Stainless steel surface passivation treatment process

Abstract

The invention relates to the field of metal surface treatment, and particularly discloses a stainless steel surface passivation treatment process. The stainless steel surface passivation treatment process comprises the following steps: pre-cleaning by adopting an alkaline cleaning agent, and soaking at 60-80 DEG C for 5-10 minutes; the pre-cleaned workpiece is placed in a passivation solution containing chromate, molybdate and a corrosion inhibitor to be subjected to passivation treatment, and dipping is conducted for 20-30 min at the temperature of 30-80 DEG C; and after passivating treatment, the workpiece is cleaned and dried. The stainless steel surface passivation treatment process has the beneficial effect that the corrosion resistance of the aviation fastener is greatly improved, and the requirements for environmental protection and efficient production are met.

Description

Technical Field

[0001] The present invention relates to the field of metal surface treatment, and more specifically, to a stainless steel surface passivation treatment process. Background Art

[0002] In today's industrial field, stainless steel has become the preferred material in many key application scenarios due to its excellent mechanical properties and outstanding corrosion resistance, and the aerospace field is the key place for it to display its skills. Aviation equipment often needs to operate in complex, changeable and harsh environments. The high strength of stainless steel can meet the needs of aircraft structural parts to withstand huge stress, and its corrosion resistance ensures that the components can maintain stable performance under conditions of high humidity, large temperature differences and contact with various chemical media, laying a solid foundation for the safety and reliability of aviation flight.

[0003] However, even though stainless steel has many advantages, its surface protection barrier faces severe tests once it encounters extreme conditions. In extreme environments such as high temperature, high humidity, strong acid and alkali or high salt spray, the surface of stainless steel is prone to oxidation reaction, forming a loose oxide layer, which accelerates corrosion and greatly reduces the overall performance of the material. This surface degradation phenomenon not only weakens the original mechanical strength of stainless steel, but may also cause potential safety hazards in key aviation components such as fasteners.

[0004] In order to enhance the surface performance of stainless steel, the industry has developed and widely applied a series of traditional surface treatment technologies. Electroplating technology uses the principle of electrochemical deposition to coat a metal coating with special properties on the surface of stainless steel, such as chrome plating to enhance hardness and wear resistance, and zinc plating to improve corrosion resistance; heat treatment methods use high temperatures to change the microstructure of the material and optimize surface properties; chemical conversion film technology uses chemical reactions to generate a dense protective film on the surface of stainless steel, such as common phosphating films and chromate conversion films. These methods have helped stainless steel expand its application boundaries, but with the development of the times and increasingly stringent requirements in multiple dimensions such as environmental protection, efficiency, and cost, their shortcomings have become increasingly prominent.

[0005] On the one hand, the electroplating process consumes a large amount of expensive metal raw materials, and the preparation, maintenance and subsequent waste liquid treatment of the electroplating solution are expensive; heat treatment has strict requirements on equipment and huge energy consumption, coupled with complex process parameter control and professional labor costs, which makes the overall processing cost rise; chemical conversion films also face the procurement of high-priced chemical reagents and the backlog of time costs caused by complicated processing procedures.

[0006] On the other hand, the heavy metal waste liquid generated by electroplating and the discharge of toxic and harmful substances such as chromate involved in the chemical conversion film process, if not handled properly, will cause irreversible and severe pollution to the soil and water sources, greatly endangering the ecological balance, which runs counter to the green and sustainable development concept advocated by the world today. Summary of the invention

[0007] In order to significantly improve the corrosion resistance of aviation fasteners and meet the needs of green environmental protection and efficient production, the present application provides a stainless steel surface passivation treatment process.

[0008] The present application provides a stainless steel surface passivation treatment process using the following technical solutions: A stainless steel surface passivation treatment process comprises the following steps: Use alkaline cleaning agent for pre-cleaning, soaking at 60-80℃ for 5-10 minutes; The pre-cleaned workpiece is placed in a passivation solution containing chromate, molybdate and corrosion inhibitor for passivation treatment, and immersed at 30-80°C for 20-30 minutes; After passivation treatment, the workpiece is cleaned and dried.

