Salt mist resistant composite surface treatment process for 17-4 stainless iron

Abstract

The invention relates to the field of metal surface treatment, in particular to a salt mist resistant composite surface treatment process for 17-4 stainless iron, which comprises the following steps: S1, immersing a workpiece in dilute nitric acid for pickling to dissolve carbide and oxide skin, then immersing in a weakly alkaline solution to neutralize acid residues, and finally washing and drying for later use; s2, the workpiece is immersed in a solution containing chromium metal ions, a complexing agent is added for reaction, the PH value is adjusted to be 4-7, iron atoms and chromium ions on the surface of the workpiece are replaced, and a continuous chromium-rich passivation film is formed on the surface of the workpiece; and S3, the workpiece is completely coated with composite sol prepared by blending zirconium oxide, a silane coupling agent containing amino or epoxy groups and organic silicon, the mixture is kept for 10-15 min, then the workpiece is taken out, centrifugal spinning, gelatinization treatment, drying and sintering are sequentially conducted, and the salt mist resistant stainless iron product is obtained. According to the process, the corrosion resistance and the wear resistance of the 17-4 stainless iron in a strong corrosion environment are improved, the protection life of the 17-4 stainless iron is prolonged, and the phenomenon of surface layer stripping is effectively avoided.

Description

Technical Field

[0001] This application relates to the field of metal surface treatment, and in particular to an anti-salt spray composite surface treatment process for 17-4 stainless steel. Background Technology

[0002] In numerous industrial sectors such as machinery parts, aerospace, automotive, and hardware, material performance plays a crucial role in product quality and reliability. 17-4PH (17Cr-4Ni), a precipitation-hardening stainless steel, also known as "stainless iron," possesses both good mechanical strength and a certain degree of corrosion resistance, making it suitable for applications requiring load-bearing capacity and operating in moderately corrosive environments. It has been widely used in these industries, providing vital material support for their development. However, in some highly corrosive environments, its performance fails to meet practical needs, limiting its wider application. To improve the salt spray resistance of 17-4 stainless iron, the industry typically employs several methods: electroplating, which uses electrochemical methods to deposit a layer of metal or alloy onto the metal surface using an electric current, thereby altering the surface properties and improving corrosion resistance; coating, which involves applying an organic or inorganic protective film to the metal surface, isolating it from external corrosive media and reducing the risk of corrosion; and phosphating, which forms a phosphate conversion film on the metal surface, further enhancing its corrosion resistance.

[0003] However, existing methods for improving the salt spray performance of 17-4 stainless steel still have significant drawbacks. These drawbacks primarily stem from the fact that 17-4 stainless steel has a relatively low chromium content and a small amount of ferrite structure, resulting in insufficient corrosion resistance in highly corrosive environments. Long-term use easily leads to surface peeling, making the protective effect unsustainable. Furthermore, existing methods such as electroplating, coating, and phosphating are costly and complex, leading to low production efficiency and increased economic burden. In addition, these methods do not meet environmental protection requirements, making large-scale adoption difficult given increasingly stringent environmental regulations. These problems prevent existing methods from meeting the demands of large-scale, low-cost production and effectively addressing the corrosion resistance issues of 17-4 stainless steel in highly corrosive environments. Summary of the Invention

[0004] To meet the demands of high-volume, low-cost production, improve the corrosion resistance and wear resistance of 17-4 stainless steel in highly corrosive environments, extend the protective life of 17-4 stainless steel, and effectively prevent surface peeling, this application provides a salt spray resistant composite surface treatment process for 17-4 stainless steel.

