CN111876783A - Metallographic chemical polishing solution and application thereof in field of austenitic stainless steel metallographic detection - Google Patents

Abstract

The invention specifically relates to a metallographic chemical polishing liquid and its application in the field of metallographic detection of austenitic stainless steel. It is difficult to achieve the ideal polishing effect when the traditional chemical polishing liquid is applied to the surface inspection of austenitic stainless steel. The present invention provides a chemical polishing liquid suitable for the metallographic inspection of 18Cr-8Ni type austenitic stainless steel. The ingredients and proportions are as follows: hydrochloric acid 120ml/L～160ml/L, phosphoric acid 120ml/L～160ml/L, sodium nitrate 50g/L～70g/L, 30% hydrogen peroxide 300ml/L, ethanol 100ml/L, thiourea 5g /L, hydrochloric acid fog inhibitor 1g/L, the balance is water. When the chemical polishing liquid is applied to austenitic stainless steel, the acid mist generated in the polishing process can be effectively suppressed, the preparation method is simple and safe, and a clear metallographic structure surface can be obtained.

Description

A metallographic chemical polishing liquid and its application in the field of metallographic detection of austenitic stainless steel

technical field

The invention belongs to the technical field of metallographic detection and polishing, and in particular relates to a metallographic chemical polishing liquid, a preparation method of the polishing liquid, and the application of the metallographic chemical polishing liquid in the field of metallographic detection of 18Cr-8Ni type austenitic stainless steel .

Background technique

The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not necessarily be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person of ordinary skill in the art.

In recent years, with the rapid development of high-parameter, large-capacity, and high-efficiency power plant boilers, higher requirements have been placed on the performance and processing performance of heated components. 18Cr-8Ni type austenitic stainless steel is widely used in the heating surface tubes of supercritical power plant boilers because of its good microstructure stability, high creep strength, excellent oxidation resistance and high temperature corrosion resistance. The heating surface tube is often under extremely harsh working conditions (especially in units with large installed capacity, the temperature of the flue gas on the outer surface of the tube exceeds 1000 °C, the temperature of the high-pressure steam flowing in the tube is above 540 °C, and the pressure reaches 16MPa. The above) operation, with the accumulation of operating time, it is inevitable that there will be defects such as tissue aging, corrosion, intergranular cracks, etc. The occurrence of these defects seriously affects the safe operation of the unit. Therefore, the metallographic detection of austenitic stainless steel is a power station. It is an important part of the boiler metal supervision project, and in the actual metal supervision process, it is necessary to carry out on-site metallographic preparation without damaging the components. Due to the complexity of on-site working conditions and the limitations of environmental conditions, on-site metallographic preparation is far more difficult than laboratory preparation. One of the main difficulties restricting the on-site metallographic preparation process is metallographic polishing.

In the process of on-site metallographic inspection, there are mainly steps such as polishing, polishing, erosion and observation. The quality of polishing will have a direct impact on the clarity of the metallographic structure. If the polishing quality is not good, some small and tiny defects (such as carbide precipitation, intergranular cracks, etc.) will not be easily found, resulting in missed inspections. Therefore, the most commonly used polishing method in the field is mechanical polishing, which is carried out by using a portable hand-held electric polishing machine with diamond polishing liquid. However, this method is limited by the shape of the workpiece and the location of the environment. It is difficult to control the polishing process, and the required polishing For a long time, the scratches are not easy to throw away, and the phenomenon of overheating in local areas is prone to occur, and the polishing effect is not ideal.

Chemical polishing is a commonly used polishing process for metallographic inspection of stainless steel. It can polish parts with complex shapes and has high inspection efficiency. In terms of functionality, chemical polishing can not only obtain a surface with physical and chemical cleanliness, but also remove the mechanical damage layer and stress layer on the surface of the stainless steel metallographic measuring point after grinding to obtain a surface with mechanical cleanliness. However, there are some shortcomings in the application of traditional chemical polishing methods to austenitic stainless steel: due to the high content of alloying elements such as Cr and Ni in austenitic stainless steel (the total mass fraction is often close to 30%), traditional metallographic chemical polishing solutions often It cannot be chemically polished due to factors such as insufficient acidity.

