A method for etching the metallographic structure of high manganese steel for low temperature use

Abstract

The invention provides an etching method for the metallographic structure of high-manganese steel for low temperature use, comprising the following steps: S1, grinding a sample with water-sandpaper, and then polishing with flannel cloth, so that the polished surface of the sample is in a mirror state; S2, preparing a nitric acid aqueous solution and an oxalic acid ethanol solution, which are respectively recorded as etchant A and etchant B; S3, immersing the polished surface of the sample in the etchant A, shaking the sample, and leaving it for 4 to 7 seconds, so that a purple corrosion film layer is generated on the polished surface of the sample; S4, taking out the sample, and wiping the polished surface of the sample with the etchant B for 5 to 8 seconds, so that the purple corrosion film layer disappears; S5, rinsing the surface of the sample with deionized water, then rinsing with anhydrous ethanol, and drying. The etching method of the invention can display grain boundaries more clearly and completely than those etched by a traditional method, is simple and fast to operate, and can completely remove the surface oxide film layer, so that the metallographic structure can be observed more clearly and accurately.

Description

Technical Field

[0001] The invention belongs to the technical field of metallographic inspection of metal materials, and in particular relates to an erosion method for the metallographic structure of high-manganese steel for low temperature use. Background Art

[0002] Low-temperature high-manganese steel, with its high strength, good toughness, wear resistance, and processability, particularly its excellent low-temperature toughness, is expected to become a low-cost alternative to 9Ni steel for large LNG storage tanks, generating significant economic benefits. Metallographic characterization of high-manganese steel is a key step in metal material performance testing and is crucial for the promotion and application of low-temperature high-manganese steel.

[0003] In the process of detecting the metallographic structure of high manganese steel, the existing technology often adopts the following four methods to corrode the metallographic structure of high manganese steel: (1) etching with 4% nitric acid ethanol; (2) etching with glycerol mixed acid (HNO3:HCl:glycerol=1:2:3); (3) etching with saturated picric acid solution; (4) etching with reagent 1 (10-15% nitric acid ethanol solution) and wiping with reagent 2 (a mixed solution of 15 parts of hydrochloric acid, 3-5 parts of glycerol, and 100 parts of ethanol solution).

[0004] The existing methods for etching the metallographic structure of high manganese steel often have problems such as complicated reagent preparation, slow etching speed, unclear and incomplete intragranular / boundary precipitation after etching, and incomplete removal of the surface oxide film, which makes it impossible to observe the metallographic structure. Summary of the Invention

[0005] In view of this, the present invention aims to propose a method for etching the metallographic structure of high manganese steel for low temperature use, so as to solve the problems in the prior art of unclear and incomplete grain boundary display, incomplete removal of surface oxide film, and interference with metallographic analysis and evaluation after etching the metallographic structure of high manganese steel for low temperature use.

[0006] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] A method for etching the metallographic structure of low-temperature high-manganese steel comprises the following steps: S1, grinding a sample with wet sandpaper, and then polishing with flannel cloth, so that the polished surface of the sample is in a mirror state; S2, preparing a nitric acid aqueous solution and an oxalic acid ethanol solution, which are respectively recorded as etchant A and etchant B; S3, immersing the polished surface of the sample in etchant A, shaking the sample, and leaving it for 4 to 7 seconds, so that a purple corrosion film is formed on the polished surface of the sample; S4, removing the sample, and wiping the polished surface of the sample with etchant B for 5 to 8 seconds to eliminate the purple corrosion film; S5, rinsing the surface of the sample with deionized water, then rinsing with anhydrous ethanol, and drying it.

[0008] Furthermore, in step S1, the sample is polished in sequence using 80-mesh, 240-mesh, 400-mesh, and 800-mesh water sandpaper.

