A method for preparing large-size TC21 titanium alloy rods at low cost

Abstract

The application relates to a low-cost preparation method of a TC21 titanium alloy large-size rod, which comprises the following steps: 1) two-fire breakdown forging of a TC21 titanium alloy ingot: first fire is high-temperature forging in a beta single-phase zone to obtain a square-section intermediate blank ingot; second fire is low-temperature upsetting and reversing elongation forging, and then high-temperature forging to obtain a square-section intermediate blank ingot with a grain size of 1mm-2mm; 2) three-fire rod modification forging: in the first and second fires, the intermediate blank ingot is first upset and then elongated to be forged into an eight-square-section blank, and in the third fire, the intermediate blank is elongated to be an twelve-square-section intermediate blank; 3) one-fire forming forging: the twelve-square-section intermediate blank is upset to be a round-section rod blank with a required size. The method improves the uniformity of the rod structure, and can prepare the required Φ350mm TC21 titanium alloy large-size rod with required structure and performance at a low cost.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of titanium alloy production and processing, and particularly relates to a preparation method of TC21 titanium alloy large-size rod. BACKGROUND

[0002] TC21 titanium alloy is a new type of high-strength, high-toughness and high-damage tolerance titanium alloy independently researched and developed by China and having independent intellectual property rights. The TC21 titanium alloy belongs to Ti-Al-Sn-Zr-Mo-Cr-Nb-Si two-phase titanium alloy, has excellent strength, plasticity, fracture toughness and low crack propagation rate, and is widely used in the aerospace industry, especially in the field of aircraft structural parts, such as key load-bearing components of large frames and beams of aircraft. Since the TC21 titanium alloy has high alloying degree and poor forging penetration, for the large-size rod with a diameter of 350 mm or more, the conventional forging method is used, the number of heating times is large, and the transverse and longitudinal organization uniformity is prone to be produced.

[0003] In order to reduce the forging cost of the TC21 titanium alloy large-size rod with a diameter of 350 mm or more, improve the organization uniformity of the TC21 titanium alloy large-size rod, and meet the development needs of the aerospace industry, a new low-cost preparation method of the TC21 titanium alloy large-size rod needs to be developed. SUMMARY

[0004] In order to overcome the above-mentioned deficiencies of the prior art, the application provides a preparation method of TC21 titanium alloy large-size rod, which provides a new preparation method of TC21 titanium alloy large-size rod by high-temperature forging, low-temperature forging + high-temperature forging and low-temperature forging on the titanium alloy ingot in sequence, 2 heating times of blooming and 4 heating times of upsetting, so as to obtain a low-cost titanium alloy large-size rod with good organization uniformity.

[0005] In order to achieve the above-mentioned purpose, the application adopts the following technical scheme.

[0006] On the one hand, the application provides a preparation method of TC21 titanium alloy large-size rod, which comprises the following steps:

[0007] Step 1), two heating times of blooming forging are performed on the TC21 titanium alloy ingot:

[0008] In the first heating time, β single-phase zone high-temperature forging is performed on the TC21 titanium alloy ingot, and a square-section intermediate blank ingot is obtained;

[0009] In the second heating time, low-temperature upsetting and reversing elongation forging are performed on the square-section intermediate blank ingot, and then high-temperature forging is performed, so that a square-section intermediate blank ingot with a grain size of 1 mm to 2 mm is obtained;

[0010] Step 2), the intermediate blank ingot obtained in step 1) is subjected to three-pass bar upsetting and drawing in the α+β two-phase region:

[0011] In the first and second passes, the intermediate blank ingot is first upset and then drawn to form an intermediate blank with an octagonal cross section, and in the third pass, the intermediate blank with the octagonal cross section is drawn to form an intermediate blank with a dodecagonal cross section;

[0012] Step 3), the intermediate blank with the dodecagonal cross section obtained in step 2) is subjected to α+β two-phase region bar forming:

[0013] The intermediate blank with the dodecagonal cross section is upset to form a TC21 titanium alloy large-size bar with a circular cross section and a desired size.

