A method for manufacturing wide and thick TC4ELI titanium alloy plates

Abstract

The invention relates to a method for manufacturing a wide-width and thick-gauge TC4ELI titanium alloy plate. The method comprises the following processes: grinding and spraying a titanium alloy flat ingot, heating, rolling, online hot straightening and annealing. Optimized spraying, heating and rolling processes, as well as flexible high-pressure water descaling and annealing processes are adopted to ultimately produce a wide-width TC4ELI titanium alloy medium and thick plate with a width of 2800 to 4000 mm and a thickness of more than 50 mm. This method solves the problem of surface cracks being easily generated during the production of thick and wide-gauge TC4ELI titanium alloy hot-rolled medium and thick plates, reduces the surface crack scrap rate from more than 10% to less than 2%, and satisfies plate shape control requirements without the need for subsequent offline straightening.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium alloy plate production, and in particular to a method for manufacturing a wide and thick TC4ELI titanium alloy plate with a thickness of more than 50 mm and a width greater than 2800 mm. Background Art

[0002] With technological advancements in aerospace, deep-sea exploration, shipbuilding, petroleum, chemical, and nuclear energy industries, demand for TC4ELI titanium alloy sheet is increasing, with requirements for high strength, high dimensional accuracy, good impact toughness, and weldability. Currently, the demand for wide-width, large-size titanium alloy sheet is growing. This is primarily due to the fact that using wide-width, large-size titanium alloy sheet with a thickness greater than 50 mm and a width greater than 2800 mm reduces the number of weld seams and weld material flaw detection during manufacturing, while also increasing resistance to impact loads during subsequent service and enhancing safety during pre-service. Furthermore, it significantly reduces factory prefabrication costs, shortens material procurement cycles, and increases construction speed. Therefore, this type of titanium alloy sheet has broad application prospects. Controlled rolling is a very effective method for simultaneously improving the strength and toughness of metal materials. However, due to the poor thermal conductivity, narrow processing window and poor process plasticity of titanium alloy, cracks are easily generated on the surface and corners of the rolled product; and the process of large deformation at a relatively low temperature will greatly increase the load on the rolling equipment, and put higher requirements on the capacity of the rolling equipment, thereby limiting the application of controlled rolling in the production of titanium alloy plates.

[0003] At present, the conventional process route of titanium alloy plates is characterized by "rushing temperature and fast rolling", that is, on the one hand, the rolling rhythm is required to be accelerated so that the heating temperature of the slab is at the upper limit of the (α+β) two-phase region or even above the alloy phase transformation point, so that the entire rolling process is in a relatively high temperature range as much as possible; on the other hand, the deformation during the rolling process should be small. The advantage of this process is that the deformation process can be completed under a lower rolling mill equipment load, but it inevitably increases the energy consumption of the entire rolling process; and the high final rolling temperature and small rolling deformation will have an adverse effect on the uniformity and refinement of the plate structure, and the improvement of comprehensive performance. In addition, due to the low elastic modulus of titanium alloy, the plate is prone to broken waves as the plate thickness increases, and the plate shape control is more difficult, resulting in the inability to meet the automatic welding requirements during subsequent use, seriously affecting customer use. This type of plate is characterized by thick rolled pieces and is extremely sensitive to rolling forces and temperature changes. During production, problems such as wave-shaped and scrapped steel are very likely to occur. The scrap rate is high, and the rolled steel plate will have a shape similar to corrugated board, resulting in excessive flatness and difficulty in achieving mass production capacity. Furthermore, due to its low elastic modulus and large rebound, the cold plate cannot be flattened and saved using cold levelers and flattening machines. This significantly increases the manufacturing cost of thick-gauge titanium alloy plates and extends the delivery cycle. Therefore, solving the plate shape problem of the TC4ELI titanium alloy with a thickness of more than 50mm and a width greater than 2800mm, while avoiding edge and surface cracks and improving its strength and toughness, is the key to the development of thick-gauge and wide-width TC4ELI titanium alloy plates.

