Forging method of TC21 titanium alloy large-specification bar

Abstract

The invention relates to the technical field of titanium alloy hot working, in particular to a forging method for a TC21 titanium alloy large-specification bar. The method comprises the following steps: (1) upsetting and drawing forging of a beta single-phase region; (2) upsetting and drawing forging in an alpha + beta two-phase region; (3) upsetting and drawing forging of a quasi-beta phase region; (4) upsetting and drawing forging in an alpha + beta two-phase region; and (5) drawing and forging an alpha + beta two-phase region. The method is simple and feasible in process, the large-specification TC21 forged rod with the diameter of 200-550 mm obtained through forging with the method is uniform in macrostructure, excellent in mechanical property and good in consistency, and the requirement for the large-specification TC21 forged rod in the aerospace field can be met.

Description

Technical Field

[0001] The invention relates to the technical field of titanium alloy hot processing, and in particular to a forging method for a large-size TC21 titanium alloy bar. Background Art

[0002] TC21 is a high-strength damage-tolerant titanium alloy developed in my country with independent intellectual property rights. It is a two-phase titanium alloy of the Ti-Al-Sn-Zr-Mo-Cr-Nb (-Ni-Si) system, and its chemical composition is similar to that of Ti-62222S. The alloy has high strength (R m ≥1100MPa), high fracture toughness (K IC ≥70MPa·m1 / 2), high damage tolerance performance and excellent fatigue resistance, etc., which are comparable to the performance of Ti-62222S high-strength and high-damage-tolerance titanium alloy used in the fifth-generation fighter F-22 of the United States. Its good welding performance also makes up for the poor welding process performance of Ti-62222S. TC21 titanium alloy is the best titanium alloy variety with comprehensive mechanical properties among my country's high-strength and toughness titanium alloys. It is suitable for the key load-bearing components (frames, beams, tail wings, etc.) of new fighter aircraft and the manufacture of large integral frames of aircraft, pylons, beams, joints, landing gears near engines, etc. Most of the TC21 titanium alloy forgings for aviation are obtained by further die forging with forging bars as blanks.

[0003] The forging process of TC21 titanium alloy bars is complex, including multiple processes such as blanking, rough forging, and radial forging. Reasonable forging process parameters are selected in different processes. Blanking of TC21 titanium alloy is to break the coarse-grained structure in the ingot, and there are no special requirements for performance. It is usually carried out in the β single-phase region to reduce deformation resistance. Rough forging is to refine the bar structure. It is generally carried out in the β single-phase region and the α+β two-phase region. Through large forging ratios and repeated upsetting and drawing, grain refinement and homogenization effects are obtained, thereby obtaining excellent mechanical properties. Radial forging is the final forming process of TC21 titanium alloy bars. It is generally carried out in the α+β two-phase region. The expected bar size is obtained through repeated drawing, while ensuring that the grains do not grow significantly.

[0004] The parameters such as forging temperature, forging ratio, forging rate and so on in each process of forging TC21 titanium alloy bar have a great influence on its microstructure and properties. In terms of forging temperature control, for ordinary forging bars, good comprehensive performance is generally required, and the final forging is carried out in the two-phase region to obtain equiaxed or dual-state microstructure. For TC21 titanium alloy forging bars with damage tolerance performance requirements, in order to improve its fracture toughness and fatigue crack growth performance, the final forging is carried out in the single-phase region to obtain a basketweave microstructure. In addition to forging temperature, forging rate is an important factor affecting titanium alloy forging bars. High forging rate can improve the production efficiency of titanium alloy forgings, reduce energy consumption and reduce costs. However, at high forging rate, titanium alloy has high deformation resistance and high requirements on equipment capacity; at the same time, due to the low thermal conductivity of titanium alloy, the deformation heat caused by high forging rate will cause overheating of the core, resulting in deformation and uneven forging microstructure. In addition to forging temperature and rate, forging ratio also plays a vital role in penetration forging deformation and refinement of TC21 titanium alloy structure. A larger upsetting forging ratio can make the core metal of the bar billet flow, refine the grains through dynamic recovery recrystallization, and reduce the structural inhomogeneity from the core to the edge of the titanium alloy bar. In summary, in order to obtain TC21 titanium alloy forging bars with uniform structure and excellent performance, it is necessary to strictly control the forging temperature, forging ratio, forging rate and other parameters of each forging process. Summary of the invention

