Dual-phase steel color metallographic coloring agent and color metallographic display method thereof

Abstract

The invention relates to a dual-phase steel color metallographic coloring agent and a color metallographic display method thereof, belongs to the technical field of decoration agents for metal metallographic display, solves the technical problem that a conventional coloring agent contains picric acid, and adopts the technical scheme that the dual-phase steel color metallographic coloring agent is prepared from the following components in percentage by volume: 40-60% of a potassium metabisulfite solution with the concentration of 2-20%, 10-30% of a solvent and the balance of water. The volume sum of the potassium metabisulfite solution and the sodium metabisulfite solution is 100%, and mixing the potassium metabisulfite solution, the sodium metabisulfite solution and the potassium metabisulfite solution at room temperature. The method sequentially comprises the steps of sampling, coarse grinding, fine grinding, coarse polishing, fine polishing, coloring agent solution preparation, dyeing, microscopic structure observation and color image acquisition. The raw materials are convenient to store and low in price, and the dyeing process is simple and reliable; the coloring agent can replace a coloring agent containing picric acid, bainite and martensite structures can be clearly distinguished, and a guarantee is provided for recognition and quantitative detection of the microstructure of the steel grade.

Description

Technical Field

[0001] The present invention belongs to the technical field of etchants for metal metallographic display, and specifically relates to a color metallographic stain for duplex steel and a method for color metallographic display thereof. Background Art

[0002] Duplex steel is a high-strength steel mainly used in automobile wheels or structural parts. The microstructure of this steel is mainly martensite or bainite, and the content of martensite or bainite has an important influence on the performance of the steel. Therefore, quantitative analysis of the martensite or bainite structure is required. In the prior art, color metallographic stains containing picric acid are usually used for metallographic analysis of the microstructure of metals.

[0003] Picric Acid, molecular formula: C6H3N3O7, chemical name: 2,4,6-trinitrophenol, is a light yellow shiny needle-like or massive crystal, odorless, with a strong bitter taste, and is an important organic compound. Physical properties of picric acid: density is 1.767 g / cm 3 ³, melting point is 122.3 °C, boiling point is above 300 °C (sublimation), flash point is 150 °C, auto-ignition point is 300 °C; it is sparingly soluble in cold water, dissolving 1.2 g in 100 g of water at 20 °C and 6.2 g at 100 °C; it is easily soluble in ethanol, benzene, ether, hot water and many other organic solvents. Chemical properties of picric acid: It has strong acidity, can decompose carbonates, and can react with common metals (except aluminum and tin) to form picrates, among which lead salts and iron salts are extremely explosive when struck; in addition, it can also form adducts with polycyclic aromatic hydrocarbons, heterocyclic compounds, phenols, and amines, and can be oxidized by strong oxidants, such as boiling nitric acid can oxidize it to oxalic acid.

[0004] Picric acid has a wide range of uses in the military field, chemical industry field, medical field and metal field. However, its physical and chemical properties determine that picric acid is very harmful. For health hazards: after contact with its dust, itching, papules, and blisters often occur on the cheeks, corners of the mouth, and both sides of the nose wings. In severe cases, the skin swells and peels, and even exfoliative dermatitis may occur; it has irritating symptoms to the eyes, nose, and respiratory tract, causing conjunctivitis and bronchitis; after absorption, the skin, conjunctiva and other mucous membranes as well as urine and secretions are all dyed yellow; short-term large amount of absorption can cause temporary loss of consciousness, and there may be symptoms such as weakness, muscle pain, anuria or polyuria. For environmental hazards: it is toxic to aquatic organisms and has long-term effects. The critical concentration for its adverse impact on water body hygiene is set at 25 mg / L.

[0005] In summary, there is an urgent need to find a stain that can replace the picric acid-containing stain for color metallographic staining of duplex steel. Summary of the Invention

[0006] The main object of the present invention is to overcome the deficiencies in the prior art, solve the technical problem of replacing the staining agent containing picric acid for the color metallographic staining of duplex steel, and provide a color metallographic staining agent for duplex steel and a method for color metallographic display thereof.

[0007] The present invention is achieved through the following technical solutions: The color metallographic staining agent for duplex steel is composed of the following components according to the volume ratio of the solution: 40% - 60% of a potassium metabisulfite (K2S2O5) solution with a concentration of 2% - 20%, 40% - 60% of a sodium metabisulfite (Na2S2O5) solution with a concentration of 10% - 48%. The sum of the volumes of the potassium metabisulfite solution and the sodium metabisulfite solution is 100%, and it is mixed at room temperature.

