A large-sized forging of Ti-6Al-4V titanium alloy with high uniformity and its manufacturing method

Abstract

The present invention provides a large-sized forging of Ti-6Al-4V titanium alloy with high uniformity and a manufacturing method, including the following preparation steps: S1. Provide a powder metallurgy sintered Ti-6Al-4V titanium alloy blank, and the cross-sectional thickness of the blank is above 120 mm; S2. Use a heating device to heat the blank to 1030 °C to 1060 °C for heat preservation and then forge it. The forging deformation amount is 30% to 38%, and a large-sized forging of titanium alloy is prepared. The present invention uses a powder metallurgy sintered Ti-6Al-4V titanium alloy blank for forging, omitting the traditional melting and blank forging processing procedures, shortening the manufacturing process of the forging, greatly reducing the production cost. At the same time, using a suitable forging process for forging, while improving the strength and plasticity, a forging with more uniform structure and properties than that obtained by traditional ingot forging is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium alloys, and particularly relates to a large-sized forging of a Ti-6Al-4V titanium alloy with high uniformity and a manufacturing method thereof. Background Art

[0002] Ti-6Al-4V titanium alloy is the titanium alloy category with the largest usage amount at present. It has excellent comprehensive mechanical properties, outstanding specific strength (the ratio of strength to density), good strength-ductility matching and high-temperature strength. Therefore, it has been widely used in the aerospace field, such as the landing gear of airplanes, fuselage crossbeams, rocket engine casings, etc.

[0003] At present, titanium alloy forgings are mainly obtained by vacuum melting of sponge titanium to obtain titanium ingots, and then blank forging and forming forging are carried out on the titanium ingots. However, in order to improve casting segregation and eliminate casting columnar crystals and improve the tissue uniformity of the billets, the titanium ingots need to be blank forged for multiple heats to obtain billets that can be used for forming forging, resulting in a long production process, low production efficiency, and the cost of hot processing reaching 45-60% of the cost of the entire forging.

[0004] Powder metallurgy is a process method that uses powders as raw materials and manufactures various products such as metals and composites through pressing and sintering. When preparing titanium alloy billets by powder metallurgy, its sintering temperature is much lower than that of traditional melting, which can minimize alloy composition segregation, will not appear coarse and uneven casting structures, and the material utilization rate is significantly improved. Based on the above advantages, the titanium alloy billets prepared by powder metallurgy can be directly subjected to forming forging without blank forging, the hot processing process flow is significantly shortened, and the cost is also reduced. Chinese Patent Application No. 202010487693.7 discloses a short-process and low-cost TC4 titanium alloy pipe preparation process, which manufactures TC4 titanium alloy pipes through powder metallurgy to make pipe blanks and radial forging, overcomes the disadvantages of many hot rolling passes and long processing cycles of traditional pipes, uses powder metallurgy to make pipe blanks, and through high- and low-temperature two-heat radial forging process methods, manufactures seamless pipes with uniform deformation and high strength, improves the deformation uniformity of the metal during the process, and ensures the dimensional uniformity of titanium alloy pipes. However, from the microstructural diagrams of the prepared TC4 titanium alloy pipes ( Figure 3 、 4 ) it can be seen that due to the large temperature difference between the inner and outer walls of the material, the microstructures of the inner and outer walls of the titanium alloy pipes are uneven, the α lamellae are not uniform in thickness, and it is easy for the titanium alloy to have defects of uneven internal and external tissues and resulting in uneven internal and external properties. Especially for large-sized titanium alloy forgings (section thickness ≥ 120 mm), during the forging process, the temperature difference between the surface and the core is large, the deformation distribution is uneven, and it is more difficult to control the uniformity of its tissue and properties.

[0005] It can be seen that there is an urgent need to provide a new method for preparing large-sized forgings of Ti-6Al-4V titanium alloy billets based on powder metallurgy technology, which can improve the defects of uneven microstructure and properties of traditional large-sized titanium alloy forgings. Summary of the Invention

[0006] The purpose of the present invention is to provide a new method for preparing large-sized forgings of Ti-6Al-4V titanium alloy billets based on powder metallurgy technology, which can improve the defects of uneven microstructure and properties of traditional large-sized titanium alloy forgings.

[0007] In the first aspect, the present invention provides a method for manufacturing large-sized forgings of Ti-6Al-4V titanium alloy, including the following preparation steps:

[0008] S1. Provide a powder metallurgy sintered Ti-6Al-4V titanium alloy billet, the cross-sectional thickness of the billet is more than 120 mm, the porosity of the billet does not exceed 4 vol%, and the chemical composition range of the billet is: Al: 5.5 - 6.75 wt%, V: 3.5 - 4.5 wt%, C ≤ 0.08 wt%, Fe ≤ 0.25 wt%, H ≤ 0.012 wt%, O ≤ 0.12 wt%, N ≤ 0.03 wt%, and the balance is Ti;

[0009] S2. Use a heating device to heat the billet to 1030°C - 1060°C for heat preservation. After the internal and external temperatures of the billet are uniform, take out the billet for forging. The time for the billet to transfer from the heating device to the forging working surface does not exceed 80 seconds, the die temperature is 300°C - 500°C, the pressing rate of the punch during forging is 8 - 12 mm / s, control the final forging temperature above 850°C, and the forging deformation amount is 30% - 38% to obtain large-sized forgings of titanium alloy.

