Graphene microcapsule-containing environment-friendly water-based anti-decarburization coating for medium-high carbon steel

Abstract

The invention provides an environment-friendly water-based anti-decarburization coating containing graphene microcapsules for medium-high carbon steel, and belongs to the field of high-temperature processing protection. The coating comprises basic powder, a binder and graphene microcapsules, wherein the basic powder comprises silicon dioxide, aluminum oxide, magnesium oxide, boric oxide and calcium oxide; the binder is sodium silicate; a shell material of the graphene microcapsule is silicon dioxide, a core material of the graphene microcapsule is graphene, and the graphene microcapsule is prepared by taking sodium silicate as a precursor through a chemical precipitation method. The invention also provides a preparation method and application of the coating. The coating is a water-based inorganic coating, the components are environment-friendly, the problem of environmental pollution caused by chromic oxide is avoided, meanwhile, graphene under protection of microcapsules is released in a high-temperature environment, the surface carbon environment of steel is changed through the high surface adsorption capacity of the graphene, and decarburization of medium-high carbon steel in the high-temperature heating process is effectively inhibited.

Description

Technical Field

[0001] The present invention belongs to the field of high-temperature processing protection, and particularly relates to an environment-friendly water-based anti-decarburization coating containing graphene microcapsules for medium and high carbon steel, its preparation method and application, which are applicable to the high-temperature heat treatment process of medium and high carbon steel. Background Art

[0002] Due to the relatively high carbon content, during the high-temperature environment in the heat treatment process, carbon elements diffuse from the inside of the steel matrix to the outside and are oxidized and consumed, which easily causes surface decarburization of medium and high carbon steel. Surface decarburization will cause mechanical property problems such as a decrease in the yield strength of the steel, a reduction in fatigue toughness and surface wear resistance. In particular, the ferrite phase in the completely decarburized layer will cause microcracks to easily occur during the use of the steel, further causing material failure. Currently, the commonly used anti-decarburization methods mainly focus on optimizing alloy components, adjusting heating systems, and using coating protection. Among them, the coating protection technology is easy to operate, has a low cost, and is applicable to a relatively wide range of product structures and production processes.

[0003] The high-temperature protection coatings for steel billets are mostly glass-ceramic-based temporary coatings. The coatings sinter to form a protective film at high temperatures, isolating the oxidation atmosphere from the matrix elements and being removed after the heat treatment stage of the steel billet. The main components of the coatings include basic powder materials, binders, and special functional components. The basic powder materials of the coatings are generally composed of low-melting-point substances (such as calcium oxide and boron oxide) and high-melting-point substances (such as silicon dioxide, alumina, and magnesium oxide). During the heating process, the low-melting-point substances first melt to fill the pores of the coating, reducing the generation of cracks; as the temperature rises, the high-melting-point substances melt to continuously ensure the protective effect of the coating. The coatings form a dense film through binders. Commonly used binders include silicates, phosphates, and inorganic composite binders. The special functional components in the coatings are used to meet the requirements of different steel grades and heating conditions. For example, chromium oxide can densify the coating and improve the barrier effect of the coating. Adding graphite-based components such as carbon powder can inhibit the oxidation of the steel matrix by consuming oxygen. However, chromium elements may be converted into hexavalent chromium in the later stage, producing highly toxic substances and causing environmental pollution, and carbon powder is prone to rapid reaction and consumption when the heat treatment temperature is too high or the time is too long.

[0004] In recent years, with the wide application of graphene materials, attempts have been made to use graphene to replace carbon powder. Graphene has a two-dimensional nanostructure and has a stronger adsorption tendency for the steel surface, which can effectively regulate the surface carbon environment and further enhance the anti-oxidation and anti-decarburization effects. Among them, Patent CN118185396A prepared a graphene coating for preventing decarburization of welded pipes using nano-graphene, polyvinyl alcohol, gelatin sheets, benzoic acid, and water. The coating utilizes the carbon-increasing effect and dispersion strengthening effect of nano-graphene. By entering the melt at the edge of the strip steel through nano-graphene and exerting its carbon-increasing and dispersion strengthening effects, decarburization at the weld part is inhibited. However, under high-temperature unprotected atmosphere conditions, graphene will rapidly oxidize and consume when directly contacting oxygen, reducing the protective effect of the coating.

