A passivation treatment process for stainless steel surface

Abstract

This application relates to the field of metal surface treatment, and specifically discloses a passivation treatment process for stainless steel surfaces. A passivation treatment process for stainless steel surfaces is as follows: pre-cleaning is carried out using an alkaline cleaning agent, and soaking is carried out at 60-80 °C for 5-10 minutes; the workpiece after pre-cleaning is placed in a passivation solution containing chromate, molybdate and corrosion inhibitor for passivation treatment, and impregnated at 30-80 °C for 20-30 minutes; after passivation treatment, the workpiece is cleaned and dried. The passivation treatment process for stainless steel surfaces of this application has the advantages of greatly improving the corrosion resistance of aviation fasteners and meeting the requirements of green environmental protection and high-efficiency production.

Description

Technical Field

[0001] This application relates to the field of metal surface treatment, and more specifically, to a passivation treatment process for stainless steel surfaces. Background Art

[0002] In today's industrial field, stainless steel materials have become the preferred materials in many key application scenarios due to their excellent mechanical properties and outstanding corrosion resistance. The aerospace field is especially where they can display their advantages. Aerospace equipment often needs to operate in complex, changeable, and harsh environments. The high strength of stainless steel can meet the requirements of aircraft structural components to withstand huge stresses, and its corrosion resistance ensures that components maintain stable performance under working conditions of high humidity, large temperature differences, and contact with various chemical media, laying a solid foundation for the safety and reliability of air travel.

[0003] However, even though stainless steel itself has many advantages, once it encounters extreme conditions, its surface protection barrier faces a severe test. In extreme environments such as high temperature, high humidity, strong acids and alkalis, or high salt spray, the surface of stainless steel is extremely prone to oxidation reactions, generating a loose oxide layer, which accelerates corrosion and greatly reduces the overall performance of the material. This surface deterioration phenomenon not only weakens the original mechanical strength of stainless steel but may also pose potential safety hazards at critical aerospace components such as fasteners.

[0004] To enhance the surface performance of stainless steel, the industry has developed and widely applied a series of traditional surface treatment technologies. The electroplating technology, based on the principle of electrochemical deposition, deposits a layer of metal coating with special properties on the surface of stainless steel. For example, chromium plating is used to enhance hardness and wear resistance, and zinc plating is used to improve corrosion resistance; heat treatment methods use high temperatures to change the microstructure of the material and optimize the surface performance; the chemical conversion film process generates a dense protective film on the surface of stainless steel through chemical reactions, such as common phosphating films, chromate conversion films, etc. These methods have helped stainless steel expand its application boundaries, but with the development of the times and the increasingly stringent requirements in multiple dimensions such as environmental protection, efficiency, and cost, their shortcomings have become more prominent.

[0005] On the one hand, the electroplating process requires a large amount of expensive metal raw materials, and the preparation, maintenance of electroplating solutions, and subsequent waste liquid treatment costs are high; heat treatment has strict requirements for equipment, consumes a large amount of energy, and with complex process parameter regulation and professional labor costs, the overall treatment cost increases; chemical conversion films also face the high cost of purchasing high - price chemical reagents and the backlog of time costs due to complex treatment processes.

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

[0007] In order to greatly improve the corrosion resistance of aviation fasteners and meet the requirements of green environmental protection and high-efficiency production, the present application provides a passivation treatment process for stainless steel surfaces.

[0008] The passivation treatment process for stainless steel surfaces provided by the present application adopts the following technical solutions:

[0009] A passivation treatment process for stainless steel surfaces includes the following steps:

[0010] Perform pre-cleaning with an alkaline cleaning agent and soak for 5 - 10 minutes under the condition of 60 - 80°C;

[0011] Place the workpiece after pre-cleaning in a passivation solution containing chromate, molybdate and corrosion inhibitor for passivation treatment, and immerse it for 20 - 30 minutes at 30 - 80°C;

[0012] After passivation treatment, clean and dry the workpiece.

