A method for preparing a large-size fan-shaped thin-wall forged piece of near-alpha titanium alloy

Abstract

The application discloses a preparation method of a near-alpha titanium alloy large-size fan-shaped thin-wall forged piece, and the preparation method comprises the following steps: 1) open-die forging; 2) intermediate forging; 3) low-temperature re-forging, punching and hole expanding; 4) ring rolling forming; and 5) machining of a finished product. The preparation method overcomes the defects of a traditional process, adopts a three-fire-time open-die forging + multi-fire-time two-phase zone forging + low-temperature punching and hole expanding + ring rolling process, and effectively improves the production efficiency of the near-alpha titanium alloy large-size forged piece, reduces the processing cost, and improves the organization uniformity and batch stability. Through actual detection, the surface roughness of the forged piece is less than 1.6 microns, ultrasonic flaw detection meets the GB / T 5193 A1 level, in a full immersion corrosion test in a mixed solution of a 6 mol / L nitric acid solution and a nuclear waste solution simulation solution, the corrosion rate is less than 0.1 mm / year, and the rest of the performance indexes all meet the technical requirements.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of titanium alloy processing, and particularly relates to a preparation method of a large-size (an outer diameter is greater than 1500 mm) fan-shaped thin-wall forged piece of near-alpha titanium alloy, so that the forged piece can be applied to a high-concentration nitric acid environment. BACKGROUND

[0002] It is known that nuclear energy, as a clean energy, has advantages of safety, high efficiency, economy and cleanness, and is one of the most hopeful future energies of human beings. At present, the human beings have applied the nuclear energy to military, energy, technology, spaceflight and other fields. Among them, the spent fuel reprocessing technology is the most extensive way of processing the spent fuel discharged from a nuclear reactor. The technology not only can fully utilize the function of nuclear fuel and improve the utilization ability of nuclear fuel to benefit human beings, but also more importantly, reduces the volume and radioactivity to create conditions for nuclear waste storage. The spent fuel reprocessing technology of nuclear power plants is the most important link in the later stage of nuclear fuel cycle, and is the key to closed cycle of nuclear fuel and sustainable development of nuclear energy.

[0003] It is known to those skilled in the art that the spent fuel reprocessor is long-term in a high-concentration boiling nitric acid, high-oxidizing ion and high-radioactivity environment, and therefore, the corrosion resistance of the acid treater is strictly required. The material usually used in the spent fuel reprocessor in the world is ultra-low-carbon austenitic stainless steel. However, the material is long-term in a strong acid and high-radioactivity environment, and is easy to cause intergranular corrosion. Titanium and titanium alloy are easy to combine with oxygen to generate an oxide film, and can be passivated in the high-concentration boiling nitric acid, high-oxidizing ion and high-radioactivity medium. According to research, the near-alpha titanium alloy has excellent corrosion resistance in the high-concentration nitric acid at high temperature, is not sensitive to irradiation and has good processability. Therefore, the near-alpha titanium alloy becomes a substitute for the ultra-low-carbon austenitic stainless steel as a material for key equipment of the spent fuel reprocessor.

[0004] The existing near-alpha titanium alloy is mainly applied to the heat exchange pipe and liquid pipeline of a spent fuel reprocessing device, and the large-size sector thin-wall forged piece of the near-alpha titanium alloy is used as a plug of a circulating tank of the device, and the service life of the device has a high requirement on the mechanical properties of the large-size sector thin-wall forged piece. Generally, the sector thin-wall forged piece is forged by upsetting and drawing a rectangular forged piece for a certain number of times, and then is forged into a sector by using a quick forging machine and a die anvil. This processing mode adopts free forging, and the titanium alloy has a high requirement on the final forging temperature in the forging process. The forging blank is small, the material temperature drops quickly, the forming must be completed by multiple times of re-furnace, the size difference of the forged piece is large, the processing allowance is large, the process controllability is poor, and the quality stability is poor. Moreover, the forming must be completed by multiple times of re-furnace, so that the microstructure and properties are affected. That is to say, the sector thin-wall forged piece prepared by using the existing free forging preparation technology has problems of high forging cost, low yield, poor batch stability, poor market core competitiveness and the like. In addition, the corrosion performance, corrosion behavior, passivation film and transition layer of the near-alpha titanium alloy, the plate processing technology, the pipe processing technology and the like are researched in China, but the preparation of the large-size sector thin-wall forged piece of the near-alpha titanium alloy is rarely researched.

[0005] Therefore, the present inventors provide a preparation method of a large-size sector thin-wall forged piece of a near-alpha titanium alloy to overcome the defects of the prior art. SUMMARY

[0006] The present application aims to overcome the above-mentioned defects of the prior art, and provides a preparation method of a large-size sector thin-wall forged piece of a near-alpha titanium alloy. The preparation method overcomes various disadvantages caused by multiple times of reforming and forming of a conventional titanium alloy sector thin-wall forged piece by using a quick forging machine and a die anvil, improves the production efficiency of the large-size sector thin-wall forged piece of the near-alpha titanium alloy, reduces the processing cost, improves the stability of batch products, and the surface roughness of the forged piece is less than 1.6 μm through actual detection, ultrasonic flaw detection meets GB / T5193 A1 level, and the rest of the performance indicators meet the technical requirements.