SUMMARY OF THE INVENTION

In view of the records in the above background art, the technical purpose of the present invention is to provide a simplified metallographic inspection and polishing method to improve the efficiency of on-site inspection. In order to achieve the technical purpose, the present invention provides a chemical polishing liquid for metallographic detection of stainless steel. It is easy to observe, and the polishing efficiency is high and the speed is easy to control.

Based on the above technical effects, the present invention provides the following technical solutions:

In a first aspect of the present invention, a metallographic chemical polishing liquid is provided, the metallographic chemical polishing liquid includes the following components: hydrochloric acid, phosphoric acid, sodium nitrate, hydrogen peroxide, ethanol, thiourea and hydrochloric acid fog inhibitor, and the balance is water.

Hydrochloric acid is a non-oxidizing inorganic strong acid and a strong corrosive agent, mainly for dissolving metals. However, the use of hydrochloric acid alone has no dissolving effect on stainless steel products. Only in combination with nitric acid and other additives, it has a certain dissolving ability to remove the oxide layer on the surface of stainless steel.

Phosphoric acid is a medium-strength ternary inorganic acid, which can increase the viscosity of the polishing solution, reduce the acidity of the polishing solution, and effectively inhibit the excessive dissolution of stainless steel. In the process of chemical polishing, on the one hand, it plays a role in dissolving the metal surface, and at the same time, an insoluble phosphate passivation film can be formed on the surface. The formation and dissolution of this passivation film can make the surface of metallographic measuring points To achieve flat, but also has the effect of polishing.

Sodium nitrate is a strong oxidant, which can dissolve with hydrochloric acid, effectively remove the oxide layer, and form a passivation film at the metallographic measuring point. Compared with using nitric acid as a raw material in the traditional polishing liquid, the present invention adopts sodium nitrate as a substitute, which can not only achieve the same good polishing effect, but also can effectively avoid yellow smoke during the polishing process, and improve the configuration safety of the polishing liquid.

Hydrogen peroxide can eliminate corrosion residues and dissolve carbon and carbides, improve the finish of stainless steel surfaces, and also eliminate NOx bumps. The addition of anhydrous ethanol can improve the stability of hydrogen peroxide in the chemical polishing liquid system and assist in improving the smoothness of the stainless steel surface.

In the process of chemical polishing, the main way to generate acid mist is that part of the surface metal is corroded by the polishing solution, and the generated hydrogen gas is accompanied by the escape, and the other part is generated by the thermal volatilization of the acid solution. The hydrochloric acid fog suppressant contains a surfactant, which can generate a certain amount of foam, which covers the surface of the polishing liquid, inhibits the volatilization of the acid, greatly reduces the hydrogen released by the corrosion of the acid liquid and the exposed metal surface, and cools the acid liquid to an acid level. Below the dew point, the acid liquid brought out is reduced, reducing the loss of acid. Reduce pollution and physical harm to testing and testing personnel. It can also remove various oil stains, slow down or inhibit the corrosion of hydrochloric acid to metals, has a good synergistic effect with hydrochloric acid, and is suitable for the use of hydrochloric acid at various temperatures.

The second aspect of the present invention provides the application of the metallographic chemical polishing solution described in the first aspect in the field of metallographic detection of austenitic stainless steel.

A third aspect of the present invention provides an austenitic stainless steel metallographic detection tool kit, the detection tool includes the metallographic chemical polishing solution described in the first aspect.

The beneficial effects of the above one or more technical solutions are:

1. Compared with the existing chemical polishing liquid, the metallographic chemical polishing liquid provided by the present invention simplifies the composition, and the configuration of the chemical polishing liquid is simpler. contamination risk.

2. The prepared chemical metallographic polishing liquid is easy to store and carry. It can be loaded with ordinary plastic reagent bottles, which can be suitable for laboratory testing, and can also be carried to the production site for metallographic testing. In addition, the properties of the ingredients are stable, not easy to deteriorate, and can be used for a long time.

