A method for manufacturing TC4ELI titanium alloy medium and thick plates with excellent high cycle fatigue performance

Abstract

The present invention relates to a method for manufacturing a TC4ELI titanium alloy medium and thick plate with excellent high-cycle fatigue performance. The method comprises the following processes: grinding, spraying, heating, rolling, online hot straightening and annealing of a titanium alloy flat ingot. The method adopts optimized spraying, heating and rolling processes, as well as flexible high-pressure water descaling and annealing processes, to ultimately prepare a wide TC4ELI titanium alloy medium and thick plate with a width of 2800 to 4000 mm and a thickness of 6 to 40 mm. The method solves the problem of surface cracks being easily generated during the production process of the wide TC4ELI titanium alloy hot-rolled medium and thick plate, reduces the scrap rate due to surface cracks from over 10% to under 1%, and achieves excellent high-cycle fatigue performance of the finished plate.

Description

Technical Field

[0001] The present invention relates to the technical field of medium and thick plate production, and in particular to a method for manufacturing a TC4ELI titanium alloy medium and thick plate with a thickness of 6 to 40 mm, a width greater than 2800 mm and excellent high-cycle fatigue performance. 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 high fatigue resistance. Currently, the demand for wide and large-sized titanium alloy sheet is growing. This is primarily because using wide and large-sized titanium alloy sheet, with a width greater than 2800 mm, reduces weld seams and the amount of weld material flaw detection required during the manufacturing process. At the same time, titanium alloy sheet must also maintain high impact load resistance and fatigue resistance to enhance service safety. 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 alloys, cracks are easily generated on the surface and edges of the rolled product. Furthermore, the large deformation caused by rolling at relatively low temperatures significantly increases the load on the rolling equipment, placing higher demands on its capacity, thus limiting its application in titanium alloy sheet production.

[0003] At present, the conventional production process 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, and at the same time, 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 kept 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 production process is that it allows the rolling mill equipment to complete the deformation process under a lower load, but it inevitably increases the energy consumption of the entire rolling process; and the excessively high final rolling temperature and the small rolling deformation will have an adverse effect on the uniformity and refinement of the plate structure and the improvement of the overall performance. It can be seen from this that how to solve the generation of surface cracks in the above-mentioned TC4ELI titanium alloy plates with a thickness of 6 to 40 mm and a width greater than 2800 mm and improve their fatigue performance are the keys to their product development and application.

[0004] To date, there has been little research, both domestically and internationally, on how to improve the high-cycle fatigue performance of wide TC4ELI titanium alloy plates and reduce their surface cracking. Chinese patent application publication number CN 103203361 A discloses a "rolling method for wide, thick TC4 titanium alloy plates." This method employs low-temperature, large-deformation, two-pass rolling. By water-cooling each pass to achieve rapid cooling, it preserves the low-temperature, large-deformation structure and ensures that the steel plate performance meets requirements. However, it does not address research on improving high-cycle fatigue performance. Chinese patent application publication number CN 108838208 A discloses a "two-pass rolling method for wide TC4 titanium alloy billets." This method employs appropriate heating and soaking processes, and employs two-pass rapid warming rolling during the rolling process, effectively preventing buckling, warping, and other phenomena caused by temperature drop during the slab rolling process. However, the thickness of the finished plates produced is 42-46mm and the width is 3800-3900mm. The manufacturing process for titanium alloy plates with a thickness of 6-40mm is not covered. Chinese patent application with publication number CN 103203361 A discloses a "rolling method for wide and thick TC4 titanium alloy plates." It uses low-temperature, large-deformation two-pass rolling. By water cooling after each pass of rolling to achieve rapid cooling, it can retain the low-temperature, large-deformation structure and thus ensure that the plate performance meets the requirements. However, its product performance cannot meet the technical requirements for deep-sea service, and the plate width is less than 2800mm. At the same time, the use of a two-pass rolling process increases energy consumption and process costs.

[0005] In the journal article "Effect of Rolling Process on the Microstructure and Mechanical Properties of TC4ELI Titanium Alloy Ultra-Wide Thick Plate" (authored by Li Rui et al., "Journal of Materials Heat Treatment", Issue 1, 2020), the mechanical properties of the plate were guaranteed by optimizing the control of the rolling phase transition point temperature range, but the width and thickness group spacing of the plate suitable for its production process and the fatigue performance requirements were not clarified.

