High wear resistant bolt and method of manufacturing same

Abstract

This invention relates to the field of bolt technology, specifically to a high wear-resistant bolt and its manufacturing method. The high wear-resistant bolt is composed of the following components by mass percentage: C 0.35%–0.42%, Si 1.2%–1.6%, Mn 0.4%–0.8%, Cr 2.0%–2.8%, B 0.002%–0.005%, Y 0.02%–0.06%, W 2.0%–3.0%, Ta 1.3%–2.2%, Zr 1.0%–1.3%, Co 1.0%–1.6%, Ni 1.0%–2.0%, Cu 1.0%–1.6%, P≤0.008%, S≤0.008%, with the balance being Fe and unavoidable impurities. The bolt surface, from the inside out, sequentially comprises an ultrasonic-assisted plasma carbonitriding layer and a graphene oxide / polytetrafluoroethylene composite sealing layer containing a bonding resin. This invention achieves high strength and high toughness of high wear-resistant bolts at ultra-low temperatures, while also solving the problems of seizing and corrosion during heavy-duty thread assembly.

Description

Technical Field

[0001] This invention relates to the field of bolt technology, specifically to a high wear-resistant bolt and its manufacturing method. Background Technology

[0002] Bolts are indispensable fasteners in high-end equipment (such as wind power, nuclear power, heavy machinery, mining and metallurgy), and their service environment often involves high stress loads, severe vibration and impact, as well as high-intensity abrasive wear and corrosive media. Therefore, modern industry places extremely stringent requirements on the strength, toughness, wear resistance, corrosion resistance, and self-lubricating properties of bolts.

[0003] Currently, the traditional method in the industry to improve the wear and corrosion resistance of bolts is to use medium-carbon low-alloy steel as the base material to ensure strength, followed by high-temperature carburizing / nitriding treatment on the surface to improve wear resistance, or applying anti-corrosion coatings (such as electroplating zinc, electroplating nickel, or Dacromet coating). However, existing technologies have the following obvious drawbacks in actual production and service assembly: First, conventional high-temperature carburizing (above 800℃) leads to coarse grains in the bolt matrix, severely reducing the low-temperature impact toughness of the core; the use of a single high-temperature quenching process in tempering heat treatment easily generates huge residual phase transformation stresses within the microstructure, causing high-strength bolts to easily fracture brittlely under low-temperature environments or severe impacts. Second, the traditional single Cr / Mo carbide has insufficient upper limit of hardness, and the strengthening layer is easily worn away under heavy-load friction; if the hardness is increased indiscriminately, the carburized layer will become brittle, directly resulting in brittle spalling under tightening torque. Third, to meet the requirements of long-term corrosion protection, the coating is usually thick and has a high coefficient of friction. This leads to difficulties in high-precision thread mating, and the threads are prone to intense friction and heat generation during high-torque tightening, causing adhesive wear (commonly known as thread seizing or sintering). Furthermore, conventional anti-corrosion coatings are easily worn away and peeled off after repeated disassembly and assembly, causing their anti-corrosion capabilities to fail instantly. Therefore, developing an alloy material and bolt manufacturing process that combines extremely high surface wear resistance, ultra-low temperature toughness, and self-lubricating anti-corrosion properties has become a pressing technical problem to be solved in the fastener industry.

[0004] Based on this, the present invention proposes a high wear-resistant bolt and its manufacturing method. Summary of the Invention

[0005] This invention proposes a high wear-resistant bolt and its manufacturing method, which solves the brittle fracture tendency of high-strength bolts under ultra-low temperature and severe impact environments, eliminates residual stress from traditional quenching, solves the problem of rapid wear and brittle spalling of traditional diffusion layers under heavy-load friction, and solves the problem of thread adhesion wear caused by thick anti-corrosion coatings, achieving a synergistic effect of self-lubrication and long-term anti-corrosion under high precision.

[0006] The technical solution of the present invention is as follows: In a first aspect, the present invention proposes a high wear-resistant bolt, wherein the bolt is composed of the following components by mass percentage: C 0.35%–0.42%, Si 1.2%–1.6%, Mn 0.4%–0.8%, Cr 2.0%–2.8%, B 0.002%–0.005%, Y 0.02%–0.06%, W 2.0%–3.0%, Ta 1.3%–2.2%, Zr 1.0%–1.3%, Co 1.0%–1.6%, Ni 1.0%–2.0%, Cu 1.0%–1.6%, P≤0.008%, S≤0.008%, with the balance being Fe and unavoidable impurities; the bolt surface has, from the inside out, an ultrasonic-assisted plasma carbonitriding layer and a graphene oxide / polytetrafluoroethylene composite sealing layer containing a bonding resin.

