Etching agent for displaying metallographic structure of martensite heat-resistant steel and display method

Abstract

The invention relates to the technical field of metallographic structure detection, in particular to an etching agent for displaying a metallographic structure of martensite heat-resistant steel and a display method, and the etching agent comprises the following components in percentage by weight: 6-12% of sodium metabisulfite, 4-8% of citric acid and 80-90% of water. By adopting the etching agent disclosed by the invention, the metallographic structure morphology of the martensite heat-resistant steel can be truly and clearly displayed without illusion, and the structure inspection can be conveniently and accurately carried out.

Description

Technical Field

[0001] This invention relates to the field of metallographic structure detection technology, specifically to an etching agent and display method for displaying the metallographic structure of martensitic heat-resistant steel. Background Technology

[0002] Martensitic heat-resistant steels are widely used in the manufacture of critical high-temperature components for thermal power generation equipment due to their good oxidation resistance, high strength, and excellent microstructural stability. Examples include P91, P92, and G115 steels for high-temperature steam pipes, headers, and fittings in power plant boilers; T91 and T92 steels for boiler heating surface tubes; and 1Cr13 and 2Cr13 steels for power plant turbine blades. The normality of the metallographic structure of these materials not only determines the service life of power plant components but also affects the operational safety of the power plant equipment. Therefore, the inspection and control of the metallographic structure is a crucial testing item during the production acceptance and operational supervision of these materials.

[0003] Currently, various etching agents are used to reveal the metallographic structure of this type of martensitic heat-resistant steel, such as commonly used ferric chloride-hydrochloric acid aqueous solution, copper chloride-hydrochloric acid aqueous solution, hydrochloric acid-picric acid alcohol solution, nitric acid-hydrochloric acid glycerol solution, and hydrofluoric acid-nitric acid aqueous solution. However, it can be seen that these etching agents are all composed of chemical reagents with strong corrosiveness, toxicity, and volatility.

[0004] This brings considerable inconvenience and safety hazards to the preparation, use, and storage of reagents. In particular, the inconvenience and safety risks of carrying, preparing, and using such reagents are even more prominent when conducting on-site metallographic inspections of in-service components of thermal power generation equipment. Leakage and injury accidents are very likely to occur during carrying and use. At the same time, the treatment of waste acid after on-site use is also more difficult, which can easily cause environmental pollution and secondary injury accidents.

[0005] As domestic thermal power units continue to develop towards larger capacity and higher parameters, the demand for in-service monitoring and inspection of such important martensitic heat-resistant steel high-temperature components in thermal power plants is increasing. Furthermore, with growing emphasis on laboratory environmental protection in recent years, the use of safe, non-toxic, and pollution-free environmentally friendly reagents has become a trend. Therefore, it is essential to invent a novel etching agent that is simple in composition, easy and quick to prepare, convenient to carry, safe and environmentally friendly to use, and non-toxic and pollution-free, to meet the needs of laboratory and on-site metallographic testing. Summary of the Invention

[0006] The purpose of this invention is to provide an etchant and a method for displaying the metallographic structure of martensitic heat-resistant steel, thereby solving the technical problem that etchants in the prior art are all composed of a combination of chemical reagents with strong corrosiveness, toxicity, and volatility.

[0007] This invention discloses an etching agent for displaying the metallographic structure of martensitic heat-resistant steel, comprising, by weight percentage, 6-12% sodium metabisulfite, 4-8% citric acid and 80-90% water.

[0008] Furthermore, it comprises, by weight percentage, 7-11% sodium metabisulfite, 4-8% citric acid, and 81-89% water.

[0009] Furthermore, it comprises, by weight percentage, 8-10% sodium metabisulfite, 6-8% citric acid, and 82-86% water.

[0010] Furthermore, the sodium metabisulfite and citric acid are of analytical grade.

[0011] A method for displaying the metallographic structure of martensitic heat-resistant steel, using the above-mentioned etching agent.

[0012] Further, the specific steps are as follows: S1. Dissolve sodium metabisulfite and citric acid in water and set aside for later use; S2. Etched sample; S3. Observe the metallographic morphology of the sample.

[0013] Furthermore, in step S1, sodium metabisulfite is first dissolved, and after the sodium metabisulfite is fully dissolved, citric acid is then dissolved.

