High-temperature anti-oxidation coating for high-density creep-resistant steel billets and preparation method thereof

Abstract

This invention discloses a high-density, creep-resistant, high-temperature anti-oxidation coating for steel billets and its preparation method. By mass percentage, the coating comprises the following components: 40%–50% pentagonal nanocomposite powder, 8%–15% inorganic binder, 2%–5% film-forming agent, 0.8%–1.5% dispersant, 1.5%–4% anti-precipitation rheology modifier, 1%–2.2% antifreeze, 0.3%–1.2% anticorrosive and antifungal agent, 0.2%–0.6% defoamer, with the balance being water. The pentagonal nanocomposite powder is composed of nano-silica, nano-alumina, nano-silicon carbide, nano-zinc oxide, and nano-lanthanum boride in a mass ratio of (5–8):(2–4):(0.8–1.5):(1–2):(0.6–1.2). The coating of this invention achieves multi-level protection—low-temperature sintering densification, high-temperature creep resistance, thermal shock self-healing, and high storage stability—through the complementary functions of its multiple components.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature protective coatings for metals, specifically relating to a high-density, creep-resistant, high-temperature anti-oxidation coating for steel billets and its preparation method. Background Technology

[0002] Under hot working conditions of 800-1200℃, such as hot rolling, forging, and high-temperature annealing, steel billets are highly susceptible to violent oxidation reactions with oxygen and water vapor in the air, generating a large amount of loose iron oxide scale. This not only causes the steel raw material to burn and reduces the yield, but also leads to excessive surface roughness of the billet, increasing the cost of subsequent finishing processes and seriously affecting the quality of the finished steel product. High-temperature anti-oxidation coatings are the most economical and efficient active protection method for steel billets during hot working. By forming a dense protective film on the surface of the billet, it isolates the high-temperature oxidizing medium from contact with the metal substrate, inhibiting the oxidation reaction.

[0003] Currently, commercially available and publicly available high-temperature anti-oxidation coatings for steel billets generally suffer from problems such as single system composition and significant performance shortcomings. Most of them adopt micron-level powders or conventional ternary and quaternary nano-oxide compound systems, which have many inherent technical defects: First, conventional powder systems have high sintering activation energy, and cannot fully ceramicize in the 800~1000℃ medium temperature range, resulting in high coating porosity, easy oxygen penetration, and poor medium-temperature protection. Second, the coating has insufficient high-temperature mechanical properties and weak creep resistance, making it prone to film relaxation, cracking, and peeling under high-temperature pressure and steel billet thermal deformation conditions, resulting in a short protective life. Third, the coating is prone to microcracks during thermal shock cycling, and traditional systems lack self-repairing capabilities; the continuous expansion of microcracks will directly lead to the failure of the protective system. Fourth, multi-component nano-powders have high surface energy, and without a dedicated dispersion system, they are prone to cross-agglomeration, causing batch-to-batch performance fluctuations. Fifth, traditional coatings are difficult to balance in terms of storage stability, low-temperature adaptability, and anti-mildew and anti-corrosion performance, failing to meet the needs of stable construction on a large scale in all seasons.

[0004] For example, patent CN200710035208.7 discloses a coating for high-temperature oxidation resistance of steel, mainly composed of SiO2, Al2O3, clay, borides, and inorganic binders, with an applicable temperature range of 900~1300℃. This solution uses conventional micron-sized inorganic powders, lacks sintering catalysis and creep resistance, and has insufficient temperature-dependent density in the coating, making it unable to self-repair after microcracks are generated by thermal shock.

[0005] Patent CN201911268467.3 discloses a high-alloy steel billet anti-oxidation coating resistant to high-temperature and long-term heating, which is prepared by using SiO2, Al2O3, and ZrO2 as the main fillers and an inorganic binder. This solution only uses conventional oxide compounding, and the system is a simple ternary oxide combination. It has poor high-temperature creep resistance and cannot achieve rapid densification at medium temperatures.

