Hot rolling method of isotropic SP700 titanium alloy wide thin plate

Abstract

The invention discloses a hot rolling method of an isotropic SP700 titanium alloy wide thin plate. The method comprises the following steps: 1, coating the surface of an SP700 titanium alloy plate blank with an anti-oxidation coating; 2, rolling for the first heating number; 3, cutting treatment; 4, quenching treatment; 5, rolling for the second heating number; 6, cutting treatment; 7, rolling for the third heating number; 8, cutting treatment; 9, fourth fire rolling; and 10, finished product heat treatment. One-heating-number near-beta rolling is conducted on the SP700 titanium alloy plate blank, follow-up beta quenching treatment and alpha-beta phase region medium-temperature reversing rolling are combined, the wide fine-grain thin plate with the B texture as the main part is prepared, and therefore the longitudinal and transverse mechanical property difference is controlled within 15 MPa, wrapping ply rolling is adopted for being assisted by reasonable pass deformation distribution, and the thickness of the thin plate is reduced. The minimum thickness of the obtained wide-width thin plate can reach 0.5 mm, the maximum width of the wide-width thin plate can reach 1800 mm, in addition, material loss of a common process is reduced, and production benefits are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of titanium and titanium alloy thin plate preparation, and particularly relates to a hot rolling method for isotropic SP700 titanium alloy wide-width thin plates. Background Art

[0002] SP700 titanium alloy is a (α + β) two-phase titanium alloy rich in β phase, with a nominal composition of Ti-4.5Al-3V-2Mo-2Fe. By increasing the isomorphous β phase elements Mo, V and the eutectoid stabilizing element Fe, the β transformation temperature is reduced, and at the same time, the diffusion ability of the β phase is improved. Therefore, compared with TC4 titanium alloy, this alloy has a lower β transformation temperature, better strength-plasticity matching, a lower superplastic forming temperature and forming plasticity. It is widely used in the fields of aerospace, marine ships, etc., and can be used to manufacture thin-walled and complex-shaped parts such as hatch doors, partitions, tail fins, shells and air ducts by superplastic forming / diffusion bonding process.

[0003] Common preparation methods for SP700 titanium alloy thin plates mostly adopt the method of hot rolling blank + cold rolling forming. This rolling process is extremely prone to generating strong T texture, resulting in the transverse tensile strength of the plate being much higher than the longitudinal direction, damaging the deformation uniformity of the plate in the subsequent superplastic forming process and affecting the forming accuracy. Moreover, the process plasticity of the plate during cold rolling is poor, and work hardening is obvious. When the thickness of the finished plate is less than 1.5 mm, the work hardening is particularly serious, and multiple vacuum stress relief annealings are required, resulting in low production efficiency. In addition, due to the limitations of the deformation method and equipment size of cold rolled plates, the product width generally does not exceed 1200 mm. With the development of China's aviation, aerospace and shipbuilding industries, the requirement for preparing larger-sized superplastic structural parts is increasing. Therefore, higher requirements are put forward for the size and isotropy of the plates. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a hot rolling method for isotropic SP700 titanium alloy wide-width thin plates in view of the above-mentioned deficiencies of the prior art. Through one-pass near-β rolling of the slab, combined with subsequent β quenching treatment and medium-temperature reverse rolling in the α-β phase region, a wide-width fine-grained thin plate mainly with B texture is prepared, so as to control the difference in mechanical properties between the longitudinal and transverse directions within 15 MPa. Among them, by using clad rolling supplemented with reasonable distribution of pass deformation amounts, the minimum thickness of the obtained wide-width thin plate can reach 0.5 mm, and the maximum width can reach 1800 mm. In addition, the material loss of common processes is also reduced, and the production efficiency is improved.