[0014] Further, in the step (1), the first pass is high-temperature forging above the β phase transition point, the initial breakdown temperature is T β +180-205℃, heating is performed by two-up two-down forging, the heating coefficient is 0.65-0.80, the total forging ratio is 1.70-2.00, after forging, the hot material is returned to the furnace, the return-to-furnace temperature is T β +105-125℃, after being taken out of the furnace, two-up two-down forging is performed, after forging, the hot material is returned to the furnace, the return-to-furnace temperature is T β +60-95℃, then two-up two-down forging is performed, and after forging, the material is air-cooled, the pressing speed in the forging process is controlled to be 20-35 mm / s, the reduction is controlled to be 100-160 mm, and the feed amount is controlled to be 280-500 mm, thereby obtaining β structure with a grain size of 5-20 mm;

[0015] The second pass is low-temperature forging below the β phase transition point, the heating temperature is T β -(30-70)℃, the heating coefficient is 0.65-0.80, upsetting and reverse drawing are performed, the total forging ratio is 1.6-2.0, after forging, the hot material is returned to the furnace, the return-to-furnace temperature is T β +(30-100)℃; then high-temperature forging above the β phase transition point is performed, the heating temperature is T β +(30-100)℃, the heating coefficient is 0.5, the total forging ratio is 1.2-1.5, after forging, the material is air-cooled, thereby obtaining an intermediate blank ingot with β structure with a grain size of 1-2 mm.

[0016] Further, in the first pass of the step 1), the upsetting and drawing deformation amount is controlled to be 37%-45% each time, and in the second pass, the deformation amount is controlled to be 35%-40%.

[0017] Further, in step 1), the reversing upsetting is that the intermediate blank ingot is first upset forged along the axial direction, then is elongated forged along the radial direction, then is tempered, then is upset along the radial direction, and then is elongated forged along the axial direction.

[0018] Further, in step 2), the heating temperature of the first and second heating times is T β -(30-70) ℃, the heating coefficient is 0.5-0.8, the deformation amount is controlled to be 30%-40%, the pressing speed is controlled to be 15-25 mm / s, the feeding amount is controlled to be 300-500 mm, the reduction amount is controlled to be 105-145 mm, the hot material is re-melted twice after each heating time, the re-melting heating temperature is T β -(30-70) ℃, the heating coefficient is 0.3-0.4.

[0019] Further, in step 2), the forging mode of the second heating time is hexagonal elongation forging to dodecahedral elongation forging, and the deformation amount is controlled to be 15%-37%.

[0020] Further, in step 2), the third heating time is reducing elongation forging, and the heating temperature is T β -(30-70) ℃, the heating coefficient is 0.5-0.8, the hot material is re-melted after each heating time, and the re-melting temperature of the hot material is T β -(30-70) ℃, the holding coefficient is 0.3-0.4, the deformation amount is controlled to be 10%-35%, the pressing speed is controlled to be 15-25 mm / s, the feeding amount is controlled to be 120-400 mm, and the reduction amount is controlled to be 40-120 mm.

[0021] Further, in step 3), the heating temperature of the round breaking is T β -(30-70) ℃, the heating coefficient is 0.5-0.8, the deformation amount is controlled to be 10%-20%, the reduction amount is controlled to be 20-30 mm, and the feeding amount is controlled to be 120-300 mm.

[0022] Further, in step 3), the required size is 350 mm≤Φ≤350+20 mm.

[0023] In another aspect, the application also provides a TC21 titanium alloy large-size rod prepared by the preparation method.

[0024] The beneficial effects of the application are as follows:

[0025] 1) The application can obtain the titanium alloy large-size rod through 6 heating times by 2 heating times of blooming and 4 heating times of open-die forging, compared with the multiple heating times of the prior art, so that the production cost is greatly reduced.

