Low-carbon and environment-friendly rust-proof cast iron body blank and rust-proof process thereof

Abstract

The application provides a low-carbon and environment-friendly rust-proof cast iron body blank and a rust-proof process, and relates to the technical field of rust-proof treatment. The thickness of the oxide film in the low-carbon and environment-friendly rust-proof cast iron body blank is 5-25 microns, the porosity of the oxide film is not higher than 15%, and the bonding force of the oxide film is not lower than 5 MPa. The low-carbon and environment-friendly cast iron body blank obtained by the rust-proof process treatment has a dense oxide layer on the surface and the inner hole wall of the cast iron part, thereby improving the corrosion resistance of the cast iron part. Moreover, without spraying paint on the outer surface of the body, the rust problem of the engine body during the in-plant flow processing can be solved, the energy consumption is greatly reduced, the low-carbon and environment-friendly effect is achieved, the production efficiency is improved, and the manufacturing cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of rust prevention technology, specifically to a low-carbon and environmentally friendly rust prevention treatment for cast iron machine blanks and its rust prevention process. Background Technology

[0002] Diesel engine blocks are generally made of cast iron. The potential difference between different components of cast iron makes it prone to electrochemical corrosion. During processing and operation, especially in high-temperature and high-humidity environments like summer, cast iron parts are easily corroded, affecting the cleanliness of the castings and significantly wasting manpower and resources. Furthermore, rust inside the engine block's water passages, oil passages, and other pores is difficult to detect and remove in a timely manner, resulting in a risk of rust even when the engine block is assembled into a complete unit and shipped from the factory, impacting engine reliability and customer satisfaction.

[0003] To prevent engine blocks from rusting during processing and handling, paint or water-based paint is typically sprayed onto the surface of the cast iron parts. However, this consumes a lot of energy, causes environmental problems, increases engine production costs, and the paint cannot reach the inside of the engine block's water passages, oil passages, and other openings, leaving the problem of rust inside these openings unresolved.

[0004] Chinese invention patent CN114507809A discloses a heat treatment process for a novel anti-corrosion and rust-resistant alloy material. It proposes that after processing raw materials such as bars, a special heat treatment process is used to enhance their salt spray resistance. The anti-corrosion ability of the metallographic structure is altered by precisely controlling the time and temperature during the heat treatment process. This patent changes the metallographic structure during heat treatment, thus altering the mechanical properties. However, the rust resistance achieved through this process is relatively weak, only ensuring that the material will not rust on the surface for at least 72 hours due to environmental influences. This is insufficient for the on-site rust prevention requirements of cast iron machine parts, which are typically in operation for at least one month.

[0005] Chinese invention patent CN106801115A discloses a heat treatment process for rust-proof steel plates. (1) Preheating treatment: The steel plate is placed in a heating furnace, and the temperature of the heating furnace is raised to 450℃-600℃; (2) Heat treatment: The temperature of the heating furnace containing the steel plate is raised to 950℃-1100℃ and held for 4 hours; (3) Quenching: The steel plate is taken out and placed in quenching oil for cooling; (4) Tempering treatment: The quenched and cooled steel plate is placed in a tempering furnace, and the temperature of the tempering furnace is raised to 550℃-600℃ and held for 2 hours. The steel plate is then taken out and placed in a sodium hydroxide and sodium nitrite solution. When the solution temperature drops to 50℃-80℃, a film-forming substance and a slow-release rust inhibitor are added to the solution, and the solution is cooled to room temperature. After the heat treatment process, the workpiece is placed in a sodium hydroxide and sodium nitrite solution. Additional steps and materials are required to passivate the workpiece for rust prevention. The process is complex, increases costs, and is not environmentally friendly. In addition, the heat treatment temperature in this patent exceeds 900℃, which will cause the oxide film to thicken too quickly, the internal stress to increase dramatically, the film to crack or peel off, and the oxide film is porous and loose (porosity >19%), resulting in weak bonding strength of the oxide film.

