As-cast duplex stainless steel with metallographic etching liquid and preparation method and use method thereof

Abstract

The application provides a metallographic etching liquid for as-cast duplex stainless steel and a preparation method and use method thereof, the metallographic etching liquid comprises: a mixture A of hydrochloric acid and copper chloride, and a mixture B of nitric acid and iron nitrate, and the metallographic etching liquid for as-cast duplex stainless steel and the preparation method and use method thereof have the advantages that the gray color contrast of a metallographic photo is good, the grain combination characteristics are intuitive and visual, the reagent is common and common, the preparation is convenient, and the success rate is extremely high.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metallographic examination of metal materials, and particularly relates to a metallographic etching solution for as-cast duplex stainless steel and a preparation method and use method thereof. BACKGROUND

[0002] Duplex stainless steel is a kind of stainless steel with austenitic and ferritic dual-phase structure, which is obtained by increasing the content of elements such as chromium, molybdenum and titanium and reducing the content of elements such as nickel and manganese on the basis of 18-8 type austenitic stainless steel, and then through solid solution treatment. The austenitic phase has high corrosion resistance and high toughness, is usually formed at high temperature, and has a face-centered cubic structure. The ferritic phase is another phase, which has lower corrosion resistance but usually has higher strength, is formed at low temperature, and has a body-centered cubic structure. The metallographic structure of duplex stainless steel is that small island-shaped austenite is distributed on the ferritic matrix, and the content of ferrite is generally about 50% to 70%. As-cast duplex stainless steel is prepared by a casting process. Since the duplex stainless steel structure contains both austenite and ferrite, it combines the corrosion resistance of austenite and the strength of ferrite, so that the duplex stainless steel performs well in some special applications, especially in environments requiring high strength and corrosion resistance, such as chemical industry, marine engineering and some special high temperature and high pressure environments.

[0003] In the prior art, the commonly used metallographic etching solution for duplex stainless steel is aqua regia and sodium metabisulfite hydrochloric acid solution, and the metallographic etching solution used for stainless steel materials also includes ferric chloride hydrochloric acid solution and hydrochloric acid nitric acid ferric chloride solution. Among them, aqua regia and sodium metabisulfite hydrochloric acid solution are mainly used to etch the metallographic structure of duplex stainless steel to display and distinguish the two phases in duplex steel; it is found through experiments that ferric chloride hydrochloric acid solution and hydrochloric acid nitric acid ferric chloride solution cannot etch duplex stainless steel, and the test surface still appears bright after long-term etching.

[0004] Grain size detection is a routine detection item in metallographic detection. Grain size is the size of crystals or the characteristic of crystal structure in a material. The size of grain size can affect the physical and mechanical properties of the material. Therefore, by detecting grain size and understanding the microstructure of the material, the performance of the material can be predicted and understood, which helps to select the appropriate material for specific application scenarios; it can help to optimize the processing technology and improve the processing performance and formability of the material, which is crucial for the processing of metal materials such as forging, rolling, and quenching; in addition, the grain size and grain boundary have an impact on the corrosion resistance of the material, smaller grains usually mean more grain boundaries, which can lead to higher corrosion resistance, so by detecting grain size, the behavior of the material in a corrosive environment can be understood; the grain structure also has an impact on the fatigue performance of metal materials, smaller grains are usually associated with higher fatigue life, by detecting grain size, the behavior of the material under fatigue loading can be better understood; the distribution and shape of grains are also related to the fracture behavior of the material, grain size detection can provide information about the fracture toughness and fracture mode of the material. Overall, grain size detection of metal materials is a key step to deeply understand and optimize the performance of the material, which helps to guide material design, processing and application. However, the existing aqua regia, sodium sulfite hydrochloric acid solution and other metallographic etching liquids can only be used to etch the metallographic structure of duplex stainless steel and distinguish the two phases in duplex steel, but they cannot display the grain morphology characteristics of duplex stainless steel. At present, there is a lack of effective metallographic etching liquid and etching method for grain size detection of as-cast duplex stainless steel. SUMMARY

[0005] The present application designs a metallographic etching liquid for as-cast duplex stainless steel and its preparation method and use method, to overcome the technical problem that the existing metallographic etching liquid cannot display the grain morphology characteristics of as-cast duplex stainless steel.

