Preparation method of low-cost short-process high-performance titanium alloy thick plate and titanium alloy thick plate

Abstract

The application discloses a low-cost short-process high-performance titanium alloy thick plate preparation method and a titanium alloy thick plate, belongs to the titanium alloy processing technical field, and is especially suitable for short-process low-cost preparation of a titanium alloy thick plate with a TC32 brand. The method comprises the following steps: smelting and preparing an ingot, less-fire-time ingot forging, less-pass large-deformation reversing hot rolling forming, and heat treatment, and the like. In the ingot forging stage, the plate is prepared by not more than 3 times of rapid breakdown forging combined with a multiple upsetting and drawing alternating mode. In the hot rolling forming stage, the less-pass large-deformation reversing hot rolling is implemented in the Tbeta vicinity temperature zone, and the total thickness reduction is controlled to be more than 40%. Then, the thick plate heat treatment and surface treatment are carried out to obtain the thick plate finished product. The method utilizes the large-deformation less-pass hot rolling forming to relieve the production pressure of the forging forming, realizes the uniformization of the plate structure, significantly weakens the anisotropy, obtains the effect of uniform grains and mechanical property improvement, and further plays the advantages of high rolling production efficiency, stable process, high surface quality and high tolerance precision.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy processing technology, specifically relating to a low-cost, short-process, high-performance titanium alloy thick plate preparation method and titanium alloy thick plate, which is particularly suitable for the short-process, low-cost preparation of titanium alloy thick plates of grade TC32. Background Technology

[0002] Titanium alloys possess characteristics such as high specific strength, good corrosion resistance, and excellent heat resistance, and are widely used in aerospace, shipbuilding, petrochemical, and high-end equipment industries. my country's independently developed TC32 titanium alloy, as a new type of medium-high strength and toughness titanium alloy, exhibits a wide hot working process window, great potential for strength-toughness matching, and comprehensive performance superior to similar medium-high strength and high toughness titanium alloys such as TC4 and TA15, demonstrating broad application prospects.

[0003] However, for critical load-bearing components, large-section, thick-gauge semi-finished products are often required to meet subsequent forming and processing needs. Constrained by the capabilities of traditional equipment and process windows, the industry has long relied on forging to obtain billets or finished products for large-size products. To obtain better microstructure and mechanical properties in the finished product, multiple forging processes with significant deformation are often necessary. Invention patent CN116790939B discloses a two-phase titanium alloy sheet, which is prepared according to the following steps: Step 11, the raw materials of the components are electrode pressed and melted in a vacuum arc remelting furnace to obtain billet one; Step 12, the obtained billet one is upsetting and free forging at 200°C above the β phase transformation temperature to obtain billet two; Step 13, the obtained billet two is forged at 100°C above the phase transformation temperature into a thick slab with a thickness of 110±5mm; Step 14, the obtained thick slab is hot rolled multiple times in the α+β phase region at 30-50°C below the phase transformation point to obtain a thin sheet with a wall thickness of 1.2mm; Step 15, the obtained thin sheet is subjected to high-temperature annealing or solution aging treatment in the two-phase region to obtain the two-phase titanium alloy sheet. This patent mainly obtains the thick slab by forging and then hot rolling to obtain the thin sheet, resulting in a long production cycle and high manufacturing cost for the thick plate. Forged thick plates are difficult to use directly; otherwise, a large machining allowance is required to ensure dimensional and positional accuracy, resulting in a large amount of machining and low material utilization. In contrast, if thick plates or near-net-shape thick plates can be obtained directly through rolling, the requirements for consistency in the size and quality of the forging billet can be reduced to a certain extent, the preparation process can be shortened, and the matching and convenience of the plates in subsequent cutting, machining, and assembly processes can be improved, thus providing a better foundation for engineering promotion.

[0004] Furthermore, titanium alloys have poor thermal conductivity and a narrow processing window. During the rolling of thick plates, they are susceptible to temperature drops, oxidation, and uneven deformation, leading to problems such as edge cracks, uneven microstructure, and excessive anisotropy. The flatness, surface quality, and tolerance accuracy of thick plates also directly affect their adaptability to subsequent processing and engineering applications. Invention patent CN112680630B discloses a vacuum heat treatment method for ultra-high toughness, medium strength, and high plasticity TC32 titanium alloy parts. The method involves placing the TC32 titanium alloy parts into a vacuum heat treatment furnace, where the vacuum pressure does not exceed 6.7 × 10⁻⁶. -2 The TC32 titanium alloy parts were heated to Tβ+10℃ in the furnace at a heating rate of 0.3℃ / s, and held for 45-90 minutes. After holding, they were cooled to Tβ-10℃ in the furnace at a cooling rate of 80-180℃ / s, and then held for 25-35 minutes. After holding, they were cooled to 500-550℃ in the furnace at a cooling rate of 0.001-0.1℃ / s, and then held for 300-380 minutes. The parts were then air-cooled after removal from the furnace. By implementing a vacuum heat treatment technique of rapid cooling in the transphase region and slow cooling in the two-phase region on the TC32 titanium alloy parts, the microstructure was precisely controlled, significantly improving the comprehensive properties of the TC32 titanium alloy, with a fracture toughness reaching 140 MPa·m. 1 / 2 The plasticity reaches 15% or more, and the strength is guaranteed to be 850MPa or more. Although this patent improves the mechanical properties of TC32 titanium alloy parts through vacuum heat treatment, it is difficult to apply to the manufacture of large titanium alloy plates with a thickness of more than 60mm and a width of more than 500mm. It is also difficult to simultaneously meet the comprehensive goals of homogenizing the microstructure of thick plates, reducing anisotropy, and improving the adaptability of thick plates for subsequent processing.

[0005] Therefore, how to provide a method for preparing titanium alloy thick plates and titanium alloy thick plates to solve the problems of high cost, long cycle, large machining volume and low material utilization caused by the reliance on multi-fire forging of existing large-size products, as well as the challenges of controlling the uniformity and anisotropy of the microstructure and the difficulty in balancing flatness and surface quality during the rolling process of thick plates, are problems that urgently need to be solved by those skilled in the art. Summary of the Invention

[0006] To address the shortcomings of the existing technology, this invention provides a low-cost, short-process method for preparing high-performance titanium alloy thick plates and a high-performance TC32 titanium alloy thick plate. The method involves pre-forging a titanium alloy ingot in the β-phase region using a limited number of passes to form a forging billet, then further upsetting and drawing the forging billet to obtain a slab. After obtaining the slab, a limited number of passes of large deformation reversal hot rolling are performed, followed by annealing and other post-treatments. This reduces the reliance on multi-pass large deformation forging and improves the process adaptability of thick plate preparation. The resulting TC32 titanium alloy thick plate exhibits comprehensive high performance, including high strength, high toughness, impact resistance, fatigue resistance, and damage tolerance.

