Special bolt for stainless steel mechanical equipment and preparation method thereof

Abstract

The invention relates to the technical field of bolts, and provides a bolt special for stainless steel mechanical equipment and a preparation method thereof. A bolt special for stainless steel mechanical equipment comprises a bolt body and a surface coating, and the surface coating is prepared from, by weight, 100 parts of epoxy resin E-44, 50-55 parts of a curing agent, 1.5-2 parts of a curing accelerator, 20-25 parts of flaky iron oxide, 10-12 parts of modified boron nitride, 2-3 parts of an ultraviolet light absorber, 3-5 parts of silicon dioxide, 1-1.5 parts of a dispersing agent, 25-35 parts of butanone and 10-12 parts of xylene. According to the bolt special for the stainless steel mechanical equipment, the corrosion resistance of the stainless steel bolt in a high-concentration acid-base solution and high-temperature and high-pressure seawater is improved.

Description

Technical Field

[0001] This invention relates to the field of bolt technology, specifically to a stainless steel bolt for mechanical equipment and its manufacturing method. Background Technology

[0002] Stainless steel bolts are crucial components for ensuring the tight connection and stable operation of various parts in mechanical equipment. In chemical production equipment, they must withstand the corrosive effects of various chemicals; in marine engineering equipment, they must resist the long-term corrosion of seawater and the impact of waves; in food processing machinery, they must meet hygiene standards and prevent rust contamination of food. Their performance directly affects the reliability and safety of the equipment. If bolts corrode or break, it can lead to equipment malfunctions or even serious safety accidents.

[0003] Suitable stainless steel materials, such as 304 and 316 austenitic stainless steels, are typically selected as the raw materials for bolts. These materials possess good corrosion resistance and comprehensive mechanical properties. Although stainless steel itself has a certain degree of corrosion resistance, existing stainless steel bolts may still corrode in some extreme environments, such as high-concentration acid and alkali solutions, and high-temperature, high-pressure seawater. This is mainly because the oxide film on the stainless steel surface can be destroyed under certain conditions, leading to direct contact between the base metal and the corrosive medium. Furthermore, defects such as microcracks and scratches may occur during bolt processing, which can also become corrosion initiation points, accelerating the corrosion process. Based on this, this invention proposes a stainless steel bolt specifically for mechanical equipment and its manufacturing method. Summary of the Invention

[0004] This invention proposes a special bolt for stainless steel mechanical equipment and its preparation method, which improves the corrosion resistance of stainless steel bolts in high-concentration acid and alkali solutions and high-temperature and high-pressure seawater.

[0005] The technical solution of the present invention is as follows: In a first aspect, the present invention proposes a special bolt for stainless steel mechanical equipment, comprising a bolt body and a surface coating, wherein the surface coating comprises the following raw materials in parts by weight: 100 parts of epoxy resin E-44, 50-55 parts of curing agent, 1.5-2 parts of curing accelerator, 20-25 parts of flake iron oxide, 10-12 parts of modified boron nitride, 2-3 parts of ultraviolet absorber, 3-5 parts of silicon dioxide, 1-1.5 parts of dispersant, 25-35 parts of methyl ethyl ketone, and 10-12 parts of xylene.

[0006] As a further technical solution, the preparation method of the surface coating includes: weighing the raw materials according to the formula, premixing the epoxy resin, curing agent, and curing accelerator, adding acetone and xylene, stirring at 200-300 rpm for 20-30 min; adjusting the speed to 500-600 rpm, continuing to add flake iron oxide, modified boron nitride, ultraviolet absorber, and silicon dioxide, and stirring for 30-40 min to obtain the coating.

[0007] As a further technical solution, the preparation method of the flake-like iron oxide includes: heating a ferric chloride solution to 70-80℃, adding NaOH solution and NaH2PO4 solution dropwise at a rate of 0.5-1 mL / min at a speed of 600-700 rpm, maintaining pH=5.0±0.2, and maintaining the temperature and speed for 2-3 hours after the addition is complete; cooling to 60±2℃, stirring continuously for 10-12 hours, collecting the precipitate by vacuum filtration, washing with water at 70±2℃, drying, and then performing air jet milling at a pressure of 0.6-0.8 MPa to obtain D. 50 =25±5m of flaky iron oxide.

