High-hardenability and high-uniformity wire rod and wire rod for bolt and manufacturing method of high-hardenability and high-uniformity wire rod

Abstract

The invention discloses a high-hardenability and high-uniformity wire rod for a bolt, which contains Fe and inevitable impurities, and further contains the following chemical elements in percentage by mass: 0.40 to 0.44 percent of C, 0.25 to 0.35 percent of Si, 0.60 to 0.80 percent of Mn, 1.0 to 1.20 percent of Cr, 0.10 to 0.20 percent of Ni, 0.10 to 0.20 percent of Mo, 0.015 to 0.040 percent of Al, 0.0006 to 0.001 percent of B and 0.003 to 0.005 percent of N. The invention further discloses a high-hardenability and high-uniformity wire rod for the bolt. The high-hardenability and high-uniformity wire rod for the bolt is prepared from the wire rod. The invention further discloses a manufacturing method of the wire rod and the wire rod. The manufacturing method comprises the steps of smelting and continuous casting; blooming and cogging; high-speed wire rod controlled rolling; cooling by a Stelmor fan to obtain a wire rod; spheroidizing and drawing are carried out; quenching and tempering heat treatment.

Description

Technical Field

[0001] The present invention relates to a steel material and a preparation method thereof, and in particular to a wire rod for bolts and a preparation method thereof. Background Art

[0002] Bolt fasteners are general basic components that can be used in electronic products, mechanical products, digital products, power equipment, ships, vehicles, new energy projects, etc.

[0003] For bolts of varying cross-sectional sizes, their mechanical properties vary even with the same tempering process due to varying degrees of hardening. A higher degree of hardening results in a greater yield strength ratio after tempering, and a greater likelihood of achieving the desired mechanical properties. A lower degree of hardening results in lower mechanical properties, impacting final quality. Therefore, hardenability is a key evaluation metric for bolts.

[0004] A Chinese patent document, CN106521316A, published on March 22, 2017, and titled "A High-Hardenability Medium-Carbon Low-Alloy Round Steel for Fasteners and Its Manufacturing Method," discloses a high-hardenability medium-carbon low-alloy round steel for fasteners. The round steel has a chemical composition percentage of C: 0.36-0.44%, Si: 0.15-0.40%, Mn: 0.80-1.00%, Cr: 1.00-1.15%, Mo: 0.05-0.25%, Ni: 0.05-0.25%, Cu: 0.05-0.25%, Al: 0.015-0.050%, B: 0.0010-0.0050%, Ti: 0.020-0.050%, with the balance being Fe and unavoidable impurities. However, this patent document primarily addresses the manufacturing method for large-size round steel bars and does not address the production of wire rods.

[0005] The Chinese patent document with publication number CN114231840A and publication date March 25, 2022, and titled "A wire rod for high hardenability medium carbon cold heading steel and its production process" discloses a wire rod for high hardenability medium carbon cold heading steel and its production process, C: 0.37%~0.40%, Si: 0.15%~0.30%, Mn: 0.70%~0.90%, Cr: 0.10-0.20%, P≤0.020%, S≤0.020%, Als 0.010%~0.030%, and the balance is iron and unavoidable impurity elements. However, its hardenability can only reach J51 / 56-1.5, J45 / 52-3, J30 / 37-5, J26 / 33-7, J25 / 27-9, J23 / 25-11, J22 / 24-13, J21 / 23-15, J20 / 22-20, and J18 / 20-25. Summary of the Invention

[0006] One of the purposes of the present invention is to provide a wire rod for bolts with high hardenability and high uniformity. The wire rod has high hardenability and good toughness through reasonable chemical composition design.

[0007] To achieve the above object, the present invention provides a high hardenability and high uniformity wire rod for bolts, which contains Fe and inevitable impurities, and further contains the following chemical elements in the following mass percentages:

[0008] C: 0.40~0.44%, Si: 0.25~0.35%, Mn: 0.60~0.80%, Cr: 1.0%~1.20%, Ni: 0.10~0. 20%, Mo: 0.10~0.20%, Al: 0.015~0.040%, B: 0.0006~0.001%, N: 0.003~0.005%.

