Wire rod for prestressed steel strand with high stress corrosion resistance, steel strand and preparation method

Abstract

The invention discloses a steel wire rod for a prestressed steel strand with high stress corrosion resistance, the steel strand and a preparation method. The steel wire rod comprises the following chemical components in percentage by mass: 0.70-0.80% of C, 0.40-0.80% of Si, 0.20-0.80% of Mn, 0.15-0.40% of Cr, 0.01-0.05% of V, less than 0.30% of Cu and less than 0.30% of Ni. S is less than or equal to 0.008%, P is less than or equal to 0.010%, N is less than or equal to 0.004%, and O is less than or equal to 0.0020%. By reducing the carbon content, improving the purity and increasing corrosion-resistant chemical elements, the stress corrosion resistance can be improved while the strength of the wire rod is guaranteed; the steel wire rod has excellent strength and plasticity, the drawing area reduction rate can be reduced, surface damage and internal defects are reduced, and the stress corrosion index of the steel strand is improved.

Description

Technical Field

[0001] The present application belongs to the technical field of iron and steel metallurgy and metal products, and specifically relates to a wire rod for high stress corrosion resistant prestressed steel strand, a steel strand and a preparation method. Background Art

[0002] Stress corrosion cracking (SCC) is a brittle fracture phenomenon of materials under the combined action of a corrosive environment and tensile stress. The national standard GB / T5224 requires a minimum stress corrosion performance of 2 hours and a median of 5 hours for steel strands, but the stress corrosion resistance required by this standard is far from meeting the requirements for the use of steel strands in corrosive environments. To improve the corrosion resistance of steel strands, hot-dip galvanizing is generally used to coat the steel wire surface with a layer of zinc or zinc-aluminum alloy, but the cost is high, reaching 1,500 yuan per ton. Alternatively, the entire surface of the steel strand can be coated with PE plastic, but this is easily damaged and has poor reliability. In particular, during tensioning construction, the surface plastic layer cannot deform with the steel strand and is damaged, losing its anti-corrosion function. Summary of the Invention

[0003] The purpose of the present application is to provide a wire rod, a steel strand and a preparation method for a highly stress corrosion resistant prestressed steel strand, so as to solve the technical problem that the stress corrosion resistance of the existing steel strand is far from meeting the requirements for use of the steel strand in a corrosive environment.

[0004] In order to achieve the above-mentioned object, the first aspect of the present application provides a wire rod for prestressed steel strand with high stress corrosion resistance, wherein the chemical composition of the wire rod comprises, in terms of mass percentage:

[0005] C 0.70-0.80%, Si 0.40-0.80%, Mn 0.20-0.80%, Cr 0.15-0.40%, V 0.01-0.05%, Cu less than 0.30%; Ni less than 0.30%; S less than or equal to 0.008%, P less than or equal to 0.010%, N less than or equal to 0.004%, O less than or equal to 0.0020%, and the balance is Fe and other inevitable impurities.

[0006] In one or more embodiments, the wire rod has a diameter of 8 to 14 mm, a tensile strength of 1180 to 1300 MPa, and a cross-sectional reduction rate of 38 to 48%.

[0007] In one or more embodiments, the troostitization rate of the wire rod is greater than or equal to 92%, and the spacing between troostite lamellae is 50-70 nm.

[0008] In order to achieve the above-mentioned object, the second aspect of the present application provides a method for preparing a wire rod for a prestressed steel strand with high stress corrosion resistance, comprising:

[0009] smelting molten steel to obtain target molten steel, wherein the chemical composition of the target molten steel comprises, by mass percentage, the following: C 0.70-0.80%, Si 0.40-0.80%, Mn 0.20-0.80%, Cr 0.15-0.40%, V 0.01-0.05%, Cu less than 0.30%; Ni less than 0.30%; S less than or equal to 0.008%, P less than or equal to 0.010%, N less than or equal to 0.004%, O less than or equal to 0.0020%, and the balance being Fe and other unavoidable impurities;

[0010] The target molten steel is cast into a shape by continuous casting of small square billets to obtain an intermediate billet;

[0011] Performing a high-speed wire rolling process on the intermediate billet to obtain a coil;

[0012] The coil is immediately immersed in a salt bath tank for online salt bath isothermal treatment. After the treatment is completed, the coil is immediately placed in a heat preservation corridor for online aging treatment and temperature control. After the treatment is completed, it is cooled to room temperature to obtain the wire rod.

