High-temperature oxidation and decarburization resistant and anti-cracking protective coating for high manganese steel and preparation method thereof

Abstract

The application discloses a high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel and a preparation method thereof. The technical scheme is as follows: alpha-Al2O3 micro powder, fused magnesite fine powder, potassium feldspar fine powder, manganese oxide powder, iron oxide powder, boron carbide powder and lanthanum oxide powder are uniformly mixed to prepare a composite powder. Metakaolin and silicon micro powder are mixed, NaOH solution and KOH solution are added and mixed; the mixed solution is placed in a plastic container, stirred, deionized water is added, water bath stirring is conducted, and a silicate gel is obtained; the silicate gel, a benzene propyl emulsion, deionized water and a silane coupling agent are mixed, water bath stirring is conducted, and a high-strength binding agent is prepared. The composite powder and the high-strength binding agent are uniformly mixed and stirred to prepare the high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel. The coating of the product prepared by the application on high manganese steel has excellent high-temperature anti-oxidation, small decarburization layer thickness and excellent anti-cracking performance, and can meet the protection requirements in the heat treatment process of high manganese steel.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of protective coatings for high manganese steel. In particular, it relates to a high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel and a preparation method thereof. BACKGROUND

[0002] High manganese steel has broad application potential in the fields of mining, automobiles, low-temperature containers, bridge construction, etc. due to its excellent wear resistance, impact resistance, toughness and corrosion resistance. Heat treatment is one of the processes in the processing of high manganese steel. In order to ensure the plasticity of high manganese steel castings and improve the alloy structure in the castings as much as possible, the heating temperature of high manganese steel needs to be controlled in the range of 1100-1300℃. At high temperatures, Mn and C elements have a strong affinity with oxygen. High content of Mn and C in the steel makes the degree of oxidation and decarburization more serious. Oxidation can form pits on the surface of high manganese steel and generate a large number of brittle phases at the grain boundaries; decarburization reduces the strength and wear resistance of high manganese steel. In addition, the high linear expansion coefficient of high manganese steel can easily induce cracks in brittle phases due to stress caused by volume changes during heat treatment. These accompanying phenomena seriously reduce the yield of high manganese steel. Therefore, protection of high manganese steel during heat treatment is crucial.

[0003] High manganese steel heat treatment protection technologies include protective coating method, low-temperature hot rolling method and vacuum heating method. Current research on protection technologies includes:

[0004] The patent technology "High-temperature oxidation-resistant coating for medium and high manganese steel and coating method" (CN115260806A) uses 20-35wt% of silicone resin, 8-20wt% of Na2SiO3, 2-10wt% of K2SiO3, 1-5wt% of H3BO3, 10-20wt% of CaO, 10-25wt% of Al2O3, 2-10wt% of MgO, 2-8wt% of SiC, 2-5wt% of aluminum powder, and 2-12wt% of CeO2 to prepare a coating. Although this coating has anti-oxidation effect at a use temperature not higher than 1300℃ for long-time holding, the thickest coating reaches 2.5mm and needs to be coated multiple times, with a maximum drying time of 10h for the second supplementary coating, which makes the process more complex and greatly increases the time and production cost. The protective stability of this coating is poor, the SiO2 content in the coating can reach 50wt%, and high content of SiO2 can easily react with oxidation products such as iron oxide and manganese oxide to generate liquid phase and cause corrosion pits. This patent technology does not provide anti-decarburization and anti-cracking effects.

[0005] The patent technology of "a billet anti-oxidation, anti-decarburization coating" (CN117304722A) is prepared by mixing the following components in mass fraction: 20-40 parts of polyphosphoric aluminum, 10-15 parts of silicon powder, 9-10 parts of silicon carbide, 3-5 parts of ferric oxide, 2-4 parts of chromium oxide, 5-15 parts of bentonite, 10-15 parts of aluminum oxide, 3-5 parts of kaolin, 2-4 parts of sillimanite, 1-2 parts of talc, 0.8-1.5 parts of aluminum silicate fiber. The prepared coating has certain anti-oxidation and anti-decarburization effect, but the anti-oxidation effect is only 62.98%, and there is no binder in the formula, so the adhesion to the substrate is low, and the coating is easy to peel off in a large area due to collision during the billet handling process, and the anti-cracking effect has not been mentioned.

