Ultrahigh corrosion-resistant retard-bonded prestressed tendon

Abstract

The invention discloses an ultrahigh corrosion-resistant retard-bonded prestressed tendon. The prestressed tendon comprises a sleeve, a plurality of reinforcing ribs and a plurality of reinforcing ribs, the steel strand is arranged in the sleeve and extends in the axial direction of the sleeve, a gap is formed between the steel strand and the inner wall of the sleeve, the tensile strength of the steel strand reaches 1860 Mpa or above, the minimum value of the stress corrosion test time of the steel strand in the solution A reaches 5 hours or above, and the median value of the stress corrosion test time of the steel strand in the solution A reaches 8 hours or above; and the slow bonding layer is arranged in a gap between the sleeve and the steel strand. The service life of the prestressed part is further prolonged by selecting the steel strand with higher stress corrosion resistance on the aspect of material intrinsic and adopting a combined slow-bonding protection measure, and the safety performance of the prestressed part within the designed service life is improved; practical reference basis is provided for application of the prestress technology and the retard-bonded prestressed tendon with higher corrosion resistance in the fields of concrete structure engineering and wind power technology.

Description

Technical Field

[0001] The present application belongs to the field of prestressed steel technology, and specifically relates to an ultra-high corrosion-resistant slow-bonding prestressed steel bar. Background Art

[0002] The durability of prestressed tendons significantly impacts the performance of prestressed structures. Therefore, the durability guarantee for prestressed tendons should be higher than that for ordinary steel bars. Especially when structures face complex environmental conditions, simply improving the quality and thickness of the concrete cover often fails to guarantee the designed service life. As the strength level of steel strands increases, their susceptibility to stress corrosion in high-stress environments increases significantly, hindering the use of ultra-high-strength steel strands.

[0003] In the field of wind power technology, prestressed components such as anchor bolts and high-strength screws currently used in wind turbine foundations are all unbonded prestressed structures. These are typically coated with Dacromet for corrosion protection. In actual use, PVC pipes are often placed over the outer surfaces of the anchor bolts and high-strength screws, creating a bondless state between the anchor bolts and high-strength screws and the concrete. After tensioning, the top of the PVC pipe is sealed to prevent water from entering. However, the waterproof sealing process for PVC pipe tops is typically complex and has drawbacks, allowing rainwater to enter the pipes. Since Dacromet loses its corrosion protection upon contact with water, foundations constructed with this approach are subject to severe corrosion of prestressed components, posing a serious threat to wind turbine safety. Currently, wind turbine towers primarily utilize external prestressed structures and prestressed cables. These external prestressed tendons are directly exposed to the external environment, particularly in harsh corrosive environments such as coastal locations. Therefore, there is an urgent need to improve the adaptability and corrosion resistance of these key components in their operating environments and extend their service life. Summary of the Invention

[0004] The purpose of this application is to provide a super-high corrosion-resistant slow-bonding prestressed tendon to solve the technical problem that the existing prestressed tendons have low corrosion resistance and cannot guarantee the designed service life.

[0005] In order to achieve the above-mentioned object, the present application provides an ultra-high corrosion-resistant slow-bonding prestressed tendon, the prestressed tendon comprising:

[0006] casing;

[0007] A steel strand arranged inside the casing, the steel strand extending axially along the casing, with a gap formed between the steel strand and the inner wall of the casing, the tensile strength of the steel strand reaching 1860 MPa or greater, and the minimum stress corrosion test time of the steel strand in solution A reaching 5 hours or greater, and the median time reaching 8 hours or greater;

[0008] The slow-bonding layer is arranged in the gap between the casing and the steel strand.

[0009] In one or more embodiments, the slow-bonding layer is an epoxy resin layer, and the slow-bonding layer evenly fills the gap between the steel strand and the sleeve, and the thickness of the controllable bonding layer in the radial direction of the steel strand is 1.15 to 1.25 mm.

[0010] In one or more embodiments, the nominal diameter of the steel strand is 21.8 to 28.6 mm, and the nominal area of the steel strand is 313 to 532 mm. 2 .

[0011] In one or more embodiments, the steel strand is obtained by twisting 7 wire rods, the nominal diameter of the steel strand is 15.2 to 21.6 mm, and the nominal area of the steel strand is 140 to 285 mm. 2 .

[0012] In one or more embodiments, the steel strand is obtained by twisting a plurality of wire rods, and the chemical composition of the wire rods comprises, by mass percentage:

[0013] 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.

[0014] In one or more embodiments, the diameter of the wire rod is 8-14 mm, the tensile strength is 1180-1300 MPa, and the cross-sectional shrinkage is 38-48%; the troostitization rate of the wire rod is greater than or equal to 92%, and the spacing between troostite lamellae is 50-70 nm.

[0015] In one or more embodiments, the steel strand is prepared by the following steps:

[0016] 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;

[0017] The target molten steel is cast into shape by continuous casting of small square billets to obtain intermediate billets;

[0018] Performing a high-speed wire rolling process on the intermediate billet to obtain a coil;

[0019] 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 to obtain a wire rod;

[0020] The steel strand is prepared by sequentially subjecting a plurality of the wire rods to the processes of pickling, phosphating, drawing, stranding and stabilization.

