Preparation method of high-performance super-large-specification TC4ELI titanium alloy ring forging

Abstract

The invention discloses a preparation method of a high-performance super-large-specification TC4ELI titanium alloy ring forging, and belongs to the technical field of high-quality titanium alloy materials. The method comprises the following steps: preparing a cast ingot; the prepared cast ingot is subjected to multi-heating-number forging; the prepared blank is subjected to ring rolling forging, and an annular blank is obtained; and the prepared annular blank is subjected to annealing treatment, and the titanium alloy ring forging is obtained. The ring forge piece is obtained by adopting a process route of smelting, pre-forming forging and ring rolling forging. A cast ingot with uniform components is prepared from high-purity raw materials, and a blank is fully deformed through multi-heating-number large-deformation forging and ring rolling forging, so that the structure uniformity is improved. A high-precision electric furnace is adopted for annealing, it is guaranteed that all positions of the material are fully heated, and therefore the TC4ELI titanium alloy ring forge piece which is uniform in overall structure and excellent in performance is obtained.

Description

Technical Field

[0001] This invention belongs to the field of high-quality titanium alloy materials technology, and relates to the manufacture of TC4ELI titanium alloy, specifically to a method for preparing high-performance, ultra-large TC4ELI titanium alloy ring forgings. Background Technology

[0002] With the upgrading of materials for deep-sea equipment, traditional pressure hulls made of steel are finding it difficult to adapt to the increasingly complex marine environment. TC4ELI titanium alloy has the characteristics of low density, high specific strength and high corrosion resistance, and is now being used in the field of deep-sea equipment. Its inherent properties enable it to maintain high service performance in the harsh environment of the deep sea.

[0003] The fabrication of large titanium alloy ring forgings is constrained by factors such as equipment capability and process route selection. High-performance ring forgings are often highly correlated with highly uniform microstructure; therefore, obtaining ring forgings with highly uniform microstructure within the limits of equipment capability is crucial. Currently, the fabrication of large titanium alloy ring forgings faces the following challenges: First, the microstructure of titanium alloys is extremely sensitive to temperature process parameters, making it prone to defects such as overheating and bright bands during forging. Second, parameters such as deformation rate and deformation amount during hot working greatly affect the internal microstructure of the material and may cause significant defects such as folding and cracking on the material surface. Third, due to the poor thermal conductivity of titanium alloys, during heat treatment, it is necessary to ensure that the core of the ring forging reaches the specified holding time while preventing excessive grain growth on the material surface due to prolonged heat treatment. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing high-performance, ultra-large TC4ELI titanium alloy ring forgings. This method solves the technical problem that the immature manufacturing process for large titanium alloy ring forgings in existing technologies leads to low microstructure uniformity and consequently poor mechanical properties. The present invention is implemented using the following technical solution: A method for preparing a high-performance, ultra-large TC4ELI titanium alloy ring forging, comprising the following steps: Step 1, Ingot Preparation: The TC4ELI titanium alloy raw material is pressed into several electrode blocks, which are then welded into complete electrodes using a plasma vacuum welding box. After three vacuum consumable arc melting processes, a large-size TC4ELI ingot is prepared.

[0005] Step two: The ingot obtained in step one is subjected to multiple forging processes to obtain a preliminary ring-shaped billet. Step 2.1, Ingot forging: First, heat to 700-800℃ and hold for 2-3 hours, then raise the temperature to 1100-1150℃ with a holding coefficient of 0.6-0.7 min / mm, rivet and upset forging and shaping into a square billet, then chamfer, grind, and air cool; then reheat to 700-800℃ and hold for 2-3 hours, then raise the temperature to 1100-1150℃ with a holding coefficient of 0.6-0.7 min / mm, after taking it out of the furnace, perform elongation and upset forging, then chamfer, grind, and air cool.

