Mn-Si-Cr-Ni bainite wire rod for steel strand and preparation method of Mn-Si-Cr-Ni bainite wire rod

Abstract

The invention relates to a Mn-Si-Cr-Ni bainite wire rod for a steel strand and a preparation method of the Mn-Si-Cr-Ni bainite wire rod, belongs to the technical field of wire rod steel, and is used for solving at least one of the problems that an existing wire rod is insufficient in strength and plasticity matching, prone to drawing wire breakage, unqualified in torsion and the like. The invention discloses a Mn-Si-Cr-Ni bainite wire rod for a steel strand. The Mn-Si-Cr-Ni bainite wire rod comprises the following chemical components in percentage by mass: 0.30 to 0.42 percent of C, 1.10 to 1.20 percent of Si, 1.25 to 1.45 percent of Mn, 0.5 to 0.7 percent of Cr, 0.25 to 0.45 percent of Ni, less than or equal to 0.008 percent of S, less than or equal to 0.015 percent of P and the balance of Fe and inevitable impurities. According to the steel wire rod, by accurately controlling the mass percent of the main elements such as C, Si, Mn, Cr and Ni, the steel wire rod has high tensile strength and can also keep good percentage reduction of area and uniform elongation at the same time, that is, when the tensile strength is larger than or equal to 1538 MPa, the percentage reduction of area is larger than or equal to 60%, and the uniform elongation is larger than or equal to 8.5%.

Description

Technical Field

[0001] This invention relates to the field of wire rod technology, and more particularly to a Mn-Si-Cr-Ni bainitic wire rod for steel strand and its preparation method. Background Technology

[0002] Wire rod is a widely used and essential industrial product, indispensable in industries such as construction and bridge building. To ensure stability and safety, wire rod typically requires high tensile strength and reduction of area, while also maintaining good machinability for subsequent stable industrial production processes such as drawing. Traditional wire rod microstructure is mostly pearlitic, with a high C-Mn-Si system composition. Strength is improved by refining the pearlite lamellar spacing through adjustments to carbon content and microalloying element content, and further enhanced by salt bath or tempering treatments to improve ductility and toughness, achieving a combined improvement in strength and plasticity. However, adjusting carbon content alone has reached a bottleneck in improving the mechanical properties of wire rod. Increasing the microalloying element content can further improve tensile strength, but this significantly sacrifices material plasticity, failing to yield high-strength wire rod steel with a good balance of strength and plasticity. Summary of the Invention

[0003] In view of the above analysis, the present invention aims to provide a Mn-Si-Cr-Ni bainitic wire rod for steel strand and its preparation method, so as to solve at least one of the following problems: insufficient strength-plasticity matching of existing wire rods, easy occurrence of wire breakage during drawing, and unqualified torsion.

[0004] In a first aspect, the present invention provides a Mn-Si-Cr-Ni bainitic wire rod for steel strand, wherein the chemical composition of the wire rod comprises, by mass percentage: C 0.30-0.42%, Si 1.10-1.20%, Mn 1.25-1.45%, Cr 0.5-0.7%, Ni 0.25-0.45%, S≤0.008%, P≤0.015%, with the remainder being Fe and unavoidable impurities.

[0005] Furthermore, the chemical composition of the wire rod also satisfies the following conditions: when C ≥ 0.36%, Ni ≤ 0.35%, and when C < 0.36%, Ni > 0.35%.

[0006] Furthermore, the diameter of the wire rod is 6–14 mm.

[0007] Secondly, the present invention provides a method for preparing the above-mentioned wire rod, comprising the following steps:

[0008] S1: Based on the chemical composition of the wire rod, the raw materials are prepared, smelted, and continuously cast to obtain a continuously cast billet;

[0009] S2: Rolling: The continuously cast billet is heated and rolled to obtain steel.

[0010] S3: Wire drawing: The steel is wired to obtain the initial wire rod;

[0011] S4: The initial wire rod is subjected to a salt bath treatment;

[0012] S5: Tempering treatment: The wire rod after salt bath treatment is tempered to obtain the wire rod.

[0013] Furthermore, in S1, the continuously cast billet is a square billet with dimensions of 180-190mm × 220-240mm.

[0014] Furthermore, in S2, the heating temperature is 1050–1100°C, and the holding time is 6–8 hours.