[0010] Optionally, the chemical composition range of the billet is: Al: 5.8 - 6.5 wt%, V: 3.8 - 4.5 wt%, C ≤ 0.06 wt%, Fe ≤ 0.20 wt%, H ≤ 0.01 wt%, O ≤ 0.12 wt%, N ≤ 0.03 wt%, and the balance is Ti.

[0011] Optionally, the microstructure of the core and the 1 / 4 near the surface of the billet is equiaxed structure, the average thickness of the α-phase in the core and the 1 / 4 near the surface is less than 20 μm, and the difference in the average thickness of the α-phase in the core and the 1 / 4 near the surface is less than 3 μm.

[0012] Optionally, the microstructure of the core and the 1 / 4 near the surface of the large-sized forgings of titanium alloy is fully lamellar α-phase, and the difference between the average thickness of the α-phase in the core and the average thickness of the α-phase in the 1 / 4 near the surface does not exceed 0.5 μm.

[0013] Optionally, the average thickness of the α-phase at the core and at 1 / 4 of the near-surface of the large-sized titanium alloy forging is below 4 μm.

[0014] Optionally, it further includes:

[0015] S3. Use a heating device to heat the titanium alloy forging obtained in step S2 to 930°C - 970°C for heat preservation. After the internal and external temperatures of the titanium alloy forging are uniform, take out the titanium alloy forging for forging. The time for the titanium alloy forging to transfer from the heating device to the forging working surface does not exceed 80 seconds. The die temperature is 300°C - 500°C, the pressing rate of the punch during forging is 6 - 10 mm / s, control the final forging temperature above 780°C, and the forging deformation amount is 25 - 40%, to obtain a second-forged large-sized titanium alloy forging;

[0016] S4. Use a heating device to heat the second-forged large-sized titanium alloy forging to 730°C - 780°C for annealing treatment to obtain an annealed large-sized titanium alloy forging.

[0017] Optionally, the microstructure at the core and at 1 / 4 of the near-surface of the annealed large-sized titanium alloy forging is primary α-phase and β transformation structure, and the difference in the average thickness of the α-phase at the core and at 1 / 4 of the near-surface does not exceed 0.5 μm.

[0018] Optionally, the average thickness of the α-phase at the core and at 1 / 4 of the near-surface of the annealed large-sized titanium alloy forging does not exceed 12 μm.

[0019] It further includes:

[0020] S5. Use a heating device to heat the annealed large-sized titanium alloy forging obtained in step S4 to 930°C - 970°C for heat preservation. After the internal and external temperatures of the annealed large-sized titanium alloy forging are uniform, take out the annealed large-sized titanium alloy forging for forging. The time for the annealed large-sized titanium alloy forging to transfer from the heating device to the forging working surface does not exceed 80 seconds. The die temperature is 300°C - 500°C, the pressing rate of the punch during forging is 6 - 10 mm / s, control the final forging temperature not lower than 780°C, and the forging deformation amount is 25 - 40%, to obtain a third-forged large-sized titanium alloy forging;

[0021] S6. Use a heating device to heat the third-forged titanium alloy forging to 730°C - 780°C for annealing treatment to obtain an annealed large-sized titanium alloy forging.

[0022] Optionally, the difference in the yield strength between the core and at 1 / 4 of the near-surface of the large-sized titanium alloy forging does not exceed 10 MPa, the difference in the tensile strength between the core and at 1 / 4 of the near-surface does not exceed 10 Mpa, and the difference in the elongation between the core and at 1 / 4 of the near-surface does not exceed 1%.

[0023] In a second aspect, the present invention provides a large-sized forging of Ti-6Al-4V titanium alloy, which is obtained by the manufacturing method of the large-sized forging of Ti-6Al-4V titanium alloy described above.

[0024] In summary, the present invention includes at least one of the following beneficial technical effects:

[0025] 1. For the manufacturing method of a large-sized forging of Ti-6Al-4V titanium alloy provided by the present invention, the Ti-6Al-4V titanium alloy billet prepared by powder metallurgy is used as the forging raw material, reducing the number of hot working heats of the forging by 4 to 8 times, solving the problems of many heating heats and long production cycle of traditional titanium alloy forgings, and reducing the cost of the forging by more than 40%.

[0026] 2. For the manufacturing method of a large-sized forging of Ti-6Al-4V titanium alloy provided by the present invention, the forging process is optimized according to the tissue characteristics of the powder metallurgy billet, controlling the initial forging temperature, forging deformation amount, final forging temperature and specific process parameters during forging, thereby refining the tissue of the large-sized forging of titanium alloy and realizing the tissue and performance uniformity between the core and the outside of the large-sized forging. The strength fluctuation between the near surface and the core is reduced from 40 - 60 MPa to within 10 MPa, a reduction of about 80%, effectively solving the problem of poor uniformity of large forgings.

[0027] 3. For the manufacturing method of a large-sized forging of Ti-6Al-4V titanium alloy provided by the present invention, while the uniformity of the large forging is greatly improved, compared with traditional Ti-6Al-4V titanium alloy forgings, the yield strength of the forgings produced by this process is also increased by about 20 MPa, and the tensile strength and elongation are basically unchanged.

[0028] 4. For the manufacturing method of a large-sized forging of Ti-6Al-4V titanium alloy provided by the present invention, it is possible to specify the process of the titanium alloy forging according to the actual deformation amount requirements, and the prepared large-sized titanium alloy has excellent mechanical properties and the uniformity of the internal and external tissue and performance. The process has high controllability and is suitable for industrial mass production. Description of the Drawings

[0029] Figure 1 It is the metallographic structure diagram of the powder metallurgy sintered Ti-6Al-4V titanium alloy billet provided by Example 1 of the present invention.

