Nickel-free, unannealed, high-strength, weather-resistant steel wire for bolts, bolts, and methods for manufacturing steel wire.

Abstract

In this invention, a nickel-free, unannealed, high-strength, weather-resistant steel wire rod for bolts is disclosed. This steel wire rod contains Fe and unavoidable impurity elements, and further contains the following chemical elements in mass percent: C: 0.05-0.14%, Si: 0.01-2.0%, Mn: 0.3-2.2%, Cr: 2.4-4.5%, Cu: 0.2-0.6%, and Al: 0.01-0.10%, where the mass percent content of Cr and C satisfies Cr / C > 20; and this steel wire rod does not contain Ni. Accordingly, in this invention, a method for manufacturing the nickel-free, unannealed, high-strength, weather-resistant steel wire rod for bolts is disclosed. The manufacturing method specifically includes the following steps: (1) smelting and casting; (2) heating; (3) rolling; and (4) cooling, including the following: after rolling, the material is cooled to 900 to 920°C at a cooling rate of 4 to 5°C / s, and then continuously cooled to room temperature at a cooling rate lower than 0.4°C / s to obtain steel wire.

Description

[Technical Field]

[0001] Technical field This disclosure relates to wires, bolts, and methods for manufacturing the same, and more particularly to high-strength and weather-resistant wires, bolts, and methods for manufacturing the same for use with bolts. [Background technology]

[0002] Background technology Weathering steel refers to low-alloy, high-strength steel that exhibits good corrosion resistance in the atmosphere by adding small amounts of alloying elements. When elements such as phosphorus, copper, and chromium are added to steel, an amorphous spinel-type oxide layer approximately 50-100 μm thick is formed between the rust layer and the substrate. This oxide layer is dense and adheres well to the substrate metal, preventing the penetration of oxygen and moisture from the atmosphere into the steel substrate, thereby slowing the progression of rust in the steel material and enhancing its atmospheric corrosion resistance. The atmospheric corrosion resistance of weathering steel is 2 to 8 times that of ordinary carbon steel, and its corrosion resistance becomes more pronounced as the period of use increases. In addition to its excellent weathering resistance, weathering steel also has excellent mechanical properties and weldability.

[0003] As critical connecting components, bolt corrosion poses a significant risk to structural safety. To delay and control bolt corrosion, prevent deterioration and degradation of bolt materials, and ensure the reliability, safety, and service life of bolts, surface corrosion protection treatments are typically applied to bolts to enhance their corrosion resistance. Surface corrosion protection treatments involve providing a protective layer to the metal surface, thereby isolating the metal from the corrosive environment and preventing or inhibiting the corrosion process.

[0004] Currently, high-strength bolts are the primary connecting components used in steel structures such as buildings, bridges, and power transmission towers. These bolts are generally treated with coating methods such as hot-dip galvanizing, electroplating, or mechanical plating to achieve corrosion protection. However, high-strength bolts experience considerable initial load torque and substantial friction between the threads. The coating itself cannot withstand such high friction, and the coating is often damaged during the initial loading process of the bolt, leading to a reduction in coating thickness. In severe cases, the base material of the bolt may even be exposed to the environment during use, thereby compromising its corrosion resistance.

[0005] The use of surface coating methods requires maintenance of the anticorrosion coating every 3-5 years, and complete reapplication every 10-15 years. This coating maintenance not only increases costs but also causes health hazards and environmental pollution during the coating process. Furthermore, some coating processes may introduce a hydrogen source into the bolt, which increases the susceptibility of high-strength bolts to hydrogen embrittlement, thereby causing a series of safety risks such as delayed fracture. Therefore, the development of high-strength weather-resistant bolt steel that does not require coating is extremely important. [Overview of the project] [Means for solving the problem]

[0006] Summary of the Invention One of the objectives of this disclosure is to provide nickel-free, anneal-free, high-strength, and weather-resistant wire for bolts, thereby achieving improved weather resistance without the addition of Ni, and its atmospheric corrosion resistance meeting the requirements for applications where coating is not required.

[0007] To achieve the above objective, this disclosure provides a wire containing, in addition to Fe and unavoidable impurities, the following chemical elements in mass percentage: C: 0.05-0.14%, Si: 0.01-2.0%, preferably Si: 0.2-1.6%, Mn: 0.3-2.2%, preferably Mn: 0.5-1.7%, Cr: 2.4-4.5%, Cu: 0.2-0.6%, Al: 0.01-0.1%; Here, the mass percentage content of Cr and C satisfies Cr / C > 20; and The wire material does not contain nickel.