[0009] Furthermore, in the high hardenability and high uniformity wire rod for bolts of the present invention, the mass percentage of chemical elements is:

[0010] C: 0.40~0.44%, Si: 0.25~0.35%, Mn: 0.60~0.80%, Cr: 1.0%~1.20%, Ni: 0.10~0.20%, Mo: 0.10~0.20%, Al: 0.015~0.040%, B: 0.0006~0.001%, N: 0.003~0.005%; the balance is Fe and inevitable impurities.

[0011] In the high hardenability and high uniformity wire rod for bolts of the present invention, the design principles of the chemical elements are specifically described as follows:

[0012] C: In the high-hardenability, high-uniformity bolt wire rod described herein, carbon is an essential element of the steel grade. Its content directly determines the strength and hardness of the wire rod and the resulting bolts. Carbon also improves the hardenability of the steel. However, excessive carbon content in the steel can lead to oversized carbides in the wire rod's microstructure, reducing the wire rod's plasticity and toughness. Therefore, to ensure the wire rod's strength, toughness, and hardenability, the present invention limits the carbon content to between 0.40% and 0.44% by weight.

[0013] Si: In the high-hardenability, high-uniformity wire rod for bolts described herein, Si can be added to the steel as a deoxidizer during the smelting process. It also provides solid solution strengthening, increasing the steel's strength. However, excessive Si content in the steel can affect its cold working properties and increase carbon diffusion, exacerbating decarburization. To maximize the beneficial effects of Si, the present invention limits its content to between 0.25% and 0.35% by weight.

[0014] Mn: In the high-hardenability, high-uniformity bolt wire rod described herein, Mn is added during the steelmaking process as a deoxidizer. It also reacts with the harmful element S in the steel to form MnS, reducing the harmful effects of S. Mn also provides solid solution strengthening. However, excessive Mn content can easily lead to central segregation in the steel. Therefore, in the present invention, the Mn content is controlled to between 0.60% and 0.80% by weight.

[0015] Cr: The addition of Cr to the high-hardenability, high-uniformity bolt wire rod described herein helps improve the material's hardenability. Cr also helps refine the quenched and tempered heat treatment structure, improving the material's strength and plasticity, resulting in better overall performance after quenching and tempering. However, excessive Cr content in the steel can form coarse carbides, deteriorating the material's plasticity and toughness. Therefore, in the present invention, the Cr content is controlled within a range of 1.0% to 1.20% by weight.

[0016] Ni: In the high hardenability and high uniformity wire rod for bolts described in the present invention, the Ni element can play a role in solid solution strengthening in the steel, improving the strength while maintaining good plasticity and toughness. In addition, the Ni element has a certain effect on improving the hardenability of the material and can lower the ductile-brittle transition temperature, improving low-temperature toughness. However, the Ni element is a precious alloy element, and adding too much will lead to increased costs. Based on this, considering the cost and effectiveness of the Ni element, the mass percentage of the Ni element is controlled between 0.10 and 0.20% in the present invention.

[0017] Mo: In the high-hardenability, high-uniformity bolt wire rod described herein, adding an appropriate amount of Mo improves the steel's hardenability, allowing martensite to form during quenching. It also refines the microstructure, increasing strength and toughness. However, Mo is a precious alloying element, and adding too much of it can increase costs. Therefore, considering the cost and utility of Ni, the Mo content in this invention is controlled to between 0.10% and 0.20% by weight.

[0018] Al: In the high-hardenability, high-uniformity wire rod for bolts described herein, Al acts as a deoxidizing element and also refines the grain size. It also stabilizes nitrogen in the steel. However, excessive Al content can easily form non-deformable inclusions such as aluminum oxide during the smelting process, negatively impacting the steel's fatigue life and delayed fracture resistance. Therefore, to ensure optimal material performance, the Al content is controlled within a range of 0.015% to 0.040% by weight in the present invention.

[0019] B: In the high-hardenability, high-uniformity wire rod for bolts described herein, the addition of element B facilitates the precipitation of ferrite. Even a small amount of element B can significantly improve the hardenability of the steel. However, excessive B content can promote temper brittleness and reduce the toughness of the material. Therefore, in the present invention, the mass percentage of element B is controlled between 0.0006% and 0.001%.

