4Cr13 stainless steel metallographic etchant and corrosion method for displaying carbide
By using an etching solution composed of glacial acetic acid, ammonium persulfate, and sodium molybdate to form a nanofilm on the surface of 4Cr13 stainless steel, the problem of difficult color development of carbides in martensitic stainless steel was solved, enabling safe, environmentally friendly, and clear observation of carbides.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHAANXI FAST AUTO DRIVE GRP CO LTD
- Filing Date
- 2026-02-02
- Publication Date
- 2026-05-08
AI Technical Summary
Existing etchants for martensitic stainless steel have problems such as difficulty in controlling corrosion time, difficulty in obtaining reagents, significant safety hazards, and difficulty in distinguishing metallographic structures. In particular, it is difficult to develop carbide color, and traditional etchants often contain highly toxic or strongly corrosive substances.
A corrosion solution composed of glacial acetic acid, ammonium persulfate, and sodium molybdate, free of bitter acids, heavy metals, and strong inorganic acids, was used to etch 4Cr13 stainless steel at 40℃~50℃ for 10min~20min. The molybdate ions formed a nanofilm on the carbide surface, producing a blue-black contrast, which significantly improved the visualization effect of the carbide.
It achieves clear color development of carbides, reduces the complexity of waste treatment after corrosion, improves operational safety and environmental friendliness, avoids the risks of highly toxicity and violent explosions, and has a color development effect superior to traditional methods.
Smart Images
Figure CN121992408A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of performance testing technology for martensitic stainless steel, and specifically relates to a metallographic etching solution for 4Cr13 stainless steel and a etching method for displaying carbides. Background Technology
[0002] Martensitic stainless steel is widely used in industrial fields due to its excellent mechanical properties, good wear resistance, and corrosion resistance. Applications include structural components such as gears and bearings, automotive parts, hot-working dies, turbine blades, oil and gas valves, cutting tools, and medical devices. Metallographic analysis is an irreplaceable analytical method for evaluating material properties, and etching agents are key to obtaining a clear metallographic structure.
[0003] Currently, the main traditional etchants for martensitic stainless steel include: high ferric chloride + hydrochloric acid aqueous solution, nitric acid + hydrochloric acid aqueous solution, picric acid + hydrochloric acid + alcohol solution, and aqua regia glycerol. They primarily differentiate the microstructure by altering the surface contrast of the material. The core drawbacks and pain points are: 1. Difficulty in controlling the corrosion time, because during FeCl3 etching, sulfur-oxygen complex inclusions in the sample matrix react with the Cl... -1 1. Under corrosion, micropores are formed after detachment, and these micropores enlarge with prolonged etching time, resulting in numerous black spots on the sample surface. This misleads inspectors, increases the difficulty of analysis, and requires the recovery of heavy metals, making waste liquid treatment complex. 2. Reagents are difficult to obtain; concentrated nitric acid is a controlled reagent and difficult to purchase. Picric acid is highly effective in identifying carbides, but due to its extreme toxicity and explosiveness, it is currently unavailable. 3. Significant safety hazards exist. Picric acid is highly toxic; even small amounts ingested or inhaled can be fatal, and trace amounts can cause gastroenteritis, hemorrhagic nephritis, and acute hepatitis. Picric acid is prone to violent explosions upon friction or vibration. Concentrated sulfuric acid, nitric acid, and hydrochloric acid are extremely corrosive, posing significant safety hazards during use. 4. Metallographic structures are difficult to distinguish; multiple structures appear simultaneously after etching, but the contrast between structures is not obvious, making it difficult to observe specific structures. For example, the wear resistance of martensitic stainless steel mainly depends on the morphology and distribution of carbides in the microstructure. When observing the metallographic structure, special attention should be paid to the morphology and distribution of carbides. Therefore, there is an urgent need for a green, environmentally friendly and readily available corrosion solution that can clearly identify the carbides in 4Cr13 stainless steel. Summary of the Invention
[0004] To address the shortcomings of the prior art, the present invention aims to provide a metallographic etching solution for 4Cr13 stainless steel and a etching method for displaying carbides. The etching solution is free of picric acid, heavy metals, and strong inorganic acids, and can be used to display carbides, thereby achieving directional identification of carbide structures in martensitic stainless steel.
