Method for controlling microstructure and homogenization of ta18 titanium alloy ingot

Abstract

The application discloses a TA18 titanium alloy ingot organization control and homogenization control method, and the TA18 titanium alloy ingot production process is improved, a composite melting process of one-time melting by adopting an electron beam cold bed furnace and two-time melting by adopting a vacuum consumable arc furnace is adopted, the large melting pool and long residence time of the electron beam cold bed furnace are utilized to solve the problem of insufficient impurity removal capacity of the vacuum consumable arc furnace melting, and the fine regulation and control and electromagnetic stirring of the vacuum consumable arc furnace are utilized to make up for the shortcoming of the relatively coarse ingot organization of the electron beam cold bed furnace melting; the problems of Al and V element segregation and Fe element micro segregation of the TA18 titanium alloy ingot can be effectively solved, the Al and V element longitudinal range of the TA18 titanium alloy ingot prepared by the application is less than or equal to 0.08wt%, the grain size is less than or equal to 8.5mm, the tensile strength fluctuation between batches of the rod prepared after subsequent processing is less than or equal to 20MPa, and the requirements of aerospace hydraulic pipes on the high uniformity and stability of the TA18 titanium alloy ingot can be met.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal material processing technology, and in particular to a method for controlling the microstructure and homogenization of TA18 titanium alloy ingots. Background Technology

[0002] TA18 titanium alloy, also known as Ti-3Al-2.5V, is a low-alloy near-alpha titanium alloy. Due to its excellent mechanical properties, corrosion resistance, and plasticity in both hot and cold working processes, it has become the preferred material for aerospace piping systems. With the development of the aerospace industry, the performance requirements for TA18 titanium alloy tubing are constantly increasing, demanding not only a high strength level of ≥862MPa tensile strength but also higher requirements for material uniformity and stability.

[0003] The uniformity of chemical composition and microstructure of TA18 titanium alloy ingots directly determines the performance stability of the final product. Although TA18 titanium alloy has a low content of alloying elements, its smelting process still faces the following technical challenges: First, the macroscopic segregation of Al and V elements; Al has a melting point of 660℃ and a density of 2.7 g / cm³. 3 V has a melting point of 1910℃ and a density of 6.1 g / cm³. 3 The two elements have vastly different melting points and densities. During vacuum arc remelting, the lower-density Al tends to float, while the higher-density V tends to sink, resulting in significant compositional deviations at the beginning and end of the ingot. Current technology uses three-stage vacuum arc remelting to control the Al and V elemental deviations to around 0.1 wt%, but this still requires further improvement to meet the requirement of ≤20 MPa tensile strength fluctuations for aerospace hydraulic pipes.

[0004] Secondly, there is the issue of microscopic segregation of Fe. In TA18 alloys, Fe, as an impurity element, requires strict control, with a Fe content ≤0.20%. During solidification, it easily accumulates between dendrites, forming microscopic segregation. This microscopic segregation is difficult to completely eliminate during subsequent hot working, leading to localized structural abnormalities and performance fluctuations.

[0005] Third, the problem of coarse as-cast microstructure; the β grain size of ingots obtained by conventional VAR melting is usually 15-30mm or even larger. The coarse as-cast microstructure is hereditary and difficult to completely eliminate even after multiple forgings, affecting the microstructure uniformity and performance stability of the final product. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for controlling the microstructure and homogenization of TA18 titanium alloy ingots, which can effectively improve the homogenization degree of the microstructure and composition of TA18 titanium alloy ingots.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by this invention is: a method for controlling the microstructure and homogenization of TA18 titanium alloy ingots, comprising the following steps: S1. Using sponge titanium, Al-V master alloy, and aluminum briquettes as raw materials, the chemical composition of the raw materials is tested and the raw materials are batched according to the test results, so that the composition of the finished TA18 titanium alloy ingot meets the requirements of Al content of 2.8-3.2% and V content of 2.3-2.7%. S2. Mix the raw materials after batching evenly, and after multiple mixing, press the material into electrode blocks on a press in one go, and weld multiple electrode blocks into consumable electrodes. S3. The consumable electrode is loaded into an electron beam cold hearth furnace for the first melting to obtain a first ingot; S4. The primary ingot is used as a consumable electrode and placed into a vacuum consumable arc furnace for a second melting process to obtain a secondary ingot. S5. Determine the β phase transformation point of TA18 titanium alloy. The secondary ingot is subjected to homogenization heat treatment at a temperature of 80-150°C above the β phase transformation point. After heat treatment, it is slowly cooled to below 600°C and then air-cooled to room temperature. S6. Inspect and peel the surface of the ingot after homogenization heat treatment to obtain the finished TA18 titanium alloy ingot.

