A zirconium alloy ultra-thin sheet for a nuclear fuel assembly grid and a preparation method thereof

Abstract

The present invention discloses a preparation method for a zirconium alloy ultra-thin sheet used for a nuclear fuel assembly grid. The preparation method includes the following steps: Step 1, perform batching and multiple vacuum levitation melting; Step 2, perform ingot breakdown forging followed by water cooling; Step 3, perform scalping and then hot extrusion; Step 4, perform multi-pass hot rolling and annealing; Step 5, perform cold rolling on a synchronous rolling mill and vacuum annealing, and then perform cold rolling on an asynchronous rolling mill and vacuum annealing. The present invention also discloses a zirconium alloy ultra-thin sheet used for a nuclear fuel assembly grid. By using an asynchronous rolling mill with different rotational speeds of the upper and lower rolling rolls in the preparation method of the present invention, the warping problem caused by uneven deformation of the upper and lower surfaces during the rolling of the sheet can be improved, and the thickness uniformity of the sheet can be increased; and a shearing force at a certain angle is introduced to break the grains along the normal direction, optimize the grain orientation distribution, and obtain a zirconium alloy ultra-thin sheet with high flatness and high thickness uniformity, which is suitable for the technical field of nuclear rare metal materials.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear rare metal materials, and in particular relates to an ultra-thin zirconium alloy plate for a nuclear fuel assembly grid and a preparation method thereof. Background Art

[0002] Zirconium alloys are widely used in structural components in reactor cores due to their excellent radiation resistance, mechanical properties and corrosion resistance, especially in the manufacture of fuel assembly grids. Fuel assembly grids are punched from ultra-thin zirconium alloy plates (such as Zr-4 and M5 alloys) and play a role in fixing and guiding fuel rods, which is crucial to ensuring the stability and safe operation of the core.

[0003] However, the processing of ultra-thin zirconium alloy plates faces many challenges. First, due to the low strain limit of zirconium alloy, its formability is poor. Especially during the rolling of thin strips, the complex stress state of the contact interface in the deformation zone exacerbates the elastic flattening of the rollers. Compared with the rolling of medium and thick plates, the elastic strain and plastic strain of thin strips are close to the same order of magnitude, which will result in only a very small amount of thinning after multiple rolling, thereby reducing processing efficiency.

[0004] In addition, zirconium alloy has a close-packed hexagonal structure (c / a is about 1.593) at room temperature. This structure has few slip systems and poor plastic deformation ability, making it difficult to manufacture high-precision ultra-thin plates through conventional cold and hot deformation processes. Ultra-thin zirconium alloy plates manufactured by traditional rolling methods often have problems such as large thickness tolerance, poor surface quality, poor flatness, and large anisotropy. During the blanking process, plates with large anisotropy are prone to uneven cuts, cracks, burrs, etc. due to differences in mechanical properties, which reduces the cutting quality, thereby affecting the qualification rate of subsequent punched products and increasing production costs. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies in the above-mentioned prior art and provide a method for preparing an ultra-thin zirconium alloy sheet for a nuclear fuel assembly grid. The preparation method adopts an asynchronous rolling mill with different upper and lower roller speeds, which can improve the warping problem caused by uneven deformation of the upper and lower surfaces during the sheet rolling process and improve the thickness uniformity of the sheet; and introduces a shear force at a certain angle to break the grains along the normal direction, optimize the grain orientation distribution, and obtain an ultra-thin zirconium alloy sheet with high flatness and high thickness uniformity, solving the problems of large thickness tolerance, poor flatness and large anisotropy of the ultra-thin zirconium alloy sheet.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing an ultra-thin zirconium alloy plate for a nuclear fuel assembly grid, characterized in that the preparation method comprises the following steps:

[0007] Step 1: According to the composition design requirements of the target product zirconium alloy ultra-thin plate, the raw materials are mixed according to the element ratio, and then vacuum suspension smelting is performed multiple times in an induction suspension furnace to obtain an alloy ingot;

