Metallographic corrosion method for high-purity ferrite and heat-treated ferritic stainless steel
By using aqueous nitric acid solution to electrolytic corrosion on high-purity ferrite and heat-treated ferrite stainless steel, the problem of being difficult to corrode clear grains in the prior art is solved, and clearer grain corrosion and ratings are achieved.
Patent Information
- Application Number
- CN202411649241.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-19
- Publication Date
- 2025-02-18
AI Technical Summary
The prior art is difficult to corrode clear grains on high-purity ferrite and heat-treated ferrite stainless steel, making it difficult to perform grain size ratings.
Electrolytic corrosion is performed using 50-80% concentration of nitric acid aqueous solution. The specific steps include coarse grinding, fine grinding and polishing the surface to be measured on the sample, and then immersing the sample in the aqueous solution of nitric acid, and electrolytic corrosion under the action of a DC power supply. , the control voltage is 1-2V, the current is 0.08-0.12A, and the power-on time is 25-35 seconds.
This method can clearly corrode the grains of high-purity ferrite and heat-treated ferrite stainless steel, which significantly improves the feasibility of grain size rating.
Smart Images
Figure CN119469971A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a metallographic corrosion method for high-purity ferrite and heat-treated ferrite stainless steel. Background Art
[0002] High-purity ferrite and heat-treated ferrite stainless steel refers to ferrite stainless steel with a Cr content of ≥20%, a pure ferrite structure and heat-treated. For most stainless steels, FeCl3 hydrochloric acid aqueous solution, copper sulfate hydrochloric acid aqueous solution and oxalic acid electrolysis can be used for metallographic corrosion. This method is also applicable to hot-rolled and low-purity ferrite stainless steels. However, when used for high-purity ferrite and heat-treated ferrite stainless steels, due to their high Cr content, low carbon content, and Mo-containing ferrite, they have excellent corrosion resistance, and the resulting grain boundaries are blurred, making it difficult to perform metallographic grain rating. Summary of the invention
[0003] The object of the present invention is to provide a metallographic etching method for high-purity ferrite and heat-treated ferrite stainless steel. The present invention has the advantages of being able to etch clear grains on high-purity ferrite and heat-treated ferrite stainless steel, and is easier to grade the grain size of high-purity ferrite and heat-treated ferrite stainless steel.
[0004] The technical solution of the present invention is: a metallographic corrosion method for high-purity ferrite and heat-treated ferrite stainless steel, obtaining samples of high-purity ferrite and heat-treated ferrite stainless steel, performing coarse grinding, fine grinding, and polishing on the surface to be tested of the sample, and cleaning the surface to be tested;
[0005] Immerse the surface of the sample to be tested in a nitric acid aqueous solution with a concentration of 50-80%;
[0006] Take a DC power supply, connect the positive pole of the DC power supply to product A, and connect the negative pole of the DC power supply to the nitric acid aqueous solution. After the DC power supply voltage is 1-2V, the current is 0.08-0.12A, and the power-on time is 25-35s, take out the sample.
[0007] In the above-mentioned metallographic corrosion method of high-purity ferrite and heat-treated ferrite stainless steel, the concentration of the nitric acid aqueous solution is 65%.
[0008] In the above-mentioned metallographic corrosion method of high-purity ferrite and heat-treated ferrite stainless steel, the nitric acid aqueous solution is prepared by uniformly mixing a nitric acid solution with a concentration of 80% and deionized water.
[0009] In the above-mentioned metallographic corrosion method of high-purity ferrite and heat-treated ferrite stainless steel, the surface to be tested of the sample is first coarsely ground with 300# sandpaper, then coarsely ground with 600# sandpaper, and then finely ground with 1000# sandpaper.
[0010] In the above-mentioned metallographic corrosion method of high-purity ferrite and heat-treated ferrite stainless steel, the surface to be tested of the sample is finely ground and then polished using a polishing paste with a particle size of 2.5 μm and a polishing cloth until the surface to be tested is bright and scratch-free.
