Heat treatment process of corrosion-resistant bolt

Abstract

The invention relates to the technical field of bolt machining, and particularly discloses a heat treatment process of a corrosion-resistant bolt. The heat treatment process of the corrosion-resistant bolt comprises the following steps that a bolt blank is cleaned and blow-dried, and a pretreated bolt blank is obtained; in the presence of methanol and liquefied gas, the pretreated bolt blank is heated, subjected to heat preservation, immersed in quenching oil to be cooled, taken out, washed with water and blow-dried, and a bolt semi-finished product is obtained; the bolt semi-finished product is heated, subjected to heat preservation and immersed in a post-treatment working solution, standing treatment is conducted for 5-10 min, stirring treatment is conducted for 10-30 min, the bolt semi-finished product is taken out and washed with water, heat preservation treatment is conducted for 40-60 min at the temperature of 100-120 DEG C, and the corrosion-resistant bolt is obtained. The post-treatment working solution is mainly prepared from the following raw materials: water, sodium nitrite, molybdate, aminated nano silicon dioxide aerogel and a dispersing agent. The corrosion-resistant bolt obtained through the heat treatment process has the advantages of being high in tensile strength and corrosion resistance, and the market requirement is met.

Description

Technical Field

[0001] This application relates to the field of bolt processing technology, and more specifically, to a heat treatment process for corrosion-resistant bolts. Background Technology

[0002] Bolts are indispensable fasteners in machinery manufacturing, automotive industry, engineering machinery, construction, and other fields. Their performance directly determines the assembly stability, operational safety, and service life of equipment. Especially in humid and salt spray environments, bolts not only need to meet the requirement of tensile strength ≥1040MPa, but also need to possess excellent corrosion resistance to avoid assembly failure and structural loosening caused by surface corrosion. Existing heat treatment processes for corrosion-resistant bolts generally involve pre-treating the bolt blank, followed by quenching and tempering to obtain corrosion-resistant bolts. To further enhance corrosion resistance, some researchers have used sodium nitrite aqueous solution during the tempering cooling stage, utilizing the sodium nitrite to form a protective film on the surface and improve the neutral salt spray resistance time. However, the neutral salt spray resistance time is only around 600 hours, and the improvement in corrosion resistance is limited, requiring further improvement. Summary of the Invention

[0003] To improve the neutral salt spray resistance time and enhance the corrosion resistance of corrosion-resistant bolts, this application provides a heat treatment process for corrosion-resistant bolts, employing the following technical solution: A heat treatment process for corrosion-resistant bolts includes the following steps: S1. Clean the bolt blank, remove surface oil, and blow dry to obtain a pre-treated bolt blank; S2. Under methanol and liquefied gas, the pretreated bolt blank is heated to 840-850℃ and held for 70-90 minutes. Then, the temperature is raised to 850-860℃ and held for 90-110 minutes. The blank is then immersed in quenching oil at 40-80℃ for cooling. The blank is then removed, washed with water, and dried to obtain a semi-finished bolt. S3. Heat the semi-finished bolts to 470-490℃, keep them warm for 110-130 minutes, immerse them in a post-treatment working solution at 10-30℃, let them stand for 5-10 minutes, stir for 10-30 minutes, take them out, wash them with water, and keep them warm at 100-120℃ for 40-60 minutes to obtain corrosion-resistant bolts. The post-treatment working fluid is mainly made of the following raw materials in parts by weight: 1000 parts water, 30-50 parts sodium nitrite, 10-20 parts molybdate, 2-4 parts aminated nano silica aerogel, and 1-3 parts dispersant.

[0004] The heat treatment process for corrosion-resistant bolts disclosed in this application involves first cleaning, quenching, and tempering the bolt blank, followed by cooling with a post-treatment working fluid to form a protective film, resulting in corrosion-resistant bolts. The synergistic effect of quenching and tempering improves the microstructure and increases tensile strength. The post-treatment working fluid not only cools the semi-finished bolts but also forms a dense organic-inorganic hybrid protective film on the surface of the semi-finished bolts through the interaction of the raw materials, further enhancing corrosion resistance. The corrosion-resistant bolts obtained by this heat treatment process exhibit a neutral salt spray resistance time >1000h and a tensile strength >1150MPa, demonstrating high tensile strength and high corrosion resistance, exhibiting excellent comprehensive performance and meeting market demands.

