Preparation method of metal surface blackening treatment agent

Abstract

The invention discloses a preparation method of a metal surface blackening treatment agent, and particularly relates to the technical field of blackening, the preparation method comprises the following steps: selecting martensitic hardened bearing steel as a base material, processing the base material into a sample with the specification of 20 * 1 * 65 mm, and controlling the surface roughness Ra to be 0.2 mu m; the preparation method comprises the following steps: mixing sulfuric acid, triethanolamine and ammonium persulfate according to a mass ratio of 1: 1: 1, adding deionized water, and fully and uniformly stirring to prepare a chemical solution; the martensitic hardened bearing steel base material obtained after electrolysis treatment and electrolyte are placed in the environment of 25 DEG C to be soaked for 15-20 min, and a uniform black oxide coating is generated on the metal surface; and taking out the treated martensitic hardened bearing steel base material, thoroughly washing the martensitic hardened bearing steel base material with deionized water to remove residual chemical reagents on the surface, and drying the martensitic hardened bearing steel base material at 50 DEG C for 2 hours to obtain the metal surface blackening treatment agent product.

Description

Technical Field

[0001] The present invention relates to the technical field of blackening, and more particularly to a method for preparing a metal surface blackening treatment agent. Background Art

[0002] Metal surface treatment technology is of great significance in the industrial field, playing a key role in improving the performance of metal materials. Black oxide coating, a common surface treatment method, has attracted much attention due to its unique properties. Black oxide coating not only imparts a deep black appearance to the metal surface, enhancing its decorative properties, but also provides excellent protective functions, such as preventing hydrogen absorption, improving corrosion resistance, and extending service life. This is particularly true in lubricant-using environments, where hydrogen generated by lubricant decomposition can penetrate the metal interior, leading to failure phenomena such as hydrogen embrittlement or white etching cracking.

[0003] Existing open literature (Preparation of thin carbon black coating and study of its microwave absorption performance, 2019) prepares thin coatings by filling carbon black (CB) in a silicone resin matrix and evaluates its microwave absorption performance. Figure 2 As shown in the study, the coating was prepared using ultrasonic dispersion and mechanical stirring. The microstructure and electromagnetic properties of the coating were analyzed using transmission electron microscopy (TEM), scanning electron microscopy (SEM), conductivity testing, dielectric properties testing, and microwave absorption testing. The study found that the oxidatively modified carbon black coating exhibited excellent microwave absorption at low thicknesses and low filler loadings. In particular, at a thickness of 1.9 mm and a filler loading of 2.3%, the effective absorption bandwidth reached 5.44 GHz, covering the entire Ku-band (12-18 GHz). However, while the oxidative modification improves performance, it also increases costs and poses environmental risks.

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

[0005] In order to overcome the above-mentioned defects of the prior art, the present invention provides a method for preparing a metal surface blackening treatment agent, which is prepared by selecting martensitic hardened bearing steel as a substrate, preparing a chemical solution composed of sulfuric acid, triethanolamine and ammonium persulfate in a ratio of 1:1:1, heating it at 130°C for 30 minutes to generate a black oxide coating, and then rinsing it with deionized water and drying it at 50°C for 2 hours to complete the preparation, so as to solve the problems raised in the above-mentioned background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions: A method for preparing a metal surface blackening treatment agent comprises the following steps: Step S1, martensitic hardened bearing steel is selected as the substrate and processed into a sample with a specification of 20×1×65 mm, and the surface roughness Ra is controlled at 0.2 μm; The martensitic hardened bearing steel is a steel material that has been processed by quenching and tempering. The surface roughness of the sample was controlled to 0.2 μm by grinding and polishing process; Step S2, mixing sulfuric acid, triethanolamine, and ammonium persulfate in a mass ratio of 1:1:1, adding deionized water, and stirring thoroughly to prepare a chemical solution; The volume of deionized water added to the chemical solution is 1000 ml to 2000 ml; Step S3, using the martensitic hardened bearing steel substrate prepared in step S1 as an anode and immersing it in the chemical solution prepared in step S2 for electrolysis. During the electrolysis, an anodic oxidation reaction occurs on the surface of the substrate to generate an oxide precursor. Step S4, soaking the electrolytically treated martensite-hardened bearing steel substrate and the electrolyte at 25° C. for 15-20 minutes to allow the electrolytically generated oxide precursor to further react and form a uniform black oxide coating; Step S5: Take out the treated martensite hardened bearing steel substrate, ultrasonically clean it with deionized water for 5 minutes to remove the chemical reagents remaining on the surface, and dry it at 50°C for 2 hours to obtain a metal surface blackening treatment agent product.