[0011] In the above-mentioned metallographic corrosion method of high-purity ferrite and heat-treated ferrite stainless steel, when cleaning the surface to be tested, first wash it with clean water, then rinse it with anhydrous ethanol, and finally blow dry the sample.
[0012] In the above-mentioned metallographic corrosion method of high-purity ferrite and heat-treated ferrite stainless steel, an austenitic stainless steel plate is immersed in a nitric acid aqueous solution and connected to the negative electrode of a DC power supply.
[0013] In the above-mentioned metallographic corrosion method of high-purity ferrite and heat-treated ferrite stainless steel, the DC power supply voltage is 1.5V, the current is 0.1A, and the power-on time is 30s.
[0014] Compared with the prior art, the present invention adopts a specific corrosion solution (aqueous nitric acid solution) to corrode a specific metal (high-purity ferrite and heat-treated ferritic stainless steel) under a specific electrolytic state, which can make the corroded grains clearer and easier to grade the grain size. It can be said that the present invention is specifically used for the metallographic corrosion treatment of high-purity ferrite and heat-treated ferritic stainless steel. BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Figure 1 This is the metallographic diagram of Example 1.
[0016] Figure 2 This is the metallographic diagram of Example 2.
[0017] Figure 3 This is the metallographic diagram of Example 3.
[0018] Figure 4 This is the metallographic diagram of Comparative Example 1.
[0019] Figure 5 This is the metallographic diagram of Comparative Example 2.
[0020] Figure 6 This is the metallographic diagram of Comparative Example 3. DETAILED DESCRIPTION
[0021] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but they are not intended to limit the present invention.
[0022] High-purity ferrite and heat-treated ferrite stainless steel, bars, chemical composition and mass percentage: Cr ≥ 20%, C ≤ 0.05%, Mn ≤ 1.5%, Ni: 0.25-0.5%, Mo: 0.02-0.05%, the balance is Fe; the heat treatment process is heating up to 750 ° C with the furnace temperature, keeping the temperature for 1.5 hours and then air cooling. It is used in all the following examples and comparative examples.
[0023] Embodiment 1 (optimal embodiment). Metallographic corrosion method of high-purity ferrite and heat-treated ferrite stainless steel: a sample with a length of 20 mm and a diameter of 6.5 mm is cut from the above-mentioned stainless steel bar, and the surface to be tested of the sample is polished with 300#, 600# and 1000# sandpapers in turn, and then a polishing paste with a particle size of 2.5 μm is applied to the polishing cloth or the surface to be tested, and the surface to be tested is polished with a polishing cloth until the surface to be tested is bright and has no scratches, and the surface to be tested is cleaned with clean water, and the surface to be tested is rinsed with anhydrous ethanol, and finally the sample is blown dry to complete the acquisition and pretreatment of the sample.
[0024] Mix 81.3 mL of 80% nitric acid solution with 18.7 mL of deionized water, add the nitric acid solution into the deionized water, and stir continuously with a glass rod until the nitric acid solution and water are evenly mixed to prepare 100 mL of 65% nitric acid aqueous solution.
[0025] Take a DC power supply, use the surface of the sample to be tested as the anode, connect it to the positive pole of the DC power supply, take the austenitic stainless steel plate as the cathode, connect it to the negative pole of the DC power supply, immerse the anode and cathode in the nitric acid aqueous solution and keep them parallel and opposite.
[0026] Turn on the DC power supply, and electrify the test surface of the corrosion sample, with a voltage of 1-2V, a current of 0.08-0.12A, and a time of 25-35s. In the embodiment, preferably: voltage 1.5V, current 0.1A, and electrification time 30s. Then cut off the power supply, take out the sample, wash it with water, then rinse it with anhydrous ethanol, and finally blow dry the sample to obtain the high-purity ferrite and heat-treated ferrite stainless steel metallographic corrosion samples.
