A method for detecting grain size of austenitic stainless steel and its application

Abstract

The present invention relates to a method for detecting the grain size of austenitic stainless steel and its application, and relates to the field of metallographic testing technology. The method comprises the following steps: displaying grain boundaries and microstructure morphology: heating the austenitic stainless steel to be evaluated to a predetermined temperature of 450-800°C, holding the temperature for 115-125 minutes, cooling, and electrolyzing the sample using an oxalic acid aqueous solution; and grain size assessment: performing grain size assessment on the electrolyzed austenitic stainless steel. This method accurately displays the morphology of the austenitic grain boundaries and microstructure of the austenitic stainless steel after solid solution, enabling inspectors to accurately assess the grain size grade and observe the microstructure morphology.

Description

Technical Field

[0001] The present invention relates to the technical field of metallographic detection, and in particular to a method for detecting the grain size of austenitic stainless steel and an application thereof. Background Art

[0002] Austenitic stainless steel refers to stainless steel with an austenitic structure at room temperature. It is non-magnetic and possesses high toughness and ductility, but relatively low strength. Due to its excellent corrosion resistance, formability, compatibility, and strength and toughness over a wide temperature range, stainless steel is widely used in heavy and light industry, consumer goods, and construction and renovation.

[0003] Nuclear-grade austenitic stainless steel is the primary material used in key equipment for my country's fourth-generation nuclear power demonstration fast reactor. Currently, a key characteristic of fourth-generation reactors is that most design operating temperatures are between 500°C and 800°C, exceeding the design temperature of pressurized water reactors (350°C). For equipment or components operating above 427°C, nuclear-grade austenitic stainless steel is selected due to its superior stability, good mechanical properties, excellent resistance to radiation damage, excellent environmental compatibility, and long-term environmental durability, resulting in more stringent requirements. Austenitic stainless steel undergoes final heat treatment in a solid solution state, resulting in an austenite structure containing numerous twins. Nuclear-grade austenitic stainless steel offers greater structural stability and stricter requirements for grain size and gradation. However, mixed and coarse grains are common in the actual production of austenitic stainless steel. Failure to accurately verify grain size and gradation can pose risks to the operation of nuclear power equipment and pose safety hazards.

[0004] Currently, the industry's most common methods for displaying the grain size of austenitic stainless steel include electrolysis with 10% oxalic acid solution, electrolytic corrosion with 60% nitric acid solution, or corrosion with copper sulfate solution, as recommended in the GB / T6394 standard. The 10% oxalic acid solution is characterized by preferential corrosion of twin boundaries, while austenite grain boundaries are only slightly corroded (or almost uncorrupted), resulting in inconspicuous grain boundaries and numerous twins, which severely interfere with the grain boundaries. While electrolytic corrosion with 60% nitric acid solution can achieve the goal of displaying grain boundaries and suppressing twinning, it still leaves grain boundaries incomplete and completely suppresses the appearance of microstructure morphology. Furthermore, 60% nitric acid is a highly concentrated acid with strong oxidizing and corrosive properties, posing a potential safety hazard. Using copper sulfate solution, however, makes it difficult to accurately determine the corrosion time and concentration, resulting in overall corrosion of the sample surface. Grain size rating often confuses austenite grain boundaries with twin boundaries, making them difficult to distinguish. These shortcomings have a significant impact on grain size rating in austenitic stainless steel, leading to misjudgment of grain size, poor reliability, and product quality. Summary of the Invention

[0005] In response to the above problems, the present invention provides a method for detecting the grain size of austenitic stainless steel. The method accurately displays the morphology of austenite grain boundaries and structure after solid solution of austenitic stainless steel, enabling inspectors to accurately judge the grain size level and observe the structure morphology.

[0006] In order to achieve the above object, the present invention provides a method for detecting the grain size of austenitic stainless steel, comprising the following steps:

[0007] Displaying grain boundaries and microstructure: Take the austenitic stainless steel to be evaluated, heat it to a predetermined temperature of 450-800°C, keep it at that temperature for 115-125 minutes, cool it, and electrolyze it with oxalic acid aqueous solution;

[0008] Grain size assessment: Grain size assessment is performed on austenitic stainless steel after electrolysis.

