Preparation method of high-impact-toughness super-large-specification Ti80 titanium alloy ring forging

Abstract

The invention discloses a preparation method of a high-impact-toughness super-large-specification Ti80 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, and a cake blank is obtained; the prepared cake blank is subjected to ring rolling forging, and an annular blank is obtained; and the prepared annular blank is subjected to heat treatment, and the titanium alloy ring forging is obtained. According to the titanium alloy ring forging process adopted by the invention, on the premise of eliminating the longitudinal welding seam, the overall structure uniformity of the pressure-resistant shell can be ensured, and the mechanical property is stable. By designing a reasonable processing route and formulating optimal processing parameters, the uniformity of the material structure is improved, and the manufacturing safety and reliability of the pressure-resistant shell are improved. The method is suitable for preparing the Ti80 titanium alloy ring forge piece with the outer diameter of 4000-10000 mm, the wall thickness of 100-500 mm and the piece weight larger than or equal to 8 t.

Description

Technical Field

[0001] This invention belongs to the field of high-quality titanium alloy material technology, and relates to the manufacture of Ti80 titanium alloy, specifically to a method for preparing ultra-large Ti80 titanium alloy ring forgings with high impact toughness. Background Technology

[0002] Titanium alloys are widely used engineering materials in the aerospace and marine fields. Among them, Ti80 alloy, with its low density, high specific strength, high corrosion resistance, and high toughness, is a specialized material for deep-sea equipment such as deep-sea submersibles. With the continuous upgrading and iteration of deep-sea equipment, the performance requirements for materials are becoming increasingly stringent. Material design must maintain excellent service performance in extreme environments such as deep-sea collisions. Therefore, there is an urgent need to develop titanium alloy products with high impact toughness to ensure that the products possess good mechanical properties and performance safety margins.

[0003] Currently, the main research and development route for large pressure hulls is the rolling and welding of large-size titanium alloy plates. Welding and forming titanium alloys is extremely difficult. Compared to traditional steel, titanium alloys require special welding processes for forming. Although Ti80 alloy has good weldability, the rolled and welded cylinder has longitudinal weld seams, making it difficult to control the microstructure around the weld seams. The presence of longitudinal weld seams leads to insufficient mechanical properties of the rolled and welded cylinder, making it difficult to meet the requirements of pressure hull materials in extreme environments such as deep-sea collisions. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing ultra-large Ti80 titanium alloy ring forgings with high impact toughness, thereby solving the technical problem of poor mechanical properties of Ti80 titanium alloy ring forgings obtained by the roll welding process in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for preparing ultra-large Ti80 titanium alloy ring forgings with high impact toughness, the method comprising: Step 1, Ingot preparation: The Ti80 titanium alloy raw material is pressed into several electrode blocks, which are then welded into complete electrodes through a plasma vacuum welding box; then, after three vacuum consumable arc melting processes, a large-size Ti80 ingot is obtained.

[0006] 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: The ingot obtained in step one is first held at 700-800℃ for 1.5-2.5 hours, then heated to 1100-1150℃ and held for a holding coefficient of 0.6-0.7 min / mm. After riveting, upsetting and shaping into a square billet, it is returned to the furnace at a temperature of 1100-1150℃ with a holding coefficient of 0.2-0.3 min / mm. After being taken out of the furnace, it is upsetting and drawing forging, then chamfered and air-cooled.

[0007] Step 2.2, forging below the phase transformation point and forging above the phase transformation point: Hold the Ti80 alloy forging billet at 20-30℃ below the β phase transformation point with a holding coefficient of 0.6-0.7 min / mm; after exiting the furnace, heat it to 30-50℃ above the β phase transformation point and hold it with a holding coefficient of 0.4-0.5 min / mm; after forging, chamfer and air cool.

