High-purity niobium plate for radio frequency superconducting cavity and rolling method thereof

Abstract

The application discloses high-purity niobium plate for radio frequency superconducting cavity and a rolling method thereof, and the rolling method comprises the following steps: one, open mill rolling to obtain open mill blank; two, surface treatment; three, open mill blank heat treatment; four, intermediate rolling to obtain intermediate blank; five, intermediate blank surface treatment; six, finished product rolling; seven, finished product blank surface treatment; eight, finished product blank heat treatment; and nine, finished product machining. Through reasonable design of the rolling process and limitation of process parameters, in combination with vacuum heat treatment and surface treatment, the application effectively breaks and refines the original organization of the high-purity niobium blank, significantly improves the grain size uniformity of the product high-purity niobium plate and the uniformity of the horizontal and vertical organizations and performances, removes the gas elements in the high-purity niobium plate, improves the RRR value of the high-purity niobium plate, makes the surface of the high-purity niobium plate uniform and consistent, is suitable for radio frequency superconducting cavity, simultaneously improves the processing yield of the high-purity niobium plate, reduces the raw material cost, and can realize batch stable production.

Description

Technical Field

[0001] This invention belongs to the field of superconducting accelerator cavity technology, specifically relating to a high-purity niobium plate for radio frequency superconducting cavities and its rolling method. Background Technology

[0002] Radio frequency (RF) superconducting acceleration is one of the key technologies in modern particle accelerators, capable of accelerating charged particle beams in continuous wave and long-pulse modes. RF superconducting accelerator cavities offer advantages such as low heat loss and high electrical conversion efficiency, and are now widely used in various high-energy accelerators and light source devices. High-purity niobium is a type II superconductor with a relatively high critical temperature (Tc = 9.2 K). Due to its high critical temperature and high critical magnetic field, it has been used to replace copper as a superconducting cavity material since 1967. The quality factor (Q value) of a high-purity niobium superconducting cavity is 10 times higher than that of a copper cavity. 5 ~10 6 It boasts advantages such as high power loss, high accelerating field gradient, and low impedance, while achieving excellent energy resolution and stability. To date, high-purity niobium is the preferred material for manufacturing radio frequency superconducting accelerator cavities.

[0003] High-purity niobium plates are mainly used to fabricate resonant cavities for radio frequency superconducting linear accelerators. They are one of the main components of radio frequency superconducting cavities, and their quality directly affects the performance of the superconducting cavity. Radio frequency superconducting cavities have extremely high requirements for the purity and performance of niobium materials. The key to processing high-purity niobium plates is to control impurity contamination, loss of RRR (residual resistivity) value, and uniformity of material properties.

[0004] Sheet rolling is an essential production step in the plastic processing of high-purity niobium sheets. The main drawbacks of existing rolling technologies are: excessive rolling deformation heat leading to a low RRR value; the introduction of impurities during processing causing a low RRR value; gaseous elements C, N, H, and O exceeding standard requirements; the difference in mechanical properties between the perpendicular and rolling directions of high-purity niobium sheets exceeding 5%; the grain size difference between the perpendicular and rolling directions of high-purity niobium sheets exceeding ASTM grade 1 (ASTM E112-13); and low yield of high-purity niobium sheet products, generally <50%. Summary of the Invention

[0005] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a rolling method for high-purity niobium plates for radio frequency superconducting cavities. This method, through rational design of the rolling process and limitation of process parameters, combined with vacuum heat treatment, significantly improves the uniformity of grain size, transverse and longitudinal microstructure and properties of the high-purity niobium plate while simultaneously refining the original microstructure of the high-purity niobium billet. It also significantly removes gaseous elements from the high-purity niobium plate, improving its RRR (Rapid Reduction Ratio) value. This solves the problems of low RRR, excessive gaseous elements, and poor mechanical properties and grain size uniformity in current high-purity niobium plates for radio frequency superconducting cavities.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a rolling method for high-purity niobium plate for radio frequency superconducting cavities, characterized in that the method includes the following steps:

[0007] Step 1, initial rolling: The niobium billet with a thickness of H and a purity of 99.5% or higher is initially rolled along the axial direction of the raw niobium ingot. After cooling, it is rolled again along the axial direction of the raw niobium ingot to complete the initial rolling and obtain an initial billet with a thickness of H1.