[0027] In the trial and error process of obtaining the solution of Example 1, it was found that electrolysis is a necessary step. Without electrolysis, it is impossible to etch out the grain boundaries by relying solely on a 65% nitric acid aqueous solution. Even if electrolysis is performed, it is difficult to etch out the grain boundaries when the voltage, current, and time exceed the above range values, but the grain boundaries can be etched out when they fall within the range values. Under the conditions of voltage 1.5V, current 0.1A, and power-on time 30s, the etched grain boundaries are the clearest, and the voltage and current values are particularly important.
[0028] Example 2. Based on Example 1, the concentration of the nitric acid aqueous solution was changed to 50%, and 62.5 mL of 80% nitric acid solution + 37.5 mL of deionized water were used, the nitric acid solution was added into the deionized water, and the nitric acid solution was continuously stirred with a glass rod until the nitric acid solution and the water were evenly mixed to obtain the nitric acid aqueous solution.
[0029] Example 3. Based on Example 1, the concentration of the nitric acid aqueous solution is directly 80% nitric acid solution.
[0030] The three samples of Examples 1, 2 and 3 were observed in turn using a Zeiss observer.Zlm Zeiss metallographic microscope, and the results were Figure 1 , Figure 2 , Figure 3 Metallographic diagram.
[0031] from Figure 1 It can be seen that the metallographic etching method of Example 1 can clearly and completely reflect the microstructure of the annealed sample, showing the characteristics of complete recrystallization. Figure 2 It can be seen that the metallographic etching method of Example 2 can achieve a certain etching effect, but the etched grain boundaries are not clear and the corrosion is uneven. Figure 3 It can be seen that the metallographic etching method of Example 3 can achieve a certain etching effect, but the etched grain boundaries are too deep, the grains have obvious over-corrosion, and there are a large number of black spots that seriously affect the rating and analysis of the grains.
[0032] Comparative Example 1 (one of the existing methods). A sample with a length of 20 mm and a diameter of 25 mm was cut from a stainless steel bar, and the surface to be tested of the sample was polished with 300#, 600# and 1000# sandpapers in turn, and then a polishing paste with a particle size of 2.5 μm was applied to the polishing cloth or the surface to be tested, and the surface to be tested was polished with the polishing cloth until the surface to be tested was bright and scratch-free, and then the surface to be tested was cleaned with clean water, and then rinsed with anhydrous ethanol, and finally the sample was dried to complete the acquisition and pretreatment of the sample.
[0033] Add 8g of ferric chloride to 100ml of deionized water, stir with a glass rod until the ferric chloride is completely dissolved, then add 25ml of hydrochloric acid to the ferric chloride aqueous solution, stir with a glass rod until the mixture is uniform, to prepare a ferric chloride hydrochloric acid aqueous solution.
[0034] Place the sample in an aqueous solution of ferric chloride and hydrochloric acid for 1 min. Take out the sample, rinse it with clean water first, then rinse it with anhydrous ethanol and blow it dry with hot air.
[0035] The Zeiss observer.Zlm Zeiss metallographic microscope was used for observation. Figure 4 Metallographic diagram. Figure 4It can be seen from the above that the grain boundaries of the heat-treated high-purity ferritic stainless steel cannot be corroded, indicating that the existing method of chemical corrosion using ferric chloride hydrochloric acid aqueous solution is not suitable for the preparation of high-purity and heat-treated ferritic stainless steel samples.
[0036] Comparative Example 2 (Existing Method 2). A sample with a length of 20 mm and a diameter of 25 mm was cut from a stainless steel bar, and the surface to be tested of the sample was polished with 300#, 600# and 1000# sandpapers in turn, and then a polishing paste with a particle size of 2.5 μm was applied to the polishing cloth or the surface to be tested, and the surface to be tested was polished with the polishing cloth until the surface to be tested was bright and scratch-free, and then the surface to be tested was washed with clean water, and then rinsed with anhydrous ethanol, and finally the sample was dried to complete the acquisition and pretreatment of the sample.
[0037] Add 1.5 g CuSO4·5H2O to 20 mL alcohol, stir with a glass rod until 1.5 g CuSO4·5H2O is completely dissolved, then add 40 ml hydrochloric acid to the ferric chloride aqueous solution, stir with a glass rod until mixed evenly, to prepare a copper sulfate hydrochloric acid aqueous solution.