[0006] Fan Yongfei et al. (Fan Yongfei, Zhang Heng. Research on intergranular oxidation of hot-rolled high manganese steel [J]. Heat Treatment, 2017, 32 (3): 32-35.) analyzed the reason for the occurrence of strip cracks at the edge of hot-rolled high manganese steel plate, and proposed to take measures such as cooling rolling, shortening high temperature holding time and controlling residual oxygen content to reduce the degree of intergranular oxidation of high manganese steel, which is expected to reduce the cracking of high manganese steel. However, cooling rolling and shortening high temperature holding time are not conducive to the subsequent rolling of high manganese steel; controlling the residual oxygen content puts high requirements on the sealing performance of the heating furnace, changes the original heat treatment process, and increases the production cost. SUMMARY

[0007] The present application aims to overcome the defects of the prior art, and provides a preparation method of a high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel. The prepared product has strong adhesion, simple coating process, excellent high-temperature anti-oxidation of the protective coating after coating on high manganese steel, small decarburization layer thickness and excellent anti-cracking performance, good compatibility with the original heat treatment process, and can meet the protection needs of high manganese steel during heat treatment.

[0008] To achieve the above-mentioned purposes, the technical scheme adopted by the present application is as follows:

[0009] Step 1, preparation of composite powder

[0010] Mix 25-70wt% of α-Al2O3 micro powder, 14-32wt% of fused magnesite fine powder, 5-26wt% of potassium feldspar fine powder, 2-6wt% of manganese oxide powder, 1-5wt% of iron oxide powder, 3-6wt% of boron carbide powder and 1-3wt% of lanthanum oxide powder uniformly to prepare a composite powder.

[0011] Step 2, preparation of high-strength binder

[0012] Step 2.1, according to the mass ratio of metakaolin: silica powder: NaOH solution: KOH solution: deionized water is 1:1.0-1.2:1.1-2.8:1.3-3.2:3.3-4.3, first mix the metakaolin and silica powder to obtain a premix, then add the NaOH solution and the KOH solution to the premix, mix to obtain a mixed solution; place the mixed solution in a plastic container, stir uniformly, react at 40-50℃ for 0.5-1h, then add the deionized water, stir in a water bath at 40-80℃ for 5-10min to obtain a silicate gel.

[0013] The concentration of the NaOH solution is 13-15mol / L, and the concentration of the KOH solution is 13-15mol / L.

[0014] Step 2.2, according to the mass ratio of the silicate gel: styrene-acrylic emulsion: deionized water: silane coupling agent is 1:0.05-0.3:0.2-0.4:0.01-0.02, mix the silicate gel, the styrene-acrylic emulsion, the deionized water and the silane coupling agent, stir in a water bath at 40-60℃ for 0.5-1.5h to obtain a high-strength binder.

[0015] Step 3, preparation of high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel

[0016] According to the mass ratio of the composite powder: the high-strength binder is 1:1-1.2, mix the composite powder and the high-strength binder uniformly to obtain a high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel.

[0017] The high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel is used by coating on the surface of high manganese steel at one time, and the thickness of the coating after drying is 300-600μm.

[0018] The Al2O3 content of the α-Al2O3 micro powder is ≥99wt%; the particle size of the α-Al2O3 micro powder is <5μm.

[0019] The MgO content of the fused magnesia is >96wt%; the particle size of the fused magnesia is <45μm.

[0020] The SiO2 content of the potassium feldspar powder is 65-72wt%; the particle size of the potassium feldspar powder is <10μm.

[0021] The MnO content of the manganese oxide powder is ≥99wt%; the particle size of the manganese oxide powder is <5μm.

[0022] The Fe2O3 content of the iron oxide powder is ≥99wt%; the particle size of the iron oxide powder is <5μm.

[0023] The B4C content of the boron carbide powder is ≥99wt%; and the particle size of the boron carbide powder is <5μm.

[0024] The Al2O3 content of the metakaolin is 39-44wt%; and the average particle size of the metakaolin is <5μm.

[0025] The SiO2 content of the silicon micro powder is >94wt%; and the average particle size of the silicon micro powder is <2μm.

[0026] Due to the above technical means, the present application has the following positive effects compared with the prior art:

[0027] The present application uses metakaolin, silicon micro powder, NaOH solution and KOH solution to dissolve a special inorganic binder, which has good high-temperature stability; in addition, a large number of silicate network structures are formed, and the introduction of high-alkalinity NaOH and KOH makes the PH value of the binder exceed 11, which is beneficial to the formation of a good bond between the protective coating (hereinafter referred to as the coating) and the high manganese steel substrate at room temperature, and a high adhesion is obtained. In addition to further improving the adhesion of the coating on the high manganese steel substrate, the organic polymer chain is inserted into the three-dimensional network structure of the silicate, which improves the flexibility of the coating, reduces the peeling of the coating due to bumps and vibrations during the conveying process of the high manganese steel, and the adhesion between the coating and the high manganese steel is strong. The prepared product is coated on the surface of the high manganese steel once, and after drying, the thickness of the coating is 300-600μm, and the coating process is simple.

