A high-strength stainless steel fastener

Abstract

The present invention provides a high-strength stainless steel fastener and a preparation method thereof, wherein the fastener comprises the following components by mass percentage: C: 0.05-0.19%, Si: ≤1.0%, Mn ≤1.0%, P ≤0.080%, S ≤0.010%, Cr: 13.00-15%, Ni: 1.5-2.2%, Mo ≤0.15%, Cu ≤0.25%, N ≤0.010%. The fastener provided by the present invention has high strength, stable elastic forging performance, no tripping, anti-locking, anti-hydrogen embrittlement and corrosion resistance, and is an ideal fastener for power transmission and transformation projects. At the same time, the production method provided by the present invention can be mass-produced, the process is simple, and a new way is explored for the production of high-strength stainless steel fasteners for power transmission and transformation using new materials.

Description

Technical Field

[0001] The invention relates to the field of power transmission and transformation engineering materials, and in particular to a high-strength stainless steel fastener. Background Art

[0002] For a long time, fasteners used in power transmission and transformation projects are mostly made of carbon steel or low alloy steel. Since power transmission and transformation projects are located in the wild in harsh environments and are exposed to the air, wind, sun and rain all year round, they are easily oxidized and corroded, which results in high maintenance costs and short service life. High-strength stainless steel fasteners for power transmission and transformation projects produced with high-strength stainless steel can solve this problem. The neutral salt spray test shows that the service life of the fasteners can reach 500 years.

[0003] In order to solve the problems of low corrosion resistance, easy oxidation and short life of power transmission and transformation fasteners, stainless steel is usually considered. However, the commonly used 304, 316 and other stainless steel fasteners are low in strength and high in price, and cannot be promoted in power transmission and transformation projects; martensitic stainless steel is easy to crack and difficult to process; duplex stainless steel is expensive. Therefore, it is necessary to provide a new type of fastener to replace the existing fasteners. Summary of the invention

[0004] In view of the deficiencies in the prior art, an object of the present invention is to provide a high-strength stainless steel fastener, which has high strength, good toughness reserve, corrosion resistance and a simple production method.

[0005] The purpose of the present invention is achieved by adopting the following technical solutions:

[0006] The present invention provides a high-strength stainless steel fastener, the improvement of which is that the fastener comprises the following components in percentage by mass:

[0007] C: 0.05~0.19%, Si: ≤1.0%, Mn≤1.0%, P≤0.080%, S≤0.010%, Cr: 13.00~15%, Ni: 1.5~2.2%, Mo≤0.15%, Cu≤0.25%, N≤0.010%.

[0008] Preferably, the fastener comprises the following components by mass percentage:

[0009] C: 0.15%, Si: 0.44%, Mn: 0.48%, P: 0.05974%, S: 0.00053%, Cr: 13.51%, Ni: 1.83%, Cu: 0.01%, N≤0.010%.

[0010] The present invention provides a method for preparing a high-strength stainless steel fastener, characterized in that the method for preparing the fastener comprises:

[0011] Step (1) hot rolling and upsetting: hot rolling the material, then annealing and straightening the hot rolled material, pickling the annealed and straightened material, and then hot upsetting or cold upsetting the material to form a semi-finished product of a bolt or nut;

[0012] Step (2) quenching and tempering: subjecting the semi-finished product obtained in step (1) to quenching and tempering treatment;

[0013] Step (3): pickling or grinding the semi-finished product obtained in step (2);

[0014] Step (4): turning the hot-forged fastener;

[0015] Step (5) thread making: thread rolling or thread rolling the semi-finished bolt product obtained in step (4), and tapping the semi-finished nut product obtained in step (3);

[0016] Step (6) passivation: passivating the semi-finished product of step (5) with a passivation solution and a coordination agent;

[0017] Step (7): Finished product inspection.

[0018] Preferably, the hot upsetting comprises:

[0019] After the pickled material is polished and blanked, the blanked section is heated, and then the blanked section material is hot-forged into semi-finished bolts and nuts.

[0020] Preferably, the cold heading comprises:

[0021] After the pickled material is polished, the material is cold-forged into finished bolts and nuts.

[0022] Preferably, the fastener is of grade 12.9 and is subjected to the following treatments in sequence:

[0023] Hot rolling and upsetting, turning and hot upsetting of the fasteners, wire making, quenching and tempering, pickling or grinding, passivation and finished product inspection.