[0006] Step 2.2, forging below the phase transformation point and forging above the phase transformation point: The TC4ELI alloy forging billet is held at 20-30℃ below the β phase transformation point with a holding coefficient of 0.6-0.7 min / mm, and then upset and rolled; after forging, it is returned to the furnace at a temperature of 1100-1150℃ with a holding coefficient of 0.2-0.3 min / mm, rolled into a round billet and air-cooled to room temperature.

[0007] Step 2.3, Pre-forming forging: The billet is punched and expanded in sequence, heated to 20-30℃ below the β phase transformation point, with a heat retention coefficient of 0.6-0.7 min / mm, and then air-cooled to obtain a preliminary annular billet.

[0008] Step 3: The preliminary annular billet obtained in Step 2 is subjected to ring rolling forging to obtain an annular billet: the billet is heated to 20-30℃ below the β phase transformation point and held at that temperature with a holding coefficient of 0.6-0.7 min / mm, and then subjected to ring rolling forging.

[0009] Step four: Anneal the annular billet obtained in step three to obtain a titanium alloy ring forging: hold at a temperature of 700-800℃ with a holding coefficient of 1.5-2.0.

[0010] The present invention also has the following technical features: Specifically, in step one, the welding current is 500-600A; during the vacuum consumable arc melting process, the melting voltage is 30-36V, the melting current is 28-31kA, the arc stabilizing current is AC 34-35A, and the arc stabilizing change period is 10-15s.

[0011] Specifically, in step 2.1, the total deformation of riveting upsetting is 70% to 80%; the total deformation of drawing upsetting forging is 70% to 80%.

[0012] Specifically, in step 2.2, the upsetting and rounding deformation is 70% to 80%; the remelting deformation is 70% to 80%.

[0013] Specifically, in step 2.3, the hole expansion deformation is 35% to 45%.

[0014] Specifically, the time for the billet to be transferred from the furnace to the forging machine during the forging process in steps 2.1 to 2.3 is less than 180 seconds.

[0015] Optionally, step three also includes: after the ring forging is completed, the ring is reheated multiple times at a temperature 20-30°C below the β phase transformation point, with a holding coefficient of 0.2-0.3 min / mm, followed by air cooling after forging.

[0016] Specifically, in step three, the deformation amount during ring rolling is 35%–45%. The deformation amount during remelting and rolling is also 35%–45%.

[0017] The above method is applicable to the preparation of TC4ELI titanium alloy ring forgings with an outer diameter of 5000-12000 mm, a wall thickness of 80-500 mm, and a single weight of ≥10 t.

[0018] The beneficial technical effects of this invention compared to the prior art are as follows: (I) This invention employs a process route of smelting-pre-forming forging-ring rolling to obtain ring forgings. High-purity raw materials are used to prepare ingots with uniform composition, and the billets are fully deformed through multi-fire, large-deformation forging and ring rolling to improve the uniformity of the microstructure. Annealing is performed in a high-precision electric furnace to ensure that all parts of the material are fully heated, thereby obtaining TC4ELI titanium alloy ring forgings with uniform overall microstructure and excellent performance.

[0019] (II) The preparation method of the present invention can prepare TC4ELI alloy ring forgings with an outer diameter of 5000-12000 mm, a wall thickness of 80-500 mm, and a single weight of ≥10t. Attached Figure Description

[0020] Figure 1 The transverse microstructure of the upper part of the TC4ELI ring forging obtained in Example 1 of this invention is shown.

[0021] Figure 2 The longitudinal microstructure of the upper part of the TC4ELI ring forging obtained in Example 1 of this invention is shown.

[0022] Figure 3 The transverse microstructure of the lower part of the TC4ELI ring forging obtained in Example 1 of this invention is shown.

[0023] Figure 4 The longitudinal microstructure of the lower part of the TC4ELI ring forging obtained in Example 1 of this invention is shown.

[0024] Figure 5 The transverse microstructure of the TC4ELI ring forging was prepared in Comparative Example 1.