[0007] The present application aims to overcome the above-mentioned defects of the prior art, and provides a preparation method of a large-size sector thin-wall forged piece of a near-alpha titanium alloy. The preparation method overcomes various disadvantages caused by multiple times of reforming and forming of a conventional titanium alloy sector thin-wall forged piece by using a quick forging machine and a die anvil, improves the production efficiency of the large-size sector thin-wall forged piece of the near-alpha titanium alloy, reduces the processing cost, improves the stability of batch products, and the surface roughness of the forged piece is less than 1.6 μm through actual detection, ultrasonic flaw detection meets GB / T5193 A1 level, and the rest of the performance indicators meet the technical requirements.

[0008] The present application aims to overcome the above-mentioned defects of the prior art, and provides a preparation method of a large-size sector thin-wall forged piece of a near-alpha titanium alloy. The preparation method overcomes various disadvantages caused by multiple times of reforming and forming of a conventional titanium alloy sector thin-wall forged piece by using a quick forging machine and a die anvil, improves the production efficiency of the large-size sector thin-wall forged piece of the near-alpha titanium alloy, reduces the processing cost, improves the stability of batch products, and the surface roughness of the forged piece is less than 1.6 μm through actual detection, ultrasonic flaw detection meets GB / T5193 A1 level, and the rest of the performance indicators meet the technical requirements.

[0009] Step one, step one, cogging forging: three times of upsetting and drawing forging is performed above the phase transition point, and high-temperature homogenization treatment is adopted in the second time of upsetting and drawing forging, so as to fully break the original as-cast structure to obtain a blank after cogging;

[0010] Step two, intermediate forging: the blank after cogging in step one is subjected to multiple times of heat preservation forging below the phase transition point in a stepwise descending manner of the heat preservation temperature of each time, so as to obtain a uniform and fine structure, and the forging mode of the last time is lengthening;

[0011] Step three, low temperature re-forging punching and hole expanding: through the mandrel hole expansion below the phase transition temperature to prepare the ring blank meeting the deformation requirement of subsequent ring rolling;

[0012] Step four, ring rolling forming: ring rolling below the phase transition temperature to the predetermined ring size;

[0013] Step five, finished product machining: removing the oxide skin on the inner and outer surfaces and the end surfaces of the ring by machining, and then cutting the ring into the required arc sector thin-walled forgings using water cutting.

[0014] Further, the specific process of the three-fire upsetting and drawing forging in the step one cogging forging is as follows:

[0015] First fire: the heating temperature is 1000-1040℃, the heating coefficient is 0.45-0.6, the upsetting and drawing forging ratio is controlled to be 1.3-1.7, the upsetting is divided into 2-3 hammering, the upsetting rate is ≤20mm / s, the drawing rate is ≤40mm / s, and the forging is air-cooled after completion;

[0016] Second fire: the heating temperature is 1150-1180℃, the holding time is 50-55 hours, the upsetting and drawing forging ratio is controlled to be 1.3-1.7, the upsetting is divided into 2-3 hammering, the upsetting rate is ≤20mm / s, the drawing rate is ≤40mm / s, the end feeding amount is 350-400mm, and the remaining feeding amount is 200-300mm, and the forging is air-cooled after completion;

[0017] Third fire: the heating temperature is 1000-1040℃, the heating coefficient is 0.45-0.6, the upsetting and drawing forging ratio is controlled to be 1.3-1.7, the upsetting is divided into 2-3 hammering, the upsetting rate is ≤20mm / s, the drawing rate is ≤40mm / s, the end feeding amount is 350-400mm, and the remaining feeding amount is 200-300mm, and the forging is air-cooled after completion.

[0018] Further, in the step one cogging forging, the work die used in the first fire is a 900mm wide upper flat anvil and a 1200mm wide lower flat anvil, and the drawing mode is radial drawing; the work dies used in the second fire and the third fire are the same, both of which are a 650mm wide upper flat anvil and a 1200mm wide lower flat anvil, and the drawing mode is axial drawing.

[0019] Further, in the step one cogging forging, the coating is uniformly coated on the surface of the blank before the second fire, the coating is a mixed solution of paint and binder, and the blank is wrapped with asbestos before being discharged for forging;

[0020] The binder is selected from model NJ-1, and is configured in a proportion of paint:binder=1:1, and is fully stirred to uniformly mix the paint and the binder, and the solution after stirring cannot have flocculation or caking phenomenon. Preferably, after the first coating is completed, the next coating is performed after 1h-6h; after the three coatings are performed, heating is performed.

[0021] Further, the intermediate forging in step two is specifically performed as follows: multiple heating and forging is performed at a temperature range of 30-70℃ below the phase transition point, the single heating temperature gradually decreases, the heating coefficient is 0.60-0.80, the upsetting and drawing forging ratio is 1.5-1.8, the upsetting rate is ≤20mm / s, the end part is deformed by using small feeding amount, the drawing rate is ≤40mm / s, the drawing mode is repeated drawing, the temperature difference of the two ends of the rod is reduced, the end feeding amount is 350-400mm, the remaining feeding amount is 200-300mm, after the final forging is completed, the inverted octagonal processing is performed, and air cooling is performed after the forging.