[0009] By adopting the above technical solution, the oil, impurities, etc. on the surface of stainless steel can be effectively removed by soaking in an alkaline cleaning agent at 60-80℃ for 5-10 minutes, providing a clean surface for subsequent passivation treatment, so that the passivation liquid can better contact and react with the stainless steel surface, thereby improving the quality and bonding strength of the passivation film. The pre-cleaned workpiece is placed in a passivation solution containing chromate, molybdate and corrosion inhibitor, and immersed at 30-80℃ for 20-30 minutes to form a passivation film on the stainless steel surface, which can effectively isolate the contact between air, water and other corrosive media and the stainless steel substrate, thereby improving the corrosion resistance of stainless steel. Timely cleaning and drying after passivation treatment can remove the passivation liquid and impurities remaining on the surface to prevent them from having adverse effects on the passivation film, further ensuring the passivation effect and the appearance quality of the workpiece. The entire process consists of only three steps: pre-cleaning, passivation treatment, and cleaning and drying. Compared with traditional heat treatment processes, it does not require complicated heating, insulation, and cooling curve control, nor does it have lengthy and cumbersome pre-treatment and post-treatment steps like the chemical conversion film process. It greatly shortens the surface treatment cycle of a single aviation fastener, improves production efficiency, and meets the needs of rapid iteration and mass production in the aerospace industry.

[0010] Optionally, the passivation solution contains 2-5% chromate, 1-3% molybdate, and 1-3% corrosion inhibitor by mass percentage, and the pH value of the passivation solution is 3-5.

[0011] By adopting the above technical solution, 2-5% chromate is added to the passivation solution. During the passivation process, chromate reacts with the surface of stainless steel to form a chromium-rich passivation film. This passivation film has good corrosion resistance and stability, and can significantly improve the corrosion resistance of stainless steel in extreme environments. The addition of 1-3% molybdate can further enhance the corrosion resistance of the passivation film. Molybdenum can synergize with elements such as chromium to optimize the structure and performance of the passivation film, making it denser and stronger, so as to better resist the erosion of extreme environments such as high temperature, high humidity, strong acid and alkali or high salt spray. The corrosion inhibitor with a content of 1-3% can slow down the corrosion rate of the metal during the passivation process, and also help to improve the quality and uniformity of the passivation film, so that the passivation film can cover the stainless steel surface more completely, reduce the formation of defects and pores, and thus enhance the corrosion resistance of stainless steel. The pH value of the passivation solution is controlled at 3-5. This acidic range is conducive to the passivation reaction, which can promote the rapid formation and growth of the passivation film, and can make the performance of the passivation film reach the optimal state, ensuring that the stainless steel has good corrosion resistance and stability in various extreme environments. Compared with the large-scale use of chromates in traditional electroplating and other processes, the passivation solution of this application greatly reduces the use of chromium elements. Due to the low amount of chromate used, pollutants such as chromium-containing wastewater generated are also reduced, reducing the risk of environmental pollution, and also reducing the pressure of subsequent environmental protection treatment, which meets the requirements of today's green industrial development.

[0012] Optionally, the passivation solution further includes 0.1-0.5% by mass of nanoparticles, wherein the nanoparticles include one of nanosilver particles, nanobarium titanate particles or titanate-modified barium titanate nanoparticles.

[0013] By adopting the above technical solution, 0.1-0.5% of nanoparticles, such as nanosilver particles, nanobarium titanate particles or titanate-modified barium titanate nanoparticles, are added to the passivation solution. These nanoparticles have the characteristics of small size effect and high surface activity. They can fill the defects and pores of the passivation film, making the passivation film denser, thereby improving the protective performance of the passivation film. The nanoparticles can also interact with other components in the passivation film to further enhance the stability and corrosion resistance of the passivation film.