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

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

[0007] Step 2: Perform the first-pass rolling on the SP700 titanium alloy slab processed in Step 1 under the condition of a temperature of 860 °C to 900 °C to obtain a first-rolled slab; the first-pass rolling is unidirectional rolling, the pass reduction rate of the first-pass rolling is 15% to 30%, and the number of passes is 6 to 8; the thickness of the first-rolled slab is 15 mm to 45 mm, and the width is 1000 mm to 1600 mm;

[0008] Step 3: Perform cutting treatment on the first-rolled slab obtained in Step 2 to obtain a plurality of first intermediate slabs; the thickness of the first intermediate slab is 15 mm to 45 mm, the width is 1000 mm to 1600 mm, and the length is 800 mm to 1500 mm;

[0009] Step 4: Perform β quenching treatment on the first intermediate slab obtained in Step 3; the specific process of the β quenching treatment is: keep the first intermediate slab at a temperature 20 °C to 70 °C above the β transformation point for 40 min to 80 min and then water-cool to below 60 °C;

[0010] Step 5: Perform the second-pass rolling on the first intermediate slab after β quenching treatment in Step 4 under the condition of a temperature of 800 °C to 860 °C to obtain a second-rolled slab; the pass reduction rate of the second-pass rolling is 15% to 30%, the number of passes is 2 to 4, and the rolling direction of the second-pass rolling is perpendicular to the rolling direction of the first-pass rolling in Step 2; the thickness of the second-rolled slab is 10 mm to 15 mm, and the width is 800 mm to 1500 mm;

[0011] Step 6: Perform cutting treatment on the second-rolled slab obtained in Step 5 to obtain a plurality of second intermediate slabs; the thickness of the second intermediate slab is 10 mm to 15 mm, the width is 800 mm to 1500 mm, and the length is 1500 mm to 2400 mm;

[0012] Step 7: Perform the third-pass rolling on the second intermediate slab obtained in Step 6 under the condition of a temperature of 780 °C to 840 °C to obtain a third-rolled slab; the pass reduction rate of the third-pass rolling is 10% to 25%, the number of passes is 2 to 4, and the rolling direction of the third-pass rolling is parallel to the rolling direction of the second-pass rolling in Step 5, and the thickness of the third-rolled slab is 4 mm to 12 mm, and the width is 800 mm to 1500 mm;

[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 4 mm to 12 mm, the width is 800 mm to 1500 mm, and the length is 1500 mm to 1800 mm;

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

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

[0016] The present invention designs a technical route of high-temperature near-β blooming rolling in the α-β phase region, homogenization quenching in the β single-phase region, and medium-temperature reverse cladding rolling in the α-β phase region. Among them, through high-temperature near-β blooming rolling in the α-β phase region, that is, the first rolling pass, billets are efficiently produced and the structure is refined, and strong texture is avoided. Through quenching in the β single-phase region, that is, β quenching treatment, full recrystallization occurs during homogenization, making the original β grains of the rolled intermediate billet uniformly fine. Needle-like martensite that is uniformly fine is obtained after quenching. Through medium-temperature reverse cladding rolling in the α-β phase region, that is, the second rolling pass, the third rolling pass, and the fourth rolling pass, and the rolling direction of the second rolling pass is perpendicular to the rolling direction of the first rolling pass, and the rolling direction of the fourth rolling pass is perpendicular to the rolling direction of the third rolling pass, ensuring that there are two reverse rolling passes during the entire rolling process, thereby minimizing the differences in the transverse and longitudinal properties of the finished plate to the greatest extent, making the plate tend to be "isotropic", and thus obtaining an isotropic fine-grained thin plate with extremely small longitudinal and transverse deviations.

[0017] In the present invention, by stacking and welding in the order of steel plate, multiple third intermediate slabs, and steel plate, the steel plate is used to cover the multiple third intermediate slabs in the middle, which has a good heat preservation effect on the multiple third intermediate slabs, ensuring that almost no heat is lost from the multiple third intermediate slabs during the deformation process, achieving an effect close to isothermal rolling; the purpose of isothermal rolling is to ensure the consistency of the temperature during the entire deformation process to achieve the purpose of controlling the uniformization of the structure.

