A method for preparing a metal surface blackening agent

Abstract

This invention discloses a method for preparing a metal surface blackening agent, specifically relating to the field of blackening technology. The preparation method includes selecting martensitic hardened bearing steel as the substrate, processing it into a sample with dimensions of 20×1×65mm, and controlling the surface roughness Ra at 0.2μm; mixing sulfuric acid, triethanolamine, and ammonium persulfate in a mass ratio of 1:1:1, adding deionized water, and stirring thoroughly to obtain a chemical solution; immersing the electrolyzed martensitic hardened bearing steel substrate along with the electrolyte in an environment of 25°C for 15-20 minutes to generate a uniform black oxide coating on the metal surface; removing the treated martensitic hardened bearing steel substrate, thoroughly rinsing it with deionized water to remove residual chemical reagents, and drying it at 50°C for 2 hours to obtain the metal surface blackening agent product.

Description

Technical Field

[0001] This invention relates to the field of blackening technology, and more specifically, to a method for preparing a metal surface blackening agent. Background Technology

[0002] Metal surface treatment technology plays a vital role in industry, particularly in improving the performance of metallic materials. Black oxide coatings, a common surface treatment method, have garnered significant attention due to their unique properties. Black oxide coatings not only impart a deep black appearance to metal surfaces, enhancing their aesthetics, but also offer excellent protective functions, such as preventing hydrogen absorption, improving corrosion resistance, and extending service life. Especially in environments using lubricants, hydrogen gas generated from lubricant decomposition can penetrate the metal, leading to failure phenomena such as hydrogen embrittlement or whitening cracks.

[0003] Existing literature (Preparation of Thin Carbon Black Coatings and Study on Their Microwave Absorption Performance, 2019) describes the preparation of thin coatings by filling a silicone resin matrix with carbon black (CB) and evaluates their microwave absorption performance. Figure 2 As shown, the study prepared coatings using ultrasonic dispersion and mechanical stirring, and analyzed the microstructure and electromagnetic properties of the coatings using transmission electron microscopy (TEM), scanning electron microscopy (SEM), conductivity testing, dielectric property testing, and microwave absorption performance testing. The study found that the oxidized carbon black coating exhibited excellent microwave absorption capabilities at low thickness and low filler content, especially at a thickness of 1.9 mm and a filler content of 2.3%, achieving an effective absorption bandwidth of 5.44 GHz, covering the entire Ku-band (12-18 GHz). However, while the oxidation modification improves performance, it increases cost and pollutes the environment.

[0004] Therefore, there is an urgent need for a method to prepare a metal surface blackening agent that is easy to operate, low in cost, and does not pollute the environment. Summary of the Invention

[0005] To overcome the aforementioned deficiencies in the prior art, this invention provides a method for preparing a metal surface blackening agent. The method involves using martensitic hardening bearing steel as the substrate, preparing a chemical solution composed of sulfuric acid, triethanolamine, and ammonium persulfate in a 1:1:1 ratio, heating at 130°C for 30 minutes to generate a black oxide coating, rinsing with deionized water, and drying at 50°C for 2 hours to complete the preparation. This method addresses the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing a metal surface blackening agent includes the following steps:

[0008] Step S1: Martensitic hardened bearing steel is selected as the base material and processed into a sample with a specification of 20×1×65mm. The surface roughness Ra is controlled at 0.2μm.

[0009] The martensitic hardening bearing steel is a steel that has undergone quenching and tempering processes.

[0010] The surface roughness of the sample was controlled to be 0.2 micrometers through grinding and polishing processes;

[0011] Step S2: Mix sulfuric acid, triethanolamine and ammonium persulfate in a mass ratio of 1:1:1, add deionized water, and stir thoroughly to obtain a chemical solution.

[0012] The volume of deionized water added to the chemical solution is 1000 ml to 2000 ml.

