Preparation method of TC4 titanium alloy coiled tape

Abstract

The invention discloses a preparation method of a TC4 titanium alloy coiled strip, which comprises the following steps: by adopting specific titanium blank forging, rolling and annealing modes, after a cast ingot is forged and cogged, a plate blank is continuously returned to a furnace for heat preservation, the plate blank is subjected to double annealing, the annealing temperature is 830-890 DEG C, and after heat preservation is performed for 4-8 hours, the plate blank is subjected to heat preservation for 3-5 hours at 450-550 DEG C; the coated titanium alloy plate blank is conveyed to a heating furnace to be heated and rolled, and a coiled strip obtained after hot rolling is completed is cooled and then subjected to cover-type furnace annealing treatment with electric heating gradient temperature rising and argon protection; and finally, the wide hot-rolled titanium coil with the width of 1500-2000 mm, the thickness of 4-10 mm and good surface quality is prepared. The problems of narrow plate width, small coil weight, poor titanium alloy coil surface quality and the like of the titanium and titanium alloy plate strip produced by the existing coil method are solved, the performance uniformity of the titanium and titanium alloy coil strip is improved, the product quality is improved to a great extent, the production cost is reduced, the yield is improved, and good economic benefits are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloys, and in particular relates to a method for preparing a TC4 titanium alloy strip. Background Art

[0002] Titanium alloy has excellent properties such as low density, high specific strength and good corrosion resistance. As an important structural material, it has been widely used in aviation, aerospace, chemical industry, ships, automobiles, weapons, sports, medical and other fields. However, the large-scale application of titanium and its alloys is limited by its many surface defects, small single coil width, small coil weight, high smelting and processing costs.

[0003] Titanium alloy coils produced by hot rolling titanium steel can improve the utilization rate of rolling lines and increase corporate profits. During the heating process of the titanium alloy slab in the heating furnace, the blast furnace or converter gas and natural gas mixed atmosphere flame with low fuel value and low cost is used for heating. However, the thermal conductivity of titanium is poor, which leads to long heating time of titanium billets in the steel enterprise heating furnace, severe surface oxidation, violent surface reaction, and severe cracking of the thick surface oxygen-rich embrittlement layer during the subsequent rolling process. For example, TC4 hot-rolled coils have serious edge cracking and surface cracking problems. The hot rolling temperature of titanium billets is generally greater than 870°C. During the medium and low temperature heating process of titanium, as the temperature rises, the film structure is composed of titanium oxides of different densities. The oxide film increases in weight, but it is a dense layer with protective properties. When the temperature exceeds 800°C, the oxide film will gradually penetrate into the matrix, the oxide film will break, and it will no longer be dense. In the hot rolling process, in order to ensure the plasticity of the titanium billet, descaling water is basically not used. This will inevitably cause the surface hard oxide scale to be pressed into the matrix, causing surface defects and affecting the surface quality of the titanium coil.

[0004] In addition, the rolling line of steel enterprises is more than twice the length of the rolling line of titanium enterprises, and the temperature control and surface quality of the billet during the rolling process are difficult to guarantee. When TA1 and TA2 titanium billets are heated to a rolling temperature of 870-910°C, the surface oxidation products are mainly TiO2 with different densities, and the oxidation rate of TC4 is much greater than that of pure titanium (TA1, TA2). TC4 has a titanium-poor, aluminum-poor, vanadium-poor, and oxygen-rich oxygen-permeated layer from the surface to the inside. The longitudinal growth of the oxide layer is stratified and the structure is loose. The stress generated by the different thermal expansion coefficients of the generated oxidation products and the matrix causes the oxide film to fall off easily, and microcracks are easily formed during the subsequent rolling process, resulting in poor surface quality and serious edge cracks of TC4 hot-rolled coils. Summary of the invention

[0005] In order to overcome the defects of the above-mentioned prior art, the purpose of the present invention is to provide a method for preparing titanium alloy strips. By adopting specific titanium billet forging methods, rolling methods and annealing methods, a wide hot-rolled titanium coil with a width of 1500-2000mm, a thickness of 4-10mm and good surface quality is finally prepared; the problems of narrow width, small coil weight and poor surface quality of titanium alloy strips in the existing coil-type method for producing titanium and titanium alloy strips are solved, the performance uniformity of titanium and titanium alloy strips is improved, the product quality is greatly improved, the production cost is reduced, the yield rate is increased, and good economic benefits are achieved.