[0008] In response to this, the present disclosure further provides a wire containing the following chemical elements in mass percentage: C: 0.05~0.14%, Si: 0.01~2.0%, preferably Si: 0.2~1.6%, Mn: 0.3~2.2%, preferably Mn: 0.5~1.7%, Cr: 2.4~4.5%, Cu: 0.2~0.6%, Al: 0.01~0.1%, the remainder being Fe and other unavoidable impurities; and The mass percentage content of Cr and C satisfies the condition Cr / C > 20.

[0009] In the wire materials described herein, the design principles for each chemical element are as follows: Carbon (C) is an important element that forms finely dispersed carbides after subsequent quenching and tempering treatments, and plays a decisive role in improving the strength of bolts. However, it should be noted that the carbon content in steel should not be too high. If the carbon content in steel is too high, it will negatively affect the atmospheric corrosion resistance of the material on the one hand, and on the other hand, it will increase the strength of the hot-rolled wire rod (making it impossible to satisfy the requirement of no annealing). Therefore, in order to ensure that the material of this disclosure achieves good atmospheric corrosion resistance and adequate strength, the carbon content in steel must be controlled within a reasonable range. In this disclosure, the mass percentage content of carbon is controlled in particular to 0.05-0.14%.

[0010] Si: The element Si has high solid solubility in steel. The addition of an appropriate amount of Si to steel can effectively increase the volume fraction of ferrite in the steel, refine the grain size, and therefore improve the toughness of the steel. Accordingly, in order to fully utilize the beneficial effects of Si, the mass percentage content of Si in the nickel-free, unannealed, high-strength, and weather-resistant wire rod for bolts according to this disclosure is controlled to 0.01 to 2.0%, preferably 0.2 to 1.6%.

[0011] Mn: The element Mn has a strong solid solution strengthening effect and is also an important strengthening and toughening element. The addition of an appropriate amount of Mn to steel can significantly lower the phase transition temperature of the steel and refine the microstructure of the steel. Based on this, and considering the beneficial effects of the element Mn, the mass percentage content of the element Mn in the nickel-free, unannealed, high-strength, and weather-resistant wire rod for bolts according to this disclosure is controlled to 0.3 to 2.2%, preferably 0.5 to 1.7%.

[0012] The presence of Cr significantly accelerates the progression of electrochemical corrosion products to a thermodynamically stable state. In rust layer analysis, the element Cr is (Fe X H Y O Z This significantly accelerates the transformation process of ) → γ-FeOOH → α-FeOOH → α-Fe2O3, promoting the formation of spinel compounds. At the same time, the Cr element in the steel partially substitutes for Fe, forming chromium iron hydroxide Cr X Fe 1-X OOH can be formed, thereby imparting cation selectivity to the α-FeOOH rust layer, and Cl - and SO4 2- This prevents the rust from penetrating the substrate surface (which provides a protective function to the rust layer). Therefore, in order to fully utilize the beneficial effects of the Cr element and ensure a significant improvement in the atmospheric corrosion resistance of the steel, the mass percentage content of the Cr element in the nickel-free, unannealed, high-strength, and weather-resistant wire rods for bolts according to this disclosure is controlled to 2.4-4.5%.

[0013] Naturally, the Cr element inevitably combines with the C element to form the precipitated Cr phase.23 It should be noted that C6 is formed, which does not contribute to the weather resistance of the steel. Therefore, in this disclosure, in order to ensure that there is enough Cr element in the steel to improve weather resistance, it is also necessary to control the mass percentage content of individual chemical elements, as well as to further control the content of Cr and C elements in the steel to satisfy Cr / C > 20.

[0014] Cu: Among alloying elements, Cu has the most significant effect on the weather resistance of the material. The addition of an appropriate amount of Cu to steel can effectively delay the anode dissolution of Fe or reduce the electronic conductivity of the rust layer, thereby slowing the rate at which electrons flow to the cathode region. At the same time, Cu in steel can also complex, producing small amounts of insoluble copper hydroxide sulfate such as Cu4(SO4)(OH) and Cu4(SO4)(OH)4. These compounds can precipitate in the pores of the rust layer and enhance the barrier effect of the corrosion product film. However, it should be noted that the Cu content in steel should not be too high, as excess Cu can cause high-temperature brittleness of steel and increase the difficulty of manufacturing. Therefore, in order to fully utilize the beneficial effects of Cu, the mass percentage content of Cu is controlled to 0.2-0.6% in the nickel-free, unannealed, high-strength, and weather-resistant wire rods for bolts according to this disclosure.

