Polishing agents, methods, and uses for EBSD samples of low-alloy weld metals.

Abstract

This invention provides abrasives, methods, and uses for preparing EBSD samples of low-alloy weld metals. [Solution] The present invention relates to an abrasive, method, and use for EBSD samples of low-alloy weld metal, wherein the abrasive mainly consists of citric acid and silica suspension. When vibration polishing is performed using this abrasive as a base, not only is pitting corrosion prevented from occurring on the low-alloy steel weld sample, but the surface deformation layer is also removed, and the hit rate of the prepared EBSD sample of low-alloy weld metal can reach 98% or more. Citric acid is commonly used as a food additive, is readily available, economical, practical, and environmentally friendly.

Description

[Technical Field]

[0001] The present invention relates to the technical field of metallographic structure inspection, and in particular to an abrasive for EBSD samples of low-alloy weld metal, a method and use thereof. [Background Art]

[0002] Welding is an important process in the manufacture of nuclear power generation equipment, and is the most critical technology that determines manufacturing quality. Welding quality is an important factor for ensuring the safe operation of nuclear power generation. EBSD (Electron Backscatter Diffraction) is widely used for improving welding quality, developing new technologies, and inspecting and analyzing weld metals, bond zones and heat-affected zones. However, as shown in Figure 1, EBSD inspection and analysis require that the sample surface is free of stress layers, oxide layers, continuous corrosion pits and large undulations, and must be clean and non-contaminated. Low-alloy steel is widely used in nuclear power generation equipment. Since the content of alloying elements in low-alloy steel is relatively low, the corrosion resistance of low-alloy steel weld metal to acids and alkalis is even lower. Welding is a process of smelting weld metal that involves structural changes in the weld metal and heat-affected zone. Compared with the base material, the structure of weld metal is more complex and special. For example, since the spatial state of its structure is mainly axial and dendritic crystals, natural micro-segregation exists in the weld metal, low-melting-point impurity elements are concentrated between the dendritic crystals, and the presence of slag inclusions in the weld metal is unavoidable. These characteristics further reduce the corrosion resistance of low-alloy steel weld metal.

[0003] Sample preparation is a crucial step in EBSD inspection, analysis, and related research. Typical EBSD sample preparation involves a rational wire-cutting, embedding, and metallographic polishing process to achieve a scratch-free, mirror-like surface. Then, the deformation layer is removed by oxygen-free vibration polishing before EBSD inspection and analysis. However, polishing agents currently used in the industry cause pitting corrosion in low-alloy steel weld metal. Therefore, EBSD samples of typical low-alloy steel weld metal must be thoroughly vibration polished in a suspension to remove the deformation layer. As shown in Figure 2, severe pitting corrosion has already occurred on the sample's surface after vibration polishing, making it impossible to meet the requirements for EBSD inspection and analysis.

[0004] To study low-alloy steel welds for nuclear power plant equipment using EBSD analysis, it is necessary to develop a manufacturing method and construction process that prevents pitting corrosion when vibrating polishing low-alloy steel weld samples in an oxygen-free environment for EBSD analysis. [Overview of the project] [Problems that the invention aims to solve]

[0005] To address the above-mentioned problems, the present invention provides an abrasive for preparing EBSD samples of low-alloy weld metal, and when vibration polishing is performed using this abrasive as a base, the hit rate of the prepared EBSD samples of low-alloy weld metal can reach 98% or more. [Means for solving the problem]

[0006] To achieve the above objective, the present invention provides an abrasive for preparing EBSD samples of low-alloy weld metals, mainly consisting of citric acid and silica suspension.

[0007] When vibration polishing is performed using the above-mentioned abrasive as a base, not only is pitting corrosion prevented from occurring on low-alloy steel weld samples, but the surface deformation layer is also removed, and the hit rate of the EBSD samples of the prepared low-alloy weld metal can reach over 98%. Citric acid is commonly used as a food additive, is readily available, economical, practical, and environmentally friendly.

[0008] In one embodiment, the pH of the abrasive is 5 to 6.

[0009] Furthermore, the present invention provides a method for producing an abrasive, which includes the steps of preparing a citric acid solution, adding the citric acid solution to a silica suspension, and obtaining an abrasive when the pH reaches 5 to 6.

[0010] Furthermore, the present invention provides a method for preparing an EBSD sample of low-alloy weld metal, comprising the steps of performing a first vibration polishing on a sample to be polished using water and the abrasive as the polishing solution, washing, performing a second vibration polishing using water as the polishing solution, washing, ultrasonic cleaning, drying, and obtaining an EBSD sample of low-alloy weld metal.