[0006] Patent CN202410263417.0 discloses a high-temperature anti-oxidation coating for steel billets, comprising components such as SiO2, Al2O3, ZrO2, SiC, and B4C. This solution improves sintering performance through borides, but it remains a conventional micron-sized powder, lacking nano-composite synergy, self-healing function, and creep-resistant strengthening mechanism, thus failing to achieve dynamic thermal shock repair and high-temperature structural stability.

[0007] Patent CN202410263404.3 discloses a high-temperature anti-oxidation coating for steel billets, mainly comprising SiO2, Al2O3, ZrO2, SiC, B4C, and carbon materials. This solution focuses on coating removal performance and does not use nanoscale powders, thus failing to meet the multiple requirements of mid-temperature densification, high-temperature creep resistance, and microcrack self-healing.

[0008] In summary, the existing publicly available solutions are all limited to simple ratio improvements of conventional oxide powders, and cannot simultaneously solve the coupled technical problems such as non-densification at medium temperatures, easy creep at high temperatures, easy cracking due to thermal shock, easy agglomeration of nanoparticles, and unstable storage. Summary of the Invention

[0009] Based on the above-mentioned defects in the prior art, the present invention provides a high-density, creep-resistant, high-temperature anti-oxidation coating for steel billets and its preparation method. The coating achieves multi-level protection through the complementary functions of multiple components, including low-temperature sintering densification, high-temperature creep resistance, thermal shock self-healing, and high storage stability.

[0010] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows: This invention provides a high-density, creep-resistant, high-temperature anti-oxidation coating for steel billets. By mass percentage, the coating comprises the following components: 40%–50% pentagonal nanocomposite powder, 8%–15% inorganic binder, 2%–5% film-forming agent, 0.8%–1.5% dispersant, 1.5%–4% anti-precipitation rheology modifier, 1%–2.2% antifreeze, 0.3%–1.2% anti-corrosion and anti-mildew agent, 0.2%–0.6% defoamer, with the balance being water. The five-element nanocomposite powder is composed of nano-silica, nano-alumina, nano-silicon carbide, nano-zinc oxide, and nano-lanthanum boride in a mass ratio of (5~8):(2~4):(0.8~1.5):(1~2):(0.6~1.2).

[0011] Further, the coating is composed of the following components by mass percentage: 43% pentaneous nanocomposite powder, 12% inorganic binder, 3.5% film-forming agent, 1.2% dispersant, 2.5% anti-precipitation rheology modifier, 2% antifreeze agent, 0.6% preservative and mildew inhibitor, 0.4% defoamer, and 34.8% water.

[0012] Furthermore, the particle size of the nano-silica, nano-alumina, nano-silicon carbide, nano-zinc oxide, and nano-lanthanum boride is controlled within 20~80nm.

[0013] Furthermore, the inorganic binder is a compound of silica sol and aluminum dihydrogen phosphate in a mass ratio of (1.5~2.5):(0.5~1.5), preferably in a mass ratio of 2:1. The inorganic binder used in this invention has both room temperature bonding and shaping functions and high temperature sintering and crosslinking functions, which can strengthen the chemical bonding and mechanical interlocking between the coating and the steel billet substrate.

[0014] Furthermore, the film-forming agent is ethylene glycol monobutyl ether, which is used to improve the powder wetting and spreading properties, and enhance the coating curing uniformity and low-temperature film-forming quality.

[0015] Furthermore, the dispersant is a modified sodium polyacrylate dispersant.

[0016] Furthermore, the anti-precipitation rheology modifier is one or both of bentonite and sodium carboxymethyl cellulose, used to construct a reversible three-dimensional network structure to bind suspended powders and inhibit sedimentation and stratification.

[0017] Furthermore, the antifreeze is a compound of glycerol and ethylene glycol in a mass ratio of (0.5~1.5):(0.5~1.5), preferably glycerol and ethylene glycol in a mass ratio of 1:1. This antifreeze can effectively reduce the freezing point of the system and is suitable for low-temperature construction conditions.