[0005] The purpose of the present invention is to provide a forging method for large-size TC21 titanium alloy bars. The method is simple and feasible. Large-size TC21 forged bars with a diameter of 200 to 550 mm are forged by the method. The high and low-magnification structures are uniform, the mechanical properties are excellent, and the consistency is good, which can meet the demand for large-size TC21 forged bars in the aerospace field.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] The present invention provides a forging method for a large-size TC21 titanium alloy bar, the method comprising the following steps:

[0008] (1) β single phase zone upsetting and forging

[0009] The TC21 titanium alloy ingot is heated and subjected to three-time upsetting forging. The first forging temperature is the phase transition point T β Above 100~200℃, the second forging temperature is the phase transition point T β Above 50~100℃, the third forging temperature is the phase transition point T β Above 30~50℃, each time of upsetting and drawing forging is three upsetting and three drawing with changing direction, after upsetting and drawing to eight directions each time, it is thrown out for air cooling and grinding;

[0010] (2) α+β two-phase region upsetting and drawing forging

[0011] The forging blank obtained in step (1) is heated to the phase transformation point T β At the temperature below 30-50℃, the steel is subjected to one-time upsetting and drawing forging. The upsetting and drawing forging is three-upsetting and three-drawing in reverse direction. After each upsetting and drawing, the steel is returned to the furnace for 60-120 minutes of heat preservation. After upsetting and drawing to eight directions, it is thrown out for air cooling and grinding.

[0012] (3) Quasi-β phase upsetting and forging

[0013] The forging blank obtained in step (2) is heated to the phase transformation point T β Above 5-15℃, carry out one-time upsetting and drawing forging. The upsetting and drawing forging is three-upsetting and three-drawing with reversing direction. After each upsetting and drawing, return to the furnace and keep warm for 60-120min. After upsetting and drawing to eight directions, throw out and air cool, grind, and cut in the middle.

[0014] (4) α+β two-phase region upsetting and drawing forging

[0015] The forging blank obtained in step (3) is heated to the phase transformation point T β At the temperature below 20-60℃, two to three times of upsetting and drawing forging are carried out. Each time of upsetting and drawing forging is three upsetting and three drawing with changing direction. After each upsetting and drawing, the forging is returned to the furnace for insulation for 60-120min. After each upsetting and drawing to eight directions, it is thrown out for air cooling and grinding.

[0016] (5) α+β two-phase stretch forging

[0017] The forging blank obtained in step (4) is heated to the phase transformation point T β Below 20 ~ 60 ℃, one-time drawing to the required size, throwing out air cooling, and grinding.

[0018] In the above technical solution, further, in step (1), the TC21 titanium alloy ingot is a cylinder with a size of Φ400~800mm*400~1500mm.

[0019] In the above technical solution, further, in step (1), step (2) and step (3), the heating coefficient is 0.7.

[0020] In the above technical solution, further, in step (1), step (2) and step (3), the reversing three upsetting and three drawing is to perform upsetting and drawing processing in three directions of XYZ respectively.

[0021] In the above technical solution, further, in step (1), step (2) and step (3), the reduction rate during each upsetting is 40-60%, and the height-to-diameter ratio during each stretching to eight sides is 1.8-2.0.

[0022] In the above technical solution, further, in step (5), the diameter of the finished forged rod is Φ200-550 mm.

[0023] Beneficial effects of the present invention:

[0024] 1. In the present invention, each upsetting and drawing forging of the TC21 large-size bar adopts the reversing upsetting and drawing forging technology. The three upsetting and drawing of the three-upsetting and three-drawing are all reversing upsetting and drawing, and the three directions of XYZ are upset once respectively. The reversing upsetting and drawing forging is used to improve the uniformity of the TC21 titanium alloy bar structure.