[0007] As a further embodiment of the present invention, step S1 includes selecting martensite-hardened bearing steel as a substrate and processing it into a sample with specifications of 20×1×65 mm, with a surface roughness Ra controlled to 0.2 μm. The martensite-hardened bearing steel is a high-performance steel that has been quenched and tempered. The sample is processed into a size of 20×1×65 mm. The surface roughness Ra of the sample is controlled to 0.2 μm through precision grinding and polishing.

[0008] As a further embodiment of the present invention, step S2, mixing sulfuric acid, triethanolamine, and ammonium persulfate in a mass ratio of 1:1:1, adding deionized water, and stirring thoroughly to prepare a chemical solution, comprising the following specific contents: mixing sulfuric acid, triethanolamine, and ammonium persulfate in a mass ratio of 1:1:1, adding 1000mL-2000mL of deionized water, and stirring thoroughly to prepare a chemical solution. A mechanical stirrer is used to stir at a speed of 300-500 rpm for more than 30 minutes to ensure that the three reagents are evenly distributed in the solution to avoid uneven reaction caused by local concentration differences.

[0009] As a further embodiment of the present invention, in step S3, the martensitic hardened bearing steel substrate prepared in step S1 is used as an 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 an oxide precursor, including the following specific contents: the electrolysis conditions are: current density 1A / dm², voltage 10V, treatment time 10 minutes, and temperature 80°C.

[0010] As a further embodiment of the present invention, the electrolytically treated martensite-hardened bearing steel substrate and the electrolyte are immersed in an environment at 25°C for 15-20 minutes to allow the electrolytically generated oxide precursor to further react and form a uniform black oxide coating. Specifically, the martensite-hardened bearing steel substrate is completely immersed in a chemical solution at a constant temperature of 25°C for 15-20 minutes to perform a blackening treatment. At this temperature, iron atoms on the steel surface react with oxygen atoms in the chemical solution to form Fe3O4 (magnetite), which is the primary component of the black oxide coating on the metal surface.

[0011] As a further embodiment of the present invention, step S5 involves removing the treated martensite-hardened bearing steel substrate, ultrasonically cleaning it with deionized water for 5 minutes to remove any residual surface chemicals, and drying it at 50°C for 2 hours to obtain a metal surface blackening treatment agent product. This includes the following specific steps: After the martensite-hardened bearing steel substrate has been blackened at 130°C for 30 minutes, it is immediately removed from the blackening treatment agent and cleaned to prevent any residual chemicals from adversely affecting the coating or substrate. The cleaning process begins with a thorough rinse with deionized water. The rinse continues for several minutes, with the operator carefully monitoring the water flow until it becomes clear and colorless, indicating that any residual surface chemicals have been completely removed and the cleaning effect has been achieved. After cleaning, the martensite-hardened bearing steel substrate is immediately dried, specifically at 50°C for 2 hours. The cleaned and dried coating exhibits a uniform and dense microstructure, with a thickness between 1.0 and 1.6 microns and Fe₃O₄ (magnetite) grain size of approximately 33 nanometers.

