Preparation method of high-efficiency and low-cost TC4 titanium alloy fine-grain bar

Abstract

The invention discloses a high-efficiency and low-cost TC4 titanium alloy fine-grain rod preparation method, which comprises the following steps of: accurately controlling the structure evolution in the hot working process of a rod material in a manner of replacing forging with rolling and combining forging and rolling, and carrying out cast ingot cogging forging for three heating numbers and low-temperature low-speed large-deformation rolling forming for four heating numbers, so as to obtain the high-efficiency and low-cost TC4 titanium alloy fine-grain rod. And finally, the TC4 titanium alloy fine-grain rod which is uniform and fine in structure and excellent in performance is obtained. The TC4 titanium alloy fine-grain bar prepared by the method reaches a leading level in the aspect of transverse and longitudinal structure uniformity and refinement. According to the preparation method, the difficulty in formulation of a forging and rolling combined process and the difficulty in structure regulation and control are broken through, the heating number of the preparation process is reduced from about 20 of a traditional radial forging process to 4 of rolling, and the preparation method of the TC4 titanium alloy fine-grain bar is efficient and low in cost.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy processing, and in particular relates to a method for preparing a titanium alloy fine-grained rod with high efficiency and low cost. Background Art

[0002] A typical application of advanced high-performance titanium alloys in the aviation field is engine blades. The bar material for blades requires that the primary α phase content is greater than 60%, the average grain size in the transverse and longitudinal directions is less than 10μm, and the room temperature tensile strength is greater than 930MPa, and the room temperature impact energy is greater than 31J. The common titanium alloy fine grain rod preparation process is free forging + radial forging process. This process has a small amount of deformation accumulated during the entire thermal deformation process, and the spheroidization and recrystallization effects of the α phase are poor. The primary α phase grain size of the prepared bar is 20-30μm, which cannot meet the use requirements. In addition, the radial forging process has problems such as many fires, low forming efficiency, poor deformation uniformity and poor organizational consistency. The use of "forging and rolling combined" instead of "free forging + radial forging" has become a more cost-effective and efficient method for preparing TC4 titanium alloy fine grain rods. Summary of the invention

[0003] In view of this, the object of the present invention is to provide a method for preparing TC4 titanium alloy fine crystal rods with high efficiency and low cost.

[0004] In order to achieve the above object, the present invention provides the following technical solutions:

[0005] On the one hand, the present invention provides a method for preparing TC4 titanium alloy fine crystal rods with high efficiency and low cost, the method comprising:

[0006] Step 1: Ingot forging and 3-fire forging:

[0007] First fire: The TC4 titanium alloy ingot is forged at a high temperature above the β phase transformation point, and air-cooled after forging;

[0008] Second fire: The billet obtained in the first fire is forged at low temperature below the β transformation point and air-cooled after forging;

[0009] The third fire: the billet obtained in the second fire is subjected to high temperature forging above the β phase transformation point, and water-cooled after forging to obtain a forging billet with a cross-sectional size of (350-400)*(350-400)mm;

[0010] Step 2: Low temperature, low speed, large deformation rolling forming 4 times:

[0011] First heat: the forging billet obtained in step 1 is subjected to low temperature rolling below the β phase transformation point, and air-cooled after rolling to obtain a square billet with a cross-sectional size of (200-250) mm*(200-250) mm;

[0012] Second fire: the square billet obtained in the first fire is subjected to low temperature rolling below the β transformation point, and air-cooled after rolling to obtain a billet with a cross-sectional size of Φ (100-160) mm;

[0013] Third fire: The bar blank obtained in the second fire is subjected to low temperature rolling below the β transformation point, and air-cooled after rolling to obtain a bar blank with a cross-sectional size of Φ (50 to 80) mm.

[0014] Fourth fire: The bar blank obtained in the third fire is subjected to low temperature rolling below the β transformation point, and air-cooled after rolling to obtain a TC4 titanium alloy fine-grained bar with a cross-sectional size of Φ (20-45) mm.