[0006] Chinese invention patent CN107739785B discloses a heat treatment process for stator cores used in air conditioners. In this patent, the heat treatment temperature exceeds 700℃, and the resulting oxide film layer is porous and loose (porosity > 15%), which leads to weak bonding strength of the oxide film layer and reduces rust prevention performance. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a low-carbon and environmentally friendly rust prevention process for cast iron engine block blanks. This method generates a dense oxide layer on the surface and inner wall of the cast iron parts, thereby improving the corrosion resistance of the cast iron parts. Moreover, it eliminates the need for painting the outer surface of the engine block, thus solving the problem of rust during in-factory processing of the engine block. This significantly reduces energy consumption, is low-carbon and environmentally friendly, and simultaneously improves production efficiency and reduces manufacturing costs.

[0008] The present invention provides a cast iron body blank with low carbon and environmental protection anti-rust treatment. The oxide film thickness of the cast iron body blank with low carbon and environmental protection anti-rust treatment is 5-25μm, the porosity of the oxide film is not higher than 15%, and the bonding force of the oxide film is not lower than 5Mpa.

[0009] Optionally, the oxide film thickness in the cast iron body blank with low-carbon and environmentally friendly rust prevention treatment is 15-25μm, and the porosity of the oxide film is not higher than 10%.

[0010] Optionally, the oxide film adhesion should be no less than 10 MPa.

[0011] Optionally, at temperatures above 30℃ and relative humidity above 50%, the rust prevention time can reach more than 3 months. Optionally, at temperatures above 30℃ and relative humidity above 50%, the rust prevention time can reach more than 6 months.

[0012] Another aspect of the present invention provides a rust prevention process for cast iron machine body blanks with low-carbon and environmentally friendly rust prevention treatment, the rust prevention process for cast iron machine body blanks includes the following steps:

[0013] S1: Clean the surface of the cast iron machine body blank;

[0014] S2: Heat-treat the cleaned cast iron blank at a certain temperature;

[0015] S3: Cooling is performed to obtain a rust-proof cast iron machine body blank;

[0016] In step S2, the temperature is 300-600℃, the holding time is 4-8h, and the heating rate of the heat treatment is 30-80℃ / h.

[0017] Optionally, the temperature in step S2 is 500-580℃. Optionally, the heating rate is 30-60℃ / h.

[0018] Furthermore, the rust prevention process of this invention is relatively simple. By controlling the heat treatment temperature, an oxide layer of a certain thickness can be formed on the surface of the casting, thereby improving the corrosion resistance of the casting. No additional rust-preventive materials are required, resulting in lower costs. It also does not alter the metallographic structure or mechanical properties of the casting, and the rust prevention time can reach more than three months. In addition, it reduces the process of spraying paint on the casting surface, improving production efficiency, reducing production costs, and is more low-carbon and environmentally friendly, reducing energy consumption.

[0019] In an exemplary embodiment of the present invention, step S2 involves subjecting the surface-cleaned cast iron machine body blank to gradient heating heat treatment at a certain temperature, including the following steps:

[0020] After surface cleaning, the cast iron blank is heated to 300-400℃ at a rate of 30-50℃ / h and held for 1-2 hours. Then, it is heated to the working temperature of 550±15℃ at a rate of 50-80℃ / h and held for 5-7 hours.

[0021] Furthermore, this invention employs gradient heating heat treatment. First, heat treatment is performed at a lower temperature, which can effectively reduce thermal stress and generate oxide nuclei, laying the foundation for the uniformity of subsequent film formation. Then, the temperature is increased to promote the lateral fusion of oxide nuclei, which promotes the uniform growth of the oxide film, reduces porosity, and improves the density and adhesion of the oxide layer.

[0022] Optionally, in step S2, the surface-cleaned cast iron blank undergoes gradient heating heat treatment at a certain temperature, including the following steps:

[0023] The surface-cleaned cast iron blank is heated to 330-360℃ at a rate of 35-45℃ / h, and then heated to a working temperature of 550±10℃ at a rate of 50-60℃ / h.

