A high-strength weather-resistant nickel-free bolt wire rod, bolt and manufacturing method thereof

Abstract

The application discloses a kind of nickel-free high-strength weather-resistant bolt wire rod, it contains Fe and inevitable impurities, it also contains the following chemical elements with mass percentage as follows: C:0.17-0.35%, Si:0.01-2.0%, Mn:0.3-2.2%, Cr:3.0-5.5%, Cu:0.3-0.5%, Al:0.001-0.1%, Ti:0.02-0.03%;And the mass percentage of Cu, Cr, C satisfies: (Cr+20Cu) / C≥40.The application also discloses a bolt, which is made of the above wire rod after at least quenching and tempering treatment.The application further discloses a manufacturing method of the above wire rod, comprising the steps of: smelting and casting, heating, controlling the heating temperature to be 1050-1100 DEG C, rolling, and cooling.

Description

Technical Field

[0001] This invention relates to a wire rod, a bolt, and a method for manufacturing the same, and more particularly to a wire rod, a bolt, and a method for manufacturing the same for high-strength weather-resistant bolts. Background Technology

[0002] Currently, high-strength bolts are the primary connectors in the steel structures of buildings, bridges, and transmission towers. These bolts typically employ coating methods, such as hot-dip galvanizing, electroplating, or mechanical plating, to achieve corrosion protection. However, high-strength bolts have high preload torque and significant friction between the threads. The coating itself cannot withstand this high friction, and it is often damaged during bolt preload, resulting in a thinner coating. In severe cases, this can even expose the bolt's base material to the service environment, reducing its corrosion resistance.

[0003] Surface coating methods require maintenance every 3-5 years and recoating every 10-15 years. This maintenance not only increases costs but also poses health hazards and environmental pollution. Furthermore, some coating processes introduce hydrogen sources into the bolts, increasing hydrogen embrittlement sensitivity in high-strength bolts and potentially leading to delayed fracture. Therefore, developing coating-free, high-strength, weather-resistant steel for bolts is of great significance.

[0004] Chinese patent document CN107177787A, published on May 24, 2017, entitled "High-strength Bolt Steel Resistant to Industrial Atmospheric Corrosion for Uncoated Steel Structures and its Manufacturing Method," discloses a high-strength bolt steel resistant to industrial atmospheric corrosion for uncoated steel structures and its manufacturing method, belonging to the technical field of atmospheric corrosion resistant steel. Its components, by weight percentage, are: C 0.16–0.45%, Si 0.01–2.0%, Mn 0.3–2.2%, P 0.025–0.12%, S 0.002–0.025%, B 0.0005–0.0100%, Ti 0.04–0.50%, V 0.01–0.20%, Al 0.02–0.10%, Cu 0.2–0.5%, Ni 0.2–1.0%, with the remainder being Fe and trace impurities. The high-strength weather-resistant bolt steel has a corrosion resistance index I≥6.3 calculated according to the chemical composition prediction formula. The bolt specifications produced are M16~30mm. After the bolts are made into bolts at the bolt processing plant, the heat treatment process is oil quenching at 840~920℃ + tempering at 380~625℃ to obtain the best strength and toughness match.

[0005] Chinese patent document CN108070796A, published on November 28, 2017, entitled "A Weathering Bolt with 1040MPa Grade Resistance to Delayed Fracture," discloses a weathering bolt with a 1040MPa grade resistance to delayed fracture. The mass percentage of its chemical composition is as follows: C: 0.21–0.32, Si: 0.10–0.50, Mn: 0.60–1.00, P: 0.008–0.020, S: ≤0.005, Cr: 0.82–1.20, Ni: 0.25–0.50, Cu: 0.25–0.50, Mo: 0.05–0.20, Nb: 0.015–0.060, V: 0. 0.15~0.090, Ti: 0.008~0.035, B: 0.0008~0.0035, Al: 0.015~0.040, Ca: 0.003~0.007, Zr: 0.015~0.045, Re: 0.010~0.045, with the balance being Fe and unavoidable impurities; the above bolts are mainly prepared using conventional high-purity chemical smelting-continuous casting-rolling technology to prepare metal raw materials into weather-resistant bolt steel materials resistant to delayed fracture; the raw materials are pickled, drawn, cut, end face chamfered, flattened, head formed, head chamfered, shot blasted, semi-finished surface treatment, diameter reduction, thread rolling, heat treatment, and finished product surface treatment according to conventional methods. Summary of the Invention