[0004] To date, there has been limited research, both domestically and internationally, on methods for effectively controlling the toughness, flatness, and surface cracking of thick, wide TC4ELI titanium alloy plates. Chinese patent application publication number CN 103203361 A discloses a "Method for Rolling Wide Thick TC4 Titanium Alloy Plates." This method utilizes low-temperature, high-deformation, two-pass rolling. By rapidly cooling the plate after each pass, water cooling is performed to preserve the low-temperature, high-deformation microstructure, thereby ensuring that the plate performance meets requirements. However, the plate shape control standards are unclear, and the plate width is less than 2800 mm. Chinese patent application publication number CN 108838208 A discloses a "Method for Two-Pass Rolling of Wide TC4 Titanium Alloy Billets." This method utilizes appropriate heating and soaking processes, along with a two-pass rapid warming rolling process, effectively preventing buckling, warping, and other phenomena caused by temperature drops during the slab rolling process. However, the plate thickness is 42-46mm and the width is 3800-3900mm, and the manufacturing process for titanium alloy plates thicker than 50mm is not covered. Chinese patent application publication number CN 103203361 A discloses a "rolling method for wide and thick TC4 titanium alloy plates," which uses low-temperature, large-deformation, two-pass rolling. By water-cooling each pass to achieve rapid cooling, the low-temperature, large-deformation structure is retained, thereby ensuring that the plate performance meets the requirements. However, the product performance cannot meet the technical requirements for deep-sea service, and the plate width is less than 2800mm. Furthermore, the use of two-pass rolling increases energy consumption and process costs.

[0005] The journal article "Effect of Rolling Process on the Microstructure and Mechanical Properties of Ultra-Wide Thick Plates of TC4ELI Titanium Alloy" (written by Li Rui et al., "Journal of Materials Heat Treatment", Issue 1, 2020) mainly ensures the mechanical properties of the plate by optimizing and controlling the rolling phase transition point temperature range, but it does not clearly explain the plate width and thickness group spacing and plate shape requirements suitable for production.

[0006] While the titanium alloy sheet manufacturing methods disclosed in the aforementioned documents improve the sheet's mechanical properties and microstructure uniformity, they fail to meet the plate shape, surface crack control, and performance requirements for deep-sea space service in ultra-wide TC4ELI titanium alloy sheets with a thickness of 50 mm or greater and a width greater than 2800 mm. The technical solution provided by the present invention effectively overcomes the shortcomings of the aforementioned prior art and addresses the issues of plate shape, surface cracking, through-thickness microstructure uniformity, and performance when producing TC4ELI titanium alloy sheets with a thickness of 50 mm or greater and a width greater than 2800 mm from titanium alloy slabs with a thickness of 200 to 400 mm. Summary of the Invention

[0007] The present invention provides a method for manufacturing wide-width and thick-gauge TC4ELI titanium alloy plates. The method adopts optimized spraying, heating and rolling processes, as well as flexible high-pressure water descaling and annealing processes, to ultimately produce wide-width medium and thick TC4ELI titanium alloy plates with a width of 2800 to 4000 mm and a thickness of more than 50 mm. The method solves the problem of surface cracks being easily generated during the production of thick-gauge and wide-width hot-rolled medium and thick TC4ELI titanium alloy plates, reduces the scrap rate due to surface cracks from more than 10% to less than 2%, and satisfies the plate shape control requirements without the need for subsequent offline straightening treatment.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for manufacturing wide and thick TC4ELI titanium alloy plates includes grinding, spraying, heating, rolling, online heat straightening, and annealing of titanium alloy flat ingots. The specific process is as follows:

[0010] 1) Grinding and spraying of titanium alloy flat ingots;

[0011] The titanium alloy slabs are subjected to full surface grinding online with temperature, and the surface of the ground titanium alloy slabs is sprayed with high temperature anti-oxidation coating;

[0012] 2) heating;

[0013] The titanium alloy slab is heated in a heating furnace. The preheating temperature is 810-860°C and the holding time is 35-60 minutes. The first heating temperature is 890-920°C and the holding time is 35-55 minutes. The second heating temperature is 965-980°C and the holding time is 45-60 minutes. The soaking temperature is 1000-1030°C and the holding time is 150-180 minutes. At the same time, the air-fuel ratio in the soaking section is controlled at 1:1.8-1:2.3 to ensure that the temperature difference between the upper and lower surfaces of the titanium alloy slab is within 20°C.

[0014] 3) rolling;

[0015] Before rolling, the roller cooling water is turned off; the titanium alloy flat ingot is rolled back and forth, first horizontally and then vertically; during horizontal rolling, the reduction rate of a single pass is 25% to 35%; during vertical rolling, at least the first three passes use a large reduction rate, and the reduction rate of a single pass is 20% to 30%; during the rolling process, the rollers are cooled in sections, and when rolling the head section, the roller cooling water volume is 150 to 200 m 3 / h; when rolling the middle section, the water volume of the roller should be 200~250m 3 / h; when rolling the tail section, the water volume of the roller is 150~200m 3 / h; in the longitudinal rolling stage, at least the first three passes are sprayed with descaling water, the descaling water pressure is 10-15MPa, and the descaling time for each pass is 10-20s; the rolling speed is 2-4.5m / s, the final rolling temperature is ≥800℃, and the post-rolling ejection speed is 4-6.5m / s; during the rolling process, the roller speed is adjusted to compensate, the upper and lower roller speed difference is controlled at -2.5% to -1.0%, and the final pass reduction is controlled within 1mm;

