High-strength bolt steel and preparation method thereof

Abstract

The invention discloses high-strength bolt steel and a preparation method thereof, and the high-strength bolt steel alloy comprises the following components in percentage by mass: 0.35%-0.45% of C, 0.03%-0.80% of O, 0.05%-1.20% of RE, 0.02%-0.70% of Si, 0.80%-1.20% of Cr, 0.05%-0.85% of Ti, 0.01%-0.05% of Nb, 0.02%-0.35% of V, 0.001%-0.1% of B, less than or equal to 0.005% of S, less than or equal to 0.015% of P and the balance of Fe. According to the high-strength bolt steel and the preparation method thereof, the obdurability and the hydrogen-induced delayed fracture resistance of the material are synchronously improved through dispersion strengthening of the high-number-density nanometer oxide, the high-strength bolt steel can be used for producing 15.8-grade high-strength bolts with the tensile strength being 1500 MPa or above, nanometer oxide particles serve as a dispersion strengthening phase and a hydrogen trap, and the high-strength bolt steel can be used for producing high-strength bolts with the tensile strength being 1500 MPa or above. While the strength and the toughness of the material are improved, the fatigue performance and the delayed fracture resistance of the material are greatly improved.

Description

Technical Field

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

[0002] Bolts are structural fasteners widely used in industrial engineering. In the steel structure industry, bolt connection is the second most widely used connection and fastening method after welding. Bolts can be classified into ordinary bolts and high-strength bolts according to their strength levels, with bolts of grade 8.8 and above being high-strength bolts. High-strength bolts are mainly applied in industries such as automobiles, aerospace, wind power, and construction machinery. With the increasing demand for higher stress design of structural components and the development of lightweighting, high-strength bolts are evolving towards higher strength levels.

[0003] Bolts are notched parts and usually bear static tensile loads, with high notch sensitivity. When the tensile strength of high-strength bolts reaches over 1200 MPa, the problems of fatigue failure and delayed fracture are very prominent, and delayed fracture or fatigue fracture is likely to occur at the notch concentration sites such as the transition between the rod and the head or the thread root. Therefore, high-strength bolt steel not only needs to have good cold heading performance, high tensile strength, relatively high plasticity and toughness, but also needs to have good resistance to delayed fracture and relatively high fatigue performance. The problem of delayed fracture has become one of the main factors hindering the development of high-strength bolt steel.

[0004] Introducing more hydrogen traps into steel is an effective way to solve the problem of delayed fracture. For example, the KNDS series of steel developed in Japan, the ADF series of steel developed in China, and the 42CrMoVNb-NJ steel, etc., have improved the resistance to delayed fracture through the dispersion precipitation of carbides, and successfully achieved the industrial production of high-strength bolts of grades 13.9 and 14.9. For bolt steels of higher strength levels, on the basis of improving the strength and toughness of the material, it is necessary to further optimize the resistance to delayed fracture of the bolt steel. In Patent CN107604243A, by adding microalloying elements Ti and Nb to 42CrMo steel, they combine with C and N elements to form carbonitride particles to form hydrogen traps, thereby enhancing the resistance to delayed fracture of the material. In Patent CN115404399A, through the optimized design of the V content, it reacts with C and N elements in the steel to precipitate vanadium-containing carbonitrides with a size of 5-50 nm, improving the resistance to delayed fracture of the material. In Patent CN111218618A, by increasing the contents of elements such as Cr and Ni, and adding elements such as Ti and Al, dispersed metal intermetallic compound hardening phases such as Ni3Al, Ni3Ti, and Ni3Mo are formed, and a hydrogen embrittlement-resistant and high-strength and tough stainless steel is developed. In Patent CN110423954A, by increasing the Cu element content, it promotes precipitation and induces the precipitation of carbides of elements such as Mo, V, and Nb, enhancing its hydrogen trap effect and inhibiting crack propagation. In Patent CN114058974A, alloying elements V, Nb, Ti, and B are added simultaneously to generate dispersed carbonitrides to refine austenite grains, improving the resistance to hydrogen-induced delayed fracture while increasing strength and toughness. In Patent CN116926410A, by optimizing the contents and ratios of elements C, Si, Mn, Ni, Cr, and Mo in the steel, and through the corresponding preparation process, a 1700 MPa high-strength bolt steel is obtained, but the hydrogen-induced delayed fracture resistance of this material is not mentioned. Patents CN115216695A, CN115094337A, and CN115216696A respectively disclose alloy steels of grades 16.9, 18.8, and 20.8, achieving high strength and taking into account the yield ratio through the synergistic effect of elements, but the hydrogen-induced delayed fracture resistance of this material is not mentioned. Patent CN110983199A improves the low-temperature performance of high-strength bolt steel by adding rare earth elements to the steel, and at the same time reduces the contents of alloying elements Ni and Cr, saving costs, but the action mode of rare earth elements and their influence on the hydrogen-induced delayed fracture resistance are not mentioned.