[0015] Further, in step 1, the specific steps of performing high temperature forging above the β phase transformation point on the titanium alloy ingot in the first fire are as follows: heating the TC4 titanium alloy ingot to a heating temperature of T β +100~200℃, heating coefficient is 0.6~0.8min / mm, after coming out of the furnace, it is subjected to 4~6 times of upsetting and drawing forging, with 2 times of tempering in the middle, and the heating temperature of tempering is T β +100~200℃, heating coefficient is 0.2~0.4min / mm, upsetting deformation is controlled at 30~80%, final forging temperature is controlled at above 800℃, and air cooling is performed after forging.

[0016] Further, in step 1, the second low temperature forging is specifically as follows: the blank obtained in the first firing is heated to a temperature of T β -(20~50)℃, heating coefficient is 0.6~0.8min / mm, upsetting and drawing are carried out twice after coming out of the furnace, the upsetting and drawing deformation is controlled at 30~80%, the final forging temperature is controlled at above 800℃, and air cooling is carried out after forging.

[0017] Further, in step 1, the third fire is performed at a high temperature above the β phase transformation point as follows: the billet obtained in the second fire is heated to a temperature of T β +50~150℃, and carry out two consecutive drawing forgings after taking out of the furnace. The drawing deformation is controlled at 30~80%, and the final forging temperature is controlled at above 800℃. After forging, it is water-cooled to obtain a forging billet with a cross-sectional size of (350~400)*(350~400)mm.

[0018] Furthermore, in step 2, the low-temperature rolling of the first fire is specifically as follows: the forging billet obtained in step 1 is heated to 900-960°C, with a heating coefficient of 0.6-0.8 min / mm, and after being taken out of the furnace, 11-15 passes of rolling are performed on a reciprocating rolling mill with a roll diameter of 1000-1500 mm to roll the billet into a square billet with a specification of (200-250) mm*(200-250) mm, the rolling deformation is controlled at 60-70%, and the rolling speed is controlled at 1-2 mm / s.

[0019] Furthermore, in step 2, the low-temperature rolling of the second fire is specifically as follows: the bar blank obtained in the first fire of step 2 is heated to 900-960°C, with a heating coefficient of 0.6-0.8 min / mm, and after being taken out of the furnace, 11-15 passes of rolling are performed using a reciprocating rolling mill with a roll diameter of 800-1200 mm to roll the bar blank to a specification of Φ (100-160) mm, the rolling deformation is controlled at 60-80%, and the rolling speed is controlled at 1-2 mm / s.

[0020] Furthermore, in step 2, the low-temperature rolling of the third fire is specifically as follows: the bar blank obtained in the second fire of step 2 is heated to 790-830°C, with a heating coefficient of 0.6-0.8 min / mm, and after being taken out of the furnace, 4-7 passes of rolling are carried out using a reciprocating rolling mill with a roll diameter of 500-800 mm to roll the bar blank to a specification of Φ (50-80) mm, the rolling deformation is controlled at 60-80%, and the rolling speed is controlled at 1-2 mm / s.

[0021] Furthermore, in step 2, the low-temperature rolling of the fourth fire is specifically as follows: the bar blank obtained in the third fire of step 2 is heated to 900-960°C, with a heating coefficient of 0.6-0.8 min / mm, and after being taken out of the furnace, 4-7 passes of rolling are carried out using a reciprocating rolling mill with a roll diameter of 500-800 mm to roll the finished bar to a specification of Φ (20-45) mm, the rolling deformation is controlled at 50-60%, and the rolling speed is controlled at 1-2 mm / s.

[0022] On the other hand, the present invention also provides a TC4 titanium alloy fine crystal rod, which is prepared by the above preparation method.

