Forging method of TC2 titanium alloy large-specification bar

Abstract

The invention discloses a forging method of a TC2 titanium alloy large-specification bar, which comprises the following steps: step 1, cogging and forging: preserving the heat of a TC2 titanium alloy ingot at T beta + 100 DEG C to T beta + 210 DEG C, performing cogging and forging for 1-2 heating numbers, completing 2-3 upsetting and drawing in each heating number of forging, controlling the total forging ratio to 8.5-12.0, and performing air cooling to obtain a first blank; the first blank is subjected to heat preservation at the temperature ranging from T beta-120 DEG C to T beta + 70 DEG C and subjected to repeated upsetting and drawing of 6-10 heating numbers, the forging ratio of each heating number ranges from 3.5 to 5.0, and a second blank is obtained; and thirdly, forming forging is conducted, specifically, the second blank is subjected to heat preservation at the temperature ranging from T beta-40 DEG C to T beta-120 DEG C, forming forging of 3-4 heating numbers is conducted, and the TC2 titanium alloy bar is obtained. The TC2 titanium alloy large-specification bar prepared through the method is uniform in macrostructure and macrostructure, excellent in mechanical property, good in batch stability, short in process and suitable for large-batch industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy processing, and in particular relates to a forging method for a large-size TC2 titanium alloy bar. Background Art

[0002] The nominal composition of TC2 alloy is Ti-4Al-1.5Mn. It is a medium-strength near-α alloy with good process plasticity and thermal stability. It can be thermally deformed in a wide temperature range and is widely used in aerospace structural parts. With the development of the aerospace industry, the requirements for load-bearing structural parts to be integrated and large-scale have been put forward, and the demand for large-size bars has gradually increased.

[0003] In the traditional forging process, in order to solve the problem of poor forgeability and difficult microstructure crushing of TC2 materials, multiple fires of upsetting at the phase transformation point are added. As the number of fires increases, the forging process becomes more difficult to control and it is difficult to ensure the stability of the batches. The cumbersome process also means a longer production cycle and higher costs. Especially for large-sized bars with a diameter greater than 200 mm, the increase in size brings about problems such as increased element segregation, coarse original grains, and uneven microstructure and performance, which affect product delivery. Therefore, it is urgent to design a method for preparing large-sized TC2 titanium alloy bars with a short process and high microstructure uniformity.

[0004] In view of this, the inventors propose a forging method for large-size TC2 titanium alloy bars to overcome the defects of the prior art. Summary of the invention

[0005] The purpose of the present invention is to provide a forging method for large-size TC2 titanium alloy bars. The large-size TC2 titanium alloy bars prepared by the method have uniform high and low-magnification structures, excellent mechanical properties, good batch stability, and a short process, and are suitable for large-scale industrial production.

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

[0007] A forging method for a large-size TC2 titanium alloy bar comprises the following steps:

[0008] Step 1: Forging:

[0009] The TC2 titanium alloy ingot is cast at T β +100℃~T β +210℃ heat preservation and 1-2 rounds of open forging, 2-3 upsettings and drawing are completed in each round of forging, the total forging ratio is controlled between 8.5 and 12.0, and the first billet is obtained by air cooling;

[0010] Step 2: Intermediate forging:

[0011] For the first blank at Tβ -120℃~T β Keep the temperature at +70℃ and perform repeated upsetting and drawing for 6 to 10 times, with the forging ratio of each time being 3.5 to 5.0, to obtain the second billet;

[0012] Step 3: Forming and forging:

[0013] For the second blank at T β -40℃~T β The TC2 titanium alloy rod is obtained by keeping the temperature at -120℃ and performing 3 to 4 forming forgings.

[0014] Preferably, in the step 1, the ingot insulation time during blank forging is not less than 20 hours.

[0015] Preferably, in the step 1, the horizontal anvil stretching method is adopted during the blank forging and all the fire stretching, and the stretching rate is 60 mm / s to 90 mm / s.