[0025] 2. The forging method of the present invention performs a first upsetting forging in the quasi-β phase region immediately after the TC21 large-sized bar is upset forged in the α+β two-phase region, and then performs upsetting forging in the α+β two-phase region, which can refine and homogenize the high and low magnification structures of the TC21 titanium alloy forged bar, and obtain a large-sized TC21 titanium alloy forged bar with uniform structure and properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a macrostructure diagram of the TC21 titanium alloy rod of Example 1;

[0027] Figure 2 This is the microstructure diagram of the core of the TC21 titanium alloy rod of Example 1;

[0028] Figure 3 The microstructure diagram of the TC21 titanium alloy rod at 1 / 2R of Example 1;

[0029] Figure 4 This is the microstructure diagram of the edge of the TC21 titanium alloy bar of Example 1;

[0030] Figure 5 is a macrostructure diagram of the TC21 titanium alloy rod of Example 2;

[0031] Figure 6 This is the microstructure diagram of the core of the TC21 titanium alloy rod of Example 2;

[0032] Figure 7 The microstructure diagram of the TC21 titanium alloy rod at 1 / 2R of Example 2;

[0033] Figure 8 This is the microstructure diagram of the edge of the TC21 titanium alloy bar of Example 2;

[0034] Fig. 9 is a macrostructure diagram of the TC21 titanium alloy rod of Example 3;

[0035] Fig.10 This is the microstructure diagram of the core of the TC21 titanium alloy rod of Example 3;

[0036] Fig.11 This is the microstructure diagram of the TC21 titanium alloy rod at 1 / 2R of Example 3;

[0037] Fig.12This is the microstructure diagram of the edge of the TC21 titanium alloy bar of Example 3;

[0038] Fig.13 is a macrostructure diagram of the TC21 titanium alloy rod of Example 4;

[0039] Fig.14 This is the microstructure diagram of the core of the TC21 titanium alloy rod of Example 4;

[0040] Fig.15 The microstructure diagram of the TC21 titanium alloy rod at 1 / 2R of Example 4;

[0041] Fig.16 This is the microstructure diagram of the edge of the TC21 titanium alloy rod of Example 4. DETAILED DESCRIPTION

[0042] The following examples may enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0043] Example 1

[0044] The forging method of the TC21 titanium alloy large-size bar in this embodiment comprises the following steps:

[0045] (1) β single phase zone upsetting and forging

[0046] The TC21 titanium alloy ingot with a specification of Φ720mm*600mm was subjected to three-time upsetting and drawing forging, with a heating coefficient of 0.7. The first time was three-time upsetting and three-drawing with reversing direction, that is, upsetting and drawing were performed in the three directions of XYZ respectively, and the forging temperature was T β The temperature is above 200℃, the reduction rate of each upsetting is 45%, and the steel is drawn to a height-to-diameter ratio of about 1.9, then thrown out for air cooling, and the surface is ground. The second time is three-way upsetting and three-drawing, that is, upsetting and drawing are performed in the three directions of XYZ respectively. The forging temperature is T β Above 100℃, each time the upsetting reduction rate is 45%, drawn to a height-to-diameter ratio of about 1.9, thrown out for air cooling, and grinding. The third fire is a reversing three-upsetting and three-drawing, that is, upsetting and drawing treatments are performed in the three directions of XYZ respectively. The forging temperature is T β Above 50℃, each time the upsetting reduction rate is 45%, drawn to a height-to-diameter ratio of about 1.9, thrown out for air cooling, and ground;

[0047] (2) α+β two-phase region upsetting and drawing forging

[0048] The forging blank obtained in step (1) is subjected to a first-time upsetting and drawing forging, and the forging method is three-way upsetting and three-drawing, that is, upsetting and drawing treatment are performed in three directions of XYZ respectively, and the forging temperature is T βBelow 30℃, heating coefficient is 0.7, each upsetting reduction is 45%, then drawn to a height-to-diameter ratio of about 1.9, after each upsetting and drawing, return to the furnace for 90 minutes of heat preservation, throw out for air cooling, and grind;

[0049] (3) Quasi-β phase upsetting and forging

[0050] The forging blank obtained in step (2) is subjected to one-time upsetting and drawing forging, the heating coefficient is 0.7, the forging method is three-way upsetting and three-drawing, that is, upsetting and drawing treatment are performed in the three directions of XYZ respectively, and the forging temperature is T β Above 15℃, each upsetting reduction rate is 45%, and the steel is drawn to a height-to-diameter ratio of about 1.9. After each upsetting and drawing, the steel is returned to the furnace for 90 minutes of heat preservation, thrown out for air cooling, surface grinding, and center cutting.