[0007] Firstly, a low-cost, short-process method for preparing high-performance titanium alloy thick plates is provided, applicable to (α+β) type two-phase titanium alloy of grade TC32. The titanium alloy comprises, by weight percentage: Al 4.5% ~ 5.5%, Mo 2.5% ~ 3.5%, Cr 2.5% ~ 3.5%, Zr 0.5% ~ 1.5%, Si 0.1% ~ 0.2%, Fe≤0.3%, C≤0.08%, N≤0.05%, H≤0.0125%, O≤0.2%, with the balance being Ti and unavoidable impurity elements. Includes the following steps: Step 1: Ingot forging. After holding the titanium alloy ingot obtained from smelting at Tβ+100℃ to Tβ+200℃, it is forged no more than 3 times. Tβ is the β phase transformation point of the titanium alloy ingot, and the total deformation is less than 40%. Then, it is upsetting and drawing repeatedly to obtain intermediate slabs with a thickness of 200~480mm. The intermediate slabs are then cut into titanium alloy slabs. Step 2: Hot rolling. After heating the titanium alloy slab to Tβ-100℃ to Tβ+50℃, it is hot rolled with a small number of passes and large deformation to obtain a thick titanium alloy plate with a total thickness reduction of more than 40%. Step 3: Heat treatment of thick plates. The titanium alloy thick plates obtained in Step 2 are subjected to double annealing treatment. Step 4: Surface treatment of the thick plate to obtain a finished TC32 titanium alloy thick plate with a thickness of 60~280mm and a width greater than or equal to 500mm.

[0008] Preferably, the β phase transformation point Tβ of the titanium alloy ingot is 880~920℃. In step one, after holding for 180~360min, no more than two forging processes are performed, and the final forging temperature is above 700℃.

[0009] It should be noted that, in this invention, the β phase transformation point Tβ refers to the phase transformation temperature limit corresponding to the gradual transformation of the titanium alloy from the α phase region to the β phase region during the heating process, that is, the critical temperature for the transformation from the α phase to the β phase.

[0010] Deformation is a core parameter characterizing the degree of plastic deformation in metallic materials, and it is quantitatively expressed through the ratio of the workpiece dimensions before and after plastic deformation. Specifically, deformation reflects the degree of change in the shape and size of a material after being subjected to external force. Since this invention aims to prepare thick titanium alloy plates, the dimensional changes are particularly focused on thickness changes, but monitoring of length and width dimensions is not excluded.

[0011] This invention, through the synergistic design of the TC32 titanium alloy composition system and the "rolling instead of forging" hot working path, shifts the main forming load of thick plates from the forging stage to the rolling stage, thereby reducing the dependence of large-size products on multi-stage, large-deformation forging. Specifically, the synergistic ratio of Al with Mo and Cr provides the alloy with a phase composition suitable for hot working in the β phase region and its adjacent temperature range. Zr and trace amounts of Si help improve microstructure stability and suppress the tendency of microstructure coarsening during high-temperature processing. The upper limit control of impurity elements such as Fe, C, N, H, and O is used to reduce the influence of interstitial elements and impurities on plasticity and cracking sensitivity, providing the material prerequisites for subsequent large-deformation rolling.

[0012] In terms of process, after the ingot is heated in the β phase region, it is forged no more than 3 times, preferably no more than 2 times, and the total deformation is low to obtain the alloy forging billet. This is the first step in the material’s transformation from “cast state” to “processed state”, laying the foundation for subsequent more refined deformation. This invention transforms ingot forging from the main forming method to a transitional link of pre-forming and defect passivation, which reduces forging costs and cycles, and also reduces the risk of structural and quality fluctuations caused by multiple forging processes. Subsequently, the alloy forging billet is subjected to multiple upsetting and drawing alternations to prepare intermediate slabs with a thickness of 200~480 mm, and then cut to make the billet shape and internal deformation state more suitable for entering the hot rolling forming stage. After the slab is heated in a set temperature zone near the β phase transformation point, it undergoes a few passes of large deformation reversal hot rolling while ensuring that the total thickness reduction reaches the specified level. This allows for sufficient cumulative plastic deformation to be introduced in a shorter process, promoting deformation penetration and microstructure homogenization within the thick plate section, reducing anisotropy caused by a single deformation path, and lowering the risk of edge cracking. On this basis, heat treatment of the thick plate combined with surface treatment can further eliminate residual stress and improve the surface condition. This ensures that the final TC32 titanium alloy thick plate with a thickness of 60~280 mm and a width greater than or equal to 500 mm achieves a balance in terms of process feasibility, preparation efficiency, and adaptability to subsequent processing, thereby achieving the overall goal of producing finished thick plates under the condition of "rolling instead of forging".

[0013] Step three, double annealing, refers to subjecting the hot-rolled semi-finished thick plate to two annealing processes to further regulate the microstructure and stabilize the overall properties. Specifically, when the first annealing is performed in the two-phase region, a two-phase double annealing method is adopted. Since the first annealing is located in the α+β two-phase region, its morphology and distribution can be adjusted while retaining a certain amount of primary α phase. The second annealing then achieves microstructure stabilization and further stress release, resulting in a biphasic microstructure characterized by equiaxed primary α phase or short rod-shaped primary α phase in the thick plate.

[0014] When the first annealing is performed in the single-phase region, a single-phase region double annealing treatment is adopted. Since the first annealing is located in the β single-phase region, the original microstructure is reconstructed at a temperature higher than the β phase transformation point. Subsequently, a lamellar transformation microstructure is formed during air cooling. The lamellar microstructure is then stabilized by the second annealing, thereby giving the thick plate a lamellar microstructure. By selecting either two-phase region double annealing or single-phase region double annealing according to the target microstructure type, thick plates can form either a biphasic microstructure or a lamellar microstructure, adapting to the requirements of strength, plasticity, and microstructure stability in different application scenarios.

[0015] Preferably, before step one, the titanium alloy raw material is smelted twice to obtain a titanium alloy ingot, and both smelting processes are performed using vacuum consumable arc melting: Primary melting: Vacuum arc ignition is used to perform primary melting to obtain primary ingots; wherein, under vacuum conditions, arc ignition and melting current, voltage and melting rate are controlled to keep the molten pool stable and achieve continuous and uniform energy input to form primary ingots with stable quality. At the same time, the vacuum environment promotes degassing of the melt and causes inclusions to float to the surface, thereby removing most of the gas and inclusions in the melt and reducing the risk of the formation of pores and inclusion defects inside the primary ingot.

[0016] More preferably, during the dynamic heat preservation process of gradually reducing the melting current after one melting is completed, the titanium alloy melt is evacuated and filled with inert gas alternately multiple times to reduce the oxygen content of the titanium alloy melt to below 500 ppm.

[0017] Secondary melting: The primary ingot is used as an electrode for remelting to obtain a titanium alloy ingot. In this process, electrode remelting achieves further purification and solidification control, which further homogenizes the alloy composition and suppresses macroscopic segregation. At the same time, under relatively stable solidification conditions, the solidification structure is refined and the probability of shrinkage defects is reduced, thus providing a more uniform and dense ingot foundation for subsequent ingot forging and thick plate rolling.

[0018] Preferably, in step one, the upsetting and pulling are performed alternately using two upsetting and two pulling operations, including a first upsetting and pulling operation and a second upsetting and pulling operation performed sequentially: The deformation of a single pier is 20-60%, the amount of each hammer blow is 20-50 mm, the downward pressure is uniform and the downward pressure rate is 10-40 mm / s; the deformation of a single elongation is 40-60%, and the deformation of the widening is 30-50%.

