Stainless steel passivation solution, preparation method and application thereof

Abstract

This invention relates to the field of surface treatment technology, providing a stainless steel passivation solution, its preparation method, and its application. The passivation solution comprises an oxidant and a rare earth metal salt. The oxidant forms a metal oxide on the stainless steel surface, and the rare earth metal salt forms a rare earth metal compound on the stainless steel surface. The metal oxide and the rare earth metal compound together constitute a passivation film on the stainless steel surface. This passivation solution forms a dense passivation film on the stainless steel surface in an orderly manner. This passivation film exhibits excellent corrosion resistance, significantly improving upon mainstream silane + resin passivation methods in testing environments such as salt spray, pitting corrosion, corrosion current, and boiling in salt water.

Description

Technical Field

[0001] This invention relates to the field of surface treatment technology, and to a stainless steel passivation solution, its preparation method and application, particularly to a chromium-free passivation solution for low-Ni stainless steel, its preparation method and application. Background Technology

[0002] Stainless steel is widely used in household appliances and kitchen appliances. 304 stainless steel can meet the needs of most scenarios, but its high cost is mainly due to its high content of the scarce element Ni. Current technological innovation focuses on developing stainless steel grades with lower Ni content but higher corrosion resistance, or using low-Ni stainless steel with passivation processes to meet corrosion resistance requirements.

[0003] There are many types of stainless steel passivation technology, and the most commonly used ones in the past are roughly as follows:

[0004] (1) Hexavalent chromium passivation. This method can generate a dense passivation film on the surface of stainless steel, which can significantly improve corrosion resistance. Moreover, even if the surface is scratched, the hexavalent chromium in the film can repair the passivation film and still maintain corrosion resistance. However, hexavalent chromium is a highly toxic and carcinogenic substance, and with increasing attention to the environment and health, its use has been gradually banned by countries around the world.

[0005] (2) Trivalent chromium passivation scheme. The principle is similar to that of hexavalent chromium, which is to generate a dense passivation film on the surface of stainless steel. Although trivalent chromium cannot directly cause cancer, trivalent chromium may be oxidized to hexavalent chromium, which still poses a serious risk.

[0006] In recent years, in order to solve environmental and health problems, many enterprises and organizations have gradually developed chromium-free passivation solutions.

[0007] For example, patent application CN113430507A discloses a chromium-free stainless steel passivating agent. By weight, the passivating agent components include 10-15 parts rare earth metal salt, 3-5 parts organic acid, 8-10 parts silane coupling agent, 3-5 parts complexing agent, 3-5 parts film curing agent, 3-5 parts accelerator, 2-3 parts water-soluble titanium dioxide, and the balance being deionized water. However, the silane coupling agent in this solution easily loses its effectiveness in high-temperature and humid environments.

[0008] For example, patent CN102168265B discloses a chromium-free composite passivating agent and its preparation method. The components, by mass percentage, are: γ-methacryloxytrimethoxysilane 3.0–10%, sodium molybdate 0.1–3.0%, cerium chloride 0.1–5.0%, phosphoric acid 0.5–4.0%, acetic acid 0.5–4.0%, water-soluble epoxy resin 15–20%, water-soluble acrylic resin 5–15%, water 10–30%, and ethanol 20–40%. In this scheme, the γ-methacryloxytrimethoxysilane is quite complex, making the product prone to "powdering" during passivation, and the large amount of ethanol used greatly limits the product's widespread application.

[0009] For example, patent CN101717930B discloses a passivating agent formulation, comprising: (a) 5-50 ml of type A alkoxysilane; alkoxysilane containing at least one epoxy functional group, or at least one alkoxysilane containing an amino functional group, or alkoxysilane containing an epoxy functional group; (b) 5-50 ml of type B alkoxysilane; bis(methylsilyl)silane containing at least one non-hydrophilic functional group; (c) the content of water-dispersible nano-silica is 5-200 mg / L; (d) the content of nano-cerium oxide is 0-200 mg / L; (e) the content of rare earth cerium salt is 10-500 mg / L; (f) water balance, containing a small amount of acetic acid and ethanol. The solution aims to form a silane coating on the surface of metal after treatment. This silane coating has excellent corrosion resistance and can extend the service life of the metal to a certain extent. However, silane is unstable and easily hydrolyzed by water. Moreover, the water-dispersible nano-silica used in this solution not only has extremely high requirements for nano-silica, but also has high requirements for the storage environment, and is very easy to agglomerate.