[0008] As an improvement to the above scheme: in step S1, the sponge titanium is grade 0A, grade 0 or grade 1 sponge titanium, and the Brinell hardness fluctuation of the sponge titanium is ≤5; the V content of the Al-V master alloy is 55-58%, the particle size of the Al-V master alloy is 5-25mm; and the purity of the aluminum granules is ≥99.7%.

[0009] As an improvement to the above scheme: in step S2, the raw materials are mixed 3 to 5 times, and the mixing time for each mixing is 90 to 150 seconds.

[0010] As an improvement to the above scheme: in step S2, the pressing pressure of the press is 75-100 MPa, the holding time is 10-30 s, and the density of the pressed electrode block is ≥3.5 g / cm³. 3 .

[0011] As an improvement to the above scheme: In step S2, multiple electrode blocks are welded into consumable electrodes by plasma arc welding under vacuum or argon protection, with a welding current of 200-400A and an argon flow rate of 10-20L / min.

[0012] As an improvement to the above scheme: In step S3, the consumable electrode is dried before the first melting, and the drying temperature is 120-150℃, and the drying time is 4-6h.

[0013] As an improvement to the above scheme: In step S3, the vacuum degree of the furnace chamber during the first melting is ≤0.65Pa; the electron beam power is controlled in stages during melting, with the power of 500-800kW during the start-up stage, 1000-1400kW during the bottom-forming stage, and 1600-1900kW during the normal melting stage; the melting speed is 800-1200kg / h, the depth of the molten pool in the cooling bed is 50-100mm, and the residence time of the melt in the cooling bed is ≥3min.

[0014] As an improvement to the above scheme: In step S4, the second melting adopts a variable current melting process, and the melting vacuum degree is ≤0.1Pa; the current in the arc initiation stage is 8-10kA and the voltage is 25-30V; the current in the normal melting stage is 10-14kA and the voltage is 30-40V, and the melting rate is 4-7kg / min; the current in the feeding stage is 6-8kA and the voltage is 25-30V; electromagnetic stirring is used to assist in the melting process, the stirring current is 1-10A, and continuous stirring or intermittent stirring is adopted, with the ratio of stirring time to interval time in intermittent stirring being 1:2-1:5.

[0015] As an improvement to the above scheme: in step S5, the homogenization heat treatment is carried out in a vacuum furnace or an argon-protected furnace, with a furnace temperature uniformity of ≤±10℃; the ingot is slowly cooled at a rate of ≤50℃ / h.

[0016] As an improvement to the above scheme: In step S6, the inspection of the ingot includes chemical composition analysis, low-magnification microstructure inspection, and ultrasonic testing; when performing chemical composition analysis, samples are taken from the head, middle, and bottom of the ingot to analyze the content of main elements Al and V and the content of impurity elements such as Fe, O, C, N, and H; when performing low-magnification microstructure inspection, the macroscopic grain size and segregation of the ingot are examined; when performing ultrasonic testing, a flat-bottomed hole with a diameter of 1.2 mm is used for testing to check for internal defects; when performing surface peeling treatment, the oxide layer and defect layer on the surface of the ingot are peeled off, and the peeling amount is 3-8 mm.