[0005] This application provides a salt spray resistant composite surface treatment process for 17-4 stainless steel, including the following steps: S1 Immerse the workpiece in dilute nitric acid to pickle and dissolve carbides and oxide scale, then immerse it in a weak alkaline solution to neutralize acid residue, and finally wash and dry it for later use. S2 involves immersing the workpiece in a solution containing chromium metal ions, adding a complexing agent to react, adjusting the pH value to 4-7, replacing iron atoms and chromium ions on the workpiece surface, and forming a continuous chromium-rich passivation film on the workpiece surface. S3 coats the entire workpiece with a composite sol, holds it for 10-15 minutes, and then takes out the workpiece and sequentially performs centrifugal spinning, gelation treatment, drying and sintering to obtain salt spray resistant stainless iron products. The composite sol is prepared by blending zirconium oxide, a silane coupling agent containing amino or epoxy groups, and organosilicon. By employing the above technical solution, in step S1, immersing the workpiece in dilute nitric acid for pickling dissolves carbides and oxide scale, resulting in a cleaner workpiece surface and providing a good foundation for subsequent processing. Subsequent immersion in a weakly alkaline solution and acid residues prevent adverse effects from acidic substances on subsequent processing. Washing and drying ensure the workpiece surface is in a suitable condition for subsequent processing. In step S2, immersing the workpiece in a solution containing chromium ions and adding a complexing agent allows for the replacement of iron atoms and chromium ions on the workpiece surface. The complex reduces Cr... 3+ The diffusion resistance promotes its migration to the workpiece surface, and the complexing agent preferentially binds to free Fe in the solution. 3+ The removal of impurity ions reduces contamination of the replacement layer. Due to chromium's good corrosion resistance, replacement allows for the formation of a continuous chromium-rich passivation film on the workpiece surface. This passivation film effectively isolates the workpiece from external corrosive media, thereby improving its corrosion resistance. Furthermore, adjusting the pH of the solution in step S2 to 4-7 ensures a suitable pH level—neither too acidic nor too alkaline—which is beneficial for chromium... 3+ Stable existence, avoiding Fe 2+Hydrolysis and precipitation. This moderate pH environment is conducive to the substitution reaction between chromium-containing metal ions and iron atoms on the workpiece surface. In step S3, the workpiece is fully coated with a composite sol composed of zirconium oxide, a silane coupling agent containing amino or epoxy groups, and organosilicon. The sol is maintained for 10-15 minutes, followed by centrifugation, gelation, drying, and sintering. The silane coupling agent enhances the bonding force between zirconium oxide and organosilicon, allowing them to mix at the molecular level and form chemical bonds that enhance interfacial adhesion, preventing phase separation. Zirconia provides temperature resistance, wear resistance, and corrosion resistance, while organosilicon imparts crack resistance, sealing, and weather resistance. The combined coating improves the overall performance of the sealing adhesive, ultimately resulting in a stainless iron product with excellent salt spray resistance, meeting the requirements for use in highly corrosive environments, while avoiding the problems of high cost, complex processes, and environmental unfriendliness associated with existing treatment methods. Preferably, the complexing agent is at least one of sulfate, oxalate, or sodium citrate. By employing the above technical solution, at least one of sulfate, oxalate, or sodium citrate is added as a complexing agent to the solution containing chromium metal ions. These complexing agents can form stable complexes with the metal ions in the solution, reducing the activity of the metal ions and allowing them to participate in the reaction more uniformly. During the replacement of iron atoms and chromium ions on the workpiece surface, this uniform reaction facilitates a more complete replacement of iron atoms and chromium ions, thereby enabling the formation of a continuous and dense chromium-rich passivation film on the workpiece surface. Preferably, the pH value of the solution in step S2 is adjusted to 5. By employing the above technical solution, adjusting the pH value of the solution in step S2 to 5 provides an optimal pH value for chromium... 3+ Stable existence, avoiding Fe2+ hydrolysis and precipitation. Preferably, the conditions for the displacement treatment in step S2 are a temperature of 60-80℃ and a reaction time of 25-40 min. By adopting the above technical solution, in step S2, the temperature of the displacement treatment is set within the range of 60-80℃ and the reaction time is set within the range of 25-40 min. Within this range, the ionic activity in the solution containing chromium metal ions is suitable, and a sufficient and appropriate displacement reaction can occur with the iron atoms on the workpiece surface. This ensures that the iron atoms and chromium ions have enough time to fully displace each other, thereby forming a continuous and dense chromium-rich passivation film on the workpiece surface. Preferably, the preparation method of the composite sol includes the following steps: Zirconia sol: Zirconium propoxide, nitric acid, silane coupling agent containing amino or epoxy groups and ethanol are mixed in a mass ratio of 5:1:5:25, stirred for 30 minutes until uniform and transparent, and heated in a water bath at 60℃ for 2 hours to obtain a zirconia sol with a particle size of 10-50 nm; Preparation of the composite sol: Zirconia sol, dispersant, and organosilicon sol are mixed in a mass ratio of 15:1:5 and ultrasonically treated for 15 minutes to obtain a uniform and stable zirconia and organosilicon blend sol. By employing the above technical solution, mixing zirconium propoxide, nitric acid, a silane coupling agent containing amino or epoxy groups, and ethanol in a specific mass ratio, followed by stirring and water bath heating, allows for complete reaction of the components, resulting in a zirconia sol with a particle size of 10-50 nm. This nano-sized zirconia sol possesses a large specific surface area and high activity. Then, mixing the zirconia sol, dispersant, and organosilicon sol in a specific mass ratio and ultrasonically treating it ensures uniform dispersion of the zirconia sol and organosilicon sol, forming a uniform and stable zirconia and organosilicon blend sol. This blended sol is applied to the salt spray resistant composite surface treatment process of 17-4 stainless steel. Nano-sized zirconia sol enhances the hardness and wear resistance of the coating, while organosilicon sol possesses good flexibility and chemical corrosion resistance. The composite coating formed by the combination of these two effectively isolates external corrosive media, improving the salt spray resistance and protective durability of 17-4 stainless steel in highly corrosive environments. Simultaneously, it reduces processing costs, simplifies the process, and meets the needs of large-scale, low-cost production. Preferably, in step S3, the workpiece is fully coated with the composite sol, and a vacuum is applied to (-0.08)-(-0.05) MPa. By adopting the above technical solution, in step S3, the workpiece is fully coated with the composite sol, and a vacuum is applied to (-0.08)-(-0.05) MPa. Vacuuming reduces environmental pressure, allowing gas to be extracted from the workpiece surface and pores, reducing the obstruction of gas to the sol's immersion. This allows the zirconium oxide and organosilicon blend sol to penetrate more fully into the tiny pores and defects on the workpiece surface, resulting in a more uniform and dense coating. Preferably, the drying process in step S3 employs a graded drying method, which includes the following steps: first, drying the workpiece in a 60°C oven for 2 hours to remove physically adsorbed water; then transferring the workpiece to a 120°C vacuum dryer for 4 hours to remove chemically bound water and prevent gel cracking. By adopting the above technical solution, the graded drying method in step S3, first drying the workpiece in a 60°C oven for 2 hours (a relatively low temperature), slowly removes physically adsorbed water from the workpiece surface, avoiding rapid evaporation of moisture at excessively high temperatures that could cause significant stress on the gel surface, thus preventing gel cracking. Then, transferring the workpiece to a 120°C vacuum dryer for 4 hours lowers the boiling point of water in a vacuum environment, allowing for more effective removal of chemically bound water at a lower temperature, further preventing gel cracking caused by stress from rapid moisture evaporation. Preferably, the sintering method in step S3 is as follows: after graded drying, the oven is heated to 400°C at a rate of 2°C / min and kept at that temperature for 2 hours to transform the gel into a dense ceramic layer while retaining some of the flexibility of the organosilicon.By adopting the above technical solution, after the graded drying process, the oven temperature is raised to 400℃ at a rate of 2℃ / min and held for 2 hours. This slow heating method allows the gel to be heated evenly, avoiding defects such as cracks caused by stress inside the gel due to rapid temperature changes. Under these temperature and time conditions, the gel can undergo sufficient physical and chemical changes, transforming into a dense ceramic layer. The dense ceramic layer has excellent barrier properties, effectively preventing external corrosive media such as salt spray from contacting the workpiece surface, thereby significantly improving the workpiece's salt spray resistance. Simultaneously, during this sintering process, some of the flexibility of the organosilicon is retained, allowing the formed protective layer to possess high hardness and corrosion resistance while also adapting to workpiece deformation to a certain extent, preventing the protective layer from cracking due to slight workpiece deformation, further enhancing the stability and durability of the protective layer, and extending the workpiece's service life. Preferably, after step S2, the workpiece is subjected to plasma treatment to remove any complexing agents that may remain from step S2. By employing the above technical solution for plasma treatment, any residual complexing agent that may have remained in step S2 can be removed, preventing the residual complexing agent from affecting subsequent processing and workpiece performance. Preferably, the working gas for plasma treatment is compressed air with a frequency of 10-50 kHz and a power density of 50-200 W / cm². 2 By adopting the above technical solution, the workpiece is subjected to plasma treatment after step S2, and the working gas is compressed air at a frequency of 10-50kHz and a pressure of 50-200W / cm². 2 At a power density of [specific value], compressed air can generate a large number of high-energy and highly reactive particles in a plasma environment at that frequency and power density. These particles come into full contact with the workpiece surface and can undergo physical and chemical reactions with any complexing agent that may remain from step S2, decomposing the complexing agent and removing it from the workpiece surface.

