Metallographic etching solution and metallographic etching method for dissimilar material welded joint

Abstract

The application discloses a metallographic corrosion liquid for dissimilar material welded joints, and relates to the technical field of metallographic preparation.The metallographic corrosion liquid comprises 35-50 ml of ethanol, 40-50 ml of nitric acid, 20-30 g of ferric chloride and 20-40 ml of glycerol according to the amount ratio.The application further discloses a metallographic corrosion method for dissimilar material welded joints, which uses the above-mentioned corrosion liquid to corrode the dissimilar metal welded joints.The application is suitable for the metallographic corrosion of nickel-based alloy / bainite steel dissimilar material welded joints, solves the problems that the corrosion time of traditional corrosion agents for dissimilar welded joint samples is difficult to accurately grasp and the corrosion liquid is difficult to be stored for a long time, and has the characteristics of smooth and stable corrosion process, good tissue display after corrosion, long-term storage resistance, simple operation and less pollution.

Description

Technical Field

[0001] This invention relates to the field of metallographic preparation technology, and in particular to a metallographic etching solution and method for welding joints of dissimilar materials. Background Technology

[0002] With the concepts of carbon neutrality and carbon peaking gaining widespread acceptance, nuclear power, as a green power generation technology, has ample market prospects and application space. In pressurized water reactor nuclear power plants, pressure vessels such as reactor pressure vessels, pressurizers, and steam generator shells are mainly made of high-strength, low-cost low-alloy steel, with a bainitic microstructure. The coolant main pipes, on the other hand, are primarily made of highly corrosion-resistant austenitic stainless steel. The connection point—the safety end—between these low-alloy steel pressure vessels and high-alloy stainless steel main pipes is a dissimilar material welded joint, typically using nickel-based alloy welding wire. Nuclear power plant operation involves significant radiation, making the reliability of dissimilar material welded joints crucial. Fractures and other safety issues can have serious consequences, and the area near the fusion line is often a weak point in performance. Therefore, accurately and effectively detecting and analyzing the metallographic microstructure of the area near the fusion line is of significant practical importance for optimizing the nickel-based alloy / bainitic steel dissimilar material welding process and ensuring the safe use of dissimilar material welded joints.

[0003] Currently, metallographic corrosion of dissimilar welded joints of nickel-based alloys and bainitic steel presents challenges. Bainitic steel is typically corroded using a nitric acid-alcohol solution, while nickel-based alloys are usually corroded using aqua regia. Aqua regia is highly corrosive and easily decomposes, making precise control difficult when working with dissimilar welded joint samples. This often results in over-corrosion of the bainitic steel side of the fusion line by aqua regia, or insufficient corrosion of the nickel-based alloy side.

[0004] Furthermore, existing etching solutions such as nitric acid-alcohol and aqua regia need to be prepared fresh for each use, making them difficult to store long-term and causing inconvenience in operation. Additionally, immersing samples in the etching solution typically contaminates the solution and wastes a significant amount of etching solution.

[0005] Therefore, those skilled in the art are dedicated to developing a metallographic etching solution and method for dissimilar material welded joints, which can be applied to the metallographic etching of nickel-based alloy / bainitic steel dissimilar material welded joints, and can maintain good etching effect even after long-term preservation. Summary of the Invention

[0006] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is that it is difficult to accurately control the corrosion of dissimilar welded joint samples by existing corrosive liquids, the corrosive liquids are difficult to preserve for a long time, and the immersion corrosion causes waste and pollution.

[0007] To achieve the above objectives, the present invention provides a metallographic etching solution for dissimilar material welded joints, comprising ethanol, nitric acid, ferric chloride and glycerol.

[0008] Furthermore, the ratio of the amounts of ethanol, nitric acid, glycerol and ferric chloride is (35-50 ml): (40-50 ml): (20-40 ml): (20-30 g).

[0009] Furthermore, the ethanol is 98% anhydrous ethanol, the nitric acid is 68% concentrated nitric acid, and the ferric chloride and glycerol are of analytical grade.

[0010] Furthermore, the metallographic etching solution is suitable for welding joints of dissimilar materials such as nickel-based alloys and bainitic steel.