[0013] By adopting the above technical solutions, soaking with an alkaline cleaning agent for 5 - 10 minutes under the condition of 60 - 80°C can effectively remove oil stains, impurities, etc. on the stainless steel surface, provide a clean surface for subsequent passivation treatment, enable the passivation solution to better contact and react with the stainless steel surface, thereby improving the quality and adhesion of the passivation film. Place the workpiece after pre-cleaning in a passivation solution containing chromate, molybdate and corrosion inhibitor, and immerse it for 20 - 30 minutes at 30 - 80°C 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. Cleaning and drying in time after passivation treatment can remove the residual passivation solution and impurities on the surface, prevent them from having an adverse effect on the passivation film, and further ensure 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 the traditional heat treatment process, it does not require complex control of the heating, heat preservation, and cooling curves, nor does it have the long 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 requirements of rapid iteration and batch production in the aerospace industry.

[0014] Optionally, the passivation solution contains 2 - 5% chromate, 1 - 3% molybdate, 1 - 3% corrosion inhibitor by mass percentage, and the pH value of the passivation solution is 3 - 5.

[0015] By adopting the above technical solution, 2-5% chromate is added to the passivation solution. During the passivation process, the chromate will react with the surface of the 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 elements can act synergistically with other 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 mist. The corrosion inhibitor with a content of 1-3% can slow down the corrosion rate of the metal during the passivation process, and at the same time contribute to improving the quality and uniformity of the passivation film, making the passivation film more completely cover the surface of the stainless steel, reducing the formation of defects and pores, and further enhancing the corrosion resistance of the stainless steel. Controlling the pH value of the passivation solution within the range of 3-5 is beneficial to the progress of the passivation reaction, 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 traditional electroplating and other processes that use a large amount of chromate, the passivation solution of this application greatly reduces the usage amount of chromium elements. Due to the low usage amount of chromate, the generation of pollutants such as chromium-containing wastewater is also reduced, reducing the environmental pollution risk, and at the same time reducing the pressure of subsequent environmental protection treatment, meeting the requirements of today's green industrial development.

[0016] Optionally, the passivation solution further includes 0.1-0.5% nanoparticles by mass percentage, and the nanoparticles include one of silver nanoparticles, barium titanate nanoparticles or titanate-modified barium titanate nanoparticles.

[0017] By adopting the above technical solution, 0.1-0.5% nanoparticles, such as one of silver nanoparticles, barium titanate nanoparticles or titanate-modified barium titanate nanoparticles, are added to the passivation solution. These nanoparticles have characteristics such as small size effect and high surface activity. They can fill the defects and pores of the passivation film to make the passivation film denser, thereby improving the protection 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.

[0018] Optionally, the preparation method of the titanate-modified barium titanate nanoparticles is as follows:

[0019] Add barium titanate nanoparticles into absolute ethanol and perform ultrasonic dispersion to obtain a suspension;

[0020] Drop isopropyl triisostearoyl titanate into the suspension. The addition amount of isopropyl triisostearoyl titanate is 3-5% of the mass of barium titanate nanoparticles. After dropping, heat the suspension to 60-80 °C and keep it warm for 3-5 hours. Stir at a speed of 3000-5000 rpm during the heat preservation period.

[0021] After the reaction ends, separate the solid product, wash and dry it to obtain titanate-modified barium titanate nanoparticles.

[0022] By adopting the above technical solution, adding barium titanate nanoparticles into absolute ethanol for ultrasonic dispersion can make the barium titanate nanoparticles evenly dispersed in the solution, avoiding the occurrence of agglomeration phenomenon, so as to ensure that the titanate can be evenly coated on the surface of barium titanate nanoparticles in the subsequent reaction, improving the quality and performance of titanate-modified barium titanate nanoparticles. Drop isopropyl triisostearoyl titanate into the suspension, and the titanate reacts with barium titanate nanoparticles to form stable chemical bonding, thus realizing the effective modification of 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 ends, through washing and drying, the unreacted impurities and by-products are removed, ensuring the purity and activity of the nanoparticles, enabling them to better play the roles of filling and strengthening in the passivation solution, and improving the protection effect of the passivation film.

[0023] Optionally, when the workpiece is passivated, pulse current assisted treatment is also carried out synchronously.

[0024] By adopting the above technical solution, carrying out pulse current assisted treatment synchronously when the workpiece is passivated can promote the passivation reaction, making the formation of the passivation film more uniform and rapid. The pulse current can change the electrochemical state of the stainless steel surface, accelerating 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 compactness and stability of the passivation film, and further improving the corrosion resistance of the stainless steel in extreme environments.

[0025] Optionally, 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.