[0006] To solve the above problems, the present application discloses a metallographic etching liquid for as-cast duplex stainless steel, comprising:

[0007] a mixture A of hydrochloric acid and copper chloride,

[0008] and a mixture B of nitric acid and iron nitrate.

[0009] Further, in the metallographic etching liquid, the mass ratio of the mixture A and the mixture B is (0.7-1.3):1.

[0010] Further, in the metallographic etching liquid, the mass ratio of the mixture A and the mixture B is 1:1.

[0011] Further, in the mixture A, the addition amount of copper chloride is 0.04-0.06 g / ml.

[0012] Further, in the mixture B, the addition amount of iron nitrate is 0.04-0.06 g / ml.

[0013] Further, the mass concentration of the hydrochloric acid is 35-40%, and the mass concentration of the nitric acid is 60-75%.

[0014] Further, the formula of the metallographic etching solution is:

[0015] a mixture A of 10-12 ml of hydrochloric acid and 0.5 g of copper chloride,

[0016] and a mixture B of 10-12 ml of nitric acid and 0.5 g of ferric nitrate.

[0017] A preparation method of a metallographic etching solution for as-cast duplex stainless steel, which is used to prepare the metallographic etching solution for as-cast duplex stainless steel, and the preparation method comprises the steps of:

[0018] S1, preparing the mixture A: a certain amount of hydrochloric acid is weighed into a container according to the weight ratio, then a certain amount of copper chloride is added into the container according to the weight ratio, and the mixture A is obtained after stirring uniformly;

[0019] S2, preparing the mixture B: a certain amount of nitric acid is weighed into a container according to the weight ratio, then a certain amount of ferric nitrate is added into the container according to the weight ratio, and the mixture B is obtained after stirring uniformly;

[0020] S3, preparing the metallographic etching solution: the mixture A and the mixture B are mixed and stirred uniformly to obtain the metallographic etching solution.

[0021] A use method of a metallographic etching solution for as-cast duplex stainless steel, which is used for the metallographic etching solution for as-cast duplex stainless steel, and the use method comprises:

[0022] First, a metallographic sample to be etched is prepared, then the metallographic etching solution is dipped with degreasing cotton, and the sample surface is wiped with degreasing cotton at room temperature for 40-50 seconds until the sample surface becomes gray, then the sample surface is rinsed and dried, and then the sample surface is placed under an optical metallographic microscope for grain size detection.

[0023] Further, the process of rinsing and drying the sample surface is as follows: first, the sample surface is rinsed with running water, then the sample surface is rinsed with anhydrous ethanol, and finally the metallographic sample surface is blown dry.

[0024] The metallographic etching solution for as-cast duplex stainless steel and the preparation method and use method thereof have the advantages of good gray color contrast of the metallographic photo, intuitive and visual grain combination characteristics, common reagents, convenient preparation, and high success rate. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1A photomicrograph of the as-cast duplex stainless steel obtained in Example 1 of the present application;

[0026] Figure 2 A photomicrograph of the as-cast duplex stainless steel obtained in Example 2 of the present application;

[0027] Figure 3 A photomicrograph of the as-cast duplex stainless steel obtained in Example 3 of the present application;

[0028] Figure 4 Another photomicrograph of the as-cast duplex stainless steel obtained in Example 3 of the present application;

[0029] Figure 5 A photomicrograph of the as-cast duplex stainless steel obtained in Comparative Example 1 of the present application;

[0030] Figure 6 Another photomicrograph of the as-cast duplex stainless steel obtained in Comparative Example 1 of the present application;

[0031] Figure 7 A photomicrograph of the as-cast duplex stainless steel obtained in Comparative Example 2 of the present application;

[0032] Figure 8 Another photomicrograph of the as-cast duplex stainless steel obtained in Comparative Example 2 of the present application;

[0033] Figure 9 A photomicrograph of the as-cast duplex stainless steel obtained in Comparative Example 3 of the present application. DETAILED DESCRIPTION

[0034] In order to make the above objects, features and advantages of the present application more clear and comprehensible, specific embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0035] A photomicrograph of the as-cast duplex stainless steel obtained in Comparative Example 3 of the present application.

