A method for producing TC4ELI titanium alloy medium and thick plates with high yield and low cost

Abstract

The present invention relates to a method for producing TC4ELI titanium alloy medium and thick plates with a high yield and low cost. The method comprises the following processes: grinding and spraying of titanium alloy flat ingots, heating, rolling, online hot straightening and annealing. The method adopts a single-fire rolling process to achieve the purpose of eliminating or minimizing grinding of the plates after rolling, thereby greatly reducing grinding labor and material costs. The method solves the problem of surface cracks being easily generated in wide-width TC4ELI titanium alloy hot-rolled medium and thick plates after rolling, and reduces the surface crack scrap rate from over 20% to below 0.5%. The mechanical properties of the produced plates are as follows: yield strength ≥880MPa, tensile strength ≥950MPa, elongation ≥12%, and room temperature transverse KV2 ≥45J.

Description

Technical Field

[0001] The invention relates to the technical field of steel rolling, in particular to a method for producing TC4ELI titanium alloy medium and thick plates with a thickness of 15 to 60 mm and a width of 2800 to 4000 mm at a high yield and low cost. Background Art

[0002] With technological advancements in aerospace, deep-sea exploration, shipbuilding, petroleum, chemical, and nuclear energy industries, 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, large-sized titanium alloy sheet. This is primarily due to the fact that using wide, large-sized titanium alloy sheet, with thicknesses ranging from 15 to 60 mm and widths ranging from 2,800 to 4,000 mm, reduces weld seams, minimizes weld material flaw detection during the manufacturing process, reduces equipment maintenance costs, and increases equipment safety. It also significantly reduces factory prefabrication costs, shortens material procurement cycles, and increases construction speed. However, due to titanium alloy's poor thermal conductivity, narrow processing window, and poor thermoplasticity, cracks are prone to forming on the surface and edges of rolled products, especially in thinner sheets. These defects become more pronounced with increasing rolling passes and decreasing finishing temperatures. In addition, the process of large deformation at a lower temperature will greatly increase the load of the rolling equipment and put forward higher requirements on the equipment capacity, thus limiting the application of the controlled rolling process in the production of wide titanium alloy plates. At present, the conventional process route of titanium alloy plates adopts two-fire rolling and "rush temperature fast rolling" production, that is, on the one hand, the rolling rhythm is required to be accelerated, and at the same time, the slab heating temperature is at the upper limit of the (α+β) two-phase region or even above the alloy phase transformation point, so as to keep the entire rolling process in a relatively high temperature range as much as possible; because the temperature of such plates drops quickly and they are very sensitive to temperature changes, many problems such as rolling scrap and severe surface cracks are very likely to occur during the production process, and the scrap rate is high; and the use of two-fire rolling and the generation of cracks on the surface will increase the amount of grinding of the finished plate in the later stage, thus greatly increasing the production cost and reducing the production efficiency. It can be seen that how to optimize the production process and use single-fire rolling to produce crack-free or less-cracked plates, thereby greatly reducing the amount of grinding and rolling costs and improving production efficiency, is the key to the development of TC4ELI titanium alloy ultra-wide plates with thickness specifications of 15 to 60 mm and width specifications of 2800 to 4000 mm.

[0003] To date, little research has been conducted domestically and internationally on how to achieve high yields and low costs in the production of ultra-wide TC4ELI titanium alloy plates with thicknesses of 15-60 mm and widths of 2800-4000 mm. Prior to the present invention, Chinese Patent Publication No. CN103203361A disclosed a "Method for Rolling Wide and Thick TC4 Titanium Alloy Plates." This method employed low-temperature, high-deformation, two-pass rolling. Water cooling after each pass achieved rapid cooling, preserving the low-temperature, high-deformation microstructure and ensuring that the plate performance met requirements. However, its performance could not meet technical requirements for deep-sea service, the plate width was less than 2800 mm, and the use of two-pass rolling increased production costs. Chinese Patent Publication No. CN108838208A disclosed a "Method for Two-Pass Rolling of Wide TC4 Titanium Alloy Billets." By employing appropriate heating and soaking processes, and employing two-pass rapid warming rolling, this method effectively prevented buckling, warping, and other phenomena in the titanium alloy billet caused by temperature drop 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. The use of double-fire rolling increases production costs and there are no clear requirements for surface quality.