[0008] As a further technical solution, the weight ratio of ferric chloride, NaOH and NaH2PO4 is 205-215g:130-135g:1-1.1g.

[0009] As a further technical solution, the preparation method of the modified boron nitride includes: acid washing and drying boron nitride, ultrasonically dispersing it in a mixture of ethanol and water to obtain a boron nitride suspension, dispersing silane coupling agent KH550 in a mixture of ethanol and water to obtain a silane hydrolysate, maintaining the temperature of the boron nitride suspension at 60-80℃, adding the hydrolysate at 300-400 rpm, and continuously stirring for 3-4 hours. After the reaction is completed, cooling, centrifugation, washing, and drying are performed to obtain the modified boron nitride.

[0010] As a further technical solution, the curing agent is polyamide 650; the curing accelerator is DMP-30; the dispersant is dispersant BYK-110; and the ultraviolet absorber is ultraviolet absorber UV-531.

[0011] As a further technical solution, the bolt body is composed of the following components by mass percentage: C 0.05%-0.07%, Cr 20.5%-22.0%, Ni 10.5%-12.0%, Mo 3.0%-3.5%, Cu 1.2%-1.8%, Si 0.2%-0.3%, Mn 4.0%-5.0%, with the balance being Fe and other unavoidable impurities.

[0012] Secondly, this invention proposes a method for preparing stainless steel bolts specifically for mechanical equipment, comprising the following steps: (1) Melt in a medium frequency induction furnace, introduce argon gas to protect against oxidation, control the temperature at 1550-1600℃, refine and deoxidize, let stand for 10-15 minutes, cast the molten steel into round billets, cool to room temperature, heat the billet to 1150-1200℃ for hot rolling, make bars of the target diameter, heat the bars to 1050-1100℃ and hold for 30 minutes, water quench and cool rapidly to obtain a uniform austenitic structure, pickle to remove oxide scale, lubricate the surface and then cold forging to obtain the bolt body; (2) The bolt body is sandblasted with 120-mesh white corundum sand to make its surface roughness Ra 3.2-4.0μm, ultrasonically cleaned with acetone and dried; a coating is prepared for the surface coating, and electrostatic spraying is performed on the treated bolt body. The coating thickness is controlled to be 40-50μm. After step curing, the stainless steel mechanical equipment special bolt is obtained.

[0013] As a further technical solution, the electrostatic spraying voltage is 60-80kV and the spraying distance is 20-30cm.

[0014] As a further technical solution, the curing step includes: pre-curing at 80±2℃ for 30-35 minutes, curing at 120±2℃ for 50-60 minutes, and curing at 150±2℃ for 2-3 hours.

[0015] The working principle and beneficial effects of this invention are as follows: The surface coating of this invention forms a three-dimensional network structure through the cross-linking reaction of epoxy resin E-44 and a curing agent, serving as the basic framework of the coating. Lamellar iron oxide is arranged in parallel layers within the coating, forming a physical shielding layer. Its lamellar structure effectively extends the penetration path of corrosive media, hindering the intrusion of corrosive substances such as water and chloride ions. Modified boron nitride, after surface modification with silane coupling agent KH550, forms a chemical bond with the epoxy matrix, not only acting as a thermally conductive reinforcing phase to improve the coating's heat resistance stability but also filling the gaps between the lamellar iron oxide, forming a "lamellar-particle" composite shielding structure. The ultraviolet absorber UV-531 absorbs ultraviolet energy and converts it into heat energy for dissipation, preventing coating cracking caused by photo-oxidative degradation of the epoxy resin. Silica, as a nano-reinforcing phase, refines the coating's microstructure and reduces porosity defects. Through the synergistic effect of physical filling and chemical bonding, the components construct a multi-layered protective system.

