A method for improving the corrosion resistance of zirconium metal by regulating the grain size

Abstract

The present invention relates to a method for improving the corrosion resistance of zirconium metal by regulating the grain size. The method comprises the following steps: annealing the zirconium metal, which is one of the following two methods: Method 1: Horizontally place the zirconium metal in a vacuum tube furnace, heat it to 500 - 800 °C; then cool it to room temperature with the furnace; or, Method 2: Horizontally place the zirconium metal in a vacuum tube furnace, heat it to 700 - 800 °C; then cool it to room temperature with the furnace, and then heat it to 800 - 850 °C to obtain zirconium metal subjected to secondary annealing treatment. By changing the heat treatment process and adjusting the heat treatment parameters of the present invention, that is, by means of variable temperature and variable time, combined with the method of secondary annealing, while obtaining zirconium alloys with different scales in the internal microstructure of the zirconium alloy, the purpose of making the production process simpler, more convenient, lower in cost, and higher in efficiency is achieved.

Description

Technical Field

[0001] The present invention relates to the field of zirconium metal, and particularly to a method for improving the corrosion resistance of zirconium metal by regulating the grain size. Background Art

[0002] Zirconium (Zr) has a low thermal neutron absorption cross-section (0.18×10 -28 m 2 ), excellent corrosion resistance in high-temperature high-pressure water and most acid-base environments, good anti-neutron irradiation performance, excellent mechanical properties and good processing properties, and is widely used as a nuclear reactor cladding material and structural material. Zirconium (Zr) is used in biological fields such as hip and knee implants due to its good corrosion resistance, biocompatibility and elastic modulus similar to bone. In addition, Zr has a lower density than stainless steel, a lower thermal expansion coefficient than titanium (Ti), and better resistance to ultraviolet irradiation, etc., and is used in aerospace and other fields, and is an ideal space structure material. At present, many scholars are still exploring corrosion-resistant zirconium and zirconium alloys.

[0003] The excellent corrosion resistance of zirconium is due to the dense oxide film on the surface layer. However, in the actual application process, due to poor wear resistance, the passivation film on the surface layer is often damaged, greatly reducing the corrosion resistance of zirconium. Especially in the nuclear industry field containing fluorine and in the chloride ion environment, Zr is prone to pitting corrosion. Pitting corrosion, also known as pore corrosion, is a corrosion form concentrated in a very small range on the metal surface and penetrating into the metal interior, and its harmfulness is great. In order to improve the corrosion resistance of zirconium metal, researchers usually adopt alloying and grain refinement means. However, compared with controlling the microstructure, the cost of alloying is higher. Therefore, it is of great significance to study the relationship between the grain size of zirconium metal and its corrosion performance.

[0004] At present, there are various means to improve the corrosion resistance of zirconium alloys, including adding trace elements, improving processing technology or surface treatment technology. These technologies include surface mechanical grinding, friction stir welding, equal-channel angular pressing, etc. However, these experiments mainly improve the surface layer of zirconium alloys, and the required instruments are expensive, with high maintenance costs and high labor costs. Moreover, due to the limited sample size, it is not easy to realize industrial production. In this regard, a large amount of research work is being carried out.

[0005] For zirconium metal, there are more studies on the relationship between grain size and mechanical properties, ignoring the influence of the microstructure grain size of zirconium alloys on corrosion performance. Currently, the research on the relationship between metal grain size and corrosion performance mainly focuses on metals such as stainless steel, aluminum and aluminum alloys, magnesium and magnesium alloys, titanium alloys, etc., and there is no research on the grain size of zirconium alloys and their corrosion resistance. Summary of the Invention

[0006] The object of the present invention is to provide a method for improving the corrosion resistance of zirconium metal by controlling the grain size in view of the problems faced by the prior art. This method anneals the rolled pure zirconium plate, and different zirconium metal blocks with different grain sizes are obtained through the change of the internal microstructure of the material during the annealing process. The present invention studies the correlation between the grain size and corrosion performance of zirconium metal under different environments by controlling the heat treatment process. The present invention changes the heat treatment process, adjusts the heat treatment parameters, that is, by means of variable temperature and variable time, combined with the method of secondary annealing, while obtaining zirconium alloys with different scales in the internal microstructure of the zirconium alloy, the production process becomes simpler, more convenient, with low cost and high efficiency.

