High-strength bolt and preparation method thereof

Abstract

The invention relates to the field of alloy steel, and provides a high-strength bolt and a preparation method thereof. The bolt is composed of the following components in percentage by mass: 0.28%-0.35% of C, 0.3%-0.35% of Si, 0.5%-0.6% of Mn, 1.2%-1.5% of Cr, 0.18%-0.22% of W, 0.1%-0.3% of Co, 0.2%-0.3% of Mo, 0.03%-0.05% of Nb, 0.02%-0.05% of Ti, 0.015%-0.03% of Al, 0.008%-0.015% of N, 0.18%-0.22% of V, 0.05%-0.12% of Ce, 0.03%-0.08% of Y, 0.03%-0.06% of Re, 0.002%-0.005% of B and the balance of Fe and other inevitable impurities. The strength of the bolt is improved, and the high-temperature stability and corrosion resistance of the bolt are further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of alloy steel, and specifically, to a high-strength bolt and a preparation method thereof. Background Art

[0002] High-strength bolts are widely used in key fields such as aerospace, rail transit, heavy machinery, and bridge construction. In the aerospace field, aircraft will bear huge loads and complex stress environments during high-speed flight, and high-strength bolts are required to ensure reliable connections between components and guarantee flight safety; in the rail transit field, the vibrations and impacts generated by trains during high-speed operation pose extremely high requirements for the performance of bolts; in heavy machinery and bridge construction, bolts need to bear heavy loads and harsh environmental conditions for a long time, and their performance is directly related to the safety and stability of the entire structure.

[0003] Currently, the mainstream preparation process of high-strength bolts uses medium-carbon alloy steels (such as 42CrMo, SCM435) as the main raw materials. These medium-carbon alloy steels have certain strength and toughness, but in order to meet the performance requirements of high-strength bolts, it is also necessary to add elements such as Cr, Ni, and Mo to improve hardenability. The improvement of hardenability can enable the steel to obtain a more uniform microstructure during the heat treatment process, thereby improving the overall performance of the bolt.

[0004] The selection of existing components and the preparation process have certain limitations in improving the performance of high-strength bolts. Although the performance of bolts can be improved to a certain extent by adding alloy elements and heat treatment processes, with the continuous improvement of the performance requirements of bolts in engineering applications, the existing processes are difficult to meet the needs of higher strength, longer fatigue life, and better corrosion resistance. For example, in some extreme environments, such as deep sea, high temperature, etc., the existing high-strength bolts may experience performance degradation or even failure. Based on this, the present invention proposes a high-strength bolt and a preparation method thereof. Summary of the Invention

[0005] The present invention proposes a high-strength bolt and a preparation method thereof, which not only improve the strength of the bolt, but also further improve the high-temperature stability and corrosion resistance of the bolt.

[0006] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a high-strength bolt, which is composed of components in the following mass percentages: C 0.28% - 0.35%, Si 0.3% - 0.35%, Mn 0.5% - 0.6%, Cr 1.2% - 1.5%, W 0.18% - 0.22%, Co 0.1% - 0.3%, Mo 0.2% - 0.3%, Nb 0.03% - 0.05%, Ti 0.02% - 0.05%, Al 0.015% - 0.03%, N 0.008% - 0.015%, V 0.18% - 0.22%, Ce 0.05% - 0.12%, Y 0.03% - 0.08%, Re 0.03% - 0.06%, B 0.002% - 0.005%, with the balance being Fe and other inevitable impurities.

[0007] As a further technical solution, the bolt is composed of components in the following mass percentages: C 0.28% - 0.35%, Si 0.3% - 0.35%, Mn 0.5% - 0.6%, Cr 1.2% - 1.5%, W 0.18% - 0.22%, Co 0.1% - 0.3%, Mo 0.2% - 0.3%, Nb 0.03% - 0.05%, Ti 0.02% - 0.05%, Al 0.015% - 0.03%, N 0.008% - 0.015%, V 0.18% - 0.22%, Ce 0.05% - 0.12%, Y 0.03% - 0.08%, Re 0.03% - 0.06%, B 0.002% - 0.005%, with the balance being Fe and other inevitable impurities, and the weight ratio of (Mo + W) / (Cr + V) is 0.22 - 0.38.

