A high-strength, heat-resistant steel strand with ultra-high fatigue performance and its production method

Abstract

This invention discloses a high-strength, heat-resistant steel for ultra-high fatigue performance and its production method. The main chemical composition and weight percentage of the steel for the steel strand are: C 0.89%~1.10%, Mn 0.70%~1.00%, Cr 0.20%~0.35%, V 0.04%~0.09%, Alt 0.015%-0.030%, and Si 1.00%~1.30%; wherein 3.0≤(Si+1.2*Mn) / (8*V)≤7.0. It is mainly micro-alloyed by Cr, V, Ni, Cu, etc., with a sorbitization rate of over 95%. The hot-rolled tensile strength Rm≥1440MPa and the reduction of area Z≥37%. This method produces steel strands with a strength ≥2330MPa, an elastic modulus of 190-210GPa, a yield strength ratio of 0.90-0.95, and high fatigue performance of ≥2 million cycles. The production process is stable and reliable, and is suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the field of steel strand technology, specifically relating to a high-strength, heat-resistant steel strand with ultra-high fatigue performance and its production method. Background Technology

[0002] High-strength prestressed steel strand is a widely used product in the metal products industry. It has the characteristics of high tensile strength, good elongation, low relaxation value, small stress loss and excellent fatigue resistance. Due to its unique properties, no more ideal product has been found to completely or exclusively replace high-strength prestressed steel strand, making it an indispensable component or material. It is widely used in railways, highways, cross-sea bridges, large buildings, water conservancy and other fields.

[0003] my country is currently in a critical period of rapid construction, leading to a rapid increase in demand for high-strength prestressed steel strands. This is especially true as domestic transportation infrastructure development progresses, with increasing demand for public facilities such as highways and railways, gradually expanding into remote mountainous areas. Some regions, due to complex geological conditions, urgently require the construction of railways and bridges with larger spans, placing higher demands on the high strength and lightweight nature of these structures. As a crucial raw material used in these large-scale construction projects, the cost and quality of steel strands directly impact the construction cost and safety of buildings.

[0004] Currently, the prestressed concrete steel strands commonly used in domestic railway and bridge construction are 1860MPa grade steel strands, with the highest strength grade in this standard being only 1960MPa. Increasing the strength of the steel used in the steel strands can significantly reduce costs. For example, replacing 1860MPa grade steel strands with 1960MPa grade high-strength steel strands can save about 20% of the steel strand usage. Therefore, larger spans, lighter weight, higher strength, and safer bridges will become an inevitable trend in the future development of the industry. Existing steel strands all use a C-Si-Mn composition system. Increasing the C, Si, and Mn content can improve strength, but it easily leads to the formation of network cementite and core martensite, severely damaging the material's performance, especially drastically reducing plasticity and toughness. This makes it impossible to meet the requirements of repeated bending and torsion during processing, and the fatigue strength also fails to meet user requirements.

[0005] Chinese patent CN116084194A discloses a high-strength fatigue-resistant steel wire rope and its manufacturing method, comprising a central strand, a first inner layer strand, a second inner layer strand, and an outer layer strand. The first inner layer strand is disposed on the outer side of the central strand, and the second inner layer strand is disposed on the outer side of the first inner layer strand. The first inner layer strands are evenly distributed on the outer side of the central strand, and the second inner layer strands are evenly distributed on the outer side of the first inner layer strand. This high-strength fatigue-resistant steel wire rope and its manufacturing method utilize an oil-impregnated fiber core to improve the strength and fatigue resistance of the steel wire rope, increase flexibility, reduce deformation, and facilitate oil lubrication of the steel wire structure within the fiber core. The double electroplating process ensures uniform electroplating of the steel wire, improving corrosion resistance. The uniform coating of adhesive on the outer side of the steel wire rope enhances its cushioning performance. However, this invention offers limited improvement in fatigue performance from the perspective of steel strand manufacturing and cannot meet the requirements for higher fatigue performance or heat resistance.