[0016] 3) Online thermal straightening;

[0017] At least three straightening passes are required; the straightening temperature for hot straightening is 720-760°C, the straightening force is 1500-2000kN, the bending amount is 1.5-3.0mm, and the tilting value is 3-6mm;

[0018] 4) Annealing treatment;

[0019] Before entering the furnace, steel plates with a thickness of more than 80 mm are placed on the upper and lower surfaces of the titanium alloy plate, and nickel-based alloy pads with good thermal conductivity are placed between the steel plate and the titanium plate; the annealing temperature is 830-880°C, the annealing time is 4-6 hours, and the plate is air-cooled after being taken out of the furnace.

[0020] Furthermore, the chemical composition of the TC4ELI titanium alloy plate is as follows by weight: O: 0.08% to 0.12%, Fe: 0.20% to 0.25%, C≤0.07%, H≤0.012%, Al: 5.5% to 6.5%, V: 3.8% to 4.5%, and the remainder is Ti and unavoidable impurity elements.

[0021] Furthermore, the TC4ELI titanium alloy plate has a thickness of more than 50 mm and a width of more than 2800 mm.

[0022] Furthermore, the preparation process of the titanium alloy flat ingot is as follows: using first-grade titanium sponge, Al-V master alloy, and high-purity Al with an Al content of ≥99.9% as furnace materials, pressing electrodes, and smelting in an EB furnace to obtain the titanium alloy flat ingot.

[0023] Furthermore, the size of the titanium alloy slab is thickness×width×length=200-400 mm×1650-1950 mm×2500-4000 mm.

[0024] Furthermore, in the step 1), the surface roughness of the titanium alloy slab after grinding is Ra≤60 μm.

[0025] Furthermore, in the step 1), the high-temperature anti-oxidation coating sprayed on the surface of the titanium alloy slab is a nano-SiO2 anti-oxidation coating with a thickness of 0.6 to 1.0 mm.

[0026] Furthermore, in step 2), 2 to 4 vacancies are left at the furnace head of the soaking section of the heating furnace.

[0027] Furthermore, in step 3), the total length of the titanium alloy ingot is L, the head section is a 1 / 4L length section, the middle section is a 1 / 4L-3 / 4L length section, and the tail section is a 1 / 4L length section.

[0028] Furthermore, the mechanical properties of the finished titanium alloy plate are: yield strength ≥890MPa, tensile strength ≥960MPa, elongation ≥15%, and transverse KV2 ≥60J at room temperature; the surface grain size of the finished titanium alloy plate is consistent with the central grain size grade, and the grain size is above level 5; the flatness of the finished titanium alloy plate is below 5mm / 2m.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1) The titanium alloy plate of the present invention has a reasonable design composition. By limiting the content of O and Fe elements, the O and Fe contents in the titanium alloy are ensured to be 0.08% to 0.12% and 0.20% to 0.25%, respectively. When the oxygen content is high, oxygen atoms enter the interior of the titanium alloy, generating second-type internal stress, causing lattice deformation of the titanium alloy, increasing resistance to dislocation movement, and improving the strength of the TC4ELI titanium alloy. Fe, as a strong β-phase stabilizing element, is added to the titanium alloy mainly to form a TiFe intermediate phase. This ensures that when the amount of O added is limited, the strength of the TC4ELI titanium alloy can be improved by increasing the impurity Fe content, thereby compensating for the insufficient strength of the TC4ELI titanium alloy caused by the limited O content.

[0031] 2) High-temperature nano-SiO2 anti-oxidation coating is sprayed on the ground titanium alloy ingot in three dimensions to prevent the titanium alloy ingot from coming into contact with open flames during the heating process in a walking beam heating furnace. This will cause a large amount of Widmanstätten β phase structure to form on the surface due to overburning, resulting in uncoordinated deformation of the two phases in the subsequent rolling process and surface cracks.

[0032] 3) A high heating temperature is adopted while ensuring the time of the soaking section and the heating section in the furnace, and the air-fuel ratio is controlled, thereby shortening the temperature difference between the surface and the core of the titanium alloy slab. At the same time, 2 to 4 vacancies are left in the furnace head of the soaking section of the heating furnace to prevent the low furnace head temperature from affecting the heating uniformity of the titanium alloy slab; thereby ensuring the uniformity of the lateral and longitudinal metal flow on the upper and lower surfaces during the rolling process of the titanium alloy plate.