[0005] In summary, regarding the core problem of delayed fracture that hinders the development of high-strength bolt steel above grade 12.9, some research has made progress. However, all existing technologies use carbide or carbonitride precipitation phases as hydrogen traps to inhibit delayed fracture problems. The precipitation phases are relatively large in size and low in number density, so their ability as hydrogen traps is limited. Moreover, the stability of carbides / carbonitrides themselves during long-term service is difficult to guarantee. When the particles grow, their shapes are irregular, and stress concentration at the interfaces easily leads to crack initiation, which may cause a decline in the fatigue performance of the material. Nano-oxides have a spherical and regular shape and excellent stability. They are dispersed in the steel with a high number density as hydrogen traps, which can significantly improve the delayed fracture resistance of the material. However, in the existing technologies and published literature, high-strength bolt steel strengthened by nano-oxide particles has not been found. Summary of the Invention

[0006] In view of the above-mentioned defects of the existing technology, the technical problem to be solved by the present invention is that existing high-strength bolt steels all use carbide or carbonitride precipitation phases as hydrogen traps to inhibit delayed fracture problems. The precipitation phases are relatively large in size and low in number density, so their ability as hydrogen traps is limited. Moreover, the stability of carbides / carbonitrides themselves during long-term service is difficult to guarantee. When the particles grow, their shapes are irregular, and stress concentration at the interfaces easily leads to crack initiation, which may cause a decline in the fatigue performance of the material, etc. The present invention provides a high-strength bolt steel and a preparation method thereof. Through composition and process design, the combination of element V with O, RE, and Si forms a core-shell structure, which promotes the uniform distribution of nano-oxides and inhibits their growth. The high number density of nano-oxides dispersed strengthening simultaneously improves the strength, toughness, and hydrogen-induced delayed fracture resistance of the material, and can be used to produce 15.8-grade high-strength bolts with a tensile strength of more than 1500 MPa. Using nano-oxide particles as the dispersed strengthening phase and hydrogen traps, while improving the strength and toughness of the material, it significantly improves the fatigue performance and delayed fracture resistance of the material.

[0007] To achieve the above object, the present invention provides a high-strength bolt steel. In this alloy, the percentages of each component by total mass are as follows: C 0.35% - 0.45%, O 0.03 - 0.80%, RE 0.05 - 1.20%, Si 0.02% - 0.70%, Cr 0.80% - 1.20%, Ti 0.05% - 0.85%, Nb 0.01% - 0.05%, V 0.02 - 0.35%, B 0.001% - 0.1%, S ≤ 0.005%, P ≤ 0.015%, and the balance is Fe.

[0008] Further, the oxygen element O content in the bolt steel is 300 - 8000 ppm, the rare earth element RE content is 500 - 12000 ppm, and the O / (RE + Ti + Si + V) component ratio is 1:(1 - 8). O and RE combine with one or several of Ti, Si, and V to form nano-oxide particles with an average particle size of less than 10 nm and a number density of not less than 2×10 23 m -3 , and the nano-oxides are uniformly and dispersedly distributed in the steel matrix.

