A hot rolling method of an isotropic sp700 titanium alloy wide sheet

Abstract

The application discloses a kind of isotropic SP700 titanium alloy wide-width sheet hot rolling method, which comprises the following steps: one, SP700 titanium alloy slab surface is coated with oxidation-resistant coating;Two, first fire rolling;Three, cutting treatment;Four, quenching treatment;Five, second fire rolling;Six, cutting treatment;Seven, third fire rolling;Eight, cutting treatment;Nine, fourth fire rolling;Ten, finished product heat treatment.The application prepares B texture mainly wide-width fine-grain sheet by one-time near-beta rolling of SP700 titanium alloy slab, combined with subsequent beta quenching treatment and alpha-beta phase zone medium-temperature reversing rolling, so as to control the difference between longitudinal and transverse mechanical properties within 15 MPa, wherein the minimum thickness of the wide-width sheet obtained by using cladding and stacking rolling with reasonable pass deformation distribution can reach 0.5 mm, and the maximum width can reach 1800 mm, and in addition, the material loss of common process is also reduced, and the production benefit is improved.

Description

Technical Field

[0001] This invention belongs to the field of titanium and titanium alloy thin plate preparation technology, specifically relating to a hot rolling method for isotropic SP700 titanium alloy wide thin plates. Background Technology

[0002] SP700 titanium alloy is a β-phase-rich (α+β) two-phase titanium alloy with a nominal composition of Ti-4.5Al-3V-2Mo-2Fe. The β-transformation temperature is lowered by increasing the isomorphous β-phase elements Mo and V, and the eutectoid stabilizing element Fe, while simultaneously improving the diffusion capacity of the β-phase. Therefore, compared to TC4 titanium alloy, this alloy exhibits a lower β-transformation temperature, better strength-plasticity matching, lower superplastic forming temperature, and improved forming plasticity. It is widely used in aerospace, marine engineering, and other fields, and can be used in superplastic forming / diffusion bonding processes to manufacture thin-walled, complex-shaped parts such as hatches, bulkheads, tail fins, hulls, and air ducts.

[0003] The common method for manufacturing SP700 titanium alloy thin sheets involves hot rolling followed by cold rolling. This rolling process easily produces strong T-textures, resulting in a transverse tensile strength that is much higher than the longitudinal strength. This impairs the uniformity of deformation during subsequent superplastic forming, affecting forming accuracy. Furthermore, cold rolling results in poor process plasticity and significant work hardening, especially severe when the finished sheet thickness is below 1.5 mm, requiring multiple vacuum stress-relief annealing processes, leading to low production efficiency. In addition, cold-rolled sheets are limited by deformation methods and equipment dimensions, with product widths generally not exceeding 1200 mm. With the development of my country's aerospace and shipbuilding industries, there is a growing demand for larger superplastic structural components, thus placing higher requirements on the dimensions and isotropy of the sheet materials. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a hot rolling method for wide thin plates of isotropic SP700 titanium alloy, addressing the shortcomings of the prior art. This method involves a single near-β rolling of the slab, combined with subsequent β-quenching and mid-temperature reversing rolling in the α-β phase region, to produce wide, fine-grained thin plates with a predominantly B-texture. This effectively controls the difference in longitudinal and transverse mechanical properties to within 15 MPa. By employing cladding rolling supplemented with a reasonable distribution of deformation per pass, the minimum thickness of the obtained wide thin plate can reach 0.5 mm, and the maximum width can reach 1800 mm. Furthermore, it reduces material waste in common processes and improves production efficiency.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a hot rolling method for wide thin plates of isotropic SP700 titanium alloy, characterized in that the method includes the following steps:

[0006] Step 1: Apply an anti-oxidation coating to the surface of the SP700 titanium alloy slab; the thickness of the SP700 titanium alloy slab is 130mm to 180mm, the width is 1000mm to 1600mm, and the length is 800mm to 1700mm.

[0007] Step 2: The SP700 titanium alloy slab processed in Step 1 is subjected to a first rolling process at a temperature of 860℃~900℃ to obtain a first rolled slab. The first rolling process is unidirectional rolling, with a pass deformation rate of 15%~30% and 6~8 passes. The thickness of the first rolled slab is 15mm~45mm and the width is 1000mm~1600mm.

[0008] Step 3: Cut the first rolled slab obtained in Step 2 to obtain multiple first intermediate slabs; the thickness of the first intermediate slab is 15mm to 45mm, the width is 1000mm to 1600mm, and the length is 800mm to 1500mm.

[0009] Step 4: Perform β-quenching on the first intermediate slab obtained in Step 3; The specific process of β-quenching is as follows: hold the first intermediate slab at a temperature of 20℃ to 70℃ above the β phase transformation point for 40 min to 80 min and then water cool it to below 60℃.