[0008] As a further technical solution, the bolt is composed of components in the following mass percentages: C 0.28% - 0.35%, Si 0.3% - 0.35%, Mn 0.5% - 0.6%, Cr 1.2% - 1.5%, W 0.18% - 0.22%, Co 0.1% - 0.3%, Mo 0.2% - 0.3%, Nb 0.03% - 0.05%, Ti 0.02% - 0.05%, Al 0.015% - 0.03%, N 0.008% - 0.015%, V 0.18% - 0.22%, Ce 0.05% - 0.12%, Y 0.03% - 0.08%, Re 0.03% - 0.06%, B 0.002% - 0.005%, with the balance being Fe and other inevitable impurities, and the weight ratio of B / (Ti + Al) is 0.025 - 0.143.

[0009] As a further technical solution, the bolt is composed of the following components by mass percentage: C 0.28% - 0.35%, Si 0.3% - 0.35%, Mn 0.5% - 0.6%, Cr 1.2% - 1.5%, W 0.18% - 0.22%, Co 0.1% - 0.3%, Mo 0.2% - 0.3%, Nb 0.03% - 0.05%, Ti 0.02% - 0.05%, Al 0.015% - 0.03%, N 0.008% - 0.015%, V 0.18% - 0.22%, Ce 0.05% - 0.12%, Y 0.03% - 0.08%, Re 0.03% - 0.06%, B 0.002% - 0.005%, the balance being Fe and other inevitable impurities, and the total amount of V + Ce + Y + Re being 0.35% - 0.44%.

[0010] As a further technical solution, a NiZr alloy layer with a thickness of 0.2 - 0.4 μm and a diamond - like carbon film with a thickness of 0.1 - 0.2 μm are sequentially deposited on the surface of the bolt.

[0011] As a further technical solution, the Zr content in the NiZr alloy layer is 15% - 20%.

[0012] In a second aspect, the present invention provides a method for preparing a high - strength bolt, and the steps include: S1. Melting and casting: Weigh the raw materials according to the ratio, melt them in a vacuum induction furnace, control the oxygen content ≤ 20 ppm, and pour them into a billet after refining; S2. Two - stage solution treatment: Under the protection of argon gas, heat up to 1150 - 1250 °C at a rate of 80 - 100 °C / h and hold for 1 - 1.5 h, then quickly cool to 900 - 940 °C under the condition of a vacuum degree ≤ 1×10 -3 Pa, and then heat up to 980 - 1020 °C at a rate of 50 - 60 °C / h and hold for 2 - 3 h, and then process and form to obtain the bolt; S3. Cryogenic treatment: Immerse it in liquid nitrogen at - 190 - 200 °C for 1.5 - 2.5 h, and then temper at 150 - 160 °C for 3 - 4 h; S4. Surface treatment: The high - strength bolt is obtained by sequentially depositing a NiZr alloy layer and a diamond - like carbon film using high - power pulsed magnetron sputtering.

[0013] As a further technical solution, the melting conditions in the vacuum induction furnace include: the melting pressure is 4×10 -3 ~6×10 -3 Pa, and the melting temperature is 1580 - 1640 °C; the refining is carried out under argon gas for 30 - 40 min.

[0014] As a further technical solution, the rapid cooling is carried out by helium gas jet quenching, and the cooling rate is ≥200°C / s.

[0015] As a further technical solution, the deposition parameters include: the pulse frequency is 500~800Hz, the peak current density is 0.8~1.2A / cm², the substrate bias voltage is -150~-300V, the deposition temperature is 200~300°C, and the vacuum degree is 0.3~0.6Pa.

[0016] The working principle and beneficial effects of the present invention are as follows: The high-strength bolt proposed by the present invention adopts a multi-element alloying design. By precisely controlling the mass percentages of elements such as C, Si, Mn, Cr, W, Co, Mo, Nb, Ti, Al, N, V, Ce, Y, Re, and B, the high strength and high toughness of the bolt matrix material are achieved. The multi-element alloying design improves the strength and toughness of the bolt through mechanisms such as solid solution strengthening, second-phase strengthening, and grain boundary strengthening of alloying elements. The control of specific element ratios optimizes the distribution and morphology of carbides, as well as the structure and properties of grain boundaries, thereby further improving the high-temperature strength and corrosion resistance of the bolt.