[0022] Further, the intermediate forging in step two is specifically performed as follows: multiple heating and forging is performed at a temperature range of 30-70℃ below the phase transition point, the single heating temperature gradually decreases, the heating coefficient is 0.60-0.80, the upsetting and drawing forging ratio is 1.5-1.8, the upsetting rate is ≤20mm / s, the end part is deformed by using small feeding amount, the drawing rate is ≤40mm / s, the drawing mode is repeated drawing, the temperature difference of the two ends of the rod is reduced, the end feeding amount is 350-400mm, the remaining feeding amount is 200-300mm, after the final forging is completed, the inverted octagonal processing is performed, and air cooling is performed after the forging.

[0023] Further, the intermediate forging in step two is specifically performed as follows: multiple heating and forging is performed at a temperature range of 30-70℃ below the phase transition point, the single heating temperature gradually decreases, the heating coefficient is 0.60-0.80, the upsetting and drawing forging ratio is 1.5-1.8, the upsetting rate is ≤20mm / s, the end part is deformed by using small feeding amount, the drawing rate is ≤40mm / s, the drawing mode is repeated drawing, the temperature difference of the two ends of the rod is reduced, the end feeding amount is 350-400mm, the remaining feeding amount is 200-300mm, after the final forging is completed, the inverted octagonal processing is performed, and air cooling is performed after the forging.

[0024] Further, the intermediate forging in step two is specifically performed as follows: multiple heating and forging is performed at a temperature range of 30-70℃ below the phase transition point, the single heating temperature gradually decreases, the heating coefficient is 0.60-0.80, the upsetting and drawing forging ratio is 1.5-1.8, the upsetting rate is ≤20mm / s, the end part is deformed by using small feeding amount, the drawing rate is ≤40mm / s, the drawing mode is repeated drawing, the temperature difference of the two ends of the rod is reduced, the end feeding amount is 350-400mm, the remaining feeding amount is 200-300mm, after the final forging is completed, the inverted octagonal processing is performed, and air cooling is performed after the forging.

[0025] Further, the intermediate forging in step two is specifically performed as follows: multiple heating and forging is performed at a temperature range of 30-70℃ below the phase transition point, the single heating temperature gradually decreases, the heating coefficient is 0.60-0.80, the upsetting and drawing forging ratio is 1.5-1.8, the upsetting rate is ≤20mm / s, the end part is deformed by using small feeding amount, the drawing rate is ≤40mm / s, the drawing mode is repeated drawing, the temperature difference of the two ends of the rod is reduced, the end feeding amount is 350-400mm, the remaining feeding amount is 200-300mm, after the final forging is completed, the inverted octagonal processing is performed, and air cooling is performed after the forging.

[0026] Further, the intermediate forging in step two is specifically performed as follows: multiple heating and forging is performed at a temperature range of 30-70℃ below the phase transition point, the single heating temperature gradually decreases, the heating coefficient is 0.60-0.80, the upsetting and drawing forging ratio is 1.5-1.8, the upsetting rate is ≤20mm / s, the end part is deformed by using small feeding amount, the drawing rate is ≤40mm / s, the drawing mode is repeated drawing, the temperature difference of the two ends of the rod is reduced, the end feeding amount is 350-400mm, the remaining feeding amount is 200-300mm, after the final forging is completed, the inverted octagonal processing is performed, and air cooling is performed after the forging.

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] This invention discloses a method for preparing large-sized fan-shaped thin-walled forgings of near-α titanium alloy. It abandons the traditional method of using a high-speed forging machine and anvil to forge rectangular forgings into a fan shape. This application first employs high-temperature forging above the phase transformation point to fully break down the original as-cast structure, obtaining a billet with a fine and uniform structure. Then, intermediate forging and low-temperature forging with punching and reaming are performed below the phase transformation point temperature. During reaming, a reaming machine is used to prepare a ring billet that meets the deformation requirements of subsequent ring rolling. The resulting machining allowance is used to produce smaller-sized products, improving material utilization and reducing production costs. Next, below the phase transformation point temperature, low-temperature ring rolling is performed to the required ring size. Hot material is recycled during the rolling process to avoid significant temperature drops on the ring surface due to prolonged rolling time, which could cause uneven deformation and differences in forging energy storage. Finally, a water jet cutting machine is used to shape the desired fan shape, resulting in the finished product. In summary, the near-α titanium alloy large-size fan-shaped thin-walled forgings prepared using this application have been verified in practice to have uniform microstructure, room temperature tensile properties and corrosion resistance that meet the material requirements for nuclear waste reprocessing melters. At the same time, the production cost is reduced due to the reduced number of remelting cycles during the forming stage. Attached Figure Description

[0029] The accompanying drawings are incorporated in and form part of this specification, and together with the description serve to explain the principles of the invention.

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a flowchart of a method for preparing a large-size fan-shaped thin-walled forging of near-α titanium alloy according to the present invention;

[0032] Figure 2 This is a photograph of the thin-walled ring component prepared in Example 1 of the present invention;

[0033] Figure 3 This is a photograph of the fan-shaped thin-walled forging prepared in Embodiment 1 of the present invention;

[0034] Figure 4 This is a low-magnification microstructure image of the fan-shaped thin-walled forging prepared in Example 1 of the present invention; Detailed Implementation

[0035] The exemplary embodiments will be described in detail herein with reference to the attached drawings. The description of the exemplary embodiments is intended to apply to all alternative embodiments, as would be understood by one skilled in the art. Overly broad disclosures are not intended to be synonymous with the exemplary embodiments of the application. Instead, they are merely examples of apparatuses consistent with some aspects of the application as detailed in the appended claims.