[0012] The technical effects and advantages of the method for preparing a metal surface blackening treatment agent disclosed herein are as follows: The method uses martensitic hardened bearing steel as a substrate, prepares a chemical solution comprising sulfuric acid, triethanolamine, and ammonium persulfate in a 1:1:1 ratio, heats the solution at 130°C for 30 minutes to generate a black oxide coating, and then rinses with deionized water and dries at 50°C for 2 hours to complete the preparation. The preparation process of the present invention involves only simple steps, such as substrate processing, solution preparation, soaking and heating, and cleaning and drying, eliminating the need for complex equipment or processes, thus simplifying the production process. The chemical reagents used are all common and inexpensive, and the processing conditions (e.g., heating at 130°C and drying at 50°C) do not require high temperature or high pressure, reducing energy consumption and equipment investment. No toxic or hazardous substances are used in the preparation process, and deionized water is used for cleaning to avoid secondary contamination. The resulting black oxide coating is uniform and dense, with a thickness controlled to 1.0-1.6 microns 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. The present invention provides an efficient, economical and environmentally friendly method for blackening metal surfaces, which effectively solves the problems of high cost and environmental pollution in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The present invention is a flow chart of a method for preparing a metal surface blackening treatment agent.

[0014] Figure 2 Experimental flow chart for the preparation of CB coating in the prior art.

[0015] Figure 3 This is an SEM image of the metal surface blackening treatment agent coating of the present invention.

[0016] Figure 4 This is a TEM image of the metal surface blackening treatment agent coating of the present invention.

[0017] Figure 5 Schematic diagram of the diffusible hydrogen content of non-coated and blackening treatment agent coated steel samples at different heating rates of the present invention. DETAILED DESCRIPTION

[0018] 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.

[0019] Example 1. See Figure 1 As shown in the flow chart, the present invention provides a method for preparing a metal surface blackening treatment agent, which comprises the following steps: Step S1, martensitic hardened bearing steel is selected as the substrate and processed into a sample with a specification of 20×1×65 mm, and the surface roughness Ra is controlled at 0.2 μm; The martensite hardened bearing steel is a steel material that has been processed by quenching and tempering processes; The surface roughness of the sample was controlled to 0.2 μm by grinding and polishing process; Step S2, mixing sulfuric acid, triethanolamine, and ammonium persulfate in a mass ratio of 1:1:1, adding deionized water, and stirring thoroughly to prepare a chemical solution; The volume of deionized water added to the chemical solution is 1000 ml to 2000 ml; Step S3, using the martensitic hardened bearing steel substrate prepared in step S1 as an anode and immersing it in the chemical solution prepared in step S2 for electrolysis. During the electrolysis, an anodic oxidation reaction occurs on the surface of the substrate to generate an oxide precursor. Step S4, soaking the electrolytically treated martensite-hardened bearing steel substrate and the electrolyte at 25° C. for 15-20 minutes to allow the electrolytically generated oxide precursor to further react and form a uniform black oxide coating; Step S5: Take out the treated martensite hardened bearing steel substrate, ultrasonically clean it with deionized water for 5 minutes to remove the chemical reagents remaining on the surface, and dry it at 50°C for 2 hours to obtain a metal surface blackening treatment agent product.

[0020] Furthermore, step S1 selects martensitic hardened bearing steel as the substrate and processes it into a sample with a specification of 20×1×65mm, with the surface roughness Ra controlled at 0.2μm, including: the martensitic hardened bearing steel is a high-performance steel that has been processed through a quenching and tempering process, and the sample is processed into a specification of 20×1×65mm. 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.

[0021] In this example, to verify that a surface roughness of Ra = 0.2μm is the optimal value for black oxide coating adhesion 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 = 0.1μm, 0.2μm, 0.4μm, and 0.6μm were used in the experiment. Coating adhesion was measured using the cross-hatch method (scoring on a scale of 0-5, with 5 being the best), and coating integrity was assessed by observing the number of surface defects (unit: defects / cm²). The experimental data is shown in Table 1: Table 1 Test results of samples with different surface roughness

[0022] Table 1 shows that when the surface roughness Ra = 0.2μm, the black oxide coating achieves the highest adhesion level (level 5) and the lowest number of surface defects (1 defect / cm²), indicating that under this condition, the mechanical fit between the coating and the substrate is the strongest and the coating integrity is optimal. In contrast, when the surface is too smooth, resulting in insufficient contact area, the adhesion level drops to level 3, and the number of defects increases to 5 defects / cm². When the surface is Ra = 0.4μm, the adhesion level is level 4, with 3 defects / cm², which still maintains good performance but is inferior to that of Ra = 0.2μm. When the surface is Ra = 0.6μm, the surface is too rough, and the coating is prone to defects in uneven areas, resulting in the adhesion level dropping to level 2, with a high number of defects / cm². These data indicate that a Ra = 0.2μm provides the best balance between adhesion and coating integrity.