[0014] Optionally, the preparation method of the titanate-modified barium titanate nanoparticles is: The barium titanate nanoparticles are added into anhydrous ethanol and ultrasonically dispersed to obtain a suspension; Add isopropyl triisostearoyl titanate dropwise to the suspension, wherein the amount of isopropyl triisostearoyl titanate added is 3-5% of the mass of the barium titanate nanoparticles. After the addition is completed, heat the suspension to 60-80° C. and keep it warm for 3-5 hours, stirring at a speed of 3000-5000 rpm during the heat preservation period. After the reaction is completed, the solid product is separated, washed and dried to obtain titanate-modified barium titanate nanoparticles.

[0015] By adopting the above technical scheme, barium titanate nanoparticles are added to anhydrous ethanol for ultrasonic dispersion, so that the barium titanate nanoparticles can be evenly dispersed in the solution to avoid the occurrence of agglomeration, thereby ensuring that the titanate ester can be evenly coated on the surface of the barium titanate nanoparticles in the subsequent reaction, and improving the quality and performance of the titanate-modified barium titanate nanoparticles. Triisostearyl isopropyl titanate is added to the suspension, and the titanate ester reacts with the barium titanate nanoparticles to form a stable chemical bond, thereby achieving effective modification of the barium titanate nanoparticles. The modified barium titanate nanoparticles have better compatibility and dispersibility, can better play a role in the passivation solution, and further improve the quality and performance of the passivation film. After the reaction is completed, it is washed and dried to remove unreacted impurities and by-products, ensuring the purity and activity of the nanoparticles, so that it can better play the role of filling, strengthening, etc. in the passivation solution, and improve the protective effect of the passivation film.

[0016] Optionally, the workpiece is also subjected to pulse current auxiliary treatment simultaneously with the passivation treatment.

[0017] By adopting the above technical solution, pulse current auxiliary treatment is carried out synchronously when the workpiece is passivated, which can promote the passivation reaction and make the formation of the passivation film more uniform and rapid. The pulse current can change the electrochemical state of the stainless steel surface, accelerate the adsorption and reaction of ions in the passivation solution on the stainless steel surface, thereby increasing the growth rate and quality of the passivation film, enhancing the density and stability of the passivation film, and further improving the corrosion resistance of stainless steel in extreme environments.

[0018] Optionally, the pulse current assisted processing uses a 50-70 Hz pulse current, the duty cycle of the pulse current is 20-30%, and the amplitude of the pulse current is 0.5-1 A / dm².

[0019] By adopting the above technical solution, the pulse current can promote the passivation reaction to the greatest extent without damaging the stainless steel substrate, so that the performance of the passivation film reaches the best state. The frequency, duty cycle and amplitude of the present application can optimize the growth rate and structure of the passivation film, making it denser and more uniform, thereby improving the corrosion resistance, wear resistance and other properties of stainless steel.

[0020] Optionally, the corrosion inhibitor includes 40-50% sodium tungstate, 30-40% sodium gluconate and 10-30% inositol hexaphosphate in terms of mass percentage.

[0021] By adopting the above technical scheme, sodium tungstate can form a protective film on the surface of stainless steel to slow down the corrosion reaction; sodium gluconate has good corrosion inhibition and coordination ability, and can form a stable complex with metal ions to further inhibit the corrosion reaction; phytic acid is a highly efficient corrosion inhibitor, which can be adsorbed on the surface of stainless steel to prevent the contact between the corrosive medium and the metal surface, and also has certain antioxidant properties. The synergistic effect of these three components can significantly improve the corrosion inhibition effect of the corrosion inhibitor, thereby enhancing the corrosion resistance of stainless steel.

[0022] Optionally, the passivation treatment temperature is 60-70° C. and the time is 25-30 minutes.

