A hypoeutectoid prestressed wire rod steel and a production process thereof

Abstract

The application belongs to the technical field of wire rod steel production, and particularly relates to a hypoeutectoid prestressed wire rod steel and a production process thereof. The chemical composition of the wire rod steel comprises, in percentage by mass, C: 0.71-0.75%, Si: 0.20-0.30%, Mn: 0.70-0.83%, P: 0.018% or less, S: 0.015% or less, Cr: 0.30-0.35%, N: 0.0055% or less, and the rest is Fe and inevitable impurities. The production process flow is "KR molten iron pretreatment + converter + LF refining furnace + continuous casting + controlled rolling and controlled cooling process + heat preservation channel slow cooling process". Through the optimized matching of "C+Mn+Cr" elements and the differential air cooling process control, the hypoeutectoid steel SWRH72BHCr wire rod meets the requirements of high strength, sorbitizing rate, metallographic structure and other comprehensive performance index requirements.

Description

Technical Field

[0001] This invention belongs to the field of wire rod production technology, and particularly relates to a hypoeutectoid prestressed wire rod and its production process. Background Technology

[0002] Prestressed steel wire and strand products, due to their high strength and low relaxation characteristics, can significantly improve the load-bearing capacity and service safety of prestressed concrete components, thereby reducing the amount of concrete and steel reinforcement used. Therefore, they are widely used in many fields such as railway and highway bridges, high-rise buildings, heavy-duty components in industrial plants, railway sleepers, utility poles, and hydropower projects. The application scenarios and application levels of this product in the domestic and international metal products industry are constantly increasing, and the demand is growing.

[0003] The application of prestressed wire rod steel is mostly concentrated in the range of eutectoid and hypereutectoid steels such as SWRH77B and SWRH82B, which can provide high strength indicators for wire rod. The production and application of hypoeutectoid prestressed steel are relatively few.

[0004] In the prior art, patent application number CN202311416967.X discloses a ferrite + pearlite microstructure SWRH72BCr-1 prestressed hot-rolled wire rod and its preparation method. This method involves adding 0.32-0.34% Cr to the SWRH72B prestressed wire rod based on controlled chemical elements. The Mn content is increased to 0.82-0.87%. The wire rod microstructure is S+P+F, with a sorbite ratio ≥82%. Air cooling is achieved using a Stellmore + water mist controlled cooling system, and this method is used for the production of 1570MPa level prestressed steel strands. This technical solution has a relatively high Mn content, increasing the segregation index and the risk of abnormal microstructure, while also increasing alloy costs. The relatively low sorbite ratio in the wire rod is not conducive to subsequent drawing. Patent application number CN201510094044.X discloses a SWRH72B-S wire rod for low-carbon, high-strength, and high-toughness steel strand and its manufacturing process. The chemical composition is C: 0.69-0.75%, Si: 0.20-0.30%, Mn: 0.60-0.75%, P≤0.020%, and S≤0.015%. It increases the reduction of area by ≥35%, making it suitable for direct high-speed continuous drawing. This composition is designed with low content of strengthening elements and good plasticity. However, this results in lower wire rod strength, making it difficult to manufacture prestressed steel wire and steel strand products, and limiting the product's adaptability in later stages.

[0005] Currently, a certain factory uses 150×150mm. 2 and 160×160mm 2 Two types of small-sized billets are used to produce SWRH72BHCr hot-rolled wire rods for hypoeutectoid prestressed steel wire and strand. The low magnification defects of the raw material billets, especially the central porosity and shrinkage cavity defects, are more prominent, and the overall performance indicators cannot meet the application needs of downstream customers. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a hypoeutectoid prestressed wire rod steel and its production process. The process route is "KR desulfurization pretreatment + converter smelting + LF refining + small billet continuous casting + heating furnace heating + controlled rolling and controlled cooling rolling + heat preservation channel" to produce prestressed wire rod steel, which meets the requirements for its drawing performance while ensuring the high strength index of the wire rod.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A hypoeutectoid prestressed wire rod steel, wherein the chemical composition of the wire rod steel comprises, by mass percentage: C: 0.71%~0.75%, Si: 0.20%~0.30%, Mn: 0.70%~0.83%, P≤0.018%, S≤0.015%, Cr: 0.30~0.35%, N≤0.0055%, with the remainder being Fe and unavoidable impurities.