[0017] The beneficial effects of this invention are as follows: This invention improves the production process of TA18 titanium alloy ingots by adopting a composite melting process that combines primary melting in an electron beam cold hearth furnace with secondary melting in a vacuum consumable arc furnace. The large molten pool and long residence time of the electron beam cold hearth furnace solve the problem of insufficient impurity removal capacity in vacuum consumable arc furnace melting. Simultaneously, the precise control and electromagnetic stirring of the vacuum consumable arc furnace compensate for the coarser ingot structure inherent in electron beam cold hearth furnace melting. Furthermore, this invention effectively solves the problem of Al and V element segregation and Fe element micro-agglomeration in TA18 titanium alloy ingots by dynamically controlling melting parameters and synergistically controlling electromagnetic stirring and homogenization heat treatment. The TA18 titanium alloy ingots prepared by this invention have a longitudinal range of Al and V elements ≤0.08wt%, a grain size ≤8.5mm, and the tensile strength fluctuation between batches of bars prepared after subsequent processing ≤20MPa, meeting the requirements of high uniformity and high stability for TA18 titanium alloy ingots in aerospace hydraulic pipes. Detailed Implementation

[0018] To facilitate understanding of the present invention, the present invention will be further described below with reference to embodiments.

[0019] The method for controlling the microstructure and homogenization of TA18 titanium alloy ingots disclosed in this invention is carried out according to the following steps: S1. Using sponge titanium, Al-V master alloy, and aluminum briquettes as raw materials, the chemical composition of the raw materials is analyzed, and the batching is carried out according to the test results. This ensures that the composition of the finished TA18 titanium alloy ingot meets the following requirements: Al content 2.8–3.2%, V content 2.3–2.7%; the sponge titanium uses grade 0A, grade 0, or grade 1 sponge titanium, with a Brinell hardness fluctuation ≤5; the Al-V master alloy has a V content of 55–58% and a particle size of 5–25 mm; the purity of the aluminum briquettes is ≥99.7%. In this step, the batch fluctuations of raw materials such as sponge titanium and Al-V master alloy are strictly controlled to minimize the impact of raw material fluctuations on the uniformity of the ingot, thereby providing a foundation for the homogenization of the ingot by improving the stability of the raw materials.

[0020] S2. Mix the prepared raw materials evenly, repeating the mixing process 3-5 times, with each mixing session lasting 90-150 seconds. Then, press the mixture into electrode blocks using a press with a pressing pressure of 75-100 MPa and a holding time of 10-30 seconds. The density of the resulting electrode blocks should be ≥3.5 g / cm³. 3 Multiple electrode blocks are welded into consumable electrodes using plasma arc welding under vacuum or argon protection. The welding current is 200-400A and the argon flow rate is 10-20L / min. Welding ensures that the weld is strong and free of oxidation.

[0021] S3. Dry the consumable electrode at a temperature of 120–150℃ for 4–6 hours to remove adsorbed moisture. After drying, place the consumable electrode in an electron beam cold hearth furnace for the first melting. The vacuum degree of the furnace chamber during the first melting is ≤0.65Pa. During melting, the electron beam power is controlled in stages: 500–800kW during the start-up stage, 1000–1400kW during the bottom-forming stage, and 1600–1900kW during the normal melting stage. The melting speed is 800–1200 kg / h, the depth of the molten pool in the cold hearth is 50–100 mm, and the residence time of the melt in the cold hearth is ≥3 min. In addition, during the first melting process in the electron beam cold hearth furnace, a laser liquid level monitoring system is used to monitor the liquid level fluctuation of the molten pool in real time. The flow of the molten pool is optimized and controlled by the electron beam scanning trajectory to ensure that the residence time of the melt in the cold hearth is ≥3 min. After the first melting, a first ingot is obtained. In this step, the first melting process, including deep purification and pre-alloying, is achieved through an electron beam cold hearth furnace. The electron beam cold hearth furnace utilizes a high-energy electron beam as a heat source, enabling melting of raw materials under vacuum conditions. The cold hearth design allows the melt sufficient residence time before entering the crystallizer, allowing high-density impurities such as high-melting-point unmelted particles to settle to the bottom of the cold hearth and be captured, while low-density impurities such as titanium nitride and oxides can float to the surface of the melt and be removed. Simultaneously, the large molten pool depth of the electron beam cold hearth furnace, reaching 50–100 mm, facilitates the full diffusion and homogenization of alloying elements, providing a pre-homogenized primary ingot for subsequent melting in a vacuum consumable arc furnace.

