Integral beta annealing aging state Ti55531 titanium alloy bar and preparation method thereof

Abstract

The invention discloses an integral beta annealing aging state Ti55531 titanium alloy bar and a preparation method thereof. The preparation method comprises the following steps: preparing raw materials, and smelting a titanium alloy cast ingot; the cast ingot is heated and subjected to heat preservation, air cooling is conducted after 1-2 heating number forging is conducted, and an intermediate blank is obtained; the intermediate blank is heated, subjected to heat preservation, forged for 4-8 heating numbers and then subjected to air cooling, and a round bar with the specification ranging from phi 100 mm to phi 160 mm is obtained; the round bar is directly subjected to overall beta annealing heat treatment to obtain a finished bar or serves as a blank to be rolled to obtain a small-specification rolled bar, and then annealing heat treatment is conducted; and finally, a finished bar is obtained. The finished bar is obtained by adopting a forging and rolling method, and the obtained finished bar is uniform in macrostructure and good in grain refinement degree; and the strength-plasticity-toughness regulation and control of the finished bar is realized. According to the method, the whole beta annealing aging heat treatment link is added, the preparation heating number is small, the process is short, and the preparation period of aeronautical parts is greatly shortened.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy materials, and in particular relates to an integral beta annealed Ti55531 titanium alloy bar, and also relates to a preparation method of the integral beta annealed Ti55531 titanium alloy bar. Background Art

[0002] The nominal composition of Ti55531 titanium alloy is Ti-5Al-5Mo-5V-3Cr-1Zr. It has the characteristics of high strength, high toughness and high hardenability. It is known as the most advanced titanium alloy material for structural parts in the world. It is suitable for the preparation of aircraft landing gear, wings, wing joints, suspension joints and other parts. It has been maturely applied in aircraft such as Airbus A308.

[0003] Ti55531 titanium alloy belongs to metastable β-type titanium alloy, with narrow forging temperature window, large deformation resistance in forging process, and poor forging permeability. At present, the production process of Ti55531 titanium alloy parts mainly includes: ingot melting, bar forming, forging, heat treatment, and machining to prepare parts, with low material utilization rate. Therefore, the manufacturing process is optimized on the basis of the original forging process. Through the overall heat treatment of bars and the preparation process of directly machining parts, the finished product can meet the requirements of aviation parts and other industries. At the same time, the forging process can be omitted, which greatly improves the material utilization rate and reduces the production cycle and production cost of parts. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing an integral beta annealed Ti55531 titanium alloy bar, so as to solve the problems of poor consistency of the structure of small-sized Ti55531 titanium alloy bars prepared by the existing forging method and high difficulty in matching the mechanical properties and plasticity. At the same time, the production cycle of small-sized Ti55531 titanium alloy bars used in the aerospace field is shortened.

[0005] The present invention also aims to provide an integral beta annealed Ti55531 titanium alloy bar.

[0006] The first technical solution adopted by the present invention is: a method for preparing an integral β-annealed Ti55531 titanium alloy bar, and the specific operation steps are as follows:

[0007] Step 1, ingot smelting: prepare raw materials, mix materials and prepare electrode blocks, weld the electrode blocks into consumable electrodes, and then perform vacuum smelting three times. After surface machining, obtain Ti55531 titanium alloy ingots with a specification of 650 mm to 750 mm;

[0008] Step 2, blank forging: heating and keeping the ingot warm, forging for 1 to 2 times and then air cooling to obtain an intermediate blank;

[0009] Step 3, intermediate forging: heating and heat-insulating the intermediate billet, forging for 4 to 8 times, and then air-cooling to obtain round bars with a specification of 100 mm to 160 mm; the round bars can be directly subjected to the overall β annealing heat treatment in step 5 to obtain finished bars or used as billets to carry out the bar rolling in step 4 to obtain small-sized rolled bars;

[0010] Step 4, bar rolling: heating and heat preservation of the round bar, rolling for 2 to 3 times and then cooling in air to obtain a rolled bar of 30 mm to 100 mm in diameter;

[0011] Step 5: Overall β annealing aging heat treatment: Place the rolled bar into a muffle furnace or a resistance box heating furnace and heat it to (T β -80~30)℃, keep warm for 30min~180min; then heat with the furnace to (T β +10~30)℃, keep warm for at least 30min; then cool to 500℃~600℃ with the furnace, keep warm for 360min~600min, the cooling rate should be controlled at 1.5℃ / min~3.5℃ / min during the cooling process; finally air cool to room temperature to obtain the finished bar; where T β is the phase transition temperature.

[0012] The present invention is also characterized in that:

[0013] The composition of Ti55531 titanium alloy rod is Ti-5Al-5Mo-5V-3Cr-1Zr, which includes Al: 4.0%~6.0%, Mo: 4.5%~6.0%, V: 4.5%~6.0%, Cr: 2.0%~3.6%, Fe: 0.2%~0.5%, Zr: 0.3%~2.0%, and the balance is Ti and unavoidable impurities.