[0023] In summary, this application has the following beneficial effects: 1. Since the present application adopts the synergistic effect of chromate, molybdate and corrosion inhibitor in the passivation solution, chromate forms a chromium-rich passivation film, molybdate synergistically optimizes the film structure, and the corrosion inhibitor slows down the corrosion rate. The three work together to make the passivation film dense and stable, greatly improving the corrosion resistance of stainless steel, and can resist erosion in extreme environments such as high temperature, high humidity, strong acid and alkali or high salt spray.

[0024] 2. Compared with the traditional electroplating process, this application produces a large amount of waste liquid containing heavy metals. Although this solution contains chromate, the dosage is precisely controlled, and other ingredients are combined to optimize the passivation effect, reduce dependence on heavy metals, reduce the discharge of heavy metal waste liquid, and reduce the risk of soil and water pollution, which is in line with the concept of green and sustainable development.

[0025] 3. The method of the present application can complete the surface passivation of the workpiece through pre-cleaning, passivation treatment, cleaning and drying. The process operation of the present application is simple, which reduces the process difficulty and operation cost, does not require complex equipment and cumbersome operations, improves production efficiency, is suitable for mass production, and can effectively meet the requirements of production efficiency and quality stability of aviation fasteners. DETAILED DESCRIPTION

[0026] The present application is further described in detail below in conjunction with the examples. It is particularly noted that if no specific conditions are specified in the following examples, the experiments are carried out according to conventional conditions or the conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following examples can be obtained from common commercial sources.

[0027] Preparation example of titanate modified barium titanate nanoparticles Preparation Example 1 Preparation of titanate-modified barium titanate nanoparticles: Select barium titanate nanoparticles with a particle size of 20-100 nm and a purity of more than 99%. Prepare triisostearyl titanate isopropyl ester and anhydrous ethanol, both of which are analytically pure.

[0028] 100g of barium titanate nanoparticles were added to 1L of anhydrous ethanol, and then placed in an ultrasonic cleaner for 30 minutes with a power setting of 250 W. During the ultrasonic process, the nanoparticles gradually dispersed in the ethanol to form a preliminary suspension. The suspension was then transferred to a high shear dispersing emulsifier and stirred at 6000 rpm for 30 minutes to fully disperse the nanoparticles in the suspension.

[0029] 4 g of isopropyl triisostearyl titanate was slowly added dropwise to the suspension with continuous stirring at a speed of 4000 rpm. After the addition was completed, the temperature of the reaction system was raised to 70±2°C and maintained at this temperature for 4 hours while continuing to stir at a speed of 4000 rpm.

[0030] After the reaction is completed, the reaction system is naturally cooled to room temperature, the modified barium titanate nanoparticles are separated from the solution by centrifugal separation, the modified barium titanate nanoparticles are washed with anhydrous ethanol, and the washed nanoparticles are placed in a vacuum drying oven and dried at 60° C. for 12 hours to obtain titanate-modified barium titanate nanoparticles.

[0031] Preparation Example 2 Preparation of titanate-modified barium titanate nanoparticles: The difference from Preparation Example 1 is that 3 g of isopropyl triisostearoyl titanate is slowly added dropwise into the suspension with a continuous stirring speed of 4000 rpm.

[0032] Preparation Example 3 Preparation of titanate-modified barium titanate nanoparticles: The difference from Preparation Example 1 is that 5 g of isopropyl triisostearoyl titanate is slowly added dropwise into the suspension with a continuous stirring speed of 4000 rpm.

[0033] Preparation Example 4 Preparation of titanate-modified barium titanate nanoparticles: The difference from Preparation Example 1 is that 2 g of isopropyl triisostearoyl titanate is slowly added dropwise into the suspension with a continuous stirring speed of 4000 rpm.

[0034] Preparation Example 5 Preparation of titanate-modified barium titanate nanoparticles: The difference from Preparation Example 1 is that 6 g of isopropyl triisostearoyl titanate is slowly added dropwise into the suspension with a continuous stirring speed of 4000 rpm.