[0030] Figure 2 It is the metallographic structure diagram of the large-sized forging of titanium alloy prepared in Example 1 of the present invention.

[0031] Figure 3 It is the metallographic structure diagram of the large-sized forging of titanium alloy prepared in Comparative Example 1 of the present invention.

[0032] Figure 4 This is the metallographic structure diagram of the large-sized titanium alloy forging prepared in Comparative Example 2 of the present invention.

[0033] Figure 5 This is the metallographic structure diagram of the large-sized titanium alloy forging prepared in Example 2 of the present invention.

[0034] Figure 6 This is the metallographic structure diagram of the large-sized titanium alloy forging prepared in Comparative Example 3 of the present invention.

[0035] Figure 7 This is the metallographic structure diagram of the annealed large-sized titanium alloy forging prepared in Example 3 of the present invention. Detailed implementation manners

[0036] To make the objectives, technical solutions and advantages of the present invention clearer and more explicit, the following further describes the present invention in detail with reference to the accompanying drawings and by way of examples. It should be understood that the specific examples described herein are only used to explain the present invention and are not used to limit the present invention.

[0037] The chemical composition range of Ti-6Al-4V titanium alloy is as follows: Al: 5.5% - 6.75%, V: 3.5% - 4.5%, and the balance is Ti and inevitable industrial impurities (C ≤ 0.08wt%, Fe ≤ 0.25wt%, H ≤ 0.012wt%, O ≤ 0.12wt%, N ≤ 0.03wt%). Ti-6Al-4V titanium alloy belongs to α+β alloy and is composed of α phase and β phase under equilibrium state. It has the characteristics of high strength, good thermal strength, plasticity, toughness, formability, weldability, corrosion resistance and biocompatibility, and has become the most widely used titanium alloy at present. Forging deformation can enable Ti-6Al-4V titanium alloy forgings to meet the design technical index requirements of shape and size, microstructure and service performance. Generally, it is considered that Ti-6Al-4V titanium alloy is very sensitive to forging deformation process. On the one hand, if the initial forging temperature exceeds the β phase transformation temperature of the titanium alloy, due to the drastic growth of β grains, Widmanstätten structure is easily formed, resulting in β brittleness. Therefore, in order to avoid the β brittleness of α+β alloy and make the α+β alloy forgings have excellent comprehensive performance, forging should be carried out below the β phase transformation temperature. On the other hand, when the forging deformation degree is 2% - 10%, the grains of the titanium alloy after deformation are very coarse. Beyond the above forging deformation degree, the greater the deformation degree, the finer the grains of the titanium alloy after deformation. And increasing the forging deformation speed is likely to lead to a decrease in plasticity and an increase in deformation resistance. Therefore, conventional α+β forging is carried out at a temperature 30 - 50°C below the β phase transformation point for heating and forging deformation, with a deformation amount of 40% - 60%, and the deformation speed cannot be too large. The inventor found during a long-term research process that for powder metallurgy sintered Ti-6Al-4V titanium alloy billets, using the traditional forging process to forge in the α+β two-phase region has a large deformation resistance and it is difficult to eliminate pores. More importantly, for large-sized billets, during the deformation process, the lattice friction in the core of the billet is intense, resulting in an increase in the β phase content in the core. In contrast, the temperature in the near-surface area drops quickly and the α phase content is higher. Therefore, after cooling, a gradient in the content change of primary α phase and β transformation structure is generated between the core and the surface of the forging, increasing the non-uniformity. Based on this, the inventor unexpectedly found that starting forging within a specific temperature range above the β phase transformation point can significantly reduce the deformation resistance of powder metallurgy billets, which is beneficial to the closure of the remaining pores in the billets during forging and improves the mechanical properties of the forgings. Further, deforming within a specific deformation degree and deformation speed range can control the occurrence of dynamic recrystallization in the core of large-sized billets, thereby making the core and surface structures uniformly refined and improving the uniformity of the internal and external structures and properties after forging. Furthermore, the overall deformation amount can be made adjustable through multiple forging deformations with specific processes, while meeting the uniformity of the internal and external structures and properties of large-sized billet forgings. The present invention is obtained on this basis.

[0038] In some embodiments of the present invention, the present invention provides a method for manufacturing a large-sized Ti-6Al-4V titanium alloy forging, comprising the following preparation steps:

[0039] S1. Provide a powder metallurgy sintered Ti-6Al-4V titanium alloy blank, the cross-sectional thickness of the blank is more than 120 mm, the porosity of the blank does not exceed 4 vol%, and the chemical composition range of the blank is: Al: 5.5-6.75 wt%, V: 3.5-4.5 wt%, C≤0.08 wt%, Fe≤0.25 wt%, H≤0.012 wt%, O≤0.12 wt%, N≤0.03 wt%, and the balance is Ti;

[0040] S2. Use a heating device to heat the blank to 1030°C - 1060°C for heat preservation. After the internal and external temperatures of the blank are uniform, take out the blank for forging. The time for the blank to transfer from the heating device to the forging working surface does not exceed 80 seconds, the die temperature is 300°C - 500°C, the pressing rate of the punch during forging is 8 - 12 mm / s, control the final forging temperature above 850°C, and the forging deformation amount is 30 - 38%, to obtain a large-sized titanium alloy forging.