[0014] Step 1 is as follows:

[0015] According to the above-mentioned Ti55531 titanium alloy bar standard, raw materials are prepared, mixed and pressed into electrode blocks, multiple electrode blocks are combined, and plasma welding is used to prepare consumable electrodes under argon protection. After three vacuum consumable melting, ingot blanks are obtained, and Ti55531 titanium alloy ingots with specifications of Ф650mm~Ф750mm are obtained after surface machining.

[0016] Step 2 is as follows:

[0017] For the Ti55531 titanium alloy ingot obtained in step 1, 1 to 2 fire forgings are performed at 250°C to 350°C above the phase transformation point, 2 to 3 upsetting and drawing operations are completed in each forging, the cumulative forging ratio of each fire is 7.0 to 13.8, the forging methods are upsetting, rounding and inverting, and the surface cracks of the material are polished after air cooling during forging; the starting forging temperature of each fire is not lower than 50°C to 150°C above the phase transformation point, and the final forging temperature is not lower than 20°C to 100°C below the phase transformation point to obtain an intermediate billet.

[0018] Step 3 is as follows:

[0019] The intermediate billet obtained in step 2 is subjected to 2-4 forgings at 80°C below the phase transformation point and 150°C above the phase transformation point, which is divided into 1-2 heatings at 40°C to 80°C below the phase transformation point and 1-2 heatings at 50°C to 150°C above the phase transformation point; the forging ratio of each fire is 2.5-6.0, the forging methods are upsetting, square drawing, flattening and inverting, the cooling method after forging is air cooling, and the surface cracks of the material are polished after forging air cooling to obtain a billet with a regular octagonal or rectangular cross section;

[0020] Among them, the initial forging temperature of each fire in the two-phase zone shall not be lower than 60℃~150℃ below the phase transformation point, and the final forging temperature shall not be lower than 150℃~250℃ below the phase transformation point; the initial forging temperature of each fire in the single-phase zone shall not be lower than 30℃~80℃ below the phase transformation point, and the final forging temperature shall not be lower than 80℃~150℃ below the phase transformation point;

[0021] The blanks forged above are reheated at 40°C to 80°C below the phase transformation point, the holding time is 6h to 9h, and then 1 to 2 rounds of forging are performed, the forging ratio of each round is 1.2 to 3.0, the forging method is upsetting and inverting, the forging process adopts the method of returning to the furnace to make up the temperature, and the material surface cracks are polished after forging; the starting forging temperature of each round is not lower than 60°C to 150°C below the phase transformation point, and the final forging temperature is not lower than 150°C to 250°C below the phase transformation point, so as to obtain the octagonal blank;

[0022] The octagonal billet is subjected to forming forging: the billet is heated to 40℃~80℃ below the phase transition point, and the holding time is 6h~9h; then 1~2 rounds of forging are carried out, the forging ratio is 0.8~2.2, the forging method is straight drawing, chamfering and rounding, and the billet shape is changed from octagonal billet to Ф100mm~Ф160mm round bar, the forging process adopts the method of returning to the furnace to make up the temperature, and the surface cracks of the material are polished after forging air cooling;

[0023] Among them, the initial forging temperature of each forming forging is not lower than 80℃~200℃ below the phase transformation point, and the final forging temperature is not lower than 150℃~300℃ below the phase transformation point.

[0024] Step 4 is as follows:

[0025] The round bar to be rolled obtained in step 3 is heated to 40°C to 80°C below the phase transition point, and the holding time is 2h to 6h; 1 to 2 rounds of rolling are performed, the rolling method is bidirectional multi-pass rolling, and the total rolling deformation of the passes is 170% to 400%, and then air-cooled, sawed, and ground to obtain a 80mm to 120mm bar blank;

[0026] The rolled bar billet is heated to 40°C to 80°C below the phase transformation point, and the holding time is 1h to 3h; one fire rolling is performed, and the rolling method is bidirectional multi-pass rolling, and the total rolling deformation is 140% to 700%. After the rolling is completed, one straightening is performed to obtain a rolled bar of Ф30mm to Ф100mm.

[0027] Step 5 is as follows:

[0028] Place the round bars or rolled bars to be heat treated in a muffle furnace or resistance box heating furnace that can control the cooling rate. The temperature error of the heat treatment furnace must be controlled within ±5°C. When multiple round bars or bars are heat treated at the same time, the interval between the bars should be controlled to be greater than 150mm. The bars are heated from room temperature to (T β -80~30)℃, keep warm for 30min~180min after reaching temperature; then heat with furnace to (T β +10~30)℃, keep warm for at least 30min; then cool to 500℃~600℃ with the furnace, keep warm for 360min~600min, and the cooling rate should be controlled at 1.5℃ / min~3.5℃ / min during the cooling process; finally, air cool it to room temperature to obtain β annealing and aging state bars, and then through machining and finishing, finally obtain finished bars of Ф30mm~Ф150mm.