[0011] The present invention also provides a metallographic etching method for welded joints of dissimilar materials, using the metallographic etching solution as described in claims 1 to 4, the method comprising the following steps:

[0012] Step 1: Measure ethanol, nitric acid, glycerol and ferric chloride to prepare the metallographic etching solution;

[0013] Step 2: The dissimilar material welded joint samples are subjected to wire cutting, inlaying, rough grinding, fine grinding, polishing, ultrasonic cleaning, alcohol rinsing and blow treatment to obtain metallographic samples;

[0014] Step 3: Place the pretreated metallographic sample flat and use the metallographic etching solution prepared in Step 1 to etch the metallographic sample.

[0015] Step 4: Clean the corroded sample with alcohol and dry it with a hair dryer.

[0016] Furthermore, step 1 also includes:

[0017] Step 1.1: Place ferric chloride into a container containing ethanol and stir thoroughly until the ferric chloride dissolves to obtain an ethanol solution of ferric chloride.

[0018] Step 1.2: Pour the ethanol solution of ferric chloride obtained in step 1.1 into nitric acid to induce an esterification reaction;

[0019] Step 1.3: After the esterification reaction is complete, pour glycerol into the solution from Step 1.2 and stir thoroughly until homogeneous.

[0020] Step 1.4: After standing for a period of time, the corrosive solution is obtained and bottled.

[0021] Furthermore, the settling time in step 1.4 is 20 to 60 minutes.

[0022] Furthermore, the etching step in step 3 specifically involves: using a dropper to drop the metallographic etching liquid onto the metallographic sample and completely covering it, utilizing the surface tension of the liquid to form a surface etching cap layer, followed by static etching.

[0023] Furthermore, the corrosion time in step 3 is 25–45 minutes.

[0024] Furthermore, in step 3, the end of corrosion is indicated by the sample corrosion surface turning silver-gray.

[0025] Aqua regia, a mixture of concentrated nitric acid and concentrated hydrochloric acid, is highly corrosive. This invention uses ferric chloride instead of concentrated hydrochloric acid; the chloride ions it provides, in combination with ethyl nitrate, indirectly achieve the corrosive effect of aqua regia. Furthermore, due to its low concentration and weak acidity, the corrosiveness is not strong, and over-corrosion is less likely. Glycerol, as an activator, can improve the corrosion effect on the sample surface. The water generated by the esterification reaction can dilute the solution, making the corrosion process more stable. The synergistic effect of these components results in excellent corrosion performance on nickel-based alloy / bainitic steel dissimilar material welded joint samples.

[0026] In addition, ethyl nitrate is produced by the esterification reaction of nitric acid and ethanol, thus avoiding the decomposition of nitric acid and the resulting decrease in corrosiveness.

[0027] Compared with the prior art, the present invention has the following beneficial technical effects:

[0028] 1. The entire corrosion process is smooth and stable, unlikely to cause over-corrosion, and the microstructure is well displayed after corrosion.

[0029] 2. The corrosive solution of the present invention maintains good corrosive effect even after long-term storage.

[0030] 3. The etching solution of this invention utilizes liquid surface tension to cover the sample surface, thus avoiding immersion etching. This allows for single-use of the etching solution, saving solution, simplifying operation, and preventing contamination caused by immersion etching.

[0031] The following will further explain the concept, specific structure, and technical effects of the present invention in conjunction with the accompanying drawings, so as to fully understand the purpose, features, and effects of the present invention. Attached Figure Description

[0032] Figure 1 This is a metallographic sample diagram of a preferred embodiment of the present invention;

[0033] Figure 2 This is a preferred embodiment of the present invention, showing the corrosion cap layer formed on a sample of a nickel-based alloy / bainitic steel dissimilar material welded joint after corrosion by an etchant.

[0034] Figure 3Metallographic microstructure of a nickel-based alloy / bainitic steel dissimilar material welded joint sample after corrosion by an etchant according to a preferred embodiment of the present invention.

[0035] Figure 4 This is a metallographic microstructure image of a nickel-based alloy / bainitic steel dissimilar material welded joint sample after being corroded by a corrosion solution for 15 days, according to a preferred embodiment of the present invention.