[0041] In the embodiments of the present application, the cross-sectional thickness of the powder metallurgy sintered Ti-6Al-4V titanium alloy blank refers to the maximum inscribed circle diameter of the cross-section after the blank is cut in a direction perpendicular to the longest axis of the blank. The blank can be obtained commercially or prepared by a conventional powder metallurgy sintering process. Optionally, the microstructure of the core and the 1 / 4 near the surface (the position at 1 / 4 cross-sectional thickness from the surface) of the blank is equiaxed structure. The average (arithmetic mean) thickness of the α-phase in the core and the 1 / 4 near the surface is 20 μm or less, preferably 10 μm or less, more preferably 8 μm or less, even more preferably 6 μm or less. The difference in the average thickness of the α-phase between the core and the 1 / 4 near the surface is 3 μm or less, preferably 2 μm or less, more preferably 1 μm or less, even more preferably 0.5 μm or less. The standard deviation of the thickness of the α-phase between the core and the 1 / 4 near the surface is 3 μm or less, preferably 2 μm or less, more preferably 1 μm or less. Optionally, the cross-sectional thickness of the blank is 150 mm or more. Further, the cross-sectional thickness of the blank is 200 mm or more. Still further, the cross-sectional thickness of the blank is 250 mm or more and 400 mm or less. The porosity of the blank = 1 - measured density of the blank / theoretical density * 100%. Optionally, the porosity of the blank is 3.5% or less. Further, the porosity of the blank is 3% or less. The temperature for forging heating and holding is preferably 1030°C to 1050°C; the heating rate for uniform rate heating is 30 to 100°C / min, preferably 50 to 80°C / min; the holding time is 30 to 200 min, preferably 40 to 150 min, preferably 40 to 80 min; the transfer time is preferably no more than 75 seconds; the die temperature is preferably 350°C to 450°C; the pressing rate of the punch is preferably 8 to 10 mm / s; the forging deformation amount is preferably 30 to 36%, more preferably 32 to 36%, even more preferably 32 to 34%.

[0042] In some embodiments of the present invention, the chemical composition range of the blank is: Al: 5.8 - 6.5 wt%, V: 3.8 - 4.5 wt%, C ≤ 0.06 wt%, Fe ≤ 0.20 wt%, H ≤ 0.01 wt%, O ≤ 0.12 wt%, N ≤ 0.03 wt%, and the balance is Ti; preferably Al: 6.0 - 6.5 wt%, V: 4.0 - 4.5 wt%, C ≤ 0.06 wt%, Fe ≤ 0.20 wt%, H ≤ 0.01 wt%, O ≤ 0.12 wt%, N ≤ 0.03 wt%, and the balance is Ti; more preferably Al: 6.1 - 6.4 wt%, V: 4.0 - 4.4 wt%, C ≤ 0.06 wt%, Fe ≤ 0.20 wt%, H ≤ 0.01 wt%, O ≤ 0.12 wt%, N ≤ 0.03 wt%, and the balance is Ti.

[0043] In some embodiments of the present invention, the microstructure of the core and the 1 / 4 part near the surface of the large-sized titanium alloy forging is all lamellar α-phase, and the difference between the average thickness of the α-phase in the core and the average thickness of the α-phase at the 1 / 4 part near the surface does not exceed 0.5 μm. The average thickness of the α-phase is the arithmetic mean. Preferably, the difference between the average thickness of the α-phase in the core and the average thickness of the α-phase at the 1 / 4 part near the surface does not exceed 0.3 μm, and more preferably is below 0.2 μm.

[0044] In some embodiments of the present invention, the average thickness of the α-phase in the core and the 1 / 4 part near the surface of the large-sized titanium alloy forging is below 4 μm, preferably below 3 μm, and more preferably below 2.7 μm. The standard deviation of the α-phase thickness in the core and the α-phase thickness at the 1 / 4 part near the surface is below 2 μm, preferably below 1.5 μm, more preferably below 1 μm, more preferably below 0.6 μm, and more preferably below 0.5 μm.

[0045] In some embodiments of the present invention, S3. Use a heating device to heat the titanium alloy forging obtained in step S2 to 930 °C - 970 °C for heat preservation. After the internal and external temperatures of the titanium alloy forging are uniform, take out the titanium alloy forging for forging. The time for the titanium alloy forging to be transferred from the heating device to the forging working surface does not exceed 80 seconds. The die temperature is 300 °C - 500 °C, the pressing rate of the punch during forging is 6 - 10 mm / s, control the final forging temperature above 780 °C, and the forging deformation amount is 25 - 40%. Preferably, heat to 940 °C - 960 °C for heat preservation, the transfer time is below 70 s; the die temperature is 350 °C - 450 °C; the pressing rate of the punch is 6 - 8 mm / s; the forging deformation amount is 25 - 35%.

[0046] S4. Use a heating device to heat the large-sized titanium alloy forging after secondary forging to 730 °C - 780 °C for annealing treatment to obtain an annealed large-sized titanium alloy forging. The preferred annealing heating temperature is 740 °C - 760 °C, and the annealing time is 0.5 - 4 h, preferably 1 - 2 h.

[0047] In some embodiments of the present invention, the microstructure of the core and the 1 / 4 part near the surface of the annealed large-sized titanium alloy forging is primary α-phase and β transformation microstructure, and the difference between the average thickness of the α-phase in the core and the average thickness of the α-phase at the 1 / 4 part near the surface does not exceed 0.5 μm. Preferably, the difference between the average thickness of the α-phase in the core and the average thickness of the α-phase at the 1 / 4 part near the surface does not exceed 0.3 μm, and more preferably is below 0.2 μm.

