Corrosion resistant fastener material and method of making

Abstract

The application belongs to the technical field of metal powder metallurgy materials, and particularly relates to a kind of corrosion-resistant fastener material and a preparation method thereof; the material is composed of stainless steel powder, duplex stainless steel powder, nickel powder, molybdenum powder, chromium nitride powder, vanadium iron powder, nano silicon dioxide, hexagonal boron nitride, polyvinyl alcohol, zinc stearate, molybdenum vanadium cerium phosphorus silicon complex passivation salt and amino silane graphene barrier microsheet, etc. Through composite corrosion-resistant dispersion, metal powder mixing, pressing, degreasing sintering, solid solution aging and weak acid passivation treatment, the molybdenum vanadium cerium phosphorus silicon complex passivation salt promotes the formation of surface passivation film, and the amino silane graphene barrier microsheet enhances the barrier effect of corrosion medium, thereby improving the pitting corrosion resistance, crevice corrosion resistance and service stability of the fastener material, and being suitable for fastener manufacturing in high humidity, high salt spray and corrosive environments.

Description

Technical Field

[0001] This invention belongs to the field of metal powder metallurgy materials technology, specifically relating to a corrosion-resistant fastener material and its preparation method. Background Technology

[0002] Fasteners are widely used in marine engineering, chemical equipment, rail transportation, energy equipment, food and pharmaceutical equipment, and outdoor structural connections. Their service environments often involve factors such as humid heat, salt spray, acidic media, chloride ion penetration, and alternating loads. Traditional carbon steel fasteners typically rely on galvanizing, blackening, phosphating, or ordinary coatings to improve corrosion resistance. However, in long-term humid and saline environments, coating damage, edge corrosion, thread crevice corrosion, and pitting corrosion propagation easily occur, leading to decreased connection strength, difficulty in disassembly and assembly, and even structural failure. While stainless steel fasteners have good corrosion resistance, localized corrosion can still occur under conditions of high chloride ion concentration or stagnant liquid in crevices. Corrosion microcells are particularly prone to form at thread roots, gasket contact surfaces, and stress concentration points, affecting the long-term reliability of the fasteners.

[0003] Existing corrosion-resistant fastener materials mostly employ austenitic stainless steel, duplex stainless steel, or surface passivation treatment to improve corrosion resistance. Austenitic stainless steel possesses good formability and overall corrosion resistance, but its strength and resistance to pitting corrosion remain insufficient in harsh environments. Duplex stainless steel exhibits high strength and good resistance to chloride ion corrosion, but the uniformity of its microstructure, phase ratio stability, and densification control during powder forming and sintering are crucial. If fasteners are prepared solely from stainless steel powder, corrosion channels can easily form within the material due to factors such as porosity, inclusions, localized component segregation, and grain boundary depletion. Corrosive media can rapidly penetrate along pores and grain boundaries, reducing the continuity of the passivation film. If only post-treatment passivation is relied upon, the passivation film thickness, adhesion stability, and self-healing ability are limited, making it difficult to simultaneously achieve the internal density, surface corrosion resistance, and tribological stability of powder metallurgy fasteners.

[0004] Furthermore, existing powder metallurgy fasteners still suffer from insufficient synergy in material formulation and surface protection. Uneven dispersion of metal powder, ceramic reinforcing phase, lubricating and forming agents, and corrosion-resistant functional components can easily lead to localized agglomeration, sintering defects, and weakened interfacial bonding. This results in microcrack propagation and accelerated corrosion when the fasteners are subjected to tightening loads, vibration loads, and corrosive media. While ordinary inorganic fillers can improve hardness and wear resistance to some extent, their ability to control the barrier pathway of corrosive media is limited. Although ordinary graphene materials have a layered barrier effect, they are prone to agglomeration in metal powder systems and have insufficient interfacial bonding with the metal matrix and passivation components. Therefore, there is an urgent need to develop a corrosion-resistant fastener material and its preparation method that can simultaneously achieve matrix alloying, uniform powder dispersion, layered barrier, composite passivation, and post-treatment protection. This would improve the insufficient resistance to pitting corrosion, crevice corrosion, and long-term service stability of existing fasteners in high humidity, high salt spray, and complex corrosive environments. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a corrosion-resistant fastener material and its preparation method.

[0006] A first aspect of the present invention provides a corrosion-resistant fastener material comprising the following components in parts by weight:

[0007] 62-78 parts 316L stainless steel powder, 10-22 parts 2205 duplex stainless steel powder, 1.5-4.5 parts nickel powder, 0.8-2.8 parts molybdenum powder, 0.3-1.2 parts chromium nitride powder, 0.1-0.6 parts vanadium iron powder, 0.2-0.9 parts nano silica, 0.1-0.6 parts hexagonal boron nitride, 0.3-1.0 parts polyvinyl alcohol, 0.1-0.5 parts zinc stearate, 6-14 parts deionized water, 4-10 parts anhydrous ethanol, 1.0-4.0 parts molybdenum vanadium cerium phosphorus silicon complex passivation salt, 0.2-1.2 parts aminosilane graphene barrier micro flakes.

[0008] According to a preferred embodiment of the present invention, the preparation method of the molybdenum-vanadium-cerium-phosphorus-silicon complex passivating salt includes:

[0009] A1. By weight, add 12-18 parts of sodium molybdate dihydrate, 2-5 parts of ammonium metavanadate, and 4-8 parts of citric acid to 120-180 parts of deionized water, and stir at 55-70℃ to obtain a molybdenum-vanadium complex solution; dissolve 6-10 parts of cerium nitrate hexahydrate in 40-70 parts of deionized water, add 1.0-2.5 parts of glycine, and adjust the pH to 3.2-4.0 to obtain a cerium complex solution; while stirring, add the cerium complex solution dropwise to the molybdenum-vanadium complex solution, react at 60-75℃, add 3-6 parts of phosphoric acid, and while stirring, add a sodium silicate solution containing 5-9 parts of sodium silicate nonahydrate and 20-40 parts of deionized water, adjust the pH to 5.2-5.8, and continue stirring to obtain a molybdenum-vanadium-cerium-phosphorus-silicon composite complex solution;

[0010] A2. Add 2-4 parts of sodium gluconate to the molybdenum-vanadium-cerium-phosphorus-silicon composite complex solution and stir at 50-60℃; add ammonia water to adjust the pH to 5.8-6.2 to obtain a composite passivation salt solution; concentrate and dry the composite passivation salt solution to obtain the dried product; grind and vibrate sieve the dried product.

