Method for single-pass rolling of thin gauge and ultra-wide TC4 titanium alloy plates

Abstract

The present invention discloses a method for single-pass rolling of thin-gauge and ultra-wide TC4 titanium alloy plates. The method adopts EB flat ingots, explosive compounding, slab heating, single-pass rolling, straightening and annealing processes to obtain thin-gauge and ultra-wide TC4 titanium alloy plates. The plate width is 3500-4300 mm, the plate thickness is 20-30 mm, and the microstructure of the thin-gauge and ultra-wide TC4 titanium alloy plates is an α+β dual-state structure. The plate has the advantages of good plate surface quality, wide plate width, and small difference in longitudinal and transverse mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium alloy material processing, in particular to a method for rolling thin-gauge and ultra-wide TC4 titanium alloy plates in one hot rolling operation. Background Art

[0002] Titanium alloys are considered strategic metals and one of the most important structural materials due to their low density, high specific strength, and high specific modulus, along with excellent heat resistance, corrosion resistance, and biocompatibility. Ti-6Al-4V (TC4) alloy is the most widely used titanium alloy, finding widespread application in traditional fields such as aviation, aerospace, navigation, and automotive, as well as in emerging sectors such as medical devices, sports equipment, and consumer electronics. It is also a key material for welded structural components, load-bearing structures, and large, integrated components.

[0003] The traditional titanium alloy processing process generally involves "two or more vacuum autoclave refining (VAR) cycles - multi-fire forging - multi-fire rolling," ultimately resulting in titanium alloy plates. This process has a long production process, high processing costs, significant processing losses, and a yield rate of less than 70% for the finished plates, which to some extent limits the widespread production and application of titanium alloys. Compared to VAR melting, electron beam cold hearth furnace melting (EB) offers a shorter process, higher efficiency, and greater controllability. The melting process can effectively eliminate high- and low-density inclusions, and can also use returned material, reducing raw material costs. Furthermore, EB melting directly produces flat ingots without the need for multi-fire forging, enabling forging-free direct rolling of flat ingots to produce titanium alloy plates.

[0004] Despite a steady increase in domestic titanium production in recent years, it remains a minor metal in the metals industry. Relying on specialized rolling mills to process titanium significantly increases the manufacturing cost of titanium alloy sheets, limiting their application and development. The "steel-titanium combination" (i.e., utilizing steel production lines to produce titanium) offers significant advantages in both cost and efficiency.

[0005] Chinese Patent Publication No. CN117583401A proposes a method for single-fire rolling of TC4 titanium alloy wide and thick plates from steel-titanium collinear TC4 titanium alloy slabs. α+β type TC4 titanium alloy wide and thick plates with a thickness of 30-60 mm, a width of 3500-4500 mm, and a length of 6000-12000 mm are prepared by single-fire rolling. However, this technology does not involve the rolling of TC4 titanium alloy thin plates below 30 mm, nor does it mention the surface quality control of wide and thick plates.

[0006] Chinese patent publication number CN118321345A proposes a TC4 titanium alloy wide and thick plate and a preparation method thereof. The EB flat ingot is coated with glass coating and then heated, and then directly rolled into a TC4 titanium alloy wide and thick plate with a thickness of 15-30 mm and a width of 1500-2500 mm. Although heating after coating the flat ingot with glass coating can effectively inhibit the surface oxidation of the titanium alloy during high temperature, the coating is prone to sticking to the roller during the subsequent rolling process, and the switching process has a greater impact on the production of the normal steel production line; in addition, the rolling process described in this technology lacks a widening process, so the width of the finished plate is relatively narrow.

[0007] In view of the above situation, it is necessary to develop a preparation method for TC4 titanium alloy plates with thinner and wider specifications and to ensure their surface quality. Summary of the Invention

[0008] In view of the defects existing in the prior art, the purpose of the present invention is to provide a method for rolling thin-gauge and ultra-wide TC4 titanium alloy plates in one fire. Pure titanium plates are coated on the upper and lower surfaces of EB flat ingots by explosive composite method, and thin-gauge and ultra-wide TC4 titanium alloy plates are obtained by one fire rolling. The entire preparation process is short, the cost is low, the yield rate is high, and the product surface is good.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] A first aspect of the present invention provides a method for rolling thin-gauge and ultra-wide TC4 titanium alloy plates in one hot rolling operation, comprising the following steps:

[0011] S1, EB flat ingot, TC4 titanium alloy EB flat ingot is prepared by smelting raw materials according to the composition ratio of TC4 titanium alloy in an EB furnace;