[0022] S4. The primary ingot is used as a consumable electrode and placed in a vacuum consumable arc furnace for a second melting process. The second melting process adopts a variable current melting process with a melting vacuum degree ≤0.1Pa. The current during the arc initiation stage is 8-10kA and the voltage is 25-30V. The current during the normal melting stage is 10-14kA and the voltage is 30-40V, with a melting rate of 4-7kg / min. The current during the feeding stage is 6-8kA and the voltage is 25-30V. Electromagnetic stirring is used to assist the melting process, with a stirring current of 1-10A. Continuous stirring or intermittent stirring is used, and the ratio of stirring time to interval time for intermittent stirring is 1:2 to 1:5. A secondary ingot is obtained after the second melting process. In this step, a "low-high-low" variable current melting process is adopted. During the arc initiation stage, a low current is used to prevent electrode breakage. During the normal melting stage, a high current is used to ensure stable melting rate. During the feeding stage, a low current is used to reduce shrinkage cavities. Combined with electromagnetic stirring assistance, an alternating magnetic field is used to drive the flow of the molten pool, which can break the dendrite growth front, refine the solidification structure, and further homogenize the composition of the ingot.

[0023] S5. Determine the β-phase transformation point of TA18 titanium alloy. The secondary ingot is then subjected to homogenization heat treatment at a temperature 80–150°C above the β-phase transformation point. This homogenization heat treatment is carried out in a vacuum furnace or argon-protected furnace, with a furnace temperature uniformity of ≤±10°C to prevent high-temperature oxidation of the ingot. After heat treatment, the ingot is slowly cooled to below 600°C at a rate ≤50°C / h, and then air-cooled to room temperature. In this step, by holding the secondary ingot at a high temperature above the β-phase transformation point for a long time, atomic high-temperature diffusion is used to eliminate microscopic segregation, especially the interdendritic segregation of Fe elements, further homogenizing the distribution of alloying elements. The slow cooling process also reduces thermal stress and prevents ingot cracking.

[0024] S6. After homogenization heat treatment, the ingot is inspected and its surface is peeled off. The inspection of the ingot includes chemical composition analysis, low-magnification microstructure inspection, and ultrasonic testing. During chemical composition analysis, samples are taken from the head, middle, and bottom of the ingot to analyze the content of main elements Al and V and impurity elements such as Fe, O, C, N, and H. During low-magnification microstructure inspection, the macroscopic grain size and segregation of the ingot are examined. During ultrasonic testing, a 1.2mm diameter flat-bottom hole with equivalent sensitivity is used to detect internal defects. During surface peeling, the oxide layer and defect layer on the surface of the ingot are removed, with a peeling amount of 3-8mm. Finally, a TA18 titanium alloy ingot with uniform microstructure and homogeneous composition is obtained.

[0025] Furthermore, this invention can also employ finite element simulation methods such as ProCAST to simulate the molten pool flow and temperature field of electron beam cold hearth furnace melting, the solidification process and composition distribution of vacuum consumable arc furnace melting, and the diffusion dynamics of homogenization heat treatment, thereby achieving precise design and optimization of process parameters and reducing trial-and-error costs.

