Passivation solution for improving corrosion resistance of X40CrMoVN16-2 high-nitrogen martensitic stainless steel

Abstract

The invention discloses a passivation solution for improving the corrosion resistance of X40CrMoVN16-2 high-nitrogen martensitic stainless steel, and belongs to the technical field of stainless steel surface treatment. The passivation solution is prepared from, by mass, 6%-10% of citric acid, 3%-5% of hydrogen peroxide, 0.8%-1.2% of sodium molybdate, 0.1%-0.16% of lauryl sodium sulfate and 0.06%-0.12% of nano-silica sol, the passivation temperature is 35-45 DEG C, and the passivation time is 50-60 min. The self-corrosion current density of a sample passivated by the passivation solution is reduced to 0.076 [mu] A.cm <-2 > from 0.892 [mu] A.cm <-2 > of an unpassivated sample, the pitting potential is increased to 1.54 V from-1.55 V of the unpassivated sample, and the corrosion resistance of the X40CrMoVN16-2 high-nitrogen martensitic stainless steel is effectively improved.

Description

Technical Field

[0001] This invention relates to a passivation solution for improving the corrosion resistance of X40CrMoVN16-2 high-nitrogen martensitic stainless steel, belonging to the field of stainless steel surface treatment technology. Background Technology

[0002] X40CrMoVN16-2 high-nitrogen martensitic stainless steel, with its core advantages of high strength, corrosion resistance, and high-temperature resistance, is widely used in petrochemical, aerospace, medical device, energy engineering, shipbuilding, and machinery manufacturing industries, especially in the manufacture of components requiring high strength and corrosion resistance. While X40CrMoVN16-2 high-nitrogen martensitic stainless steel inherently possesses a certain degree of corrosion resistance, its surface is prone to pitting corrosion in harsh working environments (such as seawater, air pollution, and chemical media), thus affecting its service life. Its inherent corrosion resistance alone is far from sufficient; therefore, passivation can further enhance its corrosion resistance. Chemical passivation is a chemical treatment process that uses a strong oxidizing medium (such as nitric acid) to remove free iron contaminants from the stainless steel surface and promotes the formation of an extremely thin, dense, inert chromium-rich oxide film (passivation film). This process effectively improves the corrosion resistance of X40CrMoVN16-2 high-nitrogen martensitic stainless steel at a relatively low cost.

[0003] Traditional stainless steel passivation methods rely on strong oxidants such as concentrated nitric acid, concentrated sulfuric acid, or chromic acid, posing significant safety hazards and stringent operational requirements. Given the harmful effects of strong acids on human health, the use of nitric acid and other strong acids is strictly limited, and nitric acid-based passivation formulations are gradually being replaced by more environmentally friendly citric acid-based formulations. The advantages of this technology are: citric acid preferentially reacts with iron, effectively removing free iron impurities from the stainless steel surface; simultaneously, thanks to the strong oxidizing properties of hydrogen peroxide, a stable and dense chromium-based oxide passivation film can be better formed on the stainless steel surface. Therefore, the citric acid-hydrogen peroxide system, as a safe, efficient, and environmentally friendly new passivation technology, shows broad application prospects.

[0004] Chinese patent (202210682128.5) discloses a stainless steel passivation solution and its application. The stainless steel passivation solution includes sulfuric acid, hydrogen peroxide and a complexing agent. After passivation, the product has improved corrosion resistance and a long service life. However, its raw materials contain sulfuric acid, which is harmful to human health and poses a high operational risk.

[0005] Chinese patent (201710177703.5) discloses a stainless steel passivation solution and its passivation method. The passivation solution comprises 40-50 parts of inorganic acid, 5-15 parts of hydrogen peroxide, 8-12 parts of cyclohexanol, 4-8 parts of octyl epoxy stearate, 4-6 parts of acetic anhydride, 2-4 parts of polyethyleneimine, 3-5 parts of carbomer resin, 2-4 parts of penetrant, 1-3 parts of corrosion inhibitor, and 10-20 parts of organic filler. This passivation solution has low hazard and minimal environmental pollution, meeting green environmental protection standards. However, the raw materials for the passivation solution are numerous, resulting in high costs, and the solution preparation is relatively cumbersome.