[0012] S2, explosive compounding, compounding a pure titanium layer with a thickness of 2 to 3 mm on the upper and lower surfaces of the TC4 titanium alloy EB flat ingot to obtain a TC4 titanium alloy slab;

[0013] S3, slab heating, put the TC4 titanium alloy slab into the furnace at (400~800)±10℃, keep it at 800℃±10℃ for 2~3h, then heat it to β transformation temperature + (20~100)℃, and keep it at temperature for more than 5h;

[0014] S4, single-hot rolling, feeds the heated TC4 titanium alloy slab into the four-roll reversing mill of the steel production line for multi-pass, medium-reduction rolling, and adopts a hot rolling process across the β-transformation temperature, while controlling the total deformation to 80-95%;

[0015] S5, straightening, using the waste heat of the rolling mill to straighten the TC4 titanium alloy slab after the first hot rolling, and then air-cooling it to room temperature on the roller table;

[0016] S6, annealing, annealing the straightened TC4 titanium alloy slab in the two-phase region to obtain a thin-gauge ultra-wide TC4 titanium alloy plate with a plate width of 3500-4300 mm and a plate thickness of 20-30 mm.

[0017] Preferably, in step S1:

[0018] The raw materials are selected from grade 0 or 0A titanium sponge, Al-V, and Al99.5; or the raw materials of the EB ingot are selected from TC4 return material, grade 0 or 0A titanium sponge, Al-V, and Al99.5;

[0019] The TC4 titanium alloy EB flat ingot has a thickness of 200 to 340 mm, a width of 1050 to 1550 mm, and a length of 1500 to 4200 mm.

[0020] Preferably, in step S2, the detonation velocity of the explosive used in the explosive compounding process is not less than 2500 mm / s.

[0021] Preferably, in step S3:

[0022] The heating rate during the heating process is 60 to 120° C. / h; and / or

[0023] The heating furnace used for heating the slab is a gas furnace, and the atmosphere in the furnace is controlled to be a slightly oxidizing atmosphere with a residual oxygen content of 100 to 500 ppm.

[0024] Preferably, in step S4, the first hot rolling comprises the following steps:

[0025] S41, rolling the heated TC4 titanium alloy slab on a four-roll reversible rolling mill of a steel production line, controlling the time interval between the TC4 titanium alloy slab being taken out of the furnace and the start of rolling to be 60 to 100 seconds;

[0026] S42, during the rolling process, first widening the TC4 titanium alloy slab along the slab width direction to a target width and then performing reversing rolling;

[0027] S43: During the rolling process, multi-pass rolling with a medium reduction amount is adopted. The reduction amount is gradually increased in the first 3 to 4 passes until the medium reduction amount is reached. The reduction amount is gradually reduced in the first 3 to 4 passes until the slab reaches the target thickness. The total deformation is controlled to be 80 to 95%;

[0028] S44, during the rolling process, a hot rolling process across the β-transformation temperature is adopted, the initial rolling temperature is controlled to be 1000-1080°C, and the final rolling temperature is ≥780°C.

[0029] Preferably, in step S43:

[0030] The multiple passes are 15 to 30 passes;

[0031] The pressing amount in the first 3 to 4 passes of the start of rolling and the first 3 to 4 passes of the end of rolling is ≤10%; the medium pressing amount is 8% to 16%.

[0032] Preferably, in step S5, during the straightening process, the deformation amount is ≤5%.

[0033] Preferably, in step S6, the annealing process is as follows:

[0034] The TC4 titanium alloy slab is placed in a furnace at 400±10℃ and kept for more than 2 hours, then heated to 600-850℃ at a heating rate of 50-80℃ / h, and the annealing time is controlled to be 2-4 hours. The furnace is then cooled to a slab temperature ≤200℃ and then taken out of the furnace and air-cooled to room temperature.

[0035] Preferably, the microstructure of the thin-gauge and ultra-wide TC4 titanium alloy plate is an α+β phase dual-state structure, the equiaxed α phase content is ≥20%, and the average grain size is below 350µm.

[0036] Preferably, the thin-gauge ultra-wide TC4 titanium alloy plate has a longitudinal tensile strength of 970±20 MPa, a longitudinal yield strength of 865±20 MPa, and a longitudinal elongation of 12.5±2.0%;

[0037] The thin-gauge, ultra-wide TC4 titanium alloy plate has a transverse tensile strength of 980±20 MPa, a transverse yield strength of 910±20 MPa, and a transverse elongation of 11.5±1.0%;

[0038] The unevenness of the thin-gauge and ultra-wide TC4 titanium alloy plate is ≤8 mm / m.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1. The present invention uses TC4 titanium alloy EB flat ingots to prepare thin-gauge and ultra-wide TC4 titanium alloy plates. The preparation process does not require multiple smelting and forging processes, and can achieve short process, low cost, low loss, and efficient preparation;

[0041] 2. The present invention uses explosive lamination of a pure titanium layer on the TC4 titanium alloy EB slab to prevent oxidation or hydrogen absorption within the alloy during heating, meeting the requirement for a high reduction rate during rolling, while reducing surface cracks and improving the surface quality of the finished plate. In addition, compared to the traditional method of applying high-temperature resistant coatings, the explosive lamination process can effectively improve the roller sticking problem during rolling and reduce the impact on steel production lines.

