High-uniformity Ti-6Al-4V titanium alloy large-size forge piece and manufacturing method

Abstract

The invention provides a high-uniformity Ti-6Al-4V titanium alloy large-size forge piece and a manufacturing method, the manufacturing method comprises the following preparation steps: S1, providing a powder metallurgy sintered Ti-6Al-4V titanium alloy blank, the section thickness of the blank being more than 120 mm; and S2, the blank is heated to 1030-1060 DEG C through a heating device, heat preservation is conducted, then forging is conducted, the forging deformation is 30%-38%, and the titanium alloy large-size forge piece is prepared. According to the method, the Ti-6Al-4V titanium alloy blank is sintered through powder metallurgy for forging, the traditional smelting and blank forging machining process is omitted, the manufacturing process of the forge piece is shortened, the production cost is greatly reduced, meanwhile, a proper forging technology is adopted for forging, and the production efficiency is greatly improved. And a forge piece which is more uniform in structure and performance compared with a traditional cast ingot forging forming method is obtained while the strength and plasticity are improved.

Description

Technical Field

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

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

[0003] At present, titanium alloy forgings are mainly obtained by vacuum melting titanium sponge to obtain titanium ingots, and then subjecting the titanium ingots to blank forging and forming forging. However, in order to improve casting segregation and eliminate casting columnar crystals, and improve the uniformity of the blank structure, the titanium ingots need to be forged for multiple times before the blanks that can be used for forming forging are obtained, resulting in a long production process and low production efficiency. The cost of hot working accounts for 45-60% of the total forging cost.

[0004] Powder metallurgy is a process that uses powder as raw material, pressurized and sintered to manufacture various products such as metals and composite materials. When using powder metallurgy to prepare titanium alloy billets, the sintering temperature is much lower than traditional smelting, which can minimize the segregation of alloy components, prevent coarse and uneven casting structures, and significantly improve material utilization. Based on the above advantages, titanium alloy billets prepared by powder metallurgy can be directly formed and forged without the need for billet forging, and the hot working process is significantly shortened, and the cost is also reduced. The Chinese patent application with application number 202010487693.7 discloses a short-process, low-cost TC4 titanium alloy pipe preparation process. TC4 titanium alloy pipes are prepared by powder metallurgy and radial forging, which overcomes the shortcomings of traditional pipe hot rolling with many passes and long processing cycles. Powder metallurgy is used to make pipe billets, and high-temperature and two-fire radial forging processes are used to produce uniformly deformed and high-strength seamless pipes, which improves the deformation uniformity of the metal in the process and ensures the uniformity of the size of the titanium alloy pipe. However, from the microstructure of the prepared TC4 titanium alloy tube ( Figure 3 , 4 ) It can be seen that due to the large temperature difference between the inner and outer walls of the material, the microstructure of the inner and outer walls of the titanium alloy tube is uneven, and the thickness of the α layer is not uniform, which easily causes the titanium alloy to have uneven internal and external structures and uneven internal and external performance defects. Especially for large-sized titanium alloy forgings (section thickness ≥ 120mm), 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 organization and performance.

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

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

[0007] In a first aspect, the present invention provides a method for manufacturing a large-size forging of a Ti-6Al-4V titanium alloy, comprising 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: 5.5-6.75wt%, V: 3.5-4.5wt%, C≤0.08wt%, Fe≤0.25wt%, H≤0.012wt%, O≤0.12wt%, N≤0.03wt%, and the balance is Ti;

[0009] S2. Use a heating device to heat the billet to 1030℃~1060℃ for insulation, so that the temperature inside and outside the billet is uniform, then take out the billet for forging, the time for the billet to be transferred from the heating device to the forging work surface is no more than 80 seconds, the mold temperature is 300℃~500℃, the pressing head pressing rate during forging is 8~12mm / s, the final forging temperature is controlled above 850℃, the forging deformation is 30%~38%, and large-size titanium alloy forgings are prepared.

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

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

[0012] Optionally, the microstructure of the core and 1 / 4 near the surface of the large-size titanium alloy forging is full 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 1 / 4 near the surface does not exceed 0.5 μm.

