Etchant and etching method for microstructure of mn-mo-ni steel for nuclear power in situ

Abstract

This invention relates to an etchant and etching method for the in-situ microstructure of Mn-Mo-Ni steel used in nuclear power plants, and relates to the field of nuclear power equipment testing. The etching method is easy to operate and can clearly and completely etch out microstructures such as tempered bainite grain boundaries, fine bainite lath / block structures, and finely dispersed carbides, meeting the specific requirements of in-situ micro-etching, such as rapid volatilization, suitable etching time, and safety and environmental protection requirements.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of nuclear power equipment detection, and discloses an etchant for in-situ microstructure of Mn-Mo-Ni steel for nuclear power and an etching method. BACKGROUND

[0002] Nuclear power equipment has extremely strict requirements on materials: high temperature and high pressure, strong radiation, long-term service (more than 60 years), and extremely high safety and reliability. High-strength Mn-Mo-Ni steel has become the main structural material of key equipment in the nuclear island (such as reactor pressure vessels, steam generator shells, and pressurizers) due to its good strength, toughness, weldability, anti-irradiation embrittlement capability, and relatively mature manufacturing process.

[0003] The core performance (high strength, high toughness, and anti-irradiation embrittlement) of Mn-Mo-Ni steel (such as SA-508 Gr.3) for nuclear power equipment is obtained through heat treatment, and the microstructure of the tempered bainite is obtained, and the high-density dislocation, fine bainite lath bundle / block structure, and fine dispersed carbide microstructure structure of the tempered bainite are the key characteristics to achieve the perfect balance of high strength and excellent toughness (especially low-temperature toughness and anti-irradiation embrittlement toughness).

[0004] In the manufacturing of nuclear power equipment, it is often necessary to perform in-situ micro-detection on key parts (such as welds, heat-affected zones, and material bodies) to evaluate the material state, diagnose failure causes, verify manufacturing quality, and provide technical support for process optimization. Etching is a key step for revealing the microstructure of materials, and its importance cannot be overemphasized. Without proper etching, the microstructure of metals (such as grain boundaries, phase composition, defects, and machining marks) is like "invisible" and cannot be effectively observed and analyzed by an optical microscope. In-situ micro-etching has special characteristics: the clear microstructure image obtained through immediate etching is required for on-site decision-making, and the success or failure of the etching step directly determines the accuracy of on-site judgment; the environment (wind, light, temperature, and space) affects the volatilization, reaction rate, and operation precision of the etchant, and also directly affects safety and environmental protection.

[0005] In the field of physical and chemical detection technology, the tempered bainite of high-strength low-alloy steel is a complex microstructure, and it is more challenging to etch for in-situ micro-detection,

[0006] The nitric acid alcohol solution commonly used in the industry can preferentially corrode carbides in low alloy steel organization due to its strong oxidizing and corrosive properties, and often shows the organization as the matrix plus carbides, and cannot show the diversity of grain orientation, so it is difficult to show the tempered bainite grain boundary, the fine bainite lath bundle / block structure morphology, and cannot evaluate the material state, diagnose the failure cause, monitor the damage progress, and verify the manufacturing and maintenance quality. Solving this technical problem has become an important research direction to promote the upgrading of nuclear power equipment manufacturing technology.

[0007] In the field of nuclear power equipment manufacturing, Mn-Mo-Ni steel is the main structural material of nuclear power equipment, and the relationship between the microstructure, composition or defect detection and analysis is related to the evaluation of material state, diagnosis of failure cause, verification of manufacturing quality and optimization of process. These works are entirely dependent on etching of microstructure. However, the nitric acid alcohol solution commonly used in the physical and chemical detection technology cannot etch the tempered bainite grain boundary, the fine bainite lath bundle / block structure of the Mn-Mo-Ni steel for nuclear power equipment, and cannot meet the special requirements of in-situ micro-etching, such as faster evaporation, appropriate etching time and safety and environmental protection.