[0038] Place the sample in a copper sulfate hydrochloric acid aqueous solution for 1 min. Take out the sample, rinse it with clean water first, then rinse it with anhydrous ethanol and blow it dry with hot air.
[0039] The Zeiss observer.Zlm Zeiss metallographic microscope was used for observation. Figure 5 Metallographic diagram. Figure 5 It can be seen from the above that the grain boundaries of the heat-treated high-purity ferritic stainless steel cannot be corroded, indicating that the existing method of chemical corrosion using copper sulfate and hydrochloric acid aqueous solution is not suitable for the preparation of high-purity and heat-treated ferritic stainless steel samples.
[0040] Comparative Example 3 (Existing Method 3): 1 g oxalic acid + 10 mL deionized water to prepare oxalic acid solution.
[0041] The pretreated sample was obtained according to the method of Example 1.
[0042] According to the electrolysis method in Example 1, the surface of the sample to be tested was immersed in the oxalic acid solution for electrolysis, and the electrolysis parameters were adjusted back to the existing voltage of 3V, current of 0.1A, and power-on time of 30s.
[0043] The Zeiss observer.Zlm Zeiss metallographic microscope was used for observation. Figure 6 Metallographic diagram. Figure 6 It can be seen from the above that the grain boundaries of the heat-treated high-purity ferritic stainless steel cannot be corroded, indicating that the existing oxalic acid electrolysis method is not suitable for the preparation of high-purity and heat-treated ferritic stainless steel samples.
Claims
1. A metallographic corrosion method for high purity ferrite and heat treated ferrite stainless steel, characterized in that: Obtain samples of high-purity ferrite and heat-treated ferrite stainless steel, perform rough grinding, fine grinding, and polishing on the surface to be tested of the sample, and clean the surface to be tested; Immerse the surface of the sample to be tested in a nitric acid aqueous solution with a concentration of 50-80%; Take a DC power supply, connect the positive pole of the DC power supply to product A, and connect the negative pole of the DC power supply to the nitric acid aqueous solution. After the DC power supply voltage is 1-2V, the current is 0.08-0.12A, and the power-on time is 25-35s, take out the sample.
2. The metallographic corrosion method of high-purity ferrite and heat-treated ferrite stainless steel according to claim 1, characterized in that: The concentration of the nitric acid aqueous solution is 65%.
3. The metallographic corrosion method of high-purity ferrite and heat-treated ferrite stainless steel according to claim 1, characterized in that: The nitric acid aqueous solution is prepared by uniformly mixing a nitric acid solution with a concentration of 80% and deionized water.
4. The metallographic corrosion method of high-purity ferrite and heat-treated ferrite stainless steel according to claim 1, characterized in that: The surface to be tested of the sample was first coarsely ground with 300# sandpaper, then coarsely ground with 600# sandpaper, and then finely ground with 1000# sandpaper.
5. The metallographic corrosion method of high-purity ferrite and heat-treated ferrite stainless steel according to claim 1, characterized in that: After fine grinding, the surface to be tested of the sample is polished using a polishing paste with a particle size of 2.5 μm and a polishing cloth until the surface to be tested is bright and scratch-free.
6. The metallographic corrosion method of high-purity ferrite and heat-treated ferrite stainless steel according to claim 1, characterized in that: When cleaning the surface to be tested, first wash it with clean water, then rinse it with anhydrous ethanol, and finally blow dry the sample.
7. The metallographic corrosion method of high-purity ferrite and heat-treated ferrite stainless steel according to claim 1, characterized in that: An austenitic stainless steel plate was immersed in the nitric acid aqueous solution and connected to the negative pole of a DC power supply.
8. The metallographic corrosion method of high-purity ferrite and heat-treated ferrite stainless steel according to claim 1, characterized in that: The DC power supply has a voltage of 1.5V, a current of 0.1A, and a power-on time of 30s.