[0008] Step 2: Surface treatment of the blank: Use a grinding wheel to grind the blank obtained in Step 1 to remove surface defects, and use a hand-held flap wheel to polish the surface of the ground blank. Then, place it in an acid solution for pickling for 15 to 20 minutes, rinse with clean water and air dry naturally.

[0009] Step 3, Heat treatment of the billet: Wipe the surface of the billet after surface treatment in step 2 with ethanol solution, and then place it in a vacuum heat treatment furnace for vacuum heat treatment.

[0010] Step 4, Intermediate Rolling: The blank after vacuum heat treatment in Step 3 is subjected to intermediate rolling to obtain an intermediate blank with a thickness of H2.

[0011] Step 5, Surface treatment of intermediate billet: Use a grinding wheel to grind the intermediate billet obtained in step 4 to remove surface defects, and use a hand-held flap wheel to polish the surface of the intermediate billet after grinding. Then, place it in an acid solution for pickling for 5 to 7 minutes, rinse with clean water and air dry naturally.

[0012] Step 6, Finished product rolling: The intermediate billet after surface treatment in step 5 is rolled into a finished product billet with a thickness of H3.

[0013] Step 7: Surface treatment of finished blanks: Sand the finished blanks obtained in Step 6 with a sander until the product thickness tolerance is within the range, then place them in an acid solution for pickling for 30s to 45s, then rinse with clean water and air dry naturally.

[0014] Step 8: Heat treatment of finished billet: Wipe the surface of the finished billet after surface treatment in step 7 with ethanol solution, and then place it in a vacuum heat treatment furnace for vacuum heat treatment.

[0015] Step 9, Finished Product Machining: The finished billet after heat treatment in Step 8 is machined using a CNC machining center to the length and width tolerance range of the product, resulting in a high-purity niobium plate product with a purity of 99.5% or higher and an RRR ≥ 350.

[0016] The above-mentioned rolling method for high-purity niobium plate for radio frequency superconducting cavities is characterized in that the deformation of the first three passes of the initial rolling in step one is more than 25%, and the rolling is suspended when the thickness of the billet after the initial rolling is 0.4 to 0.5 times the thickness before rolling, i.e., 0.4H to 0.5H. The billet after the initial rolling is cooled to room temperature by water cooling and then rolled again.

[0017] The above-mentioned rolling method for high-purity niobium plate for radio frequency superconducting cavity is characterized in that the thickness H1 of the billet in step one is 0.2 to 0.3 times the thickness before rolling, i.e., 0.2H to 0.3H.

[0018] The above-mentioned rolling method for high-purity niobium plate for radio frequency superconducting cavity is characterized in that the acid solution used in steps two, five and seven is a uniform mixture of 40% hydrofluoric acid solution, 70% nitric acid solution and water in a volume ratio of 1:3:3, and the surface of the billet after each acid pickling step is smooth, has a metallic color and is uniform, without acid traces.

[0019] The above-mentioned rolling method for high-purity niobium sheet for radio frequency superconducting cavities is characterized in that the vacuum heat treatment regime in steps three and eight is: when the vacuum degree in the furnace does not exceed 3×10 -3 After Pa, the temperature is raised to 500℃±10℃ within 60 minutes and held for 30 minutes. Then, the temperature is raised to 770℃±10℃ within 30 minutes and held for 120 minutes. The furnace is then cooled to a temperature below 100℃ before being removed from the furnace.

