A method for preparing thick plates by single-fire direct rolling of Ti80 titanium alloy EB flat ingots.

Abstract

A method for preparing thick plates from Ti80 titanium alloy EB flat ingots by single-fire direct rolling is disclosed. The method involves selecting Ti80 titanium alloy EB flat ingots, heating them through multi-stage temperature control, and then performing single-fire rolling. The rolling process involves coordinated control of heating temperature, deformation, and phase transformation. Finally, the plates undergo straightening and annealing. Under conditions where the total deformation in a single-fire rolling process is 65-93%, Ti80 titanium alloy plates with excellent shape and a thickness of 15-125 mm are obtained. The mechanical properties of the Ti80 titanium alloy thick plates produced by this invention meet the requirements. Furthermore, this invention eliminates the need for multiple forging processes involving vacuum consumable arc melting of Ti80 titanium alloy round ingots, shortening the process flow and production cycle, reducing production costs, and increasing the yield to over 70%, making it suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of metal metallurgical manufacturing, specifically to a method for preparing thick plates from Ti80 titanium alloy EB flat ingots by single-fire direct rolling. Background Technology

[0002] Ti80 titanium alloy (Ti-6Al-3Nb-2Zr-1Mo) is a near-alpha type titanium alloy with characteristics such as low density, high specific strength, high temperature resistance, and non-magnetic properties. The excellent comprehensive properties of Ti80 titanium alloy make it widely used in aerospace, chemical, and shipbuilding fields, and it also has broad application prospects in marine engineering equipment such as pressure hulls for deep-sea submersibles.

[0003] Currently, most Ti80 titanium alloy plates are produced using the "vacuum self-consumable (VAR) ingot-forging billet-hot rolling" method. This process is lengthy, has low production efficiency, and suffers from high process losses (approximately 40-50%), resulting in high production costs and hindering its widespread application in aerospace, chemical, and marine engineering equipment fields.

[0004] With technological advancements, some manufacturers are also using electron beam melting furnaces (EB furnaces) to cast titanium alloy flat ingots. These EB furnaces are renowned for their exceptional refining capabilities and are a new type of specialized equipment for melting and purification. Because melting occurs under high vacuum, the process involves high superheat temperatures and a long period of time maintaining the liquid state, effectively refining and purifying the material. Direct rolling into plates using EB furnace heating is a highly efficient, short-process thick plate manufacturing technology that also allows the use of recycled materials, reducing raw material costs.

[0005] There are also related patents for using an EB furnace to prepare titanium alloy EB flat ingot rolled plates, as follows:

[0006] 1) A method for rolling TC4 titanium alloy flat ingots and TC4 titanium alloy plates according to patent number CN112371725B involves heating TC4 titanium alloy flat ingots above their phase transformation temperature and holding them at that temperature to obtain a billet to be rolled; spraying an anti-oxidation coating onto the billet before rolling; repeating the rolling process multiple times to obtain the final billet; and finally placing the billet on a straightening machine for preliminary straightening to obtain the rolled TC4 titanium alloy plates. This patent uses electron beam cold-hearth melting of TC4 titanium alloy flat ingots as material, which are then heated and rolled into TC4 titanium alloy plates.

[0007] 2) A low-cost, short-process rolling technology for titanium alloys, patent number CN112517633 B, involves heating flat ingots melted in an electron beam cold hearth furnace to a temperature above the phase transformation point, performing a first-stage rolling, followed by water cooling to obtain a first hot-rolled slab; then performing a second-stage hot rolling to obtain a second hot-rolled slab; next, performing intermediate recrystallization annealing; then performing a third-stage hot rolling to obtain a third hot-rolled slab; and finally performing finished product annealing to obtain a titanium alloy slab with a thickness of 4mm to 12mm. This patent uses TC4 titanium alloy flat ingots obtained by electron beam cold hearth furnace melting to directly perform three-stage rolling to obtain plates with a thickness of 4mm to 12mm.

[0008] 3) A method for single-rolling thin-gauge ultra-wide TC4 titanium alloy plates using patent number CN120079718B. The method employs EB flat ingots, explosive bonding, slab heating, single-rolling, straightening and annealing processes to obtain thin-gauge ultra-wide TC4 titanium alloy plates with a width of 3500-4300 mm and a thickness of 20-30 mm. The microstructure of the thin-gauge ultra-wide TC4 titanium alloy plates is an α+β dual-state structure.

[0009] 4) A high-yield, low-cost process for producing high-quality TC4 alloy hot-rolled plates (patent number CN103045906B) involves preparing EB flat ingots, grinding and hot rolling, atmospheric annealing, sandblasting, pickling, grinding, and length setting to obtain annealed TC4 hot-rolled plates. This patent uses four heats to roll TC4 titanium alloy EB flat ingots to produce 4mm finished plates.

