Low-cost high-strength two-phase titanium alloy and manufacturing method thereof

Abstract

The invention discloses a low-cost and high-strength two-phase titanium alloy, which contains Ti and inevitable impurity elements, and also contains the following chemical elements in percentage by mass: 5.0%-7.0% of Al, 3.6%-4.5% of V, 0.4%-1.6% of Cr, 0.5%-1.3% of Fe and 0.06%-0.20% of O. The invention further discloses a manufacturing method of the two-phase titanium alloy. The manufacturing method comprises the steps that material preparation is conducted, wherein raw materials comprise sponge titanium, ferrochrome, TC4 titanium alloy return scraps and metal aluminum; smelting cast ingots; carrying out homogenization treatment; one-fire multi-pass rolling is adopted, the rolling speed is firstly slow and then fast during rough rolling, the rolling speed is firstly fast and then slow during finish rolling, online reversing is carried out between rough rolling and finish rolling, and air cooling is carried out after rolling.

Description

Technical Field

[0001] The present invention relates to an alloy and a manufacturing method thereof, in particular to a titanium alloy and a manufacturing method thereof. Background Art

[0002] Titanium alloy is an excellent lightweight, high-strength structural material that has been widely used in aviation, aerospace, navigation, petrochemicals, biomedicine, and weapons and equipment. In particular, titanium alloys have attracted significant attention in the navigation and petrochemical sectors due to the demand for lightweight and corrosion-resistant materials.

[0003] The traditional titanium alloy production process is lengthy and complex. Conventional titanium alloy sheet production typically requires multiple rounds of melting, forging, and rolling. This process significantly increases manufacturing costs. Furthermore, titanium alloy's high temperature sensitivity and processing difficulties result in a low yield and high production costs, limiting the material's widespread adoption.

[0004] Furthermore, to ensure the stability and uniformity of the microstructure and properties of titanium alloy products, machining is often used to remove certain areas during the production process, resulting in large quantities of high-quality titanium alloy scraps. The recycling and utilization of titanium alloy scraps has always been a problem plaguing the titanium industry. Summary of the Invention

[0005] One of the purposes of the present invention is to provide a low-cost, high-strength two-phase titanium alloy. The α+β two-phase titanium alloy has a high lamellar structure strength, good strength-plasticity matching, and a wide range of applications.

[0006] To achieve the above objectives, the present invention provides a low-cost, high-strength two-phase titanium alloy, which contains Ti and unavoidable impurity elements, and further contains the following chemical elements in the following mass percentages: Al: 5.0%~7.0%, V: 3.6%~4.5%, Cr: 0.4%~1.6%, Fe: 0.5%~1.3%, O: 0.06%~0.20%.

[0007] Furthermore, in the two-phase titanium alloy of the present invention, the mass percentage of each chemical element is: Al: 5.0%~7.0%, V: 3.6%~4.5%, Cr: 0.4%~1.6%, Fe: 0.5%~1.3%, O: 0.06%~0.20%; the balance is Ti and other inevitable impurity elements.

[0008] In the present invention, based on the volatilization law of each element and actual working conditions, the mass percentage of volatile Cr and Al elements is increased, Al: 5.0%~7.0% and Cr: 0.4%~1.6% to help ensure the composition uniformity of the two-phase titanium alloy.

[0009] Furthermore, Cr and Fe are both slow-eutectoid β-stabilizing elements that can significantly lower the phase transition temperature of titanium alloys. Their primary function is solid solution strengthening and increasing alloy plasticity. Therefore, a Cr content of 0.4% to 1.6% and an Fe content of 0.5% to 1.3% contribute to the formation of a two-phase titanium alloy with a good balance of strength and plasticity.