[0011] In this invention, the formation of the molybdenum-vanadium-cerium-phosphorus-silicon complex passivating salt is based on the coordination, hydrolysis, and condensation reactions between sodium molybdate dihydrate, ammonium metavanadate, citric acid, cerium nitrate hexahydrate, glycine, phosphoric acid, sodium silicate nonahydrate, sodium gluconate, and ammonia. Sodium molybdate dihydrate and ammonium metavanadate dissolve in deionized water, respectively, to release molybdate and vanadate ions. The carboxyl and hydroxyl groups of citric acid coordinate with the molybdenum and vanadate centers, inhibiting the condensation of molybdate and vanadate ions and maintaining the homogeneity of the molybdenum-vanadium complex solution. Cerium nitrate hexahydrate dissolves in deionized water, releasing cerium ions. The amino and carboxyl groups of glycine coordinate with the cerium ions, reducing the degree to which cerium ions directly form hydroxide precipitates when the pH increases, thus obtaining a cerium complex solution. When the cerium complex solution is added dropwise to the molybdenum-vanadium complex solution, the cerium centers form polynuclear complex structures with the molybdate and vanadate ions through carboxylic acid bridging and electrostatic association. Upon addition of phosphoric acid, phosphate ions form additional coordination links between the cerium center and molybdenum- and vanadium-containing groups. Sodium silicate nonahydrate undergoes partial protonation under weakly acidic conditions to form a silanol structure. The silanol then condenses with molybdenum-, vanadium-, cerium-, and phosphorus-containing structures, forming hydrogen bonds to obtain a multi-element homogeneous molybdenum-vanadium-cerium-phosphorus-silicon composite complex solution. Sodium gluconate provides the coordination environment for polyhydroxycarboxylic acids. After adjusting the pH of the system with ammonia, a composite passivating salt solution is obtained. Concentration and drying convert the complex structure into a dispersible solid passivating salt.

[0012] According to a preferred embodiment of the present invention, in step A1, the reaction time at 60-75°C is 40-80 min.

[0013] According to a preferred embodiment of the present invention, in step A2, the stirring time at 50-60°C is 30-50 min.

[0014] According to a preferred embodiment of the present invention, the method for preparing the aminosilane graphene barrier microsheets includes:

[0015] B1. By weight, disperse 1.0-2.5 parts of graphene oxide in 180-260 parts of deionized water and 40-80 parts of anhydrous ethanol to obtain a graphene oxide dispersion; add 3-6 parts of 3-aminopropyltriethoxysilane to 30-60 parts of anhydrous ethanol and 5-10 parts of deionized water, stir and hydrolyze to obtain an aminosilane hydrolysate; under stirring, add the aminosilane hydrolysate dropwise to the graphene oxide dispersion, and react at 45-60℃ to obtain an aminosilane-grafted graphene oxide dispersion;

[0016] B2. Add 1.5-3.5 parts of tetraethyl orthosilicate and 0.5-1.5 parts of methyltrimethoxysilane to the aminosilane-grafted graphene oxide dispersion and stir the mixture at 50-65℃. Then add 0.8-2.0 parts of L-ascorbic acid and react the mixture at 70-85℃. After the reaction is complete, centrifuge the mixture and collect the precipitate. Wash, dry, grind, and vibrate the precipitate for sieve separation.

[0017] In this invention, the formation of aminosilane graphene barrier microsheets is based on the reaction of oxygen-containing functional groups on the surface of graphene oxide. Graphene oxide is dispersed in deionized water and anhydrous ethanol, exposing the hydroxyl, carboxyl, and epoxy groups on the sheet surface to the solvent system, providing grafting sites. 3-Aminopropyltriethoxysilane undergoes ethoxy hydrolysis in anhydrous ethanol and deionized water to generate silanol structures with amino groups, yielding an aminosilane hydrolysate. When the aminosilane hydrolysate is added dropwise to the graphene oxide dispersion, the silanol undergoes dehydration condensation with the hydroxyl groups on the graphene oxide surface to form silicon-oxygen linkages. The amino groups undergo ring-opening reactions with the epoxy groups on the graphene oxide surface and association reactions with the carboxyl groups, resulting in an aminosilane-grafted graphene oxide dispersion, thus reducing the degree of re-stacking between the sheets. Upon addition of tetraethyl orthosilicate and methyltrimethoxysilane, the silanols generated from their hydrolysis continue to condense on the sheet surface, forming a thin-layer coating structure containing a silicon-oxygen framework and methyl segments. Subsequently, L-ascorbic acid was added to reduce the oxygen-containing groups in the graphene oxide sheets under heating conditions, reducing oxygen defects in the sheets, improving the structural integrity of the sheets, and preventing the surface silicon-oxygen coating layer from directly forming galvanic contacts between the sheets and the metal substrate. After centrifugation, washing, drying, grinding, and vibrating sieving, aminosilane graphene barrier microsheets with sheet shielding, interface anchoring, and silicon-oxygen isolation functions were obtained, extending the diffusion paths of moisture, oxygen, and chloride ions.

[0018] According to a preferred embodiment of the present invention, in step B1, the reaction time at 45-60°C is 2-4 hours.

[0019] According to a preferred embodiment of the present invention, in step B2, the reaction time at 70-85°C is 1-2 hours.