[0051] (4) α+β two-phase region upsetting and drawing forging

[0052] The forging blank obtained in step (3) is subjected to two-time upsetting and drawing forging. The forging method is three-way upsetting and three-drawing, that is, upsetting and drawing are performed in three directions, XYZ, respectively. The first-time forging temperature is the phase transition point T β Below 30℃, heating coefficient is 0.7, each upsetting reduction rate is 45%, then drawn to a height-to-diameter ratio of about 1.9, each time upsetting and drawing, return to the furnace for 60min of heat preservation, throw out for air cooling, and grind. The second forging temperature is T β Below 30℃, heating coefficient is 0.7, each upsetting reduction is 45%, then drawn to a height-to-diameter ratio of about 1.9, after each upsetting and drawing, return to the furnace for 60 minutes of heat preservation, throw out for air cooling, and grind;

[0053] (5) α+β two-phase stretch forging

[0054] The forging blank obtained in step (4) is heated to the phase transformation point T β Below 30℃, the heating coefficient of the forging billet is 0.7, and the round bar is drawn to Φ200mm×3900mm in one fire. It is not returned to the furnace, and then thrown out for air cooling and surface grinding.

[0055] The macrostructure of the large-size TC21 titanium alloy bar prepared in Example 1 is shown in Figure 1 , the microstructure diagram of the bar edge is shown in Figure 2 , the microstructure diagram of the rod at 1 / 2R is shown in Figure 3 , the microstructure diagram of the core of the rod is shown in Figure 4 .

[0056] The rod obtained in Example 1 was kept at 880°C for 1 hour and then air-cooled, and then kept at 590°C for 3 hours and then air-cooled. The properties of the rod after heat treatment are shown in Table 1.

[0057] Example 2

[0058] The forging method of the TC21 titanium alloy large-size bar in this embodiment comprises the following steps:

[0059] (1) β single phase zone upsetting and forging

[0060] The TC21 titanium alloy ingot with a specification of Φ720mm*600mm was subjected to three-time upsetting and drawing forging, with a heating coefficient of 0.7. The first time was three-time upsetting and three-drawing with reversing direction, that is, upsetting and drawing were performed in the three directions of XYZ respectively, and the forging temperature was T β The temperature is above 180℃, the reduction rate of each upsetting is 50%, and the steel is drawn to a height-to-diameter ratio of about 1.9, then thrown out for air cooling, and the surface is ground. The second time is three-way upsetting and three-drawing, that is, upsetting and drawing are performed in the three directions of XYZ respectively. The forging temperature is T β Above 90℃, each time the upsetting reduction rate is about 50%, drawn to a height-to-diameter ratio of about 1.9, thrown out for air cooling, and grinding. The third fire is a reversing three-upsetting and three-drawing, that is, upsetting and drawing treatments are performed in the three directions of XYZ respectively. The forging temperature is T β Above 45℃, each time the upsetting reduction rate is about 50%, drawn to a height-to-diameter ratio of about 1.9, thrown out for air cooling, and grinding;

[0061] (2) α+β two-phase region upsetting and drawing forging

[0062] The forging blank obtained in step (1) is subjected to a first-time upsetting and drawing forging, and the forging method is three-way upsetting and three-drawing, that is, upsetting and drawing treatment are performed in three directions of XYZ respectively, and the forging temperature is T β Below 35℃, heating coefficient is 0.7, each upsetting reduction rate is about 50%, then drawn to a height-to-diameter ratio of about 1.9, after each upsetting and drawing, return to the furnace for 100 minutes of heat preservation, throw out and air cool, and grind;

[0063] (3) Quasi-β phase upsetting and forging

[0064] The forging blank obtained in step (2) is subjected to one-time upsetting and drawing forging, the heating coefficient is 0.7, the forging method is three-way upsetting and three-drawing, that is, upsetting and drawing treatment are performed in the three directions of XYZ respectively, and the forging temperature is T β Above 10℃, each time the upsetting reduction rate is about 50%, and the steel is drawn to a height-to-diameter ratio of about 1.9. After each upsetting and drawing, the steel is returned to the furnace for 100 minutes of heat preservation, thrown out for air cooling, surface grinding, and center cutting.