[0013] Optionally, the average thickness of the α phase in the core and near the surface 1 / 4 of the titanium alloy large-size forging is less than 4 μm.

[0014] Optionally, also include:

[0015] S3. The titanium alloy forging obtained in step S2 is heated to 930°C to 970°C by a heating device for heat preservation, so that the temperature inside and outside of the titanium alloy forging is uniform, and then the titanium alloy forging is taken out for forging. The time for transferring the titanium alloy forging from the heating device to the forging working surface does not exceed 80 seconds, the mold temperature is 300°C to 500°C, the pressing rate of the ram during forging is 6 to 10 mm / s, the final forging temperature is controlled to be above 780°C, and the deformation amount of forging is 25 to 40%, so as to obtain a large-size secondary forged titanium alloy forging;

[0016] S4. Using a heating device, the secondary forged titanium alloy large-size forging is heated to 730° C. to 780° C. for annealing to obtain an annealed titanium alloy large-size forging.

[0017] Optionally, the core and 1 / 4 near the surface of the annealed titanium alloy large-size forging have primary α phase and β transformation structure, 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.

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

[0019] Also includes:

[0020] S5. The annealed titanium alloy large-size forging obtained in step S4 is heated to 930°C to 970°C by a heating device for heat preservation, so that the internal and external temperatures of the annealed titanium alloy large-size forging are uniform, and then the annealed titanium alloy large-size forging is taken out for forging, the time for the annealed titanium alloy large-size forging to be transferred from the heating device to the forging work surface does not exceed 80 seconds, the mold temperature is 300°C to 500°C, the pressure head pressing rate during forging is 6 to 10 mm / s, the final forging temperature is controlled to be not less than 780°C, the deformation amount of forging is 25 to 40%, and the three-forged titanium alloy large-size forging is obtained;

[0021] S6. Using a heating device, heat the tertiary forged titanium alloy forging to 730°C to 780°C for annealing to obtain an annealed titanium alloy large-size forging.

[0022] Optionally, the difference between the yield strength at the core and the yield strength at 1 / 4 near the surface of large-size titanium alloy 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%.

[0023] In a second aspect, the present invention provides a Ti-6Al-4V titanium alloy large-size forging obtained by the aforementioned method for manufacturing the Ti-6Al-4V titanium alloy large-size forging.

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

[0025] 1. The present invention provides a method for manufacturing large-size Ti-6Al-4V titanium alloy forgings, which uses Ti-6Al-4V titanium alloy billets prepared by powder metallurgy as forging raw materials, reduces the number of hot working fires of forgings by 4 to 8 times, solves the problems of traditional titanium alloy forgings having many heating fires and long production cycles, and reduces the cost of forgings by more than 40%.

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

[0027] 3. The present invention provides a method for manufacturing large-size forgings of Ti-6Al-4V titanium alloy. While the uniformity of large-size forgings is greatly improved, the yield strength of forgings produced by this process is also increased by about 20 MPa compared with traditional Ti-6Al-4V titanium alloy forgings, and the tensile strength and elongation remain basically unchanged.