[0026] 2) Compared with the same specification bar produced by other manufacturers for multiple times, the elongation and the reduction of area of the TC21 titanium alloy large specification bar prepared by the method of the present application is significantly higher than that of the existing same specification bar.

[0027] 3) The Φ350mm bar prepared by the method of the present application has excellent high temperature tensile properties, which can be increased by about 20-30% compared with the high temperature properties of the same specification TC4 titanium alloy at 400℃, and at the same time has excellent strength and toughness comprehensive properties at room temperature, and is expected to be used for high strength and toughness titanium alloy under high temperature conditions such as aviation and aerospace engines. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is the low-magnification microstructure diagram of the head, middle and tail cross sections of the TC21 titanium alloy Φ350mm large specification bar prepared by the forging method provided by the embodiment of the present application.

[0029] Figure 2 is the high-magnification microstructure diagram of the R / 2 position of the head, middle and tail cross sections of the TC21 titanium alloy Φ350mm large specification bar prepared by the forging method provided by the embodiment of the present application. DETAILED DESCRIPTION

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for describing particular embodiments only and is not intended to be limiting of the application.

[0031] In the present application, when a numerical interval (i.e. a numerical range) is involved, without specific indication, the numerical values distributed in the above numerical interval are considered to be continuous, and include the two numerical end points (i.e. the minimum value and the maximum value) of the numerical range, and every numerical value between the two numerical end points. Without specific indication, when the numerical interval only refers to the integers in the numerical interval, including the two end point integers of the numerical range, and every integer between the two end points, in this article, it is equivalent to directly listing every integer, for example, t is an integer selected from 1-10, which means that t is any integer selected from the group consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. In addition, when multiple ranges are provided to describe characteristics or properties, these ranges can be combined. In other words, unless otherwise indicated, the ranges disclosed herein should be understood to include any and all sub-ranges therein.

[0032] In the present application, the temperature parameter, without specific limitation, allows for constant temperature treatment, and also allows for variation within a certain temperature interval. It should be understood that the constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument. Fluctuation within a range such as ±5℃, ±4℃, ±3℃, ±2℃, ±1℃ is allowed.

[0033] The application provides a low-cost preparation method of a large-size TC21 titanium alloy rod, which comprises the following steps:

[0034] Step 1), two-pass open-die forging of a TC21 titanium alloy ingot:

[0035] In the first pass, the TC21 titanium alloy ingot is subjected to high-temperature forging in a β single-phase region to obtain a square-section intermediate blank ingot;

[0036] In the second pass, the square-section intermediate blank ingot is subjected to low-temperature upsetting and reversing elongation forging, and then high-temperature forging, to obtain a square-section intermediate blank ingot with a grain size of 1 mm to 2 mm;

[0037] Step 2), three-pass rod reforming of the intermediate blank ingot obtained in step 1):

[0038] In the first and second passes, the intermediate blank ingot is first upset and then elongated to form an octagonal-section intermediate blank, and in the third pass, the octagonal-section intermediate blank is elongated to form a dodecagonal-section intermediate blank;

[0039] Step 3), rod forming of the dodecagonal-section intermediate blank obtained in step 2):

[0040] The dodecagonal-section intermediate blank is upset to form a circular-section TC21 titanium alloy large-size rod with a desired size.

[0041] In some preferred embodiments, the application provides a low-cost preparation method of a large-size TC21 titanium alloy rod, which comprises the following steps:

[0042] Step 1, open-die forging of a TC21 titanium alloy ingot to obtain fine-grained structure. The titanium alloy ingot has a specification of a diameter of Φ720 mm and a single weight of 6 tons, and is divided into three equal parts.