[0013] In one or more embodiments, the step of smelting molten steel is specifically: performing converter smelting and LF furnace refining in sequence;

[0014] The converter smelting specifically includes feeding molten iron into a converter and mixing it with scrap steel to form molten steel, and performing desiliconization, dephosphorization, oxygen blowing and decarburization. When tapping, alloy is added to the ladle for deoxidation and alloying.

[0015] The LF furnace refining specifically involves sending the molten steel after converter smelting into the LF refining furnace for chemical composition adjustment and temperature control, and controlling the inclusions in the molten steel by soft stirring until the temperature of the molten steel reaches the continuous casting requirement. After the chemical composition of the molten steel meets the standard, the steel is tapped to obtain the target molten steel.

[0016] In one or more embodiments, in the step of using small square billet continuous casting to cast the target molten steel into shape, the superheat of the target molten steel is 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 content is 0.22±0.01L / kg, the end stirring current is 450±25A, the end stirring frequency is 8±0.5Hz, and the total reduction under light pressure is 15.0±0.2mm.

[0017] In one or more embodiments, the step of performing a high-speed wire rolling process on the intermediate billet to obtain a coil specifically comprises: heating the intermediate billet and then performing rough rolling, finish rolling and wire drawing in sequence to obtain the coil;

[0018] Among them, the heating temperature is 1080-1150°C, the starting temperature of rough rolling is 950-1000°C, the inlet temperature of finishing rolling is 850-900°C, and the spinning temperature is 820-880°C.

[0019] In one or more embodiments, the coil is immediately immersed in a salt bath tank for online salt bath isothermal treatment, immediately enters a heat preservation corridor for online aging treatment after the treatment is completed, and is cooled to room temperature after the treatment is completed.

[0020] The salt bath temperature of the online salt bath isothermal treatment is 480-535° C., the salt bath time is 60-200s, the average cooling rate of the temperature control treatment is not higher than 0.2° C. / s, and the treatment time of the temperature control treatment is not less than 30 minutes.

[0021] In order to achieve the above-mentioned purpose, the third aspect of the present application provides a steel strand, comprising the wire rod described in any of the above-mentioned embodiments or the wire rod prepared by the preparation method described in any of the above-mentioned embodiments, and the steel strand is prepared by a plurality of the wire rods through the processes of pickling, phosphating, drawing, stranding and stabilization in sequence.

[0022] In one or more embodiments, the pickling is specifically to pickle the coil in a 15-20 wt % hydrochloric acid solution for 7-10 min at a pickling temperature of 35-42° C.;

[0023] The phosphating is carried out after the pickled coil is left for 20 to 28 hours;

[0024] The drawing is specifically to draw the coil in 9 to 11 passes, with a pass reduction rate of 23 to 25%, a drawing speed not higher than 2 m / s, and a temperature rise of not higher than 100° C. per pass;

[0025] The twisting tension is greater than or equal to 80 kN, and the speed is less than or equal to 36 m / min;

[0026] The stabilization temperature of the stabilization step is 400-430°C.

[0027] Different from the prior art, the present invention has the following advantages:

[0028] This application can significantly improve the stress corrosion resistance of the wire rod while ensuring its strength by reducing carbon content, increasing purity and adding corrosion-resistant chemical elements;

[0029] The present application significantly improves the strength and plasticity of the wire rod and the homogeneity of the steel by optimizing the chemical composition ratio of the wire rod, as well as reasonable preparation process parameters and post-rolling controlled cooling process, so that the target strength can be obtained by drawing with a lower area reduction rate in the subsequent steel strand preparation process, reducing the drawing area reduction rate and significantly improving the plasticity index of the wire rod, which can reduce surface damage and internal defects of the wire rod during subsequent drawing processing, thereby improving the stress corrosion index of the steel strand;

