High-impact-toughness Ti80 titanium alloy thick plate and heat treatment control method for structure form of Ti80 titanium alloy thick plate

Abstract

The invention discloses a high-impact-toughness Ti80 titanium alloy thick plate and a heat treatment control method for the structure form of the high-impact-toughness Ti80 titanium alloy thick plate. The method comprises the steps that furnace temperature uniformity detection is conducted on a heat treatment furnace, then heat treatment is conducted according to a heat treatment system, the Ti80 titanium alloy thick plate enters the furnace at the temperature of (Tbeta-60) + / -10 DEG C, heat preservation is conducted for 0.5-1 h after the temperature is reached, the Ti80 titanium alloy thick plate is evenly heated to (Tbeta-15) + / -10 DEG C, and heat preservation is conducted for 3-4 h after the temperature is reached; in the heat treatment process, the Ti80 titanium alloy thick plate slightly moves in a heat treatment furnace; the Ti80 titanium alloy thick plate subjected to heat treatment is taken out of a furnace and then subjected to hot straightening, and it is ensured that the straightening unevenness allowable deviation of the Ti80 titanium alloy thick plate is smaller than or equal to 10 mm / m; and then the Ti80 titanium alloy thick plate subjected to hot straightening is moved and cooled on a cooling bed, and the high-impact-toughness Ti80 titanium alloy thick plate is obtained. The heat treatment process is controlled by detecting the temperature control precision of the heat treatment furnace, the structure form of the thick plate can be effectively controlled, and it is guaranteed that the thick plate has high impact toughness.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium alloys, and particularly relates to a thick plate of Ti80 titanium alloy with high impact toughness and a heat treatment control method for its microstructure. Background Art

[0002] Titanium alloys have excellent comprehensive properties such as high specific strength, good corrosion resistance, and weldability, and are widely used in the fields of aviation, aerospace, ships, petroleum, chemical engineering, etc. In recent years, with the implementation of several major engineering projects such as ocean engineering and transportation, the demand for titanium alloy plates has increased, and at the same time, higher requirements have been put forward for the specifications and performance of titanium alloy plates, especially the plate thickness and impact toughness of the plates. Under complex marine conditions, the plates are subjected to various actions such as tension, torsion, and impact, and the stress conditions are complex. Generally, as the thickness of the plate increases, the impact toughness of the central part will decrease. This is mainly because the forging and rolling penetrability of the billet core becomes worse, and the pores and microcracks in the central part of the structure are difficult to be welded together during the deformation process, and the structural uniformity is difficult to control. Therefore, ensuring that the thick titanium alloy plate has a good microstructure is the key to obtaining excellent impact toughness of the thick titanium alloy plate; and heat treatment, as the last link in controlling the microstructure of the thick titanium alloy plate, is also an extremely crucial link.

[0003] Chinese Patent CN118291901A discloses a heat treatment method for super-large-sized titanium alloy wide and thick plates. The method mainly includes the following steps: Step (1), heat the furnace to T1 (T1 = T2 - 100°C), and keep it at the temperature for 10 - 30 min after reaching the temperature; Step (2), put the wide and thick plate into the furnace and keep it warm for S1 min (S1 = 1 - 1.2d, where d is the thickness of the wide and thick plate); Step (3), heat up to T2 (1 - 100°C below the β transformation temperature), and keep it at the temperature for S2 min (S2 = 0.5 - 0.8d, where d is the thickness of the wide and thick plate) after reaching the temperature; Step (4), end the heat preservation and cool it in the furnace for 10 - 30 min; Step (5), take it out of the furnace and cool it with water, then dry it; Step (6), heat the furnace to T3 (T3 = T2 / 2 ± 100°C); Step (7), put the wide and thick plate into the furnace and keep it warm for 240 - 600 min; Step (8), end the heat preservation and cool it in the furnace to 140 - 165°C; Step (9), take the wide and thick plate out of the furnace to complete the heat treatment. After being treated by the method of the invention, super-large-sized titanium alloy wide and thick plates with high strength and good plasticity can be obtained. The limitations of this method are: (1) the applicable thickness range of the wide and thick plate is 30 - 60 mm; (2) the time occupied by cooling in the furnace after ending the heat preservation is long; (3) the method for controlling the microstructure of the wide and thick plate during the heat treatment process and the cooling process is not mentioned. Chinese Patent CN117773158A discloses a heat treatment method for additively manufactured large-sized titanium alloy thin-walled ring parts. The method mainly includes: Step (1), place the part with a substrate into a vacuum heat treatment furnace; (2) the heat treatment regime is: heat up to 200 - 300°C, keep it warm for 1 - 2 h; heat up to 400 - 500°C, keep it warm for 1 - 2 h; heat up to 600 - 700°C, keep it warm for 1 - 2 h; heat up to 800 - 850°C, keep it warm for 1 - 2 h, and then take it out of the furnace after cooling in the furnace; (3) use wire cutting to cut the part from the substrate. After being treated by this method, the microstructure in the height direction of the part changes uniformly. The limitations of this method are: (1) the applicable thickness of the part is below 5 mm; (2) an additional substrate is required during the heat treatment process, increasing the complexity of industrial implementation; (3) the time occupied by cooling in the furnace after ending the heat preservation is long.