[0026] By adopting the above technical solution, the pulse current can promote the passivation reaction to the greatest extent without damaging the stainless steel substrate, making the performance of the passivation film reach the best state. The frequency, duty cycle and amplitude of this application can optimize the growth rate and structure of the passivation film, making it more compact and uniform, thereby improving the corrosion resistance, wear resistance and other properties of the stainless steel.

[0027] Optionally, the corrosion inhibitor comprises 40-50% of sodium tungstate, 30-40% of sodium gluconate, and 10-30% of phytic acid by mass percentage.

[0028] By adopting the above technical solution, 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 performance and coordination ability, and can form stable complexes with metal ions to further inhibit the corrosion reaction; phytic acid is an efficient corrosion inhibitor, which can adsorb on the surface of stainless steel to prevent the contact between the corrosion medium and the metal surface, and at the same time 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.

[0029] Optionally, the passivation treatment temperature is 60-70 °C and the time is 25-30 minutes.

[0030] In summary, the present application has the following beneficial effects:

[0031] 1. Since the present application uses chromate, molybdate and corrosion inhibitor in the passivation solution to act together, 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 enabling it to resist erosion in extreme environments such as high temperature, high humidity, strong acid-base or high salt mist.

[0032] 2. Compared with the traditional electroplating process that produces a large amount of heavy metal waste liquid, although the present solution contains chromate, its dosage is accurately controlled, and it is combined with other components to optimize the passivation effect, reducing the dependence on heavy metals, reducing the discharge of heavy metal waste liquid, and reducing the risk of soil and water pollution, which conforms to the concept of green and sustainable development.

[0033] 3. The method of the present application can complete the passivation of the workpiece surface through pre-cleaning, passivation treatment, and cleaning and drying. The process of the present application is simple in operation, reducing the process difficulty and operation cost. It does not require complex equipment and cumbersome operations, improving the production efficiency, being suitable for mass production, and being able to effectively meet the requirements for production efficiency and quality stability of aviation fasteners, etc. Specific Embodiments

[0034] The following further elaborates on the present application with reference to embodiments. It should be specifically noted that: for those not specifying specific conditions in the following embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments can all be obtained from ordinary commercial sources.

[0035] Preparation Example of Titanate-Modified Barium Titanate Nanoparticles

[0036] Preparation Example 1

[0037] Preparation of titanate-modified barium titanate nanoparticles:

[0038] Select barium titanate nanoparticles with a particle size of 20 - 100 nm and a purity of over 99%. Prepare triisooctanoyl titanate isopropyl ester and absolute ethanol, both of which are of analytical purity.

[0039] Add 100 g of barium titanate nanoparticles to 1 L of absolute ethanol, then place it in an ultrasonic cleaner and ultrasonically treat for 30 minutes with a power setting of 250 W. During the ultrasonic process, the nanoparticles gradually disperse in ethanol to form a preliminary suspension. Then transfer the suspension to a high-shear dispersion emulsifier and stir at a speed of 6000 rpm for 30 minutes to fully disperse the nanoparticles in the suspension.

[0040] Slowly add 4 g of triisooctanoyl titanate isopropyl ester dropwise to the suspension with a continuous stirring speed of 4000 rpm. After the addition is complete, raise the temperature of the reaction system to 70 ± 2 °C and maintain it at this temperature for 4 hours while continuing to stir at a speed of 4000 rpm.

[0041] After the reaction is completed, naturally cool the reaction system to room temperature, separate the modified barium titanate nanoparticles from the solution by centrifugation, wash the modified barium titanate nanoparticles with absolute ethanol, and place the washed nanoparticles in a vacuum drying oven and dry at 60 °C for 12 hours to obtain titanate-modified barium titanate nanoparticles.

[0042] Preparation Example 2

[0043] Preparation of titanate-modified barium titanate nanoparticles: The difference from Preparation Example 1 is that 3 g of triisooctanoyl titanate isopropyl ester is slowly added dropwise to the suspension with a continuous stirring speed of 4000 rpm.

[0044] Preparation Example 3

[0045] Preparation of titanate-modified barium titanate nanoparticles: The difference from Preparation Example 1 is that 5 g of triisooctanoyl titanate isopropyl ester is slowly added dropwise to the suspension with a continuous stirring speed of 4000 rpm.

[0046] Preparation Example 4

[0047] Preparation of titanate-modified barium titanate nanoparticles: The difference from Preparation Example 1 is that 2 g of triisooctanoyl titanate isopropyl ester is slowly added dropwise to the suspension with a continuous stirring speed of 4000 rpm.