[0005] Microencapsulation technology has been widely used in material loading, encapsulation, and slow release. There are various types of shell materials for encapsulation. Among them, silica, as an inorganic material, is heat-resistant and chemically inert, and it can be tried to be used in high-temperature protective coatings for steel billets. Summary of the Invention

[0006] Aiming at the environmental pollution problems of traditional chromium-containing coatings and the problem of easy rapid consumption of graphite-containing coatings, the present invention aims to provide an environmentally friendly water-based anti-decarburization coating containing graphene microcapsules for medium and high carbon steels, its preparation method, and application. The coating is prepared from silica powder, alumina powder, magnesia powder, boron oxide powder, and calcium oxide powder as basic powders, sodium silicate as a binder, and a special functional component, graphene microcapsules.

[0007] To achieve the above object, the specific technical solutions of the present invention are as follows:

[0008] The present invention provides an environmentally friendly water-based anti-decarburization coating containing graphene microcapsules for medium and high carbon steels, which includes basic powders, a binder, and graphene microcapsules. Among them, the basic powders include silica, alumina, magnesia, boron oxide, and calcium oxide; the binder is sodium silicate; the shell material of the graphene microcapsules is silica, and the core material is graphene. The graphene microcapsules are prepared by chemical precipitation using sodium silicate as a precursor.

[0009] Preferably, the basic powders include, by mass percentage: 25% - 30% silica, 25% - 30% alumina, 15% - 20% magnesia, 10% - 15% boron oxide, 5% - 10% calcium oxide.

[0010] Preferably, the preparation method of the basic powders is: mixing silica powder, alumina powder, magnesia powder, boron oxide powder, and calcium oxide powder and then grinding, and filtering with a 200-mesh standard sieve to obtain basic powders with a particle size ≤ 0.075 mm.

[0011] Preferably, the preparation method of the graphene microcapsules includes the following steps:

[0012] S1. Dispersing graphene with petroleum ether to obtain liquid A, and dissolving cetyltrimethylammonium bromide in water to obtain liquid B;

[0013] Preferably, the mass fraction of graphene in liquid A is 0.3 - 0.6%, preferably 0.4%; the mass fraction of cetyltrimethylammonium bromide in liquid B is 0.8 - 1.2%, preferably 1%. Petroleum ether with a boiling point of 30 - 60°C is selected to facilitate the subsequent removal of organic solvents. In liquid A, if the content of graphene in the solvent is too high, it is easy to agglomerate, resulting in difficult dispersion; if the content of graphene is too low, the content of graphene in the microcapsules will decrease, thereby reducing the coating efficiency. Cetyltrimethylammonium bromide is a cationic surfactant, which is more likely to form an oil-in-water emulsion of the petroleum ether oil-water mixture.

[0014] S2. Mixing liquid A and liquid B at a mass ratio of 1:(1.5 - 3), preferably 1:2, mechanically stirring to form an oil-in-water emulsion, and adjusting the pH value to 3 - 4 with hydrochloric acid to obtain liquid C; in liquid C, if the oil phase is too much, the oil-in-water emulsion will turn into a water-in-oil emulsion, while too much water phase will cause additional material waste. Therefore, the mass of liquid B should be slightly greater than that of liquid A.

[0015] S3. Dissolving sodium silicate in water to obtain liquid D; preferably, the mass fraction of the liquid D is 7 - 9%;

[0016] S4. Dropwise adding liquid D to liquid C while stirring, standing and aging after stirring, and then filtering, washing with deionized water, and drying to obtain graphene microcapsules coated with silica on graphene. Commonly used silicon sources in the prior art, such as alkoxysilane compounds, are more likely to exist in the oil phase and are easy to crosslink with graphene in the oil phase, resulting in graphene becoming part of the microcapsule shell. Sodium silicate can exist in the water phase. Silicate ions combine with hydrogen ions on the surface of the oil phase to generate silica and water, thereby coating the oil phase without affecting graphene. Therefore, the present invention selects to use sodium silicate to generate silica.