[0010] V: V is an isomorphous β-stabilizing element that can lower the phase transition point of titanium alloys, significantly improving their strength and hardness. It can also improve the mechanical properties of titanium alloys by refining their microstructure through solid solution strengthening. At the same time, the element can improve the hot working properties of titanium alloys, making them easier to form through hot working processes such as rolling. Adding V can reduce the cracking tendency of titanium alloys and optimize their welding properties. In particular, the addition of an appropriate amount of V can enhance the corrosion resistance of titanium alloys, especially in acidic environments. Therefore, a V content of 3.6% to 4.5% helps to obtain a two-phase titanium alloy with fine structure, excellent hot working properties, and outstanding welding and corrosion resistance, thereby broadening the application range of titanium alloys.

[0011] O: O is an interstitial α-stabilizing element that forms an interstitial solid solution with titanium, significantly improving the strength and hardness of titanium alloys. Properly controlling the concentration of O in titanium alloys can improve their corrosion resistance. Therefore, an O content of 0.06% to 0.20% helps produce a two-phase titanium alloy with both high strength and excellent corrosion resistance.

[0012] Furthermore, among other inevitable impurities in the two-phase titanium alloy of the present invention, H≤0.005%, N≤0.01%, and C≤0.03%.

[0013] In the above technical solution, H, N and C are all impurity elements in titanium alloys. When technical conditions permit, the content of these impurity elements should be controlled and reduced as much as possible to ensure that the comprehensive performance of the titanium alloy meets the use requirements.

[0014] Furthermore, in the two-phase titanium alloy described in the present invention, its microstructure is a lamellar structure.

[0015] Furthermore, in the two-phase titanium alloy of the present invention, the lamellar α phase and its clusters of the lamellar structure are curved, and the lamellar α phase grain boundaries are serrated.

[0016] Furthermore, in the two-phase titanium alloy described in the present invention, its yield strength is 950~1080MPa, its tensile strength is 1000~1150MPa, and its elongation is ≥12%.

[0017] Another object of the present invention is to provide a method for manufacturing a two-phase titanium alloy. This method significantly reduces the cost of raw materials by using a high proportion of TC4 titanium alloy return material as raw material. At the same time, combined with a one-fire, multi-pass forging-free direct rolling process, it can not only improve production efficiency but also significantly reduce processing costs.

[0018] In order to achieve the above object, the present invention provides a method for manufacturing a two-phase titanium alloy, which comprises the steps of: Ingredients: Raw materials include titanium sponge, ferrochrome raw materials, TC4 titanium alloy return materials and aluminum metal; Raw material mixing and briquetting; Ingot melting; Homogenization treatment; Rolling: One-pass multi-pass rolling is adopted. The rolling speed is slow at first and then fast during rough rolling, and fast at first and then slow during finish rolling. Online reversing is performed between rough rolling and finish rolling, and air cooling is performed after rolling.

[0019] In the manufacturing method of the present invention, the use of TC4 titanium alloy return material as raw material can significantly reduce the cost of raw materials.

[0020] In the manufacturing method described herein, the purpose of raw material mixing is to prevent localized segregation in the ingot and ensure uniform distribution of elements. Furthermore, simple briquetting facilitates raw material briquette transport, placement within the furnace, and pushing the material from the furnace chamber to the melting zone during smelting. Furthermore, the applied pressure squeezes out air from the gaps between individual raw material briquette blocks or particles, facilitating subsequent vacuuming.

[0021] In the manufacturing method described in the present invention, the purpose of homogenizing the titanium alloy ingot is that Cr and Fe are both slow eutectoid β-stabilizing elements, among which Cr is volatile and the solute equilibrium distribution coefficient of Fe is much less than 1. Therefore, homogenizing can better diffuse Cr and Fe elements and prevent the occurrence of β-spot defects, thereby obtaining a titanium alloy product with uniform element distribution.

