An aqueous anti-permeation coating for steel chemical heat treatment process, its preparation method and application

Abstract

The present application belongs to the field of temporary protection of chemical heat treatment process, and particularly relates to a water-based anti-permeation coating for steel chemical heat treatment process and a preparation method and application thereof. The coating is a water-based inorganic protective coating, and the coating comprises, by mass fraction, 10-15 parts of enamel glaze powder I, 10-15 parts of enamel glaze powder II, 15-25 parts of enamel glaze powder III, 20-30 parts of quartz powder, 15-25 parts of alumina powder, 1-10 parts of iron oxide powder, 0.1-1 part of bentonite, 35-50 parts of deionized water and 10-20 parts of water glass. The water-based anti-permeation coating is used for preparing a water-based anti-permeation coating layer in a metal chemical heat treatment process, and the preparation process of the coating layer comprises the following steps: (1) preparation of the coating; (2) coating of the coating; (3) drying of the coating layer; and (4) removal of the coating layer. The present application can be used in heat treatment processes at different temperatures according to different raw material ratios, and the residual coating layer can be removed through a simple sand blasting process after the heat treatment is completed.

Description

Technical Field

[0001] This invention belongs to the temporary protection field of chemical heat treatment processes, and specifically relates to a water-based anti-seepage coating for steel chemical heat treatment processes, its preparation method and application. Background Technology

[0002] Chemical heat treatment is a metal heat treatment process that uses chemical reactions, and sometimes combined with physical methods, to alter the chemical composition and microstructure of the surface layer of steel parts, in order to obtain better technical and economic benefits than homogeneous materials. It includes processes such as carburizing, nitriding, and aluminizing. Since most failures and damages of mechanical parts originate in the surface layer, especially for parts operating under conditions that may cause wear, fatigue, metal corrosion, and oxidation, the properties of the surface layer are particularly important. Steel parts that have undergone chemical heat treatment can essentially be considered a special composite material. The core is the original steel composition, while the surface layer is a material infused with alloying elements. The bond between the core and the surface layer is a tight crystalline structure, which is much stronger than the core-surface bond obtained by surface protection techniques such as electroplating.

[0003] In the machining of gears, shafts, and other parts, the vast majority undergo heat treatment processes such as carburizing, nitriding, and carbonitriding. For design or process requirements, localized anti-seepage technology is widely used in the gear industry. Coating protection is the simplest and most reliable method. Compared to reserving a carburizing allowance and then reheating and quenching after cutting, using an anti-seepage coating to protect the carburized parts allows for direct quenching, simplifying the process, saving materials and energy, and offering significant benefits.

[0004] Although China has independently developed some coatings, their high-temperature service life is short, generally not exceeding five hours. Nitriding of some parts requires holding at 1100℃ for tens of hours, and the protective effect of domestically produced coatings is currently limited. Therefore, developing a protective coating with a long high-temperature service life and easy removal after heat treatment is of great significance for improving part performance, refining processes, and reducing costs. Summary of the Invention

[0005] The purpose of this invention is to provide a water-based anti-seepage coating for steel chemical heat treatment processes, its preparation method, and its application. It is made using only commercially available raw materials, and the preparation process is simple and low-cost. Depending on the raw material ratio, it can be used in heat treatment processes at different temperatures, and residual coatings can be removed by a simple sandblasting process after heat treatment.

[0006] The technical solution of this invention is:

[0007] A water-based anti-seepage coating for use in the chemical heat treatment process of steel. The coating is a water-based inorganic protective coating, and by weight parts, it contains 10-15 parts of enamel glaze powder one, 10-15 parts of enamel glaze powder two, 15-25 parts of enamel glaze powder three, 20-30 parts of quartz powder, 15-25 parts of alumina powder, 1-10 parts of iron oxide powder, 0.1-1 parts of bentonite, 35-50 parts of deionized water, and 10-20 parts of water glass.