[0010] However, the aforementioned patents primarily target TC4 titanium alloys, focusing on room temperature tensile properties. For Ti80 titanium alloys, however, the higher alloy content results in greater deformation resistance than TC4, a narrower hot working window, and a greater susceptibility to cracking during rolling. Furthermore, as a titanium alloy used in marine engineering equipment, Ti80 titanium alloys require not only room temperature tensile strength but also impact performance as a crucial evaluation indicator, both of which are closely related to the hot rolling process.

[0011] Therefore, there is an urgent need for a new method for preparing Ti80 titanium alloy, which can produce medium-thick Ti80 titanium alloy plates with excellent microstructure and properties and a thickness of 20-125 mm. Summary of the Invention

[0012] This invention addresses the characteristics of Ti80 titanium alloy preparation and the requirements of its application fields by providing a method for preparing thick plates from Ti80 titanium alloy EB flat ingots through single-pass direct rolling. By rationally setting the heating temperature, total deformation amount, and deformation amount per pass, this invention can obtain Ti80 titanium alloy thick plate products with excellent microstructure and properties and a thickness of 20-120mm.

[0013] The present invention discloses a method for preparing thick plates by single-fire direct rolling of Ti80 titanium alloy EB flat ingots, comprising the following steps:

[0014] S1. Select a Ti80 titanium alloy EB flat ingot with a thickness of 200-350mm, mill the surface of the flat ingot, and use an explosive bonding method to bond a pure titanium plate TA1 or pure titanium plate TA2 with a thickness of 1-3mm to the upper and lower surfaces of the flat ingot to form a Ti80 titanium alloy EB composite flat ingot. Apply an anti-oxidation and heat insulation coating to the upper surface and around the Ti80 titanium alloy EB composite flat ingot.

[0015] S2, The Ti80 titanium alloy EB composite flat ingot is fed into a heating furnace for heating. A stepped heating method is used. The Ti80 titanium alloy EB composite flat ingot is fed into the heating furnace and heated to 400~600±10℃ and held for 1~2h. Then it is heated to 800~900℃±10℃ and held for 2~3h. Finally, it is heated to Tβ+50~100℃ and held for 2h before being taken out of the furnace. Tβ is the transformation temperature of the β phase transformation point of the EB flat ingot, in ℃.

[0016] The objective of this invention is to set two heat preservation steps below the Tβ phase transformation point, at 400~600±10℃ and 800~900℃±10℃, to eliminate the temperature difference between the core and surface of the thick plate and reduce internal and external thermal stress during the heating process. The billet is selected to be heated in the β region, and the heat preservation temperature is selected to be Tβ+50~100℃ with a heat preservation coefficient of 1.2~2.0min / mm. At this time, the titanium alloy has excellent plasticity and low deformation resistance, and can withstand a huge amount of heat deformation (breaking the as-cast structure and triggering dynamic recrystallization) without cracking.

[0017] The purpose of β-zone rolling is to break down the original cast grains. The core principle is to provide sufficient driving force and necessary atomic diffusion capacity for dynamic recrystallization through "large deformation" and "suitable temperature," thereby completing the transformation from "coarse cast structure" to "fine machined structure." The adjacent strain εc∝exp(Q / RT) that triggers recrystallization, along with increasing the deformation temperature, dramatically enhances atomic diffusion capacity, making recrystallization nucleation and growth easier. This is the most effective means of reducing the critical strain.

[0018] The holding temperature of Tβ+50~100℃ is selected based on thermal simulation results and takes into account factors such as surface temperature drop during rolling. The first heating temperature is ≥Tβ+50℃. If the heating temperature is too high, the recrystallization grains will grow severely. Therefore, the billet heating temperature is controlled to ≤Tβ+100℃.

[0019] S3, single-pass rolling of sheet metal, as detailed below:

[0020] The Ti80 titanium alloy EB composite flat ingot heated from S2 is fed into a four-roll reversible rolling mill in the steel production line. The mill is used to carry out alternating horizontal and vertical rolling, and the plate is rolled into the target thickness in a single fire and multiple passes. The total deformation during the rolling process is 65-93%, the initial rolling temperature is ≥1000℃, and the final rolling temperature is controlled to be ≥750℃.

[0021] The purpose of this invention is that, in specific implementation, depending on the size of the rolling mill and the billet, it can be rolled horizontally first and then longitudinally, or rolled longitudinally first and then horizontally. Since unidirectional rolling easily causes the grains to elongate in one direction, forming texture, and the recrystallization nucleation points are limited, changing the rolling direction can generate more directional slip systems and dislocation entanglements inside the grains, weakening the texture. On the other hand, this is also a requirement of specifications, and the deformation amount of horizontal rolling is determined according to the needs of the specifications.

[0022] During rolling, the reduction in the first and second passes is 2-8%, and the deformation in subsequent passes increases to 10-20%. When the cumulative reduction reaches 45-70%, a small deformation of <10% is adopted. During rolling, the bite speed is 1.0-1.5 m / s, and the rolling speed of the remaining passes is controlled at 1.5-3.5 m / s.