[0015] Al:Al is added to steel as a deoxidizing agent and plays a role in removing oxygen. In this disclosure, controlling the mass percentage of element Al to 0.01-0.1% is beneficial for refining the grain size and improving the strength-toughness properties of the steel.

[0016] Preferably, among the unavoidable impurities of the nickel-free, unannealed, high-strength, and weather-resistant wire for bolts according to this disclosure, P ≤ 0.012% and S ≤ 0.005%.

[0017] In the nickel-free, non-annealed, high-strength and weather-resistant wire rod for bolts according to the present disclosure, both P element and S element are impurity elements in steel. Under technically feasible conditions, the content of impurity elements in steel should be minimized as much as possible in order to obtain steel with better performance and higher quality.

[0018] S, P: In the present disclosure, the presence of impurity element S deteriorates the atmospheric corrosion resistance of steel and causes high-temperature brittleness of steel. P can improve the atmospheric corrosion resistance of steel, but when the content of P element in steel is too high, the toughness and plasticity of steel will be significantly reduced, and cold brittleness will also be caused. Therefore, the content of P element and S element in steel should be minimized as much as possible. The present disclosure can adopt extremely low contents of S and P in the design, and control the mass percentage of P element to P≦0.012% and the mass percentage of S element to S≦0.005%.

[0019] Preferably, the nickel-free, non-annealed, high-strength and weather-resistant wire rod for bolts according to the present disclosure has a fine structure of ferrite + pearlite.

[0020] Preferably, the nickel-free, non-annealed, high-strength and weather-resistant wire rod for bolts according to the present disclosure has a weather resistance index I≧8.5, where I = 26.01×Cu +3.88×Ni + 1.20×Cr + 1.49×Si + 17.28×P - 7.29×Cu×Ni - 9.10×Ni×P - 33.39×Cu 2 where each chemical element symbol is replaced by the numerical value before the % symbol of the corresponding element's mass percentage content. For the nickel-free steel according to the present disclosure, the Ni element in the formula is replaced by 0.

[0021] It should be noted that for steel materials, the higher the I value, the better the atmospheric corrosion resistance. Generally, a weather resistance index I>6 indicates that the material has excellent atmospheric corrosion resistance performance.

[0022] Preferably, the nickel-free, non-annealed, high-strength and weather-resistant wire for bolts according to the present disclosure has a yield strength ≤ 400 MPa, a tensile strength ≤ 600 MPa, an elongation ≥ 25% and a cross-sectional reduction rate ≥ 60%.

[0023] Furthermore, another object of the present disclosure is to disclose a bolt manufactured from the nickel-free, non-annealed, high-strength and weather-resistant wire for bolts as described above. The bolt manufactured from the nickel-free, non-annealed, high-strength and weather-resistant wire for bolts not only exhibits mechanical properties of grade 8.8 to 10.9, but also has excellent atmospheric corrosion resistance. This bolt can be applied in a non-coated manner in bridge structures, transmission towers, solar power supports and other fields, and has good application prospects.

[0024] To achieve the above object, the present disclosure provides a bolt manufactured from the nickel-free, non-annealed, high-strength and weather-resistant wire for bolts. This bolt has a yield strength ≥ 720 MPa, preferably ≥ 820 MPa, a tensile strength ≥ 870 MPa, an elongation ≥ 16% and a cross-sectional reduction rate ≥ 55%. [[ID=Y]]

[0025] [[ID=Y]] The present disclosure further relates to a method for manufacturing the above bolt, where the method includes subjecting the wire according to any one of claims 1 to 6 to quenching and tempering treatments.

[0026] Preferably, the quenching and tempering treatments include: quenching at a temperature of 850 to 880 °C for 80 minutes, followed by oil quenching; and tempering at a temperature of 420 to 600 °C for 1 hour, followed by air cooling.

[0027] In the aforementioned technical solutions of the present disclosure, based on the nickel-free, unannealed, high-strength, and weather-resistant wire for bolts according to the present disclosure, downstream users may, when specifically manufacturing bolts, further perform pickling, phosphate treatment and saponification, drawing, cold heading, quenching and tempering, thread rolling and other processes on the nickel-free, unannealed, high-strength, and weather-resistant wire for bolts, thereby processing the wire into high-strength and weather-resistant bolts.