[0020] The above-mentioned rolling method for high-purity niobium sheet for radio frequency superconducting cavities is characterized in that, during the intermediate rolling in step four, the heat-treated billet is reversed by 90° and then intermediately rolled in a direction perpendicular to the rolling direction in step one. The deformation of the first three passes of the intermediate rolling is more than 15%, and the thickness H2 of the intermediate billet is 0.5 to 0.6 times the thickness before rolling, i.e., 0.5H1 to 0.6H1.

[0021] The above-mentioned rolling method for high-purity niobium sheet for radio frequency superconducting cavity is characterized in that the intermediate billet after grinding in step five and the finished billet after sanding in step seven have smooth and uniform surfaces, without grinding marks, and without defects such as pits, cracks, fissures, and non-niobium material inclusions that are visible to the naked eye.

[0022] The above-mentioned rolling method for high-purity niobium plate for radio frequency superconducting cavity is characterized in that the rolling direction of the finished product in step six is ​​consistent with the rolling direction of the intermediate rolling in step four, and the deformation amount of the first three rolling passes of the finished product is more than 10%.

[0023] The rolling method of the high-purity niobium plate for radio frequency superconducting cavity described above is characterized in that, in step nine, the finished billet after heat treatment is coated for protection before machining.

[0024] In addition, the present invention provides a high-purity niobium plate for radio frequency superconducting cavities, characterized in that it is prepared by the above-described method.

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

[0026] 1. This invention sequentially processes high-purity niobium billets through initial rolling, intermediate rolling, and final rolling, effectively breaking down and refining the original microstructure of the high-purity niobium billets. By controlling the reduction per pass, the total rolling deformation, and the rolling direction in each rolling process, the uniformity of the transverse and longitudinal microstructure and properties of the high-purity niobium sheet products is significantly improved. Combined with vacuum heat treatment of the initial billets and finished products, the recrystallization degree, grain size, and transverse and longitudinal grain difference of the high-purity niobium sheet products are effectively controlled, and gaseous elements in the high-purity niobium sheet products are significantly removed. While improving the uniformity of grain size in the high-purity niobium sheet products, the RRR value of the high-purity niobium sheet products is also improved, making them suitable for use in radio frequency superconducting cavities.

[0027] 2. By taking cooling measures during the initial rolling of high-purity niobium billets, this invention effectively reduces the deformation heat generated during the rolling process, avoids the introduction of gaseous impurities due to excessive rolling deformation heat causing the billet temperature to be too high, and further improves the RRR value of high-purity niobium plates.

[0028] 3. By performing surface treatment on the billet after each rolling process, the present invention effectively removes surface contaminants introduced during the processing of high-purity niobium plates, resulting in a uniform surface of the high-purity niobium plates with a surface roughness that meets the following requirements: average roughness Ra≤1.2μm and maximum roughness Rt≤10μm.

[0029] 4. By rationally designing the rolling process and limiting the process parameters, this invention significantly reduces folds and defects at the head, tail, and sides of each billet during the rolling process while ensuring stable performance of high-purity niobium plates. This effectively increases the yield of the billet to over 60%, thereby significantly reducing the raw material cost of high-purity niobium plates for radio frequency superconducting cavities.

[0030] 5. The high-purity niobium plate prepared by this invention has an RRR value (the ratio of resistance at 295K to resistance at 4.2K) of 350 or higher. The difference in mechanical properties and hardness between the perpendicular rolling direction and the rolling direction does not exceed 5%. The recrystallization rate of the high-purity niobium plate is 100%. At the same time, the difference in grain size between the perpendicular rolling direction and the rolling direction is ≤ ASTM Grade 1 (ASTM E112-13). This ensures that the RRR value, gas element content, mechanical properties, hardness, grain size and recrystallization rate of the high-purity niobium plate meet the requirements for use in radio frequency superconducting cavities.

[0031] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0032] Figure 1 This is a metallographic image of the transverse (perpendicular rolling direction) microstructure of the δ3.5mm high-purity niobium plate prepared in Example 1 of this invention.