[0015] Furthermore, in S2, the rolling process includes roughing and finishing, wherein the initial rolling temperature of the roughing is 1000–1030°C, the initial rolling temperature of the finishing is 800–900°C, and the final rolling temperature of the finishing is ≥860°C.

[0016] Furthermore, in S3, when C in the wire rod is ≥0.36%, the wire rod temperature is 780–800℃, and when C in the wire rod is <0.36%, the wire rod temperature is 840–860℃.

[0017] Furthermore, in S4, the temperature of the salt bath treatment is 360–370°C, and the salt bath time is 5–10 minutes.

[0018] Furthermore, in S4, the tempering temperature is 300–400°C, and the tempering time is 30–45 min.

[0019] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0020] 1. The wire rod of the present invention achieves high tensile strength while maintaining good reduction of area and uniform elongation by precisely controlling the mass percentage of major elements such as C, Si, Mn, Cr and Ni. That is, when the tensile strength is ≥1538MPa, the reduction of area is ≥60% and the uniform elongation is ≥8.5%.

[0021] 2. The addition of elements such as C and Ni can improve the stability of retained austenite, enabling wire rods to achieve both high strength and high plasticity. However, high C and Ni contents significantly increase the time required for bainitic phase transformation, which is detrimental to improving production efficiency. In this invention, considering both austenite stability and production efficiency, a matching design was implemented for C and Ni: when C ≥ 0.36%, Ni ≤ 0.35%; when C < 0.36%, Ni > 0.35%.

[0022] 3. The wire rod of this invention, through composition design and control of process parameters such as rolling, wire drawing, salt bath treatment, and tempering, obtains a portion of highly stable retained austenite while refining the bainitic and martensitic microstructure. Both the refined microstructure and the presence of retained austenite contribute to achieving high plasticity while maintaining high strength.

[0023] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0024] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0025] Figure 1 The X-ray diffraction pattern of the wire rod in Embodiment 1 of the present invention;

[0026] Figure 2 The microstructure of the wire rod prepared in Example 2 of this invention;

[0027] Figure 3 The wire rod stretching curve prepared in Example 3 of this invention;

[0028] Figure 4 The microstructure of the wire rod prepared in Comparative Example 1 of this invention;

[0029] Figure 5 This is a microstructure diagram of the wire rod prepared in Comparative Example 2 of the present invention;

[0030] Figure 6 This is a microstructure diagram of the wire rod prepared in Comparative Example 5 of the present invention. Detailed Implementation

[0031] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0032] A specific embodiment of the present invention discloses a Mn-Si-Cr-Ni bainitic wire rod for steel strand, wherein the chemical composition of the wire rod comprises, by mass percentage: C 0.30-0.42%, Si 1.10-1.20%, Mn 1.25-1.45%, Cr 0.5-0.7%, Ni 0.25-0.45%, S≤0.008%, P≤0.015%, with the remainder being Fe and unavoidable impurities.

[0033] Compared with the prior art, the wire rod of the present invention, by precisely controlling the mass percentage of major elements such as C, Si, Mn, Cr, and Ni, enables the wire rod to maintain good reduction of area and uniform elongation while possessing high tensile strength.

[0034] The reasons for limiting the composition of the Mn-Si-Cr-Ni bainitic wire rod used for steel strand in this invention will be explained. Hereinafter, only the percentage of mass in the composition will be used.

[0035] C: To ensure the strength of the wire rod and appropriately improve the stability of austenite. Unlike the high-carbon design in pearlitic wire rod, the carbon content here is lower, aiming to obtain a microstructure dominated by bainite and martensite, resulting in higher strength. On the other hand, the appropriate carbon content improves the stability of austenite, allowing the wire rod to retain a certain amount of untransformed austenite after salt bath treatment and remain stable at room temperature. In this invention, the C content ranges from 0.30% to 0.42%, for example, 0.30%, 0.31%, 0.32%, 0.33%, 0.34%, 0.35%, 0.36%, 0.37%, 0.38%, 0.39%, 0.40%, 0.41%, and 0.42%.

[0036] Si: A non-carbide-forming element. The addition of Si can suppress the precipitation of cementite during salt bath and tempering processes. In this invention, the Si content ranges from 1.10% to 1.20%, for example, 1.10%, 1.11%, 1.12%, 1.13%, 1.14%, 1.15%, 1.16%, 1.17%, 1.18%, 1.19%, and 1.2%.