[0006] In order to achieve the above-mentioned invention object, the present invention provides a method for preparing TC4 titanium alloy coil, the process flow of which includes: ingot smelting - slab preparation - slab coating - slab heating - black coil rolling - black coil bell furnace annealing - shot blasting - pickling; the preparation method includes the following steps:

[0007] S1 Ingot Melting

[0008] Sponge titanium, vanadium aluminum alloy and the like are used as raw materials and smelted into titanium alloy ingots through three times of vacuum consumable furnace; the mass content of alloy elements in the ingots is Al: 5%-7%, V: 3%-5%, Fe: 0.1%-0.25%, C: 0.02%-0.08%, H: 0.001%-0.01%, O: 0.1%-0.2%, N: 0.01%-0.05%, and the balance is Ti and other inevitable impurities; the above components are smelted into φ700mm ingots.

[0009] S2 Slab Preparation

[0010] The ingot is forged and molded into a slab to be rolled, and the slab size is thickness (200-300) × width (1300-1600) × Lmm. The forging process is completed through 3 to 5 fires. The initial forging temperature of the first fire is 980℃~1050℃. After three upsetting and drawing, the slab is returned to the furnace for heating. The initial forging temperature of the subsequent fire is 940℃~980℃. After repeated upsetting and drawing, a slab with a thickness of (200~300mm)×width of (1300~2000mm)×L mm is prepared. The slab is returned to the furnace for insulation and double annealing is performed. The annealing temperature is 830℃~890℃, and the insulation time is 4 to 8h. After the insulation is completed, the slab is sent to 450℃~550℃ for insulation, and the insulation time is 3 to 5h. After the insulation is completed, the slab is taken out of the furnace and cooled to room temperature. As the slab to be rolled, the average Brinell hardness of the slab surface is less than 290HB. The double annealing is beneficial to reducing the surface hardness and facilitating the subsequent coating process. Short-time high-temperature annealing activates the recrystallization process in the alloy, allowing the alloy to completely recrystallize while controlling the grains from growing excessively. The second step is short-time low-temperature annealing below the recrystallization temperature, which is beneficial to reducing the stress in the slab, thereby obtaining a titanium alloy slab with good organizational uniformity.

[0011] S3 slab cladding

[0012] The slab to be rolled is subjected to surface grinding treatment to remove the oxide layer until the bright metal is exposed, with a surface roughness of 1.6μm<Ra<3.2μm, preferably 1.8μm. The upper and lower surfaces of the titanium slab are coated with 0.8-2.0mm pure TA2 thin plates by explosive composite method, and the average Vickers hardness of the thin plates is HV5<120, preferably HV5=100. The titanium thin plate and the titanium alloy slab must be tightly combined to avoid oxidation of the titanium alloy slab surface during the heating process. The use area of ​​the titanium thin plate is less than 20m 2 , without increasing processing costs. Low-cost coating treatment can avoid direct contact between the titanium billet and the oxidizing atmosphere during heating, and improve the surface quality after deformation. Coating treatment can also avoid direct contact with the roller during the first few rolling passes, achieving the purpose of heat preservation and improving plastic deformation.

[0013] S4 Slab Heating

[0014] The coated titanium alloy slab is sent to the heating furnace for heating and rolling. After passing through the preheating zone, the first heating zone, and the second heating zone of the heating furnace, the slab is kept warm in the 980℃~1040℃ equalizing zone for 120~280min. The total time in the furnace is less than 480min, and the heating zone is less than 300min. After the insulation is completed, it is rolled out of the furnace. The coated TA2 sheet has low strength at high temperature and good thermoplasticity. After the hot rolling is completed, the obtained black skin coil is shot blasted and pickled to remove the surface oxide layer and micro defects, and a titanium alloy coil with good surface quality is obtained. One of the heating zones is from room temperature to 550℃, and the heating time is less than 120min. The secondary heating zone is 750℃~820℃, and the heating time is 120~180min. Segmented heating can avoid the uneven organization caused by overheating of the surface tissue, control the total re-furnace time, and avoid the coarse grain phenomenon due to long-term heating.

[0015] S5 black coil rolling: including rough rolling, finish rolling and slow cooling processes.