[0024] Preferably, the pickling in step (1) comprises:

[0025] Immerse in a solution of 30% sulfuric acid, 5% nitric acid and 65% water at room temperature for 15 to 50 seconds and then rinse the surface with water.

[0026] Furthermore, the purity of the sulfuric acid is ≥98%, and the purity of the nitric acid is ≥96%.

[0027] Furthermore, the polishing treatment includes polycarbonate powder or oxalic acid lubrication.

[0028] Preferably, the lubricant of the hot upsetting die during the hot upsetting in step (2) is a mixture of graphite emulsion and molybdenum disulfide emulsion.

[0029] Preferably, a weak acid is used for grinding in step (3).

[0030] Preferably, the step (6) comprises:

[0031] After the wire-made bolts and nuts are immersed in the stainless iron passivation liquid ID4000 at a temperature of 80±5°C for 15 to 30 minutes, the bolts and nuts are then immersed in the stainless iron coordination agent ID4000A, heated to 65±5°C, immersed for 10 to 15 minutes, washed with water, and then immersed in soft water with a chloride ion content of less than 25ppm for 1 to 3 minutes and then dried.

[0032] Compared with the closest prior art, the present invention has the following beneficial effects:

[0033] (1) The preparation method of a high-strength stainless steel fastener provided by the present invention has a simple process and can be mass-produced, thus exploring a new way for the production of high-strength stainless steel fasteners for power transmission and transformation using new materials;

[0034] (2) The high-strength stainless steel fastener provided by the present invention can be used in power transmission and transformation projects, which can greatly improve the service life of power transmission and transformation projects, extending the current design life of 50 years to 500 years, saving maintenance costs, reducing overall costs, and being environmentally friendly and pollution-free. It is a major move that benefits the country and the people;

[0035] (3) The high-strength stainless steel fastener provided by the present invention has high strength, good toughness reserve, stable elastic forging performance, no slipping, anti-locking, anti-hydrogen embrittlement and safe metallographic structure, and is an ideal fastener for current power transmission and transformation projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a production process flow chart of hot-forging 6.8-10.9 grade bolts in a method for preparing a high-strength stainless steel fastener provided by the present invention;

[0037] Figure 2 This is a process flow chart of hot-forging 12.9-grade bolt production in a method for preparing a high-strength stainless steel fastener provided by the present invention;

[0038] Figure 3 This is a process flow chart of cold heading bolt production in a method for preparing a high-strength stainless steel fastener provided by the present invention;

[0039] Figure 4 It is a production process flow chart of hot upsetting nuts in a method for preparing a high-strength stainless steel fastener provided by the present invention;

[0040] Figure 5The present invention provides a process flow chart for cold heading nut production in a method for preparing a high-strength stainless steel fastener. DETAILED DESCRIPTION

[0041] The specific implementation modes of the present invention will be further described in detail below in conjunction with the accompanying drawings.

[0042] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] Example 1

[0044] The present invention provides a method for preparing a high-strength stainless steel fastener, wherein the fastener comprises the following components in percentage by mass:

[0045] C: 0.05~0.19%, Si: ≤1.0%, Mn≤1.0%, P≤0.080%, S≤0.010%, Cr: 13.00~15%, Ni: 1.5~2.2%, Mo≤0.15%, Cu≤0.25%, N≤0.010%.

[0046] In the most preferred embodiment of the present invention, the fastener comprises the following components by mass percentage:

[0047] C: 0.15%, Si: 0.44%, Mn: 0.48%, P: 0.05974%, S: 0.00053%, Cr: 13.51%, Ni: 1.83%, Cu: 0.01%, N≤0.010%.