[0008] Furthermore, in the color metallographic staining agent for duplex steel, the potassium metabisulfite solution and the sodium metabisulfite solution are uniformly mixed in equal volumes.

[0009] The method for color metallographic display of duplex steel using the above-mentioned staining agent includes the following steps: S1. Prepare a metallographic specimen S1-1. Sampling: Prepare a cylindrical specimen with a shape and size of ф12×12mm or ф18×20mm, or a cubic metallographic specimen of 12×12×12mm. During sampling, prevent tissue changes caused by temperature rise or plastic deformation caused by stress. S1-2. Grinding the specimen: Rough grind to remove the unnecessary edges, sharp corners, and flash of the specimen; successively use 180#, 600#, 1000#, 1500#, and 2000# metallographic sandpapers on an automatic grinding machine for fine grinding to eliminate the grinding marks left by rough grinding. S1-3. Polishing: Mechanical polishing is carried out successively using a high-efficiency metallographic polishing agent, woolen cloth, and velvet fabric for rough polishing and fine polishing. Control the humidity and strength during polishing. The polished grinding surface is smooth, without scratches and deformation layer; then corrode with 4% nitric acid alcohol solution, polish again to eliminate the corrosion marks, and finally clean with alcohol. S2. Prepare the staining agent, prepare it at room temperature, and use it within one minute after the solution is fully mixed; S2-1. Prepare the potassium metabisulfite solution: Weigh potassium metabisulfite powder and dissolve it in water to prepare a potassium metabisulfite solution with a concentration of 2% - 20% for standby. S2-2. Prepare the sodium metabisulfite solution: Weigh sodium metabisulfite powder and dissolve it in water to prepare a potassium metabisulfite solution with a concentration of 10% - 48% for standby. S2-3. Mixing: Mix the potassium metabisulfite solution prepared in step S2-1 and the sodium metabisulfite solution according to the volume ratio to obtain the color metallographic staining agent for duplex steel for standby; S3. Stain the specimen to form an interference film: S3-1. Place the stain prepared in step S2-3 in a container; S3-2. Use tweezers to pick up the specimen and place it flat on the experimental table with the staining surface facing up. Then, use a dropper to suck up the stain and drop it drop by drop on the staining surface of the specimen. The staining time is determined by the color change on the surface of the specimen. When the color gradually turns blue and stabilizes, rinse the stain off with water; S3-4. Continue to rinse the specimen thoroughly with water, then spray an alcohol spray on the staining surface of the specimen, and finally dry it with a hair dryer to form a stable interference film on the staining surface of the specimen; S4. Observation and image acquisition of the microstructure: S4-1. Place the specimen with the staining surface facing up under a metallurgical microscope and successively use 10×, 20×, and 50× objective lenses; S4-2. Turn on the light source, select a white light source, adjust the aperture and field diaphragm, and adjust the focusing knob until the image is clear; S4-3. Adjust the color temperature and hue, collect a color electronic image. The bainite appears blue-black, the martensite appears yellow, and the remaining transparent area is the martensite-austenite island, completing the color metallography display of the duplex steel.

[0010] Further, in step S2, first, mix the potassium metabisulfite powder weighed in step S2-1 and the sodium metabisulfite powder weighed in step S2-2 evenly to obtain a mixed powder; then, let the mixed powder stand for seven days; finally, dissolve the powder after standing for seven days in water to prepare a duplex steel color metallography stain for standby.

[0011] The beneficial effects of the present invention are as follows: The present invention uses a duplex steel color metallography stain prepared by mixing a potassium metabisulfite solution and a sodium metabisulfite solution in a certain proportion. The raw materials of the stain, potassium metabisulfite and sodium metabisulfite, are convenient for storage and low in price. The staining process is simple and reliable; this stain can replace the stain containing picric acid, can clearly distinguish between bainite and martensite structures, provides a guarantee for the identification and quantitative detection of the microstructure of this steel type, promotes the research and development of products, and achieves remarkable economic and social benefits. Description of the Drawings

