High-carbon steel wire rod for ultrahigh-strength prestressed steel strand and production method of high-carbon steel wire rod

Abstract

The invention particularly relates to a high-carbon steel wire rod for an ultrahigh-strength prestressed steel strand and a production method of the high-carbon steel wire rod, and the production method comprises the working procedures of molten steel smelting, continuous casting, high-speed wire rolling and controlled cooling after rolling, the degree of superheat of molten steel, the stirring current of the crystallizer, the stirring frequency of the crystallizer, the pulling speed during continuous casting, the specific water flow of continuous casting, the tail end stirring current, the tail end stirring frequency and the total reduction of soft reduction are all optimally controlled; in the high-speed wire rolling process, the rectangular blank obtained in the continuous casting process is heated and then subjected to rough rolling and finish rolling in sequence, the heating temperature is 1080-1150 DEG C, the initial rolling temperature of rough rolling is 950-1000 DEG C, the inlet temperature of finish rolling is 850-880 DEG C, and the spinning temperature is 840-920 DEG C; the step of controlled cooling after rolling can adopt a Steyr cooling process or a salt bath process. And the production cost is greatly reduced, and the homogeneity of the steel is improved.

Description

Technical Field

[0001] The invention relates to the technical field of steel smelting, and in particular to a high-carbon steel wire rod for ultra-high-strength prestressed steel strand and a production method thereof. Background Art

[0002] With the promulgation of the new national standard, the market demand for ultra-high-strength prestressed steel strands of 2200MPa and above will surely grow rapidly. However, there is currently no special raw material wire rod for prestressed steel strands of 2200MPa and higher strength levels, and ultra-high-strength bridge cable wire rods can only be used as raw materials for trial production. Ultra-high-strength bridge cables require high torsion and other indicators while having ultra-high strength, so their raw material wire rods need to add a large amount of alloy elements and undergo secondary heat treatment, which is costly. For example, Chinese patent CN201710721505.0 discloses heat-treated wire rods and production methods for 2000MPa-grade cable steel wires. Ultra-high-strength prestressed steel strands have no strict requirements for torsion and other indicators, and the market demand is as high as millions of tons. The use of raw material wire rods for bridge cables to produce prestressed steel strands has the problems of high cost, excess quality, and insufficient supply capacity. Summary of the invention

[0003] The object of the present invention is to provide a high carbon steel wire rod for ultra-high strength prestressed steel strand and a production method thereof, so as to solve the problems raised in the above-mentioned background technology.

[0004] To achieve the above-mentioned purpose, the present invention provides the following technical solution: a high carbon steel wire rod for ultra-high strength prestressed steel strand, the chemical composition of the wire rod comprising, by mass percentage: C 0.90-0.99%, Si 0.20-0.40%, Mn 0.6-1.0%, Cr≤0.40, Al 0.020-0.040%, S≤0.020%, P≤0.020%, N≤0.004%, and the rest being Fe and other inevitable impurities.

[0005] In the chemical composition of the present invention:

[0006] C is the most important strengthening element in steel, but with the increase of C content, the segregation control of continuous casting billet becomes more difficult, which affects the homogeneity of wire rod. In the present invention, the C content is limited to 0.90-0.99%.

[0007] Si is a strengthening element and deoxidizing element in steel, and can suppress the strength loss of cold-drawn steel wire during stabilization treatment. However, too much Si will reduce the plasticity of the wire rod and increase the difficulty of mechanical peeling and removal of the oxide scale. In the present invention, the Si content is limited to 0.20-0.40%.

[0008] Mn is a strengthening element in steel, which can improve the strength and hardenability of steel and ensure a good work hardening rate of wire rod. However, too much Mn will reduce the plasticity of steel, increase the stability of austenite and increase the difficulty of controlling organizational transformation. In the present invention, the Mn content is limited to 0.6-1.0%.

[0009] Cr is a strengthening element in steel. It has the function of refining pearlite lamellae in pearlite steel to improve plasticity. However, too much Cr element will increase the difficulty of controlling wire rod segregation. The present invention limits the Cr content to ≤0.40.

[0010] Al is a deoxidizing element in steel, which can effectively remove oxygen in steel and improve the cleanliness of steel. Al can also form AlN with N to refine grains and reduce the dynamic aging of N atoms in the drawn steel wire, thus ensuring the plasticity of the steel wire. In the present invention, the Al content is limited to 0.015-0.055%.