[0028] In response to this, a further object of this disclosure is to provide a method for manufacturing nickel-free, anneal-free, high-strength, and weather-resistant wire for bolts as described above. This manufacturing method suppresses the formation of a copper-enriched phase by integrating compositional design and control process parameters in the heating process. Furthermore, by controlling the cooling process, the yield strength and tensile strength of the hot-rolled wire are reduced, workability is improved, and thereby a hot-rolled wire that meets the requirements is produced.

[0029] To achieve the above objectives, this disclosure provides a method for manufacturing nickel-free, anneal-free, high-strength, and weather-resistant wire for the above-mentioned bolts, comprising the following steps: (1) Smelting and casting to obtain cast slabs; (2) Heat the cast slab; (3) The heated cast slab is rolled; (4) Cooling: After rolling, the material is cooled to 900-920°C at a cooling rate of 4-5°C / s, and then cooled to room temperature at a cooling rate of less than 0.4°C / s to obtain the wire.

[0030] Preferably, in the manufacturing method according to the present disclosure, in step (2), the heating temperature is controlled to 1050 to 1100°C, and the residence time in the furnace is controlled to be ≤ 120 minutes, preferably 95 to 110 minutes.

[0031] Preferably, in the manufacturing method according to this disclosure, annealing is not performed after the cooling step.

[0032] In the manufacturing method designed by this disclosure, molten steel is obtained by smelting according to the chemical composition designed by this disclosure, followed by deoxidation of the molten steel, and then casting under protective conditions to obtain an ingot or slab.

[0033] In response to this, the resulting steel ingot or slab requires further processing steps of heating, rolling, and cooling. It should be noted that the temperature of the steel slab before rolling should be strictly controlled to avoid the precipitation of the copper-enriched phase due to excessive heating. Therefore, this process can be specifically controlled as follows: Before rolling, the heating temperature of the steel slab should be controlled to 1050-1100°C, and the residence time in the furnace should be controlled to ≤120 minutes, preferably 95-110 minutes.

[0034] During the cooling process, the temperature of the hot-rolled wire must be strictly controlled to avoid excessively rapid cooling below 900°C, which could cause excessive strength in the hot-rolled wire. Thus, after rolling, the wire is cooled to 900-920°C at a cooling rate of 4-5°C / s, and then further cooled to room temperature at a cooling rate of less than 0.4°C / s, thereby obtaining nickel-free, anneal-free, high-strength, and weather-resistant wire for bolts of the present disclosure.

[0035] The nickel-free, unannealed, high-strength, and weather-resistant wire rods, bolts, and methods for manufacturing the same bolts, as disclosed herein, offer the following advantages and beneficial effects: The nickel-free, unannealed, high-strength, and weather-resistant wire for bolts described herein achieves high strength and high weather resistance through rational composition adjustment and process design. The atmospheric corrosion resistance of the wire (weather resistance index I ≥ 8.5) can satisfy the requirements for uncoated applications. The nickel-free, unannealed, high-strength, and weather-resistant wire for bolts has a yield strength ≤ 400 MPa, a tensile strength ≤ 600 MPa, an elongation ≥ 25%, and a cross-sectional reduction ≥ 60%.

[0036] The nickel-free, unannealed, high-strength, and weather-resistant bolts manufactured according to this disclosure can achieve a yield strength of ≥720 MPa, preferably ≥820 MPa, a tensile strength of ≥870 MPa, an elongation of ≥16%, and a cross-sectional reduction of ≥55%. These bolts not only exhibit high strength but also possess excellent atmospheric corrosion resistance. These bolts can be applied in an uncoated manner to bridge structures, power transmission towers, solar power support structures, and other fields.

[0037] Detailed explanation The nickel-free, unannealed, high-strength, and weather-resistant wires, bolts, and methods for manufacturing them described herein are further described and explained below with reference to specific examples. However, this description and explanation should not be construed as unduly limiting the technical solutions of this disclosure.

[0038] Examples 1-6 Table 1-1 shows the mass percentage content of chemical elements in nickel-free, unannealed, high-strength, and weather-resistant wire rods for bolts in Examples 1-6.

[0039] [Table 1-1]

[0040] Table 1-2 shows the relationship between the content of certain chemical elements in nickel-free, unannealed, high-strength, and weather-resistant wires for bolts in Examples 1-6.

[0041] [Table 1-2]

[0042] Note: In Table 1-2 above, Cr and C in the formula "Cr / C" are substituted with the mass percentage content of the corresponding chemical element; also, I = 26.01×Cu + 3.88×Ni + 1.20×Cr + 1.49×Si + 17.28×P - 7.29×Cu×Ni - 9.10×Ni×P - 33.39×Cu2 In this formula, each chemical element symbol is replaced by the number preceding the % symbol representing the mass percentage content of the corresponding element.