[0020] N: In the high-hardenability, high-uniformity bolt wire rod described herein, N combines with Al and B to form nanoscale AlN, thereby refining the grain size. However, excessive N content can increase the size of microalloy precipitates in the steel, deteriorating material properties. Therefore, in the present invention, the N content is controlled within a range of 0.003% to 0.005% by weight.

[0021] Furthermore, in the high hardenability and high uniformity wire rod for bolts of the present invention, the mass percentage of each chemical element also satisfies: Cr+Mo+Ni / 3≤1.40%.

[0022] Furthermore, in the wire rod for bolts with high hardenability and high uniformity described in the present invention, the mass percentage of each chemical element also satisfies: Al / N≥3.

[0023] Furthermore, among the inevitable impurities in the wire rod for bolts with high hardenability and high uniformity according to the present invention, P≤0.01%, S≤0.01%, O≤0.002%, H≤0.0002%, and Ti≤0.001%.

[0024] In the high hardenability and high uniformity wire rod for bolts described in the present invention, P, S, O, H, and Ti are all impurity elements in the steel. Where 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. Among them:

[0025] P and S: In the high-hardenability, high-uniformity bolt wire rod described herein, P and S, as impurity elements, can segregate at austenite grain boundaries, embrittle the steel, and degrade the wire rod's performance. Therefore, the P and S content in the steel should be minimized. The present invention utilizes extremely low P and S content in its design, achieving P ≤ 0.01% by weight and S ≤ 0.01% by weight.

[0026] O: In the high-hardenability, high-uniformity bolt wire rod of the present invention, O easily forms alumina-type hard inclusions with Al, which is detrimental to the performance of the wire rod. Therefore, in the present invention, the mass percentage of O is controlled to O≤0.002%.

[0027] H: In the high hardenability and high uniformity bolt wire rod of the present invention, the presence of H element can easily lead to delayed cracking of the bolt. Therefore, in the present invention, the mass percentage of H element is controlled to H≤0.0002%.

[0028] Ti: In the high-hardenability, high-uniformity wire rod for bolts described herein, Ti combines with N to form hard inclusions such as TiN, which can affect the material's fatigue performance. Therefore, in the present invention, the Ti content is controlled to ≤ 0.001% by weight.

[0029] Furthermore, the microstructure of the wire rod for high hardenability and high uniformity bolts described in the present invention is bainite + pearlite + a small amount of ferrite, wherein the volume content of ferrite does not exceed 3%.

[0030] Another object of the present invention is to provide a high-hardenability and high-uniformity wire for bolts, which, after tempering, can meet the manufacturing requirements of high-hardenability 10.9 grade bolts.

[0031] In order to achieve the above-mentioned object, the present invention further provides a high-hardenability and high-uniformity wire rod for bolts, which is made by using the above-mentioned high-hardenability and high-uniformity wire rod for bolts.

[0032] Furthermore, the surface microstructure of the high hardenability and high uniformity bolt wire of the present invention is entirely tempered bainite, and the volume content of tempered bainite in the core microstructure exceeds 90%, with the remainder being ferrite and bainite.

[0033] Furthermore, in the high hardenability and high uniformity bolt wire described in the present invention, its yield strength is ≥970MPa, tensile strength is ≥1075MPa, cross-sectional reduction rate is ≥40%, and core-surface hardness difference is ≤20HV; hardenability J1.5 is 56-58HRC, J5 is 55-58HRC, J11 is 54-57HRC, J15 is 51-54HRC, J20 is 48-51HRC, J25 is 43-47HRC, and J30 is 41-43HRC.

[0034] Another object of the present invention is to provide a method for manufacturing wire rod for bolts with high hardenability and high uniformity.

[0035] In order to achieve the above object, the present invention also provides a method for manufacturing a wire rod for bolts with high hardenability and high uniformity, which comprises the steps of:

[0036] smelting and continuous casting;

[0037] Blooming;

[0038] High-speed wire rod controlled rolling: controlled heating temperature is 1000-1100℃, rolling start temperature is 980-1010℃, sizing temperature is 940-970℃, and spinning temperature is 890-910℃;

[0039] Stelmore fan cooling.

