Metallographic corrosive agent, metallographic corrosion method and metallographic observation method

Abstract

The invention relates to a metallographic corrosive. The metallographic corrosive comprises ferric chloride, citric acid, phosphoric acid, hydrochloric acid, hydrogen peroxide and water. According to the method, the ferric ions serve as the corrosive agent, the hydrogen peroxide serves as the oxidizing agent, the nickel-chromium-iron alloy can be efficiently corroded through the ferric ions, the generated ferrous ions are oxidized into the ferric ions through the hydrogen peroxide, and therefore the corrosion process can be continued; and by adding citric acid, generation of oxides with complex components on the surface of the nickel-chromium-iron alloy is inhibited, meanwhile, the concentration change of ferric ions is more stable through complexation, and the corrosion process is more uniform and stable. The metallographic phase corrosive agent disclosed by the invention can be used for corroding the nickel-chromium-iron alloy with relatively high efficiency, and a clear metallographic phase and a clear grain boundary are obtained.

Description

Technical Field

[0001] The present application relates to metal material surface treatment technology, and in particular to chemical corrosion of metal materials. Background Art

[0002] Nickel-chromium-iron alloy is an important corrosion-resistant material. Due to the composite effect of high nickel content and a large amount of chromium, molybdenum and other elements, it can resist corrosion damage in various corrosive environments. However, when conducting metallographic observation on nickel-chromium-iron alloy, due to its excellent corrosion resistance, the effect of using corrosive solution to corrode it is poor. The corrosion time of existing corrosive solution at room temperature is generally more than 10 minutes, and it is often difficult to corrode clear metallographic structure and grain boundaries. The corrosion time is long, the corrosion of the sample surface is uneven, some areas are severely over-corroded, and some areas cannot see clear metallographic structure. Summary of the invention

[0003] The embodiments of the present application provide a metallographic etching agent, a metallographic etching method, and a metallographic observation method to solve the technical problem that the corrosion effect of the etching solution on the nickel-chromium-iron alloy is poor.

[0004] In a first aspect, an embodiment of the present application provides a metallographic etchant, which includes: ferric chloride, citric acid, phosphoric acid, hydrochloric acid, hydrogen peroxide, and water.

[0005] In some embodiments of the present application, in the metallographic etchant, the concentration of ferric chloride is 0.01-0.05 g / mL, the concentration of citric acid is 0.002-0.012 g / mL, the concentration of phosphoric acid is 0.077-0.18 g / mL, and the concentration of hydrogen peroxide is 0.014-0.043 g / mL.

[0006] In a second aspect, an embodiment of the present application provides a metallographic etching method, the metallographic etching method comprising the following steps:

[0007] Providing a metallographic corrosive agent and an alloy sample to be corroded, wherein the material of the alloy sample is a nickel-chromium-iron alloy;

[0008] Grinding and polishing the alloy sample to form a polished surface on the alloy sample;

[0009] Immersing the polished surface in the metallographic etching agent for etching until the polished surface appears light brown;

[0010] The alloy sample is taken out, and the metallographic corrosive agent remaining on the surface of the alloy sample is cleaned to obtain a well-corroded alloy sample.

[0011] Wherein, the metallographic etching agent is the metallographic etching agent described in any embodiment of the first aspect.

[0012] In some embodiments of the present application, the polished alloy sample to be corroded is added to the metallographic corrosive agent for corrosion, and the corrosion of the alloy sample to be corroded is carried out at 60-80°C.

[0013] In some embodiments of the present application, the polished alloy sample to be corroded is added to the metallographic corrosive agent for corrosion, and the duration of the corrosion of the alloy sample to be corroded is 30 to 40 seconds.

[0014] In some embodiments of the present application, the alloy sample includes the following elemental components, measured in percentage by mass: 18% to 20% Cr, 50% to 55% Ni, 2.4% to 3% Mo, 4.75% to 5.5% Nb, 0.75% to 1.1% Ti, 0 to 1% Co, 0 to 0.7% Al, Fe and unavoidable impurities.

[0015] In some embodiments of the present application, the grinding and polishing of the alloy sample comprises the following steps:

[0016] Mechanically rough grinding the alloy sample to form a rough-ground surface on the alloy sample;

[0017] Performing mechanical fine grinding on the coarse ground surface to form a fine ground surface on the alloy sample;

[0018] The finely ground surface is polished.