[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 mitigate surface cracking in TC4ELI titanium alloy sheets with a thickness of 6 to 40 mm and a width greater than 2800 mm, while also failing to achieve the fatigue performance required for aircraft engine service. The technical solution provided by the present invention effectively overcomes the shortcomings of these prior arts and addresses the high surface crack rate and low high-cycle fatigue performance associated with producing TC4ELI titanium alloy sheets of these specifications. Summary of the Invention

[0007] The present invention provides a method for manufacturing TC4ELI titanium alloy medium and thick plates with excellent high-cycle fatigue performance. The method adopts optimized spraying process, heating process and rolling process, and adopts flexible high-pressure water descaling process and annealing process, and finally prepares TC4ELI titanium alloy wide medium and thick plates with a width of 2800-4000 mm and a thickness of 6-40 mm. The problem of surface cracks easily generated during the production process of wide TC4ELI titanium alloy hot-rolled medium and thick plates is solved, and the surface crack scrap rate is reduced from more than 10% to less than 1%. At the same time, the finished plates have excellent high-cycle fatigue performance.

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

[0009] A method for manufacturing TC4ELI titanium alloy medium and thick plates with excellent high-cycle fatigue performance includes grinding, spraying, heating, rolling, online hot 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 820-870°C and the holding time is 30-45 minutes. The first heating temperature is 890-930°C and the holding time is 35-50 minutes. The second heating temperature is 965-990°C and the holding time is 45-60 minutes. The soaking temperature is 1000-1050°C and the holding time is 120-150 minutes. At the same time, the air-fuel ratio in the soaking section is controlled at 1:1.9-1:2.4 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 EB flat steel is rolled back and forth, first horizontally and then longitudinally; the reduction rate of at least the first two passes in the horizontal rolling stage is 25% to 35%, and the rolling temperature in the horizontal rolling stage is greater than 920°C; at least the first two passes in the longitudinal rolling stage adopt a large reduction rate, with a single pass reduction rate of 30% to 45%, and at least the last two passes with a pass reduction rate of 10% to 20%; the rollers are cooled in sections during the rolling process, 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; 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 is 10-20s each time; the rolling speed is 2-4.5m / s, the final rolling temperature is ≥800℃, and the ejection speed after rolling is 4-6.5m / s;

[0016] 4) Online thermal straightening;

[0017] At least three straightening passes are performed. The straightening temperature of hot straightening is 740-770°C, the straightening force is 1500-2000kN, the bending amount is set to 1.5-2.0mm, and the tilting value is set to 2-4mm.

[0018] 5) Annealing treatment;

[0019] The annealing temperature is 780-850° C., and the annealing time is 3-4 hours.

[0020] Furthermore, the chemical composition of the TC4ELI titanium alloy medium and thick plate is as follows by weight: O: 0.09% to 0.13%, 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 medium and thick plate has a thickness of 6 to 40 mm and a width greater 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=85-200 mm×1750-1950 mm×2500-3800 mm.

[0024] Furthermore, in the step 1), the surface roughness of the titanium alloy slab after grinding is Ra≤100 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 0.8 to 1.3 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 the step 3), rolling is performed on a medium and thick plate reciprocating rolling mill; the total length of the titanium alloy flat ingot is L, the head section is a 1 / 6L length section of the head, the middle section is a 1 / 6L to 5 / 6L length section, and the tail section is a 1 / 6L length section of the tail.

[0028] Furthermore, the mechanical properties of the finished TC4ELI titanium alloy medium and thick plates are: yield strength ≥880MPa, tensile strength ≥970MPa, elongation ≥15%, room temperature transverse KV2 ≥60J, and 900°C high cycle fatigue limit stress ≥350MPa.

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

[0030] 1) The composition of the TC4ELI titanium alloy medium and thick plate of the present invention is rationally designed. By limiting the contents of O and Fe elements, the O and Fe contents in the titanium alloy plate are ensured to be 0.09% to 0.13% and 0.20% to 0.25%, respectively. When the oxygen content in the plate is high, oxygen atoms enter the interior of the titanium alloy plate to generate second-type internal stress, causing lattice deformation of the titanium alloy, increasing resistance to dislocation movement, and thereby improving the strength of the TC4ELI titanium alloy plate. As a strong β-phase stabilizing element, Fe is added to the titanium alloy plate mainly to form a TiFe intermediate phase, ensuring that when the O content is limited, the impurity Fe content is increased, 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 surface of the titanium alloy ingot from being overburned when it comes into contact with open flames during the heating process in a walking beam heating furnace. As a result, a large amount of Widmanstätten β phase structure is generated on the surface, resulting in uncoordinated deformation of the two phases in the subsequent rolling process and surface cracks.