[0036] In order to make the technical solution of the present application better understood by those skilled in the art, the present application will be described in further detail below with reference to the accompanying drawings and examples.

[0037] Please refer to Figure 1 The present application provides a preparation method of a near-alpha titanium alloy large-size fan-shaped thin-walled forging, which comprises the following steps:

[0038] Step one, open-die forging: three times of upsetting and drawing are performed above the phase transition point, and high-temperature homogenization treatment is adopted during the second time of upsetting and drawing, so as to fully break the original as-cast structure to obtain a fine β structure blank after opening.

[0039] Specifically, the first time: the heating temperature is 1000-1040℃, the heating coefficient is 0.45-0.6, the upsetting and drawing ratio is controlled to be 1.3-1.7, the upsetting is performed slowly and in 2-3 hammers, the upsetting rate is ≤20 mm / s, the drawing is performed slowly, the drawing rate is ≤40 mm / s, and the forging is air-cooled after completion. The upper anvil of the die is a 900 mm wide flat anvil, the lower anvil is a 1200 mm wide flat anvil, and the drawing mode is radial drawing.

[0040] The second time: before heating, the coating is brushed, the binder is selected to be NJ-1, the coating and the binder are mixed uniformly according to the ratio of 1:1, the stirring time is 1-10 min, and the solution after stirring cannot have flocculation or caking phenomenon. After the first coating is completed, the next coating is brushed after 1-6 h, and the coating is brushed three times before heating. The heating temperature is 1150-1180℃, the holding time is 50-55 h, the asbestos is wrapped before furnace-out forging, the upsetting and drawing ratio is 1.3-1.7, the upsetting is performed slowly and in 2-3 hammers, the upsetting rate is ≤20 mm / s, the drawing is performed slowly, the drawing rate is ≤40 mm / s, the end feeding amount is 350-400 mm, the remaining feeding amount is 200-300 mm, the forging is air-cooled after completion, the upper anvil of the die is a 650 mm flat anvil, the lower anvil is a 1200 mm flat anvil, and the drawing mode is axial drawing.

[0041] Third heating: heating temperature is 1000℃-1040℃, heating coefficient is 0.45-0.6, upsetting and drawing forging ratio is controlled between 1.3-1.7, slow and 2-3 hammer upsetting, upsetting rate ≤20mm / s, slow drawing, drawing rate ≤40mm / s, feed amount is 350mm-400mm, the rest is 200mm-300mm; after forging, air cooling, the upper anvil of the work die uses 650mm flat anvil, the lower anvil uses 1200mm flat anvil, the drawing mode is axial drawing.

[0042] Step two, intermediate forging: the billet after step one is open-die forged in a way that the temperature of each heating cycle is uniformly stepped down below the phase transition point, and the last heating cycle is drawing;

[0043] Specifically, the billet after step one is open-die forged in a way that the temperature of each heating cycle is uniformly stepped down below the phase transition point, and the last heating cycle is drawing;

[0044] Step three, low-temperature re-forging punching and expanding: the ring billet that meets the deformation requirement of subsequent ring rolling is prepared by frame expanding below the phase transition point;

[0045] Specifically, first, the billet after step two is heated below the phase transition point in a temperature range of 40℃-60℃, the heating coefficient is 0.60-0.80, and the billet is upset to meet the punching size, then punched by a suitable punch, the punch core separated from the billet is expanded, the time of each heating cycle is controlled to be ≤15min, if the time exceeds, the hot material is returned to the furnace for heat preservation until the expanding is completed, the heat preservation time is 60min-150min, until the ring billet that meets the deformation requirement of subsequent ring rolling is prepared. Hot material return is adopted to reduce the cumulative heat preservation time of the billet, avoid the alloy microstructure to be coarse, improve the production efficiency, and reduce the production cost; in addition, the punch core is the original core material of the billet, which can be used to produce smaller specifications, and improve the material utilization rate.

[0046] Further, the billet is wrapped with asbestos before re-forging, so that the cracks caused by rapid temperature reduction of the billet are avoided, and the quality of the product is improved.

[0047] Step four, ring rolling forming: below the phase transition point temperature, ring rolling to a predetermined ring size;

[0048] Specifically, the ring blank obtained in step three is subjected to heat preservation rolling in a temperature range of 40-60°C below the phase transition point, the heating coefficient is 0.60-0.80, the single-fire control rolling process time is ≤15 min, and if the time exceeds, the hot material is recycled and preserved until the rolling is completed, the recycling and preserving time is 60-150 min, and finally different specifications of ring pieces can be obtained. The whole ring rolling process avoids the large temperature drop of the surface layer of the ring blank due to the too long rolling time, causing uneven deformation of the ring blank and difference in forging energy storage.

[0049] The ring product size is determined by the final delivered product size, considering the thickness of the oxide skin and adding a machining allowance.

[0050] Step five, finished product machining: the oxide skin on the inner and outer surfaces of the ring piece in step four is removed by machining, and the ring piece is cut into a fan-shaped thin-walled forging with a required arc by water cutting.

[0051] Note: The heating coefficient unit in the present application is min / mm.