[0023] Furthermore, step S2 comprises mixing sulfuric acid, triethanolamine, and ammonium persulfate in a mass ratio of 1:1:1, adding deionized water, and stirring thoroughly to prepare a chemical solution, comprising: mixing sulfuric acid, triethanolamine, and ammonium persulfate in a mass ratio of 1:1:1, adding 1000 mL to 2000 mL of deionized water, and stirring thoroughly to prepare a chemical solution. A mechanical stirrer is used to stir at a speed of 300 to 500 rpm for more than 30 minutes to ensure that the three reagents are evenly distributed in the solution to avoid uneven reaction caused by local concentration differences.

[0024] Furthermore, in step S3, the martensitic hardened bearing steel substrate is used as the anode and immersed in a chemical solution prepared by mixing sulfuric acid, triethanolamine, and ammonium persulfate (mass ratio 1:1:1). A DC power supply (current density 1A / dm², voltage 10V, temperature 80°C, treatment time 10 minutes) is connected to perform electrolysis. During the electrolysis process, the iron atoms (Fe) on the surface of the substrate 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 and deposit on the substrate surface to form the oxide precursor Fe2O3.

[0025] Furthermore, step S4 involves immersing the electrolytically treated martensitic hardened bearing steel substrate and the electrolyte at 25°C for 15-20 minutes to allow the electrolytically generated oxide precursor to further react and form a uniform black oxide coating. This process involves completely immersing the martensitic hardened bearing steel substrate in a chemical solution at a constant temperature of 25°C for 15-20 minutes to perform a blackening treatment. At this temperature, the oxide precursor undergoes chemical and crystal structure transformations under the action of the solution, ultimately forming Fe3O4 (magnetite), the primary component of the black oxide coating.

[0026] Furthermore, the treated martensitic hardened bearing steel substrate is removed, thoroughly rinsed with deionized water to remove residual chemical reagents on the surface, and dried at 50°C for 2 hours to obtain a metal surface blackening treatment agent product, including: after the martensitic hardened bearing steel is blackened at 130°C for 30 minutes, it must be immediately removed from the blackening treatment agent and cleaned to avoid residual chemicals from adversely affecting the coating or substrate. The cleaning process first uses deionized water for thorough rinsing. The reason for using deionized water for rinsing is that it does not contain impurity ions that may react with the coating or substrate, thereby effectively avoiding secondary contamination and ensuring the chemical purity and structural integrity of the coating. During the rinsing process, deionized water can efficiently remove residual chemical reagents on the metal surface, such as sulfuric acid, triethanolamine, and ammonium persulfate. The rinsing lasts for several minutes, and the operator needs to 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. If the rinsing is not thorough, the 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 is immediately dried at 50°C for two hours. The gentle drying temperature of 50°C preserves the black oxide coating's microstructure while maintaining its stability. The two-hour drying time allows for complete evaporation of any surface moisture, preventing potential corrosion or coating flaking caused by residual moisture. The cleaned and dried coating exhibits a uniform and dense microstructure with a thickness of 1.0-1.6 microns and an Fe3O4 (magnetite) grain size of approximately 33 nanometers.