[0005] The post-treatment working solution of this application simultaneously adds sodium nitrite and molybdate to the raw materials. Sodium nitrite can rapidly form a protective film, and molybdate ions are enriched and adsorbed on the surface of the protective film, forming molybdenum-containing oxides, which improves microscopic defects. The synergistic effect between sodium nitrite and molybdate enhances the density and stability of the protective film. Aminated nano-silica aerogel is also added to the raw materials of the post-treatment solution. This aerogel can coordinate with the protective film or form a hydrogen bond, creating a support framework. The amino groups in the aerogel also coordinate with the molybdate, guiding the growth of the protective film on the aminated nano-silica aerogel network, forming a chemically bonded organic-inorganic hybrid protective film, increasing physical barrier properties and improving corrosion resistance.

[0006] Optionally, the aminated nano-silica aerogel is prepared by the following method: at a temperature of 50-70℃, an aqueous ethanol solution and 3-aminopropyltriethoxysilane are mixed, hydrophobic nano-silica aerogel is added, the mixture is stirred for 4-6 hours, filtered, washed with water, and dried to obtain the aminated nano-silica aerogel.

[0007] Optionally, the weight ratio of the hydrophobic nano-silica aerogel to 3-aminopropyltriethoxysilane is 100:(7-13).

[0008] By employing the above-mentioned technical solution, 3-aminopropyltriethoxysilane is grafted onto the surface of hydrophobic nano-silica aerogel using siloxy groups, introducing amino groups to obtain aminated nano-silica aerogel. The preparation method of this application is simple to operate and can produce stable aminated nano-silica aerogels, ensuring their performance in use.

[0009] Optionally, the mass concentration of the ethanol aqueous solution is 40-80%.

[0010] In several implementations, the mass concentration of the ethanol aqueous solution is 60%, but it can also be set to 40%, 50%, 70%, 80%, etc. as needed, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0011] Optionally, the hydrophobic nano-silica aerogel has an average particle size of 10-50 nm and a specific surface area of ​​200-500 m². 2 / g.

[0012] By adopting the above technical solution, the average particle size and specific surface area of ​​the hydrophobic nano-silica aerogel are optimized, ensuring that the aminated nano-silica aerogel has good dispersibility and adsorption capacity, which facilitates the formation of a dense and stable protective film.

[0013] In several embodiments, the hydrophobic nano-silica aerogel has an average particle size of 30 nm and a specific surface area of ​​400 m². 2 / g, and the average particle size can also be set to 10nm, 20nm, 40nm, 50nm, etc. as needed, and the specific surface area can also be set to 200m² as needed. 2 / g、250m 2 / g、300m 2 / g, 350m 2 / g、450m 2 / g、500m 2 / g, etc., but not limited to the listed values; other unlisted values ​​within this range also apply.

[0014] Optionally, the molybdate is selected from one or more combinations of sodium molybdate, potassium molybdate, ammonium molybdate, and ammonium dodecylmolybdate phosphate, and the dispersant is selected from one or more combinations of polyvinylpyrrolidone, sodium polyacrylate, ammonium polyacrylate, and sodium hexametaphosphate.

[0015] By adopting the above technical solution, the molybdate and dispersant are optimized, facilitating their selection. The dispersant exhibits excellent dispersing properties, reducing the agglomeration of aminated nano-silica aerogel and ensuring the uniformity of the protective film.

[0016] Optionally, the weight ratio of the semi-finished bolt and the post-treatment working fluid is 1:(15-25).