[0033] 4) Rolling and high-pressure water descaling: Before rolling, the roller cooling water in the rough rolling to hot straightening area is turned off to avoid a large amount of cooling water flowing on the lower surface of the intermediate billet and causing an uncontrolled temperature drop, thereby increasing the rolling passes. It is also beneficial to control the intermediate billet to maintain a horizontal or slightly upward state, creating conditions for the rolling mill to bite; the rollers are cooled in sections to avoid a large amount of cooling water flowing on the plate surface and causing an uncontrolled temperature drop, thereby increasing the rolling passes; by reasonably controlling the cooling water volume of the rollers, the roller shape is effectively controlled, and the irregular deviation and sickle bending defects caused by the uneven temperature distribution of the head, middle and tail of the intermediate billet during the rolling process are greatly improved; the properties (anisotropy) of the alloy plate are improved by reversing rolling, and a large reduction rate is used in the transverse rolling stage and the first two passes of the longitudinal rolling stage to promote the transformation During the forming process, the original β phase grains are elongated or broken, and at the same time, the precipitation of secondary α phase in the β phase is promoted, resulting in the refinement of grains from the surface to the center of the EB flat ingot; by controlling the reduction rate of the middle pass in the longitudinal rolling stage, it is possible to ensure the coordination of the deformation of the two phases and suppress the generation of cracks, while also ensuring sufficient reduction rate to promote the spheroidization of the lamellar structure into an equiaxed structure; in the first three passes of the longitudinal rolling stage, the mill sprays water to remove scales for surface cooling, so that a temperature gradient is generated between the surface and the center of the center billet, thereby making the deformation resistance of the plate surface greater than that of the center, which is conducive to the expansion of deformation from the surface to the center; during the rolling process, the roller speed compensation is adjusted to control the speed difference between the upper and lower rollers to ensure that there is no goose head wave before the initial plate shape enters the hot straightening machine, and the reduction in the last pass is controlled within 1mm to flatten the plate shape and reduce the stress in the plate.

[0034] 5) By controlling the straightening temperature, the difference in the two-phase ratio is reduced, the internal stress is fully released, and the plate is straightened after the internal stress is fully released, avoiding the generation of large internal stress due to phase change; by setting the appropriate bending roller amount and tilting value, the straightness of the straightened plate is guaranteed to be good.

[0035] 6) By increasing the annealing temperature, the lamellar α phase is promoted to become wider and the aspect ratio is reduced, ensuring the refinement of the structure. The fine structure hinders the slip during plastic deformation, thereby improving the strength of the material; at the same time, extending the furnace time promotes the increase in the size of some lamellar or needle-shaped α phases, thereby improving plastic toughness.

[0036] 7) Before annealing, steel plates with a thickness of more than 80 mm are arranged on the upper and lower surfaces of the titanium alloy plate, and nickel-based alloy pads with good thermal conductivity are placed between the steel plates and the titanium alloy plates to ensure that the titanium alloy plate is heated evenly during the annealing process. At the same time, it also prevents the titanium alloy plate from directly contacting the roller and air after being taken out of the furnace, which may cause the upper and lower surfaces to cool too quickly, and utilizes the gap between the pads and the steel plates to cool evenly and slowly. In addition, by arranging steel plates with a thickness of more than 80 mm on the upper and lower surfaces of the titanium alloy plate, the titanium alloy plate can also be flattened by the dead weight of the steel plates during high-temperature annealing, ensuring that the flatness of the high-strength TC4ELI titanium alloy plate with a thickness of more than 50 mm and a width of more than 2800 mm meets the use requirements.

[0037] 8) The present invention produces TC4ELI titanium alloy plates with a thickness of 50 mm or more and a width of 2800 mm or more through systematic optimization of various aspects, including composition, surface grinding and spraying of anti-oxidation coatings on titanium alloy slabs, heating, rolling, straightening, and heat treatment processes. This solves the problem of surface cracks that are easily generated during the production of wide and thick titanium alloy medium and thick plates, reducing the scrap rate due to surface cracks from the conventional 10% or more to less than 2%. Furthermore, the plate shape control requirements (straightness below 5 mm / 2 m) can be met without the need for subsequent offline straightening treatment. The mechanical properties of the titanium alloy plates are as follows: yield strength ≥890 MPa, tensile strength ≥960 MPa, elongation ≥15%, transverse KV2 ≥60 J at room temperature, and the surface grain size is consistent with the central grain size, with the grain size being above grade 5. DETAILED DESCRIPTION

[0038] The present invention provides a method for manufacturing a wide and thick TC4ELI titanium alloy plate, which includes grinding, spraying, heating, rolling, online heat straightening, and annealing of a titanium alloy flat ingot. The specific process is as follows:

[0039] 1) Grinding and spraying of titanium alloy flat ingots;

[0040] The titanium alloy slabs are subjected to full surface grinding online with temperature, and the surface of the ground titanium alloy slabs is sprayed with high temperature anti-oxidation coating;

[0041] 2) heating;

[0042] The titanium alloy slab is heated in a heating furnace. The preheating temperature is 810-860°C and the holding time is 35-60 minutes. The first heating temperature is 890-920°C and the holding time is 35-55 minutes. The second heating temperature is 965-980°C and the holding time is 45-60 minutes. The soaking temperature is 1000-1030°C and the holding time is 150-180 minutes. At the same time, the air-fuel ratio in the soaking section is controlled at 1:1.8-1:2.3 to ensure that the temperature difference between the upper and lower surfaces of the titanium alloy slab is within 20°C.

[0043] 3) rolling;

[0044] Before rolling, the roller cooling water is turned off; the titanium alloy flat ingot is rolled back and forth, first horizontally and then vertically; during horizontal rolling, the reduction rate of a single pass is 25% to 35%; during vertical rolling, at least the first three passes use a large reduction rate, and the reduction rate of a single pass is 20% to 30%; during the rolling process, the rollers are cooled in sections, and when rolling the head section, the roller cooling water volume is 150 to 200 m 3 / h; when rolling the middle section, the water volume of the roller should be 200~250m 3 / h; when rolling the tail section, the water volume of the roller is 150~200m 3 / h; in the longitudinal rolling stage, at least the first three passes are sprayed with descaling water, the descaling water pressure is 10-15MPa, and the descaling time for each pass is 10-20s; the rolling speed is 2-4.5m / s, the final rolling temperature is ≥800℃, and the post-rolling ejection speed is 4-6.5m / s; during the rolling process, the roller speed is adjusted to compensate, the upper and lower roller speed difference is controlled at -2.5% to -1.0%, and the final pass reduction is controlled within 1mm;

[0045] 3) Online thermal straightening;

[0046] At least three straightening passes are required; the straightening temperature for hot straightening is 720-760°C, the straightening force is 1500-2000kN, the bending amount is 1.5-3.0mm, and the tilting value is 3-6mm;

[0047] 4) Annealing treatment;

[0048] Before entering the furnace, steel plates with a thickness of more than 80 mm are placed on the upper and lower surfaces of the titanium alloy plate, and nickel-based alloy pads with good thermal conductivity are placed between the steel plate and the titanium plate; the annealing temperature is 830-880°C, the annealing time is 4-6 hours, and the plate is air-cooled after being taken out of the furnace.

[0049] Furthermore, the chemical composition of the TC4ELI titanium alloy plate is as follows by weight: O: 0.08% to 0.12%, Fe: 0.20% to 0.25%, C≤0.07%, H≤0.012%, Al: 5.5% to 6.5%, V: 3.8% to 4.5%, and the remainder is Ti and unavoidable impurity elements.

[0050] Furthermore, the TC4ELI titanium alloy plate has a thickness of more than 50 mm and a width of more than 2800 mm.

[0051] Furthermore, the preparation process of the titanium alloy flat ingot is as follows: using first-grade titanium sponge, Al-V master alloy, and high-purity Al with an Al content of ≥99.9% as furnace materials, pressing electrodes, and smelting in an EB furnace to obtain the titanium alloy flat ingot.

[0052] Furthermore, the size of the titanium alloy slab is thickness×width×length=200-400 mm×1650-1950 mm×2500-4000 mm.

[0053] Furthermore, in the step 1), the surface roughness of the titanium alloy slab after grinding is Ra≤60 μm.

[0054] Furthermore, in the step 1), the high-temperature anti-oxidation coating sprayed on the surface of the titanium alloy slab is a nano-SiO2 anti-oxidation coating with a thickness of 0.6 to 1.0 mm.

[0055] Furthermore, in step 2), 2 to 4 vacancies are left at the furnace head of the soaking section of the heating furnace.

[0056] Furthermore, in step 3), the total length of the titanium alloy ingot is L, the head section is a 1 / 4L length section, the middle section is a 1 / 4L-3 / 4L length section, and the tail section is a 1 / 4L length section.

[0057] Furthermore, the mechanical properties of the finished titanium alloy plate are: yield strength ≥890MPa, tensile strength ≥960MPa, elongation ≥15%, and transverse KV2 ≥60J at room temperature; the surface grain size of the finished titanium alloy plate is consistent with the central grain size grade, and the grain size is above level 5; the flatness of the finished titanium alloy plate is below 5mm / 2m.