[0013] Step S3: The martensitic hardened bearing steel substrate prepared in step S1 is used as the anode and immersed in the chemical solution prepared in step S2 for electrolytic treatment. During the electrolysis process, an anodic oxidation reaction occurs on the surface of the substrate to generate oxide precursors.

[0014] Step S4: Immerse the electrolyzed martensitic hardened bearing steel substrate along with the electrolyte in an environment of 25°C for 15-20 minutes to allow the oxide precursor generated by electrolysis to react further and generate a uniform black oxide coating.

[0015] Step S5: Take out the treated martensitic hardened bearing steel substrate, ultrasonically clean it with deionized water for 5 minutes to remove residual chemical reagents on the surface, and dry it at 50°C for 2 hours to obtain the metal surface blackening treatment agent product.

[0016] As a further aspect of the present invention, step S1 involves selecting martensitic hardening bearing steel as the base material and processing it into a sample with dimensions of 20×1×65mm, controlling the surface roughness Ra to 0.2μm. This includes the following specific details: the martensitic hardening bearing steel is a high-performance steel that has undergone quenching and tempering processes; the sample is processed into dimensions of 20×1×65mm. The surface roughness Ra of the sample is controlled to 0.2μm through precision grinding and polishing processes.

[0017] As a further aspect of the present invention, step S2 involves mixing sulfuric acid, triethanolamine, and ammonium persulfate in a mass ratio of 1:1:1, adding deionized water, and stirring thoroughly to obtain a chemical solution. This process includes the following specific steps: mixing sulfuric acid, triethanolamine, and ammonium persulfate in a mass ratio of 1:1:1, adding 1000 mL-2000 mL of deionized water, and stirring thoroughly to obtain a chemical solution. A mechanical stirrer is used to stir at a speed of 300-500 rpm for at least 30 minutes to ensure uniform distribution of the three reagents in the solution and to avoid uneven reaction caused by local concentration differences.

[0018] As a further aspect of the present invention, in step S3, the martensitic hardened bearing steel substrate prepared in step S1 is used as the anode and immersed in the chemical solution prepared in step S2 for electrolytic treatment. During the electrolysis process, an anodic oxidation reaction occurs on the surface of the substrate to generate oxide precursors. The specific contents include the following: the electrolysis conditions are: current density 1A / dm², voltage 10V, treatment time 10 minutes, and temperature 80°C.

[0019] As a further aspect of the present invention, the martensitic hardened bearing steel substrate after electrolytic treatment is immersed in the electrolyte at 25°C for 15-20 minutes to allow the oxide precursor generated by electrolysis to further react and form a uniform black oxide coating. This includes the following specific steps: the martensitic hardened bearing steel substrate is completely immersed in a chemical solution and subjected to a blackening treatment at a constant temperature of 25°C for 15-20 minutes. At this temperature, iron atoms on the steel surface react with oxygen atoms in the chemical solution to generate Fe3O4 (magnetite), which is the main component of the black oxide coating on the metal surface.

[0020] As a further aspect of the present invention, in step S5, the treated martensitic hardened bearing steel substrate is removed, ultrasonically cleaned with deionized water for 5 minutes to remove residual chemical reagents on the surface, and dried at 50°C for 2 hours to obtain a metal surface blackening agent product, including the following specific contents: After the martensitic hardened bearing steel undergoes blackening treatment at 130°C for 30 minutes, it must be immediately removed from the blackening agent and cleaned to avoid residual chemicals from adversely affecting the coating or substrate. The cleaning process begins with a thorough rinse using deionized water. The rinsing continues for several minutes, and the operator must carefully observe the water flow until it becomes clear and colorless, indicating that the residual chemicals on the surface have been completely removed and the cleaning effect has reached the ideal state. After cleaning, the martensitic hardened bearing steel substrate must be dried immediately, specifically at 50°C for 2 hours. The coating after cleaning and drying exhibits a uniform and dense microstructure, with a thickness controlled between 1.0-1.6 micrometers and an Fe3O4 (magnetite) grain size of approximately 33 nanometers.