[0030] The troostitization rate of the wire rod of the present application reaches more than 92%, the troostite interlamellar spacing is 50 to 70 nm, and the tensile strength reaches more than 1180 MPa; the tensile strength of the steel strand of the present application reaches 1860 MPa level, and it has excellent resistance to stress corrosion. Taking the prepared 1×7 steel strand as an example, the minimum stress corrosion time is 5 hours and the median time is 8 hours, which is significantly better than the existing 1860 MPa level steel strand, far exceeding the national standard requirements, and can meet the use requirements of the steel strand in a corrosive environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 This is a schematic flow chart of a method for preparing wire rod for prestressed steel strand with high stress corrosion resistance according to the present application;

[0033] Figure 2 This is a metallographic image of the wire rod prepared in Example 1 of the present application;

[0034] Figure 3 This is a metallographic image of the wire rod prepared in Example 2 of the present application;

[0035] Figure 4 This is a metallographic image of the wire rod prepared in Example 3 of the present application. DETAILED DESCRIPTION

[0036] In order to enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of this application.

[0037] In order to solve the problem that steel strands in the existing technology cannot achieve both high strength and stress corrosion resistance, the applicant has developed a wire rod for high stress corrosion resistant prestressed steel strands, which can be used to prepare steel strands with a strength level of 1860Mpa and have excellent stress corrosion resistance.

[0038] Specifically, the chemical composition of the wire rod for high stress corrosion resistance prestressed steel strand of the present application includes, by mass percentage:

[0039] C 0.70-0.80%, Si 0.40-0.80%, Mn 0.20-0.80%, Cr 0.15-0.40%, V 0.01-0.05%, Cu less than 0.30%; Ni less than 0.30%; S less than or equal to 0.008%, P less than or equal to 0.010%, N less than or equal to 0.004%, O less than or equal to 0.0020%, and the balance is Fe and other inevitable impurities.

[0040] The present application significantly improves the homogeneity of the steel and improves the stress corrosion index of the steel by optimizing the mass fraction of each chemical component of the wire rod.

[0041] Specifically, in this application, the C content is limited to 0.70-0.80%, which ensures the tensile strength of the wire rod while reducing the carbon content, which helps to improve the stress corrosion resistance; by limiting the Si content to 0.40-0.80%, it helps to improve the corrosion resistance and relaxation resistance of the steel; by limiting the Mn content to 0.20-0.80%, the strength and hardenability of the steel can be improved, and a good work hardening rate of the wire rod can be guaranteed; by limiting the Cr content to 0.15-0.40%, on the one hand, it is beneficial to obtain retained austenite, and on the other hand, a dense oxide film is formed on the surface of the steel, while avoiding excessive Cr content that increases the difficulty of controlling segregation; by limiting the V content to 0.01-0.05%, the carbon oxides formed by V serve as effective hydrogen traps in the steel, thereby improving the stress corrosion index of the steel; by adding Cu and Ni and limiting their content to less than 0.30%, the stress corrosion index of the steel can be significantly improved.

[0042] In addition, in order to avoid affecting the strength and plasticity of the steel, this application limits the S content to less than or equal to 0.008%, the P content to less than or equal to 0.010%, the N content to less than or equal to 0.004%, and the O content to less than or equal to 0.0020%.

[0043] Based on the aforementioned composition ratios, by reducing carbon content, increasing purity, and adding corrosion-resistant chemical elements, the stress corrosion resistance of the wire rod can be significantly improved while maintaining its strength. In one embodiment, the wire rod can have a diameter of 8 to 14 mm, a tensile strength of 1180 to 1300 MPa, and a reduction of area of ​​38 to 48%.

[0044] This application also provides a method for preparing the above-mentioned wire rod, please refer to Figure 1 , Figure 1 It is a flow chart of the method for preparing wire rod for high stress corrosion resistance prestressed steel strand of the present application.

[0045] like Figure 1 As shown, the preparation method comprises:

[0046] S100, smelting molten steel to obtain target molten steel.