[0028] The composite powder prepared by the present application is the main body of the coating, and the melting points of the α-Al2O3 micro powder, the fused magnesia fine powder, the boron carbide powder and the lanthanum oxide powder in the composite powder all exceed 2000℃, the melting point of the manganese oxide is 1650℃, the melting point of the iron oxide is 1565℃, and the theoretical melting point of the potassium feldspar is 1290℃, which can ensure that the coating can stably play a protective role in a heating furnace environment of 1100℃-1300℃. When the composite powder and the high-strength binder are mixed uniformly and dried, a colloidal structure wrapped with powder structure mainly composed of Si, Al, Na and K is formed. During the high-temperature heating process of the protective coating, these colloids can quickly form a glass liquid phase, promote the rapid sintering of the powder to form a continuous and dense coating, and can play a role in reducing the oxidation of high manganese steel in a short time, and has strong oxidation resistance.

[0029] With further temperature rise or extension of holding time, the alpha-Al2O3 micropowder, magnesium oxide fine powder, potassium feldspar, iron oxide and manganese oxide in the present application will react to form mullite, magnesium aluminum spinel, magnesium iron manganese spinel and the like, and in addition, the iron oxide and manganese oxide will also react with the Si, Al, Na and K as the main components of the colloid to form a small amount of liquid phase, the densification degree of the coating can be further increased, and it is more difficult for oxygen to diffuse to the high manganese steel substrate, and the decarburization reaction is also difficult to occur.

[0030] In the present application, the SiO2 exists in the form of nano colloidal particles in the binder mainly composed of Si, Al, Na and K in addition to part of it existing in the potassium feldspar raw material; because the SiO2 is easy to react with the iron oxide and manganese oxide to form a liquid phase to corrode the surface to form pits, the total content of SiO2 in the solid components of the coating after drying is controlled to be 15-28% in the present application, and in addition, the uniform dispersion of the small amount of generated liquid phase improves the densification of the coating, thereby ensuring the excellent oxidation and decarburization resistance of the coating.

[0031] In addition, the oxidation of boron carbide at high temperature will reduce the oxygen partial pressure in the coating, which is beneficial to reducing the oxidation and decarburization reactions; at the same time, the oxidation product B2O3 of boron carbide also has a sintering promoting effect, further improving the densification of the coating, and improving the oxidation and decarburization resistance of the coating.

[0032] The manganese oxide powder and iron oxide powder used in the present application make the Mn and Fe elements in the coating have a certain abundance, thereby effectively inhibiting the element segregation in the high manganese steel substrate, not only greatly improving the surface quality of the high manganese steel, but also reducing the thermal stress generated due to the phase difference. In addition, compared with the high thermal conductivity of metals, the present coating mainly contains Al2O3, MgO and SiO2, and also contains a small amount of liquid phase, and the thermal conductivity is significantly lower than that of metal materials; in the heating process, it also plays a role in reducing the heating speed of the high manganese steel blank. The reduction of element segregation in high manganese steel and the thermal resistance of the coating effectively reduce the surface cracks of high manganese steel after heat treatment.

[0033] The present application is compatible with the original heat treatment process under the condition of ensuring that the coating coated on the high manganese steel has excellent high temperature oxidation resistance, small decarburization layer thickness and excellent anti-cracking performance, and does not need to adjust the existing heat treatment equipment and temperature parameters. Therefore, it will not affect the subsequent rolling of high manganese steel, and will not increase the additional production cost.

[0034] The high temperature oxidation, decarburization and crack resistance protective coating for high manganese steel prepared by the present application is coated on the surface of high manganese steel at one time, and after drying, the test results are as follows: the oxidation protection rate is 90.32-92.49%; the decarburization layer thickness is <100 μm; the crack reduction rate is 30-50%; and the adhesion is 7.51-9.89 MPa.

[0035] Therefore, the high-temperature anti-oxidation, anti-decarburization, and anti-cracking protective coating for high-manganese steel prepared by this invention has strong adhesion, simple coating process, excellent high-temperature anti-oxidation properties, small decarburization layer thickness and excellent crack resistance after being coated on high-manganese steel, good compatibility with existing heat treatment processes, and can meet the protection requirements of high-manganese steel during heat treatment. Attached Figure Description

[0036] Figure 1 This is a photograph of the surface state of high-manganese steel after heat treatment following the application of a high-temperature anti-oxidation, anti-decarburization, and anti-cracking protective coating prepared according to the present invention to high-manganese steel.

[0037] Figure 2 for Figure 1 Metallographic photograph of the high-manganese steel cross-section shown. Detailed Implementation

[0038] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of protection thereof.

[0039] A high-temperature anti-oxidation, anti-decarburization, and crack-resistant protective coating for high-manganese steel and its preparation method. The preparation method of this specific embodiment is as follows:

[0040] Step 1: Preparation of composite powder

[0041] A composite powder is prepared by uniformly mixing 25–70 wt% α-Al₂O₃ micro powder, 14–32 wt% fused magnesia fine powder, 5–26 wt% potassium feldspar fine powder, 2–6 wt% manganese oxide powder, 1–5 wt% iron oxide powder, 3–6 wt% boron carbide powder, and 1–3 wt% lanthanum oxide powder.

