Preparation method of low-cost TC21 titanium alloy large-specification bar

Abstract

The invention relates to a preparation method of a low-cost TC21 titanium alloy large-specification bar, which comprises the following steps: 1) carrying out two-heating cogging forging on a TC21 titanium alloy ingot: carrying out beta single-phase region high-temperature forging at the first heating to obtain an intermediate billet ingot with a square cross section; in the second heating number, low-temperature upsetting and reversing drawing-out forging are carried out, then high-temperature forging is carried out, and an intermediate billet cast ingot with the square section and the grain size being 1-2 mm is obtained; (2) three-heating-number bar forging is carried out, specifically, in the first heating number to the second heating number, the intermediate blank cast ingot is upset and then drawn out and forged into a blank with the octagonal section in each heating number, and in the third heating number, the intermediate blank is drawn out into an intermediate blank with the twelve-square section; and (3) forming and forging for one heating number, wherein the middle blank with the twelve-square section is milled into a rod blank with the round section and the required size. By means of the method, the uniformity of the bar structure is improved, and the TC21 titanium alloy large-specification bar with the structure and performance meeting the requirements of phi 350 mm can be prepared at low cost.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy production and processing, and specifically relates to a method for preparing large-size TC21 titanium alloy bars. Background Art

[0002] TC21 titanium alloy is a new type of high-strength, high-toughness, high-damage tolerance titanium alloy independently developed by my country with independent intellectual property rights. It belongs to Ti-Al-Sn-Zr-Mo-Cr-Nb-Si two-phase titanium alloy, with excellent strength, plasticity, fracture toughness and low crack growth rate. It is widely used in the aerospace industry, especially in the field of aircraft structural parts, such as large aircraft frames, beams and other key load-bearing parts. Due to the high degree of alloying and poor forgeability of TC21 titanium alloy, for large-size bars with a diameter of more than 350mm, conventional forging methods are used, with many fires and prone to unevenness of transverse and longitudinal structures.

[0003] In order to reduce the forging cost of large-sized TC21 titanium alloy bars with a diameter of more than 350 mm, improve the organizational uniformity of large-sized TC21 titanium alloy bars, and meet the development needs of the aviation and aerospace industries, it is urgent to develop a new low-cost method for preparing large-sized TC21 titanium alloy bars. Summary of the invention

[0004] In order to overcome the above-mentioned shortcomings of the prior art, the present invention provides a method for preparing large-size TC21 titanium alloy bars, by successively subjecting the titanium alloy ingot to high-temperature forging, low-temperature forging + high-temperature forging, and low-temperature forging, and providing a new method for preparing large-size TC21 titanium alloy bars through 2 rounds of blanking and 4 rounds of forging to obtain large-size titanium alloy bars with low cost and good structural uniformity.

[0005] In order to achieve the above object, the present invention adopts the following technical solution.

[0006] On the one hand, the present invention provides a method for preparing a large-size TC21 titanium alloy bar, which comprises:

[0007] Step 1) Perform two-stage forging of the TC21 titanium alloy ingot:

[0008] In the first firing, the TC21 titanium alloy ingot is subjected to high temperature forging in the β single phase region to obtain an intermediate billet ingot with a square cross section;

[0009] In the second firing, the intermediate billet ingot with a square cross section is subjected to low temperature upsetting and reversing drawing forging, and then subjected to high temperature forging to obtain an intermediate billet ingot with a square cross section and a grain size of 1 mm to 2 mm;

[0010] Step 2), the intermediate billet ingot obtained in step 1) is subjected to α+β two-phase region three-fire bar forging:

[0011] In the first and second firings, the intermediate billet ingot is first upset and then stretched and forged into an intermediate billet with an octagonal cross section, and in the third firing, the intermediate billet with an octagonal cross section is stretched into an intermediate billet with a twelve-square cross section;

[0012] Step 3), forming the intermediate billet with a cross section of twelve squares obtained in step 2) into an α+β two-phase region rod:

[0013] The intermediate billet with a dodecagonal cross section is rounded into a large-size TC21 titanium alloy bar with a circular cross section and a required size.