[0029] The second technical solution adopted by the present invention is: an integral β-annealed Ti55531 titanium alloy rod, the Ti55531 titanium alloy rod composition is Ti-5Al-5Mo-5V-3Cr-1Zr, and includes, by mass percentage, Al: 4.0% to 6.0%, Mo: 4.5% to 6.0%, V: 4.5% to 6.0%, Cr: 2.0% to 3.6%, Fe: 0.2% to 0.5%, Zr: 0.3% to 2.0%, and the remainder is Ti and unavoidable impurities.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] Compared with the small-sized Ti55531 titanium alloy bar solution produced by traditional processes, the finished bar is obtained by the forging + rolling method. The finished bar obtained by the new solution has uniform low-magnification structure and good grain refinement. The overall β annealing aging heat treatment link is added to achieve the strength-plasticity-toughness regulation of the finished bar. The mechanical properties of the Ti55531 titanium alloy bar prepared by this method meet the standard requirements of aviation materials, with fewer preparation fires and a short process, which meets the requirements of large-scale industrial production. At the same time, the finished bar can be directly machined into parts, which greatly shortens the preparation cycle of aviation parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0033] Figure 1 This is a typical macrostructure of the Φ50 mm rod prepared in Example 4;

[0034] Figure 2 This is a typical transverse metallographic microstructure of the Φ50 mm bar prepared in Example 4 after overall heat treatment;

[0035] Figure 3 This is a typical longitudinal metallographic microstructure of the Ø50 mm bar prepared in Example 4 after overall heat treatment;

[0036] Figure 4 This is the inverse pole figure of the Ø50 mm bar prepared in Example 4 after overall heat treatment;

[0037] Figure 5 This is a typical macrostructure of the Φ150 mm rod prepared in Example 5;

[0038] Figure 6 This is a typical transverse metallographic microstructure of the Φ150 mm bar prepared in Example 5 after overall heat treatment;

[0039] Figure 7 This is a typical longitudinal metallographic microstructure of the Φ150 mm bar prepared in Example 5 after overall heat treatment;

[0040] Figure 8 This is the inverse pole figure of the Φ150 mm bar prepared in Example 5 after overall heat treatment;

[0041] Fig. 9 It is a schematic diagram of the heat treatment process flow of the present invention. DETAILED DESCRIPTION

[0042] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] Example 1

[0044] The integral beta annealed Ti55531 titanium alloy rod of the present invention has components of Ti-5Al-5Mo-5V-3Cr-1Zr, and comprises, by mass percentage, 4.0% to 6.0% of Al, 4.5% to 6.0% of Mo, 4.5% to 6.0% of V, 2.0% to 3.6% of Cr, 0.2% to 0.5% of Fe, 0.3% to 2.0% of Zr, and the remainder is Ti and unavoidable impurities.

[0045] Example 2

[0046] The raw materials processed by the preparation method of the present invention are sponge titanium and intermediate alloy. The preparation process is divided into five parts: ingot smelting → blank forging → intermediate forging → bar rolling → overall heat treatment, and finally a finished bar with a diameter of 30 mm to 150 mm is obtained. The length of the bar is in the range of 1000 mm to 6000 mm, which fully meets the production requirements of Ti55531 titanium alloy bars required by aerospace and other industries. The specific operation steps are as follows:

[0047] Step 1, ingot smelting: prepare raw materials, mix materials and prepare electrode blocks, weld the electrode blocks into consumable electrodes, and then perform vacuum smelting three times. After surface machining, obtain Ti55531 titanium alloy ingots with a specification of 650 mm to 750 mm;

[0048] Step 2, blank forging: heating and keeping the ingot warm, forging for 1 to 2 times and then air cooling to obtain an intermediate blank;

[0049] Step 3, intermediate forging: heating and heat-insulating the intermediate billet, forging for 4 to 8 times, and then air-cooling to obtain round bars with a specification of 100 mm to 160 mm; the round bars can be directly subjected to the overall β annealing heat treatment in step 5 to obtain finished bars or used as billets to carry out the bar rolling in step 4 to obtain small-sized rolled bars;

[0050] Step 4, bar rolling: heating and heat preservation of the round bar, rolling for 2 to 3 times and then cooling in air to obtain a rolled bar of 30 mm to 100 mm in diameter;

[0051] Step 5: Overall β annealing aging heat treatment: Place the rolled bar into a muffle furnace or a resistance box heating furnace and heat it to (T β-80~30)℃, keep warm for 30min~180min; then heat with the furnace to (T β +10~30)℃, keep warm for at least 30min; then cool to 500℃~600℃ with the furnace, keep warm for 360min~600min, the cooling rate should be controlled at 1.5℃ / min~3.5℃ / min during the cooling process; finally air cool to room temperature to obtain the finished bar; where T β is the phase transition temperature.

[0052] Example 3

[0053] Step 1, ingot smelting: prepare raw materials, mix materials and prepare electrode blocks, weld the electrode blocks into consumable electrodes, and then perform vacuum smelting three times. After surface machining, obtain Ti55531 titanium alloy finished ingots with a specification of 650 mm to 750 mm.