[0018] By controlling the parameters of the first rolling pass, cutting treatment, quenching treatment, second rolling pass, cutting treatment, third rolling pass, cutting treatment, and fourth rolling pass, this invention aims to simultaneously meet the stability of the finished product's performance and the flexibility of the process parameters, obtaining an isotropic SP700 titanium alloy wide-width thin plate that meets the requirements. Through heat treatment, the strain energy accumulated during the previous deformation process is released, the deformation texture is eliminated, the recrystallization of the microstructure is achieved, obtaining fine and uniform grains. At the same time, the residual stress generated during the deformation process can also be removed, making the shape of the finished product flat.

[0019] In the above hot rolling method for an isotropic SP700 titanium alloy wide-width thin plate, it is characterized in that in step one, the anti-oxidation coating is a TB920 anti-oxidation coating, and the thickness of the anti-oxidation coating is 1 mm to 2 mm. This invention uses the TB920 anti-oxidation coating to play roles such as anti-oxidation, reducing surface heat loss, preventing hydrogen absorption, etc., reducing the problem of surface cracking. By controlling the coating thickness, it achieves the anti-oxidation effect, reduces heat loss, thereby reducing surface cracking, and at the same time, it will not affect the surface quality of the slab due to excessive coating.

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

[0021] In the above hot rolling method for an isotropic SP700 titanium alloy wide-width thin plate, it is characterized in that in step two, the holding time of the first rolling pass is 3 h to 5 h, the finishing rolling temperature of the first rolling pass is not lower than 700 °C, and the total deformation rate of the first rolling pass is not lower than 70%. In this invention, the thickness of the slab before the first rolling pass is relatively large. The holding time of 3 h to 5 h ensures the uniform temperature of the slab from the core to the surface after the holding ends, and it will not cause changes in the microstructure of the slab due to long-term heating, thus affecting the microstructure and performance of the finished product. The finishing rolling temperature not being lower than 700 °C is mainly to ensure that the hot working window of the whole process will not be too large, and at the same time, it can also ensure the deformation plasticity of the last few passes. Both are for the uniformity of deformation, ensuring the uniform fragmentation of the microstructure and avoiding affecting the microstructure and performance of the finished product. The advantage of the total deformation rate not being lower than 70% is that a large enough deformation amount can fully break and refine the original microstructure, laying a good foundation for finally obtaining a fine-grained microstructure. In addition, a sufficient deformation amount can also make the plastic deformation fully penetrate to the core position of the slab, avoiding the situation where the deformation amount of the surface layer and the near-surface layer is large while the deformation amount of the core is small.

[0022] The above hot rolling method for an isotropic SP700 titanium alloy wide-width thin plate is characterized in that after the heat preservation of the β quenching treatment in step four, it is quickly sent into normal temperature water for cooling, and the time from the first intermediate slab being taken out of the furnace to being completely immersed in water does not exceed 6 s. In the present invention, the time from being taken out of the furnace to being completely immersed in water determines the lamellar thickness of the fully lamellar α structure obtained after the intermediate slab is cooled and whether there is precipitation and growth of grain boundary α phase (generally, it is required that the content of grain boundary α cannot be higher than a certain value, such as 15%). The shorter the immersion time, the smaller the lamellar thickness, and the less likely the grain boundary α is to precipitate and grow, and the better the corresponding finished product structure obtained.

[0023] The above hot rolling method for an isotropic SP700 titanium alloy wide-width thin plate is characterized in that the total deformation rate of the fourth heating rolling in step nine is not less than 70%. The present invention ensures sufficient fragmentation of the structure, fine and uniform grain size by controlling the total deformation rate.

[0024] The above hot rolling method for an isotropic SP700 titanium alloy wide-width thin plate is characterized in that the specific process of the heat treatment in step ten is: heat preservation at 700 °C - 800 °C for 1 h - 2 h. The present invention provides sufficient driving force for the recrystallization of the microstructure by controlling the heat treatment parameters and ensures that there is no abnormal grain growth. In terms of time, it provides sufficient time for the uniform progress of the recrystallization process and ensures production efficiency. The combination selection of the heat treatment temperature and time determines the size and uniformity of the grains in the microstructure.