[0009] Further, the rare earth elements include one or more of lanthanum La, yttrium Y, cerium Ce, gadolinium Gd, erbium Er, neodymium Nd, praseodymium Pr, terbium Tb, samarium Sm, dysprosium Dy, or scandium Sc elements.

[0010] In a preferred embodiment of the present invention, a method for preparing high-strength bolt steel is provided, including the following steps:

[0011] Mechanically alloying Fe, RE, Ti, V metal powders and oxide powders according to the ratio in a high-purity argon protective atmosphere to prepare an oxygen supersaturated precursor powder;

[0012] Adding the oxygen supersaturated precursor powder to the continuous casting master alloy melt to obtain a billet that meets the composition design requirements;

[0013] Hot-rolling or forging the billet to obtain a hot-rolled / forged steel billet;

[0014] Performing solution heat treatment on the hot-rolled / forged steel billet, and performing water cooling after solution heat treatment to obtain a solution alloy;

[0015] Heating and holding the solution alloy after water cooling, and then performing oil cooling;

[0016] Re-heating and holding the steel billet, and then performing air cooling to obtain the final high-strength threaded steel.

[0017] Further, mechanically alloying Fe, RE, Ti, V metal powders and oxide powders according to the ratio in a high-purity argon protective atmosphere to prepare an oxygen supersaturated precursor powder, specifically, mechanically alloying Fe, RE, Ti, V metal powders and oxide powders according to the ratio in a high-purity argon protective atmosphere;

[0018] Among them, the percentages of each raw material component in the total mass of the precursor powder are: RE 0.1 - 10.0%, Ti + V in total 0.1 - 10.0%, oxide powder 0.1 - 20.0%, and the balance is Fe; the ball milling medium is ceramic balls with a diameter of 5 - 10 mm, the ball-to-material ratio is 5:1 - 50:1, and the ball milling time is 8 - 72 hours.

[0019] Further, the oxide powder includes SiO 2 , TiO2 , V 2 O 3 One or more of the following.

[0020] Furthermore, the oxygen supersaturated precursor powder is added to the continuous casting master alloy melt to obtain a billet that meets the requirements of the composition design. The master alloy composition is C 0.35% - 0.45%, Cr 0.80% - 1.20%, Nb 0.01% - 0.05%, V 0.02 - 0.30%, B 0.001% - 0.1%, S ≤ 0.005%, P ≤ 0.015%, and the balance is Fe; when the oxygen supersaturated precursor powder is introduced, the temperature of the master alloy melt is 1570 - 1620 °C, and the weight percentage of the oxygen supersaturated precursor powder to the master alloy melt is 1 / (10 - 100).

[0021] Furthermore, the billet is hot-rolled or forged. The starting temperature of the hot rolling / forging is controlled at 1150 ± 20 °C, and the hot rolling / forging deformation is 50 - 90% to obtain a hot-rolled / forged steel billet.

[0022] Furthermore, the hot-rolled / forged steel billet is solution heat-treated at 900 - 950 °C. The holding time of the solution heat treatment is 60 - 120 min, and after the solution heat treatment, it is water-cooled to obtain a solution alloy.

[0023] Furthermore, the solution alloy after water cooling is heated to 850 ± 10 °C, held for 20 - 60 min, and oil-cooled; the steel billet is reheated to 450 ± 10 °C, held for 120 - 180 min, and air-cooled to obtain the final high-strength threaded steel.

[0024] Technical Effects

[0025] The high-strength bolt steel and its preparation method provided by the present invention are based on the characteristic that there is a high affinity between the dissolved oxygen and the dissolved rare earth elements in the steel. By introducing the mechanically alloyed precursor powder containing supersaturated dissolved oxygen and supersaturated dissolved rare earth elements into the master alloy melt, O, RE, Ti, Si, and V in the solidification structure combine and precipitate in solid phase to form nano-oxide particles, realizing a high number density of uniformly dispersed nano-oxide particles in the steel. The average particle size is less than 10 nm, and the number density is greater than 2×10 23 m -3 . The nano-oxide particles have excellent stability, can pin dislocations and grain boundaries, reduce the austenite grain size, and promote the formation of a fine tempered sorbite structure; at the same time, the high number density of nano-oxides forms excellent hydrogen traps and reduces the element diffusion rate, improving the thermal stability of the structure and the corrosion resistance of the material.