[0016] In this invention, the preparation of lamellar iron oxide involves precisely controlling the co-precipitation reaction conditions of ferric chloride and alkaline solution to induce the formation of α-FeOOH crystal nuclei, which then grow directionally into a two-dimensional lamellar structure. An air-jet milling process ensures the uniformity of the lamellar particle size, preventing a decrease in coating density due to particle coarsening. Within the coating, the lamellar iron oxide is arranged in parallel stacks, forcing corrosive media to bypass multiple layers of lamellar structures to reach the substrate, significantly extending the penetration path. Compared to spherical particles, the extended path of the lamellar structure effectively reduces the corrosion rate. Furthermore, the synergistic filling effect of the lamellar iron oxide and modified boron nitride seals the micropores in the coating, further enhancing the shielding effect.

[0017] In this invention, boron nitride is modified by removing surface impurities through acid washing, followed by surface modification using the silane coupling agent KH550. The silanol groups generated by the hydrolysis of KH550 undergo a condensation reaction with the hydroxyl groups on the boron nitride surface, forming a Si-O-BN chemical bond. Simultaneously, the amino group at the other end can undergo a ring-opening reaction with the epoxy groups in the epoxy resin. This dual-interfacial bonding significantly improves the compatibility between boron nitride and the substrate, avoiding the coating peeling problem caused by poor interfacial adhesion in unmodified boron nitride.

[0018] In this invention, the bolt body adopts a Cr-Ni-Mo-Cu quaternary alloy design, where Cr (20.5%-22.0%) forms a dense Cr2O3 passivation film on the surface, blocking the contact between the corrosive medium and the substrate; Ni stabilizes the austenitic structure, improving the material's resistance to stress corrosion cracking in high-temperature seawater; Mo and Cu synergistically enhance pitting corrosion resistance, and MoO4... 2- With Cu 2+ An adsorption film is formed in the corrosive medium to inhibit chloride ion attack. The heat treatment process, through rapid water quenching, obtains a uniform austenitic structure, avoiding the tendency for localized corrosion caused by martensitic phase transformation. After pickling to remove the oxide scale, the cold heading process retains the metal flow lines, improving the fatigue resistance of the bolts. The matrix alloying design and coating protection form a synergistic anti-corrosion system of "internal strength and external protection," significantly improving the service life of the bolts in extreme environments.

[0019] In this invention, a stepped temperature curing process is employed for coating curing, optimizing coating performance by controlling the crosslinking reaction rate. The pre-curing stage allows the epoxy resin and curing agent to react initially, forming a viscous fluid that facilitates coating leveling. The intermediate-temperature curing stage accelerates the crosslinking reaction, constructing a three-dimensional network structure. The high-temperature curing stage completes the final crosslinking, improving the coating's crosslinking density and heat resistance. This process avoids the internal stress concentration problem caused by single high-temperature curing, while ensuring a strong interfacial bond between the coating and the substrate. Experiments show that the adhesion (level 0) of the stepped-cured coating is significantly better than that of a single 120℃ cured coating (level 4), and the salt spray resistance is improved by more than 2 times, demonstrating the crucial role of process optimization in coating performance. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention. It should be noted that the curing agent in the present invention is polyamide 650; the curing accelerator is DMP-30; the dispersant is dispersant BYK-110; and the ultraviolet absorber is ultraviolet absorber UV-531.

[0021] It should also be noted that the boron nitride pretreatment steps are as follows: immerse boron nitride (product number B106032, purchased from Aladdin Reagent) in a 5% hydrochloric acid aqueous solution for 30 min, wash with deionized water until neutral, and then dry at 60℃ for 12 h.

[0022] Example 1 This embodiment provides a special stainless steel bolt for mechanical equipment, including a bolt body and a surface coating. The surface coating includes the following raw materials in parts by weight: 100 parts epoxy resin E-44, 52 parts curing agent, 1.8 parts curing accelerator, 22 parts flake iron oxide, 11 parts modified boron nitride, 2.5 parts ultraviolet absorber, 4 parts silicon dioxide, 1.2 parts dispersant, 30 parts methyl ethyl ketone, and 11 parts xylene.