[0027] This invention uses martensitic hardened bearing steel as a substrate, prepares a chemical solution composed of sulfuric acid, triethanolamine, and ammonium persulfate in a 1:1:1 ratio, heats it at 130°C for 30 minutes, and produces a black oxide coating. The coating is then rinsed with deionized water and dried at 50°C for 2 hours to complete the process. The process involves simple steps such as substrate processing, solution preparation, soaking and heating, and cleaning and drying, eliminating the need for complex equipment or processes, thus simplifying the production process. The chemical reagents used are common and inexpensive, and the processing conditions (e.g., heating at 130°C and drying at 50°C) do not require high temperatures or high pressures, reducing energy consumption and equipment investment. No toxic or hazardous substances are used in the preparation process, and deionized water is used for rinsing to avoid secondary contamination. The resulting black oxide coating is uniform and dense, with a thickness of 1.0-1.6 microns and 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 addressing the high costs and environmental pollution issues of existing technologies.

[0028] Example 2. In order to verify the performance of the metal surface blackening treatment agent coating prepared by the present invention, microstructure analysis and hydrogen absorption test were performed on the samples of the above examples. The results are as follows: Microstructure analysis: 1. Scanning electron microscope (SEM) was used to observe the surface morphology of the coating. The results showed that the coating surface was uniform and dense, without obvious cracks or pores. Figure 3 2. Transmission electron microscopy (TEM) analysis shows that the coating has a thickness range of 1.0-1.6 μm and is composed of nano-scale grains (average size of about 33 nm), the main component of which is magnetite (Fe3O4), accompanied by a small amount of hematite (Fe2O3) and residual cementite, such as Figure 4 shown.

[0029] like Figure 5 As shown in the figure, uncoated steel samples and blackening agent-coated steel samples were immersed in lubricant and heated to 200°C at different constant heating rates (10°C / h, 20°C / h, 50°C / h, and 100°C / h). The diffusible hydrogen content of the uncoated and blackening agent-coated steel samples under specific experimental conditions at different constant heating rates is shown. 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. As the heating rate further increases 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, and 100°C / h), the diffusible hydrogen content of the coated sample is very low, almost close to zero. This indicates that the blackening agent coating on the metal surface effectively prevents hydrogen generated by lubricant decomposition from entering the steel.

[0030] Example 3. In this example, martensitic hardened bearing steel is first selected as the substrate because it has high hardness, high strength, good wear resistance and fatigue resistance, and is widely used in high-load scenarios, such as bearing components of wind turbines. The steel is processed into a sample with a size of 20×1×65mm, and the surface is polished to a surface roughness of Ra=0.2μm. This level of roughness can provide sufficient contact area to enhance the adhesion of the coating while avoiding defects or decreased adhesion caused by excessively rough or smooth surfaces. Then accurately weigh 100g of sulfuric acid, 100g of triethanolamine and 100g of ammonium persulfate and mix them in a mass ratio of 1:1:1. These reagents are added to 1000mL of deionized water and stirred at an appropriate speed using a magnetic stirrer for 30 minutes until all the ingredients are completely dissolved to obtain a uniform chemical solvent. The use of deionized water can avoid interference from impurities and ensure 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 above-mentioned chemical solvent for electrolytic treatment. The martensitic hardened bearing steel substrate after electrolytic treatment was placed in a constant temperature heating furnace together with the electrolyte and kept warm at 130°C for 30 minutes. During this process, a black oxide coating was gradually generated on the metal surface through chemical reaction. The coating color was uniform and there were no obvious defects. Finally, the treated sample was removed from the blackening treatment agent and rinsed with deionized water 3 times to thoroughly remove the chemical reagents remaining on the surface. Subsequently, the sample was placed in a 50°C oven and dried for 2 hours to remove surface moisture to obtain a metal surface blackening treatment agent coating sample.

[0031] Example 4. First, prepare a metal substrate. As in Example 2, martensitic hardened bearing steel is selected as the substrate and processed into a sample with a size of 20×1×65mm. Through precision machining, the surface roughness of the sample reaches Ra=0.2μm to ensure the uniformity and stability of the coating adhesion. Next, prepare a 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. Use a stirring device to stir for 40 minutes until all the reagents are completely dissolved. Compared with 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 is completely immersed in the above-mentioned blackening treatment agent, placed in a constant temperature heating furnace, and kept warm at 130°C for 30 minutes. Finally, after the blackening treatment is completed, the sample is taken out and thoroughly rinsed with deionized water to remove the chemical reagents remaining on the surface. Subsequently, the sample was placed in a 50°C environment and dried for 2 hours to finally obtain a metal surface blackening treatment agent coating sample.

