Heat treatment control method for high impact toughness Ti80 titanium alloy thick plate and its microstructure

Abstract

The present invention discloses a heat treatment control method for a high-impact-toughness Ti80 titanium alloy thick plate and its microstructure. The method involves testing the temperature uniformity of a heat treatment furnace and then performing heat treatment according to a heat treatment schedule. The Ti80 titanium alloy thick plate is placed in the furnace at (Tβ-60) ±10°C, held at that temperature for 0.5 to 1 hour, then uniformly heated to (Tβ-15) ±10°C, and held at that temperature for 3 to 4 hours. During the heat treatment, the Ti80 titanium alloy thick plate is subjected to slight movement in the heat treatment furnace. After removal from the furnace, the heat-treated Ti80 titanium alloy thick plate is subjected to heat straightening to ensure that the allowable deviation of the straightening unevenness of the Ti80 titanium alloy thick plate is ≤10 mm / m. The heat-straightened Ti80 titanium alloy thick plate is then moved and cooled on a cooling bed to obtain a high-impact-toughness Ti80 titanium alloy thick plate. The method controls the heat treatment process by testing the temperature control accuracy of the heat treatment furnace, effectively controlling the microstructure of the thick plate and ensuring high impact toughness.

Description

Technical Field

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

[0002] Titanium alloys, with their excellent combination of properties, including high specific strength, excellent corrosion resistance, and weldability, are widely used in aviation, aerospace, shipbuilding, petroleum, and chemical industries. In recent years, with the implementation of several major engineering projects, such as marine engineering and transportation, demand for titanium alloy plate has increased, along with higher requirements for specifications and performance, particularly plate thickness and impact toughness. Under complex marine conditions, plates are subjected to a variety of forces, including tension, torsion, and impact, creating complex stress conditions. Generally, as plate thickness increases, the impact toughness of the center decreases. This is primarily due to the reduced forgeability and rollability of the core, making the porosity and microcracks in the central structure difficult to weld during deformation, and thus, controlling microstructure uniformity. Therefore, ensuring optimal microstructure in thick titanium alloy plates is crucial for achieving excellent impact toughness. Heat treatment, the final step in controlling the microstructure of thick titanium alloy plates, is also crucial.

[0003] Chinese patent CN118291901A discloses a heat treatment method for ultra-large titanium alloy wide and thick plates, which mainly includes the following steps: step (1) heating the furnace to T1 (T1=T2-100℃), and keeping the temperature for 10-30min after reaching the temperature; step (2) the wide and thick plates are put into the furnace and kept warm for S1min (S1=1-1.2d, d is the thickness of the wide and thick plates); step (3) heating the furnace to T2 (1-100℃ below the β-transformation temperature), and keeping the temperature for S2min (S2=0.5-0.8d, d is the thickness of the wide and thick plates); step (4) ending the heat preservation and cooling the furnace for 10-30min; step (5) taking the plates out of the furnace. Water cooling and drying; step (6) heating the furnace to T3 (T3=T2 / 2±100℃); step (7) the wide and thick plates are put into the furnace and kept warm for 240-600min; step (8) the heat preservation is ended and the plates are cooled with the furnace to 140-165℃; step (9) the wide and thick plates are taken out of the furnace and the heat treatment is completed; after being treated by the method of the invention, ultra-large-sized titanium alloy wide and thick plates with high strength and good plasticity can be obtained; the method has certain limitations (1) the applicable thickness range of the wide and thick plates is 30-60mm; (2) the cooling with the furnace after the heat preservation takes up a long time in the heat treatment furnace; (3) the method of controlling the structure of the wide and thick plates during the heat treatment and cooling process is not mentioned. Chinese patent CN117773158A discloses a heat treatment method for additively manufactured large-size thin-walled annular parts made of titanium alloy. The method mainly comprises the following steps: (1) placing the part with a substrate into a vacuum heat treatment furnace; (2) the heat treatment schedule is as follows: heating to 200-300°C and holding for 1-2 hours; heating to 400-500°C and holding for 1-2 hours; heating to 600-700°C and holding for 1-2 hours; heating to 800-850°C and holding for 1-2 hours, and then removing from the furnace after cooling; (3) cutting the part from the substrate using wire cutting. After treatment by this method, the microstructure of the part is uniformly transformed in the height direction. The limitations of this method are: (1) it is applicable to parts with a thickness of less than 5 mm; (2) the heat treatment process requires an additional substrate, which increases the complexity of industrial implementation; and (3) the cooling time of the heat treatment furnace after holding is long.

