Method for preparing near-alpha titanium alloy with improved dynamic performance based on microstructure regulation

Abstract

The application discloses a preparation method of near-alpha titanium alloy for improving dynamic performance based on microstructure regulation, and comprises the following steps: preparing a near-alpha titanium alloy blank; determining a key temperature interval of the near-alpha titanium alloy blank; performing first gradient heating treatment on the near-alpha titanium alloy blank based on the determined temperature interval T1-T2, and then performing high-temperature hot rolling forming, with the rolling direction being the RD direction; performing interpass stress relief annealing on the near-alpha titanium alloy slab; performing second gradient heating treatment on the near-alpha titanium alloy slab based on the determined temperature interval T3-T4, and then performing medium-temperature hot rolling forming, with the rolling direction being the RD direction rotating 90 degrees along the normal direction of the rolling surface; and performing post-rolling step annealing on the near-alpha titanium alloy slab, so that the near-alpha titanium alloy plate is prepared. Through the synergistic effect of the double rolling deformation strengthening of the key temperature interval and the alloy texture directionality strengthening, the microstructure morphology and dynamic mechanical properties of the near-alpha titanium alloy are improved.

Description

Technical Field

[0001] This invention belongs to the field of metal material preparation technology, specifically relating to a method for preparing near-α type titanium alloys based on microstructure regulation to improve dynamic properties. Background Technology

[0002] Titanium alloys, as lightweight metallic structural materials, possess comprehensive advantages such as low density, high specific strength, excellent corrosion resistance, and good weldability, making them irreplaceable in the manufacturing of high-end equipment in aerospace, weaponry, and other fields. Among them, near-α-type titanium alloys such as TA19 and TA15, with their superior high-temperature performance, fracture toughness, and creep resistance, are widely used in the manufacture of key components such as aero-engine structures and aircraft structures, playing a crucial supporting role in ensuring the structural strength, damage resistance, and long-term service reliability of these components.

[0003] In the material and process design of titanium alloys, quasi-static mechanical properties are crucial for microstructure control. Fully leveraging the strength, plasticity, and toughness potential of titanium alloys has always been an important research direction in this field, and these quasi-static mechanical properties are closely related to the microstructure characteristics of titanium alloys. Currently, significant progress has been made in improving the quasi-static mechanical properties of near-α type titanium alloys through methods such as optimized heat treatment regimes and controlled deformation processes, and the related research system is relatively mature.

[0004] However, with the increasing demands for comprehensive material performance and service reliability in high-end equipment manufacturing fields such as aerospace and weaponry, titanium alloy components not only bear conventional static loads during service but also face dynamic load conditions such as high-speed impacts and fragment collisions. Under such high strain rate loading conditions, the dynamic mechanical properties of titanium alloys have become a key indicator for evaluating service behavior, directly determining the structural integrity and functional effectiveness of components, and thus playing a crucial role in the overall performance of equipment.

[0005] Currently, research on the dynamic properties of near-α type titanium alloys has the following two main shortcomings: Firstly, most existing microstructure control techniques revolve around quasi-static mechanical performance indicators (such as strength-plasticity matching). The design criteria and process windows are based on quasi-static service conditions, without incorporating the mechanical response characteristics under dynamic loads into the control target system. This lack of consideration for dynamic mechanical properties results in titanium alloys prepared by traditional processes exhibiting excellent performance under quasi-static conditions, but may not have ideal performance under dynamic impact conditions.

[0006] Secondly, current technologies lack understanding of the deformation and failure mechanisms of near-alpha titanium alloys under dynamic loading. This results in the absence of mature and systematic preparation processes capable of specifically controlling the microstructure of near-alpha titanium alloys to improve their dynamic mechanical properties. Existing process control methods are mostly empirical attempts, lacking clear theoretical guidance and reproducible process windows, making it difficult to meet the design requirements of high-end equipment for dynamic service performance.

[0007] In summary, there is an urgent need to develop a near-α type titanium alloy preparation method based on microstructure regulation to improve dynamic properties, in order to make up for the shortcomings of existing technologies. Summary of the Invention

[0008] The purpose of this invention is to provide a method for preparing near-α type titanium alloys based on microstructure control to improve dynamic properties, so as to fully utilize the potential of dynamic mechanical properties of near-α type titanium alloys such as TA19 and TA15. This method utilizes the dual rolling deformation strengthening law in the key temperature range, and combines the directional strengthening effect of alloy texture and the directional strengthening effect of layered microstructure to achieve microstructure control of the dynamic properties of near-α type titanium alloys, thereby significantly improving the comprehensive mechanical properties of near-α type titanium alloys. This method has important engineering application value for the microstructure control and dynamic property optimization of near-α type titanium alloys.