[0011] S is easily segregated at the grain boundary and makes the grain boundary embrittled, thereby reducing the strength and plasticity of the steel. In addition, S will generate MnS with Mn, thereby reducing the solid solution strengthening effect of Mn. In the present invention, the S content is limited to ≤0.020%.

[0012] P is an impurity element in steel, which is easy to segregate at the grain boundary and make the grain boundary embrittled, thereby reducing the strength and plasticity of the steel. In the present invention, the P content is limited to ≤0.020%.

[0013] N will cause the plasticity of steel to deteriorate and increase the risk of delayed fracture of wire rod. A high N content will coarsen AlN and TiN, which is not conducive to fine grain strengthening. In addition, free nitrogen atoms will undergo dynamic aging in the steel wire and reduce the plasticity of the steel wire. The present invention limits the nitrogen content to ≤0.004%.

[0014] Based on the above chemical composition design, the high strength of the wire rod is improved by using cheap C, Mn and Si elements without adding other precious metal elements, which reduces the difficulty of molten steel smelting and reduces production costs. At the same time, the content of Al and N elements is limited to ensure that the wire rod has good plasticity.

[0015] Furthermore, the chemical composition of the wire rod includes, by mass percentage, C 0.90-0.99%, Si 0.20-0.40%, Mn 0.6-1.0%, Cr≤0.40, Al 0.020-0.040%, S≤0.020%, P≤0.020%, N≤0.004%, V 0.02-0.10, and the rest is Fe and other inevitable impurities.

[0016] V can refine grains and strengthen by precipitation. In the preferred chemical composition design, the V content is controlled to be 0.02-0.10%, which can be applied to the Stelmor air cooling process to make up for the defect of insufficient air cooling speed. According to the cooling capacity of the fan, the V content is preferably controlled to V≤0.05% to control the production cost of the wire rod.

[0017] The present invention also provides a production method of high-carbon steel wire rod for ultra-high-strength prestressed steel strand, the production method comprising the steps of molten steel smelting, continuous casting, high-strength wire rolling, and controlled cooling after rolling in sequence, in the continuous casting step, the superheat of the molten steel is controlled to be 20-25°C, the stirring current of the crystallizer is 270±25A, the stirring frequency of the crystallizer is 3±0.5Hz, the pulling speed during continuous casting is 1.2±0.05m / min, the continuous casting specific water volume is 0.22±0.01L / kg, the end stirring current is 450±25A, and the end stirring frequency is 8± 0.5Hz, total light reduction is 15.0±0.2mm; in the high-speed wire rolling process, the rectangular billet obtained in the continuous casting process is heated and then subjected to rough rolling and finish rolling, the heating temperature is 1080-1150℃, the start rolling temperature of rough rolling is 950-1000℃, the entrance temperature of finish rolling is 850-880℃, and the wire-spinning temperature is 840-920℃; the post-rolling controlled cooling process can adopt the Stelmor cooling process or the salt bath process, the Stelmor cooling process is only suitable for wire rods with a diameter of ≤9mm, and the salt bath process is not limited by the direct diameter of the wire rod.

[0018] Preferably, the post-rolling controlled cooling process can adopt the Steyr cooling process. In the Steyrmore cooling process, the spinning temperature is 880-920°C, the roller speed of the entrance section is 0.8-1.2m / s, the first 8 fans are opened at 80-100%, the 9th to 11th fans are opened at 40-60%, the 12th and subsequent fans are closed, the insulation covers corresponding to the 1st to 11th fan positions are all opened, and the remaining insulation covers are closed.

[0019] Preferably, the post-rolling controlled cooling process can adopt a salt bath process. In the salt bath process, the spinning temperature is 840-870°C, and the wire rod after spinning is directly immersed in a salt bath tank for salt bathing. The salt bath temperature is 500-560°C and the salt bath time is 120-300s.

[0020] Preferably, the metallographic structure of the wire rod is mainly troostite, the troostitization rate is ≥93%, the level of grain boundary cementite and core martensite is not greater than level 1.0; the diameter of the wire rod is ≤15mm, the tensile strength is 1280-1480MPa, and the cross-sectional shrinkage rate is 30-45%.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) Based on the high-carbon low-alloy chemical composition design scheme of the present invention, the strength and plasticity of the wire rod are improved by increasing the sorbitization rate with a reasonable post-rolling controlled cooling process, replacing the existing process route of high-alloy and secondary heat treatment of bridge wire rods, greatly reducing the production cost, and more in line with the market positioning and various application scenarios of prestressed steel strands with large quantities and wide applications;