[0004] At present, the methods for controlling the microstructure of thick titanium alloy plates through heat treatment have the following problems: (1) There is a lack of heat treatment systems for thick plates with relatively high thickness. During the heat treatment and cooling processes of thick plates, the surface and the core are prone to uneven heating and cooling, resulting in the impact toughness not meeting the requirements; (2) Furnace cooling takes a long time in heat treatment, and there is a lack of an optimal heat treatment system; (3) It is difficult to control the plate shape of thick plates during the heat treatment process and the cooling process to meet the requirements; (4) The optimal microstructure is not clear; (5) The actual production process is complex, and the state of the heat treatment furnace is often in dynamic change, and the temperature uniformity state of the heat treatment furnace is not clear. Therefore, it is necessary to develop a heat treatment control method for the microstructure of thick Ti80 titanium alloy plates with high impact toughness, which can effectively control the microstructure of thick plates and ensure that the thick plates have high impact toughness. Summary of the Invention

[0005] Aiming at the defects existing in the prior art, the object of the present invention is to provide a heat treatment control method for a thick Ti80 titanium alloy plate with high impact toughness and its microstructure, which can effectively control the microstructure of the thick plate and ensure that it has high impact toughness.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: The first aspect of the present invention provides a heat treatment control method for the microstructure of a thick Ti80 titanium alloy plate with high impact toughness, including the following steps: S1, the heat treatment furnace conducts furnace temperature uniformity detection to ensure that the furnace temperature difference is within the range of ±10°C; S2, perform heat treatment according to the heat treatment system. Put the thick Ti80 titanium alloy plate into the furnace at a temperature of (Tβ - 60) ± 10°C. After reaching the temperature, keep it warm for 0.5 - 1 h, then uniformly heat up to (Tβ - 15) ± 10°C. After reaching the temperature, keep it warm for 3 - 4 h, and then take it out of the furnace and air-cool. Tβ is the phase transformation point temperature; S3, the thick Ti80 titanium alloy plate moves slightly in the heat treatment furnace during the heat treatment process; S4, after the heat-treated thick Ti80 titanium alloy plate is taken out of the furnace, perform hot straightening to ensure that the allowable deviation of the straightening flatness of the thick Ti80 titanium alloy plate is ≤10 mm / m; S5, move and cool the hot-straightened thick Ti80 titanium alloy plate on the cooling bed until the center temperature of the slab ≤300°C, then stop moving to obtain a thick Ti80 titanium alloy plate with high impact toughness; The microstructure of the thick Ti80 titanium alloy plate with high impact toughness is a uniformly distributed equiaxed α phase + β phase transformation duplex structure.

[0007] Preferably, in step S1, the method for the heat treatment furnace to conduct furnace temperature uniformity detection is as follows: S11. Evenly distribute nine K-type detection thermocouples on three metal rods with a height of 280 - 400 mm. The distance between adjacent metal rods is 1 / 3 of the furnace width. The metal rods are fixed on a metal plate with a thickness of 10 - 20 mm inside the heat treatment furnace. S12. Raise the furnace temperature to the detection temperature and move the metal plate inside the furnace for detection. During detection, first place the metal plate at the center position of the furnace width, and then stop every two meters to collect data. When the thermocouple detects, stay at each position for 30 - 60 minutes to collect data until the furnace temperature detection of the entire heat treatment furnace is completed, ensuring that the furnace temperature difference is controlled within the range of ±10°C.