[0007] The technical solution of the present invention is as follows:

[0008] A method for improving the corrosion resistance of zirconium metal by regulating the grain size, the method comprising the following steps:

[0009] (1) Wire-cut the zirconium metal according to the required size, the zirconium metal being rolled pure zirconium, the rolled zirconium metal being obtained by multi-pass deformation at a temperature below the recrystallization temperature (750 - 800 °C), and the final deformation amount reaching 60% - 85% to obtain a rolled sheet;

[0010] The thickness of the sheet is 1 mm - 6 mm;

[0011] (2) Anneal the zirconium metal in step (1) by one of the following two methods:

[0012] Method 1: Horizontally place the zirconium metal in step (1) in a vacuum tube furnace, heat it up, and under an argon atmosphere, heat it up to 500 - 800 °C and hold for 2 - 10 hours; then cool it down to room temperature with the furnace to obtain zirconium metal that has undergone a first annealing treatment;

[0013] Or, Method 2: Horizontally place the zirconium metal in step (1) in a vacuum tube furnace, heat it up, and under an argon atmosphere, heat it up to 700 - 800 °C and hold for 2 - 4 h; then cool it down to room temperature with the furnace, and then heat it up to 800 - 850 °C and hold for 20 - 40 h to obtain zirconium metal that has undergone a second annealing treatment.

[0014] The argon is argon with a purity of 99.999%; the pressure of the argon atmosphere is slightly positive pressure (0.01 MPa - 0.101 MPa).

[0015] The heating rate in the second step is 5 - 7 °C / min.

[0016] The grain size range of the zirconium metal obtained by the present invention is 4 - 70 μm.

[0017] The substantial features of the present invention are:

[0018] The research of the present invention on the relationship between the grain size and properties of pure zirconium metal is about the relationship between the grain size of zirconium metal and its corrosion resistance, which is essentially different from the current research on the correlation between the grain size of zirconium metal and its mechanical properties.

[0019] Generally, the as-cast metal after melting will undergo a single annealing treatment at 1000 °C, which is a homogenization annealing treatment. However, the zirconium metal used in the present invention is rolled zirconium, and the annealing temperature is lower than 1000 °C, between 500 and 850 °C, with the purpose of regulating the microstructure distribution without phase transformation. Therefore, through a large number of studies and experiments, zirconium metal blocks with different grain sizes are obtained at an annealing temperature of 500 - 850 °C and a holding time of 2 - 40 hours. During the annealing process, if the temperature is too low, the microstructure change is not obvious and has no reference significance; if the temperature is too high, zircon will undergo phase transformation, resulting in an increase in variables during the overall experimental process and having no comparative significance. In addition, the purity of argon must be 99.999%. Below this purity, oxygen is likely to combine with zircon to form an oxide film on the surface of zircon, which will affect the research on the corrosion resistance of the present invention.

[0020] The technical means of the present invention is the combination of single annealing and double annealing to further prepare large grains. Appropriate double annealing can obtain the required grain size without sacrificing performance.

[0021] The main purpose of single annealing is to obtain a stable grain size that can be obtained during the annealing process, as Figure 4 shown, the obtained grain size is 20 - 40 μm; double annealing can make the material further grow after the grain size grows to the limit value, obtaining a larger grain size. As Figure 5 shown, on the basis of 20 - 40 μm, the average grain size of pure zirconium obtained is 47 μm, and the grain size range is 30 - 70 μm. Compared with the grain size of the comparative example (4 - 10 μm), the grain size has grown 7 - 8 times.