[0010] Therefore, this invention is proposed. Summary of the Invention

[0011] This invention provides a stainless steel passivation solution, its preparation method, and its application, which addresses the shortcomings of insufficient corrosion resistance in existing chromium-free passivating agents used for low-Ni stainless steel. By using a stainless steel passivation solution containing oxidants and rare earth metal salts, a dense passivation film is obtained, significantly improving the corrosion resistance of stainless steel.

[0012] Specifically, the present invention provides a stainless steel passivation solution, comprising: an oxidant and a rare earth metal salt; the oxidant is used to form a metal oxide on the stainless steel surface, and the rare earth metal salt is used to form a rare earth metal compound on the stainless steel surface, wherein the metal oxide and the rare earth metal compound together constitute a passivation film on the stainless steel surface.

[0013] In the stainless steel passivation solution provided by the present invention as described above, the mass ratio of the oxidant to the rare earth metal salt is (1-20):(1-10).

[0014] The stainless steel passivation solution provided according to the present invention, as described above, comprises, by mass percentage:

[0015] 1-20% oxidant,

[0016] 1-20% oxidizing stabilizer

[0017] 1-10% complexing agent,

[0018] 1-5% surfactant,

[0019] 1-10% corrosion inhibitor,

[0020] 1-10% rare earth metal salts,

[0021] 1-5% chelating agent,

[0022] 1-5% penetrant.

[0023] The stainless steel passivation solution provided by the present invention, as described above, includes one or more of sodium peroxide, potassium persulfate, sodium persulfate, sodium hypochlorite, and hydrogen peroxide as the oxidant.

[0024] And / or, the oxidant stabilizer includes one or more of calcium fatty acid, potassium nitrate, sodium nitrate, calcium nitrate, and sodium fatty acid;

[0025] And / or, the complexing agent comprises one or more of sodium gluconate, sodium citrate, and disodium EDTA.

[0026] And / or, the surfactant comprises one or more of nonylphenol polyoxyethylene ether, octylphenol polyoxyethylene ether, higher carbon fatty alcohol polyoxyethylene ether, and sodium dodecyl sulfonate;

[0027] And / or, the corrosion inhibitor comprises one or more of sodium D-gluconate, hexamethylenetetramine, gallic acid, silicate, molybdate, tungstate, and polyphosphate;

[0028] And / or, the rare earth metal salt includes cerium metal salt;

[0029] And / or, the chelating agent includes one or more of phytic acid, triphenylcycloimidazoline quaternary ammonium salt, hydroxyethylidene diphosphate, sodium salt of polyhydroxy polymeric organic acid, and sodium iron ethylenediamine di-o-hydroxyphenylacetate;

[0030] And / or, the penetrant is one or more of fatty alcohol polyoxyethylene ether, fatty alcohol, organosiloxane and ethylenediamine EO-PO.

[0031] In the stainless steel passivation solution provided by the present invention as described above, the oxidant is hydrogen peroxide;

[0032] The oxidant stabilizer is sodium fatty acid;

[0033] The complexing agent is disodium EDTA;

[0034] The surfactant is sodium dodecyl sulfonate;

[0035] The corrosion inhibitor is sodium molybdate;

[0036] The rare earth metal salt is cerium nitrate;

[0037] The chelating agent is phytic acid;

[0038] The penetrant is fatty alcohol polyoxyethylene ether;

[0039] Preferably, the stainless steel passivation solution comprises, by mass percentage: 5-20% hydrogen peroxide, 5-20% sodium fatty acid, 1-8% disodium EDTA, 1-8% sodium dodecyl sulfonate, 1-8% sodium molybdate, 1-8% cerium nitrate, 2-4% phytic acid, 1-4% fatty alcohol polyoxyethylene ether, and the balance being water.

[0040] More preferably, by mass percentage, the stainless steel passivation solution comprises: 10-20% hydrogen peroxide, 10-20% sodium fatty acid, 2-8% disodium EDTA, 2-8% sodium dodecyl sulfonate, 1-6% sodium molybdate, 1-5% cerium nitrate, 3-5% phytic acid, 1-3% fatty alcohol polyoxyethylene ether, and the balance being water.

[0041] More preferably, by mass percentage, it comprises: 20% hydrogen peroxide, 18% sodium fatty acid, 8% disodium EDTA, 8% sodium dodecyl sulfonate, 3% sodium molybdate, 1.5% cerium nitrate, 5% phytic acid, 1% fatty alcohol polyoxyethylene ether, and the balance being water.