[0008] Preferably, in step S12, select three temperature uniformity detection temperatures: (Tβ - 100)°C, (Tβ - 50)°C, (Tβ - 25)°C, where Tβ is the phase change point temperature.

[0009] Preferably, in step S2, the time taken to uniformly heat from (Tβ - 60) ± 10°C to (Tβ - 15) ± 10°C is 10 - 20 minutes.

[0010] Preferably, in step S3, the time interval between two adjacent micro-motions is 5 - 10 minutes. The two adjacent micro-motions alternate in moving according to half of the circumference and the circumference of the drive roller inside the heat treatment furnace.

[0011] Preferably, in step S4, the time interval from the Ti80 titanium alloy thick plate being taken out of the furnace to the first hot straightening is ≤3 minutes.

[0012] Preferably, in step S5, the Ti80 titanium alloy thick plate moves on the cooling bed and stops moving when the center temperature of the slab ≤100°C.

[0013] Preferably, in step S5, in the structure of the high impact toughness Ti80 titanium alloy thick plate, the content of equiaxed α-phase is 5 - 60%, and its grain size ≤60 μm; the impact toughness KV of this high impact toughness Ti80 titanium alloy thick plate 2 ≥48 J.

[0014] The second aspect of the present invention provides a high impact toughness Ti80 titanium alloy thick plate prepared by a heat treatment control method adopting the microstructure of the high impact toughness Ti80 titanium alloy thick plate as described in the first aspect of the present invention. Its composition by mass percentage is as follows: Al 5.0% - 7.0%, Nb 2.0% - 4.0%, Zr 1.0% - 3.0%, Mo 0.4% - 2.0%, and the balance is Ti and unavoidable impurities. The microstructure of the high impact toughness Ti80 titanium alloy thick plate is an equiaxed α phase + β phase transformation duplex structure with uniform distribution; the content of the equiaxed α phase is 5-60%, and its grain size ≤ 60μm; the impact toughness KV of the high impact toughness Ti80 titanium alloy thick plate 2 ≥ 48J.

[0015] Preferably, the tensile strength Rm of the high impact toughness Ti80 titanium alloy thick plate is 800-1000 MPa, the elongation A is 8%-20%, and the reduction of area Z is 20%-50%.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By adopting the heat treatment control method of the present invention, the microstructure of the thick plate is an equiaxed α phase + β phase transformation duplex structure, the content of the primary equiaxed α is 5-60%, and the impact toughness KV 2 ≥ 48J, which can meet the requirements of the ocean engineering for the high impact toughness of titanium alloy thick plates; 2. The present invention ensures the temperature control accuracy of the heat treatment furnace through the detection of furnace temperature uniformity, ensures the uniform heating during the heat treatment process of the thick plate by micro-movement, ensures a good plate shape of the thick plate through hot straightening, and ensures uniform heat dissipation during the movement and cooling on the cooling bed; through the above measures, the problem of non-uniform microstructure of titanium alloy thick plates can be effectively solved, the impact toughness of the core part of titanium alloy thick plates can be significantly improved, the yield rate can be increased, the cost can be reduced, and the production efficiency can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is the microstructural diagram of the high impact toughness Ti80 titanium alloy thick plate prepared in Example 1 of the present invention; Figure 2 is the microstructural diagram of the high impact toughness Ti80 titanium alloy thick plate prepared in Example 2 of the present invention; Figure 3 is the microstructural diagram of the high impact toughness Ti80 titanium alloy thick plate prepared in Example 3 of the present invention; Figure 4 is the microstructural diagram of the Ti80 titanium alloy thick plate prepared in Comparative Example 1; Figure 5 is the microstructural diagram of the Ti80 titanium alloy thick plate prepared in Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form.