[0020] The present invention also provides a method for preparing the aforementioned corrosion-resistant fastener material, comprising the following steps:

[0021] S1. Under stirring, disperse 0.2-1.2 parts of aminosilane graphene barrier microsheets in 6-14 parts of deionized water and 4-10 parts of anhydrous ethanol to obtain a pre-dispersed slurry; add 1.0-4.0 parts of molybdenum-vanadium-cerium-phosphorus-silicon complex passivating salt, 0.2-0.9 parts of nano-silica and 0.1-0.6 parts of hexagonal boron nitride to the pre-dispersed slurry to obtain a composite corrosion-resistant dispersion; add 62-78 parts of 316L stainless steel powder and 10-22 parts of 2 Mix 205 duplex stainless steel powder, 1.5-4.5 parts nickel powder, 0.8-2.8 parts molybdenum powder, 0.3-1.2 parts chromium nitride powder, and 0.1-0.6 parts ferrovanadium powder to obtain a metal composite powder; add a composite corrosion-resistant dispersion to the metal composite powder under stirring, add 0.3-1.0 parts polyvinyl alcohol and 0.1-0.5 parts zinc stearate, stir at 45-60℃, dry, crush and sieve to obtain a corrosion-resistant fastener material premix powder;

[0022] S2. Press the premixed powder of corrosion-resistant fastener material at 500-750 MPa to obtain a fastener blank; under a mixed gas of nitrogen and hydrogen, degrease and sinter the fastener blank, and obtain a sintered blank after cooling; subject the sintered blank to solution treatment and aging treatment; then place it in a passivation solution containing 100-150 parts of deionized water, 0.2-0.8 parts of citric acid and 0.4-1.2 parts of sodium citrate for passivation treatment, clean, and dry.

[0023] In this invention, the preparation of corrosion-resistant fastener materials involves a continuous process of powder composite, sintering, and surface passivation. Aminosilane graphene barrier microsheets are pre-dispersed in deionized water and anhydrous ethanol to form a slurry, which is then mixed with molybdenum-vanadium-cerium-phosphorus-silicon complex passivating salt, nano-silica, and hexagonal boron nitride to form a composite corrosion-resistant dispersion. This ensures that the sheet-like barrier phase, inorganic filler phase, and passivating salt are uniformly distributed in the liquid phase. After the composite corrosion-resistant dispersion is mixed with a metal composite powder composed of 316L stainless steel powder, 2205 duplex stainless steel powder, nickel powder, molybdenum powder, chromium nitride powder, and vanadium-iron powder, polyvinyl alcohol provides temporary bonding and film-forming properties, while zinc stearate improves powder flow and demolding during pressing, allowing the corrosion-resistant components to adhere to the surface of the metal particles and the interparticle spaces. During pressing, the metal composite powder is tightly packed, nano-silica fills the micropores between particles, and hexagonal boron nitride and aminosilane graphene barrier microsheets form a sheet-like barrier structure at the particle interface. During degreasing and sintering under a mixed nitrogen and hydrogen gas atmosphere, polyvinyl alcohol and zinc stearate are removed, and metal particles are densified through diffusion bonding. Elements such as nickel, molybdenum, chromium, and vanadium enter the matrix, promoting solid solution strengthening and enhancing passivation capabilities. The sintered blanks undergo solution treatment and aging treatment to obtain a uniform microstructure. Finally, they are treated in a passivation solution containing deionized water, citric acid, and sodium citrate. The surface oxide film is gently activated and regenerated. The molybdenum-vanadium-cerium-phosphorus-silicon complex passivation salt participates in defect sealing and film repair, working together with the lamellar barrier structure and inorganic filler phase to reduce the penetration rate of corrosive media, resulting in a dense matrix, a stable passivation film, and a lamellar barrier structure.

[0024] According to a preferred embodiment of the present invention, in step S1, the stirring time at 45-60°C is 60-120 min.

[0025] According to a preferred embodiment of the present invention, in step S2, the pH of the passivation solution is 5.0-6.2.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) This invention uses 316L stainless steel powder and 2205 duplex stainless steel powder as the main metal matrix, and combines them with nickel powder, molybdenum powder, chromium nitride powder and ferrovanadium powder to form a composite matrix with both corrosion resistance and mechanical support after sintering. Nickel powder is beneficial to improving the toughness of the matrix and the sintering bonding state, molybdenum powder is beneficial to improving the pitting corrosion resistance of the material in chlorine-containing media, and chromium nitride powder and ferrovanadium powder are beneficial to improving the hardness, wear resistance and surface passivation stability of the matrix. After the above metal components are mixed, pressed, degreased, sintered, solution treated and aged, the corrosion channels caused by porosity, segregation and insufficient interfacial bonding in the powder metallurgy material can be reduced, so that the corrosion-resistant fastener material can maintain good structural stability in humid, salt spray and weakly acidic environments.

[0028] (2) The addition of molybdenum-vanadium-cerium-phosphorus-silicon complex passivating salt in this invention provides a composite passivation effect on the surface of metal particles and in subsequent passivation treatment. The molybdenum-vanadium-cerium-phosphorus-silicon complex passivating salt is beneficial to improving the passivation film's resistance to localized corrosion and to forming a deposition sealing effect at film defects, while also improving the density and adhesion stability of the passivation film. By treating the molybdenum-vanadium-cerium-phosphorus-silicon complex passivating salt with a passivation solution containing deionized water, citric acid, and sodium citrate, a more stable composite oxide film can be formed on the surface of the sintered blank, reducing the corrosion sensitivity at the root of the thread, particle boundaries, and micropores, thereby improving the pitting corrosion resistance and crevice corrosion resistance of the corrosion-resistant fastener material.

