Processing technology of high-strength bolt

Abstract

The application relates to the technical field of fastener processing, and particularly discloses a processing technology of high-strength bolts. The processing technology of high-strength bolts comprises the following steps: pickling a steel wire rod, washing with water, blowing dry, immersing in a phosphating working solution, soaking, taking out, washing with water, blowing dry, immersing in a saponification lubricating working solution, soaking, taking out, washing with water, blowing dry, wire drawing, cold upsetting forming, wire twisting and screwing, quenching, tempering, and obtaining a high-strength bolt; the phosphating working solution is mainly made of the following raw materials: water, phosphoric acid, concentrated nitric acid, zinc oxide, sodium nitrite, manganese nitrate, copper nitrate, a corrosion inhibitor and a complexing agent. The processing technology utilizes the phosphating working solution to form a uniform, complete and tough phosphating film, improves the hardness and compactness, makes the phosphating film have the characteristics of high hardness and small grain size, is beneficial to subsequent wire drawing, cold upsetting forming and wire twisting and screwing, and the obtained high-strength bolt has the characteristic of high tensile strength, and meets the market demand.

Description

Technical Field

[0001] This application relates to the field of fastener processing technology, and more specifically, to a processing technology for high-strength bolts. Background Technology

[0002] High-strength bolts are critical fasteners in steel structure bridges, mechanical equipment, wind power projects, and automobile manufacturing. They consist of a head and a threaded rod. Bolts and nuts work together to enable detachable mechanical connections. Currently, the processing technology for high-strength bolts generally includes pickling, phosphating, saponification, wire drawing, cold heading, thread rolling, quenching, and tempering of steel wire to obtain high-strength bolts. In the phosphating process, a phosphating working solution is used to form a phosphating film on the surface of the steel wire. Conventional phosphating working solutions produce a phosphating film with slightly lower microhardness and coarse grain size. During cold heading and thread rolling, this film is prone to localized breakage or deformation under high pressure, leading to microcracks, surface scratches, and other defects in the substrate, thus affecting tensile strength. Summary of the Invention

[0003] To improve the microhardness of the phosphating film and reduce its grain size, this application provides a processing technology for high-strength bolts, employing the following technical solution: A processing method for high-strength bolts includes the following steps: S1. Pickling, washing, and drying the steel wire to obtain pickled steel wire. S2. Immerse the pickled steel wire in a phosphating working solution at a temperature of 70-90℃ for 10-15 minutes, remove it, wash it with water, and blow it dry to obtain phosphated steel wire. S3. Immerse the phosphated steel wire in a saponification lubricating working solution at a temperature of 60-80℃ for 5-10 minutes, remove it, wash it with water, and blow it dry to obtain saponification lubricated steel wire. S4. The saponified lubricating steel wire is drawn, cold-headed, twisted and spiralized to obtain a bolt blank; S5. Quench and temper the bolt blank to obtain a high-strength bolt. The phosphating working solution is mainly made of the following raw materials in parts by weight: 1000 parts water, 20-30 parts phosphoric acid, 10-20 parts concentrated nitric acid, 75-85 parts zinc oxide, 1-2 parts sodium nitrite, 8-12 parts manganese nitrate, 0.3-0.8 parts copper nitrate, 0.5-1.5 parts corrosion inhibitor, and 1-3 parts complexing agent.

[0004] The processing technology of the high-strength bolts disclosed in this application involves first pickling the steel wire, followed by phosphating to form a phosphating film, then saponification lubrication to form a saponification film. Afterwards, the bolts undergo wire drawing, cold heading, thread rolling, quenching, and tempering to obtain high-strength bolts. The synergistic effect of the raw materials in the phosphating working solution forms a uniform, complete, and tough phosphating film, increasing its hardness and density, improving defects, enhancing its microhardness, and reducing its grain size. The phosphating film exhibits a microhardness (HV) > 440 and a grain size < 9 μm, resulting in a high-hardness and small-grain-size phosphating film. This also helps resist the pressure and shear force during cold heading, eliminates stress concentration, facilitates subsequent quenching and tempering, improves the metallographic structure, and increases tensile strength, exceeding 1120 MPa, demonstrating high tensile strength and meeting market demands.

[0005] The phosphating working solution raw material of this application includes sodium nitrite, which not only promotes the conversion of the phosphating film but also eliminates the hydrogen film, increases the uniformity and integrity of the phosphating film, reduces surface defects, and improves the quality and performance of the phosphating film. Simultaneous addition of manganese nitrate and copper nitrate to the raw material allows manganese ions to participate in film formation, increasing hardness and density, improving defects, and reducing porosity. Copper ions inhibit grain growth, refine grains, increase density and uniformity, and, through the synergistic effect of manganese nitrate and copper nitrate, improve the microhardness of the phosphating film, reduce the grain size, and enable the phosphating film to exhibit superior performance, which is beneficial for improving the tensile strength of high-strength bolts.

