Low-cost preparation process of large-specification TC4 bar
By optimizing the preparation process of large-diameter TC4 bars through multi-stage forging technology, the problems of high cost and low efficiency have been solved, and efficient and low-cost production of TC4 bars has been achieved to meet the needs of aerospace and other fields.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHONGQING KINGSLEY AERONAUTICAL MATERIAL TECH CO LTD
- Filing Date
- 2025-12-31
- Publication Date
- 2026-05-15
AI Technical Summary
The existing technology for manufacturing large-diameter TC4 bars is costly and inefficient, making it difficult to meet the needs of aerospace and other fields.
A multi-stage forging process is adopted, including billet forging, recrystallization forging, two-phase zone forging, and finished product forging. By controlling the temperature range and deformation amount, combined with flattening operation, the forging process is optimized to improve the plasticity and uniformity of the material and reduce heating time and internal stress.
It significantly reduced forging costs, improved preparation efficiency, obtained large-diameter TC4 bars with good microstructure uniformity, reduced heating time and internal stress, and improved material properties.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of titanium alloy processing technology, specifically to a low-cost preparation process for large-size TC4 bars. Background Technology
[0002] Titanium alloys possess high specific strength, good ductility, and excellent fracture toughness, leading to their increasing market share in the aerospace field. Among them, TC4 (Ti-6Al-4V) is currently the most widely used and consumed grade in the entire titanium alloy industry. Its excellent forgeability, lightweight properties, economy, and relatively stable mechanical properties make it widely applicable in aerospace, shipbuilding, steam turbines, defense weaponry, and petroleum refining industries.
[0003] In recent years, with the increasing demands for damage tolerance and overall aircraft integrity in the aerospace industry, more and more parts are being assembled using large-size forgings instead of small forgings, leading to a growing demand for large-size bars. Unlike small-size bars, which have good forge penetration, large-size bars experience higher forging stress and poorer forge penetration. Conventional forging processes require numerous forging passes to obtain uniform and stable bars. Furthermore, the larger diameter of large-size bars makes forging more difficult and inefficient. Existing manufacturing processes are not only costly but also negatively impact the efficiency and quality of TC4 large-size bar production. Summary of the Invention
[0004] The present invention aims to provide a low-cost manufacturing process for large-size TC4 bars, in order to solve the problems of high cost and low manufacturing efficiency in the existing technology for manufacturing large-size TC4 bars.
[0005] This invention adopts the following technical solution: a low-cost manufacturing process for large-size TC4 bars, comprising the following steps: Step 1: Forging the billet. Heat the ingot to the T1 temperature range above the phase transformation point and hold it for a period of time. Then, forge it in 2 to 3 forging cycles. During each forging cycle, perform 2 to 3 upsetting and drawing operations. Finally, flatten the billet radially into a slab with a width-to-thickness ratio of less than or equal to 2. Step 2, recrystallization forging: The billet forged in Step 1 is squared, upturned, and flattened at a temperature T2 below the phase transformation point. Then it is returned to the furnace and heated to a temperature above the phase transformation point T3 for 1-2 forging cycles before cooling. Step 3, two-phase forging: the billet cooled in Step 2 is subjected to 3 to 6 rounding, upsetting, and flattening forgings in the temperature range of T4 below the phase transformation point temperature, and the width-to-thickness ratio of the flattened billet during forging is less than or equal to 2. Step 4: Finished product forging. The billet cooled in Step 3 is forged 2-3 times in the T5 temperature range below the phase transformation point temperature, and then cooled to obtain TC4 large-diameter bars.
[0006] The principle and beneficial effects of this scheme are as follows: In step one, the ingot is heated to above the phase transformation point temperature for high-temperature forging. Taking advantage of the material's good plasticity and low deformation resistance, the as-cast structure is efficiently broken up and defects are eliminated. Then, in step two, the ingot is first forged below the phase transformation point through squaring, upsetting, and flattening. A large amount of deformation energy is introduced through forging, providing driving force for subsequent recrystallization. Then, the ingot is heated back to above the phase transformation point temperature. During the heating process, the material undergoes strong recrystallization, resulting in refined β grains and improved microstructure uniformity. Finally, in steps three and four, two-phase forging is performed. Based on the uniform and refined β grains obtained in step two, multi-directional deformation is carried out in the two-phase region to further break up and spheroidize the α phase, ultimately obtaining TC4 large-diameter bars with high refinement and good microstructure uniformity.