[0023] In the specific process of this invention, the first and second passes use a small deformation amount of 2-8% to refine the surface microstructure and improve plasticity, thereby preventing surface cracking during subsequent rolling. Afterwards, the deformation amount is rapidly increased to 10-20%, utilizing the high plasticity of the β-phase region to rapidly fragment the original as-cast microstructure. The maximum deformation amount per pass is limited by the rolling force and torque (due to the thick billet and high torque), and does not exceed 20%.

[0024] Furthermore, the selection of rolling speed in this invention is based on the fact that when rolling in the β-phase region, a large strain rate (corresponding to fast rolling speed and large reduction) can quickly refine the grains. On the other hand, appropriately reducing the rolling speed (strain rate) allows more time for atomic diffusion and recrystallization nucleation, reducing the critical strain required for dynamic recrystallization and making it possible to trigger recrystallization with small deformation. From the perspective of rolling process, if the rolling speed is too slow, the surface temperature drop will be large, increasing the risk of cracking. If the rolling speed is too fast, the steel ejection distance will be long, and the time for the slab to re-bite the roll will also increase. Therefore, combining microstructure control and on-site rolling experience, this invention selects a bite speed of 1.0 to 1.5 m / s during rolling, and controls the rolling speed of other passes at 1.5 to 3.5 m / s.

[0025] A high-precision temperature measuring instrument is installed at the exit of the rolling mill to monitor the actual temperature of the plate in real time. If the surface temperature of the plate is >920℃ after 50-70% deformation is completed, the roller speed is reduced or the billet is briefly stopped to control the billet temperature through radiative heat dissipation on the rollers until the surface temperature reaches 900±20℃; otherwise, it directly enters the subsequent rolling process.

[0026] In order to control the temperature during the hot rolling process, especially the rapid and accurate transition to the two-phase region after rolling in the β single-phase region, which directly determines the microstructure and final properties of the product, a high-precision infrared thermometer is installed at the exit of the rolling mill to monitor the actual temperature of the plate in real time.

[0027] The first pass of subsequent rolling uses a small deformation amount of <10%, and then the deformation amount of each pass is rapidly increased to 10-25%. In the last 1-2 passes before the end of rolling, a small deformation amount of <10% is used again. The cumulative deformation amount of subsequent rolling is controlled at 30-70%, the rolling speed is controlled at 1.0-2.0 m / s, and the final rolling temperature is ≥750℃.

[0028] The principle here is that the optimal deformation range for rolling in the two-phase region is 30%–70%. When the cumulative deformation is less than 30%, the deformation energy stored in the α-lamellae is relatively small, and long α-lamellae still exist during subsequent annealing, resulting in large dispersion of material strength and toughness, and the existence of substandard products. When the cumulative deformation is greater than 70%, the anisotropy of the material increases significantly. Therefore, a stepped deformation distribution strategy is adopted for the rolling deformation in the two-phase region: the first pass uses a small deformation of <10%, and then the deformation of each pass is rapidly increased to 10–25%, but the maximum deformation of a single pass is limited by the rolling force and torque and does not exceed 25%. The last 1–2 passes again use a small deformation of <10% to control the plate shape. At the same time, in order to prevent excessive core temperature rise and microstructure deterioration caused by excessive strain rate, and also to allow sufficient time for recrystallization, the rolling speed is controlled at 1.0–2.0 m / s.

[0029] S4, sheet material straightening, details are as follows:

[0030] The Ti80 titanium alloy sheet rolled in step S3 is straightened using the residual heat of rolling. The flatness of the straightened sheet is ≤8mm / m.

[0031] S5, sheet metal annealing, details are as follows:

[0032] The straightened Ti80 titanium alloy plate from step S4 is annealed at an annealing temperature of Tβ-15℃ to Tβ-40℃ and then air-cooled to obtain a thick Ti80 titanium alloy plate with a thickness of 15 to 125 mm.

[0033] According to a method for preparing thick plates by single-pass direct rolling of Ti80 titanium alloy EB flat ingots according to the present invention, in step S1, the composition of the Ti80 titanium alloy EB flat ingots by mass percentage is: Al 5.7~6.5%, Nb 2.7~3.3%, Zr 1.8~2.3%, Mo 1.0~1.5%, 0<Si≤0.10%, 0<Fe≤0.25%, 0<C≤0.10%, 0<N≤0.05%, 0<H≤0.010%, O 0.05~0.10%, with the remainder being Ti and unavoidable impurities.

[0034] According to a method for preparing thick plates by single-fire direct rolling of Ti80 titanium alloy EB flat ingots according to the present invention, the heating furnace in step S2 is an electric heating furnace with a slightly oxidizing atmosphere, wherein the heating rate of the ingot before 800-900℃ is 60-120℃ / h; the heating rate to the target temperature of 900℃ is 40-70℃ / h; and the holding coefficient at Tβ+50-100℃ is 1.2-2.0min / mm.

[0035] As a gaseous environment, the micro-oxidation atmosphere has a relatively low oxygen concentration. During the processing of this invention, it maintains a certain degree of oxidation while avoiding excessive oxidation, thereby protecting the surface quality and performance of the material.