[0048] Preparation Example 5

[0049] Preparation of titanate-modified barium titanate nanoparticles: Different from Preparation Example 1, 6 g of isopropyl triisostearoyl titanate was slowly added dropwise to a suspension with a continuous stirring speed of 4000 rpm.

[0050] Example 1

[0051] A passivation treatment process for stainless steel surface:

[0052] The surface of the workpiece to be treated was pre-cleaned with an alkaline cleaning agent. The workpiece was immersed in a sodium hydroxide solution with a mass concentration of 5%, the solution was heated to 70 °C and kept warm for 5 - 10 minutes;

[0053] The pre-cleaned workpiece was immersed in a passivation solution. The passivation solution contained 3% potassium chromate, 2% sodium molybdate, and 2% corrosion inhibitor by mass percentage, and the rest was pure water. The pH value of the passivation solution was between 3 and 5. The passivation solution was heated to 65 °C and kept warm for 25 minutes; among them, the corrosion inhibitor component was 45% sodium tungstate, 35% sodium gluconate, and 20% phytic acid by mass percentage;

[0054] After the passivation treatment, the surface of the workpiece was immediately rinsed with flowing clean water and then air-dried naturally.

[0055] Example 2

[0056] A passivation treatment process for stainless steel surface:

[0057] The surface of the workpiece to be treated was pre-cleaned with an alkaline cleaning agent. The workpiece was immersed in a sodium hydroxide solution with a mass concentration of 5%, the solution was heated to 70 °C and kept warm for 5 - 10 minutes;

[0058] The pre-cleaned workpiece was immersed in a passivation solution. The passivation solution contained 2% potassium chromate, 1% sodium molybdate, and 1% corrosion inhibitor by mass percentage, and the rest was pure water. The pH value of the passivation solution was between 3 and 5. The passivation solution was heated to 65 °C and kept warm for 25 minutes; among them, the corrosion inhibitor component was 45% sodium tungstate, 35% sodium gluconate, and 20% phytic acid by mass percentage;

[0059] After the passivation treatment, the surface of the workpiece was immediately rinsed with flowing clean water and then air-dried naturally.

[0060] Example 3

[0061] A passivation treatment process for stainless steel surface:

[0062] The surface of the workpiece to be treated was pre-cleaned with an alkaline cleaning agent. The workpiece was immersed in a sodium hydroxide solution with a mass concentration of 5%, the solution was heated to 70 °C and kept warm for 5 - 10 minutes;

[0063] Immerse the pre-cleaned workpiece in a passivation solution. The passivation solution 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 and 5. Heat the passivation solution to 65 °C and keep it warm for 25 minutes. Among them, the corrosion inhibitor component is 45% sodium tungstate, 35% sodium gluconate, and 20% phytic acid by mass percentage.

[0064] After passivation treatment, immediately rinse the surface of the workpiece with flowing clean water, and then air dry it naturally.

[0065] Example 4

[0066] A passivation treatment process for the surface of stainless steel: Different from Example 1, the passivation solution contains 5% potassium chromate, 3% sodium molybdate, 3% corrosion inhibitor, and 0.3% silver nanoparticles by mass percentage, and the rest is pure water.

[0067] Example 5

[0068] A passivation treatment process for the surface of stainless steel: Different from Example 1, the passivation solution contains 5% potassium chromate, 3% sodium molybdate, 3% corrosion inhibitor, and 0.3% barium titanate nanoparticles by mass percentage, and the rest is pure water.

[0069] Example 6

[0070] A passivation treatment process for the surface of stainless steel: Different from Example 5, the passivation solution contains 5% potassium chromate, 3% sodium molybdate, 3% corrosion inhibitor, and 0.1% barium titanate nanoparticles by mass percentage, and the rest is pure water.

[0071] Example 7

[0072] A passivation treatment process for the surface of stainless steel: Different from Example 5, the passivation solution contains 5% potassium chromate, 3% sodium molybdate, 3% corrosion inhibitor, and 0.5% barium titanate nanoparticles by mass percentage, and the rest is pure water.

[0073] Example 8

[0074] A passivation treatment process for the surface of stainless steel: Different from Example 1, 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. Among them, the titanate-modified barium titanate nanoparticles are prepared from Preparation Example 1.