[0006] To address the aforementioned problems, this invention provides a passivation method using a passivation solution with citric acid, hydrogen peroxide, sodium molybdate, sodium dodecyl sulfate, and nano-silica sol as the main components. The passivation method utilizes the complexing effect of citric acid to remove free iron ions from the stainless steel surface, while the oxidizing properties of hydrogen peroxide regenerate a dense Cr2O3 oxide film on the surface. The synergistic effect of sodium molybdate, the surfactant sodium dodecyl sulfate, and the nano-silica sol further enhances the density and stability of the oxide film. This passivation method is not only simple and easy to operate, but also eliminates the need for strong acids such as nitric acid and sulfuric acid. Summary of the Invention

[0007] X40CrMoVN16-2 high-nitrogen martensitic stainless steel is widely used in aerospace landing gear, gas turbine blades, high-performance pump and valve shafts, and medical devices (such as orthopedic implants and surgical robot joints). However, it is prone to corrosion in humid and chloride-containing corrosive environments. Passivation treatment can effectively improve its corrosion resistance and extend its service life at a lower production cost. This invention changes the traditional strong acid passivation method and further improves the citric acid-based passivation method, providing a brand-new passivation solution.

[0008] The purpose of this invention is to provide a passivation solution that improves the corrosion resistance of X40CrMoVN16-2 high-nitrogen martensitic stainless steel. The passivation solution comprises the following components by mass percentage: 6-10% citric acid, 3-5% hydrogen peroxide, 0.8-1.2% sodium molybdate, 0.1-0.16% sodium dodecyl sulfate, 0.06%-0.12% nano silica sol, and the remainder is water to prepare the passivation solution.

[0009] Preferably, the passivation temperature of the passivation liquid of the present invention is 35-45℃.

[0010] Preferably, the passivation time of the passivation solution of the present invention is 50-60 min.

[0011] Preferably, the chemical composition of the X40CrMoVN16-2 high-nitrogen martensitic stainless steel of the present invention, by mass percentage, is as follows: C: 0.35~0.45%, Cr: 14.00~16.00%, Mo: 1.00~2.50%, N: 0.10%~0.30%, V: ≤1.50%, P: ≤0.04%, S: ≤0.015%, with the balance being Fe and unavoidable impurities.

[0012] The method of using the passivation solution described in this invention is a conventional method, specifically including the following steps: (1) Prepare a passivation solution with the following mass fractions: 6-10% citric acid, 3-5% hydrogen peroxide, 0.8-1.2% sodium molybdate, 0.1-0.16% sodium dodecyl sulfate, 0.06%-0.12% nano silica sol, and the remainder being water.

[0013] (2) Cut X40CrMoVN16-2 into 12*12*3mm pieces, and polish the sample after grinding with 100-2000# sandpaper.

[0014] (3) Clean the sample obtained in step (2) with alcohol using ultrasonic cleaning to ensure surface cleanliness.

[0015] (4) Place the sample obtained in step (3) into a 10% HNO3 solution for 5 min for acid washing and activation, then rinse it with deionized water and dry it with a hair dryer.

[0016] (5) Immerse the sample obtained in step (4) in the passivation solution prepared in step (1).

[0017] (6) Rinse the sample obtained in step (5) with deionized water and place it in an 80°C constant temperature oven to dry for 60 min.

[0018] The beneficial effects of this invention are: This invention abandons the traditional stainless steel passivation method based on strong acids such as nitric acid, hydrofluoric acid, and chromic acid. It innovatively uses citric acid, hydrogen peroxide, sodium molybdate, sodium dodecyl sulfate, and nano-silica sol as the core components of the passivation solution. Citrate ions have a strong complexing ability and can bind with iron ions (Fe2+) on the stainless steel surface. 2+ / Fe 3+ This process forms a stable, soluble complex, which preferentially dissolves and removes unstable iron oxides from the surface, leaving behind more stable chromium oxides. This results in a higher quality and more stable chromium-based passivation film on the stainless steel surface, allowing for a relative enrichment of chromium (Cr) on the stainless steel surface. This process exposes more chromium atoms, allowing hydrogen peroxide to more effectively oxidize them to Cr2O3, forming a dense oxide film.

