Method for displaying austenite grain size of martensite structure in stainless steel

Abstract

The invention discloses a display method for the austenite grain size of a martensitic structure in stainless steel. The display method comprises the following steps that S10, a sample is ground and polished; s20, applying a film forming solution to the surface of the sample; s30, drying the film forming liquid; s40, the sample is placed in an electrolytic corrosion solution to be electrolyzed; s50, cleaning and drying the sample; s60, placing the sample under a microscope for observation; the film-forming liquid comprises a film-forming agent and a solvent, and the film-forming agent is selected from at least one of polyvinylpyrrolidone and chitosan. The display method of the austenite grain size of the martensitic structure in the stainless steel is simple, and a clear interface can be obtained without strictly controlling time when the stainless steel is corroded; bubbles generated by the sample in the electrolytic corrosion process are easy to float upwards, and the surface of the sample is uniformly corroded; and the polymer film formed after the film-forming liquid is dried has an antifouling effect in a short time.

Description

Technical Field

[0001] This invention relates to the field of metallographic testing and analysis methods, specifically to a method for displaying the austenite grain size in the martensitic structure of stainless steel. Background Technology

[0002] Grain size analysis of steel is crucial for controlling the austenitizing temperature during the solution treatment of stainless steel. Chemical etching methods are commonly used in metallographic testing to reveal the austenite grain size of carbon and alloy steels.

[0003] Chinese invention patent CN120084614A discloses a method for displaying the austenite grain size of martensitic structure in stainless steel. This method, through optimization of electrolyte formulation and process parameters, can clearly display the original austenite grain size of martensitic structure in stainless steel. This solution solves the problem of unclear grain boundary display in stainless steel (such as 07Cr16Ni6 steel) using traditional methods.

[0004] However, when using this method to corrode stainless steel, the corrosion rate is relatively fast, and the corrosion time must be strictly controlled in order to achieve the best results (obtaining a clear interface).

[0005] Therefore, there is an urgent need to develop a method for displaying the austenite grain size in the martensitic structure of stainless steel. Summary of the Invention

[0006] One of the objectives of this invention is to overcome the deficiencies in the prior art and provide a method for displaying the austenite grain size of the martensitic structure in stainless steel. When stainless steel is corroded using this detection method, the corrosion rate is relatively slow and the bubbles generated during the corrosion process are easy to rise.

[0007] To solve the above-mentioned technical problems, the present invention provides a method for displaying the austenite grain size of martensitic structure in stainless steel, comprising the following steps: S10: Grinding and polishing the sample; S20: Apply film-forming liquid to the sample surface; S30: Drying film-forming solution; S40: Electrolyze the sample in an electrolytic corrosion solution; S50: Clean and dry the sample; S60: Observe the sample under a microscope; The film-forming liquid includes a film-forming agent and a solvent, wherein the film-forming agent is at least one selected from polyvinylpyrrolidone and chitosan.

[0008] A preferred technical solution is that the average molecular weight of the film-forming agent is 100,000 to 900,000. Further, the average molecular weight of the film-forming agent can be selected from point values ​​of 100,000, 200,000, 300,000, 400,000, 500,000, 600,000, 700,000, 800,000, and 900,000, or a range of two of the above point values ​​as the maximum and minimum values.

[0009] A preferred technical solution is that, by weight, the film-forming liquid comprises: 90-110 parts water, 8-10 parts polyvinylpyrrolidone, and 0.1-0.3 parts surfactant.

[0010] Furthermore, the amount of water can be selected as 90, 100, or 110 points, or a range of the above two points as the maximum and minimum values; the amount of polyvinylpyrrolidone can be selected as 8, 9, or 10 points, or a range of the above two points as the maximum and minimum values; and the amount of surfactant can be selected as 0.1, 0.2, or 0.3 points, or a range of the above two points as the maximum and minimum values.

[0011] A preferred technical solution is that the surfactant is at least one selected from fatty alcohol polyoxyethylene ether and alkylphenol polyoxyethylene ether.