[0023] (2) Based on the chemical composition design scheme of the present invention and the control of the production processes such as continuous casting, rolling and post-rolling, the homogeneity of the steel is improved. The metallographic structure of the wire rod prepared by the production method of the present invention is mainly troostite, the troostitization rate is ≥93%, and the level of grain boundary cementite and core martensite is not greater than level 1.0; the tensile strength is 1280-1480MPa, and the cross-sectional shrinkage rate is 30-45%. The wire rod has high strength and good plasticity and is suitable for the drawing processing of 2160, 2230, and 2300MPa prestressed steel strands. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The metallographic structure picture of the wire rod of Example 1 is shown;

[0025] Figure 2 The metallographic structure picture of the wire rod of Example 2 is shown;

[0026] Figure 3 A scanning electron microscope image showing the microstructure of the wire rod of Example 3;

[0027] Figure 4 A scanning electron microscope image showing the microstructure of the wire rod of Example 4;

[0028] Figure 5 The metallographic structure picture of the wire rod of Example 5 is shown. DETAILED DESCRIPTION

[0029] In order to make the purpose and technical solution of the present invention clearly and completely described, and the advantages more clearly understood, the embodiments of the present invention are further described in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are part of the embodiments of the present invention, rather than all of the embodiments, and are only used to explain the embodiments of the present invention, and are not used to limit the embodiments of the present invention. All other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example 1

[0031] See also Figure 1 The present invention provides a technical solution: a method for producing high-carbon steel wire rod for ultra-high-strength prestressed steel strand.

[0032] (1) Molten steel smelting process

[0033] The molten steel is smelted by sequential converter smelting and LF furnace refining steps, and the chemical composition of the molten steel at the end of the smelting process is shown in Table 1 in terms of mass percentage. In addition, the chemical composition of the continuous casting billet obtained in the continuous casting process and the chemical composition of the high carbon steel wire rod for ultra-high strength prestressed steel strands finally prepared are consistent with the chemical composition of the molten steel at the end of the molten steel smelting process, as shown in Table 1.

[0034] Among them, in the converter smelting step, molten iron is sent to the converter and mixed with scrap steel to form molten steel, and desiliconization, dephosphorization, oxygen blowing and decarburization are carried out. When tapping the steel, alloy is added to the ladle for deoxidation and alloying; in the refining step, the molten steel after converter smelting is sent to the LF refining furnace for chemical composition adjustment and temperature control, and the inclusions in the molten steel are controlled by soft stirring until the temperature and chemical composition meet the standards and the steel is tapped.

[0035] (2) Continuous Casting Process

[0036] The molten steel obtained in the molten steel smelting process is cast into small billets with a cross-sectional size of 180 mm×240 mm by billet continuous casting.

[0037] Among them, the superheat of the molten steel is controlled at 20°C, the stirring current of the crystallizer is 245A, the stirring frequency of the crystallizer is 2.5Hz, the pulling speed during continuous casting is 1.15m / min, the continuous casting water volume is 0.21L / kg, the end stirring current is 425A, the end stirring frequency is 7.5Hz, and the total reduction under light pressure is 14.8mm.

[0038] (3) High-speed wire rolling process

[0039] The small square billet obtained in the continuous casting process is heated and then subjected to rough rolling and finish rolling to prepare a wire rod with a diameter of 15 mm. The heating temperature is 1150°C, the start rolling temperature of the rough rolling is 1000°C, the finish rolling inlet temperature is 850°C, and the wire drawing temperature is 840°C.

[0040] (4) Salt bath process

[0041] The wire rod after spinning is directly immersed in a salt bath tank for salt bathing. The temperature of the salt bath tank is 500°C and the salt bath time is 300s.

[0042] Example 2

[0043] (1) Molten steel smelting process

[0044] The molten steel is smelted by sequentially performing converter smelting and LF furnace refining steps, so that the chemical composition of the molten steel at the end of the smelting process is shown in Table 1 in terms of mass percentage. In addition, the chemical composition of the continuous casting billet obtained in the continuous casting process and the chemical composition of the high carbon steel wire rod for ultra-high strength prestressed steel strands finally prepared are consistent with the chemical composition of the molten steel at the end of the molten steel smelting process, as shown in Table 1.