[0008] Step 2.3, Two-phase forging: The Ti80 alloy forging billet is forged in three heating cycles below the phase transformation point; the heating temperature of each cycle is 20-30℃ below the β phase transformation point, and the holding coefficient is 0.6-0.7 min / mm; each cycle is returned to the furnace twice, and the furnace temperature is 20-30℃ below the β phase transformation point, with a furnace holding coefficient of 0.2-0.3 min / mm. The billet is shaped into a square billet and air-cooled after each forging cycle.

[0009] Step 2.4, forging of the billet: The Ti80 alloy forging billet is held at 20-30℃ below the β phase transformation point, with a holding coefficient of 0.4-0.5 min / mm; after forging, it is returned to the furnace at a temperature of 20-30℃ below the β phase transformation point, with a holding coefficient of 0.2-0.3 min / mm, for upsetting and rounding deformation, and then air-cooled.

[0010] Step 2.5, Pre-forming forging: The blank is punched and expanded in sequence, the heating temperature is 20-30℃ below the β phase transformation point, the heat preservation coefficient is 0.6-0.7 min / mm, and it is air-cooled after forging to obtain a preliminary ring-shaped blank.

[0011] Step 3: The preliminary annular billet obtained in Step 2 is subjected to ring rolling forging to obtain an annular billet: it is held at 20-30℃ below the β phase transformation point with a holding coefficient of 1.0-1.5 min / mm, and then air-cooled.

[0012] Step four involves heat treating the annular billet obtained in step three to obtain a titanium alloy ring forging. The heat treatment in step four includes: holding at 195–145°C below the β phase transformation point of Ti80 titanium alloy for 1.5–2.5 hours; then heating to 95–55°C below the β phase transformation point of Ti80 titanium alloy for 1.5–2.5 hours; and then holding at 20–30°C below the phase transformation point with a holding coefficient of 2.0–2.5 min / mm.

[0013] The present invention also includes the following technical features: Specifically, in step one, the welding current is 500-600A.

[0014] Specifically, in step one, during the vacuum self-consuming 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.

[0015] Specifically, in step 2.1, the deformation amount of upsetting and drawing forging is 70-80%.

[0016] Specifically, in step 2.5, the hole expansion deformation is 30-40%.

[0017] Specifically, in steps 2.1 to 2.5, the time for the billet to be transferred from the furnace to the forging machine after each forging is less than 180 seconds.

[0018] Specifically, in step three, the deformation amount of the ring forging is 30% to 40%.

[0019] The above method is applicable to the preparation of Ti80 titanium alloy ring forgings with an outer diameter of 4000-10000 mm, a wall thickness of 100-500 mm, and a single weight of ≥8t.

[0020] The beneficial technical effects of this invention compared to the prior art are as follows: (I) The titanium alloy ring forging process used in this invention can ensure the uniformity of the overall microstructure and stable mechanical properties of the pressure shell while eliminating longitudinal welds. By designing a reasonable processing route and formulating optimal processing parameters, the uniformity of the material microstructure can be improved, thereby enhancing the safety and reliability of the pressure shell manufacturing.

[0021] (II) This invention, starting from the existing equipment level in the industry, focuses on the preparation of titanium alloy ring forgings from three aspects: ingot melting, pre-forming forging, and ring rolling forging. The ingot is prepared through three VAR (vacuum consumable arc) melting processes to improve the uniformity of the ingot composition; the pre-forming forging process includes five forging stages, using a "high-low-high-low" forging method to fully recrystallize the billet, refine the grains, and improve the uniformity of the microstructure; the ring rolling forging process employs a large deformation and multiple remelting deformation method to fully deform the billet; and annealing in the high-temperature region of the "α+β" two-phase region reduces the anisotropy of performance caused by forging, thereby obtaining high-performance titanium alloy ring forgings. Attached Figure Description

[0022] Figure 1 The transverse microstructure of the upper part of the Ti80 titanium alloy ring forging obtained in Example 1 of the present invention is shown.

[0023] Figure 2 The longitudinal microstructure of the upper part of the Ti80 titanium alloy ring forging obtained in Example 1 of this invention is shown.