[0017] By adopting the above technical solution, the weight ratio of the bolt semi-finished product and the post-treatment working fluid is optimized to ensure that the bolt semi-finished product is completely immersed in the post-treatment working fluid and forms a complete and uniform protective film on the surface of the bolt semi-finished product. In several implementation schemes, the weight ratio of the bolt semi-finished product and the post-treatment working fluid is 1:20. It can also be set to 1:15, 1:18, 1:23, 1:25, etc., as needed, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0018] Optionally, the post-treatment working solution is prepared by the following method: water, sodium nitrite, molybdate, aminated nano-silica aerogel, and dispersant are mixed evenly to obtain the post-treatment working solution.

[0019] By adopting the above technical solution, the preparation of the post-treatment working fluid is facilitated.

[0020] Optionally, the bolt blank is made of one of the following materials: 42CrMo steel, 35CrMo steel, SCM440 steel, and 10B33 steel.

[0021] By adopting the above technical solutions, the material of the bolt blank is optimized to ensure that the corrosion-resistant bolt has good mechanical properties.

[0022] Optionally, the nominal diameter of the bolt blank is 5-27mm and the nominal length is 10-200mm.

[0023] By adopting the above technical solution, the nominal diameter and nominal length of the bolt blank are optimized, ensuring a stable source of bolt blanks and guaranteeing that the corrosion-resistant bolts have good mechanical properties. In several implementation schemes, the nominal diameter of the bolt blank is 16mm and the nominal length is 80mm. The nominal diameter can also be set to 5mm, 10mm, 15mm, 20mm, 25mm, 27mm, etc., and the nominal length can also be set to 10mm, 30mm, 50mm, 100mm, 130mm, 150mm, 180mm, 200mm, etc., as needed. However, these are not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0024] Optionally, in step S2, the flow rate of methanol is 8-12 L / h, and the flow rate of liquefied petroleum gas is 0.4-0.6 m³ / h. 3 / h.

[0025] By adopting the above technical solution, the flow rates of methanol and liquefied gas are optimized to maintain a stable and uniform reducing protective atmosphere and carbon potential, thereby reducing the occurrence of oxidation or decarburization in the pretreated bolt blank and ensuring the mechanical properties of corrosion-resistant bolts.

[0026] In several implementations, the methanol flow rate is 10 L / h, but it can also be set to 8 L / h, 9 L / h, 11 L / h, 12 L / h, etc., as needed, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. In several implementations, the liquefied petroleum gas (LPG) flow rate is 0.5 m³ / h. 3 / h, and the flow rate can also be set to 0.4m as needed. 3 / h, 0.45m 3 / h, 0.55m 3 / h, 0.6m 3 / h, etc., but not limited to the listed values; other unlisted values ​​within this range also apply.

[0027] Optionally, the quenching oil is selected from one or a combination of two of ISO VG46 quenching oil and ISO VG68 quenching oil.

[0028] Optionally, the weight ratio of the pretreated bolt blank to the quenching oil is 1:(15-25).

[0029] By adopting the above technical solution, the weight ratio of the pretreated bolt blank and quenching oil is optimized, which facilitates the cooling of the pretreated bolt blank. In several implementation schemes, the weight ratio of the pretreated bolt blank to the quenching oil is 1:20. It can also be set to 1:15, 1:18, 1:23, 1:25, etc., as needed, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] In summary, this application has at least the following beneficial effects: The heat treatment process for corrosion-resistant bolts in this application utilizes the synergistic effect of quenching and tempering to improve the crystal structure and enhance tensile strength. The post-treatment working fluid not only achieves cooling but also leverages the synergistic effect of sodium nitrite, molybdate, and aminated nano-silica aerogel to form an organic-inorganic hybrid protective film, further improving corrosion resistance. The corrosion-resistant bolts obtained through this heat treatment process exhibit a neutral salt spray resistance time >1000h and a tensile strength >1150MPa, demonstrating high tensile strength and high corrosion resistance, meeting market demands. Detailed Implementation

[0031] The present application will be further described in detail below with reference to the embodiments. These embodiments are for illustrative purposes only and are not limited to the scope of application of the present application. Unless otherwise specified, the raw materials or components used in the present application can be obtained commercially or by conventional methods.