[0008] The microstructure of the wire rod is mainly composed of fine lamellar sorbite, with a sorbitization rate of ≥90%, and the remainder being pearlite and a very small amount of cementite. Martensite and network cementite structures that would affect subsequent drawing processes are not allowed. The depth of the total decarburized layer (ferrite + transition layer) on one side of the wire rod should not exceed 1.5%D (D represents the nominal diameter of the wire rod).

[0009] The wire rod has a tensile strength of 1140-1250 MPa, an elongation after fracture of ≥10%, and a reduction of area of ​​≥30%.

[0010] The rationale for the design of the components in this invention is as follows: Carbon (C) enhances the strength and hardness of steel. As a fundamental element ensuring the most critical mechanical properties of hypoeutectoid prestressed wire rod, its content is controlled within the upper-middle range. This not only meets the strength requirements of the wire rod but also reduces the consumption of other strengthening elements, thus lowering manufacturing costs. Since it is a hypoeutectoid steel, the wire rod's plasticity is guaranteed. The C content is selected and controlled between 0.71% and 0.75%.

[0011] Si: Silicon can also increase the strength and hardness of steel, but reduce its plasticity and toughness. In the steelmaking process, silicon plays a deoxidizing role. The Si content should be controlled at 0.20~0.30%.

[0012] Mn: Manganese is another major strengthening element that improves the strength of steel. It can combine with sulfur to form manganese sulfide, eliminating the "hot brittleness" of steel and improving its hardenability and wear resistance. However, excessive Mn content can exacerbate segregation, especially in 150×150mm steel. 2For small-sized billets, severe local segregation can affect the uniformity of wire rod microstructure transformation, forming locally undercooled martensite and inducing wire breakage accidents during subsequent machining. Composition design needs to utilize the element's contribution to wire rod strength while suppressing the segregation risks caused by excessive content. Therefore, Mn content control adopts the middle range of the standard range, 0.70~0.83%.

[0013] P / S: Phosphorus and sulfur are harmful elements in steel. Phosphorus dissolves in ferrite, and although it can improve the strength and hardness of steel, its greatest harm is severe segregation, which increases temper brittleness and significantly reduces the plasticity and toughness of steel, making it prone to brittle fracture during cold working, also known as "cold brittleness." Sulfur reduces the plasticity of steel, increases its brittleness, and deteriorates the quality of steel. P ≤ 0.018%, S ≤ 0.015%.

[0014] Cr: Chromium significantly improves the hardenability of steel, strengthens the matrix, refines grains, increases strength and hardness, and enhances corrosion resistance and oxidation resistance. Practical production feedback demonstrates that chromium's hardenability and oxidation resistance are outstanding, enabling wire rod to undergo phase transformation at relatively low cooling rates, resulting in a low-temperature, fine lamellar microstructure. However, excessively high Cr content in steel also presents significant drawbacks. Firstly, it limits the cooling rate during the wire rod's microstructure transformation process. This is particularly evident in small-diameter, high-Cr products, easily leading to large-area undercooled microstructures, making the wire rod brittle and resulting in scrap. Secondly, it exacerbates the risk of component segregation, increasing the likelihood of forming localized low-temperature martensite. Martensite is a harmful microstructure in subsequent wire rod drawing processes and needs to be controlled. Therefore, the composition design needs to utilize its strong hardenability to refine the grains and obtain a fine lamellar microstructure (sorbite) by using a suitable cooling rate, thereby improving the strength of the wire rod. At the same time, it is necessary to suppress the segregation risks caused by excessive Cr content and their impact on the phase transformation of the wire rod microstructure, inducing the concentrated formation of martensite at low temperatures. Therefore, the Cr content was controlled within the lower limit of the standard range, 0.30~0.35%.