[0007] In this application, a flattening operation is performed after each forging. Specifically, in the final stage of the first forging in step one, the forging billet is flattened into a slab with a width-to-thickness ratio of less than or equal to 2. In step three, the width-to-thickness ratio of the flattened billet during forging is also less than or equal to 2. The billet shape is closer to a "plate shape," which allows the forging billet to heat up more quickly and reduces the heating time, reducing the overall heating time by 20% to 40% and significantly reducing forging costs. At the same time, the heating of the forging billet is more uniform, effectively reducing the time difference in heating of different parts and preventing excessive differences in material structure. In addition, the large deformation of forging can also effectively reduce the internal stress generated inside the material during heating. During deformation, the contact and constraint between the various parts of the metal and the mold are more uniform, and the triaxial compressive stress state is more sufficient, allowing the deformation to penetrate into the core and making the strain distribution on the entire cross section more uniform.
[0008] Preferably, as an improvement, the temperature range of T1 in step one is 1150~1050℃, and the temperature range of T2 in step two is T β -(30~50)℃, the temperature range of T3 is T β +(30~50)℃, the temperature range of T4 in step three is T β - (30~50)℃, the temperature range of T5 in step four is T β - (30~50)℃.
[0009] Preferably, as an improvement, the upsetting deformation during the first forging in step one is 30% to 40%.
[0010] Preferably, as an improvement, in step one, three forging cycles are performed within the T1 temperature range, with the temperature of each forging cycle decreasing in a stepwise manner, and the temperature drop between each forging cycle being 30-50℃. After the three forging cycles are completed, air cooling is performed.
[0011] Preferably, as an improvement, in step three, when forging is performed in the temperature range of T4, the deformation range of a single upsetting is 25% to 35%.
[0012] Preferably, as an improvement, in step three, after a single forging, the furnace is reheated before the next forging is performed. A maximum of three consecutive forgings are performed, followed by cooling, and then the remaining forgings are performed.
[0013] Preferably, as an improvement, in step three, during the final forging, after the square forming and upsetting, the forging billet is not flattened and instead drawn into an octagon.
[0014] Preferably, as an improvement, in step one, the last forging is followed by air cooling; in step two, the last forging in the T2 temperature range is followed by water cooling; and in step four, the last elongation forging in the T5 temperature range is followed by air cooling.
[0015] Preferably, as an improvement, the diameter of the TC4 bar obtained in step four is 400-500 mm.
[0016] Preferably, as an improvement, a glass anti-oxidation layer is coated on the surface of the ingot before heating it in step one.
[0017] The beneficial effects of this plan are: 1. In this scheme, the temperature range of T1 in step one is 1150~1050℃, and the upsetting deformation during the first forging is 30%~40%. The temperature range is moderate, and the deformation of the 400~500mm large-diameter bar is in the medium deformation range, which can effectively break the initial coarse β grain boundaries and intragranular brittle structure, laying the foundation for subsequent refinement.
[0018] 2. In step one, three forgings are performed. After the first and second forgings are completed, the billet is returned to the furnace for reheating and then cooled in a step-by-step manner. By returning the billet to the furnace for reheating, the surface and core temperatures of the billet are uneven and the overall temperature has dropped after each forging. This method can quickly restore the billet to a uniform and stable temperature state, avoiding the formation of difficult-to-eliminate structures due to local high temperatures in the billet.
[0019] 3. In step three, at T4 at T β - The forging is carried out in a temperature range of (30~50)℃, and the deformation range of a single upsetting is 25%~35%, which is reduced compared with the deformation in step one. This avoids the α phase being severely stretched into fibers or insufficient spheroidization driving force, thereby improving the uniformity of the structure and performance.
[0020] 4. In step three, during the last forging, after the square and upsetting process, the forging billet is not flattened. Instead, it is drawn into an octagon. After the square and upsetting process, the flattening process is no longer used. Drawing the forging billet into an octagon makes it easier to complete the drawing process during the finished product forging.
