A metallographic structure display etchant and display method for a Cu-containing martensitic bearing steel

Abstract

The application discloses a metallographic structure display corrosion agent suitable for Cu-containing martensite bearing steel and a display method, and the corrosion agent contains 3-5g of picric acid, 0.9-1.3g of hydrogen peroxide, 1.2-1.8g of hydrofluoric acid, 2.5-4g of nitric acid, 0.5-1g of fatty alcohol polyoxyethylene ether, 0.4-0.8g of fatty alcohol polyoxyethylene ether sodium sulfate and 0.3-0.5g of sodium dodecyl benzene sulfonate in 80-100g of water. According to the characteristics of the Cu-containing bearing steel, the corrosion agent formula is re-designed through experiments, the multi-acid is used in combination with multiple surfactants and oxidants, and the corrosion time can be controlled and the fine crystal phase structure morphology of the tempered martensite and the reversed austenite in the bearing steel can be obviously displayed.

Description

Technical Field

[0001] This invention relates to the field of inspection technology, specifically to a metallographic microstructure revealing etchant suitable for Cu-containing martensitic bearing steel, and a method for revealing the use of the etchant. Background Technology

[0002] The microstructure of metallic materials is closely related to their mechanical properties such as strength and toughness, and metallographic observation is the most direct and effective method for studying the microstructure of metallic materials. Cu-containing martensitic bearing steel belongs to the category of martensitic aging steel. Due to its good strength, toughness, and weldability, martensitic aging steel has become the preferred material for structural components such as rocket engine shells, submarine shells, and cryogenic missiles.

[0003] The metallographic etchants typically used for maraging steels are prepared from picric acid, sulfuric acid, hydrogen peroxide, water, hydrofluoric acid, etc. However, these etchants are difficult to control in terms of the etching time of Cu-containing maraging bearing steel in the aging state, and the metallographic structure display is unsatisfactory. This is because, in the aging state, the addition of the alloying element Cu promotes the transformation of martensite to inverted austenite. This results in a relatively high content of inverted austenite in Cu-containing maraging bearing steel in the aging state. Therefore, the metallographic etchants used for T250 maraging steel are not effective for Cu-containing maraging bearing steel and need to be improved. Summary of the Invention

[0004] To address at least one of the aforementioned technical deficiencies, the present invention provides the following technical solution:

[0005] This application discloses a metallographic etching agent suitable for Cu-containing martensitic bearing steel, comprising the following solution in proportion: 3-5g picric acid, 0.9-1.3g hydrogen peroxide, 1.2-1.8g hydrofluoric acid, 2.5-4g nitric acid, 0.5-1g fatty alcohol polyoxyethylene ether, 0.4-0.8g sodium fatty alcohol polyoxyethylene ether sulfate, and 0.3-0.5g sodium dodecylbenzenesulfonate per 80-100g of water.

[0006] Furthermore, the corrosive agent is prepared as follows: a predetermined weight of hydrofluoric acid solution and nitric acid solution are added to a picric acid solution, followed by a predetermined weight of fatty alcohol polyoxyethylene ether, sodium fatty alcohol polyoxyethylene ether sulfate, and sodium dodecylbenzene sulfonate, and finally a predetermined weight of hydrogen peroxide solution is added. For the addition of hydrofluoric acid, nitric acid, etc., common solution forms can be readily available and commercially available.

[0007] The second aspect of this application discloses a method for displaying the metallographic structure of a etchant applicable to Cu-containing martensitic bearing steel, comprising the following steps:

[0008] First, drop 2-4 drops of the above-mentioned etchant onto the surface to be etched of the polished metallographic sample and let it stand for 1-2 minutes.

[0009] Second, the corroded surface of the metallographic sample from the first step is cleaned and dried.

[0010] Furthermore, the etchant is applicable to Cu-containing martensitic bearing steel with a Cu mass percentage of 0.5-3.5%, and the etchant exhibits a more pronounced crystal phase structure in bearing steel with the aforementioned copper content.