[0010] Step 5: The first intermediate slab after β-quenching in Step 4 is subjected to a second rolling process at a temperature of 800℃~860℃ to obtain a second rolled slab. The deformation rate of the second rolling pass is 15%~30%, the number of passes is 2~4, and the rolling direction of the second rolling is perpendicular to the rolling direction of the first rolling in Step 2. The thickness of the second rolled slab is 10mm~15mm, and the width is 800mm~1500mm.

[0011] Step 6: Cut the second rolled slab obtained in Step 5 to obtain multiple second intermediate slabs; the thickness of the second intermediate slab is 10mm to 15mm, the width is 800mm to 1500mm, and the length is 1500mm to 2400mm.

[0012] Step 7: The second intermediate slab obtained in Step 6 is subjected to a third rolling process at a temperature of 780℃~840℃ to obtain a third rolled slab. The deformation rate of the third rolling process is 10%~25%, the number of passes is 2~4, and the rolling direction of the third rolling process is parallel to the rolling direction of the second rolling process in Step 5. The thickness of the third rolled slab is 4mm~12mm, and the width is 800mm~1500mm.

[0013] Step 8: Cut the third rolled slab obtained in Step 7 to obtain multiple third intermediate slabs; the thickness of the third intermediate slab is 4mm to 12mm, the width is 800mm to 1500mm, and the length is 1500mm to 1800mm.

[0014] Step 9: Stack and weld the third intermediate slab obtained in Step 8 in the order of steel plate, multiple third intermediate slabs, and steel plate, and perform a fourth rolling at a temperature of 780℃~860℃ to obtain SP700 titanium alloy sheet; the deformation rate of the fourth rolling pass is 15%~30%, the number of passes is 5~8, and the rolling direction of the fourth rolling is perpendicular to the rolling direction of the third rolling in Step 7. The thickness of the SP700 titanium alloy sheet is 0.5mm~3.0mm, the width is 1500mm~1800mm, and the length is 3000mm~6000mm.

[0015] Step 10: Heat-treat the SP700 titanium alloy sheet obtained in Step 9, and then cool it to room temperature by air cooling to obtain an isotropic SP700 titanium alloy wide sheet with a thickness of 0.5mm to 3.0mm, a width of 1500mm to 1800mm, and a length of 3000mm to 6000mm.

[0016] This invention designs a technical route of high-temperature near-β billet rolling in the α-β phase region, homogenization quenching in the β single-phase region, and medium-temperature reversing cladding rolling in the α-β phase region. The high-temperature near-β billet rolling in the α-β phase region, i.e., the first rolling, efficiently forms the billet and refines the microstructure, avoiding strong texture. The β single-phase region quenching, i.e., β quenching treatment, allows for sufficient recrystallization during homogenization, resulting in uniform and fine β grains in the original rolled intermediate billet. The quenching then yields uniform and fine acicular martensite. The process involves the α-β phase region... The intermediate-temperature reversing cladding rolling process involves a second, third, and fourth rolling pass. The rolling direction of the second pass is perpendicular to the rolling direction of the first pass, and the rolling direction of the fourth pass is perpendicular to the rolling direction of the third pass. This ensures that there are two reversing rolling passes during the entire rolling process, thereby minimizing the differences in transverse and longitudinal properties of the finished sheet and making the sheet more isotropic. This results in isotropic fine-grained thin sheets with minimal longitudinal and transverse deviations.

[0017] This invention involves stacking and welding steel plates, multiple third intermediate slabs, and steel plates in sequence. The steel plates are used to cover the multiple third intermediate slabs in the middle, which provides a good heat preservation effect and ensures that the multiple third intermediate slabs lose almost no heat during the deformation process, achieving an effect close to constant temperature rolling. The purpose of constant temperature rolling is to ensure the temperature consistency throughout the deformation process, so as to control the homogenization of the microstructure.

[0018] This invention controls the parameters of the first rolling, cutting, quenching, second rolling, cutting, third rolling, cutting, and fourth rolling processes to simultaneously meet the requirements of stable finished product performance and flexible process parameters, thereby obtaining isotropic SP700 titanium alloy wide thin plates that meet the requirements. Through heat treatment, the strain energy accumulated during the early deformation process is released, deformation texture is eliminated, and recrystallization of the microstructure is achieved, resulting in fine and uniform grains. At the same time, residual stress generated during deformation is also removed, making the finished plate flat.