[0052] In order to further verify the efficacy of the preparation method of the present application, the inventors carried out the following specific examples with Ti35 alloy:

[0053] Example 1 (preparation of Φ2135 / Φ1685×L ring piece)

[0054] 1) Open die forging:

[0055] The ingot size is selected as Ф620 mm, the ingot β phase transformation point is 890 ℃, the first fire cogging heating temperature is 1020 ℃, the heating coefficient is 0.45, the upsetting and drawing forging ratio is 1.3-1.55, the slow and three-hammer upsetting is adopted, the upsetting speed is 15 mm / s, the slow drawing is adopted, the drawing speed is 30 mm / s, and the air cooling is adopted after the forging is completed. The 900 mm flat anvil is used for the upper anvil of the die, the 1200 mm flat anvil is used for the lower anvil, and the radial drawing is adopted for the drawing mode; the coating is brushed before the second fire forging, the binder is selected as type NJ-1, the coating and the binder are uniformly mixed according to the proportion of 1:1, the solution is stirred after the mixing, the solution has no flocculation or lumping phenomenon, the mixed coating is uniformly coated on the surface of the material, the first coating is completed, the next coating is brushed after 3 hours, and the heating is adopted after the coating is brushed three times. The cold material heating temperature is 1170 ℃, the holding time is 50 h, the stone wool is adopted before the furnace is discharged for forging, the forging ratio is 1.3-1.55, the slow and three-hammer upsetting is adopted, the upsetting speed is 15 mm / s, the slow drawing is adopted, the drawing speed is 30 mm / s, the end feeding amount is 350-400 mm, and the remaining feeding amount is 200-300 mm. The inverted octagonal processing is adopted after the final drawing, the air cooling is adopted after the forging is completed, the 650 mm flat anvil is used for the upper anvil of the die, the 1200 mm flat anvil is used for the lower anvil, and the axial drawing is adopted for the drawing mode; the heating temperature of the third fire is 1020 ℃, the heating coefficient is 0.45, the upsetting and drawing forging ratio is 1.3-1.55, the slow and three-hammer upsetting is adopted, the upsetting speed is 15 mm / s, the slow drawing is adopted, the drawing speed is 30 mm / s, the repeated drawing is adopted for the drawing mode, the end feeding amount is 350-400 mm, and the remaining feeding amount is 200-300 mm. The air cooling is adopted after the forging is completed, the 650 mm flat anvil is used for the upper anvil of the die, the 1200 mm flat anvil is used for the lower anvil, and the axial drawing is adopted for the drawing mode.

[0056] 2) intermediate forging:

[0057] The blank after the cogging forging of step 1) is three times holding and forging at a temperature 50-70 ℃ lower than the β phase transformation point, the single fire holding temperature is in a descending state, that is, the temperature is set as 840 ℃, 830 ℃ and 820 ℃, the heating coefficient is 0.6-0.75, the upsetting and drawing forging ratio is 1.5-1.73, the inverted octagonal processing is adopted after the final drawing, the slow upsetting is adopted, the upsetting speed is 15 mm / s, the slow drawing is adopted, the drawing speed is 30 mm / s, the end feeding amount is 350-400 mm, and the remaining feeding amount is 200-300 mm. The air cooling is adopted after the forging of each fire, the 650 mm flat anvil is used for the upper anvil and the lower anvil of the die, and the axial drawing is adopted for the drawing mode of each fire. Finally, the octagonal size is 400 mm.

[0058] 3) low temperature re-forging punching and expanding:

[0059] The blank of step 2) is heated at 50°C below the phase transition point, i.e. the temperature is set to 840°C, the heating coefficient is 0.6, after discharging, the blank is wrapped with asbestos, then is upset to a blank meeting the punching size, finally is punched by a suitable punch, in this example, the blank is upset to a height of 200mm, a Φ350mm punch is used, the punched core is separated from the blank, and is expanded, after expansion for more than 15min, the expanded blank is returned to the furnace for heat preservation for 150min until the expanded size is Φ1600 / Φ1150xL, then the blank is air cooled, thereby obtaining the required ring blank.

[0060] 4) Ring rolling forming:

[0061] The ring blank obtained in step 3) is ring rolled at 50°C below the phase transition point, i.e. the temperature is set to 840°C, the heating coefficient is 0.6, the ring rolling is performed by using a ring rolling machine, and if the ring rolling process time is more than 15min, the hot blank is returned to the furnace for heat preservation for 150min until the rolling size is Φ2155 / Φ1655xL, then the forged piece is air cooled.

[0062] 5) Machining of finished product:

[0063] The forged piece obtained in step 4) is machined by a cutting equipment to remove the oxide scale on the inner surface, the outer surface and the two end surfaces, thereby obtaining a titanium alloy ring piece (as shown in Figure 2 ) of Φ2135 / Φ1685xL, and then using water cutting, the forged piece is cut into a sector thin-walled piece (as shown in Figure 3 ) with a required arc.

[0064] wherein, Figure 4 is the macrostructure of the sector thin-walled forged piece prepared by the method of the application in Example 1, it can be seen that the macrostructure is fine and blurred crystal, which indicates that the deformation of the forging blank at each position is uniform and sufficient, the surface roughness is less than 1.6μm, the ultrasonic flaw detection meets GB / T 5193 A1 level, and the other properties meet the requirements of the technical agreement, the corrosion rate in the mixed solution of 6mol / L nitric acid solution and nuclear waste simulation solution is less than 0.1mm / year, which meets the requirements of equipment use. Table 1 below shows the room temperature mechanical properties of the ring piece product prepared in Example 1 after heat treatment, and it can be seen from the data that the results meet the requirements and have a certain amount of surplus.