[0018] Furthermore, the preservative and antifungal agent is a benzimidazole-based antifungal agent, used to effectively inhibit the growth of microorganisms and extend the shelf life of the coating.

[0019] Furthermore, the defoamer is a polyether-modified silicone defoamer, which has excellent compatibility, can eliminate construction bubbles, and prevent pinhole defects in the coating.

[0020] The mechanisms of action of each component in the pentagonal nanocomposite powder are as follows: 1. Nano SiO2 (film-forming framework phase): This powder has high surface activity and can be quickly wetted and spread at room temperature to form a continuous and uniform basic protective film. In the medium and high temperature range, it preferentially melts and softens, filling the gaps between powder particles, thereby constructing a complete ceramicized continuous network, giving the coating basic density and oxygen barrier capabilities, and acting as the core framework for coating formation and basic protection.

[0021] 2. Nano Al2O3 (high-temperature structural reinforcement phase): This powder has an extremely high melting point and excellent structural rigidity. It can maintain dimensional stability under high-temperature conditions above 1000℃, effectively suppressing thermal shrinkage, deformation and creep relaxation of the coating during high-temperature service. At the same time, it reacts with nano SiO2 to form a mullite stable phase, which improves the overall high-temperature mechanical strength and structural stability of the coating.

[0022] 3. Nano SiC (anti-ablation interface strengthening phase): This powder has excellent high-temperature chemical stability and erosion resistance, which can effectively resist high-temperature furnace gas erosion and flame erosion; at the same time, it significantly enhances the interfacial bonding strength between the coating and the steel billet metal substrate, preventing the coating from peeling, flaking and falling off during high-temperature service, thereby strengthening the integrity of the protection system.

[0023] 4. Nano ZnO (thermal shock self-healing phase): This powder can generate a low-viscosity glass phase in the medium and high temperature range, which can fill the surface micro-cracks and micro-pores generated during the hot and cold cycle in real time, realize dynamic self-repair, and block the penetration channels of oxidizing media; at the same time, it has an auxiliary antibacterial function and synergistically improves the storage stability of coatings.

[0024] 5. Nano LaB6 (Sintering Catalysis + Creep-resistant Core Phase): This powder can significantly reduce the overall sintering activation energy of the powder, enabling rapid sintering and densification in the medium temperature range of 800~1000℃, solving the problem of medium-temperature protection failure in traditional coatings; under high-temperature conditions, it can fill grain boundary voids and achieve secondary pore sealing, further improving the film density; at the same time, it greatly improves the high-temperature creep resistance of the coating, ensuring the integrity of the coating structure and preventing cracking and peeling during the high-temperature deformation of the steel billet.

[0025] The present invention also provides a method for preparing the above-mentioned high-density, creep-resistant, high-temperature anti-oxidation coating for steel billets, comprising the following steps: S1. Pretreatment of pentagonal nanocomposite powder: According to the proportion of each component of the pentagonal nanocomposite powder, nano silica, nano alumina, nano silicon carbide, nano zinc oxide and nano lanthanum boride are mixed evenly, and then dispersed at room temperature for 5~10 min to break the cross-agglomeration structure of the multi-component powder. S2. Preparation of base liquid: According to the proportion of each component of the coating, add water to the reaction vessel, and under stirring at 300~400r / min, add inorganic binder, film-forming agent and dispersant in sequence, and continue stirring for 15~20min until all components are completely dissolved to obtain base liquid; S3. High-speed dispersion of powder: The pretreated five-element nanocomposite powder obtained in step S1 is added to the base liquid obtained in step S2, and the stirring speed is increased to 800~1000 r / min. The powder is dispersed for 30~40 min. By utilizing the electrostatic repulsion and steric hindrance effect of the dispersant, the monodisperse and uniformly distributed multi-category nanopowders are achieved. S4. Additive compounding and modification: Reduce the stirring speed to 400~500r / min, add anti-precipitation rheology modifier, antifreeze agent, and preservative and mildew inhibitor, stir for 15~25min to mix evenly, then add defoamer, stir for 5~8min to completely eliminate micro bubbles in the system. S5. Filtration and maturation: Filter the liquid to remove impurities and trace agglomerates, let it stand for at least 30 minutes to defoam and mature, and obtain the finished coating.