[0029] (3) This invention employs aminosilane graphene barrier microflakes, nano-silica, and hexagonal boron nitride to construct a sheet barrier and inorganic filling structure. After silane grafting and silicon-oxygen coating, the aminosilane graphene barrier microflakes exhibit improved dispersibility and interfacial bonding in the metal powder system, extending the migration path of moisture, oxygen, and chloride ions into the matrix. Nano-silica fills the micropores between particles, increasing the interfacial density. Hexagonal boron nitride improves interfacial lubrication and sheet barrier effects. Polyvinyl alcohol provides temporary bonding, and zinc stearate improves compression molding and demolding performance, allowing the molybdenum-vanadium-cerium-phosphorus-silicon complex passivating salt, aminosilane graphene barrier microflakes, nano-silica, and hexagonal boron nitride to adhere more uniformly to the surface of the metal composite powder. This enables the corrosion-resistant fastener material to possess the effects of matrix corrosion resistance, film passivation, and sheet barrier. Detailed Implementation

[0030] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0031] Example 1

[0032] This embodiment provides a method for preparing a corrosion-resistant fastener material, the steps of which include:

[0033] Step S1: Under stirring, add 0.7g of aminosilane graphene barrier microsheets to 10g of deionized water and 7g of anhydrous ethanol, stir at 500r / min for 20min, and then ultrasonically disperse for 20min to obtain a pre-dispersed slurry; add 2.5g of molybdenum vanadium cerium phosphorus silicon complex passivating salt, 0.55g of nano silica and 0.35g of hexagonal boron nitride to the pre-dispersed slurry, stir at 500r / min for 30min to obtain a composite corrosion-resistant dispersion; add 70g of 316L stainless steel powder and 16g of... 2205 duplex stainless steel powder, 3.0g nickel powder, 1.8g molybdenum powder, 0.75g chromium nitride powder, and 0.35g ferrovanadium powder were added to a mixing device and dry-mixed at 300r / min for 40min to obtain a metal composite powder. Under stirring at 300r / min, the composite corrosion-resistant dispersion was added to the metal composite powder in three portions, stirring for 10min after each addition. After all the powder was added, 0.65g polyvinyl alcohol and 0.30g zinc stearate were added, and the mixture was stirred at 52.5℃ for 90min. Then, it was dried at 60℃ for 8h. After drying, the powder was crushed and sieved through a 150μm sieve to obtain a corrosion-resistant fastener material premix powder.

[0034] Step S2: The corrosion-resistant fastener material premix powder is loaded into a fastener mold, pressed at 625 MPa and held for 60 seconds. After demolding, a fastener blank is obtained. The fastener blank is placed under a mixture of nitrogen and hydrogen gas (nitrogen to hydrogen volume ratio 95:5). First, the temperature is increased to 500℃ at 5℃ / min and held for 60 minutes for degreasing. Then, the temperature is increased to 1280℃ at 8℃ / min and held for 120 minutes for sintering. Finally, it is cooled in the furnace to below 80℃ to obtain… Sintered blanks; the sintered blanks were solution treated at 1050℃ for 60 min and then water-cooled, followed by aging treatment at 450℃ for 120 min and air-cooled; 125 g of deionized water, 0.5 g of citric acid and 0.8 g of sodium citrate were mixed until completely dissolved, and the pH was adjusted to 5.6 to obtain a passivation solution; the sintered blanks were placed in the passivation solution and passivated at 25℃ for 30 min, and after passivation, they were washed three times with deionized water and dried at 60℃ for 2 h to obtain corrosion-resistant fastener material.

[0035] Preparation steps of molybdenum-vanadium-cerium-phosphorus-silicon complex passivating salt:

[0036] Step A1: Add 150g of deionized water to the reaction vessel. While stirring, add 15g of sodium molybdate dihydrate, 3.5g of ammonium metavanadate, and 6g of citric acid sequentially. Heat to 62.5℃ and stir at 300r / min for 45min until the solid dissolves and forms a homogeneous solution, obtaining a molybdenum-vanadium complex solution. Separately, take 55g of deionized water, add 8g of cerium nitrate hexahydrate, stir until dissolved, then add 1.75g ​​of glycine. Stir at 25℃ for 20min, adjust the pH to 3.6 with citric acid solution, obtaining a cerium complex solution. Under stirring at 00 r / min, the cerium complex solution was added dropwise to the molybdenum-vanadium complex solution over 30 min. After the addition was completed, the temperature was raised to 67.5℃ and the reaction was allowed to proceed for 60 min. Then, 4.5 g of phosphoric acid was added and stirring was continued for 10 min. 7 g of sodium silicate nonahydrate was dissolved in 30 g of deionized water to obtain a sodium silicate solution. The sodium silicate solution was added dropwise to the reaction system over 25 min under stirring at 300 r / min. The pH was adjusted to 5.5 with ammonia and citric acid solution, and stirring was continued for 30 min to obtain the molybdenum-vanadium-cerium-phosphorus-silicon composite complex solution.

[0037] Step A2: Add 3g of sodium gluconate to the molybdenum-vanadium-cerium-phosphorus-silicon composite complex solution and stir at 55℃ and 300r / min for 40min; add ammonia water to adjust the pH to 6.0 to obtain a composite passivation salt solution; concentrate the composite passivation salt solution under reduced pressure at 60℃ and -0.08MPa until there is no obvious flowing liquid, and then dry it in a 60℃ forced-air drying oven for 12h to obtain the dried product; grind the dried product for 30min and vibrate it through a 75μm sieve to obtain the molybdenum-vanadium-cerium-phosphorus-silicon complex passivation salt.

[0038] Preparation steps of aminosilane graphene barrier microsheets:

[0039] Step B1: Add 1.75g ​​of graphene oxide to a mixture of 220g of deionized water and 60g of anhydrous ethanol, stir at 500r / min for 30min, and then sonicate for 30min to obtain a graphene oxide dispersion; add 4.5g of 3-aminopropyltriethoxysilane to 45g of anhydrous ethanol and 7.5g of deionized water, stir and hydrolyze at 25℃ and 300r / min for 40min to obtain an aminosilane hydrolysate; under stirring at 300r / min, add the aminosilane hydrolysate dropwise to the graphene oxide dispersion over 30min, heat to 52.5℃ and react for 3h to obtain an aminosilane-grafted graphene oxide dispersion.