[0014] Furthermore, in the step (1), the first heat is forged at a high temperature above the β phase transformation point, and the first blanking temperature is T β +180~205℃, heating for two upsetting and two drawing forging, heating coefficient is 0.65~0.80, total forging ratio is 1.70~2.00, hot material is returned to the furnace after forging, the return temperature is T β +105~125℃, after being taken out of the furnace, two upsetting and two drawing forging are carried out, and after forging, the hot material is returned to the furnace, and the returning furnace temperature is T β +60~95℃, then double upsetting and double drawing forging, air cooling after forging, the pressing speed of the forging process is controlled at 20~35mm / s, the pressing amount is controlled at 100~160mm, and the feed amount is controlled at 280~500mm, to obtain a β structure with a grain size of 5~20mm;

[0015] The second heat is low temperature forging below the β phase transformation point temperature, and the heating temperature is T β -(30~70)℃, heating coefficient is 0.65~0.80, upsetting and reversing drawing are carried out, the total forging ratio is 1.6~2.0, and the hot material is returned to the furnace after forging, and the return temperature is T β +(30~100)℃; then forge at high temperature above the β phase transformation point, the heating temperature is T β +(30~100)℃, heating coefficient is 0.5, total forging ratio is 1.2~1.5, air cooling is performed after forging to obtain an intermediate billet ingot, which is a β structure with a grain size of 1~2mm.

[0016] Furthermore, in the first firing of step 1), the deformation amount of each upsetting is controlled within a range of 37% to 45%, and in the second firing, the deformation amount is controlled within a range of 35% to 40%.

[0017] Furthermore, in step 1), the reversing drawing is to first perform upsetting forging on the intermediate billet ingot in the axial direction, and then perform drawing forging in the radial direction; then perform tempering, and after tempering, perform radial upsetting, and then perform drawing forging in the axial direction.

[0018] Furthermore, in step 2), the heating temperature of the first and second firings is T β -(30~70)℃, heating coefficient is 0.5~0.8, deformation is controlled at 30%~40%, pressing speed is controlled at 15~25mm / s, feed amount is controlled at 300~500mm, pressing amount is controlled at 105~145mm, hot material is returned to the furnace twice after each fire forging, and the heating temperature is T β -(30~70)℃, heating coefficient is 0.3~0.4.

[0019] Furthermore, in step 2), the second forging method is hexagonal drawing forging to twelve-square drawing forging, and the deformation is controlled at 15% to 37%.

[0020] Further, in step 2), the third fire is a diameter reducing and drawing forging, and the heating temperature is T β -(30~70)℃, heating coefficient is 0.5~0.8, hot material is returned to the furnace after each firing, and the temperature of hot material is T β -(30~70)℃, thermal insulation coefficient is 0.3~0.4, deformation is controlled at 10%~35%, pressing speed is controlled at 15~25mm / s, feed amount is controlled at 120~400mm, and reduction amount is controlled at 40~120mm.

[0021] Furthermore, in step 3), the heating temperature of the rounding is T β -(30~70)℃, heating coefficient is 0.5~0.8, deformation is controlled at 10%~20%, reduction is controlled at 20~30mm, and feed amount is controlled at 120~300mm.

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

[0023] On the other hand, the present invention also provides a large-size TC21 titanium alloy bar, which is prepared by the above-mentioned preparation method.

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

[0025] 1) The present invention subjects the TC21 titanium alloy ingot to two-fire forging and four-fire forging. Compared with the multi-fire forging in the prior art, large-size titanium alloy bars can be obtained by only six fires, which greatly reduces the production cost.

[0026] 2) Compared with the bars of the same specification produced by other manufacturers through multiple firings, the elongation and cross-sectional shrinkage of the large-size TC21 titanium alloy bars prepared by the method of the present invention at room temperature are significantly higher than those of the existing bars of the same specification.

[0027] 3) The Φ350 mm rod prepared by the method of the present invention has excellent high-temperature tensile properties, which can be improved by nearly 20-30% compared with the high-temperature performance of TC4 titanium alloy of the same specification at 400°C. At the same time, it has excellent comprehensive strength and toughness properties at room temperature, and is expected to be used as a high-strength and tough titanium alloy under high-temperature conditions such as aviation and aerospace engines. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The present invention provides a low-magnification microstructure diagram of the cross-section of the head, middle and tail of a TC21 titanium alloy Φ350 mm large-size bar prepared by the forging method provided in an embodiment of the present invention.