[0006] Chinese patent CN110819899A discloses a 2100MPa grade marine engineering wire rope steel and its production method. The 2100MPa grade marine engineering wire rope steel comprises the following chemical composition by weight percentage: C 0.95%~1.10%, Si 0.10%~0.50%, Mn 0.60%~1.20%, Cr 0.10%~0.50%, Nb 0.02%~0.10%, Ni 0.01%~0.50%, Al≤0.005%, P≤0.015%, S≤0.015%, O≤0.0015%, N≤0.006%, with the remainder being Fe and unavoidable impurity elements. This invention employs specific chemical compositions and wire rod production processes to produce hot-rolled wire rods with excellent mechanical properties and a high sorbitization rate. The processed wire ropes achieve strengths exceeding 2100 MPa and exhibit good torsional and bending properties, making them suitable for manufacturing 2100 MPa-grade high-strength marine steel wire ropes. However, the material used in this invention can only be used to produce 2100 MPa-grade high-strength steel wire rope products and cannot meet higher-level requirements. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a high-strength, heat-resistant steel strand with ultra-high fatigue performance and its production method. The method primarily involves micro-alloying with Cr, V, Ni, and Cu, achieving a sorbitization rate of over 95%. The hot-rolled tensile strength Rm ≥ 1440 MPa and the reduction of area Z ≥ 37% result in steel strands with a strength ≥ 2330 MPa, an elastic modulus of 190-210 GPa, a yield strength ratio of 0.90-0.95, and high fatigue resistance ≥ 2 million cycles. The production process is stable and reliable, suitable for large-scale industrial production.

[0008] The technical solution adopted in this invention is as follows:

[0009] A high-strength, heat-resistant steel strand with ultra-high fatigue performance is disclosed. The chemical composition and weight percentage of the steel are as follows: C 0.89%–1.10%, Mn 0.70%–1.00%, Cr 0.20%–0.35%, V 0.04%–0.09%, Alt 0.015%–0.030%, Si 1.00%–1.30%, P≤0.010%, S≤0.010%, O≤0.0020%, N≤0.0065%, with the remainder being Fe and other unavoidable impurities. Specifically, 3.0≤(Si+1.2*Mn) / (8*V)≤7.0. In this formula, the values ​​of each chemical component are calculated by multiplying the content of each chemical component in the steel by 100.

[0010] The hot-rolled wire rod for ultra-high fatigue performance heat-resistant high-strength steel strand has a sorbitization rate of ≥95%, a grain size of ≥9, a central martensite of ≤1.0, and a network cementite of ≤1.0; the tensile strength of the hot-rolled wire rod is ≥1440MPa, and the reduction of area is ≥37%.

[0011] The ultra-high fatigue performance heat-resistant high-strength steel strand uses steel wires with a room temperature tensile strength ≥2320MPa, capable of withstanding ≥10 180° bends in both directions without breakage, and ≥20 360° torsion cycles with good torsional fracture. At 200℃, the wire tensile strength is ≥2180MPa with a strength loss rate ≤7.0%; at 300℃, the wire tensile strength is ≥1900MPa with a strength loss rate ≤19.0%; and at 360℃, the wire tensile strength is ≥1700MPa with a strength loss rate ≤26.0%.

[0012] The finished steel strand made from the steel used in the ultra-high fatigue performance heat-resistant high-strength steel strand has a tensile strength ≥2330MPa, an elastic modulus of 190-210GPa, a yield strength ratio of 0.90~0.95, and high fatigue performance ≥2 million cycles.

[0013] The present invention also provides a method for producing steel for ultra-high fatigue performance heat-resistant high-strength steel strand, the method comprising the following steps: smelting → refining → continuous casting → diffusion annealing → rolling → grinding and peeling → wire rod rolling → Steyrmo cooling line controlled cooling → finished wire rod.

[0014] The refining steps include LF furnace refining and RH vacuum degassing; during RH vacuum degassing, the pure degassing time is ≥15 minutes to ensure that the [H] content after vacuum treatment is ≤1.5ppm.