[0054] The specific process is: prepare raw materials, mix and press into electrode blocks, combine multiple electrode blocks under argon protection and use plasma welding to prepare consumable electrodes, then undergo three vacuum consumable smelting to obtain ingot blanks, and after surface machining, obtain Ti55531 titanium alloy finished ingots with specifications of Ф650mm~Ф750mm.

[0055] Step 2, blank forging: heating and keeping the ingot warm, forging for 1 to 2 times and then cooling in air to obtain an intermediate blank;

[0056] The specific process is: for the Ti55531 large-size titanium alloy ingot obtained in step 1, 1 to 2 fire forgings are performed at 250°C to 350°C above the phase transformation point, 2 to 3 upsetting and drawing operations are completed in each forging, the cumulative forging ratio of each fire is 7.0 to 13.8, the forging methods are upsetting, rounding and inverting, and the surface cracks of the material are polished after air cooling; the starting forging temperature of each fire is not lower than 50°C to 150°C above the phase transformation point, and the final forging temperature is not lower than 20°C to 100°C below the phase transformation point to obtain an intermediate billet.

[0057] Step 3, intermediate forging: the intermediate billet is heated and kept warm, and then forged for 4 to 8 times and then cooled in air to obtain a round bar with a specification of 100 mm to 160 mm. The round bar can be directly subjected to the overall β annealing heat treatment in step 5 to obtain a finished bar or used as a billet to perform the bar rolling in step 4 to obtain a rolled bar with a smaller specification;

[0058] The specific process is: for the intermediate billet obtained in step 2, 2 to 4 forgings are performed at 80°C below the phase transformation point and 150°C above the phase transformation point, which is divided into 1 to 2 heatings with a temperature of 40°C to 80°C below the phase transformation point and 1 to 2 heatings with a temperature of 50°C to 150°C above the phase transformation point; the forging ratio of each fire is 2.5 to 6.0, the forging methods are upsetting, square drawing, flattening and octagonal drawing, the cooling method after forging is air cooling, and the surface cracks of the material are polished after air cooling; the initial forging temperature of each fire in the two-phase zone is not lower than 60°C to 150°C below the phase transformation point, and the final forging temperature is not lower than 150°C to 250°C below the phase transformation point; the initial forging temperature of each fire in the single-phase zone is not lower than 30°C to 80°C below the phase transformation point, and the final forging temperature is not lower than 80°C to 150°C below the phase transformation point; a billet with a regular octagonal (octagonal billet) or rectangular cross-section is obtained.

[0059] The blank that has completed the above forging is reheated at 40℃~80℃ below the phase transformation point, and the holding time is 6h~9h, and then 1~2 fire forgings are carried out, and the forging ratio of each fire is 1.2~3.0, the forging method is upsetting and inverting, and the forging process adopts returning to the furnace to replenish temperature, and the material surface cracks are air-cooled and polished after forging; the starting forging temperature of each fire is not lower than 60℃~150℃ below the phase transformation point, and the final forging temperature is not lower than 150℃~250℃ below the phase transformation point to obtain an octagonal blank.

[0060] The octagonal billet is heated to 40℃~80℃ below the phase transformation point, and the holding time is 6h~9h; then 1~2 fire forgings are performed, the forging ratio is 0.8~2.2, the forging method is straight drawing, chamfering and rounding, the billet shape is changed from octagonal billet to Ф100mm~Ф160mm round bar, the forging process adopts reheating, and the surface cracks of the material are polished after forging air cooling; the initial forging temperature of each forming forging is not lower than 80℃~200℃ below the phase transformation point, and the final forging temperature is not lower than 150℃~300℃ below the phase transformation point. The round bar after forging can be directly subjected to the overall β annealing aging heat treatment in step 5 to obtain the finished bar or used as the billet to be subjected to the bar rolling in step 4 to obtain the rolled bar with smaller specifications.

[0061] Step 4, bar rolling: heating and heat preservation of the intermediate bar billet, rolling for 2 to 3 times and then cooling in air to obtain a 30 mm to 100 mm Ø rolled bar;

[0062] The specific process is: for the intermediate bar blank to be rolled obtained in step 3, heat it to 40°C to 80°C below the phase change point, and keep it warm for 2h to 6h; perform 1 to 2 rounds of rolling, the rolling method is bidirectional multi-pass rolling, and the total rolling deformation is 170% to 400%, and then obtain Ф80mm to Ф120mm bar blanks through air cooling, sawing, and grinding.

[0063] For the bar billet to be rolled into finished product, it is heated to 40℃~80℃ below the phase transformation point, and the holding time is 1h~3h; it is rolled once, the rolling method is two-way multi-pass rolling, the total rolling deformation is 140%~700%, and after rolling is completed, it is straightened once to obtain a rolled bar of Ф30mm~Ф100mm.