[0036] A mixture A of hydrochloric acid and copper chloride,

[0037] and a mixture B of nitric acid and ferric nitrate.

[0038] Further, in the photomicrograph etching solution, the mass ratio of the mixture A and the mixture B is (0.7-1.3): 1.

[0039] Preferably, in the photomicrograph etching solution, the mass ratio of the mixture A and the mixture B is 1:1.

[0040] Further, in the mixture A, the addition amount of copper chloride is 0.04-0.06 g / ml.

[0041] Preferably, in the mixture A, the addition amount of copper chloride is 0.05 g / ml.

[0042] Preferably, the mass concentration of the hydrochloric acid in the mixture A is 35-40%.

[0043] Further, the added amount of the ferric nitrate in the mixture B is 0.04-0.06 g / ml.

[0044] Preferably, the added amount of the ferric nitrate in the mixture B is 0.05 g / ml.

[0045] Preferably, the mass concentration of the nitric acid in the mixture B is 60-75%.

[0046] As a preferred embodiment of the present application, the formula of the metallographic etching solution is: 10-12 ml of hydrochloric acid, 0.5 g of copper chloride, 10-12 ml of nitric acid and 0.5 g of ferric nitrate. Of course, the amount of each raw material in the formula can be expanded or reduced in proportion.

[0047] In addition, the present application also provides a preparation method of the above-mentioned metallographic etching solution, which comprises the steps of:

[0048] S1, preparing the mixture A: weighing a certain amount of hydrochloric acid according to the weight ratio into a container, then adding a certain amount of copper chloride into the container according to the weight ratio, stirring uniformly, and then obtaining the mixture A;

[0049] S2, preparing the mixture B: weighing a certain amount of nitric acid into a container according to the weight ratio, then adding a certain amount of ferric nitrate into the container according to the weight ratio, stirring uniformly, and then obtaining the mixture B;

[0050] S3, preparing the metallographic etching solution: mixing and stirring the mixture A and the mixture B uniformly, and then obtaining the metallographic etching solution.

[0051] Further, the present application also provides a use method of the above-mentioned metallographic etching solution, which comprises the following steps: first preparing a metallographic sample to be etched, then dipping the metallographic etching solution with degreasing cotton, and using the degreasing cotton to wipe the surface of the sample at room temperature for 40-50 s until the surface of the sample becomes gray, then rinsing the surface of the sample with running water, then rinsing the surface of the sample with anhydrous ethanol, and finally blowing dry the surface of the metallographic sample with an electric hair dryer, and then observing the grain characteristics and performing grain size detection under an optical metallographic microscope.

[0052] As some embodiments of the present application, the preparation process of the metallographic sample to be etched is: the as-cast duplex stainless steel metallographic sample is subjected to rough grinding, fine grinding, polishing, cleaning and drying to obtain a bright and scratch-free polished surface.

[0053] The metallographic etching liquid for the as-cast duplex stainless steel, the preparation method and the use method thereof are described below by taking specific examples:

[0054] Example 1

[0055] The proportioning of the metallographic etching liquid:

[0056] Mixture A: 10 ml of hydrochloric acid + 0.5 g of copper chloride,

[0057] Mixture B: 10 ml of nitric acid + 0.5 g of ferric nitrate.

[0058] Preparation of the metallographic etching liquid: 10 ml of hydrochloric acid with a concentration of 35% is measured into a beaker, and 0.5 g of copper chloride is measured into the hydrochloric acid solution, and mixture A is obtained after stirring uniformly; 10 ml of nitric acid with a concentration of 60% is measured into another beaker, and 0.5 g of ferric nitrate is measured into the nitric acid solution, and mixture B is obtained after stirring uniformly; the mixture A and the mixture B are mixed to obtain the metallographic etching liquid according to the application, which is used at room temperature.

