A method for preparing a TA7 titanium alloy large-size ring material

Abstract

The application discloses a preparation method of TA7 titanium alloy large-size ring material. Firstly, a TA7 titanium alloy ingot is produced by smelting, the ingot is heated to above a phase transition point and kept for a certain time, then open-die forging is carried out, the forged blank is heated to above the phase transition point and below the phase transition point respectively and kept, a multi-fire upsetting and elongating process is adopted, a TA7 titanium alloy rod blank is prepared, finally, the rod blank is heated to a two-phase zone temperature and kept, then a forging forming is carried out, a TA7 titanium alloy pre-forging ring blank is obtained, finally, the pre-forging ring blank is heated to a two-phase zone and is formed by rolling, after heat treatment, a TA7 titanium alloy ring material finished product is obtained. The produced TA7 titanium alloy ring material can meet the requirements of users in aspects of an appearance size, comprehensive performance and flaw detection.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy preparation technology, specifically to a method for preparing large-size rings of TA7 titanium alloy. Background Technology

[0002] TA7 titanium alloy has advantages such as high specific strength, strong corrosion resistance, and good fracture toughness at both room temperature and high temperature. It is mainly used in key components such as aero-engine parts, space propulsion parts, and cryogenic storage devices. At the same time, this alloy has good weldability and corrosion resistance, can work in seawater environment, and is an ideal structural material for the shipbuilding industry.

[0003] TA7 titanium alloy has a nominal composition of Ti-5Al-2.5Sn and is a medium-strength single-phase α-type titanium alloy. Its crystal structure is close-packed hexagonal with few plastic deformation slip systems, resulting in significant difficulties in plastic processing. During industrial production, this material is extremely sensitive to temperature and prone to cracking, exhibiting significant intangible losses, which further increases the processing difficulty of TA7 titanium alloy.

[0004] Currently, TA7 titanium alloy products are being used more and more widely, with bars and discs being the most common applications, but some are also being used in large-diameter rings. TA7 titanium alloy rings manufactured using conventional forging processes currently suffer from several problems, including susceptibility to cracking and uneven deformation microstructure. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides a method for preparing large-size TA7 titanium alloy rings. The technical problem to be solved by this invention is achieved through the following technical solution:

[0006] A method for preparing large-size TA7 titanium alloy rings, comprising:

[0007] Step 1: TA7 titanium alloy ingots are produced by vacuum induction melting in a vacuum consumable arc furnace; the diameter of the TA7 titanium alloy ingots is ≥700mm and the weight is ≥3.5 tons;

[0008] Step 2: Heat the TA7 titanium alloy ingot to 1130~1200℃ and hold it for 150~660min. Then, forge it above the phase transformation point to obtain a TA7 titanium alloy cylindrical forging billet with a diameter of 400~550mm. The time from opening the furnace door to transferring the ingot to the forging machine is ≤90s.

[0009] Step 3: The TA7 titanium alloy cylindrical forging billet is radially sawn according to the design requirements to obtain multiple cylindrical billets with a height of 800~1200mm. The cylindrical billets are then heated to T. β+10~200)℃ and hold for 150~200min, then upset and draw the cylindrical billet above the phase transformation point, and then heat the cylindrical billet to T. β After holding at -20~50)℃ for 250~300min, the material is upsetting and then drawn in the two-phase region to prepare TA7 titanium alloy billets with a diameter of 400~550mm; wherein the final forging temperature is ≥850℃.