[0009] During their research, the inventors discovered that after solution treatment, austenitic stainless steel does not undergo austenitic transformation at the phase transition point temperature, so the original grain size does not change. At the same time, when austenitic stainless steel is heated to 450-800°C, the high energy of the original austenite grain boundaries is relaxed, and some carbides precipitate along the grain boundaries. The austenite grain boundaries become susceptible to electrolytic corrosion, thereby revealing the grain boundaries. Simultaneously, carbides also precipitate along the low-energy twin boundaries (CSL), and the twin boundaries disappear. Electrolysis with oxalic acid aqueous solution then effectively corrodes the austenitic stainless steel, allowing clear grain morphology to be observed under a microscope, enabling both accurate grain size measurement and observation of microstructure.

[0010] In one embodiment, the predetermined temperature is 650-725°C.

[0011] If the heating temperature is higher than 725℃, the tendency of carbides in austenitic stainless steel to grow will increase, affecting the true judgment of austenitic microstructure and grain size, and then leading to excessive corrosion and poor corrosion effect; below 650℃, the precipitation of carbides in austenitic stainless steel is not obvious, and the grain size cannot be clear, and the microstructure morphology is not obvious.

[0012] In one embodiment, the austenitic stainless steel to be evaluated is nuclear grade austenitic stainless steel.

[0013] In one embodiment, the concentration of oxalic acid in the aqueous oxalic acid solution is 0.8-1.5 mol / L.

[0014] In one embodiment, in the electrolysis step, the electrolysis voltage is 6-10V.

[0015] In one embodiment, in the electrolysis step, the electrolysis current is 3-5A.

[0016] In one embodiment, in the electrolysis step, the electrolysis time is 30-120s.

[0017] By adopting the above electrolysis conditions, the grain size of the electrolyzed austenitic stainless steel can be accurately measured and the microstructure can be observed.

[0018] In one embodiment, the step of displaying grain boundaries and microstructure further includes a cleaning step after the electrolysis step, and the cleaning includes the following steps: rinsing the electrolyzed austenitic stainless steel with water, cleaning with ethanol, and drying.

[0019] In one embodiment, the cleaning comprises the following steps: rinsing the electrolyzed austenitic stainless steel with water, cleaning with ethanol, drying, wiping with nitric acid, and then rinsing with water and ethanol in sequence, and drying.

[0020] The above cleaning steps can effectively clean the corrosion products after electrolysis of austenitic stainless steel, obtaining a cleaner and clearer field of view.

[0021] The present invention also provides application of the detection method in preparing a product for detecting the grain size of austenitic stainless steel.

[0022] In one embodiment, the austenitic stainless steel is nuclear grade austenitic stainless steel.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention provides a method for detecting the grain size of austenitic stainless steel and its application. The method accurately displays the morphology of austenite grain boundaries and microstructure after solid solution in austenitic stainless steel, enabling inspectors to accurately assess the grain size level and observe the microstructure morphology. The method is pollution-free, easy to operate, poses no safety risks to the human body, exhibits stable corrosion effects, and has excellent reproducibility. Furthermore, the austenite grain boundaries and microstructure are intact and clearly defined, minimizing interference from twin boundaries on grain boundaries, resulting in more accurate and realistic grain size assessment results. Furthermore, the method displays microstructure morphology, laying the foundation for further material microstructure assessment of stainless steel, thus providing high practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 1 is a graph showing the test results of austenitic stainless steel of Example 1 in the experimental example;

[0026] Figure 2 1 is a graph showing the test results of austenitic stainless steel of Example 2 in the experimental example;

[0027] Figure 3 1 is a graph showing the test results of austenitic stainless steel of Example 3 in the experimental example;

[0028] Figure 4 1 is a graph showing the test results of austenitic stainless steel of Example 4 in the experimental example;

[0029] Figure 5 1 is a graph showing the test results of austenitic stainless steel of Example 5 in the experimental example;

[0030] Figure 6 1 is a graph showing the test results of austenitic stainless steel of Example 6 in the experimental example;

[0031] Figure 7 1 is a graph showing the test results of austenitic stainless steel of Example 7 in the experimental example;

[0032] Figure 8 1 is a graph showing the test results of austenitic stainless steel of Example 8 in the experimental example;

[0033] Figure 9 1 is a graph showing the test results of austenitic stainless steel of comparative example 1 in the experimental example;

[0034] Figure 10 1 is a graph showing the test results of austenitic stainless steel of comparative example 2 in the experimental example;

[0035] Figure 11 1 is a graph showing the test results of austenitic stainless steel of comparative example 3 in the experimental example;

[0036] Figure 12 1 is a graph showing the test results of austenitic stainless steel of comparative example 4 in the experimental example;

[0037] Figure 13 This is a test result diagram of austenitic stainless steel of comparative example 5 in the experimental example. DETAILED DESCRIPTION

[0038] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the accompanying drawings. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present disclosure.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0040] source:

[0041] Unless otherwise specified, the reagents, materials, and equipment used in this example are all commercially available; and the experimental methods, unless otherwise specified, are all conventional experimental methods in the art.