[0015] N: Nitrogen affects the age hardening of wire rod, reduces the plasticity index during wire rod drawing, causes concentrated wire breakage accidents, and affects the drawing performance of wire rod. Therefore, N≤0.0055%.

[0016] The above composition design ensures the full utilization of the controlled rolling and cooling process capabilities of SWRH72BHCr wire rod, and that the wire rod's lamellar structure and mechanical properties meet the standard requirements. The content of elements C, Mn, and Cr is carefully controlled. This reduces the risk of compositional segregation and manufacturing cost pressures associated with high alloy content, while also fully realizing the air-cooling microstructure transformation capability of the rolled steel. This achieves optimization and unification of the steelmaking and rolling processes, resulting in hot-rolled wire rod products with consistently meeting comprehensive performance standards.

[0017] A production process for hypoeutectoid prestressed wire rod includes the following steps: KR hot metal pretreatment, converter smelting, LF furnace refining, small billet continuous casting, heating, rolling, wire drawing, coiling, slow cooling, and sampling inspection; wherein: KR molten iron pretreatment: Desulfurizing agent is injected into the molten iron ladle for desulfurization. After treatment, the sulfur content of the molten iron is ≤0.030%; this ensures the effectiveness of subsequent desulfurization and meets the low sulfur control requirements of the finished product.

[0018] Converter smelting: Top and bottom blowing converter is used for smelting. The tapping temperature is 1530-1600℃. The final tapping concentration is C≥0.45%. Slag feeding is strictly prohibited. Spot blowing is avoided. The static argon blowing time is 5-15 minutes. LF furnace refining: A slight positive pressure of 40–70 kPa is maintained inside the furnace, using submerged arc heating; the basicity of the slag is controlled at 1.8–2.3, and the soft blowing time is ≥15 min to achieve uniform steel production and reduce segregation. This mitigates abnormal wire rod microstructure caused by high C, Mn, and Cr element segregation, which can negatively impact subsequent processing performance. The LF furnace exit temperature is 1521–1527℃; the ladle exit temperature is a fundamental indicator for controlling low superheat in subsequent continuous casting processes and needs to be ensured according to the production schedule.

[0019] Small billet continuous casting: Full-process protective casting is adopted to reduce steel oxidation and nitrogen absorption, ensuring drawing performance. The tundish temperature is 1505~1514℃, and the superheat is maintained at 15~30℃ to improve the quality of the low-magnification microstructure of the billet; constant casting speed of 1.8~2.0m / min is used to reduce the risk of slag entrapment caused by liquid level fluctuations.

[0020] Heating: A walking beam furnace is used for heating. The preheating section reaches 860–900℃, the heating section reaches 1100–1140℃, and the soaking section reaches 1120–1180℃. The total heating time is 1.5–3 hours. (For 150×150mm diaphragms) 2 The small size and high alloy content of these slabs, through precise heating control and prolonged furnace heating, ensure thorough homogenization, improving the slab's plasticity and providing conditions for the welding of low-magnification defects (central porosity, shrinkage cavities, cracks) during subsequent rolling. Simultaneously, the presence of Cr significantly improves and inhibits decarburization of the slab, allowing for full utilization of its properties. Rolling: The initial rolling temperature is 1020~1050℃; the wire drawing temperature is 880~920℃; the air-cooled roller speed is 0.80~1.1m / s for the head roller; the roller speed increase is 2%~5%; the insulation cover is fully open; the Stellmore air-cooling line has a strong cooling section and a weak cooling section along the wire rod travel direction. The fan frequency of the strong cooling section is set to 40~50Hz, and the fan frequency of the weak cooling section is set to 30~45Hz; slow cooling: slow cooling is achieved through an insulation channel.