[0026] The beneficial effects of this invention are as follows: 1. This invention utilizes the low-temperature sintering catalytic properties of nano-LaB6 in pentagonal nanocomposite powder to solve the industry problem of non-density during medium-temperature sintering of traditional coatings. Full ceramicization of the coating can be achieved at 800℃. Combined with the secondary sealing effect of the multi-element powder, the oxygen barrier performance is significantly improved, reducing the high-temperature oxidation burn-off rate of the steel billet to below 8%. Utilizing the coupling of a triple mechanism of Al2O3 rigid support, LaB6 creep-resistant reinforcement, and ZnO microcrack self-healing, the coating can withstand more than 50 cycles of thermal cycling from 1200℃ to room temperature without cracking, peeling, or creep deformation, exhibiting long-term protective performance far exceeding that of traditional coatings. Through the synergistic effect of the SiC interface strengthening phase and the composite binder, the coating and the steel billet substrate form a dual structure of chemical bonding and mechanical interlocking, achieving a zero-level adhesion at room temperature, with a strong interface bond, and no curling, peeling, or detachment under high-temperature conditions.

[0027] 2. This invention utilizes a modified sodium polyacrylate dispersant to adapt to a five-element multi-category powder system, inhibiting cross-agglomeration. Combined with a three-dimensional network anti-settling structure of an anti-settling rheology modifier, the coating exhibits no stratification, sedimentation, or agglomeration after being stored at room temperature in a sealed container for more than 6 months. It can be applied directly without secondary stirring.

[0028] 3. The antifreeze of this invention is a compound of glycerol and ethylene glycol. The five-element nano-composite powder used enables the coating to be applied stably in a low temperature environment of -15℃. The anti-corrosion and anti-mildew agent effectively extends the shelf life of the coating to more than 12 months. The defoamer eliminates pinhole defects in the coating and is suitable for industrial construction in all seasons and multiple scenarios.

[0029] 4. The coating of this invention is a water-based formula with no toxic volatile components, making it safe and pollution-free. It is suitable for various construction methods such as spraying, brushing, and roller coating, and can be widely used for high-temperature heat treatment protection of various carbon steel and alloy steel billets, with broad prospects for promotion. Detailed Implementation

[0030] The technical solution of the present invention will be described in detail below with reference to specific embodiments. The following embodiments are only preferred embodiments of the present invention and are not intended to limit the present invention.

[0031] Example 1 A high-density, creep-resistant, high-temperature anti-oxidation coating for steel billets, by weight percentage, comprises the following components: 40% pentagonal nanocomposite powder, 8% inorganic binder, 2% film-forming agent, 0.8% dispersant, 1.5% anti-precipitation rheology modifier, 1% antifreeze agent, 0.3% anti-corrosion and anti-mildew agent, 0.2% defoamer, and 46.2% deionized water; wherein: The five-element nanocomposite powder is composed of nano-silica, nano-alumina, nano-silicon carbide, nano-zinc oxide, and nano-lanthanum boride in a mass ratio of 6.9:2.4:0.8:1.2:0.9. The particle size of nano-silica, nano-alumina, nano-silicon carbide, nano-zinc oxide, and nano-lanthanum boride is controlled within 20~80nm. The inorganic binder is a mixture of silica sol and aluminum dihydrogen phosphate in a mass ratio of 2:1. The film-forming agent is ethylene glycol monobutyl ether; The dispersant is modified sodium polyacrylate dispersant; The anti-precipitation rheology modifier is a compound of bentonite and sodium carboxymethyl cellulose. The antifreeze is a mixture of glycerol and ethylene glycol in a 1:1 mass ratio; The preservative and mildew inhibitor is a benzimidazole-based mildew inhibitor; The defoamer is a polyether-modified silicone defoamer.