[0042] Example 1

[0043] A method for detecting the grain size of austenitic stainless steel.

[0044] SA-965MF 316H stainless steel was used as the sample. The sample was heat treated by heating to 675°C within 5 minutes, keeping warm for 120 minutes, and slowly cooling to 500°C at a constant rate of 60°C±5°C per hour. After air cooling to room temperature, it was polished and electrolyzed with oxalic acid aqueous solution at a voltage of 10V, a current of 3.5A, and an electrolysis time of 60s.

[0045] The oxalic acid aqueous solution is prepared by using oxalic acid and distilled water, wherein the weight ratio of oxalic acid to distilled water is 1:10, and the concentration of oxalic acid in the prepared oxalic acid aqueous solution is 1.11 mol / L.

[0046] The intercept method, area method and comparison method in GBT6394-2017 metal average grain size determination method were used to evaluate the grain size.

[0047] Example 2

[0048] A method for detecting the grain size of austenitic stainless steel.

[0049] SA-479M.316H stainless steel was used as the sample. The sample was heat treated, heated to 650°C within 5 minutes, kept warm for 120 minutes, and slowly cooled to 500°C at a constant rate of 60°C±5°C per hour. After air cooling to room temperature, it was polished and electrolyzed with oxalic acid aqueous solution at a voltage of 10V, a current of 3.5A, and an electrolysis time of 60s.

[0050] The oxalic acid aqueous solution is prepared by using oxalic acid and distilled water, wherein the weight ratio of oxalic acid to distilled water is 1:10, and the concentration of oxalic acid in the prepared oxalic acid aqueous solution is 1.11 mol / L.

[0051] The intercept method, area method and comparison method in GBT6394-2017 metal average grain size determination method were used to evaluate the grain size.

[0052] Example 3

[0053] A method for detecting the grain size of austenitic stainless steel.

[0054] SA-182MGr.F316 stainless steel was used as the sample. The sample was heat treated, heated to 675°C within 5 minutes, kept warm for 120 minutes, and slowly cooled to 500°C at a constant rate of 60°C±5°C per hour. After air cooling to room temperature, it was polished and electrolyzed with oxalic acid aqueous solution at a voltage of 10V, a current of 3.5A, and an electrolysis time of 60s.

[0055] The oxalic acid aqueous solution is prepared by using oxalic acid and distilled water, wherein the weight ratio of oxalic acid to distilled water is 1:10, and the concentration of oxalic acid in the prepared oxalic acid aqueous solution is 1.11 mol / L.

[0056] The intercept method, area method and comparison method in GBT6394-2017 metal average grain size determination method were used to evaluate the grain size.

[0057] Example 4

[0058] A method for detecting the grain size of austenitic stainless steel.

[0059] S31608 IV stainless steel was used as the sample. The sample was heat treated by heating to 650°C within 5 minutes, keeping warm for 120 minutes, and slowly cooling to 500°C at a constant rate of 60°C±5°C per hour. After air cooling to room temperature, it was polished and electrolyzed with oxalic acid aqueous solution at a voltage of 10V, a current of 3.5A, and an electrolysis time of 60s.

[0060] The oxalic acid aqueous solution is prepared by using oxalic acid and distilled water, wherein the weight ratio of oxalic acid to distilled water is 1:10, and the concentration of oxalic acid in the prepared oxalic acid aqueous solution is 1.11 mol / L.

[0061] The intercept method, area method and comparison method in GBT6394-2017 metal average grain size determination method were used to evaluate the grain size.

[0062] Example 5

[0063] A method for detecting the grain size of austenitic stainless steel.

[0064] SA-240TP.304 stainless steel was used as the sample. The sample was heat treated, heated to 725°C within 5 minutes, kept warm for 120 minutes, and slowly cooled to 500°C at a constant rate of 60°C±5°C per hour. After air cooling to room temperature, it was polished and electrolyzed with oxalic acid aqueous solution at a voltage of 10V, a current of 3.5A, and an electrolysis time of 60s.