[0008] Step 2: Forging the alloy ingot obtained in step 1 and then water cooling it to obtain an alloy forging;

[0009] Step 3, peeling the alloy forging obtained in step 2 and hot extruding it to obtain an extruded slab;

[0010] Step 4: subjecting the extruded slab obtained in step 3 to multiple hot rolling and annealing treatments to obtain a hot rolled slab with a thickness not greater than 10 mm;

[0011] Step 5: After the hot-rolled billet obtained in step 4 is peeled, it is cold-rolled and vacuum-annealed on a synchronous rolling mill to obtain a plate with a thickness not greater than 1 mm, and then cold-rolled and vacuum-annealed on an asynchronous rolling mill to obtain a zirconium alloy ultra-thin plate with a thickness not greater than 0.5 mm.

[0012] The present invention sequentially prepares the zirconium alloy ultra-thin plate through vacuum suspension melting, blank forging, hot extrusion, hot rolling and annealing, and cold rolling and annealing; by hot extrusion treatment of the alloy forging in the forged state after forging, the distribution of fiber structure formed by forging can be regulated to obtain the extruded alloy; then, the extruded slab in the extruded state is hot rolled to significantly reduce the thickness of the alloy in preparation for subsequent cold rolling, and the grains can be refined, the grain size and orientation distribution can be regulated, and the billet in the recrystallized annealed state is obtained after annealing, which is not prone to edge cracking during the rolling process; finally, the hot-rolled alloy after peeling is cold-rolled by a synchronous rolling mill and cold-rolled by an asynchronous rolling mill and vacuum annealed to obtain the zirconium alloy ultra-thin plate in the recrystallized annealed state, which can refine the grains and improve the strength and plasticity of the material while achieving precise control of the thickness and flatness of the zirconium alloy ultra-thin plate.

[0013] The above-mentioned method for preparing a zirconium alloy ultra-thin plate for a nuclear fuel assembly grid is characterized in that the elements required by the composition design in step one are as follows by mass: Zr 97.5%~98.5%, Sn 1.2%~1.8%, Fe 0.1%~0.5%, Cr 0.05%~0.2%.

[0014] The above-mentioned method for preparing an ultra-thin zirconium alloy plate for a nuclear fuel assembly grid is characterized in that the raw materials in step one include zirconium and an alloy package consisting of iron foil wrapped auxiliary materials, and the auxiliary materials include chromium powder, tin particles and zirconium dioxide powder.

[0015] Since the melting points of zirconium and tin elements differ by up to 1600 °C, tin element is prone to burning loss during the smelting process, resulting in uneven composition distribution. By adding auxiliary materials in the form of iron foil wrapping, the present invention can effectively reduce the burning loss of tin, thereby improving the composition uniformity of the alloy ingot.

[0016] The preparation method of the above-mentioned ultra-thin zirconium alloy sheet for nuclear fuel assembly grid is characterized in that the placement order of the raw materials in the crucible of the induction levitation furnace is as follows: first, place a layer of zircon at the bottom, then place the alloy package, and finally place a layer of zircon above the alloy package.

[0017] The preparation method of the above-mentioned ultra-thin zirconium alloy sheet for nuclear fuel assembly grid is characterized in that the vacuum levitation melting system in step one is: the melting power is 200 kW to 350 kW, and the melting time is 5 min to 15 min.

[0018] The preparation method of the above-mentioned ultra-thin zirconium alloy sheet for nuclear fuel assembly grid is characterized in that the process of cogging forging in step two is: heating the alloy ingot to not less than 1050 °C and then holding for forging, and then water-cooling and quenching; the total deformation amount in the thickness direction of the cogging forging is not less than 50%.