[0023] Furthermore, the cross-sectional size of the TC4 titanium alloy fine crystal rod is Φ(20-45) mm.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1) The present invention provides a highly efficient and low-cost preparation method for TC4 titanium alloy fine-grained rods by using a process of 3-fire free forging + 4-fire rolling, which reduces more than a dozen fires compared to the traditional process;

[0026] 2) The titanium alloy fine-grained rod prepared by this process has a primary α phase content greater than 60%, and the average grain size in the transverse and longitudinal directions is increased from 20 to 30 μm obtained by the existing process to less than 10 μm. It also meets the various indicators of TC4 fine-grained rods for aircraft engine blades, such as room temperature tensile strength greater than 930 MPa and room temperature impact energy greater than 35 J, with a certain margin. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 (a)-(c) are respectively low-magnification microstructure diagrams of the cross-sections of the head, middle and tail of the Φ30 mm fine-grained TC4 titanium alloy rod prepared in Example 1 of the present invention.

[0028] Figure 2 (a)-(c) are respectively high-magnification microstructure diagrams at the R / 2 position of the head, middle and tail cross sections of the TC4 titanium alloy Φ30 mm fine-grained rod prepared in Example 1 of the present invention.

[0029] Figure 3 (a)-(c) are respectively high-magnification microstructure diagrams at the R / 2 position of the longitudinal sections of the head, middle and tail of the Φ30 mm fine-grained TC4 titanium alloy rod prepared in Example 1 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 method for preparing TC4 titanium alloy fine crystal rods with high efficiency and low cost, which is characterized by comprising:

[0034] Step 1: Ingot forging and forging 3 times:

[0035] First fire: The TC4 titanium alloy ingot is forged at a high temperature above the β phase transformation point, and air-cooled after forging;

[0036] Second fire: The billet obtained in the first fire is forged at low temperature below the β transformation point and air-cooled after forging;

[0037] The third fire: the billet obtained in the second fire is subjected to high temperature forging above the β phase transformation point, and water-cooled after forging to obtain a forging billet with a cross-sectional size of (350-400)*(350-400)mm;

[0038] Step 2: Low temperature, low speed, large deformation rolling forming 4 times:

[0039] First heat: the forging billet obtained in step 1 is subjected to low temperature rolling below the β phase transformation point, and air-cooled after rolling to obtain a square billet with a cross-sectional size of (200-250) mm*(200-250) mm;

[0040] Second fire: the square billet obtained in the first fire is subjected to low temperature rolling below the β transformation point, and air-cooled after rolling to obtain a billet with a cross-sectional size of Φ (100-160) mm;

[0041] Third fire: The bar blank obtained in the second fire is subjected to low-temperature rolling below the β transformation point, and air-cooled after rolling to obtain a bar blank with a cross-sectional size of Φ (50 to 80) mm.

[0042] Fourth fire: The bar blank obtained in the third fire is subjected to low temperature rolling below the β transformation point, and air-cooled after rolling to obtain a TC4 titanium alloy fine-grained bar with a cross-sectional size of Φ (20-45) mm.

[0043] In some embodiments, the present invention provides a method for preparing a TC4 titanium alloy fine crystal rod with high efficiency and low cost, comprising:

[0044] Step 1: Ingot forging and forging 3 times:

[0045] First fire: The TC4 titanium alloy ingot is forged at a high temperature above the β phase transformation point, and the TC4 titanium alloy ingot is heated to a temperature of T β +100~200℃, heating coefficient is 0.6~0.8min / mm, after coming out of the furnace, it is subjected to 4~6 times of upsetting and drawing forging, with 2 times of tempering in the middle, and the heating temperature of tempering is T β+100~200℃, heating coefficient is 0.2~0.4min / mm, upsetting deformation is controlled at 30~80%, final forging temperature is controlled at above 800℃, and air cooling is performed after forging;

[0046] Second fire: The billet obtained in the first fire is forged at low temperature below the β phase transformation point, and the billet obtained in the first fire is heated to a temperature of T β -(20~50)℃, heating coefficient is 0.6~0.8min / mm, upsetting and drawing are carried out twice after coming out of the furnace, the upsetting and drawing deformation is controlled at 30~80%, the final forging temperature is controlled at above 800℃, and air cooling is carried out after forging;

