A forming method for large-size oblique tee forgings made of near-α-type titanium alloy

Abstract

The present invention relates to the field of nonferrous metal processing, and discloses a method for forming a large-scale oblique tee forging made of a near-α-type titanium alloy. The method adopts a titanium alloy ingot, and forms a combined forging process route of open forging and intermediate forging based on the principle of uniform grain refinement of repeated recrystallization of titanium alloy. The method prepares a billet with uniform structure by reasonably setting the deformation temperature, deformation amount and deformation mode, and accurately controlling the heating and forging parameters. The billet is free forged into a large-scale oblique tee forging of 2 tons or above. With the help of a simple open V-shaped anvil and the good plasticity of titanium alloy forging, the outer contour of the forging is forged, which can significantly reduce the amount of machining and reduce the cost of forging preparation. The oblique tee forging with different angle requirements can be obtained by shaping. The forging method has strong applicability, and the streamlines of the prepared oblique tee forging are distributed along the outer contour, the forging structure is uniform, the corrosion resistance in the service environment is improved, and the service life is increased.

Description

Technical Field

[0001] The invention relates to the field of nonferrous metal processing, and in particular to a forming method for a large-size oblique tee forging made of a near-α-type titanium alloy. Background Art

[0002] In recent years, with the increasing demand for corrosion-resistant titanium alloys, in order to meet the usage requirements in specific environments, a small amount of alloying elements is added to industrial pure titanium to form a near-α-type titanium alloy containing a small amount of β phase. This type of alloy has more superior corrosion resistance in specific environments and has gradually become the main corrosion-resistant material used in various industries.

[0003] With the large-scale application of nuclear energy in my country, the research and development and production of key equipment for nuclear spent fuel reprocessing projects have received widespread attention. The tonnage of reprocessing equipment has increased year by year, leading to an increasing demand for large-scale forgings made of corrosion-resistant near-α-type titanium alloy. Large-scale oblique tees are among the most difficult key forgings to manufacture. These alloy forgings typically weigh more than 2.5 tons per piece, come in a wide variety of specifications, and are produced in small quantities for each specification, making them unsuitable for die forging. Furthermore, oblique tees primarily serve as diverters and are subjected to complex, high-pressure, and highly corrosive environments, placing high demands on their uniform corrosion resistance and microstructure. Traditionally, oblique tees are formed by welding or casting, resulting in welds or cast grain boundaries that are susceptible to corrosion, hindering the overall service life of the equipment. Furthermore, large-scale oblique tees made of near-α-type titanium alloy, due to their asymmetrical tee angles, large forging size, and diverse specifications, require die forging with complex, variable molds and high costs. Summary of the Invention

[0004] The invention provides a forming method for large-size oblique tee forgings of near-α-type titanium alloy, which reduces processing and manufacturing costs, improves corrosion resistance, has strong applicability, and is suitable for industrial production.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions: A forming method for a large-scale oblique tee forging of a near-α-type titanium alloy, comprising the following steps:

[0006] Step 1: Forging, select titanium alloy ingot, and forge the ingot to break the coarse cast structure;

[0007] Step 2: Intermediate forging: the blank that has completed the blanking forging is subjected to at least three times of upsetting forging in the temperature range of phase transformation point plus 200℃ to phase transformation point minus 60℃. The deformation of each pass is 20% to 40%, and the cumulative deformation of each pass should be greater than 60%.

[0008] Step 3: Forming forging: The intermediate forged billet is heated to below the phase transition point and kept warm. After being taken out of the furnace, the billet is forged and shaped into a square billet. The square billet is placed in a V-shaped anvil for forging, and the angle of the tee of the square billet is shaped to obtain a tee forging with the required angle.

[0009] Preferably, the weight of the ingot in step 1 is more than 1.3 times the weight of the oblique tee forging after machining.

[0010] Preferably, in step 1, the temperature is kept above the phase change point, step heating is adopted, and the holding time is calculated based on the minimum size of the blank (mm)*(0.45-0.65)min.

[0011] Preferably, in step 2, 3 to 5 upsetting forgings are performed, and the cumulative deformation amount of each upsetting forging is 70%.

[0012] Preferably, the billet that has completed 3 to 5 rounds of upsetting forging is forged at a temperature below the phase transformation point for four rounds, and the upsetting forging temperature is gradually reduced between each round.

[0013] Preferably, in the billet forged in step three, one vertex corner of the billet is the head end of the original billet.