[0036] According to a method for preparing thick plates by single-fire direct rolling of Ti80 titanium alloy EB flat ingots of the present invention, in step S2, the furnace temperature of the Ti80 titanium alloy EB composite flat ingot is increased by 15-20°C 15-30 minutes before exiting the furnace to offset the temperature drop during transfer.

[0037] According to a method for preparing thick plates by single-fire direct rolling of Ti80 titanium alloy EB flat ingots according to the present invention, the time interval between the Ti80 titanium alloy EB composite flat ingot exiting the furnace and the start of rolling in step S3 is controlled within 150 seconds.

[0038] The objective of this invention is that EB flat ingots should be transferred to the rolling mill as quickly as possible after exiting the furnace. The purpose of this is to reduce the surface temperature drop during the transfer process. Only by ensuring a sufficiently high temperature can the rolling structure be fully evolved, and at the same time, the surface of the flat ingot should not crack during the rolling process. Therefore, the time from exiting the furnace to starting rolling of the EB flat ingot should be controlled within 150 seconds. Furthermore, in order to offset the temperature drop during the transfer, the furnace temperature should be increased by 15 to 20°C 15 to 30 minutes before exiting the furnace.

[0039] According to a method for preparing thick plates by single-fire direct rolling of Ti80 titanium alloy EB flat ingots according to the present invention, before rolling in step S3, the roll cooling water, roller table cooling water and descaling water pipelines are shut off to keep the roller table dry.

[0040] According to a method for preparing thick plates by single-pass direct rolling of Ti80 titanium alloy EB flat ingots according to the present invention, in step S4, the residual heat of rolling at a temperature greater than 600°C is used to level the plate using a straightener or rolling mill, with 1 to 3 straightening passes, a straightening speed of 0.5 to 1.0 m / s, and an exit gap less than the target plate thickness by 0.5 to 1 mm.

[0041] According to a method for preparing thick plates by single-fire direct rolling of Ti80 titanium alloy EB flat ingots according to the present invention, if the rolling residual temperature is less than 600°C, the plate is returned to the furnace for reheating before hot straightening.

[0042] According to a method for preparing thick plates by single-fire direct rolling of Ti80 titanium alloy EB flat ingots according to the present invention, the microstructure of the Ti80 titanium alloy thick plate obtained in step S5 after annealing is a bimodal structure, the primary α phase is equiaxed and short rod-shaped, the α phase size is 12-25 μm, and the content is 20-30%.

[0043] According to a method for preparing thick plates by single-fire direct rolling of Ti80 titanium alloy EB flat ingots according to the present invention, the Ti80 titanium alloy thick plates obtained in step S5 have the following properties: when the plate thickness is 15-25mm, tensile strength ≥880MPa, yield strength ≥785MPa, elongation after fracture A ≥12%, and impact toughness KV2 >50J; when the plate thickness is >25mm, tensile strength ≥840MPa, yield strength ≥740MPa, elongation after fracture A ≥10%, and impact toughness KV2 >50J.

[0044] The method for preparing thick plates by single-pass direct rolling of Ti80 titanium alloy EB flat ingots according to the present invention has the following beneficial effects:

[0045] 1. A method for preparing thick plates by single-pass direct rolling of Ti80 titanium alloy EB flat ingots according to the present invention, wherein Ti80 titanium alloy EB flat ingots are directly rolled into plates in a single pass, and the rolling process is controlled by multi-stage temperature control and temperature-deformation-phase transformation synergistic control, so as to obtain Ti80 titanium alloy plates with excellent plate shape and thickness of 15-125mm under the condition that the total deformation of single-pass rolling is 65-93%;

[0046] 2. The present invention discloses a method for preparing thick plates by single-fire direct rolling of Ti80 titanium alloy EB flat ingots, wherein the mechanical properties of the Ti80 titanium alloy thick plates produced meet the requirements of "GJB 944A-2018 Specification for Titanium and Titanium Alloy Plates for Ships";

[0047] 3. The present invention provides a method for preparing thick plates by single-fire direct rolling of Ti80 titanium alloy EB flat ingots. The method uses Ti80 titanium alloy flat ingots for thick plate preparation, omitting the multiple forging processes of vacuum self-consuming electric arc melting of Ti80 titanium alloy round ingots, shortening the process flow and production cycle, reducing production costs, and increasing the yield to over 70%, making it suitable for industrial production. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the process flow for a method of preparing thick plates by single-fire direct rolling of Ti80 titanium alloy EB flat ingots according to the present invention.

[0049] Figure 2 This is a microstructure diagram of the Ti80 titanium alloy plate obtained in Example 1 of the method for preparing thick plates by single-fire direct rolling of Ti80 titanium alloy EB flat ingots according to the present invention.

[0050] Figure 3 The image shows the microstructure of the Ti80 titanium alloy plate obtained by Comparative Example 1, which is a method for preparing thick plates by single-fire direct rolling of Ti80 titanium alloy EB flat ingots according to the present invention.