[0008] The formula of enamel glaze powder one, by mass percentage, is: silicon dioxide 45-50%, aluminum oxide 5-10%, sodium oxide 10-18%, potassium oxide 5-10%, boron oxide 10-15%, calcium fluoride 3-8%, cobalt oxide 0.5-2%, and iron oxide 0.5-2%;

[0009] The formula of enamel glaze powder II, by mass percentage, is: silicon dioxide 50-55%, aluminum oxide 3-8%, sodium oxide 5-10%, potassium oxide 5-10%, boron oxide 10-15%, calcium oxide 3-8%, strontium oxide 5-10%, and cobalt oxide 0.5-2%.

[0010] The formula of enamel glaze powder 3 by mass percentage is as follows: silicon dioxide 50~55%, aluminum oxide 1~5%, sodium oxide 5~10%, potassium oxide 1~5%, boron oxide 5~10%, calcium oxide 3~8%, barium oxide 10~20%, cobalt oxide 0.5~2%, and iron oxide 0.5~2%.

[0011] The water-based anti-seepage coating used in the chemical heat treatment process of steel has a quartz powder particle size range of less than 2000 mesh.

[0012] The water-based anti-seepage coating for steel chemical heat treatment processes has an alumina powder particle size range of 1~10μm.

[0013] The water-based anti-seepage coating used in the chemical heat treatment process of steel has an iron oxide powder particle size range of 1~5μm.

[0014] The water-based anti-seepage coating used in the chemical heat treatment process of steel uses potassium silicate water glass with a modulus of 3 and sodium-based bentonite with a particle size range of less than 1 μm.

[0015] The method for preparing the water-based anti-seepage coating for the chemical heat treatment process of steel includes the following steps: (1) mixing solid raw materials evenly according to the mass fraction to obtain raw material A; (2) mixing liquid raw materials evenly according to the mass fraction to obtain raw material B; (3) pouring raw material A and raw material B into an agate ball mill jar and ball milling them in a planetary ball mill for 1 to 2 hours to obtain the water-based anti-seepage coating.

[0016] The preparation method of the water-based anti-seepage coating for the steel chemical heat treatment process, the preparation process of enamel glaze powder one, enamel glaze powder two and enamel glaze powder three is as follows: (1) Prepare the raw material powder according to the formula and mix it in a planetary ball mill for 1 to 3 hours; (2) After mixing, the powder obtained is melted at a high temperature of 1200 to 1550℃ for 2 to 4 hours and then water-quenched to form glass glaze blocks; (3) Put the glass glaze blocks into an agate jar and ball mill them in a planetary ball mill for 100 to 200 hours; (4) Pass the glass glaze powder obtained after ball milling through a 200-mesh sieve to obtain enamel glaze powder.

[0017] The application of the water-based anti-seepage coating for the chemical heat treatment process of steel, the water-based anti-seepage coating is used to prepare a water-based anti-seepage coating in the chemical heat treatment process of metal, and the preparation process of the coating includes: (1) preparation of coating; (2) application of coating; (3) drying of coating; (4) removal of coating.

[0018] The coating process is as follows: depending on the shape and size of the workpiece, brush coating, dip coating or atmospheric spraying at room temperature is selected to obtain a coating thickness of no more than 300 micrometers; the coating drying process is as follows: dry at 60~80℃ for 1~2 hours.

[0019] In the application of the water-based anti-seepage coating for the steel chemical heat treatment process, preferably, the coating thickness is 150~250 micrometers.

[0020] The application of the water-based anti-seepage coating for the steel chemical heat treatment process involves the following coating removal process: sandblasting with 80-200 mesh corundum sand at a pressure of 0.4-0.6 MPa.