[0048] In some embodiments of the present invention, the average thickness of the α-phase at the core and the 1 / 4 near-surface of the annealed large-sized titanium alloy forging does not exceed 12 μm. Preferably, the average thickness of the α-phase at the core and the 1 / 4 near-surface of the annealed large-sized titanium alloy forging does not exceed 10 μm, and more preferably is below 9 μm. The standard deviation of the α-phase thickness at the core and the 1 / 4 near-surface of the annealed large-sized titanium alloy forging is below 4 μm, preferably below 3 μm.

[0049] In some embodiments of the present invention, it further includes:

[0050] S5. Use a heating device to heat the annealed large-sized titanium alloy forging obtained in step S4 to 930 °C - 970 °C for heat preservation. After the internal and external temperatures of the annealed large-sized titanium alloy forging are uniform, take out the annealed large-sized titanium alloy forging for forging. The time for the annealed large-sized titanium alloy forging to transfer from the heating device to the forging working surface does not exceed 80 seconds. The die temperature is 300 °C - 500 °C, the pressing rate of the punch during forging is 6 - 10 mm / s, control the final forging temperature to be not lower than 780 °C, and the forging deformation amount is 25 - 40%. Obtain a three-time forged large-sized titanium alloy forging. Preferably, heat to 940 °C - 960 °C for heat preservation, and the transfer time is below 70 s; the die temperature is 350 °C - 450 °C; the pressing rate of the punch is 6 - 8 mm / s; the forging deformation amount is 25 - 35%.

[0051] S6. Use a heating device to heat the three-time forged titanium alloy forging to 730 °C - 780 °C for annealing treatment to obtain an annealed large-sized titanium alloy forging. The preferred annealing heating temperature is 740 °C - 760 °C, and the annealing time is 0.5 - 4 h, preferably 1 - 2 h.

[0052] In some embodiments of the present invention, the difference in yield strength between the core of the forged titanium alloy forging and the yield strength at the 1 / 4 near-surface does not exceed 10 MPa, the difference in tensile strength between the core of the forged titanium alloy forging and the tensile strength at the 1 / 4 near-surface does not exceed 10 Mpa, and the difference in elongation between the core and the 1 / 4 near-surface does not exceed 1%.

[0053] The present invention will be further described in detail below in combination with examples and comparative examples.

[0054] Example 1

[0055] Example 1 provides a manufacturing method for a large-sized Ti-6Al-4V titanium alloy forging, and the specific preparation steps are as follows:

[0056] S1. Provide a powder metallurgy sintered Ti-6Al-4V titanium alloy blank (raw material spherical Ti-6Al-4V alloy powder with an average diameter of 32 μm), the cross-sectional thickness is Φ250 mm, and the chemical composition range of the blank is: Al: 6.21 wt%, V: 4.28 wt%, C: 0.026 wt%, Fe: 0.04 wt%, H: 0.0072 wt%, O: 0.096 wt%, N: 0.028 wt%, and the balance is Ti. The density of the blank is 97.7%, and the porosity is 2.3%. There are no macroscopic defects such as pores and inclusions on the outer surface of the blank. Observe the metallographic structure of the powder metallurgy sintered Ti-6Al-4V titanium alloy blank, and the results are as Figure 1 shown. The core part ( Figure 1 a) and the 1 / 4 part near the surface ( Figure 1 b) are equiaxed structures. Using ImageJ software, the thickness of the α phase in the core part is measured to be 5.8 ± 1.0 μm, and the thickness of the α phase in the 1 / 4 part near the surface is 5.3 ± 0.8 μm. The thickness is represented by the combination of arithmetic mean ± standard deviation, which reflects the central tendency of the thickness and the dispersion degree of the thickness distribution, indicating that the structure of the provided powder metallurgy sintered Ti-6Al-4V titanium alloy blank is fine and the internal and external structures are uniform.

[0057] S2. Use a heating device to heat the blank to 1050 °C for heat preservation. The heating is carried out at a heating rate of 60 °C / min. After the internal and external temperatures of the blank are uniform during heat preservation, take out the blank for forging. The time for the blank to transfer from the heating device to the forging working surface is 70 s, the die temperature is 400 °C, the pressing rate of the indenter during forging is 8 mm / s, control the final forging temperature above 850 °C, the forging deformation amount is 30%, and after forging, air-cool to room temperature to prepare a large-sized titanium alloy forging.

[0058] Observe the metallographic structure of the core part and the 1 / 4 part near the surface of the large-sized titanium alloy forging prepared in Example 1, and the results are as Figure 2 shown. The core part ( Figure 2 a) and the 1 / 4 part near the surface ( Figure 2 b) are fully lamellar α phases. Using ImageJ software, the thickness of the α phase in the core part is measured to be 2.7 ± 0.5 μm, and the thickness of the α phase in the 1 / 4 part near the surface is 2.5 ± 0.4 μm. The thickness is represented by the combination of arithmetic mean ± standard deviation, which reflects the central tendency of the thickness and the dispersion degree of the thickness distribution. It can be seen from this that the average thickness of the lamellar α phase in the core part is 0.2 μm thicker than that of the outer surface, and the standard deviation of the α phase thickness in the core part and the outside is below 0.5 μm, indicating that the internal and external structures of the prepared large-sized titanium alloy forging are uniform. Through the room temperature tensile property test, the size of the tensile bar specimen is M10×60 mm, the parallel section is Φ5×30 mm, and the strain rate is 0.001 s -1, the core properties were measured: yield strength 869 MPa, tensile strength 948 MPa, elongation 15.8%; properties at 1 / 4 of the near-surface: yield strength 865 MPa, tensile strength 938 MPa, elongation 15.2%. The overall (i.e., the average value and standard deviation of the corresponding properties of the core and 1 / 4 of the near-surface) yield strength was 867 ± 3 MPa, and the tensile strength was 943 ± 7 MPa. Thus, it can be seen that the internal and external properties of the prepared large-sized titanium alloy forgings are uniform.