[0004] At present, the method of controlling the microstructure of titanium alloy thick plates by heat treatment has the following problems: (1) There is a lack of heat treatment system for thick plates with high thickness. During the heat treatment and cooling process, the surface and core of the thick plate are easily heated and cooled unevenly, which leads to the impact toughness not meeting the requirements; (2) Furnace cooling takes a long time for heat treatment, and there is a lack of a better heat treatment system; (3) The plate shape of the thick plate is difficult to control to meet the requirements during the heat treatment and cooling process; (4) The better microstructure is unknown; (5) The actual production process is complex, the state of the heat treatment furnace is often in dynamic change, and the temperature uniformity of the heat treatment furnace is unknown. Therefore, it is necessary to develop a heat treatment control method for the microstructure of high impact toughness Ti80 titanium alloy thick plates, which can effectively control the microstructure of the thick plates and ensure that the thick plates have high impact toughness. Summary of the Invention

[0005] In view of the defects existing in the prior art, the purpose of the present invention is to provide a heat treatment control method for a Ti80 titanium alloy thick 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:

[0007] A first aspect of the present invention provides a method for controlling the microstructure of a high impact toughness Ti80 titanium alloy thick plate through heat treatment, comprising the following steps:

[0008] S1, the heat treatment furnace is tested for temperature uniformity to ensure that the temperature difference is within the range of ±10℃;

[0009] 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 ° C, kept at this temperature for 0.5 to 1 hour after reaching the temperature, and then uniformly heated to (Tβ-15) ± 10 ° C, kept at this temperature for 3 to 4 hours after reaching the temperature, and then taken out of the furnace and air-cooled. Tβ is the phase transition point temperature;

[0010] S3, Ti80 titanium alloy thick plate fretting in the heat treatment furnace during heat treatment;

[0011] S4, after heat treatment, the Ti80 titanium alloy thick plate is hot straightened after being taken out of the furnace to ensure that the straightening unevenness of the Ti80 titanium alloy thick plate is allowed to be less than 10mm / m;

[0012] 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 then stopping the movement to obtain a Ti80 titanium alloy thick plate with high impact toughness;

[0013] 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.

[0014] Preferably, in step S1, the method for detecting the temperature uniformity of the heat treatment furnace is as follows:

[0015] S11, evenly distribute nine K-type detection thermocouples on three metal rods with a height of 280-400 mm, with the distance between adjacent metal rods being 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;

[0016] S12: Raise the furnace temperature to the detection temperature and move the metal plate in the furnace for detection. During the detection, first place the metal plate at the center of the furnace width, and then stop every two meters to collect data. During the thermocouple detection, stop 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.

[0017] Preferably, 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.

[0018] Preferably, in step S2, the time taken to uniformly raise the temperature from (Tβ-60)±10°C to (Tβ-15)±10°C is 10-20 min.

[0019] Preferably, 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 and the circumference of the transmission roller in the heat treatment furnace.

[0020] Preferably, 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.

[0021] Preferably, in step S5, the Ti80 titanium alloy thick plate is moved on the cooling bed and cooled until the center temperature of the slab is ≤100°C and then stops moving.

[0022] Preferably, in step S5, the microstructure of the high impact toughness Ti80 titanium alloy thick plate has an equiaxed α phase content of 5-60%, and a grain size of ≤60 μm; and the impact toughness KV2 of the high impact toughness Ti80 titanium alloy thick plate is ≥48J.

[0023] A second aspect of the present invention provides a high-impact-toughness Ti80 titanium alloy thick plate produced by the heat treatment control method for the microstructure of the high-impact-toughness Ti80 titanium alloy thick plate described in the first aspect of the present invention, wherein the composition thereof 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 being Ti and unavoidable impurities;

[0024] 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 equiaxed α phase content 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.