[0014] Furthermore, in step S2, etching is stopped when the polished surface of the sample turns silver-gray, and the sample is cleaned and dried.

[0015] Furthermore, the drying process is hot air drying.

[0016] Furthermore, step S2 etching involves wiping the polished surface of the sample with an etchant.

[0017] Further, step S2 etching involves immersing the sample in an etchant and wiping the polished surface of the sample with a degreased cotton ball.

[0018] Furthermore, in step S3, the metallographic morphology of the sample is observed using an optical microscope under bright field illumination.

[0019] Compared with the prior art, the beneficial effects of the present invention are: 1. The etching agent of this invention can display the metallographic morphology of martensitic heat-resistant steel in a true, clear and unspeculative manner, making it convenient and accurate for microstructure inspection; 2. The impregnation reagent of this invention does not use traditional strong inorganic acid reagents that are highly corrosive, irritating, volatile and toxic, but is composed of simple and environmentally friendly salts and organic acids. 3. The etching agent of this invention has the characteristics of simple composition, easy and quick preparation, convenient portability, and safe and environmentally friendly use. It can display the metallographic structure of martensitic heat-resistant steel in a true, complete and clear manner. Moreover, the new reagent has good versatility and reproducibility, and has no special requirements for sample preparation equipment and metallographic microscopes. It is a new type of environmentally friendly etching agent that is ideal for displaying the metallographic structure of martensitic heat-resistant steel, and can better meet the needs of laboratory and on-site metallographic inspection. 4. Chemical etching of alloys is actually an electrochemical corrosion process with a galvanic cell effect. The different phases of the alloy will have different electrode potentials in a specific etching solution, thus forming many tiny galvanic cell effects. This causes the anolyte phase to chemically dissolve, achieving the etching purpose and revealing the alloy's metallographic morphology. This invention follows this etching principle, breaking away from the conventional thinking that etching the metallographic structure of martensitic heat-resistant steel requires strong inorganic acid reagents. Instead, it uses a simple and environmentally friendly reagent composed of salts and organic acids, achieving the same etching effect. This is mainly because sodium metabisulfite dissolves in water and ionizes to release Na+. + OH - SO3 - and HSO3 - Citric acid ions will ionize in aqueous solution to produce (C6H5O7). 3- and H + These ions will undergo electrochemical reactions with Fe, giving the solution an etching effect and thus revealing the microstructure of the martensitic heat-resistant steel. Adjusting the component ratio will allow the solution to achieve the best etching effect on the martensitic heat-resistant steel. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a microstructure image of the T91 steel of this invention.

[0022] Figure 2 This is a microstructure image of the P91 steel of this invention.

[0023] Figure 3 This is a microstructure image of the T92 steel of this invention.

[0024] Figure 4 This is a microstructure image of the P92 steel of this invention.

[0025] Figure 5This is a microstructure image of the small-diameter G115 steel pipe of the present invention.

[0026] Figure 6 This is a microstructure image of the large-diameter G115 steel pipe of the present invention.

[0027] Figure 7 The image shows the microstructure of P92 steel as shown in Comparative Example 1, where oxalic acid was used instead of citric acid.

[0028] Figure 8 Microstructure of P92 steel with varying amounts of sodium metabisulfite, used in Comparative Example 2.

[0029] Figure 9 Microstructure of T91 steel with varying amounts of citric acid as shown in Comparative Example 3. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0031] Example 1 The etching agent and method for displaying the metallographic structure of martensitic heat-resistant steel used in this embodiment include the following steps: S1. First, measure 85ml of water into a beaker, then weigh 9g of sodium metabisulfite and 6g of citric acid into the beaker in sequence, and stir with a glass rod until completely dissolved before use.

[0032] S2. During etching, immerse the sample in the etching agent and wipe the polished surface of the sample with a degreased cotton ball until the polished surface of the sample turns silver-gray. Then take it out, rinse it with clean water, drip anhydrous ethanol on it, and blow it dry with hot air before observing and inspecting the metallographic structure of the martensitic heat-resistant steel.

[0033] S3. By placing the etched sample under bright-field illumination with an optical microscope, the metallographic morphology of the martensitic heat-resistant steel can be displayed truthfully, completely, and clearly. The results are as follows: Figure 1 As shown.