[0065] (4) α+β two-phase region upsetting and drawing forging

[0066] The forging blank obtained in step (3) is subjected to two-time upsetting and drawing forging. The forging method is three-way upsetting and three-drawing, that is, upsetting and drawing are performed in three directions, XYZ, respectively. The first-time forging temperature is the phase transition point T βBelow 35℃, heating coefficient is 0.7, each upsetting reduction rate is about 50%, then drawn to a height-to-diameter ratio of about 1.9, each time upsetting and drawing, return to the furnace for 70 minutes of heat preservation, throw out and air cool, grind, the second forging temperature is T β Below 35℃, heating coefficient is 0.7, each upsetting reduction rate is about 50%, then drawn to a height-to-diameter ratio of about 1.9, after each upsetting and drawing, return to the furnace for 70 minutes of heat preservation, throw out and air cool, and grind;

[0067] (5) α+β two-phase stretch forging

[0068] The forging blank obtained in step (4) is heated to the phase transformation point T β Below 35℃, the heating coefficient of the forging billet is 0.7, and the round bar is drawn to Φ300mm×1600mm in one fire. It is not returned to the furnace, and then thrown out for air cooling and surface grinding.

[0069] The macrostructure of the large-size TC21 titanium alloy bar prepared in Example 2 is shown in Figure 5 , the microstructure diagram of the bar edge is shown in Figure 6 , the microstructure diagram of the rod at 1 / 2R is shown in Figure 7 , the microstructure diagram of the core of the rod is shown in Figure 8 .

[0070] The rod obtained in Example 2 was kept at 880°C for 1 hour and then air-cooled, and then kept at 590°C for 3 hours and then air-cooled. The properties of the rod after heat treatment are shown in Table 1.

[0071] Example 3

[0072] The forging method of the TC21 titanium alloy large-size bar in this embodiment comprises the following steps:

[0073] (1) β single phase zone upsetting and forging

[0074] The TC21 titanium alloy ingot with a specification of Φ720mm*600mm was subjected to three-time upsetting and drawing forging, with a heating coefficient of 0.7. The first time was three-time upsetting and three-drawing with reversing direction, that is, upsetting and drawing were performed in the three directions of XYZ respectively, and the forging temperature was T β The temperature is above 190℃, the reduction rate of each upsetting is about 45%, and the steel is drawn to a height-to-diameter ratio of about 1.8, then thrown out for air cooling, and the surface is ground. The second time is three-way upsetting and three-drawing, that is, upsetting and drawing are performed in the three directions of XYZ respectively. The forging temperature is T β Above 100℃, each time the upsetting reduction rate is about 45%, drawn to a height-to-diameter ratio of about 1.8, thrown out for air cooling, and grinding. The third fire is a reversing three-upsetting and three-drawing, that is, upsetting and drawing treatments are performed in the three directions of XYZ respectively. The forging temperature is T β Above 50℃, each time the upsetting reduction rate is about 45%, drawn to a height-to-diameter ratio of about 1.8, thrown out for air cooling, and grinding;

[0075] (2) α+β two-phase region upsetting and drawing forging

[0076] The forging blank obtained in step (1) is subjected to a first-time upsetting and drawing forging, and the forging method is three-way upsetting and three-drawing, that is, upsetting and drawing treatment are performed in three directions of XYZ respectively, and the forging temperature is T β Below 30℃, heating coefficient is 0.7, each upsetting reduction rate is about 45%, then drawn to a height-to-diameter ratio of about 1.8, after each upsetting and drawing, return to the furnace for 100 minutes of heat preservation, throw out and air cool, and grind;

[0077] (3) Quasi-β phase upsetting and forging

[0078] The forging blank obtained in step (2) is subjected to one-time upsetting and drawing forging, the heating coefficient is 0.7, the forging method is three-way upsetting and three-drawing, that is, upsetting and drawing treatment are performed in the three directions of XYZ respectively, and the forging temperature is T β Above 15℃, each time the upsetting reduction rate is about 45%, and the drawing is extended to a height-to-diameter ratio of about 1.8. After each upsetting and drawing, return to the furnace for 100 minutes of heat preservation, throw out and air cool, grind the surface, and cut the material in the middle;

[0079] (4) α+β two-phase region upsetting and drawing forging

[0080] The forging blank obtained in step (3) is subjected to two-time upsetting and drawing forging. The forging method is three-way upsetting and three-drawing, that is, upsetting and drawing are performed in three directions, XYZ, respectively. The first-time forging temperature is the phase transition point T β Below 30℃, heating coefficient is 0.7, each upsetting reduction rate is about 45%, then drawn to a height-to-diameter ratio of about 1.8, each time upsetting and drawing, return to the furnace for 60 minutes of heat preservation, throw out and air cool, grind, the second forging temperature is T β Below 35℃, heating coefficient is 0.7, each upsetting reduction rate is about 45%, then drawn to a height-to-diameter ratio of about 1.8, after each upsetting and drawing, return to the furnace for 60 minutes of heat preservation, throw out and air cool, and grind;

[0081] (5) α+β two-phase stretch forging

[0082] The forging blank obtained in step (4) is heated to the phase transformation point T β Below 30℃, the heating coefficient of the forging billet is 0.7, and the round bar is drawn to Φ400mm×950mm in one fire. It is not returned to the furnace, and then thrown out for air cooling and surface grinding.