3. The chemical polishing solution provided by the present invention is easy to operate when applied to metallographic surface detection, has high on-site adaptability, does not require mechanical equipment, and has good polishing effect. The organization is clear and true.

Description of drawings

The accompanying drawings forming a part of the present invention are used to provide further understanding of the present invention, and the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, and do not constitute an improper limitation of the present invention.

Fig. 1 is the metallographic structure surface photo after chemical polishing of 18Cr-8Ni type austenitic stainless steel described in embodiment 5;

Among them, Fig. 1a shows the metallographic structure surface after only chemical polishing; Fig. 1b shows the metallographic structure surface only after chemical polishing and etching; Fig. 1c shows the metallographic structure surface after only using mechanical polishing and etching.

Detailed ways

It should be noted that the following detailed description is exemplary and intended to provide further explanation of the invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It should be noted that the terminology used herein is for the purpose of describing specific embodiments only, and is not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly dictates otherwise, the singular is intended to include the plural as well, furthermore, it is to be understood that when the terms "comprising" and/or "including" are used in this specification, it indicates that There are features, steps, operations, devices, components and/or combinations thereof.

As described in the background art, in the prior art, it is difficult to achieve ideal results when chemical polishing liquid is applied to austenitic stainless steel, and problems such as gray film, dullness, and inability to remove grinding scratches may occur. In order to solve the above technical problems, the present invention proposes a metallographic chemical polishing liquid, which is applied to the surface treatment of stainless steel, especially the surface treatment of austenitic stainless steel, which can obtain a clear metallographic structure.

In a first aspect of the present invention, a metallographic chemical polishing liquid is provided, the metallographic chemical polishing liquid includes the following components: hydrochloric acid, phosphoric acid, sodium nitrate, hydrogen peroxide, ethanol, thiourea and hydrochloric acid fog inhibitor, and the balance is water.

Preferably, the concentration of hydrochloric acid in the chemical polishing solution is 1.4-1.92 mol/L.

Further preferably, the present invention provides a preparation method of the above-mentioned hydrochloric acid, using commercially available concentrated hydrochloric acid as a raw material, 1L of chemical polishing liquid contains 120ml-160ml of commercially available analytically pure hydrochloric acid, and the configuration methods of other chemical polishing liquids of hydrochloric acid concentration are also the same. .

Further, 1 L of chemical polishing solution contains 130-150 ml of commercially available analytically pure hydrochloric acid.

In some specific embodiments with better effects, the content of the concentrated hydrochloric acid is 140 ml per L, that is, 1.68 mol/L.

In order to take into account the polishing effect and economic cost, the above-mentioned hydrochloric acid adopts analytically pure commercial concentrated hydrochloric acid, usually a concentrated hydrochloric acid product with a mass fraction of 36 to 38%. It is verified by the present invention that the above concentration deviation does not affect the chemical polishing solution configuration and polishing effect of the present invention. .

According to the research of the present invention, when the hydrochloric acid is lower than 1.4mol/L, the chemical dissolution effect of the polishing solution is small, the dissolution rate is slow, the removal of the oxide layer is incomplete, and the polishing effect is not ideal; when the concentration of the hydrochloric acid exceeds 1.92mol/L, the dissolution corrosion is caused. If the process is intensified, the stainless steel surface will be corroded, the polishing performance of the polishing solution will be reduced, and the acid mist will easily form due to serious volatilization, which will affect the sight. The test results show that when the concentration of hydrochloric acid is 1.68mol/L, the polishing speed and polishing quality can be taken into account, and the effect is the best.

Preferably, the phosphoric acid concentration is 1.8 mol/L to 2.4 mol/L.