[0040] Furthermore, in the manufacturing method of the wire rod for high hardenability and high uniformity bolts described in the present invention, during the cooling process of the Stelmore blower, the air volume of the Stelmore line blower is controlled to be 15-30% of the F1-F5 blower air volume and 0-30% of the F6-F14 blower air volume.

[0041] Another object of the present invention is to provide a method for manufacturing a wire rod for bolts with high hardenability and high uniformity, wherein the wire rod obtained by the method has high hardenability and good toughness.

[0042] In order to achieve the above object, the present invention also provides a method for manufacturing a high hardenability and high uniformity bolt wire, which comprises the steps of:

[0043] smelting and continuous casting;

[0044] Blooming;

[0045] High-speed wire rod controlled rolling: controlled heating temperature is 1000-1100℃, rolling start temperature is 980-1010℃, sizing temperature is 940-970℃, and spinning temperature is 890-910℃;

[0046] Stelmore blower cooling to obtain wire rod;

[0047] Spheroidizing and drawing: The spheroidizing temperature is 750-780℃, then furnace cooled to 400-430℃ and air cooled;

[0048] Quenching and tempering heat treatment.

[0049] Furthermore, in the method for manufacturing high hardenability and high uniformity bolt wire of the present invention, in the tempering heat treatment step, the quenching temperature is 850-870°C, oil cooling is performed after quenching, and the tempering temperature is 540-560°C, air cooling is performed after tempering.

[0050] The high hardenability and high uniformity bolt wire rod, wire material and manufacturing method thereof of the present invention have the following advantages and beneficial effects compared with the prior art:

[0051] The wire rod for bolts with high hardenability and high structural uniformity of the present invention reasonably utilizes Ni, Mo and B elements to improve the hardenability of the wire rod and the structural uniformity after modulation.

[0052] In some embodiments, the core tempered bainite content of the high hardenability and high microstructure uniformity bolt wire described in the present invention can reach more than 90%, and after tempering, its yield strength is ≥970MPa, tensile strength is ≥1075MPa, cross-sectional shrinkage is ≥40%, and the core-surface hardness difference is ≤20HV. Its hardenability reaches J1.5 of 56-58HRC, J5 of 55-58HRC, J11 of 54-57HRC, J15 of 51-54HRC, J20 of 48-51HRC, J25 of 43-47HRC, and J30 of 41-43HRC, which can effectively meet the manufacturing requirements of 10.9-grade industrial parts. DETAILED DESCRIPTION

[0053] The high hardenability and high uniformity bolt wire rod, wire material and manufacturing method thereof 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 undue limitation to the technical solution of the present invention.

[0054] Examples 1-5 and Comparative Examples 1-2

[0055] The high hardenability and high uniformity wire rods for bolts of Examples 1-5 and the comparative wire rods of Comparative Examples 1-2 were prepared by the following steps:

[0056] (1) Smelting and continuous casting: Smelting is carried out in an electric furnace or a converter, and then LF refining and VD vacuum degassing are used for refining outside the furnace to allow the refined slag to fully react with the inclusions in the steel.

[0057] In some embodiments, the VD vacuum degassing treatment time can be controlled to be more than 30 minutes to ensure that the gas elements in the molten steel are completely removed.

[0058] The molten steel is cast into large square billets with a cross-sectional size of 320 mm × 425 mm using a continuous casting machine. The chemical composition ratios of the square billets are shown in Tables 1-1 and 1-2 below. Argon gas can be used for protection during the casting process.

[0059] In some embodiments, the billet segregation can be controlled by adjusting the casting speed and soft reduction process. The overheat temperature during continuous casting can be controlled to 25-38°C, the soft reduction can be controlled to 20-25mm, and the casting speed can be controlled to 0.5-0.8m / min.

[0060] (2) Initial rolling: The large square billet obtained by continuous casting is initially rolled after high-temperature diffusion. The rolling temperature is 1000-1200℃ and rolled into small square billets of 142mm×142mm. The small square billets are tested for surface defects by magnetic particle inspection or ultrasonic inspection, and then finished by grinding wheel grinding and other finishing treatments before entering the heating furnace for high-speed wire finishing rolling.