[0042] The stainless steel passivation solution provided by the present invention, as described above, has a pH value of 6 to 7.

[0043] Secondly, the present invention also provides a method for preparing the stainless steel passivation solution as described above.

[0044] Thirdly, the present invention also provides the application of the passivation solution as described above in stainless steel;

[0045] Preferably, the application includes: generating a passivation film on a stainless steel surface, which is mainly composed of metal oxides and rare earth metal compounds;

[0046] More preferably, the application includes: the metal oxide forming a metal oxide layer in situ on the stainless steel surface, and the rare earth metal compound forming a rare earth metal compound precipitate on the metal oxide layer;

[0047] More preferably, the application includes: the phytic acid being adsorbed onto the surface of the rare earth metal compound precipitate to form an adsorption film to improve the corrosion resistance of stainless steel.

[0048] In the application provided by the present invention as described above, the stainless steel is a stainless steel with a nickel content of less than 9%, preferably 430 stainless steel.

[0049] Fourthly, the present invention also provides a stainless steel passivation method, comprising passivating the stainless steel surface with the passivation solution as described above;

[0050] Preferably, the stainless steel passivation method includes:

[0051] The stainless steel is subjected to degreasing, washing, passivation, cleaning, drying and curing in sequence;

[0052] The degreasing includes: soaking or spraying stainless steel with an alkaline degreasing solution at a temperature of 50-60°C;

[0053] The washing process includes: soaking or spraying the degreased stainless steel with pure water until the water film on the stainless steel surface is uniform and there is no stranding.

[0054] The passivation includes: stainless steel that has been sprayed or immersed in the passivation solution as described above;

[0055] The cleaning includes: stainless steel treated with pure water immersion or spraying passivation solution;

[0056] The drying and curing process includes hot air drying at 100–110°C.

[0057] This invention provides a stainless steel passivation solution, its preparation method, and its application. Using a stainless steel passivation solution containing an oxidant and rare earth metal salts, a dense structure can be formed orderly on the surface of stainless steel without a chromium-containing formulation. Specifically, this dense structure includes metal oxides and rare earth metal compounds. The metal oxides form a metal oxide layer in situ on the stainless steel surface, and the rare earth metal compounds form rare earth metal compound precipitates on the metal oxide layer, together forming a passivation film on the stainless steel surface. This passivation film exhibits excellent corrosion resistance. Compared with the mainstream silane + resin passivation solutions on the market, its corrosion resistance is significantly improved under test environments such as salt spray, pitting corrosion, corrosion current, and boiling in salt water, exceeding general expectations. Attached Figure Description

[0058] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0059] Figure 1 These are schematic diagrams of polarization curves for Embodiments 1B to 4B and Comparative Examples 1 to 2 provided by the present invention;

[0060] Figure 2 The image shows the results of boiling 430 stainless steel sheets in brine using the commercially available mature solution of citric acid + hydrogen peroxide provided by this invention.

[0061] Figure 3 The image shows the results of boiling salt water on a 430 stainless steel pot lid using the commercially available mature solution of citric acid + hydrogen peroxide provided by this invention.

[0062] Figure 4 This is a diagram showing the results of boiling 430 stainless steel sheets in brine using the passivation solution of Example 1A provided by the present invention.

[0063] Figure 5 This is a diagram showing the results of boiling salt water on a 430 stainless steel pot lid using the passivation solution of Example 1A provided by the present invention. Detailed Implementation

[0064] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0065] The following is combined Figure 1 This invention describes a stainless steel passivation solution, its preparation method, and its application.

[0066] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0067] Chromium-free passivation solutions, as a new generation of passivation methods, allow rare earth metal salts to form crystalline or amorphous precipitates during the passivation process, which helps to form a dense structure. Extensive research has been conducted on their application in this field. However, the corrosion resistance of stainless steel cannot meet market demands solely based on the structure formed by this precipitate. Therefore, existing technologies use silane coatings in conjunction with these solutions. Although this improves the corrosion resistance to some extent, the application scenarios for stainless steel products are often harsh, especially the use of pressure cookers, which require stainless steel products to have excellent corrosion resistance in high-temperature, high-pressure, and high-humidity environments.