[0010] Step 4: Heat the TA7 titanium alloy billet to T β -(20~50)℃, then proceed with upsetting, punching and reaming in sequence to obtain a TA7 titanium alloy pre-forged ring billet with an outer diameter of 600~800mm, an inner diameter of 300~500mm, and a height of 300~500mm; wherein, the deformation amount of each forging pass during reaming is 10~30%, the pressing rate is 10~40mm / s, and the final forging temperature is ≥850℃;

[0011] Step 5: Heat the TA7 titanium alloy pre-forged ring billet to T β -(20~50)℃, and after holding for a time determined according to the pre-forged ring blank wall thickness mm × heat preservation coefficient 0.5~0.8min / mm, it is rolled into shape by a ring rolling mill, with a final rolling temperature ≥800℃, to obtain TA7 titanium alloy ring semi-finished product with an outer diameter of 800~900mm, an inner diameter of 550~700mm, and a height of 300~500mm;

[0012] Step 6: Heat treat the TA7 titanium alloy ring semi-finished product at a temperature of 700~850℃ and a holding time of 60~240min. After cooling, the TA7 titanium alloy ring finished product is obtained.

[0013] Furthermore, in step 2, the forging ratio of the initial forging is 2.2~3, and the deformation speed is 20~50mm / s.

[0014] Furthermore, in step 3, the cylindrical billet is subjected to upsetting and drawing 2 to 4 times above the phase transformation point, and to upsetting and drawing 1 to 2 times in the two-phase region; wherein the forging ratio per firing is 1.3 to 4, and the deformation speed is 20 to 40 mm / s.

[0015] Furthermore, in step 3, a glass coating is applied to the surface of the cylindrical blank before each heating.

[0016] Furthermore, in step 4, the time from opening the furnace door to transferring the billet to the forging machine is ≤90s, and the tooling used for reaming needs to be preheated before reaming, with a preheating temperature ≥150℃.

[0017] Further, in step 5, the rolling forming includes a stable ring rolling stage, a rapid expansion stage, a stable rolling expansion stage, a finish rolling stage, and a rounding stage; in the stable ring rolling stage, the linear speed of the mandrel is 600~1200mm / s; in the rapid expansion stage, the feed speed of the mandrel is 3~3.5mm / revolution; in the stable rolling expansion stage, the feed speed of the mandrel is 3.5~4.5mm / revolution; in the finish rolling stage, the feed speed of the mandrel is 3~3.5mm / revolution; and in the rounding stage, the feed speed of the mandrel is 0.4~0.5mm / revolution.

[0018] Furthermore, in step 5, the diameter of the core roller is 200~500mm, and the core roller pressure is 50~300KN.

[0019] The beneficial effects of this invention are:

[0020] 1. By designing a reasonable process route, the key technology for preparing large TA7 titanium alloy forgings was finally broken through. The dimensions, comprehensive performance and flaw detection level of the prepared large TA7 titanium alloy rings can meet the user's needs.

[0021] 2. The TA7 titanium alloy ring prepared by this invention has a room temperature tensile strength of over 785 MPa, a yield strength of over 730 MPa, an elongation after fracture of over 8%, a reduction of area of ​​over 23%, and an impact toughness of over 30 J / cm2. The microstructure is mostly equiaxed α structure with no complete original β grain boundaries. Ultrasonic testing meets the Class A standard requirements of the national standard GB / T5193-2020 "Ultrasonic Testing Methods for Titanium and Titanium Alloy Processed Products". This indicates that the TA7 titanium alloy ring prepared by this method has uniform microstructure at both high and low magnification and excellent room temperature mechanical properties, making it suitable for the industrial mass production of large-size TA7 titanium alloy rings.

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0023] Figure 1 ~ is the microstructure of the TA7 titanium alloy ring material prepared in Example 1 of this invention;

[0024] Figures 2-4 This is the mechanical property test report of the TA7 titanium alloy ring material in Example 1 of the present invention;

[0025] Figure 5 The ultrasonic flaw detection results are shown for the TA7 titanium alloy ring material prepared in Example 1 of this invention.