[0019] In some embodiments of the present application, the step of cleaning the metallographic corrosive agent remaining on the surface of the alloy sample comprises the following steps:

[0020] Rinse the alloy sample with deionized water;

[0021] washing the alloy sample with ethanol;

[0022] The alloy sample is dried.

[0023] In some embodiments of the present application, the step of providing a metallographic etchant comprises the following steps:

[0024] Ferric chloride, citric acid, hydrogen peroxide solution, hydrochloric acid solution, phosphoric acid solution and deionized water are mixed to obtain the metallographic etching agent.

[0025] In a third aspect, an embodiment of the present application provides a metallographic observation method, the metallographic observation method comprising the following steps:

[0026] Providing an alloy sample according to any embodiment of the second aspect;

[0027] The polished surface of the alloy sample was observed by optical metallographic microscope.

[0028] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0029] The metallographic etchant provided in the embodiment of the present application uses trivalent iron ions as an etchant and hydrogen peroxide as an oxidant, and can efficiently corrode nickel-chromium-iron alloys through trivalent iron ions, and then oxidize the generated divalent iron ions into trivalent iron ions through hydrogen peroxide, so that the corrosion process can continue; by adding citric acid, the generation of complex oxides on the surface of the nickel-chromium-iron alloy is suppressed, and the concentration change of trivalent iron ions is made more stable through complexation, so that the corrosion process is more uniform and stable. The metallographic etchant described in the present application can corrode nickel-chromium-iron alloys with high efficiency and obtain clear metallographic phases and grain boundaries. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0031] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0032] Figure 1 is a metallographic image of the alloy sample of Example 1 of the present application;

[0033] Figure 2 This is a metallographic image of the alloy sample of Comparative Example 1 of the present application;

[0034] Figure 3 This is a metallographic image of the alloy sample of Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0036] Unless otherwise specified, the terms used herein should be understood as commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which this application belongs. In the event of a conflict, this specification takes precedence.

[0037] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0038] The existing corrosion solution has the technical problem of poor corrosion effect on nickel-chromium-iron alloy.

[0039] The technical solution provided by the embodiments of the present application is to solve the above technical problems, and the overall idea is as follows:

[0040] In a first aspect, an embodiment of the present application provides a metallographic etchant, which includes: ferric chloride, citric acid, phosphoric acid, hydrochloric acid, hydrogen peroxide, and water.

[0041] In the metallographic etchant described in the present application, the role of ferric chloride is to act as an etchant, and to undergo a redox reaction with the iron in the nickel-chromium-iron alloy, so that zero-valent iron reacts to generate divalent iron, and zero-valent nickel reacts to generate divalent nickel. Hydrogen peroxide is a strong oxidant in a strongly acidic environment, and it can also directly oxidize zero-valent iron and zero-valent nickel, but the reaction rate is relatively slow from a kinetic point of view. The main role of hydrogen peroxide is to reoxidize divalent iron into trivalent iron. It can be considered that in the whole process of the metallographic etchant corroding the nickel-chromium-iron alloy, hydrogen peroxide acts as an oxidant, and trivalent iron acts as a catalyst. In addition, with hydrogen peroxide as an oxidant, the product of hydrogen peroxide reduction is water, and no other ions are generated, which will not affect the corrosion process.