[0022] Generally, double annealing can increase the grain size of the annealed sample, and at the same time can reach a stable grain size and reduce the effect of residual stress. Although under certain conditions, more annealing and larger size are obtained, but for the present invention, it is not that the more annealing times or the larger the size, the better. The main purpose of the present invention is to regulate the grain size to improve the corrosion resistance. Therefore, while obtaining large-sized grains, the corrosion resistance of the material should not be damaged.

[0023] The beneficial effects of the present invention are as follows:

[0024] Through the practical research and application of the present invention, the corrosion resistance of zirconium metal can be improved by regulating the grain size. Within a certain range, refining the grains can enhance the corrosion resistance of the metal (compared with the surface mechanically polished pure zirconium and zirconium alloys on the current market, the corrosion resistance of the products in the present invention has been increased by 29% - 57%). In addition, it can be known from the present invention that in the actual production process, it is not necessary to add expensive metal elements or perform surface treatment to improve the corrosion resistance of zirconium metal. Just looking at the cost of the instruments used, the plasma equipment is worth hundreds of thousands to millions of yuan, while a vacuum tube furnace only costs tens of thousands of yuan. Moreover, the former requires constant monitoring and has a high labor cost. Therefore, the present invention has the advantages of lower application cost and simpler process. Description of the Drawings

[0025] Figure 1 It is the metallographic optical micrograph of the rolled pure zirconium obtained in Comparative Example 1;

[0026] Figure 2 It is the metallographic optical micrograph of the annealed pure zirconium prepared in Example 1;

[0027] Figure 3 It is the metallographic optical micrograph of the annealed pure zirconium prepared in Example 2;

[0028] Figure 4 It is the metallographic optical micrograph of the annealed pure zirconium prepared in Example 3;

[0029] Figure 5 It is the metallographic optical micrograph of the annealed pure zirconium prepared in Example 4;

[0030] Figure 6 It is the XRD pattern of the pure zirconium prepared in Comparative Example 1, Example 1, and Example 2;

[0031] Figure 7 It is the comparison chart of the polarization curves of Comparative Example 1, Example 1 - 4. Detailed Description of the Embodiments

[0032] The following further describes the embodiments of the present invention in detail to make the technology, invention purpose, and invention advantages of the present invention clearer.

[0033] The zirconium metal described in the following comparative examples and examples is rolled pure zirconium (purity 99.9%). The rolled zirconium metal is obtained by multi-pass deformation below the recrystallization temperature (750 - 800 °C), and the final deformation amount reaches 60% - 85% to obtain the rolled sheet; the thickness of the sheet is 3 mm.

[0034] Comparative Example 1

[0035] (1) Use a wire electrical discharge machine to cut the rolled pure zirconium plate into square pure zirconium blocks with dimensions of 30 mm × 10 mm × 3 mm. Put the obtained pure zirconium into alcohol and perform ultrasonic cleaning for 15 min, then dry it for later use.

[0036] (2) Observe the metallographic structure of the pure Zr obtained in this example. The results are as Figure 1 shown. It can be seen that the structure of the comparative example is equiaxed α structure. XRD analysis shows that this comparative example is α phase, as Figure 6 shown, which is consistent with the metallographic analysis results.

[0037] (3) Use the intercept method to analyze the grain size of the metallographic diagram obtained in step (2). It can be seen that the grain size of the comparative example is 4 μm to 7 μm.

[0038] Example 1

[0039] (1) Use a wire electrical discharge machine to cut the rolled pure zirconium plate into square pure zirconium blocks with dimensions of 30 mm × 10 mm × 3 mm. Put the obtained pure zirconium into alcohol and perform ultrasonic cleaning for 15 min, then dry it for later use.

[0040] (2) Place the dried sample stably in a vacuum tube furnace for annealing treatment. After sealing the tube furnace, perform three gas purging operations, introduce argon protective gas with a purity of 99.999%, and set the annealing program for annealing treatment.