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

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used in the specification of the present invention are only used for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0031] In the present invention, when it comes to numerical intervals (i.e., numerical ranges), unless otherwise specified, the optional numerical distribution is considered continuous within the above numerical interval, and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical range, and each numerical value between the two numerical endpoints. Unless otherwise specified, when the numerical interval only refers to the integers within the numerical interval, it includes the two endpoint integers of the numerical range, and each integer between the two endpoints. In this article, it is equivalent to directly listing each integer, such as t is an integer selected from 1-10, indicating that t is any integer selected from the integer group consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. In addition, when multiple ranges are provided to describe features or characteristics, these ranges can be combined. In other words, unless otherwise specified, the ranges disclosed herein should be understood to include any and all sub-ranges included therein.

[0032] The temperature parameters in the present invention, if not specifically limited, are allowed to be either constant temperature treatment or to vary within a certain temperature range. It should be understood that the constant temperature treatment allows the temperature to fluctuate within the precision range controlled by the instrument. Fluctuations within the range of ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are allowed.

[0033] The present invention provides a low-cost method for preparing large-size TC21 titanium alloy bars, comprising the following steps:

[0034] Step 1) Perform two-stage forging of the TC21 titanium alloy ingot:

[0035] In the first fire, the TC21 titanium alloy ingot is subjected to high temperature forging in the β single phase region to obtain an intermediate billet ingot with a square cross section;

[0036] In the second fire, the intermediate billet ingot with a square cross section is subjected to low temperature upsetting and reversing drawing forging, and then subjected to high temperature forging to obtain an intermediate billet ingot with a square cross section and a grain size of 1 mm to 2 mm;

[0037] Step 2), the intermediate billet ingot obtained in step 1) is subjected to three-stage bar forging:

[0038] In the first and second firings, the intermediate billet ingot is first upset and then stretched and forged into an intermediate billet with an octagonal cross section. In the third firing, the intermediate billet with an octagonal cross section is stretched into an intermediate billet with a twelve-square cross section.

[0039] Step 3), the intermediate blank with a cross section of twelve squares obtained in step 2) is subjected to rod forming:

[0040] The intermediate billet with a twelve-square cross section is rounded into a large-size TC21 titanium alloy bar with a circular cross section and a required size.

[0041] In some preferred embodiments, the present invention provides a method for preparing a large-size TC21 titanium alloy bar at a low cost, comprising the following steps:

[0042] Step 1: TC21 titanium alloy ingot is blanked to obtain fine grain structure. The titanium alloy ingot has a diameter of Φ720 mm and a single weight of 6 tons and is divided into three equal parts.

[0043] The TC21 titanium alloy ingot was forged in two fires: In the first fire, the TC21 titanium alloy ingot (specification Φ720x900mm, weight 1.7 tons) was forged at a high temperature above the β phase transformation point. β +180~205℃, heating for two upsetting and two drawing forging, the cold material heating coefficient is 0.65~0.80, the deformation of each upsetting and drawing is controlled at 37%~45%, and the total forging ratio is 1.70~2.00. After forging, the hot material is returned to the furnace, and the furnace temperature is T β+105~125℃, the heat preservation coefficient of the furnace is 0.3~0.4, and two upsetting and two drawing forging are carried out after the furnace is taken out, and the direction is increased during the drawing process to better break the grains and obtain uniform structure. The deformation of each upsetting and drawing is controlled at 37%~45%. After forging, the hot material is returned to the furnace, and the furnace temperature is T β +60~95℃, heating time for 60min-120min, heat preservation coefficient for 0.3~0.4, two upsetting and two drawing forging after out of the furnace, each upsetting and drawing deformation is controlled at 37%~45%, air cooling after forging. The pressing speed of the forging process is controlled at 20~35mm / s, the pressing amount is controlled at 100~160mm, and the feed amount is controlled at 280~500mm. A β structure with a grain size of 5~20mm is obtained.