[0006] One of the objectives of this invention is to provide a nickel-free high-strength weather-resistant bolt wire rod. This nickel-free high-strength weather-resistant bolt wire rod can achieve strong weather resistance without adding Ni, and its atmospheric corrosion resistance can meet the requirements of no coating or plating.

[0007] To achieve the above objectives, the present invention provides a nickel-free high-strength weather-resistant bolt wire rod, which contains Fe and unavoidable impurities, and also contains the following chemical elements in the following mass percentages:

[0008] C: 0.17-0.35%, Si: 0.01-2.0%, Mn: 0.3-2.2%, Cr: 3.0-5.5%, Cu: 0.3-0.5%, Al: 0.001-0.1%, Ti: 0.02-0.03%;

[0009] Furthermore, the mass percentage content of Cu, Cr, and C satisfies the following condition: (Cr + 20Cu) / C ≥ 40.

[0010] In this invention, the synergistic effect of Cr and Cu elements when added to steel simultaneously is particularly pronounced. This synergistic effect refines α-FeOOH, and Cr can replace Fe3+ in α-FeOOH to form amorphous α-(Fe1-xCrx)OOH. However, Cr will inevitably combine with C to form precipitated Cr phase. 23 C6, while the precipitated phase Cr 23 C6 does not improve the weather resistance of steel. Therefore, in the nickel-free high-strength weather-resistant bolt wire rod of the present invention, while controlling the mass percentage content of a single chemical element, it is also necessary to further control the Cr and C content in the steel to meet the following condition: (Cr+20Cu) / C≥40, so as to ensure that there are enough Cr and Cu elements in the steel to improve weather resistance.

[0011] Furthermore, in the nickel-free high-strength weather-resistant bolt wire rod described in this invention, the mass percentage content of each chemical element is as follows:

[0012] C: 0.17-0.35%, Si: 0.01-2.0%, Mn: 0.3-2.2%, Cr: 3.0-5.5%, Cu: 0.3-0.5%, Al: 0.001-0.1%, Ti: 0.02-0.03%, with the balance being Fe and other unavoidable impurities.

[0013] The design principles of each chemical element in the nickel-free high-strength weather-resistant bolt wire rod of the present invention are as follows:

[0014] C: In the nickel-free high-strength weather-resistant bolt wire rod described in this invention, carbon (C) is a crucial element for the formation of fine, dispersed carbides after subsequent quenching and tempering, playing a vital role in improving bolt strength. It is important to note that the C content in the steel should not be too high. Excessive C content can negatively impact the material's atmospheric corrosion resistance and increase the strength of the hot-rolled wire rod, making cold deformation more difficult. Therefore, to ensure good atmospheric corrosion resistance and suitable strength in the material of this invention, the C content in the steel needs to be controlled within a reasonable range. In the nickel-free high-strength weather-resistant bolt wire rod described in this invention, the mass percentage of C is controlled between 0.17% and 0.35%.

[0015] Si: In the nickel-free high-strength weather-resistant bolt wire rod of the present invention, Si has a high solid solubility. Adding an appropriate amount of Si to steel can effectively increase the volume fraction of ferrite in the steel and refine the grains, thereby improving the toughness of the steel. Therefore, in order to give full play to the beneficial effects of Si, the mass percentage of Si in the nickel-free high-strength weather-resistant bolt wire rod of the present invention is controlled between 0.01% and 2.0%.