[0035] Example 1 A stainless steel surface passivation treatment process: Pre-clean the surface of the workpiece to be treated with an alkaline cleaning agent, soak the workpiece in a sodium hydroxide solution with a mass concentration of 5%, heat the solution to 70°C and keep it warm, and soak for 5-10 minutes; The pre-cleaned workpiece is immersed in a passivation solution, which contains 3% potassium chromate, 2% sodium molybdate, 2% corrosion inhibitor by mass percentage, and the rest is pure water. The pH value of the passivation solution is between 3 and 5. The passivation solution is heated to 65°C and kept warm for 25 minutes. Among them, the corrosion inhibitor components are 45% sodium tungstate, 35% sodium gluconate and 20% inositol hexaphosphate by mass percentage. After passivation treatment, rinse the workpiece surface with running water immediately and then allow it to dry naturally.

[0036] Example 2 A stainless steel surface passivation treatment process: Pre-clean the surface of the workpiece to be treated with an alkaline cleaning agent, soak the workpiece in a sodium hydroxide solution with a mass concentration of 5%, heat the solution to 70°C and keep it warm, and soak for 5-10 minutes; The pre-cleaned workpiece is immersed in a passivation solution, which contains 2% potassium chromate, 1% sodium molybdate, 1% corrosion inhibitor by mass percentage, and the rest is pure water. The pH value of the passivation solution is between 3-5. The passivation solution is heated to 65°C and kept warm for 25 minutes. Among them, the corrosion inhibitor components are 45% sodium tungstate, 35% sodium gluconate and 20% inositol hexaphosphate by mass percentage. After passivation treatment, rinse the workpiece surface with running water immediately and then allow it to dry naturally.

[0037] Example 3 A stainless steel surface passivation treatment process: Pre-clean the surface of the workpiece to be treated with an alkaline cleaning agent, soak the workpiece in a sodium hydroxide solution with a mass concentration of 5%, heat the solution to 70°C and keep it warm, and soak for 5-10 minutes; The pre-cleaned workpiece is immersed in a passivation solution, which contains 5% potassium chromate, 3% sodium molybdate, 3% corrosion inhibitor by mass percentage, and the rest is pure water. The pH value of the passivation solution is between 3-5. The passivation solution is heated to 65°C and kept warm for 25 minutes. Among them, the corrosion inhibitor components are 45% sodium tungstate, 35% sodium gluconate and 20% inositol hexaphosphate by mass percentage. After passivation treatment, rinse the workpiece surface with running water immediately and then allow it to dry naturally.

[0038] Example 4 A stainless steel surface passivation treatment process: The difference from Example 1 is that the passivation solution contains 5% potassium chromate, 3% sodium molybdate, 3% corrosion inhibitor and 0.3% nano silver particles by mass percentage, and the rest is pure water.

[0039] Example 5 A stainless steel surface passivation treatment process: The difference from Example 1 is that the passivation solution contains 5% potassium chromate, 3% sodium molybdate, 3% corrosion inhibitor and 0.3% nano barium titanate particles by mass percentage, and the rest is pure water.

[0040] Example 6 A stainless steel surface passivation treatment process: The difference from Example 5 is that the passivation solution contains 5% potassium chromate, 3% sodium molybdate, 3% corrosion inhibitor and 0.1% nano barium titanate particles by mass percentage, and the rest is pure water.

[0041] Example 7 A stainless steel surface passivation treatment process: The difference from Example 5 is that the passivation solution contains 5% potassium chromate, 3% sodium molybdate, 3% corrosion inhibitor and 0.5% nano barium titanate particles by mass percentage, and the rest is pure water.

[0042] Example 8 A stainless steel surface passivation treatment process: The difference from Example 1 is that the passivation solution contains 5% potassium chromate, 3% sodium molybdate, 3% corrosion inhibitor and 0.3% titanate-modified barium titanate nanoparticles by mass percentage, and the rest is pure water. The titanate-modified barium titanate nanoparticles are prepared by Preparation Example 1.