[0041] The specific scheme in step (2) is as follows: Use a vacuum pump to evacuate to -0.1 MPa, then close the vacuum pump and introduce argon; the argon atmosphere is -0.04 MPa to -0.06 MPa, and repeat this three times. Introduce argon and maintain the argon atmosphere at a slightly positive pressure (0.01 MPa to 0.101 MPa). Set the annealing temperature to 500 °C, the holding time to 2 h, the heating rate to 5 °C / min, and the cooling method to furnace cooling.

[0042] (3) Wait for the temperature in the vacuum tube furnace to drop to room temperature, take out the sample, put it into alcohol for ultrasonic cleaning for 15 min, and then dry it. Use a wire electrical discharge machine to cut the annealed pure zirconium plate into square pure zirconium blocks with dimensions of 10 mm × 10 mm × 3 mm, and perform performance tests on it.

[0043] (4) Observe the metallographic structure of the pure Zr obtained in this example. The results are as Figure 2 shown. It can be seen that the structure of this example is equiaxed α structure. XRD analysis shows that this example is α phase, as Figure 6 shown, which is consistent with the metallographic analysis results.

[0044] (5) Use the intercept method to analyze the grain size of the metallographic diagram obtained in step (4). It can be seen that the grain size of this example is about 6 μm to 10 μm.

[0045] The test instrument for metallographic structure observation is a Zeiss inverted optical microscope.

[0046] Operation process: 1) First, turn “Extern” to the lowest level and rotate it counterclockwise to the left.

[0047] 2) Turn on the power switch “Powder”. When it turns green, it indicates that the power output is normal; select the RL mode;

[0048] 3) Invert the specimen and place it on the stage;

[0049] 4) Select the photography mode (the white lines from the outside to the inside aligned in sequence represent 1 bright field, 2 polarized light, 3 dark field modes. Rotate counterclockwise until you hear a click);

[0050] 5) Focus at a low magnification (the colors of the objective lenses red, yellow, green, blue, white represent objective lens magnifications of 5, 10, 20, 50, 100 times in sequence);

[0051] 6) Open the “AxioVision LE64” software from the desktop, select “Preview”, corresponding to the “magnification”, adjust the brightness and contrast, and then “take a photo”;

[0052] 7) Then add a scale, save the picture, and copy the data;

[0053] 8) Adjust the light intensity to the lowest level, turn off the power switch, and turn off the personal computer.

[0054] The test instrument for the XRD pattern is a German Bruker D8 Discover.

[0055] The operation process is as follows: Place the sample on the stage, and then scan it at a speed of 6° per minute within the range of 5 - 90°, and save the data after completion.

[0056] (6) Electrochemical performance tests were carried out on the pure Zr obtained in this example. The results are as Figure 7 shown. The polarization curve of this example shows that compared with rolled pure zirconium, the current density is larger and the corrosion resistance is slightly reduced. The specific steps of the electrochemical test are as follows: Use a CHI660E electrochemical test system to conduct electrochemical corrosion behavior on the specimen annealed at 500 °C. This experiment uses a traditional three - electrode system. The electrolyte used for measurement is 3.5% NaCl solution. The annealed specimen is used as the working electrode, the reference electrode is a calomel electrode, and the auxiliary electrode is a platinum electrode. The open - circuit potential (OCP) is measured during the immersion in the corrosive solution to obtain a stable state. When measuring the polarization curve, the scanning rate is 0.01 V / s, and the test range is from - 1.2 V to 2.5 V. The specific test data are shown in Table 1.

[0057] Example 2

[0058] (1) Use a wire electrical discharge machine to cut the rolled pure zirconium plate into square pure zirconium blocks with dimensions of 30 mm × 10 mm × 3 mm. Put the obtained pure zirconium into alcohol and perform ultrasonic cleaning for 15 min, then dry it for later use.

[0059] (2) Place the dried specimen stably in a vacuum tube furnace for annealing treatment. After sealing the tube furnace, perform gas washing three times, introduce argon as the protective gas, and set the annealing program to carry out the annealing treatment.