[0040] Step B2: Add 2.5g of tetraethyl orthosilicate and 1.0g of methyltrimethoxysilane to the aminosilane-grafted graphene oxide dispersion, and stir the mixture at 57.5℃ and 300r / min for 2h. Then add 1.4g of L-ascorbic acid and react at 77.5℃ and 300r / min for 1.5h. After the reaction is complete, centrifuge the reaction solution at 6000r / min for 10min and collect the precipitate. Wash the precipitate three times with deionized water and twice with anhydrous ethanol, and then dry it in a vacuum drying oven at 60℃ for 10h. After drying, grind the precipitate for 30min and then vibrate it through a 75μm sieve to obtain aminosilane graphene barrier microsheets.

[0041] Example 2

[0042] The difference between this embodiment and Embodiment 1 is that this embodiment provides a method for preparing a corrosion-resistant fastener material, the steps of which include:

[0043] Step S1: Under stirring, 0.2g of aminosilane graphene barrier microsheets are dispersed in 6g of deionized water and 4g of anhydrous ethanol to obtain a pre-dispersed slurry; 1.0g of molybdenum-vanadium-cerium-phosphorus-silicon complex passivating salt, 0.2g of nano-silica and 0.1g of hexagonal boron nitride are added to the pre-dispersed slurry and stirred until uniform to obtain a composite corrosion-resistant dispersion; 62g of 316L stainless steel powder, 10g of 2205 duplex stainless steel powder, 1.5g of nickel powder, 0.8g of molybdenum powder, 0.3g of chromium nitride powder and 0.1g of vanadium-iron powder are mixed to obtain a metal composite powder; under stirring, the composite corrosion-resistant dispersion is added to the metal composite powder, along with 0.3g of polyvinyl alcohol and 0.1g of zinc stearate, and stirred at 45℃ for 60min, then dried, crushed and sieved to obtain a corrosion-resistant fastener material premixed powder.

[0044] Step S2: Press the premixed powder of corrosion-resistant fastener material at 500 MPa to obtain a fastener blank; under a mixed gas of nitrogen and hydrogen, degrease the fastener blank at 500℃ for 60 min, then sinter at 1280℃ for 120 min, and obtain a sintered blank after cooling; perform solution treatment at 1050℃ for 60 min and water cooling, then age at 450℃ for 120 min and air cooling; subsequently, place it in a passivation solution containing 100 g deionized water, 0.2 g citric acid and 0.4 g sodium citrate for passivation treatment. The pH of the passivation solution is 5.0, the passivation temperature is 25℃ and the passivation time is 30 min. After passivation treatment, wash with deionized water and dry to obtain the corrosion-resistant fastener material.

[0045] Preparation steps of molybdenum-vanadium-cerium-phosphorus-silicon complex passivating salt:

[0046] Step A1: Add 12g of sodium molybdate dihydrate, 2g of ammonium metavanadate, and 4g of citric acid to 120g of deionized water. Stir at 55℃ until the solid dissolves and forms a homogeneous solution to obtain a molybdenum-vanadium complex solution. Dissolve 6g of cerium nitrate hexahydrate in 40g of deionized water, add 1.0g of glycine, stir until completely dissolved, and adjust the pH to 3.2 to obtain a cerium complex solution. While stirring, add the cerium complex solution dropwise to the molybdenum-vanadium complex solution and react at 60℃ for 40min. Add 3g of phosphoric acid, and while stirring, add a sodium silicate solution prepared from 5g of sodium silicate nonahydrate and 20g of deionized water. Adjust the pH to 5.2 and continue stirring until the system is homogeneous to obtain a molybdenum-vanadium-cerium-phosphorus-silicon composite complex solution.

[0047] Step A2: Add 2g of sodium gluconate to the molybdenum-vanadium-cerium-phosphorus-silicon composite complex solution and stir at 50℃ for 30min; add ammonia water to adjust the pH to 5.8 to obtain a composite passivation salt solution; concentrate the composite passivation salt solution and dry it at 60℃ to constant weight to obtain the dried product; grind and vibrate the dried product to obtain the molybdenum-vanadium-cerium-phosphorus-silicon complex passivation salt.

[0048] Preparation steps of aminosilane graphene barrier microsheets:

[0049] Step B1: Disperse 1.0g of graphene oxide in 180g of deionized water and 40g of anhydrous ethanol, and stir until no obvious agglomeration occurs to obtain a graphene oxide dispersion; add 3g of 3-aminopropyltriethoxysilane to 30g of anhydrous ethanol and 5g of deionized water, and stir to hydrolyze until homogeneous to obtain an aminosilane hydrolysate; under stirring, add the aminosilane hydrolysate dropwise to the graphene oxide dispersion, and react at 45℃ for 2h to obtain an aminosilane-grafted graphene oxide dispersion.

[0050] Step B2: Add 1.5g of tetraethyl orthosilicate and 0.5g of methyltrimethoxysilane to the aminosilane-grafted graphene oxide dispersion, and stir the mixture at 50°C until the system is homogeneous; then add 0.8g of L-ascorbic acid and react at 70°C for 1h; after the reaction is complete, centrifuge to separate the precipitate; wash the precipitate with deionized water and anhydrous ethanol, dry, grind and vibrate to sieve to obtain aminosilane graphene barrier microsheets.

[0051] Example 3

[0052] The difference between this embodiment and Embodiment 1 is that this embodiment provides a method for preparing a corrosion-resistant fastener material, the steps of which include:

[0053] Step S1: Under stirring, 1.2g of aminosilane graphene barrier microsheets were dispersed in 14g of deionized water and 10g of anhydrous ethanol to obtain a pre-dispersed slurry; 4.0g of molybdenum-vanadium-cerium-phosphorus-silicon complex passivating salt, 0.9g of nano-silica and 0.6g of hexagonal boron nitride were added to the pre-dispersed slurry and stirred until uniform to obtain a composite corrosion-resistant dispersion; 78g of 316L stainless steel powder, 22g of 2205 duplex stainless steel powder, 4.5g of nickel powder, 2.8g of molybdenum powder, 1.2g of chromium nitride powder and 0.6g of vanadium-iron powder were mixed to obtain a metal composite powder; under stirring, the composite corrosion-resistant dispersion was added to the metal composite powder, along with 1.0g of polyvinyl alcohol and 0.5g of zinc stearate, and stirred at 60℃ for 120min, dried, crushed and sieved to obtain a corrosion-resistant fastener material premixed powder.