[0012] Figure 1 It is a color metallography image of the duplex steel (with bainite as the main phase) corroded by the stain prepared in Example 1; Figure 2 It is a color metallography image of the duplex steel (with bainite as the main phase) corroded by the stain prepared in Example 2; Figure 3 It is a color metallography image of the duplex steel (with bainite as the main phase) corroded by the stain prepared in Comparative Example 1; Figure 4The color metallographic diagram of the duplex steel (with bainite as the main phase) corroded by the staining agent prepared in Comparative Example 2; Figure 5 The color metallographic diagram of the duplex steel (with bainite as the main phase) corroded by the staining agent prepared in Example 3; Figure 6 The color metallographic diagram of the duplex steel (with equal volume fractions of bainite and martensite) corroded by the staining agent prepared in Example 4; Figure 7 The color metallographic diagram of the duplex steel (with martensite as the main phase) corroded by the staining agent prepared in Example 5. Detailed implementation manners

[0013] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Example 1

[0014] A method for showing the color metallography of duplex steel includes the following steps: S1. Prepare a metallographic specimen S1-1. Sampling: In this Example 1, the grade of the duplex steel is 40CrNiMo. After isothermal quenching at 330°C in a salt bath furnace and holding for 10 minutes, the average grain size is 50μm. In this state, bainite is the main phase. Prepare a cylindrical metallographic specimen with a shape and size of ф12×12mm. During sampling, prevent tissue changes caused by temperature rise or plastic deformation caused by stress; S1-2. Grinding the specimen: Roughly grind off the unnecessary edges, sharp corners and flash of the specimen; successively use 180#, 600#, 1000#, 1500#, 2000# metallographic sandpapers on an automatic grinding machine for fine grinding to eliminate the grinding marks left by rough grinding; S1-3. Polishing - Mechanical polishing: Successively use a high - efficiency metallographic polishing agent, woolen cloth and velvet fabric for rough polishing and fine polishing. Control the humidity and strength during polishing. The polished grinding surface is smooth, without scratches and without a deformed layer; then corrode with 4% nitric acid alcohol solution, polish again to eliminate the corrosion marks, and finally clean with alcohol; S2. Prepare the staining agent, prepare it at room temperature and use it within one minute after the solution is fully mixed; S2-1. Prepare a potassium metabisulfite solution: Weigh 0.5g of potassium metabisulfite powder and dissolve it in 10mL of water to prepare a 5% potassium metabisulfite solution for standby; S2-2. Prepare a sodium metabisulfite solution: Weigh 1.6g of sodium metabisulfite powder and dissolve it in 10mL of water to prepare a 16% potassium metabisulfite solution for standby; S2-3. Mixing: Mix the potassium metabisulfite solution prepared in step S2-1 and the sodium metabisulfite solution according to a volume ratio of 2:3 to obtain a standby color metallographic staining agent for duplex steel; S3. Dye the specimen to form an interference film: S3-1. Place the dye prepared in step S2-3 in a container. S3-2. Use forceps to pick up the specimen and place it flat on the experimental table with the surface to be dyed facing up. Then use a dropper to suck up the dye and drop it drop by drop on the surface to be dyed of the specimen. The dyeing time is 20 s. When the color gradually turns blue and stabilizes, rinse the dye off with water. S3-4. Continue to rinse the specimen thoroughly with water, then spray an alcohol spray on the dyed surface of the specimen, and finally dry it with a hair dryer to form a stable interference film on the dyed surface of the specimen. S4. Observation and image acquisition of the microstructure: S4-1. Place the specimen with the dyed surface facing up under a metallurgical microscope and successively use 10×, 20×, and 50× objective lenses. S4-2. Turn on the light source, select a white light source, adjust the aperture and field diaphragm, and adjust the focusing knob until the image is clear. S4-3. Adjust the color temperature and hue, collect a color electronic image, and complete the color metallography display of the duplex steel. The color metallography image is as Figure 1 shown. Among them, bainite is blue-black and martensite is yellow. Thus, it can be clearly seen that the martensite structure is the main phase in the duplex steel. Example 2