[0022] In the manufacturing method described in the present invention, the use of single-pass, multi-pass, forging-free direct rolling not only improves production efficiency but also significantly reduces processing costs. The reason for the rolling speeds of rough rolling being slow first and then fast, and finishing rolling being fast first and then slow is that: during rough rolling in the single-phase region, the rolling speed is slow first and then fast. This not only stabilizes the equipment in the initial rolling stage, but also provides additional temperature compensation for the plate due to friction on the slab surface during high-speed rolling. During finishing rolling in the two-phase region, the rolling speed is fast first and then slow. After rough rolling, the equipment stability is essentially normal, preventing the plate from cooling too quickly, achieving the purpose of temperature compensation and rapid temperature increase, and ensuring stable rolling of the plate. The slow rolling speed at the end is to control the plate shape, facilitate the subsequent straightening process using the plate residual heat, and also control the microstructure, promote morphological changes in the lamellar α phase and its clusters to accumulate a large amount of deformation storage energy, facilitate subsequent annealing treatment, and thus obtain an ideal microstructure.

[0023] In addition, online reversing is performed between rough rolling and finishing rolling because texture is easily generated when metal materials are deformed in a single direction. Online reversing can weaken the texture and obtain titanium alloy plates with more uniform structure and properties.

[0024] Furthermore, in the batching step of the manufacturing method described in the present invention, the mass percentage of TC4 titanium alloy return material in all raw materials is ≥70%.

[0025] Furthermore, in the batching step of the manufacturing method described in the present invention, the ferrochrome raw material includes a ferrochrome alloy.

[0026] The use of low-cost ferrochrome alloy as ferrochrome raw material can further reduce costs.

[0027] Furthermore, in the ingot melting step of the manufacturing method described in the present invention, an electron beam cooling hearth furnace is used for melting.

[0028] In some embodiments, an electron beam cooling hearth furnace is used for smelting because: the temperature and vacuum degree of the electron beam cooling hearth furnace are relatively high during operation, which can effectively prevent the titanium alloy from combining with elements such as O, C, and N to form hard and brittle phases, thereby preventing these hard and brittle phases from acting as crack sources and rapidly expanding into crack defects during the next process.

[0029] In addition, the electron beam cold hearth furnace melting method has fewer steps than the traditional vacuum consumable melting method, and can obtain ingots with uniform element and microstructure distribution in a single refining, which not only significantly improves production efficiency but also reduces melting costs.

[0030] Furthermore, in the homogenization step of the manufacturing method described in the present invention, the homogenization temperature is 1050-1150° C., and the total homogenization time is ≥20 h.

[0031] Furthermore, in the homogenization treatment step of the manufacturing method described in the present invention, the temperature is raised to the homogenization temperature in a segmented manner, the heating rate of each segment decreases successively, and the heating rate of each segment is ≤3°C / min, and the holding time of each segment increases successively.

[0032] In some embodiments, the homogenization treatment adopts step-by-step heating and insulation because: the thermal conductivity of titanium alloy is much lower than that of alloys such as steel, and the step-by-step heating and insulation can effectively control the uniformity of temperature distribution on the surface and core of the titanium alloy ingot, thereby controlling the uniformity of element distribution.

[0033] Furthermore, in the rolling step of the manufacturing method of the present invention, the rough rolling temperature is T β + (50~100) ℃, where T β Indicates the phase transition point of titanium alloy, the rough rolling deformation is 35~70%, the rough rolling reduction per pass is ≤15%, and the rough rolling passes are ≥8 times.

[0034] Furthermore, in the rolling step of the manufacturing method of the present invention, the finishing rolling starting temperature is T β - (10 ~ 50) ℃, finishing deformation is 50 ~ 85%, finishing reduction per pass is ≤ 10%, finishing rolling passes are ≥ 10 times.

[0035] In the present invention, the reason for controlling the titanium alloy ingot to deform first in the single-phase region and then in the two-phase region is: on the one hand, the initial deformation in the single-phase region can fully break the as-cast characteristics, while the deformation in the two-phase region can obtain a microstructure with excellent comprehensive performance. One-time single-phase region + two-phase region deformation can achieve an effect similar to cross-β forging, thereby obtaining a microstructure with excellent comprehensive performance. On the other hand, the slab temperature is high and the titanium alloy has a low deformation resistance, the metal is easier to flow and obtain the target plate specifications.