[0025] The present invention has the following advantages compared with the prior art:

[0026] 1. Through the first heating rolling, the present invention efficiently makes blanks, further refines the structure, and avoids the appearance of strong texture. Through the β quenching treatment, full recrystallization occurs during homogenization, making the original β grains of the rolling intermediate blank uniformly fine. Needle-like martensite that is uniformly fine is obtained after quenching. Through the second heating rolling, the third heating rolling, and the fourth heating rolling, medium-temperature deformation avoids the growth of α phase during rolling, and reverse rolling deflects the c-axis of the α phase during rolling, and the texture type changes from the B / T texture mainly composed of T texture to the B texture after reversal, thereby obtaining an isotropic fine-grained thin plate with extremely small longitudinal and transverse deviations. Compared with cold-rolled plates, the anisotropy is significantly improved, and the grain sizes are basically the same. Finally, through heat treatment, the strain energy accumulated during the previous deformation process is released, the deformation texture is eliminated, the recrystallization of the microstructure is realized, fine and uniform grains are obtained, and at the same time, the residual stress generated during the deformation process can be removed, making the finished product flat in shape, and obtaining an isotropic SP700 titanium alloy wide-width thin plate.

[0027] 2. In the present invention, heat treatment is carried out to release the strain energy accumulated during the previous deformation process, eliminate the deformation texture, realize the recrystallization of the microstructure, obtain fine and uniform grains, and at the same time remove the residual stress generated during the deformation process, so that the finished product has a flat shape.

[0028] 3. By means of the rolling method of steel plate cladding supplemented with a reasonable rolling rhythm and the distribution of the reduction per pass, the minimum thickness of the obtained finished product can reach 0.5 mm, and the maximum width is 1800 mm. Compared with the cold-rolled finished product sheet, the rolling difficulty is greatly reduced, the production efficiency is significantly improved, the width range of the sheet is greatly increased, and the tissue uniformity is good.

[0029] 4. In the present invention, the surface cracking problem is reduced by adopting the method of surface coating with an anti-oxidation coating, and the edge cracking problem during the finished product rolling (the fourth fire rolling) is avoided by adopting the method of steel plate cladding. Both of these reduce the material loss and improve the 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is the metallographic structure diagram (500×) of the isotropic SP700 titanium alloy wide-width thin plate prepared in Example 1 of the present invention.

[0032] Figure 2 It is the metallographic structure diagram (500×) of the isotropic SP700 titanium alloy wide-width thin plate prepared in Example 2 of the present invention.

[0033] Figure 3 It is the metallographic structure diagram (500×) of the isotropic SP700 titanium alloy wide-width thin plate prepared in Example 3 of the present invention.

[0034] Figure 4 It is the influence diagram of the isotropic SP700 titanium alloy wide-width thin plate with B-type texture and the SP700 titanium alloy wide-width thin plate with T-type texture prepared in Example 1 of the present invention on the tensile strength.

[0035] Figure 5 It is the influence diagram of the isotropic SP700 titanium alloy wide-width thin plate with B-type texture and the SP700 titanium alloy wide-width thin plate with T-type texture prepared in Example 1 of the present invention on the yield strength and elongation. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] Example 1

[0037] This example includes the following steps:

[0038] Step 1: Apply a TB920 anti-oxidation coating to the surface of the SP700 titanium alloy slab by cross-coating. The thickness of the anti-oxidation coating is 2 mm. The thickness of the SP700 titanium alloy slab is 150 mm, the width is 1000 mm, and the length is 800 mm.

[0039] Step 2: Keep the SP700 titanium alloy slab processed in Step 1 at 860 °C for 4 h and then perform the first-pass rolling to obtain the first rolled slab. The first-pass rolling is unidirectional rolling and 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 °C, and the total deformation is 80%. The thickness of the first rolled slab is 30 mm, and the width is 1000 mm.

[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 30 mm, the width is 1000 mm, and the length is 850 mm.