[0009] Furthermore, in step S2, 2 to 4 parts by volume of nitric acid are added to 100 parts by volume of deionized water, and stirred evenly to prepare an etchant A; 5 to 7 g of oxalic acid are added to 100 mL of anhydrous ethanol, and stirred evenly to prepare an etchant B;

[0010] Furthermore, in step S4, an absorbent cotton ball is dipped in the etchant B and wiped along one direction on the polished surface of the sample.

[0011] Compared with the prior art, the etching method for the metallographic structure of high manganese steel for low temperature use described in the present invention has the following advantages:

[0012] A kind of low-temperature high manganese steel metallographic structure erosion method of the present invention utilizes nitric acid aqueous solution to etch, and high manganese steel is corroded, can make high manganese steel surface quickly form a film layer, and corrosion waiting time is greatly reduced;Then utilize oxalic acid ethanol solution to wipe the corroded surface of high manganese steel material, on the one hand the weak acidity of oxalic acid will not continue to corrode high manganese steel, avoids the situation such as over-corrosion, grain boundary / intragranular precipitation phase falling off, on the other hand can more thoroughly remove the film layer, make metallographic structure grain boundary clear, precipitation phase will not fall off, be conducive to improving the accuracy of precipitation phase determination;Meanwhile, the reagents used in this application are all commonly used laboratory reagents, easy to buy and store, and the proportioning operation is simple. Thus the application reagent preparation is simple and quick, can reach the crystal / boundary precipitation display clear in metallographic structure, surface oxide film is removed cleanly, and metallographic structure is observed clearly and accurately. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0014] Figure 1 The metallographic structure of the low-temperature high-manganese steel obtained in Example 1 of the present invention (etched with nitric acid aqueous solution and wiped with oxalic acid ethanol solution);

[0015] Figure 2 This is the metallographic structure of the low-temperature high-manganese steel obtained in Comparative Example 1 of the present invention (etched with 4% nitric acid solution);

[0016] Figure 3 This is the metallographic structure of the low-temperature high manganese steel obtained in Comparative Example 2 of the present invention (glycerol mixed acid etching);

[0017] Figure 4This is the metallographic structure of the low-temperature high manganese steel obtained in Comparative Example 3 of the present invention (etching with a saturated picric acid solution);

[0018] Figure 5 This is the metallographic structure of the low-temperature high-manganese steel obtained in Comparative Example 4 of the present invention (etched with 12% nitric acid ethanol solution and wiped with a mixed solution of 15 parts of hydrochloric acid, 4 parts of glycerol, and 100 parts of ethanol). DETAILED DESCRIPTION

[0019] The inventive concepts of the present disclosure will be described below using terms commonly used by those skilled in the art to convey the essence of their work to other persons skilled in the art. However, these inventive concepts can be embodied in many different forms and should not be considered limited to the embodiments described herein.

[0020] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features therein may be combined with each other.

[0021] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0022] In the process of detecting the metallographic structure of high manganese steel, the existing technology often uses the following four methods to corrode the metallographic structure of high manganese steel: (1) etching with 4% nitric acid ethanol; (2) etching with glycerol mixed acid (HNO3:HCl:glycerol=1:2:3); (3) etching with saturated picric acid solution; (4) etching with reagent 1 (10-15% nitric acid ethanol solution) and wiping with reagent 2 (a mixed solution of 15 parts hydrochloric acid, 3-5 parts glycerol, and 100 parts ethanol solution). The existing technology for corroding the metallographic structure of high manganese steel often has problems such as difficult reagent preparation, slow etching speed, unclear and incomplete intragranular / boundary precipitation after etching, and incomplete removal of the surface oxide film, which makes it impossible to observe the metallographic structure.