[0008] The existence of the above technical bottleneck urgently needs to develop an etching method for Mn-Mo-Ni steel, which can etch clear and complete tempered bainite grain boundary, fine bainite lath bundle / block structure and fine and dispersed carbides and other microstructures, and meet the special requirements of in-situ micro-etching, such as faster evaporation, appropriate etching time and safety and environmental protection. SUMMARY

[0009] In view of the above problems, the present application provides an etching method for in-situ microstructure of Mn-Mo-Ni steel for nuclear power, which is easy to operate, can clearly and completely etch the tempered bainite grain boundary, the fine bainite lath bundle / block structure and the fine and dispersed carbides and other microstructures, and meet the special requirements of in-situ micro-etching, such as faster evaporation, appropriate etching time and safety and environmental protection.

[0010] The present application provides an etching method for in-situ microstructure of Mn-Mo-Ni steel for nuclear power, comprising the following steps:

[0011] Preparation of detection surface: select detection points, obtain the detection area, surface preparation, polishing, cleaning, and obtain the detection surface;

[0012] Etching: dip the etching agent for in-situ microstructure of Mn-Mo-Ni steel for nuclear power, wipe the detection surface, carry out corrosion, remove the corrosion products, and obtain the Mn-Mo-Ni steel for nuclear power used for microstructure evaluation; the etching agent is composed of FeCl3, a reagent containing a hydrocarbon solvent, and anhydrous ethanol; the hydrocarbon solvent is solvent oil.

[0013] The reagent containing the hydrocarbon solvent is actually a solvent type metal cleaning agent. The inventors have found that the solvent type metal cleaning agent has a good etching effect when compounded with FeCl3 and anhydrous ethanol. The ferric chloride (FeCl3) can form a complex with many solvents and can be used to prepare a protective film on the surface of a metal to protect electronic components from oxidation and corrosion. The hydrocarbon solvent has the advantages of strong volatility, good stability, low toxicity, and the ability to dissolve corrosion products. The anhydrous ethanol, as a key organic solvent, can dissolve many organic substances. The three raw materials are compounded, the hydrocarbon solvent is used together with the anhydrous ethanol to change the polarity of the organic solvent, balance the electrochemical difference of the microstructure, and facilitate the highlighting of the grain boundary. In addition, the addition of the hydrocarbon solvent increases the evaporation speed of the etchant and reduces the risk of over-corrosion. Therefore, the inventors propose an etchant for the in-situ microstructure of Mn-Mo-Ni steel for nuclear power, which is obtained by compounding the above three raw materials. Based on this, an etching method for the in-situ microstructure of Mn-Mo-Ni steel for nuclear power is built. The raw materials of the etchant meet the requirements of national standards 16483-2008 and 17519-2013. The etching method is easy to operate and can clearly and completely etch the microstructure such as the tempered bainite grain boundary, fine bainite lath bundle / block structure, and fine dispersed carbide, which meets the special requirements of in-situ micro-etching, such as faster evaporation, appropriate etching time, and safety and environmental protection.

[0014] In one of the embodiments, in the etching step, corrosion is performed until the detection surface is in a matte state.

[0015] In one of the embodiments, in the etching agent, the amount ratio of FeCl3, the reagent containing the hydrocarbon solvent, and anhydrous ethanol is (2-3) g:10 mL:10 mL.

[0016] In one of the embodiments, the reagent containing the hydrocarbon solvent is composed of solvent oil and organic solvent; the solvent oil includes petroleum ether, and the organic solvent includes isopropyl alcohol.

[0017] In one of the embodiments, the mass percentage of the solvent oil in the reagent containing the hydrocarbon solvent is 30%-80%, and the rest is organic solvent.

[0018] In one of the embodiments, the surface preparation includes cleaning the area to be detected and flattening the area to be detected.

[0019] The grinding and polishing include mechanically grinding and polishing the area to be detected and spray polishing.

[0020] In one of the embodiments, the flattening is achieved by an angle grinder and a belt sander, the mechanical grinding and polishing are achieved by a grinding and polishing machine, and the spray polishing is achieved by a diamond spray.

[0021] The present invention also provides an etchant for the etching method described herein.

[0022] The present invention also provides the application of the etching method in the microstructure evaluation of Mn-Mo-Ni steel for nuclear power.

[0023] The present invention also provides the application of the etchant in the microstructure evaluation of Mn-Mo-Ni steel for nuclear power.

[0024] The present invention also provides a method for evaluating the microstructure of Mn-Mo-Ni steel for nuclear power, comprising the following steps: processing the Mn-Mo-Ni steel for nuclear power using the etching method to obtain Mn-Mo-Ni steel for nuclear power for microstructure evaluation, performing metallographic testing, and evaluating the microstructure.