[0059] Comparative Example 1

[0060] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 uses Step S2' to replace Step S2 of Example 1, and forges the powder metallurgy sintered blank using the process of traditional ingot forging blank, and the remaining preparation steps are the same as those of Example 1. Step S2' is: using a heating device to heat the blank to 965 °C for heat preservation, the heating uses a heating rate of 60 °C / min, after the heat preservation makes the internal and external temperatures of the blank uniform, take out the blank for forging, the time for the blank to transfer from the heating device to the forging working surface is 70 s, the die temperature is 400 °C, the pressing rate of the punch during forging is 8 mm / s, control the final forging temperature above 780 °C, the forging deformation amount is 50%, after forging, air-cool to room temperature to prepare a large-sized titanium alloy forging.

[0061] Observe the metallographic structure of the core and 1 / 4 of the near-surface of the large-sized titanium alloy forging prepared in Comparative Example 1, and the results are as Figure 3 shown. The core ( Figure 3 a) and 1 / 4 of the near-surface ( Figure 3 b) are primary α phase + a small amount of β transformation structure. The measured thickness of the α phase in the core is 15 ± 4 μm, and the thickness of the α phase at 1 / 4 of the near-surface is 5 ± 2 μm. The thickness is represented by the combination of arithmetic mean ± standard deviation, which reflects the central tendency of the thickness and the discrete degree of the thickness distribution. It can be seen that the average thickness of the α phase in the core is 10 μm thicker than that of the outer surface, and the standard deviations of the α phase thickness in the core and the outside are 4 μm and 2 μm, indicating that the internal and external structures of the prepared large-sized titanium alloy forgings are not uniform. Through the room temperature tensile property test, the size of the tensile bar specimen is M10×60 mm, the parallel section is Φ5×30 mm, and the strain rate is 0.001 s -1 , the core properties were measured: yield strength 840 MPa, tensile strength 910 MPa, elongation 14.4%; properties at 1 / 4 of the near-surface: yield strength 868 MPa, tensile strength 939 MPa, elongation 15.6%. The overall yield strength is 854 ± 20 MPa, and the tensile strength is 925 ± 20 MPa. Thus, it can be seen that the internal and external properties of the prepared large-sized titanium alloy forgings are not uniform.

[0062] Comparative Example 2

[0063] The difference between Comparative Example 2 and Comparative Example 1 is that in step S1 of Comparative Example 2, a Ti-6Al-4V titanium alloy blank produced by traditional casting and 5-pass forging (the chemical composition range of the blank is: Al: 6.11 wt%, V: 4.25 wt%, C: 0.044 wt%, Fe: 0.12 wt%, H: 0.0088 wt%, O: 0.074 wt%, N: 0.022 wt%, the balance is Ti, and the density of the blank is 100%) is used to replace the powder metallurgy sintered Ti-6Al-4V titanium alloy blank of Comparative Example 1. The remaining preparation steps are the same as those of Comparative Example 1, and a large-sized titanium alloy forging is prepared.

[0064] Observe the metallographic structure at the core and 1 / 4 of the near-surface of the large-sized titanium alloy forging prepared in Comparative Example 2. The results are as Figure 4 shown. At the core ( Figure 4 a) and at 1 / 4 of the near-surface ( Figure 4 b), it is primary α phase + β transformation structure. The measured thickness of the α phase at the core is 32 ± 8 μm, and the thickness of the α phase at 1 / 4 of the near-surface is 28 ± 6 μm. The thickness is expressed by the combination of arithmetic mean ± standard deviation, which reflects the central tendency of the thickness and the dispersion degree of the thickness distribution. It can be seen that the average thickness of the α phase at the core is 4 μm thicker than that of the outer surface, and the standard deviations of the α phase thickness at the core and the outside are 8 μm and 6 μm, indicating that the internal and external structures of the prepared large-sized titanium alloy forging are uneven. Through room temperature tensile property testing, the size of the tensile bar specimen is M10×60 mm, the parallel section is Φ5×30 mm, and the strain rate is 0.001 s -1 . The properties measured at the core are: yield strength 820 MPa, tensile strength 906 MPa, elongation 13.3%; the properties at 1 / 4 of the near-surface are: yield strength 862 MPa, tensile strength 942 MPa, elongation 14.2%. The overall yield strength is 841 ± 30 MPa, and the tensile strength is 924 ± 25 MPa. Thus, it can be seen that the internal and external properties of the prepared large-sized titanium alloy forging are uneven. Compared with Comparative Example 2, in Example 1, the α lamellae are finer and the structure is more uniform. The overall yield strength is increased by 26 MPa, and the overall tensile strength is increased by 19 MPa. In addition, the sample standard deviation of the overall yield strength is reduced by 27 MPa, and the property uniformity of the forging is significantly improved. By calculation, for blanks of the same specification and weight (blanking specification Φ250×420, blanking weight 92 kg), the cost of the forging in Example 1 is 17,310 yuan, and the cost of the forging in Comparative Example 2 is 30,374 yuan. The cost of Example 1 is reduced by 43%.