[0006] In summary, this application includes at least one of the following beneficial technical effects: 1. First, immerse the workpiece in dilute nitric acid for pickling, which dissolves carbides and oxide scale. Then, neutralize the acidic residue with a weak alkaline solution, followed by washing and drying. This process removes carbides, oxide scale, and acidic residue. Using a chromium-containing metal ion solution and a complexing agent, react at 60-80℃ for 25-40 minutes to replace iron atoms and chromium ions on the workpiece surface, forming a continuous chromium-rich passivation film. This film effectively isolates the workpiece from external corrosive media, improving its corrosion resistance and addressing the corrosion problems of 17-4 stainless steel in highly corrosive environments. To address the issue of insufficient corrosion resistance, a composite sol-gel treatment is employed, consisting of zirconium oxide, silane coupling agents containing amino or epoxy groups, and organosilicon. This treatment forms a uniform, continuous, and dense protective layer on the workpiece surface, significantly improving the salt spray resistance and corrosion resistance of 17-4 stainless steel, resulting in salt spray resistant stainless steel products. The entire process meets environmental protection requirements and can satisfy the needs of large-scale, low-cost production. 2. The pH value of the solution in step S2 is adjusted to 4-7. Within this pH range, the acidity or alkalinity of the solution is moderate, neither too acidic nor too alkaline, which is beneficial for Cr... 3+ Stable existence, avoiding Fe 2+ Hydrolysis and precipitation facilitate the displacement reaction; 3. The graded drying and sintering process removes physically adsorbed water and chemically bound water, preventing gel cracking. It transforms the gel into a dense ceramic layer while retaining some of the flexibility of organosilicon, giving the product high hardness and corrosion resistance while also adapting to workpiece deformation to a certain extent. This prevents the protective layer from cracking due to slight workpiece deformation, further enhancing the stability and durability of the protective layer and extending the service life of the workpiece. Detailed Implementation