[0016] Preferably, in step 2, the intermediate forging is divided into two stages, wherein in the first stage, the blank is firstly β -40℃~T β -120℃ insulation and forging, the final forging temperature is not lower than T β -250℃, then at T β +20℃~T β +70℃ for heating and heat preservation, the heat preservation time is t=0.3D~0.5D, where D is the minimum cross-sectional size of the blank, and then the blank is water-cooled after being taken out of the furnace. This process is repeated 1~2 times; in the second stage, the blank is heated at T β -40℃~T β -120℃ forging and 4-7 times of forging, the final forging temperature is not less than T β -250℃.

[0017] Preferably, in the step 2, during the intermediate forging, the first three passes of each fire drawing process use a horizontal anvil for drawing, with a drawing rate of 20mm / s to 40mm / s, and the remaining passes are axially drawn, with a feed amount of 200mm to 300mm and a drawing rate of 60mm / s to 80mm / s.

[0018] Preferably, in step 3, during the forming forging, the final forging temperature of each fire is not less than T β -250℃, double-operated reciprocating feeding, deformation per pass ≤10%, feeding amount ≤100mm, pulling rate 50mm / s~70mm / s.

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

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

[0021] 1. In the present invention, during the blank forging, the blank is kept warm for a long time at a high temperature, and the thermal diffusivity of atoms at high temperature is improved, so that the easily segregated element Mn is fully diffused within and between crystals to ensure the uniformity of the composition, providing a basis for the uniformity of the organizational properties.

[0022] 2. During the intermediate forging, the present invention sets a larger pressing amount and drawing rate at the stage below the phase transformation point to ensure that the grains are fully broken, and sets the drawing in different directions to be performed alternately to reduce the deformation texture caused by compression in a single direction, and ensure that the rod is uniformly deformed in all directions; then the hot material is returned to the furnace and kept warm for a period of time above the phase transformation point to allow the material to be fully recrystallized under the drive of high temperature. After being taken out of the furnace, no upsetting forging is performed, but direct water cooling is performed, which fully retains the fine grains after recrystallization and ensures that the rod structure is uniform and fine.

[0023] 3. The present invention simplifies the steps of intermediate forging. In the traditional forging process, the material is air-cooled after each firing. For large-sized bars, air cooling takes a long time, which greatly increases the time cost and material transportation cost. In the intermediate forging stage, the present invention quickly returns the material to the furnace after forging, thereby shortening the time and reducing the cost.

[0024] 4. The present invention adopts a deformation method of relatively low temperature, fast speed, 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 grinding. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a low-magnification microstructure diagram of the TC2 titanium alloy Φ400 mm bar forged in Example 1 of the present invention.

[0026] Figure 2 This is a high-magnification microstructure diagram of the TC2 titanium alloy Φ400 mm bar forged in Example 1 of the present invention.

[0027] Figure 3 This is a low-magnification microstructure diagram of the TC2 titanium alloy Φ350 mm bar forged in Example 2 of the present invention.

[0028] Figure 4 This is a high-magnification microstructure diagram of the TC2 titanium alloy Φ350 mm bar forged in Example 2 of the present invention.

[0029] Figure 5 This is a low-magnification microstructure diagram of the TC2 titanium alloy Φ200 mm bar forged in Example 3 of the present invention.

[0030] Figure 6 This is a high-magnification microstructure diagram of the TC2 titanium alloy Φ200 mm bar forged in Example 3 of the present invention.

[0031] Figure 7 It is a low-magnification structure diagram of the TC2 titanium alloy Φ350mm bar forged according to the comparative example of the present invention.

[0032] Figure 8 It is a high-magnification microstructure diagram of a TC2 titanium alloy Φ350 mm bar forged in the comparative example of the present invention.

[0033] Fig. 9 It is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention.

[0035] like Figure 1-Figure 9 As shown, a forging method for large-size TC2 titanium alloy bars is provided. The raw material of the large-size TC2 titanium alloy bars is 3-4 ton TC2 titanium alloy ingots produced by three-stage smelting in a vacuum consumable arc furnace. The forging method can be used to produce TC2 titanium alloy bars with a diameter of 200mm to 400mm and a length of 2000mm to 4000mm.

[0036] The steps include:

[0037] Step 1: Forging:

[0038] The TC2 titanium alloy ingot is cast at T β + (100℃~210℃) insulation and 1~2 fires of blank forging, 2~3 upsettings are completed in each fire, the total forging ratio is controlled between 8.5~12.0, and the first blank is obtained by air cooling;

[0039] The ingot insulation time during forging shall be no less than 20h.