[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] While the titanium alloy sheet manufacturing methods disclosed in the aforementioned documents improve the sheet's surface quality and mechanical properties, they do not achieve the goal of producing TC4ELI titanium alloy sheet with a high yield and low cost, with a thickness of 15 to 60 mm and a width of 2800 to 4000 mm. The technical solution provided by the present invention effectively overcomes these shortcomings and addresses the problems of frequent surface cracking, extensive post-production grinding, and increased production costs associated with secondary hot rolling when producing TC4ELI titanium alloy sheet with a thickness of 15 to 60 mm and a width of 2800 to 4000 mm using titanium alloy slabs with a thickness of less than 150 to 250 mm. Summary of the Invention

[0006] The present invention provides a method for producing TC4ELI titanium alloy medium and thick plates with a high yield and low cost. The method adopts a single-hot rolling process to achieve the purpose of eliminating or minimizing grinding of the plates after rolling, thereby greatly reducing the labor and material costs of grinding. The method solves the problem that surface cracks are easily generated in wide TC4ELI titanium alloy hot-rolled medium and thick plates after rolling, and reduces the surface crack scrap rate from more than 20% to less than 0.5%. The mechanical properties of the produced plates are as follows: yield strength ≥880MPa, tensile strength ≥950MPa, elongation ≥12%, and room temperature transverse KV2 ≥45J.

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

[0008] A method for producing TC4ELI titanium alloy medium and thick plates with a high yield and low cost, comprising the following steps: grinding and spraying a titanium alloy flat ingot, heating, rolling, online heat straightening, and annealing.

[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 780-850°C and the holding time is 25-40 minutes. The first heating temperature is 870-920°C and the holding time is 30-45 minutes. The second heating temperature is 950-970°C and the holding time is 45-60 minutes. The soaking temperature is 990-1010°C and the holding time is 100-120 minutes. At the same time, the air-fuel ratio in the soaking section is controlled at 1:1.8-1:2.2 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, and the reduction rate of each of the first two passes in the horizontal rolling stage is 20% to 25%, and the roller cooling water is turned off during the horizontal rolling stage; at least the first two passes in the longitudinal rolling stage adopt a large reduction rate, with a single-pass reduction rate of 20% to 35%, and at least the reduction rate of the last two passes is controlled below 10%; the rollers are cooled in sections during the longitudinal rolling stage, and 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 200~250m 3 / h; when rolling the tail section, the water volume of the roller is 100-150m 3 / h; the starting rolling temperature is 940-970℃, the rolling speed in the transverse rolling stage is 2-3m / s, the rolling speed in the longitudinal rolling stage is 4-6.5m / s, the final rolling temperature is ≥730℃, and the strip is quickly ejected after rolling at a speed of 5-6.5m / s;

[0015] 3) Online thermal straightening;

[0016] At least three straightening passes are performed; the straightening temperature of hot straightening is 600-700°C, the straightening force is 1500-2500kN, the bending amount is 1-3.0mm, and the tilting value is 3-6mm;

[0017] 4) Annealing treatment;

[0018] The annealing temperature is 780-850° C., and the annealing time is 3-4 hours.

[0019] Furthermore, the chemical composition of the TC4ELI titanium alloy medium and thick plate is as follows by weight: O: 0.06% to 0.11%, Fe: 0.18% to 0.25%, C≤0.07%, H≤0.012%, Al: 5.5% to 6.5%, V: 3.5% to 4.5%, and the remainder is Ti and unavoidable impurity elements.

[0020] Furthermore, the TC4ELI titanium alloy medium and thick plate has a thickness of 15 to 60 mm and a width of 2800 to 4000 mm.

[0021] 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.

[0022] Furthermore, the size of the titanium alloy slab is thickness×width×length=150-250 mm×1550-1950 mm×2500-3800 mm.