[0019] The above-mentioned hot rolling method for wide thin sheets of isotropic SP700 titanium alloy is characterized in that the anti-oxidation coating in step one is a TB920 anti-oxidation coating, and the thickness of the anti-oxidation coating is 1mm to 2mm. This invention uses a TB920 anti-oxidation coating to prevent oxidation, reduce surface heat loss, and prevent hydrogen absorption, thereby reducing surface cracking. By controlling the coating thickness, it achieves anti-oxidation effects, reduces heat loss, and thus reduces surface cracking, while also preventing excessive coating from affecting the surface quality of the slab.

[0020] It should be noted that the raw material used in the TB920 anti-oxidation coating is TB920 titanium alloy rolling process glass powder produced by Beijing Tianlichuang Glass Technology Development Co., Ltd.

[0021] The above-mentioned hot rolling method for wide thin sheets of isotropic SP700 titanium alloy is characterized in that, in step two, the holding time of the first rolling is 3h to 5h, the final rolling temperature of the first rolling is not less than 700℃, and the total deformation rate of the first rolling is not less than 70%. In this invention, the slab thickness before the first rolling pass is relatively large. The holding time of 3 to 5 hours ensures the uniformity of the overall temperature of the slab from the core to the surface after the holding time, and prevents changes in the slab's microstructure due to prolonged heating, thus avoiding affecting the finished product's microstructure and properties. The final rolling temperature of not less than 700°C is mainly to ensure that the hot working window of the entire process is not too large, and also to ensure the plastic deformation of the last few passes. Both are for the uniformity of deformation, ensuring uniform fragmentation of the microstructure, and avoiding affecting the finished product's microstructure and properties. The advantage of a total deformation rate of not less than 70% is that a sufficiently large deformation amount can fully break down and refine the original microstructure, laying a good foundation for obtaining a fine-grained microstructure. In addition, a sufficient deformation amount can also allow plastic deformation to fully penetrate into the core of the slab, avoiding a situation where the deformation amount is large on the surface and near the surface, while the deformation amount in the core is small.

[0022] The above-mentioned hot rolling method for wide thin sheets of isotropic SP700 titanium alloy is characterized in that, after the heat treatment of β quenching in step four is completed, the sheet is rapidly immersed in room temperature water for cooling, and the time from the first intermediate slab exiting the furnace to complete immersion in water does not exceed 6 seconds. In this invention, the time from exiting the furnace to complete immersion in water determines the lamellar thickness of the full-lamellar α-structure obtained after the intermediate slab cools and whether there is precipitation and growth of grain boundary α phase (generally, the grain boundary α content is required not to exceed a certain value, such as 15%). The shorter the immersion time, the smaller the lamellar thickness, the less likely grain boundary α phase is to precipitate and grow, and the better the resulting finished product microstructure.

[0023] The above-mentioned hot rolling method for wide thin sheets of isotropic SP700 titanium alloy is characterized in that the total deformation rate of the fourth rolling in step nine is not less than 70%. This invention ensures sufficient microstructural fragmentation, resulting in fine grains and uniform size by controlling the total deformation rate.

[0024] The above-mentioned hot rolling method for wide thin sheets of isotropic SP700 titanium alloy is characterized in that the specific process of heat treatment in step ten is: holding at 700℃~800℃ for 1h~2h. This invention provides sufficient driving force for microstructure recrystallization by controlling the heat treatment parameters and ensures that abnormal grain growth does not occur. In terms of time, it provides sufficient time for the uniform recrystallization process and ensures production efficiency. The combination of heat treatment temperature and time determines the size and uniformity of the microstructure grains.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1. This invention achieves efficient billet preparation and further refines the microstructure through the first rolling process, avoiding strong texture. Beta quenching ensures sufficient recrystallization during homogenization, resulting in uniform and fine β grains in the original rolled intermediate billet. Quenching yields uniform and fine acicular martensite. Second, third, and fourth rolling processes, using medium-temperature deformation, prevent the α phase from growing during rolling. Reversed rolling deflects the c-axis of the α phase, transforming the texture type from a predominantly T-texture B / T texture to a reversed B texture. This results in isotropic fine-grained thin plates with minimal longitudinal and transverse deviations. Compared to cold-rolled plates, anisotropy is significantly improved, and grain size is essentially uniform. Finally, heat treatment releases the strain energy accumulated during the initial deformation process, eliminating deformation texture and achieving recrystallization of the microstructure, resulting in fine and uniform grains. It also removes residual stress generated during deformation, ensuring a flat finished plate shape and producing isotropic SP700 titanium alloy wide thin plates.

[0027] 2. This invention releases the strain energy accumulated during the early deformation process through heat treatment, eliminates deformation texture, realizes the recrystallization of microstructure, and obtains fine and uniform grains. At the same time, it can also remove the residual stress generated during the deformation process, so that the finished plate has a flat shape.