[0025] Preferably, the high impact toughness Ti80 titanium alloy thick plate has a tensile strength Rm of 800 to 1000 MPa, an elongation A of 8% to 20%, and a cross-sectional shrinkage Z of 20% to 50%.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. By adopting the heat treatment control method of the present invention, the thick plate structure is an equiaxed α phase + β phase transformation dual-state structure, the primary equiaxed α content is 5-60%, and the impact toughness KV2 is ≥ 48J, which can meet the high impact toughness requirements of titanium alloy thick plates in marine engineering;

[0028] 2. The present invention ensures the temperature control accuracy of the heat treatment furnace through furnace temperature uniformity detection, ensures the uniformity of heating by micro-movement of the thick plate during the heat treatment process, ensures the good plate shape of the thick plate by thermal straightening, and ensures uniform heat dissipation by moving cooling on the cooling bed. Through the above measures, the problem of uneven structure of the titanium alloy thick plate can be effectively solved, the impact toughness of the core of the titanium alloy thick plate can be significantly improved, the yield rate can be increased, and it can help reduce costs and improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a microstructure diagram of a high impact toughness Ti80 titanium alloy thick plate prepared in Example 1 of the present invention;

[0030] Figure 2 This is a microstructure diagram of a high impact toughness Ti80 titanium alloy thick plate prepared in Example 2 of the present invention;

[0031] Figure 3 This is a microstructure diagram of a high impact toughness Ti80 titanium alloy thick plate prepared in Example 3 of the present invention;

[0032] Figure 4 This is the microstructure of the Ti80 titanium alloy thick plate prepared in Comparative Example 1;

[0033] Figure 5 This is the microstructure diagram of the Ti80 titanium alloy thick plate prepared in Comparative Example 2. DETAILED DESCRIPTION

[0034] The present invention will be described in detail below with reference to specific examples. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form.

[0035] The present invention provides a method for controlling the microstructure of a high impact toughness Ti80 titanium alloy thick plate through heat treatment, comprising the following steps:

[0036] S1, the heat treatment furnace is tested for temperature uniformity to ensure that the temperature difference is within the range of ±10℃;

[0037] The method for testing the temperature uniformity of the heat treatment furnace in this step is as follows:

[0038] S11, evenly distribute nine K-type detection thermocouples on three metal rods with a height of 280-400 mm, with the distance between adjacent metal rods being 1 / 3 of the width of the heat treatment furnace. The metal rods are fixed to a metal plate with a thickness of 10-20 mm in the heat treatment furnace;

[0039] 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 within the range of ±10°C.

[0040] In the above furnace temperature uniformity test process, three uniformity test temperatures can be selected: (Tβ-100)℃, (Tβ-50)℃, (Tβ-25)℃, where Tβ is the phase transition point temperature.

[0041] 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 °C, kept at this temperature for 0.5 to 1 hour, and then uniformly heated for 10 to 20 minutes to (Tβ-15) ± 10 °C, kept at this temperature for 3 to 4 hours, and then taken out of the furnace and air-cooled. Tβ is the phase transition point temperature.

[0042] S3, Ti80 titanium alloy thick plate fretting in the heat treatment furnace during heat treatment;

[0043] In this step, the interval between two adjacent micro-movements is 5-10 minutes. The two adjacent micro-movements are performed alternately based on the semi-circumference and circumference of the drive roller in the heat treatment furnace. The circumference of the drive roller is calculated based on the drive roller diameter D, i.e., π*D, and the semi-circumference of the drive roller is 1 / 2π*D.

[0044] S4, after heat treatment, the Ti80 titanium alloy thick plate is hot straightened after being taken out of the furnace to ensure that the straightening unevenness of the Ti80 titanium alloy thick plate is allowed to be less than 10mm / m;

[0045] This step is to use a straightening machine to heat straighten the Ti80 titanium alloy thick plate after heat treatment, and control the time interval from the Ti80 titanium alloy thick plate being taken out of the furnace to the first heat straightening to be ≤3 minutes.