[0019] Sodium molybdate, as a relatively mild oxidizing agent, can assist this process, making the oxidation process more stable and thorough, and can form MoO4 in the passivation film. 2- The formation of molybdate precipitates at the pitting initiation site blocks corrosion channels, thereby significantly improving pitting resistance. Sodium dodecyl sulfate (SDS), as an anionic surfactant, primarily optimizes and stabilizes the passivation process by altering the physicochemical interactions between the solution and the metal surface, resulting in a more uniform, dense, and corrosion-resistant passivation film. Nano-silica sol fills the micropores and defects in the passivation film, forming a denser and more complete physical barrier that effectively blocks corrosive media. The optimized formulation and process of this technology offer advantages such as ease of operation and the ability to be carried out at low temperatures, significantly improving operational safety, reducing overall costs, and making the entire passivation process environmentally friendly. This approach achieves a balance between environmental and economic benefits while effectively improving the corrosion resistance of X40CrMoVN16-2 high-nitrogen martensitic stainless steel. Attached Figure Description

[0020] Figure 1 These are the polarization curves of the examples and comparative examples.

[0021] Figure 2 These are the AC impedance spectra of the examples and comparative examples.

[0022] Figure 3 The examples and comparative examples show the surface corrosion after immersion in 3.5% NaCl for 24 hours, where (a) is Example 1, (b) is Example 2, (c) is Example 3, (d) is Comparative Example 1, (e) is Comparative Example 2, (f) is Comparative Example 3, (g) is Comparative Example 4, and (h) is Comparative Example 5. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0024] Example 1 A passivation solution for improving the corrosion resistance of X40CrMoVN16-2 high-nitrogen martensitic stainless steel, wherein the passivation solution comprises 8% citric acid, 4% hydrogen peroxide, 1% sodium molybdate, 0.13% sodium dodecyl sulfate, 0.09% nano silica sol, and the remainder is water.

[0025] The passivation method of the passivation solution specifically includes the following steps: (1) Prepare a passivation solution with the following mass fractions: 8% citric acid, 4% hydrogen peroxide, 1% sodium molybdate, 0.13% sodium dodecyl sulfate, 0.09% nano silica sol, and the remainder being water.

[0026] (2) Cut X40CrMoVN16-2 into 12*12*3mm pieces, and polish the sample after grinding with 100-2000# sandpaper.

[0027] (3) Clean the sample obtained in step (2) with alcohol using ultrasonic cleaning to ensure surface cleanliness.

[0028] (4) Place the sample obtained in step (3) into a 10% HNO3 solution for 5 min for acid washing and activation, then rinse it with deionized water and dry it with a hair dryer.

[0029] (5) Immerse the sample obtained in step (4) in the passivation solution (40°C) prepared in step (1) for 55 minutes.

[0030] (6) Rinse the sample obtained in step (5) with deionized water and place it in an 80°C constant temperature oven to dry for 60 min.

[0031] Example 2 A passivation solution for improving the corrosion resistance of X40CrMoVN16-2 high-nitrogen martensitic stainless steel, wherein the passivation solution comprises 6% citric acid, 3% hydrogen peroxide, 0.8% sodium molybdate, 0.1% sodium dodecyl sulfate and 0.06% nano silica sol by mass, with the remainder being water.

[0032] The passivation method of the passivation solution specifically includes the following steps: (1) Prepare a passivation solution with the following mass fractions: 6% citric acid, 3% hydrogen peroxide, 0.8% sodium molybdate, 0.1% sodium dodecyl sulfate, 0.06% nano silica sol, and the remainder being water.

[0033] (2) Cut X40CrMoVN16-2 into 12*12*3mm pieces, and polish the sample after grinding with 100-2000# sandpaper.

[0034] (3) Clean the sample obtained in step (2) with alcohol using ultrasonic cleaning to ensure surface cleanliness.