[0015] In the continuous casting process, the superheat of the molten steel is controlled at 10-40℃, and the casting speed is 2.1-2.3 mm / min.

[0016] In the diffusion annealing step, the annealing temperature is 1230-1260℃ and the holding time is 10-12h.

[0017] The billet is continuously cast into a 380mm*450mm square billet; after diffusion annealing, it is rolled into a 150mm*150mm or 160mm*160mm square billet.

[0018] In the wire rolling process, the wire is first homogenized at 1140-1160℃ for 80-100 minutes, and then rolled. The initial rolling temperature is 940-980℃, the final rolling temperature is 880-920℃, and the wire drawing temperature is 860-910℃.

[0019] In the controlled cooling process of the Stellmore cooling line, a two-stage cooling method is adopted. First, the temperature is cooled to 570-630°C at a cooling rate of 7-11°C / s to prevent the formation of network cementite. At the same time, the higher the cooling rate, the greater the supercooling and the smaller the sorbite lamellar spacing. The temperature is held for 15-35 seconds to control the back-temperature during the phase transformation. Finally, the temperature is slowly cooled to room temperature at a cooling rate of ≤4°C / s to obtain an equilibrium microstructure.

[0020] The present invention also provides an ultra-high fatigue performance heat-resistant high-strength steel strand, which is obtained by drawing and stranding the steel used for the ultra-high fatigue performance heat-resistant high-strength steel strand described in the present invention.

[0021] The diameter of the center wire of the steel strand is Φ5.10-5.25mm, the diameter of the edge wire is Φ5.04-5.06mm, and the diameter of the finished steel strand is 15.40-15.15mm.

[0022] The steel grade of this invention can be produced using conventional smelting processes in converters, electric furnaces, or other smelting furnaces, provided it falls within the aforementioned composition range. It can also produce high-carbon steel wire rod for steel ropes using conventional rolling processes on ordinary high-speed wire rod mills and under controlled cooling conditions via the Steyrmore cooling line. Furthermore, it can produce 2300MPa grade high-strength prestressed steel strands through conventional continuous drawing and stranding processes. The roles and control of each chemical component in the ultra-high fatigue performance heat-resistant high-strength steel strand provided by this invention are as follows:

[0023] C: Carbon is essential for obtaining high strength and hardness. To achieve the high strength required for high-strength steel strands, the C content must be above 0.85%. However, excessively high C content increases carbon segregation, easily leading to abnormal structures such as central martensite and network cementite, which are detrimental to drawing performance. Therefore, the C content should be controlled between 0.89% and 1.10%.

[0024] Mn: Mn is an effective element for deoxidation and desulfurization, and it can also improve the hardenability and strength of steel. However, if the Mn content is too high, it is easy to cause segregation, resulting in harmful structures such as central martensite and network cementite, which deteriorates the toughness of steel. Therefore, the Mn content is controlled between 0.70% and 1.00%.

[0025] Cr: It is a strong carbide-forming element. It exists in cementite lamellars to form alloy cementite, which improves strength. At the same time, the addition of Cr shifts the continuous cooling transformation curve of steel to the right, thereby refining the interlamellar spacing. Cr can also reduce the activity of C, which can reduce the tendency of steel surface decarburization during heating, rolling and heat treatment. This is beneficial for obtaining high fatigue resistance, and can also improve corrosion resistance and wear resistance. Therefore, the Cr content should be controlled at 0.20% to 0.35%.

[0026] V (Volume): V significantly refines grain size. Grain refinement not only improves the strength and toughness of steel but also enhances its low-temperature performance. Furthermore, V is a strong carbide-forming element; its precipitation at austenite grain boundaries during the early stages of phase transformation reduces the carbon content at grain boundaries, effectively inhibiting the formation of network cementite. Additionally, V (C, N) precipitated in ferrite can play a precipitation strengthening role. Simultaneously, due to the finer grain size, it also improves corrosion resistance. Excessive V content leads to higher costs; the V range should be controlled between 0.04% and 0.09%.