[0023] In order to solve the problems in the prior art of unclear and incomplete grain boundary display, incomplete removal of surface oxide film, and interference with metallographic analysis and evaluation after corrosion of the metallographic structure of high manganese steel for low temperature, this embodiment proposes a method for etching the metallographic structure of high manganese steel for low temperature, comprising:

[0024] S1. Grind the sample with water sandpaper and then polish it with velvet cloth until the polished surface of the sample is mirror-like;

[0025] The samples in this application all refer to high manganese steel for low temperature use. The polishing is to polish the samples sequentially through 80 mesh, 240 mesh, 400 mesh, and 800 mesh water sandpaper.

[0026] S2. Prepare nitric acid aqueous solution and oxalic acid ethanol solution, and record them as etchant A and etchant B respectively;

[0027] Among them, take 2 to 4 parts by volume of nitric acid and add it to 100 parts by volume of deionized water, stir it evenly, and prepare etching agent A; take 5 to 7g of oxalic acid and add it to 100mL of anhydrous ethanol, stir it evenly, and prepare etching agent B;

[0028] S3. Immerse the polished surface of the sample in etchant A, shake the sample, and leave it for 4 to 7 seconds. A purple corrosion film will form on the polished surface of the sample.

[0029] The etchant A can be placed in a glass culture dish, and the polished surface of the sample is immersed in the etchant A facing downward.

[0030] S4. Take out the sample and wipe the polished surface of the sample with etchant B for 5 to 8 seconds to make the purple corrosion film disappear;

[0031] Among them, the etchant B was dipped in absorbent cotton and wiped in one direction on the polished surface of the sample. The disappearance of the purple corrosion film layer can be directly observed, and the shedding of the precipitated phase can be effectively avoided.

[0032] S5. Rinse the sample surface with deionized water, then rinse with anhydrous ethanol, blow dry, and then observe the metallographic structure.

[0033] The metallographic structure can be observed under a conventional metallographic microscope. The method of observing the metallographic structure can be directly carried out in accordance with existing technical specifications and laboratory operating specifications, and will not be elaborated on.

[0034] For the corrosion of high manganese steel, whether it is the existing corrosion process or the corrosion process of this application, a film layer will be formed on the corroded surface of the high manganese steel material. When observing the metallographic structure, the film layer needs to be completely removed to avoid interference with metallographic analysis and evaluation.

[0035] For this reason, according to the electrolysis ability of nitric acid in aqueous solution being greater than the electrolysis ability of nitric acid in anhydrous ethanol, the present application utilizes nitric acid aqueous solution to etch, and high manganese steel is corroded, and a layer of film can be formed quickly on the surface of high manganese steel, and the corrosion waiting time is greatly reduced; Then utilize oxalic acid ethanol solution to wipe the corroded surface of high manganese steel material, on the one hand, the weak acidity of oxalic acid will not continue to corrode high manganese steel, avoids the situation such as over-corrosion, grain boundary / intragranular precipitation phase falling off, on the other hand, can more thoroughly remove film layer, make metallographic structure grain boundary clear, precipitation phase will not fall off, be conducive to improving the accuracy of precipitation phase determination; At the same time, the reagents adopted in the present application are all commonly used laboratory reagents, easy to buy and store, and the proportioning operation is simple. Thus the present application reagent preparation is simple and quick, can reach the crystal / boundary precipitation display clear in metallographic structure, surface oxide film is removed cleanly, and metallographic structure is observed clearly and accurately.

[0036] Using grade Mn22 steel material as a sample, Example 1 and Comparative Examples 1-4 were carried out respectively, and the specific contents are as follows.

[0037] Example 1

[0038] The corrosion method of this application was used to corrode the sample of grade Mn22 steel material, specifically:

[0039] S1. The sample was polished with 80-mesh, 240-mesh, 400-mesh, and 800-mesh water sandpaper, and then polished with velvet cloth to a mirror finish.

[0040] S2. Add 2 parts by volume of nitric acid to 100 parts by volume of deionized water, stir evenly, and prepare etchant A; add 5g of oxalic acid to 100mL of anhydrous ethanol, stir evenly, and prepare etchant B;

[0041] S3. Immerse the polished metallographic specimen with the polished surface facing downward into a glass petri dish filled with etchant A. Gently shake the specimen and wait for 5 seconds until a purple corrosion film is observed on the surface.