[0017] In the present invention, the weight ratio of (Mo + W) / (Cr + V) is 0.22~0.38. The control of this ratio helps to optimize the distribution of carbides and improve the high-temperature strength and corrosion resistance of the bolt. Mo and W, as carbide-forming elements, can form fine and uniformly distributed carbides with an appropriate ratio of Cr and V, thereby enhancing the strength of the matrix.

[0018] In the present invention, the design with the weight ratio of B / (Ti + Al) being 0.04~0.12 balances the grain boundary strengthening and the risk of embrittlement. The B element helps with grain boundary strengthening, but excessive amounts can cause grain boundary embrittlement, while the Ti and Al elements help to purify the grain boundaries. By controlling the ratio of B / (Ti + Al), grain boundary embrittlement can be avoided while ensuring grain boundary strength.

[0019] In the present invention, the total amount of V + Ce + Y + Re is designed to be 0.35%~0.44%. The grain refinement and passivation film formation effects of rare earth elements are utilized to improve the corrosion resistance and mechanical properties of the bolt. The effects of rare earth elements in steel are complex and diverse, and appropriate addition can significantly improve the properties of steel.

[0020] The present invention adopts a two-stage solution treatment process. First, it is heated from 80~100°C / h to 1150~1250°C under Ar gas protection and held for 1~1.5h, and then under a vacuum degree ≤1×10 -3Under the condition of Pa, it is quickly cooled to 900 - 940 °C, and then heated to 980 - 1020 °C at a rate of 50 - 60 °C / h and held for 2 - 3 h. This two-stage solution treatment optimizes the microstructure of the matrix through the process of dissolving and reprecipitating carbides. The cryogenic treatment further refines the grains and reduces the residual stress by utilizing the phase transformation and atomic diffusion characteristics at low temperatures. The surface treatment forms a composite structure with excellent properties by depositing a double-layer coating, significantly improving the wear resistance and corrosion resistance of the bolt.

[0021] In the present invention, after soaking in liquid nitrogen at -190 ~ -200 °C for 1.5 - 2.5 h, it is tempered at 150 - 160 °C for 3 - 4 h. The cryogenic treatment can further refine the grains, improve the hardness and wear resistance of the bolt, reduce the residual stress at the same time, and improve the dimensional stability of the bolt.

[0022] The present invention adopts high-power pulsed magnetron sputtering technology to deposit NiZr alloy layer and diamond-like carbon film (DLC) in sequence. The NiZr alloy layer, as a ductile substrate, can provide good adhesion and buffering effect; the DLC film has extremely high hardness and density, which can effectively isolate the corrosive medium and improve the corrosion resistance of the bolt. This double-layer coating design significantly improves the comprehensive performance of the bolt through the synergistic mechanism of "ductile substrate + dense protection".

[0023] Specific Embodiments The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0024] Embodiment 1 In this embodiment, a high-strength bolt is provided. The bolt is composed of the following components by mass percentage: C 0.32%, Si 0.32%, Mn 0.55%, Cr 1.35%, W 0.20%, Co 0.2%, Mo 0.25%, Nb 0.04%, Ti 0.035%, Al 0.022%, N 0.011%, V 0.20%, Ce 0.08%, Y 0.05%, Re 0.045%, B 0.0035%, and the balance is Fe and other inevitable impurities; Among them, (Mo + W) / (Cr + V) = (0.25% + 0.20%) / (1.35% + 0.20%) = 0.29; B / (Ti + Al) = 0.0035% / (0.035% + 0.022%) = 0.061; V + Ce + Y + Re = 0.20% + 0.08% + 0.05% + 0.045% = 0.375%; The preparation method of this bolt includes the following steps: S1. Melting and casting: Weigh the raw materials according to the ratio, melt them in a vacuum induction furnace, control the oxygen content to be 15 ppm, and pour them into a billet after refining; The melting conditions in the vacuum induction furnace include: the melting pressure is 5×10 -3 Pa, and the melting temperature is 1600 °C; The refining is carried out under argon conditions for 35 minutes; S2. Two-stage solution treatment: Under the protection of Ar gas, heat up to 1180 °C at a rate of 90 °C / h and hold for 1.2 h. Under the condition of a vacuum degree of 1×10 -3 Pa, use helium gas spray quenching for rapid cooling, with a cooling rate of 220 °C / s. After cooling to 920 °C, heat up to 1000 °C at a rate of 55 °C / h and hold for 2.5 h, and then process and form to obtain the bolt; S3. Cryogenic treatment: Immerse it in liquid nitrogen at -195 °C for 2 h, and then temper at 155 °C for 3 h to obtain the high-strength bolt.