[0043] Two-pass open-die forging of the TC21 titanium alloy ingot: in the first pass, the TC21 titanium alloy ingot (with a specification of Φ720x900 mm and a weight of 1.7 tons) is subjected to high-temperature forging above the β phase transition point. The first open-die forging temperature is T β +180-205℃, and the heating is performed by two-upset and two-elongation forging, with a cold material heating coefficient of 0.65-0.80, a deformation amount of each upsetting and elongation being controlled at 37%-45%, and a total forging ratio being 1.70-2.00. After forging, the material is subjected to hot charging and then recharging, and the recharging temperature is T β+105~125℃, the reheat factor is 0.3~0.4, after the furnace is discharged, two upsetting and two drawing are carried out, and the reversing is increased in the drawing process, so that the crystal grains are better broken and uniform structure is obtained, the deformation amount of each upsetting and drawing is controlled to be 37%~45%, and the hot material is continuously re-melted after forging, the re-melting temperature is T β +60~95℃, the reheat time is 60min-120min, the reheat factor is 0.3~0.4, after the furnace is discharged, two upsetting and two drawing are carried out, the deformation amount of each upsetting and drawing is controlled to be 37%~45%, and the forged product is air-cooled. The pressing speed in the forging process is controlled to be 20~35mm / s, the reduction is controlled to be 100~160mm, and the feed amount is controlled to be 280~500mm. The β structure with the grain size of 5~20mm is obtained.

[0044] The second fire is forged below the β phase transformation point temperature, the heating temperature is T β -(30~70)℃, the heating factor is 0.65~0.80, one upsetting and one drawing are carried out, the reversing drawing is increased in the drawing process, the total forging ratio is 1.2~2.0, the deformation amount is controlled to be 35%~40%, the pressing speed is controlled to be 15~30mm / s, the reduction is controlled to be 80~200mm, the feed amount is controlled to be 280~500mm, and the hot material is re-melted after forging; in order to obtain the uniformly distributed primary α phase structure, the hot material below the β phase transformation point temperature is re-melted, the heating temperature is T β -(30~70)℃, the reheat factor is 0.3~0.4, one upsetting and one drawing are carried out, the reversing drawing is increased in the drawing process, the total forging ratio is 1.6~2.0, the deformation amount is controlled to be 35%~40%, the pressing speed is controlled to be 15~30mm / s, the reduction is controlled to be 80~200mm, the feed amount is controlled to be 280~500mm, and the hot material is re-melted after forging, the re-melting temperature is the temperature on the β phase transformation point, that is, T β +(30~100)℃, the reheat factor is 0.3~0.4. The forging is carried out above the β phase transformation point temperature, the heating temperature is T β +(30~100)℃, the heating factor is 0.5, the total forging ratio is 1.2~1.5, the forged product is air-cooled, the rectangular blank with the high-diameter ratio of 1.8 is obtained, and the β structure with the grain size of 1~2mm is uniform and fine.

[0045] The reversing drawing is that the intermediate blank ingot is first forged along the axial direction, and then is drawn along the radial direction, and then is tempered, and then is forged along the radial direction.

[0046] Step 2, bar re-forging. The re-forging is carried out for three fires: the first two fires are one upsetting and one drawing, and one reversing drawing is added in the first fire and the second fire respectively, the heating temperature of each fire is T β(30-70)℃, heating coefficient is 0.5-0.8, deformation amount is controlled in 30%-40%, pressing speed is controlled in 15-25mm / s, feeding amount is controlled in 300-500mm, and pressing amount is controlled in 105-145mm, and hot material is re-furnaced twice after each forging, and the re-furnace heating temperature is T β (30-70)℃, heating coefficient is 0.3-0.4. The second-time forging mode is hexagonal drawing forging to dodecahedral drawing forging, and the deformation amount is controlled in 15%-37%. After forging, air cooling is performed to obtain a duplex structure containing primary alpha phase.

[0047] The third-time is reducing-diameter drawing forging. The heating temperature is T β (30-70)℃, heating coefficient is 0.5-0.8, and hot material is re-furnaced after each time, and the hot material re-furnace temperature is T β (30-70)℃, holding coefficient is 0.3-0.4. The drawing mode is hexagonal drawing and dodecahedral drawing, and the deformation amount is reduced in turn, and the deformation amount is controlled in 10%-35%, pressing speed is controlled in 15-25mm / s, feeding amount is controlled in 120-400mm, and pressing amount is controlled in 40-120mm. After forging, air cooling is performed.