[0042] 3. The present invention obtains thin-gauge, ultra-wide TC4 titanium alloy plates through single-fire rolling. The plates have a width of 3500 to 4300 mm and a thickness of 20 to 30 mm. They have an α+β phase dual-state structure, good surface quality, small differences in plate width, longitudinal and transverse mechanical properties, and longitudinal tensile strength of 970±20 MPa, yield strength of 865±20 MPa, and elongation of 12.5±2.0%; transverse tensile strength of 980±20 MPa, yield strength of 910±20 MPa, and elongation of 11.5±1.0%. The product performance meets and exceeds national standards and is suitable for mass production.

[0043] 4. The method of the present invention has universal applicability, a simple and efficient preparation process, a short production cycle, and high repeatability, and can be widely applied to similar α+β two-phase titanium alloys. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a flow chart of the method for rolling thin-gauge and ultra-wide TC4 titanium alloy plates in one hot rolling process according to the present invention;

[0045] Figure 2 This is a photo of the TC4 titanium alloy flat ingot after the upper and lower surfaces of the ingot were explosively bonded with pure titanium layers;

[0046] Figure 3 The microstructure of the thin-gauge and extra-wide TC4 titanium alloy plate prepared in accordance with the embodiments of the present invention; (a) the microstructure of the thin-gauge and extra-wide TC4 titanium alloy plate prepared in accordance with embodiment 1; (b) the microstructure of the thin-gauge and extra-wide TC4 titanium alloy plate prepared in accordance with embodiment 2; (c) the microstructure of the thin-gauge and extra-wide TC4 titanium alloy plate prepared in accordance with embodiment 3. DETAILED DESCRIPTION

[0047] The present invention will be described in detail below with reference to specific examples. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form.

[0048] Combine Figure 1 As shown, the present invention provides a method for single-fire rolling of thin-gauge and ultra-wide TC4 titanium alloy plates, which adopts EB flat ingot, explosive compounding, slab heating, single-fire rolling, straightening, and annealing processes, and specifically includes the following steps:

[0049] S1, EB flat ingot, TC4 titanium alloy EB flat ingot is prepared by smelting raw materials according to the composition ratio of TC4 titanium alloy in an EB furnace;

[0050] In this step, the raw materials used for TC4 titanium alloy are grade 0 or 0A titanium sponge, Al-V, and Al99.5, or TC4 return material, grade 0 or 0A titanium sponge, Al-V, and Al99.5 are used for EB ingots, depending on the composition ratio of the raw materials. The TC4 return material is shot blasted, pickled, and air-dried before being inspected for chemical composition, surface quality, and dimensions. The chemical composition must meet national standards. An EB furnace is used for smelting to produce TC4 titanium alloy EB ingots with a thickness of 200-340 mm, a width of 1050-1550 mm, and a length of 1500-4200 mm.

[0051] S2, explosive compounding, compounding a pure titanium layer with a thickness of 2 to 3 mm on the upper and lower surfaces of the TC4 titanium alloy EB flat ingot to obtain a TC4 titanium alloy slab;

[0052] In this step, a pure titanium layer with a thickness of 2 to 3 mm is laminated on the upper and lower surfaces of the TC4 titanium alloy EB flat ingot to improve the surface quality of the finished plate after heating and rolling. The detonation velocity of the explosive used in the explosive lamination process is not less than 2500 mm / s. Figure 2 As shown in the figure, the bonding area between the TC4 titanium alloy EB ingot and the pure titanium layer reaches more than 99%.

[0053] S3, slab heating, put the TC4 titanium alloy slab into the furnace at (400~800)±10℃, keep it at 800℃±10℃ for 2~3h, then heat it to β transformation temperature + (20~100)℃, and keep it at temperature for more than 5h;

[0054] During the slab heating process, the heating rate is 60-120°C / h. If the slab heating furnace is a gas-fired furnace, the furnace atmosphere should be controlled to a slightly oxidizing atmosphere with a residual oxygen content of 100-500 ppm. Furthermore, the heating temperature uniformity within the furnace should be within ±10°C to ensure uniform heating of the slab.