[0011] This method is suitable for preparing EBSD samples of low-alloy steel weld metal. Under load, the sample is free from pitting corrosion and the surface deformation layer is removed. Furthermore, vibratory polishing with ultrapure water removes an additional layer of deformation and cleans the polished surface. Ultimately, the hit rate of the EBSD sample can reach over 98%. This method has the potential to become established, is easy to operate, environmentally friendly, economical, and practical. Any operator can follow this method to prepare EBSD samples of low-alloy steel weld metal that meet the required standards.

[0012] In one embodiment, the sample to be polished is a low-alloy weld metal, the duration of the first vibration polishing is 20 to 30 minutes, and the duration of the second vibration polishing is 25 to 35 minutes.

[0013] In one embodiment, a load is applied to the sample to be polished, and the load is 550 to 650 g.

[0014] In one embodiment, the sample to be polished is obtained by cutting the sample, embedding it at room temperature, grinding it, and polishing it.

[0015] Furthermore, the present invention provides an electron backscatter diffraction analysis method for low-alloy weld metal, comprising the step of performing electron backscatter diffraction analysis using an EBSD sample of low-alloy weld metal prepared by the method described above.

[0016] Furthermore, the present invention provides the use of the electron beam backscatter diffraction analysis method in the manufacture of nuclear power generation equipment. [Effects of the Invention]

[0017] The present invention has the following beneficial effects compared to the prior art. The present invention provides an abrasive, method, and use for EBSD samples of low-alloy weld metal. When vibration polishing is performed using this abrasive as a base, not only is pitting corrosion prevented from occurring on the low-alloy steel weld sample, but the surface deformation layer is also removed, and the hit rate of the prepared EBSD sample of low-alloy weld metal can reach 98% or more. This solves the problem that when vibration polishing is performed on low-alloy steel welds, the sample cannot meet the requirements for EBSD inspection and analysis due to pitting corrosion. By performing EBSD inspection and analysis on low-alloy steel welds, welding quality can be improved and new technologies can be developed. [Brief explanation of the drawing]

[0018] [Figure 1] This is the basic form of a sample that can be used for EBSD testing and analysis. [Figure 2] This is a morphology of pitting corrosion in a low-alloy steel weld sample after normal vibration polishing. [Figure 3] This is the EBSD BC+IPF+GB map (hit rate 98.8%) of the SA-508Gr3.C11 weld in Example 1. [Figure 4]It is a BC+IPF+GB map of EBSD of the 16MND5 welded part in Example 2 (hit rate: 98.6%). [Figure 5] It is a BC+IPF+GB map of EBSD of the SA-508Gr3.C11 welded part in Comparative Example 1 (hit rate: 34.5%). [Figure 6] It is a BC+IPF+GB map of EBSD of the SA-508Gr3.C11 welded part in Comparative Example 2 (hit rate: 51.7%). MODE FOR CARRYING OUT THE INVENTION

[0019] Next, in order to facilitate understanding of the present invention, the present invention will be described comprehensively with reference to the relevant drawings. Preferred embodiments of the present invention are shown in the drawings. However, the present invention is not limited to the embodiments described in the present specification, and can be implemented in various forms. These embodiments are provided rather to make the understanding of the content disclosed in the present invention deeper and more complete.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same general meanings as understood by those skilled in the art. The terms used in the specification of the present invention do not limit the present invention, and are merely for describing specific embodiments.

[0021] (Source) Unless otherwise specified, all reagents, materials and equipment used in the present example are commercially available. Unless otherwise specified, all test methods are conventional test methods in the art.

[0022] (Definition) In the present invention, low alloy refers to that the total amount of alloy elements is less than 5%.

[0023] Weld metal refers to a metal formed by fusing the molten welding electrode or welding wire with the base metal during the welding process.

[0024] (Example 1) Welded sample made of SA-508Gr3.C11 material. 1. Sample preprocessing Weld samples made of SA-508Gr3.Cl1 were cut according to the inspection location to create samples with a length of 8-20 mm, a width of 8-20 mm, and a thickness of 2-3 mm. These were then embedded at room temperature to form a Φ40 × 20 mm sample block (the size can be determined according to the abrasive material used). After embedding, the sample was ground using 300 mesh, 600 mesh, 800 mesh, and 1200 mesh waterproof sandpaper in that order until a smooth, fine surface was obtained. Polishing was then started, and diamond sprays of 7 μm, 3.5 μm, 1.5 μm, and 0.5 μm were used in that order until a smooth, clean, mirror-like finish was achieved.

[0025] 2. Preparation of citrate suspension In Step 1, 0.05 g of analytical-grade citric acid was added to 40 mL of distilled water.