[0044] The second fire is low temperature forging below the β phase transformation point, and the heating temperature is T β -(30~70)℃, heating coefficient is 0.65~0.80, one upsetting and one drawing forging is carried out, and reversing drawing is added during the drawing process, the total forging ratio is 1.2~2.0, the deformation is controlled at 35%~40%, the pressing speed is controlled at 15~30mm / s, the pressing amount is controlled at 80~200mm, the feed amount is controlled at 280~500mm, and the hot material is returned to the furnace after forging; in order to obtain a uniformly distributed primary α phase structure, it is necessary to return the hot material below the β phase transformation point temperature once, and the heating temperature is T β -(30~70)℃, the heat preservation coefficient of the furnace is 0.3~0.4, one upsetting and one drawing forging is carried out, and the reversing drawing is added during the drawing process, the total forging ratio is 1.6~2.0, the deformation is controlled at 35%~40%, the pressing speed is controlled at 15~30mm / s, the pressing amount is controlled at 80~200mm, the feed amount is controlled at 280~500mm, and the hot material is returned to the furnace after forging. The furnace temperature is the temperature at the β phase transformation point, that is, T β +(30~100)℃, the heat preservation coefficient of the furnace is 0.3~0.4. Forging at high temperature above the β phase transformation point, the heating temperature is T β +(30~100)℃, heating coefficient is 0.5, total forging ratio is 1.2~1.5, air cooling is performed after forging, and a rectangular billet with a height-to-diameter ratio of 1.8 and a uniform and fine β structure with a grain size of 1~2mm is obtained.

[0045] The reverse direction drawing is to firstly perform upsetting forging on the intermediate billet ingot in the axial direction, and then perform drawing forging in the radial direction; then perform tempering, and after tempering, perform radial upsetting, and then perform drawing forging in the axial direction.

[0046] Step 2: Reforge the bar. Reforge 3 times: The first two times are one upsetting and one drawing, and one reversing drawing is added in the first and second times, and the heating temperature of each time is T β-(30~70)℃, heating coefficient is 0.5~0.8, deformation is controlled at 30%~40%, pressing speed is controlled at 15~25mm / s, feed amount is controlled at 300~500mm, pressing amount is controlled at 105~145mm, hot material is returned to the furnace twice after each fire forging, and the heating temperature is T β -(30~70)℃, heating coefficient is 0.3~0.4. The second forging method is hexagonal drawing forging, then twelve-square drawing forging, and the deformation is controlled at 15%~37%. After forging, air cooling is performed to obtain a dual-state structure containing a certain amount of primary α phase.

[0047] The third fire is forging with reduced diameter and drawn length. The heating temperature is T β -(30~70)℃, heating coefficient is 0.5~0.8, hot material is returned to the furnace after each firing, and the temperature of hot material is T β -(30~70)℃, insulation coefficient is 0.3~0.4. The drawing methods are hexagonal and twelve-sided drawing, the deformation amount decreases successively, the deformation amount is controlled at 10%~35%, the pressing speed is controlled at 15~25mm / s, the feed amount is controlled at 120~400mm, and the pressing amount is controlled at 40~120mm. Air cooling after forging.

[0048] Step 3: Rod forming. Forming 1 fire: V-throw, heating temperature is T β -(30~70)℃, heating coefficient is 0.5~0.8, deformation is controlled within 10%~20%, preferably within 12%, reduction is controlled within 20~30mm, feed rate is controlled within 120~300mm, final forging temperature is not less than 800℃, and air cooling is performed after forging.

[0049] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with specific embodiments and drawings of the specification. The specific embodiments described here are only used to explain the present invention, and the present invention is not limited thereto.

[0050] Example 1 Preparation of Φ350mm TC21 Titanium Alloy Large-Sized Bar

[0051] The present invention provides a method for preparing a low-cost TC21 titanium alloy large-size bar, which is implemented according to the following steps:

[0052] Ingot forging: A 1.7-ton TC21 titanium alloy ingot with a specification of Φ720mm and chemical composition that meets the requirements is selected for two-fire forging. The ingot is first heated to 1150℃ and kept warm for 430min. After it is taken out of the furnace, it is forged for the first time, and two upsetting and two drawing forgings are performed. The deformation during drawing is controlled at 42%. After forging, the hot material is returned to the furnace at a temperature of 1080℃ and kept warm for 150min. After it is taken out of the furnace, two upsetting and two drawing forgings are performed. The deformation of upsetting and drawing is controlled at 40%. After forging, the hot material is continued to be returned to the furnace at a temperature of 1040℃ and kept warm for 150min. After it is taken out of the furnace, two upsetting and two drawing forgings are performed. The deformation of upsetting and drawing is controlled at 40%. The specifications after forging are square with a cross-sectional side length of 620mm. The upsetting and drawing pressing speed of the first fire is controlled at 30mm / s. The final forging temperature is controlled above 800℃, and the material is cooled by air cooling after forging.