[0026] Figure 6 The microstructure of the TA7 titanium alloy ring material prepared in Example 2 of this invention;

[0027] Figures 7-8 This is the mechanical property test report of the TA7 titanium alloy ring material in Example 2 of the present invention;

[0028] Figure 9 The microstructure of the TA7 titanium alloy ring material prepared in Example 3 of this invention;

[0029] Figures 10-11 This is the mechanical property test report of the TA7 titanium alloy ring material in Example 3 of the present invention. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0031] Example 1

[0032] This invention provides a method for preparing a TA7 titanium alloy ring with an outer diameter of 845 mm, an inner diameter of 695 mm, and a height of 450 mm. The method specifically includes the following steps:

[0033] Step 1: According to the alloy composition of TA7 titanium alloy, select appropriate raw materials and use a hydraulic press to prepare TA7 titanium alloy electrodes with uniform composition. Then, use a vacuum induction melting furnace to obtain a TA7 titanium alloy ingot with a diameter of 704 mm and a weight of 4.0 tons. The titanium alloy ingot is composed of the following mass percentages: Al 4.7%~5.3%, Sn 2.1%~2.7%, Fe 0.38%~0.48%, O 0.10%~0.16%, and the remainder is Ti.

[0034] Specifically, the oxide scale on the surface of the TA7 titanium alloy ingot is removed by machining, and a 0.4mm thick anti-oxidation coating, TB1200-16, is applied to the surface of the machined TA7 titanium alloy ingot.

[0035] Step 2: The TA7 titanium alloy ingot is heated to 1150~1180℃ in a natural gas furnace and held at that temperature for 580 minutes before being removed from the furnace. A 10,000-ton press is used to forge the ingot above the β phase transformation point to obtain a TA7 titanium alloy cylindrical forging blank with a diameter of 450mm. Specifically, the time from opening the furnace door to transferring the ingot to the forging machine is 75s. The forging ratio of the forging blank is 2.2~3, and the deformation speed is 20~30mm / s.

[0036] Specifically, the heating process for the initial forging is as follows: the TA7 titanium alloy ingot is first preheated to a temperature of 800~850℃, held for at least 120 minutes, then heated again to 1150~1180℃, held for another 580 minutes, and then the initial forging is carried out.

[0037] Step 3: The TA7 titanium alloy cylindrical forging billet is radially sawed according to the design requirements to obtain multiple cylindrical billets with a height of 1000mm. The end of each cylindrical billet is chamfered. Then, the cylindrical billet is heated to 1050~1100℃ and held for 150min. Then, it is upsetting and drawing twice above the phase transformation point using a 10,000-ton press. The cylindrical billet is then heated to 980℃ and held for 270min. Then, it is upsetting and drawing once in the two-phase region using a 10,000-ton press to obtain a TA7 titanium alloy bar billet with a diameter of 550mm. The final forging temperature is ≥850℃, the forging ratio per forging is 1.3~3, and the deformation speed is 20~30mm / s.

[0038] In addition, before each heating cycle, a glass coating needs to be applied to the surface of the cylindrical billet. This glass coating serves to insulate and maintain the temperature, ensuring the initial and final forging temperatures. The main component of the glass coating is pure silicon dioxide (SiO2), extracted from quartz sand. Water, ethanol, or organic solvents can be added as a carrier, without the need for additional additives. For example, the liquid glass spray developed by the German company Nanopool contains only silicon dioxide and water / ethanol, forming an ultrathin film with a thickness of only 15-30 molecular layers.

[0039] Gleeble thermal simulation experiments demonstrate that the lower the forging temperature, the more prone the material is to cracking. The experiments also found that controlling the forging temperature above 700℃ can prevent cracking defects. Therefore, the forging temperature needs to be monitored in real time during the forging process. In this invention, the final forging temperature is controlled to be no less than 850℃. If the final forging temperature is lower than 850℃, the forging billet should be reheated in the furnace to ensure reduced defects. The reheating temperature is the same as the original heating temperature, and the holding time is 60-120 minutes. It is also essential to ensure that the initial forging temperature is above 900℃. After forging, the surface of the forging must be cleaned, and surface defects must be ground to prevent the defects from expanding or deepening in subsequent forging passes, which could affect subsequent forging.