[0016] Mn: In the nickel-free high-strength weather-resistant bolt wire rod of the present invention, Mn has a strong solid solution strengthening effect and is also an important toughening element. Adding an appropriate amount of Mn to steel can significantly reduce the phase transformation temperature of the steel and refine the microstructure of the steel. Based on this, considering the beneficial effects of Mn, the mass percentage of Mn in the nickel-free high-strength weather-resistant bolt wire rod of the present invention is controlled between 0.3% and 2.2%.

[0017] Cr: In the nickel-free high-strength weather-resistant bolt wire rod described in this invention, the presence of Cr significantly accelerates the development of electrochemical corrosion products towards a thermodynamically stable state. In rust layer analysis, Cr can significantly accelerate (Fe... X H Y O Z The transformation process from α-FeOOH to γ-FeOOH promotes the formation of spinel compounds. Simultaneously, Cr in steel can partially replace Fe to form ferrochromium hydroxide Cr. X Fe 1-X OOH, thus giving the α-FeOOH rust layer cation selectivity and preventing Cl- and SO42- from reacting. 2 - It penetrates into the substrate surface, giving the rust layer a protective effect. Therefore, in order to maximize the beneficial effects of Cr and ensure a significant improvement in the atmospheric corrosion resistance of steel, the mass percentage of Cr in the nickel-free high-strength weather-resistant bolt wire rod described in this invention is controlled between 3.0% and 5.5%.

[0018] Cu: In the nickel-free high-strength weather-resistant bolt wire rod described in this invention, among all alloying elements, Cu has the most significant impact on the material's weather resistance. Adding an appropriate amount of Cu to steel can effectively delay the anodic dissolution of Fe or reduce the electronic conductivity of the rust layer, thus slowing down the rate at which electrons flow to the cathode region. Simultaneously, Cu in steel can also combine to form small amounts of insoluble copper oxyhydroxide, such as Cu₄(SO₄)(OH)₂ and Cu₄(SO₄)(OH)₄. These compounds can precipitate within 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 the steel should not be too high, as excessive Cu can lead to hot brittleness and increase production difficulty. Therefore, to maximize the beneficial effects of Cu, the mass percentage of Cu in the nickel-free high-strength weather-resistant bolt wire rod described in this invention is controlled between 0.3% and 0.5%.

[0019] Al: In the nickel-free high-strength weather-resistant bolt wire rod of the present invention, Al is an added deoxidizer in the steel, which can play a deoxidizing role. In addition, Al is beneficial to refine grains and improve the strength and toughness of steel. Therefore, in the nickel-free high-strength weather-resistant bolt wire rod of the present invention, the mass percentage of Al is controlled between 0.001-0.1%.

[0020] Ti: In the nickel-free high-strength weather-resistant bolt wire rod of the present invention, Ti element can form precipitation strengthening, thereby improving strength. Therefore, in the nickel-free high-strength weather-resistant bolt wire rod of the present invention, the mass percentage content of Ti element is controlled between 0.02-0.03%.

[0021] Furthermore, in the unavoidable impurities of the nickel-free high-strength weather-resistant bolt wire rod described in this invention, P ≤ 0.012% and S ≤ 0.005%.

[0022] In the nickel-free high-strength weather-resistant bolt wire rod described in this invention, both P and S elements are impurity elements in steel. Under the condition that technical conditions permit, in order to obtain steel with better performance and higher quality, the content of impurity elements in steel should be reduced as much as possible.

[0023] S and P: In this invention, the presence of impurity element S will worsen the atmospheric corrosion resistance of steel and lead to hot brittleness. While P can improve the atmospheric corrosion resistance of steel, excessively high P content will significantly reduce the toughness and plasticity of the steel and also lead to cold brittleness. Therefore, the content of P and S elements in steel should be reduced as much as possible. This invention uses extremely low S and P contents, and the mass percentage of P element can be controlled to P≤0.012%, and the mass percentage of S element can be controlled to S≤0.005%.

[0024] Furthermore, in the nickel-free high-strength weather-resistant bolt wire rod described in this invention, its microstructure is ferrite + pearlite.

[0025] Furthermore, in the nickel-free high-strength weather-resistant bolt wire rod described in this invention, 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 values ​​of the chemical elements in the formula into the values ​​preceding the percentage sign.