[0065] Table 1: Mechanical properties of the ring piece prepared in Example 1

[0066]

[0067]

[0068] Example 2 (preparation of a Φ1980 / Φ1610xL ring piece)

[0069] 1) Upsetting forging:

[0070] The ingot specification is selected as Ф620mm, the ingot β phase transformation point is 900°C, the first fire breakdown heating temperature is 1040°C, the heating coefficient is 0.5, the upsetting and drawing forging ratio is 1.4-1.6, slow and two-hammer upsetting is adopted, the upsetting speed is 20mm / s, slow drawing is adopted, the drawing speed is 40mm / s, after the forging is completed, air cooling is adopted, the upper anvil of the work die uses a 650mm flat anvil, the lower anvil uses a 1200mm flat anvil, the drawing mode is radial drawing; the second fire forging is heated after brushing the coating, the binder is selected as type NJ-1, the coating and the binder are mixed uniformly according to the ratio of 1:1, the stirring time is 1-10min, the solution after stirring cannot have flocculation or lumping phenomenon. The mixed coating is uniformly brushed on the surface of the material, after the first coating is completed, the next coating is brushed after 6h, the coating is brushed three times and then heated. The cold material heating temperature is 1180°C, the holding time is 52h, before the furnace is discharged for forging, the material is wrapped with stone wool, the forging ratio is 1.4-1.6, slow and two-hammer upsetting is adopted, the upsetting speed is 20mm / s, slow drawing is adopted, the drawing speed is 40mm / s, the end feeding amount is 350-400mm, the rest feeding amount is 200-300mm, after the final drawing, octagonal processing is adopted, after the forging is completed, air cooling is adopted, the upper anvil of the work die uses a 650mm flat anvil, the lower anvil uses a 1200mm flat anvil, the drawing mode is axial drawing; the third fire heating temperature is 1040°C, the heating coefficient is 0.5, the upsetting and drawing forging ratio is 1.4-1.6, slow and two-hammer upsetting is adopted, the upsetting speed is 20mm / s, slow drawing is adopted, the drawing speed is 40mm / s, the end feeding amount is 350-400mm, the rest feeding amount is 200-300mm, after the forging is completed, air cooling is adopted, the upper anvil of the work die uses a 650mm flat anvil, the lower anvil uses a 1200mm flat anvil, the drawing mode is axial drawing.

[0071] 2) intermediate forging:

[0072] The blank after the breakdown forging of step 1) is three times holding and forging at a temperature 40-60°C lower than the β phase transformation point, the single fire holding temperature is in a descending state, that is, the temperature is set to 860°C, 850°C, 840°C, the heating coefficient is 0.6-0.75, the upsetting and drawing forging ratio is 1.6-1.75, after the final drawing, octagonal processing is adopted, slow upsetting is adopted, the upsetting speed is 20mm / s, slow drawing is adopted, the drawing speed is 40mm / s, the drawing mode is repeated drawing, the end feeding amount is 350-400mm, the rest feeding amount is 200-300mm. After each fire forging, air cooling is adopted, the upper anvil and the lower anvil of the work die both use a 650mm flat anvil, the fire drawing mode is axial drawing, finally the octagonal size is 400mm.

[0073] 3) low temperature re-forging punching and expanding:

[0074] The blank of step 2) is heated at 60°C below the phase transition point, i.e. the temperature is set to 840°C, the heating coefficient is 0.7, after the blank is discharged, the blank is wrapped with asbestos, then is upset to a blank meeting the punching size, finally is punched by a suitable punch, in the example, the blank is upset to a height of 250mm, a Φ350mm punch is used, the punched core is separated from the blank, and is expanded, after expansion for more than 15min, the expanded blank is returned to the furnace and is kept for 150min until the expanded size is Φ1560 / Φ1000xL, then the blank is air cooled, and the required ring blank is obtained.

[0075] 4) Ring rolling forming:

[0076] The ring blank obtained in step 3) is ring rolled at 60°C below the phase transition point, i.e. the temperature is set to 840°C, the heating coefficient is 0.6, the ring rolling is performed by using a ring rolling machine, and after the ring rolling process time is more than 15min, the hot blank is returned to the furnace and is kept for 150min until the rolling size is Φ2010 / Φ1580xL, then the forged piece is air cooled.

[0077] 5) Machining of finished product:

[0078] The forged piece obtained in step 4) is machined by a cutting equipment to remove the oxide scale parts of the inner surface, the outer surface and the two end surfaces, i.e. a titanium alloy ring piece of Φ1980 / Φ1610xL is obtained, then water cutting is used to cut a fan-shaped thin-walled forged piece with a required arc.

[0079] Table 2 below is the room temperature mechanical properties of the ring piece product prepared in example 2 after heat treatment, and the data shows that the results meet the requirements and have a certain amount of surplus.