[0058] The present invention provides a method for manufacturing a wide and thick TC4ELI titanium alloy plate with a thickness of more than 50 mm and a width of more than 2800 mm. The chemical composition of the titanium alloy plate includes, by weight percentage, the following: O 0.08% to 0.12%, Fe 0.20% to 0.25%, C ≤ 0.07%, H ≤ 0.012%, Al 5.5% to 6.5%, V 3.8% to 4.5%, and the balance is Ti and unavoidable impurity elements.

[0059] First, using first-grade titanium sponge, Al-V master alloy, and high-purity Al (Al content of more than 99.9%) as furnace charge, the electrodes are pressed and smelted in an electron beam cooling hearth furnace (EB furnace) to obtain TC4ELI titanium alloy flat ingots (hereinafter referred to as titanium alloy flat ingots) with a size of (200-400) mm thick × (1650-1950) mm wide × (2500-4000) mm long. The ingots are then rolled in a medium and heavy plate reciprocating rolling mill to obtain TC4ELI titanium alloy ultra-wide plates with a thickness of more than 50 mm and a width greater than 2800 mm. The production process includes grinding and spraying the titanium alloy flat ingots → heating → rolling → online hot straightening → annealing. The reasons for selecting the process and parameters are as follows:

[0060] 1) Grinding and spraying of titanium alloy slabs: The titanium alloy slabs are subjected to full-surface grinding online with temperature, and the grinding wheel is used to grind the entire surface in three dimensions to remove surface oxide scale and defects to achieve a surface roughness of Ra ≤ 60 μm; the surface of the ground titanium alloy slabs is sprayed with high-temperature nano-SiO2 anti-oxidation coating with a spraying thickness of 0.6 to 1.0 mm.

[0061] 2) Heating: The titanium alloy slab (thickness of 200-400mm) is fed into a walking beam heating furnace for heating, and then taken out of the furnace after passing through the preheating section, heating section and soaking section in sequence; the temperature range of the preheating section is 810-860℃, and the holding time is 35-60min. This process promotes the initial diffusion of elements such as O, Fe, C, H, Al and V in the titanium alloy slab into the matrix; the temperature range of the first heating section is 890-920℃, and the holding time is 35-55min; the temperature range of the second heating section is 965-980℃, and the holding time is 100-1100℃. The time is 45 to 60 minutes; the temperature range of the soaking section is 1000 to 1030 ° C, the holding time is 150 to 180 minutes, and the air-fuel ratio of the soaking section is controlled to be 1:1.8 to 1:2.3. After the above heating process, the temperature difference between the upper and lower surfaces of the titanium alloy ingot is guaranteed to be within 20 ° C, so that elements such as O, Fe, C, H, Al and V are fully diffused in the matrix. By controlling the time of each section in the furnace, the ratio of α and β phases is guaranteed, and by controlling the evolution and distribution state of the needle-shaped β phase in the soaking section, the performance of the titanium alloy plate is finally guaranteed. In addition, 2 to 4 vacancies are left in the furnace head of the soaking section of the heating furnace to prevent the low furnace head temperature from affecting the heating uniformity of the titanium alloy ingot.

[0062] 3) Rolling and high-pressure water descaling: Before rolling, the roller cooling water in the rough rolling to hot straightening area is turned off to avoid a large amount of cooling water flowing on the lower surface of the intermediate billet and causing uncontrolled temperature drop, thereby increasing the number of rolling passes. It is also beneficial to control the intermediate billet to remain horizontal or slightly upturned, creating conditions for the rolling mill to bite; a wide-width medium and heavy plate rolling mill is used to roll the billet (titanium alloy flat ingot) back and forth, first horizontally and then longitudinally. During transverse rolling, the reduction rate of a single pass is 25% to 35%; during longitudinal rolling, it is preferred that a large reduction rate be used in the first three passes, and the reduction rate of a single pass be 20% to 30%; by reversing rolling, the performance (anisotropy) of the titanium alloy plate is improved, and it is preferred that a large reduction rate be used in the transverse rolling stage and the first two passes of the longitudinal rolling stage to promote the elongation or crushing of the original β phase grains during the deformation process, and at the same time promote the precipitation of secondary α phase transformation in the β phase, providing driving force for the subsequent spheroidization and transformation of the β phase lamellar structure into an equiaxed structure; during the rolling process, the rollers are cooled in sections, and it is preferred that the cooling water volume of the rollers be 150 to 200 m3 when the 1 / 4L length section of the rolling head is rolled. 3 / h; when rolling the middle 1 / 4L-3 / 4L length section, the water volume of the roller is 200-250m 3 / h; when rolling the 1 / 4L length section at the tail, the water volume of the roller is 150~200m 3 / h open; by adjusting the water volume of the rolls and reasonably controlling the cooling water volume, the roll shape can be effectively controlled, and at the same time, the problems of irregular deviation during the rolling process caused by the uneven temperature distribution of the head, middle and tail of the titanium alloy flat ingot are greatly improved. It is preferred that the first three passes of the longitudinal rolling stage are sprayed with descaling water, the descaling water pressure is 10-15MPa, the descaling time for each pass is 10-20s, the rolling speed is 2-4.5m / s, the final rolling temperature is ≥800℃, and the post-rolling ejection speed is 4-6.5m / s; during the rolling process, the roll speed is adjusted to compensate, and the speed difference between the upper and lower rolls is controlled at -2.5% to -1.0% to ensure that there is no goose head wave in the initial plate shape of the titanium alloy plate before entering the pre-straightening machine; it is preferred that the reduction in the last pass is controlled within 1mm to flatten the plate shape and reduce the stress in the plate.