[0026] It should be noted that for steel, the higher the I value, the higher the atmospheric corrosion resistance of the steel. Generally speaking, materials with a weather resistance index I > 6 have very good atmospheric corrosion resistance.

[0027] Furthermore, in the nickel-free high-strength weather-resistant bolt wire rod described in this invention, its yield strength is ≥900MPa, tensile strength is ≥1000MPa, elongation is ≥10%, and reduction of area is ≥20%.

[0028] Another objective of this invention is to provide a bolt made from the aforementioned nickel-free high-strength weather-resistant bolt wire rod. This nickel-free high-strength weather-resistant bolt not only has high strength but also excellent atmospheric corrosion resistance. It can be applied to bridge structures, transmission towers, and photovoltaic supports without painting, and has good application prospects.

[0029] To achieve the above objectives, the present invention provides a bolt made from the aforementioned nickel-free high-strength weather-resistant bolt wire rod after at least a quenching and tempering treatment. The bolt has a yield strength ≥1100MPa, tensile strength ≥1200MPa, elongation ≥13%, and reduction of area ≥50%.

[0030] In some embodiments, the nickel-free high-strength weather-resistant bolt wire rod prepared based on the present invention can be further processed into high-strength and high-weather-resistant bolts through spheroidization, pickling, phosphating, drawing, cold heading, quenching and tempering, and thread rolling processes.

[0031] Another objective of this invention is to provide a method for manufacturing nickel-free high-strength weather-resistant bolt wire rod, which, in conjunction with composition design, suppresses the formation of copper-rich phase and produces hot-rolled wire rod that meets the requirements.

[0032] To achieve the above objectives, the present invention provides a method for manufacturing nickel-free high-strength weather-resistant bolt wire rod, comprising the following steps:

[0033] (1) Smelting and casting;

[0034] (2) Heating: Control the heating temperature to 1050~1100℃;

[0035] (3) Rolling;

[0036] (4) Cooling.

[0037] In this invention, by strictly controlling the temperature of the billet during the rolling process, the precipitation of copper-rich phase caused by excessive heating temperature can be avoided.

[0038] Furthermore, in step (2) of the manufacturing method described in this invention, the heating time is controlled within 120 minutes.

[0039] Furthermore, in step (4) of the manufacturing method described in this invention, after rolling, the temperature is cooled to 880-900°C at a cooling rate of 4-5°C / s, and then further cooled to room temperature at a cooling rate of less than 0.5°C / s.

[0040] The nickel-free high-strength weather-resistant bolt wire rod, bolt, and manufacturing method thereof described in this invention have the following advantages and beneficial effects:

[0041] The nickel-free high-strength weather-resistant bolt wire rod of the present invention, through reasonable component matching and process design, achieves high strength and high weather resistance, and its atmospheric corrosion resistance (weather resistance index I≥8.5) is sufficient to meet the requirements of no coating.

[0042] In some embodiments, the nickel-free high-strength weather-resistant bolt wire rod of the present invention has a yield strength ≥900MPa, a tensile strength ≥1000MPa, an elongation ≥10%, and a reduction of area ≥20%.

[0043] The bolts described in this invention not only have high strength but also excellent resistance to atmospheric corrosion. They can be applied to bridge structures, transmission towers, and photovoltaic supports without painting, which is of great significance to the development of the bolt industry and has good application prospects.

[0044] In some embodiments, the bolts of the present invention have a yield strength ≥1100MPa, a tensile strength ≥1200MPa, an elongation ≥13%, and a reduction of area ≥50%. Detailed Implementation

[0045] The following will further explain and illustrate the nickel-free high-strength weather-resistant bolt wire rod, bolt, and manufacturing method of the present invention with reference to specific embodiments. However, this explanation and illustration do not constitute an improper limitation on the technical solution of the present invention.