[0007] As a further technical solution, the bolt is composed of the following components by mass percentage: C 0.35%–0.42%, Si 1.2%–1.6%, Mn 0.4%–0.8%, Cr 2.0%–2.8%, B 0.002%–0.005%, Y 0.02%–0.06%, W 2.0%–3.0%, Ta 1.3%–2.2%, Zr 1.0%–1.3%, Co 1.0%–1.6%, Ni 1.0%–2.0%, Cu 1.0%–1.6%, P≤0.008%, S≤0.008%, with the balance being Fe and unavoidable impurities, and 4.5%≤W+Ta+Zr≤6.2%.

[0008] This invention strictly limits the content to 4.5% ≤ W + Ta + Zr ≤ 6.2%. W (tungsten), Ta (tantalum), and Zr (zirconium) have extremely strong affinity for carbon and nitrogen. During cryogenic treatment and tempering, these three elements can synergistically precipitate "W-Ta-Zr" composite carbides with a scale of 10~20 nm. Due to the multi-element solid solution effect, the microhardness of this composite carbide is much higher than that of traditional chromium carbide or molybdenum carbide. It not only provides strong precipitation reinforcement for the bolt matrix, but also acts as a hard microscopic anti-wear skeleton under extreme friction, resulting in a significant increase in the overall wear resistance of the bolt.

[0009] As a further technical solution, the bolt is composed of the following components by mass percentage: C 0.35%~0.42%, Si 1.2%~1.6%, Mn 0.4%~0.8%, Cr 2.0%~2.8%, B 0.002%~0.005%, Y 0.02%~0.06%, W 2.0%~3.0%, Ta 1.3%~2.2%, Zr 1.0%~1.3%, Co 1.0%~1.6%, Ni 1.0%~2.0%, Cu 1.0%~1.6%, P≤0.008%, S≤0.008%, with the balance being Fe and unavoidable impurities, and 3.0%≤Co+Ni+Cu≤4.5%.

[0010] This invention strictly limits the content of Co+Ni+Cu to 3.0%≤4.5%. Extremely high surface wear resistance is often accompanied by brittleness; if the matrix toughness is insufficient, the wear-resistant layer is prone to chipping. Co (cobalt) can prevent dislocation cross-slip; Ni (nickel) not only expands the austenite region but also maintains extremely high impact toughness of the matrix at low temperatures; Cu (copper) works synergistically with Ni to form dense, copper-rich anti-corrosion micro-regions at grain boundaries. Combined with isothermal quenching in a nitrate bath at 280℃~320℃ and cryogenic treatment with liquid nitrogen at -196℃, the matrix obtains a high-toughness, low-bainite and martensite multiphase structure without residual stress, giving the matrix soft buffering capacity and solving the problem of high hardness and brittle fracture. This increases the impact energy of bolts at -40℃ by more than 40%.

[0011] On the other hand, the present invention also provides a method for manufacturing a high wear-resistant bolt, the steps of which include: S1. After batching, the materials are melted to form molten steel, which is then made into steel ingots. The steel ingots are then hot-forged to obtain bolt blanks. S2. The bolt blank is machined to obtain a semi-finished bolt; S3. The semi-finished bolt is subjected to a toughening matrix heat treatment, the heat treatment including austenitizing treatment, isothermal quenching in nitrate bath, cryogenic treatment and low temperature tempering treatment in sequence, to obtain the heat-treated bolt; S4. After the heat-treated bolts are subjected to ultrasonic-assisted plasma carbonitriding treatment, they are immersed in a nanocomposite dispersion for vacuum negative pressure curing and sealing treatment to obtain high wear-resistant bolts.

[0012] As a further technical solution, in step S1, the heating temperature for hot forging is 1150-1200℃, and after forging, it is slowly cooled to room temperature at a cooling rate of less than 20℃ / h.

[0013] As a further technical solution, in step S3, the austenitizing treatment includes heating to 960-980℃ and holding for 40-60 minutes; the quenching temperature of the isothermal quenching treatment in the nitrate bath is 280-320℃ and holding for 1-2 hours.