[0036] In the present invention, the reason why the deformation amount of each pass is small and the number of passes is large during the rolling of the titanium alloy ingot is: the small deformation amount of the initial cast structure pass can prevent a single severe deformation from causing macro / micro defects such as adiabatic shear bands, cracks, plate warping and wave shapes in the titanium alloy ingot during rolling. More passes are not only more conducive to controlling the plate shape of the titanium alloy plate, but also can adjust the rolling process parameters in real time based on actual working conditions, thereby controlling the microstructure after rolling.

[0037] Furthermore, in the rolling step of the manufacturing method of the present invention, the rolling speed of the rough rolling ranges from slow to fast within the range of 2 to 5 m / s.

[0038] Furthermore, in the rolling step of the manufacturing method of the present invention, the rolling speed of the finishing rolling ranges from fast to slow within the range of 1 to 4 m / s.

[0039] Furthermore, in the rolling step of the manufacturing method of the present invention, the finishing rolling temperature is ≥750°C.

[0040] In some embodiments, the plate may be further prevented from cracking due to severe work hardening by controlling the finishing rolling temperature.

[0041] Furthermore, in the rolling step of the manufacturing method described in the present invention, the total deformation of the titanium alloy is ≥78%.

[0042] The low-cost, high-strength two-phase titanium alloy and its manufacturing method described in the present invention have the following advantages and beneficial effects compared to the prior art: The low-cost, high-strength two-phase titanium alloy of the present invention achieves good strength-plasticity matching through optimized composition design.

[0043] In some specific embodiments, the low-cost, high-strength two-phase titanium alloy of the present invention has a yield strength of 950-1080 MPa, a tensile strength of 1000-1150 MPa, and an elongation of ≥12%.

[0044] The low-cost, high-strength two-phase titanium alloy manufacturing method described in the present invention uses a high proportion of TC4 titanium alloy scrap as raw material, then adds a small amount of sponge titanium, an inexpensive ferrochromium master alloy and metallic aluminum, and uses electron beam cooling hearth furnace refining to obtain a single-melt casting titanium alloy ingot. Then, a high-efficiency, short-process forging-free direct rolling method is used to obtain a low-cost, high-strength two-phase titanium alloy plate. The entire process not only significantly reduces the raw material cost, ingot melting cost and processing cost, but also improves the performance of the material.

[0045] The low-cost and high-strength two-phase titanium alloy manufacturing method of the present invention can not only realize the large-scale utilization of TC4 titanium alloy return materials, but also obtain titanium alloy ingots with uniform target composition and microstructure distribution. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 The figure schematically shows a flow chart of the steps of the method for manufacturing the low-cost and high-strength two-phase titanium alloy according to the present invention.

[0047] Figure 2 The microstructure of the two-phase titanium alloy of Example 1 is shown.

[0048] Figure 3 The microstructure of the two-phase titanium alloy of Example 2 is shown.

[0049] Figure 4 The microstructure of the two-phase titanium alloy of Comparative Example 1 is shown. DETAILED DESCRIPTION

[0050] The low-cost, high-strength two-phase titanium alloy and its manufacturing method described in the present invention will be further explained and illustrated below in conjunction with the drawings and specific embodiments of the specification. However, such explanation and illustration do not constitute an undue limitation to the technical solution of the present invention.

[0051] Examples 1-5 and Comparative Examples Figure 1 The figure schematically shows a flow chart of the steps of the method for manufacturing the low-cost and high-strength two-phase titanium alloy according to the present invention.

[0052] like Figure 1 As shown, the two-phase titanium alloys of Examples 1-5 of the present invention are prepared by the following steps: Step 100: Ingredients: The raw materials include titanium sponge, ferrochrome or chromium and iron blocks, TC4 titanium alloy return material accounting for more than 70% by weight, and aluminum metal. In some specific embodiments, the aluminum metal may include aluminum beans.

[0053] In some specific embodiments, TC4 titanium alloy return materials need to be screened, classified, and degreased according to their shape and specifications before use, and the mass fractions of O, Al, and V elements in different parts must be detected. Combined with this data, sponge titanium with a purity of grade 1 or above, cheap ferrochrome intermediate alloys, or chromium blocks + iron blocks and aluminum beans can be specifically proportioned.