[0033] Figure 2 This is a metallographic image of the longitudinal (rolling direction) microstructure of the δ3.5mm high-purity niobium plate prepared in Example 1 of this invention.

[0034] Figure 3 This is a metallographic image of the transverse (perpendicular rolling direction) microstructure of the δ2.8mm high-purity niobium plate prepared in Example 2 of this invention.

[0035] Figure 4 This is a metallographic image of the longitudinal (rolling direction) microstructure of the δ2.8mm high-purity niobium plate prepared in Example 2 of the present invention. Detailed Implementation

[0036] The surface and performance requirements for high-purity niobium plates used in existing technologies for radio frequency superconducting cavities are as follows:

[0037] 1. Residual resistivity (RRR): Must meet the requirements of the finished high-purity niobium plate. 295K / R 4.2K ≥300.

[0038] 2. Gaseous elements: The gaseous elements of the finished high-purity niobium plates should meet the requirements of Table 1 below.

[0039] Table 1

[0040] gaseous elements C / ppm N / ppm H / ppm O / ppm Standard requirements ≤10 ≤10 ≤2 ≤10

[0041] 3. Mechanical properties and hardness: The properties of high-purity niobium plates at room temperature (295K) should meet the requirements of Table 2 below.

[0042] Table 2

[0043]

[0044] High-purity niobium plates need to be tested for mechanical properties and hardness in both the direction perpendicular to the rolling direction and the rolling direction. The difference between the two directions should be ≤15%, and the difference is calculated as (larger value - smaller value) / smaller value.

[0045] 4. Grain size and recrystallization rate: The recrystallization rate of high-purity niobium plates in both the vertical rolling direction and the rolling direction must be ≥90%, and the grain size must meet ASTM 6±1 grade (ASTM E112-13).

[0046] 5. Surface roughness: The surface roughness of the finished high-purity niobium plate in both the direction perpendicular to the rolling direction and the rolling direction must meet Ra≤1.6μm and Rt≤15μm.

[0047] Example 1

[0048] This embodiment includes the following steps:

[0049] Step 1: Initial Rolling: The high-purity niobium billet with dimensions (thickness × width × length) of δ70mm × 180mm × 620mm is initially rolled along the axial direction of the raw niobium ingot, i.e., the width direction of 180mm. The reductions for the first three passes of the initial rolling are 52.5mm, 39.3mm, and 28mm, respectively. Rolling is then paused, and the billet is cooled to room temperature using water cooling. Rolling is then resumed along the axial direction of the raw niobium ingot until the thickness reaches δ70mm × 180mm × 620mm. After completing the initial rolling process with a total deformation of 70%, the resulting billet has dimensions (thickness × width × length) of: The high-purity niobium billet is obtained through electron beam melting, forging, and billet machining.

[0050] Step 2: Surface Treatment of the Blank: The blank obtained in Step 1 is ground using a grinding wheel to remove surface defects. The surface of the ground blank is then polished using a hand-held flap wheel. Next, it is placed in an acid solution for pickling for 20 minutes, rinsed with clean water, and allowed to air dry. The dimensions (thickness × width × length) of the surface-treated blank are as follows:

[0051] Step 3: Heat treatment of the billet: The surface of the billet after surface treatment in Step 2 is wiped with an ethanol solution, and then placed in a vacuum heat treatment furnace for vacuum heat treatment; the vacuum heat treatment regime is as follows: the vacuum degree in the furnace does not exceed 3×10 -3 After Pa, the temperature is raised to 500℃±10℃ within 60 minutes and held for 30 minutes. Then, the temperature is raised to 770℃±10℃ within 30 minutes and held for 120 minutes. The furnace is then cooled to a temperature below 100℃ before being removed from the furnace.