[0021] Rolling: The initial rolling temperature is 1020–1050℃ to improve the plasticity of the billet and promote the welding of internal defects such as porosity, shrinkage cavities, or cracks. Corresponding to the heating and holding time of the billet in the furnace, the main purpose is to provide sufficient plasticity to the billet, making full use of the large compression ratio of roughing and intermediate rolling to weld low-magnification defects in the billet. This is also a process compensation for the defects of small-sized billets in the rolling system. The wire drawing temperature is 880–920℃, combined with the wire rod air-cooling process, optimizing the two key technical indicators of phase transformation undercooling and cooling rate to obtain a fine lamellar sorbite structure and improve the strength of the wire rod. The air-cooling roller speed is 0.80–1.1 m / s at the head roller; the roller speed increases gradually by 2%–5%, with the insulation cover fully open; the Stellmore air-cooling line DC fan is turned on: before the phase transformation, a continuous high cooling rate is adopted to turn on the fan, and the wire rod cooling rate is controlled at 8–10℃ / s, and the transformation is carried out at a constant temperature after reaching the sorbite transformation temperature. The motor frequency for fans 1-7 is set to 40-50Hz. During and after the phase transformation of the wire rod, the air-cooling intensity must be reduced to suppress further low-temperature transformation of the supercooled austenite, forming a finer lamellar troostite or martensite structure. This is crucial for air-cooling control. Specifically, ensuring the fan airflow can effectively suppress the release and regeneration of the latent heat of the wire rod phase transformation, fans 8-15 are turned on, with their motor frequency set to 30-45Hz; the specific setting depends on the wire rod specifications.

[0022] Slow cooling: Insulated channels are used for slow cooling to promote the effective release of H and internal stress in the wire rod and improve its plasticity. In addition, given the low temperature environment in northern steel mills during winter, it is required that after the wire rod is rolled out, it be slow cooled in the warehouse for more than 12 hours before it can be shipped out, so as to promote the full release of internal stress and hydrogen in the steel and improve the plasticity of the wire rod.

[0023] The desulfurizing agent comprises, by mass percentage: 88%–92% lime powder and 8%–12% fluorite powder.

[0024] In the continuous casting of small square billets, the electromagnetic stirring current of the crystallizer is 320A, the frequency is 3Hz, and it rotates continuously. The electromagnetic stirring current at the end is 400A, the frequency is 8Hz, and it rotates in both directions, which improves the solidification structure quality of the billet and reduces low-magnification defects.

[0025] After the small square billet is continuously cast, the billet is kept at a high temperature and cooled slowly for more than 60 hours to release hydrogen and internal stress of the billet.

[0026] In the rolling process, the fan frequency of fans 1-7# in the early stage of phase transformation on the air-cooled roller table is higher than that of fans 8-15# in the later stage of phase transformation. Simultaneously, in conjunction with the wire rod drawing temperature setting, this ensures that the wire rod achieves a higher degree of undercooling in the early phase transformation stage of the air-cooled roller table, rapidly reaching the sorbite transformation temperature and achieving a complete transformation of fine lamellar sorbite. This also prevents further cooling of the undercooled austenite that failed to complete the sorbite transformation during the early phase transformation process on the air-cooled roller table, which could lead to the formation of low-temperature troostite or martensite structures and negatively impact the wire rod's subsequent drawing performance.

[0027] The specifications of the wire rod are ø8mm~ø13mm.

[0028] After rolling, the wire rod is slowly cooled in the warehouse for more than 12 hours before being shipped out.

[0029] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention adopts a production process of "KR molten iron pretreatment + converter + LF refining furnace + continuous casting + controlled rolling and cooling process + heat preservation channel slow cooling process". Through the optimized ratio of "C + Mn + Cr" elements combined with differentiated air cooling process control, it meets the comprehensive performance requirements of hypoeutectoid steel SWRH72BHCr wire rod, such as high strength, sorbitization rate, and metallographic structure.

[0030] 2. Under the premise of maintaining the hypoeutectoid steel composition system, the present invention improves the wire rod strength to the control range of hypereutectoid steel SWRH82B through the composite strengthening effect of Mn and Cr, while maintaining good plasticity index, and achieves an excellent balance between strength and plasticity.