[0047] Third fire: The billet obtained in the second fire is forged at a high temperature above the β phase transformation point, and the billet obtained in the second fire is heated to a heating temperature of T β +50~150℃, after being taken out of the furnace, two continuous drawing forgings are carried out, the drawing deformation is controlled at 30~80%, the final forging temperature is controlled at above 800℃, and water cooling is carried out after forging to obtain a forging blank with a cross-sectional size of (350~400)*(350~400)mm;

[0048] Step 2: Low temperature, low speed, large deformation rolling forming 4 times:

[0049] First heat: the forging billet obtained in step 1 is subjected to low temperature rolling below the β phase transformation point, the forging billet obtained in step 1 is heated to 900-960° C., the heating coefficient is 0.6-0.8 min / mm, and after being taken out of the furnace, 11-15 passes of rolling are performed on a reciprocating rolling mill with a roll diameter of 1000-1500 mm to roll the billet into a square billet with a specification of (200-250) mm*(200-250) mm, the rolling deformation is controlled at 60-70%, the rolling speed is controlled at 1-2 mm / s, and air-cooling is performed after rolling to obtain a square billet with a cross-sectional size of (200-250) mm*(200-250) mm;

[0050] The second fire: the square billet obtained in the first fire is subjected to low temperature rolling below the β phase transformation point, the bar billet obtained in the first fire of step 2 is heated to 900-960°C, the heating coefficient is 0.6-0.8min / mm, and after being taken out of the furnace, a reciprocating rolling mill with a roll diameter of 800-1200mm is used for 11-15 passes of rolling to a bar billet with a specification of Φ(100-160)mm, the rolling deformation is controlled at 60-80%, the rolling speed is controlled at 1-2mm / s, and air cooling is performed after rolling to obtain a bar billet with a cross-sectional size of Φ(100-160)mm;

[0051] The third fire: the bar blank obtained in the second fire is subjected to low-temperature rolling below the β phase transformation point, the bar blank obtained in the second fire of step 2 is heated to 790-830°C, the heating coefficient is 0.6-0.8min / mm, and after being taken out of the furnace, 4-7 passes of rolling are carried out on a reciprocating rolling mill with a roll diameter of 500-800mm to roll the bar blank to a specification of Φ(50-80)mm, the rolling deformation is controlled at 60-80%, the rolling speed is controlled at 1-2mm / s, and air-cooling is performed after rolling to obtain a bar blank with a cross-sectional size of Φ(50-80)mm.

[0052] The fourth fire: the bar blank obtained in the third fire is subjected to low-temperature rolling below the β phase transformation point, the bar blank obtained in the third fire of step 2 is heated to 900-960°C, the heating coefficient is 0.6-0.8min / mm, and after being taken out of the furnace, 4-7 passes of rolling are carried out on a reciprocating rolling mill with a roll diameter of 500-800mm to roll the finished bar with a specification of Φ(20-45)mm, the rolling deformation is controlled at 50-60%, the rolling speed is controlled at 1-2mm / s, and air-cooling is performed after rolling to obtain a TC4 titanium alloy fine-grained rod with a cross-sectional size of Φ(20-45)mm.

[0053] To clarify the purpose, technical solutions and advantages of the present invention, the present invention will be described in detail below in conjunction with specific embodiments and drawings. The specific embodiments described herein are only used to explain the present invention, and the present invention is not limited thereto.