[0068] Through extensive testing, this invention has discovered that a passivation solution containing specific oxidants and rare earth metal salts can, in a chromium-free formulation, form a passivation film on the stainless steel surface by orderly forming metal oxides (primarily Fe oxides and C oxides) and rare earth metal compounds. This passivation film exhibits excellent corrosion resistance. Under the same testing conditions, it significantly improves upon mainstream passivation solutions using silane and resin under various testing environments, including salt spray, pitting, corrosion current density, and boiling salt water conditions, exceeding general expectations.

[0069] Specifically, the present invention provides a stainless steel passivation solution, comprising: an oxidant and a rare earth metal salt; the oxidant is used to form a metal oxide on the stainless steel surface, and the rare earth metal salt is used to form a rare earth metal compound on the stainless steel surface, wherein the metal oxide and the rare earth metal compound together constitute a passivation film on the stainless steel surface.

[0070] Preferably, the mass ratio of the oxidant to the rare earth metal salt is (1-20):(1-10).

[0071] Preferably, by weight percentage, it comprises:

[0072] 1-20% oxidant,

[0073] 1-20% oxidizing stabilizer

[0074] 1-10% complexing agent,

[0075] 1-5% surfactant,

[0076] 1-10% corrosion inhibitor,

[0077] 1-10% rare earth metal salts,

[0078] 1-5% chelating agent,

[0079] 1-5% penetrant.

[0080] Preferably, the oxidant includes one or more of sodium peroxide, potassium persulfate, sodium persulfate, sodium hypochlorite, and hydrogen peroxide;

[0081] And / or, the oxidant stabilizer includes one or more of calcium fatty acid, potassium nitrate, sodium nitrate, calcium nitrate, and sodium fatty acid;

[0082] And / or, the complexing agent comprises one or more of sodium gluconate, sodium citrate, and disodium EDTA.

[0083] And / or, the surfactant comprises one or more of nonylphenol polyoxyethylene ether, octylphenol polyoxyethylene ether, higher carbon fatty alcohol polyoxyethylene ether, and sodium dodecyl sulfonate;

[0084] And / or, the corrosion inhibitor comprises one or more of sodium D-gluconate, hexamethylenetetramine, gallic acid, silicate, molybdate, tungstate, and polyphosphate;

[0085] And / or, the rare earth metal salt includes cerium metal salt;

[0086] And / or, the chelating agent includes one or more of phytic acid, triphenylcycloimidazoline quaternary ammonium salt, hydroxyethylidene diphosphate, sodium salt of polyhydroxy polymeric organic acid, and sodium iron ethylenediamine di-o-hydroxyphenylacetate;

[0087] And / or, the penetrant is one or more of fatty alcohol polyoxyethylene ether, fatty alcohol, organosiloxane and ethylenediamine EO-PO.

[0088] Under the action of various additives in the passivation solution, on the one hand, the wettability of the passivation solution to the stainless steel surface is increased by specific surfactants and penetrants, while preventing the formation of fine corrosion channels in the passivation film layer. On the other hand, the environment during passivation is stabilized by oxidants, stabilizers, complexing agents, and corrosion inhibitors, so that the oxidant can oxidize Fe and Cr in the stainless steel and the auxiliary components in the passivation solution to form a dense oxide layer with good corrosion resistance, especially avoiding pitting defects. Cerium nitrate and sodium molybdate generate dense chemical conversion films such as Ce(OH)4 and CeO2 during the passivation process, achieving a significant improvement in corrosion resistance.

[0089] Furthermore, introducing chelating agents, such as phytic acid, can adsorb onto the membrane surface, forming a dense adsorption membrane, while also creating a degree of hydrophobicity to prevent corrosive substances from entering the membrane, thus improving the overall corrosion resistance.

[0090] Compared to various acidic systems such as citric acid, phosphoric acid, nitric acid, and sulfuric acid, this invention does not contain substances that are difficult to operate and control and pose certain safety risks to the environment. It is environmentally friendly, and the passivation method of this invention can be performed at a passivation temperature of 30-35°C, which is low-temperature friendly.

[0091] In the stainless steel passivation solution provided by the present invention as described above, the oxidant is hydrogen peroxide;

[0092] The oxidant stabilizer is sodium fatty acid;

[0093] The complexing agent is disodium EDTA;

[0094] The surfactant is sodium dodecyl sulfonate;

[0095] The corrosion inhibitor is sodium molybdate;

[0096] The rare earth metal salt is cerium nitrate;

[0097] The chelating agent is phytic acid;

[0098] The penetrant is fatty alcohol polyoxyethylene ether;

[0099] Preferably, the stainless steel passivation solution comprises, by mass percentage: 5-20% hydrogen peroxide, 5-20% sodium fatty acid, 1-8% disodium EDTA, 1-8% sodium dodecyl sulfonate, 1-8% sodium molybdate, 1-8% cerium nitrate, 2-4% phytic acid, 1-4% fatty alcohol polyoxyethylene ether, and the balance being water.