[0019] By subjecting the ingot to cogging forging above the β phase transformation point and water-cooling and quenching, the present invention enables elements such as chromium, tin, and iron to be completely dissolved into the zirconium matrix, which can break the as-cast columnar crystal structure, weld internal pores, and improve the material density, composition uniformity, and processing performance; by controlling the total deformation amount in the thickness direction, the as-cast structure of the alloy ingot can be transformed into a forged structure, the coarse grain structure can be fully broken, and the composition distribution can be made more uniform.

[0020] The preparation method of the above-mentioned ultra-thin zirconium alloy sheet for nuclear fuel assembly grid is characterized in that the process of hot extrusion in step three is: heating the alloy forging to 850 °C to 1050 °C and then holding, and then performing hot extrusion with an extrusion ratio of 10 to 50:1; the total deformation amount in the thickness direction of the hot extrusion is greater than 30%.

[0021] By controlling the extrusion ratio, the present invention can effectively break the forged structure, increase the plasticity and uniformity of the material; by controlling the total deformation amount in the thickness direction of the hot extrusion, the fiber structure formed by forging can be further optimized, and the fiber structure direction distribution can be adjusted, which is beneficial for subsequent processing.

[0022] The preparation method of the above-mentioned ultra-thin zirconium alloy sheet for nuclear fuel assembly grid is characterized in that the deformation amount of each pass of the asynchronous mill cold rolling in step five is 3% to 15%, and a vacuum annealing and pickling are performed once when the cumulative deformation amount is 30% to 70%.

[0023] By performing a vacuum annealing and pickling once when the cumulative deformation is 30% - 70%, the present invention can eliminate work hardening and reduce the risk of cracking.

[0024] In the preparation method of the zirconium alloy ultra-thin plate for a nuclear fuel assembly grid described above, the rotational speed ratio of the upper roll to the lower roll during cold rolling on the asynchronous rolling mill is 1:0.90 - 0.99 or 1:1.01 - 1.10.

[0025] Meanwhile, the present invention also discloses a zirconium alloy ultra-thin plate for a nuclear fuel assembly grid, which is characterized in that the zirconium alloy ultra-thin plate is obtained by the above preparation method, the thickness tolerance of the zirconium alloy ultra-thin plate is not more than 10 μm, and the flatness within a length of 500 mm of the zirconium alloy ultra-thin plate is less than 1.5 mm.

[0026] The present invention has the following advantages compared with the prior art:

[0027] 1. By dividing the cold rolling into two steps of synchronous rolling mill rolling and asynchronous rolling mill rolling, the present invention first performs synchronous rolling mill rolling to greatly reduce the thickness of the plate, and then makes the thickness reach the target thickness through asynchronous rolling mill rolling. At the same time, due to the different rotational speeds of the upper and lower rolls during asynchronous rolling mill rolling, the warping problem caused by uneven deformation of the upper and lower surfaces during the plate rolling process can be improved, and the thickness uniformity of the plate can be increased; and the different rotational speeds of the upper and lower rolls can introduce a certain angle of shear force, causing the grains to break along the normal direction and avoiding the preferred orientation of grains along the rolling direction, further optimizing the grain orientation distribution, which is beneficial for the subsequent punching process of the zirconium alloy ultra-thin plate.

[0028] 2. By performing hot extrusion, the present invention uses the triaxial compressive stress during the hot extrusion process to fully break and refine the lamellar structure formed by the ingot forging, improve the grain orientation distribution, and optimize the distribution of the compositional fiber structure caused by the ingot forging; at the same time, hot extrusion can make the distribution of the second-phase particles more uniform, thereby ensuring the uniformity of the microstructure and the stability of the processing performance.

[0029] 3. The recrystallization annealed zirconium alloy ultra-thin plate prepared by the present invention is not prone to cracking during the subsequent punching process, and the plate has uniform thickness, smooth and flat surface, the thickness tolerance and the difference between the same plates are not more than 10 μm, and the flatness of the plate within a length of 500 mm is less than 1.5 mm.

[0030] The technical solution of the present invention will be further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a physical diagram of the zirconium alloy ultra-thin plate obtained in Example 1 of the present invention.