[0023] Furthermore, in the step 1), the surface roughness of the titanium alloy slab after grinding is Ra≤100 μm.

[0024] 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 0.5 to 1.0 mm.

[0025] Furthermore, in step 2), 2 to 4 vacancies are left at the furnace head of the soaking section of the heating furnace.

[0026] Furthermore, in step 3), the total length of the titanium alloy ingot is L, the head section is a 1 / 8L length section, the middle section is a 1 / 8L to 7 / 8L length section, and the tail section is a 1 / 8L length section.

[0027] Furthermore, the mechanical properties of the finished TC4ELI titanium alloy medium and thick plates are: yield strength ≥880MPa, tensile strength ≥950MPa, elongation ≥12%, room temperature transverse KV2 ≥45J; the straightness of the finished TC4ELI titanium alloy medium and thick plates is ≤8mm / 2m.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1) Grinding and spraying process: High-temperature nano-SiO2 anti-oxidation coating is sprayed on the entire surface of the ground titanium alloy slab in three dimensions to prevent the surface of the titanium alloy slab from being overburned when it comes into contact with open flames during heating in a walking beam furnace. This will cause a large amount of Widmanstätten β phase structure on the surface, resulting in uncoordinated deformation of the two phases during the subsequent rolling process and causing surface cracks.

[0030] 2) Heating process: Use high heating temperature, ensure the time of soaking section and heating section in the furnace, control the air-fuel ratio, shorten the temperature difference between the surface and the core of the continuous casting billet; at the same time, leave 2 to 4 vacancies in the furnace head of the soaking section of the heating furnace to prevent the low furnace head temperature from affecting the uniformity of heating of the titanium alloy flat ingot; ensure the uniformity of metal flow in the horizontal and vertical directions on the upper and lower surfaces of the plate during the rolling process of the titanium alloy plate;

[0031] 3) Rolling and high-pressure water descaling process: 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, causing an uncontrolled temperature drop on the surface, 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 in. During the cross-rolling stage, the roller cooling water is turned off and the rolling speed is controlled to suppress the deformation resistance exceeding the crack propagation resistance due to uncontrolled temperature drop during the cross-rolling widening stage, thereby causing surface cracks. During the longitudinal rolling stage, the rollers are controlled using a segmented cooling process to avoid a large amount of cooling water flowing on the plate surface, causing an uncontrolled temperature drop on the plate surface, thereby increasing the number of rolling passes. The cooling water volume of the rollers is reasonably controlled to effectively control the roller shape. Significantly improve the irregular deviation and sickle bend defects caused by the uneven temperature distribution of the head, middle and tail of the intermediate billet during the rolling process; improve the performance (anisotropy) of the alloy plate by reversing rolling, adopt a large reduction rate in the first two passes of the transverse rolling stage and the longitudinal rolling stage, promote the elongation or crushing of the original β phase grains during the deformation process, and promote the precipitation of secondary α phase transformation in the β phase, resulting in the refinement of the grains from the surface of the titanium alloy flat ingot to the centripetal part, and control the reduction rate of the last two passes of the longitudinal rolling stage and the rolling speed of the longitudinal rolling stage at the same time, so as to prevent the cracks from being generated due to the uncontrolled temperature drop in the late rolling stage, and ensure the coordinated deformation of the two phases, thereby inhibiting the generation of cracks; by ensuring a sufficient reduction rate, the lamellar structure is promoted to undergo spheroidization and transform into an equiaxed structure;

[0032] 4) Straightening process: By controlling the straightening temperature, reducing the difference in the two-phase ratio, promoting the full release of internal stress, ensuring that the internal stress of the plate is fully released before straightening, and avoiding the generation of large internal stress due to phase change; setting appropriate bending roller amount and tilting value to ensure good straightness of the plate after straightening;

[0033] 5) Annealing process: By increasing the annealing temperature, the lamellar α phase is promoted to become wider, the aspect ratio is reduced, and the microstructure is refined. The fine microstructure hinders the slip during plastic deformation, thereby improving the material strength. At the same time, the furnace time is extended to promote the increase in the size of some lamellar or needle-shaped α phases, thereby improving plastic toughness.