[0026] The chemical composition of the TA18 titanium alloy ingot prepared by the microstructure control and homogenization control method of the TA18 titanium alloy ingot described in this invention, by weight percentage, is as follows: Al 2.8-3.3%, V 2.3-2.7%, Fe≤0.20%, O≤0.12%, C≤0.05%, N≤0.03%, H≤0.012%; the longitudinal range of Al and V elements is ≤0.08wt%, which is significantly better than the 0.1wt% level of the prior art using the three-stage vacuum self-consuming electric arc furnace melting technology; the macroscopic grain size of the ingot is ≤8.5mm, which is more than 50% finer than the 3-5mm macroscopic grain size of conventional vacuum self-consuming electric arc furnace ingots; the microstructure is a uniform fine-grained Widmanstätten structure, without metallurgical defects such as segregation, cracks, pores, and inclusions that are visible to the naked eye.

[0027] The TA18 titanium alloy ingot prepared by this invention is hot-processed and forged at a temperature of 1050–1150°C with a forging ratio of ≥3 to fully break down the as-cast structure. After subsequent forging, rolling, and heat treatment, titanium alloy bars are obtained. The batch-to-batch tensile strength fluctuation of the titanium alloy bars is ≤20MPa, the yield strength fluctuation is ≤15MPa, and the elongation fluctuation is ≤2%, which meets the requirements of high uniformity and high stability of materials for aerospace hydraulic pipes.

[0028] Example 1 Prepare TA18 titanium alloy ingots according to the following steps: 1) Raw Material Selection and Pretreatment. Grade 0 sponge titanium with HBW fluctuation ≤4, Al-V master alloy with V content of 58% and particle size of 10-20mm, and aluminum briquettes with purity ≥99.8% were selected. Raw material testing results: the sponge titanium contained 0.03% Fe and 0.06% O; the Al-V master alloy contained 42.5% Al, 57.2% V, and 0.08% Fe. Based on the target composition of 3.0% Al and 2.5% V, the proportions of sponge titanium, Al-V master alloy, and aluminum briquettes were calculated to be 94.2%, 4.3%, and 1.5%, respectively.

[0029] 2) Electrode preparation. A total of 2000 kg of materials was prepared and mixed in five batches, each batch lasting 120 seconds. The electrode blocks were pressed under 80 MPa pressure for 20 seconds, resulting in an electrode block density of 3.3 g / cm³. 3 The electrode blocks are welded into consumable electrodes using plasma arc welding.

[0030] 3) Electron beam cold hearth furnace primary melting. Before melting, the material is dried at 130℃ for 5 hours. The melting parameters of the electron beam cold hearth furnace are controlled as follows: vacuum degree 0.5Pa, lance start-up power 600kW, bottom-forming power 1200kW, normal melting power 1800kW, melting speed 1000kg / h, cold hearth melt pool depth 70mm, and melt residence time 3.5min. A primary ingot with a diameter of 470mm is obtained through primary melting in the electron beam cold hearth furnace.

[0031] 4) Vacuum consumable arc furnace (VCA) secondary remelting. The primary ingot is used as the consumable electrode for VCA remelting. The melting parameters of the VCA furnace are controlled as follows: vacuum degree 0.09 Pa, arc ignition current 9 kA, voltage 28 V, normal melting current 13 kA, voltage 35 V, melting rate 7.5 kg / min, feeding current 7 kA, voltage 28 V; electromagnetic stirring current 6 A, alternating stirring for 20 s. A secondary ingot with a diameter of 560 mm is obtained after secondary remelting in the VCA furnace.

[0032] 5) Homogenization heat treatment. The β phase transformation point was determined to be 925℃ using metallographic methods. The ingot was heated in a vacuum furnace to 1050℃, which is 105℃ above the β phase transformation point, and held at that temperature for 20 hours. Then it was slowly cooled to 500℃ at a rate of 30℃ / h, and finally air-cooled to room temperature.

[0033] 6) Inspection and Processing. Samples were taken from the head, middle, and bottom of the ingot for chemical composition analysis. The results were: Al 3.02%, V 2.49%, Fe 0.05%, O 0.08%, C 0.02%, N 0.01%, H 0.005%; the longitudinal range of Al was 0.06%, and the longitudinal range of V was 0.05%. Low-magnification microstructure inspection revealed a macroscopic grain size of 3.0–8.0 mm, with no visible segregation. The ultrasonic flaw detection pass rate was 99%. A 5 mm layer was removed from the surface to obtain a qualified ingot.