[0060] The specific scheme in step (2) is as follows: Use a vacuum pump to evacuate to -0.1 MPa, close the vacuum pump, and then introduce argon; the argon atmosphere is -0.04 MPa to -0.06 MPa, and repeat three times. Introduce argon and maintain the argon atmosphere at a slightly positive pressure (0.01 MPa to 0.101 MPa). Set the annealing temperature to 700 °C, the holding time to 2 h, the heating rate to 5 °C / min, and the cooling method to furnace cooling.

[0061] (3) Wait for the temperature in the vacuum tube furnace to drop to room temperature, take out the sample, put it into alcohol for ultrasonic cleaning for 15 min, and then dry it. Use a wire electrical discharge machine to cut the annealed pure zirconium plate into square pure zirconium blocks with dimensions of 10 mm × 10 mm × 3 mm, and perform performance testing on it.

[0062] (4) Observe the metallographic structure of the pure Zr obtained in this example. The results are as Figure 3 shown. It can be seen that the structure of this example is equiaxed α structure. XRD analysis shows that this example is α phase, as Figure 6 shown, which is consistent with the metallographic analysis results.

[0063] (5) Use the intercept method to analyze the grain size of the metallographic diagram obtained in step (4). It can be seen that the grain size of this example is about 9 μm to 15 μm.

[0064] (6) Perform electrochemical performance testing on the pure Zr obtained in this example. The results are as Figure 7 shown. The polarization curve of this example shows that compared with the rolled pure zirconium, the current density is larger and the corrosion resistance is slightly reduced. The specific steps of the electrochemical test are as follows: Use a CHI660E electrochemical test system to perform electrochemical corrosion behavior on the specimen annealed at 700 °C. This experiment uses a traditional three-electrode system. The electrolyte used for measurement is 3.5% NaCl solution. The annealed specimen is used as the working electrode, the reference electrode is a calomel electrode, and the auxiliary electrode is a platinum electrode. Measure the open circuit potential (OCP) during the immersion in the erosion solution to obtain a stable state. When measuring the polarization curve, the scanning rate is 0.01 V / s, and the test range is -1.2 V to 2.5 V. The specific test data is shown in Table 1.

[0065] Example 3

[0066] (1) Use a wire electrical discharge machining tool to cut the rolled pure zirconium plate into square pure zirconium blocks with dimensions of 30 mm × 10 mm × 3 mm. Place the obtained pure zirconium in alcohol and perform ultrasonic cleaning for 15 minutes, then dry it for later use.

[0067] (2) Place the dried specimen stably in a vacuum tube furnace for annealing treatment. After sealing the tube furnace, perform gas washing three times, introduce argon as the protective gas, and set the annealing program to carry out the annealing treatment.

[0068] The specific scheme in step (2) is as follows: Use a vacuum pump to evacuate to -0.1 MPa, close the vacuum pump, and then introduce argon; the argon atmosphere is -0.04 MPa to -0.06 MPa, and repeat three times. Introduce argon and maintain the argon atmosphere at a slightly positive pressure (0.01 MPa to 0.101 MPa). Set the annealing temperature to 800 °C, the holding time to 2 h, the heating rate to 5 °C / min, and the cooling method to furnace cooling.

[0069] (3) Wait for the temperature in the vacuum tube furnace to drop to room temperature, take out the sample, place it in alcohol for ultrasonic cleaning for 15 minutes, and then dry it. Use a wire electrical discharge machining tool to cut the annealed pure zirconium plate into square pure zirconium blocks with dimensions of 10 mm × 10 mm × 3 mm, and perform performance testing on it.

[0070] (4) Observe the metallographic structure of the pure Zr obtained in this example. The results are as Figure 4 shown. It can be seen that the structure of this example is equiaxed α structure. XRD analysis shows that this example is α phase, which is consistent with the metallographic analysis results.

[0071] (5) Use the intercept method to analyze the grain size of the metallographic diagram obtained in step (4). It can be seen that the grain size of this example is about 13 μm to 21 μm.