[0053] The heating temperature of the second fire of the billet is 920℃, and the temperature is kept for 430min. After it comes out of the furnace, it is upset and drawn. The drawing method is to pull and draw in reverse direction. The deformation of upsetting and drawing is controlled at 37%, and the pressing speed of upsetting and drawing is 20mm / s. The hot material is returned to the furnace after forging. The furnace temperature is 920℃, and the temperature is kept for 150min. After it comes out of the furnace, it is upset and drawn. The drawing method is to pull and draw in reverse direction. The deformation of upsetting and drawing is controlled at 37%, and the pressing speed of upsetting and drawing is 20mm / s. After forging, the hot material is returned to the furnace at a temperature of 1010°C and a holding time of 300 minutes. After being taken out of the furnace, it is subjected to upsetting and drawing. The drawing method is to draw the material in eight directions. The upsetting deformation is controlled at 37%. The upsetting pressing speed is 30 mm / s. The specification after forging is that the cross-section side length is 606 mm. The final forging temperature is controlled at above 800°C. The material after forging is cooled by air cooling to obtain an intermediate billet.

[0054] α+β two-phase zone three-fire bar forging: The intermediate billet obtained above is forged for three times. The heating temperature of the first fire is 920℃, the holding time is 420min, and after coming out of the furnace, it is upsetting and pulling. The pulling method is pulling and turning eight directions, and the upsetting deformation is controlled at 37%. After forging, the hot material is returned to the furnace, the furnace temperature is 920℃, the holding time is 150min, and after coming out of the furnace, it is upsetting and pulling. The pulling method is reversing pulling and turning eight directions, and the upsetting deformation is controlled at 37%. After forging, the hot material is continued to be returned to the furnace, the furnace temperature is 920℃, and the holding time is 150min. After coming out of the furnace, it is upsetting and pulling. The pulling method is diagonal pulling and turning eight directions, and the upsetting deformation is controlled at 37%. The upsetting and pulling pressing speed is controlled at 20mm / s. The specifications after forging are 600mm in cross-section side length, and air cooling after forging.

[0055] The second heating temperature is 920℃, the holding time is 420min, and after coming out of the furnace, it is upsetting and pulling. The pulling method is to pull and pull in reverse direction, and the deformation of upsetting and pulling is controlled at 37%. After forging, the hot material is returned to the furnace, and the furnace temperature is 150min. After coming out of the furnace, it is upsetting and pulling. The pulling method is diagonal pulling, and the deformation of upsetting and pulling is controlled at 37%. After forging, the hot material is returned to the furnace, and the furnace temperature is 920℃, and the heat preservation is 150min. After coming out of the furnace, it is upsetting and pulling. The pulling method is diagonal pulling and pulling in reverse direction, and the deformation of upsetting and pulling is controlled at 37%. The upsetting and pulling pressing speed is controlled at 20mm / s. The specifications after forging are that the side length of the section is 594mm, and air cooling is performed after forging.

[0056] The third fire is forging with diameter reduction and drawing, the heating temperature is 920℃, the holding time is 420min, and the hexagonal drawing is carried out after the furnace is taken out, the deformation is controlled at 37%, and the drawing speed is 20mm / s. After forging, the hot material is returned to the furnace, the heating temperature is 920℃, the holding time is 160min, and the hexagonal drawing is carried out after the furnace is taken out, the deformation is controlled at 20%, and the cross section is 412mm, and then the twelve-sided drawing is carried out, the deformation is controlled at 12.5%, and the drawing speed is 20mm / s. The specifications after forging are 400mm in cross-section length, and air cooling is carried out after forging.

[0057] α+β two-phase region bar forming: The bar with a cross-section length of 400mm obtained after forging is formed in one fire. The heating temperature is 920℃, the holding time is 280min, and the rounding is performed after it comes out of the furnace. The anvil is a V-shaped anvil, the deformation is controlled at 17%, the pressing speed is controlled at 20mm / s, and the specification after forging is Φ365mm.

[0058] The TC21 titanium alloy Φ365 mm rod blank prepared in Example 1 was machined to finally prepare a large-size TC21 titanium alloy rod with a diameter of Φ350 mm and a single weight of 1.3 tons.