[0011] Furthermore, the corroded surface of the metallographic sample was cleaned with water and ethanol, and then dried with a fan.

[0012] Furthermore, the metallographic sample was ground and polished using an automatic polishing machine. The grinding steps included grinding with sandpaper of 180 grit, 400 grit, 800 grit, 1200 grit, and 2000 grit in sequence; the polishing was done with black velvet polishing cloth and water-soluble diamond polishing paste.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] 1. Based on the characteristics of Cu-containing bearing steel, the present invention redesigns the corrosion agent formula through experiments. By using multiple acids in combination with various surfactants and oxidants, the corrosion time can be controlled and the fine crystalline phase morphology of tempered martensite and reverse-transformed austenite in the bearing steel can be clearly displayed. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 The image shows the metallographic structure of Example 1;

[0017] Figure 2 A metallographic photograph of Comparative Example 3;

[0018] Figure 3 The metallographic structure photograph is shown in Example 2.

[0019] Figure 4 A metallographic photograph of Comparative Example 1;

[0020] Figure 5 This is a metallographic photograph of Comparative Example 2. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0022] In the following examples: nitric acid is a commercially available type with a concentration of 63%;

[0023] The hydrofluoric acid is a commercially available type with a concentration of 40%.

[0024] The hydrogen peroxide is a commercially available type with a concentration of 30%.

[0025] The water is distilled water.

[0026] The etchant ratios in each embodiment are shown in Table 1. The preparation method is as follows: In a well-ventilated laboratory, firstly, weigh a predetermined weight of picric acid powder using a balance, then measure the aqueous solution, add the picric acid powder to the water and stir thoroughly. Secondly, measure predetermined volumes of hydrogen peroxide, hydrofluoric acid, and nitric acid, and add them sequentially to the picric acid aqueous solution and stir thoroughly. Then, add predetermined volumes of fatty alcohol polyoxyethylene ether, fatty alcohol polyoxyethylene ether sodium sulfate, and the weighed predetermined weight of sodium dodecylbenzenesulfonate to the picric acid aqueous solution, stir thoroughly, and let stand to obtain the desired metallographic etchant. Since hydrofluoric acid will react chemically with glass, pour the obtained etchant solution into a plastic reagent bottle for later use.

[0027] When using corrosive agents:

[0028] The Cu-containing martensitic bearing steel used undergoes a heat treatment process including solution treatment, cryogenic treatment, and aging. The bearing steel formula and treatment process can be found in the standard. In the following example, metallographic samples were prepared using bearing steel in an aging state.

[0029] The Cu-containing martensitic bearing steel sample was cut into metallographic specimens with a length of 10 mm, a width of 10 mm, and a height of 5 mm by wire cutting.

[0030] The metallographic sample to be tested was ground and polished using an automatic polishing machine. The grinding process involved sequentially grinding with sandpaper of 180 grit, 400 grit, 800 grit, 1200 grit, and 2000 grit. Polishing was performed using black velvet polishing cloth and water-soluble diamond polishing paste, with the turntable speed at 250-350 rpm.

[0031] Then, using stainless steel tweezers, place the metallographic sample into a glass tray with the polished etched surface facing upwards. Use a dropper to draw the corresponding etchant liquid from the plastic reagent bottle and immediately drop 2-4 drops onto the surface of the metallographic sample to be tested (i.e., the polished etched surface). The etching time is approximately 1-2 minutes, depending on the condition of the sample.

[0032] After the metallographic sample is etched, it is removed with stainless steel tweezers and the etched surface is immediately rinsed thoroughly with running water. Finally, the etched surface is rinsed again with anhydrous ethanol and dried with a hair dryer. This process yields the desired metallographic sample.

[0033] Metallographic specimens after corrosion were observed using a metallographic microscope to observe the metallographic structure of Cu-containing martensitic bearing steel at different aging temperatures.