[0040] During all the drawing times of forging, the horizontal anvil drawing method is adopted, and the drawing rate is 60mm / s to 90mm / s.

[0041] Step 2: Intermediate forging:

[0042] For the first blank at T β -120℃~T β Keep the temperature at +70℃ and perform repeated upsetting and drawing for 6 to 10 times, with the forging ratio of each time being 3.5 to 5.0, to obtain the second billet;

[0043] The intermediate forging is divided into two stages. In the first stage, the billet is first β - (40℃~120℃) keep warm and forge, the final forging temperature is not lower than T β -250℃, then the hot material is returned to the furnace at T β+ (20 ℃ ~ 70 ℃) for heating and heat preservation, the heat preservation time t = (0.3 ~ 0.5) D, (where D is the minimum cross-sectional size of the billet), and then water-cooled after being taken out of the furnace. This process is repeated 1 to 2 times. β - (40℃~120℃) keep warm and carry out 4~7 fire forgings, the final forging temperature is not less than T β -250℃.

[0044] During intermediate forging, the first three passes of each fire drawing process use horizontal anvil drawing, with a drawing rate of 20mm / s~40mm / s, and the remaining passes are axial drawing, with a feed amount of 200mm~300mm and a drawing rate of 60mm / s~80mm / s.

[0045] Step 3: Forming and forging:

[0046] For the second blank at T β -(40℃~120℃) insulation and 3~4 times of forming forging are carried out to obtain TC2 titanium alloy rods.

[0047] During forming forging, the final forging temperature of each fire shall not be lower than T β -250℃, double-operated reciprocating feeding, deformation per pass ≤10%, feeding amount ≤100mm, pulling rate 50mm / s~70mm / s.

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

[0049] Example 1 (Φ400mm rod)

[0050] 1) A TC2 ingot with a specification of Φ640 mm and a phase transformation point of 960°C to 965°C was kept at 1170°C for 20 h, forged with 3 upsetting passes in one fire, with a total forging ratio of 8.5, and air-cooled to obtain the first billet.

[0051] 2) The first billet is kept at 920°C and forged, the total forging ratio is 3.5, the first three passes of drawing are horizontal anvil drawing, the drawing rate is 20mm / s, the remaining passes are axial drawing, the feed amount is 200mm, the drawing rate is 60mm / s, the final forging temperature is 780°C, after forging, it is heated to 980°C, kept for 300min and then taken out of the furnace for water cooling. After the material is cooled and polished to remove scratches, the above operation is repeated once to obtain the second billet.

[0052] 3) The second billet is kept at 920°C and subjected to 4 upsetting and drawing forgings. The total forging ratio of each forging is 5.0. The first three drawing passes of each drawing process use a horizontal anvil for drawing at a drawing rate of 20 mm / s. The remaining passes are axially drawn with a feed amount of 200 mm and a drawing rate of 60 mm / s. The final forging temperature is 720°C to obtain the third billet.

[0053] 4) The third billet is subjected to three rounds of forming forging at 920°C, with the final forging temperature of each round not less than 710°C and the drawing rate of 50 mm / s. The bar specification obtained by the final processing is Φ400 mm and the length is 2000 mm. The structure of the large-size forging billet of TC2 titanium alloy processed in this embodiment is as follows: Figure 1 and 2 The performance data are shown in Table 1 below.

[0054] Example 2 (Φ350mm rod)

[0055] 1) A TC2 ingot with a specification of Φ640 mm and a phase transformation point of 960°C was kept at 1060°C for 30 h, forged with 2 upsettings in 2 fires, with a total forging ratio of 12, and air-cooled to obtain the first billet.

[0056] 2) The first billet is kept at 840°C and forged, the total forging ratio is 5.0, the first three passes of drawing are horizontal anvil drawing, the drawing rate is 40mm / s, the remaining passes are axial drawing, the feed amount is 300mm, the drawing rate is 80mm / s, the final forging temperature is 710°C, after forging, it is returned to the furnace and heated to 1030°C, kept for 300min, and then taken out of the furnace and water-cooled. After the material is cooled, polished and cleaned, the above operation is repeated once to obtain the second billet.