[0027] Alt (Al) is a strong deoxidizing element that improves the oxidation resistance of steel. Alt also refines austenite grains. Furthermore, Alt combines with nitrogen to form AlN, reducing dislocation pinning and significantly decreasing the tendency for blue brittleness, while also improving impact toughness. However, excessive Alt content can lead to the formation of coarse carbonitrides, resulting in excessive brittle inclusions and affecting fatigue life. The Alt content should be controlled between 0.015% and 0.030%.

[0028] Si: As a solid solution hardening element, Si can significantly improve the strength of high-carbon steel. Increasing the Si content in high-carbon steel wire rod helps reduce the segregation of carbon atoms in ferrite lamellars, thus reducing the formation of central martensite and network cementite. Simultaneously, Si can significantly delay the exothermic peak of steel wire to a higher temperature range, thereby improving the thermal stability of the steel wire. Therefore, the Si content should be controlled at 1.00%–1.03%.

[0029] S and P: Impurity elements such as S and P segregate at grain boundaries, which greatly reduces the resistance to delayed fracture. P can form micro-segregation during the solidification of molten steel, and then segregate at the grain boundaries during heating at the austenitizing temperature, significantly increasing the brittleness of the steel and thus increasing its susceptibility to delayed fracture. S forms MnS inclusions and segregates at grain boundaries, thus increasing the susceptibility of the steel to delayed fracture. Therefore, the P and S contents should be controlled at P ≤ 0.010% and S ≤ 0.010%.

[0030] O and N: Oxygen forms various oxide inclusions in steel. Under stress, stress concentration easily occurs at these oxide inclusions, leading to the initiation of microcracks and thus deteriorating the mechanical properties of the steel, especially its toughness and fatigue resistance. Therefore, in metallurgical production, measures must be taken to minimize its content, controlling O to ≤ 0.0020%. N precipitates as Fe4N in steel, with a slow diffusion rate, causing aging of the steel. N also reduces the cold workability of the steel; N should be controlled to ≤ 0.0065%.

[0031] To improve fatigue performance and meet the requirements of high-temperature applications, the content of Si and Mn elements is increased. Due to the inherent strengthening effects of Si and Mn, and the presence of vanadium carbides at high temperatures, dislocation movement is difficult, thus increasing the isomorphic temperature and ensuring high strength at 300℃ and 350℃. Therefore, the chemical composition must satisfy 3.0≤(Si+1.2*Mn) / (8*V)≤7.0. To avoid reducing toughness, the addition of Si increases the activity of C atoms in austenite, accelerating C atom migration during phase transformation. This reduces the concentration of C atom aggregation regions in the ferrite lamellae, decreasing stress concentration in C atom segregation regions during wire drawing, improving the ductility, toughness, and torsional properties of the steel wire, and reducing delamination during wire torsion.

[0032] To achieve high strength, ductility, and toughness, and obtain good resistance to delayed fracture, the hydrogen content is strictly controlled. This invention employs a "two-heat forming" process, where after continuous casting, the billet undergoes high-temperature diffusion annealing to improve billet segregation, controlling the carbon segregation index to ≤1.10. Then, after heating, the billet is subjected to high-speed wire rod rolling to achieve… The wire rod is rolled to obtain hot-rolled wire rods for heat-resistant high-strength steel strands with ultra-high fatigue performance. The microstructure of the hot-rolled wire rods has a sorbitization rate of ≥95%, a grain size of ≥9, a central martensite of ≤1.0, and a network cementite of ≤1.0. The tensile strength of the hot-rolled wire rods is ≥1440MPa, and the reduction of area is ≥37%. After being drawn, such hot-rolled wire rods can achieve a room temperature tensile strength ≥2320MPa, withstand ≥10 180° bends in both directions without breaking, and undergo ≥20 360° torsion cycles with good torsional fracture. The wires at 200℃ have a tensile strength ≥2180MPa with a strength loss rate ≤7.0%, at 300℃ they have a tensile strength ≥1900MPa with a strength loss rate ≤19.0%, and at 360℃ they have a tensile strength ≥1700MPa with a strength loss rate ≤26.0%. After being twisted, these wires can be converted into 2300MPa-level ultra-high strength steel strands. The mechanical properties of the finished steel strands can meet the following requirements: tensile strength ≥2330MPa, elastic modulus 190-210GPa, yield strength ratio 0.90~0.95, and high fatigue performance ≥2 million cycles.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] This invention employs a high-C-high-Si composition design system and uses micro-alloying with Cr, V, Ni, Cu, etc., to achieve the preparation of high-fatigue-resistant, heat-resistant, and high-strength steel strands without the need to add expensive alloying elements, resulting in low cost.