[0042] In the metallographic etchant described in the present application, the role of citric acid is to form a complex with various metal ions as a chelating agent. Part of the corrosion resistance of nickel-chromium-iron alloys comes from the face-centered cubic crystal structure of nickel. The stability of its crystal structure allows it to form alloys with a variety of metal elements. Therefore, in addition to the three elements of nickel, chromium and iron, nickel-chromium-iron alloys generally also contain a variety of metal elements such as Mo, Ti, and Nb. The excellent corrosion resistance of nickel-chromium-iron alloys depends to a considerable extent on the composite effect of these metal elements. In the presence of hydrogen peroxide in the present application, nickel-chromium-iron alloys are prone to generate oxides with complex components on the surface due to the complexity of their elemental composition. These oxides will hinder the corrosion process of nickel-chromium-iron alloys, resulting in uneven corrosion of nickel-chromium-iron alloys, and unclear metallographic structures and grain boundaries. Citric acid directly dissolves after complexing with metal ions, making the above-mentioned oxides with complex components easily dissolve in a strong acidic environment. The complexing ability of citrate is stronger than citric acid molecules. In the highly acidic metallographic etching agent described in the present application, a part of citrate can be combined with hydrogen ions to generate citric acid, and the concentration of citrate is not high, which makes citric acid have a suitable complexing ability of strength as a complexing agent in the metallographic etching agent. The complexing ability of the complexing agent is too strong, and it will be complexed with ferric iron as an etching agent in large quantities, causing the corrosion ability of ferric iron to weaken, seriously affecting the corrosion efficiency. The complexing ability of the complexing agent is too weak, and it is not enough to suppress the generation of the oxide with complex components. Through the practice of the inventor, the complexing ability of citric acid in the hydrochloric acid environment is moderate, which can avoid the above-mentioned adverse effects. In addition, in the corrosion process, because zero-valent iron is continuously oxidized to ferrous ions, ferrous ions are oxidized to ferric ions by hydrogen peroxide, and the concentration of ferric ions presents an upward trend, and citric acid can be complexed with a part of ferric ions, so that the concentration fluctuation of ferric ions is not too large, thereby keeping the corrosion process relatively stable.

[0043] In addition, it should be noted that the metallographic etchant described in the present application contains both trivalent iron ions and phosphate ions in a water-soluble environment. Ferric phosphate has a small solubility product and is precipitated under neutral and alkaline conditions, but is soluble in hydrochloric acid solution.

[0044] The present application uses trivalent iron ions as an etchant and hydrogen peroxide as an oxidant, and can efficiently corrode nickel-chromium-iron alloys through trivalent iron ions, and then oxidize the generated divalent iron ions into trivalent iron ions through hydrogen peroxide, so that the corrosion process can continue; by adding citric acid, the generation of complex oxides on the surface of the nickel-chromium-iron alloy is suppressed, and the concentration change of trivalent iron ions is made more stable through complexation, so that the corrosion process is more uniform and stable. The metallographic etchant described in the present application can corrode nickel-chromium-iron alloys with high efficiency and obtain clear metallographic phases and grain boundaries.

[0045] In some embodiments of the present application, in the metallographic etchant, the concentration of ferric chloride is 0.01-0.05 g / mL, the concentration of citric acid is 0.002-0.012 g / mL, the concentration of phosphoric acid is 0.077-0.18 g / mL, and the concentration of hydrogen peroxide is 0.014-0.043 g / mL.

[0046] The metallographic etching agent adopts the above-mentioned proportion, and can corrode the nickel-chromium-iron alloy at a faster rate and a stable corrosion rate and form a clear metallographic phase and grain boundary.

[0047] In a second aspect, an embodiment of the present application provides a metallographic etching method, the metallographic etching method comprising the following steps:

[0048] S1: providing a metallographic corrosive agent and an alloy sample to be corroded, wherein the material of the alloy sample is a nickel-chromium-iron alloy;

[0049] S2: grinding and polishing the alloy sample to form a polished surface on the alloy sample;

[0050] S3: immersing the polished surface in the metallographic etching agent for etching until the polished surface appears light brown;

[0051] S4: taking out the alloy sample, cleaning the metallographic corrosive agent remaining on the surface of the alloy sample, and obtaining a well-corroded alloy sample.

[0052] Wherein, the metallographic etching agent is the metallographic etching agent described in any embodiment of the first aspect.

[0053] Since the metallographic etching method is implemented based on the metallographic etching agent described in any embodiment of the first aspect, the specific implementation of the metallographic etching method can refer to the above embodiments and common knowledge in the field. Since the metallographic etching method adopts part or all of the technical solutions of the above embodiments, it at least has all the beneficial effects brought by the technical solutions of the above embodiments, which will not be repeated here one by one.

[0054] In some embodiments of the present application, the polished alloy sample to be corroded is added to the metallographic corrosive agent for corrosion, and the corrosion of the alloy sample to be corroded is carried out at 60-80°C.