[0054] Step 200: Raw material mixing and briquetting: Titanium sponge, TC4 titanium alloys of different specifications, ferrochrome master alloy (or chromium block + iron block) and aluminum beans are placed in a mixing device and mixed thoroughly. They are then placed in a briquetting device and pressed into raw material blocks. Finally, the raw material blocks are dried.

[0055] Step 300: Ingot Melting: The dried raw material blocks are simultaneously placed in an electron beam cooling hearth furnace for single refining to produce a titanium alloy flat ingot. In some specific embodiments, the ingot cross-sectional specifications can be controlled to: width 700-2000 mm × thickness 200-400 mm.

[0056] In some more specific embodiments, the dried raw material blocks are placed in an electron beam cooling hearth furnace, which is then sealed and vacuumed. The purpose of the vacuuming process is to extract as much air as possible from the electron beam cooling hearth furnace to prevent the titanium alloy from being oxidized during the smelting process, thereby forming defects such as hard α phase or oxide scale. When the vacuum degree in the electron beam cooling hearth furnace is ≤0.01 torr, the electron gun is turned on. When all the electron guns are turned on, the raw material blocks in the electron beam cooling hearth furnace are first pushed to the melting zone to begin melting. The molten titanium liquid flows to different areas in the electron beam cooling hearth furnace, and the electron gun power in the area is promptly confirmed and adjusted to complete refining and casting. The titanium liquid finally flows into the crystallizer and is cast into a titanium alloy ingot. The ingot pulling speed can be adjusted in time based on the material properties and actual working conditions. Finally, the tail end of the titanium alloy ingot after casting is subjected to shrinkage feeding.

[0057] In some more specific embodiments, while ensuring that the mass fraction of volatile elements meets the expected target, the refining time of the titanium liquid in the molten pool can be appropriately extended to ensure the sufficient dissolution and diffusion of the alloying elements and improve the composition segregation of the ingot.

[0058] In some more specific embodiments, the vacuum treatment is continuously performed throughout the entire smelting process, and the vacuum degree is always maintained at ≤0.01 torr.

[0059] Step 400: Homogenization treatment: the homogenization temperature is 1050-1150° C., and the total homogenization time is ≥20 h.

[0060] In some specific embodiments, prior to homogenization, the material is first subjected to head cutting, milling, chamfering, ultrasonic flaw detection, and elemental testing. A titanium alloy high-temperature glass protective agent is then evenly coated on the surface. The material is then transferred to an electric furnace, heated to the homogenization temperature, and then heated and maintained to complete the homogenization process.

[0061] In some more specific embodiments, the length of the cut end of the titanium alloy slab ingot, including the dovetail portion used to clamp the titanium alloy slab ingot during ingot pulling, can be controlled to be ≥ 100 mm. This is because when the titanium alloy slab ingot is melted and cast in an electron beam cooling furnace, the head of the slab is under the electron gun for a long time, which can easily cause defects such as severe element burnout and segregation in the head of the slab.

[0062] In some more specific embodiments, the milling depth of the titanium alloy flat ingot can be controlled to be ≥3mm, including the upper surface, lower surface, overflow surface and non-overflow surface. This is because the electron beam cooling hearth furnace chamber is in a vacuum state, and the crystallizer is exposed to the atmospheric environment. Although the water cooling system of the copper crystallizer can accelerate the solidification of the titanium liquid, the temperature is still relatively high. After contact with the air, the flat ingot continues to cool down and the surface will be oxidized. On the other hand, in the process of pulling the ingot out of the crystallizer, some surface cracks that are not controllable by human factors will inevitably appear. Milling the surface can completely remove defects such as cracks and oxide scale on the surface of the flat ingot.

[0063] In the present invention, chamfering the titanium alloy flat ingot can prevent large stress concentration during the rolling process, facilitate the uniformity of metal flow during deformation, and prevent large edge cracks from occurring in the titanium alloy plate.