[0065] The oxalic acid aqueous solution is prepared by using oxalic acid and distilled water, wherein the weight ratio of oxalic acid to distilled water is 1:10, and the concentration of oxalic acid in the prepared oxalic acid aqueous solution is 1.11 mol / L.

[0066] The intercept method, area method and comparison method in GBT6394-2017 metal average grain size determination method were used to evaluate the grain size.

[0067] Example 6

[0068] A method for detecting the grain size of austenitic stainless steel.

[0069] SA-182MCrF304H stainless steel was used as the sample. The sample was heat treated, heated to 650°C within 5 minutes, kept warm for 120 minutes, slowly cooled to 500°C at a constant rate of 60°C±5°C per hour, air-cooled to room temperature, polished, and then electrolyzed with 10% oxalic acid aqueous solution at a voltage of 10V, a current of 3.5A, and an electrolysis time of 60s.

[0070] The oxalic acid aqueous solution is prepared by using oxalic acid and distilled water, wherein the weight ratio of oxalic acid to distilled water is 1:10, and the concentration of oxalic acid in the prepared oxalic acid aqueous solution is 1.11 mol / L.

[0071] The intercept method, area method and comparison method in GBT6394-2017 metal average grain size determination method were used to evaluate the grain size.

[0072] Example 7

[0073] A method for detecting the grain size of austenitic stainless steel.

[0074] SA-240TP.316 stainless steel was used as the sample. The sample was heat treated, heated to 600°C within 5 minutes, kept warm for 120 minutes, slowly cooled to 500°C at a constant rate of 60°C±5°C per hour, air-cooled to room temperature, polished, and then electrolyzed with oxalic acid aqueous solution with a voltage of 10V, a current of 3.5A, and an electrolysis time of 60s.

[0075] The oxalic acid aqueous solution is prepared by using oxalic acid and distilled water, wherein the weight ratio of oxalic acid to distilled water is 1:10, and the concentration of oxalic acid in the prepared oxalic acid aqueous solution is 1.11 mol / L.

[0076] The intercept method, area method and comparison method in GBT6394-2017 metal average grain size determination method were used to evaluate the grain size.

[0077] Example 8

[0078] A method for detecting the grain size of austenitic stainless steel.

[0079] SA-240TP.316 stainless steel was used as the sample. The sample was heat treated, heated to 750°C within 5 minutes, kept warm for 120 minutes, and slowly cooled to 500°C at a constant rate of 60°C±5°C per hour. After air cooling to room temperature, it was polished and electrolyzed with oxalic acid aqueous solution at a voltage of 10V, a current of 3.5A, and an electrolysis time of 60s.

[0080] The oxalic acid aqueous solution is prepared by using oxalic acid and distilled water, wherein the weight ratio of oxalic acid to distilled water is 1:10, and the concentration of oxalic acid in the prepared oxalic acid aqueous solution is 1.11 mol / L.

[0081] The intercept method, area method and comparison method in GBT6394-2017 metal average grain size determination method were used to evaluate the grain size.

[0082] Comparative Example 1

[0083] A method for detecting the grain size of austenitic stainless steel.

[0084] Preparation of electrolyte: 20 g of oxalic acid was added to 200 ml of distilled water to prepare an oxalic acid aqueous solution as the electrolyte. The concentration of oxalic acid in the prepared oxalic acid aqueous solution was 1.11 mol / L.

[0085] Electrolysis: A sample of SA-965MF316H solid-solution austenitic stainless steel was ground and polished, used as the anode, and a stainless steel plate as the cathode for electrolysis. The electrolysis parameters used were: voltage 6V, current 3A, and electrolysis time 30s. The sample was then removed and rinsed with running water, then rinsed with alcohol and air-dried.

[0086] Observe under a metallographic microscope.

[0087] Comparative Example 2

[0088] A method for detecting the grain size of austenitic stainless steel.

[0089] Prepare the electrolyte: Pour 180 ml of nitric acid (mass fraction 65%-68%, high-grade purity) into 120 ml of water, stir evenly with a glass rod to make a 60% nitric acid aqueous solution as the electrolyte.

[0090] Electrolysis: A sample of SA-965MF316H solid-solution austenitic stainless steel was used as the anode. The sample was ground and polished, and the stainless steel plate was used as the cathode for electrolysis. The electrolysis parameters used were: voltage 2V, current 0.35A, and electrolysis time 60s. The sample was then removed and rinsed with running water, then rinsed with alcohol and air-dried.