[0045] Among them, in the converter smelting step, the pretreated molten iron is sent to the converter and mixed with scrap steel to form molten steel, and desiliconization, dephosphorization, oxygen blowing and decarburization are carried out. When tapping the steel, alloy is added to the ladle for deoxidation and alloying; in the refining step, the molten steel after converter smelting is sent to the LF refining furnace for chemical composition adjustment and temperature control, and the inclusions in the molten steel are controlled by soft stirring, and the steel is tapped after the temperature and chemical composition meet the standards.

[0046] (2) Continuous Casting Process

[0047] The molten steel obtained in the molten steel smelting process is cast into small billets with a cross-sectional size of 180 mm×240 mm by billet continuous casting.

[0048] Among them, the superheat of the molten steel is controlled at 21°C, the stirring current of the crystallizer is 270A, the stirring frequency of the crystallizer is 3Hz, the pulling speed during continuous casting is 1.2m / min, the continuous casting water volume is 0.22L / kg, the end stirring current is 450A, the end stirring frequency is 8Hz, and the total reduction under light pressure is 15.0mm.

[0049] (3) High-speed wire rolling process

[0050] The intermediate billet obtained in the continuous casting process is prepared into a wire rod with a diameter of 14 mm by high-speed wire rolling. The heating temperature is 1080°C, the starting temperature of rough rolling is 960°C, the entrance temperature of finishing rolling is 880°C, and the wire drawing temperature is 860°C.

[0051] (4) Salt bath process

[0052] The wire rod after spinning is directly immersed in a salt bath tank for salt bathing. The temperature of the salt bath tank is 530°C and the salt bath time is 120s.

[0053] Example 3

[0054] (1) Molten steel smelting process

[0055] The molten steel is smelted by sequential converter smelting and LF furnace refining steps, and the chemical composition of the molten steel at the end of the smelting process is shown in Table 1 in terms of mass percentage. In addition, the chemical composition of the continuous casting billet obtained in the continuous casting process and the chemical composition of the high carbon steel wire rod for ultra-high strength prestressed steel strands finally prepared are consistent with the chemical composition of the molten steel at the end of the molten steel smelting process, as shown in Table 1.

[0056] Among them, in the converter smelting step, the pretreated molten iron is sent to the converter and mixed with scrap steel to form molten steel, and desiliconization, dephosphorization, oxygen blowing and decarburization are carried out. When tapping the steel, alloy is added to the ladle for deoxidation and alloying; in the refining step, the molten steel after converter smelting is sent to the LF refining furnace for chemical composition adjustment and temperature control, and the inclusions in the molten steel are controlled by soft stirring, and the steel is tapped after the temperature and chemical composition meet the standards.

[0057] (2) Continuous Casting Process

[0058] The molten steel obtained from the molten steel smelting process was cast into a small billet with a cross-sectional size of 180mm×240mm by billet continuous casting. The superheat of the molten steel was controlled at 25°C, the stirring current of the crystallizer was 295A, the stirring frequency of the crystallizer was 3.5Hz, the pulling speed during continuous casting was 1.25m / min, the continuous casting specific water volume was 0.23L / kg, the end stirring current was 475A, the end stirring frequency was 8.5Hz, and the total reduction under light pressure was 15.2mm.

[0059] (3) High-speed wire rolling process

[0060] The intermediate billet obtained in the continuous casting process is prepared into a wire rod with a diameter of 8 mm by high-speed wire rolling. The heating temperature is 1120°C, the starting temperature of rough rolling is 950°C, the entrance temperature of finishing rolling is 870°C, and the wire-spinning temperature is 870°C.

[0061] (4) Salt bath process

[0062] The wire rod after spinning is directly immersed in a salt bath tank for salt bathing. The temperature of the salt bath tank is 560°C and the salt bath time is 90s.

[0063] Example 4

[0064] (1) Molten steel smelting process

[0065] The molten steel is smelted by sequentially performing converter smelting and LF furnace refining steps, so that the chemical composition of the molten steel at the end of the smelting process is shown in Table 1 in terms of mass percentage. In addition, the chemical composition of the continuous casting billet obtained in the continuous casting process and the chemical composition of the high carbon steel wire rod for ultra-high strength prestressed steel strands finally prepared are consistent with the chemical composition of the molten steel at the end of the molten steel smelting process, as shown in Table 1.

[0066] Among them, in the converter smelting step, the pretreated molten iron is sent to the converter and mixed with scrap steel to form molten steel, and desiliconization, dephosphorization, oxygen blowing and decarburization are carried out. When tapping the steel, alloy is added to the ladle for deoxidation and alloying; in the refining step, the molten steel after converter smelting is sent to the LF refining furnace for chemical composition adjustment and temperature control, and the inclusions in the molten steel are controlled by soft stirring, and the steel is tapped after the temperature and chemical composition meet the standards.