[0043] Example 9 A stainless steel surface passivation treatment process: The difference from Example 8 is that the titanate-modified barium titanate nanoparticles are prepared by Preparation Example 2.

[0044] Example 10 A stainless steel surface passivation treatment process: The difference from Example 8 is that the titanate-modified barium titanate nanoparticles are prepared by Preparation Example 3.

[0045] Embodiment 11 A stainless steel surface passivation treatment process: Pre-clean the surface of the workpiece to be treated with an alkaline cleaning agent, soak the workpiece in a sodium hydroxide solution with a mass concentration of 5%, heat the solution to 70°C and keep it warm, and soak for 5-10 minutes; The pre-cleaned workpiece is immersed in the passivation solution, and a 60Hz pulse current is used to perform pulse current-assisted treatment on the workpiece; wherein the duty cycle of the pulse current is 25%, the amplitude of the pulse current is 0.8A / dm², the passivation solution contains 2% potassium chromate, 1% sodium molybdate, 1% corrosion inhibitor by mass percentage, and the rest is pure water, the pH value of the passivation solution is between 3-5, the passivation solution is heated to 65°C and kept warm for 25 minutes, and the corrosion inhibitor components are 45% sodium tungstate, 35% sodium gluconate and 20% inositol hexaphosphate by mass percentage; After passivation treatment, rinse the workpiece surface with running water immediately and then allow it to dry naturally.

[0046] Example 12 A stainless steel surface passivation treatment process: The difference from Example 1 is that the corrosion inhibitor components are 40% sodium tungstate, 30% sodium gluconate and 30% inositol hexaphosphate by mass percentage.

[0047] Example 13 A stainless steel surface passivation treatment process: The difference from Example 1 is that the corrosion inhibitor components are 50% sodium tungstate, 40% sodium gluconate and 10% inositol hexaphosphate by mass percentage.

[0048] Embodiment 14 A stainless steel surface passivation treatment process: The difference from Example 1 is that the passivation solution is heated to 30°C.

[0049] Embodiment 15 A stainless steel surface passivation treatment process: The difference from Example 1 is that the passivation solution is heated to 80°C.

[0050] Comparative Example 1 A stainless steel surface passivation treatment process: The difference from Example 1 is that the passivation solution does not contain potassium chromate.

[0051] Comparative Example 2 A stainless steel surface passivation treatment process: The difference from Example 1 is that the passivation solution does not contain sodium molybdate.

[0052] Comparative Example 3 A stainless steel surface passivation treatment process: The difference from Example 1 is that the passivation solution does not contain a corrosion inhibitor.

[0053] Comparative Example 4 A stainless steel surface passivation treatment process: The difference from Example 8 is that the titanate-modified barium titanate nanoparticles are prepared by Preparation Example 4.

[0054] Comparative Example 5 A stainless steel surface passivation treatment process: The difference from Example 8 is that the titanate-modified barium titanate nanoparticles are prepared by Preparation Example 5.

[0055] Detection Methods

[0056] According to GB / T 10125-2012 "Artificial Atmosphere Corrosion Test Salt Spray Test" standard, the treated workpieces of Examples 1-15 and Comparative Examples 1-5 were tested. The workpieces used were of the same size and shape. The treated workpieces were placed in a salt spray test chamber, and the salt spray concentration was set to 5% (mass fraction) of sodium chloride solution spray. The temperature in the chamber was maintained at 35±1°C, the relative humidity was set to 95%, and the spray time was set to 72 hours. After the test, the corrosion rate was calculated.

[0057] The corrosion rate calculation formula is: v = (m1-m2) / St Where v is the corrosion rate (g / m²・h), m1 and m2 are the mass of the sample before and after the test (g), S is the surface area of ​​the sample (m²), and t is the test time (h).