[0024] In an exemplary embodiment of the present invention, step S2 further includes the following step: introducing pulsed current-assisted heat treatment technology during the heat treatment process, wherein the pulsed current density is 0.5-1.5 A / cm². 2 The pulse frequency is 50-100 Hz.

[0025] This application employs pulsed current heat treatment simultaneously on the cast iron blank during the heat treatment process, resulting in a more uniform and dense oxide film with stronger adhesion. Furthermore, the core of pulsed current-assisted heat treatment lies in utilizing the auxiliary effect of an electric field. By applying a pulsed current of a certain frequency and intensity, the atoms within the metal material undergo rearrangement, accelerating the formation of the oxide layer and thereby enhancing the material's strength, hardness, corrosion resistance, and other properties. Compared to single heat treatment, pulsed current-assisted heat treatment significantly shortens the treatment time, improves heating uniformity, and reduces thermal stress. Through the auxiliary effect of the pulsed current, the formation of the oxide layer is accelerated, further enhancing the density and adhesion of the oxide film, reducing porosity, and simultaneously shortening the heat treatment time, thus improving production efficiency.

[0026] Optionally, the pulse current density is 0.8-1.2 A / cm². 2 The pulse frequency is 60-80 Hz. Optionally, the pulse current processing time is 3-5 hours.

[0027] Optionally, the surface cleaning in step S1 includes the following steps: shot blasting the cast iron machine body blank with a power of 16-18KW. First, shot blasting removes loose sand from the surface and internal cavities, ensuring the machine body casting blank is clean and free of loose sand and adhering sand. For example, spherical steel shot with a diameter of 1-3mm can be used for shot blasting. Spherical steel shot makes the casting surface more uniform and less rough, ensuring better surface oxidation quality and a more uniform and dense oxide film during subsequent heat treatment oxidation. The power of the shot blasting equipment should not be set too high, generally 16-18KW is appropriate, the purpose being to ensure more uniform shot blasting force, improve the surface quality of the casting, and create a more uniform and dense oxide film. Optionally, the shot blasting time is 7-10 minutes.

[0028] Optionally, step S2 includes a preheating treatment before heat treatment. The preheating temperature can be 100-140℃. Before placing the machine body castings into the heat treatment kiln, the kiln should be fully preheated at 100-140℃ for at least 30 minutes with an empty furnace to thoroughly dry the moisture inside and prevent rust caused by water vapor during heat treatment. Furthermore, the temperature of the machine body castings loaded into the furnace should be less than 150℃. The machine body castings should be arranged in 2-3 layers, with each layer separated by guide rails to ensure more even heating.

[0029] Optionally, the cooling process in step S3 includes the following steps: cooling at a rate of 30-60℃ / h, removing the casting when the temperature drops to 180-220℃, and then cooling it to room temperature. Cooling the cast iron increases the adhesion of the oxide film.

[0030] Compared with the prior art, the present invention achieves at least one of the following beneficial effects:

[0031] (1) The low-carbon and environmentally friendly anti-rust treatment of the present invention forms a dense oxide layer on the surface of the cast iron blank, which isolates moisture and oxygen. Under high temperature and high humidity environment, the anti-rust time can reach more than 3 months.

[0032] (2) The rust prevention process of the cast iron body blank of the present invention reduces the painting process, reduces energy consumption and production costs, and is more environmentally friendly.

[0033] (3) The rust prevention process of the cast iron body blank of the present invention reduces thermal stress, promotes uniform growth of oxide film, and improves the density and adhesion of oxide layer by adopting a segmented heating strategy during the heat treatment process.