[0036] Figure 5 The specimens were obtained by etching a dissimilar welded joint of nickel-based alloy / bainitic steel using only a nitric acid alcohol solution.

[0037] Figure 6 These are metallographic microstructure images of dissimilar material welded joint samples of nickel-based alloys and bainitic steel after corrosion using only aqua regia.

[0038] Figure 7 The image shows a sample of a welded joint of dissimilar materials, nickel-based alloy and bainitic steel, which was first corroded with a nitric acid alcohol solution, and then corroded with aqua regia, resulting in over-corrosion of one side of the bainitic steel.

[0039] Figure 8 The image shows an incomplete corrosion of the nickel-based alloy side after the sample of the dissimilar material welded joint was first etched with a nitric acid alcohol solution and then corroded with aqua regia. Detailed Implementation

[0040] The following description, with reference to the accompanying drawings, illustrates several preferred embodiments of the present invention to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0041] In the accompanying drawings, components with the same structure are indicated by the same numerical designation, and components with similar structures or functions are indicated by similar numerical designations. The dimensions and thicknesses of each component shown in the drawings are arbitrary, and the present invention does not limit the dimensions and thicknesses of each component. To make the illustrations clearer, the thickness of some components has been appropriately exaggerated in the drawings.

[0042] Example 1

[0043] The corrosive solution consists of 50 ml of ethanol, 50 ml of 68% nitric acid, 25 g of ferric chloride, and 30 ml of glycerol. All of the ethanol, nitric acid, ferric chloride, and glycerol are of analytical grade.

[0044] A method for preparing a metallographic etching solution for dissimilar material welded joints of nickel-based alloys and bainitic steel, specifically including the following steps:

[0045] First, measure 50 ml of ethanol, 50 ml of 68% nitric acid, and 30 ml of glycerol into separate beakers. Weigh 25 g of ferric chloride onto measuring paper. Then, add the ferric chloride to the beaker containing ethanol and stir thoroughly until completely dissolved. Next, pour the dissolved ethanol solution into the nitric acid to initiate an esterification reaction. After the reaction is complete, add glycerol to the solution and stir thoroughly. Finally, let stand for 30 minutes to obtain the etching solution, which is then bottled.

[0046] The nickel-based alloy / bainitic steel dissimilar material welded joint samples underwent pretreatment including wire cutting, rough grinding, fine grinding, polishing, ultrasonic cleaning, alcohol rinsing, and blow-drying. The pretreated samples are shown below. Figure 1 As shown. The pretreated sample is then placed flat on a horizontal surface, and the etching solution is dripped onto the sample surface using a dropper until it is completely covered. The surface tension of the liquid forms a surface etching cap. At this point, the sample undergoing etching appears as shown. Figure 2 As shown. Next, allow the sample to stand for 30 minutes to etch until the etched surface turns silvery-gray. Finally, rinse the etched sample with alcohol and dry it with a hairdryer to complete the metallographic etching process. Figure 3 The image shows the metallographic microstructure of the nickel-based alloy / bainitic steel dissimilar material welded joint sample after corrosion. It can be seen that both the nickel-based alloy side and the bainitic steel side of the fusion line are well corroded, and there is no incomplete corrosion or over-corrosion.

[0047] After the prepared etching solution was left to stand for 15 days, it was used to etch a sample of a nickel-based alloy / bainitic steel dissimilar material welded joint, and the resulting metallographic microstructure is shown in the figure below. Figure 4 As shown, both the nickel-based alloy side and the bainitic steel side of the fusion line are completely corroded, with no incomplete or over-corrosion issues. This indicates that the corrosive solution can still effectively corrode dissimilar material welded joints even after a considerable period of time.

[0048] Example 2

[0049] The etching solution consisted of 40 ml ethanol, 45 ml nitric acid (68% by mass), 30 g ferric chloride, and 40 ml glycerol. All components—ethanol, nitric acid, ferric chloride, and glycerol—were of analytical grade. The preparation and use of the etching solution were the same as in Example 1, except that the standing etching time was changed to 25 min.

[0050] Example 3

[0051] The etching solution consisted of 35 ml ethanol, 40 ml 68% nitric acid, 20 g ferric chloride, and 20 ml glycerol, all of which were of analytical grade. The preparation and use of the etching solution were the same as in Example 1, except that the standing etching time was changed to 45 min.