[0059] Use of the metallographic etching liquid: first, prepare the metallographic sample to be etched, then dip the metallographic etching liquid with the degreasing cotton, and use the degreasing cotton to wipe the sample surface at room temperature for 40 s until the sample surface becomes gray, then rinse the sample surface with running water, then rinse the sample surface with anhydrous ethanol, and finally dry the sample surface with an electric hair dryer, and then the sample can be observed under an optical metallographic microscope to detect the grain size and the grain characteristics.

[0060] Figure 1 The grain morphology of the as-cast duplex stainless steel observed in Example 1 is shown in the figure, Figure 1 It can be seen that under the optical metallographic microscope, the grains of the as-cast duplex stainless steel present different gray colors, and the grains are clearly visible, and the etching effect is excellent.

[0061] Example 2

[0062] The proportioning of the metallographic etching liquid:

[0063] Mixture A: 12 ml of hydrochloric acid + 0.5 g of copper chloride;

[0064] Mixture B: 12 ml of nitric acid + 0.5 g of ferric nitrate.

[0065] Preparation of the metallographic etching solution: 12 ml of 40% hydrochloric acid was measured into a beaker, and then 0.5 g of copper chloride was measured into the hydrochloric acid solution, and a mixture A was obtained after stirring uniformly; 12 ml of 75% nitric acid was measured into another beaker, and then 0.5 g of ferric nitrate was measured into the nitric acid solution, and a mixture B was obtained after stirring uniformly; the mixture A and the mixture B were mixed to obtain the metallographic etching solution of the present application, which was used at room temperature.

[0066] Use of the metallographic etching solution: first, a metallographic sample to be etched was prepared, then the metallographic etching solution was dipped with degreasing cotton, and the sample surface was wiped with degreasing cotton at room temperature for 50 s until the sample surface became gray, then the sample surface was first rinsed with running water, then rinsed with anhydrous ethanol, and finally the metallographic sample surface was dried with an electric hair dryer, and then the metallographic sample was placed under an optical metallographic microscope to observe the grain characteristics and perform grain size detection.

[0067] Figure 2 That is, the grain morphology diagram of the as-cast duplex stainless steel observed in Example 2, from Figure 2 It can be seen that under the optical metallographic microscope, each grain of the as-cast duplex stainless steel presents different gray colors, and the grains are clearly visible, and the etching effect is excellent.

[0068] Example 3

[0069] Proportioning of the metallographic etching solution:

[0070] Mixture A: 10 ml of hydrochloric acid + 0.4 g of copper chloride,

[0071] Mixture B: 12 ml of nitric acid + 0.4 g of ferric nitrate.

[0072] Preparation of the metallographic etching solution: 10 ml of 37% hydrochloric acid was measured into a beaker, and then 0.4 g of copper chloride was measured into the hydrochloric acid solution, and a mixture A was obtained after stirring uniformly; 12 ml of 70% nitric acid was measured into another beaker, and then 0.4 g of ferric nitrate was measured into the nitric acid solution, and a mixture B was obtained after stirring uniformly; the mixture A and the mixture B were mixed to obtain the metallographic etching solution of the present application, which was used at room temperature.

[0073] Use of the metallographic etching solution: first, a metallographic sample to be etched was prepared, then the metallographic etching solution was dipped with degreasing cotton, and the sample surface was wiped with degreasing cotton at room temperature for 45 s until the sample surface became gray, then the sample surface was first rinsed with running water, then rinsed with anhydrous ethanol, and finally the metallographic sample surface was dried with an electric hair dryer, and then the metallographic sample was placed under an optical metallographic microscope to observe the grain characteristics and perform grain size detection.