[0005] To solve the above-mentioned technical problems, the present invention provides a metallographic etching solution for 4Cr13 stainless steel, which is made of the following components: 10 mL glacial acetic acid, 1 g to 2 g ammonium persulfate, 0.5 g to 1 g sodium molybdate, 80 mL anhydrous ethanol and 10 mL deionized water.
[0006] Preferably, the corrosive solution is prepared from the following components: 10 mL glacial acetic acid, 1 g to 1.5 g ammonium persulfate, 0.5 g to 0.8 g sodium molybdate, 80 mL anhydrous ethanol and 10 mL deionized water.
[0007] Preferably, the corrosive solution is made from the following components: 10 mL glacial acetic acid, 1.5 g ammonium persulfate, 0.5 g sodium molybdate, 80 mL anhydrous ethanol and 10 mL deionized water.
[0008] Preferably, the martensitic stainless steel used for metallographic analysis of the corrosion solution is 4Cr13 stainless steel.
[0009] This invention provides a method for preparing an etching solution for metallographic testing of martensitic stainless steel, comprising the following steps: Ammonium persulfate and sodium molybdate are dissolved in deionized water and stirred until completely dissolved to obtain solution A; Solution B is obtained by mixing glacial acetic acid with anhydrous ethanol; Pour solution A into solution B, stir until the mixture becomes transparent, seal and store in the dark to obtain the corrosive solution; The mass ratio of ammonium persulfate to sodium molybdate is 1~2:0.5~1; the volume ratio of glacial acetic acid to anhydrous ethanol and deionized water is 1~1.5:7~8:1~1.5.
[0010] This invention provides a method for displaying carbides in a metallographic etching solution for 4Cr13 stainless steel, comprising the following steps: 4Cr13 stainless steel is prepared for polishing and ready for use. Preparation of corrosive solution; The prepared 4Cr13 stainless steel was completely immersed in the etching solution, and the polished mirror surface of the 4Cr13 stainless steel was placed upwards. It was then etched at a temperature of 40℃~50℃ for 10min~20min. After observing that the etched surface turned yellow, the sample was removed, rinsed with anhydrous ethanol, and dried.
[0011] Preferably, the heating temperature is 50°C and the corrosion time is 15 minutes.
[0012] Preferably, the pretreatment steps for polishing the 4Cr13 stainless steel are as follows: wire cutting a 4Cr13 stainless steel test block, grinding it flat with a flat grinder, coarse grinding and fine grinding with metallographic sandpaper until polished to a mirror finish, rinsing and drying for later use.
[0013] There are two reasons for placing the polished side upwards: firstly, placing it upwards ensures that the septa are on the same horizontal plane, resulting in uniform corrosion; secondly, having the corroded side upwards facilitates observation of the corrosion process. The corrosion temperature is set to appropriately accelerate the corrosion process and shorten the corrosion time.
[0014] Preferably, the 4Cr13 stainless steel is composed of the following elements in mass percentage: C 0.36%~0.45%, Cr 12.00%~14.00%, Si≤0.60%, Mn≤0.80%, P≤0.040%, S≤0.030%, Ni≤0.60%, with the remainder being Fe and unavoidable impurities.
[0015] Compared with the prior art, the beneficial effects of the present invention are: In the corrosion solution provided in this invention, glacial acetic acid, being a weak organic acid solvent, provides an acidic environment that is more environmentally friendly and has a controllable odor than inorganic acids. It provides gentle dissolution, reducing grain boundary over-corrosion. Ammonium persulfate, a mild oxidant, releases active oxygen in the acidic environment, selectively destroying the passivation film and enhancing grain and phase boundary corrosion, while avoiding strong acids or heavy metals. Molybdate ions from sodium molybdate adsorb onto the carbide surface, forming a MoO2 / MoO3 nanofilm. Through optical interference, this produces a blue-black contrast, significantly improving the contrast of the carbide and replacing toxic picric acid. Anhydrous ethanol, an environmentally friendly organic solvent, reduces the reaction rate, improves uniformity, and is environmentally friendly.
[0016] The molybdate ions in the etching solution prepared in this invention can undergo a deposition reaction on the carbide surface of 4Cr13 stainless steel, forming a nanoscale molybdenum oxide film, which produces a blue-black contrast through optical interference. The application of molybdate in the metallography of martensitic stainless steel has not been reported in China before, perfectly solving the problem of carbide color development.