[0021] The design concept of this invention is:

[0022] This invention uses enamel powder with a melting point significantly lower than the service temperature as a binder and ceramic powder with a melting point significantly higher than the operating temperature as a filler and skeleton to construct a high-temperature protective coating. The network-forming agent, flux, and adhesive components of each enamel glaze are rationally designed to ensure that the coating partially softens and flows before reaching the target temperature, isolating it from contact with the atmosphere and alloy. Simultaneously, the appropriate selection of adhesive type and content ensures sufficient wettability of the softened glass phase on the steel surface, preventing glaze run-off. Different ratios of the three enamel glazes can adjust the coating's operating temperature and coefficient of thermal expansion, achieving a reasonable thermal expansion coefficient ratio between the coating and the alloy, thus preventing peeling from starting below a safe temperature. Quartz and alumina are used as fillers, utilizing their slow in-situ reaction with the liquid glass phase to increase the coating's service temperature to a maximum of 1100°C. The use of bentonite combined with water glass can adjust the coating's viscosity and suspension properties, while also providing the coating with sufficient strength after drying, increasing the safety of the workpiece during transportation. The addition of iron oxide provides a weak oxidant for the coating, increasing its stability at high temperatures.

[0023] The advantages and beneficial effects of this invention are:

[0024] 1. The anti-seepage coating developed in this invention is dense and can completely isolate the high-temperature reaction between the high-temperature furnace gas and the metal substrate.

[0025] 2. The anti-seepage coating developed in this invention is composed of three types of enamel glazes and fillers such as quartz, alumina, iron oxide, and bentonite. It has a very wide operating temperature and time range. By adjusting the proportion of the enamel glazes, it can be applied to different heating temperatures and times.

[0026] 3. The anti-seepage coating of the present invention has good wettability with steel parts and can still spread in a reducing atmosphere, thus completely protecting the coated area.

[0027] 4. The anti-seepage coating of the present invention has a suitable difference in the coefficient of thermal expansion with the steel frame, and can be completely removed by simple sandblasting after heat treatment.

[0028] 5. The anti-seepage coating of the present invention is a water-based inorganic coating, which is environmentally friendly and will not pollute equipment such as sandblasting machines.

[0029] 6. This invention is applicable to local protection of steel during carburizing, aluminizing, nitriding, carbonitriding and other processes at 950~1100℃. Attached Figure Description

[0030] Figure 1 This is a macroscopic photograph of the coating after it has dried (without heat treatment).

[0031] Figure 2 This is a photo of carburized steel after carburizing at 1060℃ for 5 hours.

[0032] Figure 3 This is a photo of carburized steel after being carburized at 1060℃ for 5 hours and then sandblasted.

[0033] Figure 4 Backscattered cross-section photograph of the uncoated portion of carburized steel after carburizing at 1060℃ for 5 hours.

[0034] Figure 5 Backscattered photograph of the cross-section of the coated portion of carburized steel after carburizing at 1060℃ for 5 hours.

[0035] Figure 6 Comparative photos of 1060 carburized steel 5 hours after adding water glass to the coating.

[0036] Figure 7 These are comparative photos of carburized steel after being carburized at 1060℃ for 5 hours with alumina powder partially replacing quartz powder.

[0037] Figure 8 Backscattered cross-sectional image of the uncoated portion of nitrided steel after nitriding at 1100℃ for 12 hours.

[0038] Figure 9 Backscattered photograph of the cross-section of the coated portion of nitrided steel after nitriding at 1100℃ for 12 hours.

[0039] Figure 10 Photographs of the surface of nitrided steel after nitriding at 1100℃ for 12 hours to change the enamel glaze content in the coating. Detailed Implementation

[0040] In the specific implementation process, the water-based anti-seepage coating, by weight, consists of: 10-15 parts of enamel glaze powder one, 10-15 parts of enamel glaze powder two, 15-25 parts of enamel glaze powder three, 20-30 parts of quartz powder, 15-25 parts of alumina powder, 1-10 parts of iron oxide powder, 0.1-1 part of bentonite, 35-50 parts of deionized water, and 10-20 parts of water glass. The quartz powder has a particle size range of less than 2000 mesh, the alumina powder has a particle size range of 1-10 μm, the iron oxide powder has a particle size range of 1-5 μm, the water glass is potassium silicate water glass with a modulus of 3, and the bentonite is sodium-based bentonite with a particle size of less than 1 μm. Depending on the shape and size of the workpiece, brushing, dipping, or atmospheric spraying at room temperature is selected. The resulting anti-seepage coating is composed of three types of enamel glazes and fillers such as quartz, alumina, and iron oxide.