[0034] Example 2 This embodiment, as a preferred embodiment of the present invention, provides an etching agent and method for displaying the metallographic structure of martensitic heat-resistant steel, comprising the following steps: S1. First, measure 90ml of water into a beaker, then weigh 6g of sodium metabisulfite and 4g of citric acid into the beaker in sequence, and stir with a glass rod until completely dissolved before use.

[0035] S2. During etching, use a degreased cotton ball dipped in etching agent to wipe the polished surface of the sample until the polished surface of the sample turns silver-gray. Then remove the sample, rinse it with clean water, drip anhydrous ethanol on it, and blow it dry with hot air before observing and inspecting the metallographic structure of the martensitic heat-resistant steel.

[0036] S3. By placing the etched sample under bright-field illumination with an optical microscope, the metallographic morphology of the martensitic heat-resistant steel can be displayed truthfully, completely, and clearly. The results are as follows: Figure 2 As shown.

[0037] Example 3 This embodiment, as a preferred embodiment of the present invention, provides an etching agent and method for displaying the metallographic structure of martensitic heat-resistant steel, comprising the following steps: S1. First, measure 80ml of water into a beaker, then weigh 12g of sodium metabisulfite and 8g of citric acid into the beaker in sequence, and stir with a glass rod until completely dissolved before use.

[0038] S2. During etching, immerse the sample in the etching agent and wipe the polished surface of the sample with a degreased cotton ball until the polished surface of the sample turns silver-gray. Then take it out, rinse it with clean water, drip anhydrous ethanol on it, and blow it dry with hot air before observing and inspecting the metallographic structure of the martensitic heat-resistant steel.

[0039] S3. By placing the etched sample under bright-field illumination with an optical microscope, the metallographic morphology of the martensitic heat-resistant steel can be displayed truthfully, completely, and clearly. The results are as follows: Figure 3 As shown.

[0040] Example 4 This embodiment, as a preferred embodiment of the present invention, provides an etching agent and method for displaying the metallographic structure of martensitic heat-resistant steel, comprising the following steps: S1. First, measure 85ml of water into a beaker, then weigh 6g of sodium metabisulfite and 8g of citric acid into the beaker in sequence, and stir with a glass rod until completely dissolved before use.

[0041] S2. During etching, use a degreased cotton ball dipped in etching agent to wipe the polished surface of the sample until the polished surface of the sample turns silver-gray. Then remove the sample, rinse it with clean water, drip anhydrous ethanol on it, and blow it dry with hot air before observing and inspecting the metallographic structure of the martensitic heat-resistant steel.

[0042] S3. By placing the etched sample under bright-field illumination with an optical microscope, the metallographic morphology of the martensitic heat-resistant steel can be displayed truthfully, completely, and clearly. The results are as follows: Figure 4 As shown.

[0043] Example 5 This embodiment, as a preferred embodiment of the present invention, provides an etching agent and method for displaying the metallographic structure of martensitic heat-resistant steel, comprising the following steps: S1. First, measure 83ml of water into a beaker, then weigh 12g of sodium metabisulfite and 4g of citric acid into the beaker in sequence, and stir with a glass rod until completely dissolved before use.

[0044] S2. During etching, immerse the sample in the etching agent and wipe the polished surface of the sample with a degreased cotton ball until the polished surface of the sample turns silver-gray. Then take it out, rinse it with clean water, drip anhydrous ethanol on it, and blow it dry with hot air before observing and inspecting the metallographic structure of the martensitic heat-resistant steel.

[0045] S3. By placing the etched sample under bright-field illumination with an optical microscope, the metallographic morphology of the martensitic heat-resistant steel can be displayed truthfully, completely, and clearly. The results are as follows: Figure 5 As shown.

[0046] Example 6 This embodiment, as a preferred embodiment of the present invention, provides an etching agent and method for displaying the metallographic structure of martensitic heat-resistant steel. The only change from Embodiment 1 is the increase of citric acid from 6g to 8g. The results are as follows: Figure 6 As shown.

[0047] Comparative Example 1 In this embodiment, as a comparative example of the present invention, an etching agent and method for displaying the metallographic structure of martensitic heat-resistant steel are modified from Example 1 by replacing 6g of citric acid with oxalic acid. The results are as follows: Figure 7 As shown, the image surface has a black coating, the tissue is not clearly displayed, the tissue details are difficult to distinguish, and there is an artifact of erosion.