[0057] 3) The second billet is kept at 840°C and subjected to 7 upsetting and drawing forgings, with a total forging ratio of 5.0 for each forging. The first three drawing passes of each drawing process use a transverse anvil for drawing, with a drawing rate of 40 mm / s, and the remaining passes are axially drawn, with a feed amount of 300 mm, a drawing rate of 80 mm / s, and a final forging temperature of 710°C to obtain a third billet.

[0058] 4) The third billet is subjected to three rounds of forming forging at 840°C, with the final forging temperature of each round not less than 710°C and the drawing rate of 70mm / s. The bar specification obtained by the final processing is Φ350mm and the length is 2600mm. The structure of the large-size forging billet of TC2 titanium alloy processed in this embodiment is as follows: Figure 3 and 4 The performance data are shown in Table 1 below.

[0059] Example 3 (Φ200mm rod)

[0060] 1) A TC2 ingot with a specification of Φ640 mm and a phase transformation point of 960°C to 965°C was kept at 1100°C for 30 hours, forged with 2 fires and 3 upsettings each, with a total forging ratio of 10.5, and air-cooled to obtain the first billet.

[0061] 2) The first billet is kept at 880°C and forged, the total forging ratio is 4.0, the first three passes of drawing are horizontal anvil drawing, the drawing rate is 30mm / s, the remaining passes are axial drawing, the feed amount is 250mm, the drawing rate is 70mm / s, the final forging temperature is 720°C, after forging, it is returned to the furnace and heated to 1000°C, kept for 300min, and then taken out of the furnace and water-cooled. After the material is cooled, polished and cleaned, the above operation is repeated once to obtain the second billet.

[0062] 3) The second billet is kept at 880°C and subjected to 6 upsetting and drawing forgings. The total forging ratio of each forging is 4.0. The first three drawing passes of each drawing process use a horizontal anvil for drawing, and the drawing rate is 30 mm / s. The remaining passes are axially drawn, with a feed amount of 250 mm, a drawing rate of 70 mm / s, and a final forging temperature of 720°C to obtain a third billet.

[0063] 4) The third billet is subjected to 4 rounds of forming forging at 880°C, with the final forging temperature of each round not less than 720°C and the drawing rate of 60mm / s. The bar specification obtained by the final processing is Φ200mm and the length is 4000mm. The structure of the large-size forging billet of TC2 titanium alloy processed in this embodiment is as follows: Figure 5 and 6 The performance data are shown in Table 1 below.

[0064] Comparative example (Φ350mm bar)

[0065] The comparative example adopts the traditional process of blank forging → intermediate forging → forming forging. The processing method of the large-size TC2 titanium alloy bar in the comparative example is different from that of Example 2 in that:

[0066] 1) All fires were drawn axially, and no horizontal anvil drawing was used;

[0067] 2) The intermediate forging process material is first β -40℃ completes one upsetting forging, air cooling and grinding, and then β +40℃ to complete one upsetting and drawing, air cooling after forging, the forging ratio of the two fires is 3.0. β Complete 8 rounds of repeated upsetting and drawing at -50℃, with a forging ratio of 3.0 for each round, and air cooling and grinding after each forging.

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

[0069] The microstructure of the TC2 titanium alloy Φ350mm bar processed by this comparative example is as follows: Figure 7 and 8 The performance data are shown in Table 1 below.

[0070] Figure 1 , Figure 3 , Figure 5 These are the cross-sectional and peripheral low-magnification microstructure diagrams of TC2 titanium alloy Φ400mm, Φ350mm, and Φ200mm bars. It can be seen that the low-magnification microstructure of the bar is uniform, the cross-sectional and peripheral microstructures are both fuzzy crystal cross-sections, and there is no obvious difference in the grain size between the center and edge of the cross-sectional area. Figure 7 The cross section and peripheral surface macrostructure diagram of the comparative example TC2 titanium alloy Φ350mm bar show that there are coarse grain areas in the cross section and peripheral surface of the bar, and the microstructure distribution is uneven and the uniformity is poor. The macrostructure diagram shows that the present invention has a significant effect on improving the microstructure uniformity of large-size TC2 titanium alloy bars.