[0041] The following is a further detailed description of the present invention. It should be understood that these methods are for illustrative purposes only and are not intended to limit the invention.

[0042] Example 1

[0043] In this embodiment, a local anti-seepage coating is prepared using a carburized steel as the substrate. The preparation process is as follows:

[0044] (1) Enamel glaze melting:

[0045] The formula for enamel glaze one, by weight percentage, is: silicon dioxide 48%, aluminum oxide 6%, sodium oxide 16%, potassium oxide 8%, boron oxide 15%, calcium fluoride 5%, cobalt oxide 1%, and iron oxide 1%.

[0046] The formula for enamel glaze II, by weight percentage, is: 55% silicon dioxide, 5% aluminum oxide, 10% sodium oxide, 6% potassium oxide, 12% boron oxide, 5% calcium oxide, 5% strontium oxide, and 2% cobalt oxide;

[0047] The formula for enamel glaze type 3, by weight percentage, is: silicon dioxide 54%, aluminum oxide 5%, sodium oxide 5%, potassium oxide 3%, boron oxide 8%, calcium oxide 3%, barium oxide 20%, cobalt oxide 0.5%, and iron oxide 1.5%;

[0048] The raw material powders of the above three formulations were mixed separately in a planetary ball mill at a speed of 300 rpm for 1 hour. The uniformly mixed powders were then heated and smelted. The smelting process is as follows:

[0049] Enamel Glaze 1:

[0050] Heat from room temperature to 500℃ at a constant rate for 1 hour;

[0051] Heat at a constant rate from 500℃ to 1000℃ for 30 minutes.

[0052] Heat at a constant rate from 1000℃ to 1200℃ for 20 minutes.

[0053] Maintain a constant temperature of 1200℃ for 2 hours.

[0054] Enamel Glaze II:

[0055] Heat from room temperature to 500℃ at a constant rate for 1 hour;

[0056] Heat at a constant rate from 500℃ to 1000℃ for 30 minutes.

[0057] Heat at a constant rate from 1000℃ to 1350℃ for 35 minutes.

[0058] Maintain a constant temperature of 1350℃ for 2 hours.

[0059] Enamel Glaze 3:

[0060] Heat from room temperature to 500℃ at a constant rate for 1 hour;

[0061] Heat at a constant rate from 500℃ to 1000℃ for 30 minutes.

[0062] Heat at a constant rate from 1000℃ to 1550℃ for 55 minutes.

[0063] Maintain a constant temperature of 1550℃ for 2 hours.

[0064] The above three types of enamel were quenched in water to obtain glass glaze blocks.

[0065] (2) Preparation of enamel powder: The glass glaze block obtained after water quenching is placed into an agate ball mill jar and ball milled in a planetary ball mill (300 rpm, 100 hours). The glass glaze powder obtained after ball milling is passed through a 200-mesh sieve to obtain enamel glaze powder with a particle size of less than 200 mesh.

[0066] (3) Coating preparation: According to the mass percentage, 20% enamel glaze powder one, 10% enamel glaze powder two, 20% enamel glaze powder three, 24% quartz powder, 21% alumina powder, 4.5% iron oxide powder, and 0.5% bentonite are mixed evenly to obtain a mixed powder. The coating is prepared according to the ratio of 100g mixed powder: 35ml deionized water: 20ml potassium silicate water glass. First, the deionized water and potassium silicate water glass are mixed evenly, and then the mixed powder is ball-milled in an agate ball mill jar for 2 hours to obtain a uniformly mixed coating.

[0067] (4) The coating is applied to the sandblasted carburized steel surface using a brush method, and then dried in a 70℃ drying oven for 1 hour to obtain the anti-seepage coating. For example... Figure 1 As shown, the dried coating surface is smooth and completely covers the individual surface of the alloy, with a coating thickness of 300~500μm.

[0068] (5) The carburized steel coated with this coating is placed in a carburizing furnace and heated to 1060°C at a rate of 15°C / min. After carburizing at 1060°C for 5 hours, it is cooled to room temperature with the furnace. The coating hardly peels off. Figure 2 As shown. The coating can be completely removed by sandblasting with 180-mesh corundum abrasive at a pressure of 0.5 MPa, as... Figure 3 As shown.