[0016] The slab is rolled into a hot rolled coil with a thickness of 4 to 10 mm and a width of 1500 to 2000 mm by a 20 to 50 mm continuous rolling mill. The final rolling temperature is greater than 860°C and the coiling temperature is 600°C to 650°C.

[0017] Rough rolling: After the slab is heated, it is rolled to a thickness of 40 to 60 mm through a rough rolling mill.

[0018] Finishing rolling: The slab is rolled to a thickness of 40-60 mm by the roughing mill and then rolled to 4-10 mm by the finishing mill. The finishing inlet temperature is less than 940°C and the strip threading speed is 2-5 m / s. Slow strip threading can avoid tail swinging and ensure the straightness of the strip coil. The finishing inlet temperature is controlled to be less than 940°C because the finishing zone is rolled at a high speed to avoid adiabatic heating caused by strain rate sensitivity to induce β phase transformation. After the phase transformation occurs, Widmanstatten structure is easily formed in the subsequent cooling process, and the Widmanstatten structure will deteriorate the mechanical properties of the titanium alloy strip.

[0019] Slow cooling: After finishing rolling, the steel is coiled at a temperature of 600℃~650℃. After coiling, it is moved to the slow cooling zone for pile cooling. The temperature of the slow cooling zone is 600℃ and the temperature is kept for 12~16h. After the temperature is kept, it is taken out of the furnace and air-cooled. Slow cooling in the slow cooling pit is beneficial to reducing residual stress and is conducive to subsequent uncoiling.

[0020] S6 black leather bell furnace annealing

[0021] After hot rolling, the coil is cooled and then annealed in a bell-type furnace with electric heating gradient heating and argon protection. The annealing temperature is 820℃~860℃. During the annealing process of titanium coil, the furnace is kept under positive pressure and argon protection is maintained to prevent oxygen from entering the furnace. The argon inlet pressure is 2.0~9.0kPa, and the circulation flow rate is 30~80Nm 3 / h. The annealing titanium coil adopts a three-layer stacking method with a coil spacing of 50 to 100 mm. If the coil spacing is too small, it is easily affected by the radiant heat between the titanium coils, affecting the temperature uniformity. If the spacing is too large, it will interfere with the circulating gas in the furnace, causing excessive color difference on the surface of the titanium coil. The temperature setting of the hood annealing furnace adopts a gradient heating method. The radial thermal conductivity of the titanium coil is much lower than the circumferential and axial directions. The radial thermal conductivity is affected by the surface quality of the titanium coil, the thickness of the titanium coil, the winding tension, etc. The titanium coil is heated evenly by a gradient heating method. The thermal conductivity of titanium λ = 15.24W / (m·K), which is about 1 / 4 of nickel, 1 / 5 of iron, and 1 / 14 of aluminum. The thermal conductivity of various titanium alloys is about 50% lower than that of titanium. Therefore, it is necessary to strictly control the heating rate to ensure uniform heat transfer. The gradient heating technical scheme is as follows:

[0022] ①Room temperature~550℃, heating rate 60~100℃ / h, holding time 480~600min, circulating argon gas inlet pressure 2.0~3.2kPa, circulating flow rate 30Nm 3 / h; 4-10mm hot-rolled titanium coil, preferably, 4-6mm heating rate is 60℃ / h, 6-8mm heating rate is 80℃ / h, 8-10mm heating rate is 80℃ / h, 6-8mm heating rate is 100℃ / h.

[0023] ②700℃~740℃, heating from 550℃ to 700℃~740℃, heating rate 30~60℃ / h, holding time 480~600min, circulating argon gas pressure inlet 4.0~5.0kPa, circulating flow rate 50Nm 3 / h; TC4 recrystallization temperature is about 750℃, and the heating rate of the third stage is reduced after soaking at 700℃~740℃ to ensure that the titanium coil has good structural uniformity. For 4~10mm hot-rolled titanium coil, preferably, the heating rate of 4~6mm is 30℃ / h, the heating rate of 6~8mm is 45℃ / h, the heating rate of 8~10mm is 60℃ / h, and the heating rate of 6~8mm is 40℃ / h.

[0024] ③820℃~860℃, continue to heat up to 820℃~860℃, heating rate 10~30℃ / h, insulation time 600~900min, circulating argon gas inlet pressure 5.0~7.8kPa, circulating flow rate 80Nm 3 / h, 4-10mm hot rolled titanium coil, preferably, 4-6mm heating rate is 10℃ / h, 6-8mm heating rate is 20℃ / h, 8-10mm heating rate is 60℃ / h, 6-8mm heating rate is 30℃ / h.