[0041] Step 4: Perform β quenching on the first intermediate slab obtained in Step 3. The specific process of the β quenching is as follows: Keep the first intermediate slab at a temperature 20 °C above the β transformation point for 60 min and then quickly send it into normal-temperature water to cool it below 60 °C. The time from the slab being taken out of the furnace to being completely immersed in water does not exceed 5 s.

[0042] Step 5: Perform the second-pass rolling on the first intermediate slab after β quenching in Step 4 at 800 °C to obtain the second rolled slab. The second-pass rolling is completed in four passes. The deformation rates of each pass are 20%, 25%, 22%, and 15% respectively. And the rolling direction of the second-pass rolling is perpendicular to the rolling direction of the first-pass rolling in Step 2. The thickness of the second rolled slab is 12 mm, and the width is 850 mm.

[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 12 mm, the width is 850 mm, and the length is 2400 mm.

[0044] Step 7: Perform the third-pass rolling on the second intermediate slab obtained in Step 6 at 780 °C to obtain the third rolled slab. The third-pass rolling is completed in three passes. The deformation rates of each pass are 25%, 22%, and 14% respectively. And the rolling direction of the third-pass rolling is parallel to the rolling direction of the second-pass rolling 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 6 mm, the width is 850 mm, and the length is 1500 mm;

[0046] Step 9: Stack and weld the third intermediate slabs obtained in Step 8 in the order of steel plate, 4 third intermediate slabs, and steel plate, and perform the fourth heat rolling at a temperature of 780 °C to obtain SP700 titanium alloy thin plates; the fourth heat rolling is completed in a total of six passes, and the deformation rates of each pass are: 16%, 23%, 25%, 25%, 26%, 17%. The final rolling temperature after rolling is not lower than 700 °C, and the total deformation is 80%. Moreover, the rolling direction of the fourth heat rolling is perpendicular to the rolling direction of the third heat rolling in Step 7; the thickness of the SP700 titanium alloy thin plate is 1.2 mm, the width is 1500 mm, and the length is 3500 mm;

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

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

[0049] After testing, the transverse room temperature tensile strength of the isotropic SP700 titanium alloy wide plate prepared in this embodiment is 1031 MPa - 1039 MPa, the transverse yield strength is 986 MPa - 998 MPa, the elongation after fracture is 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 plate 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 difference in the room-temperature tensile strength between the transverse and longitudinal directions of the isotropic SP700 titanium alloy wide-width thin plate prepared in this embodiment is within 10 MPa, with good isotropy and excellent performance indicators.

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

[0052] Figure 4 shows the influence of the isotropic SP700 titanium alloy wide-width thin plate with B-type texture and the SP700 titanium alloy wide-width thin plate with T-type texture prepared in Example 1 of the present invention on the tensile strength, Figure 5 shows the influence of the isotropic SP700 titanium alloy wide-width thin plate with B-type texture and the SP700 titanium alloy wide-width thin plate with T-type texture prepared in Example 1 of the present invention on the yield strength and elongation, Figure 4 where the vertical coordinate in represents the magnitude of the tensile strength Rm of the sheet, Figure 5 where the vertical coordinate in represents the magnitudes of the yield strength Rp0.2 (left vertical coordinate axis) and the elongation A (right vertical coordinate axis), Figure 5 where the upper four lines in represent the test results of the yield strength Rp0.2, and the lower four lines represent the test results of the elongation A, Figure 4 and Figure 5 where the horizontal coordinate in and is the direction of the sheet property test, RD represents the rolling direction, TD represents the transverse direction perpendicular to the rolling direction, B represents the isotropic SP700 titanium alloy wide-width thin plate with B-type texture prepared in Example 1 of the present invention, represented by a solid line in the figure, and T represents the SP700 titanium alloy wide-width thin plate with T-type texture, represented by a dashed line in the figure. It can be seen from Figure 4 and Figure 5 that the numerical differences in the three performance indicators RD and TD directions of the B-type texture are relatively small (isotropic), while those of the T-type texture are relatively large (anisotropic). The comprehensive comparison of the two figures explains from the deep mechanism that the B-type texture obtained by the present invention is an important factor for obtaining isotropic SP700 thin plates.

