Wire rod for nickel-free annealing-free high-strength weather-resistant bolt, bolt and manufacturing method thereof

Abstract

The invention discloses a nickel-free annealing-free high-strength weather-resistant wire rod for a bolt, which contains Fe and inevitable impurity elements, and further contains the following chemical elements in percentage by mass: 0.05 to 0.14 percent of C, 0.01 to 2.0 percent of Si, 0.3 to 2.2 percent of Mn, 2.4 to 4.5 percent of Cr, 0.2 to 0.6 percent of Cu, 0.01 to 0.1 percent of Al, and the balance of Fe and inevitable impurity elements. The mass percentage content of Cr and C meets the condition that Cr / C is greater than 20; and does not contain Ni. Correspondingly, the invention further discloses a manufacturing method of the steel wire rod for the nickel-free annealing-free high-strength weather-resistant bolt, and the manufacturing method specifically comprises the following steps: (1) smelting and casting; (2) heating; (3) rolling; and (4) cooling: after rolling, cooling to 900-920 DEG C at the cooling speed of 4-5 DEG C / s, and then continuously cooling to room temperature at the cooling speed of less than 0.4 DEG C / s.

Description

Technical Field

[0001] The invention relates to a wire rod, a bolt and a manufacturing method thereof, and in particular to a wire rod for high-strength weather-resistant bolts, a bolt and a manufacturing method thereof. Background Art

[0002] Weathering steel refers to low-alloy high-strength steel that has good corrosion resistance in the atmosphere by adding a small amount of alloying elements. When phosphorus, copper, chromium and other elements are added to the steel, an amorphous spinel oxide layer of about 50μm to 100μm thick will be formed between the rust layer and the matrix. The oxide layer is dense and has good adhesion to the matrix metal, which prevents oxygen and water in the atmosphere from penetrating into the steel matrix, slows down the development of rust into the depth of the steel material, and improves the atmospheric corrosion resistance of the steel material. The atmospheric corrosion resistance of weathering steel is 2 to 8 times that of ordinary carbon steel, and the longer the service time, the more prominent the corrosion resistance. In addition to good weather resistance, weathering steel also has excellent mechanical, welding and other performance properties.

[0003] Bolts are important connectors, and their corrosion will cause serious damage to the safety of the structure. In order to delay and control the corrosion of bolts, prevent the degradation and deterioration of bolt materials, and ensure the reliability, safety and service life of bolts, bolts are usually subjected to surface anti-corrosion treatment to improve their corrosion resistance. Surface anti-corrosion treatment refers to applying a protective layer on the metal surface to isolate the metal from the corrosive environment to prevent or inhibit the occurrence of the corrosion process.

[0004] At present, high-strength bolts are mainly used for connecting steel structures such as buildings, bridges, and transmission towers. These bolts are generally coated with methods such as hot-dip galvanizing, electroplating, and mechanical plating to achieve the purpose of corrosion protection. However, the pre-tightening torque of high-strength bolts is large, and the friction between the threads is large. The coating itself cannot withstand the large friction. During the pre-tightening process of the bolts, the coating is often damaged, resulting in the thinning of the coating. In severe cases, the base material of the bolt is even exposed in the service environment, reducing the corrosion resistance of the bolt.

[0005] Using the surface coating method, the anti-corrosion coating needs to be maintained every 3 to 5 years, and the anti-corrosion coating needs to be reapplied every 10 to 15 years. The coating maintenance not only increases the cost, but also causes health hazards and environmental pollution during the coating process. In addition, some coating processes will introduce hydrogen sources into the bolts. For high-strength bolts, it will increase the hydrogen embrittlement sensitivity of the parts, thereby inducing a series of safety hazards such as delayed fracture. Therefore, it is of great significance to develop high-strength weather-resistant bolt steel without coating. Summary of the invention

[0006] One of the purposes of the present invention is to provide a nickel-free annealing-free high-strength weather-resistant bolt wire rod, which can obtain strong weather resistance without adding Ni elements, and the atmospheric corrosion resistance can meet the requirements of no coating or plating.