[0035] (4) Place the sample obtained in step (3) into a 10% HNO3 solution for 5 min for acid washing and activation, then rinse it with deionized water and dry it with a hair dryer.

[0036] (5) Immerse the sample obtained in step (4) in the passivation solution (35°C) prepared in step (1) for 50 minutes.

[0037] (6) Rinse the sample obtained in step (5) with deionized water and place it in an 80°C constant temperature oven to dry for 60 min.

[0038] Example 3 A passivation solution for improving the corrosion resistance of X40CrMoVN16-2 high-nitrogen martensitic stainless steel, wherein the passivation solution comprises 10% citric acid, 5% hydrogen peroxide, 1.2% sodium molybdate, 0.16% sodium dodecyl sulfate, 0.12% nano silica sol, and the remainder is water.

[0039] The passivation method of the passivation solution specifically includes the following steps: (1) Prepare a passivation solution with the following mass fractions: 10% citric acid, 5% hydrogen peroxide, 1.2% sodium molybdate, 0.16% sodium dodecyl sulfate, 0.12% nano silica sol, and the remainder being water.

[0040] (2) Cut X40CrMoVN16-2 into 12*12*3mm pieces, and polish the sample after grinding with 100-2000# sandpaper.

[0041] (3) Clean the sample obtained in step (2) with alcohol using ultrasonic cleaning to ensure surface cleanliness.

[0042] (4) Place the sample obtained in step (3) into a 10% HNO3 solution for 5 min for acid washing and activation, then rinse it with deionized water and dry it with a hair dryer.

[0043] (5) Immerse the sample obtained in step (4) in the passivation solution (45°C) prepared in step (1) for 60 minutes.

[0044] (6) Rinse the sample obtained in step (5) with deionized water and place it in an 80°C constant temperature oven to dry for 60 min.

[0045] Comparative Example 1 The comparative examples were not treated except for grinding, polishing, and ultrasonic cleaning.

[0046] Specifically, the following steps are included: (1) Cut X40CrMoVN16-2 into 12*12*3mm pieces, and polish the sample after grinding with 100-2000# sandpaper.

[0047] (2) Clean the sample obtained in step (1) with alcohol using ultrasonic cleaning to ensure surface cleanliness. Comparative Example 2 The comparative passivation solution consisted of 3% citric acid, 10% hydrogen peroxide, 0.4% sodium molybdate, 0.05% sodium dodecyl sulfate, and 0.01% nano-silica sol by mass, with the remainder being water.

[0048] The passivation method of the passivation solution specifically includes the following steps: (1) Prepare a passivation solution with the following mass fractions: 3% citric acid, 10% hydrogen peroxide, 0.4% sodium molybdate, 0.05% sodium dodecyl sulfate, 0.01% nano silica sol, and the remainder being water.

[0049] (2) Cut X40CrMoVN16-2 into 12*12*3mm pieces, and polish the sample after grinding with 100-2000# sandpaper.

[0050] (3) Clean the sample obtained in step (2) with alcohol using ultrasonic cleaning to ensure surface cleanliness.

[0051] (4) Place the sample obtained in step (3) into a 10% HNO3 solution for 5 min for acid washing and activation, then rinse it with deionized water and dry it with a hair dryer.

[0052] (5) Immerse the sample obtained in step (4) in the passivation solution (60°C) prepared in step (1) for 30 minutes.

[0053] (6) Rinse the sample obtained in step (5) with deionized water and place it in an 80°C constant temperature oven to dry for 60 min.

[0054] Comparative Example 3 The comparative passivation solution consisted of 15% citric acid, 15% hydrogen peroxide, 2% sodium molybdate, 0.2% sodium dodecyl sulfate, and 0.2% nano-silica sol by mass, with the remainder being water.

[0055] The passivation method of the passivation solution specifically includes the following steps: (1) Prepare a passivation solution with the following mass fractions: 15% citric acid, 15% hydrogen peroxide, 2% sodium molybdate, 0.2% sodium dodecyl sulfate, 0.2% nano silica sol, and the remainder being water.