[0047] Among them, the chemical composition of the target molten steel is consistent with the chemical composition of the wire rod, which will not be repeated here, so that the wire rod with the target chemical composition can be prepared based on the target molten steel.

[0048] In one embodiment, the step of smelting molten steel may specifically include sequentially performing converter smelting and LF furnace refining.

[0049] Among them, converter smelting specifically involves feeding molten iron into a converter and mixing it with scrap steel to form molten steel, and then undergoing desiliconization, dephosphorization, and oxygen blowing for decarburization. When tapping, alloys are added to the ladle for deoxidation and alloying.

[0050] LF furnace refining specifically involves sending the molten steel after converter smelting into the LF refining furnace for chemical composition adjustment and temperature control, and controlling the inclusions in the molten steel through soft stirring until the temperature of the molten steel reaches the continuous casting requirements. After the chemical composition of the molten steel meets the standard, steel is tapped to obtain the target molten steel.

[0051] S200, adopt small billet continuous casting to cast the target molten steel into shape and obtain intermediate billet.

[0052] After the target molten steel with the temperature and chemical composition meeting the requirements is prepared, the target molten steel can be cast into shape using a continuous casting process.

[0053] In one embodiment, the size of the continuously cast billet may be 180 mm×240 mm. In other embodiments, the size of the billet may be adjusted based on actual needs, while still achieving the effects of this embodiment.

[0054] In order to ensure the tensile strength and stress corrosion resistance of the prepared wire rod, the present application optimizes the parameters of the continuous casting process. Specifically, in one embodiment, the target superheat of the molten steel can be 20-25°C, the stirring current of the crystallizer can be 270±25A, the stirring frequency of the crystallizer can be 3±0.5Hz, the pulling speed during continuous casting can be 1.2±0.05m / min, the continuous casting water content can be 0.22±0.01L / kg, the end stirring current can be 450±25A, the end stirring frequency can be 8±0.5Hz, and the total reduction under light pressure can be 15.0±0.2mm.

[0055] S300: Perform high-speed wire rolling on the intermediate billet to obtain a coil.

[0056] Among them, the high-speed wire rolling process is specifically to heat the intermediate billet and then perform rough rolling, finish rolling and wire drawing in sequence to obtain a coil.

[0057] In one embodiment, the heating temperature may be 1080-1150°C, the starting temperature of the rough rolling may be 950-1000°C, and the inlet temperature of the finishing rolling may be 850-900°C.

[0058] In order to facilitate the effect of the subsequent post-rolling controlled cooling process, the spinning temperature can be 820-880°C.

[0059] S400, immediately immersing the coil in a salt bath tank for online salt bath isothermal treatment. After the treatment is completed, the coil is immediately placed in a heat preservation corridor for online aging treatment under temperature control. After the treatment is completed, the coil is cooled to room temperature to obtain a wire rod.

[0060] After the high-speed wire rolling process, the coil still maintains the spinning temperature of the rolling process. The coil can be directly immersed in the salt bath tank without uncoiling, realizing online salt bath isothermal treatment and accurately controlling the material structure and properties.

[0061] Compared with traditional off-line salt bath heat treatment, the solution of the present application does not require the coil to be unwound, heat treated and then rewound, thus avoiding surface damage to the steel and thus helping to improve the stress corrosion index of the steel strand.

[0062] In one embodiment, the salt bath temperature of the online salt bath isothermal treatment may be 480-535° C., and the salt bath time may be 60-200 s.

[0063] After the online salt bath isothermal treatment, the coil can be immediately placed in the insulation corridor for online aging, where the temperature is slowly lowered and the coil temperature is precisely controlled, thereby refining the microstructure of the steel.

[0064] In one embodiment, the average cooling rate of the temperature control treatment is no higher than 0.2° C. / s, and the treatment time of the temperature control treatment is no less than 30 minutes.

[0065] The post-rolling controlled cooling process based on online salt bath isothermal treatment and online aging in the insulation corridor can refine the microstructure of the wire rod and significantly increase the sorbitization rate to improve the strength and plasticity of the wire rod.