[0035] This invention improves billet segregation by using high-temperature diffusion annealing after continuous casting, and controls the billet carbon segregation index to be ≤1.10.

[0036] The steel grade of this invention can be produced by conventional smelting processes in converters, electric furnaces, or other smelting furnaces according to the composition range disclosed in this invention. High-carbon steel wire rods for wire ropes can be produced by conventional rolling processes on ordinary high-speed wire rod mills and under controlled cooling conditions using the Stellmore cooling line. High-strength prestressed steel strands of 2300MPa grade can be produced through conventional continuous drawing and stranding processes. The production process is simple and the production cost is low. Attached Figure Description

[0037] Figure 1 The metallographic structure of the hot-rolled wire rod of the steel strand used in Example 1 is shown. Detailed Implementation

[0038] This invention provides a steel for ultra-high fatigue performance heat-resistant high-strength steel strand. The chemical composition and weight percentage of the steel are as follows: C 0.89%~1.10%, Mn 0.70%~1.00%, Cr 0.20%~0.35%, V 0.04%~0.09%, Alt 0.015%-0.030%, Si 1.00%~1.30%, P≤0.010%, S≤0.010%, O≤0.0020%, N≤0.0065%, with the remainder being Fe and other unavoidable impurities; wherein, 3.0≤(Si+1.2*Mn) / (8*V)≤7.0, and in the formula, the values ​​of each chemical component are calculated by multiplying the content of each chemical component in the steel by 100.

[0039] The production method of the ultra-high fatigue performance heat-resistant high-strength steel strand includes the following steps: smelting → refining → continuous casting of 380mm*450mm large square billet → diffusion annealing → rolling of 160mm*160mm small square billet → grinding and peeling → wire rod rolling → controlled cooling in the Steyrmo cooling line → finished wire rod.

[0040] The smelting process employs an electric arc furnace: oxygen is determined before tapping, and slag discharge is strictly controlled during the tapping process.

[0041] The refining steps include LF furnace refining and RH vacuum degassing;

[0042] During RH vacuum degassing, the pure degassing time should be ≥15 minutes to ensure that the [H] content after vacuum treatment is ≤1.5ppm.

[0043] In the continuous casting step, the target temperature of the molten steel in the tundish is controlled at 10-40°C above the liquidus temperature, and the casting speed is 2.1-2.3 mm / min.

[0044] In the diffusion annealing step, the annealing temperature is 1230-1260℃, and the holding time is 10-12h. High-temperature diffusion annealing can further improve the segregation of the billet, making the carbon segregation index of the billet ≤1.10.

[0045] In the wire rolling process, the wire is first homogenized at 1140-1160℃ for 80-100 minutes, and then rolled. The initial rolling temperature is 940-980℃, the final rolling temperature is 880-920℃, and the wire drawing temperature is 860-910℃.

[0046] The Stellmore cooling line employs a two-stage cooling process. First, it cools to 570–630°C at a rate of 7–11°C / s, holds for 15–35 seconds, and then slowly cools to room temperature at a rate of ≤4°C / s.