[0064] Step 5: Overall β annealing aging heat treatment: Place the rolled bar into a muffle furnace or a resistance box heating furnace that can control the cooling rate, and heat it to (T β -80~30)℃, keep warm for 30min~180min; then heat with the furnace to (T β +10~30)℃, keep warm for at least 30min; then cool to 500℃~600℃ with the furnace, keep warm for 360min~600min, the cooling rate should be controlled at 1.5℃ / min~3.5℃ / min during the cooling process; finally air cool to room temperature to obtain the finished bar.

[0065] The specific process is: place the round bar or rolled bar to be heat treated in a muffle furnace or resistance box heating furnace with controlled cooling speed. The temperature error of the heat treatment furnace must be controlled within ±5℃. It should be noted that when multiple bars are heat treated at the same time, the interval between the bars should be controlled to be greater than 150mm. The bar is heated from room temperature to (T β -80~30)℃, keep warm for 30min~180min after reaching temperature; then heat with furnace to (T β +10~30)℃, keep warm for at least 30min; then cool to 500℃~600℃ with the furnace, keep warm for 360min~600min, and the cooling rate should be controlled at 1.5℃ / min~3.5℃ / min during the cooling process; finally, air cool it to room temperature to obtain β annealing and aging state bars, and then through machining and finishing, finally obtain finished bars of Ф30mm~Ф150mm.

[0066] Example 4

[0067] The preparation method of the present invention is used to prepare finished rods with a specification of Ф50mm.

[0068] Step 1: Ingot Melting

[0069] The raw materials are prepared, mixed and pressed into electrode blocks, and multiple electrode blocks are combined under argon protection and plasma welding is used to prepare consumable electrodes. The consumable electrodes are subjected to three vacuum consumable electrode melting and surface machining to become Ti55531 titanium alloy finished ingots with a specification of Ф690mm and a weight of 4700kg. The phase change point of the ingot is 835±10℃.

[0070] Step 2: Forging

[0071] The Ti55531 titanium alloy ingot weighing 4700kg was sawn into three equal parts and forged in two rounds. The forging methods of each round include upsetting, drawing and inverting. The forging ratio of a single round is controlled at 8.0-11.5 to fully break the grains. The initial forging temperature of each round should be greater than 930℃, and the final forging temperature should be greater than 810℃. After the material is forged, the surface cracks are polished to obtain the intermediate billet.

[0072] Step 3: Intermediate forging

[0073] The intermediate billet is forged 4 times in total, specifically 1 time forging at 40℃ below the phase transformation point, 1 time forging at 100℃ above the phase transformation point, and 2 times forging at 40℃ below the phase transformation point. The first time is two-phase zone forging, the forging content is upsetting and drawing, the forging ratio is 3.0-4.5, the starting temperature should be greater than 700℃, and the final forging temperature should be greater than 600℃. The second time is single-phase zone forging, the forging content is upsetting and drawing, the forging ratio is controlled at 3.8-5.5, the starting temperature should be greater than 850℃, and the final forging temperature should be greater than 750℃. The third time is two-phase zone forging, the forging content is upsetting, drawing and inverted, the forging ratio is controlled at 1.5-2.5, the starting temperature should be greater than 700℃, and the final forging temperature should be greater than 600℃. The fourth forging is two-phase zone forging, which includes chamfering and rounding. The forging ratio is controlled at 1.0-1.5. The starting temperature should be greater than 700℃, and the final forging temperature should be greater than 600℃. After each forging, the billet is air-cooled and the surface cracks are polished. The billet size after 4 forgings is Ф160mm, with uniform structure and fully refined grains, and the size is about 300μm-400μm.

[0074] Step 4: Bar rolling

[0075] The 160mm round bar billet is heated to 60℃ below the phase change point and kept warm for 3h; it is rolled once, and the rolling method is bidirectional multi-pass rolling, and the rolling deformation is 260%. After the billet is air-cooled, it is sawed and ground to obtain a 100mm round bar billet. For the 100mm round bar billet to be rolled into the finished product, it is heated to 60℃ below the phase change point and kept warm for 2h; it is rolled once, and the rolling deformation is 330%. After rolling, the residual heat is used for straightening once, and the black skin bar with a diameter of 55mm is obtained.

[0076] Step 5: Overall β annealing heat treatment

[0077] The Ф55mm black skin bar to be heat treated is placed in a resistance box heating furnace with controlled cooling speed. It should be noted that the bar spacing is greater than 150mm. The bar is heated from room temperature to 800℃ with the furnace, and then kept warm for 1h, then heated to 870℃, kept warm for 1h, then cooled to 580℃ at a controlled cooling rate of 2.0℃ / min, kept warm for 7h, and then air-cooled to room temperature to obtain the heat-treated black skin bar, and then machined and refined to finally obtain the Ф50mm finished bar.