[0014] Preferably, the thickness of the billet in step 3 is slightly greater than the thickness of the oblique tee forging, and the width and length of the billet are close, and the width and length should ensure that the center of gravity of the billet falls near the center of the V-shaped anvil.

[0015] Preferably, the V-shaped anvil in step three is an open V-shaped anvil, and the two vertices of the long side of the open V-shaped anvil triangle are located on the two end faces of the final oblique tee forging.

[0016] Preferably, the specific forming process in step three is as follows:

[0017] (1) Place the blank in a V-shaped anvil and press it down with the upper flat anvil to the required size of the forging;

[0018] (2) Rotate the blank 90°, flatten the upper and lower end surfaces of the blank, and press it down until the forging height is reduced (0mm to 50mm);

[0019] (3) Rotate the blank 90° and move it to the upper and lower anvils, so that the upper and lower large surfaces of the blank are parallel to the anvils, and press it down to the forging size minus (0mm to 40mm). Move the blank so that the tee is located between the upper and lower anvils, and press it down to the forging size plus (150mm to 250mm);

[0020] (4) Repeat the above steps (1) to (3) 3 to 4 times until the blank has taken the shape of the forging.

[0021] (5) Repeat the above processes (1) to (3) 2 to 3 times, wherein each process presses down to the required size of the forging;

[0022] (6) Place the forging blank formed in (5) on the lower round table, and use the upper flat anvil to shape the angle of the tee to obtain the inclined tee forging with the required angle.

[0023] The present invention has the following beneficial effects:

[0024] The present invention adopts this forming method with the help of a simple open V-anvil, combined with the good forging plasticity of near-α-type titanium alloy, and forms the outer contour of the forging by forging, which can significantly reduce the amount of machining and reduce the cost of forging preparation. At the same time, oblique tee forgings with different angle requirements can be obtained by shaping, and finally, an integral forging with good structural uniformity can be obtained by forging, which is beneficial to improving the corrosion resistance of the forging in the service environment and the service life of the forging, and can produce qualified near-α-type titanium alloy 2-ton and above large-scale oblique tee forgings. The oblique tee angle can be adjusted by free forging shaping. The method has strong applicability and greatly reduces the cost of forging preparation. The streamlines of the prepared oblique tee forgings are distributed along the outer contour, the forging structure is uniform, the corrosion resistance in the service environment is improved, the service life is increased, and it is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the oblique tee forging and the final parts of the present invention.

[0026] Figure 2 It is a top view of the oblique tee forging of the present invention.

[0027] Figure 3 This is the front view of the oblique tee forging of the present invention.

[0028] Figure 4 Schematic diagram of the placement position of the billet in the V-shaped anvil according to the present invention.

[0029] Figure 5 It is a schematic diagram of the forming forging of the oblique tee forging of the present invention.

[0030] Figure 6 Schematic diagram of the final part of the present invention, a is the main view of the final part, b is the top view of the final part. DETAILED DESCRIPTION

[0031] The present invention is described in detail below with reference to the accompanying drawings. The present invention provides a technical solution: a forming method for a large-sized oblique tee forging of a near-α-type titanium alloy. The forming method is described in detail through the preparation process of a Ti35 titanium alloy oblique tee forging:

[0032] Figure 1 This is a schematic diagram of the Ti35 titanium alloy inclined tee forging and the final parts prepared this time. Figure 2 and Figure 3The top and front views of the oblique tee forging are respectively. The finished product weighs approximately 2.6 tons and consists of a 680mm Ø main pipe and a 350mm Ø branch pipe, with the branch pipe and main pipe angled at 35°. The incoming ingot undergoes repeated heating, forging, and polishing to produce a forging blank with the required microstructure. After exiting the furnace, the blank is forged and shaped into a square billet, with one of the top corners of the billet forming the head of the original billet to ensure that the streamline distribution of the forged part aligns with the streamline direction of the billet. The oblique tee forging is then heated and formed to produce the specific shape. Figure 4 This is a schematic diagram of the placement of the blank in the open V-shaped anvil before forming. As can be seen from the figure, after the blank is placed, its center of gravity should fall in the middle of the open V-shaped anvil to ensure uniform deformation of both ends of the blank during subsequent forming. Figure 5 This is a schematic diagram of the forging process for the oblique tee forging according to the present invention. As can be seen from the figure, the billet exhibits strong maneuverability and easy control throughout the forming process, and the equivalent strain distribution during deformation is uniform. The oblique tee forging was machined, and macroscopic microstructure examination of the head end revealed a uniform and consistent microstructure, demonstrating a uniform, fine structure after complete recrystallization. This indicates that the forging deformation was sufficiently uniform, ultimately resulting in a qualified oblique tee forging with a uniform, fine structure. The present invention minimizes machining removal and achieves a high yield rate. Figure 6 This is a schematic diagram of the final part of the inclined tee forging after machining. The joints between the main pipe and the branch pipe are forged as a whole. This structure avoids the welds formed by conventional welding and is more conducive to improving the service life of the parts.