[0048] Step 3, rod forming. Forming 1-time: V-drop, and the heating temperature is T β (30-70)℃, heating coefficient is 0.5-0.8, deformation amount is controlled in 10%-20%, preferably within 12%, pressing amount is controlled in 20-30mm, feeding amount is controlled in 120-300mm, and the final forging temperature is not lower than 800℃, and air cooling is performed after forging.

[0049] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application will be further described in detail below by combining with specific examples and the drawings of the specification. The specific examples described herein are only used to explain the present application, and the present application is not limited to this.

[0050] Example 1, preparation of Φ350mm TC21 titanium alloy large-size rod

[0051] The present application provides a preparation method of low-cost TC21 titanium alloy large-size rod, and the method is implemented according to the following steps:

[0052] Ingot open forging: select 1.7 tons of specification Φ720 mm TC21 titanium alloy ingot with the required chemical composition, and carry out 2 fire open forging. First, heat the ingot to 1150℃, and keep for 430 min. After discharging, carry out the first fire forging, and carry out two upsetting and two drawing forging. The deformation amount during drawing is controlled at 42%. After forging, the hot material is recycled, the recycling temperature is 1080℃, and the keeping time is 150 min. After discharging, carry out two upsetting and two drawing forging. The deformation amount of upsetting and drawing is controlled at 40%. After forging, continue to recycle the hot material, the recycling temperature is 1040℃, and the keeping time is 150 min. After discharging, carry out two upsetting and two drawing forging. The deformation amount of upsetting and drawing is controlled at 40%. The specification after forging is a square with a cross-sectional side length of 620 mm. The upsetting and drawing pressing speed of the first fire is controlled at 30 mm / s. The final forging temperature is controlled above 800℃, and the material after forging is cooled by air cooling.

[0053] The heating temperature of the second fire open forging is 920℃, and the keeping time is 430 min. After discharging, carry out one upsetting and one drawing. The drawing method is reversing drawing and inverted octagon, and the upsetting and drawing deformation amount is controlled at 37%. The upsetting and drawing pressing speed is 20 mm / s. After forging, recycle the hot material, the recycling temperature is 920℃, and the keeping time is 150 min. After discharging, carry out one upsetting and one drawing. The drawing method is reversing drawing and inverted octagon, and the upsetting and drawing deformation amount is controlled at 37%. The upsetting and drawing pressing speed is 20 mm / s. After forging, continue to recycle the hot material, the recycling temperature is 1010℃, and the keeping time is 300 min. After discharging, carry out one upsetting and one drawing. The drawing method is drawing and inverted octagon, and the upsetting and drawing deformation amount is controlled at 37%. The upsetting and drawing pressing speed is 30 mm / s. The specification after forging is a cross-sectional side length of 606 mm. The final forging temperature is controlled above 800℃, and the material after forging is cooled by air cooling to obtain an intermediate blank.

[0054] Three fire rod forging in α+β two-phase region: the intermediate blank obtained above is subjected to 3 fire forging. The first fire heating temperature is 920℃, and the keeping time is 420 min. After discharging, carry out one upsetting and one drawing. The drawing method is drawing and inverted octagon, and the upsetting and drawing deformation amount is controlled at 37%. After forging, recycle the hot material, the recycling temperature is 920℃, and the keeping time is 150 min. After discharging, carry out one upsetting and one drawing. The drawing method is reversing drawing and inverted octagon, and the upsetting and drawing deformation amount is controlled at 37%. After forging, continue to recycle the hot material, the recycling temperature is 920℃, and the keeping time is 150 min. After discharging, carry out one upsetting and one drawing. The drawing method is diagonal drawing and inverted octagon, and the upsetting and drawing deformation amount is controlled at 37%. The upsetting and drawing pressing speed is controlled at 20 mm / s. The specification after forging is a cross-sectional side length of 600 mm, and air cooling is carried out after forging.