[0032] 3) 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 titanium alloy EB flat steel, and leave 2 to 4 vacancies in the furnace head of soaking section of heating furnace to prevent the low temperature of furnace head from affecting the heating uniformity of titanium alloy flat ingot; thereby ensuring the uniformity of transverse and longitudinal metal flow on the upper and lower surfaces during the rolling process of titanium alloy plate.

[0033] 4) 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 to produce an uncontrolled temperature drop. At the same time, 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; a segmented cooling process is adopted for the rollers to avoid a large amount of cooling water flowing on the surface of the plate to produce an uncontrolled temperature drop and thereby increase the number of rolling passes. The cooling water volume of the rollers is reasonably controlled to effectively control the roller shape, which greatly improves the irregular deviation and sickle bending defects caused by uneven temperature distribution of the head, middle and tail of the intermediate billet during the rolling process. The performance (anisotropy) of titanium alloy plates is improved by reversing rolling. A large reduction rate is used in the transverse rolling stage, and the rolling temperature is restricted at the same time, thereby enhancing the diffusion of the nascent α phase, swallowing up the surrounding fine α phase, and promoting the transformation from α phase to β phase, so that the size of the nascent α phase is reduced and the content is reduced; a large reduction rate is used in 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 in the β phase, resulting in the refinement of grains from the surface to the center of the titanium alloy flat ingot. At the same time, the reduction rate of the last two passes of the longitudinal rolling stage is controlled to ensure the coordinated deformation of the two phases and inhibit 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 first three passes of the longitudinal rolling mill are sprayed with descaling water to cool the surface, so that a temperature gradient is generated between the surface and the center, so that the deformation resistance of the plate surface is greater than that of the center, which is conducive to the expansion of deformation from the surface to the center.

[0034] 5) By controlling the straightening temperature, the difference in the two-phase ratio is reduced, the internal stress is fully released, and the internal stress of the titanium alloy 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 good straightness of the straightened plate.

[0035] 6) By increasing the annealing temperature, the lamellar α phase is promoted to become wider, the aspect ratio is reduced, and the microstructure is ensured to be refined. The fine microstructure hinders the slip during plastic deformation, thereby improving the strength of the material; 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 of the material.

[0036] 7) The present invention prepares TC4ELI titanium alloy plates with a thickness of 6 to 40 mm and a width greater than 2800 mm through systematic optimization of multiple aspects such as composition, surface grinding and spraying of anti-oxidation coatings on titanium alloy slabs, heating, rolling, straightening and heat treatment processes. This solves the problems of surface cracks easily generated during the production of TC4ELI titanium alloy wide medium and thick plates and low fatigue performance of the finished products. The surface crack scrap rate is reduced from more than 10% to less than 1%, meeting the service requirements for high-cycle fatigue resistance. The mechanical properties of the plates are: yield strength ≥880 MPa, tensile strength ≥970 MPa, elongation ≥15%, room temperature transverse KV2 ≥60 J, and 900°C high-cycle fatigue limit stress ≥350 MPa. DETAILED DESCRIPTION

[0037] The present invention provides a method for manufacturing a TC4ELI titanium alloy medium and thick plate with excellent high-cycle fatigue performance, comprising the steps of grinding, spraying, heating, rolling, online heat straightening, and annealing of a titanium alloy flat ingot. The specific steps are 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 820-870°C and the holding time is 30-45 minutes. The first heating temperature is 890-930°C and the holding time is 35-50 minutes. The second heating temperature is 965-990°C and the holding time is 45-60 minutes. The soaking temperature is 1000-1050°C and the holding time is 120-150 minutes. At the same time, the air-fuel ratio in the soaking section is controlled at 1:1.9-1:2.4 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 EB flat steel is rolled back and forth, first horizontally and then longitudinally; the reduction rate of at least the first two passes in the horizontal rolling stage is 25% to 35%, and the rolling temperature in the horizontal rolling stage is greater than 920°C; at least the first two passes in the longitudinal rolling stage adopt a large reduction rate, with a single pass reduction rate of 30% to 45%, and at least the last two passes with a pass reduction rate of 10% to 20%; the rollers are cooled in sections during the rolling process, 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; 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 is 10-20s each time; the rolling speed is 2-4.5m / s, the final rolling temperature is ≥800℃, and the ejection speed after rolling is 4-6.5m / s;

[0044] 4) Online thermal straightening;

[0045] At least three straightening passes are performed. The straightening temperature of hot straightening is 740-770°C, the straightening force is 1500-2000kN, the bending amount is set to 1.5-2.0mm, and the tilting value is set to 2-4mm.