[0051] Figure 4 The image shows the microstructure of the Ti80 titanium alloy plate obtained by Comparative Example 2, which is a method for preparing thick plates by single-fire direct rolling of Ti80 titanium alloy EB flat ingots according to the present invention.

[0052] Figure 5 This is a microstructure of the Ti80 titanium alloy plate obtained by Comparative Example 3, which is a method for preparing thick plates by single-fire direct rolling of Ti80 titanium alloy EB flat ingots according to the present invention. Detailed Implementation

[0053] The following description, in conjunction with the accompanying drawings and embodiments, further describes the technical means, creative features, achieved objectives, and effects of a method for preparing thick plates from Ti80 titanium alloy EB flat ingots using single-fire direct rolling. The described embodiments are merely some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0054] Example 1 - Preparation of Ti80 titanium alloy sheet with dimensions of 83×2160×11100 mm

[0055] S1, EB flat ingots with Al 6.08%, Nb 3.05%, Zr 2.10%, Mo 1.38%, Fe 0.10%, Si 0.03%, C 0.02%, N 0.004%, H 0.003%, O 0.08% and dimensions of 350×1500×3800mm were selected. The phase transformation point Tβ was measured to be 990 ℃ by metallography. A 2mm TA2 pure titanium layer was explosively bonded to the upper and lower surfaces to obtain Ti80 titanium alloy EB composite flat ingots;

[0056] S2, Ti80 titanium alloy EB composite flat ingot heating:

[0057] The billet is heated in an electric furnace. It is fed into the furnace in a cold state and heated to 400±10℃ in 2.5 hours and held for 2 hours. Then it is heated to 900±10℃ in 3 hours and held for 3 hours. Then it is heated to 1090℃ at a rate of 40℃ / h and held for 11 hours before being taken out of the furnace and rolled.

[0058] S3, slab rolling:

[0059] Before rolling, the cooling water pipes for the rolls, the cooling water pipes for the roller table, and the descaling water pipes are shut off. The slab is quickly conveyed to the rolling mill within 80 seconds after exiting the furnace and rolled in 13 passes using a four-high reversible rolling mill. The finished plate thickness is 83mm, and the cumulative deformation during rolling is 76%. The first four passes are transverse rolling with a reduction of 30%, from 350mm to 245mm. The reduction per pass (reduction rate per pass) is 15 (4.3%), 20 (6.0%), 35 (11.1%), and 35 (12.5%) mm, respectively. Then, four passes are longitudinal rolling, from 245mm to 127mm. The reduction per pass (reduction rate per pass) is 25 (10.2%), 30 (13.6%), 30 (15.8%), 28 (17.5%), and 5 (3.8%) mm, respectively.

[0060] The first pass rolling speed is 1.0 m / s, and the rolling speed for the remaining passes is controlled between 1.5 and 2.0 m / s. After the above rolling is completed, the infrared thermometer shows that the surface temperature of the slab is 950℃. The rolling speed is then adjusted to 0.5 m / s, and the slab is moved back and forth on the roller table until the surface temperature of the slab drops to 900℃, and then rolling continues. Three passes are arranged, with a total reduction of 35%, i.e., from 127 mm to 83 mm. The reduction per pass (reduction rate per pass) is 10 (7.9%), 26 (22.2%), and 8 (8.8%) mm, respectively. The rolling speed is controlled between 1.2 and 1.5 m / s, and the final rolling temperature is 780℃.

[0061] S4, Sheet straightening:

[0062] The billet is straightened using a straightening machine with residual heat, and the flattening is done in 3 passes with a reduction of 0.5 mm per pass.

[0063] S5, sheet metal annealing:

[0064] The straightened sheet was annealed at 970℃ for 3 hours and then air-cooled to obtain a thick Ti80 titanium alloy plate with dimensions of 83×2160×11100 mm. The final Ti80 titanium alloy hot-rolled plate exhibits a straight shape and no obvious surface defects such as cracks. Figure 2 As shown, the microstructure is a bimodal structure, containing equiaxed and short rod-shaped α-grains, with a grain size of 10–25 μm. Tensile mechanical properties, strength, and impact toughness all meet national standards.

[0065] Example 2 - Preparation of Ti80 titanium alloy sheet with dimensions of 122×1080×2190mm

[0066] S1, an EB flat ingot with the following composition: Al 6.01%, Nb 3.0%, Zr 2.08%, Mo 1.32%, Fe 0.12%, Si 0.03%, C 0.02%, N 0.004%, H 0.003%, O 0.08%, and dimensions of 350×750×1100mm, was selected. The phase transformation point Tβ, measured by metallography, was 988℃. A 2mm TA2 pure titanium layer was explosively laminated onto both the upper and lower surfaces to obtain a Ti80 titanium alloy EB composite flat ingot.

[0067] S2, Ti80 titanium alloy EB composite flat ingot heating:

[0068] The billet is heated in an electric furnace. It is fed into the furnace in a cold state and heated to 400±10℃ in 2 hours and held for 1.5 hours. Then it is heated to 800±10℃ in 2 hours and held for 2 hours. Then it is heated to 1050℃ at a rate of 60℃ / h and held for 9 hours before being taken out of the furnace and rolled.