[0054] Example 1 Preparation of TC4 titanium alloy Φ30 mm fine grain rod

[0055] This embodiment provides a method for preparing a TC4 titanium alloy fine crystal rod, the method comprising:

[0056] Step 1: Ingot forging and 3-fire forging:

[0057] First fire: The TC4 titanium alloy ingot is forged at a high temperature above the β phase transformation point, and the TC4 titanium alloy ingot is heated to a temperature of T β +120℃, heating coefficient is 0.75min / mm, after coming out of the furnace, it is upsetting and drawing twice, and the upsetting and drawing deformation is controlled at 30%~40%. After forging, the hot material is returned to the furnace, and the furnace temperature is T β +70℃, heating coefficient is 0.35min / mm, after coming out of the furnace, two upsetting and drawing are carried out, and the upsetting and drawing deformation is controlled at 30%~40%. After forging, the hot material is returned to the furnace, the heating coefficient is 0.35min / mm, and the furnace temperature is T β +20℃, after being taken out of the furnace, two upsetting and drawing processes are carried out, the deformation of each upsetting and drawing process is controlled at 30% to 40%, the final forging temperature is controlled at above 800℃, and air cooling is carried out after forging;

[0058] Second fire: The billet obtained in the first fire is forged at low temperature below the β phase transformation point. The heating temperature is T β -50℃, heating coefficient is 0.75min / mm, upsetting and drawing are carried out twice after coming out of the furnace, the upsetting and drawing deformation is controlled at 30% to 40%, the final forging temperature is controlled at above 800℃, and air cooling is carried out after forging;

[0059] Third fire: The billet obtained in the second fire is forged at a high temperature above the β transformation point. The heating temperature is T β +30℃, heating coefficient is 0.75min / mm, after being taken out of the furnace, drawing forging is carried out, the drawing deformation is controlled at 30% to 40%, the final forging temperature is controlled at above 800℃, forging to a size of (350±3)*(350±3)*Lmm, and water cooling is carried out after forging;

[0060] Step 2: Low temperature, low speed, large deformation rolling forming 4 times:

[0061] First heat: The forging billet obtained in step 1 is subjected to low temperature rolling below the β phase transformation point, with a heating temperature of 900°C and a heating coefficient of 0.75min / mm. After being taken out of the furnace, it is rolled 13 times using a reciprocating rolling mill with a roller diameter of 1200mm to a square billet with a specification of 200*200mm, with the rolling deformation controlled at 60% and the rolling speed controlled at 1-2mm / s. After rolling, it is air-cooled to obtain a square billet with a cross-sectional size of 200*200mm;

[0062] Second fire: The square billet obtained in the first fire of step 2 is subjected to low-temperature rolling below the β phase transformation point, with a heating temperature of 900°C and a heating coefficient of 0.75min / mm. After being taken out of the furnace, it is rolled 13 times using a reciprocating rolling mill with a roll diameter of 1200mm to a bar billet with a specification of Φ120mm, with the rolling deformation controlled at 60% and the rolling speed controlled at 1-2mm / s. After rolling, it is air-cooled to obtain a bar billet with a cross-sectional size of Φ120mm;

[0063] The third fire: The bar obtained in the second fire of step 2 is subjected to low temperature rolling below the β phase transformation point, the heating temperature is 800°C, the heating coefficient is 0.75min / mm, and after being taken out of the furnace, it is rolled for 5 times using a reciprocating rolling mill with a roller diameter of 500mm to a bar with a specification of Φ70mm, the rolling deformation is controlled at 70%, and the rolling speed is controlled at 1-2mm / s. After rolling, it is air-cooled to obtain a bar with a cross-sectional size of Φ70mm.

[0064] The fourth fire: the bar blank obtained in the third fire of step 2 is subjected to low temperature rolling below the β phase transformation point, the heating temperature is 900°C, the heating coefficient is 0.75min / mm, and after being taken out of the furnace, it is rolled for 5 times using a reciprocating rolling mill with a roller diameter of 500mm to a bar with a specification of Φ30mm, the rolling deformation is controlled at 60%, and the rolling speed is controlled at 1-2mm / s. After rolling, it is air-cooled to obtain a TC4 titanium alloy fine-grained bar with a cross-sectional size of Φ30mm.