[0032] Preparation Example Preparation Example 1 An aminated nano-silica aerogel is prepared by the following method: At a rotation speed of 300 r / min and a temperature of 60℃, 10 kg of 3-aminopropyltriethoxysilane was added to 1500 kg of a 60% (w / w) aqueous ethanol solution and stirred for 5 min. Then, 100 kg of hydrophobic nano-silica aerogel was added and stirred for 5 h. Afterward, the mixture was filtered, washed with water, and dried to obtain aminated nano-silica aerogel.

[0033] Among them, the hydrophobic nano-silica aerogel has an average particle size of 30 nm and a specific surface area of ​​400 m². 2 / g.

[0034] Preparation Example 2 An aminated nano-silica aerogel differs from Preparation Example 1 in that the amount of 3-aminopropyltriethoxysilane added is different, and the amount of 3-aminopropyltriethoxysilane added is 7 kg.

[0035] Preparation Example 3 An aminated nano-silica aerogel differs from Preparation Example 1 in that the amount of 3-aminopropyltriethoxysilane added is different, and the amount of 3-aminopropyltriethoxysilane added is 13 kg.

[0036] Example

[0037] Example 1 A heat treatment process for corrosion-resistant bolts includes the following steps: S0, Prepare the post-treatment working solution.

[0038] The post-treatment working fluid is made from the following raw materials: 1000 kg water, 40 kg sodium nitrite, 15 kg molybdate, 3 kg aminated nano silica aerogel, and 2 kg dispersant.

[0039] Furthermore, the molybdate is selected from sodium molybdate; the dispersant is selected from polyvinylpyrrolidone, specifically polyvinylpyrrolidone PVPK30; and the aminated nano-silica aerogel is prepared using the method described in Preparation Example 1.

[0040] The post-treatment working solution was prepared by the following method: sodium nitrite, molybdate, and dispersant were added to water at a speed of 300 r / min and stirred for 5 min. Aminated nano-silica aerogel was then added and stirred for 10 min to obtain the post-treatment working solution.

[0041] S1. The bolt blank is cleaned with a sodium hydroxide aqueous solution at 60℃ and pH 12 to remove surface oil and then dried to obtain a pretreated bolt blank.

[0042] The bolt blank is made of 42CrMo steel, with a nominal diameter of 16mm and a nominal length of 80mm.

[0043] S2. Under methanol and liquefied petroleum gas conditions, the pretreated bolt blank is heated to 850℃ and held for 80 minutes, then heated to 860℃ and held for 100 minutes. It is then immersed in quenching oil at 60℃ and cooled for 20 minutes before being removed. Afterwards, it is washed with water at 60℃ to remove the surface quenching oil, and then dried to obtain the bolt semi-finished product.

[0044] The flow rate of methanol is 10 L / h, and the flow rate of liquefied petroleum gas is 0.5 m³ / h. 3 / h; The quenching oil is selected from ISO VG46 quenching oil, and the weight ratio of pretreated bolt blank to quenching oil is 1:20.

[0045] S3. Heat the semi-finished bolts to 480℃ and hold for 120 minutes. Then immerse them in a post-treatment working solution at 20℃, let them stand for 8 minutes, and then stir for 20 minutes at 300 rpm. Remove them and wash them with water. Finally, hold them at 110℃ for 50 minutes to obtain corrosion-resistant bolts.

[0046] The weight ratio of the semi-finished bolts to the post-treatment fluid is 1:20.

[0047] Example 2 A heat treatment process for corrosion-resistant bolts differs from that in Example 1 in that the raw material ratio of the post-treatment working fluid is different in step S0.

[0048] Furthermore, the post-treatment working fluid is made from the following raw materials: 1000 kg of water, 30 kg of sodium nitrite, 20 kg of molybdate, 2 kg of aminated nano-silica aerogel, and 3 kg of dispersant.