[0100] More preferably, by mass percentage, the stainless steel passivation solution comprises: 10-20% hydrogen peroxide, 10-20% sodium fatty acid, 2-8% disodium EDTA, 2-8% sodium dodecyl sulfonate, 1-6% sodium molybdate, 1-5% cerium nitrate, 3-5% phytic acid, 1-3% fatty alcohol polyoxyethylene ether, and the balance being water.

[0101] More preferably, by mass percentage, it comprises: 20% hydrogen peroxide, 18% sodium fatty acid, 8% disodium EDTA, 8% sodium dodecyl sulfonate, 3% sodium molybdate, 1.5% cerium nitrate, 5% phytic acid, 1% fatty alcohol polyoxyethylene ether, and the balance being water.

[0102] The stainless steel passivation solution provided by the present invention, as described above, has a pH value of 6 to 7.

[0103] When the above substances are prepared into a passivation solution in a specific ratio, the pH value of the passivation solution is neutral, which is more environmentally friendly compared to strong acid or strong base passivating agents.

[0104] Secondly, the present invention also provides a method for preparing the stainless steel passivation solution as described above.

[0105] Thirdly, the present invention also provides the application of the passivation solution as described above in stainless steel;

[0106] Preferably, the application includes: generating a passivation film on a stainless steel surface, which is mainly composed of metal oxides and rare earth metal compounds;

[0107] More preferably, the application includes: the metal oxide forming a metal oxide layer in situ on the stainless steel surface, and the rare earth metal compound forming a rare earth metal compound precipitate on the metal oxide layer;

[0108] More preferably, the application includes: the phytic acid being adsorbed onto the surface of the rare earth metal compound precipitate to form an adsorption film to improve the corrosion resistance of stainless steel.

[0109] When the passivation solution of this invention is used on stainless steel, the different components in the passivation solution exhibit varying reactivity and capabilities. Experimental observations show that when stainless steel enters the passivation solution, it is oxidized by the oxidizing components in the solution within a very short time, forming metal oxides on its surface. Subsequently, the rare earth metal salts in the passivation solution further form dense crystalline or amorphous precipitates on the oxide layer surface, resulting in a passivation film with significantly improved density. When the passivation solution contains phytic acid, it is ultimately adsorbed onto the surface of the precipitate to form an adsorption film, optimizing the passivation effect.

[0110] Preferably, the stainless steel is 430 stainless steel.

[0111] Fourthly, the present invention also provides a stainless steel passivation method, comprising passivating the stainless steel surface with the passivation solution as described above;

[0112] Preferably, the stainless steel passivation method includes:

[0113] The stainless steel is subjected to degreasing, washing, passivation, cleaning, drying and curing in sequence;

[0114] More preferably, the stainless steel passivation method includes:

[0115] The degreasing includes: immersing or spraying stainless steel with an alkaline degreasing solution at a temperature of 50-60°C for 5-10 minutes;

[0116] The washing process includes: soaking or spraying the degreased stainless steel with pure water until the water film on the stainless steel surface is uniform and there is no stranding.

[0117] The passivation process includes: spraying or immersing the stainless steel with the passivation solution described above; the passivation temperature is 30-35°C; and the duration is 5-6 minutes.

[0118] The cleaning includes: stainless steel treated with pure water immersion or spraying passivation solution;

[0119] The drying and curing process includes hot air drying at 100–110°C.

[0120] Example 1A Passivation Solution

[0121] A passivation solution, by mass percentage, comprises: 20% hydrogen peroxide, 18% sodium fatty acid, 8% disodium EDTA, 8% sodium dodecyl sulfonate, 3% sodium molybdate, 1.5% cerium nitrate, 5% phytic acid, 1% fatty alcohol polyoxyethylene ether, and the balance being water.

[0122] The preparation process includes: taking deionized water, adding hydrogen peroxide and sodium fatty acid, stirring continuously for about 10 minutes, and after it is evenly dispersed, adding EDTA disodium salt, sodium dodecyl sulfonate, sodium molybdate, cerium nitrate, phytic acid, and fatty alcohol polyoxyethylene ether in sequence, stirring evenly, and letting it stand for 24 hours before use.