[0078] Figure 1 This is a typical macrostructure of the rod prepared in Example 4; Figure 2 This is a typical transverse metallographic microstructure of the rod prepared in Example 4 after overall heat treatment; Figure 3 This is a typical longitudinal metallographic microstructure of the rod prepared in Example 4 after overall heat treatment; Figure 4 It is the inverse pole figure (IPF) and grain size of the rod prepared in Example 4 after overall heat treatment. Figure 1-Figure 4 It can be seen that the bar has a uniform structure after forging, and the grains are uniformly broken and refined after overall heat treatment, with good anisotropy. The room temperature performance results of the Ti55531 titanium alloy bar prepared in Example 4 are shown in Table 1. The tensile strength R m The average value can reach 1184MPa, the elongation strength R p The average value can reach 1081MPa, the average value of elongation A can reach 13.4%, the average value of cross-sectional shrinkage Z can reach 26.8%, the average value of impact absorption energy KU2 can reach 30.9J, and the fracture toughness K IC The average value can reach 80MPa·m 0.5 ; The extreme difference between the head, middle and tail is also very small, and the material consistency is very high; the strength, plasticity and toughness of the rod are well matched.

[0079] Table 1. Room temperature properties of Ti55531 titanium alloy Ф50mm bar β annealed

[0080]

[0081]

[0082] Example 5

[0083] The preparation method of the present invention is used to prepare finished rods with a specification of Ф150mm.

[0084] Step 1: Ingot Melting

[0085] The raw materials are prepared, mixed and pressed into electrode blocks, and multiple electrode blocks are combined under argon protection and plasma welding is used to prepare consumable electrodes. The consumable electrodes are subjected to three vacuum consumable electrode melting and surface machining to become Ti55531 titanium alloy finished ingots with a specification of Ф690mm and a weight of 4900kg. The phase change point of the ingot is 835±10℃.

[0086] Step 2: Forging

[0087] The Ti55531 titanium alloy ingot weighing 4900kg was sawn into three equal parts and forged in two rounds. The forging methods of each round include upsetting, drawing and inverting. The forging ratio of a single round is controlled at 8.0-11.5 to fully break the grains. The initial forging temperature of each round should be greater than 930℃, and the final forging temperature should be greater than 810℃. After the material is forged, the surface cracks are polished to obtain the intermediate billet.

[0088] Step 3: Intermediate forging

[0089] The intermediate billet is forged 4 times in total, specifically 1 time forging at 40℃ below the phase transformation point, 1 time forging at 100℃ above the phase transformation point, and 2 times forging at 40℃ below the phase transformation point. The first time is two-phase zone forging, the forging content is upsetting and drawing, the forging ratio is 3.2-4.6, the starting temperature should be greater than 700℃, and the final forging temperature should be greater than 600℃. The second time is single-phase zone forging, the forging content is upsetting and drawing, the forging ratio is controlled at 3.9-5.6, the starting temperature should be greater than 850℃, and the final forging temperature should be greater than 750℃. The third time is two-phase zone forging, the forging content is upsetting, drawing and inverted, the forging ratio is controlled at 1.6-2.7, the starting temperature should be greater than 700℃, and the final forging temperature should be greater than 600℃. The fourth forging is two-phase zone forging, which includes chamfering and rounding. The forging ratio is controlled at 1.2-1.6. The starting temperature should be greater than 700℃, and the final forging temperature should be greater than 600℃. After each forging, the billet is air-cooled and the surface cracks are polished. The billet size after 4 forgings is Ф160mm, with uniform structure and fully refined grains, and the size is about 300μm-400μm.

[0090] Step 5: Overall β annealing heat treatment

[0091] Two 160mm Ø forged bars to be heat treated are placed in a resistance box heating furnace with controlled cooling rate. Note that the distance between bars is greater than 150mm. The bars are heated from room temperature to 800℃, kept warm for 1.5h, then heated to 870℃, kept warm for 1.5h, then cooled to 570℃ at a controlled cooling rate of 2.0℃ / min, kept warm for 9h, and then air-cooled to room temperature to obtain heat-treated black bars, which are then machined and finely finished to obtain 150mm Ø finished bars.

[0092] Figure 5 This is a typical macrostructure of the rod prepared in Example 5; Figure 6 This is a typical transverse metallographic microstructure of the rod prepared in Example 5 after overall heat treatment; Figure 7 This is a typical longitudinal metallographic microstructure of the rod prepared in Example 5 after overall heat treatment; Figure 8 This is a typical IPF diagram and grain size of the rod prepared in Example 5 after overall heat treatment. Figure 5-Figure 8 It can be seen that the bar has a uniform structure after forging, and the grains are uniformly crushed and refined after overall heat treatment, with good anisotropy. The room temperature performance results of the prepared Ti55531 titanium alloy bar in Example 5 are shown in Table 2. The tensile strength R m The average value can reach 1196MPa, the elongation strength R p The average value can reach 1088MPa, the average elongation A can reach 12.4%, the average cross-sectional shrinkage Z can reach 25%, the average impact absorption energy KU2 can reach 35.1J, and the fracture toughness K IC The average value can reach 103MPa·m 0.5 ; The extreme difference between the head, middle and tail is also very small, and the material consistency is very high; the strength, plasticity and toughness of the rod are well matched.