[0055] The second heating temperature is 920 DEG C, the holding time is 420 min, after discharging, one upsetting and one drawing is carried out, the drawing mode is reversing drawing and octagonal, the upsetting and drawing deformation is controlled to be 37%. After forging, the hot material is recycled, the recycling temperature is 920 DEG C, the holding time is 150 min, after discharging, one upsetting and one drawing is carried out, the drawing mode is diagonal drawing, the upsetting and drawing deformation is controlled to be 37%. After forging, the hot material is continuously recycled, the recycling temperature is 920 DEG C, the holding time is 150 min, after discharging, one upsetting and one drawing is carried out, the drawing mode is diagonal drawing and octagonal, the upsetting and drawing deformation is controlled to be 37%. The upsetting and drawing pressing speed is controlled to be 20 mm / s. After forging, the specification is that the cross section side length is 594 mm, and the forged material is air cooled.

[0056] The third heating temperature is 920 DEG C, the holding time is 420 min, after discharging, six square drawing is carried out, the deformation is controlled to be 37%, and the drawing pressing speed is 20 mm / s. After forging, the hot material is recycled, the heating temperature is 920 DEG C, the holding time is 160 min, after discharging, six square drawing is carried out first, the deformation is controlled to be 20%, the cross section is drawn to be 412 mm, then twelve square drawing is carried out, the deformation is controlled to be 12.5%, the drawing pressing speed is 20 mm / s, and the specification after forging is that the cross section side length is 400 mm, and the forged material is air cooled.

[0057] The α+β two-phase zone bar forming: the bar material with the cross section side length of 400 mm obtained after the reforming is subjected to one-time forming. The heating temperature is 920 DEG C, the holding time is 280 min, after discharging, round forming is carried out, the anvil is V-shaped anvil, the deformation is controlled to be 17%, the pressing speed is controlled to be 20 mm / s, and the specification after forging is that the bar blank is Φ365 mm.

[0058] The Φ365 mm bar blank of TC21 titanium alloy prepared in Example 1 is subjected to mechanical processing, and finally the TC21 titanium alloy large-size bar with the diameter of Φ350 mm and the single weight of 1.3 tons is prepared.

[0059] The Φ350 mm bar prepared in Example 1 is subjected to macrostructure observation, and according to the macrostructure observation standard of the aviation standard, it can be known that the macrostructure of the head, the middle and the tail of the bar is uniform and fuzzy, and there is no visible clear grain, no visible metallurgical defects such as stratification, cracks, pores, segregation, metal and non-metallic inclusions and other visible metallurgical defects, which meets the requirements of the aviation standard. Figure 1 It can be known that the macrostructure of the head, the middle and the tail of the bar is uniform and fuzzy, and there is no visible clear grain, no visible metallurgical defects such as stratification, cracks, pores, segregation, metal and non-metallic inclusions and other visible metallurgical defects, which meets the requirements of the aviation standard.

[0060] The Φ350 mm bar prepared in Example 1 is subjected to macrostructure observation, and according to the macrostructure observation standard of the aviation standard, it can be known that the macrostructure of the head, the middle and the tail of the bar is uniform and fuzzy, and there is no visible clear grain, no visible metallurgical defects such as stratification, cracks, pores, segregation, metal and non-metallic inclusions and other visible metallurgical defects, which meets the requirements of the aviation standard. Figure 2 It can be known that the macrostructure of the head, the middle and the tail of the bar is uniform and fuzzy, and there is no visible clear grain, no visible metallurgical defects such as stratification, cracks, pores, segregation, metal and non-metallic inclusions and other visible metallurgical defects, which meets the requirements of the aviation standard.