[0080] Table 2: Mechanical properties of the ring piece prepared in example 2

[0081]

[0082] Example 3 (preparation of a Φ2220 / Φ1650xL ring piece)

[0083] 1) Upsetting forging:

[0084] The ingot specification is selected as Ф620mm, the ingot β phase transformation point is 880℃, the first fire cogging heating temperature is 1000℃, the heating coefficient is 0.6, the upsetting and drawing forging ratio is 1.45-1.7, the slow and three-hammer upsetting is adopted, the upsetting speed is 15mm / s, the slow drawing is adopted, the drawing speed is 30mm / s, the workpiece is air-cooled after the forging is completed, the 900mm flat anvil is used for the upper anvil of the die, the 1200mm flat anvil is used for the lower anvil, and the radial drawing is adopted for the drawing mode; the coating is brushed before the second fire forging, the binder is selected as type NJ-1, the coating and the binder are uniformly mixed according to the proportion of 1:1, the stirring time is 1-10min, the solution cannot have the flocculent or lump phenomenon after the stirring, the mixed coating is uniformly brushed on the surface of the material, the next brushing is performed after the first brushing is completed and 6h is interval, and the heating is performed after the coating is brushed three times. The cold material heating temperature is 1150℃, the holding time is 55h, the stone wool is wrapped before the workpiece is taken out for forging, the forging ratio is 1.45-1.7, the slow and three-hammer upsetting is adopted, the upsetting speed is 15mm / s, the slow drawing is adopted, the drawing speed is 30mm / s, the end feeding amount is 350-400mm, the rest feeding amount is 200-300mm, the inverted octagonal processing is performed after the final drawing, the workpiece is air-cooled after the forging is completed, the 650mm flat anvil is used for the upper anvil of the die, the 1200mm flat anvil is used for the lower anvil, and the axial drawing is adopted for the drawing mode; the heating temperature of the third fire is 1000℃, the heating coefficient is 0.6, the upsetting and drawing forging ratio is 1.45-1.7, the slow and three-hammer upsetting is adopted, the upsetting speed is 15mm / s, the slow drawing is adopted, the drawing speed is 30mm / s, the end feeding amount is 350-400mm, the rest feeding amount is 200-300mm, the workpiece is air-cooled after the forging is completed, the 650mm flat anvil is used for the upper anvil of the die, the 1200mm flat anvil is used for the lower anvil, and the axial drawing is adopted for the drawing mode.

[0085] 2) intermediate forging:

[0086] The blank after the cogging forging of step 1) is three times holding and forging at 30-50℃ below the β phase transformation point temperature, the single fire holding temperature is in the descending state, that is, the temperature is set as 850℃, 840℃, 830℃, the heating coefficient is 0.7-0.8, the upsetting and drawing forging ratio is 1.65-1.8, the inverted octagonal processing is performed after the final drawing, the slow upsetting is adopted, the upsetting speed is 15mm / s, the slow drawing is adopted, the drawing speed is 30mm / s, the drawing mode is the repeated drawing, the end feeding amount is 350-400mm, the rest feeding amount is 200-300mm. The workpiece is air-cooled after each fire forging, the 650mm flat anvil is used for the upper anvil and the lower anvil of the die, the axial drawing is adopted for the fire drawing mode, and the final octagonal size is 400mm.

[0087] 3) low temperature re-forging punching and expanding:

[0088] The blank of step 2) is heated at 40℃ below the phase transition point, i.e. the temperature is set to 840℃, the heating coefficient is 0.8, after discharging, the blank is wrapped with asbestos, then is upset to a blank meeting the punching size, finally is punched by a suitable punch, in the example, the blank is upset to a height of 300mm, a punch with a diameter of 380mm is used, the punched core is separated from the blank, and is expanded, after expansion for more than 15min, the expanded blank is returned to the furnace for heat preservation for 150min until the expanded size is Φ1760 / Φ1100xL, and then is air cooled, thereby obtaining the required ring blank.

[0089] 4) Ring rolling forming:

[0090] The ring blank obtained in step 3) is ring rolled at 40℃ below the phase transition point, i.e. the temperature is set to 840℃, the heating coefficient is 0.8, the ring rolling machine is used as the equipment, and the hot blank is returned to the furnace for heat preservation for 150min after the ring rolling process time is more than 15min, until the rolling size is Φ2250 / Φ1620xL, and then the forged piece is air cooled.

[0091] 5) Machining of finished product:

[0092] The forged piece obtained in step 4) is machined by a cutting equipment to remove the oxide scale parts of the inner surface, the outer surface and the two end surfaces, thereby obtaining a titanium alloy ring piece with a size of Φ2220 / Φ1650xL, and then water cutting is used to cut the forged piece into a fan-shaped thin-walled forged piece with a required arc.

[0093] Table 3 is the room temperature mechanical properties of the ring piece product prepared in Example 3 after heat treatment, and the data show that the results meet the requirements and have a certain surplus.

[0094] Table 3: Mechanical properties of the ring piece prepared in Example 3

[0095]

[0096] In summary, the above examples all use a Ф620mm ingot, and provide a forging and rolling process technology for a near-alpha titanium alloy fan-shaped thin-walled forged piece, as shown by the data in Tables 1-3, the thin-walled forged piece prepared by the present application has a tensile strength (Rm) of more than 400Mpa, a yield strength (Rp0.2) of more than 300Mpa, an elongation after fracture (A) of more than 25%, and a reduction of area (Z) of more than 70 at room temperature, which meets the requirements of the fan-shaped thin-walled forged piece for a nuclear fuel reprocessing dissolver, has uniform structure, excellent performance, low cost and is suitable for industrial production. In actual production, the ingot size is not limited to Ф620mm, and the finished product size is not limited to the size of the above examples. In actual production, the finished product size is calculated by considering the thickness of the oxide scale and the machining allowance in the forging process, and then the blank size is calculated.