[0054] Step S2: The premixed powder of corrosion-resistant fastener material is pressed at 750 MPa to obtain a fastener blank; under a mixed gas of nitrogen and hydrogen, the fastener blank is first degreased at 500℃ for 60 min, then sintered at 1280℃ for 120 min, and cooled to obtain a sintered blank; the sintered blank is solution treated at 1050℃ for 60 min and then water-cooled, then aged at 450℃ for 120 min and air-cooled; subsequently, it is placed in a passivation solution containing 150 g deionized water, 0.8 g citric acid and 1.2 g sodium citrate for passivation treatment. The pH of the passivation solution is 6.2, the passivation temperature is 25℃ and the passivation time is 30 min. After passivation treatment, it is washed with deionized water and dried to obtain the corrosion-resistant fastener material.

[0055] Preparation steps of molybdenum-vanadium-cerium-phosphorus-silicon complex passivating salt:

[0056] Step A1: Add 18g of sodium molybdate dihydrate, 5g of ammonium metavanadate, and 8g of citric acid to 180g of deionized water. Stir at 70℃ until the solids dissolve and form a homogeneous solution to obtain a molybdenum-vanadium complex solution. Dissolve 10g of cerium nitrate hexahydrate in 70g of deionized water, add 2.5g of glycine, stir until completely dissolved, and adjust the pH to 4.0 to obtain a cerium complex solution. While stirring, add the cerium complex solution dropwise to the molybdenum-vanadium complex solution and react at 75℃ for 80min. Add 6g of phosphoric acid, and while stirring, add a sodium silicate solution prepared from 9g of sodium silicate nonahydrate and 40g of deionized water. Adjust the pH to 5.8 and continue stirring until the system is homogeneous to obtain a molybdenum-vanadium-cerium-phosphorus-silicon composite complex solution.

[0057] Step A2: Add 4g of sodium gluconate to the molybdenum-vanadium-cerium-phosphorus-silicon composite complex solution and stir at 60℃ for 50min; add ammonia water to adjust the pH to 6.2 to obtain a composite passivation salt solution; concentrate the composite passivation salt solution and dry it at 60℃ to constant weight to obtain the dried product; grind and vibrate the dried product to obtain the molybdenum-vanadium-cerium-phosphorus-silicon complex passivation salt.

[0058] Preparation steps of aminosilane graphene barrier microsheets:

[0059] Step B1: Disperse 2.5g of graphene oxide in 260g of deionized water and 80g of anhydrous ethanol, and stir until no obvious agglomeration occurs to obtain a graphene oxide dispersion; add 6g of 3-aminopropyltriethoxysilane to 60g of anhydrous ethanol and 10g of deionized water, and stir to hydrolyze until homogeneous to obtain an aminosilane hydrolysate; under stirring, add the aminosilane hydrolysate dropwise to the graphene oxide dispersion, and react at 60℃ for 4h to obtain an aminosilane-grafted graphene oxide dispersion.

[0060] Step B2: Add 3.5g of tetraethyl orthosilicate and 1.5g of methyltrimethoxysilane to the aminosilane-grafted graphene oxide dispersion, and stir the mixture at 65°C until the system is homogeneous; then add 2.0g of L-ascorbic acid and react at 85°C for 2 hours; after the reaction is complete, centrifuge to separate the precipitate; wash the precipitate with deionized water and anhydrous ethanol, dry, grind and vibrate to sieve, and obtain aminosilane graphene barrier microsheets.

[0061] Comparative Example 1

[0062] The difference between this comparative example and Example 1 is that no molybdenum-vanadium-cerium-phosphorus-silicon complex passivating salt is prepared and added, and 2.5g of molybdenum-vanadium-cerium-phosphorus-silicon complex passivating salt is added in step S1. The remaining steps are the same as in Example 1.

[0063] Comparative Example 2

[0064] The difference between this comparative example and Example 1 is that aminosilane graphene barrier microsheets are not prepared and are not added, and 0.7g of aminosilane graphene barrier microsheets are not added in step S1. The remaining steps are the same as in Example 1.

[0065] Comparative Example 3

[0066] The difference between this comparative example and Example 1 is that no molybdenum-vanadium-cerium-phosphorus-silicon complex passivating salt and aminosilane graphene barrier microsheets are prepared and added. In step S1, 2.5g of molybdenum-vanadium-cerium-phosphorus-silicon complex passivating salt and 0.7g of aminosilane graphene barrier microsheets are added. The remaining steps are the same as in Example 1.

[0067] According to relevant national and industry standards, the performance of the corrosion-resistant fastener materials provided in the above embodiments and comparative examples was tested, and the test methods are as follows:

[0068] The corrosion-resistant fastener materials obtained in Examples 1-3 and Comparative Examples 1-3 were processed into test samples of the same specifications. The number of samples in each group was n=5. Before testing, the sample surface was polished step by step with P600, P1000 and P1200 sandpaper. Then, the samples were cleaned with deionized water 3 times and anhydrous ethanol 2 times, and dried at 60°C for 2 hours before use.

[0069] During the relative density test, the mass m1 of the sample in air is first measured. Then, the sample is placed in deionized water to fully immerse it and remove any air bubbles adhering to the surface. The suspended mass m2 of the sample in deionized water is measured. The relative density is calculated based on the ratio of the actual density of the sample to the theoretical density. The average value of 5 samples in each group is taken.

[0070] For the open porosity test, the sample was vacuum-immersed in deionized water at -0.08 MPa for 30 min. After removal, the surface free water was wiped off, and the saturated water mass m3 was measured. Then, the suspended mass m4 of the sample in deionized water was measured. The open porosity was calculated based on the dry mass, saturated water mass, and suspended mass. The average value of 5 samples in each group was taken.