[0019] In the aforementioned two-upsetting and two-drawing forging process, upsetting and drawing are alternated, and the amount of single deformation and single reduction are limited. This ensures that the billet achieves sufficient cumulative plastic deformation while avoiding strain concentration due to excessive instantaneous reduction. Specifically, the upsetting stage achieves basic deformation for cross-section compaction and as-cast structure fragmentation through a single deformation of 20-60%. The drawing stage, combined with a single drawing deformation of 40-60% and a superimposed widening deformation of 30-50%, facilitates the full transfer of deformation to the interior of the cross-section and improves the uniformity of cross-section deformation. At the same time, controlling the single reduction to 20-50 mm and using a uniform pressing method (reduction rate 10-40 mm / s) reduces the deformation gradient and instantaneous load impact between the surface and core of the billet, reducing the risk of crack initiation and propagation caused by local temperature drop or uneven structure. Thus, while ensuring that the forging deformation meets the requirements of subsequent rolling, the stability and forming quality of the slab forging process are improved.

[0020] Preferably, the first upsetting and drawing is carried out at a temperature of Tβ+50℃ to Tβ+100℃ in the following order: ingot flattening → flat square upsetting → axial upsetting → axial drawing → pressing flat square to obtain a flat billet. The second forging process involves recrystallizing and annealing the flat billet obtained from the first forging process, followed by widening and elongation treatment at a temperature of Tβ-50℃ to Tβ-20℃. The widening and elongation treatment is carried out in 1-2 forging passes, with a final forging temperature above 800℃.

[0021] In the above process arrangement, the first upsetting and drawing process selects a temperature range higher than Tβ for flattening, upsetting and drawing combined deformation, which can keep the material in a high plasticity state in the β phase region. This is conducive to the transfer of deformation to the center under large cross-section conditions and the breaking and homogenization of the coarse structure in the cast state. At the same time, through the sequence of "cast ingot flattening → flat upsetting → axial upsetting → axial drawing → pressing flattening", the cross-sectional shape is gradually regularized and multi-directional strain paths are formed, which reduces the risk of insufficient internal deformation, folding and local strain concentration caused by deformation in a single direction, thereby obtaining a flat billet with relatively stable structure and shape.

[0022] The second upsetting and drawing process is carried out after recrystallization annealing. On the one hand, recrystallization annealing is used to eliminate the work hardening and residual stress introduced by the first upsetting and drawing process, so that the deformation resistance and microstructure are restored to a level suitable for continued large deformation. On the other hand, the widening and elongation treatment in the α+β two-phase region below Tβ can promote grain refinement and microstructure homogenization while maintaining a certain plasticity. Furthermore, the temperature compensation and segmented deformation of multiple heating processes can reduce the uneven deformation and cracking tendency caused by temperature drop.

[0023] Preferably, in step two, the fewer-pass large deformation reversing hot rolling includes: The titanium alloy slab is heated at 880~950℃ for 250~300 minutes; After every 2 to 3 rolling passes, the billet is rotated 90°, and the longitudinal-transverse hot rolling cycle is completed alternately, with a total of 4 to 10 hot rolling passes and a thickness reduction of more than 15% per pass.

[0024] In the aforementioned hot rolling process, sufficient heating and holding within the 880-950℃ range allows the slab to maintain relatively stable deformation capacity during continuous rolling passes. Combined with a pass design featuring large deformation in fewer passes and limiting the thickness reduction per pass to no less than 15%, this facilitates the introduction of sufficient cumulative plastic deformation within a shorter rolling cycle, making deformation more likely to penetrate towards the slab thickness and promoting microstructure homogenization. Furthermore, rotating the slab 90° every 2-3 passes and alternating longitudinal and transverse rolling changes the main deformation direction and creates multi-directional strain paths. This weakens the texture strengthening and property anisotropy caused by single rolling direction, reduces the tendency to crack due to edge strain concentration, and allows the thick plate to obtain a more balanced microstructure and property base within the cross-sectional area, providing a more stable initial state for subsequent heat treatment and finishing processes.

[0025] Preferably, the reversing hot rolling adopts a four-roll reversible hot rolling mill with a roll diameter of 800~1200mm, a surface roughness Ra of less than 1.0μm, a preheating temperature of 200~350℃, and a pass interval of less than 30s.

[0026] The use of a four-roll reversible hot rolling mill enables multiple passes of forward and reverse rolling within the same stand and facilitates the completion of reversing rolling cycles in coordination with billet rotation. This reduces temperature drops and cycle fluctuations caused by intermediate transfers and mill changes, which is beneficial for maintaining continuous and stable hot deformation conditions for thick slabs during the rolling process.

[0027] Preferably, the double annealing process employs single-phase double annealing or double annealing.

[0028] Preferably, the temperature of the reversing hot rolling is maintained above 750°C, and the plate immediately proceeds to the third step of thick plate heat treatment after the reversing hot rolling is completed. The double annealing treatment employs a single-phase region double annealing process, including: The first annealing temperature is Tβ+10 to Tβ+30℃, the holding time is 30 min to 85 min, and the air is cooled. The second annealing temperature is 500℃~600℃, the holding time is 120min~240min, and it is cooled in air.

[0029] Preferably, the temperature of the reversing hot rolling is maintained above 750°C, and the plate immediately proceeds to the third step of thick plate heat treatment after the reversing hot rolling is completed. The double annealing treatment employs a two-phase region double annealing process, including: The first annealing temperature is 760℃~900℃, the holding time is 60min~120min, and the air is cooled. The second annealing temperature is 500℃~600℃, the holding time is 120min~240min, and it is cooled in air.

[0030] Preferably, at 500~600℃ after the second annealing and heat preservation, a creep straightening treatment is slowly applied to the thick plate so that the flatness of the finished titanium alloy thick plate after straightening is no more than 0.5mm / m.

[0031] Maintaining the reversing hot rolling temperature above 750℃ and immediately following the hot rolling with thick plate heat treatment can reduce the temperature drop of the thick plate between passes and during transport, as well as the resulting fluctuations in deformation resistance. This reduces the risk of cracking and plate instability caused by insufficient surface plasticity. Furthermore, heat treatment promptly releases residual rolling stress and stabilizes the microstructure. Further, after the second annealing and holding stage of heat treatment, creep straightening is applied while the thick plate temperature is still between 500 and 600℃, followed by air cooling. Utilizing the material's time-dependent viscoplastic deformation capacity within this temperature range, warpage and waviness are gradually eliminated at a lower stress level, and new stress concentrations are avoided introduced by straightening. This ensures that the flatness of the finished thick plate is stably controlled to no more than 0.5 mm / m, improving the processing stability of subsequent cutting, machining, and assembly processes.

[0032] Preferably, in step four, the surface treatment of the thick plate includes acid and alkali washing and / or surface sanding, so that the surface roughness Ra of the finished titanium alloy thick plate is below 2.5μm and there are no edge line crack defects of 45°~120°.

[0033] Removing the oxide scale and any underlying embrittlement layer from the surface of thick plates by alkaline pickling can reduce the risk of surface defects expanding in subsequent processing and provide a foundation for obtaining stable surface quality. Surface sanding helps to further remove shallow defects and the initiation source of edge microcracks, reducing the impact of scratches, adhesion, and stress concentration on surface integrity. This allows the surface roughness of the finished thick plate to be stably controlled at Ra≤2.5μm, and reduces the probability of edge crack defects, improving the applicability and safety of thick plates in cutting, machining, and assembly processes.