[0069] S3, slab rolling:

[0070] Before rolling, the roll cooling water, roller table cooling water, and descaling water are turned off. The billet is quickly conveyed to the rolling mill within 80 seconds after exiting the furnace and rolled in 12 passes using a four-high reversible rolling mill. The finished plate thickness is 123mm, and the cumulative deformation during rolling is 66%. The first four passes are transverse rolling with a total reduction of 30%, i.e., from 350mm to 245mm. The reduction per pass (reduction per pass) is 15 (4.3%), 20 (6.0%), 35 (11.1%), and 35 (12.5%) mm, respectively. Then, four passes are longitudinal rolling with a total reduction of 29%, i.e., from 245mm to 174mm. The reduction per pass (reduction per pass) is 30 (12.2%), 30 (14%), and 11 (5.9%) mm, respectively.

[0071] The first pass rolling speed was 1.0 m / s, and the rolling speed for the remaining passes was controlled between 1.5 and 2.0 m / s. After the rolling was completed, the infrared thermometer showed that the slab surface temperature was 925℃. The rolling speed was adjusted to 0.5 m / s, and then the slab was moved back and forth on the roller table until the slab surface temperature dropped to 890℃, and rolling continued. Three passes were arranged, with a total reduction of 30%, from 174 mm to 122 mm. The reduction per pass (reduction rate per pass) was 14 (8%), 28 (17.5%), and 10 (7.6%) mm, respectively. The rolling speed was controlled between 1.2 and 1.5 m / s, and the final rolling temperature was 760℃.

[0072] S4, Sheet straightening:

[0073] The billet is straightened and leveled using a rolling mill with residual heat in 3 passes, with a reduction of 0.5 to 1 mm per pass.

[0074] S5, sheet metal annealing:

[0075] The straightened sheet was annealed at 970℃ for 4 hours and then air-cooled to obtain a Ti80 titanium alloy sheet with dimensions of 122×1080×2190mm. The microstructure was bimodal, with the primary α phase size ranging from 15 to 25 μm. The tensile mechanical properties, strength, and impact toughness all met national standards.

[0076] Example 3 - Preparation of Ti80 titanium alloy plate with dimensions of 15×1250×8600mm

[0077] S1, an EB flat ingot with the following composition: Al 6.01%, Nb 3.0%, Zr 2.08%, Mo 1.32%, Fe 0.12%, Si 0.03%, C 0.02%, N 0.004%, H 0.003%, O 0.08%, and dimensions of 200×750×1100mm, was selected. The phase transformation point Tβ, measured by metallography, was 988 ℃. A 2mm TA2 pure titanium layer was explosively laminated onto both the upper and lower surfaces to obtain a Ti80 titanium alloy EB composite flat ingot.

[0078] S2, Ti80 titanium alloy EB composite flat ingot heating:

[0079] The billet is heated in an electric furnace. It is fed into the furnace in a cold state and heated to 400±10℃ in 2 hours and held for 1.5 hours. Then it is heated to 800±10℃ in 2 hours and held for 2 hours. Then it is heated to 1050℃ at a rate of 60℃ / h and held for 5 hours before being taken out of the furnace and rolled.

[0080] S3, slab rolling:

[0081] Before rolling, the roll cooling water, roller table cooling water, and descaling water are turned off. The billet is rapidly conveyed to the rolling mill within 80 seconds of exiting the furnace and rolled in 15 passes using a four-high reversible rolling mill, resulting in a finished plate thickness of 15mm and a cumulative deformation of 93%. The first four passes are transverse rolling with a reduction rate of 40%, from 200mm to 120mm, with reductions per pass (7.5%), 20 (10.8%), 25 (15.2%), and 20 (4.3%) mm respectively. Then, five passes are longitudinal rolling with a reduction rate of 58%, from 120mm to 50mm, with reductions per pass (13.3%), 20 (19.2%), 17 (20.2%), 13 (19.4%), and 4 (7.4%) mm respectively.

[0082] The first pass rolling speed was 1.0 m / s, and the rolling speed for the remaining passes was controlled between 1.5 and 2.0 m / s. After the above rolling was completed, the infrared thermometer showed that the surface temperature of the slab was 890℃, and rolling continued. Six passes were arranged, with a total reduction rate of 70%, i.e., from 50 mm to 15 mm. The reduction per pass (reduction rate per pass) was 5 (10%), 11 (24.4%), 8 (23.5%), 6 (23.1%), 4 (20%), and 1 (6.3%) mm, respectively. The rolling speed was controlled between 1.2 and 1.5 m / s, and the final rolling temperature was 750℃.

[0083] S4, Sheet straightening:

[0084] The sheet material is straightened using a straightening machine with residual heat, and the flattening is done in two passes with a reduction of 0.5 mm per pass.