[0034] (4) The rust prevention process of the cast iron blank of the present invention introduces pulse current during the heat treatment process to accelerate the formation of oxide layer, further enhance the corrosion resistance and adhesion of oxide film, and shorten the treatment time and improve production efficiency. Attached Figure Description

[0035] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0036] Figure 1 An exemplary embodiment of the rust prevention process flow diagram of Embodiment 1 of the present invention is shown;

[0037] Figure 2 An exemplary embodiment is shown, illustrating a test diagram of the oxide film thickness of a cast iron body blank treated with low-carbon and environmentally friendly rust prevention in Example 1.

[0038] Figure 3An exemplary embodiment of the test diagram showing the appearance of erythema after 30 seconds of copper sulfate dripping in Example 1 is shown;

[0039] Figure 4 An exemplary embodiment of the test diagram for testing the adhesion of the oxide layer using the vertical tensile method in Example 1 is shown;

[0040] Figure 5 An exemplary embodiment is shown, illustrating the rust prevention effect after 3 months in Example 1;

[0041] Figure 6 An exemplary embodiment is shown, illustrating a test diagram of the oxide film thickness of a cast iron body blank treated with low-carbon and environmentally friendly rust prevention in Example 2.

[0042] Figure 7 An exemplary embodiment is shown, illustrating the rust prevention effect of temperature and humidity over 4 months in Example 2;

[0043] Figure 8 An exemplary embodiment is shown, illustrating the oxide film thickness test diagram of the cast iron body blank treated with low-carbon and environmentally friendly rust prevention in Example 3;

[0044] Figure 9 An exemplary embodiment of the test graph showing no red spots after 30 seconds of copper sulfate dripping in Example 3 is shown;

[0045] Figure 10 An exemplary embodiment of the test diagram for testing the adhesion of the oxide layer using the vertical tensile method in Example 3 is shown;

[0046] Figure 11 An exemplary embodiment is shown, illustrating the rust prevention effect of temperature and humidity over 6 months in Example 3;

[0047] Figure 12 An exemplary embodiment is shown, illustrating the oxide film thickness test diagram of the cast iron body blank treated with low-carbon and environmentally friendly rust prevention in Example 4;

[0048] Figure 13 An exemplary embodiment of the test graph showing no red spots after 30 seconds of copper sulfate dripping in Example 4 is shown;

[0049] Figure 14 An exemplary embodiment of the test diagram for testing the adhesion of the oxide layer using the vertical tensile method in Example 4 is shown;

[0050] Figure 15 An exemplary embodiment is shown, illustrating the rust prevention effect of temperature and humidity after 8 months in Example 4;

[0051] Figure 16 An exemplary embodiment is shown, illustrating a test diagram of the oxide film thickness of a cast iron body blank treated with low-carbon and environmentally friendly rust prevention in Example 5.

[0052] Figure 17 An exemplary embodiment is shown, illustrating the rust prevention effect of temperature and humidity after 7 months in Example 5;

[0053] Figure 18 An exemplary embodiment is shown, illustrating the oxide film thickness test diagram of the cast iron body blank treated with low-carbon and environmentally friendly rust prevention in Comparative Example 1.

[0054] Figure 19 An exemplary embodiment is shown, illustrating the rust prevention effect of temperature and humidity over 11 months in Comparative Example 1.

[0055] Figure 20 An exemplary embodiment is shown, illustrating the oxide film thickness test diagram of the cast iron body blank treated with low-carbon and environmentally friendly rust prevention in Comparative Example 2.

[0056] Figure 21 An exemplary embodiment is shown, illustrating the rust prevention effect of temperature and humidity over 2 months in Comparative Example 2.

[0057] Figure 22 The diagram shows the test results of the oxide layer adhesion strength using the vertical tensile method. Detailed Implementation

[0058] To more clearly illustrate the overall concept of the present invention, a detailed description will be provided below with reference to the accompanying drawings and examples.

[0059] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0060] Example 1

[0061] In an exemplary embodiment of the present invention, the rust prevention process for the cast iron body blank with low-carbon and environmentally friendly rust prevention treatment includes the following steps:

[0062] (1) Shot blasting: Shot blasting treatment of cast iron to clean the surface of cast iron. The cast iron blank is shot blasted using a shot blasting power equipment with a power of 16KW. Spherical steel shot with a diameter of 2mm is used for shot blasting for 7min.