[0040] Step 4: Heat the TA7 titanium alloy billet to 960~980℃, transfer the billet to a press for upsetting, punching and reaming in sequence to obtain a TA7 titanium alloy pre-forged ring billet with an outer diameter of 750mm, an inner diameter of 500mm and a height of 450mm. During reaming, the deformation amount per heat is 10~30%, the reaming rate is 10~40mm / s, and the final forging temperature is ≥850℃.

[0041] Specifically, the time from opening the furnace door to transferring the billet to the forging machine should be ≤90s; the dies and tools used for reaming should be preheated before reaming, with a preheating temperature ≥150℃; the deformation amount of each forging pass in upsetting and punching should be 10~30%; and the forging passes required for reaming should be 2~3 times.

[0042] Step 5: Heat the TA7 titanium alloy pre-forged ring billet to 960~980℃ and hold it for 125 minutes, then roll it into shape using a ring rolling mill. The final rolling temperature is ≥800℃, resulting in a TA7 titanium alloy ring semi-finished product with an outer diameter of 845mm, an inner diameter of 695mm, and a height of 450mm.

[0043] The entire rolling forming process includes a stable ring rolling stage, a rapid expansion stage, a stable rolling expansion stage, a finish rolling stage, and a rounding stage. In the stable ring rolling stage, the linear speed of the mandrel is 600~1200mm / s; in the rapid expansion stage, the feed speed of the mandrel is 3~3.5mm / revolution; in the stable rolling expansion stage, the feed speed of the mandrel is 3.5~4.5mm / revolution; in the finish rolling stage, the feed speed of the mandrel is 3~3.5mm / revolution; and in the rounding stage, the feed speed of the mandrel is 0.4~0.5mm / revolution.

[0044] Specifically, during the entire rolling process, the core roll used for the ring rolling has a diameter of 250mm, a core roll pressure of 150KN, a clamping roll pressure of 200KN, and a tapered roll pressure of 50KN.

[0045] Step 6: Heat treat the TA7 titanium alloy ring semi-finished product at a temperature of 800~850℃ for 200min. After cooling, the TA7 titanium alloy ring finished product is obtained.

[0046] Microstructure and mechanical properties of the TA7 titanium alloy ring obtained in Example 1 were analyzed. The scanning electron microscopy results are as follows: Figure 1 As shown, the microstructure of this ring material is basically composed of equiaxed and elongated primary α phases, as well as discontinuous network α phases at the original β grain boundaries, which meets the standard requirements; performance testing is as follows. Figures 2-4 As shown, the results indicate that the room temperature tensile, impact, low-magnification microstructure, and microstructure of the TA7 titanium alloy ring all meet the technical standard requirements; the flaw detection results of the TA7 titanium alloy ring are as follows. Figure 5 As shown, the flaw detection results meet the Class A standard requirements of GB / T5193-2020 "Ultrasonic Testing Methods for Titanium and Titanium Alloy Processed Products", proving that the processing technology and heat treatment process adopted by the preparation method of this invention for the large-size TA7 titanium alloy rings are reasonable and feasible.

[0047] Example 2

[0048] This invention provides a method for preparing a TA7 titanium alloy ring with an outer diameter of 830 mm, an inner diameter of 635 mm, and a height of 310 mm. The method specifically includes the following steps:

[0049] Step 1: According to the alloy composition of TA7 titanium alloy, select appropriate raw materials and use a hydraulic press to prepare TA7 titanium alloy electrodes with uniform composition. Then, use a vacuum induction melting furnace to obtain a TA7 titanium alloy ingot with a diameter of 704 mm and a weight of 3.8 tons. The titanium alloy ingot is composed of the following mass percentages: Al 4.7%~5.3%, Sn 2.1%~2.7%, Fe 0.38%~0.48%, O 0.10%~0.16%, and the remainder is Ti.

[0050] Specifically, the oxide scale on the surface of the TA7 titanium alloy ingot is removed by machining, and a 0.5mm thick anti-oxidation coating, TB1200-16, is applied to the surface of the machined TA7 titanium alloy ingot.