[0025] In one embodiment, the method for evaluating the microstructure of the nuclear power Mn-Mo-Ni steel includes the following steps:

[0026] 1. Prepare the etching solution for later use:

[0027] Weigh 2-3g FeCl3 (analytical grade), 10ml of a reagent containing hydrocarbon solvent (containing 30-80% solvent oil by mass, with the remainder being organic solvent), and 10ml of anhydrous ethanol; pour the FeCl3, the reagent containing hydrocarbon solvent, and the anhydrous ethanol into a glass container in sequence, stir well, and then put the mixture into a glass bottle and seal it for later use.

[0028] 2. Preparation of the detection surface:

[0029] a. Selecting testing points: Identify the key or suspicious areas that need to be inspected.

[0030] b. Surface preparation:

[0031] Cleaning: Remove oil stains from the area to be inspected using a cleaning agent.

[0032] Rough grinding / leveling: Use a portable angle grinder or belt sander to remove the uneven layer on the surface and obtain a relatively flat surface of about 50×50mm.

[0033] c. Fine grinding and polishing:

[0034] Portable polishing machines use sandpaper ranging from coarse to fine: 120# → 300# → 600# → 800# → 1200#, followed by polishing with diamond spray.

[0035] d. Wipe the polished surface and surrounding area clean with anhydrous ethanol cotton balls.

[0036] e. Etching: Soak a cotton ball with the prepared etching solution in the glass bottle, squeeze out the excess solution, wipe the polished test surface, observe the test surface change from glossy to matte, and wipe the corrosion products clean with anhydrous ethanol cotton ball.

[0037] f. After observing and acquiring images using a portable metallurgical microscope, the microstructure can be evaluated.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] This invention uses ferric chloride, hydrocarbon solvents, and anhydrous ethanol as basic raw materials. Through precise proportioning, it provides a formulation and application method for an etching agent suitable for the microstructure of Mn-Mo-Ni steel used in nuclear power equipment. This invention allows for in-situ microscopic inspection of Mn-Mo-Ni steel used in nuclear power equipment. It directly assesses and analyzes the structure, composition, or defects of key areas (such as welds, heat-affected zones, and the material itself) at the microscale (typically micrometer or even nanometer level) to rapidly evaluate material condition, diagnose failure causes, verify manufacturing quality, and provide technical support for process optimization. Through the precise proportioning of ferric chloride, hydrocarbon solvents, and anhydrous ethanol, the interaction of these substances clearly and completely etches the microstructure.

[0040] The core advantages of this technology are reflected in three aspects:

[0041] Firstly, technological innovation. By precisely proportioning ferric chloride, hydrocarbon solvents, and anhydrous ethanol, the bottleneck of in-situ microscopic detection of Mn-Mo-Ni steel for nuclear power applications has been overcome, significantly improving the clarity and integrity of the microstructure. This is of great value for assessing material condition, diagnosing failure causes, verifying manufacturing quality, and optimizing processes.

[0042] Secondly, the combination of hydrocarbon solvent and anhydrous ethanol changes the polarity of the organic solvent, balances the electrochemical difference of the microstructure, and facilitates the prominent display of grain boundaries. Moreover, the addition of hydrocarbon solvent increases the evaporation rate of the etchant, reducing the risk of over-corrosion. This formula is simple, and the etching method built on this formula is easy to operate. It can clearly and completely etch tempered bainite grain boundaries, fine bainite lath bundles / block structures, and fine dispersed carbides, etc., meeting the special requirements of in-situ micro-etching, such as faster evaporation, appropriate etching time, and safety and environmental protection requirements.

[0043] Thirdly, ferric chloride, hydrocarbon solvents, and anhydrous ethanol are common raw materials used in laboratory preparation. They are inexpensive, readily available, safe, and environmentally friendly, causing no pollution to the environment. The operation process is controllable and unlikely to pose safety hazards to operators, making them particularly suitable for safe on-site operation. Attached Figure Description

[0044] Figure 1The in-situ microstructure morphology of SA-508 Gr.3 steel etched with 10% ferric chloride etchant in Example 1, 400X;

[0045] Figure 2 The in-situ microstructure morphology of SA-508 Gr.3 steel etched with 15% ferric chloride etchant in Example 2, 400X;

[0046] Figure 3 The in-situ microstructure morphology of 18MND5 steel wiped with 4% nitric acid alcohol in Comparative Example 1 is shown at 400X.