[0023] The preparation method of the surface coating includes: weighing the raw materials according to the formula, premixing the epoxy resin, curing agent, and curing accelerator, adding acetone and xylene, and stirring at 250 rpm for 25 min; adjusting the speed to 550 rpm, and continuing to add flake iron oxide, modified boron nitride, ultraviolet absorber, and silicon dioxide, and stirring for 35 min to obtain the coating.

[0024] The preparation method of flaky iron oxide includes: dissolving 210g of ferric chloride solution into 1L of 0.7mol / L solution, heating to 75℃, and adding NaOH solution and NaH2PO4 solution dropwise at a rate of 0.7mL / min at 650rpm. The NaOH solution consists of 132g of sodium hydroxide solid dissolved in 500mL of deionized water; the NaH2PO4 solution consists of 1.05g of NaH2PO4·2H2O dissolved in 50mL of deionized water, maintaining the pH at 5.0. After the addition is complete, the temperature and speed are maintained for 2.5h. The temperature is then lowered to 60℃, and stirring is continued for 11h. The precipitate is collected by vacuum filtration, washed 7 times with water at 70℃, dried at 110℃ for 16h, and then subjected to air jet milling at a pressure of 0.7MPa to obtain D. 50 =25m of flaky iron oxide.

[0025] The preparation method of modified boron nitride includes: acid washing and drying boron nitride, ultrasonically dispersing it in a mixture of ethanol and water to obtain a boron nitride suspension, dispersing silane coupling agent KH550 in a mixture of ethanol and water to obtain a silane hydrolysate, maintaining the boron nitride suspension at 70°C, adding the hydrolysate at 350 rpm, and stirring continuously for 3.5 h. After the reaction is completed, cooling, centrifugation, washing, and drying in a vacuum oven at 100°C for 12 h are performed to obtain the modified boron nitride. The bolt body is composed of the following components by mass percentage: C 0.06%, Cr 21.5%, Ni 11.5%, Mo 3.2%, Cu 1.5%, Si 0.25%, Mn 4.5%, with the balance being Fe and other unavoidable impurities.

[0026] The preparation method of this stainless steel mechanical equipment special bolt includes the following steps: (1) Melt in a medium frequency induction furnace, introduce argon gas to protect against oxidation, control the temperature at 1580℃, refine and deoxidize and stand for 12 minutes, cast the molten steel into round steel billets, cool to room temperature, heat the billet to 1180℃ for hot rolling, make bars of the target diameter, heat the bars to 1080℃ and hold for 30 minutes, water quench and cool rapidly to obtain a uniform austenitic structure, pickle to remove oxide scale, lubricate the surface and then cold forging to obtain the bolt body; (2) The bolt body was sandblasted with 120-mesh white corundum sand to make its surface roughness Ra 3.6μm. It was then ultrasonically cleaned with acetone and dried. The coating material for the surface coating was prepared and electrostatically sprayed on the treated bolt body. The electrostatic spraying voltage was 70kV, the spraying distance was 25cm, and the coating thickness was controlled to be 45μm. The bolt was pre-cured at 80℃ for 32min, cured at 120℃ for 55min, and cured at 150℃ for 2.5h to obtain the stainless steel special bolt for mechanical equipment.

[0027] Example 2 This embodiment provides a special bolt for stainless steel mechanical equipment, including a bolt body and a surface coating. The surface coating includes the following raw materials in parts by weight: 100 parts epoxy resin E-44, 50 parts curing agent, 1.5 parts curing accelerator, 20 parts flake iron oxide, 10 parts modified boron nitride, 2 parts ultraviolet absorber, 3 parts silicon dioxide, 1 part dispersant, 25 parts methyl ethyl ketone, and 10 parts xylene.

[0028] The preparation method of the surface coating includes: weighing the raw materials according to the formula, premixing the epoxy resin, curing agent, and curing accelerator, adding acetone and xylene, and stirring at 200 rpm for 20 min; adjusting the speed to 500 rpm, and continuing to add flake iron oxide, modified boron nitride, ultraviolet absorber, and silicon dioxide, and stirring for 30 min to obtain the coating.