[0037] Mn and Cr: delay the high-temperature ferrite transformation, ensuring that no high-temperature ferrite phase transformation occurs during the cooling of the wire rod to the salt bath; lower the martensitic transformation start temperature, allowing the salt bath to be carried out at a lower temperature, resulting in a fine bainite structure. In this invention, the Mn and Cr contents range from 1.25% to 1.45% (e.g., 1.25%, 1.26%, 1.27%, 1.28%, 1.29%, 1.30%, 1.31%, 1.32%, 1.33%, 1.34%, 1.35%, 1.36%, 1.37%, 1.38%, 1.39%, 1.40%, 1.41%, 1.42%, 1.43%, 1.44%) and 0.5% to 0.7% (e.g., 0.5%, 0.52%, 0.54%, 0.56%, 0.58%, 0.60%, 0.62%, 0.64%, 0.66%, 0.68%, 0.7%).

[0038] Ni improves austenite stability, similar to some of the effects of C, allowing the wire rod to retain a certain amount of untransformed austenite after salt bath treatment and remain stable at room temperature. Excessive Ni addition increases the time required for bainitic transformation, meaning that a larger amount of bainite cannot be obtained within a shorter salt bath treatment time. Especially when the C and Ni contents are high, the bainitic transformation time is significantly increased, which is detrimental to improving production efficiency. In this invention, considering both austenite stability and production efficiency, the Ni content ranges from 0.25% to 0.45%, for example, 0.25%, 0.27%, 0.29%, 0.31%, 0.33%, 0.35%, 0.37%, 0.39%, 0.41%, 0.43%, and 0.45%.

[0039] High P and S contents are detrimental to plasticity improvement. Therefore, without significantly increasing costs, P and S contents should be controlled to a minimum. In this invention, the P and S contents are controlled to be P≤0.015% and S≤0.008%, respectively.

[0040] Specifically, the chemical composition of the wire rod also satisfies the following conditions: when C ≥ 0.36%, Ni ≤ 0.35%, and when C < 0.36%, Ni > 0.35%.

[0041] It should be noted that the addition of C and Ni can improve the stability of retained austenite, enabling the wire rod to achieve both high strength and high plasticity. However, high C and Ni contents will significantly increase the time required for bainitic phase transformation, which is detrimental to improving production efficiency. In this invention, considering both austenite stability and production efficiency, a matching design was implemented for C and Ni: when C ≥ 0.36%, Ni ≤ 0.35%; when C < 0.36%, Ni > 0.35%.

[0042] Specifically, the microstructure of the wire rod includes bainite, martensite, and retained austenite. Preferably, the volume fraction of the retained austenite is 8% to 15%, for example, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%.

[0043] Specifically, the diameter of the wire rod is 6 to 14 mm, for example, 6 mm, 6.5 mm, 7 mm, 7.5 mm, 8 mm, 8.5 mm, 9 mm, 9.5 mm, 10 mm, 10.5 mm, 11 mm, 11.5 mm, 12 mm, 12.5 mm, 13 mm, 13.5 mm, and 14 mm.

[0044] Another specific embodiment of the present invention discloses a method for preparing the above-mentioned wire rod, comprising the following steps:

[0045] S1: Based on the chemical composition of the wire rod, the raw materials are prepared, smelted, and continuously cast to obtain a continuously cast billet;

[0046] S2: Rolling: The continuously cast billet is heated and rolled to obtain steel.

[0047] S3: Wire drawing: The steel is wired to obtain the initial wire rod;

[0048] S4: The initial wire rod is subjected to a salt bath treatment;

[0049] S5: Tempering treatment: The wire rod after salt bath treatment is tempered to obtain the wire rod.

[0050] Specifically, in S1, the continuously cast billet is a square billet with dimensions of 180-190mm × 220-240mm.

[0051] It should be noted that when selecting continuously cast billets with larger cross-sectional dimensions to roll into wire rods, the wire rod compression ratio is high. A higher compression ratio is beneficial for breaking down the as-cast structure, homogenizing composition and properties, resulting in wire rods with high strength, high plasticity, and uniform properties. When the cross-sectional dimension of the continuously cast billet is too large, the solidification and cooling rate of the billet core is slower, increasing the risk of central porosity and shrinkage cavities. In this invention, the billet size is a square billet of 180–190 mm × 220–240 mm.