[0017] Preferably, the mass ratio of liquid C to liquid D is 1:1, the stirring time is 0.5 - 1.5 h, the aging time is 20 - 30 h, and the drying temperature is 100 - 110°C.

[0018] The present invention also provides a preparation method of the coating, comprising the following steps:

[0019] S1. Mix the base powder, binder, and graphene microcapsules to obtain the dry coating material. Preferably, the mass ratio of the base powder, binder, and graphene microcapsules is 4:1:(0.8 - 3.2), and more preferably 4:1:2. If the binder content is too low, it will be difficult for the powder to form a film. If the binder content is too high, a large number of pores will appear in the coating. If the microcapsule content is too low or too high, it will affect the graphene content in the coating. The graphene content needs to be controlled within a specific range to control the carbon potential on the surface of the steel billet, thereby inhibiting decarburization.

[0020] S2. When in use, add an equal mass of water to the dry coating material and mix evenly to obtain the coating.

[0021] The present invention also provides the application of the coating in the field of high-temperature protection of medium and high carbon steel.

[0022] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0023] 1. The components of the coating of the present invention include a base powder, a binder, and graphene microcapsules. The base powder consists of silicon dioxide powder, aluminum oxide powder, magnesium oxide powder, boron oxide powder, and calcium oxide powder. The binder is sodium silicate. The components are environmentally friendly, do not contain toxic substances, are environmentally friendly, and can withstand temperatures up to over 1000 °C, which can meet the decarburization prevention requirements of various medium and high carbon steel heat treatment scenarios.

[0024] 2. The present invention introduces the microcapsule technology and uses silicon dioxide to coat graphene, solving the problem that the special functional components such as graphite in the coating are directly in contact with the oxidation atmosphere and rapidly consumed in a high-temperature environment. Coating graphene with silicon dioxide can reduce the direct contact between graphene and oxygen, effectively preventing graphene from being rapidly oxidized during the heat treatment heating process. At the same time, the silicon dioxide shell layer used for coating has good compatibility with the coating base material and can still function as a coating component after releasing graphene at the heat treatment temperature. Compared with directly adding graphene, graphene microcapsules have a more stable protective effect. The silicon dioxide used as the shell material in the microcapsules is one of the components of the basic powder of the coating, making the coating have better homogeneity and avoiding problems such as low-temperature decomposition and generation of toxic substances of other commonly used shell materials such as urea-formaldehyde resin.

[0025] 3. The graphene microcapsules in the coating of the present invention slowly release graphene in a high-temperature environment, have a strong adsorption effect on the surface of the steel, can change the carbon environment on the surface of the steel, and reverse the decarburization in the form of carburization, effectively achieving high-temperature protection of medium and high carbon steel during the heat treatment process. Description of the Drawings

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the accompanying drawings required for the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0027] Figure 1 Microscopic morphology diagram of graphene coated with silica sol in Comparative Example 1;

[0028] Figure 2 Microscopic morphology diagram of graphene coated with silica dioxide by ultrasonic dispersion using a cell crusher in Comparative Example 2;

[0029] Figure 3 Microscopic morphology diagrams of the graphene microcapsules and graphene prepared in the present invention, where (a) is the surface morphology of the spherical graphene microcapsules prepared in Example 1, (b) is the microcapsule fragments after the graphene microcapsules prepared in Example 1 are crushed, and (c) is the lamellar graphene used in the present invention;

[0030] Figure 4 Microscopic structure diagram of 60Si2Mn without coating protection after holding at 1000 °C for 30 min;

[0031] Figure 5 Microscopic structure diagram of 60Si2Mn protected by the coating of Example 1 of the present invention after holding at 1000 °C for 30 min;

[0032] Figure 6 Microscopic structure diagram of 60Si2Mn protected by the coating of Example 2 of the present invention after holding at 1000 °C for 30 min;

[0033] Figure 7 Microscopic structure diagram of 60Si2Mn protected by the coating of Example 3 of the present invention after holding at 1000 °C for 30 min. Detailed implementation manners

[0034] To make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments.