[0019] The present invention provides a heat treatment control method for the tissue morphology of a high impact toughness Ti80 titanium alloy thick plate, including the following steps: S1. The heat treatment furnace is subjected to furnace temperature uniformity detection to ensure that the temperature difference of the furnace is within the range of ±10°C. The method for detecting the furnace temperature uniformity of the heat treatment furnace in this step is as follows: S11. Nine K-type detection thermocouples are evenly distributed on three metal rods with a height of 280 - 400 mm. The distance between adjacent metal rods is 1 / 3 of the width of the heat treatment furnace. The metal rods are fixed on a metal plate with a thickness of 10 - 20 mm inside the heat treatment furnace. S12. The furnace temperature is raised to the detection temperature, and the metal plate inside the furnace is moved for detection. During detection, the metal plate is first placed at the center position of the furnace width, and then data is collected every time it stops after moving two meters. When the thermocouple detects, data is collected after staying at each position for 30 - 60 minutes until the furnace temperature detection of the entire heat treatment furnace is completed, ensuring that the temperature difference of the furnace is within the range of ±10°C.

[0020] During the above furnace temperature uniformity detection process, three temperature uniformity detection temperatures can be selected: (Tβ - 100)°C, (Tβ - 50)°C, (Tβ - 25)°C, where Tβ is the phase change point temperature.

[0021] S2. Heat treatment is carried out according to the heat treatment system. The Ti80 titanium alloy thick plate enters the furnace at a temperature of (Tβ - 60) ± 10°C, holds for 0.5 - 1 h after reaching the temperature, is heated uniformly for 10 - 20 minutes to (Tβ - 15) ± 10°C, holds for 3 - 4 h after reaching the temperature, and then is taken out of the furnace and air-cooled, where Tβ is the phase change point temperature. S3. The Ti80 titanium alloy thick plate moves slightly in the heat treatment furnace during heat treatment. In this step, the time interval between two adjacent slight movements is 5 - 10 minutes, and the two adjacent slight movements are alternately moved according to half of the circumference and the circumference of the drive roller inside the heat treatment furnace. Among them, the circumference of the drive roller is calculated according to the diameter D of the drive roller, that is, π * D, and the half circumference of the drive roller is 1 / 2π * D.

[0022] S4. After the heat-treated Ti80 titanium alloy thick plate is taken out of the furnace, it is subjected to hot straightening to ensure that the allowable deviation of the straightening flatness of the Ti80 titanium alloy thick plate is ≤10 mm / m. In this step, the heat-treated Ti80 titanium alloy thick plate is hot-straightened by a straightening machine, and the time interval from the Ti80 titanium alloy thick plate being taken out of the furnace to the first hot straightening is controlled to be ≤3 minutes.

[0023] S5. The hot-straightened Ti80 titanium alloy thick plate is moved and cooled on a cooling bed until the center temperature of the slab is ≤300°C, and then the movement stops to obtain a Ti80 titanium alloy thick plate with high impact toughness. In this step, the hot-straightened thick Ti80 titanium alloy plate moves and cools on the cooling bed until it stops moving when the center temperature of the slab ≤ 300°C (for example, the center temperature of the slab ≤ 100°C). The center temperature of the slab can be detected by a portable infrared thermometer.

[0024] In the present invention, first, the temperature control accuracy of the heat treatment furnace is ensured by detecting the furnace temperature uniformity, and the furnace temperature difference is within the controllable range. Secondly, the heat treatment system is optimized. The thick Ti80 titanium alloy plate is put into the furnace and kept warm at (Tβ - 60) ± 10°C, which is beneficial to ensuring uniform heating of the slab and avoiding temperature overshoot. Then, it is uniformly heated to (Tβ - 15) ± 10°C to obtain a better duplex structure. In addition, during the heat treatment process, the thick Ti80 titanium alloy plate is slightly moved in the heat treatment furnace, which can further ensure the uniformity of the thick Ti80 titanium alloy plate during heat treatment. Through hot straightening, it can be ensured that the thick Ti80 titanium alloy plate after straightening has a good plate shape. Moving and cooling the thick Ti80 titanium alloy plate on the cooling bed can ensure uniform heat dissipation of the thick Ti80 titanium alloy plate. Through the above measures, the present invention solves the problem of non-uniform structure of the thick Ti80 titanium alloy plate and regulates its microstructure morphology, making the microstructure of the thick Ti80 titanium alloy plate transform into an equiaxed α phase + β phase transformation duplex structure, significantly improving the impact toughness of the core of the thick Ti80 titanium alloy plate and increasing the yield rate.