[0046] 5) Annealing treatment;

[0047] The annealing temperature is 780-850° C., and the annealing time is 3-4 hours.

[0048] Furthermore, the chemical composition of the TC4ELI titanium alloy medium and thick plate is as follows by weight: O: 0.09% to 0.13%, 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.

[0049] Furthermore, the TC4ELI titanium alloy medium and thick plate has a thickness of 6 to 40 mm and a width greater than 2800 mm.

[0050] 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.

[0051] Furthermore, the size of the titanium alloy slab is thickness×width×length=85-200 mm×1750-1950 mm×2500-3800 mm.

[0052] Furthermore, in the step 1), the surface roughness of the titanium alloy slab after grinding is Ra≤100 μm.

[0053] 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 0.8 to 1.3 mm.

[0054] Furthermore, in step 2), 2 to 4 vacancies are left at the furnace head of the soaking section of the heating furnace.

[0055] Furthermore, in the step 3), rolling is performed on a medium and thick plate reciprocating rolling mill; the total length of the titanium alloy flat ingot is L, the head section is a 1 / 6L length section of the head, the middle section is a 1 / 6L to 5 / 6L length section, and the tail section is a 1 / 6L length section of the tail.

[0056] Furthermore, the mechanical properties of the finished TC4ELI titanium alloy medium and thick plates are: yield strength ≥880MPa, tensile strength ≥970MPa, elongation ≥15%, room temperature transverse KV2 ≥60J, and 900°C high cycle fatigue limit stress ≥350MPa.

[0057] The present invention provides a method for manufacturing a TC4ELI titanium alloy medium and thick plate with a thickness of 6 to 40 mm and a width greater than 2800 mm and excellent high-cycle fatigue performance. The chemical composition of the TC4ELI titanium alloy medium and thick plate (hereinafter referred to as titanium alloy medium and thick plate) includes, by weight percentage, O: 0.09% to 0.13%, 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.

[0058] First, using first-grade titanium sponge, Al-V master alloy, and high-purity Al (Al content above 99.9%) as the charge, the electrode is pressed and smelted in an electron beam cooling hearth furnace (EB furnace) to obtain a TC4ELI titanium alloy flat ingot (referred to as titanium alloy flat ingot) with a size of (85-200) mm thick × (1750-1950) mm wide × (2500-3800) mm long. The finished titanium alloy medium and thick plate is then rolled in a medium and thick plate reciprocating rolling mill. The production process includes grinding and spraying the titanium alloy flat ingot → heating → rolling → online hot straightening → annealing. The specific process route and reasons for selecting process parameters are as follows:

[0059] 1) Grinding and spraying of titanium alloy slabs: The titanium alloy slabs are subjected to online surface grinding with temperature, and the grinding wheel is used to grind the entire surface in three dimensions to remove surface oxide scale and defects. The surface roughness after grinding is Ra ≤ 100 μm. The surface of the ground titanium alloy slabs is sprayed with high-temperature nano-SiO2 anti-oxidation coating with a spraying thickness of 0.8 to 1.3 mm.

[0060] 2) Heating: The titanium alloy slab (thickness 85-200mm) is placed in 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 820-870℃, and the holding time is 30-45min. During this process, the elements O, Fe, C, H, Al and V in the titanium alloy slab are initially diffused into the matrix; the temperature range of the first heating section is 890-930℃, and the holding time is 35-50min; the temperature range of the second heating section is 965-990℃, and the holding time is 100-200min. The time is 45 to 60 minutes; the temperature range of the soaking section is 1000 to 1050 ° C, and the holding time is 120 to 150 minutes. At the same time, the air-fuel ratio of the soaking section is controlled to be 1:1.9 to 1:2.4 to ensure that the temperature difference between the upper and lower surfaces of the titanium alloy slab is within 20 ° C. Through this process, 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 ultimately 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 slab.