[0032] Example 5. Martensitic hardened bearing steel was selected as the substrate, which is consistent with Examples 2 and 3. The substrate was processed into a sample with a size of 20×1×65mm, and the surface roughness was made to reach Ra=0.2μm by precision machining and polishing. Accurately weigh 200g of sulfuric acid, 200g of triethanolamine and 200g of ammonium persulfate, mix them in a mass ratio of 1:1:1, and add them to 2000mL of deionized water. Use a stirring device to stir for 50 minutes until all the reagents are completely dissolved to obtain a chemical solution. Compared with Examples 2 and 3, the amount of reagents and the volume of deionized water are further increased here. The prepared metal substrate was completely immersed in the above-mentioned chemical solution, placed in a constant temperature heating furnace, and kept warm at 130°C for 30 minutes. After the blackening treatment is completed, the sample was taken out and thoroughly rinsed with deionized water to remove the chemical reagents remaining on the surface. Subsequently, the sample was placed in a 50°C environment and dried for 2 hours to finally obtain a metal surface blackening treatment agent coating sample.

[0033] In Examples 3, 4, and 5, by increasing the reagent dosage (300 g to 600 g) and the deionized water volume (1000 mL to 2000 mL), the thickness of the metal surface blackening agent coating gradually increased from 1.0-1.6 μm to 2.0-2.5 μm, and the hydrogen absorption resistance increased from 70% to 80%, demonstrating a trend of improved coating performance with increasing thickness. The experimental data are shown in Table 2.

[0034] Table 2 Performance of metal surface blackening agent coating under different reagent dosage and deionization volume conditions

[0035] 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.

[0036] Finally: 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 in the scope of protection of the present invention.

Claims

1. A method for preparing a metal surface blackening treatment agent, characterized in that: The steps include: Step S1, selecting martensite hardened bearing steel as a substrate and processing it to a surface roughness Ra controlled at 0.2 μm; the martensite hardened bearing steel is a steel material that has been processed by quenching and tempering processes, and the surface roughness is controlled at 0.2 μm by grinding and polishing processes; Step S2, mixing sulfuric acid, triethanolamine, and ammonium persulfate in a mass ratio of 1:1:1, adding deionized water, and stirring thoroughly to prepare a chemical solution; the volume of deionized water added to the chemical solution is 1000 ml to 2000 ml; Step S3, using the martensitic hardened bearing steel substrate prepared in step S1 as an anode, immersing it in the chemical solution prepared in step S2, connecting it to a DC power supply, and performing an electrolytic treatment. During the electrolysis process, an anodic oxidation reaction occurs on the surface of the substrate to generate an oxide precursor; Step S4, soaking the electrolytically treated martensite-hardened bearing steel substrate and the electrolyte at 25° C. for 15-20 minutes to allow the electrolytically generated oxide precursor to further react and form a uniform black oxide coating; Step S5: Take out the treated martensite hardened bearing steel substrate, ultrasonically clean it with deionized water for 5 minutes to remove the chemical reagents remaining on the surface, and dry it at 50°C for 2 hours to obtain a metal surface blackening treatment agent product.

2. The method for preparing a metal surface blackening treatment 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 uniformly distribute the reagent in the solution.

3. The method for preparing a metal surface blackening treatment agent according to claim 1, characterized in that: In step S4, the martensite hardened 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 form a Fe3O4 black oxide coating.

4. The method for preparing a metal surface blackening treatment agent according to claim 1, characterized in that: In step S5, deionized water is used in the rinsing process to remove sulfuric acid, triethanolamine and ammonium persulfate remaining on the surface until the water flow is clear and colorless.

5. The method for preparing a metal surface blackening treatment agent according to claim 1, characterized in that: In step S5, the drying process is performed at a temperature of 50° C. for 2 hours to completely volatilize the moisture on the coating surface without destroying the microstructure of the coating.

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

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

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

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