[0028] 3. This invention uses a steel plate cladding rolling method supplemented by a reasonable rolling rhythm and pass deformation distribution to obtain a finished product with a minimum thickness of 0.5mm and a maximum width of 1800mm. Compared with cold-rolled finished plates, the rolling difficulty is greatly reduced, the production efficiency is significantly improved, the plate width range is greatly increased, and the structure uniformity is good.

[0029] 4. This invention reduces surface cracking by using an anti-oxidation coating and avoids edge cracking during finished product rolling (fourth-stage rolling) by using a steel plate covering method. Both of these reduce material loss and improve production efficiency.

[0030] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0031] Figure 1 Metallographic image (500×) of the isotropic SP700 titanium alloy wide sheet prepared in Example 1 of this invention.

[0032] Figure 2 Metallographic image (500×) of the isotropic SP700 titanium alloy wide sheet prepared in Example 2 of this invention.

[0033] Figure 3 Metallographic image (500×) of the isotropic SP700 titanium alloy wide sheet prepared in Example 3 of the present invention.

[0034] Figure 4 The diagram shows the influence of the B-type textured isotropic SP700 titanium alloy wide sheet and the T-type textured SP700 titanium alloy wide sheet prepared in Example 1 of the present invention on tensile strength.

[0035] Figure 5 The figure shows the effect of the B-type textured isotropic SP700 titanium alloy wide sheet and the T-type textured SP700 titanium alloy wide sheet prepared in Example 1 of the present invention on yield strength and elongation. Detailed Implementation

[0036] Example 1

[0037] This embodiment includes the following steps:

[0038] Step 1: Apply a TB920 anti-oxidation coating to the surface of the SP700 titanium alloy slab. The anti-oxidation coating is 2mm thick, and the SP700 titanium alloy slab is 150mm thick, 1000mm wide, and 800mm long.

[0039] Step 2: After the SP700 titanium alloy slab processed in Step 1 is held at 860℃ for 4 hours, it is then subjected to the first rolling process to obtain the first rolled slab. The first rolling process is a unidirectional rolling process, which is completed in six passes. The deformation rates of each pass are 15%, 20%, 24%, 28%, 29%, and 25%, respectively. The final rolling temperature after rolling is not lower than 700℃, and the total deformation is 80%. The thickness of the first rolled slab is 30mm and the width is 1000mm.

[0040] Step 3: Cut the first rolled slab obtained in Step 2 to obtain four first intermediate slabs; the thickness of the first intermediate slab is 30mm, the width is 1000mm, and the length is 850mm.

[0041] Step 4: Perform β-quenching treatment on the first intermediate slab obtained in Step 3; The specific process of β-quenching treatment is as follows: after holding the first intermediate slab at a temperature 20°C above the β phase transformation point for 60 minutes, quickly send it into room temperature water to cool it to below 60°C, and the time from the slab being taken out of the furnace to being completely immersed in the water shall not exceed 5 seconds.

[0042] Step 5: The first intermediate slab after β-quenching in Step 4 is subjected to a second rolling process at a temperature of 800℃ to obtain a second rolled slab. The second rolling process is completed in four passes, with deformation rates of 20%, 25%, 22%, and 15% for each pass, respectively. The rolling direction of the second rolling process is perpendicular to the rolling direction of the first rolling process in Step 2. The thickness of the second rolled slab is 12mm and the width is 850mm.

[0043] Step 6: Cut the second rolled slab obtained in Step 5 to obtain four second intermediate slabs; the thickness of the second intermediate slab is 12mm, the width is 850mm, and the length is 2400mm.

[0044] Step 7: The second intermediate slab obtained in Step 6 is subjected to a third rolling process at a temperature of 780℃ to obtain a third rolled slab. The third rolling process is completed in three passes, with deformation rates of 25%, 22%, and 14% for each pass. The rolling direction of the third rolling process is parallel to the rolling direction of the second rolling process in Step 5. The thickness of the third rolled slab is 6 mm and the width is 850 mm.

[0045] Step 8: Cut the third rolled slab obtained in Step 7 to obtain twelve third intermediate slabs; the thickness of the third intermediate slab is 6mm, the width is 850mm, and the length is 1500mm.

[0046] Step 9: The third intermediate slab obtained in Step 8 is stacked and welded in the order of steel plate, 4 third intermediate slabs, and steel plate, and then rolled in a fourth pass at a temperature of 780℃ to obtain SP700 titanium alloy sheet. The fourth pass rolling is completed in six passes, with deformation rates of 16%, 23%, 25%, 25%, 26%, and 17% for each pass. The final rolling temperature is not lower than 700℃, the total deformation is 80%, and the rolling direction of the fourth pass rolling is perpendicular to the rolling direction of the third pass rolling in Step 7. The SP700 titanium alloy sheet has a thickness of 1.2mm, a width of 1500mm, and a length of 3500mm.