[0028] 4. The present invention provides a method for manufacturing large-size forgings of Ti-6Al-4V titanium alloy, which can specify the process of titanium alloy forgings according to the actual deformation requirements, and the prepared large-size titanium alloy has excellent mechanical properties and uniformity of internal and external structure and performance, high process controllability, and is suitable for industrial mass production. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0031] Figure 3 This is the metallographic structure diagram of the large-sized titanium alloy forging 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 titanium alloy large-size forging prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the present invention clearer and more specific, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments 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: Al: 5.5%-6.75%, V: 3.5%-4.5%, 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, which is composed of α phase and β phase in equilibrium. It has the characteristics of high strength, thermal strength, plasticity, toughness, formability, weldability, corrosion resistance and good biocompatibility, and has become the most widely used titanium alloy. Forging deformation can make Ti-6Al-4V titanium alloy forgings meet the design technical index requirements of shape, size, microstructure and performance. It is generally believed 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 violent growth of the β grains, it is easy to form Widmanstatten structure, resulting in β brittleness. Therefore, in order to avoid the β brittleness of the α+β alloy and make the α+β alloy forgings have excellent comprehensive properties, forging should be carried out below the β phase transformation temperature; on the other hand, when the forging deformation degree is 2% to 10%, the grains of the titanium alloy after deformation are very coarse. When the forging deformation degree exceeds 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 reduced plasticity and increased deformation resistance. Therefore, conventional α+β forging is carried out at 30 to 50°C below the β phase transformation point, heating and forging deformation, deformation of 40% to 60%, and deformation speed cannot be too large. The inventors found in a long research process that for powder metallurgy sintered Ti-6Al-4V titanium alloy billets, the traditional forging process forging in the α+β two-phase region has high deformation resistance and is difficult to eliminate pores. More importantly, for large-sized billets, during the deformation process, the core lattice friction of the billet is intense, resulting in an increase in the β-phase content in the core. In contrast, the temperature of the area near the surface drops rapidly and the α-phase content is higher. Therefore, after cooling, the core and surface of the forging produce a gradient of primary α-phase and β-transformed structure content changes, and the inhomogeneity increases. Based on this, the inventors unexpectedly found that above the β-phase transformation point, the α-phase transformation point is more uniform than the α-phase transformation point. Starting forging within a specific temperature range can significantly reduce the deformation resistance of the powder metallurgy billet, which is conducive to the closure of the residual pores in the billet during the forging process, and improves the mechanical properties of the forging. Further, deformation within a specific deformation degree and deformation speed range can control the dynamic recrystallization of the core of the large-sized billet, so that the core and surface structures are uniformly refined, and the uniformity of the internal and external structures and properties after forging is improved. Furthermore, the overall deformation amount can be controlled through multiple specific process forging deformations, and at the same time, the uniformity of the internal and external structures and properties of the large-sized billet forgings is met. 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-size Ti-6Al-4V titanium alloy forging, comprising the following preparation steps:

[0039] 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: 5.5-6.75wt%, V: 3.5-4.5wt%, C≤0.08wt%, Fe≤0.25wt%, H≤0.012wt%, O≤0.12wt%, N≤0.03wt%, and the balance is Ti;

[0040] S2. Use a heating device to heat the billet to 1030℃~1060℃ for insulation, so that the temperature inside and outside the billet is uniform, then take out the billet for forging, the time for the billet to be transferred from the heating device to the forging work surface is no more than 80 seconds, the mold temperature is 300℃~500℃, the pressing head pressing rate during forging is 8~12mm / s, the final forging temperature is controlled above 850℃, the forging deformation is 30~38%, and large-size titanium alloy forgings are prepared.

[0041] The cross-sectional thickness of the powder metallurgy sintered Ti-6Al-4V titanium alloy billet in the embodiment of the present application refers to the maximum inscribed circle diameter of the cross section after the billet is cut off from the direction perpendicular to the longest axis of the billet, and the billet can be obtained commercially or prepared by a conventional powder metallurgy sintering process. Optionally, the organization of the core and the near surface 1 / 4 of the billet (the position of the 1 / 4 cross-sectional thickness from the surface) is an equiaxed organization, and the average (arithmetic mean) thickness of the α phase at the core and the near surface 1 / 4 is 20 μm or less, preferably 10 μm or less, more preferably 8 μm or less, more preferably 6 μm or less, the average thickness difference of the α phase at the core and the near surface 1 / 4 is 3 μm or less, preferably 2 μm or less, more preferably 1 μm or less, more preferably 0.5 μm or less, and the thickness standard deviation of the α phase at the core and the near surface 1 / 4 is 3 μm or less, preferably 2 μm or less, and more preferably 1 μm or less. Optionally, the cross-sectional thickness of the blank is more than 150 mm, further, the cross-sectional thickness of the blank is more than 200 mm, and further the cross-sectional thickness of the blank is more than 250 mm and less than 400 mm. The porosity of the blank = 1-measured density of the blank / theoretical density * 100%, optionally, the porosity of the blank is less than 3.5%, and further the porosity of the blank is less than 3%. The temperature of forging heating and heat preservation is preferably 1030℃~1050℃; the rate of uniform heating and heating is 30~100℃ / min, preferably 50~80℃ / min; the heat preservation time is 30~200min, preferably 40~150min, preferably 40~80min; the transfer time is preferably not more than 75 seconds; the mold temperature is preferably 350℃~450℃; the pressure head pressing rate is preferably 8~10mm / s; the forging deformation is preferably 30~36%, more preferably 32~36%, more preferably 32~34%.