[0056] (2) Cut X40CrMoVN16-2 into 12*12*3mm pieces, and polish the sample after grinding with 100-2000# sandpaper.

[0057] (3) Clean the sample obtained in step (2) with alcohol using ultrasonic cleaning to ensure surface cleanliness.

[0058] (4) Place the sample obtained in step (3) into a 10% HNO3 solution for 5 min for acid washing and activation, then rinse it with deionized water and dry it with a hair dryer.

[0059] (5) Immerse the sample obtained in step (4) in the passivation solution (25°C) prepared in step (1) for 90 minutes.

[0060] (6) Rinse the sample obtained in step (5) with deionized water and place it in an 80°C constant temperature oven to dry for 60 min.

[0061] Comparative Example 4 The comparative passivation solution consisted of 10% citric acid, 5% hydrogen peroxide, and the remainder was water.

[0062] The passivation method of the passivation solution specifically includes the following steps: (1) Prepare a passivation solution with 10% citric acid, 5% hydrogen peroxide and the remainder water.

[0063] (2) Cut X40CrMoVN16-2 into 12*12*3mm pieces, and polish the sample after grinding with 100-2000# sandpaper.

[0064] (3) Clean the sample obtained in step (2) with alcohol using ultrasonic cleaning to ensure surface cleanliness.

[0065] (4) Place the sample obtained in step (3) into a 10% HNO3 solution for 5 min for acid washing and activation, then rinse it with deionized water and dry it with a hair dryer.

[0066] (5) Immerse the sample obtained in step (4) in the passivation solution (40°C) prepared in step (1) for 60 minutes.

[0067] (6) Rinse the sample obtained in step (5) with deionized water and place it in an 80°C constant temperature oven to dry for 60 min.

[0068] Comparative Example 5 The comparative passivation solution consisted of 12% citric acid, 10% hydrogen peroxide, 0.4% sodium molybdate, and 0.05% sodium dodecyl sulfate by mass, with the remainder being water.

[0069] The passivation method of the passivation solution specifically includes the following steps: (1) Prepare a passivation solution with 12% citric acid, 10% hydrogen peroxide, 0.4% sodium molybdate, 0.05% sodium dodecyl sulfate, and the remainder being water.

[0070] (2) Cut X40CrMoVN16-2 into 12*12*3mm pieces, and polish the sample after grinding with 100-2000# sandpaper.

[0071] (3) Clean the sample obtained in step (2) with alcohol using ultrasonic cleaning to ensure surface cleanliness.

[0072] (4) Place the sample obtained in step (3) into a 10% HNO3 solution for 5 min for acid washing and activation, then rinse it with deionized water and dry it with a hair dryer.

[0073] (5) Immerse the sample obtained in step (4) in the passivation solution (25°C) prepared in step (1) for 90 minutes.

[0074] (6) Rinse the sample obtained in step (5) with deionized water and place it in an 80°C constant temperature oven to dry for 60 min.

[0075] Corrosion resistance test: Examples 1 to 3 and Comparative Examples 1 to 5 were subjected to potentiodynamic polarization curve testing and AC impedance spectroscopy testing in 3.5% NaCl solution to analyze parameters such as self-corrosion current density, pitting potential, and polarization resistance; immersion experiments were conducted in 3.5% NaCl solution, and the time when corrosion first appeared on the sample was recorded and the surface corrosion was observed after 24 hours of immersion; the test results are shown in Table 1.

[0076] Table 1. Surface corrosion of the samples As can be seen from the parameters of the polarization curves in Table 1, the self-corrosion current density of Example 1 is the lowest at 0.076 μA·cm. -2 The self-corrosion current density of Comparative Example 1 is 0.892 μA·cm. -2 The pitting potential was reduced by more than an order of magnitude; the pitting potential of Example 1 was 0.154V, which was 0.309V higher than that of Comparative Example 1 (-0.155V). The pitting potentials of Examples 1-3 were all increased, and the improvement was significant. The pitting potentials of the Examples were higher than those of the Comparative Examples. Comparative Examples 2-5 showed an increase in pitting potential compared to Comparative Example 1, but the effect was not significant. Figure 1 It can be seen that the polarization curves of Examples 1-3 show obvious passivation plateaus, and the polarization curves shift significantly to the right compared with Comparative Examples 1-5, indicating improved corrosion resistance. This proves that the corrosion resistance of X40CrMoVN16-2 high-nitrogen martensitic stainless steel is greatly improved after passivation with passivation solution (6-10% citric acid, 3-5% hydrogen peroxide, 0.8-1.2% sodium molybdate, 0.1-0.16% sodium dodecyl sulfate, 0.06%-0.12% nano silica sol, passivation temperature 35-45℃, passivation time 50-60min).