[0025] Figure 6 The longitudinal microstructure of the TC4ELI ring forging was obtained in Comparative Example 2.

[0026] The technical solution of the present invention will be further described below with reference to the embodiments. Detailed Implementation

[0027] It should be noted that all raw materials used in this invention, unless otherwise specified, are those known in the art. For example, the specific composition of TC4ELI titanium alloy is: Al 6.5 wt%, vanadium 4.2 wt%, iron 0.08 wt%, oxygen 0.10 wt%, hydrogen 0.001 wt%, carbon 0.03 wt%, nitrogen 0.01 wt%, with the balance being Ti; its β phase transformation point is 985℃.

[0028] Following the above technical solutions, specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0029] Example 1: This embodiment provides a method for preparing high-performance, ultra-large TC4ELI titanium alloy ring forgings. This method is used to prepare TC4ELI titanium alloy ring forgings with an outer diameter > 6000 mm, a wall thickness of 100 mm, and a single weight > 10 t. The specific steps include the following: Step 1, Ingot Preparation: High-purity sponge titanium is used as the main raw material for Ti element addition, supplemented with Al-V master alloy, iron particles, aluminum particles and titanium dioxide to add other required metal elements. It is pressed into several electrode blocks, which are then welded into complete electrodes through a plasma vacuum welding box with a welding current of 550A. The TC4ELI large-size ingot is prepared through three vacuum self-consuming arc melting processes. During the vacuum self-consuming arc melting process, the melting voltage is 32V, the melting current is 30kA, the arc stabilization current is AC 35A, and the arc stabilization change period is 10s.

[0030] Step two: The ingot obtained in step one is subjected to multiple forging processes to obtain a preliminary ring-shaped billet. Step 2.1, Ingot forging: First, heat to 800℃ and hold for 2 hours, then raise the temperature to 1150℃ and hold for 10 hours. Rivet and upset the billet to form a square billet with a height-to-width ratio of 1.0, with a total deformation of 80%. After forging, chamfering is performed, with a chamfering reduction L = (0.15~0.2) × the diagonal length of the square billet cross-section. After forging, the billet is ground, and the depth-to-width ratio is less than 1:9. After forging, the billet is air-cooled. Then, heat to 800℃ again and hold for 2 hours, then raise the temperature to 1150℃ and hold for 15 hours. After being taken out of the furnace, the billet is drawn and upset forged, with a deformation of 80%. After forging, chamfering is performed, with a chamfering reduction L = (0.15~0.2) × the diagonal length of the square billet cross-section. After forging, the billet is ground, and the depth-to-width ratio is less than 1:9. After forging, the billet is air-cooled.

[0031] Step 2.2, forging below the phase transformation point and forging above the phase transformation point: The TC4ELI alloy forging billet was held at 25°C below the β phase transformation point for 15 hours, then upset and rolled into a round shape with a deformation of 75%. After forging, it was returned to the furnace at a temperature of 1100°C for 6 hours with a deformation of 75%. The billet was rolled into a round shape and then air-cooled to room temperature.

[0032] Step 2.3, Pre-forming Forging: The blank is subjected to punching and reaming processes in sequence. The selected punch diameter is d = D × (0.25 ~ 0.3), where D is the blank diameter. The heating temperature is 25℃ below the β phase transformation point, the holding time is 16h, the reaming deformation is 40%, and the blank is air-cooled after forging to obtain a preliminary annular blank.

[0033] In this embodiment, the time for the billet to be transferred from the furnace to the forging machine during the forging process in steps 2.1 to 2.3 is less than 180 seconds.

[0034] Step 3: The preliminary annular billet obtained in Step 2 is subjected to ring rolling forging to obtain an annular billet. The billet is heated to 25°C below the β phase transformation point and held for 3 hours, then rolled into a ring forging with a deformation of 40%. It can be reheated multiple times, with the reheating temperature at 25°C below the β phase transformation point and the reheating holding time at 1 hour. The deformation of the ring after reheating is 40%, and it is then air-cooled.