[0123] Examples 2A-4A passivation solutions

[0124] Prepare the passivation solution according to the formula in Table 1. The preparation process is the same as in Example 1A.

[0125] Table 1

[0126] Components Example 1A Example 2A Example 3A Example 4A hydrogen peroxide 20.0％ 18.0％ 22.0％ 24.0％ Sodium fatty acids 18.0％ 16.0％ 20.0％ 22.0％ Disodium EDTA 8.0％ 7.0％ 6.0％ 6.0％ Sodium dodecyl sulfonate 8.0％ 8.0％ 9.0％ 9.0％ Sodium molybdate 3.0％ 3.0％ 3.0％ 3.0％ Cerium nitrate 1.5％ 1.5％ 1.5％ 1.5％ Phytic acid 5.0％ 6.0％ 7.0％ 7.0％ Fatty alcohol polyoxyethylene ether 1.0％ 1.0％ 1.5％ 1.5％ water margin margin margin margin

[0127] Example 1B Passivation Method

[0128] A passivation method for stainless steel includes the following steps:

[0129] (1) Material preparation:

[0130] Passivation material: 430 stainless steel, brushed finish, 0.8mm thick.

[0131] Passivation solution: Take the passivation solution prepared in Example 1A and test its pH value to be 6-7.

[0132] (2) Degreasing: Use an alkaline degreasing solution at 55°C to degrease the surface of 430 stainless steel by soaking or spraying for 5 to 10 minutes.

[0133] (3) Washing: Use immersion or spraying to wash with pure water until the water film on the degreased stainless steel surface is uniform and there is no stranding.

[0134] (4) Passivation: The passivation solution obtained in step (1) is used to passivate the washed stainless steel by spraying or immersion. The temperature of the system during passivation is 30-35℃ and the duration is 5-6 minutes.

[0135] (5) Cleaning: After passivation, rinse with pure water by soaking or spraying twice, 1 minute each time;

[0136] (6) Drying and curing: Dry with hot air at 100-110℃ for 10 min;

[0137] (7) Inspection: After being placed for at least 36 hours, the corrosion resistance is tested.

[0138] Passivation methods in Examples 2B-4B

[0139] It is basically the same as Example 1B, except that the passivation solution in Example 1A is replaced with the passivation solutions in Examples 2A to 4A respectively.

[0140] Comparative Example 1: Passivation Method

[0141] Considering that the current market mainly uses silane + resin passivation solutions, this invention uses such products as a reference to verify the effectiveness of the invention, as detailed below:

[0142] Silane + resin passivating agents, whose main components are: non-ferrous metal corrosion inhibitor: 9-10%; silane coupling agent: 5-6%; film-forming agent: 4-5%; flash rust inhibitor: 2-3%; water: balance. Their main components are: waterborne polyurethane resin: 9-10%; silane coupling agent: 5-6%; film-forming agent: 4-5%; flash rust inhibitor: 2-3%; water: balance.

[0143] The passivation process mainly includes: dewaxing, passivation, and sealing.

[0144] Comparative Example 2

[0145] The cleaning step was performed only on the 430 stainless steel prepared in Example 1B.

[0146] Comparative Example 3

[0147] The method is basically the same as that in Example 1B, except that the hydrogen peroxide and sodium fatty acid in the passivation solution in Example 1A are replaced with citric acid. The composition of the passivation solution is as follows: citric acid, 38%; disodium EDTA, 8.0%; sodium dodecyl sulfonate, 8.0%; sodium molybdate, 3.0%; cerium nitrate, 1.5%; phytic acid, 5.0%; fatty alcohol polyoxyethylene ether, 1.0%; water, balance.

[0148] Comparative Example 4

[0149] The method is basically the same as that in Example 1B, except that the passivation solution in Example 1A does not contain cerium nitrate. The composition of the passivation solution is as follows: 20% hydrogen peroxide, 18% sodium fatty acid, 8% disodium EDTA, 8% sodium dodecyl sulfonate, 3% sodium molybdate, 5% phytic acid, 1% fatty alcohol polyoxyethylene ether, and the balance is water.