[0025] The increase in the argon inlet pressure in the above steps ② and ③ can prevent the large flow of room temperature argon from meeting the high temperature in the furnace, causing furnace pressure fluctuations.

[0026] ④ After the insulation is completed, cool down to 550℃ at a rate of 10~30℃ / h. After 300~360min of insulation, cut off the heating power supply, remove the heating cover, and continue to pass argon gas for cooling. When the average temperature in the furnace is cooled to <180℃, remove the inner cover and carry out air cooling.

[0027] S7 finished product

[0028] After shot blasting and pickling, the surface roughness of the finished TC4 coil is 2 to 8 μm and the silver is bright. The diameter of the shot blasting steel ball is 0.6 to 1.0 mm, and the mixed addition, the proportion of 0.6 mm steel ball is greater than 60%, and the shot blasting operation speed is 1.5 to 3.0 m / min; the immersion + spray pickling is adopted, and the pickling liquid ratio, the volume ratio of hydrofluoric acid: nitric acid: sulfuric acid is (1:5 to 10:1), the concentration ratio of hydrofluoric acid solution is 22 to 36 g / L, the concentration ratio of nitric acid solution is 120 to 180 g / L, and the concentration ratio of sulfuric acid solution is 20 to 40 g / L. The pickling liquid ratio has good surface quality, and the pickling temperature should be controlled within the range of 40℃ to 60℃. If the temperature is too high, the acid will evaporate quickly and the concentration will fluctuate greatly. If the temperature is too low, the pickling efficiency will be low. The thinning amount of the TC4 plate can be controlled within the range of 40℃ to 60℃, and it does not affect the size of the finished product. The immersion pickling residence time is 2 to 5 minutes, followed by spray pickling.

[0029] Furthermore, the performance of the TC4 titanium alloy coiled product prepared by the above method was tested: the finished plate was annealed at 830 ° C, and the tensile specimen was prepared and tested according to GB / T 228.1-2021. The room temperature mechanical properties of the 4-5 mm plate were: 925 MPa ≤ R m ≤1150MPa, R p0.2 ≥870MPa, A≥10%, in line with the mechanical properties requirements of GB / T3621-2022 titanium and titanium alloy strips. Room temperature mechanical properties of 5-10mm plates: 895MPa≤R m ≤1100MPa, R p0.2 ≥825MPa, A≥10%, in line with the mechanical properties requirements of titanium and titanium alloy strips in GB / T3621-2022. The metallographic structure of the finished sample head and tail was inspected, and it was a uniform equiaxed α phase + transformed β structure.

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

[0031] The present invention adopts specific titanium billet forging method, rolling method, annealing and post-treatment method to finally prepare wide hot-rolled titanium coils with a width of 1500-2000 mm, a thickness of 4-10 mm and good surface quality; solves the problems of narrow plate width, small coil weight and poor surface quality of titanium alloy coils in the existing coil-to-coil method for producing titanium and titanium alloy plates and strips, improves the performance uniformity of titanium and titanium alloy coils, greatly improves product quality, reduces production costs, increases the yield rate, and has good economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The metallographic structure diagram of the head of the TC4 titanium alloy strip finished product sample prepared in the embodiment;

[0033] Figure 2 The metallographic structure diagram of the tail of the TC4 titanium alloy coiled strip finished product sample prepared in the embodiment. DETAILED DESCRIPTION

[0034] The present invention is further described below in conjunction with specific examples, but the present invention is not limited in any way. To avoid redundant description, the raw materials in the following examples are all commercially available products unless otherwise specified, and the methods used are all conventional methods unless otherwise specified.