[0047] Figure 4 The image shows the in-situ microstructure of SA-508 Gr.3 steel etched with an anhydrous ethanol solution containing 10% ferric chloride in Comparative Example 2, at 400X. Detailed Implementation

[0048] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0049] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0050] Unless otherwise specified, all reagents, materials, and equipment used in this embodiment are commercially available; unless otherwise specified, all test methods are conventional test methods in this field.

[0051] The etchant preparation method for the in-situ microstructure of Mn-Mo-Ni steel for nuclear power plants, and the microstructure evaluation method for Mn-Mo-Ni steel for nuclear power plants, are detailed below in various embodiments of this invention:

[0052] 1. Prepare the etching solution for later use:

[0053] Weigh 2-3g of FeCl3 (analytical grade), 10ml of a reagent containing hydrocarbon solvent (containing 30-80% solvent oil by mass, with the remainder being organic solvent), and 10ml of anhydrous ethanol; pour the FeCl3, hydrocarbon solvent, and anhydrous ethanol into a glass container in sequence and stir well to obtain an etching agent with a FeCl3 mass concentration of 10%-15%, and seal it in a glass bottle for later use;

[0054] 2. Preparation of the detection surface:

[0055] a. Selecting testing points: Identify the key or suspicious areas that need to be inspected.

[0056] b. Surface preparation:

[0057] Cleaning: Remove oil stains from the area to be inspected using a cleaning agent.

[0058] Rough grinding / leveling: Use a portable angle grinder or belt sander to remove the uneven layer on the surface and obtain a relatively flat surface of about 50×50mm.

[0059] c. Fine grinding and polishing:

[0060] Portable polishing machines use sandpaper ranging from coarse to fine: 120# → 300# → 600# → 800# → 1200#, followed by polishing with diamond spray.

[0061] d. Wipe the polished surface and surrounding area clean with anhydrous ethanol cotton balls.

[0062] e. Etching: Soak a cotton ball with the prepared etching solution in the glass bottle, squeeze out the excess solution, wipe the polished test surface, observe the test surface change from glossy to matte, and wipe the corrosion products clean with anhydrous ethanol cotton ball.

[0063] f. After observing and acquiring images using a portable metallurgical microscope, the microstructure can be evaluated.

[0064] The reagent containing hydrocarbon solvent in the following examples is: a solvent oil containing 30-80% by mass and the balance being isopropanol. Specifically, Jinrun JRH-101 nuclear metal solvent cleaner is used, which was purchased from Jinrun (Dalian) Fine Chemical Technology Co., Ltd. This nuclear metal solvent cleaner is composed of 30-80% by mass of solvent oil (i.e., petroleum ether) with CAS number 8032-32-4 and 20-70% by mass of isopropanol with CAS number 67-63-0.

[0065] Example 1

[0066] The equipment is made of SA-508 Gr.3 material. After determining the inspection surface and removing oil stains, use a portable grinder to grind the inspection surface to a flat surface of about 50×50mm. Use sandpaper from coarse to fine: 120# → 300# → 600# → 800# → 1200#. Then polish with diamond spray. Wipe the polished surface and surrounding area clean with anhydrous ethanol cotton balls. Soak cotton balls with 10% ferric chloride etching agent prepared in a glass bottle, squeeze out the excess liquid, and wipe the polished inspection surface to etch. Observe the inspection surface change from glossy to matte. Wipe the corrosion products clean with anhydrous ethanol cotton balls.

[0067] After observing and acquiring images using a portable metallographic microscope, the microstructure can be evaluated: fine-sized effective grains of tempered bainite, small lath bundles / blocks with clear orientation, fine and dispersed carbides, and a clear and complete microstructure are observed, meeting the requirements of SA-508 Gr.3 for nuclear power applications. Figure 1 .

[0068] Example 2

[0069] The equipment is made of SA-508 Gr.3 material. After determining the test surface and removing oil stains, use a portable grinder to grind the test surface to a flat surface of about 50×50mm. Use sandpaper from coarse to fine: 120# → 300# → 600# → 800# → 1200#. Then polish with diamond spray. Wipe the ground surface and surrounding area clean with anhydrous ethanol cotton balls. Soak cotton balls with 15% ferric chloride etching agent prepared in a glass bottle, squeeze out the excess solution, and wipe the ground test surface to etch. Observe the test surface change from glossy to matte. Wipe the corrosion products clean with anhydrous ethanol cotton balls.

