer 3. The optimal tank voltage is based on the following: if the tank voltage is too low (below 5.0V), the dissolution rate is slow and the production efficiency is low; if the tank voltage is too high (above 20.0V), the side reactions are aggravated, energy consumption is increased, and there are safety hazards. After the metal isolation layer 3 is completely dissolved, the outer titanium alloy tube billet 5 and the inner titanium alloy solid mandrel 2 can be separated without damage.

[0030] Furthermore, if the titanium alloy tube blank 5 and the solid rod still do not separate after electrochemical corrosion, physical separation is achieved by cooling with liquid nitrogen and then hydraulically ejecting the mandrel: the deep cooling with liquid nitrogen creates a shrinkage difference between the titanium alloy and the residual separator, and combined with hydraulic ejection, reliable separation of the stuck mandrel can be achieved.

[0031] The present invention will be further described below with reference to embodiments.

[0032] Example 1 TA16 titanium alloy forged bar is selected, with an outer diameter D0 = 200 mm and a length of 600 mm; the predetermined dimensions of the finished tube blank are: outer diameter D... t =50mm, inner diameter d t =25mm. Calculate the distance R from the center of the drilled hole to the center of the end face of the round bar according to the formula. 孔 =0.5×(25 / 50×200-3)=48.5mm. A 3mm diameter hole is drilled on the end face of the round bar using an EDM high-speed drilling machine, with the outer side of the hole 50mm from the center of the bar blank. After drilling, a 100mm through hole is machined around the outer side of the hole using an extended medium-speed wire EDM, and the 100mm solid mandrel is completely removed, with a cutting kerf width of about 0.3mm. Then, 3mm is removed from the outer surface of the solid mandrel using wire EDM, and the mandrel is machined to 94mm, removing the remaining part from the EDM drilling. A 1mm copper sheet and a 1mm iron sheet, both coated with a graphite-type boron nitride coating, are sequentially wrapped around the outer wall of the mandrel as a metal isolation layer. After the tubular blank is pre-cooled with liquid nitrogen, the mandrel with the metal isolation layer is assembled into the tubular blank, then placed in an oven to dry, and the two ends are welded and sealed to form an "outer titanium tube - metal isolation". The composite billet, consisting of an inner titanium core and a single layer, is fed into a trolley heating furnace and held at 880℃ for 90 minutes (the phase transformation point of TA16 titanium alloy is approximately 920~950℃, and this heating temperature is within 40~80℃ below the phase transformation point). After holding, the composite billet is fed into a heavy-duty reinforced transverse periodic rolling mill and rolled in 6 passes to reduce its diameter, with a single pass section reduction rate of 18%. After rolling, the head and tail welding areas are removed and the billet is cut into sections according to length. The billet is immersed in a dilute sulfuric acid washing solution prepared by mixing deionized water and 98% concentrated sulfuric acid at a volume ratio of 10:1. The billet is connected to the anode, and the melting tank is connected to the cathode. The tank voltage is controlled at 5.0~20.0V to electrochemically dissolve the copper and iron isolation layers, separating the titanium alloy tube billet and the solid bar billet. The separated tube billet is cold-rolled to prepare seamless titanium tubes, and the solid bar is drawn to prepare titanium alloy welding wire.

[0033] The TA16 titanium alloy seamless tube prepared in this embodiment has a wall thickness uniformity deviation of ≤0.06mm, a welding wire surface defect of ≤0.08mm, and an overall titanium alloy raw material utilization rate of 95.2%. The prepared seamless titanium tube has uniform wall thickness and good surface quality of the bar and wire.

Claims

1. A method for integrated composite rolling of titanium alloy tubes and bars, characterized in that, Includes the following steps: S1. Take a forged titanium alloy round bar, drill a hole on the end face of the round bar, and then use wire cutting to cut around the outside of the hole to completely remove the central cylindrical core material, forming an outer tubular blank and an inner solid core bar. S2. After the outer surface of the solid mandrel is regularized, a metal isolation layer is applied. S3. The mandrel covered with the metal isolation layer is assembled into the tubular blank, and the two ends are welded and sealed to form an integrated composite blank of outer titanium tube-metal isolation layer-inner titanium core. S4. Heat and hold the composite billet at the specified temperature, then perform multi-pass rolling to reduce the diameter. S5. After rolling into a finished product, the head and tail are cut off, and the metal isolation layer is dissolved and removed to achieve separation of the outer titanium alloy tube blank and the inner titanium alloy solid mandrel. S6. The separated tube blanks are cold-rolled to prepare seamless titanium tubes, and solid mandrels are drawn to prepare titanium alloy rods and wires.

2. The method for integrated composite rolling of titanium alloy tubes and bars as described in claim 1, characterized in that, In step S1, the diameter of the forged titanium alloy round bar is φ100~220mm and the length is 600~800mm; a high-speed EDM drilling machine is used to drill holes on the end face of the round bar, and the hole diameter is controlled to be less than 3mm.

3. The method for integrated composite rolling of titanium alloy tubes and bars as described in claim 2, characterized in that, At the location where the hole is drilled on the end face of the round bar, follow formula R. 孔 =0.5×(d) t / D t ×D0-3) is determined, where D0 is the outer diameter of the round bar, D t d represents the predetermined outer diameter of the titanium alloy tube blank obtained in step S5. t R is the predetermined inner diameter of the titanium alloy tube blank obtained in step S5. 孔 This is the distance from the center of the hole to the center of the end face of the round bar.

4. The method for integrated composite rolling of titanium alloy tubes and bars as described in claim 1, characterized in that, In step S2, 3mm is first removed from the outer surface of the solid mandrel by wire cutting, and then a metal isolation layer with a thickness not exceeding 3mm is coated.

5. The method for integrated composite rolling of titanium alloy tubes and bars as described in claim 4, characterized in that, The metal isolation layer consists of a 1mm thin copper sheet and a 1mm iron sheet, both coated with a graphite-type boron nitride coating, sequentially covering the outer surface of the solid mandrel.

6. The method for integrated composite rolling of titanium alloy tubes and bars as described in claim 1, characterized in that, In step S3, the tubular blank is pre-cooled with liquid nitrogen before assembly, and the composite blank is placed in an oven to dry after assembly.

7. The method for integrated composite rolling of titanium alloy tubes and bars as described in claim 1, characterized in that, In step S4, the heating and heat preservation process is as follows: the composite billet is fed into a trolley heating furnace and kept at 40~80℃ below the phase transformation point of titanium alloy for 90~120 minutes.

8. The method for integrated composite rolling of titanium alloy tubes and bars as described in claim 1, characterized in that, In step S4, the multi-pass rolling adopts a heavy-duty reinforced transverse periodic rolling mill or a high-speed continuous rolling mill, and the single-pass section shrinkage rate is controlled at 15%~22%.

9. The method for integrated composite rolling of titanium alloy tubes and bars as described in claim 1, characterized in that, In step S5, the dissolution and removal of the metal isolation layer is carried out by electrochemical corrosion: the rolled billet is immersed in a dilute sulfuric acid washing solution prepared by deionized water and 98% concentrated sulfuric acid at a volume ratio of 10:1, the billet is connected to the anode, and the tank voltage is controlled at 5.0~20.0V to dissolve the metal isolation layer.

10. The method for integrated composite rolling of titanium alloy tubes and bars as described in claim 9, characterized in that, If the titanium alloy tube blank and the solid rod still do not separate after electrochemical corrosion, physical separation is achieved by cooling with liquid nitrogen and then hydraulically ejecting the mandrel.

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