[0031] 3. This invention controls the Mn content, avoiding abnormal microstructures (such as martensite or bainite) caused by increased segregation. Simultaneously, the addition of Cr refines the original austenite grains, providing excellent microstructure preparation for phase transformation. A "fast at the beginning, slow at the end" cooling method is employed, providing sufficient undercooling in the early stage of phase transformation to obtain fine lamellar sorbite, while reducing the cooling intensity in the later stage effectively suppresses the transformation of undercooled austenite to martensite, ensuring the uniformity and stability of the microstructure. The sorbitization rate of the wire rod reaches over 90%, and the decarburized layer depth is controlled to ≤1.5D.

[0032] 4. This invention utilizes small-sized cast billets, high initial rolling temperatures, and considers the influence of the cooling rate and lamellar structure of the wire rod on its strength indicators, resulting in wire rods with ideal comprehensive performance. The tensile strength of the wire rod steel is 1140–1250 MPa, elongation after fracture ≥10%, and reduction of area ≥30%. This invention compensates for the adverse effects of low magnification defects in small-sized cast billets on the wire rod microstructure, resulting in high-performance prestressed wire rod products. Attached Figure Description

[0033] Figure 1 This is a comparative microstructure diagram of the disc strip of the present invention.

[0034] Figure 2 This is a microstructure diagram of the bar in Embodiment 1 of the present invention.

[0035] Figure 3 This is a microstructure diagram of the disc strip in Embodiment 2 of the present invention.

[0036] Figure 4 This is a microstructure diagram of the disc strip in Embodiment 3 of the present invention.

[0037] Figure 5 This is a microstructure diagram of the disc strip in Embodiment 4 of the present invention. Detailed Implementation

[0038] The present invention will now be described in detail with reference to the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0039] The production process of hypoeutectoid SWRH72BHCr prestressed wire rod steel includes the following steps: Step S1, KR molten iron pretreatment: Desulfurizing agent (90% lime powder + 10% fluorite powder) is injected into the molten iron ladle for desulfurization. After treatment, the molten iron S is required to be ≤0.030% to ensure the subsequent desulfurization effect and the low sulfur control requirements of the finished product.

[0040] Step S2, Converter smelting: Smelting is carried out in a top-and-bottom blown converter. The tapping temperature is ≥1530℃, and the final tapping concentration (C) is ≥0.45%. Slag feeding is strictly prohibited, and spot blowing should be avoided. The static argon blowing time is ≥5 minutes.

[0041] Step S3, LF furnace refining: Maintain a slight positive pressure of 40-70 kPa inside the furnace, using submerged arc heating. Control the basicity of the slag to 1.8-2.3, with a soft blowing time ≥15 min, and maintain the LF furnace temperature at 1521-1527℃. The ladle soft blowing time must be guaranteed to achieve uniform steel structure and reduce segregation. This reduces abnormal wire rod microstructure caused by high C, Mn, and Cr element segregation, which affects subsequent processing performance. The ladle temperature at the furnace is a fundamental indicator for controlling low superheat in subsequent continuous casting processes and needs to be ensured according to the production schedule.

[0042] Step S4, Continuous Casting: A full-process protective casting process is adopted to reduce steel oxidation and nitrogen absorption, ensuring drawing performance. The crystallizer electromagnetic stirring current is 320A, frequency 3Hz, continuously rotating; the end electromagnetic stirring current is 400A, frequency 8Hz, rotating in both directions, improving the solidification structure quality of the billet and reducing low-magnification defects. The tundish temperature is 1505℃~1514℃, superheat is maintained ≤30℃, and the casting speed is 2.0m / min, a constant casting speed to reduce liquid level fluctuations and lower the risk of slag entrapment.

[0043] The steel billets are kept at a low temperature and cooled slowly for more than 60 hours after being removed from the production line. This promotes the release of hydrogen and stress in the steel, ensuring a reliable raw material supply for subsequent wire rod rolling.

[0044] Step S5, Heating Process: A walking beam furnace is used for heating. The preheating zone is 860–900℃, the heating zone is 1100–1140℃, and the soaking zone is 1120–1180℃. The total heating time is 1.5–3 hours. This is the key process control for this product, primarily targeting 150×150mm PVC sheets. 2 and 160×160mm 2 The small size and high alloy content of these billets, through precise heating control and prolonged furnace heating, allow for thorough homogenization and improved billet plasticity. This provides conditions for the welding of low-magnification defects (central porosity, shrinkage cavities, and cracks) during subsequent rolling. Simultaneously, the presence of Cr significantly improves and inhibits decarburization of the billet, which is fully utilized.