[0034] Example 1

[0035] Metallographic specimens were prepared by cutting samples of martensitic bearing steel containing Cu (0.5% by weight) in the aged state. Etching agents were prepared according to the proportions in Table 1 and the preparation method described above, and the etching operation was carried out by the above method.

[0036] Example 2

[0037] Metallographic specimens were prepared by cutting samples of martensitic bearing steel containing Cu (2.5% by weight) in the aged state. Etching agents were prepared according to the proportions in Table 1 and the preparation method described above, and the etching operation was carried out by the above method.

[0038] Comparative Example 1

[0039] Metallographic specimens were prepared by cutting samples of martensitic bearing steel containing Cu (0.3% by weight) in an aged state, and the remaining samples were subjected to corrosion operations in accordance with Example 1.

[0040] Comparative Example 2

[0041] Metallographic specimens were prepared by cutting samples of martensitic bearing steel containing Cu (3.7% by weight) in an aged state, and the remaining samples were subjected to corrosion operations in accordance with Example 2.

[0042] Comparative Example 3

[0043] Metallographic specimens were prepared by cutting samples of martensitic bearing steel containing Cu (0.5% by weight) in the aged state. The conventional etchants used are listed in Table 1. The preparation method was conventional, and the usage method was the same as in Example 1.

[0044] Table 1

[0045]

[0046]

[0047] Note: The unit of measurement in the table is g;

[0048] The metallographic structures of the metallographic samples after corrosion in the above embodiments and comparative examples are shown in the attached figures. Figure 1 , Figure 2 It can be seen that, for the same metallographic sample, the etchant of the present invention can better reveal the metallographic structure compared with traditional etchants.

[0049] from Figure 1 , Figure 3 , Figure 4 , Figure 5 It can be seen that this etchant has a narrow range of applications, and is only suitable for displaying the metallographic structure of bearing steel with limited Cu content.

[0050] Furthermore, as can be seen from the examples, the corrosion time of this etchant is relatively stable, more controllable, and convenient to operate.

[0051] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principle of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for displaying the use of a metallographic structure display reagent for a Cu-containing martensitic bearing steel, characterized by: The method comprises the following steps: First, 2-4 drops of etchant are dropped on the etching surface of the polished metallographic sample to be tested, and the sample is left for 1-2 min, wherein the etchant comprises the following proportioned solutions: 3-5 g of picric acid, 0.9-1.3 g of hydrogen peroxide, 1.2-1.8 g of hydrofluoric acid, 2.5-4 g of nitric acid, 0.5-1 g of fatty alcohol polyoxyethylene ether, 0.4-0.8 g of fatty alcohol polyoxyethylene ether sodium sulfate, and 0.3-0.5 g of sodium dodecyl benzene sulfonate in 80-100 g of water; Second, the etching surface of the metallographic sample in the first step is cleaned and dried, and the etching surface of the metallographic sample is cleaned with water and ethanol and dried with a fan; The etchant is suitable for a Cu-containing martensitic bearing steel, and the mass percentage of Cu in the steel is 0.5-3.5%.

2. The method for displaying the use of a metallographic structure revealing etchant for a Cu-containing martensitic bearing steel according to claim 1, characterized in that: The metallographic sample is ground and polished by using an automatic polishing machine, and the grinding steps include sequentially using sandpaper with mesh sizes of 180, 400, 800, 1200 and 2000; and the polishing is performed by using black velvet polishing cloth and water-soluble diamond grinding paste.

3. The method for displaying the use of a metallographic structure revealing etchant for a Cu-containing martensitic bearing steel according to claim 1, characterized in that: The etchant is prepared as follows: predetermined weights of hydrofluoric acid solution, nitric acid solution, fatty alcohol polyoxyethylene ether, fatty alcohol polyoxyethylene ether sodium sulfate, and sodium dodecyl benzene sulfonate are added to a picric acid solution, and finally, a predetermined weight of hydrogen peroxide solution is added.

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