[0017] The molybdate in this etching solution can also directionally etch carbides in the metallographic structure, making the contrast between the carbides and other structures significantly different. This allows for accurate observation of the distribution and morphology of the carbides, resulting in a clearer structure. Because the etching solution prepared by this invention contains no strong acid, no picric acid (an explosive), and no heavy metals, the main waste after etching is converted into biodegradable acetate / molybdate, making it more environmentally friendly. Furthermore, this etching solution does not produce any volatile highly toxic gases during preparation (compared to aqua regia and mixed acids), and compared to picric acid, it poses no explosion risk, requiring only basic ventilation, making the preparation process safer. Attached Figure Description
[0018] Figure 1 This is a metallographic image of the carbide structure of 4Cr13 stainless steel in Example 1 of the present invention.
[0019] Figure 2 This is a metallographic image of the uncorroded carbide structure of 4Cr13 stainless steel in Comparative Example 1 of this invention.
[0020] Figure 3 This is a metallographic image of the uncorroded carbide structure of 4Cr13 stainless steel in Comparative Example 2 of the present invention.
[0021] Figure 4 This is a metallographic image of the uncorroded carbide structure of 4Cr13 stainless steel in Comparative Example 3 of the present invention.
[0022] Figure 5 This is a physical diagram of the preparation of the corrosive solution for Comparative Example 4 of the present invention.
[0023] Figure 6 The image shows the metallographic structure of the 4Cr13 stainless steel used in Comparative Example 5 of this invention, which has a carbide microstructure.
[0024] Figure 7 The image shows the metallographic structure of the 4Cr13 stainless steel used in Comparative Example 6 of this invention, which has a carbide microstructure.
[0025] Figure 8 The image shows the metallographic structure of the 4Cr13 stainless steel used in Comparative Example 7 of this invention, which has a carbide microstructure. Detailed Implementation
[0026] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods.
[0027] It should be noted that when numerical ranges are involved in this invention, it should be understood that the two endpoints of each numerical range, as well as any value between the two endpoints, can be selected. Since the steps and methods used are the same as in Examples 1 to 8, preferred embodiments are described to avoid redundancy. However, this invention is not limited to these embodiments and can be implemented in other ways within the scope of the technical solutions defined in the appended claims. All raw materials, reagents, instruments, and equipment used in the following embodiments of this invention can be purchased commercially or prepared using existing methods.
[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, using preferred embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.
[0029] This invention provides an etching solution for metallographic testing of martensitic stainless steel, a preparation method thereof, and a method for displaying carbide corrosion. The etching solution is free of picric acid, heavy metals, and strong inorganic acids, and can be used to display carbides, thereby achieving directional identification of carbide structures in martensitic stainless steel.
[0030] The following are specific examples of preparing metallographic etching solutions for 4Cr13 stainless steel.
[0031] Example 1 A method for preparing a metallographic etching solution for 4Cr13 stainless steel includes the following steps: Dissolve 1.5g of ammonium persulfate and 0.5g of sodium molybdate in 10mL of deionized water and stir until completely dissolved to obtain solution A.
[0032] Solution B is obtained by mixing 10 mL of glacial acetic acid with 80 mL of anhydrous ethanol.
[0033] Pour solution A into solution B and stir until the mixture becomes transparent. Seal and store in the dark to obtain the etching solution. The etching solution for metallographic testing of 4Cr13 stainless steel is made of the following components: 10mL glacial acetic acid, 1.5g ammonium persulfate, 0.5g sodium molybdate, 80mL anhydrous ethanol and 10mL deionized water.
[0034] Example 2 A method for preparing a metallographic etching solution for 4Cr13 stainless steel includes the following steps: Dissolve 1g of ammonium persulfate and 0.8g of sodium molybdate in 15mL of deionized water and stir until completely dissolved to obtain solution A.
[0035] Solution B is obtained by mixing 15 mL of glacial acetic acid with 70 mL of anhydrous ethanol.
[0036] Pour solution A into solution B and stir until the mixture becomes transparent. Seal and store in the dark to obtain the etching solution. The etching solution for metallographic testing of 4Cr13 stainless steel is made from the following components: 15mL glacial acetic acid, 1g ammonium persulfate, 0.8g sodium molybdate, 70mL anhydrous ethanol and 15mL deionized water.