[0051] Step 2: The TA7 titanium alloy ingot is heated to 1160~1190℃ in a natural gas furnace and held at that temperature for 400 minutes before being removed from the furnace. A 10,000-ton press is used to forge the ingot above the β phase transformation point to obtain a TA7 titanium alloy cylindrical forging blank with a diameter of 430mm. Specifically, the time from opening the furnace door to transferring the ingot to the forging machine is 80s. The forging ratio of the forging blank is 2.2~2.5, and the deformation speed is 25~35mm / s.

[0052] Specifically, the heating process for the initial forging is as follows: the TA7 titanium alloy ingot is first preheated to a temperature of 800~850℃, held for at least 120 minutes, then heated again to 1160~1190℃, held for another 400 minutes, and then the initial forging is carried out.

[0053] Step 3: The TA7 titanium alloy cylindrical forging billet is radially sawed according to the design requirements to obtain multiple cylindrical billets with a height of 900mm. The end of each cylindrical billet is chamfered. Then, the cylindrical billet is heated to 1080~1150℃ and held for 180min. Then, it is upsetting and drawing twice in the two-phase region using a 10,000-ton press. The cylindrical billet is then heated to 990℃ and held for 300min. Then, it is upsetting and drawing twice in the two-phase region using a 10,000-ton press to obtain TA7 titanium alloy bar billets with a diameter of 550mm. The final forging temperature is ≥850℃, the forging ratio per forging is 1.3~2.5, and the deformation speed is 25~35mm / s.

[0054] In addition, a glass coating needs to be applied to the surface of the cylindrical billet before each heating. This glass coating serves to insulate and keep the temperature, ensuring the initial and final forging temperatures. This glass coating has been described in Example 1 and will not be repeated here.

[0055] Gleeble thermal simulation experiments demonstrate that the lower the forging temperature, the more prone the material is to cracking. The experiments also found that controlling the forging temperature above 700℃ can prevent cracking defects. Therefore, the forging temperature needs to be monitored in real time during the forging process. In this invention, the final forging temperature is controlled to be no less than 850℃. If the final forging temperature is lower than 850℃, the forging billet should be reheated in the furnace to ensure reduced defects. The reheating temperature is the same as the original heating temperature, and the holding time is 60-120 minutes. It is also essential to ensure that the initial forging temperature is above 900℃. After forging, the surface of the forging must be cleaned, and surface defects must be ground to prevent the defects from expanding or deepening in subsequent forging passes, which could affect subsequent forging.

[0056] Step 4: Heat the TA7 titanium alloy billet to 980~1000℃, transfer the billet to a press for upsetting, punching and reaming in sequence to obtain a TA7 titanium alloy pre-forged ring billet with an outer diameter of 730mm, an inner diameter of 480mm and a height of 310mm; wherein, the deformation amount of each forging is 10~30% during reaming, the reaming rate is 10~40mm / s, and the final forging temperature is ≥850℃.

[0057] Specifically, the time from opening the furnace door to transferring the billet to the forging machine should be ≤90s; the dies and tools used for reaming should be preheated before reaming, with a preheating temperature ≥150℃; the deformation amount of each forging pass in upsetting and punching should be 10~30%; and the forging passes required for reaming should be 2~3 times.

[0058] Step 5: Heat the TA7 titanium alloy pre-forged ring billet to 980~1000℃ and hold it for 163 minutes, then roll it into shape using a ring rolling mill. The final rolling temperature is ≥800℃, resulting in a TA7 titanium alloy ring semi-finished product with an outer diameter of 830mm, an inner diameter of 635mm, and a height of 310mm.

[0059] The entire rolling forming process includes a stable ring rolling stage, a rapid expansion stage, a stable rolling expansion stage, a finish rolling stage, and a rounding stage. In the stable ring rolling stage, the linear speed of the mandrel is 600~1200mm / s; in the rapid expansion stage, the feed speed of the mandrel is 3~3.5mm / revolution; in the stable rolling expansion stage, the feed speed of the mandrel is 3.5~4.5mm / revolution; in the finish rolling stage, the feed speed of the mandrel is 3~3.5mm / revolution; and in the rounding stage, the feed speed of the mandrel is 0.4~0.5mm / revolution.