[0025] The microstructure of the thick Ti80 titanium alloy plate with high impact toughness obtained after the above heat treatment is a uniformly distributed equiaxed α phase + β phase transformation duplex structure; among them, the content of the equiaxed α phase is 5 - 60%, and its grain size ≤ 60μm. The thickness of the thick Ti80 titanium alloy plate with high impact toughness is 60 - 200 mm; the impact toughness KV of the thick Ti80 titanium alloy plate with high impact toughness 2 ≥48J.

[0026] The composition of the thick Ti80 titanium alloy plate with high impact toughness prepared by using the heat treatment control method of the above-mentioned microstructure morphology of the thick Ti80 titanium alloy plate with high impact toughness is as follows by mass percentage: Al 5.0% - 7.0%, Nb 2.0% - 4.0%, Zr 1.0% - 3.0%, Mo 0.4% - 2.0%, and the balance is Ti and unavoidable impurities; The microstructure of the thick Ti80 titanium alloy plate with high impact toughness is a uniformly distributed equiaxed α phase + β phase transformation duplex structure; the content of the equiaxed α phase is 5 - 60% (such as 30 - 35%, etc.), and its grain size ≤ 60μm; the impact toughness KV of the thick Ti80 titanium alloy plate with high impact toughness 2 ≥48J, such as the impact toughness KV 2 is 50 - 90 J, 50 - 60 J, etc.

[0027] The tensile strength Rm of the high impact toughness Ti80 titanium alloy thick plate is 800 - 1000 MPa, the elongation A is 8% - 20%, and the reduction of area Z is 20% - 50%.

[0028] The following further introduces the heat treatment control method of the high impact toughness Ti80 titanium alloy thick plate and its microstructure in combination with specific examples.

[0029] Example 1

[0030] The high impact toughness Ti80 titanium alloy thick plate of this example is composed of the following components by mass percentage: Al 5.8%, Nb 2.9%, Zr 1.6%, Mo 1.0%, and the balance is Ti and inevitable impurities; the high impact toughness Ti80 titanium alloy thick plate is prepared by the following method: (1) Furnace temperature uniformity detection of the heat treatment furnace: 9 K-type detection thermocouples are evenly distributed on 3 metal rods with a height of 280 mm. The distance between adjacent metal rods is 1 / 3 of the furnace width (the furnace width is 3 m), that is, the distance between adjacent metal rods is 1 m, and the metal rods are fixed on a 10-mm-thick metal plate in the heat treatment furnace. During detection, the furnace temperature is raised to the detection temperature (select 3 temperature uniformity detection temperatures 900 °C (Tβ = 1000 °C), 950 °C, 975 °C), and the metal plate in the furnace is moved for detection. The metal plate is placed at the center position of the furnace width, and data is collected every time it stops after moving 2 meters. The detection thermocouple stays at each position for 30 minutes to collect data until the temperature measurement of the entire heat treatment furnace is completed, and the furnace temperature difference is within the range of ±8 °C.

[0031] (2) The heat treatment system is as follows: Enter the furnace at 940 ± 10 °C, hold for 0.5 hour after reaching the temperature; uniformly heat up for 10 min to 985 ± 10 °C, hold for 3.5 hours after reaching the temperature, and then air cool after taking out of the furnace.

[0032] (3) During the heat treatment process, the thick plate has slight movement. The specific process is as follows: The time interval between two adjacent slight movements is 5 min, and the two adjacent slight movements alternate according to half of the circumference and the circumference of the driving roller in the heat treatment furnace.

[0033] (4) After taking out of the furnace, the thick plate is hot straightened by a straightening machine. The specific process is as follows: The time interval from taking out of the furnace to the first pass of straightening is 1 min, and the allowable deviation of straightening flatness is 10 mm / m.

[0034] (5) Move and cool on the cooling bed. The specific process is as follows: After straightening, move and cool on the cooling bed until the center temperature of the slab is lower than 300 °C (detected by a portable infrared thermometer), then stop moving to obtain a high impact toughness Ti80 titanium alloy thick plate with a thickness of 135 mm.

[0035] Figure 1This is the microstructure diagram of the high impact toughness Ti80 titanium alloy thick plate obtained after annealing heat treatment. The microstructure of the high impact toughness Ti80 titanium alloy thick plate is equiaxed α phase + β phase transformation duplex structure; among them, the content of primary equiaxed α phase is 30%, the size is 0 - 30 μm, and it is evenly distributed. The impact toughness KV of the high impact toughness Ti80 titanium alloy thick plate 2 = 50 J, the tensile strength Rm = 850 MPa, the elongation A = 15%, and the reduction of area Z = 30%.