[0052] Step 4, Intermediate Rolling: After heat treatment in Step 3, the billet is rotated 90° and then intermediate rolled along a direction perpendicular to the rolling direction in Step 1, i.e., a length of 620mm. The reductions for the first three passes of intermediate rolling are 17.4mm, 14.6mm, and 12.4mm, respectively. Rolling continues until the thickness reaches [a certain value]. The total deformation during intermediate rolling is 50%, resulting in dimensions (thickness × width × length) of: intermediate billet;

[0053] Step 5: Surface Treatment of Intermediate Billet: The intermediate billet obtained in Step 4 is ground using a grinding wheel to remove surface defects. The surface of the ground intermediate billet is then polished using a hand-held flap wheel. It is then placed in an acid solution for pickling for 7 minutes, rinsed with clean water, and allowed to air dry. The dimensions (thickness × width × length) of the obtained surface-treated intermediate billet are as follows:

[0054] Step Six: Finished Billet Rolling: The intermediate billet, after surface treatment in Step Five, is rolled into a finished product along a length of 1240mm. The reductions for the first three passes are 8.8mm, 7.9mm, and 7.1mm, respectively. Rolling continues until the thickness reaches [a specific value is missing]. The total deformation of the finished product during rolling is 64%, resulting in dimensions (thickness × width × length) of: Finished blanks;

[0055] Step 7: Surface Treatment of Finished Blank: The finished blank obtained in Step 6 is sanded using a sander until it falls within the product thickness tolerance range. During sanding, a 400# sanding belt is used to sand both sides of the finished blank until the thickness reaches [total tolerance]. Then, it is placed in an acid solution for pickling for 45 seconds, rinsed with clean water, and air-dried naturally. The dimensions (thickness × width × length) of the finished blank after surface treatment are as follows:

[0056] Step 8, Finished Product Heat Treatment: Wipe the surface of the finished billet after surface treatment in Step 7 with an ethanol solution, and then place it in a vacuum heat treatment furnace for vacuum heat treatment; the vacuum heat treatment regime is as follows: the vacuum degree in the furnace does not exceed 3×10 -3 After Pa, the temperature is raised to 500℃±10℃ within 60 minutes and held for 30 minutes. Then, the temperature is raised to 770℃±10℃ within 30 minutes and held for 120 minutes. The furnace is then cooled to a temperature below 100℃ before being removed from the furnace.

[0057] Step Nine, Finished Product Machining: Using a CNC machining center, the heat-treated finished blanks from Step Eight are machined to within the product's length and width tolerances. Before machining, the CNC machining center equipment is cleaned, and the heat-treated finished blanks are coated for protection. Four pieces with dimensions (thickness × width × length) are obtained. High-purity niobium plate products with a purity of 99.5% or higher and an RRR of 350 or higher.

[0058] In steps two, five, and seven of this embodiment, the acid solutions used are all uniformly mixed with 40% hydrofluoric acid solution, 70% nitric acid solution, and water in a volume ratio of 1:3:3. The surface of the billet after each pickling step is smooth, has a metallic color, and is uniform, without any traces of acid. The surface of the intermediate billet after grinding in step five and the finished billet after sanding in step seven is smooth and uniform, without grinding marks, pits, cracks, fissures, non-niobium material inclusions, or other defects visible to the naked eye.

[0059] Figure 1 This is a metallographic image of the transverse (perpendicular to the rolling direction) microstructure of the δ3.5mm high-purity niobium plate prepared in Example 1 of this invention. Figure 1 It can be seen that all grains in this structure are 100% recrystallized, and the grains are equiaxed, uniform in size, and the main grain size is ASTM 5.5 to 6 (0.055 mm to 0.045 mm).

[0060] Figure 2 This is a metallographic image of the longitudinal (rolling direction) microstructure of a δ3.5mm high-purity niobium plate prepared in Example 1 of this invention. Figure 2 It can be seen that all grains in this structure are 100% recrystallized, and the grains are equiaxed, uniform in size, and the main grain size is ASTM 5.5 to 6 (0.055 mm to 0.045 mm).

[0061] The performance components of the high-purity niobium plate product prepared in this embodiment were tested, and the test results are shown in Table 3 below.