[0006] Optionally, the weight ratio of the pickled steel wire and the phosphating working solution is 1:(10-20).

[0007] By adopting the above technical solution, the weight ratio of pickled steel wire and phosphating working solution is optimized to ensure that the phosphating working solution fully wets and coats the pickled steel wire and forms a uniform and complete phosphating film, thus ensuring the quality and performance of the phosphating film.

[0008] In several implementation schemes, the weight ratio of pickled steel wire and phosphating working solution is 1:15. It can also be set to 1:10, 1:12, 1:8, 1:20, etc. as needed, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0009] Optionally, the corrosion inhibitor is selected from one or more combinations of benzotriazole, methylbenzotriazole, benzimidazole, and heptadecanylimidazoline.

[0010] By adopting the above technical solution, the corrosion inhibitor is optimized, making it easier to select the appropriate inhibitor. Furthermore, the corrosion inhibitor can adsorb onto the surface of the pickled steel wire to form a protective film, effectively inhibiting excessive corrosion of the pickled steel wire by the phosphating working solution, and facilitating the formation of a uniform and complete phosphating film.

[0011] Optionally, the complexing agent is selected from one or more combinations of citric acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, and tartaric acid.

[0012] Optionally, the complexing agent is selected from a combination of citric acid and ethylenediaminetetraacetic acid, and the weight ratio of citric acid to ethylenediaminetetraacetic acid is (1-3):(1-3).

[0013] By adopting the above technical solution, the complexing agent is optimized, facilitating its selection. The complexing agent can effectively maintain the stability of the phosphating working solution, ensure uniform growth of phosphating film grains, reduce phosphating film defects, and guarantee the quality and performance of the phosphating film.

[0014] In several implementations, the weight ratio of citric acid to ethylenediaminetetraacetic acid is 1:1. However, the weight ratio can also be set to 1:2, 1:3, 2:1, 2:3, 3:1, 3:2, etc., as needed, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0015] Optionally, the saponified lubricating working fluid is mainly made from the following raw materials in parts by weight: 1000 parts water, 8-12 parts sodium stearate, 2-4 parts sodium carbonate, and 1-3 parts trisodium phosphate.

[0016] By adopting the above technical solution, the raw materials and raw material ratio of the saponified lubricating working fluid are optimized. Sodium stearate can be adsorbed on the surface of the phosphating film and combine with the metal ions on the surface of the phosphating film to form a dense saponified film, thereby increasing lubricity.

[0017] Optionally, the weight ratio of the phosphated steel wire and the saponified lubricating fluid is 1:(10-20).

[0018] By adopting the above technical solution, the weight ratio of phosphated steel wire and saponified lubricating fluid is optimized to ensure that the saponified lubricating fluid fully wets and coats the surface of the phosphated steel wire and forms a uniform saponified film, thus ensuring good lubricity.

[0019] In several implementation schemes, the weight ratio of phosphated steel wire and saponified lubricating fluid is 1:10. It can also be set to 1:12, 1:15, 1:8, 1:20, etc. as needed, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] Optionally, in step S1, during the pickling process, hydrochloric acid is dissolved in water for pickling, the mass concentration of the hydrochloric acid aqueous solution is 4-10%, and the pickling time is 10-15 min.

[0021] By adopting the above technical solution, the pickling process is optimized to remove impurities and rust from the surface of the steel wire, which is beneficial for subsequent phosphating and the formation of a phosphating film, increases the adhesion of the phosphating film, and reduces the occurrence of peeling.

[0022] In several embodiments, the mass concentration of the hydrochloric acid aqueous solution is 6%, but it can also be set to 4%, 5%, 8%, 10%, etc., as needed, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. In several embodiments, the pickling time is 12 minutes, but it can also be set to 10 minutes, 11 minutes, 13 minutes, 14 minutes, 15 minutes, etc., as needed, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0023] Optionally, the weight ratio of the steel wire and the hydrochloric acid aqueous solution is 1:(10-20).

[0024] In several implementation schemes, the weight ratio of steel wire and hydrochloric acid aqueous solution is 1:15. It can also be set to 1:10, 1:12, 1:8, 1:20, etc. as needed, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] Optionally, in step S5, the quenching temperature is 840-860℃ and the time is 90-110min.

