A forging method of TC2 titanium alloy large-size bar

Abstract

The application discloses a forging method of TC2 titanium alloy large-size rod, which comprises the following steps: step one, open-die forging: the TC2 titanium alloy ingot is kept at T β +100 DEG C to T β +210 DEG C and is subjected to 1-2 times of open-die forging, 2-3 upsetting and drawing are completed per time of forging, the total forging ratio is controlled to be between 8.5 and 12.0, and first billets are obtained through air cooling; step two, intermediate forging: the first billets are kept at T β -120 DEG C to T β +70 DEG C and are subjected to 6-10 times of repeated upsetting and drawing, the forging ratio per time is 3.5-5.0, and second billets are obtained; step three, forming forging: the second billets are kept at T β -40 DEG C to T β -120 DEG C and are subjected to 3-4 times of forming forging, and TC2 titanium alloy rods are obtained. The TC2 titanium alloy large-size rod prepared by the method has uniform high-low magnification structure, excellent mechanical properties, good batch stability, a relatively short process and is suitable for large-batch industrial production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of titanium alloy processing, and particularly relates to a forging method of TC2 titanium alloy large-size bar. BACKGROUND

[0002] TC2 alloy has a nominal composition of Ti-4Al-1.5Mn, is a medium-strength near-alpha alloy, has good process plasticity and thermal stability, can be hot deformed in a relatively wide temperature range, and is widely used in aerospace structural parts. With the development of the aerospace industry, the overall and large-scale requirements are put forward for load-bearing structural parts, and the demand for large-size bars gradually increases.

[0003] In the traditional forging process, in order to solve the problems of poor forging penetration and difficult organization fragmentation of TC2 material, multiple upsetting and drawing at phase change points are added. With the increase of fire times, the forging process is more difficult to control, and it is difficult to ensure the stability of the batch. The cumbersome process also means a longer production cycle and higher cost. Especially for large-size bars with a diameter greater than 200 mm, the increase in size brings problems such as aggravation of element segregation, coarse original grains, and uneven organization performance, which affect product delivery. Therefore, it is urgent to design a TC2 titanium alloy large-size bar preparation method with a short process and high uniformity of organization.

[0004] Therefore, the present application provides a forging method of TC2 titanium alloy large-size bar to overcome the defects of the prior art. SUMMARY

[0005] The purpose of the present application is to provide a forging method of TC2 titanium alloy large-size bar, which has uniform high and low magnification organization, excellent mechanical properties, good batch stability, a short process, and is suitable for large-scale industrial production.

[0006] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] A forging method of TC2 titanium alloy large-size bar, comprising the following steps:

[0008] Step one, breakdown forging:

[0009] The TC2 titanium alloy ingot is heated to T β +100℃~T β +210℃, and is kept for 1-2 times of breakdown forging, 2-3 times of upsetting and drawing are completed for each forging, the total forging ratio is controlled to be 8.5-12.0, and a first blank is obtained by air cooling;

[0010] Step two, intermediate forging:

[0011] The first blank is heated to Tβ -120℃ ~ T β +70℃ and repeated upsetting and drawing for 6-10 times, with a forging ratio of 3.5-5.0 each time, to obtain a second blank;

[0012] Step three, shape forging:

[0013] The second blank is heated at T β -40℃ ~ T β -120℃ and shape forged for 3-4 times to obtain a TC2 titanium alloy rod.

[0014] Preferably, in the first step, the holding time of the ingot during the open-die forging is not less than 20 hours.

[0015] Preferably, in the first step, the ingot is drawn using a cross-anvil drawing method at a drawing speed of 60-90 mm / s during the drawing of all times of the open-die forging.

[0016] Preferably, in the second step, the intermediate forging is divided into two stages, in which, in the first stage, the blank is first heated at T β -40℃ ~ T β -120℃ and forged, with a final forging temperature of not less than T β -250℃, and then heated at T β +20℃ ~ T β +70℃ and held for a time t = 0.3D-0.5D, where D is the minimum cross-sectional dimension of the blank, and then cooled in water after being discharged, and the process is repeated 1-2 times; in the second stage, the blank is heated at T β -40℃ ~ T β -120℃ and forged for 4-7 times, with a final forging temperature of not less than T β -250℃.