[0046] Examples 1-6

[0047] In this invention, the nickel-free high-strength weather-resistant bolt wire rods of Examples 1-6 are all prepared using the following steps:

[0048] (1) Smelting and casting: molten steel is obtained by smelting and after the molten steel is calmed, it is cast into a 142mm×142mm square billet under protective conditions.

[0049] (2) Heating: The prepared billet is transported to a heating furnace for heating, and the heating temperature is controlled at 1050-1100℃, and the time in the furnace is controlled within 120 minutes;

[0050] (3) Rolling;

[0051] (4) Cooling: After rolling, the temperature is cooled to 880-900℃ at a cooling rate of 4-5℃ / s, and then cooled to room temperature at a cooling rate of less than 0.5℃ / s to obtain the corresponding 12.9 grade nickel-free high-strength weather-resistant bolt wire rod.

[0052] Tables 1-1 and 1-2 list the mass percentage of each chemical element in the nickel-free high-strength weather-resistant bolt wire rods of Examples 1-6 of the present invention.

[0053] Table 1-1. (wt%, balance Fe and other unavoidable impurities besides P and S)

[0054]

[0055]

[0056] Table 1-2.

[0057] serial number (Cr+20Cu) / C I Example 1 41.4 11.7 Example 2 44.3 11.9 Example 3 44.4 11.3 Example 4 48.8 11.2 Example 5 55.5 10.2 Example 6 76.5 10.4

[0058] Note: In Table 1-2 above, Cr and C in the formula "(Cr+20Cu) / C" should be 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 Furthermore, each chemical element in the formula is replaced with the value preceding the percentage sign of its corresponding mass percentage content.

[0059] Table 2 lists the specific process parameters of the nickel-free high-strength weather-resistant bolt wire rods of Embodiments 1-6 of the present invention in the heating and cooling steps.

[0060] Table 2.

[0061]

[0062] Samples were taken from the nickel-free high-strength weather-resistant bolt wire rods obtained in Examples 1-6, and the microstructure of each example was observed using a metallographic microscope. The inventors found through microstructural observation that the microstructure of the nickel-free high-strength weather-resistant bolt wire rods of Examples 1-6, manufactured using the method described in this invention, consisted entirely of ferrite and pearlite.

[0063] In addition, samples of the nickel-free high-strength weather-resistant bolt wire rods obtained in Examples 1-6 were taken again, and relevant mechanical property tests were performed on the wire rod samples of each example. The results of the mechanical property tests are listed in Table 3. The relevant mechanical property test methods are as follows:

[0064] Tensile test: Under room temperature conditions, according to GBT228-2002 Metallic Materials Room Temperature Tensile Test Method, the yield strength, tensile strength, elongation and reduction of area of ​​the high strength weathering bolt wire rods of Examples 1-6 were tested to obtain the results.

[0065] Table 3 lists the mechanical property test results of the nickel-free high-strength weather-resistant bolt wire rods of Examples 1-6 of the present invention.

[0066] Table 3.

[0067]

[0068] As can be seen from Table 3 above, the nickel-free high-strength weather-resistant bolt wire rods of Examples 1-6 of the present invention have excellent mechanical properties, with yield strengths all greater than 900 MPa, tensile strengths all greater than 1000 MPa, elongation all greater than 10%, and reduction of area all greater than 20%. Furthermore, as can be seen from Tables 1-2 above, the nickel-free high-strength weather-resistant bolt wire rods of Examples 1-6 of the present invention have excellent corrosion resistance, with weather resistance index I all greater than 8.5, meeting the requirements for no-coating.

[0069] Furthermore, in order to verify that the nickel-free high-strength weather-resistant bolt wire rod prepared by the present invention can be further processed into bolts with excellent performance, further spheroidizing treatment, pickling, phosphating, drawing, cold heading, quenching and tempering treatment, and thread rolling processes can be carried out on the nickel-free high-strength weather-resistant bolt wire rod prepared in Examples 1-6 of the present invention, so as to obtain nickel-free high-strength weather-resistant bolts with excellent performance corresponding to Examples 1-6.