[0015] A method for color metallography display of duplex steel, comprising the following steps: S1. Prepare a metallographic specimen S1-1. Sampling: In this Example 2, the grade of the duplex steel is 40CrNiMo. After isothermal quenching at 330 °C in a salt bath furnace and holding for 10 min, the average grain size is 50 μm. In this state, bainite is the main phase. Prepare a cylindrical metallographic specimen with a shape and size of ф18×20 mm. During sampling, prevent tissue changes caused by temperature rise or plastic deformation caused by stress. S1-2. Grinding the sample: Roughly grind off the unnecessary edges, corners, and flash of the specimen; successively use 180#, 600#, 1000#, 1500#, and 2000# metallographic sandpapers on an automatic grinding machine for fine grinding to eliminate the grinding marks left by rough grinding. S1-3. Mechanical polishing: Successively use a high-efficiency metallographic polishing agent, woolen cloth, and velvet fabric for rough polishing and fine polishing. Control the humidity and strength during polishing. The polished grinding surface is smooth, without scratches and deformation layer; then corrode with 4% nitric acid alcohol solution, polish again to eliminate the corrosion marks, and finally clean with alcohol. S2. Preparation of the dye, prepared at room temperature, and used within one minute after the solution is fully mixed. S2-1. Preparation of potassium metabisulfite solution: Weigh 1.0 g of potassium metabisulfite powder and dissolve it in 10 mL of water to prepare a 10% potassium metabisulfite solution for standby. S2-2. Preparation of sodium metabisulfite solution: Weigh 3.2 g of sodium metabisulfite powder and dissolve it in 10 mL of water to prepare a 32% potassium metabisulfite solution for standby. S2-3. Mixing: Mix the potassium metabisulfite solution and sodium metabisulfite solution prepared in step S2-1 in a volume ratio of 1:1 to obtain a duplex stainless steel color metallographic stain for standby. S3. Specimen staining to form an interference film: S3-1. Place the stain prepared in step S2-3 in a container. S3-2. Use forceps to pick up the specimen and place it flat on the experimental table with the staining surface facing up. Then, use a dropper to suck up the stain and drop it drop by drop on the staining surface of the specimen. The staining time is 15 s. When the color gradually turns blue and stabilizes, rinse the stain off with water. S3-4. Continue to rinse the specimen thoroughly with water, then spray alcohol spray on the staining surface of the specimen, and finally dry it with a hair dryer to form a stable interference film on the staining surface of the specimen. S4. Observation and image acquisition of the microstructure: S4-1. Place the specimen with the staining surface facing up under a metallurgical microscope and successively use 10×, 20×, and 50× objective lenses. S4-2. Turn on the light source, select a white light source, adjust the aperture and field diaphragm, and adjust the focusing knob until the image is clear. S4-3. Adjust the color temperature and color tone, collect color electronic images, complete the duplex stainless steel color metallographic display. The color metallographic diagram is as Figure 2 shown. Among them, bainite is blue-black, martensite is yellow, and the remaining transparent area is martensite-austenite island. It can be clearly seen that bainite tissue is the main phase in the duplex stainless steel. Comparative Example 1

[0016] In this Comparative Example 1, at room temperature, only 3.2 g of sodium metabisulfite was dissolved in 10 mL of water to prepare a 32% sodium metabisulfite solution as a stain. The remaining steps are the same as those in Example 2 and will not be elaborated here. The duplex stainless steel color metallographic display was completed. The color metallographic diagram is as Figure 3 shown. Although the morphology of bainite tissue can be seen, there are white and black area interferences in the phase diagram, and the distinguishability of each phase is not obvious, causing certain difficulties for subsequent statistical volume fraction. Comparative Example 2

[0017] In Comparative Example 2, at room temperature, only 1.0 g of potassium metabisulfite was dissolved in 10 mL of water to prepare a 10% potassium metabisulfite solution as a staining agent. The remaining steps were the same as those in Example 2 and will not be elaborated here. After the color metallography of the duplex steel was completed, the color metallograph was as shown in Figure 4 . Although the morphology of the bainite structure could be seen, the color differences among the various structures in the phase diagram were not significant, and the discrimination was not obvious, causing certain difficulties for subsequent statistical volume fraction calculation.