[0037] Example 3 A method for preparing a metallographic etching solution for 4Cr13 stainless steel includes the following steps: Dissolve 2g of ammonium persulfate and 1g of sodium molybdate in 12mL of deionized water and stir until completely dissolved to obtain solution A.
[0038] Solution B is obtained by mixing 12 mL of glacial acetic acid with 75 mL of anhydrous ethanol.
[0039] Pour solution A into solution B and stir until the mixture becomes transparent. Seal and store in the dark to obtain the etching solution. The etching solution for metallographic testing of 4Cr13 stainless steel is made of the following components: 12mL glacial acetic acid, 1g ammonium persulfate, 0.8g sodium molybdate, 75mL anhydrous ethanol and 12mL deionized water.
[0040] Example 4 A method for preparing a metallographic etching solution for 4Cr13 stainless steel includes the following steps: Dissolve 1.2g of ammonium persulfate and 0.6g of sodium molybdate in 10mL of deionized water and stir until completely dissolved to obtain solution A.
[0041] Solution B is obtained by mixing 10 mL of glacial acetic acid with 80 mL of anhydrous ethanol.
[0042] Pour solution A into solution B and stir until the mixture becomes transparent. Seal and store in the dark to obtain the etching solution. The etching solution for metallographic testing of 4Cr13 stainless steel is made of the following components: 10 mL glacial acetic acid, 1.2 g ammonium persulfate, 0.6 g sodium molybdate, 80 mL anhydrous ethanol and 10 mL deionized water.
[0043] Example 5 A method for preparing a metallographic etching solution for 4Cr13 stainless steel includes the following steps: Dissolve 1.5g of ammonium persulfate and 0.5g of sodium molybdate in 15mL of deionized water and stir until completely dissolved to obtain solution A.
[0044] Solution B is obtained by mixing 10 mL of glacial acetic acid with 80 mL of anhydrous ethanol.
[0045] Pour solution A into solution B and stir until the mixture becomes transparent. Seal and store in the dark to obtain the etching solution. The etching solution for metallographic testing of 4Cr13 stainless steel is made of the following components: 10mL glacial acetic acid, 1.5g ammonium persulfate, 0.5g sodium molybdate, 80mL anhydrous ethanol and 15mL deionized water.
[0046] Examples 1 to 5 above can all prepare 4Cr13 metallographic etching solutions. The 4Cr13 metallographic etching solution prepared in Example 1 is preferred for displaying carbide corrosion in the following examples.
[0047] Example 6 A method for displaying carbides in a 4Cr13 metallographic etching solution includes the following steps: 4Cr13 stainless steel with the following elemental composition by mass percentage: C 0.36%, Cr 12.00%, Si≤0.60%, Mn≤0.80%, P≤0.040%, S≤0.030%, Ni≤0.60%, with the remainder being Fe and unavoidable impurities, was wire-cut, ground flat with a flat grinder, and then coarsely and finely ground with metallographic sandpaper until polished to a mirror finish. It was then rinsed and dried for later use.
[0048] The spare 4Cr13 stainless steel was completely immersed in the organic etching solution prepared in Example 1, and the polished mirror surface of the 4Cr13 stainless steel was placed upwards. The container holding the etching solution was placed in a constant temperature water bath at 50°C and etched for 15 minutes. After observing that the etched surface turned yellow, the sample was removed, rinsed with anhydrous ethanol, and dried.
[0049] Example 7 A method for displaying carbides in a 4Cr13 metallographic etching solution includes the following steps: 4Cr13 stainless steel with the following elemental composition by mass percentage: C 0.45%, Cr 14.00%, Si≤0.60%, Mn≤0.80%, P≤0.040%, S≤0.030%, Ni≤0.60%, with the remainder being Fe and unavoidable impurities, was wire-cut, ground flat with a flat grinder, and then coarsely and finely ground with metallographic sandpaper until polished to a mirror finish. It was then rinsed and dried for later use.