[0017] Preferably, in the second step, during the intermediate forging, the first three passes of the drawing process use cross-anvil drawing at a drawing speed of 20-40 mm / s, and the remaining passes use axial drawing at a feeding amount of 200-300 mm and a drawing speed of 60-80 mm / s.

[0018] Preferably, in the third step, during the shape forging, the final forging temperature of each time is not less than T β -250℃, a double-operating reciprocating feeding is used, the pass deformation is ≤10%, the feeding amount is ≤100 mm, and the drawing speed is 50-70 mm / s.

[0019] Preferably, the forging method can be used to produce a TC2 titanium alloy rod with a diameter of 200-400 mm and a length of 2000-4000 mm.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] 1、The present application can ensure the homogeneity of the composition and provide the basis for the homogeneity of the structure and performance by keeping the blank in high-temperature state for a long time during the rough forging, improving the thermal diffusion of atoms at high temperature and making the easily segregated element Mn fully diffuse in the intracrystalline and intercrystalline.

[0022] 2、The present application can ensure the uniform deformation of the bar in all directions by setting a large reduction and elongation rate in the stage below the phase transition point during the intermediate forging, ensuring the grains to be fully broken and setting the elongation in different directions alternately to reduce the deformation texture caused by the single direction compression; and the hot material is then returned to the furnace and kept at a temperature above the phase transition point for a period of time, so that the material is fully recrystallized under the driving of high temperature, and after being discharged, the material is directly water-cooled without being upset and drawn, so that the fine grains after recrystallization are fully retained and the uniform and fine structure of the bar is ensured.

[0023] 3、The present application simplifies the steps of the intermediate forging, and the material is air-cooled after each traditional forging process, which takes a long time for the air-cooling of the large-size bar, greatly increasing the time cost and the material transfer cost; in the present application, the material is quickly returned to the furnace after the intermediate forging, so that the time is shortened and the cost is reduced.

[0024] 4、The present application adopts the deformation mode of low temperature, fast small feed and small deformation in the forming forging, which can effectively break the grains on the circumferential surface, ensure the surface forging quality and reduce the material loss caused by polishing. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 Fig. 1 is a macrostructure diagram of the TC2 titanium alloy Φ400mm bar forged by the embodiment 1 of the present application.

[0026] Figure 2 Fig. 2 is a high-magnification structure diagram of the TC2 titanium alloy Φ400mm bar forged by the embodiment 1 of the present application.

[0027] Figure 3 Fig. 3 is a macrostructure diagram of the TC2 titanium alloy Φ350mm bar forged by the embodiment 2 of the present application.

[0028] Figure 4 Fig. 4 is a high-magnification structure diagram of the TC2 titanium alloy Φ350mm bar forged by the embodiment 2 of the present application.

[0029] Figure 5 Fig. 5 is a macrostructure diagram of the TC2 titanium alloy Φ200mm bar forged by the embodiment 3 of the present application.

[0030] Figure 6 Fig. 6 is a high-magnification structure diagram of the TC2 titanium alloy Φ200mm bar forged by the embodiment 3 of the present application.

[0031] Figure 7 is a macrostructure diagram of the TC2 titanium alloy Φ350 mm bar forged by the comparative example of the present application.

[0032] Figure 8 is a macrostructure diagram of the TC2 titanium alloy Φ350 mm bar forged by the comparative example of the present application.

[0033] Figure 9 is a flow chart of the method of the present application. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below in combination with the drawings of the present application.

[0035] As shown in Figures 1-9 A forging method of a TC2 titanium alloy large-size bar, the raw material of the TC2 titanium alloy large-size bar is a 3-4 ton TC2 titanium alloy ingot produced by three-time melting in a vacuum consumable arc furnace, and the forging method can be used to produce a TC2 titanium alloy bar with a diameter of 200-400 mm and a length of 2000-4000 mm.

[0036] The method comprises the following steps:

[0037] Step one, open-die forging:

[0038] The TC2 titanium alloy ingot is kept at T β +(100-210 ℃) and subjected to 1-2 times of open-die forging, 2-3 upsetting and drawing are completed for each time of forging, the total forging ratio is controlled to be 8.5-12.0, and a first blank is obtained by air cooling;

[0039] The keeping time of the ingot during open-die forging is not less than 20 h.

[0040] During open-die forging, the drawing rate is 60-90 mm / s.