[0026] Optionally, in step S5, the tempering temperature is 470-490℃ and the time is 110-130min.

[0027] By adopting the above technical solutions, the quenching temperature and quenching time are optimized to ensure that the bolt blank forms a uniform and fine martensitic structure. The tempering temperature and tempering time are also optimized to effectively eliminate internal stress and improve toughness and plasticity.

[0028] In several implementations, the quenching process uses a quenching temperature of 850°C and a quenching time of 100 min. However, the quenching temperature can be set to 840°C, 845°C, 855°C, 860°C, etc., and the quenching time can be set to 90 min, 95 min, 105 min, 110 min, etc., as needed. But it is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0029] In several implementations, the tempering process is performed at a tempering temperature of 480°C for 120 minutes. However, the tempering temperature can be set to 470°C, 475°C, 485°C, 490°C, etc., and the tempering time can be set to 110 minutes, 115 minutes, 125 minutes, 130 minutes, etc., as needed. However, it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0030] In summary, this application has at least the following beneficial effects: The processing technology of the high-strength bolts disclosed in this application involves first pickling the steel wire, followed by phosphating to form a phosphating film, then saponification lubrication to form a saponification film. Afterwards, the bolts undergo wire drawing, cold heading, thread rolling, quenching, and tempering to obtain the high-strength bolts. Utilizing a phosphating working solution, sodium nitrite, manganese nitrate, and copper nitrate are added to the raw material. This not only forms a uniform, complete, and tough phosphating film but also increases its hardness and density, improves defects, and enhances its performance. Furthermore, the phosphating film exhibits a microhardness (HV) > 440 and a grain size < 9 μm, resulting in high hardness and small grain size. Simultaneously, the phosphating film helps resist the pressure and shear force during cold heading, eliminates stress concentration, facilitates subsequent quenching and tempering, improves the metallographic structure, and increases tensile strength (> 1120 MPa), enabling the high-strength bolts to exhibit high tensile strength and meet 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] Example

[0033] Example 1 A processing method for high-strength bolts includes the following steps: S0, prepare phosphating working fluid and saponification lubricating working fluid.

[0034] Preparation of phosphating working solution: The phosphating working solution is made from the following raw materials: 1000 kg water, 25 kg phosphoric acid, 15 kg concentrated nitric acid, 80 kg zinc oxide, 1.4 kg sodium nitrite, 10 kg manganese nitrate, 0.5 kg copper nitrate, 1 kg corrosion inhibitor, and 2 kg complexing agent.

[0035] Furthermore, the corrosion inhibitor is selected from benzotriazole; the complexing agent is selected from a combination of citric acid and ethylenediaminetetraacetic acid, and the weight ratio of citric acid to ethylenediaminetetraacetic acid is 1:1.

[0036] The phosphating working solution is prepared by the following method: at a speed of 500 r / min, concentrated nitric acid is added to water and stirred for 2 min; phosphoric acid is added and stirred for 2 min; sodium nitrite, manganese nitrate, and copper nitrate are added and stirred for 5 min; corrosion inhibitor and complexing agent are added and stirred for 2 min; zinc oxide is added and stirred for 10 min to obtain the phosphating working solution.

[0037] Preparation of saponified lubricating working fluid: The saponified lubricating working fluid is made from the following raw materials: 1000 kg of water, 10 kg of sodium stearate, 3 kg of sodium carbonate, and 2 kg of trisodium phosphate.

[0038] The saponified lubricating working fluid is prepared by the following method: sodium carbonate and trisodium phosphate are added to water at a speed of 500 r / min and stirred for 5 min. Sodium stearate is then added and stirred for 10 min to obtain the saponified lubricating working fluid.

[0039] S1. Immerse the steel wire in a 6% hydrochloric acid solution for 12 minutes, remove it, wash it with water, and blow it dry to obtain pickled steel wire.

[0040] The steel wire is made of ML40Cr steel and has a diameter of 18mm; the weight ratio of the steel wire to the hydrochloric acid solution is 1:15.

[0041] S2. Immerse the pickled steel wire in a phosphating working solution at 80°C for 12 minutes, remove it, wash it with water, and blow it dry to obtain phosphated steel wire.

[0042] The weight ratio of pickled steel wire and phosphating working solution is 1:15.

[0043] S3. Immerse the phosphated steel wire in a saponification lubricating working solution at a temperature of 70°C for 8 minutes, remove it, wash it with water, and blow it dry to obtain saponified lubricated steel wire.

[0044] The weight ratio of phosphated steel wire and saponified lubricating fluid is 1:10.

[0045] S4. The saponified lubricating steel wire is drawn, cold-forged, twisted and spiral-formed to obtain the bolt blank.