[0026] Based on a new material design concept, the high-strength bolt steel provided by the present invention solves the problems of decreased fatigue performance and serious tendency of delayed fracture in high-strength bolt steel through the method of nano-oxide dispersion strengthening. Its tensile strength at room temperature is 1550 - 1750 MPa, the yield strength is 1230 - 1460 MPa, and it has a good yield ratio (about 0.8); the constant load delayed fracture strength ratio is ≥0.82, and it has excellent resistance to delayed fracture; at the same time, it has high fatigue performance, good corrosion resistance and thermal stability. This high-strength bolt steel is used to produce high-strength bolts of grade 15.8 and above for use in complex environments, which can effectively improve the service life, safety and reliability of the bolts, and has significant economic benefits.

[0027] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, features and effects of the present invention. Description of the Drawings

[0028] Figure 1 is a process flow chart for the preparation of high-strength bolt steel according to a preferred embodiment of the present invention;

[0029] Figure 2 is a high-resolution transmission electron microscope image of nano-oxides in high-strength bolt steel according to a preferred embodiment (Embodiment 2) of the present invention. Detailed Embodiments

[0030] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0031] In the following description, specific details such as specific internal programs and technologies are presented for the purpose of illustration rather than limitation, so as to thoroughly understand the embodiments of the present invention. However, those skilled in the art should clearly understand that the present invention can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits and methods are omitted to avoid unnecessary details from interfering with the description of the present invention.

[0032] An embodiment of the present invention provides a high-strength bolt steel. In this alloy, the percentages of each component in the total mass are as follows: C 0.35% - 0.45%, O 0.03 - 0.80%, RE 0.05 - 1.20%, Si 0.02% - 0.70%, Cr 0.80% - 1.20%, Ti 0.05% - 0.85%, Nb 0.01% - 0.05%, V 0.02 - 0.35%, B 0.001% - 0.1%, S ≤ 0.005%, P ≤ 0.015%, and the balance is Fe.

[0033] Among them, the content of oxygen element O in the bolt steel is 300 - 8000 ppm, the content of rare earth element RE is 500 - 12000 ppm, and the component ratio of O / (RE + Ti + Si + V) is 1:(1 - 8). O and RE combine with one or several of Ti, Si, and V to form nano-oxide particles with an average particle size less than 10 nm, and the number density is not less than 2×10 23 m -3 , and the nano-oxides are uniformly and dispersedly distributed in the steel matrix.

[0034] The rare earth elements include one or more of lanthanum La, yttrium Y, cerium Ce, gadolinium Gd, erbium Er, neodymium Nd, praseodymium Pr, terbium Tb, samarium Sm, dysprosium Dy, or scandium Sc elements.

[0035] The following will use specific examples to illustrate a high-strength bolt steel of the present invention. Unless otherwise specified, the ratios of the components in the following examples and comparative examples of the present invention are all mass ratios.

[0036] Examples 1 - 6: High-strength bolt steels with actual components meeting the design requirements, and the component mass percentages are shown in Table 1.

[0037] Comparative Examples 1 - 3: High-strength bolt steels with actual components not meeting the design requirements, and the component mass percentages are shown in Table 1.

[0038] The main difference between each example and comparative example is the component difference, and the component difference mainly comes from the component difference of the oxygen supersaturated precursor powder raw material (Table 2) and the component difference of the intermediate alloy melt (Table 3). The balance not shown in Tables 1 - 3 is Fe and inevitable impurities. S and P are harmful impurity elements, and they all meet the design requirements and have the same content in each example and comparative example. In the following examples and comparative examples, the RE element selects Y. The above other rare earth elements can replace Y, and under the condition that other components remain unchanged, the other rare earth elements can achieve the same effect as Y after adjusting the element content.