[0074] Figures 3-4 That is, the metallographic photo of the as-cast duplex stainless steel observed in Example 3, fromFigures 3-4 It can be seen that under the optical metallographic microscope, the grains of the as-cast duplex stainless steel present different gray colors, the grains are clearly visible, and the corrosion effect is excellent. This is because different grains have different orientations, and the corrosion degree of the grains is different. The rich contrast color makes the grain morphology easier to identify, and is more conducive to the analysis of the grain size.

[0075] Comparative Example 1

[0076] The as-cast duplex stainless steel was corroded with aqua regia (30 ml of 37% hydrochloric acid + 10 ml of 68% nitric acid) for 1 minute, and the metallographic structure thereof was ferrite + austenite, wherein the ferrite was light gray, and the austenite was white bright, as shown in Figure 5 ; the grain characteristics were not visible, as shown in Figure 6 .

[0077] Comparative Example 2

[0078] The as-cast duplex stainless steel was corroded with a sodium metabisulfite hydrochloric acid aqueous solution (90 ml of water + 10 ml of 37% hydrochloric acid + 1 g of sodium metabisulfite) for 40 seconds. This corrosion solution is a color metallographic etchant, which stains the ferrite phase into a dark color and the austenite into a white bright color, thereby realizing the differentiation of the two phases, as shown in Figure 7 ; but it cannot show the grain characteristics, as shown in Figure 8 .

[0079] Comparative Example 3

[0080] The as-cast duplex stainless steel was corroded with a ferric chloride hydrochloric acid aqueous solution (50 ml of water + 10 ml of 37% hydrochloric acid + 5 g of ferric chloride) and a hydrochloric acid nitric acid ferric chloride aqueous solution (20 ml of hydrochloric acid + 5 ml of nitric acid + 5 g of ferric chloride + 100 ml of water) respectively for 3 minutes, and the results were that both of them could not corrode the duplex stainless steel, wherein the metallographic photograph obtained by the ferric chloride hydrochloric acid aqueous solution corrosion is shown in Figure 9 .

[0081] It should be noted that in Comparative Examples 1-3, the corrosion method used is as follows: first prepare the metallographic sample to be corroded, then dip the degreasing cotton with the metallographic etchant, and use the degreasing cotton to wipe the surface of the sample for a certain time until the surface of the sample becomes gray, then first rinse the surface of the sample with running water, then rinse the surface of the sample with anhydrous ethanol, and finally blow dry the surface of the metallographic sample and place it under the optical metallographic microscope for detection.

[0082] From the above, it can be seen that the as-cast duplex stainless steel has strong corrosion resistance, and the existing corrosion liquids:

[0083] (1) the ferric chloride hydrochloric acid aqueous solution, the hydrochloric acid nitric acid ferric chloride aqueous solution, etc. cannot corrode the duplex stainless steel;

[0084] (2) Hydrochloric acid and nitric acid are both strong acids with strong corrosive properties. The aqua regia formed by hydrochloric acid and nitric acid in a ratio of 3:1 can only corrode the morphological characteristics of ferrite and austenite two phases, but cannot show the grain morphology characteristics; the corrosion of the sodium metabisulfite hydrochloric acid aqueous solution itself is not very strong, but it has good dyeing effect, can realize the dyeing of ferrite, so as to achieve the purpose of showing two phases. However, the two corrosion liquids still cannot achieve good display of the grains. The aqua regia and the sodium metabisulfite hydrochloric acid aqueous solution are relatively uniform in corroding the whole sample surface, and no different gray corrosion according to the grain orientation occurs.

[0085] In the corrosion liquid used in the present application, copper chloride has the same anion as hydrochloric acid, and ferric nitrate has the same anion as nitric acid. Such combination enables the corrosion liquid to produce special corrosion effect on grains in different orientations, that is, different grains present different gray gradients, so as to realize the identification of grains and achieve the purpose of grain size detection. It should be noted that the present application realizes the corrosion of different gray colors of grain surfaces, not the corrosion of grain boundaries, and the observation and grading of grains are realized by the different colors of grains.