[0085] S5, sheet metal annealing:

[0086] The straightened sheet was annealed at 970℃ for 1.5 hours and then air-cooled to obtain a Ti80 titanium alloy sheet with dimensions of 15×1250×8600mm. The microstructure was bimodal, with primary α grains of 15–20 μm in size. The tensile mechanical properties, strength, and impact toughness all met national standards.

[0087] The embodiments and comparative examples of the method for preparing thick plates by single-pass rolling of Ti80 titanium alloy EB flat ingots according to the present invention are distinguished as follows:

[0088] Comparative Example 1:

[0089] The difference between Comparative Example 1 and Example 1 is that the thickness was continuously rolled from 350 mm to 83 mm without temperature control in between, the cumulative rolling deformation was 76%, and the final rolling temperature was 840°C.

[0090] Heat is generated during rolling, and during continuous rolling, the heat is difficult to dissipate fully, keeping the core at a high temperature. Figure 3As shown, the microstructure after annealing remains a lamellar structure that has not fully recrystallized. Tensile mechanical properties, yield strength, and impact toughness all fail to meet national standards.

[0091] Comparative Example 2:

[0092] The difference between Comparative Example 2 and Example 2 is that the rolling deformation was 30% before intermediate temperature measurement and 28% after temperature control, with a cumulative deformation of 50%, while all other conditions remained unchanged.

[0093] Due to insufficient deformation, such as Figure 4 As shown, the microstructure consists of lamellar α layers that are not fully broken. The tensile mechanical properties and yield strength do not meet national standards.

[0094] Comparative Example 3:

[0095] The difference between Comparative Example 3 and Example 3 is that the rolling deformation was 30% before intermediate temperature measurement (single phase region), and 90% after temperature control, with a cumulative deformation of 93%.

[0096] Large deformation in the single-phase region can produce fine equiaxed β grains and broken grain boundaries, providing an excellent starting point for subsequent two-phase rolling. In the two-phase region, these fine β grains transform into dense α+β bundles, and the primary α phase is more easily spheroidized and recrystallized. In this comparative example, the rolling deformation of 30% before intermediate temperature measurement (single-phase region) is insufficient to fully break the original β grains. At this point, coarse, elongated β grains and continuous α grain boundaries are formed. Even two-phase rolling cannot completely eliminate this inherent defect. Figure 5 As shown, a distinct banded structure will be produced. After annealing, the anisotropy is obvious, and the yield strength along the rolling direction is low, failing to meet national standards.

[0097] Table 1 below is a comparison table of the embodiments and comparative examples:

[0098]

[0099] Based on the above embodiments and the comparison with Table 1 and the comparative examples, it can be seen that the method of preparing thick plates by single-fire direct rolling of Ti80 titanium alloy EB flat ingots according to the present invention, through multi-stage temperature control heating and coordinated control of temperature-deformation-phase transformation during the rolling process, obtains Ti80 titanium alloy plates with excellent plate shape and thickness of 15-125mm under the condition of a total deformation of 65-93% in a single-fire rolling. The mechanical properties of the produced Ti80 titanium alloy thick plates meet the requirements. Moreover, the present invention omits the multiple forging process of vacuum self-consuming arc melting Ti80 titanium alloy round ingots, shortens the process flow and production cycle, reduces production costs, and increases the yield to over 70%, making it suitable for industrial production.

[0100] In the description of this invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0101] Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0102] Meanwhile, those skilled in the art should recognize that the above embodiments are only used to illustrate this application and are not intended to limit this application. Any changes or modifications to the above embodiments within the spirit and essence of this application will fall within the scope of the claims of this application.

Claims

1. A method for preparing thick plates by single-pass direct rolling of Ti80 titanium alloy EB flat ingots, characterized in that, The method includes the following steps: S1. Select a Ti80 titanium alloy EB flat ingot with a thickness of 200-350mm, mill the surface of the flat ingot, and use an explosive bonding method to bond a pure titanium plate TA1 or pure titanium plate TA2 with a thickness of 1-3mm to the upper and lower surfaces of the flat ingot to form a Ti80 titanium alloy EB composite flat ingot. Apply an anti-oxidation and heat insulation coating to the upper surface and around the Ti80 titanium alloy EB composite flat ingot. S2. The Ti80 titanium alloy EB composite flat ingot is fed into a heating furnace and heated first to 400~600±10℃ and held for 1~2h, then heated to 800~900℃±10℃ and held for 2~3h, and finally heated to Tβ+50~100℃ and held before being taken out of the furnace. Tβ is the transformation temperature of the β phase transformation point of the EB flat ingot, in ℃. S3, single-pass rolling of sheet metal, as detailed below: The Ti80 titanium alloy EB composite flat ingot heated from S2 is fed into a four-roll reversible rolling mill and rolled alternately in the transverse and longitudinal directions. The total deformation during the rolling process is 65-93%, the initial rolling temperature is ≥1000℃, and the final rolling temperature is controlled to be ≥750℃. During rolling, the reduction in the first and second passes is 2-8%, and the deformation in subsequent passes increases to 10-20%. When the cumulative reduction reaches 45-70%, a small deformation of <10% is adopted. During rolling, the bite speed is 1.0-1.5 m / s, and the rolling speed of the remaining passes is controlled at 1.5-3.5 m / s. A temperature measuring instrument is installed at the exit of the rolling mill to detect the surface temperature of the plate. If the surface temperature of the plate is >920℃ after 50-70% deformation is completed, the roller speed is reduced or the billet is briefly stopped. The billet temperature is controlled by the radiative heat dissipation of the billet on the roller, until the surface temperature reaches 900±20℃. Otherwise, it directly enters the subsequent rolling process. The first pass of subsequent rolling uses a small deformation amount of <10%, and then the deformation amount of each pass is rapidly increased to 10-25%. In the last 1-2 passes before the end of rolling, a small deformation amount of <10% is used again. The cumulative deformation amount of subsequent rolling is controlled at 30-70%, the rolling speed is controlled at 1.0-2.0 m / s, and the final rolling temperature is ≥750℃. S4, sheet material straightening, details are as follows: The Ti80 titanium alloy sheet rolled in step S3 is straightened using the residual heat of rolling. The flatness of the straightened sheet is ≤8mm / m. S5, sheet metal annealing, details are as follows: The straightened Ti80 titanium alloy plate from step S4 is annealed at an annealing temperature of Tβ-15℃ to Tβ-40℃ and then air-cooled to obtain a thick Ti80 titanium alloy plate with a thickness of 15 to 125 mm.