[0029] The preparation method of flaky iron oxide includes: dissolving 205g of ferric chloride solution to prepare 1L of a 0.7mol / L solution, heating to 70℃, and adding NaOH solution and NaH2PO4 solution dropwise at a rate of 0.5 mL / min at 600 rpm. The NaOH solution consists of 130g of sodium hydroxide solid dissolved in 500mL of deionized water; the NaH2PO4 solution consists of 1g of NaH2PO4·2H2O dissolved in 5mL of deionized water, maintaining the pH at 5.0. After the addition is complete, maintain the temperature and speed for 2 hours. Cool to 60℃, stir continuously for 10 hours, collect the precipitate by vacuum filtration, wash seven times with water at 70℃, dry at 110℃ for 16 hours, and then perform air jet milling at a pressure of 0.6MPa to obtain D. 50 =25m of flaky iron oxide.

[0030] The preparation method of modified boron nitride includes: washing and drying boron nitride with acid, ultrasonically dispersing it in a mixture of ethanol and water to obtain a boron nitride suspension, dispersing silane coupling agent KH550 in a mixture of ethanol and water to obtain a silane hydrolysate, maintaining the temperature of the boron nitride suspension at 60°C, adding the hydrolysate at 300 rpm, and stirring continuously for 3 hours. After the reaction is completed, cooling is performed, followed by centrifugation, washing, and drying in a vacuum oven at 100°C for 12 hours to obtain the modified boron nitride. The bolt body is composed of the following components by mass percentage: C 0.05%, Cr 20.5%, Ni 10.5%, Mo 3.0%, Cu 1.2%, Si 0.2%, Mn 4.0%, with the balance being Fe and other unavoidable impurities.

[0031] The preparation method of this stainless steel special bolt for mechanical equipment includes the following steps: (1) Melt in a medium frequency induction furnace, introduce argon gas to protect against oxidation, control the temperature at 1550℃, refine and deoxidize and stand for 10 minutes, cast the molten steel into round steel billets, cool to room temperature, heat the billet to 1150℃ for hot rolling, make bars of the target diameter, heat the bars to 1050℃ and hold for 30 minutes, water quench and cool quickly to obtain a uniform austenitic structure, pickle to remove oxide scale, lubricate the surface and then cold forging to obtain the bolt body; (2) The bolt body is sandblasted with 120-mesh white corundum sand to make its surface roughness Ra 3.2μm, ultrasonically cleaned with acetone and dried; the coating material for the surface coating is prepared and electrostatically sprayed on the treated bolt body. The electrostatic spraying voltage is 60kV, the spraying distance is 20cm, and the coating thickness is controlled to be 40μm. After pre-curing at 80℃ for 30min, curing at 120℃ for 50min, and curing at 150℃ for 2h, the stainless steel special bolt for mechanical equipment is obtained.

[0032] Example 3 This embodiment provides a special bolt for stainless steel mechanical equipment, including a bolt body and a surface coating. The surface coating includes the following raw materials in parts by weight: 100 parts epoxy resin E-44, 55 parts curing agent, 2 parts curing accelerator, 25 parts flake iron oxide, 12 parts modified boron nitride, 3 parts ultraviolet absorber, 5 parts silicon dioxide, 1.5 parts dispersant, 35 parts methyl ethyl ketone, and 12 parts xylene.

[0033] The preparation method of the surface coating includes: weighing the raw materials according to the formula, premixing the epoxy resin, curing agent, and curing accelerator, adding acetone and xylene, and stirring at 300 rpm for 30 min; adjusting the speed to 600 rpm, and continuing to add flake iron oxide, modified boron nitride, ultraviolet absorber, and silicon dioxide, and stirring for 40 min to obtain the coating.

[0034] The preparation method of flaky iron oxide includes: dissolving 215g of ferric chloride solution into 1L of 0.7 mol / L solution, heating to 80℃, and adding NaOH solution and NaH2PO4 solution dropwise at a rate of 1mL / min at 700rpm. The NaOH solution consists of 135g of sodium hydroxide solid dissolved in 500mL of deionized water; the NaH2PO4 solution consists of 1.1g of NaH2PO4·2H2O dissolved in 50mL of deionized water, maintaining pH=5.0. After the addition is complete, the temperature and speed are maintained for 3h. The temperature is then lowered to 60℃, and stirring is continued for 12h. The precipitate is collected by vacuum filtration, washed 7 times with water at 70℃, dried at 110℃ for 16h, and then subjected to air jet milling at a pressure of 0.8MPa to obtain D. 50 =25m of flaky iron oxide.