[0055] S4, single-hot rolling, feeds the heated TC4 titanium alloy slab into the four-roll reversing mill of the steel production line for multi-pass, medium-reduction rolling, and adopts a hot rolling process across the β-transformation temperature, while controlling the total deformation to 80-95%;

[0056] In this step, the first heat rolling specifically includes the following steps:

[0057] S41, rolling the heated TC4 titanium alloy slab on a four-roll reversible rolling mill of a 4300mm steel production line, controlling the time interval from the TC4 titanium alloy slab being taken out of the furnace to the start of rolling to be 60 to 100 seconds;

[0058] S42, during the rolling process, first widening the TC4 titanium alloy slab along the slab width direction to a target width and then performing reversing rolling;

[0059] In this step, during the first-pass rolling process, the slab is widened to the target width along the width direction and then reversed for rolling. The first 2 to 3 passes after reversing should increase the pressing amount to increase the deformation heat, and then the pressing amount should be stabilized until the target thickness is reached.

[0060] S43: During the rolling process, multi-pass rolling with a medium reduction amount is adopted. The reduction amount is gradually increased in the first 3 to 4 passes until the medium reduction amount is reached. The reduction amount is gradually reduced in the first 3 to 4 passes until the slab reaches the target thickness. The total deformation is controlled to be 80 to 95%;

[0061] In this step, multiple passes and medium rolling pressure are used to control the deformation degree of the slab to avoid excessive deformation, heat or plastic instability; wherein, multiple passes are 15 to 30 passes; the rolling pressure is gradually increased in the first 3 to 4 passes of rolling until the medium rolling pressure is reached, and the rolling pressure should be gradually reduced in the first 3 to 4 passes of rolling until the slab reaches the target thickness; in a specific embodiment, the rolling pressure in the first 3 to 4 passes of rolling and the first 3 to 4 passes of rolling is ≤10%; the remaining medium rolling pressure is 8% to 16%.

[0062] S44, during the rolling process, a hot rolling process across the β-transformation temperature is adopted, the initial rolling temperature is controlled to be 1000-1080°C, and the final rolling temperature is ≥780°C.

[0063] In this step, a hot rolling process across the β-transformation temperature is adopted (the initial rolling temperature is controlled at 1000-1080°C, and the final rolling temperature is ≥780°C). The dual-state structure is obtained by utilizing the structural deformation of the β phase region and the dynamic recrystallization of the two-phase region. At the same time, the deformation amount is controlled at 80%-95% to ensure that the grains are fully broken, so that the average grain size of the slab is below 350µm.

[0064] S5, straightening, using the waste heat of the rolling mill to straighten the TC4 titanium alloy slab after the first hot rolling, and then air-cooling it to room temperature on the roller table;

[0065] During the above straightening process, the deformation is ≤5%.

[0066] S6, annealing, annealing the straightened TC4 titanium alloy slab in the two-phase region to obtain a thin-gauge ultra-wide TC4 titanium alloy plate with a plate width of 3500-4300 mm and a plate thickness of 20-30 mm.

[0067] In this step, the plate is annealed in the two-phase region. The specific annealing process is as follows:

[0068] The TC4 titanium alloy slab is placed in a furnace and held at 400±10℃ for more than 2 hours. It is then heated to 600-850℃ at a heating rate of 50-80℃ / h. The annealing time is controlled to be 2-4 hours. The slab is then cooled in the furnace to a temperature of ≤200℃ and then removed from the furnace and air-cooled to room temperature. If a gas-fired furnace is used for annealing, the atmosphere in the furnace must be controlled to a slightly oxidizing atmosphere with a residual oxygen content of 100-500ppm. The heating temperature uniformity in the heating furnace must be within the range of ±10℃ to ensure uniform annealing of the slab.

[0069] Under the above-mentioned large deformation, after hot rolling process across the β transformation temperature and two-phase region annealing treatment, the microstructure of the thin-gauge ultra-wide TC4 titanium alloy plate prepared above is an α+β phase dual-state structure, the equiaxed α phase content is ≥20% (for example, 20% to 30%), and the average grain size is below 350µm.

[0070] The properties of the thin-gauge, ultra-wide TC4 titanium alloy plate prepared above are as follows: longitudinal tensile strength 970±20MPa, longitudinal yield strength 865±20MPa, longitudinal elongation 12.5±2.0%; transverse tensile strength 980±20MPa, transverse yield strength 910±20MPa, transverse elongation 11.5±1.0%; unevenness ≤8mm / m.