[0050] The prepared 4Cr13 stainless steel was completely immersed in the etching solution prepared in Example 1, with the polished mirror surface of the 4Cr13 stainless steel facing upwards. The container holding the etching solution was placed in a constant temperature water bath at 40°C and etched for 20 minutes. After observing that the etched surface turned yellow, the sample was removed, rinsed with anhydrous ethanol, and dried. Example 8 A method for displaying carbides in a 4Cr13 metallographic etching solution includes the following steps: 4Cr13 stainless steel with the following elemental composition by mass percentage: C 0.40%, Cr 13.00%, Si≤0.60%, Mn≤0.80%, P≤0.040%, S≤0.030%, Ni≤0.60%, with the remainder being Fe and unavoidable impurities, was wire-cut, ground flat with a flat grinder, and then coarsely and finely ground with metallographic sandpaper until polished to a mirror finish. It was then rinsed and dried for later use.
[0051] The spare 4Cr13 stainless steel was completely immersed in the organic etching solution prepared in Example 1, and the polished mirror surface of the 4Cr13 stainless steel was placed upwards. The container holding the etching solution was placed in a constant temperature water bath at 45°C and etched for 10 minutes. After observing that the etched surface turned yellow, the sample was removed, rinsed with anhydrous ethanol, and dried.
[0052] Comparative Example 1 The only difference between Comparative Example 1 and Example 6 is the etching solution, in which 1.5g of ammonium persulfate was not added.
[0053] Comparative Example 2 The only difference between Comparative Example 2 and Example 6 is the etching solution, in which 0.5g of sodium molybdate was not added.
[0054] The only difference between Comparative Example 3 and Example 6 is the etching solution, in which sodium molybdate and ammonium persulfate were added at masses of 0.1 and 3 g, respectively.
[0055] Comparative Example 4 The only difference between Comparative Example 4 and Example 6 is the etching solution, in which sodium molybdate and ammonium persulfate were added in a solution with masses of 2 and 0.1 g, respectively.
[0056] Comparative Example 5 The only difference between Comparative Example 5 and Example 6 is that there is no restriction on placing the polished 4Cr13 stainless steel mirror side up.
[0057] Comparative Example 6 The only difference between Comparative Example 6 and Example 6 is that the heating temperature is 60°C and the corrosion time is 5 minutes.
[0058] Comparative Example 7 The only difference between Comparative Example 7 and Example 6 is that the heating temperature is 30°C and the corrosion time is 25 min.
[0059] The methods given in Examples 6 to 8 above can all be used to display the corrosion of carbides. The 4Cr13 stainless steel after corrosion in Example 6 is preferably tested using a ZEISS Observer Alm inverted metallographic microscope.
[0060] Figure 1 The image shows the metallographic structure of the 4Cr13 stainless steel after corrosion in Example 6. Figure 1 It can be seen that, when observed under bright field using a ZEISS Observer Alm inverted metallographic microscope, the matrix appears yellow, the carbides appear black, the carbides are fine granular, and there is a tendency for banding in some areas.
[0061] Figures 2-4The etching solutions prepared in Comparative Examples 1 to 3 were used to display the metallographic images of 4Cr13 stainless steel that had not been corroded in the carbide corrosion test. It was found that because the etching solution prepared in Comparative Example 1 lacked ammonium persulfate, the etching solution prepared in Comparative Example 2 lacked sodium molybdate, and the mass ratio of sodium molybdate to ammonium persulfate in the etching solution prepared in Comparative Example 3 was not within the range of 1~2:0.5~1, the etching solutions prepared in Comparative Examples 1 to 3 could not be used to complete the metallographic test of 4Cr13 stainless steel when used to display carbide corrosion.
[0062] Figure 5 The etching solutions prepared for Comparative Example 4, consisting of sodium molybdate and ammonium persulfate with masses of 2 and 0.1 g respectively, were prepared by... Figure 5 It is evident that corrosion tests cannot be performed on solutions with precipitates.
[0063] Figure 6 Metallographic image of a polished mirror-finished 4Cr13 stainless steel specimen, viewed sideways, showing corrosion testing of carbides. Figure 6 It can be seen that the right side of the metallographic test image of the corrosion test is darker than the left side. This is because the right side of the 4Cr13 stainless steel is placed below the corrosion solution, while the left side is placed above the corrosion solution. Since the heat source providing the corrosion solution is located below the polished mirror surface of the 4Cr13 stainless steel and closer to the heat source, the right side of the 4Cr13 stainless steel immersed in the corrosion solution corrodes faster and is darker in color, which is not conducive to displaying carbide corrosion.