[0007] In order to achieve the above object, the present invention provides a nickel-free annealing-free high-strength weather-resistant bolt wire rod, which contains Fe and inevitable impurities, and further contains the following chemical elements in the following mass percentages:

[0008] 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%, Al: 0.01-0.1%;

[0009] And the mass percentage of Cr and C satisfies: Cr / C>20;

[0010] The nickel-free annealing-free high-strength weather-resistant bolt wire rod does not contain Ni.

[0011] Correspondingly, the present invention also provides a nickel-free annealing-free high-strength weather-resistant bolt wire rod, the mass percentage of each chemical element of which is:

[0012] 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%, Al: 0.01-0.1%, the balance is Fe and other inevitable impurities;

[0013] And the mass percentage of Cr and C satisfies: Cr / C>20.

[0014] In the nickel-free annealing-free high-strength weather-resistant bolt wire rod of the present invention, the design principles of each chemical element are specifically described as follows:

[0015] C: In the nickel-free annealing-free high-strength weather-resistant bolt wire rod described in the present invention, C is an important element that forms fine dispersed carbides after subsequent quenching and tempering treatment, and it plays a vital role in improving the strength of the bolts. However, it should be noted that the C content in the steel should not be too high. When the C content in the steel is too high, on the one hand, it will affect the atmospheric corrosion resistance of the material, and on the other hand, it will increase the strength of the hot-rolled wire rod, and it will not be able to meet the strength requirements of annealing-free. Therefore, in order to ensure that the material of the present invention obtains good atmospheric corrosion resistance and suitable strength, it is necessary to control the C element in the steel within a reasonable range. In the present invention, the mass percentage of the C element is specifically controlled between 0.05-0.14%.

[0016] Si: In the nickel-free annealing-free high-strength weather-resistant bolt wire rod of the present invention, Si element has a high solid solubility in steel. Adding an appropriate amount of Si element to the steel can effectively increase the volume fraction of ferrite in the steel and refine the grains, thereby helping to improve the toughness of the steel. Therefore, in order to give full play to the beneficial effects of Si element, in the nickel-free annealing-free high-strength weather-resistant bolt wire rod of the present invention, the mass percentage of Si element is controlled between 0.01-2.0%.

[0017] Mn: In the nickel-free annealing-free high-strength weather-resistant bolt wire rod described in the present invention, the Mn element has a strong solid solution strengthening effect, and it is also an important toughening element. Adding an appropriate amount of Mn element to the steel can significantly reduce the phase transition temperature of the steel and refine the microstructure of the steel. Based on this, considering the beneficial effects of the Mn element, in the nickel-free annealing-free high-strength weather-resistant bolt wire rod described in the present invention, the mass percentage of the Mn element is controlled between 0.3-2.2%.

[0018] Cr: In the nickel-free annealing-free high-strength weather-resistant bolt wire rod of the present invention, the presence of Cr element will significantly accelerate the development of electrochemical corrosion products to a thermodynamically stable state. In the rust layer analysis, Cr element can significantly accelerate (Fe X H Y O Z )→γ-FeOOH→α-FeOOH→α-Fe2O3, promoting the formation of spinel compounds. At the same time, the Cr element in the steel can partially replace Fe to form chromium iron hydroxide Cr X Fe 1-X OOH, thus making the α-FeOOH rust layer cation-selective and preventing Cl - 、SO4 2- Therefore, in order to bring into play the beneficial effect of Cr element and ensure the significant improvement of the atmospheric corrosion resistance of steel, the mass percentage of Cr element in the nickel-free annealing-free high-strength weather-resistant bolt wire rod of the present invention is controlled between 2.4-4.5%.

[0019] Of course, it should be noted that the Cr element will inevitably combine with the C element to form the precipitated phase Cr 23 C6, precipitated phase Cr 23 C6 cannot improve the weather resistance of steel. Therefore, in the present invention, while controlling the mass percentage of a single chemical element, it is also necessary to further control the content of Cr and C elements in the steel to satisfy: Cr / C>20, so as to ensure that there is enough Cr element in the steel to improve the weather resistance.