[0018] Comparing with the attached drawings of the specification Figures 2 to 4 , it shows that this staining agent can clearly display the metallographic structure. Example 3

[0019] A method for color metallography display of duplex steel includes the following steps: S1. Prepare a metallographic specimen S1-1. Sampling: In this Example 3, the grade of the duplex steel is 40CrNiMo. After isothermal quenching at 330 °C in a salt bath furnace and holding for 10 min, the average grain size is 50 μm. In this state, bainite is the main phase. A cubic metallographic specimen with a shape and size of 12×12×12 mm is prepared. During sampling, prevent tissue changes caused by temperature rise or plastic deformation caused by stress. S1-2. Grinding the sample: Roughly grind off the unnecessary edges, sharp corners and flash of the sample; successively use 180#, 600#, 1000#, 1500#, 2000# metallographic sandpapers on an automatic grinding machine for fine grinding to eliminate the grinding marks left by rough grinding. S1-3. Polishing: Mechanically polish successively with high-efficiency metallographic polishing agent, woolen cloth and velvet fabric for rough polishing and fine polishing. Control the humidity and strength during polishing. The polished grinding surface is smooth, without scratches and deformation layer; then corrode with 4% nitric acid alcohol solution, polish again to eliminate the corrosion marks, and finally wash with alcohol. S2. Preparation of the staining agent, prepared at room temperature and used within one minute after the solution is fully mixed; S2-1. Preparation of potassium metabisulfite solution: Weigh 2 g of potassium metabisulfite powder and dissolve it in 10 mL of water to prepare a 20% potassium metabisulfite solution for standby. S2-2. Preparation of sodium metabisulfite solution: Weigh 4.8 g of sodium metabisulfite powder and dissolve it in 10 mL of water to prepare a 48% sodium metabisulfite solution for standby. S2-3. Mixing: Mix the potassium metabisulfite solution and sodium metabisulfite solution prepared in step S2-1 according to a volume ratio of 1:1 to prepare a color metallography staining agent for duplex steel for standby. S3. Staining the specimen to form an interference film: S3-1. Place the staining agent prepared in step S2-3 in a container; S3-2. Use tweezers to pick up the specimen and place it flat on the experimental bench with the surface to be dyed facing up. Then use a dropper to suck up the dyeing agent and drop it drop by drop on the surface to be dyed of the specimen. The dyeing time is 10 s. When the color gradually turns blue and stabilizes, rinse the dyeing agent off with water; S3-4. Continue to rinse the specimen thoroughly with water, then spray an alcohol spray on the dyed surface of the specimen, and finally dry it with a hair dryer to form a stable interference film on the dyed surface of the specimen; S4. Observation and image acquisition of the microstructure: S4-1. Place the specimen with the dyed surface facing up under the metallographic microscope and use the objective lens of 10×, 20×, and 50× in sequence; S4-2. Turn on the light source, select the white light source, adjust the aperture and field diaphragm, and adjust the focusing knob to make the image clear; S4-3. Adjust the color temperature and hue, collect the color electronic image, complete the color metallography display of the duplex steel, and the color metallography image is as Figure 5 shown, in which the bainite is blue-black, the martensite is yellow, and the remaining transparent area is the martensite-austenite island. It can be clearly seen that the bainite is the main phase in the microstructure. Example 4

[0020] A method for color metallography display of duplex steel, comprising the following steps: S1. Prepare a metallographic specimen S1-1. Sampling: In this Example 4, the grade of the duplex steel is 40CrNiMo. After isothermal quenching at 330 °C in a salt bath furnace and holding for 10 min, the average grain size is 30 μm. In this state, the bainite and martensite each account for half. Prepare a cubic metallographic specimen with a shape and size of 12×12×12 mm. During sampling, prevent tissue changes caused by temperature rise or plastic deformation caused by stress; S1-2. Grinding the sample: Roughly grind off the unnecessary edges, corners, and flash of the specimen; successively use 180#, 600#, 1000#, 1500#, and 2000# metallographic sandpapers to finely grind on an automatic grinding machine to eliminate the grinding marks left by rough grinding; S1-3. Polishing - Mechanical polishing: Successively use high - efficiency metallographic polishing agent, woolen cloth, and velvet fabric for rough polishing and fine polishing. Control the humidity and strength during polishing. The polished surface is smooth, without scratches and deformation layer; then corrode with 4% nitric acid alcohol solution, polish again to eliminate the corrosion marks, and finally wash with alcohol; S2. Preparation of the dyeing agent, prepared at room temperature, and used within one minute after the solution is fully mixed; First, weigh 1 g of potassium metabisulfite powder and mix it evenly with 3.2 g of sodium metabisulfite powder to obtain a mixed powder; then, let the mixed powder stand for seven days; finally, dissolve the powder after standing for seven days in 10 mL of water to prepare a duplex stainless steel colored metallographic stain for standby. The concentration of the potassium metabisulfite solution in the duplex stainless steel colored metallographic stain is 10%, and the concentration of the sodium metabisulfite solution is 32%; S3. Stain the specimen to form an interference film: S3-1. Place the stain prepared in step S2-3 in a container; S3-2. Use forceps to pick up the specimen and place it flat on the experimental table with the surface to be stained facing up. Then, use a dropper to suck up the stain and drop it drop by drop on the surface to be stained of the specimen. The staining time is 10 s. When the color gradually turns blue and stabilizes, rinse the stain off with water; S3-4. Continue to rinse the specimen thoroughly with water, then spray an alcohol spray on the stained surface of the specimen, and finally dry it with a hair dryer to form a stable interference film on the stained surface of the specimen; S4. Observation and image acquisition of the microstructure: S4-1. Place the specimen with the stained surface facing up under a metallurgical microscope and use objective lenses of 10×, 20×, and 50× in sequence; S4-2. Turn on the light source, select a white light source, adjust the aperture and field diaphragm, and adjust the focusing knob until the image is clear; S4-3. Adjust the color temperature and hue, collect a color electronic image, and complete the duplex stainless steel colored metallographic display. The colored metallographic diagram is as Figure 6 shown. Among them, bainite is blue-black, martensite is yellow, and the remaining transparent area is martensite-austenite island. It can be clearly seen that the volume fractions of bainite and martensite in the microstructure are equal. Example 5