[0042] Step 2: Preparation of high-strength binder

[0043] Step 2.1: Prepare the materials according to the mass ratio of metakaolin:silica powder:NaOH solution:KOH solution:deionized water A of 1:1.0-1.2:1.1-2.8:1.3-3.2:3.3-4.3. First, mix the metakaolin and silica powder to obtain a premix. Then, add the NaOH solution and KOH solution to the premix and mix to obtain a mixed solution. Place the mixed solution in a plastic container, stir evenly, and react at 40-50°C for 0.5-1 h. Then, add the deionized water A and stir in a water bath at 40-80°C for 5-10 min to obtain aluminosilicate gel.

[0044] The concentration of the NaOH solution is 13–15 mol / L, and the concentration of the KOH solution is 13–15 mol / L.

[0045] Step 2.2, the silicate gel, the styrene-acrylic emulsion, the deionized water B and the silane coupling agent are mixed according to the mass ratio of 1:0.05-0.3:0.2-0.4:0.01-0.02, and stirred at 40-60℃ for 0.5-1.5h to prepare the high-strength binder.

[0046] Step 3, preparation of high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high-manganese steel

[0047] The composite powder and the high-strength binder are uniformly stirred according to the mass ratio of 1:1-1.2 to prepare the high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high-manganese steel.

[0048] The high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high-manganese steel is used by coating on the surface of high-manganese steel once, and the thickness of the coating after drying is 300-600μm.

[0049] The SiO2 content of the potassium feldspar powder is 65-72wt%.

[0050] The Al2O3 content of the metakaolin is 39-44wt%.

[0051] In the specific embodiment:

[0052] The Al2O3 content of the α-Al2O3 micro powder is ≥99wt%, and the particle size of the α-Al2O3 micro powder is <5μm.

[0053] The MgO content of the electrically fused magnesite is >96wt%, and the particle size of the electrically fused magnesite is <45μm.

[0054] The particle size of the potassium feldspar powder is <10μm.

[0055] The MnO content of the manganese oxide powder is ≥99wt%, and the particle size of the manganese oxide powder is <5μm.

[0056] The Fe2O3 content of the iron oxide powder is ≥99wt%, and the particle size of the iron oxide powder is <5μm.

[0057] The B4C content of the boron carbide powder is ≥99wt%, and the particle size of the boron carbide powder is <5μm.

[0058] The average particle size of the metakaolin is <5μm.

[0059] The SiO2 content of the silicon micro powder is >94wt%, and the average particle size of the silicon micro powder is <2μm.

[0060] Example 1

[0061] A high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel and a preparation method thereof. The preparation method of the embodiment is:

[0062] Step 1, preparation of composite powder

[0063] 50wt% of α-Al2O3 micro powder, 23wt% of fused magnesia fine powder, 15wt% of potassium feldspar fine powder, 4wt% of manganese oxide powder, 3wt% of iron oxide powder, 4wt% of boron carbide powder and 1wt% of lanthanum oxide powder are uniformly mixed to prepare a composite powder.

[0064] Step 2, preparation of high-strength binder

[0065] Step 2.1, according to the mass ratio of metakaolin: silicon powder: NaOH solution: KOH solution: deionized water A is 1:1.1:1.5:2.1:4.3, first mix the metakaolin and silicon powder to obtain a premix, then add the NaOH solution and the KOH solution to the premix, mix to obtain a mixed solution; the mixed solution is placed in a plastic container and stirred uniformly, and then reacted at 45°C for 0.75h, then add the deionized water A, and stir for 7min under the condition of water bath at 60°C to obtain a silicate gel.

[0066] The concentration of the NaOH solution is 14mol / L, and the concentration of the KOH solution is 14mol / L.

[0067] Step 2.2, according to the mass ratio of the silicate gel: styrene-acrylic emulsion: deionized water B: silane coupling agent is 1:0.15:0.3:0.017, mix the silicate gel, the styrene-acrylic emulsion, the deionized water B and the silane coupling agent, and stir for 0.75h under the condition of water bath at 50°C to prepare a high-strength binder.

[0068] Step 3, preparation of high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel

[0069] According to the mass ratio of the composite powder: the high-strength binder is 1:1.1, the composite powder and the high-strength binder are stirred uniformly to prepare a high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel.

[0070] The high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel is used by coating on the surface of high manganese steel at one time, and the thickness of the coating after drying is 450μm.

[0071] The SiO2 content in the potassium feldspar powder is 69wt%.

[0072] The Al2O3 content of the metakaolin is 41wt%.

[0073] The high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel prepared by the present application is coated on the surface of high manganese steel once, and after drying, the test results show that the oxidation protection rate is 91.36%, the decarburization layer thickness is <70 μm, the crack reduction rate is 37%, and the adhesion is 8.32 MPa.