[0046] 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 then stopping the movement to obtain a Ti80 titanium alloy thick plate with high impact toughness;

[0047] In this step, the Ti80 titanium alloy thick plate after heat straightening is moved and cooled on the cooling bed until the center temperature of the slab is ≤300°C (for example, the center temperature of the slab is ≤100°C), and the movement is stopped. The center temperature of the slab can be detected by a portable infrared thermometer.

[0048] In this invention, the temperature uniformity test is first performed to ensure the temperature control accuracy of the heat treatment furnace, keeping the furnace temperature difference within a controllable range. Next, the heat treatment schedule is optimized, with the Ti80 titanium alloy thick plate entering the furnace at (Tβ-60) ±10°C for insulation. This ensures uniform heating of the slab and prevents temperature overshoot. The temperature is then uniformly raised to (Tβ-15) ±10°C, resulting in a superior bimodal microstructure. Furthermore, the Ti80 titanium alloy thick plate is slightly moved within the heat treatment furnace during the heat treatment process to further ensure uniform heating. Thermal straightening ensures that the straightened Ti80 titanium alloy thick plate has a good shape. Moving the Ti80 titanium alloy thick plate on a cooling bed for cooling ensures uniform heat dissipation. Through the above measures, the present invention solves the problem of uneven microstructure of Ti80 titanium alloy thick plates and regulates their microstructure morphology, so that the microstructure of the Ti80 titanium alloy thick plates is transformed into an equiaxed α phase + β phase transformation dual-state structure, which significantly improves the impact toughness of the core of the Ti80 titanium alloy thick plates and increases the yield rate.

[0049] The high-impact-toughness Ti80 titanium alloy thick plate obtained after the above heat treatment exhibits a uniformly distributed equiaxed α-phase + β-phase transformation dual-state structure. The equiaxed α-phase content is 5-60%, and its grain size is ≤60μm. The high-impact-toughness Ti80 titanium alloy thick plate has a thickness of 60-200mm and an impact toughness KV2 of ≥48J.

[0050] The high-impact-toughness Ti80 titanium alloy thick plate prepared by the heat treatment control method for the microstructure of the high-impact-toughness Ti80 titanium alloy thick plate has the following composition 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 being Ti and unavoidable impurities;

[0051] 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 equiaxed α phase content is 5~60% (for example, 30~35%, etc.), and its grain size is ≤60μm; the impact toughness KV2 of the high impact toughness Ti80 titanium alloy thick plate is ≥48J, for example, the impact toughness KV2 is 50~90 J, 50~60 J, etc.

[0052] 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 cross-sectional shrinkage Z is 20%-50%.

[0053] The heat treatment control method of the high impact toughness Ti80 titanium alloy thick plate and its microstructure of the present invention is further introduced below with reference to specific examples.

[0054] Example 1

[0055] The high impact toughness Ti80 titanium alloy thick plate of this embodiment is composed of the following components by weight: Al 5.8%, Nb 2.9%, Zr 1.6%, Mo 1.0%, and the balance is Ti and unavoidable impurities; the high impact toughness Ti80 titanium alloy thick plate is prepared by the following steps:

[0056] (1) Temperature uniformity test of the heat treatment furnace: 9 K-type thermocouples are evenly distributed on 3 metal rods with a height of 280mm. The distance between adjacent metal rods is 1 / 3 of the furnace width (furnace width is 3m), that is, the distance between adjacent metal rods is 1m. The metal rods are fixed on a 10mm thick metal plate in the heat treatment furnace. During the test, the furnace temperature is raised to the test temperature (3 uniformity test temperatures are selected: 900℃ (Tβ=1000℃), 950℃, and 975℃). The metal plate in the furnace is moved for testing. The metal plate is placed at the center of the furnace width. Data is collected every two meters. The test thermocouples stay at each position for 30 minutes to collect data until the temperature measurement of the entire heat treatment furnace is completed. The furnace temperature difference is within the range of ±8℃.