The research of the present invention shows that the concentration of phosphoric acid has a great influence on the polishing quality. When the concentration of phosphoric acid is lower than 1.8mol/L, the phosphate conversion film on the surface of the metallographic measuring point is discontinuous, which cannot inhibit the metallographic measuring point under the action of hydrochloric acid and nitric acid. If corrosion occurs, the polishing solution only has a corrosive effect on the metallographic measuring point; when the concentration of phosphoric acid exceeds 2.4mol/L, the thickness and formation speed of the phosphate conversion film on the surface of the stainless steel will be increased, the progress of the dissolution reaction will be inhibited, and the polishing effect will not be achieved. Effect. When the concentration of phosphoric acid is 1.8mol/L, the polishing quality is the best, which can not only dissolve, but also form an insoluble phosphate conversion film on the stainless steel surface, thereby effectively inhibiting the overdissolution of metals.

The present invention also provides a preparation method of the above phosphoric acid, which uses commercially available concentrated phosphoric acid (analytical purity, mass fraction ≥ 85%) as a raw material for preparation, wherein the phosphoric acid concentration is 1.8mol/L～2.4mol/L, which is Add 120ml to 160ml of commercially available concentrated phosphoric acid to 1L of chemical polishing solution. The concentration of the commercially available analytically pure concentrated phosphoric acid product is usually the mass fraction ≥ 85%. It is verified by the present invention that the above concentration deviation does not affect the configuration and polishing effect of the chemical polishing solution of the present invention.

Preferably, the sodium nitrate content is 50g/L～70g/L.

When the concentration of sodium nitrate in the solution is less than 50g/L, the oxide layer on the surface of the metallographic measuring point is difficult to remove, and there will be pits and pits on the surface; when the concentration of sodium nitrate exceeds 70g/L, the stainless steel surface will be passivated effect, reducing the dissolution rate. The test results show that the polishing quality is the best when the concentration of sodium nitrate is 60g/L.

Preferably, the sodium nitrate is an analytically pure product with a mass fraction of ≥99%.

Preferably, the hydrogen peroxide concentration is 80-100 ml/L. Hydrogen peroxide is a viscous liquid. In the chemical polishing liquid provided by the present invention, the concentration of the hydrogen peroxide is 80-100 ml of pure hydrogen peroxide per liter of the polishing liquid. Since the commercially available hydrogen peroxide in this field is usually analytically pure hydrogen peroxide (30% by mass), when using the above commercially available products to prepare chemical polishing solution, 280-320ml of 30% hydrogen peroxide needs to be added to each liter of chemical polishing solution. Hydrogen oxide products.

Preferably, the concentration of the absolute ethanol is 80-120 ml/L.

Preferably, the content of the thiourea is 4-6 g/L.

Preferably, the content of the hydrochloric acid fog suppressant is 0.8-1.2 g/L.

In some specific embodiments of the above-mentioned preferred technical solutions, the proportions of the components of the chemical polishing solution per liter are as follows: commercially available analytically pure concentrated hydrochloric acid 140ml, commercially available analytically pure concentrated phosphoric acid 140ml, sodium nitrate 60g, 30% peroxide Hydrogen 300ml, anhydrous ethanol 100ml, thiourea 5g, hydrochloric acid fog suppressant 1g, the balance is distilled water.

In some specific embodiments of the above-mentioned preferred technical solutions, the proportions of the components of the chemical polishing solution per liter are as follows: 130ml of commercially available analytically pure concentrated hydrochloric acid, 160ml of commercially available analytically pure concentrated phosphoric acid, 50g of sodium nitrate, 30% hydrogen peroxide 280ml, 110ml of absolute ethanol, 6g of thiourea, 0.8g of hydrochloric acid fog suppressant, and the balance is distilled water.

In some specific embodiments of the above-mentioned preferred technical solutions, the proportions of the components of the chemical polishing solution per liter are as follows: 150ml of commercially available analytically pure concentrated hydrochloric acid, 120ml of commercially available analytically pure concentrated phosphoric acid, 70g of sodium nitrate, 30% hydrogen peroxide 310ml, 80ml of absolute ethanol, 4g of thiourea, 1.2g of hydrochloric acid fog suppressant, and the balance is distilled water.

Preferably, the preparation method of the chemical gold image polishing liquid is as follows: measure distilled water, anhydrous ethanol and hydrogen peroxide and mix them evenly, then add hydrochloric acid and phosphoric acid and stir evenly, and then add sodium nitrate, thiourea and hydrochloric acid fog suppressant in sequence .