[0061] Table 1 provides the room temperature tensile properties of the head, middle and tail cross-sections of the Φ350 mm large-diameter TC21 titanium alloy rod prepared by the forging method.

[0062] Table 1 Room temperature tensile properties of the head, middle and tail cross-sections of the rod at the R / 2 position

[0063]

[0064] As can be seen from Table 1, the test results meet the requirements of the aviation standard, have good uniformity and a certain amount of surplus, and the differences in the longitudinal and transverse directions of the head, middle and tail of the rod are small.

[0065] Table 2 provides the fracture toughness of the head, middle and tail cross-sections of the Φ350 mm large-diameter TC21 titanium alloy rod prepared by the forging method at the D / 2-D / 4 position in different directions, and the average value of the fracture toughness in different directions is 90.0 MPa·m 1 / 2 As can be seen from Table 2, the fracture toughness in different directions of different parts of the rod meets the requirements of the aviation standard, has good uniformity and a certain amount of surplus.

[0066] Table 2 Fracture toughness of the head, middle and tail cross-sections of the rod at the R / 2 position in different directions

[0067]

[0068] Table 3 provides the U-type impact value of the head, middle and tail cross-sections of the Φ350 mm large-diameter TC21 titanium alloy rod prepared by the forging method at the R / 2 position in different directions. As can be seen from Table 3, the impact values in different directions of different parts of the rod meet the requirements of the aviation standard, have good uniformity and a certain amount of surplus.

[0069] Table 3 U-type impact toughness of the head, middle and tail cross-sections of the rod at the R / 2 position in different directions

[0070]

[0071]

[0072] Table 4 provides the high-temperature tensile properties of the head, middle and tail cross-sections of the Φ350 mm large-diameter TC21 titanium alloy rod prepared by the forging method at the R / 2 position. As can be seen from Table 4, the high-temperature tensile strength at the R / 2 position of the transverse direction of the rod is high.

[0073] Table 4 High-temperature tensile properties of the head, middle and tail cross-sections of the rod at the R / 2 position at 400℃

[0074] Position Direction Rm (MPa) [R P0.2 (MPa)]]> A (％) Z(％) Head Transverse 868 699 19.9 57.0 Mid Transverse 856 696 18.3 57.8 Tail Transverse 871 704 19.5 54.4

[0075] The TC21 titanium alloy ingot with a single weight of 6 tons is subjected to 2 times of blooming and 4 times of forging forming, so that the production cost is greatly reduced The rod performance and structure are excellent. Compared with the TC21 titanium alloy rod with a diameter of 350 mm produced by multiple times of production disclosed in CN 103510030 A, the elongation and the area reduction of the rod of the same specification prepared by using the method of the application are significantly higher, the average elongation can be increased by nearly 1 times, the area reduction can be increased by nearly 1.68 times, the tensile strength is only reduced by 6.7%, the yield strength is only reduced by 7.2%, the plasticity is greatly improved, the fracture toughness is equivalent to that of West Superconducting, and both are 90 MPa.m 1 / 2 .

[0076] It should be pointed out that the above-described embodiments are only preferred embodiments of the application. For ordinary skilled in the art, some modifications, improvements and equivalent replacements can be made to the application without departing from the principles of the application, and these modifications, improvements and equivalent replacements are also considered to fall within the protection scope of the claims of the application.