[0032] Figure 2 This is the metallographic structure diagram of the zirconium alloy ultra-thin sheet obtained in Example 1 of the present invention.

[0033] Figure 3 This is the test result diagram of the tensile mechanical properties of the zirconium alloy ultra-thin sheet obtained in Example 1 of the present invention.

[0034] Figure 4 This is the physical diagram of the zirconium alloy ultra-thin sheet obtained in Comparative Example 1 of the present invention.

[0035] Figure 5 This is the metallographic structure diagram of the zirconium alloy ultra-thin sheet obtained in Comparative Example 1 of the present invention.

[0036] Figure 6 This is the test result diagram of the tensile mechanical properties of the zirconium alloy ultra-thin sheet obtained in Comparative Example 1 of the present invention. Detailed implementation manners

[0037] Example 1

[0038] The elements required by the composition design of this example are in mass percentages as follows: Zr 97.5%, Sn 1.8%, Fe 0.5%, Cr 0.2%; the preparation method includes the following steps:

[0039] Step 1: According to the composition design requirements, the raw materials are proportioned according to the element ratio. An alloy package is formed by wrapping chromium powder, tin grains and zirconia powder with iron foil. The raw materials are mixed and placed in the crucible of an induction levitation furnace for 3 times of vacuum levitation melting to obtain an alloy ingot with a diameter of 100 mm and a mass of 50 kg; the placement order of the raw materials in the crucible of the induction levitation furnace is: first place a layer of zircon at the bottom, then place the alloy package, and finally place a layer of zircon above the alloy package; the zircon used is atomic-level sponge zircon with the brand number HZr-01; the system of the vacuum levitation melting is: the vacuum degree is not greater than 1×10 - ² Pa, the melting power is 200 kW, and the melting time is 15 min;

[0040] Step 2: After peeling the alloy ingot obtained in Step 1, perform cogging forging. Heat it to 1050 °C and keep it warm for 4 h, then perform three upsetting and three drawing on a quick forging machine to obtain an alloy forging with a cross-sectional diameter of 50 mm, and then perform water quenching; the final forging temperature of the forging is above 700 °C, and the total deformation amount in the thickness direction of the cogging forging is 50%;

[0041] Step 3: After peeling the alloy forging obtained in Step 2, place it in a resistance furnace and heat it to 1050 °C and keep it warm for 3 h, then perform hot extrusion with an extrusion ratio of 10:1 and an extrusion speed of 3 mm / s to obtain an extrusion slab with a cross-sectional size of 40 mm × 30 mm; the total deformation amount in the thickness direction of the hot extrusion is 40%;

[0042] Step 4: Subject the extruded slab obtained in Step 3 to multi-pass hot rolling and annealing treatments, grind the surface scale after air cooling, and obtain a hot-rolled blank with a thickness of 3 mm; the hot rolling temperature is 750 °C, the deformation per pass is not less than 20%, and the cumulative deformation is 60%; the annealing temperature is 700 °C, and the annealing duration is 1.5 h.

[0043] Step 5: After subjecting the hot-rolled blank obtained in Step 4 to cold rolling on a synchronous rolling mill with a rolling speed of 10 m / min, perform vacuum annealing at 600 °C for 1 h and pickling for 2 min to obtain a sheet with a thickness of 1 mm; then perform cold rolling on an asynchronous rolling mill with a rotational speed ratio of the upper roll to the lower roll of 1:1.10 and a tension of 30 MPa for the front and rear coiling and uncoiling rollers in the length direction for 5 passes, with a deformation per pass of 15%. After the cumulative deformation reaches 70%, obtain a slab with a thickness of 0.5 mm, perform vacuum annealing at 600 °C for 1 h, and then pickle until the surface of the slab is smooth; then perform cold rolling on an asynchronous rolling mill with a deformation per pass of 10%, a rotational speed ratio of the upper roll to the lower roll of 1:1.05, and a tension of 20 MPa for the front and rear coiling and uncoiling rollers in the length direction, and perform vacuum annealing at 600 °C for 1 h to obtain a zirconium alloy ultra-thin sheet with a thickness of 0.2 mm; the pickling solution is made of hydrofluoric acid and nitric acid with a mass ratio of 1:8, the mass concentration of hydrofluoric acid is 47%, and the mass concentration of nitric acid is 68%.