[0097] The foregoing is considered as illustrative only of the principles of the application. Numerous modifications and changes will readily occur to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application.

[0098] It is to be understood that the application is not limited to the details of the above-described embodiments and that various modifications and changes can be made without departing from the scope of the present application. The scope of the application should be determined by the appended claims.

Claims

1. A method of producing a near-alpha titanium alloy large-size fan-shaped thin-walled forged piece, characterized in that, The preparation method comprises the following steps: Step one, cogging forging: three times of upsetting and drawing forging are performed above the phase transition point, and uniformizing treatment is adopted in the second time of upsetting and drawing forging, so as to fully break the original cast state structure to obtain the blank after cogging; Step two, intermediate forging: the blank after cogging in step one is forged in multiple times of holding at temperature below the phase transition point in a stepped manner, so as to obtain uniform and fine structure, and the last time of forging is elongation; Step three, low-temperature re-forging punching and hole expanding: a ring blank meeting the deformation requirement of subsequent ring rolling is prepared by using a mandrel to expand the hole below the phase transition point; Step four, ring rolling forming: ring rolling is performed below the phase transition point to a predetermined ring size; Step five, finished product machining: the oxide skin on the inner and outer surfaces and the end surfaces of the ring in step four is removed by machining, and the ring is cut into a sector thin-walled forged piece with a required arc by using water cutting; The specific process of the three times of upsetting and drawing forging in step one is as follows: First time: the heating temperature is 1000-1040 DEG C, the heating coefficient is 0.45-0.6, the upsetting and drawing forging ratio is controlled to be 1.3-1.7, 2-3 hammers are used for upsetting, the upsetting speed is ≤20 mm / s, the elongation speed is ≤40 mm / s, and air cooling is performed after forging; Second time: the heating temperature is 1150-1180 DEG C, the holding time is 50-55 hours, the upsetting and drawing forging ratio is controlled to be 1.3-1.7, 2-3 hammers are used for upsetting, the upsetting speed is ≤20 mm / s, the elongation speed is ≤40 mm / s, the end feeding amount is 350-400 mm, and the remaining feeding amount is 200-300 mm, and air cooling is performed after forging; Third time: the heating temperature is 1000-1040 DEG C, the heating coefficient is 0.45-0.6, the upsetting and drawing forging ratio is controlled to be 1.3-1.7, 2-3 hammers are used for upsetting, the upsetting speed is ≤20 mm / s, the elongation speed is ≤40 mm / s, the end feeding amount is 350-400 mm, and the remaining feeding amount is 200-300 mm, and air cooling is performed after forging; The specific process of the intermediate forging in step two is as follows: multiple times of holding at temperature and forging are performed in the temperature range of 30-70 DEG C below the phase transition point, the heating coefficient is 0.60-0.80, the upsetting speed is ≤20 mm / s, the elongation speed is ≤40 mm / s, the elongation mode is repeated elongation, the end feeding amount is 350-400 mm, the remaining feeding amount is 200-300 mm, inverted octagonal processing is performed after final forging, and air cooling is performed after forging; The step three uses asbestos to wrap the blank before the low-temperature re-forging, and the specific process of the step three is as follows: the blank after the step two is heated to 40-60 ℃ below the phase transition point, the heating coefficient is 0.60-0.80, the blank is upset to meet the punching size, then the blank is punched by a suitable punch, the punch core separated from the blank is expanded, the single-fire-time control expansion process time is ≤15 min, and if the time exceeds, the hot material is returned to the furnace for heat preservation until the expansion is completed, until the ring blank meeting the subsequent ring rolling deformation requirement is prepared. The specific process of the step four is as follows: the blank after the step three is heat preserved at 40-60 ℃ below the phase transition point, the heating coefficient is 0.60-0.80, the single-fire-time control rolling process time is ≤15 min, and if the time exceeds, the hot material is returned to the furnace for heat preservation until the rolling is completed.

2. The method of producing a near-alpha titanium alloy large-size fan-shaped thin-walled forge piece according to claim 1, characterized in that, In the step one, the first fire uses a 900 mm wide upper flat anvil and a 1200 mm wide lower flat anvil, and the elongation is radial elongation; the second fire and the third fire use the same tooling, which is a 650 mm wide upper flat anvil and a 1200 mm wide lower flat anvil, and the elongation is axial elongation.

3. The method of producing a near-alpha titanium alloy large-size fan-shaped thin-walled forge piece according to claim 1, characterized in that, In the step one, the second fire is coated with a coating before heating, the coating is a mixed solution of paint and binder, and the blank is wrapped with asbestos before being discharged for forging; The binder is selected as NJ-1, the paint and the binder are mixed at a ratio of 1:1, and the solution after stirring should not have flocculation or caking phenomenon.

4. The method of producing a near-alpha titanium alloy large-size fan-shaped thin-walled forge piece according to claim 1, characterized in that, In the step two, the tooling used is a flat anvil with a width of 650 mm, and the elongation is axial elongation.

5. The method of producing a near-alpha titanium alloy large-size fan-shaped thin-walled forge piece according to claim 1, characterized in that, In the step four, the equipment used is a ring rolling machine.

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