[0065] Example 2

[0066] The difference between Example 2 and Example 1 is that in step S2, the blank of Example 2 is heated to 1030 °C and held until the internal and external temperatures of the blank are uniform, and the forging deformation amount is 38%. The remaining preparation steps are the same as those in Example 1, and a large-sized titanium alloy forging is prepared.

[0067] Observe the metallographic structure at the center and 1 / 4 of the near-surface of the large-sized titanium alloy forging prepared in Example 2. The results are as Figure 5 shown. At the center ( Figure 5 a) and at 1 / 4 of the near-surface ( Figure 5 b), it is all lamellar α phase. The measured thickness of the α phase at the center is 2.7 ± 0.3 μm, and the thickness of the α phase at 1 / 4 of the near-surface is 2.6 ± 0.3 μm. The thickness is expressed by the combination of arithmetic mean ± standard deviation, which reflects the central tendency of the thickness and the dispersion degree of the thickness distribution. It can be seen that the average thickness of the lamellar α phase at the center is 0.1 μm thicker than that of the outer surface, and the standard deviation of the α phase thickness at the center and the outside is below 0.5 μm, indicating that the internal and external structures of the prepared large-sized titanium alloy forging are uniform. Through the room-temperature tensile property test, the size of the tensile bar specimen is M10×60 mm, the parallel section is Φ5×30 mm, and the strain rate is 0.001 s -1 . The properties measured at the center are: yield strength 860 MPa, tensile strength 942 MPa, and elongation 15.0%; the properties at 1 / 4 of the near-surface are: yield strength 854 MPa, tensile strength 934 MPa, and elongation 14.5%. The overall yield strength is 857 ± 4 MPa, and the tensile strength is 938 ± 6 MPa. Thus, it can be seen that the internal and external properties of the prepared large-sized titanium alloy forging are uniform.

[0068] Comparative Example 3

[0069] The difference between Comparative Example 3 and Example 1 is that in step S1, the forging deformation amount is 55%. The remaining preparation steps are the same as those in Example 1, and a large-sized titanium alloy forging is prepared.

[0070] Observe the metallographic structure at the center and 1 / 4 of the near-surface of the large-sized titanium alloy forging prepared in Comparative Example 3. The results are as Figure 6 shown. At the center ( Figure 6 a) and at 1 / 4 of the near-surface ( Figure 6 b), it is Widmanstätten structure. The measured thickness of the α phase at the center is 4.2 ± 0.9 μm, and the thickness of the α phase at 1 / 4 of the near-surface is 3.5 ± 0.6 μm. The thickness is expressed by the combination of arithmetic mean ± standard deviation, which reflects the central tendency of the thickness and the dispersion degree of the thickness distribution. It can be seen that the average thickness of the α phase at the center is 0.7 μm thicker than that of the outer surface, and the standard deviation of the α phase thickness at the center and the outside is greater than 0.5 μm. Through the room-temperature tensile property test, the size of the tensile bar specimen is M10×60 mm, the parallel section is Φ5×30 mm, and the strain rate is 0.001 s-1 , the core properties were measured: yield strength of 824 MPa, tensile strength of 933 MPa, and elongation of 13.6%; the properties at 1 / 4 of the near-surface: yield strength of 836 MPa, tensile strength of 940 MPa, and elongation of 14.5%. The overall yield strength was 830 ± 8 MPa, and the tensile strength was 937 ± 5 MPa. Compared with Example 1, the forging in Comparative Example 3 was produced with a forging deformation of 55%, resulting in coarsening of the internal and external structures, a 37 MPa decrease in yield strength, a 6 MPa decrease in tensile strength, and a decrease in elongation of approximately 1.5%.

[0071] Example 3

[0072] Based on the large-sized titanium alloy forging obtained in Example 1, Example 3 performed a second forging heat treatment, which specifically included the following steps:

[0073] S3. Using a heating device, the titanium alloy forging obtained in step S2 of Example 1 was heated to 950 °C and held for heat preservation. After the internal and external temperatures of the titanium alloy forging were uniform, the titanium alloy forging was taken out for forging. The time for the titanium alloy forging to transfer from the heating device to the forging working surface was 70 s, the die temperature was 400 °C, the pressing rate of the indenter during forging was 8 mm / s, the final forging temperature was controlled above 780 °C, and the forging deformation was 25%, obtaining a large-sized titanium alloy forging after secondary forging;

[0074] S4. Using a heating device, the large-sized titanium alloy forging after secondary forging was heated to 750 °C for annealing treatment, with a heat preservation time of 1.5 h. After heat preservation, it was air-cooled to room temperature to obtain an annealed large-sized titanium alloy forging.

[0075] Observing the metallographic structure of the core and 1 / 4 of the near-surface of the large-sized titanium alloy forging prepared in Example 3, the results are as Figure 7 shown. The core ( Figure 7 a) and 1 / 4 of the near-surface ( Figure 7 b) are short rod-shaped primary α-phase and β-transformed structure. The measured thickness of the α-phase in the core is 9 ± 3 μm, and the thickness of the α-phase at 1 / 4 of the near-surface is 9 ± 2 μm. The thickness is represented by the combination of arithmetic mean ± standard deviation, reflecting the central tendency of the thickness and the dispersion degree of the thickness distribution. It can be seen that the average thickness of the α-phase in the core is the same as that of the outer surface, indicating that the internal and external structures of the prepared large-sized titanium alloy forging are uniform. Through room temperature tensile property testing, the size of the tensile bar specimen is M10 × 60 mm, the parallel section is Φ5 × 30 mm, and the strain rate is 0.001 s -1, the core properties were measured: yield strength 861 MPa, tensile strength 940 MPa, elongation 16.8%; the properties at 1 / 4 of the near-surface: yield strength 864 MPa, tensile strength 948 MPa, elongation 17.2%. The overall yield strength was 863 ± 2 MPa, and the tensile strength was 944 ± 6 MPa. Thus, it can be seen that the internal and external properties of the prepared large-sized titanium alloy forgings are uniform.