[0035] Comparative Example 1

[0036] Preparation of Graphene Microcapsules (Coating Graphene with Silica Sol): Select petroleum ether with a boiling point between 30 and 60 °C, and prepare a mixed solution of graphene and petroleum ether, denoted as Liquid A, where the mass fraction of graphene is 0.4%. Prepare an aqueous solution with a mass fraction of 1% of cetyltrimethylammonium bromide, denoted as Liquid B. Mix Liquid A and Liquid B in a mass ratio of 1:2, and mechanically disperse to form an oil-in-water emulsion, and add hydrochloric acid to adjust the pH value to 3, denoted as Liquid C. While stirring, add an equal mass of basic silica sol dropwise to Liquid C. After stirring for 1 h, let it stand and age for 24 h, then filter and wash with deionized water, and dry at 100 °C to remove petroleum ether, obtaining graphene microcapsules with silica-coated graphene.

[0037] Comparative Example 2

[0038] Preparation of Graphene Microcapsules (Changing the Dispersion Method): Select petroleum ether with a boiling point between 30 and 60 °C, and prepare a mixed solution of graphene and petroleum ether, denoted as Liquid A, where the mass fraction of graphene is 0.4%. Prepare an aqueous solution with a mass fraction of 1% of cetyltrimethylammonium bromide, denoted as Liquid B. Mix Liquid A and Liquid B in a mass ratio of 1:2, and ultrasonically disperse at a power of 600 W for 30 min using a cell disruptor, and add hydrochloric acid to adjust the pH value to 3, denoted as Liquid C. Prepare a sodium silicate solution with a mass fraction of 8.5%, denoted as Liquid D. While stirring, add Liquid D dropwise to Liquid C, and the mass ratio of Liquid C to Liquid D is 1:1. After stirring for 1 h, let it stand and age for 24 h, then filter and wash with deionized water, and dry at 100 °C to remove petroleum ether, obtaining graphene microcapsules with silica-coated graphene.

[0039] Example 1

[0040] Preparation of Basic Powder: Mix and grind 28% silica powder, 28% alumina powder, 19% magnesia powder, 16% boron oxide powder, and 9% calcium oxide powder by mass percentage, and filter with a 200-mesh standard sieve to obtain basic powder with a particle size ≤ 0.075 mm.

[0041] Preparation of Graphene Microcapsules: Select petroleum ether with a boiling point between 30 and 60 °C, prepare a mixed solution of graphene and petroleum ether, denoted as liquid A, where the mass fraction of graphene is 0.4%. Prepare an aqueous solution with a mass fraction of 1% of cetyltrimethylammonium bromide, denoted as liquid B. Mix liquid A and liquid B in a mass ratio of 1:2, mechanically disperse to form an oil-in-water emulsion, and add hydrochloric acid to adjust the pH value to 3, denoted as liquid C. Prepare a sodium silicate solution with a mass fraction of 8.5%, denoted as liquid D. While stirring, slowly add liquid D to liquid C, and the mass ratio of liquid C to liquid D is 1:1. After stirring for 1 h, let it stand for aging for 24 h, then filter and wash with deionized water, and dry at 100 °C to remove petroleum ether, obtaining graphene microcapsules with silica-coated graphene.

[0042] Mix the above-mentioned basic powder, graphene microcapsules and binder sodium silicate in a mass ratio of 4:0.8:1, and mechanically stir and mix evenly to obtain the coating. When in use, add an equal mass of water to the coating and mix evenly, spray it on the surface of 60Si2Mn steel billet at room temperature, and then perform a high-temperature treatment on 60Si2Mn at 1000 °C for 30 min.

[0043] Example 2

[0044] Preparation of Basic Powder: Mix 27% silica powder, 28% alumina powder, 20% magnesia powder, 15% boron oxide powder, and 10% calcium oxide powder by mass percentage, grind them, and filter through a 200-mesh standard sieve to obtain basic powder with a particle size ≤ 0.075 mm.