[0150] Experimental Example 1

[0151] The stainless steel products obtained from Examples 1B to 4B and Comparative Examples 1 to 3 were tested, and the testing process is as follows:

[0152] (1) Salt spray corrosion performance

[0153] The neutral salt spray test was conducted in accordance with GB / T 10125-2021 "Salt spray test for corrosion testing in artificial atmosphere". The test results were evaluated in accordance with GB / T 6461-2002 "Rating of specimens and test pieces of metal and other inorganic coatings on metal substrates after corrosion test". The duration up to grade 9 on the surface was recorded, and observations were made every 12 hours.

[0154] (2) Pitting potential

[0155] The test was conducted in accordance with GB / T 17899-1999, "Method for measuring pitting potential of stainless steel".

[0156] Polarization tests were conducted in the company's laboratory. The corrosion resistance of the samples was characterized using a CHI660E electrochemical workstation. Stainless steel was used as the working electrode, Pt wire as the counter electrode, and a saturated calomel electrode as the reference electrode. The solution temperature was room temperature during testing. Before testing, the samples were immersed in the solution until the potential stabilized. Then, a potentiodynamic scanning test was performed, scanning from 400mV - 0.05mV relative to the open circuit potential to above the anodic breakage potential at a scan rate of 2mV / s. The self-corrosion current density of the samples was determined using the Tafel extrapolation method. A lower self-corrosion current density indicates stronger corrosion resistance.

[0157] (3) Boil salt water

[0158] Stainless steel products were made into test pieces, which were then placed in a pressure cooker. A 1% salt solution was added to the cooker up to the maximum mark. The cooker was then closed and operated continuously. During the test, the test was conducted every 12 hours, and the time when rust appeared was recorded.

[0159] The test results are shown in Table 2 below:

[0160] Table 2

[0161]

[0162] The test results of Comparative Example 1, Comparative Example 2, and the 430 stainless steel passivated by the stainless steel passivation solution provided by the present invention show that the stainless steel products obtained by the method provided by the present invention have significantly improved corrosion resistance compared with the unpassivated 430 stainless steel. The passivation effect is better than the mainstream passivation scheme using silane + resin in the market.

[0163] The test results above show that Example 1B exhibits the best corrosion resistance. However, Comparative Examples 3 and 4 demonstrate that when hydrogen peroxide and sodium fatty acid are replaced with citric acid, rare earth metal compounds precipitate on the substrate surface. The adhesion and compatibility between the precipitate and the metal are far inferior to those with metal oxides, resulting in numerous defects between the grains during the crystallization of the rare earth metal compound precipitate. These defects become corrosive media, especially Cl-. - Compared to the absence of rare earth metal compound precipitation, the precipitation of rare earth metal compounds can significantly prolong the Cl channel. - While time can delay corrosion by improving the substrate's moisture content, it's far from sufficient. When only a hydrogen peroxide system forms a metal oxide film, the surface is merely a thin, dense layer. In corrosion tests, when the oxide film is intact, it can provide relatively good corrosion resistance. However, as corrosion progresses, Cl... - The corrosion continues until it penetrates the oxide film layer to the junction of the thin film and the substrate, corroding the substrate. The corrosion products from the corroded substrate cause volume expansion at this point, leading to the breakdown of the oxide film and loss of its protective ability. When stainless steel enters a passivation solution capable of generating oxides and precipitating rare earth metal compounds, it is oxidized by the oxidizing components in the passivation solution in a very short time, forming metal oxides on its surface. Subsequently, the rare earth metal salts in the passivation solution further form dense crystalline or amorphous precipitates on the oxide layer surface. The rare earth metal compound precipitates have excellent adhesion and compatibility with the previously formed oxide layer. Due to the template effect, the precipitates are denser, further significantly improving the corrosion resistance of the passivation film.

[0164] Currently, there is little research on the use of oxidizing passivation solutions to improve corrosion resistance. To further verify the effectiveness of this invention, a commercially available, mature solution, a citric acid + hydrogen peroxide system (main components: hydrogen peroxide 15%; citric acid >7%; sorbic acid: 4-6%; polyethylene glycol: 0.2-1.1%; deionized water: balance), was used in comparison with the solution in Example 1A above. After passivation, 430 stainless steel sheets and 430 stainless steel pot lids were subjected to a 1% NaCl brine boiling test. The test results for the citric acid + hydrogen peroxide system are as follows: Figure 2 and Figure 3 As shown. The test results of Example 1A are as follows. Figure 4 and Figure 5 As shown, this indicates that the technical solution provided by the present invention has significantly better corrosion resistance on 430 stainless steel products than the citric acid + double oxide passivation solution.