[0053] Example 2

[0054] This embodiment includes the following steps:

[0055] Step 1: Perform surface cross-coating treatment of the TB920 anti-oxidation coating on the SP700 titanium alloy slab; the thickness of the anti-oxidation coating is 1 mm, the thickness of the SP700 titanium alloy slab is 130 mm, the width is 1500 mm, and the length is 1200 mm;

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

[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 15 mm, the width is 1500 mm, and the length is 1100 mm.

[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: Keep the first intermediate slab at a temperature 50°C above the β transformation point for 40 minutes and then quickly send it into normal-temperature water to cool it to below 60°C. The time from the slab being taken out of the furnace to being completely immersed in water is 5 s.

[0059] Step 5: Perform the second-pass rolling on the first intermediate slab after β quenching treatment in Step 4 at 830°C to obtain the second rolled slab. The second-pass rolling is completed in a total of two passes. The deformation rate of each pass is 20% and 17% respectively, and the rolling direction of the second-pass rolling is perpendicular to the rolling direction of the first-pass rolling in Step 2. The thickness of the second rolled slab is 10 mm and the width is 1100 mm.

[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 10 mm, the width is 1100 mm, and the length is 2100 mm.

[0061] Step 7: Perform the third-pass rolling on the second intermediate slab obtained in Step 6 at 810°C to obtain the third rolled slab. The third-pass rolling is completed in a total of four passes. The deformation rate of each pass is 20%, 25%, 25%, and 11% respectively, and the rolling direction of the third-pass rolling is parallel to the rolling direction of the second-pass rolling 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 4 mm, the width is 1100 mm, and the length is 1600 mm.

[0063] Step 9: Stack and weld the third intermediate slab obtained in Step 8 in the order of steel plate, 4 titanium plates, and steel plate, and perform the fourth rolling pass under the condition of a temperature of 820 °C to obtain an SP700 titanium alloy thin plate; the fourth rolling pass is completed in a total of seven passes, and the deformation rates of each pass are: 15%, 21%, 23%, 24%, 23%, 25%, 25%. The final rolling temperature after rolling is not lower than 700 °C, the total deformation is 88%, and the rolling direction of the fourth rolling pass is perpendicular to the rolling direction of the third rolling pass in Step 7; the thickness of the SP700 titanium alloy thin plate is 0.5 mm, the width is 1600 mm, and the length is 6000 mm;

[0064] Step 10: Perform heat treatment on the SP700 titanium alloy thin plate obtained in Step 9. The specific process of the heat treatment is: keep it at 750 °C for 2 h, and then cool it to room temperature by air cooling to obtain an isotropic SP700 titanium alloy wide plate with a thickness of 0.5 mm, a width of 1600 mm, and a length of 6000 mm.

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

[0066] After testing, the transverse room temperature tensile strength of the isotropic SP700 titanium alloy wide plate prepared in this embodiment is 1018 MPa - 1027 MPa, the transverse yield strength is 974 MPa - 982 MPa, the elongation after fracture is 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 plate 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 difference in the transverse and longitudinal room temperature tensile strengths of the isotropic SP700 titanium alloy wide plate prepared in this embodiment is within 11 MPa, the isotropy is good, and all performance indicators are excellent.

[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 by cross-coating; the thickness of the anti-oxidation coating is 2 mm, the thickness of the SP700 titanium alloy slab is 180 mm, the width is 1600 mm, and the length is 1700 mm;

[0071] Step 2: Keep the SP700 titanium alloy slab processed in Step 1 at a temperature of 900 °C for 5 h and then perform the first-pass rolling to obtain the first rolled slab; the first-pass rolling is unidirectional rolling and is completed in a total of six passes. The deformation rates of each pass are: 16%, 18%, 21%, 24%, 27%, and 17%. The final rolling temperature after rolling is not lower than 700 °C, and the total deformation is 75%; the thickness of the first rolled slab is 45 mm, and the width is 1600 mm;

[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 45 mm, the width is 1600 mm, and the length is 1500 mm;