[0075] Example 9

[0076] A passivation treatment process for the surface of stainless steel: Different from Example 8, the titanate-modified barium titanate nanoparticles are prepared from Preparation Example 2.

[0077] Example 10

[0078] A passivation treatment process for stainless steel surface: The difference from Example 8 is that the titanate-modified barium titanate nanoparticles are prepared by Preparation Example 3.

[0079] Example 11

[0080] A passivation treatment process for stainless steel surface:

[0081] Pre-clean the surface of the workpiece to be treated with an alkaline cleaning agent. Immerse the workpiece in a sodium hydroxide solution with a mass concentration of 5%, heat the solution to 70 °C and keep it warm for 5 - 10 minutes.

[0082] Immerse the pre-cleaned workpiece in the passivation solution, and at the same time perform pulse current-assisted treatment on the workpiece with a 60 Hz pulse current. Among them, the duty cycle of the pulse current is 25%, the amplitude of the pulse current is 0.8 A / dm², the passivation solution contains 2% potassium chromate, 1% sodium molybdate, and 1% corrosion inhibitor by mass percentage, and the rest is pure water. The pH value of the passivation solution is between 3 - 5. Heat the passivation solution to 65 °C and keep it warm for 25 minutes. The corrosion inhibitor components are 45% sodium tungstate, 35% sodium gluconate, and 20% phytic acid by mass percentage.

[0083] After the passivation treatment, immediately rinse the surface of the workpiece with flowing water, and then perform natural air drying.

[0084] Example 12

[0085] A passivation treatment process for stainless steel surface: The difference from Example 1 is that the corrosion inhibitor components are 40% sodium tungstate, 30% sodium gluconate, and 30% phytic acid by mass percentage.

[0086] Example 13

[0087] A passivation treatment process for stainless steel surface: The difference from Example 1 is that the corrosion inhibitor components are 50% sodium tungstate, 40% sodium gluconate, and 10% phytic acid by mass percentage.

[0088] Example 14

[0089] A passivation treatment process for stainless steel surface: The difference from Example 1 is that the passivation solution is heated to 30 °C.

[0090] Example 15

[0091] A passivation treatment process for stainless steel surface: The difference from Example 1 is that the passivation solution is heated to 80 °C.

[0092] Comparative Example 1

[0093] A passivation treatment process for stainless steel surface: The difference from Example 1 is that the passivation solution does not contain potassium chromate.

[0094] Comparative Example 2

[0095] A passivation treatment process for stainless steel surface: The difference from Example 1 is that the passivation solution does not contain sodium molybdate.

[0096] Comparative Example 3

[0097] A passivation treatment process for stainless steel surface: The difference from Example 1 is that the passivation solution does not contain corrosion inhibitor.

[0098] Comparative Example 4

[0099] A passivation treatment process for stainless steel surface: The difference from Example 8 is that the titanate-modified barium titanate nanoparticles are prepared by Preparation Example 4.

[0100] Comparative Example 5

[0101] A passivation treatment process for stainless steel surface: The difference from Example 8 is that the titanate-modified barium titanate nanoparticles are prepared by Preparation Example 5.

[0102] Detection method

[0103] According to the standard of GB / T 10125-2012 "Artificial atmosphere corrosion test - Salt spray test", the treated workpieces of Examples 1-15 and Comparative Examples 1-5 are tested. The sizes and shapes of the workpieces used are the same. The treated workpieces are placed in a salt spray test chamber, and a sodium chloride solution with a salt spray concentration of 5% (mass fraction) is sprayed. The temperature in the chamber is maintained at 35±1°C, the relative humidity is set at 95%, and the spray time is set at 72 hours. After the test, the corrosion rate is calculated.

[0104] The corrosion rate calculation formula is: v = (m1 - m2) / St

[0105] Where, v is the corrosion rate (g / m²・h), m1 and m2 are the masses 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).