[0035] A method for preparing a TC4 titanium alloy strip comprises the following steps:

[0036] S1 Ingot smelting: Sponge titanium, vanadium aluminum alloy, etc. are used as raw materials and smelted into titanium alloy ingots through three vacuum consumable furnaces;

[0037] S2 slab preparation: After the ingot is forged and opened, the slab is returned to the furnace for heat preservation and double annealing is performed. The annealing temperature is 830℃~890℃. After heat preservation for 4~8h, the slab is further kept at 450℃~550℃ for 3~5h. After the heat preservation is completed, the slab is taken out of the furnace and cooled to room temperature to be used as the slab to be rolled;

[0038] S3 slab cladding: grinding the surface of the slab to be rolled to remove the oxide layer until the bright metal is exposed, with a surface roughness of 1.6μm<Ra<3.2μm, preferably 1.8μm, and cladding the upper and lower surfaces of the titanium slab with 0.8-2.0mm pure TA2 thin plates by explosive composite method;

[0039] S4 slab heating: the coated titanium alloy slab is sent to the heating furnace for heating and rolling. After passing through the preheating zone, the first heating zone and the second heating zone of the heating furnace, the slab is kept in the 980℃~1040℃ soaking zone for 120~280min. The total time in the furnace is less than 480min, and the heating zone is less than 300min. After the end of the soaking, the slab is taken out of the furnace for rolling.

[0040] S5 black coil rolling: including rough rolling, finishing rolling and slow cooling process;

[0041] S6 black coil bell furnace annealing: After the hot rolling, the coil is cooled and then annealed in a bell furnace with electric heating gradient heating and argon protection. The annealing temperature is 820℃~860℃; the argon pressure is 2.0~9.0kPa, and the circulation flow rate is 30~80Nm 3 / h;

[0042] After S7 shot blasting and pickling, the finished TC4 coil with a surface roughness of 2 to 8 μm is obtained.

[0043] The matters not described in the following embodiments are the same as the description of the above specific implementation methods.

[0044] Example

[0045] A method for preparing a TC4 titanium alloy strip, the specific process flow is as follows:

[0046] S1 Ingot Melting

[0047] Sponge titanium, vanadium aluminum alloy and the like are used as raw materials and smelted into titanium alloy ingots through three times of vacuum consumable furnace smelting. The mass content of alloy elements in the ingots is Al: 5%, V: 3%, Fe: 0.1%, C: 0.02%, H: 0.001%, O: 0.1%, N: 0.01%, and the balance is Ti and unavoidable impurities; the above components are smelted into φ700mm ingots.

[0048] S2 Slab Preparation

[0049] The ingot is forged and opened to prepare the slab to be rolled, with a slab size of 200mm (thickness) × 1300mm (width) × 6000mm (length). The forging is completed through 3 fires. The initial forging temperature of the first fire is 980℃. After three upsetting and drawing, it is returned to the furnace for warming. The initial forging temperature of the subsequent fire is 940℃. After repeated upsetting and drawing, the thickness of 200mm×width 1300mm×L mm is prepared. The slab is returned to the furnace for insulation and double annealing is performed. The annealing temperature is 830℃ and the insulation time is 4h. After the insulation is completed, the slab is sent to 450℃ for insulation time for 3h. After the insulation is completed, it is taken out of the furnace and cooled to room temperature as the slab to be rolled. The average Brinell hardness of the slab surface is 280HB.

[0050] S3 slab cladding

[0051] The surface of the slab to be rolled is polished to remove the oxide layer until the bright metal is exposed, with a surface roughness of Ra=1.8μm. 0.8mm pure TA2 thin plates are coated on the upper and lower surfaces of the titanium slab by explosive composite method, and the average Vickers hardness of the thin plates is HV5=98.

[0052] S4 Slab Heating

[0053] The coated titanium alloy slab is sent to the heating furnace for heating and rolling. After passing through the preheating zone, the first heating zone, and the second heating zone of the heating furnace, the slab is kept in the 980℃ equalizing zone for 120 minutes. The total time in the furnace is 460 minutes, and the heating zone is 280 minutes. After the insulation is completed, it is rolled out of the furnace. The coated TA2 sheet has low strength at high temperature and good thermoplasticity. After rolling, the obtained hot-rolled coil is shot blasted and pickled and then removed to obtain a titanium alloy coil with good surface quality. Among them, the first heating zone is from room temperature to 550℃, and the heating time is 100 minutes; the secondary heating zone is 750℃, and the heating time is 120 minutes.

[0054] S5 black leather roll rolling

[0055] Rough rolling: The slab is rolled into a hot-rolled coil with a thickness of 4 mm and a width of 1500 mm through a 20-50 mm continuous rolling mill. The final rolling temperature is 870°C and the coiling temperature is 600°C.