[0009] To address the problems existing in the prior art, this invention provides a method for preparing near-α type titanium alloys based on microstructure regulation to improve dynamic properties. The preparation method includes the following steps in sequence: Step 1: Prepare near-α type titanium alloy billets, which must simultaneously meet the following three requirements: (1) The near-α type titanium alloy billet has a biphase structure; (2) The last heat treatment of the near-α type titanium alloy billet is a two-phase region forging, and its forging deformation is not less than 40%; (3) The microstructure of the near-α type titanium alloy billet includes an equiaxed α phase and a β-transformed phase matrix structure, wherein the volume fraction of the equiaxed α phase is 5-50%; Step 2: Determine the critical temperature range for near-α type titanium alloy billets. The determination method includes the following steps: S1. Several small-sized test blocks were cut from the near-α type titanium alloy billet. The test blocks were heat-treated in a temperature range of 800-1050℃ with a temperature step of 10-20℃. The holding time was 1 hour. After the holding time, the test blocks were water-cooled to room temperature. S2. The microstructure of each test block after heat treatment was tested to obtain the microstructure morphology of the test blocks at different heat treatment temperatures. S3. The isoaxial primary α phase content, the original coarse secondary α phase content, and the newly formed secondary α phase content of each test block after heat treatment were quantitatively evaluated. The curves of the content of each type of α phase as a function of heat treatment temperature were plotted. Among them, the temperature range in the high temperature range where only the isoaxial primary α phase and the newly formed secondary α phase exist was recorded as T1-T2. The temperature range in the medium temperature range where only the isoaxial primary α phase and the original coarse secondary α phase exist was recorded as T3-T4. Step 3: Based on the determined temperature range T1-T2, the near-α type titanium alloy billet is subjected to the first gradient heating treatment in a heat treatment furnace. Then, the near-α type titanium alloy billet is transferred to a rolling mill for 3-5 passes of high-temperature hot rolling, with a cumulative deformation of 30-60%. The rolling direction is RD. After the high-temperature hot rolling is completed, the billet is air-cooled to room temperature. Step 4: Use a heat treatment furnace to perform stress-relieving annealing on the near-α type titanium alloy slab after high-temperature hot rolling, and air cool to room temperature after annealing. Step 5: Based on the determined temperature range T3-T4, the near-α type titanium alloy slab after stress-relief annealing in the rolling mill is subjected to a second gradient heating treatment in a heat treatment furnace. Then, the near-α type titanium alloy slab is transferred to the rolling mill for 3-5 passes of medium-temperature hot rolling, with a cumulative deformation of 25-50%. The rolling direction is RD rotating 90° along the normal direction of the rolling surface. After the medium-temperature hot rolling is completed, the slab is air-cooled to room temperature. Step 6: The near-α type titanium alloy slab after medium-temperature hot rolling is subjected to step annealing in a heat treatment furnace. After annealing, it is air-cooled to room temperature to obtain near-α type titanium alloy sheet with excellent dynamic properties.

[0010] Preferably, in step one, the near-α type titanium alloy billet is a square billet with a length, width and height of not less than 100 mm.

[0011] In any of the above schemes, preferably, in step two, the length, width, and height of the test block are all 10-20 mm; the temperature range T1-T2 is the temperature range in which only equiaxed primary α phase and newly formed secondary α phase exist, T1 is the lower boundary temperature of this temperature range, and T2 is the upper boundary temperature of this temperature range; the temperature range T3-T4 is the temperature range in which only equiaxed primary α phase and primitive coarse secondary α phase exist, T3 is the lower boundary temperature of this temperature range, and T4 is the upper boundary temperature of this temperature range.

[0012] In any of the above schemes, the preferred embodiment is that, in step three, the process of the first gradient heating treatment is as follows: first, the heat treatment furnace is heated to T1; then, the near-α type titanium alloy billet is placed into the heat treatment furnace and held for (K1×H0+10) min; finally, the temperature is increased to T at a heating rate of 40-60℃ / h. h Insulation time (K2×H0+30) min.

[0013] Where: H0 is the minimum dimension of the near-α type titanium alloy billet in the length, width, and height directions, in mm; K1 is the temperature coefficient, with a set value of 0.4-0.6 mm. -1 K2 is the temperature coefficient, with a set value of 0.6-0.8 mm. -1 (T1+T2) / 2≤T h <T2.