[0061] 3) Rolling and High-Pressure Water Descaling: Before rolling, the roller cooling water is turned off between roughing and hot straightening to prevent excessive cooling water from flowing along the lower surface of the intermediate bar, causing uncontrolled temperature drops and increasing the number of rolling passes. This also helps maintain the intermediate bar in a horizontal or slightly tilted state, creating favorable conditions for mill engagement. The billet (titanium alloy flat ingot) is rolled in a wide plate mill, first in transverse and then longitudinal rolling. During transverse rolling, the preferred reduction ratio for the first two passes is 25%-35%, and the rolling temperature during the transverse rolling stage is >920°C. This stage enhances the diffusion of the nascent α phase, incorporating surrounding fine α phases while promoting the α-to-β phase transformation, reducing the size and content of the nascent α phase. During longitudinal rolling, a high reduction ratio is preferably used in the first two passes, with a single pass reduction ratio of 30%-45%, and the final two passes with a reduction ratio of 10%-20%. The performance (anisotropy) of titanium alloy plates is improved by reversing rolling. A large reduction rate is used in the first two passes of the transverse rolling stage and the longitudinal rolling stage to promote the elongation or crushing of the original β-phase grains during the deformation process, providing a driving force for the subsequent spheroidization and transformation of the β-phase lamellar structure into an equiaxed structure. In the process of rolling titanium alloy flat ingots, the rollers are cooled in sections. It is preferred that the roller cooling water volume be 100-150m3 when the length section of the rolling head is 1 / 6L. 3 / h, when rolling the middle 1 / 6L-5 / 6L length section, the water volume of the roller should be 200~250m 3 / h; when rolling the tail 1 / 6L length section, the roller water volume is 100~150m 3 / h. By adjusting the water flow to the rolls and rationally controlling the cooling water volume, the roll shape can be effectively controlled, and the irregular deviation during rolling caused by the uneven temperature distribution of the head, middle, and tail of the titanium alloy flat ingot can be greatly improved. During the first three passes of the longitudinal rolling stage, the mill is sprayed with descaling water at a pressure of 10-15 MPa and a descaling time of 10-20 seconds per pass; the rolling speed is 2-4.5 m / s, the final rolling temperature is ≥800°C, and the post-rolling ejection speed is 4-6.5 m / s.

[0062] 4) Online hot straightening: Hot straightening is preferably carried out in three steps. The straightening temperature of hot straightening is 740-770℃, the straightening force is between 1500-2000kN, the bending roller amount is set at 1.5-2.0mm, and the tilting value is set at 2-4mm. 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 the generation of large internal stress due to rapid phase change. By setting appropriate bending roller amount, straightening force and tilting value, the straightness of the straightened plate is guaranteed to be good.

[0063] 5) Annealing: The annealing temperature is 780-850°C and the annealing time is 3-4 hours. By increasing the annealing temperature, the lamellar α phase is widened, the aspect ratio is reduced, and the fine structure hinders the slip during plastic deformation, thereby improving the fatigue strength of the material. By extending the time in the furnace, the size of some lamellar phases is increased, and the plastic toughness of the material is improved.

[0064] The present invention adopts the above-mentioned composition and process to realize the production of TC4ELI titanium alloy medium and thick plates with excellent high-cycle fatigue performance and a thickness of 6 to 40 mm and a width greater than 2800 mm. The problem of surface cracks easily generated during the production of wide-width TC4ELI titanium alloy medium and thick plates is solved. The scrap rate of surface cracks is reduced from more than 10% to less than 1%, and the service requirements for high-cycle fatigue resistance are met. The mechanical properties of the produced plates are: yield strength ≥880 MPa, tensile strength ≥970 MPa, elongation ≥15%, room temperature transverse KV2 ≥60 J, and 900°C high-cycle fatigue limit stress ≥350 MPa.

[0065] 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.

[0066] [Example]

[0067] 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 flat ingots in each embodiment, Table 3 shows the ingot rolling process parameters in each embodiment, Table 4 shows the high-pressure water descaling process parameters in the longitudinal rolling stage in each embodiment, Table 5 shows the straightening parameters and annealing process parameters in each embodiment, and Table 6 shows the finished product size, performance and quality indicators of the TC4ELI titanium alloy medium and thick plates in each embodiment.