Claims

1. A method of producing a large-diameter bar of TC21 titanium alloy, characterized in that, The method comprises the following steps: Step 1), two-fire open-die forging of a TC21 titanium alloy ingot: In the first fire, the TC21 titanium alloy ingot is subjected to high-temperature forging in a beta single-phase region to obtain a square-section intermediate ingot; In the second fire, the square-section intermediate ingot is subjected to low-temperature upsetting and reversing elongation forging, and then high-temperature forging, to obtain a square-section intermediate ingot with a grain size of 1mm-2mm; In the step 1), the first forging is carried out at a high temperature above the β phase transformation point, the first breakdown temperature is T β +180~205℃, the heating is carried out by two upsetting and two drawing forging, the heating coefficient is 0.65~0.80, the total forging ratio is 1.70~2.00, the hot material is returned to the furnace after the forging, the return-to-furnace temperature is T β +105~125℃, the two upsetting and two drawing forging is carried out after the furnace is discharged, the hot material is returned to the furnace after the forging, the return-to-furnace temperature is T β +60~95℃, the two upsetting and two drawing forging is carried out again, the air cooling is carried out after the forging, the pressing speed in the forging process is controlled to be 20~35mm / s, the reduction is controlled to be 100~160mm, the feed amount is controlled to be 280~500mm, and the β organization with the grain size of 5~20mm is obtained. In the step 1), the second heating is low temperature forging below the β phase transformation point temperature, the heating temperature is T β -(30-70) °C, the heating coefficient is 0.65-0.80, upsetting and reversing elongation are carried out, the total forging ratio is 1.6-2.0, and hot material is recycled after forging, the recycling temperature is T β +(30-100) °C; then high temperature forging above the β phase transformation point temperature is carried out, the heating temperature is T β +(30-100) °C, the heating coefficient is 0.5, the total forging ratio is 1.2-1.5, and air cooling is carried out after forging, so that the intermediate blank ingot is obtained, which is β structure with grain size of 1-2 mm. Step 2), α+β two-phase region three-fire bar modification forging of the intermediate ingot obtained in step 1): In the first and second fires, the intermediate ingot is first upset and then elongated to obtain an octagonal-section intermediate material; In the third fire, the octagonal-section intermediate material is elongated to an twelve-sided-section intermediate material; In step 2), the heating temperature of the first 2 heating times is T β - (30-70) °C, the heating coefficient is 0.5-0.8, the deformation amount is controlled at 30%-40%, the pressing speed is controlled at 15-25 mm / s, the feeding amount is controlled at 300-500 mm, the reduction is controlled at 105-145 mm, and after each heating time, the hot material is re-melted twice, and the re-melting heating temperature is T β - (30-70) °C, the heating coefficient is 0.3-0.4; In step 2), the third heating is a reducing and elongating forging, and the heating temperature is T β - (30-70) °C, the heating coefficient is 0.5-0.8, the hot material is recycled after each heating, and the hot material recycling temperature is T β - (30-70) °C, the holding coefficient is 0.3-0.4, the deformation is controlled at 10%-35%, the pressing speed is controlled at 15-25 mm / s, the feeding amount is controlled at 120-400 mm, and the reduction is controlled at 40-120 mm; Step 3), α+β two-phase region bar forming of the twelve-sided-section intermediate material obtained in step 2): The twelve-sided-section intermediate material is upset to a circular-section TC21 titanium alloy large-diameter bar with a desired size; In step 3), the heating temperature of the broken round is T β - (30-70) °C, heating coefficient is 0.5-0.8, deformation amount is controlled at 10%-20%, reduction amount is controlled at 20-30 mm, and feeding amount is controlled at 120-300 mm; In step 3), the desired size is 350mm≤Φ≤350+20mm.

2. The method of making TC21 titanium alloy large-scale bar according to claim 1, characterized in that, In the first fire of step 1), the upsetting and elongation deformation amount is controlled to be 37%-45% each time, and in the second fire, the deformation amount is controlled to be 35%-40%.

3. The method of making TC21 titanium alloy large-scale bar according to claim 1, characterized in that, In step 1), the reversing elongation is that the intermediate ingot is first subjected to axial upsetting forging, and then radial elongation forging; and then tempering, followed by radial upsetting and subsequent axial elongation forging.

4. The method of making TC21 titanium alloy large-scale bar according to claim 1, characterized in that, In step 2), the forging mode of the second fire is hexagonal elongation forging to twelve-sided elongation forging, and the deformation amount is controlled to be 15%-37%.

5. A TC21 titanium alloy large-size bar, characterized in that, The method is prepared by any one of claims 1-4.

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