[0057] (2) The heat treatment system is as follows: enter the furnace at 940±10℃, keep it at this temperature for 0.5 hours; evenly heat it to 985±10℃ for 10 minutes, keep it at this temperature for 3.5 hours, and then take it out of the furnace and air cool it.

[0058] (3) The thick plate is slightly moved during the heat treatment process. The specific process is as follows: the interval between two adjacent micro-movements is 5 minutes, and the two adjacent micro-movements are alternately moved according to the half circumference of the transmission roller and the circumference of the transmission roller in the heat treatment furnace.

[0059] (4) After being taken out of the furnace, the thick plate is straightened by a straightening machine. The specific process is: the time interval between the thick plate being taken out of the furnace and the first straightening is 1 minute, and the allowable deviation of the straightening unevenness is 10 mm / m.

[0060] (5) Moving cooling on the cooling bed. The specific process is: after straightening, moving cooling on the cooling bed until the center temperature of the slab is lower than 300 °C (detected by a portable infrared thermometer) and then stopping the movement to obtain a high impact toughness Ti80 titanium alloy thick plate with a thickness of 135 mm.

[0061] Figure 1 This is a microstructure diagram of the high-impact-toughness Ti80 titanium alloy thick plate obtained after annealing heat treatment in this example. The microstructure of this high-impact-toughness Ti80 titanium alloy thick plate is a dual-phase structure consisting of an equiaxed α phase and a β phase transformation. The primary equiaxed α phase accounts for 30%, with a uniform distribution ranging from 0 to 30 μm. This high-impact-toughness Ti80 titanium alloy thick plate has an impact toughness KV2 of 50 J, a tensile strength Rm of 850 MPa, an elongation A of 15%, and a reduction of area Z of 30%.

[0062] Example 2

[0063] The high impact toughness Ti80 titanium alloy thick plate of this embodiment is composed of the following components by weight: 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 steps:

[0064] (1) Temperature uniformity test of the heat treatment furnace: 9 K-type thermocouples are evenly distributed on 3 metal rods with a height of 300mm. The distance between adjacent metal rods is 1 / 3 of the furnace width (furnace width is 3.3m), that is, the distance between adjacent metal rods is 1.1m. The metal rods are fixed on a 15mm thick metal plate in the heat treatment furnace. During the test, the furnace temperature is raised to the test temperature (3 uniformity test temperatures are selected: 890℃ (Tβ=990℃), 940℃, and 965℃). The metal plate in the furnace is moved for testing. The metal plate is placed at the center of the furnace width. Data is collected every two meters. The test thermocouples stay at each position for 35 minutes to collect data until the temperature measurement of the entire heat treatment furnace is completed. The furnace temperature difference is within the range of ±7℃.

[0065] (2) The heat treatment system is as follows: enter the furnace at 930±10℃, keep it at this temperature for 0.5 hours; evenly heat it up to 975±10℃ for 15 minutes, keep it at this temperature for 3.5 hours, and then take it out of the furnace and air cool it.

[0066] (3) The thick plate is slightly moved during the heat treatment process. The specific process is as follows: the interval between two adjacent micro-movements is 10 minutes, and the two adjacent micro-movements are alternately moved according to the half circumference of the transmission roller and the circumference of the transmission roller in the heat treatment furnace.

[0067] (4) After being taken out of the furnace, the thick plate is straightened by a straightening machine. The specific process is: the time interval from the thick plate being taken out of the furnace to the first straightening is 1.5 minutes, and the allowable deviation of the straightening unevenness is 5 mm / m.

[0068] (5) Moving cooling on the cooling bed. The specific process is: after straightening, moving cooling on the cooling bed until the center temperature of the slab is lower than 200 °C (detected by a portable infrared thermometer) and then stopping the movement to obtain a high impact toughness Ti80 titanium alloy thick plate with a thickness of 130 mm.

[0069] Figure 2 This is a microstructure diagram of the high-impact-toughness Ti80 titanium alloy thick plate obtained after annealing heat treatment in this example. The microstructure of this high-impact-toughness Ti80 titanium alloy thick plate is a dual-phase structure consisting of an equiaxed α phase and a β phase transformation. The primary equiaxed α phase accounts for 30%, with a uniform distribution of 0-35 μm in size. The high-impact-toughness Ti80 titanium alloy thick plate has an impact toughness KV2 of 55 J, a tensile strength Rm of 860 MPa, an elongation A of 17%, and a reduction of area Z of 32%.