The second aspect of the present invention provides the application of the metallographic chemical polishing solution described in the first aspect in the field of metallographic detection of austenitic stainless steel.

Preferably, the austenitic stainless steel contains about 18% of Cr and 8% to 10% of Ni, that is, 18Cr-8Ni type austenitic stainless steel.

Preferably, the polishing method of the metallographic chemical polishing solution includes the following steps: dipping the metallographic chemical polishing solution with a water-absorbing material to wipe the metallographic surface, and observing the scratches on the surface, after the scratches disappear, clean the surface. the metallographic surface and dried.

Further preferably, in the cleaning step, anhydrous ethanol is used for cleaning.

Preferably, the polishing method of the metallographic chemical polishing solution includes the following steps: adding the workpiece to be polished into the metallographic chemical polishing solution to soak, and then wiping the metallographic surface with a water-absorbing material.

Further preferably, the water-absorbing material includes, but is not limited to, absorbent cotton, non-woven fabric, woolen wool or velvet.

A third aspect of the present invention provides an austenitic stainless steel metallographic detection tool kit, the detection tool includes the metallographic chemical polishing solution described in the first aspect.

Preferably, in the austenitic stainless steel metallographic detection kit, the raw materials of the metallographic chemical polishing solution, hydrochloric acid, phosphoric acid, sodium nitrate, hydrogen peroxide, ethanol, thiourea, hydrochloric acid fog inhibitor and water are independent Packaging, mix well in container before use.

Preferably, in the austenitic stainless steel metallographic detection tool kit, the metallographic chemical polishing solution is a reagent pre-mixed with each raw material according to the proportions.

Preferably, the austenitic stainless steel metallographic detection tool kit further includes other polishing tools, including but not limited to bamboo clips, tweezers, absorbent cotton, polishing cloth, anhydrous ethanol, and the like.

In order to enable those skilled in the art to understand the technical solutions of the present invention more clearly, the technical solutions of the present invention will be described in detail below with reference to specific embodiments. The components in the following examples are all commercially available products unless otherwise specified.

Example 1

In this embodiment, a metallographic chemical polishing liquid and a preparation method are provided. The components and proportions of the metallographic chemical polishing liquid are as follows: hydrochloric acid 130ml/L, phosphoric acid 160ml/L, sodium nitrate 50g/L, 30% Hydrogen peroxide 280ml/L, absolute ethanol 110ml/L, thiourea 6g/L, hydrochloric acid fog suppressant 0.8g/L, and the balance is distilled water.

Wherein, the hydrochloric acid is 130ml/L and the configuration is as follows: 130ml of concentrated hydrochloric acid with a mass fraction of 36-38% is added to each L of metallographic chemical polishing solution.

The configuration method of the phosphoric acid 160ml/L is as follows: 160ml of concentrated phosphoric acid with a concentration of ≥85% by mass is added to each L of the metallographic chemical polishing solution.

The configuration method of the 30% hydrogen peroxide 280ml/L is as follows: 280ml of hydrogen peroxide with a mass fraction of 30% is added to each L of metallographic chemical polishing liquid.

The hydrochloric acid fog inhibitor is Yuantai YT-1101 type.

In this embodiment, a preparation method of the metallographic chemical polishing solution is also provided, taking the preparation of 100ml solution as an example, including the following steps:

Step 1: Measure 29ml-36ml of distilled water, 10ml of absolute ethanol and 30ml of hydrogen peroxide with a volume fraction of 30% with a measuring cylinder, and pour them into a beaker;

Step 2: Measure 12-16ml of concentrated hydrochloric acid and 12-16ml of concentrated phosphoric acid with a measuring cylinder, respectively, add them into the beaker, and stir them evenly after adding;

Step 3: Weigh 5-7 g of sodium nitrate with a balance, add it into a beaker, and stir until it is completely dissolved;

Step 4: Weigh 0.5 g of thiourea and 0.1 g of hydrochloric acid fog suppressant with a balance, add them into a beaker, and stir evenly.