[0048] Example 2

[0049] Based on the same inventive concept, the present invention provides a hot upsetting production method for 6.8-10.9 grade bolts of high-strength stainless steel fasteners, such as Figure 1 As shown, the production method of the bolt includes:

[0050] Step 2-A hot rolling and polishing: hot rolling the material, annealing the hot rolled material, straightening and pickling the annealed material, grinding the pickled material, and finally polishing the ground material, wherein the material is cut into a flat end surface at one end and chamfered at the other end, and a center hole is punched at the chamfered end;

[0051] Step 2-B hot upsetting: heating the material of the blanking section obtained in step 2-A, and then hot upsetting it into bolts and turning the hexagonal flash;

[0052] Step 2-C: Quenching and tempering treatment: the bolts obtained in step 2-B are subjected to quenching and tempering treatment;

[0053] Step 2-D: pickling or grinding: subjecting the bolts obtained in step 2-C to shot blasting, pickling passivation or grinding passivation treatment;

[0054] Step 2-E: Turning the pitch diameter: Turn the pitch diameter of the bolt obtained in step 2-D to the required size;

[0055] Step 2-F: Thread rolling or thread twisting of the bolts obtained in step 2-E to produce threaded parts;

[0056] Step 2-G Passivation: Step 2-F The bolts after thread making are passivated using a passivation liquid and a coordination agent;

[0057] Step 2-H Finished product inspection: inspect the appearance, dimensional accuracy, mechanical properties and corrosion resistance of the bolts obtained in step 2-G, and finally obtain the finished product.

[0058] In the most preferred embodiment of the present invention, the pickling treatment in step 2-A comprises:

[0059] The annealed material is placed in a solution of 30% sulfuric acid + 5% nitric acid + 65% water, and soaked at room temperature for 15 to 50 seconds. After the material workpiece is taken out of the pickling tank, the black reactant on the surface of the workpiece is quickly washed with a high-pressure water gun.

[0060] Specifically, the purity of the sulfuric acid is ≥98%, and the purity of the nitric acid is ≥96%.

[0061] In the most preferred embodiment of the present invention, polycarbonate powder or oxalic acid is used for lubrication during the polishing process in step 2-A.

[0062] In the most preferred embodiment of the present invention, during the hot upsetting in step 2-B, graphite emulsion and molybdenum disulfide emulsion are mixed as lubricants for the hot upsetting die.

[0063] In the most preferred embodiment of the present invention, weak acid grinding is used in step 2-D.

[0064] In the most preferred embodiment of the present invention, step 2-G comprises:

[0065] Soak the bolts made from wire in step 2-F in stainless iron passivation solution ID4000 at 80±5°C for 15 to 30 minutes, then soak the bolts in stainless iron coordination agent ID4000A at 65±5°C for 10 to 15 minutes, and finally take out, rinse with clean water and dry.

[0066] Specifically, before drying, the method further includes: soaking the bolts in soft water with a chloride ion content of less than 25 ppm for 1 to 3 minutes and then drying the bolts.

[0067] Example 3

[0068] Based on the same inventive concept, the present invention provides a hot upsetting production method for 12.9 grade bolts of high-strength stainless steel fasteners, such as Figure 2 As shown, the production method of the bolt includes:

[0069] Step 3-a: hot rolling and polishing: the material is hot rolled and annealed, the annealed material is straightened and pickled and passivated, the pickled material is ground, and the ground material is polished and cut, wherein the material is cut into a flat end face at one end and a chamfered end at the other end, and a center hole is punched at the chamfered end;

[0070] Step 3-b: hot upsetting: heating the material of the blanking section obtained in step 3-a, and then hot upsetting it into bolts and cutting off the hexagonal burrs;

[0071] Step 3-c: turning the middle diameter: turning the middle diameter of the bolt obtained in step 3-b to the required size;

[0072] Step 3-d: Thread rolling or thread rolling of the bolt obtained in step 3-c to produce the threaded part;

[0073] Step 3-e: quenching and tempering treatment: the bolts obtained in step 3-d are subjected to quenching and tempering treatment;

[0074] Step 3-f: pickling or grinding: subjecting the bolts obtained in step 3-e to shot blasting, pickling passivation or grinding passivation treatment;

[0075] Step 3-g: passivation: Step 3-f: the bolts after wire making are passivated using a passivation liquid and a coordination agent;

[0076] Step 3-h: Finished product inspection: inspect the appearance, dimensional accuracy, mechanical properties and corrosion resistance of the bolts obtained in step 3-g, and finally obtain the finished product.

[0077] In the most preferred embodiment of the present invention, the pickling treatment in step 3-a comprises:

[0078] The annealed material is placed in a solution of 30% sulfuric acid + 5% nitric acid + 65% water, and soaked at room temperature for 15 to 50 seconds. After the material workpiece is taken out of the pickling tank, the black reactant on the surface of the workpiece is quickly washed with a high-pressure water gun.