[0047] Step 10: Heat-treat the SP700 titanium alloy sheet obtained in Step 9. The specific heat treatment process is as follows: hold at 700℃ for 1.5h, and then cool to room temperature by air cooling to obtain an isotropic SP700 titanium alloy wide sheet with a thickness of 1.2mm, a width of 1500mm, and a length of 3500mm.

[0048] Figure 2 Metallographic image (500×) of the isotropic SP700 titanium alloy wide sheet prepared in this embodiment. Figure 2 It can be seen that the metallographic structure of the SP700 titanium alloy wide sheet prepared in this embodiment is a uniform and fine equiaxed α+β structure, the original β grains are fully broken, and there is no continuous and straight grain boundary α phase.

[0049] Testing revealed that the isotropic SP700 titanium alloy wide sheet prepared in this embodiment exhibits a transverse room temperature tensile strength of 1031 MPa–1039 MPa, a transverse yield strength of 986 MPa–998 MPa, and an elongation after fracture of 16.5%–17.5%. The longitudinal room temperature tensile strength is 1029 MPa–1033 MPa, the longitudinal yield strength is 971 MPa–976 MPa, and the elongation after fracture is 17%–20%. The transverse high-temperature tensile strength is 738 MPa–741 MPa, the transverse yield strength is 619 MPa–625 MPa, the longitudinal high-temperature tensile strength is 723 MPa–724 MPa, and the longitudinal yield strength is 581 MPa–584 MPa. The transverse grain size of the isotropic SP700 titanium alloy wide sheet prepared in this embodiment is 2.4 μm–2.6 μm, and the longitudinal grain size is 2.1 μm–2.6 μm.

[0050] In summary, the isotropic SP700 titanium alloy wide sheet prepared in this embodiment has a difference of less than 10 MPa in transverse and longitudinal room temperature tensile strength, good isotropy, and excellent performance indicators.

[0051] The test results of the isotropic SP700 titanium alloy wide sheet with B-type texture and the SP700 titanium alloy wide sheet with T-type texture prepared in this embodiment are shown in the figure. Figure 4 and Figure 5 .

[0052] Figure 4 The influence of the B-textured isotropic SP700 titanium alloy wide sheet and the T-textured SP700 titanium alloy wide sheet prepared in Example 1 of this invention on tensile strength. Figure 5 The effects of B-textured and T-textured isotropic SP700 titanium alloy wide sheets prepared in Example 1 of this invention on yield strength and elongation. Figure 4 The longitudinal axis represents the tensile strength Rm of the plate. Figure 5 The vertical axis represents the yield strength Rp0.2 (left vertical axis) and the elongation A (right vertical axis). Figure 5 The top four lines represent the test results for yield strength Rp0.2, and the bottom four lines represent the test results for elongation A. Figure 4 and Figure 5 The horizontal axis represents the direction of the plate performance test. RD represents the rolling direction, TD represents the horizontal axis perpendicular to the rolling direction, B represents the isotropic SP700 titanium alloy wide sheet with B-type texture prepared in Example 1 of this invention, represented by a solid line in the figure, and T represents the SP700 titanium alloy wide sheet with T-type texture, represented by a dashed line in the figure. Figure 4 and Figure 5 As can be seen from the figures, the numerical differences in the three performance indicators RD and TD in the two directions of the B-type texture are relatively small (isotropic), while the T-type texture is relatively large (anisotropic). The comprehensive comparison of the two figures illustrates from a deeper mechanism perspective that the B-type texture obtained by this invention is an important factor in obtaining isotropic SP700 thin plates.

[0053] Example 2

[0054] This embodiment includes the following steps:

[0055] Step 1: Apply a TB920 anti-oxidation coating to the surface of the SP700 titanium alloy slab. The anti-oxidation coating is 1mm thick, and the SP700 titanium alloy slab is 130mm thick, 1500mm wide, and 1200mm long.

[0056] Step 2: After the SP700 titanium alloy slab processed in Step 1 is held at 880℃ for 3 hours, it is then subjected to the first rolling process to obtain the first rolled slab. The first rolling process is a unidirectional rolling process, which is completed in eight passes. The deformation rates of each pass are 15%, 20%, 28%, 29%, 27%, 24%, 24%, and 21%, respectively. The final rolling temperature after rolling is not lower than 700℃, and the total deformation is 88%. The thickness of the first rolled slab is 15mm and the width is 1500mm.

[0057] Step 3: Cut the first rolled slab obtained in Step 2 to obtain eight first intermediate slabs; the thickness of the first intermediate slab is 15mm, the width is 1500mm, and the length is 1100mm.