[0025] Example 2 In this example, a high-strength bolt is provided. The bolt is composed of the following components by mass percentage: C 0.35%, Si 0.35%, Mn 0.6%, Cr 1.2%, W 0.22%, Co 0.1%, Mo 0.3%, Nb 0.03%, Ti 0.02%, Al 0.015, N 0.008, V 0.18%, Ce 0.12%, Y 0.08%, Re 0.06%, B 0.005%, and the balance is Fe and other inevitable impurities; Among them, (Mo + W) / (Cr + V) = (0.30% + 0.22%) / (1.2% + 0.18%) = 0.38; B / (Ti + Al) = 0.005% / (0.02% + 0.015%) = 0.143; V + Ce + Y + Re = 0.18% + 0.12% + 0.08% + 0.06% = 0.44%; The preparation method of this bolt includes the following steps: S1. Melting and casting: Weigh the raw materials according to the ratio, melt them in a vacuum induction furnace, control the oxygen content ≤ 20 ppm, and pour them into a billet after refining; The melting conditions in the vacuum induction furnace include: the melting pressure is 6×10 -3 Pa, and the melting temperature is 1640 °C; The refining is carried out under argon conditions for 40 minutes; S2. Two-stage solution treatment: Under the protection of Ar gas, heat up to 1250°C at a rate of 100°C / h and hold for 1.5 h. Under the condition of a vacuum degree of 0.5×10 -3 Pa, carry out rapid cooling by helium gas spraying quenching, with a cooling rate of 250°C / s. After cooling to 940°C, heat up to 1020°C at a rate of 60°C / h and hold for 3 h, then process and form to obtain bolts; S3. Cryogenic treatment: Immerse in liquid nitrogen at -200°C for 2.5 h, and then temper at 160°C for 4 h to obtain high-strength bolts.

[0026] Example 3 In this example, a high-strength bolt is provided. The bolt is composed of the following components by mass percentage: C 0.28%, Si 0.35%, Mn 0.5%, Cr 1.5%, W 0.18%, Co 0.3%, Mo 0.2%, Nb 0.03%, Ti 0.05%, Al 0.03%, N 0.015%, V 0.22%, Ce 0.05%, Y 0.03%, Re 0.03%, B 0.002%, and the balance is Fe and other inevitable impurities; Among them, (Mo + W) / (Cr + V) = (0.20% + 0.18%) / (1.5% + 0.22%) = 0.22; B / (Ti + Al) = 0.002% / (0.05% + 0.03%) = 0.025; V + Ce + Y + Re = 0.22% + 0.05% + 0.03% + 0.03% = 0.33%; The preparation method of this kind of bolt includes the following steps: S1. Melting and casting: Weigh raw materials according to the ratio, melt in a vacuum induction furnace, control the oxygen content to be 10 ppm, and pour into a billet after refining; The melting conditions in the vacuum induction furnace include: the melting pressure is 4×10 -3 Pa, and the melting temperature is 1580°C; The refining is carried out under argon gas conditions for 30 min; S2. Two-stage solution treatment: Under the protection of Ar gas, heat up to 1150°C at a rate of 80°C / h and hold for 1 h. Under the condition of a vacuum degree of 0.8×10 -3 Pa, carry out rapid cooling by helium gas spraying quenching, with a cooling rate of 210°C / s. After cooling to 900°C, heat up to 980°C at a rate of 50°C / h and hold for 2 h, then process and form to obtain bolts; S3. Cryogenic treatment: Immerse in liquid nitrogen at -190°C for 1.5 h, and then temper at 150°C for 3 h to obtain high-strength bolts.