[0020] Cu: In the nickel-free annealing-free high-strength weather-resistant bolt wire rod described in the present invention, among all the alloying elements, the Cu element has the most significant effect on the weather resistance of the material. Adding an appropriate amount of Cu element to the steel can effectively delay the anodic dissolution of Fe or reduce the electronic conductivity of the rust layer, thereby reducing the rate at which electrons flow to the cathode area. At the same time, the Cu element in the steel can also cooperate and form a small amount 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 improve the barrier effect of the corrosion product film. However, it should be noted that the Cu content in the steel should not be too high. Too much Cu will cause hot brittleness of the steel and increase the difficulty of production. Therefore, in order to give full play to the beneficial effects of the Cu element, in the nickel-free annealing-free high-strength weather-resistant bolt wire rod described in the present invention, the mass percentage of the Cu element is controlled between 0.2-0.6%.

[0021] Al: In the nickel-free annealing-free high-strength weather-resistant bolt wire rod of the present invention, Al is a deoxidizer added to the steel, which can play a role in deoxidation. In the present invention, the mass percentage of the Al element is controlled between 0.01-0.1%, which is conducive to grain refinement and improvement of the strength and toughness of the steel.

[0022] Furthermore, among the inevitable impurities of the nickel-free annealing-free high-strength weather-resistant bolt wire rod of the present invention, P≤0.012%, and S≤0.005%.

[0023] In the nickel-free annealing-free high-strength weather-resistant bolt wire rod described in the present invention, the P element and the S element are both impurity elements in the steel. If technical conditions permit, in order to obtain steel with better performance and higher quality, the content of impurity elements in the steel should be reduced as much as possible.

[0024] S, P: In the present invention, the presence of impurity element S will deteriorate the atmospheric corrosion resistance of steel and cause hot brittleness of steel; while P can improve the atmospheric corrosion resistance of steel, when the content of P in steel is too high, it will significantly reduce the toughness and plasticity of steel and cause cold brittleness. Therefore, the content of P and S elements in steel should be reduced as much as possible. The present invention adopts extremely low S and P contents in design, and can control the mass percentage of P element to P≤0.012%, and the mass percentage of S element to S≤0.005%.

[0025] Furthermore, in the nickel-free annealing-free high-strength weather-resistant bolt wire rod described in the present invention, its microstructure is ferrite+pearlite.

[0026] Furthermore, in the nickel-free annealing-free high-strength weather-resistant bolt wire rod of the present invention, the weather resistance index I≥8.5, wherein 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 ; Each chemical element in the formula is substituted into the value before the mass percentage sign. For the nickel-free steel of the present invention, the Ni element in the formula is substituted into 0.

[0027] It should be noted that, for steel, the larger the I value, the higher the atmospheric corrosion resistance of the steel. Generally speaking, a material with a weather resistance index I>6 means that it has very good atmospheric corrosion resistance.

[0028] Furthermore, the nickel-free annealing-free high-strength weather-resistant bolt wire rod described in the present invention has a yield strength of ≤400MPa, a tensile strength of ≤600MPa, an elongation of ≥25%, and a cross-sectional shrinkage of ≥60%.

[0029] In addition, another object of the present invention is to disclose a bolt prepared from the above-mentioned nickel-free annealing-free high-strength weather-resistant bolt wire rod. The bolt prepared using the nickel-free annealing-free high-strength weather-resistant bolt wire rod not only has mechanical properties of grade 8.8-10.9, but also has very excellent atmospheric corrosion resistance. It can be used in bridge structures, transmission towers, photovoltaic brackets and other fields without painting, and has good application prospects.

[0030] In order to achieve the above-mentioned purpose, the present invention proposes a bolt, which is made by using the nickel-free annealing-free high-strength weather-resistant bolt wire rod of the present invention after at least tempering treatment, and the bolt has a yield strength of ≥720MPa, a tensile strength of ≥870MPa, an elongation of ≥16%, and a cross-sectional shrinkage rate of ≥55%.