[0063] (2) Preheating: The heat treatment furnace is preheated to prevent water vapor from causing corrosion of the cast iron parts. Before the cast iron blank is put into the heat treatment furnace, the heat treatment furnace is fully preheated at 100°C. The furnace is heated empty for 30 minutes to completely dry the moisture in the furnace and avoid water vapor generated during the heat treatment process from causing corrosion of the cast iron parts.

[0064] (3) Loading the furnace: The cast iron parts are loaded into the furnace and stacked evenly to ensure uniform heating. The castings of the machine body are placed in 2-3 layers, and each layer is separated by guide rails to ensure more uniform heating of the castings.

[0065] (4) Heating the cast iron parts to form an oxide film on the surface. Place the cast iron parts in the furnace and heat them at a rate of 60℃ / h until they reach 550℃.

[0066] (5) Heat preservation treatment of cast iron makes the oxide film more uniform and dense, and the bonding force better. After reaching the target temperature, the casting is kept in a constant temperature environment of 550℃ for 6 hours to make the oxide film of the casting more uniform and dense.

[0067] (6) Cooling the cast iron improves the adhesion of the oxide film. After heat preservation, cool the casting in the furnace at a rate of 30℃ / h. When the temperature drops to 200℃, remove the casting and then cool it to 60℃ in a natural room temperature environment to increase the adhesion of the oxide film. Refer to the rust prevention process flow chart. Figure 1 As shown.

[0068] Example 2

[0069] In an exemplary embodiment of the present invention, the rust prevention process for the cast iron body blank with low-carbon and environmentally friendly rust prevention treatment includes the following steps:

[0070] (1) Use shot blasting equipment to blast the cast iron machine body blank. Set the power to 18KW, use spherical steel shot with a diameter of 2mm, and blast for 10min.

[0071] (2) Before the cast iron blank is put into the heat treatment kiln, the heat treatment kiln is preheated to 140°C. The kiln is heated for 30 minutes with the furnace empty to completely dry the moisture in the furnace and prevent the water vapor generated during the heat treatment process from causing the cast iron parts to rust.

[0072] (3) The castings of the machine body are placed in 2-3 layers. In order to make the castings heat more evenly, each layer is separated by guide rails.

[0073] (4) Heat the surface-cleaned cast iron blank to 300°C at a rate of 30°C / h, hold for 1 hour, and then heat to 565°C at a rate of 50°C / h.

[0074] (5) Maintain the casting in a constant temperature environment of 565℃ for 6 hours to make the oxide film of the casting more uniform and dense.

[0075] (6) After the heat preservation is completed, the furnace is cooled at a rate of 60℃ / h. When the temperature drops to 220℃, the casting is taken out and then cooled in a natural room temperature environment to obtain a cast iron body blank with low carbon environmental protection and rust prevention treatment.

[0076] Example 3

[0077] In an exemplary embodiment of the present invention, the rust prevention process for the cast iron body blank with low-carbon and environmentally friendly rust prevention treatment includes the following steps:

[0078] (1) Use shot blasting equipment to blast the cast iron machine body blank. Set the power to 17KW, use spherical steel shot with a diameter of 2mm, and blast for 10min.

[0079] (2) Before the cast iron blank is put into the heat treatment kiln, the heat treatment kiln should be fully preheated at 120°C. The kiln should be heated empty for 30 minutes to completely dry the moisture in the furnace and avoid the water vapor generated during the heat treatment process from causing the cast iron parts to rust.

[0080] (3) The castings of the machine body are placed in 2-3 layers. In order to make the castings heat more evenly, each layer is separated by guide rails.

[0081] (4) Heat the surface-cleaned cast iron blank to 350°C at a rate of 40°C / h, hold for 1 hour, and then heat to 550°C at a rate of 55°C / h.