[0021] 5. Before heating the ingot in step one, coat the surface of the ingot with a glass anti-oxidation layer to reduce the oxidation of the ingot surface during the heating process, which would affect the material properties. Attached Figure Description
[0022] Figure 1 This is a low-magnification microstructure image of the T-end of the TC4 bar in Embodiment 1 of the present invention.
[0023] Figure 2 This is a low-magnification microstructure image of the W end of the TC4 bar in Embodiment 1 of the present invention.
[0024] Figure 3 This is a 200x magnification microstructure diagram of the transverse D / 4 section of the TC4 bar at the T end in Embodiment 1 of the present invention.
[0025] Figure 4 This is a 200x magnification microstructure diagram of the transverse D / 4 section of the W end of the TC4 bar in Embodiment 1 of the present invention.
[0026] Figure 5 This is a low-magnification microstructure image of the T-end of the TC4 bar in Embodiment 2 of the present invention.
[0027] Figure 6 This is a low-magnification microstructure image of the W end of the TC4 bar in Embodiment 2 of the present invention.
[0028] Figure 7 This is a 200x magnification microstructure diagram of the transverse D / 4 section of the TC4 bar at the T end in Embodiment 2 of the present invention.
[0029] Figure 8 This is a 200x magnification microstructure diagram of the transverse D / 4 section of the W end of the TC4 bar in Embodiment 2 of the present invention.
[0030] Figure 9 This is a low-magnification microstructure of the T-end of the TC4 bar in Comparative Example 1 of this invention.
[0031] Figure 10 This is a low-magnification microstructure of the W end of the TC4 bar in Comparative Example 1 of this invention.
[0032] Figure 11 This is a 200x magnification microstructure diagram of the transverse D / 4 section of the TC4 bar at the T end in Comparative Example 1 of this invention.
[0033] Figure 12 This is a 200x magnification microstructure diagram of the transverse D / 4 of the W end of the TC4 bar in Comparative Example 1 of this invention. Detailed Implementation
[0034] The following detailed description illustrates the specific implementation method: Example
[0035] This first embodiment describes a low-cost manufacturing process for large-diameter TC4 bars, comprising the following steps: Step 1: Forging. The ingot is heated to a temperature range of T1 above the phase transformation point and held for a period of time before being forged 2 to 3 times. The temperature range of T1 is 1150 to 1050°C. Each forging is followed by 2 to 3 upsetting and drawing operations, with a deformation of 30% to 40%. The forging blank is then flattened radially into a slab with a width-to-thickness ratio of less than or equal to 2. In this embodiment, after holding at the T1 temperature range, 3 forging operations are performed. The temperature of each forging operation decreases in a stepwise manner, with a temperature drop of 30 to 50°C. After all forging operations are completed, the blank is air-cooled.
[0036] Step 2: Recrystallization forging. The billet forged in Step 1 is squared, upset, and flattened at a temperature T2 below the phase transformation point temperature. The temperature range of T2 is T... β - (30~50)℃; then return to the furnace and heat to above the phase transformation point of T3, perform at least one forging pass, and then cool by water cooling, wherein the temperature range of T3 is T β + (30~50)℃.
[0037] Step 3: Two-phase forging. The billet cooled in Step 2 is subjected to 3-6 rounding, upsetting, and flattening forging processes within a temperature range of T4, below the phase transformation point temperature. The T4 temperature range is T... β - (30~50)℃, the deformation of a single upsetting and drawing during forging is 25%~35%, and the width-to-thickness ratio of the flattened billet during forging is less than or equal to 2; at the same time, after the single-fire forging in step three, the billet is returned to the furnace for reheating before the next forging is carried out. A maximum of three consecutive fire forgings are carried out before cooling, and the cooling method is air cooling. Then, the surface oxide scale and cracks are removed by grinding, and then the remaining fire forgings are carried out. When carrying out the last fire forging, the flattened square forging is not carried out after the square and upsetting, and the billet is drawn into an octagon.
[0038] Step 4: Finished product forging. The billet cooled in Step 3 is subjected to 2-3 drawing forgings within the T5 temperature range, below the phase transformation point temperature. The T5 temperature range is T... β - (30~50)℃, then cooled to obtain TC4 large-diameter bars, and after the last drawing and forging, air-cooled, the diameter of the obtained TC4 bars is 400~500mm.