[0067] (2) Continuous Casting Process

[0068] The molten steel obtained from the molten steel smelting process was cast into a small billet with a cross-sectional size of 180 mm × 240 mm by billet continuous casting. The superheat of the molten steel was controlled at 25°C, the stirring current of the crystallizer was 280A, the stirring frequency of the crystallizer was 3Hz, the pulling speed during continuous casting was 1.22m / min, the continuous casting specific water volume was 0.22L / kg, the end stirring current was 450A, the end stirring frequency was 8Hz, and the total reduction under light pressure was 15.0mm.

[0069] (3) High-speed wire rolling process

[0070] The intermediate billet obtained in the continuous casting process is prepared into a wire rod with a diameter of 8 mm by high-speed wire rolling. The heating temperature is 1120°C, the starting temperature of rough rolling is 950°C, the entrance temperature of finishing rolling is 880°C, and the wire drawing temperature is 920°C.

[0071] (4) Stelmor cooling process

[0072] The Stelmor cooling line is used to control the temperature and cool the rolled wire rod. The roller speed of the entrance section is 1.2m / s, the first 8 fans are opened at 100%, 100%, 100%, 100%, 90%, 90%, 80%, and 80% in sequence, the 9th to 11th fans are opened at 60%, 50%, and 40% in sequence, the 12th and subsequent fans are turned off, the insulation covers corresponding to the 1st to 11th fan positions are all opened, and the other insulation covers are closed.

[0073] Example 5

[0074] (1) Molten steel smelting process

[0075] The molten steel is smelted by sequentially performing converter smelting and LF furnace refining steps, so that the chemical composition of the molten steel at the end of the smelting process is shown in Table 1 in terms of mass percentage. In addition, the chemical composition of the continuous casting billet obtained in the continuous casting process and the chemical composition of the high carbon steel wire rod for ultra-high strength prestressed steel strands finally prepared are consistent with the chemical composition of the molten steel at the end of the molten steel smelting process, as shown in Table 1.

[0076] Among them, in the converter smelting step, the pretreated molten iron is sent to the converter and mixed with scrap steel to form molten steel, and desiliconization, dephosphorization, oxygen blowing and decarburization are carried out. When tapping the steel, alloy is added to the ladle for deoxidation and alloying; in the refining step, the molten steel after converter smelting is sent to the LF refining furnace for chemical composition adjustment and temperature control, and the inclusions in the molten steel are controlled by soft stirring, and the steel is tapped after the temperature and chemical composition meet the standards.

[0077] (2) Continuous Casting Process

[0078] The molten steel obtained from the molten steel smelting process was cast into a small billet with a cross-sectional size of 180 mm × 240 mm by billet continuous casting. The superheat of the molten steel was controlled at 25°C, the stirring current of the crystallizer was 290A, the stirring frequency of the crystallizer was 3.3Hz, the pulling speed during continuous casting was 1.23m / min, the continuous casting specific water volume was 0.23L / kg, the end stirring current was 460A, the end stirring frequency was 8Hz, and the total reduction under light pressure was 15mm.

[0079] (3) High-speed wire rolling process

[0080] The intermediate billet obtained in the continuous casting process is prepared into a wire rod with a diameter of 8 mm by high-speed wire rolling. The heating temperature is 1150°C, the starting temperature of rough rolling is 980°C, the entrance temperature of finishing rolling is 880°C, and the wire-spinning temperature is 880°C.

[0081] (4) Stelmor cooling process

[0082] The Stelmor cooling line is used to control the temperature and cool the rolled wire rod. The roller speed of the entrance section is 0.8m / s, the first 8 fans are opened at 100%, 100%, 100%, 100%, 100%, 90%, 90%, and 80% respectively, the 9th to 11th fans are opened at 50%, 50%, and 40% respectively, the 12th and subsequent fans are turned off, the insulation covers corresponding to the 1st to 11th fan positions are all opened, and the other insulation covers are closed.

[0083] Table 1

[0084]

[0085]

[0086] The wire rods of Examples 1-5 were sampled and subjected to metallographic structure testing and mechanical property testing according to the same testing method. The specific testing methods and test results are as follows:

[0087] (1) In terms of metallographic structure, a wire rod with a length of 10 cm was taken from the head of the wire rod to prepare a metallographic sample. After mechanical polishing and nitric acid alcohol corrosion, the sample was placed under a metallographic microscope for structural observation, or electrolytic polishing and scanning electron microscope observation. It was found that the structure of the wire rods of Examples 1-5 was a troostite structure, as shown in Table 2. The metallographic structure pictures of the wire rods of Examples 1-5 are as follows: Figures 1 to 5 shown.