[0035] The preparation method of modified boron nitride includes: washing and drying boron nitride with acid, ultrasonically dispersing it in a mixture of ethanol and water to obtain a boron nitride suspension, dispersing silane coupling agent KH550 in a mixture of ethanol and water to obtain a silane hydrolysate, maintaining the boron nitride suspension at 80°C, adding the hydrolysate at 400 rpm, and stirring continuously for 4 hours. After the reaction is completed, cooling is performed, followed by centrifugation, washing, and drying in a vacuum oven at 100°C for 12 hours to obtain the modified boron nitride. The bolt body is composed of the following components by mass percentage: C 0.07%, Cr 22.0%, Ni 12.0%, Mo 3.5%, Cu 1.8%, Si 0.3%, Mn 5.0%, with the balance being Fe and other unavoidable impurities.

[0036] The preparation method of this stainless steel special bolt for mechanical equipment includes the following steps: (1) Melt in a medium frequency induction furnace, introduce argon gas to protect against oxidation, control the temperature at 1600℃, refine and deoxidize and stand for 15 minutes, cast the molten steel into round steel billets, cool to room temperature, heat the billet to 1200℃ for hot rolling, make bars of the target diameter, heat the bars to 1100℃ and hold for 30 minutes, water quench and cool quickly to obtain a uniform austenitic structure, pickle to remove oxide scale, lubricate the surface and then cold forging to obtain the bolt body; (2) The bolt body is sandblasted with 120-mesh white corundum sand to make its surface roughness Ra 4.0μm, ultrasonically cleaned with acetone and dried; the coating material for the surface coating is prepared and electrostatically sprayed on the treated bolt body. The electrostatic spraying voltage is 80kV, the spraying distance is 30cm, and the coating thickness is controlled to be 50μm. After pre-curing at 80℃ for 35min, curing at 120℃ for 60min, and curing at 150℃ for 3h, the stainless steel special bolt for mechanical equipment is obtained.

[0037] Comparative Example 1 In Comparative Example 1, the total amount of filler in the coating was halved, with 11 parts of flake iron oxide and 5.5 parts of modified boron nitride. The rest was the same as in Example 1, and the preparation steps were the same as in Example 1.

[0038] Comparative Example 2 In Comparative Example 2, the flake-shaped iron oxide was replaced with an equal mass of ordinary spherical iron oxide (purchased from Beijing Zhongke Yannuo New Material Technology Co., Ltd., item number: BM11352), and the rest was the same as in Example 1, with the same preparation steps.

[0039] Comparative Example 3 In Comparative Example 3, the flaky iron oxide was completely removed from the surface coating material, and the rest was the same as in Example 1, with the same preparation steps.

[0040] Comparative Example 4 In Comparative Example 4, unmodified boron nitride was used, and the rest was the same as in Example 1, with the same preparation steps.

[0041] Comparative Example 5 In Comparative Example 5, modified boron nitride was completely removed from the surface coating raw material, and the rest was the same as in Example 1, with the same preparation steps.

[0042] Comparative Example 6 In Comparative Example 6, the pH value was changed to 3.0 in the preparation of flaky iron oxide, and the rest was the same as in Example 1. The preparation steps were the same as in Example 1.

[0043] Comparative Example 7 In Comparative Example 7, the air jet milling pressure was 0.2 MPa during the preparation of flaky iron oxide, and the rest was the same as in Example 1. The preparation steps were the same as in Example 1.

[0044] Comparative Example 8 In Comparative Example 8, the maximum curing temperature of the coating was changed to 120°C, and the rest was the same as in Example 1. The preparation steps were the same as in Example 1.

[0045] Comparative Example 9 In Comparative Example 9, the Cr content of the bolt body was reduced to 18.5%, while the rest was the same as in Example 1, and the preparation steps were the same as in Example 1.