[0082] (5) The casting is kept at a constant temperature of 550°C for 6 hours. During the constant temperature treatment, pulsed current is introduced to assist the heat treatment, with a pulsed current density of 0.8 A / cm. 2 The pulse frequency is 60Hz and the pulse current processing time is 4h.

[0083] (6) After the heat preservation is completed, the furnace is cooled at a rate of 40℃ / h. When the temperature drops to 200℃, the casting is taken out and then cooled in a natural room temperature environment to obtain a cast iron body blank with low carbon environmental protection and rust prevention treatment.

[0084] Example 4

[0085] Based on Example 3, the main difference is that in step (5), a pulsed current is introduced to assist the heat treatment during the isothermal process, with a pulsed current density of 1.2 A / cm². 2 The pulse frequency is 80Hz, and the pulse current processing time is 5 hours. Other steps are the same as in Example 3.

[0086] Example 5

[0087] Based on Example 1, the main difference is that in step (5), a pulsed current is introduced to assist the heat treatment during the isothermal process, with a pulsed current density of 1.2 A / cm². 2 The pulse frequency is 80Hz, and the pulse current processing time is 5 hours. Other steps are the same as in Example 1.

[0088] Comparative Example 1

[0089] Based on Example 1, the main difference is that in step (4), the temperature is increased at a rate of 60°C / h until it reaches 950°C. In step (5), the casting is kept at a constant temperature of 950°C for 4 hours. The other steps are the same as in Example 1.

[0090] Comparative Example 2

[0091] Based on Example 1, the main difference is that in step (4), the temperature is increased at a rate of 60°C / h until it reaches 750°C. In step (5), the casting is kept at a constant temperature of 750°C for 4 hours. The other steps are the same as in Example 1.

[0092] Test case

[0093] The cast iron blanks prepared with low-carbon and environmentally friendly rust-proof treatment according to the above examples and comparative examples were tested for oxide film thickness, porosity, adhesion, and rust-proof effect. The test results are shown in Table 1. Table 2 shows the quantitative test performance of porosity in Example 1; Table 3 shows the quantitative test performance of porosity in Example 2; Table 4 shows the quantitative test performance of porosity in Example 3; Table 5 shows the quantitative test performance of porosity in Example 4; Table 6 shows the quantitative test performance of porosity in Example 5; Table 7 shows the quantitative test performance of porosity in Comparative Example 1; and Table 8 shows the quantitative test performance of porosity in Comparative Example 2.

[0094] Qualitative test of porosity: No red spots appeared after 30 seconds of copper sulfate drop, indicating that the oxide film has good continuity and porosity (GB / T15519 "Specifications and Test Methods for Chemical Conversion Membranes").

[0095] Quantitative Porosity Testing: Electrochemical methods are one of the important means to evaluate the porosity of oxide films on material surfaces. They primarily reflect the compactness of the oxide film indirectly by measuring its corrosion resistance. Porosity = Corrosion current density of the sample with oxide film / Corrosion current density of the substrate without oxide film × 100%.

[0096] Rust prevention test: The cast iron blanks with low carbon and environmentally friendly rust prevention treatment prepared in the above examples and comparative examples were placed in an environment with a temperature of 38°C and a relative humidity of 80%, and the time for the oxide layer to rust was observed.

[0097] Adhesion strength test: The adhesion strength of the oxide layer was tested using the vertical tensile method. See the test diagram for reference. Figure 22 As shown.

[0098] Table 1

[0099]

[0100] Table 2

[0101]

[0102] Table 3

[0103]

[0104] Table 4

[0105]

[0106] Table 5

[0107]

[0108] Table 6

[0109]

[0110] Table 7

[0111]

[0112] Table 8

[0113]

[0114] Referring to Tables 1-8, the oxide film thickness in the cast iron blank treated with the low-carbon and environmentally friendly rust prevention process of this invention is 5-25μm, the oxide film porosity is not higher than 15%, and the oxide film adhesion is not lower than 5Mpa.