[0088] (2) In terms of mechanical properties, referring to the test method and definition of GB / T228 standard, the mechanical properties of the wire rod were tested using a tensile testing machine, and the tensile strength and cross-sectional shrinkage of the wire rods of Examples 1-5 were measured as shown in Table 2.

[0089] Table 2

[0090] Example Diameter / mm Sodium thiocyanate rate Grain boundary cementite Martensite tensile strength Sectional shrinkage 1 15 95 0.5 0.5 1450 32 2 14 95 0 0 1380 38 3 8 95 0 0 1480 45 4 8 93 0.5 1.0 1320 36 5 8 93 1.0 0.5 1280 35

[0091] The wire rods of Examples 1-5 produced according to this embodiment can be used to process 1×7 structure 2230-2300 MPa grade ultra-high strength steel strands.

[0092] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A high carbon steel wire rod for ultra-high strength prestressed steel strand, characterized in that: The chemical composition of the wire rod includes, by mass percentage, C 0.90-0.99%, Si 0.20-0.40%, Mn 0.6-1.0%, Cr≤0.40, Al 0.020-0.040%, S≤0.020%, P≤0.020%, N≤0.004%, and the rest is Fe and other inevitable impurities.

2. The high carbon steel wire rod for ultra-high strength prestressed steel strand according to claim 1, characterized in that: The chemical composition of the wire rod includes, by mass percentage, C 0.90-0.99%, Si 0.20-0.40%, Mn 0.6-1.0%, Cr≤0.40, Al 0.020-0.040%, S≤0.020%, P≤0.020%, N≤0.004%, V 0.02-0.10, and the rest is Fe and other inevitable impurities.

3. A method for producing high carbon steel wire rod for ultra-high strength prestressed steel strand, characterized in that: The production method comprises the steps of molten steel smelting, continuous casting, high-speed wire rolling and controlled cooling after rolling in sequence. In the continuous casting step, the superheat of the molten steel is controlled to be 20-25°C, the stirring current of the crystallizer is 270±25A, the stirring frequency of the crystallizer is 3±0.5Hz, the pulling speed during continuous casting is 1.2±0.05m / min, the continuous casting water volume is 0.22±0.01L / kg, the end stirring current is 450±25A, and the end stirring frequency is 3±0.5Hz. The frequency is 8±0.5Hz, and the total reduction under light pressure is 15.0±0.2mm; in the high-speed wire rolling process, the rectangular billet obtained in the continuous casting process is heated and then subjected to rough rolling and finish rolling, the heating temperature is 1080-1150℃, the start rolling temperature of rough rolling is 950-1000℃, the finish rolling entrance temperature is 850-880℃, and the wire drawing temperature is 840-920℃; the post-rolling controlled cooling process can adopt the Steyr cooling process or the salt bath process.

4. The method for producing high carbon steel wire rod for ultra-high strength prestressed steel strand according to claim 3, characterized in that: The post-rolling controlled cooling process can adopt the Steyr cooling process. In the Steyrmore cooling process, the spinning temperature is 880-920°C, the roller speed of the entrance section is 0.8-1.2m / s, the first 8 fans are opened at 80-100%, the 9th to 11th fans are opened at 40-60%, the 12th and subsequent fans are closed, the insulation covers corresponding to the 1st to 11th fan positions are all opened, and the remaining insulation covers are closed.

5. The method for producing high carbon steel wire rod for ultra-high strength prestressed steel strand according to claim 3, characterized in that: The post-rolling controlled cooling process can adopt a salt bath process. In the salt bath process, the spinning temperature is 840-870°C, and the wire rod after spinning is directly immersed in a salt bath tank for salt bathing. The salt bath temperature is 500-560°C and the salt bath time is 120-300s.

6. The method for producing high carbon steel wire rod for ultra-high strength prestressed steel strand according to claim 3, characterized in that: The metallographic structure of the wire rod is mainly troostite, the troostitization rate is ≥93%, the level of grain boundary cementite and core martensite is not greater than level 1.0; the diameter of the wire rod is ≤15mm, the tensile strength is 1280-1480MPa, and the cross-sectional shrinkage is 30-45%.

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