[0042] S4. After taking out the sample, use absorbent cotton dipped in etchant B to wipe it in one direction for 5 seconds. It is observed that the purple film on the metallographic grinding surface of the sample disappears.

[0043] S5. After wiping the sample in step S4, rinse the sample surface with deionized water, then rinse with anhydrous ethanol, and blow dry; observe the metallographic structure under a metallographic microscope, and the results are shown as follows: Figure 1 shown.

[0044] Comparative Example 1

[0045] The sample was etched with 4% nitric acid ethanol solution, specifically:

[0046] S1, consistent with step S1 of Example 1;

[0047] S2, adding 4 parts by volume of nitric acid to 100 parts by volume of ethanol, stirring evenly to obtain a 4% nitric acid ethanol solution;

[0048] S3. Immerse the polished surface of the metallographic specimen in 4% nitric acid ethanol solution, gently shake the specimen, and leave it for 52 seconds;

[0049] S4. Rinse the sample surface with deionized water, then rinse with anhydrous ethanol, and blow dry; observe the metallographic structure under a metallographic microscope, and the results are as follows: Figure 2 shown.

[0050] Comparative Example 2

[0051] The sample was etched with glycerol mixed acid (HNO3:HCl:glycerol=1:2:3), specifically:

[0052] S1, consistent with step S1 of Example 1;

[0053] S2. Mix HNO3, HCl, and glycerol in a volume ratio of 1:2:3 and stir evenly to obtain a glycerol mixed acid;

[0054] S3. Immerse the polished surface of the metallographic specimen in glycerol mixed acid, gently shake the specimen, and leave it for 223 seconds;

[0055] S4. Rinse the sample surface with deionized water, then rinse with anhydrous ethanol, and blow dry; observe the metallographic structure under a metallographic microscope, and the results are as follows: Figure 3 shown.

[0056] Comparative Example 3

[0057] The sample was etched with a saturated picric acid solution. Specifically:

[0058] S1, consistent with step S1 of Example 1;

[0059] S2. Gradually add excess picric acid to water and stir until the solution is saturated to obtain a saturated picric acid solution;

[0060] S3. Immerse the polished surface of the metallographic specimen in a saturated picric acid solution, gently shake the specimen, and leave it for 156 seconds.

[0061] S4. Rinse the sample surface with deionized water, then rinse with anhydrous ethanol, and blow dry; observe the metallographic structure under a metallographic microscope, and the results are as follows: Figure 4 shown.

[0062] Comparative Example 4

[0063] The sample was treated by etching with reagent 1 (12% nitric acid ethanol solution) and wiping with reagent 2 (a mixture of 15 parts hydrochloric acid, 4 parts glycerol, and 100 parts ethanol solution). Specifically:

[0064] S1, consistent with step S1 of Example 1;

[0065] S2. Add 12 parts by volume of nitric acid to 100 parts by volume of ethanol and stir to prepare reagent 1; mix 15 parts of hydrochloric acid, 4 parts of glycerol and 100 parts of ethanol solution and stir to prepare reagent 2;

[0066] S3. Immerse the polished surface of the metallographic specimen in reagent 1, gently shake the specimen, and leave it for 40 seconds;

[0067] S4. After taking out the sample, dip the absorbent cotton in reagent 2 and wipe it in one direction for 5 seconds.

[0068] S5. After wiping the sample in step S4, rinse the sample surface with deionized water, then rinse with anhydrous ethanol, and blow dry; observe the metallographic structure under a metallographic microscope, and the results are shown as follows: Figure 5 shown.

[0069] The metallographic structures of Example 1 and Comparative Examples 1-4 were observed (see attached Figure 1-5 As shown), comparison and summary, we can see that:

[0070] The etching speed of Example 1 is faster, the surface film is removed thoroughly, the grain boundaries are clear, and the microstructure observation effect is good. Figure 1 .