[0052] Specifically, in S2, the heating temperature is 1050-1100℃, for example, 1050℃, 1055℃, 1060℃, 1065℃, 1070℃, 1075℃, 1080℃, 1085℃, 1090℃, 1100℃, and the holding time is 6-8h, for example, 6h, 6.2h, 6.4h, 6.6h, 6.8h, 7h, 7.2h, 7.4h, 7.6h, 7.8h, 8h.

[0053] Specifically, the rolling process includes rough rolling and finish rolling.

[0054] Preferably, the initial rolling temperature of the roughing mill is 1000–1030℃, for example, 1000℃, 1002℃, 1004℃, 1006℃, 1008℃, 1010℃, 1012℃, 1014℃, 1016℃, 1018℃, 1020℃, 1022℃, 1024℃, 1026℃, 1028℃, or 1030℃, and the initial rolling temperature of the finishing mill is... The temperature ranges from 800 to 900℃, for example, 800℃, 810℃, 820℃, 830℃, 840℃, 850℃, 860℃, 870℃, 880℃, 890℃, and 900℃. The finishing rolling temperature is ≥860℃, for example, 860℃, 865℃, 870℃, 875℃, 880℃, 885℃, 890℃, 895℃, and 900℃.

[0055] It should be noted that when the rolling heating temperature is high, the surface of the steel billet suffers from severe decarburization; when the heating temperature is low, the deformation resistance increases, resulting in low production efficiency. In this invention, the heating temperature is 1050–1100℃. Simultaneously, the final rolling temperature in the finishing rolling stage is controlled to be ≥860℃. To obtain a finer austenite grain size, this invention adopts the lowest possible final rolling temperature. Furthermore, to avoid the introduction of ferrite due to excessively low rolling temperatures, the final rolling temperature is controlled to be above 860℃.

[0056] Specifically, in S3, when the C content in the wire rod is ≥0.36%, the wire drawing temperature is 780–800℃, for example, 780℃, 782℃, 784℃, 786℃, 788℃, 790℃, 792℃, 794℃, 796℃, 798℃, and 800℃. When the C content in the wire rod is <0.36%, the wire drawing temperature is 840–860℃, for example, 840℃, 842℃, 846℃, 848℃, 850℃, 852℃, 854℃, 856℃, 858℃, and 860℃.

[0057] It should be noted that, in order to obtain high-strength, high-ductility wire rods and improve production efficiency, different process parameters were designed based on the effects of alloying elements in this invention. To shorten the time between wire drawing and salt bath treatment, the wire drawing temperature was kept as low as possible; however, if the wire drawing temperature is too low, ferrite will form. In this invention, different wire drawing temperatures were designed for different carbon contents: when the carbon content is high (C≥0.36%), the ferrite phase transformation temperature is low, and a lower wire drawing temperature (780~800℃) was designed; when the carbon content is low (C<0.36%), the ferrite phase transformation temperature is high, and a higher wire drawing temperature (840~860℃) was designed.

[0058] Specifically, in S4, the salt bath treatment includes online salt bath treatment or offline salt bath treatment.

[0059] Specifically, in S4, the temperature of the salt bath treatment is 360-370℃, for example, 360℃, 362℃, 364℃, 365℃, 366℃, 368℃, or 370℃, and the salt bath time is 5-10 minutes, for example, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, or 10 minutes.

[0060] It should be noted that the microstructure in this invention is bainite + martensite + retained austenite. The purpose of salt bath treatment is to obtain bainite. During the salt bath treatment, elements such as carbon and manganese in the bainitic ferrite diffuse into the untransformed austenite, allowing some of the untransformed austenite to remain at room temperature. Martensite is obtained during the cooling process to room temperature after the salt bath, thus achieving a balance between high strength and high plasticity. To obtain a microstructure of fine bainite + fine martensite + highly stable retained austenite, the salt bath temperature and time need to be carefully matched. Higher temperatures result in larger bainite microstructures, while lower temperatures hinder the diffusion of carbon and manganese. In this invention, the salt bath temperature is 360–370°C, and the salt bath time is 5–10 minutes.