[0014] In any of the above schemes, the preferred embodiment is that, in step four, the process of stress-relieving annealing during rolling is as follows: annealing temperature 200-400℃, annealing time (K3×H1+60) min; where: H1 is the thickness of the near-α type titanium alloy slab after high-temperature hot rolling, mm; K3 is the temperature coefficient, and its set value is the average value of K1 and K2.

[0015] In any of the above schemes, preferably, in step five, the process of the second gradient heating treatment is as follows: first, the heat treatment furnace is heated to T3; then, the near-α type titanium alloy slab after inter-roll stress-relief annealing is placed in the heat treatment furnace and held for (K1×H2+10) min; finally, the temperature is increased to T at a heating rate of 40-60℃ / h. m Insulation time: (K2×H2+30) min.

[0016] Where: H2 is the thickness of the near-α type titanium alloy slab after stress-relief annealing during rolling, in mm; K1 is the temperature coefficient, with a set value of 0.4-0.6 mm. -1 K2 is the temperature coefficient, with a set value of 0.6-0.8 mm. -1 (T3+T4) / 2≤T m <T4.

[0017] In any of the above schemes, it is preferred that, in step six, the post-rolling stepped annealing includes four annealing stages; the first stepped annealing temperature is 200℃, the second stepped annealing temperature is 300℃, and the third stepped annealing temperature is 400℃, and the holding time for the first three stepped annealing stages is (K3×H3) min; where: H3 is the thickness of the near-α type titanium alloy slab after medium-temperature hot rolling, mm; K3 is a temperature coefficient, the set value of which is the average value of K1 and K2.

[0018] In any of the above schemes, preferably, in step six, the fourth-step annealing temperature and holding time for different grades of near-α titanium alloys shall not exceed the conventional annealing temperature and conventional holding time for the corresponding grades. More preferably, the fourth-step annealing temperature for different grades of near-α titanium alloys is 0.6-0.8 times the conventional annealing temperature for the corresponding grades, and the holding time is 0.8-0.9 times the conventional holding time for the corresponding grades.

[0019] Compared with existing technologies, the present invention provides a near-α type titanium alloy preparation method based on microstructure regulation to improve dynamic properties, which has the following advantages: (1) This invention obtains the microstructure content of equiaxed α phase, primary coarse secondary α phase, and newly formed secondary α phase with heat treatment temperature through accurate identification of key temperature ranges, and designs gradient heat treatment regimes and (high temperature, medium temperature) hot rolling processes accordingly. By using rolling to obtain elongated equiaxed α phase and secondary α phase oriented along the thickness direction, the deformation coordination ability and crack propagation path of the microstructure under dynamic load are effectively optimized, thereby significantly improving the impact resistance of near-α type titanium alloys.

[0020] (2) This invention breaks through the limitations of traditional processes that only focus on the control of microstructure around quasi-static mechanical properties, and establishes a complete process chain for dynamic mechanical properties: "microstructure identification → key temperature range determination → gradient heating treatment design → multi-directional rolling". Through the synergistic effect of dual rolling deformation strengthening in the key temperature range and the directional strengthening of alloy texture, the synergistic improvement of the microstructure morphology and dynamic mechanical properties of near-α type titanium alloys is achieved.

[0021] (3) This invention fully utilizes the microstructure evolution and hot forming characteristics of near-α titanium alloys. All process steps can be completed using only conventional heat treatment furnaces and conventional rolling equipment, without the need for additional special equipment or complex control systems. The process window is wide and the operability is strong. At the same time, this method is applicable to the preparation of various grades of near-α titanium alloys such as TA19 and TA15, and has high material adaptability and feasibility. It can be directly applied to the preparation of key components of high-end equipment such as aero-engine structures and aircraft structures, and has important engineering application value for the microstructure control and dynamic performance improvement of near-α titanium alloys. Attached Figure Description

[0022] Figure 1 A micrograph of the microstructure of a TA15 near-α titanium alloy billet in a preferred embodiment of the near-α titanium alloy preparation method based on microstructure regulation to improve dynamic properties according to the present invention; Figure 2 for Figure 1 The curves showing the change of α phase content of various types in TA15 near-α titanium alloy billet with heat treatment temperature in the illustrated embodiment. Figure 3 for Figure 1 Microstructure photograph of the TA15 near-α type titanium alloy sheet with excellent dynamic properties prepared in the example shown. Detailed Implementation

[0023] To further understand the invention, the following detailed description of the invention will be provided in conjunction with specific embodiments.