[0064] In the present invention, the titanium alloy surface is uniformly coated with a titanium alloy high-temperature glass protective agent because titanium alloy is extremely easy to oxidize at high temperatures to form an oxide scale, wherein the oxide scale is composed of a surface oxide layer and an oxygen-rich α layer close to the substrate. The former is easy to break and fall off during rolling or cooling, and the latter is hard and brittle and easily serves as a crack source during deformation. As the temperature rises, the oxygen element will continue to penetrate into the interior of the titanium alloy. The titanium alloy high-temperature glass protective agent will form a glass-like protective film at high temperatures, which can significantly reduce the contact area between the titanium alloy surface and the air and effectively prevent the influence of the oxygen element in the air on the titanium alloy flat ingot. In addition, the titanium alloy high-temperature glass protective agent also reduces the friction of the plate during rolling, thereby reducing the uneven deformation of the plate; at the same time, it plays a heat-insulating role to prevent the temperature of the plate from dropping too quickly.

[0065] In some specific embodiments, the temperature can be raised to a uniform temperature in a segmented manner, with the heating rate of each segment decreasing successively and the heating rate of each segment being ≤3°C / min, and the holding time of each segment increasing successively.

[0066] Step 500: rolling: a titanium alloy plate is obtained by single-fire multi-pass rolling. The rolling speed is first slow and then fast during rough rolling, and the rolling speed is first fast and then slow during finish rolling. The plate is air-cooled after rolling.

[0067] In some specific implementations, the cross-section (perpendicular to the rolling direction) of the titanium alloy plate may be controlled to have a specification of: 2400-5000 mm in transverse direction and 20-80 mm in thickness.

[0068] In some specific embodiments, the transfer time of the insulated titanium alloy flat ingot on the roller conveyor can be controlled to ≤60 seconds. The reason for controlling the transfer time of the titanium alloy flat ingot is that after the titanium alloy is removed from the furnace, the lower surface contacts the roller conveyor and the upper surface and sides contact the air, causing the overall temperature to drop rapidly. If the transfer time is too long, the surface temperature of the plate will be too low, which may easily cause cracks due to work hardening. In addition, the different boundary conditions between the upper and lower surfaces result in a large temperature difference, which may easily cause warping defects during rolling.

[0069] In some embodiments, the rough rolling temperature is T β + (50 ~ 100) ℃, rough rolling deformation is 35 ~ 70%, rough rolling reduction per pass ≤ 15%, rough rolling passes ≥ 8 times.

[0070] In some embodiments, the slab is reversed online after reaching a specified length, and the finishing rolling starting temperature is T β - (10 ~ 50) ℃, finishing deformation is 50 ~ 85%, finishing reduction per pass is ≤ 10%, finishing rolling passes are ≥ 10 times.

[0071] In some embodiments, the rough rolling speed is slow at first and then fast in the range of 2~5m / s, the finishing rolling speed is fast at first and then slow, and the finishing rolling speed is fast at first and then slow in the range of 4m / s~1m / s. When rolling is completed, the residual temperature of the plate is used to perform online straightening treatment on the rolling mill.

[0072] In some embodiments, the finishing rolling temperature may be controlled to be ≥750°C.

[0073] In some embodiments, the total deformation of the titanium alloy can be controlled to be ≥78%.

[0074] During the entire titanium alloy plate rolling process, the water control system including the dephosphorization water is closed.

[0075] Table 1 lists the mass percentage of each chemical element in the two-phase titanium alloys of Examples 1-5 of the present invention and the comparative alloys of the comparative example.

[0076] Table 1. (wt%, the balance is Ti and other unavoidable impurities except H, N and C) Note: The comparative example is TC4 titanium alloy.

[0077] Table 2-1 and Table 2-2 list the specific process parameters of the two-phase titanium alloys of Examples 1-5 of the present invention and the comparative alloy of Comparative Example 1.