[0071] The method for rolling thin-gauge and ultra-wide TC4 titanium alloy plates in one heat of the present invention is further described below with reference to specific examples.

[0072] Example 1

[0073] This embodiment is the preparation of thin and ultra-wide TC4 sheets with specifications of 22×3500×6000. The specific preparation method is as follows:

[0074] (1) An electron beam cooling hearth furnace was used to produce a TC4 titanium alloy EB flat ingot with a specification of 200×1240×1880 by one melting. Its chemical composition and content are: Al is 5.946wt%, V is 4.13wt%, Fe is 0.046wt%, C is 0.06wt%, N is 0.01wt%, H is 0.002wt%, O is 0.19wt%, and the rest is Ti and unavoidable impurities;

[0075] (2) Explosive compounding: a 2 mm thick TA1 pure titanium layer is compounded on the upper and lower surfaces of the TC4 titanium alloy EB flat ingot to obtain a TC4 titanium alloy slab; wherein, the detonation velocity of the explosive used in the explosive compounding process is not less than 2500 mm / s.

[0076] (3) The TC4 titanium alloy slab is put into the furnace at 800℃, kept warm for 2-3h, and then heated to 1080℃ (β-transformation temperature is 980℃) at a heating rate of 60-100℃ / h and kept warm for 4-5h. The outlet temperature of the heating furnace is controlled at 1060-1080℃.

[0077] (4) Before rolling, the cooling water and dephosphorization water of the conveyor roller table were turned off, and the slab was transported to the rolling mill within 90 seconds. The slab was rolled back and forth for 24 passes using a 4300mm four-roll reversible rolling mill. The first 12 passes were for widening to the target width, followed by reversing rolling. The slab was rolled to the target thickness through 12 passes with a total deformation of 89%. The initial rolling temperature was 1075°C, and the final rolling temperature was higher than 780°C. The process control parameters for each pass are shown in Table 1. The reduction in the first 3 to 4 passes at the start of rolling and the first 3 to 4 passes at the end of rolling was ≤10%; the remaining medium reduction was 8% to 16%.

[0078] (5) After rolling is completed, the waste heat of the rolling mill is used for online straightening (deformation ≤ 5%), and then air-cooled to room temperature on the roller table;

[0079] (6) The plate is annealed in the two-phase region, kept in the furnace at 400℃ for 2-3 hours, heated to 750-780℃ at a heating rate of 60-100℃ / h and annealed for 2-3 hours, then cooled to 200℃ and air-cooled to room temperature.

[0080] The thin and ultra-wide TC4 titanium alloy plates obtained after annealing have qualified plate shapes, with unevenness ≤8mm / m, and excellent surface quality without conventional folding and pitting defects;

[0081] Combine Figure 3 As shown in (a), the microstructure of the thin-gauge ultra-wide TC4 titanium alloy plate prepared in this embodiment is an α+β phase dual-state structure, the equiaxed α phase content is in the range of 20% to 30%, and the average grain size is below 350µm.

[0082] The performance of this thin-gauge, ultra-wide TC4 titanium alloy plate is as follows: longitudinal tensile strength 972MPa, longitudinal yield strength 865MPa, longitudinal elongation 12.5%; transverse tensile strength 988MPa, transverse yield strength 911MPa, transverse elongation 11.5%. The product performance meets and exceeds national standard requirements.

[0083] Table 1 Rolling process parameters of 22×3500×6000 thin and ultra-wide TC4 sheet

[0084]

[0085] Example 2

[0086] This embodiment is the preparation of thin and ultra-wide TC4 sheets with specifications of 25×3500×7170. The specific preparation method is as follows:

[0087] (1) An electron beam cooling hearth furnace was used to produce a TC4 titanium alloy EB flat ingot with a specification of 200×1240×2530 by one-time melting. The chemical composition and content of the ingot are as follows: Al is 6.349wt%, V is 4.21wt%, Fe is 0.067wt%, C is 0.02wt%, N is 0.01wt%, H is 0.002wt%, O is 0.18wt%, and the rest is Ti and unavoidable impurities;

[0088] (2) Explosive compounding: a 2 mm thick TA1 pure titanium layer is compounded on the upper and lower surfaces of the TC4 titanium alloy EB flat ingot to obtain a TC4 titanium alloy slab; wherein, the detonation velocity of the explosive used in the explosive compounding process is not less than 2500 mm / s.

[0089] (3) The slab is placed in the furnace at 400°C and kept warm for 2-3 hours. It is then heated to 800°C at a heating rate of 60-100°C / h and kept warm for 2 hours. It is then heated to 1050°C (β-transus temperature is 980°C) at a heating rate of 60-100°C / h and kept warm for 5-6 hours. The outlet temperature of the heating furnace is controlled at 1030-1050°C.