[0036] Example 2

[0037] The high impact toughness Ti80 titanium alloy thick plate of this example is composed of the following components by mass percentage: Al 5.9%, Nb 3.2%, Zr 1.8%, Mo 1.1%, and the balance is Ti and inevitable impurities; the high impact toughness Ti80 titanium alloy thick plate is prepared by the following method steps: (1) Furnace temperature uniformity detection in the heat treatment furnace: 9 K-type detection thermocouples are evenly distributed on 3 metal rods with a height of 300 mm. The distance between adjacent metal rods is 1 / 3 of the furnace width (the furnace width is 3.3 m), that is, the distance between adjacent metal rods is 1.1 m, and the metal rods are fixed on a 15-mm-thick metal plate in the heat treatment furnace. During detection, the furnace temperature is raised to the detection temperature (select 3 uniform temperature detection temperatures 890 °C (Tβ = 990 °C), 940 °C, 965 °C), and the metal plate in the furnace is moved for detection. The metal plate is placed at the center position of the furnace width, and data is collected every time it stops after moving 2 meters. The detection thermocouple stays at each position for 35 minutes to collect data until the temperature measurement of the entire heat treatment furnace is completed, and the furnace temperature difference is within the range of ±7 °C.

[0038] (2) The heat treatment system is as follows: enter the furnace at 930 ± 10 °C, hold for 0.5 hour after reaching the temperature; uniformly heat up for 15 min to 975 ± 10 °C, hold for 3.5 hours after reaching the temperature, and then air cool after taking out of the furnace.

[0039] (3) During the heat treatment process, the thick plate undergoes micro-movement. The specific process is as follows: the time interval between two adjacent micro-movements is 10 min, and the two adjacent micro-movements are alternately moved according to the half circumference and the circumference of the driving roller in the heat treatment furnace.

[0040] (4) After taking out of the furnace, the thick plate is hot straightened by a straightening machine. The specific process is as follows: the time interval from taking out of the furnace to the first pass of straightening is 1.5 min, and the allowable deviation of straightening flatness is 5 mm / m.

[0041] (5) Move and cool on the cooling bed. The specific process is as follows: after straightening, move and cool on the cooling bed, and stop moving until the center temperature of the slab is lower than 200 °C (detected by a portable infrared thermometer) to obtain a high impact toughness Ti80 titanium alloy thick plate with a thickness of 130 mm.

[0042] Figure 2 Microstructure diagram of the high impact toughness Ti80 titanium alloy thick plate obtained after annealing treatment in this embodiment. The microstructure of the high impact toughness Ti80 titanium alloy thick plate is equiaxed α phase + β phase transformation duplex structure; among them, the content of primary equiaxed α phase is 30%, the size is 0 - 35 μm, and it is evenly distributed. The impact toughness KV of the high impact toughness Ti80 titanium alloy thick plate 2 = 55 J, the tensile strength Rm = 860 MPa, the elongation A = 17%, and the reduction of area Z = 32%.

[0043] Example 3

[0044] The high impact toughness Ti80 titanium alloy thick plate in this embodiment is composed of the following components by mass percentage: Al 6.0%, Nb 3.1%, Zr 1.5%, Mo 1.0%, and the balance is Ti and unavoidable impurities; the Ti80 high impact toughness titanium alloy thick plate is prepared by a method including the following steps: (1) Furnace temperature uniformity detection in the heat treatment furnace: 9 K-type detection thermocouples are evenly distributed on 3 metal rods with a height of 285 mm. The distance between adjacent metal rods is 1 / 3 of the furnace width (the furnace width is 3.6 m), that is, the distance between adjacent metal rods is 1.2 m, and the metal rods are fixed on a 10-mm-thick metal plate. During detection, the furnace temperature is raised to the detection temperature (select 3 uniform temperature detection temperatures 880 °C (Tβ = 980 °C), 930 °C, 955 °C), and the metal plate in the furnace is moved for detection. The metal plate is placed at the center position of the furnace width, and data is collected every time it stops after moving 2 meters. The detection thermocouple stays at each position for 30 minutes to collect data until the temperature measurement of the entire heat treatment furnace is completed, and the furnace temperature difference is within the range of ±10 °C.