[0068] Table 1 Chemical composition of titanium alloy medium and thick plates in various embodiments (wt, %)

[0069] Example O Fe C H Al V 1 0.10 0.21 0.06 0.009 5.6 3.9 2 0.11 0.22 0.07 0.011 5.8 4.5 3 0.09 0.25 0.03 0.006 6.3 4.2 4 0.13 0.23 0.07 0.012 5.9 4.4 5 0.12 0.24 0.04 0.007 6.4 3.8

[0070] Note: Others are residual Ti and unavoidable impurity elements

[0071] Table 2 Grinding requirements and heating system of titanium alloy slabs in each embodiment

[0072]

[0073] Table 3 Rolling process parameters of each embodiment

[0074]

[0075] Table 4 High-pressure water descaling process parameters in the longitudinal rolling stage of each embodiment

[0076]

[0077] Table 5 Straightening parameters and annealing process parameters of each embodiment

[0078] Example Hot straightening temperature / ℃ Thermal straightening force / kN Roll bending amount / mm Tilt value / mm Annealing temperature / ℃ Annealing time / h 1 745 1550 1.5 3.6 785 3.2 2 755 1950 2.0 2.6 830 3.5 3 770 1850 1.8 3.8 845 4.0 4 755 1750 1.7 3.0 850 3.8 5 740 1900 1.9 3.2 810 3.9

[0079] Table 6 Dimensions, properties and quality indicators of finished products of TC4ELI titanium alloy medium and thick plates in various embodiments

[0080]

[0081] As can be seen, compared with existing technologies, the present invention provides a method for manufacturing TC4ELI titanium alloy medium and thick plates with a thickness of 6-40 mm and a width greater than 2800 mm, exhibiting excellent high-cycle fatigue performance. The technical solution provided by the present invention solves the problems of TC4ELI titanium alloy wide medium and thick plates prone to surface cracking and poor fatigue performance. The surface crack rejection rate has been reduced from over 10% in the initial stage to below 1%, meeting the service requirements for high-cycle fatigue resistance.

[0082] 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 TC4ELI titanium alloy medium and thick plates with excellent high cycle fatigue performance, characterized in that: The TC4ELI titanium alloy medium and thick plate has a thickness of 6 to 40 mm and a width greater than 2800 mm. The chemical composition of the TC4ELI titanium alloy medium and thick plate is as follows by weight: O: 0.09% to 0.13%, Fe: 0.20% to 0.25%, C 0.06% to 0.07%, H ≤ 0.012%, Al: 6.4% to 6.5%, V: 3.8% to 4.5%, with the remainder being Ti and unavoidable impurity elements. The manufacturing method includes grinding and spraying a titanium alloy flat ingot, 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 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, pressing electrodes, and smelting in an EB furnace to obtain the titanium alloy slab ingot; the titanium alloy slab ingot has a size of thickness × width × length = 85-200 mm × 1750-1950 mm × 2500-3800 mm; the titanium alloy slab ingot is subjected to hot online full-surface grinding, and the surface of the ground titanium alloy slab is sprayed with a high-temperature anti-oxidation coating; the surface roughness Ra of the ground titanium alloy slab is ≤100 μm; 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 0.8-1.3 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 820 to 870°C, with a holding time of 30 to 35 minutes. The first heating section temperature is 890 to 910°C, with a holding time of 35 to 50 minutes. The second heating section temperature is 965 to 990°C, with a holding time of 45 to 60 minutes. The soaking section temperature is 1000 to 1050°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 1:1.9 to 1:2.4 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 EB flat steel is rolled back and forth on the medium and thick plate reciprocating rolling mill, first horizontally and then longitudinally; the reduction rate of at least the first two passes in the horizontal rolling stage is 25% to 35%, and the rolling temperature in the horizontal rolling stage is greater than 920°C; at least the first two passes in the longitudinal rolling stage adopt a large reduction rate, a single pass reduction rate of 30% to 45%, and a reduction rate of at least the last two passes of 10% to 20%; the rollers are cooled in sections during the rolling process, the total length of the titanium alloy flat ingot is L, the head section is the head 1 / 6L length section, the middle section is the 1 / 6L to 5 / 6L length section, and the tail section is the tail 1 / 6L 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 200~250m 3 / h; when rolling the tail section, the water volume of the roller is 100-150m 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 is 10-20s each time; the rolling speed is 2-4.5m / s, the final rolling temperature is ≥800℃, and the ejection speed after rolling is 4-6.5m / s; 4) Online thermal straightening; At least three straightening passes are performed. The straightening temperature of hot straightening is 740-770°C, the straightening force is 1500-2000kN, the bending amount is set to 1.5-2.0mm, and the tilting value is set to 2-4mm. 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 ≥970MPa, elongation ≥15%, room temperature transverse KV2 ≥60J, 900℃ high cycle fatigue limit stress ≥350MPa.

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