[0077] Table 2. Polarization resistance Rp As can be seen from Table 2, the polarization resistance Rp of Examples 1-3 is significantly greater than that of Comparative Examples 1-5; among them, Rp of Example 1 is 90.71 KΩcm. 2 Compared to Comparison Example 1 (unpassivated), Rp = 12.95 KΩcm 2It increased by about 7 times; the larger the Rp, the better the passivation film density, the more stable it is, and the better its corrosion resistance; from Figure 2 The AC impedance spectra show that the impedance arc radii of Examples 1-3 are larger than those of Comparative Examples 1-5. The impedance arc radii of Comparative Examples 2-5 are larger than those of Comparative Example 1 (unpassivated), but the increase is not large enough. However, the impedance arc radii of Examples 1-3 are significantly larger, indicating that the environmentally friendly passivation method of the present invention has a good passivation effect and greatly improves the corrosion resistance of X40CrMoVN16-2 martensitic stainless steel.

[0078] From Table 1, it can be seen that the time it took for corrosion to initially appear on the sample surface after immersion in 3.5% NaCl in Examples 1-3 and Comparative Examples 1-5 is longer than 26 hours compared to 4 hours in Comparative Example 1. Figure 3 (a), (b), and (c) show that after soaking in 3.5% NaCl for 24 hours, no corrosion was observed on the surface of Examples 1-3, and the surface remained bright and mirror-like, indicating that the passivation film quality was qualified; while from Figure 3 (d)-(h) Comparative Examples 1-5 were subjected to varying degrees of corrosion, especially as Figure 3 (d) Comparative Example 1 shows the largest corrosion range and the most severe corrosion. Among them, Figures (e) and (f) show relatively mild corrosion, while Figures (g) and (h) show a larger corrosion range. Compared with Examples 1-3, Comparative Examples 2 and 3 demonstrate that the passivation solution concentration, passivation temperature, and passivation time must be within a reasonable range. Comparative Examples 4 and 5 demonstrate that adding appropriate amounts of sodium molybdate, sodium dodecyl sulfate, and nano-silica sol to citric acid-hydrogen peroxide can effectively improve corrosion resistance in chloride ion environments.

Claims

1. A passivation liquid for improving the corrosion resistance of X40CrMoVN16-2 high-nitrogen martensitic stainless steel, characterized by, The passivation solution comprises the following components in percentage by mass: 6-10% citric acid, 3-5% hydrogen peroxide, 0.8-1.2% sodium molybdate, 0.1-0.16% sodium dodecyl sulfate, 0.06%-0.12% nano-silica sol, and the rest is water.

2. The passivation solution for improving the corrosion resistance of X40CrMoVN16-2 high-nitrogen martensitic stainless steel according to claim 1, characterized in that: The passivation temperature is 35-45 DEG C.

3. The passivation solution for improving the corrosion resistance of X40CrMoVN16-2 high-nitrogen martensitic stainless steel according to claim 1, characterized in that: The passivation time is 50-60 min.

4. The passivation solution for improving the corrosion resistance of X40CrMoVN16-2 high-nitrogen martensitic stainless steel according to claim 1, characterized by: The chemical composition of the X40CrMoVN16-2 high-nitrogen martensitic stainless steel is as follows in percentage by mass: C: 0.35-0.45%, Cr: 14.00-16.00%, Mo: 1.00-2.50%, N: 0.10%-0.30%, V: ≤1.50%, P: ≤0.04%, S: ≤0.015%, and the balance is Fe and inevitable impurities.

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