[0031] In the above technical scheme of the present invention, based on the nickel-free, annealing-free, high-strength, weather-resistant wire rod for bolts described in the present invention, when preparing the bolts, downstream users can further perform pickling, phosphorus saponification, drawing, cold heading, tempering treatment, thread rolling and other processes on the nickel-free, annealing-free, high-strength, weather-resistant wire rod for bolts, thereby processing them into high-strength and high-weather-resistant bolts.

[0032] In certain embodiments, the specific quenching and tempering heat treatment process adopted by downstream users may be: quenching temperature 850°C-880°C, keeping warm for 80 minutes and then oil quenching; tempering temperature 420-600°C, keeping warm for 1 hour and then air cooling.

[0033] Correspondingly, another object of the present invention is to provide a method for manufacturing the above-mentioned nickel-free annealing-free high-strength weather-resistant bolt wire rod, which combines component design with the control of the wire rod rolling process to suppress the formation of copper-rich phase, and reduces the strength of the hot-rolled wire rod through a controlled cooling process to produce hot-rolled wire rod that meets the requirements.

[0034] In order to achieve the above object, the present invention proposes a method for manufacturing the above-mentioned nickel-free annealing-free high-strength weather-resistant bolt wire rod, which comprises the steps of:

[0035] (1) Smelting and casting;

[0036] (2) Heating;

[0037] (3) rolling;

[0038] (4) Cooling: After rolling, cool to 900-920°C at a cooling rate of 4-5°C / s, and then continue to cool to room temperature at a cooling rate lower than 0.4°C / s.

[0039] Furthermore, in the manufacturing method of the present invention, in step (2), the heating temperature is controlled to be 1050-1100° C., and the time in the furnace is controlled to be within 120 minutes.

[0040] In the manufacturing method designed by the present invention, after molten steel is obtained by smelting according to the chemical composition designed by the present invention, the molten steel can be cast into steel ingots or steel billets under protective conditions after being calmed.

[0041] Accordingly, the obtained ingot or billet needs to be further heated, rolled and cooled. It should be noted that the temperature of the billet should be strictly controlled during the rolling process to avoid the precipitation of copper-rich phase due to excessive heating temperature. Therefore, the specific control process can be as follows: the heating temperature of the billet should be controlled at 1050-1100°C before rolling, and the furnace time should be controlled within 120 minutes.

[0042] The temperature of the wire rod must be strictly controlled during the cooling process to avoid too fast cooling below 900°C resulting in too high strength of the hot-rolled wire rod. Therefore, after rolling, it 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 lower than 0.4°C / s, thereby obtaining the nickel-free annealing-free high-strength weather-resistant bolt wire rod described in the present invention.

[0043] The nickel-free annealing-free high-strength weather-resistant bolt wire rod, bolt and manufacturing method thereof of the present invention have the following advantages and beneficial effects:

[0044] The nickel-free annealing-free high-strength weather-resistant bolt wire rod of the present invention has high strength and high weather resistance through reasonable component matching and process design, and its atmospheric corrosion resistance (weather resistance index I≥8.5) can meet the requirements of no coating and plating. The nickel-free annealing-free high-strength weather-resistant bolt wire rod has a yield strength of ≤400MPa, a tensile strength of ≤600MPa, an elongation of ≥25%, and a cross-sectional shrinkage of ≥60%.

[0045] The bolts made of nickel-free annealing-free high-strength weather-resistant bolt wire rods of the present invention can achieve a yield strength of ≥720MPa, a tensile strength of ≥870MPa, an elongation of ≥16%, and a cross-sectional shrinkage of ≥55%. The bolts not only have high strength, but also have excellent atmospheric corrosion resistance, and can be applied to bridge structures, transmission towers, photovoltaic brackets and other fields without painting. DETAILED DESCRIPTION

[0046] The nickel-free, annealing-free, high-strength, weather-resistant bolt wire rod, bolts, and their manufacturing methods described in the present invention will be further explained and illustrated below in conjunction with specific embodiments. However, such explanation and illustration do not constitute an improper limitation on the technical solution of the present invention.

[0047] Examples 1-6

[0048] Table 1-1 lists the mass percentages of the chemical elements in the nickel-free annealing-free high-strength weather-resistant bolt wire rods of Examples 1-6.