[0046] The bolt blank has a diameter of 16mm and a length of 155mm.

[0047] S5. The bolt blank is quenched for 100 minutes in methanol and liquefied gas at 850℃, followed by oil cooling. Then, it is tempered for 120 minutes at 480℃ and air-cooled to obtain a high-strength bolt.

[0048] The flow rate of methanol is 10 L / h, and the flow rate of liquefied petroleum gas is 0.5 m³ / h.3 / h.

[0049] Example 2 A processing technology for high-strength bolts differs from that of Example 1 in that the raw material ratios of the phosphating working fluid and the saponification lubricating working fluid are different in step S0.

[0050] Furthermore, the phosphating working solution is made from the following raw materials: 1000 kg water, 20 kg phosphoric acid, 10 kg concentrated nitric acid, 85 kg zinc oxide, 2 kg sodium nitrite, 8 kg manganese nitrate, 0.8 kg copper nitrate, 0.5 kg corrosion inhibitor, and 3 kg complexing agent.

[0051] The saponified lubricating working fluid is made from the following raw materials: 1000 kg of water, 8 kg of sodium stearate, 4 kg of sodium carbonate, and 3 kg of trisodium phosphate.

[0052] Example 3 A processing technology for high-strength bolts differs from that of Example 1 in that the raw material ratios of the phosphating working fluid and the saponification lubricating working fluid are different in step S0.

[0053] Furthermore, the phosphating working solution is made from the following raw materials: 1000 kg water, 30 kg phosphoric acid, 20 kg concentrated nitric acid, 75 kg zinc oxide, 1 kg sodium nitrite, 12 kg manganese nitrate, 0.3 kg copper nitrate, 1.5 kg corrosion inhibitor, and 1 kg complexing agent.

[0054] The saponified lubricating working fluid is made from the following raw materials: 1000 kg of water, 12 kg of sodium stearate, 2 kg of sodium carbonate, and 1 kg of trisodium phosphate.

[0055] Comparative Example Comparative Example 1 A processing technology for high-strength bolts differs from that of Example 1 in that, in step S0, sodium nitrite, manganese nitrate, and copper nitrate are not added to the raw materials of the phosphating working solution.

[0056] Comparative Example 2 A processing technology for high-strength bolts differs from that of Example 1 in that, in step S0, manganese nitrate and copper nitrate are not added to the raw materials of the phosphating working solution.

[0057] Comparative Example 3 A processing technology for high-strength bolts differs from that of Example 1 in that, in step S0, an equal amount of manganese nitrate is used to replace copper nitrate in the raw materials of the phosphating working solution.

[0058] Comparative Example 4 A processing technology for high-strength bolts differs from that of Example 1 in that, in step S0, an equal amount of copper nitrate is used to replace manganese nitrate in the raw materials of the phosphating working solution.

[0059] Performance testing (1) The saponified lubricated steel wire obtained in step S3 of Examples 1-3 and Comparative Examples 1-4 were taken as samples, and the following performance tests were performed on the saponified lubricated steel wire. The test results are shown in Table 1.

[0060] In particular, the microhardness of the phosphate film on the surface of saponified lubricated steel wire was tested according to GB / T 4340.1-2024 "Metallic materials - Vickers hardness test - Part 1: Test method".

[0061] According to GB / T 13298-2015 "Methods for Inspection of Microstructure of Metals", the grain size of the phosphate film on the surface of saponified lubricated steel wire was tested.

[0062] (2) The high-strength bolts obtained in step S5 of Examples 1-3 and Comparative Examples 1-4 were taken as samples, and the following performance tests were performed on the high-strength bolts. The test results are shown in Table 1.

[0063] In accordance with GB / T3098.1-2010 "Mechanical Properties of Fasteners - Bolts, Screws and Studs", the tensile strength of high-strength bolts was tested.

[0064] Table 1 Test Results

[0065] As shown in Table 1, the saponified lubricated steel wire obtained by the processing technology of this application has high microhardness of the phosphate film, with a microhardness HV of 445-455, exhibiting the characteristic of high hardness of the phosphate film. It also has low phosphate film grain size, with a grain size of 8.3-8.6 μm, exhibiting the characteristic of small grain size. Furthermore, the phosphate film can form a strong, dense, and uniform phosphate film, which is beneficial for subsequent wire drawing, cold heading, and wire twisting. The high-strength bolts obtained by the processing technology of this application have high tensile strength, with a tensile strength of 1127-1142 MPa, exhibiting the characteristic of high tensile strength and meeting market demand.