[0074] Example 2

[0075] A high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel and a preparation method thereof. The preparation method of the present embodiment is as follows:

[0076] Step 1, preparation of composite powder

[0077] 70wt% of α-Al2O3 micro powder, 14wt% of fused magnesite fine powder, 5wt% of potassium feldspar fine powder, 2wt% of manganese oxide powder, 2wt% of iron oxide powder, 5wt% of boron carbide powder and 2wt% of lanthanum oxide powder are uniformly mixed to prepare the composite powder.

[0078] Step 2, preparation of high-strength binder

[0079] Step 2.1, according to the mass ratio of metakaolin: silicon powder: NaOH solution: KOH solution: deionized water A is 1:1.0:1.1:3.2:3.7, first mix the metakaolin and silicon powder to obtain a premix, then add the NaOH solution and the KOH solution to the premix, mix to obtain a mixed solution; place the mixed solution in a plastic container, stir uniformly, react at 40℃ for 0.5h, then add the deionized water A, stir for 5min under the condition of 80℃ water bath to obtain a silicate gel.

[0080] The concentration of the NaOH solution is 13mol / L, and the concentration of the KOH solution is 13mol / L.

[0081] Step 2.2, according to the mass ratio of the silicate gel: styrene-acrylic emulsion: deionized water B: silane coupling agent is 1:0.1:0.25:0.013, mix the silicate gel, the styrene-acrylic emulsion, the deionized water B and the silane coupling agent, stir for 1h under the condition of 40℃ water bath to prepare a high-strength binder.

[0082] Step 3, preparation of high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel

[0083] According to the mass ratio of the composite powder: the high-strength binder is 1:1, the composite powder and the high-strength binder are stirred uniformly to prepare a high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel.

[0084] The high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel is coated on the surface of the high manganese steel once, and the thickness of the coating after drying is 300 mu m.

[0085] The SiO2 content in the potassium feldspar powder is 65 wt%.

[0086] The Al2O3 content in the metakaolin is 44 wt%.

[0087] The high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel prepared by the method has the following properties: the oxidation protection rate is 92.49%; the decarburization layer thickness is less than 40 mu m; the crack reduction rate is 50%; and the adhesion is 7.51 MPa.

[0088] Example 3

[0089] A high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel and a preparation method thereof are disclosed.

[0090] Step 1, preparation of composite powder

[0091] 25 wt% of alpha-Al2O3 micro powder, 32 wt% of fused magnesite fine powder, 26 wt% of potassium feldspar fine powder, 3 wt% of manganese oxide powder, 5 wt% of iron oxide powder, 6 wt% of boron carbide powder and 3 wt% of lanthanum oxide powder are uniformly mixed to prepare the composite powder.

[0092] Step 2, preparation of high-strength binder

[0093] Step 2.1, the mass ratio of metakaolin: silica micro powder: NaOH solution: KOH solution: deionized water A is 1:1.2:2.0:2.5:3.3, the metakaolin and the silica micro powder are mixed first to obtain a premix, then the NaOH solution and the KOH solution are added to the premix, mixed to obtain a mixed solution; the mixed solution is placed in a plastic container and stirred uniformly, and then the deionized water A is added, and the mixture is stirred for 8 min under the condition of a water bath at 40 DEG C to obtain a silicate gel.

[0094] The concentration of the NaOH solution is 13.5 mol / L, and the concentration of the KOH solution is 15 mol / L.

[0095] Step 2.2, the mass ratio of the silicate gel: styrene-acrylic emulsion: deionized water B: silane coupling agent is 1:0.3:0.4:0.02, the silicate gel, the styrene-acrylic emulsion, the deionized water B and the silane coupling agent are mixed, and the mixture is stirred for 1.5 h under the condition of a water bath at 60 DEG C to prepare a high-strength binder.

[0096] Step 3, preparation of high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel

[0097] The high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel is prepared by mixing the composite powder and the high-strength binder in a mass ratio of 1:1.2 and stirring them uniformly.

[0098] The high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel is used by being coated on the surface of high manganese steel once, and the thickness of the coating after drying is 500 μm.

[0099] The SiO2 content in the potassium feldspar powder is 72 wt%.

[0100] The Al2O3 content in the metakaolin is 39 wt%.

[0101] The high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel prepared by the method has an oxidation protection rate of 90.32% after being coated on the surface of high manganese steel once and dried, a decarburization layer thickness of <100 μm, a crack reduction rate of 30%, and an adhesion of 8.94 MPa.