[0026] In Step 2, 20 mL of the citric acid aqueous solution prepared in Step 1 was added to 20 mL of SiO2 suspension and stirred until homogeneous. The pH was then measured using pH test paper and should have been between 5 and 6.

[0027] In step 3, 200 mL of distilled water was added to the vibrating disc, and the citric acid suspension prepared in step 2 was uniformly injected into it.

[0028] 3. Vibration polishing After pretreatment, the sample was placed in a vibratory polishing mold, a 600g weight was applied, and the sample was vibrated for 25 minutes. The sample was then removed and rinsed with water for 2 minutes. The citric acid / SiO2 suspension in the polishing plate was discarded and rinsed clean. After that, 250mL of distilled water was added, and the sample was vibrated for another 30 minutes. After completing the vibratory polishing, the sample was removed and rinsed with water for 2 minutes. It was then placed in a beaker, anhydrous ethanol was added, and ultrasonic cleaning was performed for 10 minutes. After drying with hot air, the sample was removed from the embedded mold and subjected to EBSD inspection and analysis using a SEM. The hit rate reached 98.8%, each map was clearly visible, and the collected data was complete. The results are shown in Figure 3.

[0029] (Example 2) Weld sample made of 16MND5 material 1. Sample preprocessing Weld samples made of 16MND5 material were cut according to the inspection location to create samples with a length of 8-20mm, a width of 8-20mm, and a thickness of 2-3mm. These were then embedded at room temperature to form a Φ40×20mm sample block (the size can be determined according to the abrasive material used). After embedding, the sample was ground using 300 mesh, 600 mesh, 800 mesh, and 1200 mesh waterproof sandpaper in that order until a smooth, fine surface was obtained. Polishing was then started, using 7μm, 3.5μm, 1.5μm, and 0.5μm diamond spray in that order until a smooth, clean, mirror-like finish was achieved.

[0030] 2. Preparation of citrate suspension In Step 1, 0.05 g of analytical-grade citric acid was added to 40 mL of distilled water.

[0031] In Step 2, 20 mL of the citric acid aqueous solution prepared in Step 1 was added to 20 mL of SiO2 suspension and stirred until homogeneous. The pH was then measured using pH test paper and should have been between 5 and 6.

[0032] In step 3, 200 mL of distilled water was added to the vibrating disc, and the citric acid suspension prepared in step 2 was uniformly injected into it.

[0033] 3. Vibration polishing After pretreatment, the sample was placed in a vibratory polishing mold, a 600g weight was applied, and vibratory polishing was performed for 25 minutes. The sample was then removed and rinsed with water for 2 minutes. The citric acid / SiO2 suspension in the polishing plate was discarded and rinsed clean. After that, 250mL of distilled water was added, and vibratory polishing was performed for another 30 minutes. After completing the vibratory polishing, the sample was removed and rinsed with water for 2 minutes. It was then placed in a beaker, anhydrous ethanol was added, and ultrasonic cleaning was performed for 10 minutes. After drying with hot air, the sample was removed from the embedded mold and subjected to EBSD inspection and analysis using a SEM. The hit rate reached 98.6%, each map was clearly visible, and the collected data was complete. The results are shown in Figure 4.

[0034] (Comparative Example 1) Welded sample made of SA-508Gr3.C11 material. 1. Sample preprocessing Weld samples made of SA-508Gr3.C11 material were cut according to the inspection location to create samples with a length of 8-20 mm, a width of 8-20 mm, and a thickness of 2-3 mm. These were then embedded at room temperature to form a Φ40 × 20 mm sample block (the size can be determined according to the abrasive material used). After embedding, the sample was ground using 300 mesh, 600 mesh, 800 mesh, and 1200 mesh waterproof sandpaper in that order until a smooth, fine surface was obtained. Polishing was then started, and diamond sprays of 7 μm, 3.5 μm, 1.5 μm, and 0.5 μm were used in that order until a smooth, clean, mirror-like finish was achieved.

[0035] 2. Preparation of the suspension 200 mL of distilled water was added to the vibrating disc, and 20 mL of SiO2 suspension was uniformly injected.

[0036] 3. Vibration polishing After pretreatment, the sample was placed in a vibratory polishing mold, a 600g weight was applied, and vibratory polishing was performed for 25 minutes. The sample was then removed and rinsed with water for 2 minutes. The SiO2 suspension in the polishing plate was discarded and rinsed clean. After that, 250mL of distilled water was added, and vibratory polishing was performed for another 30 minutes. After completing the vibratory polishing, the sample was removed and rinsed with water for 2 minutes. It was then placed in a beaker, anhydrous ethanol was added, and ultrasonic cleaning was performed for 10 minutes. After drying with hot air, the sample was removed from the embedding mold and subjected to EBSD inspection and analysis using a SEM. The hit rate was only 34.5%, indicating severe pitting corrosion. Each map was not clearly visible, and the microstructure could not be distinguished, so analyzing the collected data was meaningless. The results are shown in Figure 5.