[0044] The physical object of the zirconium alloy ultra-thin sheet prepared in this embodiment is as Figure 1 shown. The surface of this zirconium alloy ultra-thin sheet is flat, the plate shape is good, the thickness tolerance and the difference in the same plate are not more than 10 μm, and the flatness is less than 1.5 mm within a length range of 500 mm; perform metallographic structure analysis on this zirconium alloy ultra-thin sheet, as Figure 2 shown. The tissue state is a recrystallized tissue; perform tensile mechanical property tests on the rolling direction and the transverse direction of this zirconium alloy ultra-thin sheet, and the results are as Figure 3 shown. The difference in the yield strength mechanical properties between the rolling direction and the transverse direction is small, indicating that the anisotropy of the zirconium alloy ultra-thin sheet is small, which is beneficial to the subsequent stamping forming of the zirconium alloy ultra-thin sheet.

[0045] Comparative Example 1

[0046] The difference between this comparative example and Example 1 is that: in this comparative example, hot extrusion treatment is not performed, and the cold rolling on the asynchronous rolling mill in Step 5 is replaced with cold rolling on a synchronous rolling mill.

[0047] The physical object of the zirconium alloy ultra-thin sheet prepared in this comparative example is as Figure 4As shown, there are corrugations in the middle of the ultra-thin zirconium alloy sheet, and the sheet shape is poor. The flatness is greater than 2 mm within a length of 500 mm, indicating that cold rolling with an asynchronous rolling mill can optimize the surface quality and flatness of the ultra-thin zirconium alloy sheet; the metallographic structure of the ultra-thin zirconium alloy sheet is analyzed as follows Figure 5 As shown, the alloy structure has not undergone complete recrystallization. Compared with Example 1, the grain boundary degree of the alloy structure in this comparative example is lower, the grains are coarser and more uneven, which is not conducive to subsequent stamping; the tensile mechanical properties of the ultra-thin zirconium alloy sheet in the rolling direction and the transverse direction are tested, and the results are as follows Figure 6 As shown, compared with Example 1, the mechanical properties of the yield strength in the rolling direction and the transverse direction of the ultra-thin zirconium alloy sheet in this comparative example have a large difference, indicating that the anisotropy of the ultra-thin zirconium alloy sheet is large, and problems such as uneven cut, cracks, and burrs are likely to occur during subsequent stamping. Therefore, the preparation method of Example 1 can effectively reduce the anisotropy of the ultra-thin zirconium alloy sheet structure.

[0048] The thicknesses of the ultra-thin zirconium alloy sheets of Example 1 and Comparative Example 1 are tested, and the results are shown in Table 1.

[0049] Table 1 Thickness test results of ultra-thin zirconium alloy sheets of Example 1 and Comparative Example 1 / mm

[0050]

[0051] It can be seen from Table 1 that the thickness tolerance of the ultra-thin zirconium alloy sheet in Comparative Example 1 is larger than that in Example 1, indicating that the preparation method of Example 1 can effectively reduce the thickness tolerance.