[0102] Example 4

[0103] A high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel and a preparation method thereof. The preparation method of the embodiment is as follows:

[0104] Step 1, preparation of composite powder

[0105] The composite powder is prepared by uniformly mixing 60 wt% of α-Al2O3 micro powder, 17.5 wt% of fused magnesite fine powder, 10 wt% of potassium feldspar fine powder, 6 wt% of manganese oxide powder, 1 wt% of iron oxide powder, 3 wt% of boron carbide powder and 2.5 wt% of lanthanum oxide powder.

[0106] Step 2, preparation of high-strength binder

[0107] Step 2.1, the metakaolin, silicon micro powder, NaOH solution, KOH solution and deionized water A are mixed in a mass ratio of 1:1.15:2.8:1.3:3.75, the metakaolin and silicon micro powder are first mixed to obtain a premix, then the NaOH solution and the KOH solution are added to the premix and mixed to obtain a mixed solution; the mixed solution is placed in a plastic container and stirred uniformly, and then the deionized water A is added and stirred for 10 min in a water bath at 70°C to obtain a silicate gel.

[0108] The concentration of the NaOH solution is 15 mol / L, and the concentration of the KOH solution is 14.5 mol / L.

[0109] Step 2.2, the silicate gel: styrene-acrylate emulsion: deionized water B: silane coupling agent are mixed in a mass ratio of 1:0.05:0.2:0.01, and stirred in a water bath at 45 DEG C for 0.5 h to prepare a high-strength binder.

[0110] Step 3, preparation of high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel

[0111] The composite powder and the high-strength binder are uniformly stirred in a mass ratio of 1:1.15 to prepare a high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel.

[0112] The high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel is used by being coated on the surface of the high manganese steel at one time, and the thickness of the coating after drying is 600 microns.

[0113] The SiO2 content in the potassium feldspar powder is 70 wt%.

[0114] The Al2O3 content in the metakaolin is 43 wt%.

[0115] The high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel prepared by the present application is coated on the surface of the high manganese steel at one time, and after drying, the oxidation protection rate is 90.76%, the decarburization layer thickness is <80 microns, the crack reduction rate is 35%, and the adhesion is 9.89 MPa.

[0116] The adhesion test method of the protective coating obtained by the present embodiment is as follows:

[0117] First, the surfaces of a plurality of high manganese steel samples are cleaned, and then the prepared high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel is uniformly coated on the surfaces of the plurality of high manganese steel samples at one time, and dried at room temperature. The thickness of the coating after drying is 300-600 microns, and a plurality of high manganese steel samples coated with the protective coating are obtained.

[0118] The test column is bonded to one of the high manganese steel samples coated with the protective coating by using an epoxy adhesive, and is placed in a 60 DEG C oven for 2.5 h. After cooling, the adhesion of the coating is obtained according to the "Pull-off Method for Adhesion of Coatings" (GB / T5210-2006).

[0119] σ = F / A (1)

[0120] In formula (1), F represents the force, A represents the area, and σ represents the adhesion.

[0121] Σ represents the adhesion of the protective coating, MPa.

[0122] F represents the tensile force when the protective coating is damaged, N;

[0123] A represents the cross-sectional area of the test column, mm 2 .

[0124] The test method for the oxidation protection rate of the protective coating obtained by the present embodiment is as follows:

[0125] The heating furnace is heated to a predetermined temperature, and another high manganese steel sample coated with a protective coating is placed in the heating furnace. After heat preservation for 1-3 h, it is taken out and cooled in water at 5-15 ℃. The oxidation loss rate β is calculated according to the Black Metallurgy Industry Standard “Determination and Calculation of Oxidation Loss of Billets” (YB / T4773-2019). g The oxidation protection rate OPR of the high manganese steel sample coated with the protective coating is.

[0126]

[0127] In formula (2):

[0128] OPR represents the oxidation protection rate, %;

[0129] β g0 represents the oxidation loss rate of the high manganese steel sample without the protective coating, %;

[0130] β g1 represents the oxidation loss rate of the high manganese steel sample coated with the protective coating, %.

[0131] The present embodiment has the following positive effects compared with the prior art:

[0132] The present embodiment uses metakaolin, silicon powder, NaOH solution and KOH solution to dissolve a special inorganic binder, which has good high-temperature stability. In addition, due to the formation of a large number of three-dimensional network structures of silicate and the introduction of high-alkalinity NaOH and KOH, the PH value of the binder exceeds 11, which is conducive to the formation of good bonding between the protective coating (hereinafter referred to as the coating) and the high manganese steel substrate at room temperature, and the adhesion is high. In addition to further improving the adhesion of the coating on the high manganese steel substrate, the organic polymer chain is inserted into the three-dimensional network structure of silicate, which improves the flexibility of the coating, reduces the peeling of the coating due to bumps and vibrations during the transportation of high manganese steel, and the adhesion of the coating to high manganese steel is strong. The product is coated on the surface of high manganese steel at one time, and the thickness of the coating after drying is 300-600 μm, and the coating process is simple.