[0034] Secondly, the present invention also provides a high-performance TC32 titanium alloy thick plate prepared by the aforementioned method, wherein the TC32 titanium alloy thick plate has a room temperature tensile strength ≥950MPa, a yield strength ≥825MPa, an elongation ≥8%, and an impact toughness ≥50J / cm. 2 .

[0035] This titanium alloy thick plate is produced through a process combining low-temperature, low-deformation forging with a combination of short-pass, high-deformation hot rolling. This results in a more uniform grain distribution within the plate's cross-section, improved microstructure, and significantly reduced anisotropy. It also exhibits good macroscopic mechanical property stability and consistent overall performance. By employing a rolling-instead-of-forging process, the quality of thick plates is ensured while reducing the difficulty and cycle time of forging at the ingot end, alleviating production pressure in traditional forging processes. Furthermore, the advantages of rolling—high production efficiency, process stability, good surface quality, and high dimensional tolerance control—are fully utilized, making the resulting TC32 titanium alloy thick plate a viable alternative to TC4 forgings.

[0036] The method for preparing TC32 titanium alloy thick plates and the titanium alloy thick plates provided by this invention have at least the following beneficial effects: (1) This invention, by coordinating the titanium alloy composition system with the preparation path of “melting and ingot making - low-deformation forging and billet making - multiple upsetting and drawing alternating plate making - low-deformation hot rolling forming - double annealing and surface treatment and other post-treatments”, enables thick plates to be directly obtained as finished products or near-finished products by rolling, reducing the dependence on multiple forgings to obtain large-size forgings, reducing intermediate turnover and machining allowance, thereby shortening the preparation process and reducing manufacturing costs and cycle.

[0037] (2) By implementing a small number of large deformation reversal hot rollings within a set temperature window and ensuring sufficient cumulative thickness reduction, and by promptly entering post-treatment such as double annealing after hot rolling, this invention is conducive to promoting deformation penetration and microstructure homogenization within the thick plate cross section, weakening the texture strengthening and performance anisotropy caused by a single rolling direction, reducing the risk of edge cracking and plate shape fluctuation, and improving the quality stability of the thick plate.

[0038] (3) By setting a two-phase region double annealing treatment system or a single-phase region double annealing treatment system, the present invention enables the thick plate to further obtain a dual-state structure or lamellar structure after rolling, thereby broadening the post-processing window and providing support for the microstructure control and comprehensive mechanical property optimization under different performance requirements. In addition, creep leveling and surface treatment are carried out at 500~600℃ after the second annealing treatment, which can eliminate warping and waviness without introducing significant secondary damage, so that the flatness of the finished thick plate meets the requirements, while improving the surface roughness and reducing the probability of edge crack defects, thereby improving the applicability and engineering reliability of the thick plate in the cutting, machining and assembly processes. Attached Figure Description

[0039] Figure 1 This is a microstructure diagram of the TC32 titanium alloy thick plate product from Example 2 of the present invention; Figure 2 This is a microstructure diagram of the TC32 titanium alloy thick plate product from Example 4 of the present invention. Detailed Implementation

[0040] To better understand the above technical solutions, a detailed description of the specific implementation methods will be provided below. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0041] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0042] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0043] This invention provides a low-cost, short-process method for preparing high-strength and high-toughness TC32 titanium alloy thick plates, which can be used to prepare finished TC32 titanium alloy thick plates with a thickness of 60-280 mm.

[0044] The titanium alloy, by mass percentage, comprises the following composition: Al 4.5~5.5%, Mo 2.5~3.5%, Cr 2.5~3.5%, Zr 0.5~1.5%, Si 0.1~0.2%, Fe≤0.3%, C≤0.08%, N≤0.05%, H≤0.0125%, O≤0.2%, with the balance being Ti and unavoidable impurity elements. The preparation method specifically includes the following steps: S1. Melting and casting: Titanium alloy ingots are produced by batching and melting according to the titanium alloy ratio.

[0045] In one preferred embodiment, the smelting in step S1 includes primary smelting and secondary smelting, both of which employ vacuum consumable arc melting: the prepared raw materials are pressed or assembled into consumable electrodes and cleaned before being loaded into a vacuum consumable arc melting furnace. A vacuum is drawn and leaks are checked to ensure the furnace pressure is stably controlled below 10 Pa. Vacuum arc ignition is completed in a water-cooled copper crystallizer, and primary smelting is performed to obtain a primary ingot. During the arc ignition stage, the current is controlled at 3-6 kA to achieve stable arc ignition. After entering the stable smelting stage, the current is controlled at 8-18 kA and the voltage at 20-35 V. The electrode descent speed is linked to the melting rate to stabilize the melting rate at 2-10 kg / min, and the molten pool is kept stable by adjusting the electrode feed and arc length. After primary smelting, the ingot is cooled and removed from the furnace under vacuum or inert gas protection conditions. Subsequently, the primary ingot is surface-cleaned and loaded into the furnace as a consumable electrode for secondary melting. Vacuum is drawn and the pressure inside the furnace is controlled below 10 Pa. Vacuum arc ignition is repeated and secondary remelting is performed to obtain titanium alloy ingots. During the secondary remelting stage, the current is controlled at 10~20 kA, the voltage at 20~35V, and the melting rate at 2~8 kg / min. The electrode feed rate is adjusted in real time according to the stable state of the molten pool to avoid molten pool fluctuations.

[0046] In one preferred embodiment, the furnace body is subjected to pressure holding and leak detection or pressure rise rate test before primary melting and secondary remelting, so that the pressure rise rate is controlled below 0.5 Pa / min; the primary ingot is mechanically peeled and decontaminated before being used as the secondary electrode, with a peeling thickness of 2~5 mm, and oil and dust are removed by wiping with anhydrous ethanol or acetone; during the melting process, the melting current, voltage and melting rate are adjusted by a closed-loop control method that continuously measures the arc voltage and current, and after the melting is completed, the head and tail of the ingot are cut off to remove the unstable melting section.

[0047] S2. Forging: The titanium alloy ingot obtained by melting is heated to Tβ+100℃ to Tβ+200℃, where Tβ is the β phase transformation point of the titanium alloy ingot. The Tβ of TC32 titanium alloy is about 880~920℃. After holding at the temperature, the alloy forging is obtained by no more than 3 forgings, and the total deformation is less than 40%.

[0048] In one optional embodiment, the ingot is heated in a protective atmosphere or vacuum furnace at a heating rate of 2-6°C / min. Once the furnace temperature reaches the target temperature, it is held for 180-360 minutes to keep the temperature difference across the ingot cross-section within 20°C and maintain the final forging temperature above 700°C. Forging is performed using a hydraulic press or high-speed forging machine. The reduction in a single forging is 10-30mm, the deformation is 10-20%, and the cumulative forging count is 1-3 times with the total deformation controlled to be less than 40%, for example, 15-39%. During forging, the cycle time is controlled to ensure manageable temperature drop on the billet surface, and forging continues after reheating if necessary. Initial forging is used for pre-forming and defect passivation of the ingot. During forging, multi-point temperature measurement is used to control the billet exit temperature and forging cycle time. After each forging, the ends and surface of the billet are inspected and trimmed to ensure that the forged billet has a regular shape and no obvious defect expansion on the surface when entering step S3.