[0069] (6) The coated surface was found to have no carburized layer upon inspection, such as Figure 4 As shown; the uncoated surface shows obvious carburization, such as Figure 5 As shown.

[0070] Comparative Example 1

[0071] The difference from Example 1 is that the potassium silicate water glass in the coating is increased to 30 ml, otherwise the contents remain the same. The carburized steel coated with this material is placed in a carburizing furnace and heated to 1060°C at a rate of 15°C / min. Figure 6As shown, after carburizing at 1060℃ for 5 hours and then cooling to room temperature in the furnace, the coating foamed severely, and its protective performance decreased.

[0072] Comparative Example 2

[0073] The difference from Example 1 is that the quartz powder content in the coating is reduced to 17%, and the alumina powder content is increased to 28%, while the rest remains the same. The carburized steel coated with this coating is placed in a carburizing furnace and heated to 1060°C at a rate of 15°C / min. Figure 7 As shown, after carburizing at 1060℃ for 5 hours and then cooling to room temperature in the furnace, the coating almost completely peeled off.

[0074] Example 2

[0075] In this embodiment, a local anti-seepage coating is prepared using a nitriding steel as the substrate. The preparation process is as follows:

[0076] (1) Enamel glaze melting: The preparation process of the three enamel glazes is the same as that in Example 1.

[0077] (2) Coating preparation: According to the mass percentage, enamel glaze powder I 15%, enamel glaze powder II 10%, enamel glaze powder III 20%, quartz powder 28%, alumina powder 22%, iron oxide powder 4.5%, and bentonite 0.5%. The above solid raw materials are mixed evenly to obtain a mixed powder. The coating is prepared according to the ratio of 100g mixed powder: 35ml deionized water: 20ml potassium silicate water glass. First, the deionized water and potassium silicate water glass are mixed evenly, and then the mixed powder is ball-milled in an agate ball mill jar for 2 hours to obtain a uniformly mixed coating.

[0078] (3) The coating is applied to the nitrided steel surface after sandblasting by brushing and then dried in a drying oven at 70°C for 1 hour. The surface of the anti-seepage coating after drying is flat and completely covers the individual surface of the alloy. The coating thickness is 300~500 micrometers.

[0079] (4) The nitrided steel coated with the coating was placed in a nitriding furnace and heated to 1100°C at a rate of 15°C / min. After nitriding at 1100°C for 12 hours, the coating was cooled to room temperature with the furnace and almost no peeling occurred. The coating could be completely removed by sandblasting with 180-mesh corundum sand at a pressure of 0.5 MPa.

[0080] (5) The coated surface was found to have no nitriding layer upon inspection, such as Figure 8 As shown; nitriding is obvious on the uncoated surface, such as Figure 9 As shown.

[0081] Comparative Example 3

[0082] The difference from Example 2 is that the amount of enamel glaze powder in the coating is increased by 2% to 17%, the amount of enamel glaze powder in the coating is increased by 30%, the amount of quartz powder in the coating is decreased to 19%, and the amount of alumina powder in the coating is decreased to 14%, while the rest remain the same. The nitrided steel coated with this material is placed in a nitriding furnace and heated to 1100°C at a rate of 15°C / minute. Figure 10 As shown, after nitriding at 1100℃ for 12 hours and then cooling to room temperature in the furnace, the coating shrinks severely and its protective performance decreases.

[0083] The results show that the performance indicators of the high-temperature anti-seepage coating obtained by this invention are as follows: When carburizing or nitriding alloy steels such as carburized steel and nitrided steel, after the surface is coated with the coating, no seepage layer appears in the coated area after chemical heat treatment at a heating rate of 15℃ / min and a temperature of 950~1100℃, and the service life exceeds 40 hours. After heat treatment, it can be directly quenched, and the coating will partially peel off on its own. The remaining coating can be removed by simple sandblasting.