[0056] Finishing rolling: The slab is rolled to a thickness of 40mm by the roughing mill and then rolled to 4mm by the finishing mill. The finishing inlet temperature is 920℃ and the threading speed is 5m / s. Slow threading can avoid tail swinging and ensure the straightness of the coil. The finishing inlet temperature is controlled at 920℃.

[0057] Slow cooling: After finishing rolling, the steel is coiled at a temperature of 600°C. After coiling, the steel is moved into the slow cooling zone for pile cooling at a temperature of 600°C. The steel is kept warm for 12 hours. After the heat preservation is completed, the steel is taken out of the furnace for air cooling.

[0058] S6 black leather bell furnace annealing

[0059] After hot rolling, the coil is cooled and then annealed in a bell-type furnace with electric heating and argon protection. The annealing temperature is 820°C. During the annealing process of the titanium coil, the furnace is kept under positive pressure and argon is circulated to prevent oxygen from entering the furnace. The argon pressure is 2.0kPa and the circulation flow rate is 30Nm 3 / h. Annealing titanium coils are stacked in three layers with a coil spacing of 50mm. The heating rate is strictly controlled to ensure uniform heat transfer:

[0060] 1) Room temperature ~ 550℃, heating rate 60℃ / h, holding time 480min, circulating argon pressure 2.0kPa, circulating flow rate 30Nm 3 / h; 4mm hot rolled titanium coil, heating rate 60℃ / h.

[0061] 2) 700℃, heating from 550℃ to 700℃, heating rate 30℃ / h, holding time 480min, circulating argon pressure 4.0kPa, circulating flow rate 50Nm 3 / h.

[0062] 3) 820℃, from 700℃ to 820℃, heating rate 10℃ / h, holding time 600min, circulating argon pressure 5.0kPa, circulating flow rate 80Nm 3 / h. After rolling, the head and tail samples of the coiled strip were taken for metallographic inspection, which showed a uniform equiaxed α phase + transformed β structure. Figure 1 and Figure 2 .

[0063] 4) After the insulation is completed, the temperature is lowered to 550°C at a rate of 10°C / h. After 300 minutes of insulation, the heating power is cut off, the heating cover is removed, and argon gas is continuously introduced for cooling. When the average temperature in the furnace is cooled to 180°C, the inner cover is removed and air cooling is performed.

[0064] S7 finished product

[0065] After shot blasting and pickling, a silver-bright TC4 coil with a thickness of 4mm, a width of 1500mm and a surface roughness of 3-4μm was obtained. The diameter of the shot blasting steel ball is 0.6-1.0mm, 0.6mm diameter steel balls account for 60%, and the remaining mixed diameter steel balls account for 40%. The shot blasting operation speed is 1.5-3.0m / min, and immersion + spray pickling is adopted. The pickling liquid ratio is hydrofluoric acid: nitric acid: sulfuric acid liquid ratio (1:5:1), the immersion pickling residence time is 5min, followed by spray pickling, the pickling temperature is controlled in the range of 40℃~60℃, the hydrofluoric acid concentration ratio is 22g / L, the nitric acid concentration ratio is 120g / L, and the sulfuric acid concentration ratio is 20g / L.

[0066] Performance Testing

[0067] After the finished plate is annealed at 830℃, the tensile specimens are prepared and tested according to GB / T228.1-2021. The room temperature mechanical properties are: R m =980MPa, R p0.2 =880MPa, A=12%, which meets the mechanical property requirements of titanium and titanium alloy strips in GB / T 3621-2022. After annealing, the head and tail samples of the coiled strip were taken for metallographic inspection, which showed a uniform equiaxed α phase + transformed β structure. Figure 1 and Figure 2 .