[0070] Example 3

[0071] The high impact toughness Ti80 titanium alloy thick plate of this embodiment is composed of the following components in percentage by weight: 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 comprising the following steps:

[0072] (1) Temperature uniformity test of the heat treatment furnace: 9 K-type thermocouples are evenly distributed on 3 metal rods with a height of 285mm. The distance between adjacent metal rods is 1 / 3 of the furnace width (furnace width is 3.6m), that is, the distance between adjacent metal rods is 1.2m. The metal rods are fixed on a 10mm thick metal plate. During the test, the furnace temperature is raised to the test temperature (3 uniformity test temperatures are selected: 880℃ (Tβ=980℃), 930℃, and 955℃). The metal plate in the furnace is moved for testing. The metal plate is placed at the center of the furnace width. Data is collected every two meters. The test thermocouples stay at each position for 30 minutes to collect data until the temperature measurement of the entire heat treatment furnace is completed. The furnace temperature difference is within the range of ±10℃.

[0073] (2) The heat treatment system is as follows: enter the furnace at 920±10℃, keep it at this temperature for 0.5 hours; evenly heat it up to 965±10℃ for 20 minutes, keep it at this temperature for 3.5 hours, and then take it out of the furnace and air cool it.

[0074] (3) The thick plate is slightly moved during the heat treatment process. The specific process is as follows: the interval between two adjacent micro-movements is 5 minutes, and the two adjacent micro-movements alternately move half the circumference of the roller and the circumference of the roller.

[0075] (4) After being taken out of the furnace, the thick plate is straightened by a straightening machine. The specific process is: the time interval from the thick plate being taken out of the furnace to the first straightening is 2 minutes, and the allowable deviation of the straightening unevenness is 10 mm / m.

[0076] (5) Moving cooling on the cooling bed. The specific process is: after straightening, moving cooling on the cooling bed until the center temperature of the slab is lower than 100 °C (detected by a portable infrared thermometer) and then stopping the movement to obtain a high impact toughness Ti80 titanium alloy thick plate with a thickness of 160 mm.

[0077] Figure 3 This is a microstructure diagram of the high-impact-toughness Ti80 titanium alloy thick plate obtained after annealing heat treatment in this example. The microstructure of this high-impact-toughness Ti80 titanium alloy thick plate is a dual-phase structure consisting of an equiaxed α phase and a β phase transformation. The primary equiaxed α phase contains 35% of the material and is uniformly distributed, with a size of 0 to 30 μm. The titanium alloy has an impact toughness of KV2 = 60 J, a tensile strength of Rm = 860 MPa, an elongation of A = 20%, and a reduction of area of Z = 25%.

[0078] Comparative Example 1

[0079] Heat treatment control method for the microstructure of Ti80 titanium alloy thick plate in this comparative example:

[0080] The only difference between this comparative example and the above-mentioned Example 1 is that step (3) is not performed, that is, the thick plate is not slightly moved during the heat treatment process. The other process parameters are the same as those of Example 1. The microstructure of the Ti80 titanium alloy thick plate prepared in Comparative Example 1 is as follows: Figure 4 As shown in the figure, the microstructure of Ti80 titanium alloy contains Widmanstätten structure and the content of primary equiaxed α phase is relatively low. The impact toughness KV2 of Ti80 titanium alloy is 48J, the tensile strength Rm is 835MPa, the elongation A is 18%, and the reduction of area Z is 23%.

[0081] Comparative Example 2

[0082] Heat treatment control method for the microstructure of Ti80 titanium alloy thick plate in this comparative example:

[0083] The only difference between this comparative example and the above-mentioned Example 1 is that step (5) is not performed, that is, the thick plate is not moved and cooled during the cooling process. The other process parameters are the same as those of Example 1. The microstructure of the Ti80 titanium alloy thick plate prepared in Comparative Example 1 is as follows: Figure 5 As shown in Figure 1, its microstructure contains Widmanstätten structure and the content of primary equiaxed α phase is relatively low. The impact toughness KV2 of Ti80 titanium alloy is 46J, the tensile strength Rm is 825MPa, the elongation A is 16%, and the cross-sectional reduction Z is 20%.