[0021] The technical effects and advantages of the preparation method of the metal surface blackening treatment agent of this invention are as follows: This invention uses martensitic hardening bearing steel as the substrate, prepares a chemical solution by mixing sulfuric acid, triethanolamine and ammonium persulfate in a 1:1:1 ratio, heats at 130°C for 30 minutes to generate a black oxide coating, rinses with deionized water, and dries at 50°C for 2 hours to complete the preparation. The preparation process of this invention involves only simple steps such as substrate processing, solution preparation, soaking and heating, and cleaning and drying, without the need for complex equipment or processes, thus simplifying the production process; the chemical reagents used are all common and inexpensive substances, and the processing conditions (such as heating at 130°C and drying at 50°C) do not require high temperature and high pressure, reducing energy consumption and equipment investment; no toxic or harmful substances are used in the preparation process, and deionized water is used for cleaning to avoid secondary pollution; the generated black oxide coating is uniform and dense, with a thickness controlled at 1.0-1.6 micrometers, and the Fe3O4 grain size is about 33 nanometers, which not only prevents hydrogen absorption but also improves corrosion resistance and extends service life. This invention provides an efficient, economical, and environmentally friendly method for blackening metal surfaces, effectively solving the problems of high cost and environmental pollution in existing technologies. Attached Figure Description

[0022] Figure 1 This is a flowchart of a method for preparing a metal surface blackening agent according to the present invention.

[0023] Figure 2 An experimental flowchart for the preparation of CB coatings using existing technology.

[0024] Figure 3 This is a SEM image of the metal surface blackening agent coating of the present invention.

[0025] Figure 4 This is a TEM image of the metal surface blackening agent coating of the present invention.

[0026] Figure 5 This is a schematic diagram showing the diffusible hydrogen content of uncoated and blackened steel samples under different heating rates according to the present invention. Detailed Implementation

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0028] Example 1. See Figure 1 The flowchart shown illustrates a method for preparing a metal surface blackening agent according to the present invention, which includes the following steps:

[0029] Step S1: Martensitic hardened bearing steel is selected as the base material and processed into a sample with a specification of 20×1×65mm. The surface roughness Ra is controlled at 0.2μm.

[0030] The martensitic hardened bearing steel is a steel that has undergone quenching and tempering processes.

[0031] The surface roughness of the sample was controlled to be 0.2 micrometers through grinding and polishing processes;

[0032] Step S2: Mix sulfuric acid, triethanolamine and ammonium persulfate in a mass ratio of 1:1:1, add deionized water, and stir thoroughly to obtain a chemical solution.

[0033] The volume of deionized water added to the chemical solution is 1000 ml to 2000 ml.

[0034] Step S3: The martensitic hardened bearing steel substrate prepared in step S1 is used as the anode and immersed in the chemical solution prepared in step S2 for electrolytic treatment. During the electrolysis process, an anodic oxidation reaction occurs on the surface of the substrate to generate oxide precursors.

[0035] Step S4: Immerse the electrolyzed martensitic hardened bearing steel substrate along with the electrolyte in an environment of 25°C for 15-20 minutes to allow the oxide precursor generated by electrolysis to react further and generate a uniform black oxide coating.

[0036] Step S5: Take out the treated martensitic hardened bearing steel substrate, ultrasonically clean it with deionized water for 5 minutes to remove residual chemical reagents on the surface, and dry it at 50°C for 2 hours to obtain the metal surface blackening treatment agent product.

[0037] Further, in step S1, martensitic hardening bearing steel is selected as the base material and processed into a sample with dimensions of 20×1×65mm. The surface roughness Ra is controlled at 0.2μm. This includes: the martensitic hardening bearing steel is a high-performance steel that has undergone quenching and tempering processes; the sample is processed into a size of 20×1×65mm; and the surface roughness Ra of the sample is controlled at 0.2μm through precision grinding and polishing processes. Surface roughness Ra refers to the arithmetic mean deviation of the surface profile; the smaller the value, the smoother the surface.