[0060] Specifically, during the entire rolling process, the core roll used for the ring rolling has a diameter of 200mm, a core roll pressure of 250KN, a clamping roll pressure of 350KN, and a tapered roll pressure of 85KN.

[0061] Step 6: Heat treat the TA7 titanium alloy ring semi-finished product at a temperature of 750~800℃ for 120 minutes. After cooling, the TA7 titanium alloy ring finished product is obtained.

[0062] Microstructure and mechanical properties of the TA7 titanium alloy ring obtained in Example 2 were analyzed. The scanning electron microscopy results are as follows: Figure 6 As shown, the microstructure of this ring material is basically composed of equiaxed and elongated primary α phases, as well as discontinuous network α phases at the original β grain boundaries, which meets the standard requirements; performance testing is as follows. Figures 7-8 As shown, the results indicate that the room temperature tensile properties, impact properties, low-magnification microstructure, and microstructure of the TA7 titanium alloy ring all meet the technical standard requirements.

[0063] Example 3

[0064] This invention provides a method for preparing a TA7 titanium alloy ring with an outer diameter of 830 mm, an inner diameter of 635 mm, and a height of 312 mm. The method specifically includes the following steps:

[0065] Step 1: According to the alloy composition of TA7 titanium alloy, select appropriate raw materials and use a hydraulic press to prepare TA7 titanium alloy electrodes with uniform composition. Then, use a vacuum induction melting furnace to obtain a TA7 titanium alloy ingot with a diameter of 704 mm and a weight of 3.6 tons. The titanium alloy ingot is composed of the following mass percentages: Al 4.7%~5.3%, Sn 2.1%~2.7%, Fe 0.38%~0.48%, O 0.10%~0.16%, and the remainder is Ti.

[0066] Specifically, the oxide scale on the surface of the TA7 titanium alloy ingot is removed by machining, and a 0.5mm thick anti-oxidation coating, TB1200-16, is applied to the surface of the machined TA7 titanium alloy ingot.

[0067] Step 2: The TA7 titanium alloy ingot is heated to 1170~1200℃ in a natural gas furnace and held at that temperature for 350 minutes before being removed from the furnace. A 10,000-ton press is used to forge the ingot above the β phase transformation point to obtain a TA7 titanium alloy cylindrical forging blank with a diameter of 450mm. Specifically, the time from opening the furnace door to transferring the ingot to the forging machine is 85s. The forging ratio of the forging blank is 2.4~3, and the deformation speed is 35~40mm / s.

[0068] Specifically, the heating process for the initial forging is as follows: the TA7 titanium alloy ingot is first preheated to a temperature of 800~850℃, held for at least 120 minutes, then heated again to 1170~1200℃, held for another 350 minutes, and then the initial forging is carried out.

[0069] Step 3: The TA7 titanium alloy cylindrical forging billet is radially sawed according to the design requirements to obtain multiple cylindrical billets with a height of 1000mm. The end of each cylindrical billet is chamfered. Then, the cylindrical billet is heated to 1060~1170℃ and held for 200min. Then, it is upsetting and drawing twice above the phase transformation point using a 10,000-ton press. The cylindrical billet is then heated to 970℃ and held for 250min. Then, it is upsetting and drawing once in the two-phase region using a 10,000-ton press to obtain a TA7 titanium alloy bar billet with a diameter of 550mm. The final forging temperature is ≥850℃, the forging ratio per forging is 2.5~3.5, and the deformation speed is 35~40mm / s.

[0070] In addition, before each heating, a glass coating needs to be applied to the surface of the cylindrical billet. This glass coating serves to insulate and keep the temperature, ensuring the initial and final forging temperatures. This glass coating has been described in Example 1 and will not be repeated here.