[0012] A preferred technical solution is that, after the film-forming solution in S30 dries, a polymer film with an average thickness of 8-14 μm is formed. Further, the average thickness of the polymer film can be selected as a point value of 8, 9, 10, 11, 12, 13, or 14 μm, or a range of two of the above point values ​​as the maximum and minimum values.

[0013] A preferred technical solution is that, in step S40, the sample is immersed in the electrolytic corrosion solution for 2-6 seconds before electrolysis. Further, the immersion time can be selected as a point value of 2, 3, 4, 5, or 6 seconds, or as a range between the maximum and minimum values ​​of the above two points.

[0014] The preferred technical solution is that the drying method used in S30 is vacuum drying.

[0015] A preferred technical solution is that the sample comprises martensitic precipitation hardening stainless steel; further, the martensitic precipitation hardening stainless steel is 07Cr16Ni6 steel.

[0016] A preferred technical solution is that the electrolytic corrosion solution includes nitric acid, sulfuric acid, and water; The mass fraction of nitric acid in the electrolytic corrosion solution is 30%~36%, and the mass fraction of sulfuric acid is 1%~3%. Further, the mass fraction of nitric acid in the electrolytic corrosion solution can be selected from points of 30%, 31%, 32%, 33%, 34%, 35%, and 36%, or a range of the above two points as the maximum and minimum values; the mass fraction of sulfuric acid can be selected from points of 1%, 2%, and 3%, or a range of the above two points as the maximum and minimum values.

[0017] A preferred technical solution is that, in step S40, the electrolysis voltage is 4.1~4.6V, the electrolysis time is 50~70s, and the electrolysis power supply is a constant voltage DC power supply. Further, the electrolysis voltage can be selected from points of 4.1, 4.2, 4.3, 4.4, 4.5, and 4.6V, or a range of two of these points as the maximum and minimum values; the electrolysis time can be selected from points of 50, 55, 60, 65, and 70s, or a range of two of these points as the maximum and minimum values.

[0018] The advantages and beneficial effects of this invention are as follows: The method for displaying the austenite grain size of the martensitic structure in stainless steel is simple and can obtain a clear interface without strict time control during the corrosion of stainless steel. During the electrolytic corrosion process, the bubbles generated in the sample tend to rise to the surface, resulting in more uniform corrosion of the sample surface. The polymer film formed after the film-forming solution dries has a short-term antifouling effect. Attached Figure Description

[0019] Figure 1 This is the metallographic image corresponding to the sample in Example 1; Figure 2 This is the metallographic image corresponding to the sample in Example 2; Figure 3 This is the metallographic image corresponding to the sample in Example 3; Figure 4 This is the metallographic image corresponding to the sample in Example 4; Figure 5 This is the metallographic image corresponding to the sample in Example 5; Figure 6 This is the metallographic image corresponding to the sample in Example 6; Figure 7 This is the metallographic image corresponding to the sample in Example 7; Figure 8 This is the metallographic image corresponding to the sample in Example 8; Figure 9 This is the metallographic image corresponding to the sample in Comparative Example 1; Figure 10 This is the metallographic image corresponding to the sample in Comparative Example 2; Figure 11This is the metallographic image corresponding to the sample in Comparative Example 3; Figure 12 This is the metallographic image corresponding to the sample in Comparative Example 4. Detailed Implementation

[0020] The specific embodiments of the present invention will be further described below with reference to examples. These examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0021] 1. Examples and Comparative Examples Example 1

[0022] Preparation of the polyvinylpyrrolidone solution (film-forming solution) in Example 1: A polyvinylpyrrolidone solution was prepared by mixing 100 parts of deionized water, 9 parts of polyvinylpyrrolidone (film-forming agent), and 0.2 parts of fatty alcohol polyoxyethylene ether.

[0023] Preparation of the electrolytic etching solution in Example 1: An electrolytic corrosion solution is prepared by mixing 120 mL of deionized water, 100 mL of nitric acid (65% by mass), and 3 mL of concentrated sulfuric acid (98% by mass).