[0079] Specifically, the purity of the sulfuric acid is ≥98%, and the purity of the nitric acid is ≥96%.

[0080] In the most preferred embodiment of the present invention, polycarbonate powder or oxalic acid is used for lubrication during the polishing process in step 3-a.

[0081] In the most preferred embodiment of the present invention, during the hot upsetting in step 3-b, graphite emulsion and molybdenum disulfide emulsion are mixed as a lubricant for the hot upsetting die.

[0082] In the most preferred embodiment of the present invention, weak acid grinding is used in step 3-f.

[0083] In the most preferred embodiment of the present invention, step 3-g comprises:

[0084] Soak the bolts after pickling or grinding in step 3-f in stainless iron passivation liquid ID4000 at a temperature of 80±5°C for 15 to 30 minutes, then soak the bolts in stainless iron coordination agent ID4000A, heat to 65±5°C, soak for 10 to 15 minutes, and finally take out, rinse with clean water and dry.

[0085] Specifically, before drying, the method further includes: soaking the bolts in soft water with a chloride ion content of less than 25 ppm for 1 to 3 minutes and then drying the bolts.

[0086] Example 4

[0087] Based on the same inventive concept, the present invention provides a cold heading production method for bolts of high-strength stainless steel fasteners, such as Figure 3 As shown, the production method of the bolt includes:

[0088] Step 4-A hot rolling and polishing: the material is hot rolled, and the hot rolled material is annealed, and then the annealed material is straightened and pickled and passivated, and the material is polished;

[0089] Step 4-B cold forging: cold forging the blanking section obtained in step 4-A into a bolt;

[0090] Step 4-C: Threading the bolts obtained in step 4-B to produce threaded parts;

[0091] Step 4-D: Quenching and tempering treatment: the bolts obtained in step 4-C are subjected to quenching and tempering treatment;

[0092] Step 4-E: pickling or grinding: pickling or grinding the bolts obtained in step 4-D;

[0093] Step 4-F Passivation: Step 4-E The bolts after wire making are passivated using a passivation liquid and a coordination agent;

[0094] Step 4-G Finished Product Inspection: Inspect the appearance, dimensional accuracy, mechanical properties and corrosion resistance of the bolts obtained in step 4-F, and finally obtain the finished product.

[0095] In the most preferred embodiment of the present invention, the pickling treatment in step 4-A comprises:

[0096] The annealed material is placed in a solution of 30% sulfuric acid + 5% nitric acid + 65% water, and soaked at room temperature for 15 to 50 seconds. After the material workpiece is taken out of the pickling tank, the black reactant on the surface of the workpiece is quickly washed with a high-pressure water gun.

[0097] Specifically, the purity of the sulfuric acid is ≥98%, and the purity of the nitric acid is ≥96%.

[0098] In the most preferred embodiment of the present invention, polycarbonate powder or oxalic acid is used for lubrication during the polishing process in step 4-A.

[0099] In the most preferred embodiment of the present invention, weak acid grinding is used in step 4-E.

[0100] In the most preferred embodiment of the present invention, step 4-F comprises:

[0101] Soak the pickled or ground bolts in step 4-E in stainless iron passivation liquid ID4000 at 80±5°C for 15 to 30 minutes, then soak the bolts in stainless iron coordination agent ID4000A, heat to 65±5°C, soak for 10 to 15 minutes, and finally take out, rinse with clean water and dry.

[0102] Specifically, before drying, the method further includes: soaking the bolts in soft water with a chloride ion content of less than 25 ppm for 1 to 3 minutes and then drying the bolts.

[0103] Example 5

[0104] Based on the same inventive concept, the present invention provides a hot upsetting production method for nuts of high-strength stainless steel fasteners, such as Figure 4 As shown, the method is the same as the hot upsetting production method of 12.9 grade bolts.