[0078] Table 2-1. Table 2-2. The two-phase titanium alloys of Examples 1-5 and the comparative alloys of the comparative example were sampled and subjected to mechanical property tests and microstructural observations. Mechanical properties test and microstructure observation position: Based on the national standard GB / T 23604-2024, the middle of the head of the titanium alloy plate is more than 1000mm away from the edge, about one-third of the width in the width direction and one-quarter or one-half of the thickness in the thickness direction to obtain national standard tensile and microstructure samples; the microstructure can be obtained through inlaying, polishing, corrosion and other processes, and its observation position is the center position of the obtained sample.

[0079] Figure 2 The microstructure of the two-phase titanium alloy of Example 1 is shown.

[0080] like Figure 2 As shown, the microstructure of Example 1 of the present invention exhibits a typical lamellar structure. After rolling, the lamellar α phase and its clustered morphology are essentially curved, and the lamellar α phase boundaries are jagged, indicating that the lamellar α phase is undergoing dynamic spheroidization or recrystallization. This microstructure contains a large amount of deformation storage energy, which facilitates further manipulation of microstructure and performance in subsequent processes. Furthermore, the grain boundaries of the original high-temperature β grains also undergo significant dynamic spheroidization, resulting in relatively complete fragmentation. Combined with the morphological characteristics of the lamellar α phase, this indicates that the plate of Example 1 underwent forming across the phase transition point during rolling.

[0081] Figure 3 The microstructure of the two-phase titanium alloy of Example 2 is shown.

[0082] like Figure 3 As shown, the microstructure of Example 2 of the present invention exhibits similar characteristics to Example 1 in terms of its internal lamellar α phase and its clustered morphology, both exhibiting a substantially curved shape. Furthermore, the lamellar α phase grain boundaries exhibit a serrated shape, indicating that the microstructure under these conditions is also undergoing dynamic spheroidization or recrystallization. Furthermore, the original high-temperature β grain boundaries undergo relatively complete shattering due to dynamic spheroidization during rolling. Combined with the lamellar α phase morphology, this indicates that the plate in Example 2 also underwent forming across the phase transformation point during rolling.

[0083] Figure 4 The microstructure of the two-phase titanium alloy of the comparative example is shown.

[0084] like Figure 4As shown, the microstructure of the comparative example is a typical lamellar structure, with the inner lamellar α phase being straighter than that of Examples 1 and 2, and the lamellar α phase grain boundaries being relatively smooth. Furthermore, the grain boundaries of the original high-temperature β grains are generally wavy, indicating that the original high-temperature β grains are undergoing dynamic recovery at high temperatures. The presence of a very small amount of equiaxed α phase formed by the broken grain boundaries of the original high-temperature β grains in the microstructure indicates that the alloy undergoes a quasi-β forging-like formation during rolling using the current process.

[0085] In addition, combined Figure 2 、 Figure 3 and Figure 4 It can be seen that the deformation of the comparative example is close to the maximum, but the microstructure lamellar α phase does not undergo obvious bending and the degree of grain boundary breakage of the original high-temperature β grains is much lower than that of Examples 1 and 2, indicating that the two-phase titanium alloy flat ingot prepared by the method of the present invention is more conducive to the organizational evolution at the rolling rate of "rough rolling first slow and then fast, finishing rolling first fast and then slow", especially the morphological change of the lamellar α phase, and a more excellent microstructure can be obtained.

[0086] The obtained two-phase titanium alloys of Examples 1-5 and the comparative example were sampled again and subjected to mechanical property tests, and the test results are listed in Table 3. Mechanical properties testing: Tensile testing was performed on a Zwick Z100 electronic universal testing machine at a quasi-static rate. Each batch of tests was repeated at least three times, and the average value was taken to avoid data errors caused by processing defects and human measurement errors.

[0087] Table 3 lists the performance test results of the two-phase titanium alloys of Examples 1-5 of the present invention and the comparative example.

[0088] Table 3. As can be seen from Table 3 above, the yield strength of the two-phase titanium alloys of Examples 1-5 of the present invention are all between 959 and 1046 MPa, the tensile strength is all between 1025 and 1148 MPa, and the elongation is all greater than 12%. Compared with the TC4 titanium alloy in the comparative example, the strength is higher and the comprehensive performance of strength-plasticity matching is better.