[0090] (4) Before rolling, the cooling water and dephosphorization water of the conveyor roller table were turned off, and the slab was transported to the rolling mill within 90 seconds. The slab was rolled back and forth for 21 passes using a 4300mm four-roll reversible rolling mill. The first 10 passes were for widening to the target width, followed by reversing rolling. The slab was rolled to the target thickness in 11 passes with a total deformation of 87.5%. The initial rolling temperature was 1045°C, and the final rolling temperature was higher than 780°C. The process control parameters for each pass are shown in Table 2. The reduction in the first 3 to 4 passes at the start of rolling and the first 3 to 4 passes at the end of rolling was ≤10%; the remaining medium reduction was 8% to 16%.

[0091] (5) After rolling is completed, the waste heat of the rolling mill is used for online straightening (deformation ≤ 5%), and then air-cooled to room temperature on the roller table;

[0092] (6) The plate is annealed in the two-phase region, kept in the furnace at 400 °C for 2 hours, heated to 750-780 °C at a heating rate of 60-100 °C / h and annealed for 2-3 hours, then cooled to 200 °C and air-cooled to room temperature.

[0093] The thin and ultra-wide TC4 titanium alloy plates obtained after annealing have qualified plate shapes, with unevenness ≤8mm / m, and excellent surface quality without conventional folding and pitting defects;

[0094] Combine Figure 3As shown in (b), the microstructure of the thin-gauge ultra-wide TC4 titanium alloy plate prepared in this embodiment is an α+β phase dual-state structure, the equiaxed α phase content is in the range of 20% to 30%, and the average grain size is below 350µm.

[0095] The performance of this thin-gauge, ultra-wide TC4 titanium alloy plate is as follows: longitudinal tensile strength 961MPa, yield strength 855MPa, and elongation 11.0%; transverse tensile strength 1000MPa, yield strength 921MPa, and elongation 10.5%. The product performance meets and exceeds national standard requirements.

[0096] Table 2 Rolling process parameters of 25×3500×7170 ultra-wide TC4 sheet

[0097]

[0098] Example 3

[0099] This embodiment is the preparation of a thin and ultra-wide TC4 sheet with a specification of 30×4000×7300. The specific preparation method is as follows:

[0100] (1) An electron beam cooling hearth furnace was used to produce a TC4 titanium alloy EB flat ingot with a specification of 200×1240×3540 by one-time melting. The chemical composition and content of the ingot were as follows: Al: 6.108wt%, V: 4.03wt%, Fe: 0.048wt%, C: 0.05wt%, N: 0.01wt%, H: 0.002wt%, O: 0.15wt%, and the rest were Ti and unavoidable impurities.

[0101] (2) Explosive compounding: a 2 mm thick TA1 pure titanium layer is compounded on the upper and lower surfaces of the TC4 titanium alloy EB flat ingot to obtain a TC4 titanium alloy slab; wherein, the detonation velocity of the explosive used in the explosive compounding process is not less than 2500 mm / s.

[0102] (3) The slab is put into the furnace at 400-800℃, kept warm for 2-4 hours, and then heated to 1020℃ (β-transform temperature is 980℃) at a heating rate of 60-100℃ / h, and kept warm for 5-6 hours. The outlet temperature of the heating furnace is controlled at 1000-1020℃.

[0103] (4) Before rolling, the cooling water and dephosphorization water of the conveyor roller table were turned off, and the slab was transported to the rolling mill within 90 seconds. The slab was rolled back and forth for 16 passes using a 4300mm four-roll reversible rolling mill. The first 8 passes were for widening to the target width, followed by reversing rolling. The slab was rolled to the target thickness through 8 passes with a total deformation of 82.5%. The initial rolling temperature was 1015°C, and the final rolling temperature was higher than 780°C. The process control parameters for each pass are shown in Table 3. The reduction in the first 3 to 4 passes at the start of rolling and the first 3 to 4 passes at the end of rolling was ≤10%; the remaining medium reduction was 8% to 16%.

[0104] (5) After rolling is completed, the waste heat of the rolling mill is used for online straightening (deformation ≤ 5%), and then air-cooled to room temperature on the roller table;

[0105] (6) The plate is annealed in the two-phase region, kept in the furnace at 400 °C for 2 hours, heated to 750-780 °C at a heating rate of 60-100 °C / h and annealed for 2 hours, then cooled to 200 °C and air-cooled to room temperature.