[0039] Table 1 Chemical compositions of the steels in the examples and comparative examples of the present invention (wt.%)

[0040] C O Y Si Cr Ti Nb V B Example 1 0.36 0.05 0.08 0.04 0.90 0.15 0.03 0.12 0.001 Example 2 0.36 0.20 0.30 0.18 0.90 0.15 0.03 0.12 0.001 Example 3 0.38 0.08 0.12 0.07 0.90 0.15 0.03 0.12 0.001 Example 4 0.38 0.18 0.23 0.16 0.90 0.15 0.03 0.12 0.001 Example 5 0.42 0.07 0.11 0.06 0.90 0.15 0.03 0.12 0.001 Example 6 0.42 0.19 0.35 0.16 0.90 0.15 0.03 0.12 0.001 Comparative Example 1 0.31 0.02 0.03 0.01 0.90 0.15 0.03 0.12 0.001 Comparative Example 2 0.31 0.90 1.30 0.82 0.90 0.15 0.03 0.12 0.001 Comparative Example 3 0.47 0.02 0.03 0.01 0.90 0.15 0.03 0.12 0.001

[0041] Table 2 Composition of oxygen supersaturated precursor powder raw materials in the examples and comparative examples of the present invention (wt.%)

[0042]

[0043]

[0044] Table 3 Composition of master alloys in the examples and comparative examples of the present invention (wt.%)

[0045] C Cr Nb V B Example 1 0.39 0.90 0.03 0.12 0.001 Example 2 0.39 0.90 0.03 0.12 0.001 Example 3 0.41 0.90 0.03 0.12 0.001 Example 4 0.41 0.90 0.03 0.12 0.001 Example 5 0.43 0.90 0.03 0.12 0.001 Example 6 0.43 0.90 0.03 0.12 0.001 Comparative Example 1 0.33 0.90 0.03 0.12 0.001 Comparative Example 2 0.33 0.90 0.03 0.12 0.001 Comparative Example 3 0.49 0.90 0.03 0.12 0.001

[0046] As Figure 1 shown, the above examples and comparative examples are all produced according to the following process flow:

[0047] S1. According to the ratio in Table 2, mechanically alloyize Fe, Y, Ti, V metal powders and SiO 2 oxide powder under the protection of high-purity argon atmosphere; the ball milling medium is Al 2 O 3 ceramic balls with a diameter of 5 mm, the ball-to-material ratio is 15:1, and the ball milling time is 36 hours.

[0048] S2. Add the oxygen supersaturated precursor powder prepared in S1 to the continuous casting master alloy melt to obtain a billet that meets the composition design requirements; when the oxygen supersaturated precursor powder is introduced, the temperature of the master alloy melt is 1580 ± 10 °C, the retention time is 5 - 10 min, and the weight percentage of the oxygen supersaturated precursor powder to the master alloy melt is 1 / 20; this step can also be replaced by die casting.

[0049] The master alloy is prepared by smelting in an electric furnace followed by refining in an LF furnace and RH vacuum degassing. Specifically: Weigh the materials according to the master alloy composition and conduct smelting in an electric furnace, controlling the end impurities at S≤0.010% and P≤0.015%; slag blocking during tapping, adding deoxidizers and alloys, and after tapping is completed, evenly sprinkle an appropriate amount of rare earth particles on the steel slag surface according to the amount of slag flowing down. The LF furnace refining is specifically as follows: Bottom blowing argon in the ladle, adding pre-melted refining slag and lime to make slag, with the basicity R being 3 - 6, and according to the composition analysis results in front of the LF furnace, add alloys during the early and middle stages of refining to adjust the contents of Cr, V, Nb, and B. The RH vacuum degassing is specifically as follows: If the vacuum degree ≤100Pa, then maintain the vacuum in the early stage for ≥10 minutes; if 100Pa < vacuum degree ≤200Pa, then maintain the vacuum in the early stage for ≥15 minutes; maintain the vacuum in the later stage for ≥10 minutes. According to the composition analysis results in the early stage of vacuum, if component adjustment is required in the middle stage, then ensure a vacuum holding time of more than 5 minutes after adjustment. After breaking the vacuum, conduct rare earth wire feeding treatment. Conduct soft blowing argon treatment before tapping out, with the soft blowing time ≥10 minutes. Adopt full-process protected casting, use a protective sleeve + argon seal between the ladle and the tundish, and use an immersion nozzle between the tundish and the mold. Introduce oxygen supersaturated precursor powder into the molten steel through the tundish, and achieve uniform dispersion of the oxygen supersaturated precursor powder in the way of combining end electromagnetic stirring and light and heavy reduction. During the casting process, the liquid level, drawing speed, and superheat are stable to obtain a cast slab.