[0055] It is easy to understand that the beneficial effect of corroding the alloy sample to be corroded at 60-80° C. is that it can not only make the corrosion efficiency higher, but also keep the corrosion stable without uneven corrosion or unstable corrosion process.

[0056] As an example, the corrosion of the alloy sample to be corroded can be carried out at 60°C, 65°C, 70°C, 75°C, or 80°C.

[0057] In some embodiments of the present application, the polished alloy sample to be corroded is added to the metallographic corrosive agent for corrosion, and the duration of the corrosion of the alloy sample to be corroded is 30 to 40 seconds.

[0058] It is easy to understand that, under the premise that the corrosion of the alloy sample to be corroded is carried out at 60-80° C., the surface of the alloy sample to be corroded can usually be corroded in 30-40 seconds to form a clear metallographic phase and grain boundary.

[0059] In some embodiments of the present application, the alloy sample includes the following elemental components, measured in percentage by mass: 18% to 20% Cr, 50% to 55% Ni, 2.4% to 3% Mo, 4.75% to 5.5% Nb, 0.75% to 1.1% Ti, 0 to 1% Co, 0 to 0.7% Al, and the balance is Fe and unavoidable impurities.

[0060] In some embodiments of the present application, the grinding and polishing of the alloy sample comprises the following steps:

[0061] S21: mechanically rough grinding the alloy sample to form a rough ground surface on the alloy sample;

[0062] S22: mechanically fine-grinding the coarse-ground surface to form a fine-ground surface on the alloy sample;

[0063] S23: polishing the finely ground surface.

[0064] In some embodiments of the present application, the step of cleaning the metallographic corrosive agent remaining on the surface of the alloy sample comprises the following steps:

[0065] S41: Rinse the alloy sample with deionized water;

[0066] S42: washing the alloy sample with ethanol;

[0067] S43: Drying the alloy sample.

[0068] It is easy to understand that washing the alloy sample with deionized water first and then with ethanol can effectively remove inorganic and organic substances remaining on the surface of the alloy sample.

[0069] In some embodiments of the present application, the step of providing a metallographic etchant comprises the following steps:

[0070] S11: Mix ferric chloride, citric acid, hydrogen peroxide solution, hydrochloric acid solution, phosphoric acid solution, and deionized water to obtain the metallographic etching agent.

[0071] In a third aspect, an embodiment of the present application provides a metallographic observation method, the metallographic observation method comprising the following steps:

[0072] S5: providing an alloy sample according to any embodiment of the second aspect;

[0073] S6: Observe the polished surface of the alloy sample through an optical metallographic microscope.

[0074] The metallographic observation method is implemented based on the alloy sample described in any embodiment of the second aspect. The specific implementation of the metallographic observation method can refer to the above embodiments and common knowledge in the art. Since the metallographic observation method adopts part or all of the technical solutions of the above embodiments, it at least has all the beneficial effects brought by the technical solutions of the above embodiments, which will not be repeated here one by one.

[0075] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to industry standards. If there is no corresponding industry standard, then the conditions recommended by the manufacturer are followed.

[0076] Example 1

[0077] First, this embodiment provides a metallographic etching agent, which is prepared by the following method:

[0078] The metallographic etching agent is obtained by mixing 1.5 ml of ferric chloride, 0.6 ml of citric acid, 5 ml of 30% hydrogen peroxide solution, 35 ml of 34% hydrochloric acid solution, 15 ml of 85% phosphoric acid solution and 40 ml of deionized water.

[0079] Then, this embodiment provides a metallographic etching method, which comprises the following steps:

[0080] Providing an alloy sample to be corroded, wherein the material of the alloy sample is nickel-chromium-iron alloy;

[0081] Mechanically rough grinding the alloy sample to form a rough-ground surface on the alloy sample;

[0082] Performing mechanical fine grinding on the coarse ground surface to form a fine ground surface on the alloy sample;

[0083] Polishing the finely ground surface to form a polished surface on the alloy sample;

[0084] After heating the metallographic etching agent to 80° C., immersing the polished surface in the metallographic etching agent for etching, and the etching lasts for 30 seconds. After the etching is completed, the polished surface appears light brown;

[0085] The alloy sample is taken out, and firstly rinsed with deionized water, and then rinsed with ethanol, and then the washed alloy sample is dried to obtain a well-corroded alloy sample.