[0058] Table 1 Test data statistics Corrosion rate / (g / m²・h) Example 1 0.00041 Example 2 0.00047 Example 3 0.00044 Example 4 0.00037 Example 5 0.00035 Example 6 0.00038 Example 7 0.00036 Example 8 0.00031 Example 9 0.00033 Example 10 0.00032 Embodiment 11 0.00036 Example 12 0.00039 Example 13 0.00040 Embodiment 14 0.00045 Embodiment 15 0.00043 Comparative Example 1 0.00867 Comparative Example 2 0.00358 Comparative Example 3 0.00153 Comparative Example 4 0.00038 Comparative Example 5 0.00032 Combining Example 1 and Comparative Examples 1-3 and Table 1, it can be seen that the passivation solution in Example 1 contains potassium chromate, sodium molybdate and a corrosion inhibitor, and its corrosion rate is 0.00041 g / m²・h. After removing potassium chromate from Comparative Example 1, the corrosion rate increased to 0.00867 g / m²・h; after removing sodium molybdate from Comparative Example 2, the corrosion rate became 0.00358 g / m²・h; after removing the corrosion inhibitor from Comparative Example 3, the corrosion rate reached 0.00153 g / m²・h. This shows that potassium chromate plays a key role in the passivation process and can promote the formation of a chromium-containing oxide film on the surface of stainless steel, in which trivalent chromium ensures the stability of the film, and hexavalent chromium can self-repair when the film is damaged, which contributes significantly to reducing the corrosion rate. Sodium molybdate and potassium chromate work together to optimize the structure of the passivation film, fill the pores, and further improve the corrosion resistance. Its absence will increase the corrosion rate. Corrosion inhibitors can inhibit corrosion reactions in many ways, and build a protective barrier through adsorption, chelation, etc. Lack of corrosion inhibitors also leads to an increase in corrosion rate. This shows that potassium chromate, sodium molybdate and corrosion inhibitors each play an important role in the passivation process, and only by working together can a better passivation effect be achieved, effectively reducing the corrosion rate of stainless steel in a salt spray environment.

[0059] Combining Examples 8-10 and Comparative Examples 4-5 and Table 1, it can be seen that the amount of titanate modifier added has an effect on the modification effect of barium titanate nanoparticles. When the amount added is lower than the range of this application, the modification effect is poor due to insufficient amount of modifier, and the improvement of the passivation effect of the obtained titanate modified barium titanate nanoparticles becomes smaller; and when the amount added exceeds the range of this application, it does not further improve the passivation effect, so it is best within the range of this application.

[0060] It can be seen from Examples 1-3 and Table 1 that the corrosion rate fluctuates with the change of the content of potassium chromate, sodium molybdate and corrosion inhibitor, but is generally at a low level, and the content of each component needs to be reasonably matched to achieve a good passivation effect. Within the scope of this application, the component ratio of the passivation solution in Example 1 is the best for this application, so as to achieve efficient and economical passivation protection and ensure good corrosion resistance of stainless steel in a salt spray environment.

[0061] Combining Example 1 and Examples 4, 5, and 8 with Table 1, it can be seen that the addition of nanosilver particles, nanobarium titanate particles, and titanate-modified barium titanate nanoparticles can further reduce the corrosion rate of stainless steel to a certain extent, indicating that these nanoparticles have an enhancing effect on the corrosion resistance of the passivation film. Among them, the enhancement effect of titanate-modified barium titanate nanoparticles is relatively more obvious. After modification, it has better compatibility with the passivation solution and the stainless steel surface, can more effectively participate in the construction of the passivation film, optimize the structure of the film, and enhance the barrier ability to corrosive media, thereby better improving the corrosion resistance of stainless steel in a salt spray environment.