[0106] The thin and ultra-wide TC4 titanium alloy plates obtained after annealing have qualified plate shapes, with unevenness ≤ 6mm / m, and excellent surface quality without conventional folding and pitting defects;

[0107] Combine Figure 3 As shown in (c), the microstructure of the thin-gauge ultra-wide TC4 titanium alloy plate prepared in this embodiment is an α+β phase dual-state structure, the equiaxed α phase content is in the range of 20% to 30%, and the average grain size is below 350µm.

[0108] The performance of this thin-gauge, ultra-wide TC4 titanium alloy plate is as follows: longitudinal tensile strength 954MPa, yield strength 870MPa, elongation 13.6%; transverse tensile strength 965MPa, yield strength 892MPa, elongation 12.2%. The product performance meets and exceeds national standard requirements.

[0109] Table 3 Rolling process parameters of 30×4000×7300 ultra-wide TC4 sheet

[0110]

[0111] Comparative Example

[0112] This comparative example is the preparation of an ultra-wide TC4 sheet with a specification of 30×4000×8000. The specific preparation method is as follows:

[0113] (1) Press TC4 alloy blocks and weld them into electrodes in a vacuum welding box;

[0114] (2) The electrode was subjected to three vacuum consumable melting processes to obtain an F860 TC4 titanium alloy ingot;

[0115] (3) The ingot is put into the furnace at 400-800℃, heated to 1150℃ and kept warm for 8-10h, then forged and upset. The billet after upsetting is repeatedly returned to the furnace for upsetting, and then air-cooled and ground;

[0116] (4) The ground blank is put into the furnace at 400-800℃, heated to 970℃ and kept at this temperature for 6-8h, then upset and drawn, and then air-cooled and ground;

[0117] (5) The repaired billet is put into the furnace at 400-800℃, heated to 950℃ and kept warm for 6-8h, then forged and widened to the size of the slab for milling;

[0118] (6) After milling, the plate is heated in a soaking furnace and rolled into finished plate using a 4300mm four-roll reversible rolling mill.

[0119] The size of the finished plate prepared in this comparative example is 30×4000×8000mm, and the microstructure is α+β phase equiaxed structure, with equiaxed α phase content greater than 40%. The properties are as follows: longitudinal tensile strength 910MPa, longitudinal yield strength 830MPa, longitudinal elongation 11%; transverse tensile strength 940MPa, transverse yield strength 850MPa, transverse elongation 10%. Compared with the embodiment, steps (3)-(5) in this comparative example are forging processes. After the ingot is subjected to three vacuum consumable smelting processes, it is then heated in a furnace three times and then widened after three upsetting processes to obtain a forged blank. The microstructure of the finished plate has a higher equiaxed α phase content (greater than 40%), and the plate exhibits the characteristics of an equiaxed structure. However, the microstructure is controlled by forging multiple upsetting deformations and controlling the uniform deformation in all directions. In addition, the strength and plasticity of the finished plate are slightly insufficient. Although the product performance meets the national standards, the entire preparation process is time-consuming and costly.

[0120] In summary, the present invention obtains the ingot by a single EB and obtains the finished plate by a single-fire direct rolling. The uniform deformation control of the structure is achieved by a large width-aspect ratio and transverse and longitudinal reversing rolling during the rolling process, which is obviously innovative. The entire preparation process is simple and efficient, with a short production cycle and high repeatability, and can be widely applied to similar α+β two-phase titanium alloys.

[0121] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, and all of these should be included in the scope of the claims of the present invention.

Claims

1. A method for rolling thin-gauge and ultra-wide TC4 titanium alloy plates in one heat, characterized in that: The following steps are involved: S1, preparing an EB flat ingot, preparing raw materials according to the composition ratio of TC4 titanium alloy, and using an EB furnace to smelt and prepare a TC4 titanium alloy EB flat ingot; S2, explosive compounding, compounding a pure titanium layer with a thickness of 2 to 3 mm on the upper and lower surfaces of the TC4 titanium alloy EB flat ingot to obtain a TC4 titanium alloy slab; S3, slab heating, put the TC4 titanium alloy slab into the furnace at (400~800)±10℃, keep it at 800℃±10℃ for 2~3h, then heat it to β transformation temperature + (20~100)℃, and keep it at temperature for more than 5h; S4, single-hot rolling, feeds the heated TC4 titanium alloy slab into the four-roll reversing mill of the steel production line for multi-pass, medium-reduction rolling, and adopts a hot rolling process across the β-transformation temperature, while controlling the total deformation to 80-95%; S5, straightening, using the waste heat of the rolling mill to straighten the TC4 titanium alloy slab after the first hot rolling, and then air-cooling it to room temperature on the roller table; S6, annealing, annealing the straightened TC4 titanium alloy slab in the two-phase region to obtain a thin-gauge ultra-wide TC4 titanium alloy plate with a plate width of 3500-4300 mm and a plate thickness of 20-30 mm; In step S4, the first hot rolling comprises the following steps: S41, rolling the heated TC4 titanium alloy slab on a four-roll reversible rolling mill of a steel production line, controlling the time interval between the TC4 titanium alloy slab being taken out of the furnace and the start of rolling to be 60 to 100 seconds; S42, during the rolling process, first widening the TC4 titanium alloy slab along the slab width direction to a target width and then performing reversing rolling; S43: During the rolling process, multi-pass rolling with a medium reduction amount is adopted. The reduction amount is gradually increased in the first 3 to 4 passes until the medium reduction amount is reached. The reduction amount is gradually reduced in the first 3 to 4 passes until the slab reaches the target thickness. The total deformation is controlled to be 80 to 95%; S44, during the rolling process, a hot rolling process across the β-transformation temperature is adopted, the initial rolling temperature is controlled to be 1000-1080°C, and the final rolling temperature is ≥780°C.