[0024] Figure 3 The microstructure of the lower transverse part of the Ti80 titanium alloy ring forging obtained in Example 1 of this invention is shown.

[0025] Figure 4 The lower longitudinal microstructure of the Ti80 titanium alloy ring forging obtained in Example 1 of this invention is shown.

[0026] Figure 5 The microstructure of the Ti80 titanium alloy ring forging prepared in Comparative Example 1 is shown.

[0027] Figure 6 The microstructure of the Ti80 titanium alloy ring forging prepared in Comparative Example 2 is shown.

[0028] The technical solution of the present invention will be further described below with reference to the embodiments. Detailed Implementation

[0029] 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 Ti80 titanium alloy is: Al 6.3 wt%, Nb 3.1 wt%, Zr 2.1 wt%, Mo 1.3 wt%, with the balance being Ti; its β phase transformation point is 995℃.

[0030] 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.

[0031] Example 1: This embodiment provides a method for preparing ultra-large Ti80 titanium alloy ring forgings with high impact toughness. This method is used to prepare Ti80 titanium alloy ring forgings with an outer diameter ≥6000mm, a wall thickness ≥140mm, and a single weight ≥8t. The specific steps include the following: Step 1, Prepare the ingot: High-purity sponge titanium was used as the main raw material for Ti, supplemented with Al-Nb master alloy, Al-Mo master alloy, aluminum foil, aluminum granules and sponge zirconium to add other required metal elements. The mixture was pressed into several electrode blocks and welded into complete electrodes in a plasma vacuum welding box with a welding current of 550A. Then, Ti80 large-size ingots were obtained by three vacuum arc melting processes. During the vacuum arc melting process, the melting voltage was 32V, the melting current was 30kA, the arc stabilization current was AC 35A, and the arc stabilization change period was 10s.

[0032] 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: Place the ingot obtained in Step 1 into a resistance heating furnace, first heat it to 800℃ and hold it for 2 hours, then raise the temperature to 1150℃ and hold it for 11 hours, then rivet and upset it and shape it into a square billet with a height-to-diameter ratio of 2.0; after forging, return it to the furnace at a temperature of 1150℃ and hold it for 6 hours, then remove it from the furnace and perform upsetting and drawing forging, with a deformation of 80%; after forging, chamfer it with a chamfering reduction of L = 0.1 × the diagonal length of the square billet cross section, and then air cool it.

[0033] Step 2.2, forging below the phase transformation point and forging above the phase transformation point: Hold the Ti80 alloy forging billet at 30°C below the β phase transformation point for 14 hours; after taking it out of the furnace, heat it to 50°C above the β phase transformation point and hold it for 10 hours, with a deformation of 70%; after forging, chamfer the edges, with a chamfering reduction L = 0.1 × the diagonal length of the square billet cross section, and air cool it after chamfering.

[0034] Step 2.3, Two-phase forging: The Ti80 alloy forging billet is forged in three heating cycles below the phase transformation point. The heating temperature is 30°C below the β phase transformation point, and the heating time is 10h. Each heating cycle is reheated twice in the furnace. The reheating temperature is 30°C below the β phase transformation point, and the reheating holding time is 5h. The deformation is 70%. After forging, the billet is chamfered. The chamfering reduction is L=0.1×diagonal length of the billet cross section. After chamfering, the billet is air-cooled.

[0035] Step 2.4, forging of the billet: The Ti80 alloy forging billet is heated at 30°C below the β phase transformation point for 10 hours; after forging, it is returned to the furnace at a temperature 30°C below the β phase transformation point and held at the furnace for 6 hours. Upsetting and rounding deformation are then performed, with a deformation amount of 70%, to obtain the billet.

[0036] Step 2.5, Pre-forming forging: The billet is subjected to punching and reaming processes in sequence. The heating temperature is 30°C below the β phase transformation point, the holding time is 10h, the reaming deformation is 35%, the punch diameter is selected = 0.25 × billet diameter, and the billet is air-cooled after forging to obtain a preliminary annular billet.