[0063] 4) Online hot straightening: Hot straightening is preferably carried out in three steps. The straightening temperature of hot straightening is 720-760℃, the straightening force is between 1500-2000kN, the bending roller amount is set to 1.5-3.0mm, and the tilting value is set to 3-6mm. By reducing the difference in the two-phase ratio, the internal stress is fully released, and the internal stress of the titanium alloy plate is fully released before straightening, avoiding large internal stress due to rapid phase change. By setting appropriate bending roller amount, straightening force and tilting value, the straightness of the plate after straightening is guaranteed to be good.

[0064] 5) Annealing treatment: Before entering the furnace, steel plates with a thickness of more than 80 mm are placed on the upper and lower surfaces of the titanium alloy plate, and nickel-based alloy pads with good thermal conductivity are placed between the steel plates and the titanium alloy plate (head-middle-tail, 3 can be placed in each position, a total of 9); the annealing temperature is 830-880 ° C, the time is 4-6 hours, and the plate is air-cooled after being taken out of the furnace. Placing thick steel plates and heat-resistant nickel-based alloy pads on the upper and lower surfaces can ensure that the titanium alloy plate is heated evenly during the annealing process, and at the same time avoid direct contact between the titanium alloy plate and the roller and air after being taken out of the furnace, resulting in excessively fast cooling of the upper and lower surfaces. The gap between the pads and the steel plates is used for uniform and slow cooling; in addition, by arranging steel plates with a thickness of more than 80 mm on the upper and lower surfaces, the titanium alloy plate can be flattened by the weight of the steel plates during high-temperature annealing.

[0065] By adopting the above-mentioned components and process scheme, the present invention solves the problem of surface cracks easily generated during the production of TC4ELI titanium alloy wide and thick-gauge plates with a thickness of more than 50 mm and a width of more than 2800 mm. The surface crack scrap rate is reduced from the conventional more than 10% to less than 2%. At the same time, the plate shape control requirements (straightness less than 5 mm / 2 m) can be met without subsequent offline straightening treatment. The mechanical properties of the prepared titanium alloy plates are: yield strength ≥890 MPa, tensile strength ≥960 MPa, elongation ≥15%, room temperature transverse KV2 ≥60 J, the surface grain size is consistent with the center grain size grade, and the grain size is above grade 5.

[0066] The following examples are implemented on the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operating processes, but the protection scope of the present invention is not limited to the following examples.

[0067] [Example]

[0068] Table 1 shows the chemical composition of the titanium alloy plates in each embodiment, Table 2 shows the grinding requirements and heating system of the titanium alloy slabs in each embodiment, Table 3 shows the rolling process parameters of each embodiment, Table 4 shows the high-pressure water descaling process parameters in the longitudinal rolling stage of each embodiment, Table 5 shows the straightening parameters and annealing process parameters of each embodiment, and Table 6 shows the finished product size, performance and quality indicators of the TC4ELI titanium alloy plates in each embodiment.

[0069] Table 1 Chemical composition of titanium alloy plates in various embodiments (wt, %)

[0070]

[0071]

[0072] Note: The remainder is Ti and unavoidable impurity elements

[0073] Table 2 Grinding requirements and heating system of titanium alloy slabs in each embodiment

[0074]

[0075] Table 3 Rolling process parameters of each embodiment

[0076]

[0077] Table 4 High-pressure water descaling process parameters in the longitudinal rolling stage of each embodiment

[0078]

[0079] Table 5 Straightening parameters and annealing process parameters of each embodiment

[0080]

[0081] Table 6 Dimensions, properties and quality indicators of finished TC4ELI titanium alloy plates of various examples

[0082]

[0083] It can be seen that compared with the existing technology, the manufacturing method of a wide and thick TC4ELI titanium alloy plate described in the present invention solves the problems in plate shape, surface cracks, thickness direction uniformity and performance when using 200-400mm thick titanium alloy slabs to produce TC4ELI titanium alloy plates with a thickness of more than 50mm and a width greater than 2800mm.