[0061] Specifically, in S4, the tempering temperature is 300-400℃, such as 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃, or 400℃. For example, the tempering time is 30-45 minutes, such as 30 minutes, 32 minutes, 34 minutes, 36 minutes, 38 minutes, 40 minutes, 42 minutes, 44 minutes, or 45 minutes.

[0062] It should be noted that, as mentioned above, during the salt bath treatment, elements such as carbon and manganese in the bainitic ferrite diffuse into the untransformed austenite. Some of the untransformed austenite has a high carbon content and can be stably retained to room temperature; some of the less carbon-rich untransformed austenite will transform into martensite during cooling to room temperature; another portion of the untransformed austenite is highly carbon-rich, but not enough to lower the martensite transformation initiation temperature below room temperature, thus transforming into martensite during cooling to room temperature. The resulting martensite has a high carbon content and is brittle. In this invention, tempering is employed to avoid the adverse effects of high-carbon martensite on plasticity. Furthermore, during tempering, supersaturated carbon atoms in the martensite and bainite continue to diffuse into the austenite, further improving the stability of the retained austenite. In this invention, the tempering temperature is 300–400°C, and the tempering time is 30–45 minutes. If the temperature is too high, carbides will precipitate in the retained austenite, reducing the retained austenite content and hindering the improvement of the uniform elongation of the wire rod.

[0063] The wire rod of this invention, through composition design and control of process parameters such as rolling, wire drawing, salt bath treatment, and tempering, obtains partially stable retained austenite while refining the bainitic and martensitic microstructure. Both the refined microstructure and the presence of retained austenite contribute to achieving high plasticity while maintaining high strength.

[0064] The advantages of precise control of wire rod composition and process parameters of the present invention are demonstrated below with specific embodiments and comparative examples. The chemical composition (%) of the wire rods in the embodiments and comparative examples is shown in Table 1, with the balance being Fe and unavoidable impurities. The specific process parameters are shown in Table 2, and the microstructure and mechanical properties are shown in Table 3.

[0065] Example

[0066] The preparation method of Mn-Si-Cr-Ni bainitic wire rod for steel strand in the embodiment is as follows:

[0067] S1: According to the chemical composition of the wire rod, the raw materials are prepared, smelted and continuously cast to obtain a continuously cast billet with a cross-sectional size of 180~190mm×220~240mm.

[0068] S2: Rolling: The continuously cast billet is heated to 1050-1100℃ and held for 6-8 hours. Rough rolling and finish rolling are performed sequentially. The initial rolling temperature of the rough rolling is 1000-1030℃, the initial rolling temperature of the finish rolling is 800-900℃, and the final rolling temperature of the finish rolling is ≥860℃ to obtain steel.

[0069] S3: Wire drawing: The steel is wired. When C in the wire rod is ≥0.36%, the wire drawing temperature is 780-800℃. When C in the wire rod is <0.36%, the wire drawing temperature is 840-860℃, to obtain the initial wire rod.

[0070] S4: The initial wire rod is subjected to a salt bath treatment at a temperature of 360-370°C for 5-10 minutes.

[0071] S5: Tempering treatment: The wire rod after salt bath treatment is tempered at a temperature of 300-400℃ for 30-45 minutes to obtain the wire rod.

[0072] The preparation method of the comparative wire rod is similar to that of the example, and the differences in process parameters are shown in Table 2.

[0073] Table 1. Chemical composition (%) of wire rods from the examples and comparative examples

[0074]

[0075] Table 2 shows the process parameters involved in each embodiment and comparative example.

[0076]

[0077] Table 3. Microstructure and mechanical properties of the wire rods in each embodiment and comparative example.

[0078]

[0079] The wire rod of the present invention has a tensile strength of ≥1538MPa, preferably 1538~1613MPa, a reduction of area of ​​≥60%, preferably 60~68%, and a uniform elongation of ≥8.5%, preferably 8.5~12%.

[0080] The X-ray diffraction pattern of the wire rod in Example 1 is as follows: Figure 1 As shown, the volume fraction of retained austenite was 11.38% as determined by X-ray diffraction.

[0081] The microstructure of the wire prepared in Example 2 is as follows: Figure 2 As shown, the microstructure is mainly bainite + martensite, and the volume fraction of retained austenite was found to be 8% using X-ray diffraction.

[0082] The wire rod tensile curve prepared in Example 3 is as follows: Figure 3 As shown, the tensile strength is 1613 MPa.