[0058] Step 4: Perform β-quenching treatment on the first intermediate slab obtained in Step 3; The specific process of the β-quenching treatment is as follows: after holding the first intermediate slab at a temperature 50°C above the β phase transformation point for 40 minutes, quickly send it into room temperature water to cool to below 60°C, and the time from the slab being taken out of the furnace to being completely immersed in the water is 5 seconds.

[0059] Step 5: The first intermediate slab after β-quenching in Step 4 is subjected to a second rolling process at a temperature of 830℃ to obtain a second rolled slab. The second rolling process is completed in two passes, with deformation rates of 20% and 17% for each pass, respectively. The rolling direction of the second rolling process is perpendicular to the rolling direction of the first rolling process in Step 2. The thickness of the second rolled slab is 10mm and the width is 1100mm.

[0060] Step 6: Cut the second rolled slab obtained in Step 5 to obtain eight second intermediate slabs; the thickness of the second intermediate slab is 10mm, the width is 1100mm, and the length is 2100mm.

[0061] Step 7: The second intermediate slab obtained in Step 6 is subjected to a third rolling process at a temperature of 810℃ to obtain a third rolled slab. The third rolling process is completed in four passes, with deformation rates of 20%, 25%, 25%, and 11% for each pass. The rolling direction of the third rolling process is parallel to the rolling direction of the second rolling process in Step 5. The thickness of the third rolled slab is 4 mm and the width is 1100 mm.

[0062] Step 8: Cut the third rolled slab obtained in Step 7 to obtain twenty-four third intermediate slabs; the thickness of the third intermediate slab is 4mm, the width is 1100mm, and the length is 1600mm.

[0063] Step 9: The third intermediate slab obtained in Step 8 is stacked and welded in the order of steel plate, 4 titanium plates, and steel plate, and then rolled in a fourth pass at a temperature of 820℃ to obtain SP700 titanium alloy sheet. The fourth pass rolling is completed in seven passes, with deformation rates of 15%, 21%, 23%, 24%, 23%, 25%, and 25% for each pass. The final rolling temperature is not lower than 700℃, the total deformation is 88%, and the rolling direction of the fourth pass rolling is perpendicular to the rolling direction of the third pass rolling in Step 7. The SP700 titanium alloy sheet has a thickness of 0.5mm, a width of 1600mm, and a length of 6000mm.

[0064] Step 10: Heat-treat the SP700 titanium alloy sheet obtained in Step 9. The specific heat treatment process is as follows: hold at 750℃ for 2 hours, and then cool to room temperature by air cooling to obtain an isotropic SP700 titanium alloy wide sheet with a thickness of 0.5 mm, a width of 1600 mm, and a length of 6000 mm.

[0065] Figure 3 Metallographic image (500×) of the isotropic SP700 titanium alloy wide sheet prepared in this embodiment. Figure 3 It can be seen that the metallographic structure of the isotropic SP700 titanium alloy wide sheet prepared in this embodiment is a uniform and fine equiaxed α+β structure, the original β grains are fully broken, and there is no continuous and straight grain boundary α phase.

[0066] Testing revealed that the isotropic SP700 titanium alloy wide sheet prepared in this embodiment exhibits a transverse room temperature tensile strength of 1018 MPa–1027 MPa, a transverse yield strength of 974 MPa–982 MPa, and an elongation after fracture of 16.5%–17.5%. The longitudinal room temperature tensile strength is 1016 MPa–1021 MPa, the longitudinal yield strength is 969 MPa–972 MPa, and the elongation after fracture is 17%–20%. The transverse high-temperature tensile strength is 732 MPa–734 MPa, the transverse yield strength is 601 MPa–608 MPa, the longitudinal high-temperature tensile strength is 736 MPa–739 MPa, and the longitudinal yield strength is 600 MPa–601 MPa. The transverse grain size of the isotropic SP700 titanium alloy wide sheet prepared in this embodiment is 1.7 μm–1.8 μm, and the longitudinal grain size is 1.8 μm–2.0 μm.

[0067] In summary, the isotropic SP700 titanium alloy wide sheet prepared in this embodiment has a difference of less than 11 MPa in transverse and longitudinal room temperature tensile strength, good isotropy, and excellent performance indicators.

[0068] Example 3

[0069] This embodiment includes the following steps:

[0070] Step 1: Apply a TB920 anti-oxidation coating to the surface of the SP700 titanium alloy slab. The anti-oxidation coating is 2mm thick, and the SP700 titanium alloy slab is 180mm thick, 1600mm wide, and 1700mm long.