[0048] Comparative Example 2 In this embodiment, as a comparative example of the present invention, an etching agent and method for displaying the metallographic structure of martensitic heat-resistant steel are shown. The only change from Example 1 is that the amount of sodium metabisulfite is increased from 9g to 16g. The results are as follows: Figure 8 As shown, the image is heavily tinted, affecting the clarity of the tissue and the observation of tissue details.

[0049] Comparative Example 3 In this embodiment, as a comparative example of the present invention, an etching agent and method for displaying the metallographic structure of martensitic heat-resistant steel are shown. The only change from Example 1 is the reduction of citric acid from 6g to 3g. The results are as follows: Figure 9 As shown, the tissue etching is incomplete and unclear, and the sample surface is easily stained during the etching process, making etching difficult to control.

[0050] from Figures 1-6It can be seen that the etching agent of this invention abandons the conventional thinking that strong inorganic acid reagents with strong corrosiveness, irritation, volatility, and toxicity are required to display the metallographic structure of martensitic heat-resistant steel. It innovatively adopts a simple and environmentally friendly composition of salts and organic acids. This makes the etching agent of this invention simple in composition, easy and quick to prepare, convenient to carry, and safe and environmentally friendly to use. It can realistically, clearly, completely, and without artifacts display the metallographic structure of martensitic heat-resistant steel. Furthermore, the new reagent has good versatility and reproducibility, and has no special requirements for sample preparation equipment and metallographic microscopes. It is a relatively ideal new environmentally friendly etching agent for displaying the metallographic structure of martensitic heat-resistant steel, which can better meet the needs of laboratory and on-site metallographic examination. Simultaneously, from... Figures 7-9 It can be seen that changing the composition of the etching agent and the ratio of reagent dosage in this invention will affect the etching effect, causing etching defects such as etching film, coloring, and unclearness, which will affect the observation and differentiation of the tissue.

[0051] The above are the embodiments listed in this example. However, this example is not limited to the optional embodiments described above. Those skilled in the art can arbitrarily combine the above methods to obtain other various embodiments. Anyone can derive other various forms of embodiments based on the inspiration of this example. The above specific embodiments should not be construed as limiting the scope of protection of this example. The scope of protection of this example should be determined by the claims, and the specification can be used to interpret the claims.

Claims

1. An etching agent for revealing the metallographic structure of martensitic heat-resistant steel, characterized in that: It comprises 6-12% sodium metabisulfite, 4-8% citric acid and 80-90% water by weight percentage.

2. The etching agent for revealing the metallographic structure of martensitic heat-resistant steel according to claim 1, characterized in that: It contains 7-11% sodium metabisulfite, 4-8% citric acid and 81-89% water by weight percentage.

3. The etching agent for revealing the metallographic structure of martensitic heat-resistant steel according to claim 1, characterized in that: It contains 8-10% sodium metabisulfite, 6-8% citric acid and 82-86% water by weight percentage.

4. An etching agent for revealing the metallographic structure of martensitic heat-resistant steel according to any one of claims 1-3, characterized in that: The sodium metabisulfite and citric acid were of analytical grade.

5. A method for displaying the metallographic structure of martensitic heat-resistant steel, characterized in that: Use an etching agent that reveals the metallographic structure of martensitic heat-resistant steel according to any one of claims 1-4.

6. The method for displaying the metallographic structure of martensitic heat-resistant steel according to claim 5, characterized in that: The specific steps are as follows: S1. Dissolve sodium metabisulfite and citric acid in water and set aside for later use; S2. Etched sample; S3. Observe the metallographic morphology of the sample.

7. The method for displaying the metallographic structure of martensitic heat-resistant steel according to claim 6, characterized in that: In step S1, sodium metabisulfite is first dissolved, and after the sodium metabisulfite is fully dissolved, citric acid is then dissolved.

8. A method for displaying the metallographic structure of martensitic heat-resistant steel according to claim 6, characterized in that: In step S2, etching is stopped when the polished surface of the sample turns silver-gray, and the sample is then cleaned and dried.

9. A method for displaying the metallographic structure of martensitic heat-resistant steel according to claim 6, characterized in that: Step S2 etching involves wiping the polished surface of the sample with an etchant.

10. A method for displaying the metallographic structure of martensitic heat-resistant steel according to claim 6, characterized in that: Step S2 etching involves immersing the sample in the etching agent and wiping the polished surface of the sample with a degreased cotton ball.

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