[0007] The present application will be further described in detail below with reference to the embodiments.

[0008] Introduction to some raw materials: Polyethylene glycol: Tianjin Zhonghe Shengtai Chemical Co., Ltd., CAS No.: 25322-68-3; Organosilicon sol: Guangzhou Fuer Chemical Technology Co., Ltd., CAS No.: 112926-00-8. Example

[0009] Example 1 A salt spray resistant composite surface treatment process for 17-4 stainless steel is prepared by the following method: S1 The workpiece is immersed in 10% dilute nitric acid for 20 minutes, then immersed in 5% sodium hydroxide solution for 20 minutes, and finally rinsed with deionized water for 10 minutes and dried for later use. S2 involves immersing the workpiece in a 5% chromium sulfate solution, adding a complexing agent of 0.25% sodium oxalate, adjusting the pH of the solution to 5 with dilute sulfuric acid, and reacting for 30 minutes at a constant temperature water bath of 70°C to replace the iron atoms and chromium ions on the surface of the workpiece, thereby forming a continuous chromium-rich passivation film on the surface of the workpiece. S3 involves coating the entire workpiece with a composite sol made of zirconium oxide, a silane coupling agent containing amino or epoxy groups, and organosilicon. The coating is held for 10 minutes, then the workpiece is removed and sequentially subjected to centrifugation, gelation treatment, drying, and sintering to obtain a salt spray resistant stainless steel product. The coating amount in step S3 is 200 g / m². 2 .