[0050] S3. Hot roll the cast slab, control the starting temperature of hot rolling at 1150±20°C, keep it warm for 1.5 hours, and the hot rolling deformation amount is 80% to obtain a hot rolled steel billet.

[0051] S4. Solution heat treat the hot rolled steel billet at 925°C, with the holding time of solution heat treatment being 80min, and water cool after solution heat treatment to obtain a solution alloy.

[0052] S5. Heat the water-cooled solution alloy to 850±10°C, keep it warm for 40min, and oil cool.

[0053] S6. Reheat the steel billet to 450±10°C, keep it warm for 150min, and air cool to obtain the final high-strength bolt steel.

[0054] Conduct transmission electron microscopy microanalysis on the bolt steels produced in the above-mentioned examples and comparative examples, count the size and number density of nano-oxides, and the analysis results are shown in Table 4.

[0055] In all examples, the average size of nano-oxide particles is less than 10nm, and the number density is greater than 2×10 23 m -3 . Especially when the RE / O mass ratio is about 1.5:1, the number density and size of the particles match well. For example, the high-resolution transmission electron microscopy image of nano-oxides in the microstructure of Example 2 is as Figure 2As shown, there are a large number of well-crystallized nano-oxide particles with a size ranging from 3 to 5 nm in the microstructure. The average size is 3.5 nm, and the number density reaches 9.6×10 23 m -3 . In the comparative example, when the contents of O, RE, and Si are not within the composition design range, the distribution parameters of the nano-oxides cannot reach the above values.

[0056] Samples were cut from the bolt steels produced in the above examples and comparative examples and processed into standard specimens for tensile, impact, fatigue, and stress corrosion cracking resistance tests. The test results are shown in Table 5.

[0057] The strength of all examples meets the requirements of tensile strength ≥ 1550 MPa, elongation after fracture ≥ 13%, yield ratio ≤ 0.83, impact energy at -20°C ≥ 45 J, and constant load stress corrosion cracking strength ratio ≥ 0.82, showing good strength and toughness and stress corrosion cracking resistance. Within the designed composition range, the higher the C content, the higher the tensile strength of the material, while the elongation after fracture and impact performance decrease. When the C content is the same, the higher the contents of O and RE, the higher the tensile strength of the material, while the elongation after fracture and impact energy slightly decrease. In the comparative example, when the contents of O, RE, and Si are not within the composition design range, obvious changes occur in the tensile strength, elongation after fracture, yield ratio, impact energy, and stress corrosion cracking resistance of the material, and the parameter values of the examples cannot be reached.

[0058] Table 4 Dimensions and number densities of nano-oxides in the examples and comparative examples of the present invention

[0059]

[0060]

[0061] Table 5 Dimensions and number densities of nano-oxides in the examples and comparative examples of the present invention

[0062]

[0063] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative efforts. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field of the present invention through logical analysis, reasoning, or limited experiments based on the concept of the present invention on the basis of the prior art should fall within the protection scope determined by the claims.

Claims

1. A high-strength bolt steel, characterized in that: The percentage of each component in the alloy in terms of total mass is: C 0.35%-0.45%, O 0.03%-0.80%, RE 0.05%-1.20%, Si 0.02%-0.70%, Cr 0.80%-1.20%, Ti 0.05%-0.85%, Nb 0.01%-0.05%, V 0.02%-0.35%, B 0.001%-0.1%, S≤0.005%, P≤0.015%, and the balance is Fe.