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

[0043] In some embodiments of the present invention, the microstructure of the core and the 1 / 4 near the surface of the large-size titanium alloy forging is a full 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. The average thickness of the α phase is the arithmetic mean, and preferably, 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 0.3 μm, and more preferably is less than 0.2 μm.

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

[0045] In some embodiments of the present invention, S3. The titanium alloy forging obtained in step S2 is heated to 930°C to 970°C by a heating device for heat preservation, so that the temperature inside and outside of the titanium alloy forging is uniform, and then the titanium alloy forging is taken out for forging, and 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 mold temperature is 300°C to 500°C, the pressure head pressing rate during forging is 6 to 10 mm / s, the final forging temperature is controlled above 780°C, the forging deformation is 25 to 40%, and a large-size secondary forged titanium alloy forging is obtained. Preferably, it is heated to 940°C to 960°C for heat preservation, the transfer time is less than 70s; the mold temperature is 350°C to 450°C; the pressure head pressing rate is 6 to 8 mm / s; the forging deformation is 25 to 35%.

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

[0047] In some embodiments of the present invention, the core and the 1 / 4 near the surface of the annealed titanium alloy large-size forging have primary α phase and β transformation structure, 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. Preferably, 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 0.3 μm, and more preferably is less than 0.2 μm.

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

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

[0050] S5. Use a heating device to heat the annealed titanium alloy large-size forging obtained in step S4 to 930℃~970℃ for heat preservation, so that the internal and external temperatures of the annealed titanium alloy large-size forging are uniform, then take out the annealed titanium alloy large-size forging for forging, the time for the annealed titanium alloy large-size forging to be transferred from the heating device to the forging work surface does not exceed 80 seconds, the mold temperature is 300℃~500℃, the pressure head pressing rate during forging is 6~10mm / s, the final forging temperature is controlled not less than 780℃, the forging deformation is 25~40%, and the three-time forged titanium alloy large-size forging is obtained. Preferably, heating to 940℃~960℃ for heat preservation, the transfer time is less than 70s; the mold temperature is 350℃~450℃; the pressure head pressing rate is 6~8mm / s; the forging deformation is 25~35%.

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

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

[0053] The present invention is described in detail below in conjunction with embodiments and comparative examples.

[0054] Example 1

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

[0056] S1. Provide powder metallurgy sintered Ti-6Al-4V titanium alloy billet (raw material spherical Ti-6Al-4V alloy powder, average diameter of 32μm), cross-sectional thickness of Φ250mm, chemical composition range of billet: Al: 6.21wt%, V: 4.28wt%, C: 0.026wt%, Fe: 0.04wt%, H: 0.0072wt%, O: 0.096wt%, N: 0.028wt%, balance Ti, billet density of 97.7%, porosity of 2.3%, billet outer surface without pores, inclusions and other macro defects. Observe the metallographic structure of powder metallurgy sintered Ti-6Al-4V titanium alloy billet, the results are as follows Figure 1 As shown, the heart ( Figure 1 a) and near the surface 1 / 4 ( Figure 1 b) is an equiaxed structure. The thickness of the core α phase is measured by ImageJ software to be 5.8±1.0μm, and the thickness of the α phase at 1 / 4 near the surface is 5.3±0.8μm. The thickness is expressed by a combination of arithmetic mean±standard deviation, which reflects the central trend of the thickness and the degree of discreteness of the thickness distribution, indicating that the powder metallurgy sintered Ti-6Al-4V titanium alloy billet has a fine structure and uniform internal and external structures.