[0049] S3. Upsetting and drawing plate: The alloy forging billet is heated to at least Tβ-50℃, and the alloy forging billet is upset and drawn into an intermediate plate with a thickness of 200~480 mm by multiple alternating upsetting and drawing processes. The intermediate plate is then cut into titanium alloy plate.

[0050] In one preferred embodiment, the alloy forging billet is heated and held in a heating furnace for 60-180 minutes to ensure uniform temperature of the billet cross section before being upset. During the upset process, the single pressing amount and pressing rate are controlled and necessary heat compensation is used to ensure that the final forging temperature is above 800°C. Finally, the billet is upset to the target thickness and then cut to obtain a slab.

[0051] In one preferred embodiment, the alternating upsetting and drawing process in step S3 adopts a two-upsetting and two-drawing method, which includes a first upsetting and drawing and a second upsetting and drawing performed sequentially. The process parameters of the two upsetting and two-drawing are: the deformation amount of a single upsetting is 20~60%, the reduction amount of a single pressing is 20~50 mm, and the pressing is uniform with a pressing rate of 10~40 mm / s; the deformation amount of a single drawing length is 40~60%, and the deformation amount of widening is 30~50%.

[0052] In a more preferred embodiment, the first upsetting and drawing is carried out at a temperature 50-100°C higher than Tβ, and includes ingot flattening, flat square upsetting, axial upsetting, axial drawing, and pressing flat square to obtain a flat billet; the second upsetting and drawing is carried out after the flat billet recrystallization annealing at a temperature 50-20°C lower than Tβ for widening and drawing treatment.

[0053] In one preferred embodiment, the recrystallization annealing is carried out at a temperature of 700~850℃, held for 30~120min and then air-cooled or furnace-cooled to reduce the influence of work hardening and residual stress on subsequent widening and elongation; uniform pressing is used to reduce instantaneous impact load and local strain concentration, reduce the risk of large crack initiation, thereby improving the stability of the plate making process while ensuring the upsetting deformation.

[0054] The above specific implementation method can also combine S2 billet forging and S3 upsetting and drawing into a single ingot forging, in order to distinguish it from the previous smelting and ingot making and the subsequent hot rolling forming.

[0055] S4. Hot rolling: After heating the titanium alloy slab to Tβ-100℃ to Tβ+50℃, it is hot rolled with a small number of passes and large deformation reversal, with a total thickness reduction of more than 40%, to obtain a titanium alloy thick plate with a thickness of 65mm~285mm and a width of ≥500mm.

[0056] In one preferred embodiment, the heating in step S4 is carried out under inert gas protection, and the slab is heated at 880~950℃ for 250~300 min. After the slab is taken out of the furnace, the loose oxide layer on the surface is cleaned and it is quickly rolled on the machine. The interval between passes is controlled within 30s. If necessary, short-term reheating is used and rolling continues.

[0057] In one preferred embodiment, the few-pass large deformation reversing hot rolling in step S4 satisfies the following: after every 2 to 3 rolling passes, the billet is rotated 90°, and the longitudinal and transverse hot rolling cycles are alternately completed, with a cumulative hot rolling pass of 4 to 10 passes and a pass thickness reduction of more than 15%.

[0058] In one preferred embodiment, the reversing hot rolling adopts a four-roll reversible hot rolling mill with a roll diameter of 800~1200 mm, a roll surface roughness Ra≤1.0μm, a roll preheating temperature of 200~350℃, and a pass interval of less than 30s.

[0059] In a more preferred embodiment, the temperature of the reversing hot rolling is maintained above 750°C, wherein the final rolling temperature or the exit rolling temperature is used as the temperature control caliber; during the rolling process, online temperature measurement and cycle control are used to ensure that the temperature meets the requirements, and after rolling, the thickness is checked to confirm that the total thickness reduction meets the process requirements.

[0060] S5. Heat treatment of thick plates: The titanium alloy thick plates after reversing hot rolling are immediately subjected to double annealing treatment, including two-phase region (α+β) double annealing treatment or single-phase region (β) double annealing treatment: A. Two-phase region (α+β) double annealing treatment: While retaining a certain amount of primary α phase, its morphology, size, and distribution are adjusted. A second annealing process further releases residual stress and stabilizes the microstructure, resulting in a thick plate with a biphasic microstructure characterized by equiaxed primary α phases or short rod-shaped primary α phases, including: The first annealing temperature is 760℃~900℃, the holding time is 60min~120min, and the air is cooled. The second annealing temperature is 500℃~600℃, the holding time is 120min~240min, and it is cooled in air.

[0061] B. Double annealing treatment in the single-phase region: The first annealing is located in the β single-phase region, where the original microstructure is reconstructed at a temperature higher than the β phase transformation point, and a lamellar transformation microstructure is formed during the subsequent air cooling process. The second annealing then stabilizes this microstructure, resulting in a lamellar microstructure in the obtained thick plate, including: The first annealing temperature is Tβ+10 to Tβ+30℃, the holding time is 30 min to 85 min, and the air is cooled. The second annealing temperature is 500℃~600℃, the holding time is 120min~240min, and it is cooled in air.

[0062] In one preferred embodiment, at 500~600℃ after the second annealing and heat preservation, a creep leveling treatment is slowly applied to the thick plate so that the flatness of the finished titanium alloy thick plate is no more than 0.5mm / m, and then it is air-cooled.

[0063] S6. Surface treatment of thick plates, including but not limited to acid and alkali washing, surface sanding, etc. After physical and chemical testing, the finished titanium alloy thick plates of the required specifications are obtained, namely, TC32 titanium alloy thick plates with a thickness of 60~280mm and a width greater than or equal to 500mm.

[0064] In one optional embodiment, alkaline washing uses an alkaline solution with a mass fraction of 2-10%, a temperature of 40-80℃, and a time of 10-40 min; acid washing uses a mixed acid system containing fluorine and nitric acid, a temperature of 15-35℃, and a time of 1-10 min; after acid washing, the surface is thoroughly cleaned with deionized water and dried; when there are still local defect areas on the surface after acid washing, or when surface sanding is performed directly, the surface roughness Ra of the finished titanium alloy thick plate is ≤2.5μm, and there are no edge line crack defects of 45°-120°; wherein, 45°-120° is the range of the angle between the crack extension direction and the edge line direction of the plate projected on the plate surface.

[0065] Example 1 This embodiment uses a target smelting total charge of 1000 kg of titanium alloy, comprising: 50.00 kg of aluminum, 30.00 kg of molybdenum, 30.00 kg of chromium, 10.00 kg of zirconium, 1.50 kg of silicon, and the balance being 878.50 kg of sponge titanium. The β-phase transformation point Tβ of this TC32 titanium alloy is approximately 910℃. A low-cost, short-process method for preparing high-performance TC32 titanium alloy thick plates is adopted, and the specific steps are as follows: S1. Melting and Ingot Making: The above raw materials are loaded into a vacuum self-consuming arc melting furnace according to the proportion. After vacuuming and leak detection, the pressure inside the furnace is stabilized and controlled below 10 Pa. Vacuum arc ignition and self-consuming arc melting are carried out in a water-cooled copper crystallizer to obtain titanium alloy ingots. The current is controlled at 4kA during the arc ignition stage. After entering the stable melting stage, the current is controlled at 12kA and the voltage is controlled at 28V. The melting rate is controlled at 6kg / min by the electrode feed speed. After melting, the titanium alloy ingots are cooled and removed from the furnace under inert gas protection.