[0071] Figure 2 , Figure 4 , Figure 6 These are the R / 2 high-magnification organization diagrams of TC2 titanium alloy Φ400mm, Φ350mm, and Φ200mm bars. It can be seen that the primary α phase of the bar is equiaxed or short rod-shaped, without long strips of α phase and original β grain boundaries. The organization is uniform and fine, without streamlines or clustered distribution. Figure 8 This is a high-magnification microstructure diagram of the comparative example TC2 titanium alloy Φ350mm rod. It can be seen that compared with the embodiment of the present invention, the grains of the comparative example are coarser, indicating that the present invention has a significant improvement effect on the grain refinement of the large-size TC2 titanium alloy rod.

[0072] Table 1 shows the room temperature tensile performance data of TC2 titanium alloy bars of three embodiments and one comparative example. All performance sampling positions are R / 2, and all are heat treated with the same system of sample blanks. It can be seen from the data in Table 1 that the room temperature tensile tensile strength and yield strength of the large-size TC2 titanium alloy bars forged by the present invention are significantly improved compared with the comparative example, and the elongation and area reduction are equivalent to those of the comparative example.

[0073] Table 1 Room temperature tensile properties of TC2 titanium alloy bars of the embodiment and a 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 large-size TC2 titanium alloy bars forged by the present invention is significantly improved, the strength and yield of the bars are improved by refining the microstructure, the risk of local failure of the material is reduced, and the hot material return is increased, the forging cycle is shortened, and the cost is reduced, which is suitable for industrial application and development.

Claims

1. A forging method for large-size TC2 titanium alloy bars, characterized in that: The following steps are involved: Step 1: Forging: The TC2 titanium alloy ingot is cast at T β +100℃~T β +210℃ heat preservation and 1-2 rounds of open forging, 2-3 upsettings and drawing are completed in each round of forging, the total forging ratio is controlled between 8.5 and 12.0, and the first billet is obtained by air cooling; Step 2: Intermediate forging: For the first blank at T β -120℃~T β Keep the temperature at +70℃ and perform repeated upsetting and drawing for 6 to 10 times, with the forging ratio of each time being 3.5 to 5.0, to obtain the second billet; Step 3: Forming and forging: For the second blank at T β -40℃~T β The TC2 titanium alloy rod is obtained by keeping the temperature at -120℃ and performing 3 to 4 rounds of forming forging.

2. The forging method of TC2 titanium alloy large-size bars according to claim 1 is characterized in that: In the step 1, the ingot insulation time during the blank forging is not less than 20 hours.

3. The forging method of TC2 titanium alloy large-size bars according to claim 1 is characterized in that: In the step 1, the horizontal anvil stretching method is adopted during the forging of the blank for all the fires, and the stretching rate is 60 mm / s to 90 mm / s.

4. The forging method of TC2 titanium alloy large-size bars according to claim 1, characterized in that: In step 2, the intermediate forging is divided into two stages, in which the first stage of the billet is first β -40℃~T β -120℃ insulation and forging, the final forging temperature is not lower than T β -250℃, then at T β +20℃~T β +70℃ for heating and heat preservation, the heat preservation time is t=0.3D~0.5D, where D is the minimum cross-sectional size of the blank, and then the blank is water-cooled after being taken out of the furnace. This process is repeated 1~2 times; in the second stage, the blank is heated at T β -40℃~T β -120℃ forging and 4-7 times of forging, the final forging temperature is not less than T β -250℃.

5. The forging method of TC2 titanium alloy large-size bars according to claim 1, characterized in that: In the step 2, during the intermediate forging, the first three passes of each fire drawing process use a horizontal anvil for drawing, with a drawing rate of 20mm / s to 40mm / s, and the remaining passes are axially drawn, with a feed amount of 200mm to 300mm and a drawing rate of 60mm / s to 80mm / s.

6. The forging method of TC2 titanium alloy large-size bars according to claim 1, characterized in that: In the step 3, during the forming forging, the final forging temperature of each fire is not less than T β -250℃, double-operated reciprocating feeding, deformation per pass ≤10%, feeding amount ≤100mm, pulling rate 50mm / s~70mm / s.

7. The forging method of TC2 titanium alloy large-size bars according to claim 1, characterized in that: The forging method can be used to produce TC2 titanium alloy bars with a diameter of 200 mm to 400 mm and a length of 2000 mm to 4000 mm.

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