[0070] In some embodiments, the quenching and tempering heat treatment process is as follows: quenching temperature 850℃-880℃, holding temperature for 80 minutes followed by oil quenching; tempering temperature 420-600℃, holding temperature for 1 hour followed by air cooling.

[0071] Mechanical properties were tested on the nickel-free high-strength weather-resistant bolts obtained in Examples 1-6, and the test results are listed in Table 3. The relevant mechanical property testing methods are described below:

[0072] Tensile test: Under room temperature conditions, according to GBT228-2002 Metallic Materials Room Temperature Tensile Test Method, the yield strength, tensile strength, elongation and reduction of area of ​​the nickel-free high-strength weathering bolts obtained in Examples 1-6 were tested.

[0073] Table 4 lists the mechanical property test results of the nickel-free high-strength weather-resistant bolts of Examples 1-6 of the present invention.

[0074] Table 4.

[0075]

[0076] As can be seen from Table 4 above, the yield strength of the nickel-free high-strength weather-resistant bolts in Examples 1-6 of the present invention is greater than 1100MPa, the tensile strength is greater than 1220MPa, the elongation is ≥13%, and the reduction of area is ≥51%. They have excellent mechanical properties and can therefore be applied to bridge structures, transmission towers, and photovoltaic supports.

[0077] It should be noted that the combination of the technical features in this case is not limited to the combination methods described in the claims of this case or the combination methods described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way, unless they contradict each other.

[0078] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made thereto are those that can be directly derived or easily conceived by those skilled in the art from the content disclosed in the present invention, and should all fall within the protection scope of the present invention.

Claims

1. A nickel-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: 0.17-0.35%, Si: 0.01-2.0%, Mn: 0.3-2.2%, Cr: 3.0-5.5%, Cu: 0.3-0.5%, Al: 0.001-0.1%, Ti: 0.02-0.03%; Furthermore, the mass percentage content of Cu, Cr, and C satisfies the following condition: (Cr + 20Cu) / C ≥ 40.

2. The nickel-free high-strength weather-resistant bolt wire rod as described in claim 1, characterized in that, Its mass percentage content of each chemical element is as follows: C: 0.17-0.35%, Si: 0.01-2.0%, Mn: 0.3-2.2%, Cr: 3.0-5.5%, Cu: 0.3-0.5%, Al: 0.001-0.1%, Ti: 0.02-0.03%, with the balance being Fe and other unavoidable impurities.

3. The nickel-free high-strength weather-resistant bolt wire rod as described in claim 1 or 2, characterized in that, In unavoidable impurities, P ≤ 0.012% and S ≤ 0.005%.

4. The nickel-free high-strength weather-resistant bolt wire rod as described in claim 1 or 2, characterized in that, Its microstructure consists of ferrite and pearlite.

5. The nickel-free high-strength weather-resistant bolt wire rod as described in 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 values ​​of the chemical elements in the formula into the values ​​preceding the percentage sign.

6. The nickel-free high-strength weather-resistant bolt wire rod as described in claim 1 or 2, characterized in that, Its yield strength is ≥900MPa, tensile strength is ≥1000MPa, elongation is ≥10%, and reduction of area is ≥20%.

7. A bolt, characterized in that, It is made from nickel-free high-strength weather-resistant bolt wire rod as described in any one of claims 1-6, which has undergone at least quenching and tempering treatment. The bolt has a yield strength ≥1100MPa, tensile strength ≥1200MPa, elongation ≥13%, and reduction of area ≥50%.

8. The method for manufacturing nickel-free high-strength weather-resistant bolt wire rod as described in any one of claims 1-6, characterized in that, It includes the following steps: (1) Smelting and casting; (2) Heating: Control the heating temperature to 1050~1100℃; (3) Rolling; (4) Cooling.

9. The manufacturing method as described in claim 8, characterized in that, In step (2), the heating time is controlled within 120 minutes.

10. The manufacturing method as described in claim 8, characterized in that, In step (4), after rolling, the temperature is cooled to 880-900°C at a cooling rate of 4-5°C / s, and then cooled to room temperature at a cooling rate of less than 0.5°C / s.

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