[0057] S2. Use a heating device to heat the billet to 1050℃ and keep it warm. The heating rate is uniform at 60℃ / min. After the temperature inside and outside the billet is kept uniform, the billet is taken out for forging. The time for the billet to be transferred from the heating device to the forging work surface is 70s. The mold temperature is 400℃. The pressing rate of the ram during forging is 8mm / s. The final forging temperature is controlled above 850℃. The forging deformation is 30%. After forging is completed, it is air-cooled to room temperature to prepare large-size titanium alloy forgings.

[0058] The metallographic structure of the core and 1 / 4 of the surface of the large-sized titanium alloy forging prepared in Example 1 was observed. Figure 2 As shown, the heart ( Figure 2 a) and near the surface 1 / 4 ( Figure 2 b) is the full lamellar α phase. The thickness of the core α phase measured by ImageJ software is 2.7±0.5μm, and the thickness of the α phase near the surface 1 / 4 is 2.5±0.4μm. The thickness is expressed by a combination of arithmetic mean ± standard deviation, reflecting the central trend of the thickness and the degree of dispersion of the thickness distribution. It can be seen that the average thickness of the lamellar α phase in the core is 0.2μm thicker than the outer surface, and the standard deviation of the thickness of the α phase in the core and the outside is below 0.5μm, indicating that the internal and external structures of the prepared large-size titanium alloy forgings are uniform. Through room temperature tensile performance testing, the tensile rod specimen size is M10×60mm, the parallel section is Φ5×30mm, and the strain rate is 0.001s -1, the core performance was measured: yield strength 869MPa, tensile strength 948MPa, elongation 15.8%; the performance near the surface 1 / 4: yield strength 865MPa, tensile strength 938MPa, elongation 15.2%. The overall (i.e. the average and standard deviation of the corresponding performance of the core and the near surface 1 / 4) yield strength 867±3MPa, tensile strength 943±7MPa. It can be seen that the prepared large-size titanium alloy forgings have uniform internal and external properties.

[0059] Comparative Example 1

[0060] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 uses step S2' instead of step S2 of Example 1, and the powder metallurgy sintered billet is forged using the traditional ingot casting to forging billet process, and the remaining preparation steps are the same as Example 1. Step S2' is: using a heating device to heat the billet to 965°C for insulation, and the heating uses a uniform heating rate of 60°C / min. After insulation makes the temperature inside and outside the billet uniform, the billet is taken out for forging, the time for the billet to be transferred from the heating device to the forging work surface is 70s, the mold temperature is 400°C, the pressing head pressing rate during forging is 8mm / s, the final forging temperature is controlled above 780°C, the forging deformation is 50%, and after forging is completed, it is air-cooled to room temperature to prepare large-size titanium alloy forgings.

[0061] The metallographic structure of the core and 1 / 4 of the surface of the large-size titanium alloy forging prepared in Comparative Example 1 was observed. Figure 3 As shown, the heart ( Figure 3 a) and near the surface 1 / 4 ( Figure 3 b) is the primary α phase + a small amount of β transformation structure. The thickness of the core α phase is measured to be 15±4μm, and the thickness of the α phase near the surface 1 / 4 is 5±2μm. The thickness is expressed by a combination of arithmetic mean ± standard deviation, reflecting the central trend of the thickness and the degree of dispersion of the thickness distribution. It can be seen that the average thickness of the core α phase is 10μm thicker than the outer surface, and the standard deviation of the thickness of the core and the outer α phase is 4μm and 2μm, indicating that the internal and external structures of the prepared large-size titanium alloy forgings are uneven. Through room temperature tensile performance testing, the tensile rod specimen size is M10×60mm, the parallel section is Φ5×30mm, and the strain rate is 0.001s -1 , the core performance was measured: yield strength 840MPa, tensile strength 910MPa, elongation 14.4%; the performance near the surface 1 / 4: yield strength 868MPa, tensile strength 939MPa, elongation 15.6%. The overall yield strength is 854±20MPa, and the tensile strength is 925±20MPa. It can be seen that the internal and external properties of the prepared large-size titanium alloy forgings are uneven.