[0038] In this embodiment, to verify that a surface roughness Ra = 0.2 μm is the optimal value for the adhesion of the black oxide coating and to achieve a balance between adhesion and coating integrity, samples with different surface roughnesses were selected for testing. Four groups of samples with Ra = 0.1 μm, 0.2 μm, 0.4 μm, and 0.6 μm were used in the experiment. The coating adhesion was measured using a cross-cut adhesion test (rated from 0 to 5, with 5 being the best). The coating integrity was assessed by observing the number of surface defects (unit: defects / cm²). The experimental data are shown in Table 1.

[0039] Table 1 Test results of samples with different surface roughness

[0040]

[0041] As shown in Table 1, when the surface roughness Ra = 0.2 μm, the black oxide coating achieves the highest adhesion grade (level 5) while having the fewest surface defects (1 defect / cm²), indicating that under this condition, the mechanical interlocking between the coating and the substrate is strongest, and the coating integrity is optimal. In contrast, when Ra = 0.1 μm, the surface is too smooth, resulting in insufficient contact area, causing the adhesion grade to drop to level 3 and the defect number to increase to 5 defects / cm²; when Ra = 0.4 μm, the adhesion grade is level 4, and the defect number is 3 defects / cm², still maintaining good performance but not as good as Ra = 0.2 μm; when Ra = 0.6 μm, the surface is too rough, and defects easily form in the coating at uneven areas, causing the adhesion grade to drop to level 2 and the defect number to reach as high as 8 defects / cm². These data indicate that Ra = 0.2 μm achieves the best balance between adhesion and coating integrity.

[0042] Further, in step S2, sulfuric acid, triethanolamine, and ammonium persulfate are mixed in a mass ratio of 1:1:1, and deionized water is added. The mixture is stirred thoroughly to obtain a chemical solution. This solution comprises: sulfuric acid, triethanolamine, and ammonium persulfate mixed in a mass ratio of 1:1:1, and 1000 mL-2000 mL of deionized water is added. After thorough stirring, a chemical solution is obtained. A mechanical stirrer is used to stir at a speed of 300-500 rpm for at least 30 minutes to ensure that the three reagents are evenly distributed in the solution and to avoid uneven reaction caused by local concentration differences.

[0043] Further, in step S3, the martensitic hardened bearing steel substrate, acting as the anode, is immersed in a chemical solution prepared from a mixture of sulfuric acid, triethanolamine, and ammonium persulfate (mass ratio 1:1:1), and electrolysis is performed by connecting a DC power supply (current density 1 A / dm², voltage 10 V, temperature 80 °C, processing time 10 minutes). During electrolysis, the iron atoms (Fe) on the substrate surface undergo an anodic oxidation reaction, losing electrons to generate Fe. 2+ or Fe 3+Ions. These ions combine with oxygen or other anions in the solution to deposit on the substrate surface, forming the oxide precursor Fe2O3.

[0044] Further, in step S4, the martensitic hardened bearing steel substrate after electrolytic treatment, along with the electrolyte, is immersed in an environment of 25°C for 15-20 minutes to allow the oxide precursor generated by electrolysis to react further, forming a uniform black oxide coating. This includes: the martensitic hardened bearing steel substrate being completely immersed in a chemical solution and soaked at a constant temperature of 25°C for 15-20 minutes for blackening treatment. At this temperature, the oxide precursor undergoes chemical and crystal structure transformation under the action of the solution, ultimately generating Fe3O4 (magnetite), which is the main component of the black oxide coating.