[0039] Specifically, in this embodiment, a TC4 titanium alloy ingot is used. βThe temperature is 997℃, the initial diameter is Φ740, and a Φ400 bar is forged according to the forging method of this invention. The process steps are as follows: Step 1: Forging the billet. First, raise the furnace temperature to 850℃, then hold it in the furnace for 2 hours. Next, raise the furnace temperature to 1150℃ with a holding coefficient of 0.5. Then, perform three-stage forging. During the initial forging, after the billet is taken out of the furnace, place it on a high-speed forging machine for rolling forging, and then perform upsetting and drawing forging. The upsetting and drawing deformation is 35%. After forging, return it to the furnace for heating. The dimensions after forging are 450×800×L. Then, lower the furnace temperature to 1100℃ with a holding coefficient of 0.3. After taking it out of the furnace, forge the billet to □600×L, and then perform reverse upsetting and drawing forging in the X and Y directions. After forging, return it to the furnace for heating. The dimensions after forging are □600×L. Finally, the furnace temperature was reduced to 1050℃ with a heat retention coefficient of 0.3. After exiting the furnace, the billet was upsetting and drawn on the Z-axis using a high-speed forging machine, then diagonally elongated, and finally forged into a flat square with dimensions of 450×800×L. After forging, it was air-cooled.
[0040] Step Two: Recrystallization Forging. The furnace temperature is raised to 950℃ for loading, with a holding coefficient of 0.7. After unloading, the forging billet is shaped to □600×L, then subjected to upsetting forging. The billet is then forged to 450×800×L and returned to the furnace. The furnace temperature is then raised to 1050℃ for heating, with a holding coefficient of 0.5. After unloading, the forging billet is shaped to □600×L, then subjected to upsetting forging. The billet is then forged to 450×800×L and water-cooled.
[0041] Step 3: Two-phase forging. The furnace temperature is raised to 950℃ before loading the billet into the furnace, with a holding coefficient of 0.7. After unloading, the billet is shrunk to □600×L, then subjected to upsetting forging. The billet is then forged to 450×800×L, and this process is repeated 6 times. The upsetting deformation is 35%. After each forging cycle, the billet is returned to the furnace for reheating before the next forging cycle. A maximum of three consecutive forging cycles are performed before cooling, which is done by air cooling. During the final forging cycle, after shrunk and upsetting, the billet is not flattened; instead, it is drawn to an octagonal length of 620×L.
[0042] Step 4: Finished product forging. The furnace temperature is raised to 950℃ and loaded into the furnace, with a holding coefficient of 0.7. After being taken out of the furnace, the forging billet is drawn to an octagonal length of 480×L and then returned to the furnace. The furnace temperature is then reheated to 950℃ and loaded into the furnace again, with a holding coefficient of 0.3. After being taken out of the furnace, the bar is drawn to a length of Φ410×L, resulting in a TC4 large-diameter bar that can be machined to Φ400×L.
[0043] Comparative Example 1: In Comparative Example 1, TC4 titanium alloy ingots were used, T β The temperature is 992℃, the initial diameter is Φ740, and a Φ400 bar stock is forged using conventional forging methods. The process steps are as follows: Step 1: Initial forging. First, raise the furnace temperature to 850℃, then hold the forged billet at that temperature for 2 hours. Next, raise the furnace temperature to 1150℃ with a holding coefficient of 0.5. Then, perform three-stage forging. During initial forging, after exiting the furnace, place the ingot on a high-speed forging mill for rolling, followed by upsetting and drawing. The upsetting and drawing deformation is 35%. After forging, reheat in the furnace. The final forging dimension is □650×L. Next, lower the furnace temperature to 1100℃ with a holding coefficient of 0.3. After exiting the furnace, forge the slab to □650×L, then perform reverse upsetting and drawing in the X and Y directions. After forging, reheat in the furnace. The final forging dimension is □650×L. Finally, lower the furnace temperature to 1050℃ with a holding coefficient of 0.3. After exiting the furnace, perform Z-axis upsetting and drawing on a high-speed forging mill, followed by diagonal drawing. The final forging dimension is □650×L. Air cool after forging.
[0044] Step Two: Recrystallization Forging. The furnace temperature is raised to 950℃, with a holding coefficient of 0.7. After removal from the furnace, the billet is upset forged to a diameter of 650mm x L, and then air-cooled. The furnace temperature is then raised to 1050℃, with a holding coefficient of 0.7. After removal from the furnace, the billet is upset forged to a diameter of 650mm x L, and then water-cooled.