Example 2

In this embodiment, another metallographic chemical polishing solution is provided. The raw materials and proportions of the metallographic chemical polishing solution are as follows: hydrochloric acid 130ml/L, phosphoric acid 160ml/L, sodium nitrate 50g/L, 30% peroxide Hydrogen 280ml/L, absolute ethanol 110ml/L, thiourea 6g/L, hydrochloric acid fog suppressant 0.8g/L, and the balance is distilled water.

The hydrochloric acid fog inhibitor is Yuantai YT-1101 type.

The preparation method of the metallographic chemical polishing solution is the same as that described in Example 1.

Example 3

In this embodiment, another metallographic chemical polishing solution is provided. The raw materials and proportions of the metallographic chemical polishing solution are as follows: hydrochloric acid 150ml/L, phosphoric acid 120ml/L, sodium nitrate 70g/L, 30% peroxide Hydrogen 310ml/L, absolute ethanol 80ml/L, thiourea 4g/L, hydrochloric acid fog suppressant 1.2g/L, and the balance is distilled water.

The hydrochloric acid fog inhibitor is Yuantai YT-1101 type.

The preparation method of the metallographic chemical polishing solution is the same as that described in Example 1.

Example 4

In this embodiment, a metallographic chemical polishing solution is provided. The components and proportions of the metallographic chemical polishing solution are as follows: hydrochloric acid 130ml/L, phosphoric acid 160ml/L, sodium nitrate 50g/L, 30% hydrogen peroxide 280ml/L, thiourea 6g/L, hydrochloric acid fog suppressant 0.8g/L, and the balance is distilled water.

The metallographic chemical polishing solution described in the configured examples 1-4 was put into a plastic bottle and sealed, placed at room temperature for preservation, and the pH value of the metallographic chemical polishing solution was detected every 10 days. The test results and the appearance results of the polishing liquid are shown in Table 1 below:

The results of stability testing of metallographic chemical polishing solutions described in Table 1 Examples 1-4

Example 5

In this embodiment, the 18Cr-8Ni type austenitic stainless steel is polished with the metallographic chemical polishing solution configured in Embodiment 1, including the following steps:

(1) Prepare the chemical polishing liquid according to the required proportion;

(2) Hold absorbent cotton with tweezers, dip 3-5ml of chemical polishing solution, wipe evenly and forcefully on the metallographic surface of the stainless steel to be inspected, and constantly observe the change of scratches on the surface of the sample;

(3) The wiping time is controlled at 20-30s. When the scratches on the metallographic grinding surface are observed to disappear gradually, rinse the metallographic grinding surface with anhydrous alcohol and dry it.

The polished stainless steel surface is shown in Figure 1. It can be seen from Figure 1a that only the surface of the austenitic stainless steel treated with the metallographic polishing solution described in Example 1 is eroded flat and clear, without unevenness. Fig. 1b shows the metallographic surface after polishing and etching with the chemical polishing liquid described in Example 1, and Fig. 1c shows the metallographic surface after only mechanical polishing and etching. Comparing Fig. 1b and Fig. 1c, it can be seen that the metallographic surface obtained after polishing and eroding with the polishing liquid of the present invention is equivalent to the metallographic surface obtained after mechanical polishing and etching, which proves that the polishing effect of the polishing liquid is basically comparable to that of mechanical polishing. , and the mechanical polishing is limited by the work site and equipment, and the chemical polishing liquid provided in the present invention can make up for this defect very well.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. The metallographic chemical polishing solution is characterized by comprising the following components: hydrochloric acid, phosphoric acid, sodium nitrate, hydrogen peroxide, ethanol, thiourea, a hydrochloric acid fog inhibitor and the balance of water.

2. The metallographic chemical polishing solution according to claim 1, wherein the hydrochloric acid concentration is 1.4 to 1.92 mol/L.

Or the concentration of the phosphoric acid is 1.8 mol/L-2.4 mol/L;

or the content of the sodium nitrate is 50 g/L-70 g/L.