[0066] S2. Forging: The titanium alloy ingot is heated to 1050℃ (140℃ higher than Tβ) and held for 240 minutes before two forging processes. The total deformation during forging is controlled to be about 35%. After forging, an alloy forging billet is obtained. S3. Upsetting and Drawing Plate: The alloy forging billet is heated to 880℃ (at least Tβ-50℃) and then subjected to two upsetting and two drawing processes (multiple alternating upsetting and drawing) to a thickness of 200 mm and cut into titanium alloy plate blanks, including the first upsetting and drawing and the second upsetting and drawing processes performed sequentially: The first upsetting and drawing process involves holding the billet at approximately 1000℃ for 120 minutes, followed by sequential processes of ingot flattening, flat square upsetting, axial upsetting, axial drawing, and pressing into a flat square to obtain a flat billet. The second drawing process involves widening and elongating the billet after recrystallization annealing (annealing temperature of approximately 800℃, holding for 90 minutes followed by air cooling) at approximately 880℃.

[0067] The single upsetting deformation is about 30%, the single pressing is about 30 mm, and the pressing is done at a uniform speed of about 20 mm / s; the single drawing deformation is about 50%, and the widening deformation is 40%. During the upsetting process, the final forging temperature is kept above 700℃ by controlling the single pressing cycle and coordinating with necessary heating.

[0068] S4. Hot Rolling: The titanium alloy slab is heated to approximately 900℃ (belonging to the temperature range of 100℃ lower than Tβ to 50℃ higher than Tβ) and then subjected to a small number of passes of large deformation reversing hot rolling using a four-high reversible hot rolling mill. The roll diameter of the four-high reversible hot rolling mill is 1000mm, the surface roughness Ra is below 1.0μm, the preheating temperature is 300℃, and the pass interval is within 30s. During the rolling process, the slab is rotated 90° after every 2 passes, and the longitudinal and transverse hot rolling cycles are alternately completed. A total of 6 hot rolling passes are completed, and the thickness reduction of each pass is more than 15%. The slab thickness is rolled from 200 mm to 164 mm, 135 mm, 112 mm, 94 mm, 78 mm, and 65 mm in sequence, with a total thickness reduction of more than 67%. The final rolling temperature is used as the control caliber to keep the final rolling temperature above 750℃.

[0069] S5. Thick plate heat treatment: The titanium alloy thick plate after reversal hot rolling is immediately subjected to single-phase (β phase) double annealing treatment, including: The first annealing temperature is 930℃, the holding time is 60min, and it is cooled in air. The second annealing temperature is 550℃, the holding time is 180 minutes, and it is cooled in air.

[0070] S6. Surface treatment of thick plates: The surface of the titanium alloy thick plates is sanded to obtain TC32 titanium alloy thick plates with a thickness of about 60mm and a width of about 550mm.

[0071] Example 2 The difference between this embodiment and embodiment 1 is that step S1 adopts a vacuum self-consuming arc melting process of primary melting and secondary remelting. Specifically, the raw materials are prepared into consumable electrodes according to the specified ratio, and after surface cleaning, they are loaded into the furnace. A vacuum is drawn and leaks are checked to control the furnace pressure below 10 Pa. After vacuum arc ignition, a primary melting process is performed to obtain a primary ingot. The arc ignition current is 4 kA, and the stable melting stage current is 12 kA, voltage is 28 V, and melting rate is 6 kg / min. After the primary melting, the ingot is cooled and removed from the furnace under inert gas protection. The ingot undergoes mechanical peeling and decontamination treatment, with a peel thickness of approximately 3 mm. During the dynamic heat preservation stage after the primary melting and as the melting current gradually decreases, the furnace is alternately evacuated and filled with inert gas multiple times until the oxygen content of the melt is controlled below 500 ppm. The primary ingot is then used as a consumable electrode, vacuumed, loaded into the furnace, and the furnace pressure is still controlled below 10 Pa for a secondary remelting to obtain a titanium alloy ingot. The stable stage of the secondary remelting has a current of 15 kA, voltage of 26 V, and melting rate of 5 kg / min. The remaining steps are the same as in Example 1, resulting in a TC32 titanium alloy thick plate with a thickness of approximately 60 mm and a width of approximately 550 mm. Its microstructure is shown in [Figure 1]. Figure 1 .

[0072] Example 3 The difference between Example 3 and Example 2 is that: In step S3, the upsetting and drawing process involves two upsetting and two drawing operations (multiple alternating upsetting and drawing) to a thickness of 280 mm, which is then cut into titanium alloy blanks. In step S4 hot rolling forming, the billet is rotated 90° after every two rolling passes, alternating between longitudinal and transverse hot rolling cycles. A total of 6 hot rolling passes are completed, with each pass reducing the thickness by more than 15%. The slab thickness is rolled from 280 mm to 236 mm, 200 mm, 170 mm, 144 mm, 122 mm, and 103.5 mm, with a total thickness reduction of approximately 63%. In the thick plate surface treatment in step S6, the surface of the titanium alloy thick plate is sanded to obtain a finished TC32 titanium alloy thick plate with a thickness of about 100 mm and a width of about 535 mm.

[0073] Example 4 The difference between Example 4 and Example 2 is that: In step S3, the upsetting and drawing process involves two upsetting and two drawing operations (multiple alternating upsetting and drawing) to a thickness of 480 mm, which is then cut into titanium alloy slab blanks. In step S4 hot rolling forming, the billet is rotated 90° after every two rolling passes, alternating between longitudinal and transverse hot rolling cycles. The cumulative number of hot rolling passes is 4, and the thickness reduction in each pass is more than 10%. The slab thickness is rolled from 480 mm to 400 mm, 340 mm, 288 mm, and 244 mm in sequence, with a total thickness reduction of about 49%. In step S6, the surface treatment of the thick plate involves sanding the surface of the titanium alloy thick plate to obtain a finished TC32 titanium alloy thick plate with a thickness of approximately 240 mm and a width of approximately 530 mm. Its microstructure is shown in [image missing]. Figure 2 .

[0074] Example 5 The difference between this embodiment and Embodiment 2 is that step S5, the heat treatment of the thick plate, also includes creep leveling. Specifically, the second annealing temperature is 550℃, and after holding for 180 minutes, creep leveling is performed using a staged loading and holding method followed by slow unloading, and then air cooling. After leveling, the flatness of the thick plate is no greater than 0.5 mm / m; the remaining steps are the same as in Embodiment 2.

[0075] Example 6 The difference between this embodiment and embodiment 2 is that recrystallization annealing is omitted between the first and second upsetting, while the remaining steps are the same as in embodiment 2.