[0045] Step 3: Two-phase zone forging. The furnace temperature is raised to 950℃ and the billet is loaded into the furnace with a heat preservation coefficient of 0.7. After being taken out of the furnace, it is upset forging. The billet is then forged to □650×L. This process is repeated 6 times. The upsetting deformation is 35%. After each forging, the billet is returned to the furnace for reheating before the next forging. This process is repeated for three consecutive forging cycles before cooling. The cooling method is air cooling.
[0046] Step 4: Finished product forging. The furnace temperature is raised to 950℃ and loaded into the furnace, with a holding coefficient of 0.7. After being taken out of the furnace, the forging billet is drawn to an octagonal length of 480×L and then returned to the furnace. The furnace temperature is then reheated to 950℃ and loaded into the furnace again, with a holding coefficient of 0.3. After being taken out of the furnace, the bar is drawn to a length of Φ410×L, resulting in a TC4 large-diameter bar that can be machined to Φ400×L.
[0047] The finished bar stock from Example 1 was tested, and according to... Figures 1-4 The test results show that the low-magnification structure of the bar is a uniform fuzzy crystal, and the overall D / 4 microstructure has uniform grains, small grain size, and no complete original β grain boundaries.
[0048] The finished bars in Comparative Example 1 were tested, and according to... Figures 9-12 The test results show that the low-magnification structure of the bar is a uniform fuzzy crystal, but the microstructure is somewhat different, consisting of elongated α and equiaxed α structures.
[0049] Compared with Comparative Example 1, Implementation Case 1 reduced the heating time by about 28%, which greatly reduced the forging heating cost. At the same time, with the same pairwise phase zone forging, the flattening forging method used in Implementation Case 1 significantly improved the core of the forging billet compared with the comparative example. Example
[0050] The material processed in this implementation case is a TC4 titanium alloy ingot. β The temperature is 996℃, the initial diameter is Φ830, and a Φ400 bar is forged according to the forging method of this invention. The process steps are as follows: Step 1: Initial forging. First, raise the furnace temperature to 850℃ and hold for 2 hours. Then, raise the temperature to 1150℃ with a holding coefficient of 0.5. Perform three-stage forging. During initial forging, after exiting the furnace, place the ingot on a high-speed forging mill for rolling, followed by upsetting and drawing forging. The upsetting and drawing deformation is 35%. After forging, reheat in the furnace. The final dimensions are 480×870×L. Next, lower the furnace temperature to 1100℃ with a holding coefficient of 0.3. After exiting the furnace, forge the slab to □650×L, then perform reverse upsetting and drawing forging in the X and Y directions. After forging, reheat in the furnace. The final dimensions are □650×L. The furnace temperature was reduced to 1050℃ with a heat retention coefficient of 0.3. After exiting the furnace, the billet was upsetting and drawn on the Z-axis using a high-speed forging machine, then diagonally elongated, and finally forged into a flat square with dimensions of 480×870×L. The billet was then air-cooled after forging.
[0051] Step Two: Recrystallization Forging: The furnace temperature is raised to 950℃ for loading, with a holding coefficient of 0.7. After unloading, the forging billet is shaped to □650×L, then subjected to upsetting and drawing forging. The billet is then forged to 480×870×L and returned to the furnace. The furnace temperature is then raised to 1050℃ for heating, with a holding coefficient of 0.5. After unloading, the forging billet is shaped to □650×L, then subjected to upsetting and drawing forging. The billet is then forged to 480×870×L and water-cooled after forging.
[0052] Step 3: Two-phase zone forging: Raise the furnace temperature to 950℃ and load the furnace, with a heat preservation coefficient of 0.7. After taking it out of the furnace, shrink the forging billet to □650×L, and then perform upsetting and drawing forging. Then forge the forging billet to 480×870×L, and repeat the process 6 times.