[0083] The macrostructure of the large-size TC21 titanium alloy bar prepared in Example 3 is shown in Fig. 9 , the microstructure diagram of the bar edge is shown in Fig.10 , the microstructure diagram of the rod at 1 / 2R is shown in Fig.11 , the microstructure diagram of the core of the rod is shown in Fig.12 .

[0084] The rods prepared in Example 3 were kept at 880°C for 1 hour and then air-cooled, and then kept at 590°C for 3 hours and then air-cooled. The properties of the rods after heat treatment are shown in Table 1.

[0085] Example 4

[0086] The forging method of the TC21 titanium alloy large-size bar in this embodiment comprises the following steps:

[0087] (1) β single phase zone upsetting and forging

[0088] The TC21 titanium alloy ingot with a specification of Φ720mm*1000mm was subjected to three-time upsetting and drawing forging, with a heating coefficient of 0.7. The first time was three-time upsetting and three-drawing with reversing direction, that is, upsetting and drawing were performed in the three directions of XYZ respectively, and the forging temperature was T β The temperature is above 190℃, the reduction rate of each upsetting is about 45%, and the steel is drawn to a height-to-diameter ratio of about 1.8, then thrown out for air cooling, and the surface is ground. The second time is three-way upsetting and three-drawing, that is, upsetting and drawing are performed in the three directions of X, Y and Z respectively. The forging temperature is T β Above 90℃, each time the upsetting reduction rate is about 45%, drawn to a height-to-diameter ratio of about 1.8, thrown out for air cooling, and grinding. The third fire is a reversing three-upsetting and three-drawing, that is, upsetting and drawing treatment are performed in the three directions of XYZ respectively. The forging temperature is T β Above 50℃, each time the upsetting reduction rate is about 45%, drawn to a height-to-diameter ratio of about 1.8, thrown out for air cooling, and grinding;

[0089] (2) α+β two-phase region upsetting and drawing forging

[0090] The forging blank obtained in step (1) is subjected to a first-time upsetting and drawing forging, and the forging method is three-way upsetting and three-drawing, that is, upsetting and drawing treatment are performed in three directions of XYZ respectively, and the forging temperature is T β Below 35℃, heating coefficient is 0.7, each upsetting reduction rate is about 45%, then drawn to a height-to-diameter ratio of about 1.8, after each upsetting and drawing, return to the furnace for 100 minutes of heat preservation, throw out and air cool, and grind;

[0091] (3) Quasi-β phase upsetting and forging

[0092] The forging blank obtained in step (2) is subjected to one-time upsetting and drawing forging, the heating coefficient is 0.7, the forging method is three-way upsetting and three-drawing, that is, upsetting and drawing treatment are performed in the three directions of XYZ respectively, and the forging temperature is T β Above 10℃, each time the upsetting reduction rate is about 45%, and the drawing is extended to a height-to-diameter ratio of about 1.8. After each upsetting and drawing, return to the furnace for 100 minutes of heat preservation, throw out and air cool, grind the surface, and cut the material in the middle;

[0093] (4) α+β two-phase region upsetting and drawing forging

[0094] The forging blank obtained in step (3) is subjected to two-time upsetting and drawing forging. The forging method is three-way upsetting and three-drawing, that is, upsetting and drawing are performed in three directions, XYZ, respectively. The first-time forging temperature is the phase transition point T β Below 35℃, heating coefficient is 0.7, each upsetting reduction rate is about 45%, then drawn to a height-to-diameter ratio of about 1.8, each time upsetting and drawing, return to the furnace for 60 minutes of heat preservation, throw out and air cool, grind, the second forging temperature is T β Below 35℃, heating coefficient is 0.7, each upsetting reduction rate is about 45%, then drawn to a height-to-diameter ratio of about 1.8, after each upsetting and drawing, return to the furnace for 60 minutes of heat preservation, throw out and air cool, and grind;

[0095] (5) α+β two-phase stretch forging

[0096] The forging blank obtained in step (4) is heated to the phase transformation point T β Below 35℃, the heating coefficient of the forging billet is 0.7, and the round bar is drawn to Φ550mm×800mm in one fire. It is not returned to the furnace, and then thrown out for air cooling and surface grinding.