[0076] Example 4

[0077] On the basis of Example 3 and Example 4, the third heat forging was carried out, and specifically, the following steps were further included:

[0078] S5. Use a heating device to heat the titanium alloy forging obtained in step S4 of Example 3 to 950 °C for heat preservation. After the internal and external temperatures of the titanium alloy forging are uniform, take out the titanium alloy forging for forging. The time for the titanium alloy forging to transfer from the heating device to the forging working surface is 70 s, the die temperature is 400 °C, the pressing rate of the indenter during forging is 8 mm / s, control the final forging temperature above 780 °C, and the forging deformation amount is 30% to obtain a large-sized titanium alloy forging after three times of forging;

[0079] S4. Use a heating device to heat the large-sized titanium alloy forging after three times of forging to 750 °C for annealing treatment, the heat preservation time is 1.5 h, and after the heat preservation is completed, air-cool to room temperature to obtain an annealed large-sized titanium alloy forging.

[0080] Through room temperature tensile property testing, the size of the tensile bar specimen is M10×60 mm, the parallel section is Φ5×30 mm, and the strain rate is 0.001 s -1 , the core properties were measured: yield strength 858 MPa, tensile strength 940 MPa, elongation 15.9%; the properties at 1 / 4 of the near-surface: yield strength 862 MPa, tensile strength 942 MPa, elongation 15.5%. The overall yield strength was 860 ± 3 MPa, and the tensile strength was 941 ± 1 MPa. Thus, it can be seen that the internal and external properties of the prepared large-sized titanium alloy forgings are uniform.

[0081] The above are all the preferred embodiments of the present invention, and the protection scope of the present invention is not limited accordingly. Therefore, all equivalent changes made according to the mechanism, shape, and principle of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for manufacturing a large-size forging of a Ti-6Al-4V titanium alloy, characterized in that: The preparation method comprises the following steps: S1. providing a powder metallurgy sintered Ti-6Al-4V titanium alloy blank, wherein the cross-sectional thickness of the blank is greater than 120 mm, the porosity of the blank is less than 4 vol%, and the chemical composition range of the blank is: Al: 5.5-6.75 wt%, V: 3.5-4.5 wt%, C≤0.08 wt%, Fe≤0.25 wt%, H≤0.012 wt%, O≤0.12 wt%, N≤0.03 wt%, and the balance is T i; S2. The blank is heated to 1030°C~1060°C by a heating device for heat preservation, so that the temperature inside and outside the blank is uniform, and then the blank is taken out for forging. The time for transferring the blank from the heating device to the forging work surface does not exceed 80 seconds, the mold temperature is 300°C~500°C, the pressing rate of the ram during forging is 8~12mm / s, the final forging temperature is controlled above 850°C, the deformation amount of forging is 30%~38%, and a large-size titanium alloy forging is prepared; S3. Use a heating device to heat the large-sized titanium alloy forging obtained in step S2 to 930℃~970℃ for heat preservation, so that the temperature inside and outside of the large-sized titanium alloy forging is uniform, then take out the large-sized titanium alloy forging for forging, the time for the large-sized titanium alloy forging to be transferred from the heating device to the forging work surface shall not exceed 80 seconds, the mold temperature shall be 300℃~500℃, the pressing rate of the ram during forging shall be 6~10mm / s, the final forging temperature shall be controlled above 780℃, the deformation amount of forging shall be 25~40%, and the secondary forged titanium alloy large-sized forging shall be obtained; S4. Use a heating device to heat the secondary forged titanium alloy large-sized forging to 730℃~780℃ for annealing to obtain the annealed titanium alloy large-sized forging; S5. Use The heating device heats the annealed titanium alloy large-size forgings obtained in step S4 to 930°C~970°C for insulation, so that the internal and external temperatures of the annealed titanium alloy large-size forgings are uniform, and then the annealed titanium alloy large-size forgings are taken out for forging. The time for the annealed titanium alloy large-size forgings to be transferred from the heating device to the forging work surface does not exceed 80 seconds, the mold temperature is 300°C~500°C, the pressing rate of the ram during forging is 6~10mm / s, the final forging temperature is controlled not lower than 780°C, the forging deformation is 25~40%, and the three-time forged titanium alloy large-size forgings are obtained; S6. The three-time forged titanium alloy large-size forgings are heated to 730°C~780°C by the heating device for annealing to obtain the final annealed titanium alloy large-size forgings.

2. The method for manufacturing a large-size Ti-6Al-4V titanium alloy forging according to claim 1, characterized in that: The difference between the yield strength at the core and the yield strength at 1 / 4 near the surface of the final annealed titanium alloy large-size forgings does not exceed 10MPa, the difference between the tensile strength at the core and the tensile strength at 1 / 4 near the surface does not exceed 10Mpa, and the difference between the elongation at the core and the elongation at 1 / 4 near the surface does not exceed 1%.

3. A Ti-6Al-4V titanium alloy large-size forging obtained by the manufacturing method of the Ti-6Al-4V titanium alloy large-size forging according to claim 1 or 2.

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