[0035] Step four: Anneal the annular billet obtained in step three to obtain a titanium alloy ring forging. The TC4ELI ring forgings were annealed at a temperature of 780℃ for 3 hours. After being removed from the furnace, they were air-cooled on a flat surface to ensure uniform cooling of the billet.

[0036] Verification of the effect of Example 1 (see Table 1 below) Figures 1 to 4 ): Table 1. Mechanical properties of the TC4ELI ring forgings in Example 1

[0037] like Figures 1-4 As shown, the microstructure of the ring forging consists of equiaxed α and β transformed phases, exhibiting an equiaxed structure. The primary α phase content is approximately 50% or more, and the microstructure is uniform between the upper and lower parts with minimal differences. Table 1 shows that the mechanical properties of the upper and lower parts of the ring forging are essentially identical, with the average yield strength and impact absorption energy (KV2) being 869 MPa and 48.3 J, respectively. The ring forging in Example 1 exhibits a good balance of strength and plasticity, demonstrating high overall performance.

[0038] Comparative Example 1: This comparative example presents a method for preparing a high-performance, ultra-large TC4ELI titanium alloy ring forging. The method is basically the same as that in Example 1, except that the heating temperature below the phase transformation point is different in steps 2.2, 2.3 and step 3.

[0039] In this comparative example, step 2.2 includes: holding the TC4ELI alloy forging billet at 45°C (i.e., 940°C) below the β phase transformation point for 15 hours, then upsetting and rounding it with a deformation of 75%; after forging, the billet is returned to the furnace at a temperature of 1100°C for 6 hours with a deformation of 75%, and then rounded to obtain a cake billet and air-cooled to room temperature.

[0040] In this comparative example, step 2.3 includes: punching and expanding the blank in sequence, selecting a punch diameter d=D×(0.25~0.3), where D is the blank diameter; heating temperature is 45℃ below the β phase transformation point, holding time is 16h, expansion deformation is 40%, and air cooling is performed after forging.

[0041] In this comparative example, step three includes: heating the billet to 45°C below the β phase transformation point and holding it for 3 hours, then performing ring forging with a deformation of 40%; it can be reheated multiple times, with the reheating temperature at 45°C below the β phase transformation point and the reheating holding time at 1 hour, resulting in a ring deformation of 40% after forging, followed by air cooling.

[0042] In this comparative example, the billet was difficult to deform during forging, requiring multiple reheating processes, and severe surface cracking occurred, affecting processing efficiency. The final titanium alloy ring forging exhibited an uneven microstructure. Figure 5 and Figure 6 The study found that the ring forging contained large areas of elongated strips and coarse α phases, indicating problems such as incomplete forging of the billet during the forging process. The mechanical properties of the ring forging are shown in Table 2. Compared with Example 1, the tensile strength and impact absorption energy decreased by 26 MPa and 15.3 J, respectively. The impact performance was significantly reduced and the performance safety margin was small, making it unsuitable for extreme environments such as deep-sea collisions.

[0043] Table 2. Mechanical properties of the TC4ELI ring forgings in Comparative Example 1

[0044] Comparative Example 2: This comparative example presents a method for preparing high-performance, ultra-large TC4ELI titanium alloy ring forgings. This method is basically the same as that in Example 1, except that the annealing temperature in step four is different.

[0045] In this comparative example, step four includes: annealing the TC4ELI ring forging at a temperature of 850℃ for 3 hours, then air-cooling it after removing it from the furnace to ensure uniform cooling of the billet.

[0046] In this comparative example, the mechanical properties of the final titanium alloy ring forging are shown in Table 3. Compared with Example 1, it maintains good plasticity. However, its tensile strength and impact absorption energy are reduced by 24 MPa and 15.6 J, respectively. The impact performance is significantly reduced and the performance safety margin is small, making it unsuitable for extreme environments such as deep-sea collisions.