[0061] (3) High-speed wire rod controlled rolling: the heating temperature is controlled to be 1000-1100℃, the rolling temperature is 980-1010℃, the sizing temperature is 940-970℃, the spinning temperature is 890-910℃, and the wire rod specification is Φ20-30mm.

[0062] In some more specific embodiments, the heating and holding time can be controlled to 1 to 2 hours to ensure uniform heating of the blank.

[0063] (4) Stelmore fan cooling: After the wire rod is rolled, it enters the Stelmore air cooling line for controlled cooling. The air volume of the Stelmore line fan is controlled to be 15-30% of the air volume of the F1-F5 fan and 0-30% of the air volume of the F6-F14 fan.

[0064] The high hardenability and high uniformity bolt wires of Examples 1-5 and the comparative wires of Comparative Examples 1-2 were prepared based on the wire rods obtained in the Examples and Comparative Examples by further following the steps below:

[0065] (5) Spheroidizing and drawing: Spheroidizing annealing is performed before cold heading to obtain uniform and fine spheroidized pearlite. The spheroidizing temperature is 750-780°C, then furnace cooled to 400-430°C and air cooled;

[0066] (6) Quenching and tempering heat treatment: quenching temperature is 850-870℃, oil cooling after quenching, tempering temperature is 540-560℃, air cooling after tempering.

[0067] It should be noted that the chemical element composition and related process design of the high hardenability and high uniformity bolt wire rods of Examples 1-5 all meet the design specification requirements of the present invention. However, the chemical element composition and related process design of the comparative wire rods of Comparative Examples 1-2 do not meet the design specification requirements of the present invention.

[0068] Tables 1-1 and 1-2 list the mass percentages of the chemical elements in the high hardenability and high uniformity wire rods for bolts of Examples 1-5 and the comparative wire rods of Comparative Examples 1-2.

[0069] Table 1-1. (wt%, the balance is Fe and other inevitable impurities except P, S, O, H and Ti)

[0070]

[0071]

[0072] Table 1-2. (wt%, the balance is Fe and other inevitable impurities except P, S, O, H and Ti)

[0073] serial number Cr+Mo+Ni / 3 Al / N P S O H Ti Example 1 1.40 6.11 0.005 0.008 0.0015 0.00010 0.0009 Example 2 1.26 3.00 0.006 0.009 0.0017 0.00015 0.0008 Example 3 1.27 13.33 0.006 0.008 0.0009 0.00012 0.0009 Example 4 1.38 7.25 0.005 0.006 0.0012 0.00019 0.0009 Example 5 1.35 6.80 0.008 0.007 0.0019 0.00020 0.0010 Example 6 1.22 7.62 0.007 0.008 0.0018 0.00013 0.0010 Comparative Example 1 1.05 5.83 0.005 0.009 0.0020 0.00018 0.0016 Comparative Example 2 1.25 6.44 0.007 0.007 0.0015 0.00013 0.0018

[0074] Table 2 lists the specific process parameters of the high hardenability and high uniformity bolt wire rods of Examples 1-5 and the comparative wire rods of Comparative Examples 1-2 in the manufacturing method and the process parameters of the subsequent wire rods.

[0075] Table 2-1.

[0076]

[0077] Table 2-2.

[0078]

[0079]

[0080] The high hardenability and high uniformity bolt wire rods obtained in Examples 1-5 and the comparative wire rods of Comparative Examples 1-2 were sampled respectively, and the microstructure of each example was observed using a metallographic microscope. The microstructure observation results are listed in Table 3 below.

[0081] Table 3 lists the microstructure observation results of the high hardenability and high uniformity wire rods for bolts of Examples 1-5 of the present invention and the comparative wire rods of Comparative Examples 1-2.

[0082] Table 3.