[0049] Example 3 A heat treatment process for corrosion-resistant bolts differs from that in Example 1 in that the raw material ratio of the post-treatment working fluid is different in step S0.

[0050] Furthermore, the post-treatment working fluid is made from the following raw materials: 1000 kg of water, 50 kg of sodium nitrite, 10 kg of molybdate, 4 kg of aminated nano-silica aerogel, and 1 kg of dispersant.

[0051] Example 4 A heat treatment process for corrosion-resistant bolts differs from that in Example 1 in that, in step S0, the source of the aminated nano-silica aerogel in the post-treatment working fluid is different, and the aminated nano-silica aerogel is prepared using the method of Preparation Example 2.

[0052] Example 5 A heat treatment process for corrosion-resistant bolts differs from that in Example 1 in that, in step S0, the source of the aminated nano-silica aerogel in the raw materials of the post-treatment working fluid is different, and the aminated nano-silica aerogel is prepared using the method of Preparation Example 3.

[0053] Comparative Example Comparative Example 1 A heat treatment process for corrosion-resistant bolts, which differs from Example 1 in that, in step S0, an equal amount of sodium nitrite is used to replace molybdate in the raw materials of the post-treatment working fluid.

[0054] Comparative Example 2 A heat treatment process for corrosion-resistant bolts, which differs from Example 1 in that, in step S0, an equal amount of molybdate is used to replace sodium nitrite in the raw materials of the post-treatment working fluid.

[0055] Comparative Example 3 A heat treatment process for corrosion-resistant bolts, which differs from Example 1 in that, in step S0, aminated nano-silica aerogel is not added to the raw materials of the post-treatment working fluid.

[0056] Comparative Example 4 A heat treatment process for corrosion-resistant bolts, which differs from Example 1 in that, in step S0, an equal amount of nano-silica aerogel is used to replace the aminated nano-silica aerogel in the raw materials of the post-treatment working fluid.

[0057] Performance testing Corrosion-resistant bolts obtained in Examples 1-5 and Comparative Examples 1-4 were used as samples, and the following performance tests were performed on the corrosion-resistant bolts. The test results are shown in Table 1.

[0058] In accordance with GB / T10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test", the resistance time of corrosion-resistant bolts to neutral salt spray was tested.

[0059] The tensile strength of corrosion-resistant bolts was tested in accordance with GB / T3098.1-2010 "Mechanical Properties of Fasteners - Bolts, Screws and Studs".

[0060] Table 1 Test Results

[0061] As shown in Table 1, the corrosion-resistant bolts obtained by the heat treatment process of this application have a higher neutral salt spray resistance time, ranging from 1080 to 1250 hours, demonstrating high corrosion resistance. They also exhibit good tensile strength, exceeding 1150 MPa, showcasing excellent mechanical properties. In other words, the corrosion-resistant bolts of this application possess the advantages of high tensile strength and high corrosion resistance, exhibiting excellent comprehensive performance and meeting market demands.

[0062] Comparative Examples 1-2 and Example 1 were compared. Sodium nitrite was added to the post-treatment working solution of Comparative Example 1; molybdate was added to the post-treatment working solution of Comparative Example 2; and both sodium nitrite and molybdate were added to the post-treatment working solution of Example 1. It can be seen that the simultaneous addition of sodium nitrite and molybdate to the post-treatment working solution significantly improves the neutral salt spray resistance time. This may be because sodium nitrite can rapidly form a protective film, and the molybdate ions in molybdate are enriched and adsorbed on the surface of the protective film, improving microscopic defects. Simultaneously, the molybdate ions can also form molybdenum-containing oxides, achieving a positive synergistic effect, improving the density and stability of the protective film, and thus increasing the neutral salt spray resistance time.