[0053] Step 4: Finished Product Forging: The furnace temperature is raised to 950℃, with a holding coefficient of 0.7. After removal from the furnace, the forged billet is drawn to an octagonal length of 520×L and then returned to the furnace. The heating temperature is then increased to 950℃, with a holding coefficient of 0.3. After removal from the furnace, the bar is drawn to Φ450×L and then returned to the furnace. The temperature is then reheated to 950℃, with a holding coefficient of 0.3. After removal from the furnace, the bar is drawn to Φ410×L, resulting in a TC4 large-diameter bar that can be machined to Φ400×L.
[0054] The finished bars from Implementation Case Two were tested, and according to... Figures 5-8 The test results show that the low-magnification structure of the bar is a uniform fuzzy crystal, with little difference in microstructure at the D / 4 position, relatively uniform overall grain size, small grain size, and no complete original β grain boundaries. Example
[0055] The difference between Example 3 and Example 1 is that: in step 1, before heating the ingot, a glass anti-oxidation layer is coated on the surface of the ingot. The model of the glass anti-oxidation layer is TB1200-16:NJ-1=1:1. By setting a glass anti-oxidation layer on the surface of the ingot, the oxidation of the surface of the ingot during the heating process is reduced, thereby improving the quality of the bar preparation.
[0056] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.
Claims
1. A low-cost manufacturing process for large-size TC4 bars, comprising the following steps: Step 1: Forging the billet. Heat the ingot to the T1 temperature range above the phase transformation point and hold it for a period of time. Then, forge it in 2 to 3 forging cycles. During each forging cycle, perform 2 to 3 upsetting and drawing operations. Finally, flatten the billet radially into a slab with a width-to-thickness ratio of less than or equal to 2. Step 2, recrystallization forging: The billet forged in Step 1 is squared, upturned, and flattened at a temperature T2 below the phase transformation point. Then it is returned to the furnace and heated to a temperature above the phase transformation point T3 for 1-2 forging cycles before cooling. Step 3, two-phase forging: the billet cooled in Step 2 is subjected to 3 to 6 rounding, upsetting, and flattening forgings in the temperature range of T4 below the phase transformation point temperature, and the width-to-thickness ratio of the flattened billet during forging is less than or equal to 2. Step 4: Finished product forging. The billet cooled in Step 3 is forged 2-3 times in the T5 temperature range below the phase transformation point temperature, and then cooled to obtain TC4 large-diameter bars.
2. The low-cost manufacturing process for large-size TC4 bars according to claim 1, characterized in that: In step one, the temperature range of T1 is 1150–1050℃, and in step two, the temperature range of T2 is T... β -(30~50)℃, the temperature range of T3 is T β +(30~50)℃, the temperature range of T4 in step three is T β - (30~50)℃, the temperature range of T5 in step four is T β - (30~50)℃.
3. The low-cost manufacturing process for large-size TC4 bars according to claim 1, characterized in that: In step one, during the first forging process, the upsetting deformation is 30% to 40%.
4. The low-cost manufacturing process for large-size TC4 bars according to claim 3, characterized in that: In step one, three forging processes are carried out within the T1 temperature range. The temperature of each forging process decreases in a stepwise manner, with a temperature drop of 30-50℃ between each process. After the three forging processes are completed, air cooling is performed.
5. The low-cost manufacturing process for large-size TC4 bars according to claim 1, characterized in that: In step three, when forging is performed in the temperature range of T4, the deformation range of a single upsetting is 25% to 35%.
6. The low-cost manufacturing process for large-size TC4 bars according to claim 5, characterized in that: In step three, after a single forging, the furnace is returned to reheat before the next forging. A maximum of three consecutive forgings are performed before cooling, and then the remaining forgings are performed.
7. The low-cost manufacturing process for large-size TC4 bars according to claim 7, characterized in that: In step three, during the final forging, after the square and upsetting processes, the blank is not flattened during forging; instead, it is drawn into an octagon.
8. The low-cost manufacturing process for large-size TC4 bars according to claim 1, characterized in that: In step one, the last forging is followed by air cooling; in step two, the last forging in the T2 temperature range is followed by water cooling; and in step four, the last elongation forging in the T5 temperature range is followed by air cooling.
9. The low-cost manufacturing process for large-size TC4 bars according to claim 1, characterized in that: In step four, the final diameter of the TC4 bar is 400-500 mm.
10. The low-cost manufacturing process for large-size TC4 bars according to claim 1, characterized in that: Before heating the ingot in step one, a glass anti-oxidation layer is coated on the surface of the ingot.