[0033] Step 1: Forging

[0034] The ingot weighs approximately 3750kg, and the alloy's phase transition point is 890°C. The ingot is heated in a stepwise manner to 1020°C and held for 300 minutes. After exiting the furnace, it undergoes a shaping forging process with a single upsetting and a single drawing pass, resulting in a deformation of approximately 40%. After forging, it is air-cooled. After surface cracks are removed by grinding, the billet is heated in a stepwise manner to 1020°C and held for 350 minutes. After exiting the furnace, it undergoes a double upsetting and double drawing forging process, resulting in a single-pass deformation of approximately 25% and a cumulative deformation of approximately 50%. After forging, it is air-cooled. The open forging process is completed in two passes, with a total cumulative deformation of approximately 90%.

[0035] Step 2: Intermediate Forging

[0036] The billet is subjected to three rounds of "high, low, high" upsetting forging in a cycle within the temperature range of phase transformation point plus 200°C to phase transformation point minus 60°C. The deformation of each single pass is about 35%, and the cumulative deformation is about 70%. During this process, re-melting is used for heat preservation. After the third round of forging is completed, the cross-section of the billet is octagonal and the billet is air-cooled.

[0037] The blank that has completed the above three-forging process is then forged for the fourth time at a temperature below the phase transformation point. The specific process is as follows:

[0038] After the billet is polished to remove surface cracks, it is kept at 860℃ for 530 minutes. After being taken out of the furnace, it is forged by two upsetting and two drawing. The deformation of a single pass is about 35%, and the cumulative deformation is 70%. After forging, it is air-cooled.

[0039] After the surface cracks of the blank are removed by grinding, it is kept at 850℃ for 530 minutes. After being taken out of the furnace, it is forged by two upsetting and two drawing. The deformation of a single pass is about 35%, and the cumulative deformation is 70%. After the last drawing, the cross-section of the blank is octagonal. After forging, it is air-cooled.

[0040] After the surface cracks of the blank are removed by grinding, the process of holding at 850℃ and forging after being taken out of the furnace is repeated.

[0041] After grinding to remove surface cracks, the billet is held at 840°C for 530 minutes. After exiting the furnace, it undergoes two upsetting and two drawing forging passes, with a single-pass deformation of approximately 35% and a cumulative deformation of 70%. After forging, it is air-cooled. Both ends of the billet are polished and macroscopically inspected. The macroscopic structure at the ends of the billet is uniform and fine, meeting the requirements.

[0042] Step 3: Forming and forging

[0043] After the surface cracks are removed by grinding, the square billet is kept at 840℃ for 530 minutes. After being taken out of the furnace, the billet is pressed into a square billet with a thickness of 650mm, a width of 950mm, and a length of 1050mm by diagonal drawing. Then the forming process is carried out as follows:

[0044] (1) Press the top corner of the blank near the original head end to 500mm between the upper and lower flat anvils, and then press the blank Figure 4 Place the open V-shaped anvil in the position shown, with the 500mm thick top corner located in the V-shaped anvil, and press Figure 5 In the forming process 1, press down to 1100mm with the upper flat anvil.

[0045] (2) Rotate the blank 90° and move it to the lower round table. Figure 5 In the forming process 2, press down to 1050mm with the upper flat anvil.

[0046] (3) Rotate the blank 90° and move it to the lower anvil. Figure 5 In the forming process 3, the upper anvil is used to press the two large surfaces down to 700mm. The blank is moved so that the tee is located between the upper and lower anvils, and the two small surfaces are pressed down to 600mm.

[0047] (4) Repeat the above (1) to (3) processes three times, then return the billet to 840℃ and keep it at this temperature for 60 minutes before taking it out of the furnace.

[0048] (5) Take out the furnace blank and shape it. Repeat the process from (1) to (3) three times. Each process is pressed down to the required size of the forging. The forging has been basically formed. Figure 5 The forming processes 4 and 5 are shown in FIG.

[0049] (6) Place the forging that has been deformed in (5) on the round table and press Figure 5 In the intermediate forming process 6, the upper anvil edge fillet is used to trim the angle of the tee of the forging to obtain an oblique tee forging that meets the requirements. At the same time, the upper anvil edge fillet is used to trim the fillet at the transition between the tee and the forging body. After trimming is completed, the forging dimensions are measured until the forging meets the requirements.