[0070] After observing and acquiring images using a portable metallographic microscope, the microstructure can be evaluated: fine-sized effective grains of tempered bainite, small lath bundles / blocks with clear orientation, fine and dispersed carbides, and a clear and complete microstructure are observed, meeting the requirements of SA-508 Gr.3 for nuclear power applications. Figure 2 .

[0071] Comparative Example 1

[0072] The equipment is made of SA-508 Gr.3 material. After determining the test surface and removing oil stains, use a portable grinder to grind the test surface to a flat surface of about 50×50mm. Use sandpaper from coarse to fine: 120# → 300# → 600# → 800# → 1200#. Then polish with diamond spray. Wipe the ground surface and surrounding area clean with anhydrous ethanol cotton balls. Soak cotton balls with a prepared 4% nitric acid alcohol solution and wipe the ground test surface. Observe the test surface change from shiny to matte. Wipe away the corrosion products with anhydrous ethanol cotton balls.

[0073] Microstructural assessment can be performed after observation and image acquisition using a portable metallographic microscope: If the microstructure is unclear or incomplete, and only carbides can be observed, it cannot be used to evaluate the base material of SA-508 Gr.3 equipment for nuclear power plants. (See...) Figure 3 .

[0074] Comparative Example 2

[0075] The equipment is made of SA-508 Gr.3 material. After determining the test surface and removing oil stains, use a portable grinder to grind the test surface to a flat surface of about 50×50mm. Use sandpaper from coarse to fine: 120# → 300# → 600# → 800# → 1200#. Then polish with diamond spray. Wipe the ground surface and surrounding area clean with anhydrous ethanol cotton balls. Soak cotton balls with a 10% anhydrous ethanol solution of ferric chloride (prepared by 2g ferric chloride and 20mL anhydrous ethanol) and wipe the ground test surface. Observe the test surface change from shiny to matte. Wipe away the corrosion products with anhydrous ethanol cotton balls.

[0076] Microstructural assessment can be performed after observation and image acquisition using a portable metallurgical microscope: If the microstructure is unclear or incomplete, the SA-508 Gr.3 base material for nuclear power equipment cannot be evaluated. (See...) Figure 4 .

Claims

1. A method for etching the in-situ microstructure of Mn-Mo-Ni steel for nuclear power plants, characterized in that, Includes the following steps: Preparation of the test surface: Select the test point to obtain the area to be tested, prepare the surface, grind and polish, clean, and obtain the test surface; Etching: Dip the surface of the test surface in the etching agent for the in-situ microstructure of nuclear power Mn-Mo-Ni steel, and etch it to remove the corrosion products to obtain nuclear power Mn-Mo-Ni steel for microstructure evaluation; the etching agent is composed of FeCl3, a reagent containing petroleum ether, and anhydrous ethanol; the ratio of FeCl3, the reagent containing petroleum ether, and anhydrous ethanol is (2-3) g: 10 mL: 10 mL; The petroleum ether-containing reagent is composed of petroleum ether and an organic solvent, wherein the mass percentage of petroleum ether in the petroleum ether-containing reagent is 30%-80%, and the organic solvent includes isopropanol.

2. The etching method according to claim 1, characterized in that, The surface preparation includes: cleaning the area to be inspected and leveling the area to be inspected; The polishing process includes: mechanically polishing the area to be inspected and spray polishing.

3. The etchant used in the etching method according to any one of claims 1-2.

4. The application of the etching method according to any one of claims 1-2 in the microstructure evaluation of Mn-Mo-Ni steel for nuclear power.

5. The application of the etchant according to claim 3 in the microstructure evaluation of Mn-Mo-Ni steel for nuclear power.

6. A method for evaluating the microstructure of Mn-Mo-Ni steel for nuclear power plants, characterized in that, The process includes the following steps: processing nuclear power Mn-Mo-Ni steel using the etching method described in any one of claims 1-2 to obtain nuclear power Mn-Mo-Ni steel for microstructure evaluation, performing metallographic testing, and evaluating the microstructure.

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