[0034] 7) Performance Verification. The ingots were forged, rolled into titanium alloy bars with a diameter of 30 mm, and then annealed. The room temperature mechanical properties of 10 batches of titanium alloy bars were tested. The test results were as follows: the average tensile strength was 805 MPa, with a fluctuation range of 800–820 MPa; the average yield strength was 750 MPa, with a fluctuation range of 740–760 MPa; the average elongation was 18.5%, with a fluctuation range of 17.5%–19.5%.

[0035] Example 2 The preparation steps of Example 2 are basically the same as those of Example 1. The difference is that in Example 2, intermittent electromagnetic stirring is used in the secondary remelting stage of the vacuum self-consuming electric arc furnace, and the ratio of stirring time to interval time is 1:3.

[0036] The ingot obtained in Example 2 was inspected. The inspection results showed that the longitudinal range of Al element was 0.07%, the longitudinal range of V element was 0.06%, and the macroscopic grain size was 2.0–7.0 mm. The performance fluctuation of the ingot obtained in Example 2 was slightly greater than that in Example 1, but it still met the requirements for aerospace grade.

[0037] Example 3 The preparation steps of Example 3 are basically the same as those of Example 1. The difference is that Example 3 uses ProCAST software to simulate the electron beam cold hearth furnace melting process of TA18 titanium alloy to study the effects of casting temperature, billet speed and heat transfer coefficient on the morphology of the molten pool and solidification structure.

[0038] The ingot obtained in Example 3 was inspected. The inspection results showed that the longitudinal range of Al element was 0.05%, the longitudinal range of V element was 0.05%, and the macroscopic grain size was 2.0–6.0 mm. The tensile strength fluctuation of the ingot obtained in Example 3 was ≤15 MPa, and the yield strength fluctuation was ≤12 MPa.

[0039] Comparative Example 1 TA18 titanium alloy ingots were prepared using a traditional three-stage vacuum arc remelting method. The resulting ingots were inspected, and the results showed that the longitudinal range of Al was 0.22%, the longitudinal range of V was 0.21%, and the macroscopic grain size was 3–15 mm. The ingots were then processed according to the subsequent processing steps of Example 1 to obtain titanium alloy bars. The tensile strength fluctuation of the bars was 35 MPa, and the yield strength fluctuation was 28 MPa. The performance stability of Comparative Example 1 was significantly worse than that of Examples 1 to 3.

[0040] The comparison between Examples 1 to 3 and Comparative Example 1 shows that the present invention successfully solves the problems of compositional segregation, coarse microstructure and performance fluctuation in TA18 titanium alloy ingots. The present invention can obtain TA18 titanium alloy ingot products with high uniformity and high stability.

Claims

1. A method for controlling the microstructure and homogenization of TA18 titanium alloy ingots, characterized in that: Includes the following steps: S1. Using sponge titanium, Al-V master alloy, and aluminum briquettes as raw materials, the chemical composition of the raw materials is tested and the raw materials are batched according to the test results, so that the composition of the finished TA18 titanium alloy ingot meets the requirements of Al content of 2.8-3.2% and V content of 2.3-2.7%. S2. Mix the raw materials after batching evenly, and after multiple mixing, press the material into electrode blocks on a press in one go, and weld multiple electrode blocks into consumable electrodes. S3. The consumable electrode is loaded into an electron beam cold hearth furnace for the first melting to obtain a first ingot; S4. The primary ingot is used as a consumable electrode and placed into a vacuum consumable arc furnace for a second melting process to obtain a secondary ingot. S5. Determine the β phase transformation point of TA18 titanium alloy. The secondary ingot is subjected to homogenization heat treatment at a temperature of 80-150°C above the β phase transformation point. After heat treatment, it is slowly cooled to below 600°C and then air-cooled to room temperature. S6. Inspect and peel the surface of the ingot after homogenization heat treatment to obtain the finished TA18 titanium alloy ingot.