[0086] Therefore, it is not difficult to obtain that the metallographic corrosion liquid for as-cast duplex stainless steel and the preparation method and use method thereof have the following advantages:

[0087] Firstly, the gray color contrast of the metallographic photo is good, and the grain combination characteristics are intuitive and visual. The corrosion method can make the grains of the as-cast duplex stainless steel present different gray colors, so that the grains present high contrast gray under the microscope. This high contrast helps to more clearly observe and analyze the combination characteristics of the grains, such as the boundaries and shapes of the grains.

[0088] Secondly, the reagents are common and easy to prepare. The reagents used in the present application are relatively common and easy to prepare, which is an advantage for laboratory work, because it means that no complex or expensive reagents are needed, thereby improving the feasibility and economy of the detection.

[0089] Thirdly, the success rate is extremely high. The corrosion method disclosed in the present application is very reliable when processing as-cast duplex stainless steel samples, and the success rate is very high. The method has strong applicability to samples and can stably produce clear grain micrographs under various conditions.

[0090] Although the present application has been disclosed in its currently best mode, the present application is not limited to it. In the description of the specification, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are contained in at least one embodiment or example of the present application. The exemplary description of the above terms in the specification does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Any person skilled in the art can make various modifications and changes without departing from the spirit and scope of the present application, and the protection scope of the present application should be subject to the scope defined by the claims.

Claims

1. A metallographic etching solution for cast duplex stainless steel, characterized in that, Comprise: a mixture A of hydrochloric acid and copper chloride, and a mixture B of nitric acid and ferric nitrate; In the metallographic etching solution, the mass ratio of the mixture A and the mixture B is (0.7-1.3):1, in the mixture A, the added amount of copper chloride is 0.04-0.06 g / ml, in the mixture B, the added amount of ferric nitrate is 0.04-0.06 g / ml, the mass concentration of the hydrochloric acid is 35-40%, and the mass concentration of the nitric acid is 60-75%.

2. The metallographic etching solution for as-cast duplex stainless steel according to claim 1, characterized by, In the metallographic etching solution, the mass ratio of the mixture A and the mixture B is 1:

1.

3. The metallographic etching solution for as-cast duplex stainless steel according to claim 1 or 2, characterized by, The formula of the metallographic etching solution is: a mixture A of 10-12 ml of hydrochloric acid and 0.5 g of copper chloride, and a mixture B of 10-12 ml of nitric acid and 0.5 g of ferric nitrate.

4. A method for preparing a metallographic etching solution for as-cast duplex stainless steel, characterized by, The preparation method is used for preparing the metallographic etching solution for as-cast duplex stainless steel according to any one of claims 1-3, and comprises the steps of: S1, preparing the mixture A: weighing a certain amount of hydrochloric acid according to the weight ratio into a container, then adding a certain amount of copper chloride into the container according to the weight ratio, stirring uniformly, and obtaining the mixture A; S2, preparing the mixture B: weighing a certain amount of nitric acid into a container according to the weight ratio, then adding a certain amount of ferric nitrate into the container according to the weight ratio, stirring uniformly, and obtaining the mixture B; S3, preparing the metallographic etching solution: mixing and stirring the mixture A and the mixture B uniformly, and obtaining the metallographic etching solution.

5. A method for using a metallographic etching solution for as-cast duplex stainless steel, characterized by, The use method is used for the metallographic etching solution for as-cast duplex stainless steel according to any one of claims 1-3, and comprises: firstly preparing a metallographic sample to be etched, then dipping the metallographic etching solution with degreasing cotton, and using the degreasing cotton to wipe the surface of the sample at room temperature for 40-50 s until the surface of the sample becomes gray, then rinsing and drying the surface of the sample, and placing the sample under an optical metallographic microscope for grain size detection.

6. The method of using a metallographic etching solution for as-cast duplex stainless steel according to claim 5, characterized in that, The process of rinsing and drying the surface of the sample is as follows: firstly rinsing the surface of the sample with running water, then rinsing the surface of the sample with anhydrous ethanol, and finally blowing dry the surface of the metallographic sample.

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