[0045] Step S6, Rolling process: Initial rolling temperature: 1030~1050℃; key process control corresponds to the heating and holding time of the billet in the furnace, mainly to provide sufficient plasticity to the billet, fully utilize the large compression ratio of roughing and intermediate rolling, and weld low-magnification defects in the billet. This is also a process compensation for the defects of small-sized billets in the rolling system. It is an effective combination of actual steelmaking and rolling production.

[0046] Wire drawing temperature: 880~920℃; this is a relatively high wire drawing temperature for medium and high carbon wire rod. It is a temperature regime specifically designed to achieve the mechanical property requirements of SWRH72BHCr hypoeutectoid steel to meet the requirements of hypereutectoid SWRH82B wire rod. Utilizing the cooling capacity of the air-cooling line in the rolling mill, the strength is improved by increasing the undercooling of the wire rod to obtain a fine lamellar sorbite structure.

[0047] Air-cooled roller conveyor speed: 0.80~1.1m / s for the head roller conveyor; speed increment between each section of the roller conveyor is 2%~5%. By adjusting the speed of the air-cooled roller conveyor, the overlapping points of the wire rod are effectively staggered, resulting in uniform cooling of the wire rod and stable microstructure control.

[0048] Fans: During the early stage of phase transformation, fans 1-7# operate at 40-50Hz, and during the later stage of phase transformation, fans 8-15# operate at 30-45Hz. The characteristic of this process is that by controlling the rapid cooling in the early stage of phase transformation and the weak cooling after phase transformation of the wire rod structure, a fine lamellar sorbite structure is obtained, while the further low-temperature transformation of supercooled austenite into martensite, a hard structure, is suppressed. This promotes the stability of wire rod drawing in the later stage and reduces the wire breakage rate.

[0049] Step S7 employs a heat-insulated channel for slow cooling, fully utilizing the residual heat of the wire rod after it leaves the production line. During transport within the sealed channel, the wire rod undergoes rapid aging, allowing for the rapid release of hydrogen and rolling stress within the rod. This shortens the natural aging time of the post-rolling wire rod, benefiting downstream customers' drawing applications. This process is particularly effective during winter production periods.

[0050] The chemical composition of the wire rods in the examples is shown in Table 1. The main production processes of the wire rods in the examples and comparative examples are shown in Tables 2 and 3. The performance of the wire rods in the examples and comparative examples is shown in Table 4.

[0051] Table 1 Chemical composition of wire rod in the examples (wt%):

[0052] Table 2. Main Production Process of Wire Rod in Example 1:

[0053] Note: Table 2 shows the process temperature control for different embodiments.

[0054] Table 3. Main Production Process of Wire Rod in Embodiment 2 of the Invention

[0055] Table 4 Performance of the wire rod in the embodiments of the present invention

[0056] As shown in Table 4 and Figure 1-5 As shown, the wire rod produced by this invention features good microstructure uniformity, high sorbite content, and stable mechanical properties. The tensile strength of the wire rod is consistently in the upper-middle range of 1140–1250 MPa, with elongation after fracture ≥10% and reduction of area ≥30%. Its microstructure exhibits a sorbite content consistently above 90%, with the sorbite content of large-diameter ø12mm wire rod reaching a controlled level of 95%. This is highly beneficial for subsequent drawing processes. More importantly, the low-range control of Mn and Cr alloy content in the embodiments significantly reduces manufacturing costs and enhances market competitiveness. This wire rod demonstrates excellent adaptability to subsequent processing by users, meeting market demands.

[0057] The successful application of this invention proves that the technical solution has successfully resolved the conflict between the composition and performance requirements of hypoeutectoid steel strand wire rod, achieving a dual improvement in economic benefits and product quality, and providing technical accumulation for the market expansion of prestressed steel strand products.