[0032] The preparation method of the coating in this embodiment includes the following steps: S1. Pretreatment of pentagonal nanocomposite powder: According to the proportion of each component of pentagonal nanocomposite powder, nano silica, nano alumina, nano silicon carbide, nano zinc oxide and nano lanthanum boride are mixed evenly and then dispersed at room temperature for 8 minutes to break the cross-agglomeration structure of multi-component powder. S2. Preparation of base liquid: According to the proportion of each component of the coating, add deionized water to the reaction vessel, and under stirring at 350 r / min, add inorganic binder, film-forming agent and dispersant in sequence, and continue stirring for 18 min until each component is completely dissolved to obtain base liquid; S3. High-speed dispersion of powder: The pretreated five-element nanocomposite powder obtained in step S1 is added to the base liquid obtained in step S2, the stirring speed is increased to 900 r / min, and high-speed dispersion is carried out for 35 min. With the help of the electrostatic repulsion and steric hindrance effect of the dispersant, the monodisperse and uniform distribution of multiple types of nanopowders is achieved. S4. Additive compounding and modification: Reduce the stirring speed to 450 r / min, add anti-precipitation rheology modifier, antifreeze agent, and preservative and mildew inhibitor, stir for 20 min to mix evenly, then add defoamer, stir for 6 min to completely eliminate micro bubbles in the system. S5. Filtration and maturation: The liquid is filtered through a 200-mesh filter to remove impurities and trace agglomerated particles. The mixture is allowed to stand for at least 30 minutes to defoam and mature, and the finished coating is obtained.

[0033] Example 2 A high-density, creep-resistant, high-temperature anti-oxidation coating for steel billets, by weight percentage, comprises the following components: 43% pentagonal nanocomposite powder, 12% inorganic binder, 3.5% film-forming agent, 1.2% dispersant, 2.5% anti-precipitation rheology modifier, 2% antifreeze agent, 0.6% anti-corrosion and anti-mildew agent, 0.4% defoamer, and 34.8% deionized water; wherein: The pentagonal nanocomposite powder is composed of nano-silica, nano-alumina, nano-silicon carbide, nano-zinc oxide, and nano-lanthanum boride in a mass ratio of 7.5:2.7:0.9:1.2:0.6. The particle size of nano-silica, nano-alumina, nano-silicon carbide, nano-zinc oxide, and nano-lanthanum boride is controlled within 20~80nm. The inorganic binder is a mixture of silica sol and aluminum dihydrogen phosphate in a mass ratio of 2:1. The film-forming agent is ethylene glycol monobutyl ether; The dispersant is modified sodium polyacrylate dispersant; The anti-precipitation rheology modifier is a compound of bentonite and sodium carboxymethyl cellulose. The antifreeze is a mixture of glycerol and ethylene glycol in a 1:1 mass ratio; The preservative and mildew inhibitor is a benzimidazole-based mildew inhibitor; The defoamer is a polyether-modified silicone defoamer.

[0034] The preparation method is the same as in Example 1.

[0035] Example 3 A high-density, creep-resistant, high-temperature anti-oxidation coating for steel billets, by weight percentage, comprises the following components: 50% pentagonal nanocomposite powder, 15% inorganic binder, 5% film-forming agent, 1.5% dispersant, 4% anti-precipitation rheology modifier, 2.2% antifreeze, 1.2% anti-corrosion and anti-mildew agent, 0.6% defoamer, and 20.5% deionized water; wherein: The pentagonal nanocomposite powder is composed of nano-silica, nano-alumina, nano-silicon carbide, nano-zinc oxide, and nano-lanthanum boride in a mass ratio of 7.25:2.5:0.75:1.25:0.75. The particle size of nano-silica, nano-alumina, nano-silicon carbide, nano-zinc oxide, and nano-lanthanum boride is controlled within 20~80nm. The inorganic binder is a mixture of silica sol and aluminum dihydrogen phosphate in a mass ratio of 2:1. The film-forming agent is ethylene glycol monobutyl ether; The dispersant is modified sodium polyacrylate dispersant; The anti-precipitation rheology modifier is a compound of bentonite and sodium carboxymethyl cellulose. The antifreeze is a mixture of glycerol and ethylene glycol in a 1:1 mass ratio; The preservative and mildew inhibitor is a benzimidazole-based mildew inhibitor; The defoamer is a polyether-modified silicone defoamer.