[0083] serial number microstructure Ferrite volume content (%) Example 1 Bainite + pearlite + ferrite 2.5 Example 2 Bainite + pearlite + ferrite 2.3 Example 3 Bainite + pearlite + ferrite 2.0 Example 4 Bainite + pearlite + ferrite 2.7 Example 5 Bainite + pearlite + ferrite 2.8 Example 6 Bainite + pearlite + ferrite 2.0 Comparative Example 1 Bainite + pearlite + ferrite 3.5 Comparative Example 2 Bainite + pearlite + ferrite 3.8

[0084] In addition, samples were taken from the high hardenability and high uniformity bolt wires of Examples 1-5 of the present invention and the comparative wires of Comparative Examples 1-2, and the microstructures of each example were observed using a metallographic microscope. The microstructure observation results are listed in Table 4 below.

[0085] Table 4 lists the microstructure observation results of the high hardenability and high uniformity bolt wires of Examples 1-5 of the present invention and the comparative wires of Comparative Examples 1-2.

[0086] Table 4.

[0087] serial number Surface microstructure Core microstructure Volume content of tempered bainite in core microstructure (%) Example 1 tempered troostite Tempered troostite + ferrite + bainite 93 Example 2 tempered troostite Tempered bainite + ferrite + bainite 95 Example 3 tempered troostite Tempered bainite + ferrite + bainite 97 Example 4 tempered troostite Tempered troostite + ferrite + bainite 96 Example 5 tempered troostite Tempered troostite + ferrite + bainite 95 Example 6 tempered troostite Tempered troostite + ferrite + bainite 98 Comparative Example 1 tempered troostite Tempered troostite + ferrite + bainite 90 Comparative Example 2 tempered troostite Tempered troostite + ferrite + bainite 90

[0088] In addition, samples were taken from the high hardenability and high uniformity bolt wires of Examples 1-5 and the comparative wires of Comparative Examples 1-2, and relevant mechanical property tests were performed on the wire samples of each Example and Comparative Example. The obtained mechanical property test results are listed in Tables 5-1 and 5-2. The relevant mechanical property test methods are as follows:

[0089] Tensile test: At room temperature, the tensile strength and area reduction of the high carbon steel hot-rolled wire rods of the embodiments and comparative examples were determined according to GB / T 228.1-2010 "Tensile testing of metallic materials - Part 1: Room temperature test methods".

[0090] Hardness testing method: The core and surface hardness of each embodiment and comparative example were tested according to GB / T 4340.1-2009 "Vickers hardness test for metallic materials - Part 1: Test method".

[0091] End quench hardness testing method: The end quench hardness of each embodiment and comparative example was tested according to GB / T 225-2006 "End quench test method for hardenability of steel (Jominy test)".

[0092] Tables 5-1 and 5-2 list the mechanical property test results of the high hardenability and high uniformity bolt wires of Examples 1-5 of the present invention and the comparative wires of Comparative Examples 1-2.

[0093] Table 5-1.

[0094]

[0095]

[0096] Table 5-2.

[0097]

[0098] As can be seen from Tables 5-1 and 5-2 above, the high-hardenability, high-uniformity bolt wires of Examples 1-5 of the present invention all have a yield strength greater than or equal to 995 MPa, a tensile strength greater than or equal to 1075 MPa, a reduction of area greater than or equal to 40%, and a core-to-surface hardness difference less than 20 HV. Furthermore, the hardenability J1.5 of the high-hardenability, high-uniformity bolt wires of Examples 1-5 ranges from 56.1 to 58 HRC, J11 ranges from 54 to 55.9 HRC, J15 ranges from 51.2 to 54 HRC, J20 ranges from 48 to 49.8 HRC, J25 ranges from 43.2 to 45.8 HRC, and J30 ranges from 41.4 to 43 HRC. This demonstrates that the high-hardenability, high-uniformity bolt wires of Examples 1-5 can effectively meet the demands of industrial parts manufacturing.

[0099] However, the chemical element composition and related process design of the comparative wire rod of Example 1-2 do not meet the requirements of the design specification of the present invention, resulting in its final mechanical properties not meeting its design requirements.

[0100] 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.

[0101] 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 therefrom that can be directly derived from or easily conceived by those skilled in the art based on the disclosure of the present invention are intended to fall within the scope of protection of the present invention.