[0024] Example 1: According to a preferred embodiment of the method for preparing near-α type titanium alloys based on microstructure regulation to improve dynamic properties, taking the rolling process and heat treatment regime of TA15 near-α type titanium alloy as an example, the preparation method includes the following steps in sequence: Step 1: Prepare near-α type titanium alloy billets, which must simultaneously meet the following three requirements: (1) The near-α type titanium alloy billet has a dual-state structure; (2) The last forging of the near-α type titanium alloy billet is a two-phase region forging, and its forging deformation is not less than 40%; (3) The microstructure of the near-α type titanium alloy billet includes an equiaxed α phase and a β transformation phase matrix structure, wherein the volume fraction of the equiaxed α phase is 5-50%.

[0025] In this embodiment, the near-α type titanium alloy billet is a square billet with a length, width and height of 600mm, 500mm and 100mm respectively; the forging deformation in the last forging is 40%; and the volume fraction of equiaxed α phase is about 35%.

[0026] Step 2: Determine the critical temperature range for near-α type titanium alloy billets. The determination method includes the following steps: S1. Several small-sized test blocks were cut from the near-α type titanium alloy billet. The test blocks were heat-treated in a temperature range of 800-1050℃ with a temperature step of 10-20℃. The holding time was 1 hour. After the holding time, the test blocks were water-cooled to room temperature. S2. Microstructure tests were performed on each heat-treated test block to obtain the microstructure morphology of the test blocks at different heat treatment temperatures. S3. The isoaxial primary α phase content, the original coarse secondary α phase content, and the newly formed secondary α phase content of each test block after heat treatment were quantitatively evaluated. Curves of the content of each type of α phase as a function of heat treatment temperature were plotted. Among them, the temperature range in the high temperature range where only equiaxed primary α phase and newly formed secondary α phase exist was recorded as T1-T2, and the temperature range in the medium temperature range where only equiaxed primary α phase and original coarse secondary α phase exist was recorded as T3-T4.

[0027] In this embodiment, the length, width and height of the test block are all 12mm; the test block is heat-treated in 10℃ temperature steps within the temperature range of 800-1050℃. After microstructure testing and quantitative evaluation, T1=950℃, T2=1020℃, T3=800℃ and T4=850℃ are finally determined.

[0028] Step 3: Based on the determined temperature range T1-T2, the near-α type titanium alloy billet is subjected to the first gradient heating treatment in a heat treatment furnace. Then, the near-α type titanium alloy billet is transferred to a rolling mill for 3-5 passes of high-temperature hot rolling, with a cumulative deformation of 30-60%. The rolling direction is RD. After the high-temperature hot rolling is completed, the billet is air-cooled to room temperature.

[0029] The process of the first gradient heating treatment is as follows: First, the heat treatment furnace is heated to T1; then, the near-α type titanium alloy billet is placed into the heat treatment furnace and held for (K1×H0+10) min; finally, the temperature is increased to T at a heating rate of 40-60℃ / h. h Insulation time (K2×H0+30) min.

[0030] Where: H0 is the minimum dimension of the near-α type titanium alloy billet in the length, width, and height directions, in mm; K1 is the temperature coefficient, with a set value of 0.4-0.6 mm. -1 K2 is the temperature coefficient, with a set value of 0.6-0.8 mm. -1 (T1+T2) / 2≤T h <T2.

[0031] In this embodiment, T1 = 950℃, T2 = 1020℃, H0 = 100mm, and K1 = 0.5mm. -1 K2=0.7mm -1 T h =985℃. The process of the first gradient heat treatment is as follows: first, the heat treatment furnace is heated to 950℃; then, the near-α type titanium alloy billet is placed in the heat treatment furnace and held for 60 minutes; finally, the temperature is increased to 985℃ at a heating rate of 50℃ / h and held for 100 minutes. After 5 passes of high-temperature hot rolling, the cumulative deformation is 50%, and a near-α type titanium alloy slab with a thickness of 50mm is obtained.

[0032] Step 4: Use a heat treatment furnace to perform stress-relieving annealing on the near-α type titanium alloy slab after high-temperature hot rolling, and air cool to room temperature after annealing.

[0033] The process of stress-relief annealing during rolling is as follows: annealing temperature 200-400℃, annealing time (K3×H1+60) min; where: H1 is the thickness of the near-α type titanium alloy slab after high-temperature hot rolling, mm; K3 is the temperature coefficient, and its set value is the average value of K1 and K2.

