A shape control method for TC4ELI titanium alloy medium and thick plates with a thickness greater than 50 mm

Abstract

The present invention relates to a plate shape control method for a TC4ELI titanium alloy medium and thick plate with a thickness greater than 50 mm. The production process of the TC4ELI titanium alloy medium and thick plate comprises grinding and spraying of titanium alloy flat ingots, heating, rolling, online hot straightening, stacking slow cooling and annealing. The plate shape control requirements of the TC4ELI titanium alloy are met without the need for subsequent offline warm straightening or cold straightening. This solves the problem of wavy defects caused by thick rolled pieces, large deformation resistance and large springback during the production of such titanium alloy plates, thereby improving the first-pass pass rate of the product and reducing the scrap rate.

Description

Technical Field

[0001] The present invention relates to the technical field of medium and thick plate production, and in particular to a plate shape control method for high-strength TC4ELI titanium alloy medium and thick plates with a thickness greater than 50 mm and a width greater than 2800 mm. Background Art

[0002] With technological advancements in aerospace, deep-sea exploration, shipbuilding, marine engineering, chemical engineering, and the nuclear power industry, demand for titanium alloy TC4ELI sheet is increasing, with requirements for high strength, high dimensional accuracy, good impact toughness, and weldability. Currently, there is growing demand for wide-width, large-size titanium alloy sheet. 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 of 2800 to 4000 mm can reduce weld seams, minimize weld material flaw detection during the manufacturing process, lower equipment maintenance costs, and increase equipment safety. It can also significantly reduce factory prefabrication costs, shorten material procurement cycles, and increase construction speed. However, due to the low elastic modulus of titanium alloy and the increased susceptibility to breaking waves as the sheet thickness increases, plate shape control is also difficult, resulting in the inability to meet automatic welding requirements during subsequent use, seriously impacting customer use and delaying delivery times. The production of this type of plate is characterized by thick rolled pieces and extreme sensitivity to rolling forces and temperature fluctuations. This makes it prone to numerous problems during production, such as wavy shapes and scrap. This leads to a high scrap rate, and the finished steel plate exhibits a corrugated shape, resulting in excessive flatness and difficulty in achieving mass production capacity. Furthermore, due to its low elastic modulus and high rebound, cold plates cannot be flattened and salvaged using cold levelers and flattening machines. These factors significantly increase the manufacturing cost of thick titanium alloy plate and extend lead times. Therefore, addressing the shape issues of TC4ELI titanium alloy plate with thicknesses exceeding 50 mm and widths greater than 2800 mm, and improving its first-pass pass rate, is crucial for the development of this product specification.

[0003] To date, little research has been conducted domestically or internationally on shape control methods for TC4ELI titanium alloy sheets with thicknesses greater than 40 mm and widths greater than 2800 mm. 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 steel plate after each pass, water cooling is performed to maintain the low-temperature, high-deformation microstructure, thereby ensuring that the steel plate's performance meets requirements. However, the 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 thickness of the steel plates produced is 42 to 46 mm and the width is 3800 to 3900 mm, and the manufacturing process of titanium alloy plates with a thickness greater than 50 mm is not involved.

[0004] The journal article "Effect of Rolling Process on the Microstructure and Mechanical Properties of Ultra-Wide Thick Plates of TC4ELI Titanium Alloy" (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 indicators such as the plate width and thickness group spacing suitable for production, surface quality status and yield rate.

[0005] Although the steel plate shape control method disclosed in the above documents solves the shape problem of TC4ELI titanium alloy plates with certain thickness specifications, it is not suitable for controlling the shape problem of high-strength TC4ELI titanium alloy plates with a thickness of more than 50 mm. Summary of the Invention

[0006] The present invention provides a plate shape control method for TC4ELI titanium alloy medium and thick plates with a thickness greater than 50 mm. The plate shape control requirements of TC4ELI titanium alloy can be met without subsequent offline warm straightening or cold straightening treatment. This solves the problem of wavy defects caused by thick rolled pieces, large deformation resistance, and large springback during the production of such titanium alloy plates, thereby improving the first-time pass rate of the product and reducing the scrap rate.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for controlling the shape of a TC4ELI titanium alloy medium and thick plate having a thickness greater than 50 mm is disclosed. The production process of the TC4ELI titanium alloy medium and thick plate includes grinding and spraying of titanium alloy flat ingots, heating, rolling, online hot straightening, stacking and slow cooling, and annealing. The specific process is as follows:

[0009] 1) Grinding and spraying of titanium alloy flat ingots;

[0010] 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;

[0011] 2) heating;

[0012] The titanium alloy slab is heated in a heating furnace. The preheating temperature is 800-850°C and the holding time is 45-60 minutes. The first heating temperature is 880-910°C and the holding time is 35-45 minutes. The second heating temperature is 955-970°C and the holding time is 35-45 minutes. The soaking temperature is 980-1020°C and the holding time is 120-150 minutes. At the same time, the air-fuel ratio in the soaking section is controlled at 1:1.7-1:2.3 to ensure that the temperature difference between the upper and lower surfaces of the titanium alloy slab is within 20°C.

[0013] 3) rolling;

[0014] Before rolling, the roller cooling water is turned off; the titanium alloy flat ingot is rolled back and forth, first horizontally and then vertically, with a single-pass reduction rate of 20% to 25% in the horizontal rolling stage and a large reduction rate of 20% to 30% in at least the first two passes of the longitudinal rolling stage; the rollers are cooled in sections during the rolling process, and when rolling the head section, the roller cooling water volume is 100 to 150 m 3 / h; when rolling the middle section, the water volume of the roller should be 150~200m 3 / h; when rolling the tail section, the water volume of the roller is 100-150m 3 / h; during the rolling process, the roller speed is adjusted to compensate, and the speed difference between the upper and lower rollers is controlled at -3% to -1.5%. The final rolling reduction is controlled within 1mm; the starting rolling temperature is 940-970℃, the rolling speed is 3-5m / s, and the final rolling temperature is ≥800℃; after the final rolling, the whole length of the plate is descaled using high-pressure water from the rolling mill, with a descaling machine pressure of 20-25MPa, and the plate is quickly ejected after rolling at a speed of 5-6.5m / s;

[0015] 4) Online thermal straightening;

[0016] Three straightening steps are performed, with a straightening temperature of 720-750°C, a straightening force of 1500-1800 kN, a roller bending amount of 2-3.0 mm, and a tilting value of 4-7 mm;

[0017] 5) Stacking and slow cooling;

[0018] When stacking and slow cooling, the temperature of titanium alloy medium and thick plates is lower than 600℃, and the stacking time is 24 to 48 hours;

[0019] 6) Annealing treatment;

[0020] Before entering the furnace, steel plates with a thickness of more than 60 mm are placed on the upper and lower surfaces of the titanium alloy medium and thick plates, and nickel-based alloy pads are placed between the steel plates and the titanium alloy medium and thick plates; the annealing temperature is 860-890°C, the annealing time is 4-6 hours, and the plates are air-cooled after being taken out of the furnace.

[0021] Furthermore, the chemical composition of the TC4ELI titanium alloy medium and thick plate is as follows by weight: O: 0.07% to 0.11%, Fe: 0.20% to 0.25%, C≤0.08%, H≤0.012%, Al: 5.5% to 6.5%, V: 3.5% to 4.5%, and the remainder is Ti and unavoidable impurity elements.

[0022] Furthermore, the width of the TC4ELI titanium alloy medium and thick plate is greater than 2800 mm.

[0023] Furthermore, the preparation process of the titanium alloy flat ingot is: using first-grade sponge titanium, 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 produce the titanium alloy flat ingot.

[0024] Furthermore, the size of the titanium alloy slab is thickness×width×length=200-350 mm×1550-1950 mm×2500-4000 mm.

[0025] Furthermore, in step 1), the surface roughness of the titanium alloy slab after grinding is Ra≤80 μm.

[0026] 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 0.9 mm.

[0027] Furthermore, in step 2), 2 to 4 vacancies are left at the furnace head of the soaking section of the heating furnace.