2. The method for rolling thin-gauge and ultra-wide TC4 titanium alloy plates in one heat as claimed in claim 1, characterized in that: In the step S1: The raw materials are grade 0 or 0A titanium sponge, Al-V and Al99.5; the thickness of the TC4 titanium alloy EB ingot is 200-340 mm, the width is 1050-1550 mm, and the length is 1500-4200 mm.

3. The method for rolling thin-gauge and ultra-wide TC4 titanium alloy plates in one heat as claimed in claim 1, characterized in that: In the step S1: The raw materials of the EB ingot are TC4 return material, grade 0 or 0A titanium sponge, Al-V and Al99.5; The TC4 titanium alloy EB flat ingot has a thickness of 200 to 340 mm, a width of 1050 to 1550 mm, and a length of 1500 to 4200 mm.

4. The method for rolling thin-gauge and ultra-wide TC4 titanium alloy plates in one heat as claimed in claim 1, characterized in that: In step S2, the detonation velocity of the explosive used in the explosive compounding process is not less than 2500 mm / s.

5. The method for rolling thin gauge and ultra-wide TC4 titanium alloy plates in one heat as claimed in claim 1, characterized in that: In the step S3: The heating rate during the heating process is 60 to 120° C. / h; and / or The heating furnace used for heating the slab is a gas furnace, and the atmosphere in the furnace is controlled to be a slightly oxidizing atmosphere with a residual oxygen content of 100 to 500 ppm.

6. The method for rolling thin gauge and ultra-wide TC4 titanium alloy plates in one heat as claimed in claim 1, characterized in that: In step S43: The multiple passes are 15 to 30 passes; The pressing amount in the first 3 to 4 passes of the start of rolling and the first 3 to 4 passes of the end of rolling is ≤10%; the medium pressing amount is 8% to 16%.

7. The method for rolling thin gauge and ultra-wide TC4 titanium alloy plates in one heat as claimed in claim 1, characterized in that: In the step S5, during the straightening process, the deformation amount is ≤5%.

8. The method for rolling thin gauge and ultra-wide TC4 titanium alloy plates in one heat as claimed in claim 1, characterized in that: In step S6, the annealing process is as follows: The TC4 titanium alloy slab is placed in a furnace at 400±10℃ and kept for more than 2 hours, then heated to 600-850℃ at a heating rate of 50-80℃ / h, and the annealing time is controlled to be 2-4 hours. The furnace is then cooled to a slab temperature ≤200℃ and then taken out of the furnace and air-cooled to room temperature.

9. The method for rolling thin and ultra-wide TC4 titanium alloy plates in one heat as claimed in claim 1, characterized in that: The microstructure of the thin-gauge and ultra-wide TC4 titanium alloy plate is an α+β phase dual-state structure, the equiaxed α phase content is ≥20%, and the average grain size is below 350µm.

10. The method for single-pass rolling of thin-gauge and ultra-wide TC4 titanium alloy plates according to any one of claims 1 to 9, characterized in that: The thin-gauge, ultra-wide TC4 titanium alloy plate has a longitudinal tensile strength of 970±20 MPa, a longitudinal yield strength of 865±20 MPa, and a longitudinal elongation of 12.5±2.0%; The thin-gauge, ultra-wide TC4 titanium alloy plate has a transverse tensile strength of 980±20 MPa, a transverse yield strength of 910±20 MPa, and a transverse elongation of 11.5±1.0%; The unevenness of the thin-gauge and ultra-wide TC4 titanium alloy plate is ≤8 mm / m.

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