[0010] The centrifugal spinning conditions were 1000 rpm for 1 min; the gelation treatment conditions were: standing for 1 h in an environment with 50% humidity; the drying method was a staged drying method: first, the workpiece was dried in a 60℃ oven for 2 h to remove physically adsorbed water; then the workpiece was transferred to a 120℃ vacuum dryer for 4 h; the sintering method was: the oven was heated to 400℃ at a rate of 2℃ / min and held for 2 h. The composite sol in this embodiment is prepared by the following steps: Zirconia sol: 70% zirconium propoxide, 10% nitric acid, amino-containing silane coupling agent and 75% ethanol are mixed in a mass ratio of 5:1:5:25, stirred for 30 minutes until uniform and transparent, and heated in a water bath at 60°C for 2 hours to obtain a zirconium oxide sol with a particle size of 10-50 nm; the amino-containing silane coupling agent is γ-aminopropyltriethoxysilane coupling agent.

[0011] A composite sol was prepared by mixing zirconia sol, dispersant, and organosilicon sol in a mass ratio of 15:1:5 and ultrasonically treating the mixture for 15 minutes to obtain a uniform and stable zirconia and organosilicon blend sol. Polyethylene glycol was used as the dispersant.

[0012] Example 2 The difference between Example 2 and Example 1 is that sodium sulfate is used as the complexing agent.

[0013] Example 3 The difference between Example 3 and Example 1 is that the complexing agent used is sodium citrate.

[0014] Example 4 The difference between Example 4 and Example 1 is that the pH value of the solution in step S2 is adjusted to 7.

[0015] Example 5 Example 5 differs from Example 1 in that it uses a silane coupling agent containing an epoxy group, specifically γ-glycidoxypropyltrimethoxysilane coupling agent.

[0016] Example 6 The difference between Example 6 and Example 1 is that in step S3, the workpiece is fully coated with composite sol and vacuumed to (-0.08) MPa.

[0017] Example 7 The difference between Example 7 and Example 1 is that: after step S2, the workpiece is subjected to plasma treatment to remove any residual complexing agent that may have remained in step S2. The working gas for plasma treatment is compressed air, with a frequency of 10-50 kHz and a power density of 50-200 W / cm². 2 .

[0018] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the zirconium oxide sol was replaced with an equal amount of organosilicon sol.

[0019] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the organosilicon sol was replaced with an equal amount of zirconium oxide sol.

[0020] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the γ-aminopropyltriethoxysilane coupling agent was replaced with an equal amount of zirconium propoxide.

[0021] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the pH value of the solution in step S2 is adjusted to 2.

[0022] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that the pH value of the solution in step S2 is adjusted to 9.

[0023] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that the composite sol was replaced in equal amounts with C610 sealing agent produced by Suzhou Jiuchen Environmental Protection Technology Co., Ltd.

[0024] Performance testing Salt spray resistant stainless steel products obtained in Examples 1-7 and Comparative Examples 1-6 were used as samples. Corrosion resistance and wear resistance of each sample were measured using the corresponding test methods. Specific data are shown in Table 1.

[0025] Test Methods / Experimental Methods Corrosion Resistance Test: Acidic Salt Spray Test: The test standard is GB / T 10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test". The test uses a 5% NaCl solution with added copper salt, pH=6.5, and the salt spray chamber temperature is maintained at 37℃. Copper salt accelerates corrosion. Continuous spraying is used on all surfaces of the workpiece. The test duration is 14 days. The corrosion area of ​​each sample surface is observed at the same time each day, and the number of days it takes for rust to appear is recorded. Samples showing rust within 4 days are considered unqualified; samples showing rust within 4 to 7 days are considered qualified (Class B); samples showing rust after 7 days are considered qualified (Class A); and samples showing rust after 14 days are considered qualified (Class A+).

[0026] Abrasion resistance: The test standard GB / T 1768-2006 "Determination of Abrasion Resistance of Paints and Varnishes - Rotary Rubber Grinding Wheel Method" was selected. A 12.7mm thick rubber grinding wheel with an outer diameter of 51.6mm was used, and the turntable speed was 60 r / min. The test environment was 23℃ and 50% relative humidity. Samples that passed the acid salt spray test were cut to standard dimensions of 100mm × 100mm. A 500g weight was applied to the rubber grinding wheel, and the samples were polished to simulate actual friction pressure. The number of friction cycles was set to 1000, and the wear was recorded. Standard sandpaper with a grit size of P300 was used as the abrasion medium. The abrasion resistance was evaluated by measuring the mass change of each sample before and after wear. Based on the test results, the abrasion resistance of each sample coating was classified into four levels: excellent, good, medium, and poor. The grades are classified according to the following standards: Excellent: mass loss ≤50mg / 1000 rpm, or wear depth ≤10μm; Good: Mass loss is 50-100 mg / 1000 rpm, or wear depth is 10-20 μm; Medium: mass loss is 100-200 mg / 1000 rpm, or wear depth is 20-50 μm; Poor: Mass loss > 200 mg / 1000 rpm, or wear depth > 50 μm.