[0072] (6) Perform electrochemical performance testing on the pure Zr obtained in this example. The results are as Figure 7 shown. The polarization curve of this example shows that compared with the rolled pure zirconium, the current density increases and the corrosion resistance decreases. The specific steps of the electrochemical test are as follows: Use a CHI660E electrochemical test system to perform electrochemical corrosion behavior on the specimen annealed at 800 °C. This experiment uses a traditional three-electrode system. The electrolyte used for measurement is 3.5% NaCl solution. The annealed specimen is used as the working electrode, the reference electrode is a calomel electrode, and the auxiliary electrode is a platinum electrode. Measure the open circuit potential (OCP) during the immersion in the corrosive solution to obtain a stable state. When measuring the polarization curve, the scanning rate is 0.01 V / s, and the test range is -1.2 V to 2.5 V. The specific test data is shown in Table 1.

[0073] Example 4

[0074] (1) Use a wire electrical discharge machining (EDM) machine to cut the rolled pure zirconium plate into square pure zirconium blocks with dimensions of 30 mm × 10 mm × 3 mm. Place the obtained pure zirconium in alcohol and ultrasonically clean it for 15 min, then dry it for later use.

[0075] (2) Place the dried specimen stably in a vacuum tube furnace for annealing treatment. After sealing the tube furnace, perform gas washing three times, introduce argon as the protective gas, and set the annealing program to carry out the annealing treatment.

[0076] The specific scheme in step (2) is as follows: Use a vacuum pump to evacuate to -0.1 MPa, close the vacuum pump, and then introduce argon. The argon atmosphere is -0.04 MPa to -0.06 MPa, and repeat this three times. Introduce argon and maintain the argon atmosphere at a slightly positive pressure (0.01 MPa to 0.101 MPa). Set the annealing temperature to 800 °C, the holding time to 2 h, the heating rate to 5 °C / min, and the cooling method to furnace cooling. After the first stage ends, set the annealing temperature to 850 °C again, the holding time to 40 h, the heating rate to 5 °C / min, and the cooling method to furnace cooling.

[0077] (3) Wait for the temperature in the vacuum tube furnace to drop to room temperature, take out the sample, place it in alcohol and ultrasonically clean it for 15 min, and then dry it. Use a wire electrical discharge machining (EDM) machine to cut the annealed pure zirconium plate into square pure zirconium blocks with dimensions of 10 mm × 10 mm × 3 mm, and perform performance tests on it.

[0078] (4) Observe the metallographic structure of the pure Zr obtained in this example. The results are as Figure 5 shown. It can be seen that the structure of this example is equiaxed α structure.

[0079] (5) Use the intercept method to analyze the grain size of the metallographic diagram obtained in step (4). It can be seen that the grain size of this example is about 40 μm to 70 μm.

[0080] (6) Perform electrochemical performance tests on the pure Zr obtained in this example. The results are as Figure 7 shown. The polarization curve of this example shows that compared with the pure zirconium annealed at 800 °C for 2 h, the current density is smaller, the corrosion potential increases, and the corrosion resistance is slightly improved. The specific steps of the electrochemical test are as follows: Use a CHI660E electrochemical test system to perform electrochemical corrosion behavior on the annealed specimen. This experiment uses a traditional three-electrode system. The electrolyte used for measurement is 3.5% NaCl solution. The annealed specimen is used as the working electrode, the reference electrode is a saturated calomel electrode, and the auxiliary electrode is a platinum electrode. Measure the open circuit potential (OCP) during immersion in the corrosive solution to obtain a stable state. When measuring the polarization curve, the scanning rate is 0.01 V / s, and the test range is -1.2 V to 2.5 V. The specific test data are shown in Table 1.

[0081] Table 1: Electrochemical test results of Examples 1-4 of the present invention

[0082]

[0083] It can be seen from Figures 1 - 5 that the grain size of the comparative example is the smallest, about 4 μm, and the grain sizes of Examples 1-4 gradually increase from 6 μm to about 47 μm. Compared with the comparative example, the grain size becomes more than 10 times larger.