[0062] Comparative Example 2

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

[0064] The metallographic structure of the core and 1 / 4 of the surface of the large-size titanium alloy forging prepared in Comparative Example 2 was observed. Figure 4 As shown, the heart ( Figure 4 a) and near the surface 1 / 4 ( Figure 4 b) is the primary α phase + β transformation structure. The thickness of the core α phase is measured to be 32±8μm, and the thickness of the α phase near the surface 1 / 4 is 28±6μm. The thickness is expressed by a combination of arithmetic mean ± standard deviation, reflecting the central trend of the thickness and the degree of dispersion of the thickness distribution. It can be seen that the average thickness of the core α phase is 4μm thicker than the outer surface, and the standard deviation of the core and outer α phase thickness is 8μm and 6μm, indicating that the internal and external structures of the prepared large-size titanium alloy forgings are uneven. Through room temperature tensile performance testing, the tensile rod specimen size is M10×60mm, the parallel section is Φ5×30mm, and the strain rate is 0.001s -1 , the core performance was measured: yield strength 820MPa, tensile strength 906MPa, elongation 13.3%; performance near the surface 1 / 4: yield strength 862MPa, tensile strength 942MPa, elongation 14.2%. The overall yield strength is 841±30MPa, and the tensile strength is 924±25MPa. It can be seen that the internal and external properties of the prepared large-size titanium alloy forgings are uneven. Compared with Example 2, the α layer of Example 1 is finer and more uniform in structure, the overall yield strength is increased by 26MPa, and the overall tensile strength is increased by 19MPa. In addition, the sample standard deviation of the overall yield strength is reduced by 27MPa, and the performance uniformity of the forging is significantly improved. By calculation, the billet of the same specifications and weight (cutting specifications Φ250×420, cutting weight 92kg), the forging cost of Example 1 is 17,310 yuan, and the forging cost of Comparative Example 2 is 30,374 yuan, and 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 billet of Example 2 is heated to 1030°C and kept warm until the temperature inside and outside the billet is uniform, the forging deformation is 38%, and the remaining preparation steps are the same as Example 1 to prepare large-sized titanium alloy forgings.

[0067] The metallographic structure of the core and 1 / 4 of the surface of the large-sized titanium alloy forging prepared in Example 2 was observed. Figure 5 As shown, the heart ( Figure 5 a) and near the surface 1 / 4 ( Figure 5 b) is a full lamellar α phase. The thickness of the core α phase is measured to be 2.7±0.3μm, and the thickness of the α phase near the surface 1 / 4 is 2.6±0.3μm. The thickness is expressed by a combination of arithmetic mean ± standard deviation, reflecting the central trend of the thickness and the degree of dispersion of the thickness distribution. It can be seen that the average thickness of the lamellar α phase in the core is 0.1μm thicker than the outer surface, and the standard deviation of the thickness of the α phase in the core and the outside is below 0.5μm, indicating that the internal and external structures of the prepared large-size titanium alloy forgings are uniform. Through room temperature tensile performance testing, the tensile rod specimen size is M10×60mm, the parallel section is Φ5×30mm, and the strain rate is 0.001s -1 , the core performance was measured: yield strength 860MPa, tensile strength 942MPa, elongation 15.0%; the performance near the surface 1 / 4: yield strength 854MPa, tensile strength 934MPa, elongation 14.5%. The overall yield strength is 857±4MPa, and the tensile strength is 938±6MPa. It can be seen that the prepared large-size titanium alloy forgings have uniform internal and external properties.