[0052] Example 2

[0053] The elements required by the composition design of this example are in mass percentages as follows: Zr 98.5%, Sn 1.2%, Fe 0.25%, Cr 0.05%; the preparation method includes the following steps:

[0054] Step 1: According to the composition design requirements, the raw materials are proportioned according to the element ratio. An alloy package is formed by wrapping chromium powder, tin grains, and zirconia powder with an iron foil. The raw materials are mixed and placed in the crucible of an induction levitation furnace for 3 times of vacuum levitation melting to obtain an alloy ingot with a diameter of 100 mm and a mass of 50 kg; the placement order of the raw materials in the crucible of the induction levitation furnace is as follows: first, a layer of zircon is placed at the bottom, then the alloy package is placed, and finally a layer of zircon is placed above the alloy package; the zircon used is atomic-level sponge zircon with a grade of HZr-01; the vacuum levitation melting regime is: the vacuum degree is 1×10 -3 Pa, the melting power is 350 kW, and the melting time is 5 min;

[0055] Step 2: After scalping the alloy ingot obtained in Step 1, perform cogging forging. Heat it to 1050°C and hold for 4 hours, then perform three upsetting and three drawing operations on a quick forging machine to obtain an alloy forging with a cross-sectional diameter of 50 mm, and then perform water quenching; the final forging temperature is above 700°C, and the total deformation amount in the thickness direction during cogging forging is 50%;

[0056] Step 3: After scalping the alloy forging obtained in Step 2, place it in a resistance furnace and heat it to 950°C and hold for 3 hours, then perform hot extrusion with an extrusion ratio of 10:1 and an extrusion speed of 3 mm / s to obtain an extrusion slab with cross-sectional dimensions of 40 mm × 30 mm; the deformation amount in the thickness direction during hot extrusion is 40%;

[0057] Step 4: Perform multi-pass hot rolling and annealing on the extrusion slab obtained in Step 3, and after air cooling, grind the surface oxide scale to obtain a hot-rolled blank with a thickness of 3 mm; the temperature of hot rolling is 750°C, the deformation amount per pass is not less than 20%, and the cumulative deformation amount is 60%; the annealing temperature is 700°C, and the annealing duration is 1.5 hours;

[0058] Step 5: After cold rolling the hot-rolled blank obtained in Step 4 on a synchronous rolling mill with a rolling speed of 10 m / min, perform vacuum annealing at 600°C for 1 hour and pickling for 2 minutes to obtain a sheet with a thickness of 1 mm; then perform cold rolling on an asynchronous rolling mill with a rotational speed ratio of the upper roll to the lower roll of 1:1.01 and a tension of 30 MPa for the front and rear coiling and uncoiling rollers in the length direction for 3 passes, with a deformation amount of 3% per pass. After the cumulative deformation amount reaches 30%, obtain a slab with a thickness of 0.5 mm, perform vacuum annealing at 600°C for 1 hour, and then pickle until the surface of the slab is smooth; then perform cold rolling on an asynchronous rolling mill with a single-pass deformation amount of 10%, a rotational speed ratio of the upper roll to the lower roll of 1:1.05, and a tension of 20 MPa for the front and rear coiling and uncoiling rollers in the length direction, perform vacuum annealing at 600°C for 1 hour to obtain a zirconium alloy ultra-thin sheet with a thickness of 0.2 mm; the pickling solution is made of hydrofluoric acid and nitric acid with a mass ratio of 1:8, the mass concentration of hydrofluoric acid is 47%, and the mass concentration of nitric acid is 68%.

[0059] The zirconium alloy ultra-thin sheet prepared in this example has a flat surface and good plate shape. The thickness tolerance and the difference in the same sheet are both not greater than 10 μm, and the flatness is less than 1.5 mm within a length range of 500 mm.

[0060] Example 3

[0061] For the elements required by the composition design of this example, the mass ratio is: Zr 98.2%, Sn 1.6%, Fe 0.1%, Cr 0.1%; the preparation method includes the following steps:

[0062] Step 1: According to the composition design requirements, the raw materials are prepared according to the element ratio, and the chromium powder, tin particles and zirconium dioxide powder are wrapped in iron foil to form an alloy bag. The raw materials are mixed and placed in the crucible of the induction suspension furnace for vacuum suspension melting three times to obtain an alloy ingot with a diameter of 100 mm and a mass of 50 kg. The order of placing the raw materials in the crucible of the induction suspension furnace is: first place a layer of zirconium at the bottom, then place the alloy bag, and finally place a layer of zirconium on the alloy bag. The zirconium uses atomic-level sponge zirconium with a grade of HZr-01. The system of vacuum suspension melting is: the vacuum degree is 1×10 -3 Pa, smelting power is 300kW, smelting time is 10min;