2. A high-strength bolt steel as claimed in claim 1, characterized in that: The bolt steel has an oxygen content of 300 to 8000 ppm, a rare earth element RE content of 500 to 12000 ppm, and an O / (RE+Ti+Si+V) composition ratio of 1:(1 to 8). O and RE are combined with one or more of Ti, Si, and V to form nano-oxide particles with an average particle size of less than 10 nm and a number density of not less than 2×10 23 m -3 , nano-oxides are evenly dispersed in the steel matrix.

3. A high-strength bolt steel as claimed in claim 2, characterized in that: The rare earth elements include one or more of lanthanum La, yttrium Y, cerium Ce, gadolinium Gd, erbium Er, neodymium Nd, praseodymium Pr, terbium Tb, samarium Sm, dysprosium Dy or scandium Sc.

4. A method for preparing the high-strength bolt steel according to any one of claims 1 to 3, characterized in that: The following steps are involved: Fe, RE, Ti, V metal powders and oxide powders are mechanically alloyed in a high-purity argon protective atmosphere according to the proportions to prepare oxygen-supersaturated precursor powders; The oxygen supersaturated precursor powder is added to the continuous casting master alloy melt to obtain a casting billet that meets the composition design requirements; Hot rolling or forging the cast billet to obtain a hot rolled / forged billet; The hot-rolled / forged steel billet is subjected to a solution heat treatment, and then water-cooled after the solution heat treatment to obtain a solid solution alloy; The water-cooled solid solution alloy is heated, kept warm, and then oil-cooled; The billet is reheated, kept warm, and then air-cooled to obtain the final high-strength rebar.

5. The method for preparing high-strength bolt steel according to claim 4, characterized in that: Mechanically alloying Fe, RE, Ti, V metal powders and oxide powders according to a ratio in a high-purity argon protective atmosphere to prepare an oxygen-supersaturated precursor powder, specifically, mechanically alloying Fe, RE, Ti, V metal powders and oxide powders according to a ratio in a high-purity argon protective atmosphere; The percentage of each raw material component in the total mass of the precursor powder is: RE 0.1-10.0%, Ti+V total 0.1-10.0%, oxide powder 0.1-20.0%, and the balance is Fe; the ball milling medium is a ceramic ball with a diameter of 5-10 mm, the ball-to-material ratio is 5:1-50:1, and the ball milling time is 8-72 hours.

6. The method for preparing high-strength bolt steel according to claim 5, characterized in that: The oxide powder includes one or more of SiO2, TiO2, and V2O3.

7. The method for preparing high-strength bolt steel according to claim 4, characterized in that: The oxygen supersaturated precursor powder is added to a continuous casting master alloy melt to obtain a casting billet that meets the composition design requirements. The master alloy composition is C0.35%-0.45%, Cr 0.80%-1.20%, Nb 0.01%-0.05%, V 0.02%-0.30%, B0.001%-0.1%, S≤0.005%, P≤0.015%, and the balance is Fe. When the oxygen supersaturated precursor powder is introduced, the temperature of the master alloy melt is 1570-1620°C, and the weight percentage of the oxygen supersaturated precursor powder to the master alloy melt is 1 / (10-100).

8. The method for preparing high-strength bolt steel according to claim 4, characterized in that: The cast billet is hot rolled or forged, the hot rolling / forging starting temperature is controlled at 1150±20° C., and the hot rolling / forging deformation amount is 50-90%, so as to obtain a hot rolled / forged steel billet.

9. The method for preparing high-strength bolt steel according to claim 4, characterized in that: The hot rolled / forged steel billet is subjected to a solid solution heat treatment at 900-950° C., the holding time of the solid solution heat treatment is 60-120 minutes, and the solid solution heat treatment is followed by water cooling to obtain a solid solution alloy.

10. The method for preparing high-strength bolt steel according to claim 4, characterized in that: The solid solution alloy after water cooling is heated to 850±10℃, kept warm for 20-60min, and oil-cooled; the steel billet is reheated to 450±10℃, kept warm for 120-180min, and air-cooled to obtain the final high-strength rebar.

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