[0071] During the tensile strength test, the sample is processed into a tensile specimen with a uniform gauge length. The specimen surface must not have obvious burrs, cracks, or indentations. Uniaxial tension is applied at 25℃ with a loading rate of 1 mm / min. The maximum load before fracture is recorded, and the tensile strength is calculated based on the ratio of the maximum load to the original cross-sectional area of ​​the specimen. Five specimens are tested in each group, and the average value is taken.

[0072] For the first corrosion time test of neutral salt spray, the sample was placed in a salt spray test chamber, using a 50 g / L sodium chloride solution, at a test temperature of 35 ℃, with the pH of the collected solution controlled at 7.0, and the angle between the sample and the vertical direction at 20°. During continuous spraying, the sample was taken out and observed once every 24 hours. The time when visible pitting, corrosion spots or red rust first appeared on the sample surface was taken as the first corrosion time of neutral salt spray. The average of the first corrosion time of 5 samples in each group was taken.

[0073] During pitting potential testing, the non-test surface of the sample is encapsulated with insulating material, leaving only 1 cm exposed. 2 The exposed area was used as the working surface. A 3.5% sodium chloride solution was used as the corrosive medium. After standing at 25°C for 30 minutes to stabilize, a potentiodynamic scanning was performed at a scanning rate of 1 mV / s. The potential corresponding to the continuous and rapid increase in current density was taken as the pitting potential. Five samples were tested in each group and the average value was taken.

[0074] For corrosion current density testing, the same sample encapsulation method and 3.5% sodium chloride solution corrosion medium were used as in pitting potential testing. After stabilizing in an open circuit at 25℃ for 30 minutes, polarization testing was performed. The polarization curves were extrapolated to obtain the corrosion current density. Five samples were tested in each group and the average value was taken.

[0075] The performance test data above are shown in Table 1.

[0076] Table 1 Performance Test Results

[0077] Relative density / % 98.6 97.8 98.3 97.1 96.9 95.8 Open porosity / % 0.42 0.58 0.49 0.86 0.93 1.35 Tensile strength / MPa 782 748 769 721 706 672 First corrosion time of neutral salt spray / h 1320 1080 1248 720 816 456 Pitting potential / V 0.61 0.54 0.58 0.39 0.44 0.28 <![CDATA[Corrosion current density / μA / cm 2 > 0.18 0.26 0.21 0.62 0.51 1.18

[0078] As can be seen from the above, Examples 1-3 show significant improvements in density, mechanical properties, and corrosion resistance compared to Comparative Examples 1-3. This indicates that the present invention solves the problems of high porosity, easy penetration of corrosive media along particle gaps, insufficient passivation film stability, and limited resistance to pitting and crevice corrosion in existing powder metallurgy fastener materials by using molybdenum-vanadium-cerium-phosphorus-silicon complex passivation salt and aminosilane graphene barrier micro-flakes in a synergistic manner.

[0079] The relative density of Examples 1-3 was 97.8-98.6%, which was higher than that of Comparative Examples 1-3 (95.8-97.1%), and the open porosity was 0.42-0.58%, which was lower than that of Comparative Examples 1-3 (0.86-1.35%). This indicates that the distribution of molybdenum-vanadium-cerium-phosphorus-silicon complex passivation salt, aminosilane-graphene barrier microflakes, nano-silica, and hexagonal boron nitride on the surface of the metal composite powder and in the interparticle gaps is beneficial to reducing interconnected pores and defect channels, and improving the density of the sintered blank.

[0080] The tensile strength of Examples 1-3 was 748-782 MPa, which was higher than that of Comparative Examples 1-3 (672-721 MPa). This indicates that after introducing molybdenum-vanadium-cerium-phosphorus-silicon complex passivating salt and aminosilane graphene barrier microflakes into the composite matrix formed by 316L stainless steel powder, 2205 duplex stainless steel powder, nickel powder, molybdenum powder, chromium nitride powder and vanadium-iron powder, the internal porosity of the material was reduced and the interparticle interface bonding state was improved, thereby reducing the possibility of crack propagation induced by porosity and interfacial defects during tensile testing.

[0081] The initial corrosion time of neutral salt spray in Examples 1-3 was 1080-1320 h, significantly longer than the 456-816 h in Comparative Examples 1-3; the pitting potential was 0.54-0.61 V, higher than the 0.28-0.44 V in Comparative Examples 1-3; and the corrosion current density was 0.18-0.26 μA / cm. 2 This is lower than the 0.51-1.18 μA / cm of comparative examples 1-3. 2 This indicates that the corrosion reaction rate on the material surface is reduced, and the resistance to pitting corrosion is improved.

[0082] Comparative Example 1, without the addition of molybdenum-vanadium-cerium-phosphorus-silicon complex passivation salt, showed a reduced initial corrosion time of 720 h for neutral salt spray, a pitting potential of 0.39 V, and a corrosion current density of 0.62 μA / cm². 2 This indicates that the lack of molybdenum-vanadium-cerium-phosphorus-silicon complex passivation salt weakens the surface composite passivation and defect sealing effects.

[0083] Comparative Example 2, without the addition of aminosilane graphene barrier microsheets, showed an initial corrosion time of 816 hours under neutral salt spray, a pitting potential of 0.44 V, and a corrosion current density of 0.51 μA / cm². 2 This indicates that without the layered barrier structure, moisture, oxygen, and chloride ions can more easily migrate into the matrix.

[0084] Comparative Example 3, which did not include molybdenum-vanadium-cerium-phosphorus-silicon complex passivation salt and aminosilane graphene barrier microsheets, had the highest open porosity, lowest tensile strength, shortest first corrosion time under neutral salt spray, lowest pitting potential, and highest corrosion current density. This indicates that it is difficult to simultaneously form a stable passivation film and an effective diffusion barrier structure by relying solely on metal composite powder, nano-silica, and hexagonal boron nitride.

[0085] Therefore, Examples 1-3 improve the service stability of corrosion-resistant fastener materials in salt spray and chlorine-containing environments through the combined effects of composite matrix densification, molybdenum-vanadium-cerium-phosphorus-silicon complex passivation salt-assisted passivation, and aminosilane-graphene barrier microsheet shielding.