[0063] Step 2: After the alloy ingot obtained in step 1 is peeled, it is forged, heated to 1050°C and kept warm for 4 hours, and then three-piercing and three-drawing are performed on a fast forging machine to obtain an alloy forging with a cross-sectional diameter of 50 mm, and then water-cooled quenching; the final forging temperature of the forging is above 700°C, and the total deformation of the forging along the thickness direction is 50%;

[0064] Step 3: After the alloy forging obtained in step 2 is peeled, it is placed in a resistance furnace and heated to 1000°C and then kept warm for 3 hours, and then hot extrusion is performed with an extrusion ratio of 30:1 and an extrusion speed of 3 mm / s to obtain an extruded slab with a cross-sectional size of 40 mm×30 mm; the deformation amount of the hot extrusion along the thickness direction is 40%;

[0065] Step 4: The extruded slab obtained in step 3 is subjected to multiple hot rolling and annealing treatments, and the surface oxide scale is polished after air cooling to obtain a hot-rolled billet with a thickness of 3 mm; the hot rolling temperature is 750°C, the deformation amount of each pass is not less than 20%, and the cumulative deformation amount is 60%; the annealing temperature is 700°C, and the annealing time is 1.5h;

[0066] Step 5: After subjecting the hot-rolled blank obtained in Step 4 to cold rolling on a synchronous rolling mill at a rolling speed of 10 m / min, perform vacuum annealing at 600 °C for 1 h and pickling for 2 min to obtain a sheet with a thickness of 1 mm; then perform cold rolling on an asynchronous rolling mill along the length direction with a rotational speed ratio of the upper roll to the lower roll of 1:1.05 and a tension of 30 MPa for the front and rear coiling and uncoiling rolls in 4 passes, with a deformation amount of 10% for each pass. After the cumulative deformation amount reaches 50%, a slab with a thickness of 0.5 mm is obtained, and after vacuum annealing at 600 °C for 1 h, it is pickled until the surface of the slab is smooth; then perform cold rolling on an asynchronous rolling mill along the length direction with a single-pass deformation amount of 10%, a rotational speed ratio of the upper roll to the lower roll of 1:1.05, and a tension of 20 MPa for the front and rear coiling and uncoiling rolls, and perform vacuum annealing at 600 °C for 1 h to obtain a zirconium alloy ultra-thin sheet with a thickness of 0.2 mm; the pickling solution is made of hydrofluoric acid and nitric acid with a mass ratio of 1:8, the mass concentration of hydrofluoric acid is 47%, and the mass concentration of nitric acid is 68%.

[0067] The zirconium alloy ultra-thin sheet prepared in this embodiment has a flat surface and a good sheet shape. The thickness tolerance and the difference in thickness within the same sheet are both not greater than 10 μm, and the flatness is less than 1.5 mm within a length range of 500 mm.

[0068] Example 4

[0069] The difference between this embodiment and Example 3 lies in that: the extrusion ratio in hot extrusion in Step 3 is 50:1; the rotational speed ratios of the upper roll to the lower roll during the two cold rollings on the asynchronous rolling mill in Step 5 are 1:0.90 and 1:0.95 respectively, and a zirconium alloy ultra-thin sheet with a thickness of 0.1 mm is obtained.

[0070] The zirconium alloy ultra-thin sheet prepared in this embodiment has a flat surface and a good sheet shape. The thickness tolerance and the difference in thickness within the same sheet are both not greater than 10 μm, and the flatness is less than 1.5 mm within a length range of 500 mm.