[0047] Table 3. Mechanical properties of the TC4ELI ring forgings in Comparative Example 2

[0048] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for preparing high-performance super-size TC4 ELI titanium alloy ring forgings, characterized in that, The method comprises the following steps: Step one, preparing an ingot; Step two, performing multi-fire forging on the ingot prepared in step one to obtain a preliminary ring blank; Step three, performing ring rolling on the preliminary ring blank prepared in step two to obtain a ring blank; Step four, performing annealing treatment on the ring blank prepared in step three to obtain a titanium alloy ring forge piece; The annealing treatment of step four comprises: holding at a temperature of 700-800℃, and a holding coefficient of 1.5-2.

0.

2. The method of producing high performance, oversized TC4 ELI titanium alloy ring forgings of claim 1, wherein, Step one comprises: pressing the TC4ELI titanium alloy raw material into several electrode blocks, welding the electrode blocks into a complete electrode through a plasma vacuum welding box, and preparing a TC4ELI large-size ingot through three vacuum consumable arc melting.

3. The method of producing a high-performance, oversized TC4 ELI titanium alloy ring forge piece of claim 2, wherein In step one, the welding current is 500-600A.

4. The method of producing high performance, oversized TC4 ELI titanium alloy ring forgings of claim 2, wherein, In step one, during the vacuum consumable arc melting process, the melting voltage is 30-36V, the melting current is 28-31kA, the stable arc current is 34-35A, and the stable arc change period is 10-15s.

5. The method of producing high performance, oversized TC4 ELI titanium alloy ring forgings of claim 1, wherein, Step two comprises: step 2.1, bloom forging of the ingot; step 2.2, forging below the phase transition point and forging above the phase transition point; and step 2.3, preforming forging.

6. The method of producing high performance, oversized TC4 ELI titanium alloy ring forgings of claim 5, wherein, Step 2.1 comprises: firstly heating to 700-800℃ and holding for 2-3h, and then heating to 1100-1150℃, with a holding coefficient of 0.6-0.7 min / mm, upsetting and sizing to a square billet, chamfering, trimming, and air cooling after forging; and then again heating to 700-800℃ and holding for 2-3h, and then heating to 1100-1150℃, with a holding coefficient of 0.6-0.7 min / mm, performing elongation upsetting forging after discharging, and chamfering, trimming, and air cooling after forging.

7. The method of producing high performance, oversized TC4 ELI titanium alloy ring forgings of claim 5, wherein, Step 2.2 comprises: holding the TC4ELI alloy forge blank at 20-30℃ below the beta phase transition point, with a holding coefficient of 0.6-0.7 min / mm, and performing upsetting and rolling; after forging, returning to the furnace at a temperature of 1100-1150℃, with a holding coefficient of 0.2-0.3 min / mm, and rolling to obtain a pie billet and air cooling to room temperature.

8. The method of producing high performance, oversized TC4 ELI titanium alloy ring forgings of claim 5, wherein, Step 2.3 comprises: sequentially punching and expanding the pie billet, with a heating temperature of 20-30℃ below the beta phase transition point and a holding coefficient of 0.6-0.7 min / mm, and air cooling after forging.

9. The method of producing high performance, oversized TC4 ELI titanium alloy ring forgings of claim 1, wherein, Step three comprises: heating the blank to 20-30℃ below the beta phase transition point and holding, with a holding coefficient of 0.6-0.7 min / mm, and performing ring rolling.

10. The method of producing a high-performance, oversized TC4 ELI titanium alloy ring forge piece of claim 9, wherein, Step three further comprises: after the ring rolling is completed, returning to the furnace multiple times at a temperature of 20-30℃ below the beta phase transition point, with a holding coefficient of 0.2-0.3 min / mm, and air cooling after forging.

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