[0034] 6) The present invention adopts a single-fire rolling process to prepare TC4ELI titanium alloy ultra-wide plates with a thickness specification of 15 to 60 mm and a width specification of 2800 to 4000 mm. Through the optimization of multiple aspects such as composition, surface grinding of titanium alloy flat ingots and spraying of anti-oxidation coatings, heating, rolling, straightening and heat treatment processes, the surface crack scrap rate of the rolled plates is reduced from more than 20% to less than 0.5%; at the same time, no subsequent offline straightening treatment is required to meet the plate shape control requirements (straightness below 8 mm / 2 m). The mechanical properties of the prepared plates are: yield strength ≥880 MPa, tensile strength ≥950 MPa, elongation ≥12%, and room temperature lateral KV2 ≥45 J. DETAILED DESCRIPTION

[0035] The present invention discloses a method for producing TC4ELI titanium alloy medium and thick plates with high yield and low cost, comprising the following steps: grinding and spraying a titanium alloy flat ingot, heating, rolling, online heat straightening, and annealing.

[0036] 1) Grinding and spraying of titanium alloy flat ingots;

[0037] 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;

[0038] 2) heating;

[0039] The titanium alloy slab is heated in a heating furnace. The preheating temperature is 780-850°C and the holding time is 25-40 minutes. The first heating temperature is 870-920°C and the holding time is 30-45 minutes. The second heating temperature is 950-970°C and the holding time is 45-60 minutes. The soaking temperature is 990-1010°C and the holding time is 100-120 minutes. At the same time, the air-fuel ratio in the soaking section is controlled at 1:1.8-1:2.2 to ensure that the temperature difference between the upper and lower surfaces of the titanium alloy slab is within 20°C.

[0040] 3) rolling;

[0041] Before rolling, the roller cooling water is turned off; the titanium alloy flat ingot is rolled back and forth, first horizontally and then vertically, and the reduction rate of each of the first two passes in the horizontal rolling stage is 20% to 25%, and the roller cooling water is turned off during the horizontal rolling stage; at least the first two passes in the longitudinal rolling stage adopt a large reduction rate, with a single-pass reduction rate of 20% to 35%, and at least the reduction rate of the last two passes is controlled below 10%; the rollers are cooled in sections during the longitudinal rolling stage, and 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 200~250m 3 / h; when rolling the tail section, the water volume of the roller is 100-150m 3 / h; the starting rolling temperature is 940-970℃, the rolling speed in the transverse rolling stage is 2-3m / s, the rolling speed in the longitudinal rolling stage is 4-6.5m / s, the final rolling temperature is ≥730℃, and the strip is quickly ejected after rolling at a speed of 5-6.5m / s;

[0042] 3) Online thermal straightening;

[0043] At least three straightening passes are performed; the straightening temperature of hot straightening is 600-700°C, the straightening force is 1500-2500kN, the bending amount is 1-3.0mm, and the tilting value is 3-6mm;

[0044] 4) Annealing treatment;

[0045] The annealing temperature is 780-850° C., and the annealing time is 3-4 hours.

[0046] Furthermore, the chemical composition of the TC4ELI titanium alloy medium and thick plate is as follows by weight: O: 0.06% to 0.11%, Fe: 0.18% to 0.25%, C≤0.07%, H≤0.012%, Al: 5.5% to 6.5%, V: 3.5% to 4.5%, and the remainder is Ti and unavoidable impurity elements.

[0047] Furthermore, the TC4ELI titanium alloy medium and thick plate has a thickness of 15 to 60 mm and a width of 2800 to 4000 mm.

[0048] 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.

[0049] Furthermore, the size of the titanium alloy slab is thickness×width×length=150-250 mm×1550-1950 mm×2500-3800 mm.

[0050] Furthermore, in the step 1), the surface roughness of the titanium alloy slab after grinding is Ra≤100 μm.

[0051] 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 0.5 to 1.0 mm.