[0084] From the comprehensive examples and comparative examples, the microstructure of the high impact toughness Ti80 titanium alloy thick plate prepared by the embodiment of the present invention is regulated by the heat treatment control method, forming a uniformly distributed equiaxed α phase + β phase transformation dual-state structure, thereby improving the performance of the material.

[0085] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, and all of these should be included in the scope of the claims of the present invention.

Claims

1. A heat treatment control method for the microstructure of a high impact toughness Ti80 titanium alloy thick plate, 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°C; three uniformity test temperatures are selected in the furnace temperature uniformity test: (Tβ-100)°C, (Tβ-50)°C, and (Tβ-25)°C, where Tβ is the phase transition point temperature; 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 then uniformly heated to (Tβ-15)±10℃, kept warm for 3~4h after reaching the temperature, and then taken out of the furnace and air-cooled. Tβ is the phase transition point temperature; S3, Ti80 titanium alloy thick plate micro-moves in the heat treatment furnace during heat treatment; two adjacent micro-movements are alternating according to the half circumference and circumference of the transmission roller in the heat treatment furnace; S4, after heat treatment, the Ti80 titanium alloy thick plate is hot straightened after being taken out of the furnace to ensure that the straightening unevenness of the Ti80 titanium alloy thick plate is allowed to be less than 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 then stopping the movement to obtain a Ti80 titanium alloy thick plate with high impact toughness; The high-impact-toughness Ti80 titanium alloy thick plate has a thickness of 60 to 200 mm, a microstructure of uniformly distributed equiaxed α phase + β phase transformation dual-state structure, an equiaxed α phase content of 5 to 60%, and a grain size of ≤60 μm; the high-impact-toughness Ti80 titanium alloy thick plate has an impact toughness KV2 ≥48 J.

2. The method for controlling the microstructure of a high impact toughness Ti80 titanium alloy thick plate according to claim 1, wherein: In step S1, the method for detecting the temperature uniformity of the heat treatment furnace is as follows: S11, evenly distribute nine K-type detection thermocouples on three metal rods with a height of 280 to 400 mm, with the distance between adjacent metal rods being 1 / 3 of the furnace width. The metal rods are fixed to a metal plate with a thickness of 10 to 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. During the detection, first place the metal plate at the center of the furnace width, and then stop every two meters to collect data. During the thermocouple detection, 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 heat treatment control method for 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 to 20 minutes.

4. The method for controlling the microstructure of a high impact toughness Ti80 titanium alloy thick plate according to claim 1, wherein: In step S3, the interval between two adjacent micro-movements is 5 to 10 minutes.

5. The method for controlling the microstructure of a high impact toughness Ti80 titanium alloy thick plate according to claim 1, wherein: 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 minutes.

6. The method for controlling the microstructure of a high impact toughness Ti80 titanium alloy thick plate according to claim 1, wherein: In step S5, the Ti80 titanium alloy thick plate is moved on the cooling bed and cooled until the center temperature of the slab is ≤100° C., and then the movement is stopped.

7. A high impact toughness Ti80 titanium alloy thick plate produced 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 6, 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 thickness of the high-impact-toughness Ti80 titanium alloy thick plate is 60 to 200 mm, and the microstructure is a uniformly distributed equiaxed α phase + β phase transformation dual-state structure; the equiaxed α phase content is 5 to 60%, and its grain size is ≤60 μm; the impact toughness KV2 of the high-impact-toughness Ti80 titanium alloy thick plate is ≥48J.

8. The high impact toughness Ti80 titanium alloy thick plate according to claim 7, characterized in that: The high-impact toughness Ti80 titanium alloy thick plate has a tensile strength Rm of 800-1000 MPa, an elongation A of 8%-20%, and a section shrinkage Z of 20%-50%.

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