[0133] The composite powder prepared in the embodiment is the main body of the coating, and the melting points of the α-Al2O3 micropowder, the fused magnesia fine powder, the boron carbide powder and the lanthanum oxide powder in the composite powder are all higher than 2000℃, the melting point of the manganese oxide is 1650℃, the melting point of the iron oxide is 1565℃, and the theoretical melting point of the potassium feldspar is 1290℃, so it can be ensured that the coating can stably play a protective role in the heating furnace environment of 1100℃-1300℃. When the composite powder and the high-strength binding agent are uniformly mixed and dried, a colloidal wrapped powder structure mainly composed of Si, Al, Na and K is formed. When the protective coating is heated at high temperature, these colloids can quickly form a glass liquid phase, promote the rapid sintering of the powder to form a continuous and dense coating, and can play a role in reducing the oxidation of the high manganese steel in a short time, and has strong oxidation resistance.

[0134] With further temperature rise or prolongation of the holding time, the α-Al2O3 micropowder, the magnesium oxide fine powder, the potassium feldspar, the iron oxide and the manganese oxide in the embodiment will react to form mullite, magnesium-aluminum spinel, magnesium-iron-manganese spinel and the like, and in addition, the iron oxide and the manganese oxide will also react with the colloids mainly composed of Si, Al, Na and K to form a small amount of liquid phase, so the densification degree of the coating can be further increased, and it is more difficult for oxygen to diffuse to the high manganese steel substrate, and the decarburization reaction is also difficult to occur.

[0135] In the embodiment, in addition to part of the SiO2 being present in the potassium feldspar raw material, more SiO2 exists in the binding agent mainly composed of Si, Al, Na and K in the form of nano colloidal particles; because SiO2 is easy to react with the iron oxide and the manganese oxide to form a liquid phase to corrode the surface and form pits, the total content of SiO2 in the solid components of the coating after drying is controlled to be 15%-28% in the embodiment, and in addition, the dispersion of the small amount of generated liquid phase improves the denseness of the coating, and thus the excellent anti-oxidation and anti-decarburization performance of the coating is ensured.

[0136] In addition, the oxidation of boron carbide at high temperature will reduce the oxygen partial pressure in the coating, which is beneficial to reducing the oxidation and decarburization reaction; at the same time, the oxidation product B2O3 of boron carbide also has a sintering-promoting effect, further improving the denseness of the coating, and improving the anti-oxidation and anti-decarburization performance of the coating.

[0137] The manganese oxide powder and iron oxide powder used in this specific embodiment ensure a certain abundance of Mn and Fe elements in the coating, effectively suppressing elemental segregation in the high-manganese steel matrix. This not only significantly improves the surface quality of the high-manganese steel but also reduces thermal stress caused by phase differences. Furthermore, compared to the high thermal conductivity of metals, this coating, primarily composed of Al2O3, MgO, and SiO2 with a small amount of liquid phase, has a significantly lower thermal conductivity than metallic materials. This also helps to reduce the heating rate of the high-manganese steel billet during the heating process. The reduction in elemental segregation in the high-manganese steel and the thermal resistance of the coating effectively reduce surface cracks in the high-manganese steel after heat treatment.

[0138] The high-manganese steel high-temperature anti-oxidation, anti-decarburization, and crack-resistant protective coating prepared according to this specific embodiment is shown in the attached figure. Figure 1 The image shows the surface condition of the high manganese steel prepared in Example 2 after being coated with a high-temperature anti-oxidation, anti-decarburization, and anti-cracking protective coating and then heat-treated at 1250℃ for 3 hours. Figure 2 for Figure 1 Metallographic photograph of the high-manganese steel cross-section shown. From Figure 1 It can be seen that the lighter-colored areas represent unoxidized high-manganese steel substrates, while the darker-colored areas represent oxidized high-manganese steel substrates. Figure 1 Most of the area is light-colored, indicating that it is the unoxidized high-manganese steel substrate, demonstrating the excellent anti-oxidation effect of the coating; from Figure 2 It can be seen that the thickness of the decarburized layer is less than 40μm, and the oxide layer has no obvious cracks. This specific embodiment, while ensuring excellent high-temperature oxidation resistance, a thin decarburized layer, and excellent crack resistance after coating on high-manganese steel, is highly compatible with existing heat treatment processes and requires no adjustment to existing heat treatment equipment or temperature parameters. Therefore, it will not affect the subsequent rolling of high-manganese steel, nor will it increase additional production costs.

[0139] The high-manganese steel prepared in this specific embodiment is coated with a high-temperature anti-oxidation, anti-decarburization, and anti-cracking protective coating in one go. After drying, the following tests were conducted: the oxidation protection rate was 90.32-92.49%; the decarburization layer thickness was <100μm; the crack reduction rate was 30-50%; and the adhesion was 7.51-9.89MPa.