[0052] Furthermore, in step 2), 2 to 4 vacancies are left at the furnace head of the soaking section of the heating furnace.

[0053] Furthermore, in step 3), the total length of the titanium alloy ingot is L, the head section is a 1 / 8L length section, the middle section is a 1 / 8L to 7 / 8L length section, and the tail section is a 1 / 8L length section.

[0054] Furthermore, the mechanical properties of the finished TC4ELI titanium alloy medium and thick plates are: yield strength ≥880MPa, tensile strength ≥950MPa, elongation ≥12%, room temperature transverse KV2 ≥45J; the straightness of the finished TC4ELI titanium alloy medium and thick plates is ≤8mm / 2m.

[0055] The present invention provides a method for producing TC4ELI titanium alloy medium and thick plates with a high yield rate and low cost, with a thickness specification of 15 to 60 mm and a width specification of 2800 to 4000 mm. The chemical composition of the TC4ELI titanium alloy medium and thick plates comprises, by weight percentage, O: 0.06% to 0.11%, Fe: 0.18% to 0.25%, C≤0.07%, H≤0.012%, Al: 5.5% to 6.5%, V: 3.5% to 4.5%, and the balance being Ti and unavoidable impurity elements.

[0056] 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 electrode is 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 (150-250) mm thick × (1550-1950) mm wide × (2500-3800) mm long. After rolling on a medium and heavy plate reciprocating rolling mill, TC4ELI titanium alloy ultra-wide plates are obtained. The specific production process includes grinding and spraying the titanium alloy flat ingots → heating → rolling → online hot straightening → annealing. The process and parameter selection reasons are explained as follows:

[0057] 1) Grinding and spraying of titanium alloy slabs: The titanium alloy slabs are subjected to online surface grinding with temperature, such as using a grinding wheel to grind the entire surface of the titanium alloy slab in three dimensions, removing the surface oxide scale and defects to make the surface roughness Ra ≤ 100μm, and then spraying high-temperature nano-SiO2 anti-oxidation coating on the surface of the ground titanium alloy slab with a spraying thickness of 0.5 to 1.0mm.

[0058] 2) Heating: The titanium alloy slab (thickness of 150-250 mm) is sent into a walking beam heating furnace for heating. The titanium alloy slab is 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 780-850 ° C, and the holding time is 25-40 minutes. The purpose is 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 stage is 870-920℃, and the holding time is 30-45min; the temperature range of the second heating stage is 950-970℃, and the holding time is 45-60min; the temperature range of the soaking stage is 990-1010℃, and the holding time is 100-120min. At the same time, the air-fuel ratio of the soaking stage is controlled to be 1:1.8-1:2.2 to ensure that the temperature difference between the upper and lower surfaces of the titanium alloy slab is within 20℃. The purpose of controlling the above parameters is to allow the elements such as O, Fe, C, H, Al and V in the titanium alloy slab to fully diffuse into the matrix; the time in each stage is controlled to ensure the ratio of α and β phases, and the evolution and distribution state of the needle-shaped β phase in the soaking stage is controlled to ultimately ensure the performance of the alloy titanium medium and thick plate. In addition, 2-4 vacancies are left at the furnace head of the soaking stage of the heating furnace to prevent the low furnace head temperature from affecting the heating uniformity of the titanium alloy slab.