[0106] Table 1 Statistical data of the test

[0107] 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 Example 11 0.00036 Example 12 0.00039 Example 13 0.00040 Example 14 0.00045 Example 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

[0108] Combined with 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 corrosion inhibitor, and its corrosion rate is 0.00041 g / m²·h. After removing potassium chromate in Comparative Example 1, the corrosion rate increased to 0.00867 g / m²·h; after removing sodium molybdate in Comparative Example 2, the corrosion rate became 0.00358 g / m²·h; after removing the corrosion inhibitor in 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, which can promote the formation of a chromium-containing oxide film on the surface of stainless steel. Trivalent chromium ensures the stability of the film, and hexavalent chromium can self-repair when the film is damaged, contributing significantly to reducing the corrosion rate. Sodium molybdate synergizes with potassium chromate to optimize the structure of the passivation film, fill the pores, and further improve the corrosion resistance. The lack of it will cause the corrosion rate to increase to some extent. The corrosion inhibitor can inhibit the corrosion reaction from multiple aspects and build a protective barrier through adsorption, chelation, etc. The lack of the corrosion inhibitor also leads to an increase in the corrosion rate. This indicates that potassium chromate, sodium molybdate and the corrosion inhibitor each play an important role in this 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.

[0109] Combined with Examples 8-10 and Comparative Examples 4-5 and Table 1, it can be seen that the addition amount of the titanate modifier has an impact on the modification effect of barium titanate nanoparticles. When the addition amount is lower than the scope of this application, due to insufficient dosage of the modifier, the modification effect is poor, and the improvement amplitude of the passivation effect of the obtained titanate-modified barium titanate nanoparticles becomes smaller; when the addition amount exceeds the scope of this application, there is no further improvement in the passivation effect, so it is the best within the scope of this application.

[0110] Combined with Examples 1-3 and Table 1, it can be seen that with the change of the contents of potassium chromate, sodium molybdate and the corrosion inhibitor, the corrosion rate fluctuates, but the overall level is relatively low. The contents of each component need to be reasonably matched to achieve a better passivation effect. The component ratio of the passivation solution in Example 1 within the scope of this application is the best in this application to achieve efficient and economical passivation protection and ensure good corrosion resistance of stainless steel in a salt spray environment.

[0111] Combined with Example 1 and Examples 4, 5, 8 and Table 1, it can be seen that the addition of silver nanoparticles, barium titanate nanoparticles and titanate-modified barium titanate nanoparticles can all further reduce the corrosion rate of stainless steel to a certain extent, indicating that these nanoparticles all enhance the corrosion resistance of the passivation film. Among them, the improvement effect of titanate-modified barium titanate nanoparticles is relatively more obvious. After modification, its compatibility with the passivation solution and the surface of stainless steel is better, and it can more effectively participate in the construction of the passivation film, optimize the structure of the film, enhance the barrier ability to corrosion media, and thus better improve the corrosion resistance of stainless steel in a salt spray environment.

[0112] Combined with Example 1 and Examples 5 - 7 and Table 1, it can be seen that the addition amount of nano - barium titanate particles has an impact on the corrosion rate. Within a certain range, changing the content of nano - barium titanate particles will cause corresponding changes in the corrosion rate. The addition amount 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 relatively high; if the addition amount is too large, problems such as uneven dispersion of nano - particles will affect the quality of the passivation film.

[0113] Combined with Example 1 and Example 11 and Table 1, it can be seen 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, enhances the barrier ability to corrosion media, and thus shows better corrosion resistance in the salt - spray test. This indicates 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 combination with traditional passivation processes to further optimize the protection effect.

[0114] Combined with Example 1 and Examples 12 - 15 and Table 1, it can be seen that the change in the proportion of each component of the corrosion inhibitor will affect the corrosion rate, and the component proportion of the corrosion inhibitor in Example 1 of this application is the optimal in this application. The heating temperature of the passivation solution also has an impact on the corrosion rate. Too high or too low temperature will cause the corrosion rate to increase. Controlling the temperature at 60 - 70 °C can ensure that each component in the passivation solution plays a better role, promote the effective formation of the passivation film, and maintain good corrosion resistance.

[0115] This specific embodiment is only an interpretation of this application, and it is not a limitation of this application. After reading this specification, those skilled in the art can make modifications to this embodiment without creative contributions as needed, but as long as it is within the scope of the claims of this application, it is protected by the patent law.

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; The passivation solution contains 2-5% chromate, 1-3% molybdate, 1-3% corrosion inhibitor, and 0.1-0.5% titanate-modified barium titanate nanoparticles by mass percentage, and the pH value of the passivation solution is 3-5; 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 complete, 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.

2. 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.

3. The stainless steel surface passivation treatment process according to claim 2, characterized in that: The pulse current auxiliary treatment adopts 50-70Hz pulse current, the duty cycle of the pulse current is 20-30%, and the amplitude of the pulse current is 0.5-1A / dm 2 .

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

5. 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.