[0065] Figure 1 The figure shows the low magnification structure diagram of the cross section of the head, middle and tail of the TC4 titanium alloy Φ30mm fine grain rod prepared in Example 1 of the present invention. Figure 1 It can be seen that the low-magnification structure has no cracks, folds, pores, metal or non-metallic inclusions, segregation, shrinkage tails and other metallurgical defects visible to the naked eye. There are no obvious clear grains visible to the naked eye, and it is uniformly blurred.

[0066] Figure 2 and 3 The high-magnification microstructure diagrams of the head, middle, tail cross sections, and longitudinal section R / 2 position of the TC4 titanium alloy Φ30mm fine-grained rod prepared in Example 1 of the present invention are shown in FIG. Figure 2 and 3 It can be seen that the high-magnification structure is composed of equiaxed α phase and a small amount of lamellar primary α phase. The high-magnification structure is fine and uniform in the horizontal and vertical directions. No abnormal thermal structure is seen. There is no continuous α network structure on the original β grain boundary. The primary α phase content is as high as 70%, and the average longitudinal grain size of the rod is less than 10μm. The equiaxed is good and there is no obvious elongation.

[0067] Table 3 shows the mechanical properties of the longitudinal sample taken at the R / 2 position of the cross section of the TC4 titanium alloy Φ30mm fine-grained rod prepared in Example 1. It can be seen that the test results meet the requirements of the TC4 fine-grained rod standard for aircraft engine blades with a certain margin.

[0068] Table 3 Mechanical properties of longitudinal samples taken at the R / 2 position of the bar cross section

[0069]

[0070] The present invention breaks through the difficulties in formulating the forging and rolling combined process and the difficulties in controlling the structure, and reduces the preparation process from about 20 times of the traditional radial forging process to 3-4 times of rolling, providing an efficient and low-cost method for preparing titanium alloy fine-grained rods. The prepared titanium alloy fine-grained rods meet the requirements of aviation standards, have good uniformity and have a certain amount of surplus.

[0071] 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 TC4 titanium alloy fine crystal rods with high efficiency and low cost, characterized in that: include: Step 1: Ingot forging and forging 3 times: First fire: The TC4 titanium alloy ingot is forged at a high temperature above the β phase transformation point, and air-cooled after forging; Second fire: The billet obtained in the first fire is forged at low temperature below the β transformation point and air-cooled after forging; The third fire: the billet obtained in the second fire is subjected to high temperature forging above the β phase transformation point, and water-cooled after forging to obtain a forging billet with a cross-sectional size of (350-400)*(350-400)mm; Step 2: Low temperature, low speed, large deformation rolling forming 4 times: First heat: the forging billet obtained in step 1 is subjected to low temperature rolling below the β phase transformation point, and air-cooled after rolling to obtain a square billet with a cross-sectional size of (200-250) mm*(200-250) mm; Second fire: the square billet obtained in the first fire is subjected to low temperature rolling below the β transformation point, and air-cooled after rolling to obtain a billet with a cross-sectional size of Φ (100-160) mm; Third fire: The bar blank obtained in the second fire is subjected to low-temperature rolling below the β transformation point, and air-cooled after rolling to obtain a bar blank with a cross-sectional size of Φ (50 to 80) mm. Fourth fire: The bar blank obtained in the third fire is subjected to low temperature rolling below the β transformation point, and air-cooled after rolling to obtain a TC4 titanium alloy fine-grained bar with a cross-sectional size of Φ (20-45) mm.

2. The method for preparing TC4 titanium alloy fine crystal rods with high efficiency and low cost according to claim 1, characterized in that: In step 1, the specific steps of performing high temperature forging above the β phase transformation point on the titanium alloy ingot in the first fire are as follows: heating the TC4 titanium alloy ingot to a heating temperature of T β +100~200℃, heating coefficient is 0.6~0.8min / mm, after coming out of the furnace, it is subjected to 4~6 times of upsetting and drawing forging, with 2 times of tempering in the middle, and the heating temperature of tempering is T β +100~200℃, heating coefficient is 0.2~0.4min / mm, upsetting deformation is controlled at 30~80%, final forging temperature is controlled at above 800℃, and air cooling is performed after forging.