[0105] Example 6

[0106] Based on the same inventive concept, the present invention provides a cold heading production method for nuts of high-strength stainless steel fasteners, such as Figure 5 As shown, the production method of the nut includes:

[0107] Step 6-A hot rolling and polishing: the material is hot rolled, and the hot rolled material is annealed, and then the annealed material is straightened, and then the straightened material is ground, and finally the ground material is polished and cut;

[0108] Step 6-B hot forging: cold forging the material of the blanking section obtained in step 6-A into a nut shape;

[0109] Step 6-C: quenching and tempering treatment: the nut obtained in step 6-B is subjected to quenching and tempering treatment;

[0110] Step 6-D: pickling or grinding: subjecting the nuts obtained in step 6-C to shot blasting, pickling passivation or grinding passivation treatment;

[0111] Step 6-E: Pressing: Pressing the nut obtained in step 6-D;

[0112] Step 6-F: Step 6-E: The nut is tapped to produce the threaded part;

[0113] Step 6-G Passivation: Step 6-F The nuts after wire making are passivated using a passivation liquid and a coordination agent;

[0114] Step 6-H Finished product inspection: inspect the appearance, dimensional accuracy, mechanical properties and corrosion resistance of the nut obtained in step 6-G, and finally obtain the finished product.

[0115] In the most preferred embodiment of the present invention, the pickling treatment in step 6-A comprises:

[0116] The annealed material is placed in a solution of 30% sulfuric acid + 5% nitric acid + 65% water, and soaked at room temperature for 15 to 50 seconds. After the material workpiece is taken out of the pickling tank, the black reactant on the surface of the workpiece is quickly washed with a high-pressure water gun.

[0117] Specifically, the purity of the sulfuric acid is ≥98%, and the purity of the nitric acid is ≥96%.

[0118] In the most preferred embodiment of the present invention, polycarbonate powder or oxalic acid is used for lubrication during the polishing process in step 6-A.

[0119] In the most preferred embodiment of the present invention, weak acid grinding is used in step 6-D.

[0120] In the most preferred embodiment of the present invention, step 6-G comprises:

[0121] Soak the bolts after wire making in step 6-F in stainless iron passivation liquid ID4000 at 80±5℃ for 15 to 30 minutes, then soak the bolts in stainless iron coordination agent ID4000A, heat to 65±5℃, soak for 10 to 15 minutes, and finally take out, rinse with clean water and dry.

[0122] Specifically, before drying, the method further includes: soaking the bolts in soft water with a chloride ion content of less than 25 ppm for 1 to 3 minutes and then drying the bolts.

[0123] The conditioning in Examples 2-6 was performed according to the specifications in Table 1.

[0124] Table 1 Quenching and tempering process of the present invention

[0125]

[0126] Among them, the calculation formula for the quenching and tempering holding time in a box-type electric heating furnace during quenching and tempering treatment is:

[0127] 10.9 grade bolt quenching preheating holding time t = 2.5 (heating coefficient) × D × K (minutes);

[0128] The quenching and holding time of 8.8, 9.8, 10.9 and 12.9 grade bolts is t=2.5 (heating coefficient) × D × K (minutes);

[0129] The tempering and holding time for grade 6.8, 8.8, 9.8, 10.9 and 12.9 bolts is t=4.5 (heating coefficient) × D + 15 (minutes).

[0130] Annealing process in Example 2-6:

[0131] Annealing temperature: 720℃, holding time: t=5.0(heating coefficient)×D×K(minutes), cooling method: air cooling; D—effective thickness or diameter of workpiece (mm) K—furnace charging and discharging correction coefficient (refer to Table 2);

[0132] Table 2 Furnace charging and discharging coefficient

[0133]

[0134] If heated in a salt bath furnace, the time required should be reduced by one fifth compared to the heating time in a box furnace.