[0037] (Comparative Example 2) Welded sample made of SA-508Gr3.C11 material. 1. Sample preprocessing Weld samples made of SA-508Gr3.C11 material were cut according to the inspection location to create samples with a length of 8-20 mm, a width of 8-20 mm, and a thickness of 2-3 mm. These were then embedded at room temperature to form a Φ40 × 20 mm sample block (the size can be determined according to the abrasive material used). After embedding, the sample was ground using 300 mesh, 600 mesh, 800 mesh, and 1200 mesh waterproof sandpaper in that order until a smooth, fine surface was obtained. Polishing was then started, and diamond sprays of 7 μm, 3.5 μm, 1.5 μm, and 0.5 μm were used in that order until a smooth, clean, mirror-like finish was achieved.

[0038] 2. Preparation of glacial acetic acid suspension In Step 1, 1 mL of glacial acetic acid was added to 40 mL of distilled water.

[0039] In Step 2, 3 mL of the glacial acetic acid solution prepared in Step 1 was added to 20 mL of SiO2 suspension and stirred until homogeneous. The pH was then measured using pH test paper and should have been between 5 and 6.

[0040] In step 3, 230 mL of distilled water was added to the vibrating disc, and the glacial acetic acid suspension prepared in step 2 was uniformly injected.

[0041] 3. Vibration polishing After pretreatment, the sample was placed in a vibratory polishing mold, a 600g weight was applied, and the sample was vibrated for 25 minutes. The sample was then removed and rinsed with water for 2 minutes. The glacial acetic acid / SiO2 suspension in the polishing plate was discarded and rinsed clean. After that, 250mL of distilled water was added, and the sample was vibrated for another 30 minutes. After completing the vibratory polishing, the sample was removed and rinsed with water for 2 minutes. It was then placed in a beaker, anhydrous ethanol was added, and ultrasonic cleaning was performed for 10 minutes. After drying with hot air, the sample was removed from the embedding mold and subjected to EBSD inspection and analysis using a SEM. The hit rate was only 51.7%, and each map was not clearly visible, making it impossible to distinguish the microstructure. Therefore, analyzing the collected data is meaningless. The results are shown in Figure 6.

[0042] The technical features of the embodiments described above can be combined in any way, and for the sake of simplicity, not all possible combinations of the technical features in the embodiments described above are described. However, as long as there is no inconsistency in these combinations of technical features, any of them shall be considered to be described herein.

[0043] The embodiments described above illustrate only a few of the present invention, but they are described concretely and in detail and should not be understood as limiting the scope of the patent for this invention. Those skilled in the art should note that various modifications and improvements can be made without departing from the concept of the present invention, and these also fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention is subject to the claims set forth below.

Claims

1. An abrasive for preparing EBSD samples of low-alloy steel weld metal, characterized by mainly consisting of citric acid and silica suspension, with a pH of 5 to 6 for the abrasive.

2. A method for producing an abrasive according to claim 1, characterized by comprising the steps of preparing a citric acid solution, adding the citric acid solution to a silica suspension, and obtaining an abrasive when the pH reaches 5 to 6.

3. A method for producing an EBSD sample of low-alloy steel weld metal, comprising the steps of: performing a first vibration polishing on a sample to be polished using water and the abrasive described in claim 1 as the polishing solution; washing the sample; performing a second vibration polishing on a sample to be polished using water as the polishing solution; washing the sample; ultrasonic cleaning; drying the sample; and obtaining an EBSD sample of low-alloy steel weld metal.

4. The method according to claim 3, characterized in that the sample to be polished is a low-alloy steel weld metal, the duration of the first vibration polishing is 20 to 30 minutes, and the duration of the second vibration polishing is 25 to 35 minutes.

5. The method according to claim 3, characterized in that a load is applied to the sample to be polished, and the load is 550 to 650 g.

6. The method according to claim 3, characterized in that the sample to be polished is obtained by cutting the sample, embedding it at room temperature, grinding it, and polishing it.

7. A method for electron beam backscatter diffraction analysis of low-alloy steel weld metal, characterized by comprising the step of performing electron beam backscatter diffraction analysis using an EBSD sample of low-alloy steel weld metal prepared by the method described in claim 3.

8. Use of the electron beam backscatter diffraction analysis method according to claim 7 in the manufacture of a nuclear power plant.

Images