[0059] The Φ350 mm rod prepared in Example 1 was observed at low magnification. Figure 1 It can be seen that there is no delamination, cracks, pores, segregation, metal and non-metallic inclusions and other metallurgical defects visible to the naked eye at the head, middle and tail of the rod macrostructure, no clear grains visible to the naked eye, and the macrostructure is uniform and blurred, meeting the requirements of aviation standards.

[0060] The Φ350 mm rod prepared in Example 1 was observed under high magnification. Figure 2 It can be seen that the high-magnification structure of the head, middle and tail cross-sections of the TC21 titanium alloy Φ350mm large-size bar at the R / 2 position is composed of equiaxed α phase and a small amount of short rod-shaped primary α phase. The high-magnification structure is uniform, and no abnormal thermal structure is seen. The high-magnification structure of the bar microstructure is uniform, meeting the requirements of aviation standards.

[0061] Table 1 provides the room temperature tensile properties of the TC21 titanium alloy Φ350mm large-size bar prepared by the forging method in different directions at the R / 2 position of the head, middle and tail cross sections.

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

[0063]

[0064] It can be seen from Table 1 that the test results all meet the requirements of aviation standards, have good uniformity and a certain amount of margin, and have small differences in the transverse and longitudinal directions of the head, middle and tail of the bar.

[0065] Table 2 provides the fracture toughness of the head, middle and tail cross sections of the TC21 titanium alloy Φ350mm large-size bar prepared by this forging method at different directions at positions D / 2 to D / 4. The average fracture toughness in different directions is 90.0MPa·m 1 / 2 It can be seen from Table 2 that the fracture toughness of different parts and directions of the rod meets the requirements of aviation standards, with good uniformity and a certain degree of redundancy.

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

[0067]

[0068] Table 3 provides the U-shaped impact values ​​of the head, middle and tail cross sections R / 2 positions of the TC21 titanium alloy Φ350mm large-size bar prepared by this forging method in different directions. It can be seen from Table 3 that the impact values ​​of different parts and directions of the bar meet the requirements of aviation standards, with good uniformity and a certain degree of redundancy.

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

[0070]

[0071]

[0072] Table 4 provides the high temperature tensile properties of the head, middle and tail cross sections of the TC21 titanium alloy Φ350mm large-size bar prepared by the forging method at the R / 2 position. It can be seen from Table 4 that the high temperature tensile strength at the transverse R / 2 position of different parts of the bar is high.

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

[0074] Location direction Rm(MPa) <![CDATA[R P0.2 (MPa)]]> A (％) Z(％) head Horizontal 868 699 19.9 57.0 middle Horizontal 856 696 18.3 57.8 tail Horizontal 871 704 19.5 54.4

[0075] The present invention greatly reduces the production cost by subjecting the 6-ton single-weight TC21 titanium alloy ingot to 2-fire blanking and 4-fire forging. Compared with the bars of the same specification produced by other manufacturers with multiple fires, the TC21 titanium alloy produced by this process is The rod has excellent performance and structure. Compared with the TC21 titanium alloy φ350mm rod produced by multiple firings disclosed in CN 103510030 A, the room temperature tensile elongation and cross-sectional shrinkage of the same specification rod prepared by the method of the present invention are significantly higher, the average elongation can be increased by nearly 1 times, and the cross-sectional shrinkage can be increased by nearly 1.68 times. While greatly improving the plasticity, the tensile strength is only reduced by 6.7%, and the yield strength is only reduced by 7.2%. The fracture toughness is comparable to that of Western Superconducting, both of which are 90MPa·m 1 / 2 .

[0076] It should be noted that the above-described embodiments are only preferred embodiments of the present invention. For those skilled in the art, without departing from the principles of the present invention, the present invention may be modified, improved and replaced with equivalents, and these modifications, improvements and equivalent replacements are also considered to fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing large-size TC21 titanium alloy bars, characterized in that: include: Step 1) Perform two-stage forging of the TC21 titanium alloy ingot: In the first firing, the TC21 titanium alloy ingot is subjected to high temperature forging in the β single phase region to obtain an intermediate billet ingot with a square cross section; In the second firing, the intermediate billet ingot with a square cross section is subjected to low temperature upsetting and reversing drawing forging, and then subjected to high temperature forging to obtain an intermediate billet ingot with a square cross section and a grain size of 1 mm to 2 mm; Step 2), the intermediate billet ingot obtained in step 1) is subjected to α+β two-phase region three-fire bar forging: In the first and second firings, the intermediate billet ingot is first upset and then stretched and forged into an intermediate billet with an octagonal cross section, and in the third firing, the intermediate billet with an octagonal cross section is stretched into an intermediate billet with a twelve-square cross section; Step 3), forming the intermediate billet with a cross section of twelve squares obtained in step 2) into an α+β two-phase region rod: The intermediate billet with a dodecagonal cross section is rounded into a large-size TC21 titanium alloy bar with a circular cross section and a required size.