[0062] Table 3

[0063]

[0064] Comparing the performance composition test results of the high-purity niobium plate in Table 3 with the surface and performance requirements of the high-purity niobium plate for radio frequency superconducting cavities in Tables 1 and 2, it can be seen that the surface of the high-purity niobium plate prepared in this embodiment is uniform, and its RRR value, gas element content, mechanical properties, hardness, grain size and recrystallization rate all meet the requirements for use in radio frequency superconducting cavities.

[0065] Example 2

[0066] This embodiment includes the following steps:

[0067] Step 1: Initial Rolling. The high-purity niobium billet with dimensions (thickness × width × length) of δ60mm × 150mm × 280mm is initially rolled along the axial direction of the raw niobium ingot, i.e., the width direction of 150mm. The first three passes of the initial rolling have reductions of 45mm, 30mm, and 22mm respectively. Rolling is paused when the thickness reaches 30mm. The billet is then cooled to room temperature using water cooling before being rolled again along the axial direction of the raw niobium ingot until the thickness reaches δ60mm. After completing the initial rolling process with a total deformation of 80%, the resulting billet has dimensions (thickness × width × length) of: The high-purity niobium billet is obtained through electron beam melting, forging, and billet machining.

[0068] Step 2: Surface Treatment of the Blank: The blank obtained in Step 1 is ground using a grinding wheel to remove surface defects. The surface of the ground blank is then polished using a hand-held flap wheel. Next, it is placed in an acid solution for pickling for 15 minutes, rinsed with clean water, and allowed to air dry. The dimensions (thickness × width × length) of the surface-treated blank are as follows:

[0069] Step 3: Heat treatment of the billet: The surface of the billet after surface treatment in Step 2 is wiped with an ethanol solution, and then placed in a vacuum heat treatment furnace for vacuum heat treatment; the vacuum heat treatment regime is as follows: the vacuum degree in the furnace does not exceed 3×10 -3 After Pa, the temperature is raised to 500℃±10℃ within 60 minutes and held for 30 minutes. Then, the temperature is raised to 770℃±10℃ within 30 minutes and held for 120 minutes. The furnace is then cooled to a temperature below 100℃ before being removed from the furnace.

[0070] Step 4, Intermediate Rolling: After heat treatment in Step 3, the billet is rotated 90° and then intermediate rolled along a direction perpendicular to the rolling direction in Step 1, i.e., a length of 280mm. The reductions for the first three passes of intermediate rolling are 9.9mm, 8.4mm, and 7.2mm, respectively. The total deformation of intermediate rolling is 40%, resulting in dimensions (thickness × width × length) of... intermediate billet;

[0071] Step 5: Surface Treatment of Intermediate Billet: The intermediate billet obtained in Step 4 is ground using a grinding wheel to remove surface defects. The surface of the ground intermediate billet is then polished using a hand-held flap wheel. It is then placed in an acid solution for pickling for 5 minutes, rinsed with clean water, and allowed to air dry. The dimensions (thickness × width × length) of the obtained surface-treated intermediate billet are as follows:

[0072] Step Six: Finished Billet Rolling: The intermediate billet, after surface treatment in Step Five, is rolled along a length of 455mm. The reductions in the first three passes of the finished billet rolling are 6.2mm, 5.5mm, and 4.9mm, respectively. Rolling continues until the thickness reaches [a specific value is missing]. The total deformation of the finished product during rolling is 60%, resulting in dimensions (thickness × width × length) of: Finished blanks;

[0073] Step 7: Surface Treatment of Finished Blank: The finished blank obtained in Step 6 is sanded using a sander until it falls within the product thickness tolerance range. During sanding, a 400# sanding belt is used to sand both sides of the finished blank until the thickness reaches [total tolerance]. Then, it is placed in an acid solution for pickling for 30 seconds, rinsed with clean water, and air-dried naturally. The dimensions (thickness × width × length) of the finished blank after surface treatment are as follows:

[0074] Step 8, Finished Product Heat Treatment: Wipe the surface of the finished billet after surface treatment in Step 7 with an ethanol solution, and then place it in a vacuum heat treatment furnace for vacuum heat treatment; the vacuum heat treatment regime is as follows: the vacuum degree in the furnace does not exceed 3×10 -3 After Pa, the temperature is raised to 500℃±10℃ within 60 minutes and held for 30 minutes. Then, the temperature is raised to 770℃±10℃ within 30 minutes and held for 120 minutes. The furnace is then cooled to a temperature below 100℃ before being removed from the furnace.

[0075] Step Nine, Finished Product Machining: Using a CNC machining center, the heat-treated finished blanks from Step Eight are machined to within the product's length and width tolerances. Before machining, the CNC machining center equipment is cleaned, and the heat-treated finished blanks are coated for protection. Six pieces with dimensions (thickness × width × length) are obtained. High-purity niobium plate products with a purity of 99.5% or higher and an RRR of 350 or higher.

[0076] In steps two, five, and seven of this embodiment, the acid solutions used are all uniformly mixed with 40% hydrofluoric acid solution, 70% nitric acid solution, and water in a volume ratio of 1:3:3. The surface of the billet after each pickling step is smooth, has a metallic color, and is uniform, without any traces of acid. The surface of the intermediate billet after grinding in step five and the finished billet after sanding in step seven is smooth and uniform, without grinding marks, pits, cracks, fissures, non-niobium material inclusions, or other defects visible to the naked eye.

[0077] Figure 3 This is a metallographic image of the transverse (perpendicular to the rolling direction) microstructure of the δ2.8mm high-purity niobium plate prepared in Example 1 of this invention. Figure 3 It can be seen that all grains in this structure are 100% recrystallized, and the grains are equiaxed, uniform in size, and the main grain size is ASTM 6 to 6.5 (0.0378 mm to 0.045 mm).

[0078] Figure 4 This is a metallographic image of the longitudinal (rolling direction) microstructure of a δ2.8mm high-purity niobium plate prepared in Example 1 of this invention. Figure 4 It can be seen that all grains in this structure are 100% recrystallized, and the grains are equiaxed, uniform in size, and the main grain size is ASTM 6 to 6.5 (0.0378 mm to 0.045 mm).

[0079] The performance components of the high-purity niobium plate product prepared in this embodiment were tested, and the test results are shown in Table 4 below.

[0080] Table 4

[0081]

[0082]

[0083] Comparing the performance composition test results of the high-purity niobium plate in Table 4 with the surface and performance requirements of the high-purity niobium plate for radio frequency superconducting cavities in Tables 1-2, it can be seen that the surface of the high-purity niobium plate prepared in this embodiment is uniform, and its RRR value, gas element content, mechanical properties, hardness, grain size and recrystallization rate all meet the requirements for use in radio frequency superconducting cavities.