[0071] Gleeble thermal simulation tests demonstrate that the lower the forging temperature, the more prone the material is to cracking. The tests also found that controlling the forging temperature above 700℃ can prevent cracking defects. Therefore, the forging temperature needs to be monitored in real time during the forging process. If the final forging temperature is below 850℃, the forging billet should be reheated in the furnace to ensure reduced defects. The reheating temperature should be the same as the original heating temperature, and the holding time should be 60-120 minutes. It is essential to ensure that the initial forging temperature is above 900℃. After forging, the surface of the forging must be cleaned, and surface defects should be ground to prevent the defects from expanding or deepening in subsequent forging passes, which could affect subsequent forging.

[0072] Step 4: Heat the TA7 titanium alloy billet to 990~1020℃, transfer the billet to a press for upsetting, punching and reaming in sequence to obtain a TA7 titanium alloy pre-forged ring billet with an outer diameter of 730mm, an inner diameter of 480mm and a height of 312mm; wherein, the deformation amount of each forging is 10~30% during reaming, the reaming rate is 10~40mm / s, and the final forging temperature is ≥850℃.

[0073] Specifically, the time from opening the furnace door to transferring the billet to the forging machine should be ≤90s; the dies and tools used for reaming should be preheated before reaming, with a preheating temperature ≥150℃; the deformation amount of each forging pass in upsetting and punching should be 10~30%; and the forging passes required for reaming should be 2~3 times.

[0074] Step 5: Heat the TA7 titanium alloy pre-forged ring billet to 960~980℃ and hold it for 125 minutes, then roll it into shape using a ring rolling mill. The final rolling temperature is ≥800℃, resulting in a TA7 titanium alloy ring semi-finished product with an outer diameter of 845mm, an inner diameter of 695mm, and a height of 450mm.

[0075] The entire rolling forming process includes a stable ring rolling stage, a rapid expansion stage, a stable rolling expansion stage, a finish rolling stage, and a rounding stage. In the stable ring rolling stage, the linear speed of the mandrel is 600~1200mm / s; in the rapid expansion stage, the feed speed of the mandrel is 3~3.5mm / revolution; in the stable rolling expansion stage, the feed speed of the mandrel is 3.5~4.5mm / revolution; in the finish rolling stage, the feed speed of the mandrel is 3~3.5mm / revolution; and in the rounding stage, the feed speed of the mandrel is 0.4~0.5mm / revolution.

[0076] Specifically, during the entire rolling process, the core roll used for the ring rolling has a diameter of 200mm, a core roll pressure of 250KN, a clamping roll pressure of 150KN, and a tapered roll pressure of 35KN.

[0077] Step 6: The TA7 titanium alloy ring semi-finished product is subjected to heat treatment at a temperature of 700~750℃ and a holding time of 80min. After cooling, the TA7 titanium alloy ring finished product is obtained.

[0078] Microstructure and mechanical properties of the TA7 titanium alloy ring obtained in Example 3 were analyzed. The scanning electron microscopy results are as follows: Figure 9 As shown, the microstructure of this ring material is basically composed of equiaxed and elongated primary α phases, as well as discontinuous network α phases at the original β grain boundaries, which meets the standard requirements; performance testing is as follows. Figures 10-11 As shown, the results indicate that the room temperature tensile properties, impact properties, low-magnification microstructure, and microstructure of the TA7 titanium alloy ring all meet the technical standard requirements.

[0079] Based on the test reports of Examples 1 to 3, the TA7 titanium alloy ring prepared by this invention has a tensile strength of over 785 MPa, an elongation after fracture of over 8%, a reduction of area of ​​over 23%, and an impact toughness of over 30 J / cm2. Through data analysis, the TA7 ring exhibits a good match between strength, plasticity, and toughness, and has excellent comprehensive performance.