[0071] Step 2: After the SP700 titanium alloy slab processed in Step 1 is held at 900℃ for 5 hours, it is then subjected to the first rolling process to obtain the first rolled slab. The first rolling process is a unidirectional rolling process, which is completed in six passes. The deformation rates of each pass are 16%, 18%, 21%, 24%, 27%, and 17%, respectively. The final rolling temperature after rolling is not lower than 700℃, and the total deformation is 75%. The thickness of the first rolled slab is 45mm and the width is 1600mm.

[0072] Step 3: Cut the first rolled slab obtained in Step 2 to obtain four first intermediate slabs; the thickness of the first intermediate slab is 45mm, the width is 1600mm, and the length is 1500mm.

[0073] Step 4: Perform β-quenching treatment on the first intermediate slab obtained in Step 3; The specific process of β-quenching treatment is as follows: after holding the first intermediate slab at a temperature of 70°C above the β phase transformation point for 80 minutes, quickly send it into room temperature water to cool to below 60°C, and the time from the slab being taken out of the furnace to being completely immersed in the water is 5 seconds.

[0074] Step 5: The first intermediate slab after β-quenching in Step 4 is subjected to a second rolling process at a temperature of 860℃ to obtain a second rolled slab. The second rolling process is completed in four passes, with deformation rates of 22%, 26%, 27%, and 21% for each pass, respectively. The rolling direction of the second rolling process is perpendicular to the rolling direction of the first rolling process in Step 2. The thickness of the second rolled slab is 15mm and the width is 1500mm.

[0075] Step 6: Cut the second rolled slab obtained in Step 5 to obtain twelve second intermediate slabs; the thickness of the second intermediate slab is 15mm, the width is 1500mm, and the length is 1500mm.

[0076] Step 7: The second intermediate slab obtained in Step 6 is subjected to a third rolling process at a temperature of 840℃ to obtain a third rolled slab. The third rolling process is completed in two passes, with deformation rates of 11% and 10% for each pass. The rolling direction of the third rolling process is parallel to the rolling direction of the second rolling process in Step 5. The thickness of the third rolled slab is 12mm and the width is 1500mm.

[0077] Step 8: Cut the third rolled slab obtained in Step 7 to obtain twelve third intermediate slabs; the thickness of the third intermediate slab is 12mm, the width is 1500mm, and the length is 1800mm.

[0078] Step 9: The third intermediate slab obtained in Step 8 is stacked and welded in the order of steel plate, two titanium plates, and another steel plate. It is then subjected to a fourth rolling process at 860℃ to obtain an SP700 titanium alloy sheet. This fourth rolling process consists of five passes with deformation rates of 16%, 23%, 25%, 28%, and 23% for each pass. The final rolling temperature is not lower than 700℃, and the total deformation is 75%. The rolling direction of the fourth rolling process is perpendicular to the rolling direction of the third rolling process in Step 7. The SP700 titanium alloy sheet has a thickness of 3.0 mm, a width of 1800 mm, and a length of 5000 mm.

[0079] Step 10: Heat-treat the SP700 titanium alloy sheet obtained in Step 9. The specific heat treatment process is as follows: hold at 800℃ for 1 hour, and then cool to room temperature by air cooling to obtain an isotropic SP700 titanium alloy wide sheet with a thickness of 3.0 mm, a width of 1800 mm, and a length of 5000 mm.

[0080] Figure 4 Metallographic image (500×) of the isotropic SP700 titanium alloy wide sheet prepared in this embodiment. Figure 4 It can be seen that the metallographic structure of the isotropic SP700 titanium alloy wide sheet prepared in this embodiment is a uniform and fine equiaxed α+β structure, the original β grains are fully broken, and there is no continuous and straight grain boundary α phase.

[0081] Testing revealed that the isotropic SP700 titanium alloy wide sheet prepared in this embodiment exhibits a transverse room temperature tensile strength of 1011 MPa–1020 MPa, a transverse yield strength of 974 MPa–983 MPa, and an elongation after fracture of 15%–16%. The longitudinal room temperature tensile strength is 1008 MPa–1013 MPa, the longitudinal yield strength is 958 MPa–961 MPa, and the elongation after fracture is 18%–19.5%. The transverse high-temperature tensile strength is 730 MPa–741 MPa, the transverse yield strength is 588 MPa–596 MPa, the longitudinal high-temperature tensile strength is 723 MPa–728 MPa, and the longitudinal yield strength is 576 MPa–577 MPa. The transverse grain size of the isotropic SP700 titanium alloy wide sheet prepared in this embodiment is 2.3 μm–2.6 μm, and the longitudinal grain size is 2.2 μm–2.5 μm.

[0082] In summary, the isotropic SP700 titanium alloy wide sheet prepared in this embodiment has a difference of less than 12 MPa in transverse and longitudinal room temperature tensile strength, good isotropy, and excellent performance indicators.