[0062] Combining Example 1 and Examples 5-7 with Table 1, it can be seen that the amount of nano-barium titanate particles added has an effect on the corrosion rate. Within a certain range, changing the content of nano-barium titanate particles will change the corrosion rate accordingly. The addition of 0.3% in Example 5 can make the corrosion rate reach a relatively lower value. If the addition amount is reduced, the enhancement effect on the passivation film is limited, and the corrosion rate is high; if the addition amount is too much, there will be problems such as uneven dispersion of nanoparticles, which affects the quality of the passivation film.

[0063] It can be seen from Example 1 and Example 11 and Table 1 that pulse current assisted treatment can improve the passivation effect and reduce the corrosion rate. The introduction of pulse current changes the electrochemical environment during the passivation process, accelerates the formation process of the passivation film, makes its structure more dense and uniform, and enhances the barrier ability to corrosive media, thereby showing better corrosion resistance in the salt spray test, indicating that pulse current assisted treatment is an effective means to improve the passivation effect of stainless steel and enhance corrosion resistance, and can be used in conjunction with traditional passivation processes to further optimize the protection effect.

[0064] It can be seen from Example 1 and Examples 12-15 and Table 1 that the change in the proportion of each component of the corrosion inhibitor will affect the corrosion rate. The proportion of the components of the corrosion inhibitor in Example 1 of the present application is the best in the present application. The heating temperature of the passivation solution also affects the corrosion rate. Too high or too low a temperature will increase the corrosion rate. Controlling the temperature at 60-70°C can ensure that the components in the passivation solution play a better role, promote the effective formation of the passivation film, and maintain good corrosion resistance.

[0065] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A stainless steel surface passivation treatment process, characterized in that: The following steps are involved: Use alkaline cleaning agent for pre-cleaning, soaking at 60-80℃ for 5-10 minutes; The pre-cleaned workpiece is placed in a passivation solution containing chromate, molybdate and corrosion inhibitor for passivation treatment, and immersed at 30-80°C for 20-30 minutes; After passivation treatment, the workpiece is cleaned and dried.

2. The stainless steel surface passivation treatment process according to claim 1, characterized in that: The passivation solution contains 2-5% of chromate, 1-3% of molybdate, and 1-3% of corrosion inhibitor by mass percentage, and the pH value of the passivation solution is 3-5.

3. The stainless steel surface passivation treatment process according to claim 2, characterized in that: The passivation solution also includes 0.1-0.5% of nanoparticles by mass, and the nanoparticles include one of nanosilver particles, nanobarium titanate particles or titanate-modified barium titanate nanoparticles.

4. The stainless steel surface passivation treatment process according to claim 3, characterized in that: The preparation method of the titanate-modified barium titanate nanoparticles is as follows: The barium titanate nanoparticles are added into anhydrous ethanol and ultrasonically dispersed to obtain a suspension; Add isopropyl triisostearoyl titanate dropwise to the suspension, wherein the amount of isopropyl triisostearoyl titanate added is 3-5% of the mass of the barium titanate nanoparticles. After the addition is completed, heat the suspension to 60-80° C. and keep it warm for 3-5 hours, stirring at a speed of 3000-5000 rpm during the heat preservation period. After the reaction is completed, the solid product is separated, washed and dried to obtain titanate-modified barium titanate nanoparticles.

5. The stainless steel surface passivation treatment process according to claim 1, characterized in that: The workpiece is also subjected to pulse current auxiliary treatment synchronously when undergoing the passivation treatment.

6. The stainless steel surface passivation treatment process according to claim 5, characterized in that: The pulse current assisted treatment uses a 50-70 Hz pulse current, the duty cycle of the pulse current is 20-30%, and the amplitude of the pulse current is 0.5-1 A / dm².

7. The stainless steel surface passivation treatment process according to claim 1, characterized in that: The corrosion inhibitor comprises, by mass percentage, 40-50% sodium tungstate, 30-40% sodium gluconate and 10-30% inositol hexaphosphate.

8. The stainless steel surface passivation treatment process according to claim 1, characterized in that: The passivation treatment temperature is 60-70° C. and the time is 25-30 minutes.