[0084] The polarization curves of Comparative Example 1 and Examples 1-4 of the present invention are as Figure 7 shown. All examples were tested in a 3.5% NaCl solution, and the test equipment was a CHI660E electrochemical test system. The data obtained from the test was used to fit and analyze the polarization curves of the alloys in Examples 1-4 through CHI660E software. Figure 7 It can be seen that the corrosion potentials of Examples 1-3 are not very different, but the corrosion current density of Example 1 is the smallest, indicating that its corrosion resistance is the best; among them, the corrosion current density of Example 4 is the largest, and the corrosion resistance decreases.

[0085] Table 1 shows the corrosion performance test results of Examples 1-4. The corrosion potential represents the tendency of the alloy to corrode, but it is not the only reference basis for corrosion performance; the smaller the corrosion current density, the slower the corrosion rate of the alloy, and the more corrosion-resistant the alloy. It can be seen from Table 1 that the corrosion current densities of Examples 1-4 are monotonic, indicating that within a certain range, the larger the grain size, the worse the corrosion resistance tends to be. Investigating pure zircon obtained by other treatment methods, it can be obtained that the corrosion current density of pure zircon treated by surface mechanical grinding is 10 -7 ~10 -8 or so, and the corrosion current density of zirconium alloy is 10 -6 order of magnitude~10 -8 order of magnitude or so. Therefore, it can be seen that the corrosion resistance of the products in the present invention has been improved by 29% - 57%.

[0086] The present invention is described by examples, but it does not limit the present invention. Referring to the description of the present invention, other changes in the disclosed examples are easily conceivable by researchers in the field of zirconium and zirconium alloys, and such changes should fall within the scope defined by the claims of the present invention patent.

[0087] Matters not covered by the present invention are well-known techniques.

Claims

1. A method for improving the corrosion resistance of zirconium metal by controlling the grain size, characterized in that this method comprises the following steps: (1) Wire-cut the zirconium metal according to the required size. The zirconium metal is rolled pure zirconium, which is obtained by multi-pass deformation at 750 - 800 °C, and the final deformation amount reaches 60% - 85% to obtain plate-shaped zirconium metal; (2) Anneal the zirconium metal in step (1) by one of the following two methods: Method 1: Horizontally place the zirconium metal in step (1) in a vacuum tube furnace, heat it up, and under an argon atmosphere, heat it up to 500 - 800 °C and keep it warm for 2 - 10 hours; then cool it down to room temperature with the furnace to obtain zirconium metal after one annealing treatment; Or, Method 2: Horizontally place the zirconium metal in step (1) in a vacuum tube furnace, heat it up, and under an argon atmosphere, heat it up to 700 - 800 °C and keep it warm for 2 - 4 h; then cool it down to room temperature with the furnace and then heat it up to 800 - 850 °C and keep it warm for 20 - 40 h to obtain zirconium metal after two annealing treatments.

2. The method for improving the corrosion resistance of zirconium metal by controlling the grain size according to claim 1, characterized in that the purity of the zirconium metal is 99.9%.

3. The method for improving the corrosion resistance of zirconium metal by controlling the grain size according to claim 1, characterized in that the thickness of the plate is 1 mm - 6 mm.

4. The method for improving the corrosion resistance of zirconium metal by controlling the grain size according to claim 1, characterized in that the argon is argon with a purity of 99.999%; the pressure of the argon atmosphere is a slightly positive pressure of 0.01 MPa - 0.101 MPa.

5. The method for improving the corrosion resistance of zirconium metal by controlling the grain size according to claim 1, characterized in that the heating rate of Method 1 and Method 2 in step (2) is 5 - 7 °C / min.

6. The method for improving the corrosion resistance of zirconium metal by controlling the grain size according to claim 1, characterized in that the grain size range of the obtained zirconium metal is 4 - 70 μm.

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