[0050] After the inclined tee forging is formed, it can be machined according to the part drawing after appropriate heat treatment to form the final part, such as Figure 6 Final parts diagram.

[0051] The above content is a further detailed description of the present invention in conjunction with specific preferred embodiments. It cannot be determined that the specific implementation of the present invention is limited to these descriptions. It should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limiting the present invention.

Claims

1. A forming method for a large-sized oblique tee forging made of a near-α-type titanium alloy, characterized in that: The following steps are involved: Step 1: Open forging: select titanium alloy ingot, forge the ingot to break the coarse cast structure, heat the ingot to 1020℃ in a step-by-step manner and keep it warm for 300 minutes, then perform one upsetting and one drawing forging after it comes out of the furnace, and air cool it after forging. After the billet is polished to remove surface cracks, heat it to 1020℃ in a step-by-step manner and keep it warm for 350 minutes, then perform two upsetting and two drawing forging after it comes out of the furnace, and air cool it after forging. Open forging is completed in two batches. Step 2: Intermediate forging: The blank that has completed the blanking forging is subjected to a "high-low-high" upsetting forging cycle for at least three times in the temperature range of 200°C above the phase transformation point to 60°C below the phase transformation point. The deformation of each pass is 20% to 40%, and the cumulative deformation of each pass should be greater than 60%. Then, four times of forging are carried out at a temperature below the phase transformation point, and the upsetting forging temperature between each pass is gradually reduced. Step 3: Forming forging. The billet that has completed the intermediate forging is heated to below the phase transformation point and kept warm. After it comes out of the furnace, the billet is forged and shaped into a square billet. The square billet is placed in the lower V-shaped anvil for forging. The upper flat anvil is used to shape the angle of the billet tee to obtain oblique tee forgings with different angle requirements.

2. The forming method of a large-sized oblique tee forging of a near-α-type titanium alloy according to claim 1, characterized in that: The weight of the ingot in step 1 is more than 1.3 times the weight of the oblique tee forging after machining.

3. The forming method of a large-sized oblique tee forging of a near-α-type titanium alloy according to claim 1, characterized in that: In the step 1, the temperature is kept above the phase transition point, and the holding time is calculated based on the minimum size of the blank (mm) * (0.45~0.65) min.

4. The forming method of a large-sized oblique tee forging of a near-α-type titanium alloy according to claim 1, characterized in that: In the step 2, 3 to 5 upsetting forgings are performed, and the cumulative deformation amount of each upsetting forging is 70%.

5. The forming method of a large-sized oblique tee forging of a near-α-type titanium alloy according to claim 1, characterized in that: The square billet forged in step 3 has a top corner serving as the head end of the original billet.

6. The forming method of a large-sized oblique tee forging of a near-α-type titanium alloy according to claim 1, characterized in that: In the step 3, the thickness of the billet is slightly greater than the thickness of the oblique tee forging, and the width and length of the billet are close to each other, and the width and length should ensure that the center of gravity of the billet falls near the center of the V-shaped anvil.

7. The forming method of a large-sized oblique tee forging of a near-α-type titanium alloy according to claim 1, characterized in that: The V-shaped anvil in step three is an open V-shaped anvil, and the two vertices of the long side of the open V-shaped anvil triangle are located on the two end surfaces of the final oblique tee forging.

8. The forming method of a large-sized oblique tee forging of a near-α-type titanium alloy according to claim 1, characterized in that: The specific forming process in step 3 is as follows: (1) Place the blank in the V-shaped anvil and press it down with the upper flat anvil to the required size of the forging; (2) Rotate the blank 90°, flatten the upper and lower end surfaces of the blank, and press it down to the forging height minus (0mm~50mm); (3) Rotate the blank 90° and move it to the upper and lower anvils, so that the upper and lower large surfaces of the blank are parallel to the anvils, and press it down to the forging size minus (0mm~40mm). Move the blank so that the tee is located between the upper and lower anvils, and press it down to the forging size plus (150mm~250mm); (4) Repeat the above (1) to (3) processes 3 to 4 times, and the blank has begun to take the shape of the forging; (5) Repeat the above processes (1) to (3) 2 to 3 times, and press down to the required size of the forging in each process; (6) Place the forging blank formed in (5) on the lower round table, and use the upper flat anvil to shape the angle of the tee to obtain the required angle of the inclined tee forging.

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