[0080] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing large-size TA7 titanium alloy rings, characterized in that, include: Step 1: TA7 titanium alloy ingots are produced by vacuum induction melting in a vacuum consumable arc furnace; the diameter of the TA7 titanium alloy ingots is ≥700mm and the weight is ≥3.5 tons; Step 2: Heat the TA7 titanium alloy ingot to 1130~1200℃ and hold it for 150~660min. Then, forge it above the phase transformation point to obtain a TA7 titanium alloy cylindrical forging billet with a diameter of 400~550mm. The time from opening the furnace door to transferring the ingot to the forging machine is ≤90s. Step 3: The TA7 titanium alloy cylindrical forging billet is radially sawn according to the design requirements to obtain multiple cylindrical billets with a height of 800~1200mm. The cylindrical billets are then heated to T. β +10~200)℃ and hold for 150~200min, then upset and draw the cylindrical billet above the phase transformation point, and then heat the cylindrical billet to T. β After holding at -20~50)℃ for 250~300min, the material is upsetting and then drawn in the two-phase region to prepare TA7 titanium alloy billets with a diameter of 400~550mm; wherein the final forging temperature is ≥850℃. Step 4: Heat the TA7 titanium alloy billet to T β -(20~50)℃, then proceed with upsetting, punching and reaming in sequence to obtain a TA7 titanium alloy pre-forged ring billet with an outer diameter of 600~800mm, an inner diameter of 300~500mm and a height of 300~500mm; wherein, the deformation amount of each forging pass during reaming is 10~30%, the pressing rate is 10~40mm / s, and the final forging temperature is ≥850℃; Step 5: Heat the TA7 titanium alloy pre-forged ring billet to T β -(20~50)℃, and after holding for a time determined according to the pre-forged ring blank wall thickness mm × heat preservation coefficient 0.5~0.8min / mm, it is rolled into shape by a ring rolling mill, with a final rolling temperature ≥800℃, to obtain TA7 titanium alloy ring semi-finished product with an outer diameter of 800~900mm, an inner diameter of 550~700mm, and a height of 300~500mm; Step 6: Heat treat the TA7 titanium alloy ring semi-finished product at a temperature of 700~850℃ and a holding time of 60~240min. After cooling, the TA7 titanium alloy ring finished product is obtained.

2. The method for preparing large-size TA7 titanium alloy rings according to claim 1, characterized in that, In step 2, the forging ratio of the initial forging is 2.2~3, and the deformation speed is 20~50mm / s.

3. The method for preparing large-size TA7 titanium alloy rings according to claim 1, characterized in that, In step 3, the cylindrical billet is subjected to upsetting and drawing 2 to 4 times above the phase transformation point, and upsetting and drawing 1 to 2 times in the two-phase region; wherein the forging ratio per firing is 1.3 to 4, and the deformation speed is 20 to 40 mm / s.

4. The method for preparing large-size TA7 titanium alloy rings according to claim 3, characterized in that, Before each heating cycle, a glass coating is applied to the surface of the cylindrical blank.

5. The method for preparing large-size TA7 titanium alloy rings according to claim 1, characterized in that, In step 4, the time from opening the furnace door to transferring the billet to the forging machine is ≤90s. Before expanding the hole, the tooling used for expanding the hole needs to be preheated, and the preheating temperature is ≥150℃.

6. The method for preparing large-size TA7 titanium alloy rings according to claim 1, characterized in that, In step 5, the rolling forming includes a stable ring rolling stage, a rapid expansion stage, a stable rolling expansion stage, a finish rolling stage, and a rounding stage. In the stable ring rolling stage, the linear speed of the mandrel is 600~1200mm / s; in the rapid expansion stage, the feed speed of the mandrel is 3~3.5mm / revolution; in the stable rolling expansion stage, the feed speed of the mandrel is 3.5~4.5mm / revolution; in the finish rolling stage, the feed speed of the mandrel is 3~3.5mm / revolution; and in the rounding stage, the feed speed of the mandrel is 0.4~0.5mm / revolution.

7. The method for preparing large-size TA7 titanium alloy rings according to claim 6, characterized in that, The core roller has a diameter of 200~500mm and a core roller pressure of 50~300KN.

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