Claims

1. A water-based anti-seepage coating for use in the chemical heat treatment process of steel, characterized in that, This coating is a water-based inorganic protective coating used for localized protection of steel during carburizing, aluminizing, nitriding, or carbonitriding processes at 950-1100℃. By weight, it comprises: 10-15 parts enamel glaze powder one, 10-15 parts enamel glaze powder two, 15-25 parts enamel glaze powder three, 20-30 parts quartz powder, 15-25 parts alumina powder, 1-10 parts iron oxide powder, 0.1-1 parts bentonite, 35-50 parts deionized water, and 10-20 parts water glass. The quartz powder has a particle size range of less than 2000 mesh, the alumina powder has a particle size range of 1-10 μm, the iron oxide powder has a particle size range of 1-5 μm, the water glass is potassium silicate water glass with a modulus of 3, and the bentonite is sodium-based bentonite with a particle size range of less than 1 μm. The formula of enamel glaze powder one, by mass percentage, is: silicon dioxide 45-50%, aluminum oxide 5-10%, sodium oxide 10-18%, potassium oxide 5-10%, boron oxide 10-15%, calcium fluoride 3-8%, cobalt oxide 0.5-2%, and iron oxide 0.5-2%; The formula of enamel glaze powder II, by mass percentage, is: silicon dioxide 50-55%, aluminum oxide 3-8%, sodium oxide 5-10%, potassium oxide 5-10%, boron oxide 10-15%, calcium oxide 3-8%, strontium oxide 5-10%, and cobalt oxide 0.5-2%. The formula of enamel glaze powder 3 by mass percentage is as follows: silicon dioxide 50~55%, aluminum oxide 1~5%, sodium oxide 5~10%, potassium oxide 1~5%, boron oxide 5~10%, calcium oxide 3~8%, barium oxide 10~20%, cobalt oxide 0.5~2%, and iron oxide 0.5~2%.

2. A method for preparing a water-based anti-seepage coating for steel chemical heat treatment as described in claim 1, characterized in that, The process includes the following steps: (1) Mixing solid raw materials evenly according to the mass fraction to obtain raw material A; (2) Mixing liquid raw materials evenly according to the mass fraction to obtain raw material B; (3) Pour raw material A and raw material B into an agate ball mill jar and ball mill them in a planetary ball mill for 1 to 2 hours to obtain a water-based anti-seepage coating.

3. The method for preparing a water-based anti-seepage coating for steel chemical heat treatment according to claim 2, characterized in that, The preparation process of enamel glaze powder 1, enamel glaze powder 2 and enamel glaze powder 3 is as follows: (1) Prepare raw material powder according to the formula and mix it in a planetary ball mill for 1 to 3 hours; (2) After mixing, the powder obtained is melted at a high temperature of 1200 to 1550℃ for 2 to 4 hours and then water-quenched to form glass glaze blocks; (3) Put the glass glaze blocks into an agate jar and ball mill them in a planetary ball mill for 100 to 200 hours; (4) Pass the glass glaze powder obtained after ball milling through a 200-mesh sieve to obtain enamel glaze powder.

4. The application of the water-based anti-seepage coating as described in claim 2 for the chemical heat treatment process of steel, characterized in that, Water-based waterproof coatings are used in the chemical heat treatment process of metals to prepare water-based waterproof coatings. The preparation process of the coating includes: (1) preparation of the coating; (2) application of the coating; (3) drying of the coating; and (4) removal of the coating. The coating process is as follows: depending on the shape and size of the workpiece, brush coating, dip coating or atmospheric spraying at room temperature is selected to obtain a coating thickness of no more than 300 micrometers; the coating drying process is as follows: dry at 60~80℃ for 1~2 hours.

5. The application of the water-based anti-seepage coating for the chemical heat treatment process of steel according to claim 4, characterized in that, The coating thickness is 150~250 micrometers.

6. The application of the water-based anti-seepage coating for the chemical heat treatment process of steel according to claim 4, characterized in that, The coating removal process is as follows: use 80~200 mesh corundum sand to blast remove it under a pressure of 0.4~0.6MPa.

Images