[0097] The macrostructure of the large-size TC21 titanium alloy bar prepared in Example 4 is shown in Fig.13 , the microstructure diagram of the bar edge is shown in Fig.14 , the microstructure diagram of the rod at 1 / 2R is shown in Fig.15 , the microstructure diagram of the core of the rod is shown in Fig.16 .

[0098] The rod obtained in Example 4 was kept at 880°C for 1 hour and then air-cooled, and then kept at 590°C for 3 hours and then air-cooled. The properties of the rod after heat treatment are shown in Table 1.

[0099] Table 1 Mechanical properties of TC21 forged rods after heat treatment in Examples 1-4

[0100]

[0101] The above embodiments are only preferred embodiments of the present invention and are not intended to limit the implementation methods. The protection scope of the present invention shall be subject to the scope defined in the claims. Other different forms of changes or modifications may be made based on the above description. Obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A forging method for large-size TC21 titanium alloy bars, characterized in that: The method comprises the following steps: (1) β single phase zone upsetting and forging The TC21 titanium alloy ingot is heated and subjected to three-time upsetting forging. The first forging temperature is the phase transition point T β Above 100~200℃, the second forging temperature is the phase transition point T β Above 50~100℃, the third forging temperature is the phase transition point T β Above 30~50℃, each time of upsetting and drawing forging is three upsetting and three drawing with changing direction, after upsetting and drawing to eight directions each time, it is thrown out for air cooling and grinding; (2) α+β two-phase region upsetting and drawing forging The forging blank obtained in step (1) is heated to the phase transformation point T β At the temperature below 30-50℃, the steel is subjected to one-time upsetting and drawing forging. The upsetting and drawing forging is three-upsetting and three-drawing in reverse direction. After each upsetting and drawing, the steel is returned to the furnace for 60-120 minutes of heat preservation. After upsetting and drawing to eight directions, it is thrown out for air cooling and grinding. (3) Quasi-β phase upsetting and forging The forging blank obtained in step (2) is heated to the phase transformation point T β Above 5-15℃, carry out one-time upsetting and drawing forging. The upsetting and drawing forging is three-upsetting and three-drawing with reversing direction. After each upsetting and drawing, return to the furnace and keep warm for 60-120min. After upsetting and drawing to eight directions, throw out and air cool, grind, and cut in the middle. (4) α+β two-phase region upsetting and drawing forging The forging blank obtained in step (3) is heated to the phase transformation point T β At the temperature below 20-60℃, two to three times of upsetting and drawing forging are carried out. Each time of upsetting and drawing forging is three upsetting and three drawing with changing direction. After each upsetting and drawing, the forging is returned to the furnace for insulation for 60-120min. After each upsetting and drawing to eight directions, it is thrown out for air cooling and grinding. (5) α+β two-phase stretch forging The forging blank obtained in step (4) is heated to the phase transformation point T β Below 20 ~ 60 ℃, one-time drawing to the required size, throwing out air cooling, and grinding.

2. The forging method of TC21 titanium alloy large-size bars according to claim 1 is characterized in that: In step (1), the TC21 titanium alloy ingot is a cylinder with a size of Φ400-800mm*400-1500mm.

3. The forging method of TC21 titanium alloy large-size bars according to claim 1, characterized in that: In step (1), step (2) and step (3), the heating coefficient is 0.

7.

4. The forging method of TC21 titanium alloy large-size bars according to claim 1, characterized in that: In step (1), step (2) and step (3), the reversing three upsetting and three drawing is to perform upsetting and drawing processing in three directions of XYZ respectively.

5. The forging method of TC21 titanium alloy large-size bars according to claim 1, characterized in that: In step (1), step (2) and step (3), the reduction rate during each upsetting is 40-60%, and the height-to-diameter ratio during each stretching to eight sides is 1.8-2.

0.

6. The forging method of TC21 titanium alloy large-size bars according to claim 1, characterized in that: In step (5), the diameter of the finished forged rod is Φ200-550 mm.

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