[0093] Table 2. Room temperature properties of Ti55531 titanium alloy Ф150mm bar β annealed

[0094]

[0095] Example 6

[0096] The invention discloses a preparation method of an integral beta annealing aged Ti55531 titanium alloy bar, the steps comprising: step 1, ingot smelting: preparing raw materials, mixing materials and preparing electrode blocks, welding the electrode blocks into consumable electrodes, performing vacuum smelting three times, and obtaining Ti55531 titanium alloy finished ingots with a size of 650 mm to 750 mm after surface machining; step 2, blank forging: heating and heat-insulating the ingot, performing 1 to 2 fires of forging and then cooling in the air to obtain an intermediate blank; step 3, intermediate forging: heating and heat-insulating the intermediate blank, performing 4 to 8 fires of forging and then cooling in the air to obtain a round bar with a size of 100 mm to 160 mm, and the round bar can directly perform the integral beta annealing heat treatment in step 5 to obtain a finished bar or be used as a blank to perform the bar in step 4 Rolling obtains rolled bars with smaller specifications; Step 4, bar rolling: heat and keep the intermediate bar billet, roll it for 2 to 3 times and then cool it in air to obtain rolled bars with a diameter of 30 mm to 100 mm; Step 5, overall β annealing aging heat treatment: put the rolled bar into a muffle furnace or a resistance box heating furnace that can control the cooling rate, heat it to (Tβ-80 to 30)°C with the furnace, and keep it for 30min to 180min; then heat it to (Tβ+10 to 30)°C with the furnace, and keep it for at least 30min; then cool it to 500°C to 600°C with the furnace, keep it for 360min to 600min, and the cooling rate should be controlled at 1.5°C / min to 3.5°C / min during the cooling process; finally, air cool it to room temperature to obtain a finished bar.

[0097] See the heat treatment process flow diagram for details. Figure 1 The method of the invention belongs to the technical field of nonferrous metal processing. The small-size bars of Ti55531 titanium alloy in the beta annealing state prepared by the method of the invention have small grain size, good organizational uniformity, and good matching of plasticity and toughness.

[0098] The above are only preferred embodiments of the present invention. The present invention will not be limited to the embodiments shown herein, but should conform to the widest scope consistent with the principles and novel features disclosed herein. Any simple modification, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing an integral β-annealed Ti55531 titanium alloy bar, characterized in that: The specific steps are as follows: Step 1, ingot smelting: prepare raw materials, mix materials and prepare electrode blocks, weld the electrode blocks into consumable electrodes, and then perform vacuum smelting three times. After surface machining, obtain Ti55531 titanium alloy ingots with a specification of 650 mm to 750 mm; Step 2, blank forging: heating and keeping the ingot warm, forging for 1 to 2 times and then air cooling to obtain an intermediate blank; Step 3, intermediate forging: heating and heat-insulating the intermediate billet, forging for 4 to 8 times, and then air-cooling to obtain round bars with a specification of 100 mm to 160 mm; the round bars can be directly subjected to the overall β annealing heat treatment in step 5 to obtain finished bars or used as billets to carry out the bar rolling in step 4 to obtain small-sized rolled bars; Step 4, bar rolling: heating and heat preservation of the round bar, rolling for 2 to 3 times and then cooling in air to obtain a rolled bar of 30 mm to 100 mm in diameter; Step 5: Overall β annealing aging heat treatment: Place the rolled bar into a muffle furnace or a resistance box heating furnace and heat it to (T β -80~30)℃, keep warm for 30min~180min; then heat with the furnace to (T β +10~30)℃, keep warm for at least 30min; then cool to 500℃~600℃ with the furnace, keep warm for 360min~600min, the cooling rate should be controlled at 1.5℃ / min~3.5℃ / min during the cooling process; finally air cool to room temperature to obtain the finished bar; where T β is the phase transition temperature.

2. The method for preparing the integral β-annealed Ti55531 titanium alloy bar according to claim 1, characterized in that: The Ti55531 titanium alloy rod composition is Ti-5Al-5Mo-5V-3Cr-1Zr, which includes, by mass percentage, 4.0% to 6.0% Al, 4.5% to 6.0% Mo, 4.5% to 6.0% V, 2.0% to 3.6% Cr, 0.2% to 0.5% Fe, 0.3% to 2.0% Zr, and the remainder is Ti and unavoidable impurities.

3. The method for preparing the integral β-annealed Ti55531 titanium alloy bar according to claim 2, characterized in that: Step 1 is as follows: According to the standard of Ti55531 titanium alloy bar, raw materials are prepared, mixed and pressed into electrode blocks. Multiple electrode blocks are combined and prepared into consumable electrodes by plasma welding under argon protection. After three times of vacuum consumable melting, ingot blanks are obtained. After surface machining, Ti55531 titanium alloy ingots with specifications of Ф650mm~Ф750mm are obtained.