[0028] Furthermore, in the step 3), a medium and thick plate reciprocating rolling mill is used for rolling; taking the total length of the titanium alloy flat ingot as L, the head section is the head 1 / 4L length section, the middle section is the 1 / 4L to 3 / 4L length section, and the tail section is the tail 1 / 4L length section.

[0029] Furthermore, the straightness of the finished TC4ELI titanium alloy medium and thick plates is ≤3mm / 2m.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1) High-temperature nano-SiO2 anti-oxidation coating is sprayed in three directions on the ground EB flat ingot to ensure that the flat ingot is in contact with the open flame during the heating process of the walking beam heating furnace, resulting in overburning on the surface and a large amount of Widmanstätten β phase structure on the surface, which causes uncoordinated deformation of the two phases in the subsequent rolling process and produces surface cracks.

[0032] 2) Use high heating temperature, ensure the soaking section and heating section in the furnace time, control the air-fuel ratio, shorten the temperature difference between the surface and the core of the continuous casting billet, and leave 2 to 4 vacancies in the furnace head of the soaking section of the heating furnace to prevent the furnace head temperature from being low and affecting the heating uniformity of the titanium alloy flat ingot; thereby ensuring the uniformity of the transverse and longitudinal metal flow on the upper and lower surfaces of the plate during the rolling process of the titanium alloy plate.

[0033] 3) Rolling and high-pressure water descaling: Before rolling, the cooling water of the rollers in the rough rolling to hot straightening interval is turned off (to avoid a large amount of cooling water flowing on the lower surface of the intermediate billet, causing an uncontrolled temperature drop on its surface, increasing the rolling passes, and also helping to control the intermediate billet to remain horizontal or slightly upturned, creating conditions for the rolling mill to bite); the rollers are controlled by a segmented cooling process (to avoid a large amount of cooling water flowing on the surface of the plate, causing an uncontrolled temperature drop on the surface of the plate, increasing the rolling passes, and reasonably controlling the cooling water volume of the rollers to effectively control the roller shape, greatly improving 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). During the rolling process, the roller speed is adjusted to compensate and the speed difference between the upper and lower rollers is controlled to ensure that there is no goose head wave in the initial plate shape before entering the pre-straightening machine. The reduction in the last pass is controlled to be within 1mm to flatten the plate shape and reduce the internal stress of the plate.

[0034] 4) By setting requirements for the straightening temperature, the difference in the two-phase ratio is reduced, the internal stress is fully released, and the internal stress of the plate is fully released before straightening to avoid large internal stress due to phase change. The appropriate bending roller amount and tilting value are set to ensure that the straightness of the straightened plate is good.

[0035] 5) The titanium alloy plates are immediately transported to the slow cooling area for stacking and slow cooling. At the same time, the slow cooling temperature is limited to ensure that the temperature drop of the plates is consistent, while also avoiding the phase transition zone with greater stress at 600°C, thereby ensuring the final shape of the plates before heat treatment.

[0036] 6) Before annealing, steel plates with a thickness of more than 60 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 plate and the titanium plate to ensure that the titanium plate is heated evenly during the annealing process. At the same time, it also prevents the titanium plate from directly contacting the roller and air after being taken out of the furnace, resulting in excessively fast cooling of the upper and lower surfaces. At the same time, the gap between the pad and the steel plate is used for uniform and slow cooling. In addition, by arranging steel plates with a thickness of more than 60 mm on the upper and lower surfaces, the deadweight of the steel plate during high-temperature annealing can also be used to flatten the plate shape of the titanium plate, ensuring that the high-strength TC4ELI titanium alloy plate with a thickness of more than 50 mm and a width of more than 2800 mm has an unevenness of less than 3 mm / 2 m, meeting the use requirements. DETAILED DESCRIPTION

[0037] The present invention discloses a method for controlling the shape of a TC4ELI titanium alloy medium and thick plate having a thickness greater than 50 mm. The production process of the TC4ELI titanium alloy medium and thick plate includes grinding and spraying of titanium alloy flat ingots, heating, rolling, online hot straightening, stacking and slow cooling, and annealing. The specific process is as follows:

[0038] 1) Grinding and spraying of titanium alloy flat ingots;

[0039] 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;

[0040] 2) heating;

[0041] The titanium alloy slab is heated in a heating furnace. The preheating temperature is 800-850°C and the holding time is 45-60 minutes. The first heating temperature is 880-910°C and the holding time is 35-45 minutes. The second heating temperature is 955-970°C and the holding time is 35-45 minutes. The soaking temperature is 980-1020°C and the holding time is 120-150 minutes. At the same time, the air-fuel ratio in the soaking section is controlled at 1:1.7-1:2.3 to ensure that the temperature difference between the upper and lower surfaces of the titanium alloy slab is within 20°C.