[0045] Further, the treated martensitic hardened bearing steel substrate is removed and thoroughly rinsed with deionized water to remove residual chemical reagents from the surface. It is then dried at 50°C for 2 hours to obtain the metal surface blackening treatment agent product. This includes the following: after the martensitic hardened bearing steel has undergone blackening treatment at 130°C for 30 minutes, it must be immediately removed from the blackening agent and cleaned to avoid adverse effects of residual chemicals on the coating or substrate. The cleaning process begins with a thorough rinsing with deionized water. Deionized water is used because it does not contain impurity ions that may react with the coating or substrate, effectively avoiding secondary contamination and ensuring the chemical purity and structural integrity of the coating. During rinsing, deionized water efficiently removes residual chemical reagents from the metal surface, such as sulfuric acid, triethanolamine, and ammonium persulfate. Rinsing continues for several minutes, and the operator must carefully observe the water flow until it becomes clear and colorless, indicating that the residual chemicals have been completely removed and the cleaning effect is ideal. If rinsing is incomplete, residual reagents may cause coating defects in subsequent steps and even affect the long-term durability of the substrate. After cleaning, the martensitic hardened bearing steel substrate must be dried immediately, specifically at 50°C for 2 hours. The gentle drying temperature of 50°C does not damage the microstructure of the black oxide coating while maintaining its stability, and the 2-hour drying time is sufficient to completely evaporate the moisture on the coating surface, avoiding potential corrosion or coating peeling caused by residual moisture. The cleaned and dried coating exhibits a uniform and dense microstructure, with a thickness controlled between 1.0 and 1.6 micrometers, and the Fe3O4 (magnetite) grain size is approximately 33 nanometers.

[0046] This invention uses martensitic hardening bearing steel as the substrate and prepares a chemical solution consisting of sulfuric acid, triethanolamine, and ammonium persulfate in a 1:1:1 ratio. The solution is heated at 130°C for 30 minutes to generate a black oxide coating, which is then rinsed with deionized water and dried at 50°C for 2 hours to complete the preparation. The preparation process involves only simple steps such as substrate processing, solution preparation, immersion heating, and cleaning and drying, requiring no complex equipment or processes, thus simplifying the production flow. The chemical reagents used are all common and inexpensive substances, and the processing conditions (such as heating at 130°C and drying at 50°C) do not require high temperature and high pressure, reducing energy consumption and equipment investment. No toxic or harmful substances are used in the preparation process, and deionized water is used for cleaning to avoid secondary pollution. The resulting black oxide coating is uniform and dense, with a thickness controlled at 1.0-1.6 micrometers and an Fe3O4 grain size of approximately 33 nanometers. This coating not only prevents hydrogen absorption but also improves corrosion resistance and extends service life. This invention provides an efficient, economical, and environmentally friendly method for blackening metal surfaces, effectively solving the problems of high cost and environmental pollution in existing technologies.

[0047] Example 2. To verify the performance of the metal surface blackening agent coating prepared according to the present invention, microstructure analysis and hydrogen absorption tests were performed on the samples from the above examples. The results are as follows:

[0048] Microstructure analysis: 1. The surface morphology of the coating was observed using a scanning electron microscope (SEM). The results showed that the coating surface was uniform and dense, with no obvious cracks or pores. Figure 3 As shown. 2. Transmission electron microscopy (TEM) analysis showed that the coating thickness ranged from 1.0 to 1.6 μm, composed of nanoscale grains (average size approximately 33 nm), with magnetite (Fe3O4) as the main component, accompanied by small amounts of hematite (Fe2O3) and residual cementite, such as... Figure 4 As shown.