[0091] Observe under a metallographic microscope.

[0092] Comparative Example 3

[0093] A method for detecting the grain size of austenitic stainless steel.

[0094] Prepare etching solution: Mix 20g copper sulfate (CuSO4·5H2O) + 80ml hydrochloric acid + 80ml distilled water to prepare copper sulfate aqueous solution as the etchant;

[0095] Erosion: Use SA-965MF316H solid solution austenitic stainless steel as the sample. Grind and polish the sample and immerse it in the above-mentioned corrosive agent for 30 seconds. When the surface turns light white, take it out and clean it with running water, then rinse it with alcohol and blow it dry.

[0096] Observe under a metallographic microscope.

[0097] Comparative Example 4

[0098] A method for detecting the grain size of austenitic stainless steel.

[0099] SA-240TP.316 stainless steel was used as the sample. The sample was heat treated, heated to 430°C within 5 minutes, kept warm for 120 minutes, and slowly cooled to 500°C at a constant rate of 60°C±5°C per hour. After air cooling to room temperature, it was polished and electrolyzed with oxalic acid aqueous solution at a voltage of 10V, a current of 3.5A, and an electrolysis time of 60s.

[0100] The oxalic acid aqueous solution is prepared by using oxalic acid and distilled water, wherein the weight ratio of oxalic acid to distilled water is 1:10, and the concentration of oxalic acid in the prepared oxalic acid aqueous solution is 1.11 mol / L.

[0101] The intercept method, area method and comparison method in GBT6394-2017 metal average grain size determination method were used to evaluate the grain size.

[0102] Comparative Example 5

[0103] A method for detecting the grain size of austenitic stainless steel.

[0104] SA-240TP.316 stainless steel was used as the sample. The sample was heat treated, heated to 820°C within 5 minutes, kept warm for 120 minutes, and slowly cooled to 500°C at a constant rate of 60°C±5°C per hour. After air cooling to room temperature, it was polished and electrolyzed with 10% oxalic acid aqueous solution at a voltage of 10 V, a current of 3.5 A, and an electrolysis time of 60 seconds.

[0105] The oxalic acid aqueous solution is prepared by using oxalic acid and distilled water, wherein the weight ratio of oxalic acid to distilled water is 1:10, and the concentration of oxalic acid in the prepared oxalic acid aqueous solution is 1.11 mol / L.

[0106] The intercept method, area method and comparison method in GBT6394-2017 metal average grain size determination method were used to evaluate the grain size.

[0107] Experimental example

[0108] The grain size test results of each embodiment and comparative example are compared and analyzed.

[0109] Results: The grain size morphology of the corroded austenitic stainless steel obtained in each embodiment and comparative example was observed under a metallographic microscope. Figure 1-13 The grain size detection parameters and results are shown in the following table.

[0110] Table 1 Grain size test parameters and results of corroded austenitic stainless steel obtained in each embodiment and comparative example

[0111] Steel Type Grain size grade Example 1 SA-965MF 316H 4 Example 2 SA-479M.316H 3.5 Example 3 SA-182MGr.F316 3 Example 4 S31608IV 3 Example 5 SA-240TP.304 3 Example 6 SA-182MCrF304H 3 Example 7 SA-240TP.316 6.5 Example 8 SA-240TP.316 7

[0112] Result analysis: The austenitic stainless steel of Example 1 was observed under a metallographic microscope. Figure 1 As shown, the grain boundaries are clear and complete. The test results using the interception method are level 4, the area method test results are level 4, and the comparison method test results are level 4. The test results of the three test methods specified in the standard are highly consistent. The test results are true, valid and reproducible.

[0113] The austenitic stainless steel of Example 2 was observed under a metallographic microscope. Figure 2 As shown, the grain boundaries are clear and complete. The test results using the interception method are level 3.5, the area method test results are level 3.5, and the comparison method test results are level 3.5. The test results of the three test methods specified in the standard are highly consistent. The test results are true, valid and reproducible.

[0114] The austenitic stainless steel of Example 3 was observed under a metallographic microscope. Figure 3 As shown, the grain boundaries are clear and complete. The test results using the interception method are level 3, the area method test results are level 3, and the comparison method test results are level 3. The test results of the three test methods specified in the standard are highly consistent. The test results are true, valid, and reproducible.