[0021] A method for duplex stainless steel colored metallographic display, comprising the following steps: S1. Prepare a metallographic specimen S1-1. Sampling: In this Example ⑤, the grade of the duplex stainless steel is 40CrNiMo. After isothermal quenching at 330 °C in a salt bath furnace and holding for 10 min, the average grain size is 13 μm. Martensite is the main phase in this state. Prepare a cylindrical metallographic specimen with a shape and size of ф18×20 mm. Prevent tissue changes caused by temperature rise or plastic deformation caused by stress during sampling; S1-2. Grinding: Roughly grind off the unnecessary edges, sharp corners, and flash of the specimen; successively use 180#, 600#, 1000#, 1500#, and 2000# metallographic sandpapers to finely grind on an automatic grinding machine from coarse to fine to eliminate the grinding marks left by rough grinding; S1-3. Mechanical polishing: successively use high-efficiency metallographic polishing agent, woolen cloth and velvet fabric for rough polishing and fine polishing in sequence. Control the humidity and strength during polishing. After polishing, the ground surface is smooth, without scratches and deformation layer; then etch with 4% nitric acid alcohol solution, and then polish to eliminate the etching marks, and finally clean with alcohol; S2. Preparation of staining agent, which is prepared at room temperature and used within one minute after the solution is fully mixed; S2-1. Preparation of potassium metabisulfite solution: Weigh 1.0 g of potassium metabisulfite powder and dissolve it in 10 mL of water to prepare a 10% potassium metabisulfite solution for standby; S2-2. Preparation of sodium metabisulfite solution: Weigh 3.2 g of sodium metabisulfite powder and dissolve it in 10 mL of water to prepare a 32% potassium metabisulfite solution for standby; S2-3. Mixing: Mix the potassium metabisulfite solution and sodium metabisulfite solution prepared in step S2-1 according to a volume ratio of 1:1 to obtain a duplex stainless steel color metallographic staining agent for standby; S3. Specimen staining to form an interference film: S3-1. Place the staining agent prepared in step S2-3 in a container; S3-2. Use tweezers to pick up the specimen and place it flat on the experimental table with the surface to be stained facing up. Then use a dropper to suck the staining agent and drop it drop by drop on the surface to be stained of the specimen. The staining time is 15 s. When the color gradually turns blue and stabilizes, rinse the staining agent with water; S3-4. Continue to rinse the specimen thoroughly with water, then spray alcohol spray on the stained surface of the specimen, and finally dry it with a hair dryer to form a stable interference film on the stained surface of the specimen; S4. Observation and image acquisition of microstructures: S4-1. Place the specimen with the stained surface facing up under a metallographic microscope, and successively use objective lens with magnifications of 10×, 20×, and 50×; S4-2. Turn on the light source, select a white light source, adjust the aperture and field diaphragm, and adjust the focusing knob to obtain a clear image; S4-3. Adjust the color temperature and hue, collect color electronic images, complete the duplex stainless steel color metallographic display. The color metallographic diagram is as Figure 7 shown, in which bainite is blue-black, martensite is yellow, and the remaining transparent area is martensite-austenite island. Thus, it can be clearly seen that the martensite structure is the main phase in the duplex stainless steel.