[0086] Wherein, the alloy sample includes the following elemental components in terms of mass percentage: 20% Cr, 50% Ni, 2.4% Mo, 5.5% Nb, 0.75% Ti, 0.3% Co, 0.7% Al, and the remainder is Fe and unavoidable impurities.

[0087] The polished surface of the alloy sample was observed by an optical metallographic microscope, and the obtained metallographic image was as follows: Figure 1 .Depend on Figure 1 It can be seen that the alloy sample has a distinct metallographic structure and a complete grain structure, and there is no uneven corrosion or over-corrosion.

[0088] Example 2

[0089] First, this embodiment provides a metallographic etching agent, which is prepared by the following method:

[0090] The metallographic etching agent is obtained by mixing 3 g of ferric chloride, 0.8 g of citric acid, 10 mL of 30% hydrogen peroxide solution, 25 mL of 34% hydrochloric acid solution, 10 mL of 85% phosphoric acid solution, and 30 mL of deionized water.

[0091] Then, this embodiment provides a metallographic etching method, which comprises the following steps:

[0092] Providing an alloy sample to be corroded, wherein the material of the alloy sample is nickel-chromium-iron alloy;

[0093] Mechanically rough grinding the alloy sample to form a rough-ground surface on the alloy sample;

[0094] Performing mechanical fine grinding on the coarse ground surface to form a fine ground surface on the alloy sample;

[0095] Polishing the finely ground surface to form a polished surface on the alloy sample;

[0096] After the metallographic etching agent is heated to 80° C., the polished surface is immersed in the metallographic etching agent for etching, and the etching lasts for 32 seconds. After the etching is completed, the polished surface appears light brown;

[0097] The alloy sample is taken out, and firstly rinsed with deionized water, and then rinsed with ethanol, and then the washed alloy sample is dried to obtain a well-corroded alloy sample.

[0098] Wherein, the alloy sample includes the following elemental components in terms of mass percentage: 20% Cr, 50% Ni, 2.4% Mo, 5.5% Nb, 0.75% Ti, 0.3% Co, 0.7% Al, and the remainder is Fe and unavoidable impurities.

[0099] By observing the polished surface of the alloy sample through an optical metallographic microscope, it can be observed that the alloy sample has a distinct metallographic structure, a complete grain structure, and no uneven corrosion or over-corrosion.

[0100] Example 3

[0101] First, this embodiment provides a metallographic etching agent, which is prepared by the following method:

[0102] The metallographic etching agent is obtained by mixing 1.9 g of ferric chloride, 0.7 g of citric acid, 8 mL of 30% hydrogen peroxide solution, 30 mL of 34% hydrochloric acid solution, 12 mL of 85% phosphoric acid solution, and 35 mL of deionized water.

[0103] Then, this embodiment provides a metallographic etching method, which comprises the following steps:

[0104] Providing an alloy sample to be corroded, wherein the material of the alloy sample is nickel-chromium-iron alloy;

[0105] Mechanically rough grinding the alloy sample to form a rough-ground surface on the alloy sample;

[0106] Performing mechanical fine grinding on the coarse ground surface to form a fine ground surface on the alloy sample;

[0107] Polishing the finely ground surface to form a polished surface on the alloy sample;

[0108] After the metallographic etching agent is heated to 70° C., the polished surface is immersed in the metallographic etching agent for etching, and the etching lasts for 40 seconds. After the etching is completed, the polished surface appears light brown;

[0109] The alloy sample is taken out, and firstly rinsed with deionized water, and then rinsed with ethanol, and then the washed alloy sample is dried to obtain a well-corroded alloy sample.

[0110] Wherein, the alloy sample includes the following elemental components in terms of mass percentage: 20% Cr, 50% Ni, 2.4% Mo, 5.5% Nb, 0.75% Ti, 0.3% Co, 0.7% Al, and the remainder is Fe and unavoidable impurities.

[0111] By observing the polished surface of the alloy sample through an optical metallographic microscope, it can be observed that the alloy sample has a distinct metallographic structure, a complete grain structure, and no uneven corrosion or over-corrosion.