[0083] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method of hot rolling an isotropic SP700 titanium alloy wide sheet, characterized by, The method comprises the following steps: Step one, the SP700 titanium alloy slab is coated with an oxidation-resistant coating; the thickness of the SP700 titanium alloy slab is 130-180 mm, the width is 1000-1600 mm, and the length is 800-1700 mm; Step two, the SP700 titanium alloy slab treated in step one is subjected to first-pass rolling at a temperature of 860-900 ℃ to obtain a first-pass rolled slab; the first-pass rolling is unidirectional rolling, the pass deformation rate of the first-pass rolling is 15-30%, and the pass number is 6-8; the thickness of the first-pass rolled slab is 15-45 mm, the width is 1000-1600 mm; Step three, the first-pass rolled slab obtained in step two is cut to obtain a plurality of first intermediate slabs; the thickness of the first intermediate slab is 15-45 mm, the width is 1000-1600 mm, and the length is 850-1500 mm; Step four, the first intermediate slab obtained in step three is subjected to beta quenching; the specific process of the beta quenching is that the first intermediate slab is kept at a temperature of 20-70 ℃ above the beta phase transition point for 40-80 min and then water-cooled to below 60 ℃; Step five, the first intermediate slab subjected to the beta quenching in step four is subjected to second-pass rolling at a temperature of 800-860 ℃ to obtain a second-pass rolled slab; the pass deformation rate of the second-pass rolling is 15-30%, the pass number is 2-4, and the rolling direction of the second-pass rolling is perpendicular to the rolling direction of the first-pass rolling in step two; the thickness of the second-pass rolled slab is 10-15 mm, and the width is 850-1500 mm; Step six, the second-pass rolled slab obtained in step five is cut to obtain a plurality of second intermediate slabs; the thickness of the second intermediate slab is 10-15 mm, the width is 850-1500 mm, and the length is 1500-2400 mm; Step seven, the second intermediate slab obtained in step six is subjected to third-pass rolling at a temperature of 780-840 ℃ to obtain a third-pass rolled slab; the pass deformation rate of the third-pass rolling is 10-25%, the pass number is 2-4, and the rolling direction of the third-pass rolling is parallel to the rolling direction of the second-pass rolling in step five; the thickness of the third-pass rolled slab is 4-12 mm, and the width is 850-1500 mm; Step eight, the third-pass rolled slab obtained in step seven is cut to obtain a plurality of third intermediate slabs; the thickness of the third intermediate slab is 4-12 mm, the width is 850-1500 mm, and the length is 1500-1800 mm; Step nine, the third intermediate slab obtained in step eight is stacked and welded according to the order of steel plate, multiple third intermediate slabs and steel plate, and fourth rolling is carried out at a temperature of 780-860 DEG C, to obtain SP700 titanium alloy sheet; the pass deformation rate of the fourth rolling is 15-30%, the pass number is 5-7, and the rolling direction of the fourth rolling is perpendicular to the rolling direction of the third rolling in step seven; the thickness of the SP700 titanium alloy sheet is 0.5-3.0 mm, the width is 1500-1800 mm, and the length is 3500-6000 mm; Step ten, the SP700 titanium alloy sheet obtained in step nine is heat treated, and then cooled to room temperature by air cooling, to obtain isotropic SP700 titanium alloy wide sheet with a thickness of 0.5-3.0 mm, a width of 1500-1800 mm, and a length of 3500-6000 mm.

2. The method of claim 1, wherein the method is a hot rolling method of an isotropic SP700 titanium alloy wide sheet, characterized by, The anti-oxidation coating in step one is TB920 anti-oxidation coating, and the thickness of the anti-oxidation coating is 1-2 mm.

3. The method of claim 1, wherein the method is a hot rolling method of an isotropic SP700 titanium alloy wide sheet, characterized by, The holding time of the first rolling in step two is 3-5 h, the finish rolling temperature of the first rolling is not lower than 700 DEG C, and the total deformation rate of the first rolling is not lower than 70%.

4. The method of claim 1, wherein the method is a hot rolling method of an isotropic SP700 titanium alloy wide sheet, characterized by, After the holding of the beta quenching treatment in step four, the first intermediate slab is rapidly sent into normal temperature water for cooling, and the time from the first intermediate slab being discharged to completely entering the water is not more than 6 s.

5. The method of claim 1, wherein the method is a hot rolling method of an isotropic SP700 titanium alloy wide sheet, characterized by, The total deformation rate of the fourth rolling in step nine is not lower than 70%.

6. The method of claim 1, wherein the method is a hot rolling method of an isotropic SP700 titanium alloy wide sheet, characterized by, The specific process of the heat treatment in step ten is: holding at 700-800 DEG C for 1-2 h.

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