[0042] 3) rolling;

[0043] Before rolling, the roller cooling water is turned off; the titanium alloy flat ingot is rolled back and forth, first horizontally and then vertically, with a single-pass reduction rate of 20% to 25% in the horizontal rolling stage and a large reduction rate of 20% to 30% in at least the first two passes of the longitudinal rolling stage; the rollers are cooled in sections during the rolling process, and when rolling the head section, the roller cooling water volume is 100 to 150 m 3 / h; when rolling the middle section, the water volume of the roller should be 150~200m 3 / h; when rolling the tail section, the water volume of the roller is 100-150m 3 / h; during the rolling process, the roller speed is adjusted to compensate, and the speed difference between the upper and lower rollers is controlled at -3% to -1.5%. The final rolling reduction is controlled within 1mm; the starting rolling temperature is 940-970℃, the rolling speed is 3-5m / s, and the final rolling temperature is ≥800℃; after the final rolling, the whole length of the plate is descaled using high-pressure water from the rolling mill, with a descaling machine pressure of 20-25MPa, and the plate is quickly ejected after rolling at a speed of 5-6.5m / s;

[0044] 4) Online thermal straightening;

[0045] Three straightening steps are performed, with a straightening temperature of 720-750°C, a straightening force of 1500-1800 kN, a roller bending amount of 2-3.0 mm, and a tilting value of 4-7 mm;

[0046] 5) Stacking and slow cooling;

[0047] When stacking and slow cooling, the temperature of titanium alloy medium and thick plates is lower than 600℃, and the stacking time is 24 to 48 hours;

[0048] 6) Annealing treatment;

[0049] Before entering the furnace, steel plates with a thickness of more than 60 mm are placed on the upper and lower surfaces of the titanium alloy medium and thick plates, and nickel-based alloy pads are placed between the steel plates and the titanium alloy medium and thick plates; the annealing temperature is 860-890°C, the annealing time is 4-6 hours, and the plates are air-cooled after being taken out of the furnace.

[0050] Furthermore, the chemical composition of the TC4ELI titanium alloy medium and thick plate is as follows by weight: O: 0.07% to 0.11%, Fe: 0.20% to 0.25%, C≤0.08%, H≤0.012%, Al: 5.5% to 6.5%, V: 3.5% to 4.5%, and the remainder is Ti and unavoidable impurity elements.

[0051] Furthermore, the width of the TC4ELI titanium alloy medium and thick plate is greater than 2800 mm.

[0052] 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.

[0053] Furthermore, the size of the titanium alloy slab is thickness×width×length=200-350 mm×1550-1950 mm×2500-4000 mm.

[0054] Furthermore, in step 1), the surface roughness of the titanium alloy slab after grinding is Ra≤80 μm.

[0055] 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 0.9 mm.

[0056] Furthermore, in step 2), 2 to 4 vacancies are left at the furnace head of the soaking section of the heating furnace.

[0057] Furthermore, in the step 3), a medium and thick plate reciprocating rolling mill is used for rolling; taking the total length of the titanium alloy flat ingot as L, the head section is the head 1 / 4L length section, the middle section is the 1 / 4L to 3 / 4L length section, and the tail section is the tail 1 / 4L length section.

[0058] Furthermore, the straightness of the finished TC4ELI titanium alloy medium and thick plates is ≤3mm / 2m.

[0059] The present invention provides a method for controlling the shape of a high-strength TC4ELI titanium alloy medium and thick plate with a thickness of more than 50 mm and a width of more than 2800 mm. The chemical composition of the titanium alloy medium and thick plate includes, by weight percentage, O: 0.07% to 0.11%, Fe: 0.20% to 0.25%, C≤0.08%, H≤0.012%, Al: 5.5% to 6.5%, V: 3.5% to 4.5%, and the balance is Ti and unavoidable impurity elements.