[0049] like Figure 5As shown, uncoated steel samples and steel samples coated with a blackening agent were immersed in lubricant and heated to 200°C at different constant heating rates (10°C / h, 20°C / h, 50°C / h, 100°C / h). The diffusible hydrogen content of the uncoated and blackening agent coated steel samples under specific experimental conditions is shown in the figure. It can be seen that as the heating rate increases from 10°C / h to 20°C / h, the diffusible hydrogen content of the uncoated sample increases significantly, reaching a peak at 20°C / h. When the heating rate is further increased to 50°C / h and 100°C / h, the diffusible hydrogen content gradually decreases. At all heating rates (10°C / h, 20°C / h, 50°C / h, 100°C / h), the diffusible hydrogen content of the coated samples is very low, almost close to zero. This indicates that the blackening agent coating on the metal surface can effectively prevent hydrogen generated by the decomposition of the lubricant from entering the interior of the steel.

[0050] Example 3. In this example, martensitic hardening bearing steel was first selected as the base material due to its high hardness, high strength, and good wear resistance and fatigue resistance, making it widely used in high-load applications, such as bearing components of wind turbines. The steel was machined into a sample with dimensions of 20×1×65mm, and the surface was polished to achieve a surface roughness of Ra=0.2μm. This roughness level provides sufficient contact area to enhance coating adhesion while avoiding defects or decreased adhesion caused by excessively rough or smooth surfaces. Next, 100g of sulfuric acid, 100g of triethanolamine, and 100g of ammonium persulfate were accurately weighed and mixed in a mass ratio of 1:1:1. These reagents were added to 1000mL of deionized water and stirred with a magnetic stirrer at an appropriate speed for 30 minutes until all components were completely dissolved, resulting in a homogeneous chemical solvent. The use of deionized water avoids interference from impurities, ensuring the purity of the solution and the stability of subsequent reactions. Subsequently, the prepared metal substrate was used as the anode and immersed in the aforementioned chemical solvent for electrolytic treatment. The electrolyzed martensitic hardened bearing steel substrate, along with the electrolyte, was placed in a constant-temperature heating furnace and held at 130°C for 30 minutes. During this process, a black oxide coating gradually formed on the metal surface through a chemical reaction. The coating was uniform in color and free of obvious defects. Finally, the treated sample was removed from the blackening agent and rinsed three times with deionized water to thoroughly remove any residual chemical reagents from the surface. The sample was then placed in a 50°C oven and dried for 2 hours to remove surface moisture, yielding a metal surface blackening agent coating sample.

[0051] Example 4. First, prepare the metal substrate. Similar to Example 2, martensitic hardened bearing steel was selected as the substrate and machined into a sample with dimensions of 20×1×65mm. Precision machining was used to achieve a surface roughness of Ra=0.2μm to ensure the uniformity and stability of the coating adhesion. Next, prepare the chemical solution. Accurately weigh 150g of sulfuric acid, 150g of triethanolamine, and 150g of ammonium persulfate, mix them in a mass ratio of 1:1:1, and add them to 1500mL of deionized water. Stir for 40 minutes until all reagents are completely dissolved. Compared to Example 2, this step increases the amount of reagents and the volume of deionized water, thereby increasing the reagent concentration. Subsequently, the prepared metal substrate was completely immersed in the above blackening treatment agent and placed in a constant temperature heating furnace, where it was kept at 130°C for 30 minutes. Finally, after the blackening treatment was completed, the sample was removed and thoroughly rinsed with deionized water to remove any residual chemical reagents from the surface. Subsequently, the sample was dried in a 50°C environment for 2 hours to finally obtain a metal surface blackening agent coating sample.

[0052] Example 5. Martensitic hardened bearing steel was selected as the substrate, consistent with Examples 2 and 3. The substrate was machined into a sample with dimensions of 20×1×65mm, and the surface roughness was achieved to Ra=0.2μm through precision machining and polishing. 200g of sulfuric acid, 200g of triethanolamine, and 200g of ammonium persulfate were accurately weighed and mixed in a mass ratio of 1:1:1, then added to 2000mL of deionized water. The mixture was stirred for 50 minutes until all reagents were completely dissolved to obtain a chemical solution. Compared to Examples 2 and 3, the amount of reagents and the volume of deionized water were further increased here. The prepared metal substrate was completely immersed in the above chemical solution and placed in a constant temperature heating furnace, where it was kept at 130°C for 30 minutes. After the blackening treatment was completed, the sample was removed and thoroughly rinsed with deionized water to remove any residual chemical reagents from the surface. Subsequently, the sample was dried in an environment of 50°C for 2 hours to finally obtain a metal surface blackening agent coating sample.