[0068] Comparative Example 3

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

[0070] The metallographic structure of the core and 1 / 4 of the surface of the large-size titanium alloy forging prepared in Comparative Example 3 was observed. Figure 6 As shown, the heart ( Figure 6 a) and near the surface 1 / 4 ( Figure 6 b) is the Widmanstätten structure, the thickness of the core α phase is measured to be 4.2±0.9μm, and the thickness of the α phase near the surface 1 / 4 is 3.5±0.6μm. The thickness is expressed by a combination of arithmetic mean ± standard deviation, reflecting the central trend of the thickness and the degree of dispersion of the thickness distribution. It can be seen that the average thickness of the core α phase is 0.7μm thicker than the outer surface, and the standard deviation of the thickness of the core and the outer α phase is greater than 0.5μm. Through the room temperature tensile performance test, the tensile rod specimen size is M10×60mm, the parallel section is Φ5×30mm, and the strain rate is 0.001s-1 , the core performance was measured: yield strength 824MPa, tensile strength 933MPa, elongation 13.6%; the performance near the surface 1 / 4: yield strength 836MPa, tensile strength 940MPa, elongation 14.5%. The overall yield strength is 830±8MPa, and the tensile strength is 937±5MPa. Compared with Example 1, the forgings produced by Comparative Example 3 with a forging deformation of 55% have coarsened internal and external structures, a reduction in yield strength of 37MPa, a reduction in tensile strength of 6MPa, and a reduction in elongation of about 1.5%.

[0071] Example 3

[0072] Example 3 Based on the large-size titanium alloy forging obtained in Example 1, a second fire forging is performed, which specifically includes the following steps:

[0073] S3. The titanium alloy forging obtained in step S2 of Example 1 is heated to 950°C by a heating device for heat preservation, so that the temperature inside and outside the titanium alloy forging is uniform, and then the titanium alloy forging is taken out for forging. The time for transferring the titanium alloy forging from the heating device to the forging work surface is 70s, the die temperature is 400°C, the pressing rate of the ram during forging is 8mm / s, the final forging temperature is controlled to be above 780°C, the deformation amount of forging is 25%, and a large-sized secondary forged titanium alloy forging is obtained;

[0074] S4. Use a heating device to heat the secondary forged titanium alloy large-size forgings to 750°C for annealing treatment, and the insulation time is 1.5 hours. After the insulation is completed, air-cool it to room temperature to obtain annealed titanium alloy large-size forgings.

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

[0076] Example 4

[0077] On the basis of Example 4 and Example 3, a third fire forging is performed, which specifically includes the following steps:

[0078] S5. The titanium alloy forging obtained in step S4 of Example 3 is heated to 950°C by a heating device for heat preservation, so that the temperature inside and outside the titanium alloy forging is uniform, and then the titanium alloy forging is taken out for forging. The time for transferring the titanium alloy forging from the heating device to the forging work surface is 70s, the mold temperature is 400°C, the pressing rate of the ram during forging is 8mm / s, the final forging temperature is controlled to be above 780°C, the deformation amount of forging is 30%, and a large-sized titanium alloy forging is obtained after three-time forging;

[0079] S4. The three-forged titanium alloy large-size forgings are heated to 750°C for annealing by a heating device, and the heat preservation time is 1.5 hours. After the heat preservation is completed, the large-size forgings are air-cooled to room temperature to obtain annealed titanium alloy large-size forgings.

[0080] Through the room temperature tensile performance test, the tensile rod sample size is M10×60mm, the parallel section is Φ5×30mm, and the strain rate is 0.001s -1 The core performance was measured as follows: yield strength 858MPa, tensile strength 940MPa, elongation 15.9%; the performance near the surface 1 / 4: yield strength 862MPa, tensile strength 942MPa, elongation 15.5%. The overall yield strength is 860±3MPa, and the tensile strength is 941±1MPa. It can be seen that the prepared large-size titanium alloy forgings have uniform internal and external properties.

[0081] The above are all preferred embodiments of the present invention, and the protection scope of the present invention is not limited thereto. Therefore, any equivalent changes made according to the mechanism, shape, and principle of the present invention should be included in 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 method comprises the following preparation steps: 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: 5.5-6.75wt%, V: 3.5-4.5wt%, C≤0.08wt%, Fe≤0.25wt%, H≤0.012wt%, O≤0.12wt%, N≤0.03wt%, and the balance is Ti; S2. Use a heating device to heat the billet to 1030℃~1060℃ for insulation, so that the temperature inside and outside the billet is uniform, then take out the billet for forging, the time for the billet to be transferred from the heating device to the forging work surface is no more than 80 seconds, the mold temperature is 300℃~500℃, the pressing head pressing rate during forging is 8~12mm / s, the final forging temperature is controlled above 850℃, the forging deformation is 30%~38%, and large-size titanium alloy forgings are prepared.