[0068] For any person skilled in the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or to modify it into an equivalent embodiment with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the content of the technical solution of the present invention should still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a TC4 titanium alloy strip, characterized in that: The preparation method comprises the following steps: S1 Ingot smelting: Sponge titanium and vanadium aluminum alloy are used as raw materials and smelted into titanium alloy ingots through three vacuum consumable furnaces; S2 slab preparation: After the ingot is forged and opened, the slab is returned to the furnace for heat preservation and double annealing is performed. The annealing temperature is 830℃~890℃. After heat preservation for 4~8h, the slab is further kept at 450℃~550℃ for 3~5h. After the heat preservation is completed, the slab is taken out of the furnace and cooled to room temperature to be used as the slab to be rolled; S3 slab cladding: The slab to be rolled is surface-grinded to remove the oxide layer until the bright metal is exposed, with a surface roughness of 1.6μm<Ra<3.2μm. The upper and lower surfaces of the titanium slab are respectively coated with 0.8-2.0mm pure TA2 thin plates by explosive composite method; S4 slab heating: the coated titanium alloy slab is sent to the heating furnace for heating and rolling. After passing through the preheating zone, the first heating zone and the second heating zone of the heating furnace, the slab is kept in the 980℃~1040℃ soaking zone for 120~280min. The total time in the furnace is less than 480min, and the heating zone is less than 300min. After the end of the soaking, the slab is taken out of the furnace for rolling. S5 black coil rolling: including rough rolling, finishing rolling and slow cooling process; S6 black coil bell furnace annealing: After the hot rolling, the coil is cooled and then annealed in a bell furnace with electric heating gradient heating and argon protection. The annealing temperature is 820℃~860℃; the argon pressure is 2.0~9.0kPa, and the circulation flow rate is 30~80Nm 3 / h; After S7 shot blasting and pickling, the finished TC4 coil with a surface roughness of 2 to 8 μm is obtained.

2. The preparation method according to claim 1, characterized in that: The alloy element mass content of the ingot in step S1 is Al: 5%-7%, V: 3%-5%, Fe: 0.1%-0.25%, C: 0.02%-0.08%, H: 0.001%-0.01%, O: 0.1%-0.2%, N: 0.01%-0.05%, and the remainder is Ti and unavoidable impurities.

3. The preparation method according to claim 1, characterized in that: The forging process in step S2 is completed through 3 to 5 fires. The initial forging temperature of the first fire is 980°C to 1050°C, and the steel is returned to the furnace for temperature replenishment after three upsetting and stretching processes. The initial forging temperature of the subsequent fires is 940°C to 980°C, and a slab with a thickness of (200 to 300 mm) × width of (1300 to 2000 mm) × L mm is prepared through repeated upsetting and stretching processes.

4. The preparation method according to claim 1, characterized in that: The average Vickers hardness of the pure TA2 sheet in step S3 is HV5<120, and the use area of ​​the titanium sheet is <20m 2 .

5. The preparation method according to claim 1, characterized in that: In step S4, the first heating zone is heated from room temperature to 550°C, and the heating time is less than 120 minutes. The secondary heating zone is heated from 750°C to 820°C, and the heating time is 120 to 180 minutes.

6. The preparation method according to claim 1, characterized in that: Rough rolling in step S5: the slab is rolled into a hot rolled coil with a thickness of 4 to 10 mm and a width of 1500 to 2000 mm by a 20 to 50 mm continuous rolling mill, the final rolling temperature is greater than 860°C, and the coiling temperature is 600°C to 650°C.

7. The preparation method according to claim 1, characterized in that: In step S5, the finishing rolling entrance temperature is less than 940°C, and the strip threading speed is 2-5m / s; after finishing rolling, the strip is curled at a temperature of 600°C-650°C, and after curling, the strip is moved into a slow cooling zone for stack cooling at a temperature of 600°C for 12-16h.

8. The preparation method according to claim 1, characterized in that: The gradient heating process described in step S6 includes: room temperature to 550°C, a heating rate of 60 to 100°C / h, and a holding time of 480 to 600 min; heating from 550°C to 700°C to 740°C at a heating rate of 30 to 60°C / h, and a holding time of 480 to 600 min; continuing to heat to 820°C to 860°C, a heating rate of 10 to 30°C / h, and a holding time of 600 to 900 min; after the insulation is completed, the temperature is gradually reduced to 550°C at a rate of 10 to 30°C / h, and after insulation for 300 to 360 min, the heating power is cut off, the heating cover is removed, and argon gas is continuously introduced for cooling. When the average temperature in the furnace is cooled to <180°C, the inner cover is removed and air cooling is performed.

9. The preparation method according to claim 1, characterized in that: In step S7, the volume ratio of hydrofluoric acid: nitric acid: sulfuric acid in the pickling solution is 1:5-10:1; the concentration of the hydrofluoric acid solution is 22-36 g / L, the concentration of the nitric acid solution is 120-180 g / L; and the concentration of the sulfuric acid solution is 20-40 g / L.

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