[0053] In Examples 3, 4, and 5 above, by increasing the amount of reagent (300g to 600g) and the volume of deionized water (1000mL to 2000mL), the final metal surface blackening agent coating thickness gradually increased from 1.0-1.6μm to 2.0-2.5μm, and the hydrogen absorption resistance increased from 70% to 80%, showing a trend of improved coating performance with increasing thickness. Experimental data are shown in Table 2.

[0054] Table 2 Performance of metal surface blackening agent coatings under different reagent dosages and deionization volumes

[0055]

[0056] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

[0057] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a metal surface blackening agent, characterized in that, Includes the following steps: Step S1: Martensitic hardening bearing steel is selected as the base material and processed to have a surface roughness Ra controlled at 0.2 μm; the martensitic hardening bearing steel is steel that has undergone quenching and tempering processes, and the surface roughness is controlled at 0.2 micrometers through grinding and polishing processes. Step S2: Sulfuric acid, triethanolamine, and ammonium persulfate are mixed in a mass ratio of 1:1:1, deionized water is added, and the mixture is stirred thoroughly to obtain a chemical solution; the volume of deionized water added to the chemical solution is 1000 ml to 2000 ml. Step S3: The martensitic hardened bearing steel substrate prepared in step S1 is used as the anode and immersed in the chemical solution prepared in step S2. A DC power supply is connected to perform electrolytic treatment. During the electrolysis process, an anodic oxidation reaction occurs on the surface of the substrate to generate oxide precursors. Step S4: Immerse the electrolyzed martensitic hardened bearing steel substrate along with the electrolyte in an environment of 25°C for 15-20 minutes to allow the oxide precursor generated by electrolysis to react further and generate a uniform black oxide coating. Step S5: Take out the treated martensitic hardened bearing steel substrate, ultrasonically clean it with deionized water for 5 minutes to remove residual chemical reagents on the surface, and dry it at 50°C for 2 hours to obtain the metal surface blackening treatment agent product. Specifically, in step S4, the martensitic hardening bearing steel substrate is immersed in a chemical solution, and the iron atoms on the steel surface react with the oxygen atoms in the solution to generate a Fe3O4 black oxide coating.

2. The method for preparing a metal surface blackening agent according to claim 1, characterized in that, In step S2, a mechanical stirrer is used to stir the solution at a speed of 300-500 rpm for more than 30 minutes to ensure that the reagent is evenly distributed in the solution.

3. The method for preparing a metal surface blackening agent according to claim 1, characterized in that, In step S5, the rinsing process uses deionized water to remove residual sulfuric acid, triethanolamine, and ammonium persulfate from the surface until the water is clear and colorless.

4. The method for preparing a metal surface blackening agent according to claim 1, characterized in that, In step S5, the drying process is carried out at 50°C for 2 hours to completely evaporate the moisture on the coating surface without damaging the coating's microstructure.

5. The method for preparing a metal surface blackening agent according to claim 1, characterized in that, The thickness of the generated black oxide coating is controlled between 1.0 and 1.6 micrometers, and the Fe3O4 grain size is 33 nanometers.

6. The method for preparing a metal surface blackening agent according to claim 1, characterized in that, When the surface roughness Ra of the martensitic hardening bearing steel is 0.2 μm, the adhesion grade of the black oxide coating is level 5, and the number of surface defects is 1 / cm².

7. The method for preparing a metal surface blackening agent according to claim 1, characterized in that, In step S3, the electrolysis conditions are: current density 1A / dm², voltage 10V, processing time 10 minutes, and temperature 80°C.

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