[0066] Based on the wire rod and its preparation method of the above-mentioned embodiments, by optimizing the chemical composition ratio of the wire rod and reasonable preparation process parameters and post-rolling controlled cooling process, the strength and plasticity of the wire rod and the homogeneity of the steel are significantly improved, so that it can be drawn with a lower area reduction rate in the subsequent steel strand preparation process to obtain the target strength, reduce the drawing area reduction rate and significantly improve the plasticity index of the wire rod, which can reduce the surface damage and internal defects of the wire rod during subsequent drawing processing, thereby improving the stress corrosion index of the steel strand.

[0067] The present application also provides a steel strand, which is prepared from a plurality of wire rods according to any of the above embodiments.

[0068] Specifically, the steel strand is prepared from a plurality of wire rods through the processes of pickling, phosphating, drawing, stranding and stabilization in sequence.

[0069] In one embodiment, the pickling is performed by pickling the coil in a 15-20 wt % hydrochloric acid solution for 7-10 minutes at a pickling temperature of 35-42°C.

[0070] In one embodiment, phosphating is performed after the pickled coil is left for 20 to 28 hours;

[0071] In one embodiment, the drawing is performed by drawing the coil in 9 to 11 passes, with a pass reduction rate of 23 to 25%, a drawing speed not exceeding 2 m / s, and a temperature rise of not exceeding 100° C. per pass.

[0072] Based on the above-mentioned S400 post-rolling controlled cooling process, the wire rod has strong plasticity, so the target strength can be achieved with a lower drawing reduction rate, which effectively reduces the surface damage and internal defects of the wire rod, thereby helping to improve the stress corrosion resistance.

[0073] In one embodiment, the twisting tension may be greater than or equal to 80 KN, the speed may be less than or equal to 36 m / min, and the stabilization temperature of the stabilization process may be 400-430°C.

[0074] In one embodiment, the steel strand may be a 1860 MPa grade 1*7 steel strand.

[0075] The effects of the technical solution of this application are further elaborated in detail below with reference to specific embodiments.

[0076] Example 1:

[0077] A 1860MPa grade 1*7 steel strand is prepared by the following process:

[0078] (1) Molten steel smelting process

[0079] The molten steel is smelted by sequentially performing converter smelting and LF furnace refining steps to obtain the target molten steel. The chemical composition of the target molten steel is shown in Table 1 below in terms of mass percentage.

[0080] Among them, in the converter smelting step, molten iron is fed into the converter and mixed with scrap steel to form molten steel, and desiliconization, dephosphorization, oxygen blowing and decarburization are carried out. When tapping, alloy is added to the ladle for deoxidation and alloying;

[0081] During 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. The steel is tapped after the temperature and chemical composition meet the standards. The target superheat of the molten steel is 20°C.

[0082] (2) Continuous casting process

[0083] The target molten steel was cast into billets with a cross-sectional size of 180 mm × 240 mm by billet continuous casting.

[0084] Among them, the target 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 content 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.

[0085] (3) High-speed wire rolling process

[0086] 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 1150℃, the starting rolling temperature of the rough rolling is 1000℃, the finishing rolling entrance temperature is 850℃, and the wire drawing temperature is 850℃.

[0087] (4) Post-rolling controlled cooling process

[0088] The coils after spinning are directly immersed in a salt bath for salt bathing. The temperature of the salt bath is 515℃ and the salt bath time is 120s. The coils after salt bath isothermal treatment are immediately placed in a heat preservation corridor for slow cooling. The treatment time is 30min and the average cooling rate is 0.15℃ / s.

[0089] (5) Steel strand processing procedures

[0090] The coil is pickled, phosphated and drawn to produce wire rod, which is then twisted and stabilized to produce 1860MPa grade steel strand.

[0091] Among them, pickling uses an aqueous solution of hydrochloric acid with a concentration of 19wt%, pickling for 8 minutes at a temperature of 35°C. After pickling, the coil is placed for 24 hours before entering the phosphating process; drawing uses 11 passes, with a pass reduction rate of 23%, a drawing speed of 2m / s, and a temperature rise of 100°C per pass; the twisting tension is 80kN, the speed is 36m / min, and the stabilization temperature is 400°C.