2. The method for manufacturing a large-size Ti-6Al-4V titanium alloy forging according to claim 1, characterized in that: The core and 1 / 4 near the surface of the blank have equiaxed structures, the average thickness of the α phase in the core and 1 / 4 near the surface is less than 20 μm, and the average thickness difference of the α phase in the core and 1 / 4 near the surface is less than 3 μm.

3. The method for manufacturing a large-size Ti-6Al-4V titanium alloy forging according to claim 1, characterized in that: The core and 1 / 4 near the surface of the large-size titanium alloy forging have a full-lamellar α phase structure, 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.

4. The method for manufacturing a large-size Ti-6Al-4V titanium alloy forging according to claim 3, characterized in that: The average thickness of the α phase in the core and near 1 / 4 of the surface of the large-size titanium alloy forging is less than 4 μm.

5. The method for manufacturing a large-size Ti-6Al-4V titanium alloy forging according to claim 1, characterized in that: Also includes: S3. The titanium alloy forging obtained in step S2 is heated to 930°C to 970°C by a heating device for heat preservation, so that the temperature inside and outside of the titanium alloy forging is uniform, and then the titanium alloy forging is taken out for forging. The time for transferring the titanium alloy forging from the heating device to the forging working surface does not exceed 80 seconds, the mold temperature is 300°C to 500°C, the pressing rate of the ram during forging is 6 to 10 mm / s, the final forging temperature is controlled to be above 780°C, and the deformation amount of forging is 25 to 40%, so as to obtain a large-size secondary forged titanium alloy forging; S4. Using a heating device, the secondary forged titanium alloy large-size forging is heated to 730° C. to 780° C. for annealing to obtain an annealed titanium alloy large-size forging.

6. The method for manufacturing a large-size Ti-6Al-4V titanium alloy forging according to claim 5, characterized in that: The core and 1 / 4 near the surface of the annealed titanium alloy large-size forging have primary α phase and β transformation structure, 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.

7. The method for manufacturing a large-size Ti-6Al-4V titanium alloy forging according to claim 6, characterized in that: The average thickness of the α phase in the core and near the surface 1 / 4 of the annealed titanium alloy large-size forging does not exceed 12 μm.

8. The method for manufacturing a large-size Ti-6Al-4V titanium alloy forging according to claim 5, characterized in that: Also includes: S5. Using a heating device, heat the annealed titanium alloy large-size forging obtained in step S4 to 930°C to 970°C for heat preservation, so that the internal and external temperatures of the annealed titanium alloy large-size forging are uniform, take out the annealed titanium alloy large-size forging for forging, the time for transferring the annealed titanium alloy large-size forging from the heating device to the forging work surface does not exceed 80 seconds, the mold temperature is 300°C to 500°C, the pressure head pressing rate during forging is 6 to 10 mm / s, the final forging temperature is controlled to be not less than 780°C, the forging deformation is 25 to 40%, and a three-forged titanium alloy large-size forging is obtained; S6. Using a heating device, heat the tertiary forged titanium alloy forging to 730°C to 780°C for annealing to obtain an annealed titanium alloy large-size forging.

9. The method for manufacturing a large-size Ti-6Al-4V titanium alloy forging according to any one of claims 1 to 8, characterized in that: The difference between the yield strength at the core and the yield strength at 1 / 4 near the surface of large-size titanium alloy forgings shall not exceed 10MPa, the difference between the tensile strength at the core and the tensile strength at 1 / 4 near the surface shall not exceed 10Mpa, and the difference between the elongation at the core and the elongation at 1 / 4 near the surface shall not exceed 1%.

10. A Ti-6Al-4V titanium alloy large-size forging obtained by the method for manufacturing a Ti-6Al-4V titanium alloy large-size forging according to any one of claims 1 to 9.

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