[0034] In this embodiment, H1 = 50 mm, K3 = 0.6 mm -1 The process parameters for stress-relief annealing during rolling are as follows: annealing temperature 300℃, annealing time 90min.

[0035] Step 5: Based on the determined temperature range T3-T4, the near-α type titanium alloy slab after stress-relief annealing in the rolling mill is subjected to a second gradient heating treatment in a heat treatment furnace. Then, the near-α type titanium alloy slab is transferred to the rolling mill for 3-5 passes of medium-temperature hot rolling, with a cumulative deformation of 25-50%. The rolling direction is RD rotating 90° along the normal direction of the rolling surface. After the medium-temperature hot rolling is completed, the slab is air-cooled to room temperature.

[0036] The process of the second gradient heating treatment is as follows: First, the heat treatment furnace is heated to T3; then, the near-α type titanium alloy slab after inter-roll stress-relief annealing is placed in the heat treatment furnace and held for (K1×H2+10) min; finally, the temperature is increased to T at a heating rate of 40-60℃ / h. m Insulation time: (K2×H2+30) min.

[0037] Where: H2 is the thickness of the near-α type titanium alloy slab after stress-relief annealing during rolling, in mm; K1 is the temperature coefficient, with a set value of 0.4-0.6 mm. -1 K2 is the temperature coefficient, with a set value of 0.6-0.8 mm. -1 (T3+T4) / 2≤T m <T4.

[0038] In this embodiment, T3 = 800℃, T4 = 850℃, H2 ≈ H1 = 50mm, K1 = 0.5mm -1 K2=0.7mm -1 T m =835℃. The process of the second gradient heat treatment is as follows: first, the heat treatment furnace is heated to 800℃; then, the near-α type titanium alloy slab after inter-roll stress-relief annealing is placed in the heat treatment furnace and held for 35 minutes; finally, the temperature is raised to 835℃ at a heating rate of 50℃ / h and held for 65 minutes. After four passes of medium-temperature hot rolling, the cumulative deformation is 40%, and a near-α type titanium alloy slab with a thickness of approximately 30 mm is obtained.

[0039] Step 6: The near-α type titanium alloy slab after medium-temperature hot rolling is subjected to step annealing in a heat treatment furnace. After annealing, it is air-cooled to room temperature to obtain near-α type titanium alloy sheet with excellent dynamic properties.

[0040] The post-rolling stepped annealing includes four annealing stages; the first step annealing temperature is 200℃, the second step annealing temperature is 300℃, and the third step annealing temperature is 400℃. The holding time for the first three steps of annealing is (K3×H3) min; where: H3 is the thickness of the near-α type titanium alloy slab after medium-temperature hot rolling, mm; K3 is the temperature coefficient, and its set value is the average value of K1 and K2.

[0041] The fourth-step annealing temperature and holding time of TA15 near-α titanium alloy shall not exceed its conventional annealing temperature and conventional holding time. More preferably, the fourth-step annealing temperature of TA15 is 0.6-0.8 times its conventional annealing temperature, and the holding time is 0.8-0.9 times its conventional holding time.

[0042] In this embodiment, H3 = 30 mm, K3 = 0.6 mm -1 The holding time for the first three annealing steps is 18 minutes. For TA15 near-alpha titanium alloy, the fourth annealing temperature is 0.7 times its conventional annealing temperature, and the holding time is 0.8 times its conventional holding time. The conventional annealing temperature for TA15 near-alpha titanium alloy is approximately 700-850℃, and the conventional holding time is approximately 1-4 hours.

[0043] Compared with the prior art, the embodiments of the present invention have the following beneficial effects: (1) By accurately identifying the key temperature range, the microstructure content of equiaxed α phase, original coarse secondary α phase and newly formed secondary α phase changes with the heat treatment temperature, and a gradient heating treatment system and (high temperature, medium temperature) hot rolling process are designed accordingly. (2) A complete process chain for dynamic mechanical properties is established: "microstructure identification → key temperature range determination → gradient heating treatment design → multi-directional rolling". Through the synergistic effect of dual rolling deformation strengthening and alloy texture directionality strengthening in the key temperature range, the synergistic improvement of the microstructure morphology and dynamic mechanical properties of near-α type titanium alloy is achieved. (3) The microstructure evolution law and hot forming law of near-α type titanium alloy are fully utilized. All process steps can be completed using only conventional heat treatment furnace and conventional rolling equipment. There is no need to add special equipment or complex control system. The process window is wide and the operability is strong.