2. The method for controlling the microstructure and homogenization of TA18 titanium alloy ingots as described in claim 1, characterized in that: In step S1, the sponge titanium is grade 0A, grade 0 or grade 1 sponge titanium, and the Brinell hardness fluctuation of the sponge titanium is ≤5; the V content of the Al-V master alloy is 55-58%, the particle size of the Al-V master alloy is 5-25mm; and the purity of the aluminum granules is ≥99.7%.

3. The method for controlling the microstructure and homogenization of TA18 titanium alloy ingots as described in claim 1, characterized in that: In step S2, the raw materials are mixed 3 to 5 times, and each mixing time is 90 to 150 seconds.

4. The method for controlling the microstructure and homogenization of TA18 titanium alloy ingots as described in claim 1, characterized in that: In step S2, the pressing pressure of the press is 75–100 MPa, the holding time is 10–30 s, and the density of the pressed electrode block is ≥3.5 g / cm³. 3 .

5. The method for controlling the microstructure and homogenization of TA18 titanium alloy ingots as described in claim 1, characterized in that: In step S2, multiple electrode blocks are welded into consumable electrodes by plasma arc welding under vacuum or argon protection. The welding current is 200-400A and the argon flow rate is 10-20L / min.

6. The method for controlling the microstructure and homogenization of TA18 titanium alloy ingots as described in claim 1, characterized in that: In step S3, the consumable electrode is dried before the first melting, with a drying temperature of 120-150°C and a drying time of 4-6 hours.

7. The method for controlling the microstructure and homogenization of TA18 titanium alloy ingots as described in claim 1, characterized in that: In step S3, the vacuum degree of the furnace chamber during the first melting is ≤0.65Pa; the electron beam power is controlled in stages during melting, with the power being 500-800kW during the start-up stage, 1000-1400kW during the bottom-forming stage, and 1600-1900kW during the normal melting stage; the melting speed is 800-1200kg / h, the depth of the molten pool in the cooling bed is 50-100mm, and the residence time of the melt in the cooling bed is ≥3min.

8. The method for controlling the microstructure and homogenization of TA18 titanium alloy ingots as described in claim 1, characterized in that: In step S4, the second melting adopts a variable current melting process with a melting vacuum degree ≤0.1Pa; the current during the arc initiation stage is 8-10kA and the voltage is 25-30V; the current during the normal melting stage is 10-14kA and the voltage is 30-40V, with a melting rate of 4-7kg / min; the current during the feeding stage is 6-8kA and the voltage is 25-30V; electromagnetic stirring is used to assist in the melting process, with a stirring current of 1-10A, and continuous stirring or intermittent stirring is adopted, with the ratio of stirring time to interval time in intermittent stirring being 1:2-1:

5.

9. The method for controlling the microstructure and homogenization of TA18 titanium alloy ingots as described in claim 1, characterized in that: In step S5, the homogenization heat treatment is carried out in a vacuum furnace or an argon-protected furnace, with a furnace temperature uniformity of ≤±10℃; the ingot is slowly cooled at a rate of ≤50℃ / h.

10. The method for controlling the microstructure and homogenization of TA18 titanium alloy ingots as described in claim 1, characterized in that: In step S6, the inspection of the ingot includes chemical composition analysis, low-magnification microstructure inspection, and ultrasonic testing. During chemical composition analysis, samples are taken from the head, middle, and bottom of the ingot to analyze the content of main elements Al and V, and impurity elements such as Fe, O, C, N, and H. During low-magnification microstructure inspection, the macroscopic grain size and segregation of the ingot are examined. During ultrasonic testing, a 1.2mm diameter flat-bottomed hole with equivalent sensitivity is used to detect internal defects. During surface peeling, the oxide layer and defect layer on the ingot surface are removed, with a peeling amount of 3–8mm.