[0037] In steps 2.1 to 2.5 of this embodiment, the time for the billet to be transferred from the furnace to the forging machine after each forging is less than 180 seconds.

[0038] Step 3: The preliminary annular billet obtained in Step 2 is subjected to ring rolling forging to obtain an annular billet. The forging process involves holding the metal at 30°C below the β phase transformation point for 15 hours, resulting in a deformation of 35%. After forging, the metal is returned to the furnace at 30°C below the β phase transformation point for 2 hours. The metal is then rolled into a ring after exiting the furnace, resulting in a deformation of 35%, followed by air cooling.

[0039] Step four: Heat treat the annular billet obtained in step three to obtain a titanium alloy ring forging. The furnace temperature is 195°C (800°C) below the β phase transformation point. The furnace temperature is then raised to 195°C (850°C) below the β phase transformation point and held for 2 hours. The temperature is then raised to 55°C (940°C) below the β phase transformation point and held for 2 hours. Finally, the temperature is raised to 25°C (970°C) below the phase transformation point and held for 6.7 hours. After the furnace is removed, the titanium alloy ring forging is leveled and air-cooled to ensure uniform cooling of the billet.

[0040] Verification of the effect of Example 1 (see Table 1 below) Figures 1 to 4 ): Table 1. Mechanical properties of Ti80 titanium alloy ring forgings from Example 1

[0041] like Figures 1-4 As shown, the microstructure of the titanium alloy ring forging consists of equiaxed α and β transformed phases, exhibiting a bimodal structure. The primary α phase content is approximately 15%–20%, and the microstructure is uniform in both the upper and lower parts, without any streamlined morphology. Table 1 shows that the mechanical properties of the upper and lower parts of the titanium alloy ring forging are relatively similar, with an average yield strength of 780 MPa and an elongation after fracture of 16.7%, and an average impact energy (KV²) of 65.3 J. Example 1's titanium alloy ring forging demonstrates a good balance between strength and plasticity, exhibiting high overall performance and meeting the technical requirements for pressure hull materials in deep-sea equipment.

[0042] Comparative Example 1: This comparative example presents a method for preparing ultra-large Ti80 titanium alloy ring forgings with high impact toughness. The method is basically the same as that in Example 1, except that the heat treatment temperature in step four is different.

[0043] In this comparative example, step four includes: the furnace temperature is 195°C below the β phase transition point, the furnace temperature is raised to 195°C below the β phase transition point, and the temperature is held for 6.7 hours.

[0044] In this comparative example, the final titanium alloy ring forging has a large number of coarse equiaxed primary α grains in its microstructure. The titanium alloy ring forging has good toughness, but poor strength and impact performance. Compared with Example 1, the strength-plasticity match is poor, making it difficult to meet the technical requirements of deep-sea equipment for pressure-resistant shell materials.

[0045] Comparative Example 2: This comparative example presents a method for preparing ultra-large Ti80 titanium alloy ring forgings with high impact toughness. The method is basically the same as that in Example 1, except that the heat treatment temperature in step four is different.

[0046] In this comparative example, step four includes: the furnace temperature is 195°C below the β phase transition point, the furnace temperature is raised to 195°C below the β phase transition point, and the temperature is held for 2 hours; then the temperature is raised to 40°C below the β phase transition point and held for 6.7 hours.

[0047] In this comparative example, the final titanium alloy ring forging exhibits an equiaxed microstructure. In mechanical property testing, its plasticity is comparable to that of Example 1, but its tensile strength is lower than that of GJB943A-2018, and its yield strength ratio is >0.91, indicating poor structural safety. This makes it difficult to meet the technical requirements for pressure-resistant shell materials in extreme environments such as deep-sea collisions. The microstructure and mechanical properties of the titanium alloy ring forgings in Comparative Example 1 and Comparative Example 2 are as follows: Figures 5 to 6 As shown in Table 2.