[0063] Comparative Examples 3-4 and Example 1 were compared. In Comparative Example 4, nano-silica aerogel was added to the post-treatment working solution compared to Comparative Example 3; in Example 1, aminated nano-silica aerogel was added to the post-treatment working solution compared to Comparative Example 3. It can be seen that adding aminated nano-silica aerogel to the post-treatment working solution significantly improves the neutral salt spray resistance time. This is likely because the aminated nano-silica aerogel not only provides skeletal support, but its amino groups also improve dispersibility and coordinate with molybdate, guiding the growth of the protective film on the aminated nano-silica aerogel network to form a chemically bonded organic-inorganic hybrid protective film, increasing physical barrier properties and improving corrosion resistance.

[0064] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A heat treatment process for corrosion-resistant bolts, characterized in that: Includes the following steps: S1. Clean the bolt blank, remove surface oil, and blow dry to obtain a pre-treated bolt blank; S2. Under methanol and liquefied gas, the pretreated bolt blank is heated to 840-850℃ and held for 70-90 minutes. Then, the temperature is raised to 850-860℃ and held for 90-110 minutes. The blank is then immersed in quenching oil at 40-80℃ for cooling. The blank is then removed, washed with water, and dried to obtain a semi-finished bolt. S3. Heat the semi-finished bolts to 470-490℃, keep them warm for 110-130 minutes, immerse them in a post-treatment working solution at 10-30℃, let them stand for 5-10 minutes, stir for 10-30 minutes, take them out, wash them with water, and keep them warm at 100-120℃ for 40-60 minutes to obtain corrosion-resistant bolts. The post-treatment working fluid is mainly made of the following raw materials in parts by weight: 1000 parts water, 30-50 parts sodium nitrite, 10-20 parts molybdate, 2-4 parts aminated nano silica aerogel, and 1-3 parts dispersant.

2. The heat treatment process for corrosion-resistant bolts according to claim 1, characterized in that: The aminated nano-silica aerogel was prepared by the following method: at a temperature of 50-70℃, an aqueous ethanol solution and 3-aminopropyltriethoxysilane were mixed, hydrophobic nano-silica aerogel was added, the mixture was stirred for 4-6 hours, filtered, washed with water, and dried to obtain the aminated nano-silica aerogel.

3. The heat treatment process for corrosion-resistant bolts according to claim 2, characterized in that: The weight ratio of the hydrophobic nano-silica aerogel to 3-aminopropyltriethoxysilane is 100:(7-13).

4. The heat treatment process for corrosion-resistant bolts according to claim 2, characterized in that: The hydrophobic nano-silica aerogel has an average particle size of 10-50 nm and a specific surface area of ​​200-500 m². 2 / g.

5. The heat treatment process for corrosion-resistant bolts according to claim 1, characterized in that: The molybdate is selected from one or more combinations of sodium molybdate, potassium molybdate, ammonium molybdate, and ammonium dodecylmolybdate phosphate, and the dispersant is selected from one or more combinations of polyvinylpyrrolidone, sodium polyacrylate, ammonium polyacrylate, and sodium hexametaphosphate.

6. The heat treatment process for corrosion-resistant bolts according to claim 1, characterized in that: The weight ratio of the semi-finished bolts and the post-treatment working fluid is 1:(15-25).

7. The heat treatment process for corrosion-resistant bolts according to claim 1, characterized in that: The post-treatment working solution is prepared by the following method: water, sodium nitrite, molybdate, aminated nano-silica aerogel, and dispersant are mixed evenly to obtain the post-treatment working solution.

8. The heat treatment process for corrosion-resistant bolts according to claim 1, characterized in that: The bolt blank is made of one of the following materials: 42CrMo steel, 35CrMo steel, SCM440 steel, or 10B33 steel.

9. The heat treatment process for corrosion-resistant bolts according to claim 1, characterized in that: The nominal diameter of the bolt blank is 5-27mm, and the nominal length is 10-200mm.

10. The heat treatment process for corrosion-resistant bolts according to claim 1, characterized in that: In step S2, the flow rate of methanol is 8-12 L / h, and the flow rate of liquefied petroleum gas is 0.4-0.6 m³ / h. 3 / h.

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