[0041] Step two, intermediate forging:

[0042] The first blank is kept at T β -120 ℃ to T β +70 ℃ and subjected to 6-10 times of repeated upsetting and drawing, the forging ratio for each time is 3.5-5.0, and a second blank is obtained;

[0043] The intermediate forging is divided into two stages, in which the blank is first kept at T β -(40-120 ℃) and forged, the final forging temperature is not less than T β -250 ℃, and then the hot blank is returned to the furnace at T β+ (20℃~70℃) for heat preservation, the heat preservation time t = (0.3~0.5) D, (wherein D is the minimum cross-sectional dimension of the blank), water cooling after discharging, repeat the process 1~2 times. The second stage blank is at T β - (40℃~120℃) for heat preservation and 4~7 times of forging, the final forging temperature is not less than T β -250℃.

[0044] During intermediate forging, the first three passes of the elongation process use cross anvil elongation, the elongation rate is 20mm / s~40mm / s, the remaining passes are axial elongation, the feed amount is 200mm~300mm, and the elongation rate is 60mm / s~80mm / s.

[0045] Step three, shape forging:

[0046] The second blank is at T β - (40℃~120℃) for heat preservation and 3~4 times of shape forging, to obtain TC2 titanium alloy rod.

[0047] During shape forging, the final forging temperature of each pass is not less than T β -250℃, using double operation reciprocating feed, pass deformation ≤10%, feed amount ≤100mm, elongation rate 50mm / s~70mm / s.

[0048] In order to further verify the effect of the forging method of the application, the inventors carried out the following specific examples:

[0049] Example 1 (Φ400mm rod)

[0050] 1) The TC2 ingot with a specification of Φ640mm and a phase transition point of 960℃~965℃ is heat preserved at 1170℃ for 20h, and is forged for 1 pass and 3 times of upsetting and drawing, the total forging ratio is 8.5, and the first blank is obtained by air cooling.

[0051] 2) The first blank is heat preserved at 920℃ and forged, the total forging ratio of forging is 3.5, the first three passes of elongation are cross anvil elongation, the elongation rate is 20mm / s, the remaining passes are axial elongation, the feed amount is 200mm, the elongation rate is 60mm / s, the final forging temperature is 780℃, after forging, the material is reheated to 980℃, heat preserved for 300min, and then discharged and water cooled. After the material is cooled, polished and the damage is removed, the above operation is repeated once to obtain the second blank.

[0052] 3) The second blank is heat preserved at 920℃ and forged for 4 times of upsetting and drawing, the total forging ratio of each pass is 5.0, the first three passes of the elongation process of each pass use cross anvil elongation, the elongation rate is 20mm / s, the remaining passes are axial elongation, the feed amount is 200mm, the elongation rate is 60mm / s, the final forging temperature is 720℃, and the third blank is obtained.

[0053] 4) The third blank is formed and forged at 920°C for 3 heating times, each with a final forging temperature of no less than 710°C, and a drawing speed of 50 mm / s. The final rod has a specification of Φ400 mm and a length of 2000 mm. The microstructure of the TC2 titanium alloy large-scale forged blank processed according to this embodiment is shown in FIGS. 1 and 2, and the performance data is shown in Table 1. Figure 1 and 2

[0054] Example 2 (Φ350 mm rod)

[0055] 1) A TC2 ingot with a specification of Φ640 mm and a phase transition point of 960°C is heated at 1060°C for 30 h, and forged for 2 heating times, each with 2 upsetting and drawing, for a total forging ratio of 12, to obtain a first blank.

[0056] 2) The first blank is heated at 840°C and forged, with a total forging ratio of 5.0. The first three passes before drawing use cross anvil drawing at a drawing speed of 40 mm / s, and the remaining passes use axial drawing at a drawing speed of 80 mm / s and a feed amount of 300 mm. The final forging temperature is 710°C. After forging, the material is reheated to 1030°C, held for 300 min, and then water cooled. After the material is cooled, polished, and the defects are removed, the above operation is repeated once to obtain a second blank.

[0057] 3) The second blank is heated at 840°C and forged for 7 heating times, each with a total forging ratio of 5.0. The first three passes before the drawing process in each heating time use cross anvil drawing at a drawing speed of 40 mm / s, and the remaining passes use axial drawing at a drawing speed of 80 mm / s and a feed amount of 300 mm. The final forging temperature is 710°C. The third blank is obtained.