[0024] The sample testing process in Example 1 includes: S1: Grind the sample surface to a mirror finish using a metallographic disc grinder; S2: Apply a layer of polyvinylpyrrolidone solution to the surface of the sample to be tested, with a thickness of 0.2 mm. S4: Place the sample in a vacuum drying oven to dry (the surface of the sample to be tested is flat). After the polyvinylpyrrolidone solution on the sample surface dries, a polyvinylpyrrolidone film is formed. The film thickness of the polyvinylpyrrolidone film is measured to be 10.1 μm using an ellipsometry. S5: Using a stainless steel plate as the cathode, the sample is placed in the electrolytic corrosion solution (as the anode). Electrolysis begins after the sample is immersed for 5 seconds. The electrolysis voltage is 4.5V, the electrolysis time is 60 seconds, and the electrolysis power supply is a constant voltage DC power supply. S6: Remove the sample, rinse and dry it, and then observe it under a microscope.

[0025] The film-forming agent in Example 1 was polyvinylpyrrolidone K60 (density 1.69 g / cm³). 3 The sample in Example 1 was 07Cr16Ni6 steel.

[0026] Example 2

[0027] The sample testing process in Example 2 is based on Example 1, except that the electrolysis time in S5 is 50s.

[0028] Example 3

[0029] The sample testing process in Example 3 is based on Example 1, except that the electrolysis time in S5 is 70s.

[0030] Example 4

[0031] The sample testing process in Example 4 is based on Example 1, except that the electrolysis time in S5 is 45s.

[0032] Example 5

[0033] The sample testing process in Example 5 is based on Example 1, except that the electrolysis time in S5 is 75s.

[0034] Example 6

[0035] The sample testing process in Example 6 was based on Example 1, except that the film-forming agent was polyvinylpyrrolidone K30 (density 1.144 g / cm³). 3 And the coating thickness in S2 is 0.136mm.

[0036] Example 7

[0037] The sample testing process in Example 7 was based on Example 1, except that the film-forming agent was polyvinylpyrrolidone K90 (density 1.69 g / cm³). 3 ).

[0038] Example 8

[0039] The sample testing process in Example 8 was based on Example 1, except that the sample was dried at normal pressure in S4. The film thickness of the polyvinylpyrrolidone film in Example 8 was measured to be 10.5 μm using an ellipsometry.

[0040] Comparative Example 1 Comparative Example 1 used the same electrolytic etching solution as Example 1.

[0041] The testing process for the sample in Comparative Example 1 included: S1: Grind the sample surface to a mirror finish using a metallographic disc grinder; S2: Using a stainless steel plate as the cathode, the sample is placed in the electrolytic corrosion solution (as the anode), the electrolysis voltage is 4.5V, the electrolysis time is 17s, and the electrolysis power supply is a constant voltage DC power supply. S3: Remove the sample, rinse and dry it, and then observe it under a microscope.

[0042] Comparative Example 2 The sample testing process of Comparative Example 2 was based on Comparative Example 1, except that the electrolysis time in S2 was 12s.

[0043] Comparative Example 3 The sample testing process of Comparative Example 3 was based on Comparative Example 1, except that the electrolysis time in S2 was 22s.

[0044] Comparative Example 4 Preparation of the electrolytic etching solution for Comparative Example 4: An electrolytic corrosion solution is prepared by mixing 120 mL of deionized water, 100 mL of nitric acid (65% by mass), 3 mL of concentrated sulfuric acid (98% by mass), and 192 mg of polyvinylpyrrolidone K60.

[0045] The testing process for the sample in Comparative Example 4 included: S1: Grind the sample surface to a mirror finish using a metallographic disc grinder; S2: Using a stainless steel plate as the cathode, the sample is placed in the electrolytic corrosion solution (as the anode), the electrolysis voltage is 4.5V, the electrolysis time is 60s, and the electrolysis power supply is a constant voltage DC power supply. S3: Remove the sample, rinse and dry it, and then observe it under a microscope.

[0046] 2. Corrosion phenomena of samples in the examples and comparative examples During the corrosion of the samples, it was observed that the bubbles on the surface of the sample in Example 1 rose faster, while the bubbles on the surface of the samples in Examples 6, 7, and Comparative Example 4 rose slower.

[0047] 3. Performance test results of the examples and comparative samples Examples 1-5 and Comparative Examples 1-3 show that when using the detection method of the present invention to corrode stainless steel, a clear interface can be obtained without strict time control.