2. The method for preparing thick plates by single-pass direct rolling of Ti80 titanium alloy EB flat ingots as described in claim 1, characterized in that, In step S1, the composition of the Ti80 titanium alloy EB flat ingot by mass percentage is as follows: Al 5.7-6.5%, Nb 2.7-3.3%, Zr 1.8-2.3%, Mo 1.0-1.5%, 0 < Si ≤ 0.10%, 0 < Fe ≤ 0.25%, 0 < C ≤ 0.10%, 0 < N ≤ 0.05%, 0 < H ≤ 0.010%, O 0.05-0.10%, with the remainder being Ti and unavoidable impurities.

3. The method for preparing thick plates by single-pass direct rolling of Ti80 titanium alloy EB flat ingots as described in claim 1, characterized in that, The heating furnace in step S2 is an electric heating furnace with a slightly oxidizing atmosphere. The heating rate of the ingot before 800-900℃ is 60-120℃ / h; the heating rate to the target temperature of 900℃ is 40-70℃ / h; and the holding coefficient at Tβ+50-100℃ is 1.2-2.0min / mm.

4. The method for preparing thick plates by single-fire direct rolling of Ti80 titanium alloy EB flat ingots as described in claim 1, characterized in that, In step S2, the furnace temperature of the Ti80 titanium alloy EB composite flat ingot is increased by 15-20°C 15-30 minutes before it is taken out of the furnace.

5. The method for preparing thick plates by single-fire direct rolling of Ti80 titanium alloy EB flat ingots as described in claim 1, characterized in that, The time interval between the Ti80 titanium alloy EB composite flat ingot being taken out of the furnace and the start of rolling in step S3 is controlled within 150 seconds.

6. The method for preparing thick plates by single-fire direct rolling of Ti80 titanium alloy EB flat ingots as described in claim 1, characterized in that, Before rolling in step S3, the roll cooling water, roller table cooling water and descaling water pipelines are shut off to keep the roller table dry.

7. The method for preparing thick plates by single-fire direct rolling of Ti80 titanium alloy EB flat ingots as described in claim 1, characterized in that, In step S4, the residual heat from rolling at a temperature greater than 600°C is used to level the plate using a straightener or rolling mill. The straightening passes are 1 to 3 times, the straightening speed is 0.5 to 1.0 m / s, and the exit gap is 0.5 to 1 mm less than the target plate thickness.

8. The method for preparing thick plates by single-fire direct rolling of Ti80 titanium alloy EB flat ingots as described in claim 7, characterized in that, If the residual rolling temperature is less than 600°C, the material should be returned to the furnace for reheating before hot straightening.

9. The method for preparing thick plates by single-fire direct rolling of Ti80 titanium alloy EB flat ingots as described in claim 1, characterized in that, The Ti80 titanium alloy thick plate obtained in step S5 has a bimodal microstructure after annealing. The primary α phase is equiaxed and short rod-shaped, with a size of 12-25 μm and a content of 20-30%.

10. The method for preparing thick plates by single-fire direct rolling of Ti80 titanium alloy EB flat ingots as described in claim 1, characterized in that, The Ti80 titanium alloy thick plate obtained in step S5 has the following properties: when the plate thickness is 15-25mm, the tensile strength is ≥880MPa, the yield strength is ≥785MPa, the elongation after fracture A is ≥12%, and the impact toughness KV2 is >50J; when the plate thickness is >25mm, the tensile strength is ≥840MPa, the yield strength is ≥740MPa, the elongation after fracture A is ≥10%, and the impact toughness KV2 is >50J.

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