Claims

1. A corrosion-resistant fastener material, characterized in that, Includes the following components in parts by weight: 62-78 parts 316L stainless steel powder, 10-22 parts 2205 duplex stainless steel powder, 1.5-4.5 parts nickel powder, 0.8-2.8 parts molybdenum powder, 0.3-1.2 parts chromium nitride powder, 0.1-0.6 parts vanadium iron powder, 0.2-0.9 parts nano silica, 0.1-0.6 parts hexagonal boron nitride, 0.3-1.0 parts polyvinyl alcohol, 0.1-0.5 parts zinc stearate, 6-14 parts deionized water, 4-10 parts anhydrous ethanol, 1.0-4.0 parts molybdenum vanadium cerium phosphorus silicon complex passivation salt, 0.2-1.2 parts aminosilane graphene barrier micro flakes.

2. The corrosion-resistant fastener material according to claim 1, characterized in that, The preparation method of the molybdenum-vanadium-cerium-phosphorus-silicon complex passivating salt includes: A1. By weight, add 12-18 parts of sodium molybdate dihydrate, 2-5 parts of ammonium metavanadate, and 4-8 parts of citric acid to 120-180 parts of deionized water, and stir at 55-70℃ to obtain a molybdenum-vanadium complex solution; dissolve 6-10 parts of cerium nitrate hexahydrate in 40-70 parts of deionized water, add 1.0-2.5 parts of glycine, and adjust the pH to 3.2-4.0 to obtain a cerium complex solution; while stirring, add the cerium complex solution dropwise to the molybdenum-vanadium complex solution, react at 60-75℃, add 3-6 parts of phosphoric acid, and while stirring, add a sodium silicate solution containing 5-9 parts of sodium silicate nonahydrate and 20-40 parts of deionized water, adjust the pH to 5.2-5.8, and continue stirring to obtain a molybdenum-vanadium-cerium-phosphorus-silicon composite complex solution; A2. Add 2-4 parts of sodium gluconate to the molybdenum-vanadium-cerium-phosphorus-silicon composite complex solution and stir at 50-60℃; add ammonia water to adjust the pH to 5.8-6.2 to obtain a composite passivation salt solution; concentrate and dry the composite passivation salt solution to obtain the dried product; grind and vibrate sieve the dried product.

3. The corrosion-resistant fastener material according to claim 2, characterized in that, In step A1, the reaction time is 40-80 minutes at 60-75℃.

4. The corrosion-resistant fastener material according to claim 2, characterized in that, In step A2, the stirring time at 50-60℃ is 30-50 minutes.

5. The corrosion-resistant fastener material according to claim 1, characterized in that, The preparation method of the aminosilane graphene barrier microsheets includes: B1. By weight, disperse 1.0-2.5 parts of graphene oxide in 180-260 parts of deionized water and 40-80 parts of anhydrous ethanol to obtain a graphene oxide dispersion; add 3-6 parts of 3-aminopropyltriethoxysilane to 30-60 parts of anhydrous ethanol and 5-10 parts of deionized water, stir and hydrolyze to obtain an aminosilane hydrolysate; under stirring, add the aminosilane hydrolysate dropwise to the graphene oxide dispersion, and react at 45-60℃ to obtain an aminosilane-grafted graphene oxide dispersion; B2. Add 1.5-3.5 parts of tetraethyl orthosilicate and 0.5-1.5 parts of methyltrimethoxysilane to the aminosilane-grafted graphene oxide dispersion and stir the mixture at 50-65℃. Then add 0.8-2.0 parts of L-ascorbic acid and react the mixture at 70-85℃. After the reaction is complete, centrifuge the mixture and collect the precipitate. Wash, dry, grind, and vibrate the precipitate for sieve separation.

6. The corrosion-resistant fastener material according to claim 5, characterized in that, In step B1, the reaction time is 2-4 hours at 45-60℃.

7. The corrosion-resistant fastener material according to claim 5, characterized in that, In step B2, the reaction time is 1-2 hours at 70-85℃.

8. A method for preparing a corrosion-resistant fastener material according to any one of claims 1-7, characterized in that, step... include: S1. Under stirring, disperse 0.2-1.2 parts of aminosilane graphene barrier microsheets in 6-14 parts of deionized water and 4-10 parts of anhydrous ethanol to obtain a pre-dispersed slurry; add 1.0-4.0 parts of molybdenum-vanadium-cerium-phosphorus-silicon complex passivating salt, 0.2-0.9 parts of nano-silica and 0.1-0.6 parts of hexagonal boron nitride to the pre-dispersed slurry to obtain a composite corrosion-resistant dispersion; add 62-78 parts of 316L stainless steel powder and 10-22 parts of 2 Mix 205 duplex stainless steel powder, 1.5-4.5 parts nickel powder, 0.8-2.8 parts molybdenum powder, 0.3-1.2 parts chromium nitride powder, and 0.1-0.6 parts ferrovanadium powder to obtain a metal composite powder; add a composite corrosion-resistant dispersion to the metal composite powder under stirring, add 0.3-1.0 parts polyvinyl alcohol and 0.1-0.5 parts zinc stearate, stir at 45-60℃, dry, crush and sieve to obtain a corrosion-resistant fastener material premix powder; S2. Press the premixed powder of corrosion-resistant fastener material at 500-750 MPa to obtain a fastener blank; under a mixed gas of nitrogen and hydrogen, degrease and sinter the fastener blank, and obtain a sintered blank after cooling; subject the sintered blank to solution treatment and aging treatment; then place it in a passivation solution containing 100-150 parts of deionized water, 0.2-0.8 parts of citric acid and 0.4-1.2 parts of sodium citrate for passivation treatment, clean, and dry.

9. The method for preparing the corrosion-resistant fastener material according to claim 8, characterized in that, In step S1, the stirring time at 45-60℃ is 60-120 minutes.

10. The method for preparing the corrosion-resistant fastener material according to claim 8, characterized in that, In step S2, the pH of the passivation solution is 5.0-6.2.