[0115] Figure 2 An exemplary embodiment is shown, illustrating the oxide film thickness test diagram of the cast iron body blank treated with low-carbon and environmentally friendly rust prevention in Example 1. It can be seen that the oxide film thickness in Example 1 is approximately 9 μm. Figure 3 An exemplary embodiment of the test diagram showing the appearance of erythema after 30 seconds of copper sulfate dripping in Example 1 is shown. Figure 4 An exemplary embodiment of the test diagram for testing the adhesion of the oxide layer using the vertical tensile method of Example 1 is shown. Figure 5 An exemplary embodiment of Example 1 is shown, illustrating the rust prevention effect after 3 months. It can be seen that rust appeared after a temperature and humidity test after 3 months.

[0116] Figure 6 An exemplary embodiment is shown, illustrating the oxide film thickness test diagram of the cast iron body blank treated with low-carbon and environmentally friendly rust prevention in Example 2. It can be seen that the oxide film thickness in Example 2 is approximately 13 μm. Figure 7 An exemplary embodiment of Example 2 is shown, illustrating the rust prevention effect under temperature and humidity conditions after 4 months. It can be seen that no rust was observed during the 4-month temperature and humidity test.

[0117] Figure 8An exemplary embodiment is shown, illustrating the oxide film thickness test diagram of the cast iron body blank treated with low-carbon and environmentally friendly rust prevention in Example 3. It can be seen that the oxide film thickness in Example 3 is approximately 16 μm. Figure 9 An exemplary embodiment of the test diagram of copper sulfate droplet 30s without red spots is shown in Example 3, which to some extent proves that the oxide film has good continuity and porosity. Figure 10 An exemplary embodiment of the test diagram for testing the adhesion of the oxide layer using the vertical tensile method in Example 3 is shown. Figure 11 An exemplary embodiment of the temperature and humidity rust prevention effect after 6 months is shown in Example 3. It can be seen that no rust was observed during the 6-month temperature and humidity test.

[0118] Figure 12 An exemplary embodiment is shown, illustrating the oxide film thickness test diagram of the cast iron body blank treated with low-carbon and environmentally friendly rust prevention in Example 4. It can be seen that the oxide film thickness in Example 4 is approximately 25 μm. Figure 13 An exemplary embodiment of the test diagram of copper sulfate drop test for 30 seconds in Example 4 is shown, which shows that no red spots appeared, which to some extent proves that the oxide film has good continuity and porosity. Figure 14 An exemplary embodiment of the test diagram for testing the adhesion of the oxide layer using the vertical tensile method in Example 4 is shown. Figure 15 An exemplary embodiment of the temperature and humidity rust prevention effect after 8 months is shown in Example 4. It can be seen that no rust was observed during the 8-month temperature and humidity test.

[0119] Figure 16 An exemplary embodiment is shown, illustrating the oxide film thickness test diagram of the cast iron body blank treated with low-carbon and environmentally friendly rust prevention in Example 5. It can be seen that the oxide film thickness in Example 5 is approximately 20 μm. Figure 17 An exemplary embodiment of the temperature and humidity rust prevention effect after 7 months is shown in Example 5. It can be seen that no rust was observed during the 7-month temperature and humidity test.

[0120] Figure 18 An exemplary embodiment is shown, which illustrates the oxide film thickness test diagram of the cast iron body blank treated with low-carbon and environmentally friendly rust prevention in Comparative Example 1. It can be seen that the oxide film thickness of Comparative Example 1 is about 30 μm. Figure 19 An exemplary embodiment is shown, illustrating the rust prevention effect under temperature and humidity after 1 month in Comparative Example 1. It can be seen that rust occurred during the 1-month temperature and humidity test.

[0121] Figure 20 An exemplary embodiment of the oxide film thickness test diagram of the cast iron body blank treated with low carbon environmental protection rust prevention in Comparative Example 2 is shown. It can be seen that the oxide film thickness of Comparative Example 2 is about 25 μm. Figure 21 An exemplary embodiment is shown, illustrating the rust prevention effect under temperature and humidity conditions after 2 months in Comparative Example 2. It can be seen that rust occurred during the 2-month temperature and humidity test.