[0043] In this disclosure, the nickel-free, unannealed, high-strength, and weather-resistant wires for bolts in Examples 1 to 6 were all manufactured by employing the following specific process: (1) Smelting and casting are carried out according to the chemical compositions shown in Tables 1-1 and 1-2: Smelting is carried out according to the designed composition, and after deoxidation of the molten steel, the molten steel is cast under protective conditions to obtain a 142 mm × 142 mm slab. (2) Heating: The obtained 142 mm × 142 mm slab was transferred to a heating furnace, the heating temperature was controlled to 1050-1100°C, and the residence time in the furnace was controlled to within 120 minutes. (3) Roll. (4) Cooling: After rolling, the rolled product was cooled to 900-920°C at a cooling rate of 4-5°C / s, and then cooled to room temperature at a cooling rate of less than 0.4°C / s to obtain nickel-free, unannealed, high-strength, and weather-resistant wire for bolts with a diameter of 10-26 mm.

[0044] In this disclosure, steels for six furnaces were smelted and manufactured according to the chemical compositions designed in Tables 1-1 and 1-2, corresponding to Examples 1-6. The chemical elemental compositions and associated process designs of the nickel-free, unannealed, high-strength, and weather-resistant wire rods for bolts in Examples 1-6 all met the requirements of the design specifications of this disclosure.

[0045] Table 2 lists the specific process parameters in the aforementioned process steps for nickel-free, unannealed, high-strength, and weather-resistant wires for bolts in Examples 1-6.

[0046] [Table 2]

[0047] Samples were taken from the tip of the finished nickel-free, unannealed, high-strength, and weather-resistant wire for bolts in Examples 1 to 6, and observed using a scanning electron microscope (SEM). The inventors observed that the microstructure of the nickel-free, unannealed, high-strength, and weather-resistant wire for bolts in Examples 1 to 6 was ferrite + pearlite.

[0048] In response to this, following the observations and analyses described above, further samples were taken of the finished nickel-free, unannealed, high-strength, and weather-resistant wires for bolts in Examples 1-6, and relevant mechanical property tests were performed on the wire samples from each example. The results of the mechanical property tests are shown in Table 3.

[0049] The relevant mechanical properties testing methods are as follows: Tensile tests: Under room temperature conditions, yield strength, tensile strength, elongation, and reduction in section were measured for nickel-free, unannealed, high-strength, and weather-resistant wires for bolts in Examples 1-6, according to the standard GB / T 228-2002 "Metallic materials - Tensile tests at room temperature".

[0050] Table 3 shows the results of mechanical property tests for the finished nickel-free, unannealed, high-strength, and weather-resistant wires used for bolts in Examples 1 to 6.

[0051] [Table 3]

[0052] As can be seen from Table 3 and in combination with Tables 1-2, the nickel-free, unannealed, high-strength, and weather-resistant wires for bolts in Examples 1-6 of this disclosure not only exhibited excellent corrosion resistance (all with a weathering index I greater than 8.5), but also showed yield strengths of less than 400 MPa and tensile strengths of less than 600 MPa, all of which satisfied the strength requirements for unannealed applications; at the same time, the elongation was greater than 25% and the reduction in cross-sectional area was greater than 60%. The atmospheric corrosion resistance of the nickel-free, unannealed, high-strength, and weather-resistant wires for bolts in Examples 1-6 can meet the requirements for uncoated applications.

[0053] To further demonstrate that the unannealed high-strength weather-resistant wire for bolts according to this disclosure can be further processed into bolts having superior performance, the unannealed high-strength weather-resistant wire for bolts in Examples 1 to 6 of this disclosure can be further subjected to pickling, phosphate treatment and saponification, drawing, cold heading, quenching and tempering, and thread rolling processes to produce high-strength weather-resistant bolts having superior performance.

[0054] It should be noted that in some embodiments of this disclosure, the specific quenching and tempering heat treatment processes employed were as follows: quenching at a temperature of 850–880°C for 80 minutes, followed by oil quenching; and tempering at a temperature of 420–600°C for 1 hour, followed by air cooling.

[0055] Therefore, the inventors conducted mechanical property tests on each of the high-strength weather-resistant bolts manufactured in Examples 1 to 6. The results of the mechanical property tests are shown in Table 4 below. The tensile test method employed by the inventors during the mechanical property tests of the high-strength weather-resistant bolts manufactured in Examples 1 to 6 was the same as the method described above for Table 3, and will not be repeated here.