Claims

1. A wire rod for bolts with high hardenability and high uniformity, comprising Fe and unavoidable impurities, characterized in that: It also contains the following chemical elements in the following mass percentages: C: 0.40~0.44%, Si: 0.25~0.35%, Mn: 0.60~0.80%, Cr: 1.0%~1.20%, Ni: 0.10~0.20%, Mo: 0.10~0.20%, Al: 0.015~0.040%, B: 0.0006~0.001%, N：0.003～0.005％。 2. The high hardenability and high uniformity wire rod for bolts according to claim 1, characterized in that: The mass percentage of its chemical elements is: C: 0.40~0.44%, Si: 0.25~0.35%, Mn: 0.60~0.80%, Cr: 1.0%~1.20%, Ni: 0.10~0.20%, Mo: 0.10~0.20%, Al: 0.015~0.040%, B: 0.0006~0.001%, N: 0.003-0.005%; the balance is Fe and unavoidable impurities.

3. The high hardenability and high uniformity wire rod for bolts according to claim 1 or 2, characterized in that: The mass percentage of each chemical element also meets the following requirement: Cr+Mo+Ni / 3≤1.40%.

4. The high hardenability and high uniformity wire rod for bolts according to claim 1 or 2, characterized in that: The mass percentage of each chemical element also meets the following requirement: Al / N≥3.

5. The high hardenability and high uniformity wire rod for bolts according to claim 1 or 2, characterized in that: Among the unavoidable impurities, P≤0.01%, S≤0.01%, O≤0.002%, H≤0.0002%, Ti≤0.001%.

6. The wire rod for bolts with high hardenability and high uniformity according to claim 1, wherein: Its microstructure is bainite + pearlite + a small amount of ferrite, and the volume content of ferrite does not exceed 3%.

7. A high hardenability and high uniformity bolt wire, characterized in that: The bolt is made of the wire rod with high hardenability and high uniformity as claimed in any one of claims 1 to 6.

8. The high hardenability and high uniformity bolt wire according to claim 7, characterized in that: Its surface microstructure is entirely tempered bainite, and the volume content of tempered bainite in its core microstructure exceeds 90%, with the rest being ferrite and bainite.

9. The high hardenability and high uniformity bolt wire according to claim 7, characterized in that: Its yield strength is ≥970MPa, tensile strength is ≥1075MPa, section shrinkage is ≥40%, core-surface hardness difference is ≤20HV; hardenability J1.5 is 56-58HRC, J5 is 55-58HRC, J11 is 54-57HRC, J15 is 51-54HRC, J20 is 48-51HRC, J25 is 43-47HRC, and J30 is 41-43HRC.

10. The method for manufacturing a wire rod for bolts with high hardenability and high uniformity according to any one of claims 1 to 6, characterized in that: It includes the steps of: smelting and continuous casting; Blooming; High-speed wire rod controlled rolling: controlled heating temperature is 1000-1100℃, rolling start temperature is 980-1010℃, sizing temperature is 940-970℃, and spinning temperature is 890-910℃; Stelmore fan cooling.

11. The method for manufacturing a wire rod for bolts with high hardenability and high uniformity according to claim 10, wherein: During the cooling process of the Stelmore fan, the air volume of the Stelmore line fan is controlled to be 15-30% of the air volume of the F1-F5 fans and 0-30% of the air volume of the F6-F14 fans.

12. The method for producing a high hardenability and high uniformity bolt wire according to any one of claims 7 to 9, wherein: It includes the steps of: smelting and continuous casting; Blooming; High-speed wire rod controlled rolling: controlled heating temperature is 1000-1100℃, rolling start temperature is 980-1010℃, sizing temperature is 940-970℃, and spinning temperature is 890-910℃; Stelmore blower cooling to obtain wire rod; Spheroidizing and drawing: The spheroidizing temperature is 750-780℃, then furnace cooled to 400-430℃ and air cooled; Quenching and tempering heat treatment.

13. The method for producing a high hardenability and high uniformity bolt wire according to claim 12, wherein: In the quenching and tempering heat treatment step, the quenching temperature is 850-870°C, oil cooling is performed after quenching, the tempering temperature is 540-560°C, and air cooling is performed after tempering.

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