[0045] (2) The heat treatment system is as follows: Enter the furnace at 920 ± 10 °C, and keep warm for 0.5 hour after reaching the temperature; uniformly heat up for 20 min to 965 ± 10 °C, keep warm for 3.5 hours after reaching the temperature, and then air-cool after taking out of the furnace.

[0046] (3) During the heat treatment process, the thick plate undergoes micro-motion. The specific process is as follows: The time interval between two adjacent micro-motions is 5 min, and the two adjacent micro-motions alternately move half of the roller circumference and the roller circumference.

[0047] (4) After taking out of the furnace, the thick plate is hot-straightened by a straightening machine. The specific process is as follows: The time interval from taking out of the furnace to the first pass of straightening is 2 min, and the allowable deviation of straightening flatness is 10 mm / m.

[0048] (5) Move and cool on the cooling bed. The specific process is as follows: After straightening, move and cool on the cooling bed until the center temperature of the slab is lower than 100 °C (detected by a portable infrared thermometer), then stop moving to obtain a high impact toughness Ti80 titanium alloy thick plate with a thickness of 160 mm.

[0049] Figure 3 This is the microstructure diagram of the high impact toughness Ti80 titanium alloy thick plate obtained after annealing treatment in this embodiment. The microstructure of the high impact toughness Ti80 titanium alloy thick plate is equiaxed α phase + β phase transformation duplex structure, in which the content of primary equiaxed α phase is 35%, the size is 0 - 30 μm, and it is evenly distributed. The impact toughness KV of the titanium alloy 2 = 60 J, the tensile strength Rm = 860 MPa, the elongation A = 20%, and the reduction of area Z = 25%.

[0050] Comparative Example 1 The heat treatment control method for the microstructure of the Ti80 titanium alloy thick plate in this comparative example: The difference between this comparative example and the above-mentioned Example 1 is only that step (3) is not executed, that is, the thick plate does not undergo micro-motion during the heat treatment process, and the remaining process parameters are the same as those in Example 1. The microstructure of the Ti80 titanium alloy thick plate prepared in Comparative Example 1 is as Figure 4 shown. There is Widmanstätten structure in its microstructure, and the content of primary equiaxed α phase is less. The impact toughness KV of the Ti80 titanium alloy 2 = 48 J, the tensile strength Rm = 835 MPa, the elongation A = 18%, and the reduction of area Z = 23%.

[0051] Comparative Example 2 The heat treatment control method for the microstructure of the Ti80 titanium alloy thick plate in this comparative example: The difference between this comparative example and the above-mentioned Example 1 is only that step (5) is not executed, that is, the thick plate does not undergo moving cooling during the cooling process, and the remaining process parameters are the same as those in Example 1. The microstructure of the Ti80 titanium alloy thick plate prepared in Comparative Example 1 is as Figure 5 shown. There is Widmanstätten structure in its microstructure, and the content of primary equiaxed α phase is less. The impact toughness KV of the Ti80 titanium alloy 2 = 46 J, the tensile strength Rm = 825 MPa, the elongation A = 16%, and the reduction of area Z = 20%.

[0052] From the comprehensive perspective of the examples and comparative examples, the heat treatment control method prepared in the embodiments of the present invention regulates the microstructure of the high impact toughness Ti80 titanium alloy thick plate, forms a uniformly distributed equiaxed α phase + β phase transformation duplex structure, and improves the performance of the material.

[0053] It should be noted that the above-mentioned examples are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for controlling the microstructure of a high impact toughness Ti80 titanium alloy thick plate by heat treatment, characterized in that: The following steps are involved: S1, the heat treatment furnace is tested for temperature uniformity to ensure that the temperature difference of the furnace is within the range of ±10℃; S2, heat treatment is carried out according to the heat treatment system. The Ti80 titanium alloy thick plate is put into the furnace at a temperature of (Tβ-60) ±10℃, kept warm for 0.5-1h after reaching the temperature, and evenly heated to (Tβ-15) ±10℃, kept warm for 3-4h after reaching the temperature, and then taken out of the furnace for air cooling. Tβ is the phase transition point temperature; S3, the Ti80 titanium alloy thick plate fretting in the heat treatment furnace during heat treatment; S4, after the heat treatment, the Ti80 titanium alloy thick plate is heat straightened after being taken out of the furnace to ensure that the allowable deviation of the straightening unevenness of the Ti80 titanium alloy thick plate is ≤10mm / m; S5, moving and cooling the Ti80 titanium alloy thick plate after heat straightening on a cooling bed until the center temperature of the slab is ≤300°C and the movement is stopped to obtain a Ti80 titanium alloy thick plate with high impact toughness; The microstructure of the high impact toughness Ti80 titanium alloy thick plate is a uniformly distributed equiaxed α phase+β phase transformation dual-state structure.