[0027] Example 4 In this embodiment, a high-strength bolt is provided. The bolt is composed of components with the following mass percentages: C 0.32%, Si 0.32%, Mn 0.55%, Cr 1.35%, W 0.20%, Co 0.2%, Mo 0.25%, Nb 0.04%, Ti 0.035%, Al 0.022%, N 0.011%, V 0.20%, Ce 0.08%, Y 0.05%, Re 0.045%, B 0.0035%, and the balance is Fe and other inevitable impurities; Among them, (Mo + W) / (Cr + V) = (0.25 + 0.20) / (1.35 + 0.20) = 0.29; B / (Ti + Al) = 0.0035 / (0.035 + 0.022) = 0.061; V + Ce + Y + Re = 0.20% + 0.08% + 0.05% + 0.045% = 0.375%; In this embodiment, a NiZr alloy layer with a thickness of 0.3 μm and a diamond-like carbon film with a thickness of 0.15 μm are sequentially deposited on the surface of the bolt, and the Zr content in the NiZr alloy layer is 17%; The preparation method of this bolt includes the following steps: S1. Melting and casting: Weigh the raw materials according to the ratio, melt them in a vacuum induction furnace, control the oxygen content to be 15 ppm, and pour them into a billet after refining; the melting conditions in the vacuum induction furnace include: the melting pressure is 5×10 -3 Pa, and the melting temperature is 1600 °C; the refining is carried out under argon gas conditions for 35 min; S2. Two-stage solution treatment: Under the protection of Ar gas, heat it to 1180 °C at a rate of 90 °C / h and hold for 1.2 h, and carry out rapid cooling by helium gas spray quenching under the condition of a vacuum degree of 1×10 -3 Pa, with a cooling rate of 220 °C / s. After cooling to 920 °C, heat it to 1000 °C at a rate of 55 °C / h and hold for 2.5 h, and then process it into shape to obtain the bolt; S3. Cryogenic treatment: Immerse it in liquid nitrogen at -195 °C for 2 h, and then temper it at 155 °C for 3 - 4 h to obtain the high-strength bolt substrate; S4. Surface treatment: Ultrasonically clean the high-strength bolt substrate with acetone and ethanol for 15 min respectively, dry it and then load it into the coating equipment; carry out glow cleaning for 15 min under the conditions of an argon gas flow rate of 130 sccm, a gas pressure of 0.5 Pa, a bias voltage of -800 V, and an anode layer ion source of 180 W; sequentially deposit the NiZr alloy layer and the diamond-like carbon film by high-power pulsed magnetron sputtering to obtain the high-strength bolt; The NiZr alloy layer target is a NiZr alloy target, and the deposition parameters include: the pulse frequency is 600 Hz, the peak current density is 1.2 A / cm², and the substrate bias voltage is -200 V; the deposition temperature is 300 °C, and the vacuum degree is 0.6 Pa; The diamond-like carbon film target is a high-purity graphite target (99.99%), and the deposition parameters include: the pulse frequency is 500 Hz, the peak current density is 0.8 A / cm², and the substrate bias voltage is -150 V; the deposition temperature is 200 °C, and the vacuum degree is 0.3 Pa.

[0028] Example 5 In Example 5, B is 0.005%, Ti is 0.02%, Al is 0.015%, B / (Ti + Al) = 0.143, and the rest is the same as in Example 1. The preparation steps are the same as in Example 1.

[0029] Example 6 In Example 6, V is 0.2%, Ce is 0.12%, Y is 0.08%, Re is 0.06%, V + Ce + Y + Re = 0.46%, and the rest is the same as in Example 1. The preparation steps are the same as in Example 1.

[0030] Example 7 In Example 7, Cr is 1.5%, V is 0.22%, Mo is 0.18%, W is 0.18%, (Mo + W) / (Cr + V) = 0.20, and the rest is the same as in Example 1. The preparation steps are the same as in Example 1.

[0031] Example 8 In Example 8, the Zr content in the NiZr alloy layer is 25%.

[0032] Example 9 In Example 9, only the DLC film is deposited, without the NiZr layer, and the rest is the same as in Example 1.