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

[0074] Step 5: Perform the second-pass rolling on the first intermediate slab after β quenching treatment in Step 4 at a temperature of 860 °C to obtain the second rolled slab; the second-pass rolling is completed in a total of four passes. The deformation rates of each pass are: 22%, 26%, 27%, and 21%. And the rolling direction of the second-pass rolling is perpendicular to the rolling direction of the first-pass rolling in Step 2; the thickness of the second rolled slab is 15 mm, and the width is 1500 mm;

[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 15 mm, the width is 1500 mm, and the length is 1500 mm;

[0076] Step 7: Subject the second intermediate slab obtained in Step 6 to the third rolling pass at a temperature of 840 °C to obtain a third rolled slab; the third rolling pass is completed in two passes, and the deformation rates of each pass are 11% and 10% respectively. Moreover, the rolling direction of the third rolling pass is parallel to the rolling direction of the second rolling pass in Step 5. The thickness of the third rolled slab is 12 mm, and the width is 1500 mm.

[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 12 mm, the width is 1500 mm, and the length is 1800 mm.

[0078] Step 9: Stack and weld the third intermediate slabs obtained in Step 8 in the order of steel plate, 2 titanium plates, and steel plate, and then subject them to the fourth rolling pass at a temperature of 860 °C to obtain an SP700 titanium alloy thin plate; the fourth rolling pass is completed in five passes, and the deformation rates of each pass are 16%, 23%, 25%, 28%, and 23% respectively. The final rolling temperature after rolling is not lower than 700 °C, and the total deformation is 75%. Moreover, the rolling direction of the fourth rolling pass is perpendicular to the rolling direction of the third rolling pass in Step 7. The thickness of the SP700 titanium alloy thin plate is 3.0 mm, the width is 1800 mm, and the length is 5000 mm.

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

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

[0081] After testing, the transverse room-temperature tensile strength of the isotropic SP700 titanium alloy wide-width thin plate prepared in this embodiment is 1011 MPa to 1020 MPa, the transverse yield strength is 974 MPa to 983 MPa, the elongation after fracture is 15% to 16%, the longitudinal room-temperature tensile strength is 1008 MPa to 1013 MPa, the longitudinal yield strength is 958 MPa to 961 MPa, and the elongation after fracture is 18% to 19.5%; the transverse high-temperature tensile strength is 730 MPa to 741 MPa, the transverse yield strength is 588 MPa to 596 MPa, the longitudinal high-temperature tensile strength is 723 MPa to 728 MPa, and the longitudinal yield strength is 576 MPa to 577 MPa; the transverse grain size of the isotropic SP700 titanium alloy wide-width thin plate prepared in this embodiment is 2.3 μm to 2.6 μm, and the longitudinal grain size is 2.2 μm to 2.5 μm.

[0082] In summary, the difference in the transverse and longitudinal room-temperature tensile strengths of the isotropic SP700 titanium alloy wide-width thin plate prepared in this embodiment is within 12 MPa, the isotropy is good, and all performance indicators are excellent.

