Zirconium alloy ultrathin plate for nuclear fuel assembly grillwork and preparation method of zirconium alloy ultrathin plate

Abstract

The invention discloses a preparation method of a zirconium alloy ultra-thin plate for a nuclear fuel assembly grillwork. The preparation method comprises the following steps that 1, burdening and multiple times of vacuum suspension smelting are conducted; secondly, water cooling is conducted after cogging forging is conducted; step 3, performing hot extrusion after peeling; fourthly, multi-pass hot rolling and annealing are conducted; fifthly, cold rolling and vacuum annealing are conducted through a synchronous rolling mill, and then cold rolling and vacuum annealing are conducted through an asynchronous rolling mill; the invention further discloses the zirconium alloy ultrathin plate for the nuclear fuel assembly grillwork. According to the preparation method, the asynchronous rolling mill with the upper and lower rollers at different rotating speeds is adopted for rolling, the warping problem caused by uneven deformation of the upper and lower surfaces in the plate rolling process can be solved, and the plate thickness uniformity is improved; and a shearing force with a certain angle is introduced to crush the crystal grains in the normal direction, so that the orientation distribution of the crystal grains is optimized, the zirconium alloy ultrathin plate with high flatness and high thickness uniformity is obtained, and the method 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 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 vacuum suspension smelting is performed multiple times in an induction suspension furnace to obtain an alloy ingot; Step 2: Forging the alloy ingot obtained in step 1 and then water cooling it to obtain an alloy forging; Step 3, peeling the alloy forging obtained in step 2 and hot extruding it to obtain an extruded slab; 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 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.

[0007] 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.

[0008] 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%.

[0009] 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.

[0010] Since the melting points of zirconium and tin differ by 1600°C, tin is easily burned during the smelting process, resulting in uneven distribution of components. The present invention can effectively reduce the burning of tin by adding auxiliary materials in the form of iron foil wrapping, thereby improving the uniformity of the composition of the alloy ingot.

[0011] 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 are placed in the crucible of an induction suspension furnace in the following order: first place a layer of zirconium at the bottom, then place an alloy package, and finally place a layer of zirconium above the alloy package.

[0012] The above-mentioned method for preparing an ultra-thin zirconium alloy plate for a nuclear fuel assembly grid is characterized in that the vacuum suspension smelting system in step 1 is: the smelting power is 200kW~350kW, and the smelting time is 5min~15min.

[0013] The above-mentioned method for preparing an ultra-thin zirconium alloy plate for a nuclear fuel assembly grid is characterized in that the process of the blank forging in step 2 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 blank forging along the thickness direction is not less than 50%.

[0014] The present invention performs open forging at a temperature above the β phase transformation point and water-cooling quenching on the ingot, so that elements such as chromium, tin, and iron are completely dissolved into the zirconium matrix, the cast columnar crystal structure can be broken, the internal pores can be welded, and the material density, component uniformity and processing performance can be improved; by controlling the total deformation along the thickness direction, the cast structure of the alloy ingot can be transformed into a forged structure, the coarse grain structure can be fully broken, and the component distribution can be more uniform.

[0015] The above-mentioned method for preparing an ultra-thin zirconium alloy plate for a nuclear fuel assembly grid is characterized in that the hot extrusion process in step three is: heating the alloy forging to 850°C~1050°C and then keeping it warm, and then hot extruding with an extrusion ratio of 10~50:1; the total deformation of the hot extrusion along the thickness direction is greater than 30%.

[0016] The present invention can effectively break the forged structure and increase the plasticity and uniformity of the material by controlling the extrusion ratio; and can further optimize the fiber structure formed by forging and adjust the fiber structure direction distribution by controlling the total deformation along the thickness direction of the hot extrusion, which is beneficial to subsequent processing.

[0017] The above-mentioned method for preparing an ultra-thin zirconium alloy sheet for a nuclear fuel assembly grid is characterized in that the deformation amount of each pass of the asynchronous cold rolling in step five is 3% to 15%, and vacuum annealing and pickling are performed once when the cumulative deformation amount is 30% to 70%.

[0018] The present invention can eliminate work hardening and reduce the risk of cracking by performing vacuum annealing and pickling once when the cumulative deformation is 30% to 70%.

[0019] The above-mentioned method for preparing an ultra-thin zirconium alloy plate for a nuclear fuel assembly grid is characterized in that the rotation speed ratio of the upper roll and the lower roll during cold rolling by the asynchronous rolling mill in step five is 1:0.90~0.99 or 1:1.01~1.10.

[0020] At the same time, the present invention also discloses a zirconium alloy ultra-thin plate for a nuclear fuel assembly grid, characterized in that the zirconium alloy ultra-thin plate is obtained by the above-mentioned preparation method, the thickness tolerance of the zirconium alloy ultra-thin plate is not greater than 10μm, and the flatness of the zirconium alloy ultra-thin plate within a length range of 500mm is less than 1.5mm.