[0014] As a further technical solution, in step S3, the cryogenic treatment is to place the sample in liquid nitrogen at -196℃ and keep it at that temperature for 12-24 hours; the low-temperature tempering treatment is to heat the sample to 200-250℃ and keep it at that temperature for 2-3 hours.

[0015] As a further technical solution, in step S4, the co-diffusion temperature of the ultrasonic-assisted plasma carbonitriding treatment is 460-490℃, a mixture of ammonia and propane is introduced, the infiltration time is 4-6h, and ultrasonic vibration with a frequency of 20-30kHz is applied to the bolts during the co-diffusion process, and the bolts are cooled with the furnace.

[0016] To avoid compromising the strength and toughness of the matrix, this invention significantly reduces the infiltration temperature to 460℃~490℃. Atomic diffusion is extremely slow at conventional low temperatures; therefore, this invention introduces ultrasonic vibrations of 20~30kHz during the infiltration process. The alternating stress and microscopic acoustic flow effect generated by the ultrasound in the metal lattice significantly reduce the diffusion activation energy of C and N atoms, not only increasing the infiltration rate by 40% but also eliminating microscopic pores within the infiltration layer, forming an extremely dense compound outer coating.

[0017] As a further technical solution, in step S4, the vacuum negative pressure curing and sealing process is as follows: the bolt after ultrasonic-assisted plasma carbonitriding treatment is immersed in a nanocomposite dispersion, and pressure is maintained for 15-30 minutes under a vacuum of -0.08MPa to -0.1MPa. After removal, it is cured into a film at 180-200℃.

[0018] This invention utilizes vacuum negative pressure to press graphene oxide, which provides two-dimensional mechanical support and a barrier layer, along with polytetrafluoroethylene (PTFE) to reduce friction and a bonding resin, into micropores and cure them into a film. This composite layer reduces the dry friction coefficient of threads to below 0.05, not only reducing the "seizing" phenomenon during high-torque assembly, but also maintaining the dual functions of solid lubrication and physical water-blocking and corrosion prevention even after multiple disassemblies and reassemblies, achieving a dual leap in high wear resistance and corrosion resistance.

[0019] As a further technical solution, in step S4, the nanocomposite dispersion is composed of 2%-3% graphene oxide, 8%-10% polytetrafluoroethylene, 15%-20% waterborne polyamide-imide resin, and the balance being deionized water, which are ultrasonically dispersed and mixed.

[0020] The working principle and beneficial effects of this invention are as follows: This invention achieves a synergistic effect of ultra-low temperature high strength and toughness of the substrate and low friction self-lubrication of the surface by optimizing the alloy element ratio and combining an ultrasonic-assisted plasma carbonitriding layer with a graphene oxide / polytetrafluoroethylene composite sealing layer containing a bonding resin. This improves the tensile strength and low temperature impact performance of the substrate and effectively solves the "seizing" problem during heavy-duty thread assembly.

[0021] This invention significantly improves the wear resistance and corrosion resistance of bolts by adding W, Ta, and Zr to form a dense carbonitriding layer and a composite sealing layer. It also enhances the surface microhardness, wear resistance, and neutral salt spray resistance of the material, achieving a dual breakthrough in long-term corrosion protection and high wear resistance. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] It should be noted that the graphene oxide (GO) used in this invention is SE1233 type single-layer graphene oxide powder produced by Changzhou Sixth Element Materials Technology Co., Ltd.; the polytetrafluoroethylene (PTFE) is TE-3893 type submicron-level aqueous dispersion produced by Shanghai Sanaifu New Materials Technology Co., Ltd.; and the aqueous polyamide-imide resin (PAI) is 4200 type aqueous polyamide-imide resin sold by Dongguan Juheng Plastic Raw Materials Co., Ltd.