[0112] Comparative Example 1

[0113] The difference between this comparative example and Example 1 is that citric acid and phosphoric acid are not added to the metallographic etchant in this comparative example. Since phosphoric acid has a large volume, the lack of phosphoric acid will have a great impact on the concentration of other components of the metallographic etchant, so an equal volume of deionized water is used instead. The details are as follows:

[0114] First, this comparative example provides a metallographic etching agent, which is prepared by the following method:

[0115] The metallographic etching agent is obtained by mixing 1.5 mL of ferric chloride, 5 mL of a 30% hydrogen peroxide solution, 35 mL of a 34% hydrochloric acid solution, and 55 mL of deionized water.

[0116] Then, this comparative example provides a metallographic corrosion method, which comprises the following steps:

[0117] Providing an alloy sample to be corroded, wherein the material of the alloy sample is nickel-chromium-iron alloy;

[0118] Mechanically rough grinding the alloy sample to form a rough-ground surface on the alloy sample;

[0119] Performing mechanical fine grinding on the coarse ground surface to form a fine ground surface on the alloy sample;

[0120] Polishing the finely ground surface to form a polished surface on the alloy sample;

[0121] After heating the metallographic etching agent to 80° C., immersing the polished surface in the metallographic etching agent for etching, and the etching lasts for 30 seconds. After the etching is completed, the polished surface appears light brown;

[0122] The alloy sample is taken out, and firstly rinsed with deionized water, and then rinsed with ethanol, and then the washed alloy sample is dried to obtain a well-corroded alloy sample.

[0123] Wherein, the alloy sample includes the following elemental components in terms of mass percentage: 20% Cr, 50% Ni, 2.4% Mo, 5.5% Nb, 0.75% Ti, 0.3% Co, 0.7% Al, and the remainder is Fe and unavoidable impurities.

[0124] The polished surface of the alloy sample was observed by optical metallographic microscope, and the metallographic image obtained is as follows: Figure 2 .Depend on Figure 2 Uneven corrosion was clearly observed, some areas were over-corroded, and the metallographic structure and grain boundaries were unclear.

[0125] Comparative Example 2

[0126] The difference between this comparative example and Example 1 is that the metallographic etching agent in this comparative example contains only nitric acid and hydrochloric acid. At the same time, the duration of etching is also different. The details are as follows:

[0127] First, this comparative example provides a metallographic etching agent, which is prepared by the following method:

[0128] The metallographic etching agent is obtained by mixing 15 mL of a 65% nitric acid solution, 35 mL of a 34% hydrochloric acid solution, and 50 mL of deionized water.

[0129] Then, this comparative example provides a metallographic corrosion method, which comprises the following steps:

[0130] Providing an alloy sample to be corroded, wherein the material of the alloy sample is nickel-chromium-iron alloy;

[0131] Mechanically rough grinding the alloy sample to form a rough-ground surface on the alloy sample;

[0132] Performing mechanical fine grinding on the coarse ground surface to form a fine ground surface on the alloy sample;

[0133] Polishing the finely ground surface to form a polished surface on the alloy sample;

[0134] After the metallographic etching agent is heated to 80° C., the polished surface is immersed in the metallographic etching agent for etching. The etching lasts for 18 minutes. After the etching is completed, the polished surface appears light brown.

[0135] The alloy sample is taken out, and firstly rinsed with deionized water, and then rinsed with ethanol, and then the washed alloy sample is dried to obtain a well-corroded alloy sample.

[0136] Wherein, the alloy sample includes the following elemental components in terms of mass percentage: 20% Cr, 50% Ni, 2.4% Mo, 5.5% Nb, 0.75% Ti, 0.3% Co, 0.7% Al, and the remainder is Fe and unavoidable impurities.

[0137] The polished surface of the alloy sample was observed by optical metallographic microscope, and the metallographic image obtained is as follows: Figure 3 .Depend on Figure 3It can be observed that the corrosion degree of the alloy sample is very low. This means that after 18 minutes of continuous corrosion, the corrosion effect of the metallographic etchant of Comparative Example 2 is not as good as the corrosion effect of the metallographic etchant of Example 1 which is only 30 seconds of corrosion. And Comparative Example 2 also has the problem of unclear metallographic structure and grain boundary.