[0045] Preparation of Graphene Microcapsules: Select petroleum ether with a boiling point between 30 and 60 °C, prepare a mixed solution of graphene and petroleum ether, denoted as liquid A, where the mass fraction of graphene is 0.4%. Prepare an aqueous solution with a mass fraction of 1% of cetyltrimethylammonium bromide, denoted as liquid B. Mix liquid A and liquid B in a mass ratio of 1:2, mechanically disperse to form an oil-in-water emulsion, and add hydrochloric acid to adjust the pH value to 3.5, denoted as liquid C. Prepare a sodium silicate solution with a mass fraction of 8.5%, denoted as liquid D. While stirring, slowly add liquid D to liquid C, and the mass ratio of liquid C to liquid D is 1:1. After stirring for 1 h, let it stand for aging for 24 h, then filter and wash with deionized water, and dry at 100 °C to remove petroleum ether, obtaining graphene microcapsules with silica-coated graphene.

[0046] Mix the above-mentioned basic powder, graphene microcapsules and binder sodium silicate in a mass ratio of 4:2:1, and mechanically stir and mix evenly to obtain the coating. When in use, add an equal mass of water to the coating and mix evenly, spray it on the surface of 60Si2Mn steel billet at room temperature, and then perform a high-temperature treatment on 60Si2Mn at 1000 °C for 30 min.

[0047] Example 3

[0048] Prepare the base powder: Mix and grind 28% silica powder, 30% alumina powder, 19% magnesia powder, 14% boron oxide powder, and 9% calcium oxide powder by mass percentage, and filter through a 200-mesh standard sieve to obtain the base powder with a particle size ≤ 0.075 mm.

[0049] Prepare graphene microcapsules: Select petroleum ether with a boiling point between 30 and 60 °C, prepare a mixed solution of graphene and petroleum ether, denoted as liquid A, where the mass fraction of graphene is 0.4%. Prepare an aqueous solution with a mass fraction of 1% of cetyltrimethylammonium bromide, denoted as liquid B. Mix liquid A and liquid B in a mass ratio of 1:2, mechanically disperse to form an oil-in-water emulsion, and add hydrochloric acid to adjust the pH value to 4, denoted as liquid C. Prepare a sodium silicate solution with a mass fraction of 8.5%, denoted as liquid D. Slowly add liquid D to liquid C while stirring, and the mass ratio of liquid C to liquid D is 1:1. After stirring for 1 h, let it stand for aging for 24 h, then filter and wash with deionized water, and dry at 100 °C to remove petroleum ether to obtain graphene microcapsules coated with silica.

[0050] Mix the above base powder, graphene microcapsules, and binder sodium silicate in a mass ratio of 4:3.2:1, mechanically stir and mix evenly to obtain the coating. When in use, add an equal mass of water to the coating and mix evenly, spray it on the surface of the 60Si2Mn steel billet at room temperature, and then perform a high-temperature treatment on 60Si2Mn at 1000 °C for 30 min.

[0051] Test the high-temperature protection performance of the three examples in the present invention, and the product effects of Examples 1-3 are measured as shown in Table 1.

[0052] Table 1

[0053]

[0054] Figure 1 It is the microscopic morphology diagram of graphene coated with silica sol in Comparative Example 1. It can be seen that directly using silica sol to coat graphene through the shrinkage of the silica gel network cannot form spherical capsules, but tends to form irregular blocky samples, and graphene exists in the silica block in an embedded manner. This is because the shrinkage process of the silica gel network formed by pure silica sol takes time, and the gradually added silica sol is more likely to connect and form a whole when they are in contact before shrinkage, so individual independent microcapsules cannot be formed.

[0055] Figure 2It is the microscopic morphology diagram of graphene coated with silica dispersed by a cell crusher in Comparative Example 2. It can be seen that there are smooth massive samples and rough-surfaced massive samples in the ultrasonically dispersed samples. Because ultrasonic dispersion destroys the water-in-oil system, causing demulsification and oil-water separation, resulting in coating failure.

[0056] Figure 3 In (a) is the surface morphology of the spherical graphene microcapsules prepared in Example 1, indicating that spherical graphene microcapsules were successfully prepared. (b) is the microcapsule fragments after the graphene microcapsules prepared in Example 1 were crushed. (c) is the lamellar graphene used in the present invention. It can be seen that the graphene is coated inside the microcapsules.