[0089] It should be noted that the combination of the various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

[0090] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therefrom that can be directly derived from or easily conceived by those skilled in the art based on the disclosure of the present invention are intended to fall within the scope of protection of the present invention.

Claims

1. A low-cost, high-strength two-phase titanium alloy containing Ti and unavoidable impurity elements, characterized in that: It also contains the following chemical elements in the following mass percentages: Al: 5.0%~7.0%, V: 3.6%~4.5%, Cr: 0.4%~1.6%, Fe: 0.5%~1.3%, O: 0.06%~0.20%.

2. The two-phase titanium alloy according to claim 1, characterized in that The mass percentage of each chemical element is: Al: 5.0%~7.0%, V: 3.6%~4.5%, Cr: 0.4%~1.6%, Fe: 0.5%~1.3%, O: 0.06%~0.20%; the balance is Ti and other inevitable impurity elements.

3. The two-phase titanium alloy according to claim 1 or 2, characterized in that Among other inevitable impurities, H≤0.005%, N≤0.01%, and C≤0.03%.

4. The two-phase titanium alloy according to claim 1 or 2, characterized in that Its microstructure is lamellar.

5. The two-phase titanium alloy according to claim 4, characterized in that The lamellar α phase and its bundles in the lamellar structure are curved, and the lamellar α phase grain boundaries are serrated.

6. The two-phase titanium alloy according to claim 1 or 2, characterized in that Its yield strength is 950~1080MPa, tensile strength is 1000~1150MPa, and elongation is ≥12%.

7. The method for producing a two-phase titanium alloy according to any one of claims 1 to 6, wherein: Including steps: Ingredients: Raw materials include titanium sponge, ferrochrome raw materials, TC4 titanium alloy return materials and aluminum metal; Raw material mixing and briquetting; Ingot melting; Homogenization treatment; Rolling: One-pass multi-pass rolling is adopted. The rolling speed is slow at first and then fast during rough rolling, and fast at first and then slow during finish rolling. Online reversing is performed between rough rolling and finish rolling, and air cooling is performed after rolling.

8. The manufacturing method according to claim 7, wherein: In the batching step, the mass percentage of TC4 titanium alloy return material in the total raw materials is ≥70%.

9. The manufacturing method according to claim 7, wherein: In the batching step, the ferrochrome raw material includes ferrochrome alloy.

10. The manufacturing method according to claim 7, wherein: In the ingot melting step, an electron beam cooling hearth furnace is used for melting.

11. The manufacturing method according to claim 7, wherein: In the homogenization step, the homogenization temperature is 1050-1150° C., and the total homogenization time is ≥20 h.

12. The manufacturing method according to claim 11, wherein: In the homogenization treatment step, the temperature is raised to the homogenization temperature in a segmented manner, the heating rate of each segment decreases successively, and the heating rate of each segment is ≤3°C / min, and the holding time of each segment increases successively.

13. The manufacturing method according to claim 7, wherein: In the rolling step, the rough rolling temperature is T β + (50 ~ 100) ℃, rough rolling deformation is 35 ~ 70%, rough rolling reduction per pass ≤ 15%, rough rolling passes ≥ 8 times.

14. The manufacturing method according to claim 7, wherein: In the rolling step, the finishing rolling starting temperature is T β - (10 ~ 50) ℃, finishing deformation is 50 ~ 85%, finishing reduction per pass is ≤ 10%, finishing rolling passes are ≥ 10 times.

15. The manufacturing method according to claim 7, wherein: In the rolling step, the rolling speed of the rough rolling is from slow to fast in the range of 2 to 5 m / s.

16. The manufacturing method according to claim 7, wherein: In the rolling step, the rolling speed of the finishing rolling ranges from fast to slow within the range of 1 to 4 m / s.

17. The manufacturing method according to claim 7, wherein: In the rolling step, the finishing rolling temperature is ≥750°C.

18. The manufacturing method according to claim 7, wherein: During the rolling step, the total deformation of the titanium alloy is ≥78%.

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