[0084] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for manufacturing a wide and thick TC4ELI titanium alloy plate, characterized in that: The chemical composition of the TC4ELI titanium alloy plate is as follows by weight: O: 0.08% to 0.12%, Fe: 0.20% to 0.25%, C ≤ 0.07%, H ≤ 0.012%, Al: 5.5% to 6.5%, V: 3.8% to 4.5%, with the remainder being Ti and unavoidable impurity elements; the TC4ELI titanium alloy plate has a thickness of at least 50 mm and a width of at least 2800 mm; the manufacturing method includes grinding and spraying of titanium alloy slabs, heating, rolling, online hot straightening, and annealing. The specific process is as follows: 1) Grinding and spraying of titanium alloy flat ingots; The titanium alloy slab is prepared by using first-grade titanium sponge, Al-V master alloy, and high-purity Al with an Al content of ≥99.9% as furnace charge, pressing electrodes, and smelting in an EB furnace to obtain a titanium alloy slab; the titanium alloy slab has a size of thickness × width × length = 200-400 mm × 1650-1950 mm × 2500-4000 mm; the titanium alloy slab is subjected to hot online full-surface grinding, and the surface roughness after grinding is Ra ≤ 60 μm; the surface of the ground titanium alloy slab is sprayed with a high-temperature anti-oxidation coating, which is a nano-SiO2 anti-oxidation coating with a thickness of 0.6-1.0 mm; 2) heating; The titanium alloy slab is heated in a heating furnace, with 2 to 4 vacancies left at the furnace head of the soaking section. The preheating section temperature is 810 to 860°C, with a holding time of 35 to 60 minutes. The first heating section temperature is 890 to 915°C, with a holding time of 35 to 55 minutes. The second heating section temperature is 965 to 980°C, with a holding time of 45 to 60 minutes. The soaking section temperature is 1000 to 1030°C, with a holding time of 155 to 180 minutes. At the same time, the air-fuel ratio in the soaking section is controlled at 1:1.8 to 1:2.3 to ensure that the temperature difference between the upper and lower surfaces of the titanium alloy slab is within 20°C. 3) rolling; Before rolling, the roller cooling water is turned off; the titanium alloy flat ingot is rolled back and forth, first horizontally and then vertically; during horizontal rolling, the reduction rate of a single pass is 25% to 35%; during vertical rolling, at least the first three passes adopt a large reduction rate, and the reduction rate of a single pass is 20% to 30%; during the rolling process, the rollers are cooled in sections, the total length of the titanium alloy flat ingot is L, the head section is the head 1 / 4L length section, the middle section is the 1 / 4L-3 / 4L length section, and the tail section is the tail 1 / 4L length section; when rolling the head section, the roller cooling water volume is 150 to 200m 3 / h; when rolling the middle section, the water volume of the roller should be 200~250m 3 / h; when rolling the tail section, the water volume of the roller is 150~200m 3 / h; in the longitudinal rolling stage, at least the first three passes are sprayed with descaling water, the descaling water pressure is 10-15MPa, and the descaling time for each pass is 10-20s; the rolling speed is 2-4.5m / s, the final rolling temperature is ≥800℃, and the post-rolling ejection speed is 4-6.5m / s; during the rolling process, the roller speed is adjusted to compensate, the upper and lower roller speed difference is controlled at -2.5% to -1.0%, and the final pass reduction is controlled within 1mm; 4) Online thermal straightening; At least three straightening passes are required; the straightening temperature for hot straightening is 720-760°C, the straightening force is 1500-2000kN, the bending amount is 1.5-3.0mm, and the tilting value is 3-6mm; 5) Annealing treatment; Before entering the furnace, steel plates with a thickness of more than 80 mm are placed on the upper and lower surfaces of the titanium alloy plate, and nickel-based alloy pads with good thermal conductivity are placed between the steel plate and the titanium plate; the annealing temperature is 830-880°C, the annealing time is 4.2-6 hours, and the plate is air-cooled after being taken out of the furnace; The mechanical properties of the finished titanium alloy plate are: yield strength ≥890MPa, tensile strength ≥960MPa, elongation ≥15%, and transverse KV2 ≥60J at room temperature; the surface grain size of the finished titanium alloy plate is consistent with the center grain size grade, and the grain size is above grade 5; the straightness of the finished titanium alloy plate is below 5mm / 2m.

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