4. The method for preparing the integral β-annealed Ti55531 titanium alloy bar according to claim 3, characterized in that: Step 2 is as follows: For the Ti55531 titanium alloy ingot obtained in step 1, 1 to 2 fire forgings are performed at 250°C to 350°C above the phase transformation point, 2 to 3 upsetting and drawing operations are completed in each forging, the cumulative forging ratio of each fire is 7.0 to 13.8, the forging methods are upsetting, rounding and inverting, and the surface cracks of the material are polished after air cooling during forging; the starting forging temperature of each fire is not lower than 50°C to 150°C above the phase transformation point, and the final forging temperature is not lower than 20°C to 100°C below the phase transformation point to obtain an intermediate billet.

5. The method for preparing the integral β-annealed Ti55531 titanium alloy bar according to claim 4, characterized in that: Step 3 is as follows: The intermediate billet obtained in step 2 is subjected to 2-4 forgings at 80°C below the phase transformation point and 150°C above the phase transformation point, which is divided into 1-2 heatings at 40°C to 80°C below the phase transformation point and 1-2 heatings at 50°C to 150°C above the phase transformation point; the forging ratio of each fire is 2.5-6.0, the forging methods are upsetting, square drawing, flattening and inverting, the cooling method after forging is air cooling, and the surface cracks of the material are polished after forging air cooling to obtain a billet with a regular octagonal or rectangular cross section; Among them, the initial forging temperature of each fire in the two-phase zone shall not be lower than 60℃~150℃ below the phase transformation point, and the final forging temperature shall not be lower than 150℃~250℃ below the phase transformation point; the initial forging temperature of each fire in the single-phase zone shall not be lower than 30℃~80℃ below the phase transformation point, and the final forging temperature shall not be lower than 80℃~150℃ below the phase transformation point; The blanks forged above are reheated at 40°C to 80°C below the phase transformation point, the holding time is 6h to 9h, and then 1 to 2 rounds of forging are performed, the forging ratio of each round is 1.2 to 3.0, the forging method is upsetting and inverting, the forging process adopts the method of returning to the furnace to make up the temperature, and the material surface cracks are polished after forging; the starting forging temperature of each round is not lower than 60°C to 150°C below the phase transformation point, and the final forging temperature is not lower than 150°C to 250°C below the phase transformation point, so as to obtain the octagonal blank; The octagonal billet is subjected to forming forging: the billet is heated to 40℃~80℃ below the phase transition point, and the holding time is 6h~9h; then 1~2 rounds of forging are carried out, the forging ratio is 0.8~2.2, the forging method is straight drawing, chamfering and rounding, and the billet shape is changed from octagonal billet to Ф100mm~Ф160mm round bar, the forging process adopts the method of returning to the furnace to make up the temperature, and the surface cracks of the material are polished after forging air cooling; Among them, the initial forging temperature of each forming forging is not lower than 80℃~200℃ below the phase transformation point, and the final forging temperature is not lower than 150℃~300℃ below the phase transformation point.

6. The method for preparing the integral β-annealed Ti55531 titanium alloy bar according to claim 5, characterized in that: Step 4 is as follows: The round bar to be rolled obtained in step 3 is heated to 40°C to 80°C below the phase transition point, and the holding time is 2h to 6h; 1 to 2 rounds of rolling are performed, the rolling method is bidirectional multi-pass rolling, and the total rolling deformation of the passes is 170% to 400%, and then air-cooled, sawed, and ground to obtain a 80mm to 120mm bar blank; The rolled bar billet is heated to 40°C to 80°C below the phase transformation point, and the holding time is 1h to 3h; one fire rolling is performed, and the rolling method is bidirectional multi-pass rolling, and the total rolling deformation is 140% to 700%. After the rolling is completed, one straightening is performed to obtain a rolled bar of Ф30mm to Ф100mm.

7. The method for preparing the integral β-annealed Ti55531 titanium alloy bar according to claim 6, characterized in that: Step 5 is as follows: Place the round bars or rolled bars to be heat treated in a muffle furnace or resistance box heating furnace that can control the cooling rate. The temperature error of the heat treatment furnace must be controlled within ±5°C. When multiple round bars or bars are heat treated at the same time, the interval between the bars should be controlled to be greater than 150mm. The bars are heated from room temperature to (T β -80~30)℃, keep warm for 30min~180min after reaching temperature; then heat with furnace to (T β +10~30)℃, keep warm for at least 30min; then cool to 500℃~600℃ with the furnace, keep warm for 360min~600min, and the cooling rate should be controlled at 1.5℃ / min~3.5℃ / min during the cooling process; finally, air cool it to room temperature to obtain β annealing and aging state bars, and then through machining and finishing, finally obtain finished bars of Ф30mm~Ф150mm.

8. Integral β-annealed Ti55531 titanium alloy bar, characterized in that: The Ti55531 titanium alloy rod composition is Ti-5Al-5Mo-5V-3Cr-1Zr, which includes, by mass percentage, 4.0% to 6.0% Al, 4.5% to 6.0% Mo, 4.5% to 6.0% V, 2.0% to 3.6% Cr, 0.2% to 0.5% Fe, 0.3% to 2.0% Zr, and the remainder is Ti and unavoidable impurities.

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