[0049] Table 1-1. (wt%, the balance is Fe and other inevitable impurities except P and S)

[0050]

[0051] Table 1-2 lists the content relationship between some chemical elements in the nickel-free annealing-free high-strength weather-resistant bolt wire rods of Examples 1-6.

[0052] Table 1-2.

[0053]

[0054]

[0055] Note: In the above Table 1-2, the Cr and C in the formula "Cr / C" are substituted with the mass percentage of the corresponding chemical elements; and 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 , and each chemical element in the formula is substituted into the value before the percentage sign of the mass percentage content of the corresponding element.

[0056] In the present invention, the nickel-free annealing-free high-strength weather-resistant bolt wire rods of Examples 1-6 are specifically prepared by the following steps:

[0057] (1) Smelting and casting are carried out according to the chemical composition shown in Table 1-1 and Table 1-2: Smelting is carried out according to the designed composition, and after the molten steel is calmed, it is cast into a 142mm×142mm square billet under protective conditions.

[0058] (2) Heating: The obtained 142 mm × 142 mm square billet is transported to a heating furnace for heating, and the heating temperature is controlled to be 1050-1100° C., and the time in the furnace is controlled within 120 min.

[0059] (3) Rolling.

[0060] (4) Cooling: After rolling, cool to 900-920°C at a cooling rate of 4-5°C / s, and then continue to cool to room temperature at a cooling rate lower than 0.4°C / s to obtain the corresponding Nickel-free, annealing-free, high-strength, weather-resistant wire rod for bolts.

[0061] In the present invention, 6 heats of steel, namely, Examples 1-6, were smelted and prepared according to the chemical compositions designed in Tables 1-1 and 1-2. The chemical element composition and related process design of the nickel-free annealing-free high-strength weather-resistant bolt wire rods of Examples 1-6 all meet the design specification requirements of the present invention.

[0062] Table 2 lists the specific process parameters of the nickel-free, annealing-free, high-strength, weather-resistant bolt wire rods of Examples 1-6 in the above process steps.

[0063] Table 2

[0064]

[0065] The obtained finished products of Examples 1-6, nickel-free annealing-free high-strength weather-resistant bolt wire rods, were sampled and observed. The inventors observed and found that the microstructures of the nickel-free annealing-free high-strength weather-resistant bolt wire rods of Examples 1-6 were all ferrite+pearlite.

[0066] Accordingly, after completing the above observations and analyses, the nickel-free, annealing-free, high-strength, weather-resistant bolt wire rods of the finished product embodiments 1-6 can be further sampled again, and the wire rod samples of each embodiment can be subjected to relevant mechanical property tests. The obtained mechanical property test results are listed in Table 3.

[0067] The relevant mechanical properties test methods are as follows:

[0068] Tensile test: At room temperature, according to GBT228-2002 metal material room temperature tensile test method, the yield strength, tensile strength, elongation and cross-sectional shrinkage of the nickel-free annealing-free high-strength weather-resistant bolt wire rods of Examples 1-6 were tested.

[0069] Table 3 lists the mechanical property test results of the nickel-free annealing-free high-strength weather-resistant bolt wire rods obtained in finished product embodiments 1-6.

[0070] Table 3.

[0071]

[0072] As shown in Table 3, combined with Tables 1-2, it can be seen that the nickel-free annealing-free high-strength weather-resistant bolt wire rods of Examples 1-6 of the present invention have excellent corrosion resistance (weathering resistance index I is greater than 8.5), and their yield strength is less than 400MPa, and their tensile strength is less than 600MPa, which meets the strength requirements of annealing-free, and their elongation is greater than 25%, and their cross-sectional shrinkage is greater than 60%. The atmospheric corrosion resistance of the nickel-free annealing-free high-strength weather-resistant bolt wire rods of Examples 1-6 can meet the requirements of coating-free.

[0073] To further illustrate that the annealing-free high-strength weather-resistant bolt wire rod of the present invention can be further used to prepare bolts with excellent performance. Based on the annealing-free high-strength weather-resistant bolt wire rod of Examples 1-6 of the present invention, the following steps can be further performed: pickling, phosphorus saponification, drawing, cold heading, quenching and tempering, and thread rolling, so as to obtain high-strength weather-resistant bolts with excellent performance.