2. The method for controlling the microstructure of a high impact toughness Ti80 titanium alloy thick plate according to claim 1, characterized in that: In step S1, the method for detecting the temperature uniformity of the heat treatment furnace is as follows: S11, 9 K-type detection thermocouples are evenly distributed on 3 metal rods with a height of 280-400 mm, and the interval between adjacent metal rods is 1 / 3 of the furnace width. The metal rods are fixed on a metal plate with a thickness of 10-20 mm in the heat treatment furnace; S12, raise the furnace temperature to the detection temperature, and move the metal plate in the furnace for detection. When testing, first place the metal plate at the center of the furnace width, and then stop every two meters to collect data. When thermocouple testing, stay at each position for 30 to 60 minutes to collect data until the furnace temperature detection of the entire heat treatment furnace is completed, ensuring that the furnace temperature difference is controlled within the range of ±10°C.

3. The method for controlling the microstructure of a high impact toughness Ti80 titanium alloy thick plate according to claim 2, characterized in that: In step S12, three temperature uniformity detection temperatures are selected: (Tβ-100)°C, (Tβ-50)°C, and (Tβ-25)°C, where Tβ is the phase transition point temperature.

4. The method for controlling the microstructure of a high impact toughness Ti80 titanium alloy thick plate according to claim 1, characterized in that: In step S2, the time taken to uniformly increase the temperature from (Tβ-60)±10°C to (Tβ-15)±10°C is 10-20 minutes.

5. The method for controlling the microstructure of a high impact toughness Ti80 titanium alloy thick plate according to claim 1, characterized in that: In step S3, the interval between two adjacent micro-movements is 5 to 10 minutes, and the two adjacent micro-movements are performed alternately according to the half circumference of the transmission roller and the circumference of the transmission roller in the heat treatment furnace.

6. The method for controlling the microstructure of a high impact toughness Ti80 titanium alloy thick plate according to claim 1, characterized in that: In step S4, the time interval between the Ti80 titanium alloy thick plate being taken out of the furnace and the first heat straightening being performed is ≤3 min.

7. The method for controlling the microstructure of a high impact toughness Ti80 titanium alloy thick plate according to claim 1, characterized in that: In step S5, the Ti80 titanium alloy thick plate is moved on the cooling bed and cooled until the center temperature of the plate is ≤100°C and then stops moving.

8. The method for controlling the microstructure of a high impact toughness Ti80 titanium alloy thick plate according to claim 1, characterized in that: In step S5, in the structure of the high impact toughness Ti80 titanium alloy thick plate, the equiaxed α phase content is 5-60%, and the grain size thereof is ≤60 μm; and the impact toughness KV2 of the high impact toughness Ti80 titanium alloy thick plate is ≥48J.

9. A high impact toughness Ti80 titanium alloy thick plate prepared by the heat treatment control method for the microstructure of a high impact toughness Ti80 titanium alloy thick plate according to any one of claims 1 to 8, characterized in that: Its composition is as follows by mass percentage: Al 5.0% to 7.0%, Nb 2.0% to 4.0%, Zr 1.0% to 3.0%, Mo 0.4% to 2.0%, and the balance is Ti and unavoidable impurities; The microstructure of the high impact toughness Ti80 titanium alloy thick plate is a uniformly distributed equiaxed α phase + β phase transformation dual-state structure; the content of the equiaxed α phase is 5-60%, and its grain size is ≤60μm; the impact toughness KV2 of the high impact toughness Ti80 titanium alloy thick plate is ≥48J.

10. The high impact toughness Ti80 titanium alloy thick plate according to claim 9, characterized in that: The tensile strength Rm of the high impact toughness Ti80 titanium alloy thick plate is 800-1000MPa, the elongation A is 8%-20%, and the section shrinkage Z is 20%-50%.

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