[0059] 3) Rolling: Before rolling, the roller cooling water in the rough rolling to hot straightening section is turned off, and the billet (titanium alloy flat ingot) is rolled back and forth using a wide medium and thick plate mill, first horizontally and then vertically. During the horizontal rolling stage, the reduction rate of each of the first two passes is preferably 20% to 25%, and the roller cooling water is turned off during the horizontal rolling stage; during the vertical rolling stage, a large reduction rate is preferably used in the first two passes, with a single pass reduction rate of 20% to 35%, and the reduction rate of the last two passes is preferably controlled below 10%. The performance (anisotropy) of the alloy plate is improved by reversing rolling. A large reduction rate is used in the horizontal rolling stage and the first two passes of the vertical rolling stage to promote the elongation or crushing of the original β phase grains during the deformation process, while promoting the precipitation of secondary α phase transformation in the β phase. At the same time, the reduction rate of the middle pass and the last two passes of the vertical rolling stage is controlled to ensure the coordinated deformation of the two phases and suppress the generation of cracks, while also ensuring sufficient reduction rate to promote the spheroidization and transformation of the lamellar structure into an equiaxed structure. The rollers are cooled in sections during the longitudinal rolling phase. During the rolling process, the cooling water volume of the rollers is 100-150m3 for the 1 / 8L length section of the billet (full length L). 3 / h; for the 1 / 8L to 7 / 8L length section, the roller water volume is 200 to 250m 3 / h; in the tail 1 / 8L length section, the roller water volume is 100~150m 3 / h. By adjusting the water volume of the rolls and reasonably controlling the cooling water volume, the roll shape can be effectively controlled, while avoiding problems such as irregular deviation during the rolling process due to uneven temperature distribution at the head, middle and tail of the titanium alloy flat ingot. The starting rolling temperature in the rolling stage is 940-970℃, the rolling speed in the horizontal rolling stage is 2-3m / s, the rolling speed in the longitudinal rolling stage is 4-6.5m / s, the final rolling temperature is ≥730℃, and the ingot is quickly ejected after rolling at a speed of 5-6.5m / s.

[0060] 4) Online Hot Straightening: Hot straightening is performed in at least three passes at a temperature of 600-700°C, a straightening force of 1500-2500 kN, a roll bending amount of 1-3.0 mm, and a tilting value of 3-6 mm. By reducing the difference in the two-phase ratio, internal stress is fully released, ensuring that the internal stress of the plate after rolling is fully released. Straightening is then performed to avoid the generation of large internal stresses due to rapid phase changes. Appropriate straightening force, roll bending amount, and tilting value are set to ensure good straightness of the plate after straightening.

[0061] 5) Annealing: The annealing temperature is 780-850°C for 3-4 hours. By increasing the annealing temperature, the lamellar α phase is widened and the aspect ratio is reduced. The fine structure hinders the slip during plastic deformation, thereby improving the material strength. At the same time, by extending the furnace time, the size of some lamellar or needle-shaped α phases is promoted to increase, thereby improving the plastic toughness.

[0062] The surface crack scrap rate of TC4ELI titanium alloy medium and thick plates produced using the above process is reduced from more than 20% to less than 0.5%. At the same time, no subsequent offline straightening treatment is required to meet the plate shape control requirements (straightness below 8mm / 2m). The mechanical properties of TC4ELI titanium alloy medium and thick plates are: yield strength ≥880MPa, tensile strength ≥950MPa, elongation ≥12%, and room temperature transverse KV2 ≥45J.

[0063] To make the objectives, technical solutions, and technical effects of the present invention more clear, the process parameters of each production process in the embodiments of the present invention are now described in detail. However, the following embodiments are only some of the embodiments of the present invention, not all of them. In combination with the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0064] [Example]

[0065] Table 1 shows the chemical composition of the 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 the titanium alloy slabs in each embodiment, Table 4 shows the straightening parameters and annealing process parameters of the titanium alloy slabs in each embodiment, and Table 5 shows the dimensions, properties and quality indicators of the TC4ELI titanium alloy medium and thick plates in each embodiment.

[0066] Table 1 Chemical composition of the plates of each embodiment (wt, %)

[0067] Example O Fe C H Al V 1 0.07 0.21 0.06 0.009 5.6 3.7 2 0.11 0.19 0.07 0.011 5.9 4.5 3 0.09 0.25 0.03 0.006 6.3 4.2 4 0.11 0.22 0.07 0.012 5.7 4.3 5 0.06 0.24 0.04 0.007 6.1 3.6

[0068] Note: The balance is Ti and unavoidable impurity elements

[0069] Table 2 Grinding requirements and heating system of titanium alloy slabs in each embodiment

[0070]

[0071] Table 3 Rolling process parameters of titanium alloy slabs in various embodiments