3. The method for preparing TC4 titanium alloy fine crystal rods with high efficiency and low cost according to claim 1, characterized in that: In step 1, the second low temperature forging is specifically as follows: the blank obtained in the first firing is heated to a temperature of T β -(20~50)℃, heating coefficient is 0.6~0.8min / mm, upsetting and drawing are carried out twice after coming out of the furnace, the upsetting and drawing deformation is controlled at 30~80%, the final forging temperature is controlled at above 800℃, and air cooling is carried out after forging.

4. The method for preparing TC4 titanium alloy fine crystal rods with high efficiency and low cost according to claim 1, characterized in that: In step 1, the third fire is performed at a high temperature above the β phase transformation point as follows: the billet obtained in the second fire is heated to a temperature of T β +50~150℃, and carry out two consecutive drawing forgings after taking out of the furnace. The drawing deformation is controlled at 30~80%, and the final forging temperature is controlled at above 800℃. After forging, it is water-cooled to obtain a forging billet with a cross-sectional size of (350~400)*(350~400)mm.

5. The method for preparing TC4 titanium alloy fine crystal rods with high efficiency and low cost according to claim 1, characterized in that: In step 2, the low-temperature rolling of the first fire is specifically as follows: the forging billet obtained in step 1 is heated to 900-960°C, with a heating coefficient of 0.6-0.8 min / mm, and after being taken out of the furnace, 11-15 passes of rolling are performed using a reciprocating rolling mill with a roll diameter of 1000-1500 mm to roll the billet into a square billet with a specification of (200-250) mm*(200-250) mm, the rolling deformation is controlled at 60-70%, and the rolling speed is controlled at 1-2 mm / s.

6. The method for preparing TC4 titanium alloy fine crystal rods with high efficiency and low cost according to claim 1, characterized in that: In step 2, the low-temperature rolling of the second fire is specifically as follows: the bar blank obtained in the first fire of step 2 is heated to 900-960°C, with a heating coefficient of 0.6-0.8 min / mm, and after being taken out of the furnace, 11-15 passes of rolling are performed using a reciprocating rolling mill with a roll diameter of 800-1200 mm to roll the bar blank to a specification of Φ (100-160) mm, the rolling deformation is controlled at 60-80%, and the rolling speed is controlled at 1-2 mm / s.

7. The method for preparing TC4 titanium alloy fine crystal rods with high efficiency and low cost according to claim 1, characterized in that: In step 2, the low-temperature rolling of the third fire is specifically as follows: the bar blank obtained in the second fire of step 2 is heated to 790-830°C, with a heating coefficient of 0.6-0.8 min / mm. After being taken out of the furnace, a reciprocating rolling mill with a roll diameter of 500-800 mm is used for 4-7 rolling passes to roll the bar blank with a specification of Φ (50-80) mm, the rolling deformation is controlled at 60-80%, and the rolling speed is controlled at 1-2 mm / s.

8. The method for preparing TC4 titanium alloy fine crystal rods with high efficiency and low cost according to claim 1, characterized in that: In step 2, the low-temperature rolling of the 4th fire is specifically as follows: the bar blank obtained in the 3rd fire of step 2 is heated to 900-960°C, with a heating coefficient of 0.6-0.8 min / mm, and after being taken out of the furnace, it is rolled by a reciprocating rolling mill with a roll diameter of 500-800 mm for 4-7 passes to a finished bar with a specification of Φ (20-45) mm, the rolling deformation is controlled at 50-60%, and the rolling speed is controlled at 1-2 mm / s.

9. A TC4 titanium alloy fine crystal rod, characterized in that: The method is prepared according to any one of claims 1 to 8.

10. The TC4 titanium alloy fine crystal rod according to claim 9, characterized in that: The cross-sectional size of the TC4 titanium alloy fine crystal rod is Φ(20-45) mm.

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