[0044] Example 2: According to another preferred embodiment of the method for preparing near-α type titanium alloys based on microstructure regulation to improve dynamic properties of the present invention, its process flow, technical principle, and beneficial effects are basically the same as those of Embodiment 1, except that: In step one, the near-α type titanium alloy billet is a square billet with a length, width and height of 400mm, 300mm and 120mm respectively; the forging deformation in the last forging is 50%; and the volume fraction of equiaxed α phase is about 40%.

[0045] In step two, the length, width and height of the test block are all 20mm; the test block is heat-treated in 15℃ temperature steps within the temperature range of 800-1050℃. After microstructure testing and quantitative evaluation, T1=965℃, T2=1040℃, T3=800℃ and T4=860℃ are finally determined.

[0046] In step three, T1 = 965℃, T2 = 1040℃, H0 = 120mm, and K1 = 0.6mm. -1 K2=0.8mm -1 T h =1020℃. The process of the first gradient heat treatment is as follows: first, the heat treatment furnace is heated to 965℃; then, the near-α type titanium alloy billet is placed in the heat treatment furnace and held for 82 minutes; finally, the temperature is increased to 1020℃ at a heating rate of 40℃ / h and held for 126 minutes. After 5 passes of high-temperature hot rolling, the cumulative deformation is 40%, and a near-α type titanium alloy slab with a thickness of approximately 72mm is obtained.

[0047] In step four, H1 = 72mm, K3 = 0.7mm -1 The process parameters for stress-relief annealing during rolling are as follows: annealing temperature 200℃, annealing time 110.4min.

[0048] In step five, T3 = 800℃, T4 = 860℃, H2 ≈ H1 = 72mm, K1 = 0.6mm -1 K2=0.8mm -1 T m =845℃. The process of the second gradient heat treatment is as follows: first, the heat treatment furnace is heated to 800℃; then, the near-α type titanium alloy slab after inter-roll stress-relief annealing is placed in the heat treatment furnace and held for 53.2 min; finally, the temperature is raised to 845℃ at a heating rate of 40℃ / h and held for 87.6 min. After 3-5 medium-temperature hot rolling formings, the cumulative deformation is 35%, and a near-α type titanium alloy slab with a thickness of 46.8 mm is obtained.

[0049] Step six involves post-rolling stepped annealing, comprising four annealing stages. The first stepped annealing temperature is 200℃, the second is 300℃, and the third is 400℃; H3 = 46.8mm, K3 = 0.7mm. -1The holding time for the first three steps of annealing was 32.8 min. For TA15 near-α type titanium alloy, the fourth step of annealing temperature was 0.8 times its conventional annealing temperature, and the holding time was 0.8 times its conventional holding time.

[0050] Example 3: According to another preferred embodiment of the method for preparing near-α type titanium alloys based on microstructure regulation to improve dynamic properties of the present invention, its process flow, technical principle, and beneficial effects are basically the same as those of Embodiment 1, except that: In step one, the near-α type titanium alloy billet is a square billet with a length, width and height of 800mm, 600mm and 150mm respectively; the forging deformation in the last forging is 45%; and the volume fraction of equiaxed α phase is about 50%.

[0051] In step two, the length, width and height of the test block are all 10mm; the test block is heat-treated in 20℃ temperature steps within the temperature range of 800-1050℃. After microstructure testing and quantitative evaluation, T1=960℃, T2=1040℃, T3=800℃ and T4=840℃ are finally determined.

[0052] In step three, T1 = 960℃, T2 = 1040℃, H0 = 150mm, and K1 = 0.4mm. -1 K2=0.6mm -1 T h =1020℃. The process of the first gradient heat treatment is as follows: first, the heat treatment furnace is heated to 960℃; then, the near-α type titanium alloy billet is placed in the heat treatment furnace and held for 70 minutes; finally, the temperature is increased to 1020℃ at a heating rate of 60℃ / h and held for 120 minutes. After four passes of high-temperature hot rolling, the cumulative deformation is 50%, resulting in a near-α type titanium alloy slab with a thickness of 75mm.

[0053] In step four, H1 = 75mm, K3 = 0.5mm -1 The process parameters for stress-relief annealing during rolling are as follows: annealing temperature 400℃, annealing time 97.5min.