[0060] First, using first-grade titanium sponge, Al-V master alloy, and high-purity Al (Al content above 99.9%) as the charge, the electrodes are pressed and smelted in an electron beam cooling hearth furnace (EB furnace) to obtain TC4ELI titanium alloy flat ingots (referred to as titanium alloy flat ingots) with dimensions of (200-350) mm thick × (1550-1950) mm wide × (2500-4000) mm long. These ingots are then rolled on a medium and heavy plate reciprocating mill to obtain titanium alloy medium and heavy plates. The production process includes grinding and spraying the titanium alloy flat ingots → heating → rolling → online hot straightening → stacking and slow cooling → annealing. The specific process, process parameters, and principles are as follows:

[0061] 1) Grinding and spraying: The titanium alloy slab is subjected to full-surface grinding online with temperature, and a grinding wheel is used to grind the entire surface in three dimensions to remove surface oxide scale and other defects. The surface roughness after grinding is Ra ≤ 80μm; then the surface of the ground titanium alloy slab is sprayed with high-temperature nano-SiO2 anti-oxidation coating with a spraying thickness of 0.6 to 0.9mm.

[0062] 2) Heating of titanium alloy slab: The titanium alloy slab (thickness of 200-350mm) is fed into a step-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 800-850℃, and the holding time is 45-60min, in order to promote 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 880-910℃, and the holding time is 35-45min; the temperature range of the second heating section is 955-970℃, and the holding time is 20-30min. The heating time is 35-45 minutes; the temperature range of the soaking section is 980-1020℃, and the holding time is 120-150 minutes. At the same time, the air-fuel ratio of the soaking section is controlled to be 1:1.7-1:2.3 to ensure that the temperature difference between the upper and lower surfaces of the titanium alloy slab is within 20℃. Through the above heating process, the elements such as O, Fe, C, H, Al and V in the titanium alloy slab 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 the evolution and distribution state of the needle-shaped β phase in the soaking section is controlled, ultimately ensuring the performance of the titanium alloy plate. In addition, 2-4 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.

[0063] 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 prevent a large amount of cooling water from flowing on the lower surface of the intermediate billet, causing an uncontrolled temperature drop on the surface. This increases the number of rolling passes and is also beneficial for controlling the intermediate billet to remain horizontal or slightly upturned, creating conditions for the rolling mill to bite in. A wide plate mill is used to roll the billet (titanium alloy flat ingot) back and forth, first horizontally and then vertically. During horizontal rolling, the reduction rate per pass is controlled at 20% to 25%. During vertical rolling, a large reduction rate is preferably used in the first two passes, and the reduction rate per pass is controlled at 20% to 30%. By reversing rolling, the properties (anisotropy) of the titanium alloy plate are improved. The first two passes of the transverse rolling stage and the longitudinal rolling stage use a large reduction rate 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 in the β phase, providing a driving force for the subsequent spheroidization and transformation of the β phase lamellar structure into an equiaxed structure; during the rolling of titanium alloy flat ingots (full length is L), the rollers are cooled in sections, and it is preferred that the roller cooling water volume is 100-150m3 when the 1 / 4L length section of the rolling head is rolled. 3 / h; when rolling 1 / 4L-3 / 4L length section, the water volume of the roller is 150~200m 3 / h; when rolling the 1 / 4L length section at the tail, the water volume of the roller is 100-150m 3 / h is turned on. By adjusting the water volume of the rolling rollers and reasonably controlling the cooling water volume, the roller 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. During the rolling process, the roller speed is adjusted to compensate, and the speed difference between the upper and lower rollers is controlled at -3% to -1.5% to ensure that the initial plate shape of the titanium alloy plate has no goose head waves before entering the pre-straightening machine; it is preferred that the final reduction is controlled within 1mm, which is conducive to flattening the plate shape and reducing the internal stress of the plate. The starting rolling temperature during rolling is 940-970℃, the rolling speed is 3-5m / s, and the final rolling temperature is ≥800℃. After the last rolling, the high-pressure water of the rolling mill is used to descale the entire length surface of the titanium alloy plate. The pressure of the descaling machine is 20-25MPa, and it is quickly thrown out after rolling, with a throwing speed of 5-6.5m / s.