[0048] Table 2. Mechanical properties of Ti80 titanium alloy ring forgings in comparative examples

[0049] 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 of making a high impact toughness, ultra-large size Ti80 titanium alloy ring forge, characterized in that, The method comprises: 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 forging on the preliminary ring blank prepared in step two to obtain a ring blank; Step four, performing heat treatment on the ring blank prepared in step three to obtain a titanium alloy ring forging; The heat treatment of step four comprises: holding at 195-145 ℃ below the beta phase transition point of Ti80 titanium alloy for 1.5-2.5 h; then heating to 95-55 ℃ below the beta phase transition point of Ti80 titanium alloy and holding for 1.5-2.5 h; and then holding at 20-30 ℃ below the phase transition point with a holding coefficient of 2.0-2.5 min / mm.

2. The method of producing high-impact-toughness, ultra-large-size Ti80 titanium alloy ring swages as set forth in claim 1, characterized in that, Step two comprises: step 2.1, open-die forging of the ingot; step 2.2, forging below the phase transition point and forging above the phase transition point; step 2.3, two-phase zone forging; step 2.4, pie blank forging; and step 2.5, pre-forming forging.

3. The method of producing high-impact-toughness, ultra-large-size Ti80 titanium alloy ring swages of claim 2, wherein Step 2.1 comprises: first holding the ingot prepared in step one at 700-800 ℃ for 1.5-2.5 h, and then heating to 1100-1150 ℃ for holding, with a holding coefficient of 0.6-0.7 min / mm, upsetting and sizing to a square billet, re-furnacing at 1100-1150 ℃ with a re-furnace holding coefficient of 0.2-0.3 min / mm, and then performing upsetting and elongation forging after discharging, and then chamfering and air cooling after forging.

4. The method of producing high-impact-toughness, ultra-large-size Ti80 titanium alloy ring forgings according to claim 2, characterized by, Step 2.2 comprises: holding the Ti80 alloy forged blank at 20-30 ℃ below the beta phase transition point with a holding coefficient of 0.6-0.7 min / mm, heating to 30-50 ℃ above the beta phase transition point after discharging, holding with a holding coefficient of 0.4-0.5 min / mm, and then chamfering and air cooling after forging.

5. The method of producing high-impact-toughness, ultra-large-size Ti80 titanium alloy ring forgings according to claim 2, characterized in that, Step 2.3 comprises: three-fire heating forging of the Ti80 alloy forged blank below the phase transition point; the heating temperature of each fire is 20-30 ℃ below the beta phase transition point, with a holding coefficient of 0.6-0.7 min / mm; re-furnacing twice after each fire, with a re-furnace temperature of 20-30 ℃ below the beta phase transition point and a re-furnace holding coefficient of 0.2-0.3 min / mm, and sizing to a square billet, and air cooling after each fire forging.

6. The method of producing high-impact-toughness, ultra-large-size Ti80 titanium alloy ring forgings according to claim 2, characterized in that, Step 2.4 comprises: holding the Ti80 alloy forged blank at 20-30 ℃ below the beta phase transition point with a holding coefficient of 0.4-0.5 min / mm, re-furnacing after forging at 20-30 ℃ below the beta phase transition point with a re-furnace holding coefficient of 0.2-0.3 min / mm, and then performing upsetting and rolling deformation, and air cooling after forging.

7. The method of producing high-impact-toughness, ultra-large-size Ti80 titanium alloy ring forgings of claim 2, wherein Step 2.5 comprises: sequentially performing punching and hole expanding processes on the pie blank, 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.

8. The method of producing high-impact-toughness, ultra-large-size Ti80 titanium alloy ring forgings according to claim 2, characterized by, In step two, the time for transferring the blank to the forging machine after each forging is less than 180 s.

9. The method of producing high-impact-toughness, ultra-large-size Ti80 titanium alloy ring forgings according to claim 1, characterized in that, Step three comprises: holding at 20-30 ℃ below the beta phase transition point with a holding coefficient of 1.0-1.5 min / mm, and then performing ring rolling forging, and air cooling after forging.

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