[0076] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that: in Comparative Example 1, the total deformation exceeds 40% through ingot forging and other processes in step S2; in step S4, reversing hot rolling is performed using a four-roll reversible hot rolling mill, resulting in a thickness reduction of less than 15% per pass and a total thickness reduction of less than 40%. Steps S2 and S4 respectively include: S2. After heating the ingot to 1050℃ and holding it for 240 minutes, it is forged 6 times to obtain an alloy forging billet. The total deformation of the forging is about 60%. Then, it is upsetting and drawing twice to a thickness of about 100 mm and cut into titanium alloy slabs. S4. After heating a 100mm thick titanium alloy slab to approximately 900℃, it is hot rolled in reverse direction using a four-roll reversible hot rolling mill. After every two rolling passes, the slab is rotated 90°, alternating between longitudinal and transverse hot rolling cycles. The total number of hot rolling passes is 4, and the slab thickness is rolled from 100mm to 88mm, 80mm, 72mm, and 65mm in sequence, with a total thickness reduction of approximately 35% (thickness reduction per pass is less than 15%, and the total thickness reduction is less than 40%).

[0077] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the heat treatment of the thick plate in step S5 adopts the usual heat treatment method of holding at 750°C for 120 minutes and then air cooling.

[0078] Test methods and results 1. Room temperature tensile properties: Refer to the standard for room temperature tensile testing of metallic materials (such as GB / T 228.1). Take tensile specimens along the rolling direction L and transverse direction T on the thick plate (the sampling thickness should be marked according to the sampling location specification). At least 3 parallel specimens should be taken in the same direction, and the test results should be recorded and averaged. Wherein, L is the rolling direction, T is the transverse direction, Rm is the tensile strength, Rp0.2 is the specified non-proportional elongation strength (i.e., yield strength), and A is the elongation after fracture.

[0079] 2. Impact toughness (J / cm) 2 Referring to GB / T 229-2020 "Charpy Impact Test Method for Metallic Materials", V-notch Charpy impact specimens were prepared on thick plates, and pendulum impact tests were conducted at room temperature. Each group of samples consisted of at least three parallel specimens, and the average impact absorption energy was taken. When using standard specimens, the impact absorption energy can be divided by the effective cross-sectional area at the notch to convert it into impact toughness (J / cm²). 2 ) is used to represent.

[0080] The test results of samples from Examples 1-6 and Comparative Examples 1-2 are shown in Table 1: Table 1. Results of room temperature mechanical properties test

[0081] As shown in Table 1, the thick plate samples obtained in Examples 1-6 all exhibit high room temperature strength and good plasticity. Among them, Examples 2-5, while maintaining relatively small differences in longitudinal and transverse properties, show a better overall strength-plasticity ratio than Example 1. This indicates that by improving smelting cleanliness, implementing double annealing, and creep leveling based on rolling instead of forging, it is beneficial to further improve the mechanical properties and overall stability of the thick plate. In Example 6, after omitting recrystallization annealing, both strength and plasticity decreased, indicating that intermediate annealing during the upsetting and drawing process has a positive effect on subsequent microstructure homogenization and performance improvement. In contrast, Comparative Example 1, due to excessive forging and insufficient hot rolling deformation, still follows the traditional method of forging as the main deformation method. The strength, plasticity, and anisotropy control effect of the thick plate are significantly worse than those of the Example group. Comparative Example 2, after conventional annealing, also has lower overall mechanical properties than the Example group that used double annealing. In summary, this invention, through the process route of replacing forging with rolling, can effectively obtain TC32 titanium alloy thick plates with excellent overall performance and small directional differences while reducing the forging burden and streamlining the process. The impact toughness of Examples 1-5 is not less than 55 J / cm², indicating that the present invention, by replacing forging with rolling and combining it with reasonable upsetting and drawing, reversing hot rolling and heat treatment processes, can ensure both strength and good impact toughness. Among them, the impact toughness of Examples 2 and 3 increases with increasing plate thickness. In contrast, Example 6, after omitting intermediate recrystallization annealing, has an impact toughness higher than 50 J / cm². 2 But less than 55 J / cm 2 The impact toughness of Comparative Examples 1 and 2 was significantly lower than that of the Example Group due to the difference in process, indicating that heavy forging and light rolling or insufficient heat treatment are not conducive to obtaining TC32 titanium alloy thick plates with both high strength and high toughness.

[0082] 3. Microstructural Characteristics: Following standard metallographic examination methods (referring to GB / T 13298 Class II Metallographic Examination Methods standard), metallographic samples were prepared at 1 / 2T and 1 / 2L positions on the thick plate samples of Examples 2 and 4. After grinding, polishing, and etching, the samples were observed using an optical microscope. (See Appendix) Figure 1-2 The titanium alloy thick plate samples processed by this invention exhibit good uniformity in microstructure. Combined with the previous mechanical property tests and results, it is evident that the thick plate demonstrates excellent overall performance and high quality stability.

[0083] 4. Hardness and Thickness Consistency (Vickers Hardness HV10): Referring to the generally accepted hardness testing standard (GB / T 4340.1 Vickers Hardness), hardness lattice tests were performed along the thickness direction at positions of 1 / 4T and 1 / 2T. The average value and range were statistically analyzed. The hardness range was used to characterize the thickness consistency. Hardness test data for Examples 1-6 and Comparative Examples 1-2 are shown in Table 2. Table 2 Hardness Test Results

[0084] As shown in Table 2, the thick plates obtained in Examples 1-5 exhibit higher hardness at the 1 / 4T and 1 / 2T positions, and the hardness range is controlled at a low level, indicating that the process of the present invention can effectively promote the homogenization of the microstructure in the thickness direction of the thick plate and improve performance consistency. In particular, the thickness hardness difference in Examples 2-5 is even lower, indicating that higher metallurgical cleanliness, thickening paths, and heat treatment are all beneficial for further refining the microstructure, improving microstructure homogeneity, and overall hardness. In Example 6, after omitting recrystallization annealing, the hardness range increases, indicating that intermediate annealing has a positive effect on improving the microstructure after upsetting and drawing and enhancing the uniformity of subsequent rolling. In contrast, the overall hardness of Comparative Examples 1 and 2 is lower, and the hardness range is also larger, indicating that excessive forging burden or the use of only conventional annealing treatment is not conducive to obtaining TC32 titanium alloy thick plates with uniform microstructure and stable performance.

[0085] 5. Chemical composition and interstitial element content (wt% or ppm): Refer to the common practice for the inspection of chemical composition of titanium and titanium alloys (refer to the GB / T 4698 series of methods and standards). Take samples from the finished thick plate along the thickness direction and use ICP-OES to determine the content of elements such as Al, Mo, Cr, Zr, Si, and Fe. Use inert gas melting infrared or thermal conductivity method to determine the content of O, N, H, and C, and compare them with the formula window item by item.

[0086] 6. Surface roughness Ra (μm) and surface defect inspection: Refer to the common specifications for surface roughness measurement (you can refer to GB / T 1031 or equivalent standards), measure Ra at multiple points on the plate surface and take the average. At the same time, visually inspect and record defects such as folds, tears, and indentations with a magnifying glass to ensure the surface compatibility for subsequent cutting and machining.

[0087] 7. Flatness (mm / m) and dimensional tolerance (mm): Referring to the common methods for inspecting the geometric accuracy of thick plates, the warping amount is measured in segments along the length direction using a platform and feeler gauge or laser measurement method, converted into mm / m index, and the dimensional data such as plate thickness, plate width, and diagonal difference are recorded to verify the support of hot rolling post-processing and leveling (if any) for the matching of engineering assembly and processing. 8. Sensitivity to edge cracks and surface cracking (crack length, density, or acceptance criteria): Referring to the approach of internal control of edge crack defects (the reference document regards eddy current testing as one of the key quality inspection links after finishing), visually inspect the edges of thick plates and use penetrant testing or eddy current testing to screen for microcracks. Record the crack extension direction and the angle between the edge line (e.g., 45-120° range) and the defect length according to a uniform standard.