[0024] Example 1 A high wear-resistant composite reinforced bolt, comprising the following components by mass percentage: C 0.38%, Si 1.40%, Mn 0.60%, Cr 2.40%, B 0.003%, Y 0.04%, W 2.50%, Ta 1.80%, Zr 1.10%, Co 1.20%, Ni 1.50%, Cu 1.10%, P 0.005%, S 0.004%, with the balance being Fe and other unavoidable impurities; The manufacturing method of high wear-resistant bolts includes the following steps: S1. Melting and Hot Forging: Weigh the raw materials according to the proportion, and use a dual process of vacuum induction melting and electroslag remelting to form molten steel and make steel ingots; heat the steel ingots to 1180℃ for multi-directional hot forging, and then slowly cool them to room temperature at a cooling rate of 15℃ / h to obtain bolt blanks; S2. Machining: Cold heading and thread rolling are performed on the bolt blank to obtain a semi-finished bolt; S3. Heat treatment to strengthen and toughen the matrix: The semi-finished bolt is heated to 970℃ and held for 50 min to austenitize; then it is quickly quenched in a nitrate bath at 300℃ and held for 1.5 h for isothermal quenching; after being removed, it is immediately placed in liquid nitrogen at -196℃ for cryogenic treatment for 18 h; after returning to room temperature, it is heated to 220℃ and held for 2.5 h for low-temperature tempering to obtain the heat-treated bolt; S4. Ultrasonic-assisted co-infiltration: The heat-treated bolts are placed in a plasma co-infiltration furnace, and a mixture of ammonia and propane is introduced at 475°C for 5 hours. During the co-infiltration process, ultrasonic vibration at a frequency of 25kHz is applied to the bolts. After cooling to room temperature with the furnace, the bolts that have undergone ultrasonic-assisted plasma carbonitriding are immersed in a nanocomposite dispersion composed of 2.5% GO (graphene oxide), 9% PTFE (polytetrafluoroethylene), 18% waterborne polyamide-imide resin and 70.5% deionized water. The dispersion is held under a vacuum of -0.09MPa for 20 minutes. After removal, the bolts are cured at 190°C to form a film, resulting in a high-wear-resistant composite reinforced bolt.

[0025] Example 2 A high wear-resistant composite reinforced bolt, comprising: C 0.35%, Si 1.20%, Mn 0.40%, Cr 2.00%, B 0.002%, Y 0.02%, W 2.00%, Ta 1.50%, Zr 1.00%, Co 1.00%, Ni 1.00%, Cu 1.00%, P 0.006%, S 0.005%, with the balance being Fe; The manufacturing method is the same as in Example 1, except that the parameters for step S3 are: austenitization at 960℃ for 40 min; isothermal quenching in a nitrate bath at 280℃ for 1 h; cryogenic treatment at -196℃ for 12 h; and tempering at 200℃ for 3 h. Step S4 involves an ultrasonic frequency of 20 kHz for 4 h, and the nanocomposite dispersion is composed of 2% GO, 10% PTFE, 15% waterborne polyamide-imide resin, and 73% water.

[0026] Example 3 A high wear-resistant composite reinforced bolt, comprising: C 0.42%, Si 1.60%, Mn 0.80%, Cr 2.80%, B 0.005%, Y 0.06%, W 3.00%, Ta 2.00%, Zr 1.20%, Co 1.50%, Ni 2.00%, Cu 1.00%, P 0.005%, S 0.004%, with the balance being Fe; The manufacturing method is the same as in Example 1, except that the parameters for step S3 are: austenitization at 980℃ for 60 min; isothermal quenching in a nitrate bath at 320℃ for 2 h; cryogenic treatment at -196℃ for 24 h; and tempering at 250℃ for 2 h. Step S4 uses an ultrasonic frequency of 30 kHz for 6 h, and the nanocomposite dispersion ratio is 3% GO, 8% PTFE, 20% waterborne polyamide-imide resin, and 69% water.

[0027] Example 4 The chemical composition of the bolt and steps S1, S2, and S3 in this embodiment are exactly the same as in Example 1. The difference is that in step S4, there is no "ultrasonic vibration" and conventional low-temperature plasma carbonitriding is performed only in a static state; the rest of the steps in S4 remain unchanged.

[0028] Example 5 The chemical composition of the bolt and steps S1, S2, and S4 in this embodiment are exactly the same as in Example 1. The difference is that in step S3, instead of "isothermal quenching in a salt bath and cryogenic treatment", conventional direct oil quenching is used: the semi-finished bolt is heated to 970°C and held for 50 minutes before being directly quenched in room temperature quenching oil, followed by low-temperature tempering at 220°C.

[0029] Example 6 The chemical composition of this embodiment is exactly the same as that of Example 1.

[0030] The difference lies in the fact that the manufacturing method does not involve S4 "ultrasonic-assisted infiltration" and "composite sealing". After the S3 substrate heat treatment is completed, only the bolt surface is treated with conventional blackening and anti-rust oil.

[0031] Comparative Example 1 This comparative example provides a high-strength bolt composed of the following components by mass percentage: W 1.5%, Ta 1.0%, Zr 0.8%, with the remaining components being exactly the same as in Example 1; the manufacturing method is also exactly the same as in Example 1.