[0071] Example 5

[0072] The difference between this embodiment and Example 3 lies in that: the rotational speed ratios of the upper roll to the lower roll during the two cold rollings on the asynchronous rolling mill in Step 5 are 1:0.95 and 1:0.99 respectively, and a zirconium alloy ultra-thin sheet with a thickness of 0.2 mm is obtained.

[0073] The zirconium alloy ultra-thin sheet prepared in this embodiment has a flat surface and a good sheet shape. The thickness tolerance and the difference in thickness within the same sheet are both not greater than 10 μm, and the flatness is less than 1.5 mm within a length range of 500 mm.

[0074] 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 structural transformations made to the above embodiments according to the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing an ultra-thin zirconium alloy sheet for a nuclear fuel assembly grid, characterized in that: The preparation method comprises the following steps: Step 1: According to the composition design requirements of the target product zirconium alloy ultra-thin plate, the raw materials are mixed according to the element ratio, and then the induction suspension furnace is used for multiple vacuum suspension smelting to obtain an alloy ingot; the elements required by the composition design are as follows: Zr 97.5%~98.5%, Sn 1.2%~1.8%, Fe 0.1%~0.5%, Cr 0.05%~0.2% by mass; Step 2: Forging the alloy ingot obtained in step 1 and then water cooling it to obtain an alloy forging; the process of forging is: heating the alloy ingot to not less than 1050° C., then keeping it warm for forging, and then water quenching; the total deformation of the forging along the thickness direction is not less than 50%; Step 3, the alloy forging obtained in step 2 is peeled and then hot extruded to obtain an extruded slab; the hot extrusion process is: the alloy forging is heated to 850°C~1050°C and then kept warm, and then hot extruded with an extrusion ratio of 10~50:1; the total deformation of the hot extrusion along the thickness direction is greater than 30%; Step 4: subjecting the extruded slab obtained in step 3 to multiple hot rolling and annealing treatments to obtain a hot rolled slab with a thickness not greater than 10 mm; Step 5, after the hot-rolled billet obtained in step 4 is peeled, it is cold-rolled and vacuum annealed by a synchronous rolling mill to obtain a plate with a thickness of no more than 1 mm, and then cold-rolled and vacuum annealed by an asynchronous rolling mill to obtain a zirconium alloy ultra-thin plate with a thickness of no more than 0.5 mm; the deformation amount of each cold rolling by the asynchronous rolling mill is 3%~15%, and vacuum annealing and pickling are performed once when the cumulative deformation amount is 30%~70%; the speed ratio of the upper roll and the lower roll during the cold rolling by the asynchronous rolling mill is 1:0.90~0.99 or 1:1.01~1.

10.

2. The method for preparing a zirconium alloy ultra-thin plate for a nuclear fuel assembly grid according to claim 1, characterized in that: The raw materials in step 1 include zirconium and an alloy package consisting of iron foil wrapped auxiliary materials, and the auxiliary materials include chromium powder, tin particles and zirconium dioxide powder.

3. The method for preparing a zirconium alloy ultra-thin sheet for a nuclear fuel assembly grid according to claim 2, characterized in that: The raw materials are placed in the crucible of the induction suspension furnace in the following order: a layer of zirconium is placed at the bottom first, then the alloy bag is placed, and finally a layer of zirconium is placed above the alloy bag.

4. The method for preparing a zirconium alloy ultra-thin plate for a nuclear fuel assembly grid according to claim 1, characterized in that: The vacuum suspension smelting system in step 1 is: smelting power is 200kW~350kW, and smelting time is 5min~15min.

5. An ultra-thin zirconium alloy plate for a nuclear fuel assembly grid, characterized in that: The zirconium alloy ultra-thin plate is obtained by the preparation method described in any one of claims 1 to 4, the thickness tolerance of the zirconium alloy ultra-thin plate is not greater than 10 μm, and the flatness of the zirconium alloy ultra-thin plate within a length range of 500 mm is less than 1.5 mm.

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