[0054] In step five, T3 = 800℃, T4 = 840℃, H2 ≈ H1 = 75mm, K1 = 0.4mm -1 K2=0.6mm -1 T m=830℃. The process of the second gradient heat treatment is as follows: first, the heat treatment furnace is heated to 800℃; then, the near-α type titanium alloy slab after inter-roll stress-relief annealing is placed in the heat treatment furnace and held for 40 minutes; finally, the temperature is raised to 830℃ at a heating rate of 60℃ / h and held for 75 minutes. After four passes of medium-temperature hot rolling, the cumulative deformation is 40%, and a near-α type titanium alloy slab with a thickness of 45mm is obtained.

[0055] Step six involves post-rolling stepped annealing, comprising four annealing stages. The first stepped annealing temperature is 200℃, the second stepped annealing temperature is 300℃, and the third stepped annealing temperature is 400℃; H3 = 45mm, K3 = 0.5mm. -1 The holding time for the first three steps of annealing was 22.5 min. For TA15 near-α type titanium alloy, the fourth step annealing temperature was 0.6 times its conventional annealing temperature, and the holding time was 0.9 times its conventional holding time.

[0056] The TA15 near-α type titanium alloy plates prepared in the above three embodiments were subjected to comprehensive mechanical property tests. The test methods, test environment and test equipment were the same. The test results are shown in Table 1.

[0057]

[0058] The test results in Table 1 show that the three embodiments improved the comprehensive mechanical properties of near-α type titanium alloys, especially the dynamic mechanical properties, through the synergistic effect of dual rolling deformation strengthening and alloy texture directionality strengthening in the key temperature range.

[0059] Special Note: The technical solution of this invention involves numerous parameters, and the synergistic effects between these parameters must be comprehensively considered to achieve the beneficial effects and significant progress of this invention. Furthermore, the value ranges of each parameter in the technical solution were obtained through extensive experimentation. For each parameter and the combinations thereof, the inventors have recorded a large amount of experimental data; however, due to space limitations, the specific experimental data is not disclosed here.

[0060] It will be readily understood by those skilled in the art that this invention includes any combination of the inventive description and specific embodiments outlined in the foregoing specification, as well as the various parts shown in the accompanying drawings. Due to space limitations and for the sake of brevity, not all of these combinations have been described in detail. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for preparing near-α type titanium alloys based on microstructure regulation to improve dynamic properties, characterized in that, The preparation method includes the following steps in sequence: Step 1: Prepare near-α type titanium alloy billets, which must simultaneously meet the following three requirements: (1) The near-α type titanium alloy billet has a biphase structure; (2) The last heat treatment of the near-α type titanium alloy billet is a two-phase region forging, and its forging deformation is not less than 40%; (3) The microstructure of the near-α type titanium alloy billet includes an equiaxed α phase and a β-transformed phase matrix structure, wherein the volume fraction of the equiaxed α phase is 5-50%; Step 2: Determine the critical temperature range for near-α type titanium alloy billets. The determination method includes the following steps: S1. Several small-sized test blocks were cut from the near-α type titanium alloy billet. The test blocks were heat-treated in a temperature range of 800-1050℃ with a temperature step of 10-20℃. The holding time was 1 hour. After the holding time, the test blocks were water-cooled to room temperature. S2. The microstructure of each test block after heat treatment was tested to obtain the microstructure morphology of the test blocks at different heat treatment temperatures. S3. The isoaxial primary α phase content, the original coarse secondary α phase content, and the newly formed secondary α phase content of each test block after heat treatment were quantitatively evaluated. The curves of the content of each type of α phase as a function of heat treatment temperature were plotted. Among them, the temperature range in the high temperature range where only the isoaxial primary α phase and the newly formed secondary α phase exist was recorded as T1-T2. The temperature range in the medium temperature range where only the isoaxial primary α phase and the original coarse secondary α phase exist was recorded as T3-T4. Step 3: Based on the determined temperature range T1-T2, the near-α type titanium alloy billet is subjected to the first gradient heating treatment in a heat treatment furnace. Then, the near-α type titanium alloy billet is transferred to a rolling mill for 3-5 passes of high-temperature hot rolling, with a cumulative deformation of 30-60%. The rolling direction is RD. After the high-temperature hot rolling is completed, the billet is air-cooled to room temperature. Step 4: Use a heat treatment furnace to perform stress-relieving annealing on the near-α type titanium alloy slab after high-temperature hot rolling, and air cool to room temperature after annealing. Step 5: Based on the determined temperature range T3-T4, the near-α type titanium alloy slab after stress-relief annealing in the rolling mill is subjected to a second gradient heating treatment in a heat treatment furnace. Then, the near-α type titanium alloy slab is transferred to the rolling mill for 3-5 passes of medium-temperature hot rolling, with a cumulative deformation of 25-50%. The rolling direction is RD rotating 90° along the normal direction of the rolling surface. After the medium-temperature hot rolling is completed, the slab is air-cooled to room temperature. Step 6: The near-α type titanium alloy slab after medium-temperature hot rolling is subjected to step annealing in a heat treatment furnace. After annealing, it is air-cooled to room temperature to obtain near-α type titanium alloy sheet with excellent dynamic properties.