[0027] The experimental data above are shown in Table 1.

[0028] Table 1. Experimental data of Examples 1-7 and Comparative Examples 1-6 The experimental analysis results are as follows: Regarding corrosion resistance: First, the experimental results in Table 1 show that Examples 1-3 and Example 5 all achieved Class A qualification, indicating that under the conditions that the complexing agent is sodium oxalate, sodium sulfate, sodium citrate, and the silane coupling agent is γ-aminopropyltriethoxysilane or γ-glycidoxypropyltrimethoxysilane, and the pH value of the solution in step S2 is 5 or 7, this anti-salt spray composite surface treatment process can give 17-4 stainless iron products good corrosion resistance, and rust will not appear for more than 7 days or even 14 days in acidic salt spray test.

[0029] Secondly, the results of Example 4 show that when the pH value of the solution in step S2 of Example 4 is adjusted to 7, the corrosion resistance drops to the qualified Class B, indicating that pH value has a certain impact on corrosion resistance, and the corrosion resistance is better when the pH value is 5. The results of Examples 6 and 7 show that in Example 6, the vacuum was drawn to (-0.08) MPa when coating the composite sol in step S3, and in Example 7, plasma treatment was performed after step S2. Both of them achieved the qualified Class A+ corrosion resistance, indicating that vacuum treatment and plasma treatment help to further improve the corrosion resistance of the product, make the coating more dense and uniform, and thus better resist salt spray corrosion.

[0030] By comparing the experimental results of the examples with those of the comparative examples, it was found that comparative examples 1-5 were all unqualified, while comparative example 6 was qualified (Class B). Comparative Example 1 replaced an equal amount of zirconium oxide sol with organosilicon sol; Comparative Example 2 replaced an equal amount of organosilicon sol with zirconium oxide sol; and Comparative Example 3 replaced an equal amount of γ-aminopropyltriethoxysilane coupling agent with n-zirconium propoxide. This demonstrates that the synergistic effect of zirconium oxide sol, organosilicon sol, and silane coupling agent significantly improves the corrosion resistance of the product. If any one of these three is missing, the resulting salt spray resistant stainless iron product is prone to rusting under strong corrosive environments. Clearly, the acidic salt spray test results for Comparative Examples 1-3 all showed rusting within 96 hours. The silane coupling agent enhances the bonding force between zirconium oxide and organosilicon, allowing them to mix at the molecular level and form chemical bonds that enhance interfacial adhesion, preventing phase separation. Zirconium oxide provides temperature resistance, wear resistance, and corrosion resistance, while organosilicon imparts crack resistance, sealing, and weather resistance. The combined coating of these two components improves the overall performance of the sealing adhesive, ultimately resulting in a stainless iron product with excellent salt spray resistance.

[0031] The pH values ​​of the solutions in step S2 of Comparative Examples 4 and 5 were adjusted to 2 and 9, respectively, and the results were both unqualified. This indicates that excessive acidity or alkalinity can disrupt the displacement reaction between chromium metal ions and iron atoms on the workpiece surface, thus ultimately affecting the salt spray resistance of the product. Comparative Example 6 replaced the composite sol with an equal amount of C610 sealant produced by Suzhou Jiuchen Environmental Protection Technology Co., Ltd. Although it showed some corrosion resistance, it was far inferior to the composite sol treatment effect in Examples 1-7 of this application, demonstrating that the composite sol formulation of this application has a unique advantage in corrosion resistance.

[0032] In terms of wear resistance: The wear resistance of Examples 1-5 remained good after salt spray testing, indicating that under current process conditions, the product has good wear resistance and can meet the requirements for long-term use in highly corrosive environments. Examples 6 and 7 achieved excellent wear resistance. Combined with the corrosion resistance results, it can be seen that vacuum treatment and plasma treatment not only improved corrosion resistance but also significantly enhanced wear resistance, making the coating more robust and reducing mass loss and wear track depth during the wear process.