[0165] The passivating agent of the present invention can form a dense passivation film on the surface of stainless steel, which can significantly improve the corrosion resistance of the stainless steel surface. At the same time, the passivating agent is environmentally friendly and non-toxic, easy to operate, does not affect the appearance of the stainless steel surface, and has high adhesion of the passivation film.

[0166] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A stainless steel passivation solution, characterized in that, include: Oxidizing agents and rare earth metal salts; The oxidant is used to form a metal oxide on the stainless steel surface, and the rare earth metal salt is used to form a rare earth metal compound on the stainless steel surface. The metal oxide and the rare earth metal compound together constitute a passivation film on the stainless steel surface. By weight percentage, including: 1~20% oxidant, wherein the oxidant is hydrogen peroxide; 1~20% oxidant stabilizer, wherein the oxidant stabilizer is sodium fatty acid; 1~10% complexing agent, wherein the complexing agent comprises one or more of sodium gluconate, sodium citrate and disodium EDTA; 1~5% surfactant, wherein the surfactant includes one or more of nonylphenol polyoxyethylene ether, octylphenol polyoxyethylene ether, higher carbon fatty alcohol polyoxyethylene ether and sodium dodecyl sulfonate; 1~10% corrosion inhibitor, wherein the corrosion inhibitor comprises one or more of sodium D-gluconate, hexamethylenetetramine, gallic acid, silicate, molybdate, tungstate and polyphosphate; 1~10% rare earth metal salts, including cerium metal salts; 1~5% chelating agent, wherein the chelating agent includes one or more of phytic acid, triphenylcycloimidazoline quaternary ammonium salt, hydroxyethylidene diphosphate, sodium salt of polyhydroxy polymeric organic acid, and sodium iron ethylenediamine di-o-hydroxyphenylacetate; 1~5% penetrant, wherein the penetrant is one or more of fatty alcohol polyoxyethylene ether, fatty alcohol, organosiloxane and ethylenediamine EO-PO; The passivation solution has a pH value of 6-7.

2. The stainless steel passivation solution according to claim 1, characterized in that, The mass ratio of the oxidant to the rare earth metal salt is (1~20):(1~10).

3. The stainless steel passivation solution according to claim 1 or 2, characterized in that, The complexing agent is disodium EDTA; The surfactant is sodium dodecyl sulfonate; The corrosion inhibitor is sodium molybdate; The rare earth metal salt is cerium nitrate; The chelating agent is phytic acid; The penetrant is fatty alcohol polyoxyethylene ether.

4. The stainless steel passivation solution according to claim 3, characterized in that, The stainless steel passivation solution comprises, by mass percentage: 5-20% hydrogen peroxide, 5-20% sodium fatty acid, 1-8% disodium EDTA, 1-8% sodium dodecyl sulfonate, 1-8% sodium molybdate, 1-8% cerium nitrate, 2-4% phytic acid, 1-4% fatty alcohol polyoxyethylene ether, and the balance being water.

5. The stainless steel passivation solution according to claim 4, characterized in that, The stainless steel passivation solution comprises, by mass percentage: 10-20% hydrogen peroxide, 10-20% sodium fatty acid, 2-8% disodium EDTA, 2-8% sodium dodecyl sulfonate, 1-6% sodium molybdate, 1-5% cerium nitrate, 3-5% phytic acid, 1-3% fatty alcohol polyoxyethylene ether, and the balance being water.

6. The application of the passivation solution according to any one of claims 1 to 5 in stainless steel.

7. The application according to claim 6, characterized in that, The applications include: generating a passivation film on a stainless steel surface, which is mainly composed of metal oxides and rare earth metal compounds.

8. The application according to claim 7, characterized in that, The application includes: the metal oxide forming an in-situ metal oxide layer on the stainless steel surface, and the rare earth metal compound forming a rare earth metal compound precipitate on the metal oxide layer.

9. The application according to claim 8, characterized in that, The application includes: the phytic acid is adsorbed on the surface of the rare earth metal compound precipitate to form an adsorption film to improve the corrosion resistance of stainless steel.

10. The application according to claim 6, characterized in that, The stainless steel is stainless steel with a nickel content of less than 9%.

11. The application according to claim 6, characterized in that, The stainless steel is 430 stainless steel.

12. A method for passivating stainless steel, characterized in that, The passivation solution described in any one of claims 1 to 5 is used to passivate the surface of stainless steel.

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