[0066] Comparative Examples 1 and 2 were compared. In Comparative Example 2, sodium nitrite was added to the raw materials of the phosphating working solution compared to Comparative Example 1. This shows that adding sodium nitrite to the raw materials of the phosphating working solution can increase the microhardness of the phosphating film and reduce the grain size of the phosphating film. This may be because sodium nitrite not only promotes the conversion of the phosphating film but also eliminates the hydrogen film, increases the uniformity and integrity of the phosphating film conversion, reduces surface defects of the phosphating film, and improves the performance of the phosphating film.

[0067] Comparative Examples 2-4 and Example 1 were compared. In Comparative Example 3, manganese nitrate was added to the raw materials of the phosphating working solution compared to Comparative Example 2; in Comparative Example 4, copper nitrate was added to the raw materials of the phosphating working solution compared to Comparative Example 2; and in Example 1, both manganese nitrate and copper nitrate were added to the raw materials of the phosphating working solution compared to Comparative Example 2. It can be seen that the simultaneous addition of manganese nitrate and copper nitrate to the raw materials of the phosphating working solution, and their synergistic effect, significantly increases the microhardness of the phosphating film and reduces the grain size. This may be because manganese ions can participate in film formation, increasing the hardness and density of the phosphating film, improving defects, reducing porosity, and increasing integrity. Copper ions can inhibit grain growth, refine grains, increase the density and uniformity of the phosphating film, and improve its performance. During cold heading, the phosphating film can effectively resist pressure and shear force, eliminate stress concentration, and facilitate subsequent quenching and tempering, improving the metallographic structure, reducing defects, and increasing tensile strength.

[0068] 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 processing technology for high-strength bolts, characterized in that: Includes the following steps: S1. Pickling, washing, and drying the steel wire to obtain pickled steel wire. S2. Immerse the pickled steel wire in a phosphating working solution at a temperature of 70-90℃ for 10-15 minutes, remove it, wash it with water, and blow it dry to obtain phosphated steel wire. S3. Immerse the phosphated steel wire in a saponification lubricating working solution at a temperature of 60-80℃ for 5-10 minutes, remove it, wash it with water, and blow it dry to obtain saponification lubricated steel wire. S4. The saponified lubricating steel wire is drawn, cold-headed, twisted and spiralized to obtain a bolt blank; S5. Quench and temper the bolt blank to obtain a high-strength bolt. The phosphating working solution is mainly made of the following raw materials in parts by weight: 1000 parts water, 20-30 parts phosphoric acid, 10-20 parts concentrated nitric acid, 75-85 parts zinc oxide, 1-2 parts sodium nitrite, 8-12 parts manganese nitrate, 0.3-0.8 parts copper nitrate, 0.5-1.5 parts corrosion inhibitor, and 1-3 parts complexing agent.

2. The processing technology for a high-strength bolt according to claim 1, characterized in that: The weight ratio of the pickled steel wire and the phosphating working solution is 1:(10-20).

3. The processing technology for a high-strength bolt according to claim 1, characterized in that: The corrosion inhibitor is selected from one or more combinations of benzotriazole, methylbenzotriazole, benzimidazole, and heptadecanylimidazoline.

4. The processing technology for a high-strength bolt according to claim 1, characterized in that: The complexing agent is selected from one or more combinations of citric acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, and tartaric acid.

5. The processing technology for a high-strength bolt according to claim 1, characterized in that: The complexing agent is selected from a combination of citric acid and ethylenediaminetetraacetic acid, and the weight ratio of citric acid to ethylenediaminetetraacetic acid is (1-3):(1-3).

6. The processing technology for a high-strength bolt according to claim 1, characterized in that: The saponified lubricating working fluid is mainly made from the following raw materials in parts by weight: 1000 parts water, 8-12 parts sodium stearate, 2-4 parts sodium carbonate, and 1-3 parts trisodium phosphate.

7. The processing technology for a high-strength bolt according to claim 1, characterized in that: The weight ratio of the phosphated steel wire and the saponified lubricating fluid is 1:(10-20).

8. The processing technology for a high-strength bolt according to claim 1, characterized in that: In step S1, during the pickling process, hydrochloric acid is dissolved in water for pickling. The mass concentration of the hydrochloric acid aqueous solution is 4-10%, and the pickling time is 10-15 minutes.

9. The processing technology for a high-strength bolt according to claim 1, characterized in that: In step S5, during the quenching process, the quenching temperature is 840-860℃ and the time is 90-110min.

10. The processing technology for a high-strength bolt according to claim 1, characterized in that: In step S5, during the tempering process, the tempering temperature is 470-490℃ and the time is 110-130min.

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