[0058] 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 equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A hypoeutectoid prestressed wire rod, characterized in that, The chemical composition of the wire rod, by mass percentage, includes: C: 0.71%~0.75%, Si: 0.20%~0.30%, Mn: 0.70%~0.83%, P≤0.018%, S≤0.015%, Cr: 0.30~0.35%, N≤0.0055%, with the remainder being Fe and unavoidable impurities.

2. The hypoeutectoid prestressed wire rod steel according to claim 1, characterized in that, The microstructure of the wire rod is mainly composed of fine lamellar sorbite with a sorbitization rate of ≥90%, and the remainder is pearlite and a very small amount of cementite. The decarburized layer depth is ≤1.5D.

3. The hypoeutectoid prestressed wire rod steel according to claim 1, characterized in that, The wire rod has a tensile strength of 1140-1250 MPa, an elongation after fracture of ≥10%, and a reduction of area of ​​≥30%.

4. The production process of hypoeutectoid prestressed wire rod steel according to any one of claims 1-3, characterized in that, The process includes the following steps: KR molten iron pretreatment, converter smelting, LF furnace refining, small billet continuous casting, heating, rolling, wire drawing, coiling, slow cooling, and sampling inspection; among which: KR molten iron pretreatment: Desulfurizing agent is injected into the molten iron ladle for desulfurization, and the S content of the molten iron after treatment is ≤0.030%; Converter smelting: Top and bottom blowing converter is used for smelting. The tapping temperature is 1530-1600℃. The final tapping concentration is C≥0.45%. Slag feeding is strictly prohibited. Spot blowing is avoided. The static argon blowing time is 5-15 minutes. LF furnace refining: Maintain a slight positive pressure of 40-70 kPa inside the furnace and use submerged arc heating; control the basicity of the steel slag to 1.8-2.3, the soft blowing time to ≥15 min, and the LF furnace temperature at the station to 1521-1527℃; Small billet continuous casting: adopt full-process protective casting, tundish temperature 1505~1514℃, superheat maintained at 15~30℃, constant casting speed 1.8~2.0m / min; Heating: Heating is carried out in a walking beam furnace. The preheating temperature is 860-900℃, the heating temperature is 1100-1140℃, the soaking temperature is 1120-1180℃, and the total heating time is 1.5-3 hours. Rolling: The initial rolling temperature is 1020~1050℃; the wire drawing temperature is 880~920℃; the air-cooled roller speed is 0.80~1.1m / s for the head roller; the roller speed increase is 2%~5%; the insulation cover is fully open; the Stellmore air-cooling line has a strong cooling section and a weak cooling section along the wire rod travel direction. The fan frequency of the strong cooling section is set to 40~50Hz, and the fan frequency of the weak cooling section is set to 30~45Hz; slow cooling: slow cooling is achieved through an insulation channel.

5. The production process of hypoeutectoid prestressed wire rod steel according to claim 4, characterized in that, The desulfurizing agent comprises, by mass percentage: 88%–92% lime powder and 8%–12% fluorite powder.

6. The production process of hypoeutectoid prestressed wire rod steel according to claim 4, characterized in that, In the aforementioned continuous casting of small billets, the electromagnetic stirring current of the crystallizer is 320A, the frequency is 3Hz, and it rotates continuously; the electromagnetic stirring current at the end is 400A, the frequency is 8Hz, and it rotates in both directions.

7. The production process of hypoeutectoid prestressed wire rod steel according to claim 4, characterized in that, After the small square billet is continuously cast, the billet is kept warm and cooled for more than 60 hours after it leaves the production line.

8. The production process of hypoeutectoid prestressed wire rod steel according to claim 4, characterized in that, In the rolling process, the cooling rate of the fan in the strong cooling section is higher than that of the fan in the weak cooling section.

9. The production process of hypoeutectoid prestressed wire rod steel according to claim 4, characterized in that, The specifications of the wire rod are ø8mm~ø13mm.

10. The production process of hypoeutectoid prestressed wire rod steel according to claim 4, characterized in that, After rolling, the wire rod is slowly cooled in the warehouse for more than 12 hours before being shipped out.

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