[0138] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0139] In the present application, in the absence of any contrary description, the directional words used, such as "upper" and "lower", are specifically the directions of the drawings in the accompanying drawings. In addition, in the description of the present application specification, the terms "including", "comprising", etc. refer to "including but not limited to". Moreover, the terms "including", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or equipment. In the absence of further restrictions, the elements defined by the sentence "including..." do not exclude the existence of other identical elements in the process, method, article or equipment including the elements. In this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that there can be three relationships, for example, A and / or B, which can represent: A exists alone, A and B exist at the same time, and B exists alone. For the association relationship of more than three associated objects described by "and / or", it means that any one of these three associated objects can exist alone, or any at least two of them exist at the same time. For example, for A, and / or B, and / or C, it can be represented that any one of A, B, and C exists alone, or any two of them exist at the same time, or three of them exist at the same time. In this article, "at least one" refers to one or more, and "multiple" refers to two or more. "At least one", "the following at least one (individual)" or similar expressions refer to any combination of these items, including any combination of single (individual) or plural (individual). For example, "at least one (individual) of a, b, or c", or "at least one (individual) of a, b, and c", can all represent: a, b, c, ab (i.e. a and b), ac, bc, or abc, wherein a, b, and c can be single or multiple, respectively.

[0140] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A metallographic etching agent, characterized in that: The metallographic etching agent includes: ferric chloride, citric acid, phosphoric acid, hydrochloric acid, hydrogen peroxide and water.

2. The metallographic etching agent according to claim 1, characterized in that: In the metallographic etching agent, the concentration of ferric chloride is 0.01-0.05 g / mL, the concentration of citric acid is 0.002-0.012 g / mL, the concentration of phosphoric acid is 0.077-0.18 g / mL, and the concentration of hydrogen peroxide is 0.014-0.043 g / mL.

3. A metallographic etching method, characterized in that: The metallographic corrosion method comprises the following steps: Providing a metallographic corrosive agent and an alloy sample to be corroded, wherein the material of the alloy sample is a nickel-chromium-iron alloy; Grinding and polishing the alloy sample to form a polished surface on the alloy sample; Immersing the polished surface in the metallographic etching agent for etching until the polished surface appears light brown; The alloy sample is taken out, and the metallographic corrosive agent remaining on the surface of the alloy sample is cleaned to obtain a well-corroded alloy sample. Wherein, the metallographic etching agent is the metallographic etching agent described in any one of claims 1 to 2.

4. The metallographic etching method according to claim 3, characterized in that: The polished alloy sample to be corroded is added into the metallographic corrosive agent for corrosion, and the corrosion of the alloy sample to be corroded is carried out at 60-80°C.

5. The metallographic etching method according to claim 4, characterized in that: The polished alloy sample to be corroded is added into the metallographic corrosive agent for corrosion, and the duration of corrosion of the alloy sample to be corroded is 30 to 40 seconds.

6. The metallographic etching method according to claim 3, characterized in that: Calculated by mass percentage, the alloy sample includes the following elemental components: 18% to 20% Cr, 50% to 55% Ni, 2.4% to 3% Mo, 4.75% to 5.5% Nb, 0.75% to 1.1% Ti, 0 to 1% Co, 0 to 0.7% Al, Fe and unavoidable impurities.

7. The metallographic etching method according to claim 3, characterized in that: The grinding and polishing of the alloy sample comprises the following steps: Mechanically rough grinding the alloy sample to form a rough-ground surface on the alloy sample; Performing mechanical fine grinding on the coarse ground surface to form a fine ground surface on the alloy sample; The finely ground surface is polished.

8. The metallographic etching method according to claim 3, characterized in that: The cleaning of the metallographic corrosive agent remaining on the surface of the alloy sample comprises the following steps: Rinse the alloy sample with deionized water; washing the alloy sample with ethanol; The alloy sample is dried.

9. The metallographic etching method according to claim 3, characterized in that: The provision of a metallographic etching agent comprises the following steps: Ferric chloride, citric acid, hydrogen peroxide solution, hydrochloric acid solution, phosphoric acid solution and deionized water are mixed to obtain the metallographic etching agent.

10. A metallographic observation method, characterized in that: The metallographic observation method comprises the following steps: Providing an alloy sample according to any one of claims 3 to 9; The polished surface of the alloy sample was observed by optical metallographic microscope.

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