[0047] The present invention also provides an ultra-high fatigue performance heat-resistant high-strength steel strand, which is obtained by drawing and stranding the steel used in the ultra-high fatigue performance heat-resistant high-strength steel strand of the present invention.

[0048] The diameter of the center wire of the steel strand is Φ5.10mm, the diameter of the edge wire is Φ5.06mm, and the diameter of the finished steel strand is 15.2mm.

[0049] The present invention will now be described in detail with reference to the embodiments.

[0050] The chemical composition and weight percentage of the steel used for the steel strands in each embodiment and comparative example are shown in Table 1.

[0051] Table 1

[0052]

[0053] The steel used for the steel strand in all embodiments and comparative examples follows the production route as follows: electric furnace smelting → LF refining + RH vacuum degassing → continuous casting of 380*450mm large square billets → diffusion annealing → rolling of 160mm*160mm small square billets → grinding and peeling → wire rod rolling → controlled cooling in the Steyrmo cooling line → finished wire rod. The finished wire rod is... Specifications of the wire.

[0054] The production process parameters of the steel used for the steel strands in each embodiment and comparative example are shown in Table 2.

[0055] Table 2

[0056]

[0057] The microstructure and grain size of the hot-rolled wire rods used for steel strands in each embodiment and comparative example are shown in Table 3. The hot-rolled wire rods have a sorbitization rate ≥95%, a grain size ≥9.5 grade, central martensite ≤1.0 grade, and network cementite ≤1.0 grade. The hot-rolled tensile strength Rm ≥1440MPa and the reduction of area Z ≥37%, exhibiting high strength and high toughness.

[0058] Table 3

[0059]

[0060] The steel strands in each embodiment and comparative example were prepared from hot-rolled steel wire rods through drawing and stranding to form steel strands with a center wire diameter of Φ5.10mm, an edge wire diameter of Φ5.06mm, and a finished steel strand diameter of 15.2mm. The properties of each steel strand are shown in Table 4. The finished steel strands have a strength ≥2330MPa, an elastic modulus of 190-210GPa, a yield strength ratio of 0.90~0.95, and high fatigue performance ≥2 million cycles.

[0061] Table 4

[0062]

[0063]

[0064] Table 4 lists the test methods for each performance component: All properties of the steel strand were tested according to GB / T 21839-2019 "Test Methods for Steel for Prestressed Concrete". Mechanical properties (including Rm, modulus of elasticity, and yield strength ratio) were tested using tensile tests, and fatigue strength was tested using axial fatigue force tests.

[0065] The steel wire exhibits good ductility and toughness. At room temperature, its strength is ≥2320 MPa. It can withstand ≥10 180° bends in both directions without breaking, and ≥20 360° twists with a good torsional fracture surface. The heat resistance is evaluated using high-temperature strength: at 200℃, the strength is ≥2180 MPa with a strength loss rate ≤7.0%; at 300℃, the strength is ≥1900 MPa with a strength loss rate ≤19.0%; and at 360℃, the strength is ≥1700 MPa with a strength loss rate ≤26.0%. The steel wire demonstrates excellent high-temperature performance.

[0066] Table 5. Wire properties of embodiments and comparative examples of the present invention.

[0067]

[0068] Table 5 lists the test methods for each performance characteristic as follows: Mechanical properties at room temperature were tested using the room temperature test method for metallic materials in GB / T 228.1-2010 "Metallic materials, tensile testing—Part 1: Tests at room temperature". 180° bending was tested using the bending test method in GB / T 21839-2019 "Steel for prestressed concrete". 360° torsion was tested using the torsion test method in GB / T 21839-2019 "Steel for prestressed concrete".