3. The metallographic chemical polishing solution according to claim 1, wherein the hydrogen peroxide concentration is 80 to 100 ml/L;

or the concentration of the ethanol is 80-120 ml/L;

or the content of the thiourea is 4-6 g/L;

or the content of the hydrochloric acid fog inhibitor is 0.8-1.2 g/L.

4. The metallographic chemical polishing solution according to claim 2 or 3, wherein each liter of the chemical polishing solution comprises the following components in percentage by weight: 140ml of commercial analytical pure concentrated hydrochloric acid, 140ml of commercial analytical pure concentrated phosphoric acid, 60g of sodium nitrate, 300ml of 30% hydrogen peroxide, 100ml of absolute ethyl alcohol, 5g of thiourea, 1g of hydrochloric acid fog inhibitor and the balance of distilled water;

or the chemical polishing solution per liter comprises the following components in proportion: 130ml of commercial analytical pure concentrated hydrochloric acid, 160ml of commercial analytical pure concentrated phosphoric acid, 50g of sodium nitrate, 280ml of 30% hydrogen peroxide, 110ml of absolute ethyl alcohol, 6g of thiourea, 0.8g of hydrochloric acid antifogging agent and the balance of distilled water;

or the chemical polishing solution per liter comprises the following components in proportion: 150ml of commercial analytically pure concentrated hydrochloric acid, 120ml of commercial analytically pure concentrated phosphoric acid, 70g of sodium nitrate, 310ml of 30% hydrogen peroxide, 80ml of absolute ethyl alcohol, 4g of thiourea, 1.2g of hydrochloric acid antifogging agent and the balance of distilled water.

5. The metallographic chemical polishing solution according to claim 1, wherein the chemical gold image polishing solution is prepared by the following method: weighing distilled water, absolute ethyl alcohol and hydrogen peroxide, uniformly mixing, then adding hydrochloric acid and phosphoric acid, uniformly stirring, and then sequentially adding sodium nitrate, thiourea and a hydrochloric acid antifogging agent.

6. Use of the metallographic chemical polishing solution according to any one of claims 1 to 5 in the field of metallographic examination of austenitic stainless steel.

7. The application of the metallographic chemical polishing solution in the field of metallographic detection of austenitic stainless steel according to claim 6, wherein the austenitic stainless steel contains about 18% of Cr and 8-10% of Ni, namely 18Cr-8Ni type austenitic stainless steel.

8. The application of the metallographic chemical polishing solution in the field of metallographic detection of austenitic stainless steel as defined in claim 6, wherein the polishing method of the metallographic chemical polishing solution comprises the following steps: dipping a water-absorbing material in the metallographic chemical polishing solution to wipe the metallographic surface, and cleaning and drying the metallographic surface after scratches disappear by observing the surface scratch condition;

preferably, the cleaning step is performed by using absolute ethyl alcohol;

or, the polishing method of the metallographic chemical polishing solution comprises the following steps: adding a workpiece to be polished into the metallographic chemical polishing solution for soaking, and wiping the metallographic surface by adopting a water absorbing material;

preferably, the water absorbing material includes, but is not limited to, absorbent cotton, non-woven fabric, wool, or velvet.

9. An austenitic stainless steel metallographic examination kit, characterized in that the examination kit comprises a metallographic chemical polishing solution according to any one of claims 1 to 5.

10. The kit for metallographic examination of austenitic stainless steel according to claim 9, wherein in the kit for metallographic examination of austenitic stainless steel, the raw materials of the chemical polishing solution for metallographic phase, hydrochloric acid, phosphoric acid, sodium nitrate, hydrogen peroxide, ethanol, thiourea, antifogging agent for hydrochloric acid and water are packaged separately and mixed well in a container before use;

or in the austenitic stainless steel metallographic detection kit, the metallographic chemical polishing solution is a reagent prepared by premixing all raw materials according to a ratio;

or, the austenitic stainless steel metallographic detection kit further comprises other polishing tools, and the other polishing tools include, but are not limited to, bamboo clips, tweezers, absorbent cotton, polishing cloth or absolute ethyl alcohol.

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