[0135] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A high-strength stainless steel fastener, characterized in that: The fastener comprises the following components by mass percentage: C: 0.05~0.19%, Si: ≤1.0%, Mn≤1.0%, P≤0.080%, S≤0.010%, Cr: 13.00~15%, Ni: 1.5~2.2%, Mo≤0.15%, Cu≤0.25%, N≤0.010%; The steps for preparing the fasteners are as follows: Step (1) hot-rolling and upsetting: hot-rolling treatment is performed, and then the hot-rolled material is annealed and straightened, and then the annealed and straightened material is pickled, and then hot-forged to form a semi-finished product of a bolt or cold-forged to form a semi-finished product of a nut; Step (2) quenching and tempering: subjecting the semi-finished product obtained in step (1) to quenching and tempering treatment; Step (3): pickling or grinding the semi-finished product obtained in step (2); Step (4): turning the semi-finished product of the hot-forged bolt; Step (5) thread making: thread rolling or thread rolling the semi-finished bolt product obtained in step (4), and tapping the semi-finished nut product obtained in step (3); Step (6) passivation: passivating the semi-finished product of step (5) with a passivation solution and a coordination agent; Step (7): Finished product inspection; In step (1), the annealing temperature is 720°C, the holding time is t=5.0×D×K, and the cooling method is air cooling; In step (2), the quenching medium is oil and the cooling method is water cooling; In step (2), fasteners of grades 9.8, 10.9 and 12.9 can be prepared: When preparing 9.8 grade fasteners, quenching and tempering treatment is adopted, the quenching temperature is 900℃ and the tempering temperature is 570℃; When preparing 10.9 grade fasteners, quenching and tempering treatment is adopted, the quenching preheating temperature is 700℃, the quenching temperature is 980℃, and the tempering temperature is 530℃; When preparing 12.9 grade fasteners, quenching and tempering treatment is adopted, the quenching preheating temperature is 700℃, the quenching temperature is 980℃, and the tempering temperature is 200℃; Among them, the quenching preheating holding time for preparing 10.9 grade fasteners is t = 2.5 × D × K; The quenching and holding time for preparing grade 8.8, grade 9.8, grade 10.9, and grade 12.9 fasteners is t = 2.5 × D × K; The tempering holding time for preparing grade 6.8, 8.8, 9.8, 10.9, and 12.9 fasteners is t=4.5×D+15; D is the effective thickness or diameter of the fastener, mm; K is the correction factor for charging and discharging, which is 1.0, 1.3, 1.4, 1.7 or 2.

0.

2. The fastener according to claim 1, characterized in that The fastener comprises the following components by mass percentage: C: 0.15%, Si: 0.44%, Mn: 0.48%, P: 0.05974%, S: 0.00053%, Cr: 13.51%, Ni: 1.83%, Cu: 0.01%, N≤0.010%.

3. A method for preparing a fastener according to any one of claims 1 to 2, characterized in that: The method for preparing the fastener comprises: Step (1) hot-rolling and upsetting: hot-rolling treatment is performed, and then the hot-rolled material is annealed and straightened, and then the annealed and straightened material is pickled, and then hot-forged to form a semi-finished product of a bolt or cold-forged to form a semi-finished product of a nut; Step (2) quenching and tempering: subjecting the semi-finished product obtained in step (1) to quenching and tempering treatment; Step (3): pickling or grinding the semi-finished product obtained in step (2); Step (4): turning the semi-finished product of the hot-forged bolt; Step (5) thread making: thread rolling or thread rolling the semi-finished bolt product obtained in step (4), and tapping the semi-finished nut product obtained in step (3); Step (6) passivation: passivating the semi-finished product of step (5) with a passivation solution and a coordination agent; Step (7): Finished product inspection.

4. The method according to claim 3, characterized in that The hot upsetting comprises: After the pickled material is polished and blanked, the blanking section is heated, and then the blanking section material is hot-forged into a semi-finished bolt product.

5. The method according to claim 3, characterized in that The cold heading comprises: After the pickled material is polished, the material is cold-forged into a semi-finished nut.

6. The method according to claim 3, characterized in that The pickling in step (1) comprises: Immerse in a solution of 30% sulfuric acid, 5% nitric acid and 65% water at room temperature for 15 to 50 seconds and then rinse the surface with water.

7. The method according to claim 6, characterized in that: The purity of the sulfuric acid is ≥98%, and the purity of the nitric acid is ≥96%.

8. The method according to claim 4, characterized in that The polishing process includes polycarbonate powder or oxalic acid lubrication.

9. The method according to claim 3, characterized in that During the hot upsetting in step (2), the lubricant of the hot upsetting die is a mixture of graphite emulsion and molybdenum disulfide emulsion.

10. The method according to claim 3, characterized in that In the step (3), a weak acid is used for grinding.

11. The method according to claim 3, characterized in that The step (6) comprises: After the wire-made bolts and nuts are immersed in the stainless iron passivation liquid ID4000 at a temperature of 80±5°C for 15 to 30 minutes, the bolts and nuts are then immersed in the stainless iron coordination agent ID4000A, heated to 65±5°C, immersed for 10 to 15 minutes, washed with water, and then immersed in soft water with a chloride ion content of less than 25ppm for 1 to 3 minutes and then dried.

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