[0140] Therefore, the high-temperature anti-oxidation, anti-decarburization, and anti-cracking protective coating for high-manganese steel prepared in this specific embodiment has strong adhesion, simple coating process, excellent high-temperature anti-oxidation properties, small decarburization layer thickness and excellent crack resistance after being coated on high-manganese steel, good compatibility with existing heat treatment processes, and can meet the protection requirements of high-manganese steel during heat treatment.

Claims

1. A method for preparing a high-temperature anti-oxidation, anti-decarburization, and crack-resistant protective coating for high-manganese steel, characterized in that... The steps of the preparation method are: Step 1, preparation of composite powder 25-70wt% of α-Al2O3 micro powder, 14-32wt% of fused magnesite fine powder, 5-26wt% of potassium feldspar fine powder, 2-6wt% of manganese oxide powder, 1-5wt% of iron oxide powder, 3-6wt% of boron carbide powder and 1-3wt% of lanthanum oxide powder are uniformly mixed to prepare composite powder; Step 2, preparation of high-strength binder Step 2.1, according to the mass ratio of metakaolin: silica powder: NaOH solution: KOH solution: deionized water of 1: 1.0-1.2: 1.1-2.8: 1.3-3.2: 3.3-4.3, first mix the metakaolin and silica powder to obtain a premix, then add the NaOH solution and the KOH solution to the premix, mix to obtain a mixed solution; the mixed solution is placed in a plastic container and stirred uniformly, and is reacted at 40-50℃ for 0.5-1h, then the deionized water is added and stirred at 40-80℃ for 5-10min to obtain a silicate gel; The concentration of the NaOH solution is 13-15mol / L, and the concentration of the KOH solution is 13-15mol / L; Step 2.2, according to the mass ratio of the silicate gel: styrene-acrylic emulsion: deionized water: silane coupling agent of 1: 0.05-0.3: 0.2-0.4: 0.01-0.02, the silicate gel, the styrene-acrylic emulsion, the deionized water and the silane coupling agent are mixed and stirred at 40-60℃ for 0.5-1.5h to prepare a high-strength binder; Step 3, preparation of high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel According to the mass ratio of the composite powder: the high-strength binder of 1: 1-1.2, the composite powder and the high-strength binder are stirred uniformly to prepare a high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel.

2. The method for preparing high temperature oxidation, decarburization and cracking resistant coating for high manganese steel according to claim 1, characterized in that: The Al2O3 content of the α-Al2O3 micro powder is ≥99wt%; the particle size of the α-Al2O3 micro powder is <5μm.

3. The preparation method of the high-temperature anti-oxidation, anti-decarburization, and crack-resistant protective coating for high-manganese steel according to claim 1, characterized in that: The MgO content of the fused magnesite fine powder is >96wt%; the particle size of the fused magnesite fine powder is <45μm.

4. The method for preparing high temperature oxidation, decarburization and cracking resistant coating for high manganese steel according to claim 1, characterized in that: The SiO2 content of the potassium feldspar fine powder is 65-72wt%; the particle size of the potassium feldspar fine powder is <10μm.

5. The process for the preparation of high temperature oxidation, decarburization and cracking resistant protective coating for high manganese steel as claimed in claim 1 wherein the process comprises of the steps of: The MnO content of the manganese oxide powder is ≥99wt%; the particle size of the manganese oxide powder is <5μm.

6. The process for the preparation of high temperature oxidation, decarburization and cracking resistant protective coating for high manganese steel as claimed in claim 1, wherein the process comprises of the steps of: The Fe2O3 content of the iron oxide powder is ≥99wt%; the particle size of the iron oxide powder is <5μm.

7. The process for the preparation of high temperature oxidation, decarburization and cracking resistant protective coating for high manganese steel as claimed in claim 1 wherein the process comprises of the steps of: The B4C content of the boron carbide powder is ≥99wt%; the particle size of the boron carbide powder is <5μm.

8. The process for the preparation of high temperature oxidation, decarburization and cracking resistant protective coating for high manganese steel as claimed in claim 1 wherein the process comprises of the steps of: The Al2O3 content of the metakaolin is 39-44wt%; the average particle size of the metakaolin is <5μm.

9. The preparation method of the high-temperature anti-oxidation, anti-decarburization, and crack-resistant protective coating for high-manganese steel according to claim 1, characterized in that: The SiO2 content of the silica powder is >94wt%; the average particle size of the silica powder is <2μm.

10. A high-temperature anti-oxidation, anti-decarburization, and crack-resistant protective coating for high-manganese steel, characterized in that... The high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel is prepared according to the preparation method of the high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel in any one of claims 1-9. The high-temperature anti-oxidation, anti-decarburization and anti-cracking protective coating for high manganese steel is coated on the surface of the high manganese steel once, and the thickness of the coating after drying is 300-600 microns.

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