[0021] Compared with the prior art, the present invention has the following advantages: 1. The present invention divides cold rolling into two steps: synchronous rolling and asynchronous rolling. First, the synchronous rolling is performed to significantly reduce the thickness of the plate, and then the asynchronous rolling is performed to make the thickness reach the target thickness. At the same time, due to the different rotation speeds of the upper and lower rollers during the asynchronous rolling, the warping problem caused by the uneven deformation of the upper and lower surfaces during the rolling process of the plate can be improved, and the uniformity of the plate thickness can be improved; and the different rotation speeds of the upper and lower rollers can introduce a shear force of a certain angle, so that the grains are broken along the normal direction, avoiding the preferential orientation of the grains along the rolling direction, further optimizing the grain orientation distribution, and facilitating the subsequent punching of the zirconium alloy ultra-thin plate.

[0022] 2. The present invention uses hot extrusion and the three-dimensional compressive stress in the hot extrusion process to fully break the lamellar structure formed by the open forging, refine the grains, improve the grain orientation distribution, and optimize the fiber structure distribution of the components formed by the open 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.

[0023] 3. The recrystallized annealed zirconium alloy ultra-thin plate prepared by the present invention is not easy to crack during subsequent punching processing, and the plate has uniform thickness, smooth surface, thickness tolerance and plate difference are both no more than 10μm, and the plate flatness is less than 1.5mm within a length of 500mm.

[0024] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a physical picture of the zirconium alloy ultra-thin plate obtained in Example 1 of the present invention.

[0026] Figure 2 This is the metallographic structure diagram of the zirconium alloy ultra-thin plate obtained in Example 1 of the present invention.

[0027] Figure 3This is a graph showing the tensile mechanical properties test results of the zirconium alloy ultra-thin plate obtained in Example 1 of the present invention.

[0028] Figure 4 This is a physical picture of the zirconium alloy ultra-thin plate obtained in Comparative Example 1 of the present invention.

[0029] Figure 5 This is the metallographic structure diagram of the zirconium alloy ultra-thin plate obtained in Comparative Example 1 of the present invention.

[0030] Figure 6 This is a graph showing the tensile mechanical properties test results of the zirconium alloy ultra-thin plate obtained in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0031] Example 1 The elements required by the composition design of this embodiment are as follows: Zr 97.5%, Sn 1.8%, Fe 0.5%, Cr 0.2% by mass; the preparation method includes the following steps: 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 not more than 1×10 - ²Pa, melting power is 200kW, melting time is 15min; 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%; Step 3: After the alloy forging obtained in step 2 is peeled, it is placed in a resistance furnace and heated to 1050° C. and then kept warm for 3 hours, and then hot extrusion is performed with an extrusion ratio of 10:1 and an extrusion speed of 3 mm / s to obtain an extruded slab with a cross-sectional size of 40 mm×30 mm; the total deformation of the hot extrusion along the thickness direction is 40%; 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; Step 5: The hot rolled billet obtained in step 4 is cold rolled on a synchronous rolling mill at a rolling speed of 10 m / min, and then vacuum annealed at 600°C for 1 h and pickled for 2 min to obtain a plate with a thickness of 1 mm; then, the hot rolled billet is cold rolled on an asynchronous rolling mill with a rotation speed ratio of the upper and lower rolls of 1:1.10 and a tension of 30 MPa for the front and rear retractable rolls for 5 passes in the length direction, with a deformation amount of 15% in each pass, and a slab with a thickness of 0.5 mm is obtained after the cumulative deformation amount reaches 70%, and then cold rolled on a synchronous rolling mill for 6 passes. After vacuum annealing at 00℃ for 1h, pickling is performed until the surface of the slab is smooth; then, cold rolling is performed on an asynchronous rolling mill along the length direction with a deformation amount of 10% per pass, a rotation speed ratio of the upper roller and the lower roller of 1:1.05, and a tension of 20MPa between the front and rear retractable rollers; vacuum annealing is performed at 600℃ for 1h to obtain a zirconium alloy ultra-thin plate with a thickness of 0.2mm; the pickling solution is made of hydrofluoric acid and nitric acid in a mass ratio of 1:8, the mass concentration of the hydrofluoric acid is 47%, and the mass concentration of the nitric acid is 68%.