2. The method for preparing large-size TC21 titanium alloy bars according to claim 1, characterized in that: In the step (1), the first heat is forged at a high temperature above the β phase transformation point, and the first blanking temperature is T β +180~205℃, heating for two upsetting and two drawing forging, heating coefficient is 0.65~0.80, total forging ratio is 1.70~2.00, hot material is returned to the furnace after forging, the return temperature is T β +105~125℃, after being taken out of the furnace, two upsetting and two drawing forging are carried out, and after forging, the hot material is returned to the furnace, and the returning furnace temperature is T β +60~95℃, then double upsetting and double drawing forging, air cooling after forging, the pressing speed of the forging process is controlled at 20~35mm / s, the pressing amount is controlled at 100~160mm, and the feed amount is controlled at 280~500mm, to obtain a β structure with a grain size of 5~20mm; The second heat is low temperature forging below the β phase transformation point temperature, and the heating temperature is T β -(30~70)℃, heating coefficient is 0.65~0.80, upsetting and reversing drawing are carried out, the total forging ratio is 1.6~2.0, and the hot material is returned to the furnace after forging, and the return temperature is T β +(30~100)℃; then forge at high temperature above the β phase transformation point, the heating temperature is T β +(30~100)℃, heating coefficient is 0.5, total forging ratio is 1.2~1.5, air cooling is performed after forging to obtain an intermediate billet ingot, which is a β structure with a grain size of 1~2mm.

3. The method for preparing large-size TC21 titanium alloy bars according to claim 2, characterized in that: In the first firing of step 1), the deformation amount of each upsetting is controlled within 37% to 45%, and in the second firing, the deformation amount is controlled within 35% to 40%.

4. The method for preparing large-size TC21 titanium alloy bars according to claim 2, characterized in that: In step 1), the reversing drawing is to firstly perform upsetting forging on the intermediate billet ingot in the axial direction, and then perform drawing forging in the radial direction; then perform tempering, and after tempering, perform radial upsetting, and then perform drawing forging in the axial direction.

5. The method for preparing large-size TC21 titanium alloy bars according to claim 1, characterized in that: In step 2), the heating temperature of the first and second firings is T β -(30~70)℃, heating coefficient is 0.5~0.8, deformation is controlled at 30%~40%, pressing speed is controlled at 15~25mm / s, feed amount is controlled at 300~500mm, pressing amount is controlled at 105~145mm, hot material is returned to the furnace twice after each fire forging, and the heating temperature is T β -(30~70)℃, heating coefficient is 0.3~0.

4.

6. The method for preparing large-size TC21 titanium alloy bars according to claim 1, characterized in that: In step 2), the second forging method is hexagonal forging to twelve-square forging, and the deformation is controlled at 15% to 37%.

7. The method for preparing large-size TC21 titanium alloy bars according to claim 1, characterized in that: In step 2), the third fire is a diameter reduction and drawing forging, and the heating temperature is T β -(30~70)℃, heating coefficient is 0.5~0.8, hot material is returned to the furnace after each firing, and the temperature of hot material is T β -(30~70)℃, thermal insulation coefficient is 0.3~0.4, deformation is controlled at 10%~35%, pressing speed is controlled at 15~25mm / s, feed amount is controlled at 120~400mm, and reduction amount is controlled at 40~120mm.

8. The method for preparing large-size TC21 titanium alloy bars according to claim 1, characterized in that: In step 3), the heating temperature of the rounding is T β -(30~70)℃, heating coefficient is 0.5~0.8, deformation is controlled at 10%~20%, reduction is controlled at 20~30mm, and feed amount is controlled at 120~300mm.

9. The method for preparing large-size TC21 titanium alloy bars according to claim 1, characterized in that: In step 3), the required size is 350mm≤Φ≤350+20mm.

10. A large-size TC21 titanium alloy bar, characterized in that: The method is prepared according to any one of claims 1 to 9.

Images