[0046] Comparative Example 10 In Comparative Example 10, the Ni content of the bolt body was reduced to 8.5%, and the rest was the same as in Example 1. The preparation steps were the same as in Example 1.

[0047] Test Example 1: The stainless steel mechanical equipment bolts prepared in Examples 1-3 and Comparative Examples 1-8 were subjected to the following tests: Tensile strength: The tensile strength of the bolt at room temperature was tested in accordance with GB / T 228.1-2021 "Metallic materials, tensile testing - Part 1: Test method at room temperature"; Salt spray resistance: In accordance with ASTM B117 standard, the bolts were subjected to a salt spray test using a 10% NaCl solution to observe how long it took for pitting corrosion to occur; High-temperature salt water resistance: The bolts were immersed in a 10% NaCl solution at 80℃ for 720 hours, and the weight loss was tested. Adhesion: Tested according to ASTM D3359 standard. Use a blade to draw a grid on the coating surface, apply tape and then peel it off. Evaluate the adhesion level based on the area of ​​coating peeling (0-5, with 0 being the best). Acid resistance: The weight loss was tested by immersion in a 10% sulfuric acid aqueous solution at 35°C for 720 hours. Alkali resistance: The weight loss was tested by immersing the sample in a 10% sodium hydroxide aqueous solution at 35°C for 720 hours. The results are shown in Table 1 below: Table 1

[0048] Based on the foregoing, it can be seen that in Comparative Example 1, the insufficient amount of lamellar iron oxide and modified boron nitride led to the collapse of the physical barrier function of the coating, resulting in decreased salt spray resistance and increased acid / alkali weight loss. In Comparative Example 2, the spherical particles could not form a parallel stacked structure, shortening the corrosion path, resulting in decreased salt spray resistance compared to Example 1 and increased high-temperature brine weight loss. In Comparative Example 3, the key physical shielding layer was missing, causing the coating's protective function to fail, with salt spray resistance of only 950h and increased acid weight loss. In Comparative Example 4, the poor interfacial bonding of the unmodified BN caused local peeling of the coating, reducing adhesion to level 2 and decreasing salt spray resistance by 23%. In Comparative Example 5 (without boron nitride), the loss of the thermally conductive reinforcing phase reduced the coating's thermal stability, resulting in a high-temperature brine weight loss of 1.75mg.

[0049] In Comparative Example 6, the acidic environment inhibited the growth of lamellar crystals, resulting in distorted product morphology. The performance was close to that of spherical iron oxide, with a salt spray resistance of 1450h and an acid weight loss of 2.30mg. In Comparative Example 7, insufficient crushing pressure led to particle coarsening (D50>25μm), reduced coating density, and a salt spray resistance of 2050h, which was still 34% lower than that of Example 1. In Comparative Example 8, curing at 120℃ resulted in insufficient crosslinking density, leading to a porous coating structure. The adhesion was the worst (level 4), and the salt spray resistance plummeted to 1250h.

[0050] In Comparative Example 9, insufficient chromium content led to passivation film failure, resulting in a collapse of the substrate's corrosion resistance. The tensile strength plummeted to 895 MPa, and the salt spray resistance for 1450 h was only 47% of that in Example 1. In Comparative Example 10, excessively low nickel content triggered an austenitic-martensite phase transformation, accelerating localized corrosion. The tensile strength was 905 MPa, and the alkali resistance weight loss was 1.20 mg, an increase of 150%.

[0051] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A special bolt for stainless steel mechanical equipment, characterized in that, The product includes a bolt body and a surface coating. The surface coating comprises the following raw materials in parts by weight: 100 parts epoxy resin E-44, 50-55 parts curing agent, 1.5-2 parts curing accelerator, 20-25 parts flake iron oxide, 10-12 parts modified boron nitride, 2-3 parts ultraviolet absorber, 3-5 parts silica, 1-1.5 parts dispersant, 25-35 parts methyl ethyl ketone (MEK), and 10-12 parts xylene.