[0083] The microstructure of the wire prepared in Comparative Example 1 is as follows: Figure 4 As shown, due to the low salt bath temperature, the bainite transformation takes a long time. Within the designed salt bath time, the bainite transformation is insufficient, and the microstructure is mainly composed of a small amount of bainite and a large amount of martensite. Although a high strength of 1642 MPa is obtained, the reduction of area and uniform elongation are low, at 42% and 3.0% respectively, which do not meet the requirements for high plasticity.

[0084] The microstructure of the wire prepared in Comparative Example 2 is as follows: Figure 5 As shown, due to the high salt bath temperature, the bainite structure is large in size and contains large blocky martensite / austenite islands, requiring a long transformation time. Within the designed salt bath time, the bainite transformation is insufficient, and the microstructure is mainly composed of a small amount of bainite and a large amount of martensite. The strength is 1398 MPa, and the reduction of area and uniform elongation are 48% and 5.0%, respectively, which do not meet the requirements of high strength and high plasticity.

[0085] The wire rod of Comparative Example 3 did not contain Ni in its chemical composition, resulting in insufficient stability of the residual austenite and a low uniform elongation of 6.5%, which did not meet the requirements for high plasticity.

[0086] In the preparation method of the wire rod in Comparative Example 4, the tempering temperature was relatively high. Although a higher reduction in area and uniform elongation were obtained, the strength decreased significantly to 1373 MPa, which did not meet the high strength requirements.

[0087] Compared with Example 1, Comparative Example 5 did not meet the requirements for the wire-spinning temperature in its preparation method. The wire-spinning temperature was 780°C, and ferrite was introduced during the wire-spinning process. The microstructure was as follows: Figure 6 As shown, the wire rod strength decreased significantly to 1213 MPa, failing to meet the high strength requirement.

[0088] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A Mn-Si-Cr-Ni bainitic wire rod for steel strand, characterized in that, The chemical composition of the wire rod, by mass percentage, includes: C 0.30-0.42%, Si 1.10-1.20%, Mn 1.25-1.45%, Cr 0.5-0.7%, Ni 0.25-0.45%, S≤0.008%, P≤0.015%, with the remainder being Fe and unavoidable impurities.

2. The Mn-Si-Cr-Ni bainitic wire rod for steel strand according to claim 1, characterized in that, The chemical composition of the wire rod also satisfies the following conditions: when C ≥ 0.36%, Ni ≤ 0.35%; when C < 0.36%, Ni > 0.35%.

3. The Mn-Si-Cr-Ni bainitic wire rod for steel strand according to claim 1 or 2, characterized in that, The diameter of the wire rod is 6-14 mm.

4. A method for preparing the wire rod according to any one of claims 1-3, characterized in that, Includes the following steps: S1: Based on the chemical composition of the wire rod, the raw materials are prepared, smelted, and continuously cast to obtain a continuously cast billet; S2: Rolling: The continuously cast billet is heated and rolled to obtain steel. S3: Wire drawing: The steel is wired to obtain the initial wire rod; S4: The initial wire rod is subjected to a salt bath treatment; S5: Tempering treatment: The wire rod after salt bath treatment is tempered to obtain the wire rod.

5. The preparation method according to claim 4, characterized in that, In S1, the continuously cast billet is a square billet with dimensions of 180-190mm × 220-240mm.

6. The preparation method according to claim 4, characterized in that, In S2, the heating temperature is 1050-1100℃, and the holding time is 6-8h.

7. The preparation method according to claim 4, characterized in that, In S2, the rolling process includes roughing and finishing. The initial rolling temperature of the roughing rolling is 1000-1030℃, the initial rolling temperature of the finishing rolling is 800-900℃, and the final rolling temperature of the finishing rolling is ≥860℃.

8. The preparation method according to claim 4, characterized in that, In S3, when C ≥ 0.36% in the wire rod, the wire drawing temperature is 780–800℃, and when C < 0.36% in the wire rod, the wire drawing temperature is 840–860℃.

9. The preparation method according to claim 4, characterized in that, In S4, the temperature of the salt bath treatment is 360–370°C, and the salt bath time is 5–10 min.

10. The preparation method according to claim 4, characterized in that, In S4, the tempering temperature is 300-400℃ and the tempering time is 30-45 minutes.

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