[0056] Table 4 shows the mechanical properties of the high-strength weather-resistant bolts manufactured in Examples 1 to 6.

[0057] [Table 4]

[0058] As can be seen from Table 4 above, the yield strength R of the bolts manufactured in Examples 1 to 6 p0.2 The tensile strength was greater than 720 MPa, the elongation was greater than 870 MPa, the cross-sectional reduction was ≥16%, and the cross-sectional reduction was ≥55%. These bolts have excellent mechanical properties, and their strength reaches grade 8.8 to 10.9, and therefore can be applied in an uncoated form to bridge structures, power transmission towers, solar power support structures, and other fields.

[0059] It should be noted that the combinations of technical features described herein are not limited to those described in the claims or in any particular embodiment. All technical features described herein may be freely combined or associated in any way, provided that they do not conflict with each other.

[0060] Furthermore, it should be noted that the embodiments listed above are merely specific embodiments of the present disclosure. Clearly, the present disclosure is not limited to the above embodiments. Similar variations or modifications that a person skilled in the art can directly derive or readily conceive of based on the content disclosed herein are included within the scope of protection of the present disclosure.

Claims

1. In addition to Fe and unavoidable impurities, the following chemical elements are present in mass percentage in the wire: C: 0.05–0.14%, Si: 0.01–2.0%, preferably Si: 0.2–1.6%, Mn: 0.3–2.2%, preferably Mn: 0.5–1.7%, Cr: 2.4–4.5%, Cu: 0.2–0.6%, Al: 0.01–0.1%; Here, the mass percentage content of Cr and C satisfies Cr / C > 20; and The wire material does not contain nickel.

2. It contains the following chemical elements in mass percentage: C: 0.05–0.14%, Si: 0.01–2.0%, preferably Si: 0.2–1.6%, Mn: 0.3–2.2%, preferably Mn: 0.5–1.7%, Cr: 2.4–4.5%, Cu: 0.2–0.6%, Al: 0.01–0.1%, the remainder being Fe and other unavoidable impurities; and The wire according to claim 1, wherein the mass percentage content of Cr and C satisfies Cr / C > 20.

3. The wire according to claim 1 or 2, wherein among the unavoidable impurities, P ≤ 0.012% and S ≤ 0.005%.

4. The wire according to claim 1 or 2, wherein the wire has a ferrite + pearlite microstructure.

5. The wire material has a weather resistance index I ≥ 8.5, where I = 26.01 × Cu + 3.88 × Ni + 1.20 × Cr + 1.49 × Si + 17.28 × P - 7.29 × Cu × Ni - 9.10 × Ni × P - 33.39 × Cu 2 The wire according to claim 1 or 2, wherein each chemical element symbol is replaced by the number preceding the % symbol of the mass percentage content of the corresponding element.

6. The wire rod according to claim 1 or 2, having a yield strength of ≤400 MPa, a tensile strength of ≤600 MPa, an elongation of ≥25%, and a reduction in cross-sectional area of ​​≥60%.

7. A bolt manufactured from a wire rod according to any one of claims 1 to 6, having a yield strength of ≥720 MPa, preferably ≥820 MPa, a tensile strength of ≥870 MPa, an elongation of ≥16%, and a reduction in cross-sectional area of ​​≥55%.

8. A method for manufacturing a bolt according to claim 7, comprising subjecting a wire rod according to any one of claims 1 to 6 to a quenching and tempering treatment, and preferably comprising: quenching at a temperature of 850 to 880°C for 80 minutes, followed by oil quenching; and tempering at a temperature of 420 to 600°C for 1 hour, followed by air cooling.

9. A method for manufacturing a wire according to any one of claims 1 to 6, comprising the following steps: (1) Smelting and casting to obtain cast slabs; (2) Heat the cast slab; (3) Roll the heated cast slab; (4) Cooling: After rolling, the material is cooled to 900-920°C at a cooling rate of 4-5°C / s, and then cooled to room temperature at a cooling rate of less than 0.4°C / s to obtain the wire.

10. The manufacturing method according to claim 9, wherein in step (2), the heating temperature is controlled to 1050 to 1100°C, and the residence time in the furnace is controlled to within 120 minutes, preferably 95 to 110 minutes.

11. The manufacturing method according to claim 9 or 10, wherein annealing is not performed after the cooling step.

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