2. The stainless steel mechanical equipment bolt according to claim 1, characterized in that, The preparation method of the surface coating includes: weighing the raw materials according to the formula, premixing the epoxy resin, curing agent, and curing accelerator, adding acetone and xylene, stirring at 200-300 rpm for 20-30 min; adjusting the speed to 500-600 rpm, and continuing to add flake iron oxide, modified boron nitride, ultraviolet absorber, and silicon dioxide, stirring for 30-40 min to obtain the coating.

3. The stainless steel mechanical equipment bolt according to claim 1, characterized in that, The method for preparing the flake-like iron oxide includes: heating a ferric chloride solution to 70-80℃, adding NaOH solution and NaH2PO4 solution dropwise at a rate of 0.5-1 mL / min at a rotation speed of 600-700 rpm, maintaining the pH at 5.0±0.2, and maintaining the temperature and rotation speed for 2-3 hours after the addition is complete; cooling to 60±2℃, stirring continuously for 10-12 hours, collecting the precipitate by vacuum filtration, washing with water at 70±2℃, drying, and then performing air jet milling at a pressure of 0.6-0.8 MPa to obtain D. 50 =25±5m of flaky iron oxide.

4. The stainless steel mechanical equipment bolt according to claim 3, characterized in that, The weight ratio of ferric chloride, NaOH and NaH2PO4 is 205-215g: 130-135g: 1-1.1g.

5. A stainless steel mechanical equipment bolt according to claim 1, characterized in that, The method for preparing the modified boron nitride includes: acid washing and drying boron nitride, ultrasonically dispersing it in a mixture of ethanol and water to obtain a boron nitride suspension, dispersing silane coupling agent KH550 in a mixture of ethanol and water to obtain a silane hydrolysate, maintaining the boron nitride suspension at a temperature of 60-80℃, adding the hydrolysate at 300-400 rpm, and continuously stirring for 3-4 hours. After the reaction is completed, cooling, centrifugation, washing, and drying are performed to obtain the modified boron nitride.

6. The stainless steel mechanical equipment bolt according to claim 1, characterized in that, The curing agent is polyamide 650; the curing accelerator is DMP-30; the dispersant is dispersant BYK-110; and the ultraviolet absorber is ultraviolet absorber UV-531.

7. A stainless steel mechanical equipment bolt according to claim 1, characterized in that, The bolt body is composed of the following components by mass percentage: C 0.05%-0.07%, Cr 20.5%-22.0%, Ni 10.5%-12.0%, Mo 3.0%-3.5%, Cu 1.2%-1.8%, Si 0.2%-0.3%, Mn 4.0%-5.0%, with the balance being Fe and other unavoidable impurities.

8. A method for preparing a stainless steel mechanical equipment bolt, used to prepare the stainless steel mechanical equipment bolt according to any one of claims 1 to 7, characterized in that the steps include... include: (1) Melt in a medium frequency induction furnace, introduce argon gas to protect against oxidation, control the temperature at 1550-1600℃, refine and deoxidize, let stand for 10-15 minutes, cast the molten steel into round billets, cool to room temperature, heat the billet to 1150-1200℃ for hot rolling, make bars of the target diameter, heat the bars to 1050-1100℃ and hold for 30 minutes, water quench and cool rapidly to obtain a uniform austenitic structure, pickle to remove oxide scale, lubricate the surface and then cold forging to obtain the bolt body; (2) The bolt body is sandblasted with 120-mesh white corundum sand to make its surface roughness Ra 3.2-4.0μm, ultrasonically cleaned with acetone and dried; a coating is prepared for the surface coating, and electrostatic spraying is performed on the treated bolt body. The coating thickness is controlled to be 40-50μm. After step curing, the stainless steel mechanical equipment special bolt is obtained.

9. The method for preparing a stainless steel mechanical equipment bolt according to claim 8, characterized in that, The electrostatic spraying voltage is 60-80kV, and the spraying distance is 20-30cm.

10. The method for preparing a stainless steel mechanical equipment bolt according to claim 8, characterized in that, The curing steps include: pre-curing at 80±2℃ for 30-35 minutes, curing at 120±2℃ for 50-60 minutes, and curing at 150±2℃ for 2-3 hours.

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