[0033] Example 10 In Example 10, only the NiZr layer is deposited, without the DLC film, and the rest is the same as in Example 1.

[0034] Comparative Example 1 In Comparative Example 1, the content of Ti is 0%, and the rest is the same as in Example 1.

[0035] Comparative Example 2 In Comparative Example 2, the content of Al is 0%, and the rest is the same as in Example 1.

[0036] Test Example 1: The bolts prepared in the foregoing Examples 1-10 and Comparative Examples 1-2 were tested as follows: Mechanical properties: Refer to GB / T 228.1-2021 "Tensile test for metallic materials - Part 1: Test method at room temperature" to test the tensile strength and yield strength of bolts at room temperature; refer to GB / T 228.2-2015 "Tensile test for metallic materials - Part 2: Test method at high temperature" to test the tensile strength of bolts at different temperatures; Neutral salt spray resistance: Use a 5% mass concentration of NaCl aqueous solution to continuously spray the bolts and record the initial rust time of the bolts; The results are shown in Table 1 below: Table 1

[0037] Combined with the above content, it can be seen that Examples 1-3 improve the substrate performance by optimizing the composition. The coatings in Examples 4-7 not only enhance the wear resistance through the synergistic effect of the tough substrate of NiZr and the dense protection of the DLC film, but also greatly improve the corrosion resistance by physically isolating the corrosive medium; Among them, Example 4 achieves a comprehensive improvement in room temperature tensile strength and salt spray resistance time through the double-layer coating design of NiZr alloy layer (0.3μm) and diamond-like carbon film (0.15μm); The tensile strength of Example 4 at 300°C (1557 MPa) is significantly higher than that of Example 1 (1253 MPa), verifying that the coating can still effectively inhibit oxidation and grain boundary weakening at high temperatures. However, the substrate materials of Examples 1-3 have a slightly faster strength decay at high temperatures due to the aggravated carbide coarsening trend. In Example 5, the B / (Ti+Al) ratio is unbalanced, and the tensile strength and salt spray resistance time are reduced, indicating that excessive B will weaken the grain boundary purification effect of Ti / Al, resulting in grain boundary embrittlement and increased corrosion sensitivity. In Example 6, when V+Ce+Y+Re=0.46%, the total amount of rare earths is too high, and the strength and salt spray resistance time are lower than those in Example 4, indicating that excessive rare earths may cause inclusion aggregation, offsetting the positive effects of grain refinement and passivation film formation. In Example 7, when (Mo+W) / (Cr+V)=0.20, the tensile strength and salt spray resistance time are significantly reduced, confirming that the low Mo / W ratio cannot optimize the carbide distribution, resulting in a decrease in high temperature strength and corrosion resistance. After removing Ti or Al from Comparative Examples 1-2, the yield strength and salt spray resistance time are greatly reduced, indicating that Ti / Al is the core element of matrix stability by purifying grain boundaries and inhibiting high temperature oxidation. In Example 8, when Zr=25% in the NiZr layer, the salt spray resistance time is lower than that in Example 4, because excessive Zr causes the coating toughness to decrease and the interface bonding force to weaken. When only the DLC film or the NiZr layer is used in Examples 9-10, the salt spray resistance time is significantly inferior to that of the double-layer coating, which proves that the toughness buffer of NiZr and the dense protection of DLC are indispensable.

[0038] The above are only the 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 shall be included within the protection scope of the present invention.

Claims

1. A high-strength bolt, characterized in that: The bolt is composed of the following components in mass percentage: C 0.28%~0.35%, Si 0.3%~0.35%, Mn 0.5%~0.6%, Cr 1.2%~1.5%, W 0.18%~0.22%, Co 0.1%~0.3%, Mo 0.2%~0.3%, Nb 0.03%~0.05%, Ti 0.02%~0.05%, Al 0.015%~0.03%, N 0.008%~0.015%, V 0.18%~0.22%, Ce 0.05%~0.12%, Y 0.03%~0.08%, Re 0.03%~0.06%, B 0.002%~0.005%, and the balance is Fe and other inevitable impurities.