[0122] In summary, the low-carbon and environmentally friendly cast iron engine block blank obtained by the rust-prevention process of this invention produces a dense oxide layer on the surface and inner wall of the cast iron parts, thereby improving the corrosion resistance of the cast iron parts (for example, at temperatures above 30°C and relative humidity above 50%, the rust prevention time can reach more than 3 months). Moreover, it eliminates the need for painting the outer surface of the engine block, solving the problem of rust during in-factory processing, significantly reducing energy consumption, promoting low carbon emissions and environmental protection, while simultaneously improving production efficiency and reducing manufacturing costs.

[0123] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A rust-proofing process for cast iron machine body blanks with low-carbon and environmentally friendly rust-proofing treatment, characterized in that, Rust prevention process for the cast iron machine body blank Includes the following steps: S1: Clean the surface of the cast iron machine body blank; S2: Heat-treat the cleaned cast iron blank at a certain temperature; S3: Cooling is performed to obtain a rust-proof cast iron machine body blank; In step S2, the temperature is 300-600℃, the holding time is 4-8h, and the heating rate of the heat treatment is 30-80℃ / h. Step S2 further includes the following step: introducing pulsed current-assisted heat treatment technology during the heat treatment process, with a pulsed current density of 0.5-1.5 A / cm². 2 The pulse frequency is 50-100 Hz; In step S2, the surface-cleaned cast iron blank undergoes gradient heating heat treatment at a certain temperature, including the following steps: After surface cleaning, the cast iron blank is heated to 300-400℃ at a rate of 30-50℃ / h, and then heated to a working temperature of 550±15℃ at a rate of 50-80℃ / h. The oxide film thickness in the cast iron blank treated with low-carbon and environmentally friendly rust prevention is 15-25μm, the porosity of the oxide film is not higher than 10%, the adhesion of the oxide film is not less than 10Mpa, and the rust prevention time can reach more than 6 months when the temperature is above 30℃ and the relative humidity is above 50%.

2. The rust prevention process for cast iron machine body blanks with low-carbon and environmentally friendly rust prevention treatment according to claim 1, characterized in that, In step S2, the surface-cleaned cast iron blank undergoes gradient heating heat treatment at a certain temperature, including the following steps: The surface-cleaned cast iron blank is heated to 330-360℃ at a rate of 35-45℃ / h, and then heated to a working temperature of 550±10℃ at a rate of 50-60℃ / h.

3. The rust prevention process for cast iron machine body blanks with low-carbon and environmentally friendly rust prevention treatment according to claim 1, characterized in that, The pulse current density is 0.8-1.2 A / cm². 2 The pulse frequency is 60-80 Hz.

4. The rust prevention process for cast iron machine body blanks with low-carbon and environmentally friendly rust prevention treatment according to claim 1, characterized in that, The surface cleaning in step S1 includes the following steps: shot blasting the cast iron machine blank with a shot blasting power of 16-18KW.

5. The rust prevention process for cast iron machine body blanks with low-carbon and environmentally friendly rust prevention treatment according to claim 1, characterized in that, Cooling is performed in step S3, including the following steps: cooling at a rate of 30-60℃ / h, removing the casting when the temperature drops to 180-220℃, and then cooling at room temperature.

6. A cast iron body blank prepared by a rust-proofing process for a cast iron body blank with low-carbon and environmentally friendly rust-proofing treatment as described in any one of claims 1-5, characterized in that, The oxide film thickness in the cast iron blank treated with low-carbon and environmentally friendly rust prevention is 15-25μm, the porosity of the oxide film is not higher than 10%, the adhesion of the oxide film is not less than 10Mpa, and the rust prevention time can reach more than 6 months when the temperature is above 30℃ and the relative humidity is above 50%.

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