[0058] 4) The third blank is formed and forged at 840°C for 3 heating times, each with a final forging temperature of no less than 710°C, and a drawing speed of 70 mm / s. The final rod has a specification of Φ350 mm and a length of 2600 mm. The microstructure of the TC2 titanium alloy large-scale forged blank processed according to this embodiment is shown in FIGS. 1 and 2, and the performance data is shown in Table 1. Figure 3 and 4

[0059] Example 3 (Φ200 mm rod)

[0060] 1) A TC2 ingot with a specification of Φ640 mm and a phase transition point of 960°C-965°C is heated at 1100°C for 30 h, and forged for 2 heating times, each with 3 upsetting and drawing, for a total forging ratio of 10.5, to obtain a first blank.

[0061] ​​2) The first blank is kept at 880°C and forged, with a total forging ratio of 4.0, and the first three passes are cross-anvil elongation, with an elongation rate of 30 mm / s, and the remaining passes are axial elongation, with a feed amount of 250 mm and an elongation rate of 70 mm / s, and the final forging temperature is 720°C, and after forging, the material is reheated to 1000°C, kept for 300 min, and then taken out of the furnace and water-cooled. After the material is cooled, polished, and the defects are removed, the above operation is repeated once to obtain a second blank.

[0062] 3) The second blank is kept at 880°C and subjected to 6 times of upsetting and elongation forging, with a total forging ratio of 4.0 for each time, and the first three passes of each time are cross-anvil elongation, with an elongation rate of 30 mm / s, and the remaining passes are axial elongation, with a feed amount of 250 mm and an elongation rate of 70 mm / s, and the final forging temperature is 720°C, to obtain a third blank.

[0063] 4) The third blank is kept at 880°C and subjected to 4 times of forming forging, with a final forging temperature of no less than 720°C for each time, and an elongation rate of 60 mm / s, and finally a rod with a specification of Φ200 mm and a length of 4000 mm is processed. The microstructure of the TC2 titanium alloy large-size forging blank processed by the embodiment is shown in Figure 5 and 6 , and the performance data are shown in Table 1.

[0064] Comparative Example (Φ350 mm rod)

[0065] The comparative example adopts a traditional cogging forging → intermediate forging → forming forging process. The difference between the processing method of the TC2 titanium alloy large-size rod of the comparative example and that of Example 2 is that:

[0066] 1) Axial elongation is used in all times, without using cross-anvil elongation;

[0067] 2) In the intermediate forging process, the material is first completed with 1 time of upsetting and elongation forging at T β -40°C, and after air cooling and polishing, it is completed with 1 time of upsetting and elongation at T β +40°C, and after forging, it is air-cooled, and the forging ratio of the two times is 3.0. Then, it is completed with 8 times of repeated upsetting and elongation at T β -50°C, with a forging ratio of 3.0 for each time, and after each time of forging, it is air-cooled and polished.

[0068] 3) The forming forging is completed in 2 times, with a single pass reduction of 15%, a feed amount of 200 mm, and an elongation rate of 40 mm / s.

[0069] The microstructure of the TC2 titanium alloy Φ350 mm rod processed by the comparative example is shown in Figure 7 and 8 , and the performance data are shown in Table 1.

[0070] Figure 1 ,Figure 3 , Figure 5 The low-magnification microstructure of the cross section and the peripheral surface of the TC2 titanium alloy Φ400mm, Φ350mm and Φ200mm rod, respectively, can be seen that the low-magnification microstructure of the rod is uniform, and the microstructure of the cross section and the peripheral surface is all fuzzy crystal transverse, and there is no obvious difference in grain size between the center and the edge of the cross section. Figure 7 The low-magnification microstructure of the cross section and the peripheral surface of the TC2 titanium alloy Φ350mm rod of the comparative example can be seen that there is a coarse crystal region in the cross section and the peripheral surface of the rod, and the microstructure is unevenly distributed, and the uniformity is poor. The low-magnification microstructure shows that the present application has obvious improvement effect on the microstructure uniformity of the large-size rod of the TC2 titanium alloy.

[0071] Figure 2 , Figure 4 , Figure 6 The R / 2 high-magnification microstructure of the TC2 titanium alloy Φ400mm, Φ350mm and Φ200mm rod, respectively, can be seen that the primary α phase of the rod is all equiaxed or short rod-shaped, there is no long strip-shaped α phase and original β grain boundary, the microstructure is uniform and fine, and there is no streamline or cluster distribution. Figure 8 The high-magnification microstructure of the TC2 titanium alloy Φ350mm rod of the comparative example can be seen that, compared with the embodiment of the present application, the grain of the comparative example is more coarse, which shows that the present application has obvious improvement effect on the grain refinement of the large-size rod of the TC2 titanium alloy.