[0083] The above are only the preferred embodiments of the present invention and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent changes made to the above embodiments based on the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A hot rolling method for an isotropic SP700 titanium alloy wide sheet, characterized in that, The method includes the following steps: Step 1: Perform surface coating treatment of an anti-oxidation coating on the SP700 titanium alloy slab; the thickness of the SP700 titanium alloy slab is 130 mm to 180 mm, the width is 1000 mm to 1600 mm, and the length is 800 mm to 1700 mm; Step 2: Perform the first-pass rolling on the SP700 titanium alloy slab treated in Step 1 under the condition that the temperature is 860 °C to 900 °C to obtain a first-rolled slab; the first-pass rolling is unidirectional rolling, the pass reduction rate of the first-pass rolling is 15% to 30%, and the number of passes is 6 to 8; the thickness of the first-rolled slab is 15 mm to 45 mm, and the width is 1000 mm to 1600 mm; Step 3: Perform cutting treatment on the first-rolled slab obtained in Step 2 to obtain a plurality of first intermediate slabs; the thickness of the first intermediate slab is 15 mm to 45 mm, the width is 1000 mm to 1600 mm, and the length is 850 mm to 1500 mm; Step 4: Perform β quenching treatment on the first intermediate slab obtained in Step 3; the specific process of the β quenching treatment is: keep the first intermediate slab at a temperature 20 °C to 70 °C above the β transformation point for 40 min to 80 min and then water-cool it to below 60 °C; Step 5: Perform the second-pass rolling on the first intermediate slab after β quenching treatment in Step 4 under the condition that the temperature is 800 °C to 860 °C to obtain a second-rolled slab; the pass reduction rate of the second-pass rolling is 15% to 30%, and the number of passes is 2 to 4, and the rolling direction of the second-pass rolling is perpendicular to the rolling direction of the first-pass rolling in Step 2; the thickness of the second-rolled slab is 10 mm to 15 mm, and the width is 850 mm to 1500 mm; Step 6: Perform cutting treatment on the second-rolled slab obtained in Step 5 to obtain a plurality of second intermediate slabs; the thickness of the second intermediate slab is 10 mm to 15 mm, the width is 850 mm to 1500 mm, and the length is 1500 mm to 2400 mm; Step 7: Perform the third-pass rolling on the second intermediate slab obtained in Step 6 under the condition that the temperature is 780 °C to 840 °C to obtain a third-rolled slab; the pass reduction rate of the third-pass rolling is 10% to 25%, and the number of passes is 2 to 4, and the rolling direction of the third-pass rolling is parallel to the rolling direction of the second-pass rolling in Step 5, and the thickness of the third-rolled slab is 4 mm to 12 mm, and the width is 850 mm to 1500 mm; Step 8: Perform cutting treatment on the third-rolled slab obtained in Step 7 to obtain a plurality of third intermediate slabs; the thickness of the third intermediate slab is 4 mm to 12 mm, the width is 850 mm to 1500 mm, and the length is 1500 mm to 1800 mm; Step Nine: Stack and weld the third intermediate slab obtained in Step Eight in the order of steel plate, multiple third intermediate slabs, and steel plate, and perform the fourth rolling pass under the condition of a temperature of 780°C to 860°C to obtain an SP700 titanium alloy thin plate; the pass reduction rate of the fourth rolling pass is 15% to 30%, the number of passes is 5 to 7, and the rolling direction of the fourth rolling pass is perpendicular to the rolling direction of the third rolling pass in Step Seven. The thickness of the SP700 titanium alloy thin plate is 0.5 mm to 3.0 mm, the width is 1500 mm to 1800 mm, and the length is 3500 mm to 6000 mm; Step Ten: Heat-treat the SP700 titanium alloy thin plate obtained in Step Nine, and then cool it to room temperature by air cooling to obtain an isotropic SP700 titanium alloy wide plate with a thickness of 0.5 mm to 3.0 mm, a width of 1500 mm to 1800 mm, and a length of 3500 mm to 6000 mm.

2. The hot rolling method of an isotropic SP700 titanium alloy wide sheet according to claim 1, 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 1 mm to 2 mm.

3. The hot rolling method of an isotropic SP700 titanium alloy wide sheet according to claim 1, characterized in that, The holding time of the first rolling pass in Step Two is 3 h to 5 h, the final rolling temperature of the first rolling pass is not lower than 700°C, and the total reduction rate of the first rolling pass is not lower than 70%.

4. A hot rolling method for an isotropic SP700 titanium alloy wide sheet according to claim 1, characterized in that, After the holding of the β quenching treatment in Step Four, it is quickly sent into normal temperature water for cooling, and the time from the first intermediate slab out of the furnace to being completely immersed in water does not exceed 6 s.

5. The hot rolling method of an isotropic SP700 titanium alloy wide sheet according to claim 1, characterized in that, The total reduction rate of the fourth rolling pass in Step Nine is not lower than 70%.

6. A hot rolling method for an isotropic SP700 titanium alloy wide sheet according to claim 1, characterized in that, The specific process of the heat treatment in Step Ten is: hold at 700°C to 800°C for 1 h to 2 h.

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