[0084] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A rolling method for high-purity niobium sheet for radio frequency superconducting cavities, characterized in that, The method includes the following steps: Step 1, Initial Rolling: The niobium billet with a thickness of H and a purity of 99.5% or higher is initially rolled along the axial direction of the raw niobium ingot. After cooling, it is rolled again along the axial direction of the raw niobium ingot to complete the initial rolling, resulting in an initial billet with a thickness of H1. The deformation of the first three passes of the initial rolling is 25% or more. When the thickness of the billet after the initial rolling is 0.4 to 0.5 times the thickness before rolling (i.e., 0.4H to 0.5H), rolling is paused, and the billet after the initial rolling is cooled to room temperature using water cooling before being rolled again. Step 2: Surface treatment of the blank: Use a grinding wheel to grind the blank obtained in Step 1 to remove surface defects, and use a hand-held flap wheel to polish the surface of the ground blank. Then, place it in an acid solution for pickling for 15 to 20 minutes, rinse with clean water and air dry naturally. Step 3, Heat treatment of the billet: Wipe the surface of the billet after surface treatment in step 2 with ethanol solution, and then place it in a vacuum heat treatment furnace for vacuum heat treatment. Step 4, Intermediate Rolling: The blank after vacuum heat treatment in Step 3 is subjected to intermediate rolling to obtain an intermediate blank with a thickness of H2. During intermediate rolling, the heat-treated blank is rotated 90° and then rolled in a direction perpendicular to the blank rolling direction in Step 1. The deformation of the first three passes of intermediate rolling is more than 15%. Step 5, Surface treatment of intermediate billet: Use a grinding wheel to grind the intermediate billet obtained in step 4 to remove surface defects, and use a hand-held flap wheel to polish the surface of the intermediate billet after grinding. Then, place it in an acid solution for pickling for 5 to 7 minutes, rinse with clean water and air dry naturally. Step 6, Finished product rolling: The intermediate billet after surface treatment in Step 5 is rolled into a finished product billet with a thickness of H3; the direction of the finished product rolling is the same as the direction of the intermediate rolling in Step 4, and the deformation of the first three passes of the finished product rolling is more than 10%. Step 7: Surface treatment of finished blanks: Sand the finished blanks obtained in Step 6 with a sander until the product thickness tolerance is within the range, then place them in an acid solution for pickling for 30s~45s, then rinse with clean water and air dry naturally. Step 8: Heat treatment of finished billet: Wipe the surface of the finished billet after surface treatment in step 7 with ethanol solution, and then place it in a vacuum heat treatment furnace for vacuum heat treatment. Step 9, Finished Product Machining: The finished billet after heat treatment in Step 8 is machined using a CNC machining center to the length and width tolerance range of the product, resulting in a high-purity niobium plate product with a purity of 99.5% or higher and an RRR ≥ 350.

2. The rolling method for a high-purity niobium plate for a radio frequency superconducting cavity according to claim 1, characterized in that, The thickness H1 of the billet in step one is 0.2 to 0.3 times the thickness before rolling, i.e., 0.2H to 0.3H.

3. The rolling method for a high-purity niobium plate for a radio frequency superconducting cavity according to claim 1, characterized in that, The acid solutions used in steps two, five, and seven are all made by uniformly mixing 40% hydrofluoric acid solution, 70% nitric acid solution, and water in a volume ratio of 1:3:

3. The surface of the billet after each pickling step is smooth, has a metallic color, and is uniform, without any traces of acid solution.

4. The rolling method for a high-purity niobium plate for a radio frequency superconducting cavity according to claim 1, characterized in that, The vacuum heat treatment regime described in steps three and eight is as follows: when the vacuum degree inside the furnace does not exceed 3 × 10⁻⁶. -3 After Pa, the temperature is raised to 500℃±10℃ within 60 minutes and held for 30 minutes. Then, the temperature is raised to 770℃±10℃ within 30 minutes and held for 120 minutes. The furnace is then cooled to a temperature below 100℃ before being removed from the furnace.

5. The rolling method for a high-purity niobium plate for a radio frequency superconducting cavity according to claim 1, characterized in that, The thickness H2 of the intermediate billet mentioned in step four is 0.5 to 0.6 times the thickness before rolling, i.e., 0.5H1 to 0.6H1.

6. The rolling method for a high-purity niobium plate for a radio frequency superconducting cavity according to claim 1, characterized in that, The intermediate blanks after grinding in step five and the finished blanks after sanding in step seven have smooth and uniform surfaces, without grinding marks, pits, cracks, or non-niobium material inclusions visible to the naked eye.

7. The rolling method for a high-purity niobium plate for a radio frequency superconducting cavity according to claim 1, characterized in that, Step nine describes the process of applying a protective coating to the heat-treated finished blank before machining.

8. A high-purity niobium plate for radio frequency superconducting cavities, characterized in that, Prepared by the method described in any one of claims 1 to 7.

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