[0057] Figure 4 It is the microstructure of 60Si2Mn without protection during the heat treatment process. Figures 5 to 7 They are respectively the microstructures of 60Si2Mn protected by the coating of the present invention in Examples 1 to 3. As shown in the figure, the completely decarburized layer was eliminated in Example 1 and Example 2, and the decarburization degree of 60Si2Mn was significantly reduced, while only a part of the completely decarburized layer was reduced in Example 3. This is because the essence of steel decarburization is related to the carbon concentration gradient between the inside of the steel matrix and the external environment. Only by reasonably controlling the content of graphene can the best decarburization prevention effect be achieved.

[0058] As mentioned above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claimed rights.

Claims

1. An environmentally friendly water-based anti-decarburization coating containing graphene microcapsules for medium and high carbon steel, characterized in that: The invention comprises basic powder, a binder and graphene microcapsules, wherein the basic powder comprises silicon dioxide, aluminum oxide, magnesium oxide, boron oxide and calcium oxide; the binder is sodium silicate; the shell material of the graphene microcapsules is silicon dioxide, the core material is graphene, and the graphene microcapsules are prepared by a chemical precipitation method using sodium silicate as a precursor.

2. The environmentally friendly water-based anti-decarburization coating containing graphene microcapsules for medium- and high-carbon steel according to claim 1, characterized in that: The basic powder comprises, by mass percentage, 25% to 30% silicon dioxide, 25% to 30% aluminum oxide, 15% to 20% magnesium oxide, 10% to 15% boron oxide, and 5% to 10% calcium oxide.

3. The environmentally friendly water-based anti-decarburization coating containing graphene microcapsules for medium-high carbon steel according to claim 2, characterized in that: The preparation method of the basic powder is: silicon dioxide powder, aluminum oxide powder, magnesium oxide powder, boron oxide powder and calcium oxide powder are mixed and ground, and filtered with a 200-mesh standard sieve to obtain a basic powder with a particle size of ≤0.075 mm.

4. The environmentally friendly water-based anti-decarburization coating containing graphene microcapsules for medium- and high-carbon steel according to claim 1, characterized in that: The preparation method of the graphene microcapsules comprises the following steps: S1. Using petroleum ether to disperse graphene to obtain liquid A, and dissolving hexadecyltrimethylammonium bromide in water to obtain liquid B; S2, mixing liquid A and liquid B, mechanically stirring to form an oil-in-water emulsion, and adjusting the pH value to 3-4 with hydrochloric acid to obtain liquid C; S3, dissolving sodium silicate in water to obtain liquid D; S4. Liquid D is added dropwise to liquid C while stirring, and the mixture is allowed to stand for aging after stirring, and then filtered and washed with deionized water, and dried to obtain graphene microcapsules of silica-coated graphene.

5. The environmentally friendly water-based anti-decarburization coating containing graphene microcapsules for medium- and high-carbon steel according to claim 4, characterized in that: In S1, the mass fraction of graphene in liquid A is 0.3-0.6%, the mass fraction of hexadecyltrimethylammonium bromide in liquid B is 0.8-1.2%, and petroleum ether with a boiling point of 30-60°C is selected.

6. The environmentally friendly water-based anti-decarburization coating containing graphene microcapsules for medium- and high-carbon steel according to claim 5, characterized in that: In S2, liquid A and liquid B are mixed in a mass ratio of 1:(1.5~3).

7. The environmentally friendly water-based anti-decarburization coating containing graphene microcapsules for medium- and high-carbon steel according to claim 5, characterized in that: In S3, the mass fraction of the liquid D is 7-9%; In S4, the mass ratio of liquid C to liquid D is 1:1, the stirring time is 0.5~1.5h, the aging time is 20~30h, and the drying temperature is 100~110℃.

8. The method for preparing the coating according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1, mixing the base powder, the binder and the graphene microcapsules to obtain a coating dry material; S2. When using, add an equal mass of water to the coating dry material, mix well, and obtain the coating.

9. The method for preparing the coating according to claim 8, characterized in that: In S1, the mass ratio of the base powder, the binder and the graphene microcapsules is 4:1:(0.8~3.2).

10. Use of the coating according to any one of claims 1 to 7 in the field of high-temperature protection of medium- and high-carbon steel.

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