[0033] In contrast, the comparative examples 1-5 failed the salt spray resistance test, indicating that their wear resistance is also meaningless given their substandard corrosion resistance. Table 1 shows that Comparative Example 6 exhibits poor wear resistance, a stark contrast to Examples 1-7. This demonstrates that while the C610 sealant produced by Suzhou Jiuchen Environmental Protection Technology Co., Ltd. provides some corrosion resistance, its wear resistance is poor, making it prone to surface peeling under prolonged exposure to strong corrosive environments, as mentioned in the background section, leading to easy corrosion. In contrast, this application uses a composite sol-gel formulation to treat the pores, maintaining strong wear resistance and preventing surface peeling even under prolonged exposure to strong corrosive environments. This further proves the effectiveness of the composite sol-gel formulation and overall treatment process in improving the corrosion and wear resistance of the product. The process in this application demonstrates significant advantages in both corrosion and wear resistance, possessing high practical value and promotional significance.

[0034] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A salt spray resistant composite surface treatment process for 17-4 stainless steel, characterized in that, Includes the following steps: S1 The workpiece is immersed in dilute nitric acid to pickle and dissolve carbides and oxide scale, then immersed in a weak alkaline solution to neutralize acid residue, and finally washed with water and dried for later use. S2 involves immersing the workpiece in a solution containing chromium metal ions, adding a complexing agent to react, adjusting the pH value to 4-7, replacing iron atoms and chromium ions on the workpiece surface, and forming a continuous chromium-rich passivation film on the workpiece surface. S3 coats the entire workpiece with a composite sol, holds it for 10-15 minutes, and then takes out the workpiece and sequentially performs centrifugal spinning, gelation treatment, drying and sintering to obtain salt spray resistant stainless iron products. The composite sol is composed of zirconium oxide, silane coupling agents containing amino or epoxy groups, and organosilicon blend sol.

2. The process according to claim 1, characterized in that, The complexing agent is at least one of sulfate, oxalate, or sodium citrate.

3. The process according to claim 1, characterized in that, In step S2, the solution pH is adjusted to 5.

4. The process according to claim 1, characterized in that, The conditions for the displacement treatment in step S2 are a temperature of 60-80℃ and a reaction time of 25-40 min.

5. The process according to claim 1, characterized in that, The preparation method of the zirconium oxide and organosilicon blend sol includes the following steps: Zirconia sol: Zirconium propoxide, nitric acid, silane coupling agent containing amino or epoxy groups and ethanol are mixed in a mass ratio of 5:1:5:25, stirred for 30 minutes until uniform and transparent, and heated in a water bath at 60°C for 2 hours to obtain zirconia sol with a particle size of 10-50 nm. Preparation of composite sol: Zirconia sol, dispersant and organosilicon sol are mixed in a mass ratio of 15:1:5 and ultrasonically treated for 15 minutes to obtain a uniform and stable zirconia and organosilicon blend sol.

6. The process according to claim 1, characterized in that, In step S3, the workpiece is fully coated with the composite sol, and a vacuum is applied to a pressure of (-0.08) - (-0.05) MPa.

7. The process according to claim 1, characterized in that, In step S3, the drying process adopts a graded drying method, which includes the following steps: first, the workpiece is dried in an oven at 60°C for 2 hours to remove physically adsorbed water; then, the workpiece is transferred to a vacuum dryer at 120°C for 4 hours to remove chemically bound water and prevent gel cracking.

8. The process according to claim 7, characterized in that, The sintering method described in step S3 is as follows: After graded drying, the oven is heated to 400°C at a rate of 2°C / min and held for 2 hours to transform the gel into a dense ceramic layer while retaining some of the flexibility of the organosilicon.

9. The process according to claim 1, characterized in that, After step S2, the workpiece is subjected to plasma treatment to remove any complexing agent that may remain from step S2.

10. The process according to claim 9, characterized in that, The working gas for plasma treatment is compressed air with a frequency of 10-50 kHz and a power density of 50-200 W / cm².

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