[0052] Comparative Example 1

[0053] The metallographic microstructure of the nickel-based alloy / bainitic steel dissimilar material welded joint specimen was obtained by etching with only nitric acid alcohol solution. See attached image. Figure 5 It can be seen that it only affects one side of bainitic steel.

[0054] Comparative Example 2

[0055] The metallographic microstructure of the nickel-based alloy / bainitic steel dissimilar material welded joint specimens was obtained by etching with aqua regia only. See [image of microstructure]. Figure 6 It can be seen that the nickel-based alloy side has been corroded to reveal a metallographic microstructure, but the bainitic steel side has already been corroded.

[0056] Comparative Example 3

[0057] First, the welded joint specimens of nickel-based alloy / bainitic steel dissimilar materials were etched with nitric acid alcohol solution, followed by etching with aqua regia, resulting in over-etching of the bainitic steel side of the fusion line. The resulting metallographic structure is shown in [reference needed]. Figure 7 It is evident that the aqua regia etching process near the fusion line presents significant challenges.

[0058] Comparative Example 4

[0059] The welded joint specimen of nickel-based alloy / bainitic steel dissimilar materials was first etched with nitric acid alcohol solution, and then etched with aqua regia, ensuring that the nickel-based alloy side of the fusion line was not fully etched. The resulting metallographic structure is shown in the figure. Figure 8 It is evident that when using two different etchants, the aqua regia etching process near the weld line presents challenges.

[0060] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A metallographic etching solution for welded joints of dissimilar materials, characterized in that, It is composed of ethanol, nitric acid, ferric chloride and glycerol, wherein the nitric acid is 68% concentrated nitric acid, the ethanol is 98% anhydrous ethanol, and the ratio of ethanol, nitric acid, glycerol and ferric chloride is (35~50ml): (40~50ml): (20~40ml): (20~30g). The dissimilar material welded joint is a nickel-based alloy / bainitic steel dissimilar material welded joint.

2. The metallographic etching solution for dissimilar material welded joints as described in claim 1, characterized in that, The ferric chloride and glycerol were of analytical grade.

3. A metallographic etching method for welded joints of dissimilar materials, characterized in that, Using the metallographic etching solution as described in any one of claims 1 to 2, the method comprises the following steps: Step 1: Measure ethanol, nitric acid, glycerol and ferric chloride to prepare the metallographic etching solution; Step 2: The dissimilar material welded joint samples are subjected to wire cutting, inlaying, rough grinding, fine grinding, polishing, ultrasonic cleaning, alcohol rinsing and blow treatment to obtain metallographic samples; Step 3: Place the pretreated metallographic sample flat and use the metallographic etching solution prepared in Step 1 to etch the metallographic sample. Step 4: Clean the corroded sample with alcohol and dry it with a hair dryer; Step 1 further includes: Step 1.1: Place ferric chloride into a container containing ethanol and stir thoroughly until the ferric chloride dissolves to obtain an ethanol solution of ferric chloride. Step 1.2: Pour the ethanol solution of ferric chloride obtained in step 1.1 into nitric acid to induce an esterification reaction; Step 1.3: After the esterification reaction is complete, pour glycerol into the solution from Step 1.2 and stir thoroughly until homogeneous. Step 1.4: After standing for a period of time, the corrosive solution is obtained and bottled; The etching step in step 3 is as follows: the metallographic etching liquid is dripped onto the metallographic sample using a dropper and completely covered, and a surface etching cap layer is formed by the surface tension of the liquid, followed by static etching. The dissimilar material welded joint is a nickel-based alloy / bainitic steel dissimilar material welded joint.

4. The metallographic corrosion method for dissimilar material welded joints as described in claim 3, characterized in that, The settling time in step 1.4 is 20~60 minutes.

5. The metallographic corrosion method for dissimilar material welded joints as described in claim 3, characterized in that, The corrosion time in step 3 is 25~45 minutes.

6. The metallographic corrosion method for dissimilar material welded joints as described in claim 3, characterized in that, In step 3, the end of corrosion is indicated when the corrosion surface of the sample turns silver-gray.

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