[0022] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any variations or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. Duplex steel color metallographic stain, characterized in that, It is composed of the following components according to the volume ratio of the solution: 40% - 60% of potassium metabisulfite solution with a concentration of 2% - 20%, 40% - 60% of sodium metabisulfite solution with a concentration of 10% - 48%. The sum of the volumes of the potassium metabisulfite solution and the sodium metabisulfite solution is 100%, and it is mixed at room temperature.

2. The two-phase steel color metallographic stain according to claim 1, characterized in that, In the duplex steel color metallographic stain, the potassium metabisulfite solution and the sodium metabisulfite solution are uniformly mixed in equal volumes.

3. A method for color metallographic display of duplex steel using the stain described in claim 1, characterized in that, It includes the following steps: S1. Prepare a metallographic specimen S1-1. Sampling: Prepare a cylindrical specimen with a shape and size of ф12×12mm or ф18×20mm, or a cubic metallographic specimen of 12×12×12mm. During sampling, prevent tissue changes caused by temperature rise or plastic deformation caused by stress. S1-2. Grinding the specimen: Rough grinding to remove unnecessary edges, sharp corners and flash; successively use 180#, 600#, 1000#, 1500#, 2000# metallographic sandpaper to perform fine grinding on an automatic grinding machine in sequence to eliminate the grinding marks left by rough grinding. S1-3. Polishing - Mechanical polishing: Successively use high - efficiency metallographic polishing agent, woolen cloth and velvet fabric for rough polishing and fine polishing in sequence. Control the humidity and strength during polishing. The polished grinding surface is smooth, without scratches and deformation layer; then corrode with 4% nitric acid alcohol solution, polish again to eliminate the corrosion marks, and finally clean with alcohol. S2. Preparation of the stain, prepare at room temperature and use it within one minute after the solution is fully mixed. S2-1. Preparation of potassium metabisulfite solution: Weigh potassium metabisulfite powder and dissolve it in water to prepare a potassium metabisulfite solution with a concentration of 2% - 20% for standby. S2-2. Preparation of sodium metabisulfite solution: Weigh sodium metabisulfite powder and dissolve it in water to prepare a potassium metabisulfite solution with a concentration of 10% - 48% for standby. S2-3. Mixing: Mix the potassium metabisulfite solution prepared in step S2-1 and the sodium metabisulfite solution according to the volume ratio to obtain a duplex steel color metallographic stain for standby. S3. Staining the specimen to form an interference film: S3-1. Place the stain prepared in step S2-3 in a container. S3-2. Use tweezers to pick up the specimen and place it flat on the experimental table with the surface to be stained facing up. Then use a dropper to suck the stain and drop it drop by drop on the surface to be stained of the specimen. The staining time is determined by the color change of the specimen surface. When the color gradually turns blue and stabilizes, rinse the stain off with water. S3-4. Continue to rinse the specimen thoroughly with water, then spray alcohol spray on the stained surface of the specimen, and finally dry it with a hair dryer to form a stable interference film on the stained surface of the specimen. S4. Observation and image acquisition of the microstructure: S4-1. Place the specimen with the stained surface facing up under a metallographic microscope, and successively use 10×, 20×, 50× objective lenses. S4-2. Turn on the light source, select a white light source, adjust the aperture and field diaphragm, and adjust the focusing knob to obtain a clear image. S4-3. Adjust the color temperature and color tone, collect color electronic images. The bainite appears blue - black, the martensite appears yellow, and the remaining transparent area is the martensite - austenite (M - A) island, completing the duplex steel color metallographic display.

4. The method for color metallographic display of duplex steel according to claim 3, characterized in that, In the step S2, first, the potassium metabisulfite powder weighed in the step S2-1 and the sodium metabisulfite powder weighed in the step S2-2 are mixed evenly to obtain a mixed powder; then, the mixed powder is left standing for seven days; finally, the powder after standing for seven days is dissolved in water to prepare a duplex stainless steel color metallographic stain for standby.

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