2. A high-strength bolt according to claim 1, characterized in that: The bolt is composed of the following components in mass percentage: C 0.28%~0.35%, Si 0.3%~0.35%, Mn 0.5%~0.6%, Cr 1.2%~1.5%, W 0.18%~0.22%, Co0.1%~0.3%, Mo 0.2%~0.3%, Nb 0.03%~0.05%, Ti 0.02%~0.05%, Al 0.015%~0.03%, N0.008%~0.015%, V 0.18%~0.22%, Ce 0.05%~0.12%, Y 0.03%~0.08%, Re 0.03%~0.06%, B0.002%~0.005%, the balance is Fe and other inevitable impurities, and the weight ratio of (Mo+W) / (Cr+V) is 0.22~0.

38.

3. A high-strength bolt according to claim 2, characterized in that: The bolt is composed of the following components in mass percentage: C 0.28%~0.35%, Si 0.3%~0.35%, Mn 0.5%~0.6%, Cr 1.2%~1.5%, W 0.18%~0.22%, Co0.1%~0.3%, Mo 0.2%~0.3%, Nb 0.03%~0.05%, Ti 0.02%~0.05%, Al 0.015%~0.03%, N0.008%~0.015%, V 0.18%~0.22%, Ce 0.05%~0.12%, Y 0.03%~0.08%, Re 0.03%~0.06%, B0.002%~0.005%, the balance is Fe and other inevitable impurities, and the B / (Ti+Al) weight ratio is 0.025~0.

143.

4. A high strength bolt according to claim 3, characterized in that: The bolt is composed of the following components in mass percentage: C 0.28%~0.35%, Si 0.3%~0.35%, Mn 0.5%~0.6%, Cr 1.2%~1.5%, W 0.18%~0.22%, Co0.1%~0.3%, Mo 0.2%~0.3%, Nb 0.03%~0.05%, Ti 0.02%~0.05%, Al 0.015%~0.03%, N0.008%~0.015%, V 0.18%~0.22%, Ce 0.05%~0.12%, Y 0.03%~0.08%, Re 0.03%~0.06%, B0.002%~0.005%, the balance is Fe and other inevitable impurities, and the total amount of V+Ce+Y+Re is 0.35%~0.44%.

5. A high strength bolt according to claim 3, characterized in that: A NiZr alloy layer with a thickness of 0.2-0.4 μm and a diamond-like carbon film with a thickness of 0.1-0.2 μm are sequentially deposited on the surface of the bolt.

6. A high strength bolt according to claim 5, characterized in that: The Zr content in the NiZr alloy layer is 15% to 20%.

7. A method for preparing a high-strength bolt according to any one of claims 1 to 6, characterized in that the steps include: S1. Melting and casting: weigh the raw materials according to the proportion, melt them in a vacuum induction furnace, control the oxygen content to ≤20ppm, and cast them into billets after refining; S2, two-stage solution treatment: under argon protection conditions, heat up to 1150~1250℃ at 80~100℃ / h and keep for 1~1.5h. -3 After rapidly cooling to 900-940°C under Pa conditions, the temperature is raised to 980-1020°C at 50-60°C / h and maintained for 2-3h, and then processed and formed to obtain a bolt; S3. Cryogenic treatment: Soak in liquid nitrogen at -190~-200℃ for 1.5~2.5h, then temper at 150~160℃ for 3~4h; S4. Surface treatment: The high-strength bolt is obtained by sequentially depositing a NiZr alloy layer and a diamond-like carbon film using high-power pulsed magnetron sputtering.

8. The method for preparing a high-strength bolt according to claim 7, characterized in that: The smelting conditions in the vacuum induction furnace include: a smelting pressure of 4×10 -3 ~6×10 -3 Pa, the melting temperature is 1580~1640℃; the refining is carried out under argon gas conditions for 30~40min.

9. The method for preparing a high-strength bolt according to claim 7, characterized in that: The rapid cooling adopts helium spray quenching, and the cooling rate is ≥200°C / s.

10. The method for preparing a high-strength bolt according to claim 7, characterized in that: The deposition parameters include: pulse frequency of 500~800Hz, peak current density of 0.8~1.2A / cm², substrate bias of -150~-300V, deposition temperature of 200~300℃, and vacuum degree of 0.3~0.6Pa.

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