[0064] 4) Online hot straightening: Hot straightening is preferably carried out in three steps. The straightening temperature of hot straightening is 720-750℃, the straightening force is between 1500-1800kN, the bending roll amount is set to 2-3.0mm, and the tilting value is set to 4-7mm. By reducing the difference in the two-phase ratio, 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 rapid phase change. By setting appropriate bending roll amount, straightening force and tilting value, the straightness of the straightened titanium alloy plate is guaranteed to be good.

[0065] 5) Stacking and slow cooling: The titanium alloy plates after hot straightening are immediately transported to the slow cooling area for stacking. The temperature of the titanium alloy plates must be lower than 600°C during stacking, and the stacking time is 24 to 48 hours. Since the cooling rates of the lower and upper surfaces of thick-gauge steel plates are different, stacking and slow cooling can ensure that the temperature drop of the plates tends to be consistent, while avoiding the phase transition zone with greater stress at 600°C, thereby ensuring the final plate shape of the titanium alloy plates before heat treatment.

[0066] 6) Annealing treatment: Before entering the furnace, steel plates with a thickness of more than 60 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. Preferably, 3 pads are placed at each part of the head, middle and tail, for a total of 9 pads. The annealing temperature is 860-890 ° C, the annealing 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 of the titanium alloy plate can ensure that the titanium alloy plate is heated evenly during the annealing process, and at the same time prevent the titanium alloy plate from directly contacting 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, arranging thick steel plates on the upper and lower surfaces of the titanium alloy plate can also use the weight of the steel plates to flatten the titanium alloy plate during high-temperature annealing.

[0067] The present invention utilizes the aforementioned composition and controlled rolling and cooling scheme to overcome the shortcomings of existing technologies, achieving shape control for high-strength TC4ELI titanium alloy medium and thick plates with thicknesses exceeding 50 mm and widths exceeding 2800 mm. The finished titanium alloy medium and thick plates achieve a flatness of less than 3 mm / 2 m, meeting application requirements.

[0068] 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.

[0069] [Example]

[0070] Table 1 shows the chemical composition of the titanium alloy medium and thick 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 of the titanium alloy slabs in each embodiment, Table 4 shows the reduction in each pass during rolling in each embodiment, Table 5 shows the straightening parameters and annealing process parameters of the titanium alloy plates in each embodiment, and Table 6 shows the dimensions, properties and quality indicators of the finished TC4ELI titanium alloy medium and thick plates in each embodiment.

[0071] Table 1 Chemical composition of titanium alloy medium and thick plates in various embodiments (wt, %)

[0072] Example O Fe C H Al V 1 0.07 0.21 0.06 0.009 5.6 3.7 2 0.09 0.25 0.07 0.012 5.8 4.0 3 0.10 0.24 0.05 0.006 6.5 3.6 4 0.08 0.22 0.08 0.003 5.7 4.2 5 0.11 0.20 0.03 0.007 6.4 3.8

[0073] Note: The remainder is Ti and unavoidable impurity elements

[0074] Table 2 Grinding requirements and heating system of titanium alloy slabs in each embodiment

[0075]

[0076] Table 3 Rolling process parameters of each embodiment

[0077]

[0078] Table 4 Straightening, stacking parameters and annealing process parameters of titanium alloy plates in various embodiments

[0079]

[0080] Table 5 Dimensions and quality indicators of the finished TC4ELI titanium alloy plates of various examples

[0081] Example Finished product specifications (thickness × width × length) / mm × mm × mm Straightness mm / 2m 1 60×3300×5691.9 2 2 65×2900×5470.8 1 3 50×3300×7563.6 3 4 75×3800×4863.1 2 5 85×3900×6607.3 1

[0082] Thus, compared with the prior art, the present invention provides a method for controlling the shape of high-strength TC4ELI titanium alloy sheets with a thickness of 50 mm or greater and a width of 2800 mm or greater. The technical solution provided by the present invention effectively overcomes the aforementioned shortcomings and solves the shape problem of TC4ELI titanium alloy sheets with a thickness of 50 mm or greater and a width greater than 2800 mm produced from titanium alloy slabs with a thickness of 200-350 mm. The sheet flatness is reduced to less than 3 mm / 2 m, meeting the requirements for use.