[0036] The preparation method is the same as in Example 1.

[0037] Comparative Example 1 The coating uses commercially available conventional high-temperature anti-oxidation coating for steel billets, with micron-sized silica and micron-sized alumina as binary composite powders. The composition is 43% binary composite powder, 12% inorganic binder, 3.5% film-forming agent, and the remainder is deionized water.

[0038] Comparative Example 2 The formula consists of 41% quaternary nanocomposite powder (mass ratio of nano silica: nano alumina: nano silicon carbide: nano zinc oxide = 7.5:2.7:0.9:1.2), 12% inorganic binder (mass ratio of silica sol: aluminum dihydrogen phosphate = 2:1), 3.5% film-forming agent, 1.2% dispersant, 2.5% anti-precipitation rheology modifier, 2% antifreeze agent, 0.6% preservative and mildew inhibitor, 0.4% silicone defoamer, and 36.8% deionized water.

[0039] Test Example 1 According to national general testing standards, the coatings of Examples 1-3 and Comparative Examples 1-2 were subjected to uniform performance tests, and the test results are as follows: 1. Adhesion test (GB / T 9286-1998): Examples 1-3 all had an adhesion level of 0 at room temperature, and no cracking, peeling or curling was observed after being burned at 1200℃ for 2 hours; Comparative Examples 1 and 2 had an adhesion level of only 2 at room temperature, and large areas of peeling and failure occurred after being burned at high temperature.

[0040] 2. High-temperature oxidation resistance: After a 4-hour heat treatment at 1200℃, the oxidation loss rate of the billets in Examples 1-3 was ≤8%; the loss rate of the comparative examples was ≥15%, indicating extremely poor protective performance.

[0041] 3. High-temperature thermal shock stability: After 50 cycles of hot and cold cycling from 1200℃ to room temperature, the coatings in Examples 1-3 showed no cracks, no peeling, and the structure remained intact; in Comparative Example 2, a large number of microcracks appeared after 20 cycles, and in Comparative Example 1, large-area peeling occurred after 10 cycles.

[0042] 4. High-temperature creep resistance: After being subjected to constant temperature and pressure at 1200℃ for 2 hours, the coatings in Examples 1-3 showed no deformation, relaxation, or cracking; the coatings in Comparative Examples 1-2 all showed obvious creep deformation and local cracking.

[0043] 5. Storage stability: After 6 months of sealed storage at room temperature, the coatings in Examples 1-3 showed no stratification, sedimentation, or powder agglomeration and could be applied directly; while Comparative Examples 1-2 showed severe stratification, bottom hardening, and powder agglomeration and sedimentation.

[0044] 6. Low temperature compatibility: After standing at -15℃ for 72 hours, the coatings in Examples 1-3 showed no freezing, no thickening, and no component analysis; the coatings in Comparative Examples 1-2 were completely frozen, and the system failed after thawing.

[0045] 7. Storage and mildew resistance: After 12 months of sealed storage at room temperature, the coatings in Examples 1-3 showed no mildew, no odor, and no performance degradation; while the coatings in Comparative Examples 1-2 showed turbidity, mildew, and deterioration after 3 months of storage.

[0046] In summary, the test results show that the present invention achieves multi-level protection, including low-temperature sintering densification, high-temperature creep resistance, thermal shock self-healing, and high storage stability, through a multi-level synergistic system of five-element nanoparticles.