[0072] Table 1 is the room temperature tensile property data of the TC2 titanium alloy rod of three embodiments and one comparative example. The sampling position of all properties is R / 2, and all are the same system sample blank heat treatment. From the data in Table 1, it can be seen that the room temperature tensile strength and yield strength of the large-size rod of the TC2 titanium alloy forged by the present application are obviously improved compared with the comparative example, and the elongation and area reduction are equivalent to the comparative example.

[0073] Table 1 is the room temperature tensile property data of the TC2 titanium alloy rod of three embodiments and one comparative example. The sampling position of all properties is R / 2, and all are the same system sample blank heat treatment. From the data in Table 1, it can be seen that the room temperature tensile strength and yield strength of the large-size rod of the TC2 titanium alloy forged by the present application are obviously improved compared with the comparative example, and the elongation and area reduction are equivalent to the comparative example.

[0074] Rm / MPa Rp0.2 / MPa A / ％ Z / ％ Example 1 714 634 18.5 39 Example 2 727 672 22.5 48 Example 3 745 675 20 42 Comparative Example 698 623 18 44

[0075] In summary, the microstructure uniformity of the large-size rod of the TC2 titanium alloy forged by the present application is obviously improved, the strength and yield of the rod are improved by refining the microstructure, the risk of local failure of the material is reduced, the hot material is recycled, the forging cycle is shortened, the cost is reduced, and it is suitable for industrial application and development.

Claims

1. A forging method of TC2 titanium alloy large-size bar characterized by, The method comprises the following steps: Step one, cogging forging: The TC2 titanium alloy ingot is heated at T β +100℃ to T β +210℃, and is subjected to 1-2 times of open-die forging, 2-3 upsetting and drawing are completed per time of forging, the total forging ratio is controlled to be 8.5-12.0, and a first blank is obtained by air cooling; Step two, intermediate forging: T β -120°C to T β +70°C for 6 to 10 repeated upsetting and drawing, with a forging ratio of 3.5 to 5.0 per pass, to obtain a second billet; The intermediate forging is divided into two stages, in the first stage the blank is heated at T β -40°C to T β -120°C, and forged, the final forging temperature being not less than T β -250°C, then the hot material is remelted at T β +20°C to T β +70°C, the holding time being t=0.3D to 0.5D, where D is the minimum cross-sectional dimension of the blank, and the blank is discharged and water cooled, and the process is repeated 1 to 2 times; in the second stage the blank is heated at T β -40°C to T β -120°C, and forged 4 to 7 times, the final forging temperature being not less than T β -250°C; In the intermediate forging, the first three passes before the elongation process of each heating uses cross anvil elongation, and the elongation rate is 20 mm / s-40 mm / s; the remaining passes use axial elongation, the feed amount is 200 mm-300 mm, and the elongation rate is 60 mm / s-80 mm / s. Step three, forming forging: The second blank is heated to T β -40°C to T β -120°C and formed by 3 to 4 heating and forging to obtain a TC2 titanium alloy rod.

2. The method of claim 1, wherein the TC2 titanium alloy large-scale rod is forged by a method comprising: In the step one, the holding time of the ingot during the cogging forging is not less than 20 h.

3. The method of claim 1, wherein the TC2 titanium alloy large-size bar is forged at a temperature of 950°C to 1,050°C. In the step one, the cross anvil elongation is used in the elongation of all the passes of the cogging forging, and the elongation rate is 60 mm / s-90 mm / s.

4. The method of claim 1, wherein the TC2 titanium alloy large-size bar is forged at a temperature of 950-1050°C. In the third step, the temperature of each fire finish forging is not lower than T β -250℃, using double-operated reciprocating feeding, pass deformation ≤10%, feeding amount ≤100mm, elongation rate 50mm / s~70mm / s.

5. The method of claim 1, wherein the TC2 titanium alloy large-size bar is forged at a temperature of 950°C to 1,050°C. The forging method can be used for producing TC2 titanium alloy rods with a diameter of 200 mm-400 mm and a length of 2000 mm-4000 mm.

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