[0074] It should be noted that, in some embodiments of the present invention, the specific tempering heat treatment process is: quenching temperature 850℃-880℃, keeping warm for 80min and then oil quenching; tempering temperature 420-600℃, keeping warm for 1h and then air cooling.

[0075] Therefore, for the high-strength weather-resistant bolts prepared in Examples 1-6, the inventors conducted mechanical property tests on the mechanical properties of each bolt, and the mechanical property test results are listed in the following Table 4. When conducting mechanical property tests on the high-strength weather-resistant bolts prepared in Examples 1-6, the tensile test method used by the inventors is the same as that in Table 3 above, and will not be repeated here.

[0076] Table 4 lists the mechanical properties of the high-strength weather-resistant bolts prepared in Examples 1-6.

[0077] Table 4.

[0078]

[0079] As shown in Table 4 above, the yield strength Rp0.2 of the bolts prepared corresponding to Examples 1-6 are all greater than 720 MPa, the tensile strength is greater than 870 MPa, the elongation is ≥16%, and the cross-sectional shrinkage is ≥55%. The mechanical properties are excellent, and the strength reaches 8.8-10.9. Therefore, the bolts are applied to bridge structures, transmission towers, photovoltaic brackets and other fields without painting.

[0080] It should be noted that the combination of the various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

[0081] It should also be noted that the above-listed embodiments are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therewith can be directly derived or easily associated with the contents disclosed by those skilled in the art from the present invention, and all should belong to the protection scope of the present invention.

Claims

1. A nickel-free, annealing-free, high-strength, weather-resistant bolt wire rod containing Fe and unavoidable impurities, characterized in that: It also contains the following chemical elements in the following mass percentages: 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%, Al: 0.01-0.1%; And the mass percentage of Cr and C satisfies: Cr / C>20; The nickel-free annealing-free high-strength weather-resistant bolt wire rod does not contain Ni.

2. The nickel-free annealing-free high-strength weather-resistant bolt wire rod according to claim 1, characterized in that: The mass percentage of each chemical element is: 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%, Al: 0.01-0.1%, the balance is Fe and other inevitable impurities; And the mass percentage of Cr and C satisfies: Cr / C>20.

3. The nickel-free annealing-free high-strength weather-resistant bolt wire rod according to claim 1 or 2, characterized in that: Among the inevitable impurities, P ≤ 0.012%, S ≤ 0.005%.

4. The nickel-free annealing-free high-strength weather-resistant bolt wire rod according to claim 1 or 2, characterized in that: Its microstructure is ferrite + pearlite.

5. The nickel-free annealing-free high-strength weather-resistant bolt wire rod according to claim 1 or 2, characterized in that: Its 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 ; Substitute the numerical value before the mass percentage sign for each chemical element in the formula.

6. The nickel-free annealing-free high-strength weather-resistant bolt wire rod according to claim 1 or 2, characterized in that: Its yield strength is ≤400MPa, tensile strength is ≤600MPa, elongation is ≥25%, and section shrinkage is ≥60%.

7. A bolt, which is made by using the nickel-free annealing-free high-strength weather-resistant bolt wire rod as described in any one of claims 1 to 6 and subjected to at least quenching and tempering treatment, wherein the bolt has a yield strength of ≥720MPa, a tensile strength of ≥870MPa, an elongation of ≥16%, and a cross-sectional shrinkage of ≥55%.

8. The method for manufacturing the nickel-free annealing-free high-strength weather-resistant bolt wire rod according to any one of claims 1 to 6, characterized in that: It includes the steps of: (1) Smelting and casting; (2) Heating; (3) rolling; (4) Cooling: After rolling, cool to 900-920°C at a cooling rate of 4-5°C / s, and then continue to cool to room temperature at a cooling rate lower than 0.4°C / s.

9. The manufacturing method according to claim 8, characterized in that: In step (2), the heating temperature is controlled to be 1050-1100°C, and the time in the furnace is controlled to be within 120 minutes.

Images