2. The method for preparing near-α type titanium alloys based on microstructure regulation to improve dynamic properties according to claim 1, characterized in that, In step one, the near-α type titanium alloy billet is a square billet with a length, width and height of not less than 100 mm.

3. The method for preparing near-α type titanium alloys based on microstructure regulation to improve dynamic properties according to claim 2, characterized in that, In step two, the length, width, and height of the test block are all 10-20 mm; the temperature range T1-T2 is the temperature range where only equiaxed primary α phase and newly formed secondary α phase exist, T1 is the lower boundary temperature of this temperature range, and T2 is the upper boundary temperature of this temperature range; the temperature range T3-T4 is the temperature range where only equiaxed primary α phase and primitive coarse secondary α phase exist, T3 is the lower boundary temperature of this temperature range, and T4 is the upper boundary temperature of this temperature range.

4. The method for preparing near-α type titanium alloys based on microstructure regulation to improve dynamic properties according to claim 3, characterized in that, In step three, the process of the first gradient heating treatment is as follows: First, the heat treatment furnace is heated to T1; then, the near-α type titanium alloy billet is placed into the heat treatment furnace and held for (K1×H0+10) min; finally, the temperature is increased to T at a heating rate of 40-60℃ / h. h Insulation time (K2×H0+30) min; Where: H0 is the minimum dimension of the near-α type titanium alloy billet in the length, width, and height directions, in mm; K1 is the temperature coefficient, with a set value of 0.4-0.6 mm. -1 K2 is the temperature coefficient, with a set value of 0.6-0.8 mm. -1 (T1+T2) / 2≤T h <T2.

5. The method for preparing near-α type titanium alloys based on microstructure regulation to improve dynamic properties according to claim 4, characterized in that, In step four, the process of stress-relief annealing during rolling is as follows: annealing temperature 200-400℃, annealing time (K3×H1+60) min; where: H1 is the thickness of the near-α type titanium alloy slab after high-temperature hot rolling, mm; K3 is the temperature coefficient, and its set value is the average value of K1 and K2.

6. The method for preparing near-α type titanium alloys based on microstructure regulation to improve dynamic properties according to claim 5, characterized in that, In step five, the process of the second gradient heating treatment is as follows: First, the heat treatment furnace is heated to T3; then, the near-α type titanium alloy slab after inter-roll stress-relief annealing is placed into the heat treatment furnace and held for (K1×H2+10) min; finally, the temperature is increased to T at a heating rate of 40-60℃ / h. m Insulation time (K2×H2+30) min; Where: H2 is the thickness of the near-α type titanium alloy slab after stress-relief annealing during rolling, in mm; K1 is the temperature coefficient, with a set value of 0.4-0.6 mm. -1 K2 is the temperature coefficient, with a set value of 0.6-0.8 mm. -1 (T3+T4) / 2≤T m <T4.

7. The method for preparing near-α type titanium alloys based on microstructure regulation to improve dynamic properties according to claim 6, characterized in that, In step six, the post-rolling stepped annealing includes four annealing stages; the first stepped annealing temperature is 200℃, the second stepped annealing temperature is 300℃, and the third stepped annealing temperature is 400℃. The holding time for the first three stepped annealing stages is (K3×H3) min; where: H3 is the thickness of the near-α type titanium alloy slab after medium-temperature hot rolling, in mm; K3 is the temperature coefficient, and its set value is the average value of K1 and K2.

8. The method for preparing near-α type titanium alloys based on microstructure regulation to improve dynamic properties according to claim 7, characterized in that, In step six, the fourth-step annealing temperature and holding time for different grades of near-α type titanium alloys shall not exceed the conventional annealing temperature and conventional holding time for the corresponding grades.

9. The method for preparing near-α type titanium alloys based on microstructure regulation to improve dynamic properties according to claim 8, characterized in that, In step six, the fourth-step annealing temperature of different grades of near-α type titanium alloys is 0.6-0.8 times the conventional annealing temperature of the corresponding grades, and the holding time is 0.8-0.9 times the conventional holding time of the corresponding grades.

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