[0088] The test results of Examples 1-6 and Comparative Examples 1-2 are shown in Table 3, where O, N, and H represent the interstitial element content (expressed in ppm). Ultrasonic testing results are used to characterize the level of internal defect control. Flatness is expressed in mm / m, surface roughness in Ra, and edge cracks at 45-120° and the maximum crack length are used to characterize the edge crack defect control and adaptability to subsequent processing. Table 3 Quality Indicators for Component Cleanliness and Engineering Compatibility

[0089] As shown in Table 3, the O, N, and H contents of Examples 1-6 are all within the composition window defined by this invention, indicating that the process of this invention has good composition controllability. Among them, Examples 2-6, due to the use of a smelting method combining primary smelting, dynamic heat preservation purification, and secondary remelting, have significantly lower interstitial element contents than Examples 1 and Comparative Examples 1-2, indicating that this smelting purification process helps improve metallurgical cleanliness. The ultrasonic test results of Examples 1-6 are all qualified, indicating that good internal quality can still be obtained under the rolling-forging route. After adding creep leveling, the flatness of Example 5 can be better controlled within 0.5 mm / m, indicating that this treatment has a significant effect on the shape control of thick plates; the surface roughness of each example is at a low level, and no 45-120° edge line crack defects are observed at the edges, indicating that the process of this invention has good engineering adaptability. In contrast, although Comparative Example 1 still met the window requirements in terms of composition, due to excessive forging load and insufficient hot rolling thickness reduction, its ultrasonic testing showed localized high echoes, significantly worsened flatness and surface roughness, and edge cracks, indicating that this route is not conducive to obtaining thick plate finished products with stable quality. Although Comparative Example 2 did not show obvious edge cracks, its flatness and surface quality were still lower than those of the example group using double annealing treatment, indicating that the heat treatment regime of thick plates also has an important impact on the final engineering adaptability.

[0090] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if these modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include these modifications and modifications.

Claims

1. A low-cost, short-process method for preparing high-performance titanium alloy thick plates, characterized in that, This invention applies to (α+β) type two-phase titanium alloy of grade TC32, wherein the composition of the titanium alloy, by weight percentage, includes: Al 4.5% ~ 5.5%, Mo 2.5% ~ 3.5%, Cr 2.5% ~ 3.5%, Zr 0.5% ~ 1.5%, Si 0.1% ~ 0.2%, Fe≤0.3%, C≤0.08%, N≤0.05%, H≤0.0125%, O≤0.2%, with the balance being Ti and unavoidable impurity elements; Includes the following steps: Step 1: Ingot forging. After holding the titanium alloy ingot obtained from smelting at Tβ+100℃ to Tβ+200℃, it is forged no more than 3 times. Tβ is the β phase transformation point of the titanium alloy ingot, and the total deformation is less than 40%. Then, it is upsetting and drawing repeatedly to obtain intermediate slabs with a thickness of 200~480mm. The intermediate slabs are then cut into titanium alloy slabs. Step 2: Hot rolling. After heating the titanium alloy slab to Tβ-100℃ to Tβ+50℃, it is hot rolled with a small number of passes and large deformation to obtain a thick titanium alloy plate with a total thickness reduction of more than 40%. Step 3: Heat treatment of thick plates. The titanium alloy thick plates obtained in Step 2 are subjected to double annealing treatment. Step 4: Surface treatment of the thick plate to obtain a finished TC32 titanium alloy thick plate with a thickness of 60~280mm and a width greater than or equal to 500mm.

2. The preparation method according to claim 1, characterized in that, The β phase transformation point Tβ of the titanium alloy ingot is 880~920℃. In step one, after holding for 180~360min, no more than two forging processes are carried out, and the final forging temperature is above 700℃.

3. The preparation method according to claim 2, characterized in that, In step one, multiple upsetting and pulling operations are performed alternately using two upsetting and two pulling techniques, including a first upsetting and pulling operation followed by a second upsetting and pulling operation: The deformation of a single pier is 20-60%, the amount of each hammer blow is 20-50 mm, and the downward pressure is uniform with a downward speed of 10-40 mm / s. The single elongation deformation is 40-60%, and the widening deformation is 30-50%.

4. The preparation method according to claim 3, characterized in that, The first upsetting and drawing process is carried out at a temperature of Tβ+50℃ to Tβ+100℃ in the following order: ingot flattening → upsetting of flat square → axial upsetting → axial drawing → pressing of flat square to obtain flat billet. The second forging process involves recrystallizing and annealing the flat billet obtained from the first forging process, followed by widening and elongation treatment at a temperature of Tβ-50℃ to Tβ-20℃. The widening and elongation treatment is carried out in 1-2 forging passes, with a final forging temperature above 800℃.

5. The preparation method according to any one of claims 1-4, characterized in that, Step two, the less-pass large deformation reversing hot rolling includes: The titanium alloy slab is heated at 880~950℃ for 250~300 minutes; After every 2 to 3 rolling passes, the billet is rotated 90°, and the longitudinal-transverse hot rolling cycle is completed alternately, with a total of 4 to 10 hot rolling passes and a thickness reduction of more than 15% per pass.

6. The preparation method according to claim 5, characterized in that, The reversing hot rolling adopts a four-roll reversible hot rolling mill with a roll diameter of 800~1200mm, a surface roughness Ra of less than 1.0μm, a preheating temperature of 200~350℃, and a pass interval of less than 30s.

7. The preparation method according to claim 5, characterized in that, The temperature of the reversing hot rolling is maintained above 750℃. Immediately after the reversing hot rolling is completed, the plate enters step three for thick plate heat treatment. The double annealing treatment employs a single-phase region double annealing process, including: The first annealing temperature is Tβ+10 to Tβ+30℃, the holding time is 30 min to 85 min, and the air is cooled. The second annealing temperature is 500℃~600℃, the holding time is 120min~240min, and it is cooled in air.

8. The preparation method according to claim 5, characterized in that, The temperature of the reversing hot rolling is maintained above 750℃. Immediately after the reversing hot rolling is completed, the plate enters step three for thick plate heat treatment. The double annealing treatment employs a two-phase region double annealing process, including: The first annealing temperature is 760℃~900℃, the holding time is 60min~120min, and the air is cooled. The second annealing temperature is 500℃~600℃, the holding time is 120min~240min, and it is cooled in air.

9. The preparation method according to claim 7 or 8, characterized in that, At 500~600℃ after the second annealing and heat preservation, a creep leveling treatment is slowly applied to the thick plate so that the flatness of the finished titanium alloy thick plate is no more than 0.5mm / m.

10. A high-performance TC32 titanium alloy thick plate, characterized in that, The TC32 titanium alloy thick plate is prepared by the low-cost, short-process, high-performance titanium alloy thick plate preparation method according to any one of claims 1-9. The TC32 titanium alloy thick plate has a room temperature tensile strength ≥950MPa, a yield strength ≥825MPa, an elongation ≥8%, and an impact toughness ≥50J / cm. 2 .

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