[0032] Comparative Example 2 This comparative example provides a high-strength bolt composed of the following components by mass percentage: Co 0.5%, Ni 0.8%, Cu 0.5%, with the remaining components being exactly the same as in Example 1; the manufacturing method is also exactly the same as in Example 1.

[0033] Test Example 1: The bolts manufactured in Examples 1-6 and Comparative Examples 1-2 were subjected to the following tests: Mechanical properties: The room temperature tensile strength of the matrix was tested according to GB / T 228.1-2021; the Charpy impact absorption energy (AKv) at -40℃ was tested according to GB / T 229-2020 to evaluate the core toughness; the surface micro-Vickers hardness (HV0.1) was tested. Friction and wear performance: A reciprocating friction and wear tester was used to conduct 100,000 dry friction and wear tests under a load of 50N, and the dry thread friction coefficient and volume wear amount (mg) were recorded. Resistance to neutral salt spray: Refer to GB / T 10125-2021, conduct continuous neutral salt spray tests using 5% NaCl aqueous solution, and record the time when obvious red rust appears on the surface (maximum observation time 2500h).

[0034] The results are shown in Table 1 below: Table 1

[0035] As can be seen from the foregoing, the high wear-resistant composite reinforced bolts provided in Embodiments 1-3 of the present invention, through the optimized "W-Ta-Zr" and "Co-Ni-Cu" binary microalloy system and the sound field-assisted surface strengthening process, have successfully achieved ultra-high strength and toughness (tensile strength ≥1610MPa, impact energy ≥65J at -40℃), extremely low friction and wear, and excellent corrosion resistance.

[0036] Furthermore, the omission of ultrasonic vibration assistance in Example 4 resulted in insufficient diffusion motive force for C and N atoms at low temperatures, leading to a significant decrease in the density and hardness of the infiltrated layer (down to 950 HV) and an increase in wear to 5.2 mg. This strongly demonstrates the core function of ultrasonic cavitation and acoustic flow effects in improving the quality of the low-temperature co-infiltrated layer.

[0037] In Example 5, conventional direct oil quenching was used without isothermal quenching and cryogenic treatment. The impact energy in this example dropped significantly to 35 J, indicating that conventional oil quenching generated enormous residual stress within the material, failing to produce a lower bainitic matrix with excellent strength and toughness, leading to severe deterioration of the material's toughness. The "isothermal quenching + cryogenic treatment" method of this invention can eliminate residual stress and induce the precipitation of nanoscale carbides, achieving a perfect balance between extremely high surface hardness and excellent core toughness.

[0038] In Example 6, plasma co-infiltration and nano-sealing were omitted, and conventional rust-preventive oil was used for treatment. Its friction coefficient was as high as 0.28, resulting in extremely high wear, and the corrosion protection time was only 72 hours, which could not meet the requirements of modern harsh working conditions for bolt self-lubrication and long-term corrosion protection.

[0039] In Comparative Example 1, the total amount of (W+Ta+Zr) was insufficient, resulting in a lack of cryogenically precipitated composite superhard carbides. Consequently, the surface hardness dropped significantly to 820 HV, and the wear rate surged to 12.5 mg. This directly demonstrates that a sufficient combination of W, Ta, and Zr plays an irreplaceable role in constructing the surface and matrix micro-wear-resistant framework and ensuring the material reaches its ultimate wear resistance.

[0040] In Comparative Example 2, the total amount of (Co+Ni+Cu) was insufficient. Although its surface hardness and wear resistance were acceptable, its impact energy at -40℃ dropped sharply to 22J, exhibiting obvious low-temperature embrittlement, and its corrosion resistance also decreased significantly. This indicates that without the synergistic solid solution strengthening of Co, Ni, and Cu, the matrix lost its soft buffering capacity and could not support the extremely hard surface infiltrated layer, making it highly susceptible to brittle fracture and infiltrated layer peeling under impact.

[0041] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high wear-resistant bolt, characterized in that, The bolt is composed of the following components by mass percentage: C 0.35%–0.42%, Si 1.2%–1.6%, Mn 0.4%–0.8%, Cr 2.0%–2.8%, B 0.002%–0.005%, Y 0.02%–0.06%, W 2.0%–3.0%, Ta 1.3%–2.2%, Zr 1.0%–1.3%, Co 1.0%–1.6%, Ni 1.0%–2.0%, Cu 1.0%–1.6%, P≤0.008%, S≤0.008%, with the balance being Fe and unavoidable impurities. The bolt surface has, from the inside out, an ultrasonic-assisted plasma carbonitriding layer and a graphene oxide / polytetrafluoroethylene composite sealing layer containing bonding resin.