[0032] The zirconium alloy ultra-thin plate prepared in this embodiment is as follows Figure 1 As shown in the figure, the surface of the zirconium alloy ultra-thin plate is flat, the plate shape is good, the thickness tolerance and the same plate difference are not greater than 10μm, and the flatness is less than 1.5mm within the length range of 500mm. The metallographic structure of the zirconium alloy ultra-thin plate is analyzed, as shown in the figure. Figure 2 As shown, the microstructure is a recrystallized microstructure. The tensile mechanical properties of the zirconium alloy ultra-thin sheet were tested in the rolling direction and the transverse direction. The results are shown in Figure 3 As shown, the difference in 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 conducive to the subsequent punching and forming of the zirconium alloy ultra-thin sheet.

[0033] Comparative Example 1 The difference between this comparative example and Example 1 is that: this comparative example does not perform hot extrusion treatment, and the asynchronous rolling mill cold rolling in step 5 is replaced by synchronous rolling mill cold rolling.

[0034] The actual zirconium alloy ultra-thin plate prepared in this comparative example is as follows Figure 4 As shown in the figure, the zirconium alloy ultra-thin plate has corrugations in the middle, the plate shape is poor, and the flatness is greater than 2mm within a length range of 500mm, indicating that the use of asynchronous rolling mill cold rolling can optimize the surface quality and flatness of the zirconium alloy ultra-thin plate; the metallographic structure of the zirconium alloy ultra-thin plate is analyzed, as shown in the figure. Figure 5 As shown, the alloy structure has not completely recrystallized. Compared with Example 1, the alloy structure of this comparative example has a low grain boundary degree, coarser grains and uneven grains, which is not conducive to subsequent punching. The tensile mechanical properties of the zirconium alloy ultra-thin sheet in the rolling direction and transverse direction are tested. The results are as follows Figure 6As shown, compared with Example 1, the rolling direction and transverse yield strength mechanical properties of the zirconium alloy ultra-thin plate in this comparative example are quite different, indicating that the anisotropy of the zirconium alloy ultra-thin plate is relatively large, and problems such as uneven cuts, cracks, burrs, etc. are prone to occur in the subsequent punching process. Therefore, the preparation method of Example 1 can effectively reduce the anisotropy of the zirconium alloy ultra-thin plate structure.

[0035] The thickness of the zirconium alloy ultra-thin plates of Example 1 and Comparative Example 1 was tested, and the results are shown in Table 1.

[0036] Table 1 Thickness test results of zirconium alloy ultra-thin plates of Example 1 and Comparative Example 1 (mm)

[0037] It can be seen from Table 1 that the thickness tolerance of the zirconium alloy ultra-thin plate of Comparative Example 1 is larger than that of Example 1, indicating that the preparation method of Example 1 can effectively reduce the thickness tolerance.

[0038] Example 2 The elements required by the composition design of this embodiment are as follows: Zr 98.5%, Sn 1.2%, Fe 0.25%, Cr 0.05% by mass; the preparation method includes the following steps: 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 350kW, smelting time is 5min; 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%; Step 3: After peeling the alloy forging obtained in step 2, place it in a resistance furnace, heat it to 950°C, and then keep it warm for 3 hours, and then perform hot extrusion with an extrusion ratio of 10:1 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%; 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; Step 5: The hot rolled billet obtained in step 4 is cold rolled on a synchronous rolling mill at a rolling speed of 10 m / min, and then vacuum annealed at 600°C for 1 h and pickled for 2 min to obtain a plate with a thickness of 1 mm; then, the hot rolled billet is cold rolled on an asynchronous rolling mill with a rotation speed ratio of the upper and lower rolls of 1:1.01 and a tension of 30 MPa for the front and rear retractable rolls for 3 passes in the length direction, with a deformation amount of 3% in each pass, and a slab with a thickness of 0.5 mm is obtained after the cumulative deformation amount reaches 30%, and then cold rolled for 6 passes. After vacuum annealing at 00℃ for 1h, pickling is performed until the surface of the slab is smooth; then, cold rolling is performed on an asynchronous rolling mill along the length direction with a single-pass deformation of 10%, a rotation speed ratio of the upper roller and the lower roller of 1:1.05, and a tension of 20MPa between the front and rear retractable rollers, and vacuum annealing is performed at 600℃ for 1h to obtain a zirconium alloy ultra-thin plate with a thickness of 0.2mm; the pickling solution is made of hydrofluoric acid and nitric acid in a mass ratio of 1:8, the mass concentration of the hydrofluoric acid is 47%, and the mass concentration of the nitric acid is 68%.

[0039] The surface of the zirconium alloy ultra-thin plate prepared in this embodiment is flat and has a good plate shape. The thickness tolerance and the same plate difference are both no more than 10 μm, and the flatness is less than 1.5 mm within a length range of 500 mm.