[0092] Examples 2 to 4:

[0093] A 1860MPa grade 1*7 steel strand, the preparation method of which is basically the same as that of Example 1, except that: 1. the chemical composition content of the wire rods in Examples 2 to 4 is different from that in Example 1; 2. the parameters of each process in Examples 2 to 3 are different from those in Example 1.

[0094] The chemical composition contents of the wire rods of Examples 1 to 4 can be found in Table 1 below, and the process parameters of Examples 1 to 3 can be found in Table 2 below.

[0095] Table 1

[0096]

[0097]

[0098] Table 2

[0099]

[0100]

[0101] Effect example 1:

[0102] The metallographic structure of the wire rods prepared in Examples 1 to 3 was tested, and the testing method included:

[0103] A 10 cm long wire rod was taken from the head of the wire rod to make a metallographic sample. After mechanical polishing and nitric acid etching, the sample was placed under a metallographic microscope for tissue observation. Figures 2 to 4 , Figure 2 This is a metallographic image of the wire rod prepared in Example 1 of the present application. Figure 3 This is a metallographic image of the wire rod prepared in Example 2 of the present application. Figure 4 This is a metallographic image of the wire rod prepared in Example 3 of the present application.

[0104] From the above tests, it was found that the structures of the wire rods of Examples 1-3 were all sorbite structures, and their metallographic data are shown in Table 3 below. The sorbitization rates of Examples 1 to 3 all reached 92% or above, and the spacing between sorbite lamellae was 50 to 70 nm, indicating that the wire rods had excellent strength and toughness.

[0105] Table 3

[0106]

[0107]

[0108] Effect example 2:

[0109] The mechanical properties of the wire rods prepared in Examples 1 to 3 were tested using a tensile testing machine. The test method was based on the test method and definition of GB / T228 standard, and the data in Table 4 below were obtained.

[0110] Table 4

[0111]

[0112] As can be seen from the above data, the tensile strength of the wire rods prepared in Examples 1 to 3 reaches 1250 MPa and above, and the cross-sectional shrinkage rate reaches 40% and above, showing excellent mechanical properties.

[0113] Effect example 3:

[0114] The steel strands prepared in Examples 1 to 3 were subjected to strength tests according to the standard GB / T 5224-2020, and the data in Table 5 below were obtained.

[0115] Table 5

[0116]

[0117]

[0118] As can be seen from the data in the above table, the tensile strength of the steel strands of Examples 1 to 3 all reached 1890 MPa or above, and they have excellent mechanical properties.

[0119] Effect example 4:

[0120] The steel strands prepared in Examples 1 to 3 were tested for stress corrosion resistance. The test method was based on the standard GB / T15970.6-2007, and the data in Table 6 below were obtained.

[0121] Table 6

[0122]

[0123] As can be seen from the above data, the steel strands prepared in Examples 1 to 3 all have excellent stress corrosion resistance, with the minimum stress corrosion value reaching 5.5h and the median reaching 8h, far exceeding the national standard requirements and meeting the use requirements of steel strands in corrosive environments.

[0124] It will be apparent to those skilled in the art that the present application is not limited to the details of the exemplary embodiments described above, and that the present application can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the present application is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0125] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A wire rod for prestressed steel strand with high stress corrosion resistance, characterized in that: The chemical composition of the wire rod includes, by mass percentage: C 0.70-0.80%, Si 0.40-0.80%, Mn 0.20-0.80%, Cr 0.15-0.40%, V 0.01-0.05%, Cu less than 0.30%, Ni less than 0.30%, S less than or equal to 0.008%, P less than or equal to 0.010%, N less than or equal to 0.004%, O less than or equal to 0.0020%, and the balance is Fe and other inevitable impurities.

2. The wire rod for prestressed steel strand with high stress corrosion resistance according to claim 1, characterized in that: The diameter of the wire rod is 8-14 mm, the tensile strength is 1180-1300 MPa, and the cross-sectional shrinkage rate is 38-48%.

3. The wire rod for prestressed steel strand with high stress corrosion resistance according to claim 1, characterized in that: The troostitization rate of the wire rod is greater than or equal to 92%, and the spacing between troostite lamellae is 50-70 nm.