2. A high wear-resistant bolt according to claim 1, characterized in that, The bolt is composed of the following components by mass percentage: C 0.35%–0.42%, Si 1.2%–1.6%, Mn 0.4%–0.8%, Cr 2.0%–2.8%, B 0.002%–0.005%, Y 0.02%–0.06%, W 2.0%–3.0%, Ta 1.3%–2.2%, Zr 1.0%–1.3%, Co 1.0%–1.6%, Ni 1.0%–2.0%, Cu 1.0%–1.6%, P≤0.008%, S≤0.008%, with the balance being Fe and unavoidable impurities, and 4.5%≤W+Ta+Zr≤6.2%.

3. A high wear-resistant bolt according to claim 1, characterized in that, The bolt is composed of the following components by mass percentage: C 0.35%–0.42%, Si 1.2%–1.6%, Mn 0.4%–0.8%, Cr 2.0%–2.8%, B 0.002%–0.005%, Y 0.02%–0.06%, W 2.0%–3.0%, Ta 1.3%–2.2%, Zr 1.0%–1.3%, Co 1.0%–1.6%, Ni 1.0%–2.0%, Cu 1.0%–1.6%, P≤0.008%, S≤0.008%, with the balance being Fe and unavoidable impurities, and 3.0%≤Co+Ni+Cu≤4.5%.

4. A method for manufacturing a high wear-resistant bolt as described in any one of claims 1-3, characterized in that the step include: S1. After batching, the materials are melted to form molten steel, the molten steel is made into steel ingots, and then the steel ingots are hot-forged to obtain bolt blanks; S2. The bolt blank is machined to obtain a semi-finished bolt; S3. The semi-finished bolt is subjected to a toughening matrix heat treatment, the heat treatment including austenitizing treatment, isothermal quenching in nitrate bath, cryogenic treatment and low temperature tempering treatment in sequence, to obtain the heat-treated bolt; S4. After the heat-treated bolts are subjected to ultrasonic-assisted plasma carbonitriding treatment, they are immersed in a nanocomposite dispersion for vacuum negative pressure curing and sealing treatment to obtain high wear-resistant bolts.

5. The method for manufacturing high wear-resistant bolts according to claim 4, characterized in that, In step S1, the heating temperature for hot forging is 1150-1200℃, and after forging, it is slowly cooled to room temperature at a cooling rate of less than 20℃ / h.

6. The method for manufacturing high wear-resistant bolts according to claim 4, characterized in that, In step S3, the austenitizing treatment includes heating to 960-980℃ and holding for 40-60 minutes; the quenching temperature of the isothermal quenching treatment in the nitrate bath is 280-320℃ and the holding time is 1-2 hours.

7. The method for manufacturing high wear-resistant bolts according to claim 4, characterized in that, In step S3, the cryogenic treatment involves placing the sample in liquid nitrogen at -196°C and holding it for 12-24 hours; the low-temperature tempering treatment involves heating the sample to 200-250°C and holding it for 2-3 hours.

8. The method for manufacturing high wear-resistant bolts according to claim 4, characterized in that, In step S4, the co-diffusion temperature of the ultrasonic-assisted plasma carbonitriding treatment is 460-490℃, a mixture of ammonia and propane is introduced, the infiltration time is 4-6 hours, ultrasonic vibration with a frequency of 20-30kHz is applied to the bolts during the co-diffusion process, and the bolts are cooled with the furnace.

9. The method for manufacturing high wear-resistant bolts according to claim 4, characterized in that, In step S4, the vacuum negative pressure curing and sealing process is as follows: the bolts after ultrasonic-assisted plasma carbonitriding treatment are immersed in a nanocomposite dispersion, and pressure is maintained at a vacuum of -0.08MPa to -0.1MPa for 15-30 minutes. After removal, the bolts are cured into a film at 180-200℃.

10. The method for manufacturing high wear-resistant bolts according to claim 4, characterized in that, In step S4, the nanocomposite dispersion is composed of 2%-3% graphene oxide, 8%-10% polytetrafluoroethylene, 15%-20% waterborne polyamide-imide resin, and the balance being deionized water, which are ultrasonically dispersed and mixed by mass percentage.

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