[0069] The above detailed description of a high-strength, heat-resistant steel strand with ultra-high fatigue performance and its production method, with reference to the embodiments, is illustrative rather than limiting. Several embodiments can be listed within the defined scope. Therefore, variations and modifications that do not depart from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A high-strength, heat-resistant steel strand with ultra-high fatigue performance, characterized in that, The chemical composition and weight percentage of the steel used for the ultra-high fatigue performance heat-resistant high-strength steel strand are as follows: C 0.89%~1.10%, Mn 0.70%~1.00%, Cr 0.20%~0.35%, V 0.04%~0.09%, Alt 0.015%~0.030%, Si 1.00%~1.30%, P≤0.010%, S≤0.010%, O≤0.0020%, N≤0.0065%, with the remainder being Fe and other unavoidable impurities; among which, 3.0≤(Si+1.2*Mn) / (8*V)≤7.0; The production method of the steel for ultra-high fatigue performance heat-resistant high-strength steel strand includes the following steps: smelting → refining → continuous casting → diffusion annealing → rolling → grinding and peeling → wire rod rolling → controlled cooling in the Steyrmo cooling line → finished wire rod. The ultra-high fatigue performance heat-resistant high-strength steel strand uses steel wires with a room temperature tensile strength ≥2320MPa, capable of withstanding ≥10 180° bends in both directions without breakage, and ≥20 360° torsion cycles with good torsional fracture. At 200℃, the wire tensile strength is ≥2180MPa with a strength loss rate ≤7.0%; at 300℃, the wire tensile strength is ≥1900MPa with a strength loss rate ≤19.0%; and at 360℃, the wire tensile strength is ≥1700MPa with a strength loss rate ≤26.0%.

2. The steel for ultra-high fatigue performance heat-resistant high-strength steel strand according to claim 1, characterized in that, The hot-rolled wire rod for ultra-high fatigue performance heat-resistant high-strength steel strand has a sorbitization rate of ≥95%, a grain size of ≥9, a central martensite of ≤1.0, and a network cementite of ≤1.0; the tensile strength of the hot-rolled wire rod is ≥1440MPa, and the reduction of area is ≥37%.

3. The steel for ultra-high fatigue performance heat-resistant high-strength steel strand according to claim 1, characterized in that, The finished steel strand made from the steel used in the ultra-high fatigue performance heat-resistant high-strength steel strand has a tensile strength ≥2330MPa, an elastic modulus of 190-210GPa, a yield strength ratio of 0.90~0.95, and high fatigue performance ≥2 million cycles.

4. A method for producing steel for ultra-high fatigue performance heat-resistant high-strength steel strand as described in any one of claims 1-3, characterized in that, The production method includes the following steps: smelting → refining → continuous casting → diffusion annealing → rolling → grinding and peeling → wire rod rolling → Steyrmo cooling line controlled cooling → finished wire rod.

5. The production method according to claim 4, characterized in that, The refining steps include LF furnace refining and RH vacuum degassing; during RH vacuum degassing, the pure degassing time is ≥15 minutes to ensure that the [H] content after vacuum treatment is ≤1.5ppm.

6. The production method according to claim 4, characterized in that, In the continuous casting process, the superheat of the molten steel is controlled at 10-40℃, and the casting speed is 2.1-2.3 mm / min.

7. The production method according to claim 4, characterized in that, In the diffusion annealing step, the annealing temperature is 1230-1260℃ and the holding time is 10-12h.

8. The production method according to claim 4, characterized in that, In the wire rolling process, the wire is first homogenized at 1140-1160℃ for 80-100 minutes, and then rolled. The initial rolling temperature is 940-980℃, the final rolling temperature is 880-920℃, and the wire drawing temperature is 860-910℃.

9. The production method according to claim 4, characterized in that, The Stellmore cooling line employs a two-stage cooling process. First, it cools to 570–630°C at a rate of 7–11°C / s, holds for 15–35 seconds, and then slowly cools to room temperature at a rate of ≤4°C / s.

10. A heat-resistant, high-strength steel strand with ultra-high fatigue performance, characterized in that, The high-strength, heat-resistant steel strand with ultra-high fatigue performance as described in any one of claims 1-3 is obtained by drawing and stranding.

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