[0115] The austenitic stainless steel of Example 4 was observed under a metallographic microscope. Figure 4 As shown, the grain boundaries are clear and complete. The test results using the interception method are level 3, the area method test results are level 3, and the comparison method test results are level 3. The test results of the three test methods specified in the standard are highly consistent. The test results are true, valid, and reproducible.

[0116] The austenitic stainless steel of Example 5 was observed under a metallographic microscope. Figure 5As shown, the grain boundaries are clear and complete. The test results using the interception method are level 3, the area method test results are level 3, and the comparison method test results are level 3. The test results of the three test methods specified in the standard are highly consistent. The test results are true, valid, and reproducible.

[0117] The austenitic stainless steel of Example 6 was observed under a metallographic microscope. Figure 6 As shown, the grain boundaries are clear and complete. The test results using the interception method are level 3, the area method test results are level 3, and the comparison method test results are level 3. The test results of the three test methods specified in the standard are highly consistent. The test results are true, valid, and reproducible.

[0118] The austenitic stainless steel of Example 7 was observed under a metallographic microscope. Figure 7 As shown, the grain boundaries are not particularly clear, but relatively complete. The intercept method test results are 6.5, the area method test results are 6.5, and the comparison method test results are 6.5. The test results of the three test methods specified in the standard are highly consistent, and the test results are true, valid, and reproducible. However, compared with Examples 1-6, the test results of Example 7 are not obvious in the grain boundaries, and the effect is poor.

[0119] The austenitic stainless steel of Example 8 was observed under a metallographic microscope. Figure 8 As shown, the grain boundaries are clear but incomplete, indicating excessive corrosion. The intercept method test results are level 7, the area method test results are level 7, and the comparison method test results are level 7. The test results of the three test methods specified in the standard are highly consistent, and the test results are authentic, effective, and reproducible. However, compared with Examples 1-6, the test results of Example 8 show incomplete grain boundaries and excessive corrosion, and the effect is poor.

[0120] The grain boundaries and microstructure of the austenitic stainless steel after corrosion obtained in each embodiment are complete and clear, which minimizes the interference of twin boundaries on grain boundaries, and the grain size assessment results are more real and accurate; at the same time, the microstructure is clearly displayed, laying the foundation for further evaluation of the microstructure of stainless steel.

[0121] The results of Comparative Example 1 are as follows Figure 9 As shown in Figure 2, the grain boundaries of austenitic stainless steel are not obvious, and there are many twins, which seriously interfere with the grain boundaries. Figure 10 As shown in Figure 2, the grain boundaries of austenitic stainless steel are incomplete and the appearance of the microstructure is completely suppressed. Figure 11 As shown in FIG, the austenite grain boundaries and twin boundaries of austenitic stainless steel are mixed together and difficult to identify. Figure 12 As shown in FIG, the austenite grain boundaries of austenitic stainless steel are not obvious and are mixed with the twin boundaries, making them difficult to identify. Figure 13 As shown in the figure, the austenite grain boundaries of austenitic stainless steel are incomplete and discontinuous, and the effect is not good.

[0122] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0123] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for detecting the grain size of austenitic stainless steel, characterized in that: The following steps are involved: Displaying grain boundaries and microstructure: Take the austenitic stainless steel to be evaluated, heat it to a predetermined temperature of 650-725°C, keep it at that temperature for 115-125 minutes, cool it, and electrolyze it with an oxalic acid aqueous solution; the oxalic acid concentration in the oxalic acid aqueous solution is 0.8-1.5 mol / L; the electrolysis voltage is 6-10 V, the current is 3-5 A, and the electrolysis time is 30-120 seconds; Grain size assessment: Grain size assessment is performed on austenitic stainless steel after electrolysis.

2. The detection method according to claim 1, wherein The austenitic stainless steel to be assessed is nuclear grade austenitic stainless steel.

3. The detection method according to claim 1, wherein The step of displaying grain boundaries and tissue morphology also includes a cleaning step after the electrolysis step, and the cleaning includes the following steps: rinsing the electrolyzed austenitic stainless steel with water, cleaning with ethanol, and drying.

4. The detection method according to claim 3, characterized in that The cleaning comprises the following steps: rinsing the electrolyzed austenitic stainless steel with water, cleaning with ethanol, drying, wiping with nitric acid, and then rinsing with water and ethanol in sequence, and drying.

5. Use of the detection method according to any one of claims 1 to 4 in the preparation of a product for detecting the grain size of austenitic stainless steel.

6. The use according to claim 5, characterized in that The austenitic stainless steel is nuclear grade austenitic stainless steel.

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