[0047] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A high-density, creep-resistant, high-temperature anti-oxidation coating for steel billets, characterized in that, The coating, by weight percentage, comprises the following components: 40%–50% pentaneous nanocomposite powder, 8%–15% inorganic binder, 2%–5% film-forming agent, 0.8%–1.5% dispersant, 1.5%–4% anti-precipitation rheology modifier, 1%–2.2% antifreeze, 0.3%–1.2% preservative and mildew inhibitor, 0.2%–0.6% defoamer, with the balance being water; The five-element nanocomposite powder is composed of nano-silica, nano-alumina, nano-silicon carbide, nano-zinc oxide, and nano-lanthanum boride in a mass ratio of (5~8):(2~4):(0.8~1.5):(1~2):(0.6~1.2).

2. The high-density, creep-resistant, high-temperature anti-oxidation coating for steel billets according to claim 1, characterized in that, The coating comprises, by weight percentage, the following components: 43% pentagonal nanocomposite powder, 12% inorganic binder, 3.5% film-forming agent, 1.2% dispersant, 2.5% anti-precipitation rheology modifier, 2% antifreeze agent, 0.6% preservative and mildew inhibitor, 0.4% defoamer, and 34.8% water.

3. The high-density, creep-resistant, high-temperature anti-oxidation coating for steel billets according to claim 1, characterized in that, The particle sizes of the nano-silica, nano-alumina, nano-silicon carbide, nano-zinc oxide, and nano-lanthanum boride are all controlled within the range of 20-80 nm.

4. The high-density, creep-resistant, high-temperature anti-oxidation coating for steel billets according to claim 1, characterized in that, The inorganic binder is a mixture of silica sol and aluminum dihydrogen phosphate in a mass ratio of (1.5~2.5):(0.5~1.5).

5. The high-density, creep-resistant, high-temperature anti-oxidation coating for steel billets according to claim 1, characterized in that, The film-forming agent is ethylene glycol monobutyl ether; The dispersant is a modified sodium polyacrylate dispersant.

6. The high-density, creep-resistant, high-temperature anti-oxidation coating for steel billets according to claim 1, characterized in that, The anti-precipitation rheology modifier is one or both of bentonite and sodium carboxymethyl cellulose.

7. The high-density, creep-resistant, high-temperature anti-oxidation coating for steel billets according to claim 1, characterized in that, The antifreeze is a mixture of glycerol and ethylene glycol in a mass ratio of (0.5~1.5):(0.5~1.5).

8. The high-density, creep-resistant, high-temperature anti-oxidation coating for steel billets according to claim 1, characterized in that, The preservative and antifungal agent is a benzimidazole-based antifungal agent.

9. The high-density, creep-resistant, high-temperature anti-oxidation coating for steel billets according to claim 1, characterized in that, The defoamer is a polyether-modified silicone defoamer.

10. A method for preparing a high-density, creep-resistant, high-temperature anti-oxidation coating for steel billets according to any one of claims 1-9, characterized in that, Includes the following steps: S1. Pretreatment of pentagonal nanocomposite powder: According to the proportion of each component of pentagonal nanocomposite powder, nano silica, nano alumina, nano silicon carbide, nano zinc oxide and nano lanthanum boride are mixed evenly and then dispersed at room temperature for 5~10 min. S2. Preparation of base liquid: According to the proportion of each component of the coating, add water to the reaction vessel, and under stirring at 300~400r / min, add inorganic binder, film-forming agent and dispersant in sequence, and continue stirring for 15~20min until all components are completely dissolved to obtain base liquid; S3. High-speed dispersion of powder: Add the pretreated five-element nanocomposite powder obtained in step S1 to the base liquid obtained in step S2, increase the stirring speed to 800~1000r / min, and disperse for 30~40min. S4. Additive compounding and modification: Reduce the stirring speed to 400~500r / min, add anti-precipitation rheology modifier, antifreeze agent, and preservative and mildew inhibitor, stir for 15~25min, then add defoamer and stir for 5~8min; S5. Filtration and maturation: Filter the liquid and let it stand for at least 30 minutes to obtain the finished coating.