[0048] The uneven corrosion of the sample in Comparative Example 4 and the uniform corrosion of the sample in Example 1 may be due to the following reasons: after the sample in Comparative Example 4 was corroded, bubbles were generated on the surface. The polyvinylpyrrolidone, which was uniformly dispersed in the electrolytic corrosion solution, increased the viscosity of the electrolytic corrosion solution and hindered the bubbles from rising. In Example 1, the polyvinylpyrrolidone coated on the sample surface dissolved continuously during the electrolysis process (the polyvinylpyrrolidone diffused to the surroundings) while carrying the bubbles away from the sample surface.

[0049] The uneven localized corrosion of the samples in Examples 6 and 7, compared to the uniform corrosion of the sample in Example 1, may be due to the increased degree of polymerization of polyvinylpyrrolidone. This increases the repulsive force between bubbles in the electrolytic etching solution (facilitating bubble rise) while simultaneously increasing the viscosity of the solution (disadvantaging bubble rise). Overall, the degree of polymerization of polyvinylpyrrolidone in Example 1 is conducive to bubble rise on the sample surface.

[0050] The reason why the corrosion of the sample in Example 8 was uneven, while the corrosion of the sample in Example 1 was uniform, may be that vacuum drying facilitates the removal of internal bubbles in the polyvinylpyrrolidone solution coated on the surface of the sample in Example 1 during the drying process, resulting in a more uniform thickness of the polyvinylpyrrolidone film on the surface of the sample in Example 1 (and a more consistent bubble removal rate at various locations of the sample).

[0051] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for displaying the austenite grain size in the martensitic structure of stainless steel, characterized in that, Includes the following steps: S10: Grinding and polishing the sample; S20: Apply film-forming liquid to the sample surface; S30: Drying film-forming solution; S40: Electrolyze the sample in an electrolytic corrosion solution; S50: Clean and dry the sample; S60: Observe the sample under a microscope; The film-forming liquid includes a film-forming agent and a solvent, wherein the film-forming agent is at least one selected from polyvinylpyrrolidone and chitosan.

2. The method for displaying the austenite grain size of martensitic structure in stainless steel according to claim 1, characterized in that, The average molecular weight of the film-forming agent is 100,000 to 900,000.

3. The method for displaying the austenite grain size of martensitic structure in stainless steel according to claim 1, characterized in that, The film-forming solution comprises, by weight, 90-110 parts water, 8-10 parts polyvinylpyrrolidone, and 0.1-0.3 parts surfactant.

4. The method for displaying the austenite grain size of martensitic structure in stainless steel according to claim 3, characterized in that, The surfactant is selected from at least one of fatty alcohol polyoxyethylene ether and alkylphenol polyoxyethylene ether.

5. The method for displaying the austenite grain size of martensitic structure in stainless steel according to claim 1, characterized in that, After drying, the film-forming solution in S30 forms a polymer film with an average thickness of 8~14μm.

6. The method for displaying the austenite grain size of martensitic structure in stainless steel according to claim 1, characterized in that, Before electrolyzing the sample in S40, the sample should be immersed in the electrolytic corrosion solution for 2-6 seconds.

7. The method for displaying the austenite grain size of martensitic structure in stainless steel according to claim 1, characterized in that, The drying method used for S30 is vacuum drying.

8. The method for displaying the austenite grain size of martensitic structure in stainless steel according to claim 1, characterized in that, The samples included martensitic precipitation-hardening stainless steel. Furthermore, the martensitic precipitation hardening stainless steel is 07Cr16Ni6 steel.

9. The method for displaying the austenite grain size of martensitic structure in stainless steel according to claim 1, characterized in that, The electrolytic corrosion solution includes nitric acid, sulfuric acid, and water; The electrolytic corrosion solution contains 30% to 36% nitric acid and 1% to 3% sulfuric acid by mass.

10. The method for displaying the austenite grain size of martensitic structure in stainless steel according to claim 1, characterized in that, In S40, the electrolysis voltage is 4.1~4.6V, the electrolysis time is 50~70s, and the electrolysis power supply is a constant voltage DC power supply.

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