4. A method for preparing a wire rod for a prestressed steel strand with high stress corrosion resistance, characterized in that: include: smelting molten steel to obtain target molten steel, wherein the chemical composition of the target molten steel comprises, by mass percentage, the following: C 0.70-0.80%, Si 0.40-0.80%, Mn 0.20-0.80%, Cr 0.15-0.40%, V 0.01-0.05%, Cu less than 0.30%; Ni less than 0.30%; S less than or equal to 0.008%, P less than or equal to 0.010%, N less than or equal to 0.004%, O less than or equal to 0.0020%, and the balance being Fe and other unavoidable impurities; The target molten steel is cast into a shape by continuous casting of small square billets to obtain an intermediate billet; Performing a high-speed wire rolling process on the intermediate billet to obtain a coil; The coil is immediately immersed in a salt bath tank for online salt bath isothermal treatment. After the treatment is completed, the coil is immediately placed in a heat preservation corridor for online aging treatment and temperature control. After the treatment is completed, it is cooled to room temperature to obtain the wire rod.

5. The preparation method according to claim 4, characterized in that The steps of smelting molten steel are specifically: performing converter smelting and LF furnace refining in sequence; The converter smelting specifically includes feeding molten iron into a converter and mixing it with scrap steel to form molten steel, and performing desiliconization, dephosphorization, oxygen blowing and decarburization. When tapping, alloy is added to the ladle for deoxidation and alloying. The LF furnace refining specifically involves sending the molten steel after converter smelting into the LF refining furnace for chemical composition adjustment and temperature control, and controlling the inclusions in the molten steel by soft stirring until the temperature of the molten steel reaches the continuous casting requirement. After the chemical composition of the molten steel meets the standard, the steel is tapped to obtain the target molten steel.

6. The preparation method according to claim 4, characterized in that In the step of using small square billet continuous casting to cast the target molten steel into shape, the superheat of the target molten steel is 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 content is 0.22±0.01L / kg, the end stirring current is 450±25A, the end stirring frequency is 8±0.5Hz, and the total reduction under light pressure is 15.0±0.2mm.

7. The preparation method according to claim 4, characterized in that The step of performing high-speed wire rolling on the intermediate billet to obtain the coil specifically comprises: heating the intermediate billet and then performing rough rolling, finish rolling and wire laying in sequence to obtain the coil; Among them, the heating temperature is 1080-1150°C, the starting temperature of rough rolling is 950-1000°C, the inlet temperature of finishing rolling is 850-900°C, and the spinning temperature is 820-880°C.

8. The preparation method according to claim 4, characterized in that The coil is immediately immersed in a salt bath tank for online salt bath isothermal treatment, and immediately enters a heat preservation corridor for online aging treatment after the treatment is completed, and is cooled to room temperature after the treatment is completed. The salt bath temperature of the online salt bath isothermal treatment is 480-535° C., the salt bath time is 60-200s, the average cooling rate of the temperature control treatment is not higher than 0.2° C. / s, and the treatment time of the temperature control treatment is not less than 30 minutes.

9. A steel strand, characterized in that: The steel strand comprises the wire rod described in any one of claims 1 to 3 or the wire rod prepared by the preparation method described in any one of claims 4 to 8, wherein the steel strand is prepared by sequentially subjecting a plurality of the wire rods to pickling, phosphating, drawing, stranding and stabilization processes.

10. The steel strand according to claim 9, characterized in that The pickling step specifically comprises pickling the coil in a 15-20 wt% hydrochloric acid solution for 7-10 minutes at a pickling temperature of 35-42° C. The phosphating is carried out after the pickled coil is left for 20 to 28 hours; The drawing is specifically to draw the coil in 9 to 11 passes, with a pass reduction rate of 23 to 25%, a drawing speed not higher than 2 m / s, and a temperature rise of not higher than 100° C. per pass; The twisting tension is greater than or equal to 80 kN, and the speed is less than or equal to 36 m / min; The stabilization temperature of the stabilization step is 400-430°C.

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