[0083] 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 controlling the shape of a TC4ELI titanium alloy medium and thick plate with a thickness greater than 50 mm, characterized in that: The chemical composition of the TC4ELI titanium alloy medium and thick plate is as follows by weight: O: 0.07% to 0.11%, Fe: 0.20% to 0.25%, C ≤ 0.08%, H ≤ 0.012%, Al: 5.5% to 6.5%, V: 3.5% to 4.5%, and the balance is Ti and unavoidable impurity elements; the width of the TC4ELI titanium alloy medium and thick plate is not less than 2800 mm, and the straightness of the finished product is ≤ 3 mm / 2 m; The production process of TC4ELI titanium alloy medium and thick plates includes titanium alloy flat ingot grinding and spraying, heating, rolling, online hot straightening, stacking slow cooling and annealing. The specific process is as follows: 1) Grinding and spraying of titanium alloy flat ingots; The titanium alloy slab ingot has a size of thickness × width × length = 200-350 mm × 1550-1950 mm × 2500-4000 mm. The titanium alloy slab ingot 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, smelting in an EB furnace by pressing electrodes to obtain the titanium alloy slab ingot; performing hot online full-surface grinding of the titanium alloy slab to achieve a surface roughness Ra of ≤80 μm after grinding; spraying a high-temperature anti-oxidation coating on the surface of the ground titanium alloy slab; 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 0.6-0.9 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 800 to 850°C, with a holding time of 45 to 60 minutes. The first heating section temperature is 885 to 910°C, with a holding time of 35 to 45 minutes. The second heating section temperature is 955 to 970°C, with a holding time of 35 to 45 minutes. The soaking section temperature is 980 to 1020°C, with a holding time of 120 to 150 minutes. At the same time, the air-fuel ratio in the soaking section is controlled at 1:1.7 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 by a medium and thick plate reciprocating rolling mill, first horizontal rolling and then longitudinal rolling, the single-pass reduction rate in the horizontal rolling stage is 20% to 25%, and at least the first two passes in the longitudinal rolling stage adopt a large reduction rate, and the single-pass reduction rate is 20% to 30%; during the rolling process, the rollers are cooled in sections, with the full length of the titanium alloy flat ingot being L, the head section is the head 1 / 4L length section, the middle section is the 1 / 4L to 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 100 to 150m 3 / h; when rolling the middle section, the water volume of the roller should be 150~200m 3 / h; when rolling the tail section, the water volume of the roller is 100-150m 3 / h; during the rolling process, the roller speed is adjusted to compensate, and the speed difference between the upper and lower rollers is controlled at -3% to -1.5%. The final rolling reduction is controlled within 1mm; the starting rolling temperature is 940-970℃, the rolling speed is 3-5m / s, and the final rolling temperature is ≥800℃; after the final rolling pass, the entire length of the plate is descaled using high-pressure water from the rolling mill. The descaling water pressure is 20-25MPa, and the plate is quickly ejected after rolling at a speed of 5-6.5m / s; 4) Online thermal straightening; Three straightening steps are performed, with a straightening temperature of 720-750°C, a straightening force of 1500-1800 kN, a roller bending amount of 2-3.0 mm, and a tilting value of 4-7 mm; 5) Stacking and slow cooling; When stacking and slow cooling, the temperature of titanium alloy medium and thick plates is lower than 600℃, and the stacking time is 24 to 48 hours; 6) Annealing treatment; Before entering the furnace, steel plates with a thickness of more than 60 mm are placed on the upper and lower surfaces of the titanium alloy medium and thick plates, and nickel-based alloy pads are placed between the steel plates and the titanium alloy medium and thick plates; the annealing temperature is 860-890°C, the annealing time is 4.2-6 hours, and the plates are air-cooled after being taken out of the furnace.

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