[0040] Example 3 The elements required by the composition design of this embodiment are as follows: Zr 98.2%, Sn 1.6%, Fe 0.1%, Cr 0.1% by mass; the preparation method includes the following steps: 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; 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%; 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%; 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; Step 5: The hot rolled billet obtained in step 4 is cold rolled on a synchronous rolling mill at a rolling speed of 10 m / min, and then vacuum annealed at 600°C for 1 h and pickled for 2 min to obtain a plate with a thickness of 1 mm; then, the hot rolled billet is cold rolled on an asynchronous rolling mill with a rotation speed ratio of the upper and lower rolls of 1:1.05 and a tension of 30 MPa for the front and rear retractable rolls for 4 passes in the length direction, with a deformation amount of 10% in each pass, and a slab with a thickness of 0.5 mm is obtained after the cumulative deformation amount reaches 50%, and then cold rolled for 6 passes. After vacuum annealing at 00℃ for 1h, pickling is performed until the surface of the slab is smooth; then, cold rolling is performed on an asynchronous rolling mill along the length direction with a single-pass deformation of 10%, a rotation speed ratio of the upper roller and the lower roller of 1:1.05, and a tension of 20MPa between the front and rear retractable rollers, and vacuum annealing is performed at 600℃ for 1h to obtain a zirconium alloy ultra-thin plate with a thickness of 0.2mm; the pickling solution is made of hydrofluoric acid and nitric acid in a mass ratio of 1:8, the mass concentration of the hydrofluoric acid is 47%, and the mass concentration of the nitric acid is 68%.

[0041] The surface of the zirconium alloy ultra-thin plate prepared in this embodiment is flat and has a good plate shape. The thickness tolerance and the same plate difference are both no more than 10 μm, and the flatness is less than 1.5 mm within a length range of 500 mm.

[0042] Example 4 The difference between this embodiment and embodiment 3 is that the extrusion ratio of hot extrusion in step 3 is 50:1; the rotation speed ratio of the upper roll and the lower roll during the two asynchronous cold rolling in step 5 is 1:0.90 and 1:0.95 respectively, and a zirconium alloy ultra-thin plate with a thickness of 0.1 mm is obtained.

[0043] The surface of the zirconium alloy ultra-thin plate prepared in this embodiment is flat and has a good plate shape. The thickness tolerance and the same plate difference are both no more than 10 μm, and the flatness is less than 1.5 mm within a length range of 500 mm.

[0044] Example 5 The difference between this embodiment and embodiment 3 is that in step 5, the speed ratios of the upper roll and the lower roll during the two asynchronous cold rolling operations are 1:0.95 and 1:0.99, respectively, to obtain a zirconium alloy ultra-thin plate with a thickness of 0.2 mm.

[0045] The surface of the zirconium alloy ultra-thin plate prepared in this embodiment is flat and has a good plate shape. The thickness tolerance and the same plate difference are both no more than 10 μm, and the flatness is less than 1.5 mm within a length range of 500 mm.

[0046] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural transformation made to the above embodiment based on the technical essence of the present invention still falls 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 vacuum suspension smelting is performed multiple times in an induction suspension furnace to obtain an alloy ingot; Step 2: Forging the alloy ingot obtained in step 1 and then water cooling it to obtain an alloy forging; Step 3, peeling the alloy forging obtained in step 2 and hot extruding it to obtain an extruded slab; 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 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.

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 elements required for the composition design described in step 1 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%.

3. 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.

4. The method for preparing a zirconium alloy ultra-thin sheet for a nuclear fuel assembly grid according to claim 3, 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.

5. 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.

6. The method for preparing a zirconium alloy ultra-thin plate for a nuclear fuel assembly grid according to claim 1, characterized in that: The process of the open forging in step 2 is: heating the alloy ingot to not less than 1050° C., then keeping it warm for forging, and then water-cooling quenching; the total deformation of the open forging along the thickness direction is not less than 50%.

7. The method for preparing a zirconium alloy ultra-thin plate for a nuclear fuel assembly grid according to claim 1, characterized in that: The hot extrusion process in step three is: heating the alloy forging to 850°C~1050°C and then keeping it warm, and then performing hot extrusion with an extrusion ratio of 10~50:1; the total deformation of the hot extrusion along the thickness direction is greater than 30%.

8. The method for preparing a zirconium alloy ultra-thin plate for a nuclear fuel assembly grid according to claim 1, characterized in that: In step 5, the deformation amount of each cold rolling by the asynchronous rolling mill is 3% to 15%, and vacuum annealing and pickling are performed once when the cumulative deformation amount is 30% to 70%.

9. The method for preparing a zirconium alloy ultra-thin plate for a nuclear fuel assembly grid according to claim 1, characterized in that: In step 5, the rotation speed ratio of the upper roll and the lower roll during the cold rolling of the asynchronous rolling mill is 1:0.90~0.99 or 1:1.01~1.

10.

10. 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 9, 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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