[0064] Figure 7 Metallographic images of 4Cr13 stainless steel showing carbide corrosion test results, by Figure 7 It can be seen that the metallographic test pattern of the corrosion test shows a light color, insufficient and uneven color development, and incomplete display of carbides. This is because the heating temperature is 45~50℃ higher than the set temperature, which will accelerate the corrosion reaction to a certain extent, but the corrosion time is shorter than the set time, resulting in insufficient corrosion. At the same time, the higher temperature will accelerate the precipitation of the corrosion solution. Therefore, this corrosion method for displaying carbides is not suitable for displaying carbide corrosion.
[0065] Figure 8 Metallographic images of 4Cr13 stainless steel showing carbide corrosion test results, by Figure 8 It can be seen that the metallographic test images from the corrosion test show uneven color development, with varying shades in some areas. This is because when the temperature is 45-50℃ lower than the set temperature, the corrosion reaction is delayed. Although the corrosion time is longer than the set time, the corrosion reaction still proceeds slowly at lower temperatures. Therefore, this corrosion method for displaying carbides is not suitable for displaying carbide corrosion.
[0066] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.
Claims
1. A metallographic etching solution for 4Cr13 stainless steel, characterized in that, This etchant is used to etch 4Cr13 stainless steel and is made from the following components: 10 mL to 15 mL of glacial acetic acid, 1 g to 2 g of ammonium persulfate, 0.5 g to 1 g of sodium molybdate, 70 mL to 80 mL of anhydrous ethanol, and 10 mL to 15 mL of deionized water.
2. The martensitic stainless steel metallographic etching solution according to claim 1, characterized in that, The corrosive solution is made from the following components: 10 mL glacial acetic acid, 1 g to 1.5 g ammonium persulfate, 0.5 g to 0.8 g sodium molybdate, 80 mL anhydrous ethanol, and 10 mL deionized water.
3. The metallographic etching solution for 4Cr13 stainless steel according to claim 1, characterized in that, The corrosive solution is made from the following components: 10 mL glacial acetic acid, 1.5 g ammonium persulfate, 0.5 g sodium molybdate, 80 mL anhydrous ethanol, and 10 mL deionized water.
4. The method for preparing the metallographic etching solution for 4Cr13 stainless steel according to claim 1, characterized in that, Includes the following steps: Ammonium persulfate and sodium molybdate are dissolved in deionized water and stirred until completely dissolved to obtain solution A; Solution B is obtained by mixing glacial acetic acid with anhydrous ethanol; Pour solution A into solution B, stir until the mixture becomes transparent, seal and store in the dark to obtain the corrosive solution; The mass ratio of ammonium persulfate to sodium molybdate is 1~2:0.5~1; the volume ratio of glacial acetic acid to anhydrous ethanol and deionized water is 1~1.5:7~8:1~1.
5.
5. The corrosion method for displaying carbides in the metallographic etching solution of 4Cr13 stainless steel according to claim 1, characterized in that, Includes the following steps: 4Cr13 stainless steel is prepared for polishing and ready for use. Preparation of corrosive solution; The prepared 4Cr13 stainless steel was completely immersed in the etching solution, and the polished mirror surface of the 4Cr13 stainless steel was placed upwards. It was then etched at a temperature of 40℃~50℃ for 10min~20min. After observing that the etched surface turned yellow, the sample was removed, rinsed with anhydrous ethanol, and dried.
6. The corrosion method for revealing carbides according to claim 5, characterized in that, The heating temperature was 50℃ and the corrosion time was 15 minutes.
7. The corrosion method for revealing carbides according to claim 5, characterized in that, The steps for pre-polishing treatment of the 4Cr13 stainless steel are as follows: a 4Cr13 stainless steel test block is wire-cut, ground flat, and then coarsely and finely ground with metallographic sandpaper until it is polished to a mirror finish. After rinsing and drying, it is ready for use.
8. The corrosion method for revealing carbides according to claim 5, characterized in that, The 4Cr13 stainless steel is composed of the following elements by mass percentage: C 0.36%~0.45%, Cr 12.00%~14.00%, Si≤0.60%, Mn≤0.80%, P≤0.040%, S≤0.030%, Ni≤0.60%, with the remainder being Fe and unavoidable impurities.