[0072]

[0073] Table 4 Straightening parameters and annealing process parameters of titanium alloy slabs in various embodiments

[0074] Example Hot straightening temperature / ℃ Thermal straightening force / kN Roll bending amount / mm Tilt value / mm Annealing temperature / ℃ Annealing time / h 1 650 1500 1.5 3.6 785 3.2 2 685 2200 2.6 4.7 820 3.5 3 630 2350 1.8 5.9 815 3.7 4 645 1750 2.7 3.2 840 3.8 5 670 1800 1.9 5.3 835 3.1

[0075] Table 5 Dimensions, properties and quality indicators of TC4ELI titanium alloy medium and thick plates in various examples

[0076]

[0077] It can be seen that the production method described in the present invention solves the problem that surface cracks are easily generated when using a single-fire rolling process to produce wide-width TC4ELI titanium alloy hot-rolled medium and thick plates. After the improvement, the surface crack scrap rate is reduced from the usual more than 20% to less than 0.5%, achieving the purpose of no need for or less grinding of the plate after rolling, greatly reducing the labor and material costs of grinding.

[0078] 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 producing TC4ELI titanium alloy medium and thick plates with high yield and low cost, characterized in that: The chemical composition of the TC4ELI titanium alloy medium and thick plate is as follows by weight: O: 0.06% to 0.11%, Fe: 0.18% to 0.25%, C≤0.07%, H≤0.012%, Al: 5.5% to 6.5%, V: 3.5% to 4.5%, with the balance being Ti and unavoidable impurity elements; the TC4ELI titanium alloy medium and thick plate has a thickness of 15 to 60 mm and a width of 2800 to 4000 mm; the production method includes grinding and spraying of titanium alloy slabs, heating, rolling, online hot straightening, and annealing treatment, 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 = 150-250 mm × 1550-1950 mm × 2500-3800 mm; the titanium alloy slab is subjected to hot online full-surface grinding, and the surface roughness after grinding is Ra ≤ 100 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 0.5-1.0 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 780 to 850°C, with a holding time of 25 to 35 minutes. The first heating section temperature is 905 to 915°C, with a holding time of 30 to 45 minutes. The second heating section temperature is 950 to 970°C, with a holding time of 45 to 60 minutes. The soaking section temperature is 990 to 1010°C, with a holding time of 100 to 115 minutes. At the same time, the air-fuel ratio in the soaking section is controlled at 1:1.8 to 1:2.2 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, with a reduction rate of 20% to 25% for at least the first two passes of the horizontal rolling stage, and the roller cooling water is turned off during the horizontal rolling stage; a large reduction rate is used for at least the first two passes of the vertical rolling stage, with a single-pass reduction rate of 20% to 35%, and the reduction rate of at least the last two passes is controlled below 10%; The rollers are cooled in sections during the longitudinal rolling stage. The total length of the titanium alloy flat ingot is L, the head section is 1 / 8L in length, the middle section is 1 / 8L to 7 / 8L in length, and the tail section is 1 / 8L in length. 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 200~250m 3 / h; when rolling the tail section, the water volume of the roller is 100-150m 3 / h; the starting rolling temperature is 940-970℃, the rolling speed in the transverse rolling stage is 2-3m / s, the rolling speed in the longitudinal rolling stage is 4-6.5m / s, the final rolling temperature is ≥730℃, and the strip is quickly ejected after rolling at a speed of 5-6.5m / s; 4) Online thermal straightening; At least three straightening passes are performed; the straightening temperature of hot straightening is 630-700°C, the straightening force is 1500-2500kN, the bending amount is 1-3.0mm, and the tilting value is 3-6mm; 5) Annealing treatment; The annealing temperature is 780-785°C, and the annealing time is 3-4 hours; The mechanical properties of TC4ELI titanium alloy medium and thick plate products are: yield strength ≥880MPa, tensile strength ≥950MPa, elongation ≥12%, room temperature transverse KV2 ≥45J; the straightness of TC4ELI titanium alloy medium and thick plate products is ≤8mm / 2m.

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