[0071] The etching of comparative example 1 was slow, the surface film layer was not removed, and the tissue observation was greatly affected. Figure 2 , and there are a lot of unremoved yellow-brown membrane layers in the picture.

[0072] The etching of comparative example 2 is slow, the grain boundary display is incomplete, the tissue contrast is poor, and the tissue display is unclear. Figure 3 , and there are a lot of unremoved light yellow film layers in the picture.

[0073] The etching of comparative example 3 was slow, the surface film layer was not removed, and the structure was uneven. Figure 4 , the picture shows a large amount of yellow film that has not been removed.

[0074] The etching time of Comparative Example 4 is shorter than that of Comparative Examples 1-3, but the surface film is not completely removed, which affects the tissue observation. Figure 5 , the picture shows a yellowish-brown film layer that has not been completely removed.

[0075] A comparison reveals that the four existing etching methods often suffer from issues such as slow etching speed, unclear intragranular / boundary precipitation, difficulty controlling film wiping, and incomplete film removal. This is because the existing methods leave a residual film after etching high-manganese steel, and wiping with strong acids such as nitric acid and hydrochloric acid is time-constrained and should not be done for extended periods. This makes it difficult to completely remove the film, hindering metallographic observation.

[0076] The present application solves the above-mentioned problem by using a dilute nitric acid aqueous solution to etch the surface in the first step, quickly generating a purple film layer, and then using an oxalic acid anhydrous ethanol solution to wipe and remove the film layer in the second step. The first step of this method accelerates the etching speed, and the second step utilizes the weak acidity of oxalic acid, which is easy to control during the wiping process, so that the wiping time can be appropriately extended, and the wiping can be repeated, so that the film layer is completely removed, and the grain boundary / intracrystalline precipitate phase is not affected. Compared with the prior art, the method of the present application has a simple solution ratio, a short etching time, and a complete removal of the film layer, avoiding the problem of loss of the intracrystalline / boundary precipitate phase due to wiping. In addition, since oxalic acid is easily soluble in anhydrous ethanol, the ratio of oxalic acid and anhydrous ethanol can be adjusted according to the difficulty of removing the film layer. This makes the etching method involved in the present application have the advantages of clear and complete display of grain boundaries, simple and rapid operation, and simple reagent ratio compared to the traditional method.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for etching the metallographic structure of high manganese steel for low temperature use, characterized in that: The method comprises: S1. Grind the sample with water sandpaper and then polish it with velvet cloth until the polished surface of the sample is mirror-like; S2. Prepare nitric acid aqueous solution and oxalic acid ethanol solution, and record them as etchant A and etchant B respectively; S3. Immerse the polished surface of the sample in etchant A, shake the sample, and leave it for 4 to 7 seconds. A purple corrosion film will form on the polished surface of the sample. S4. Take out the sample and wipe the polished surface of the sample with etchant B for 5 to 8 seconds to make the purple corrosion film disappear; S5. Rinse the sample surface with deionized water, then rinse with anhydrous ethanol, and blow dry; In step S2, 2 to 4 parts by volume of nitric acid are added to 100 parts by volume of deionized water, and stirred evenly to prepare an etchant A; 5 to 7 g of oxalic acid are added to 100 mL of anhydrous ethanol, and stirred evenly to prepare an etchant B.

2. The method for etching the metallographic structure of high manganese steel for low temperature use according to claim 1, characterized in that: In step S1 , the sample is polished in sequence using 80-mesh, 240-mesh, 400-mesh, and 800-mesh water sandpaper.

3. The method for etching the metallographic structure of high manganese steel for low temperature use according to claim 1, characterized in that: In step S4, an absorbent cotton ball is dipped in the etchant B and wiped along one direction on the polished surface of the sample.

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