[0021] 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.

[0022] 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;

[0023] 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.

[0024] 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.

[0025] 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.

[0026] In one or more embodiments, in the step of preparing the steel strand by sequentially subjecting the plurality of wire rods to pickling, phosphating, drawing, stranding and stabilizing processes,

[0027] 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.

[0028] The phosphating is carried out after the pickled coil is left for 20 to 28 hours;

[0029] 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;

[0030] The twisting tension is greater than or equal to 80 kN, and the speed is less than or equal to 36 m / min;

[0031] The stabilization temperature of the stabilization step is 400-430°C.

[0032] Different from the prior art, the beneficial effects of this application are:

[0033] The prestressed tendons of this application achieve high corrosion resistance of ultra-high-strength prestressed steel strands, and further effectively protect and prevent corrosion by placing external casings on the steel strands, significantly extending their service life. By selecting steel strands with higher stress corrosion resistance based on the inherent material properties, and by adopting combined slow-bonding protection measures, the service life of the prestressed components is further extended, thereby improving their safety performance within the designed service life. This provides a practical reference for the application of prestressing technology and highly corrosion-resistant slow-bonding prestressed tendons in concrete structural engineering and wind power technology.

[0034] 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;

[0035] The troostitization rate of the wire rod of the present application reaches more than 92%, the troostite lamellar spacing is 50-70nm, and the tensile strength reaches more than 1180Mpa; the tensile strength of the steel strand of the present application reaches 1860Mpa level, and it has excellent stress corrosion resistance. 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 1860Mpa level steel strand, far exceeding the national standard requirements, and can meet the use requirements of steel strands in corrosive environments. Based on the existing standard of meeting the minimum value of 2 hours and the median time of 5 hours for the design service life of 50 years, the prestressed tendons applied by the present invention can be estimated to have a service life of about 80 years based on the corrosion resistance time. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] 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.

[0037] Figure 1 This is a structural diagram of an embodiment of the ultra-high corrosion-resistant slow-bonding prestressed tendon of the present application;

[0038] Figure 2 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;

[0039] Figure 3 This is a metallographic image of the wire rod prepared in Example 1 of the present application;

[0040] Figure 4 This is a metallographic image of the wire rod prepared in Example 2 of the present application;

[0041] Figure 5 This is a metallographic image of the wire rod prepared in Example 3 of the present application. DETAILED DESCRIPTION

[0042] 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.

[0043] In order to solve the technical problem that the existing prestressed tendons have low corrosion resistance and cannot guarantee the designed service life, the applicant has developed a new type of prestressed tendon. This prestressed component can achieve ultra-high strength prestressed steel strands with high stress corrosion resistance and further effectively protect the external casing of the steel strands from corrosion, which can significantly extend their service life, is conducive to reducing carbon emissions and reducing material consumption, and is also conducive to accelerating project progress and improving structural safety.

[0044] Specifically, see Figure 1 , Figure 1 It is a structural schematic diagram of an embodiment of the ultra-high corrosion-resistant slow-bonding prestressed tendons of the present application.

[0045] like Figure 1As shown, the prestressed tendon is applied to a concrete member 400 , and includes a sleeve 100 arranged in the concrete member 400 , and a steel strand 200 arranged inside the sleeve 100 .

[0046] The steel strand 200 is extended axially along the casing 100 , and a gap is formed between the steel strand 200 and the inner wall of the casing 100 .

[0047] The prestressed tendon further includes a slow-bonding layer 300 arranged at the gap between the sleeve 100 and the steel strand 200 .

[0048] It can be understood that wrapping the steel strand 200 with the slow-bonding layer 300 can effectively protect the steel strand 200 from corrosion, thereby increasing its service life.

[0049] In this embodiment, the prestressed tendons are arranged in the concrete member 400. In other embodiments, the prestressed tendons can also be directly exposed and used, and the effects of this embodiment can be achieved.

[0050] To ensure the protective effect, the slow-bonding layer 300 in this embodiment can be an epoxy resin layer, and the slow-bonding layer 300 evenly fills the gap between the steel strand 200 and the sleeve 100. The thickness of the slow-bonding layer 300 in the radial direction of the steel strand 200 is 1.15 to 1.25 mm.

[0051] Specifically, in one embodiment, a single-component epoxy resin obtained by mixing epoxy resin, a thermotropic latent curing agent, a modifier, and a filler can be injected into the gap between the steel strand 200 and the sleeve 100 to form a slow-bonding layer 300 after curing.

[0052] In this embodiment, the sleeve 100 may be a plastic sleeve 100. In other embodiments, the sleeve 100 may be made of other materials as long as it can wrap the slow-bonding layer 300 and can achieve the effect of this embodiment.

[0053] For further information, see Figure 2 In this embodiment, the specification of the steel strand 200 is 1*7, that is, it is obtained by twisting 7 wire rods 2011021. The nominal diameter of the steel strand 200 can be 15.2~21.6mm, and the nominal area of the steel strand 200 can be 140~285mm. 2 .

[0054] In other embodiments, the steel strand 200 may be obtained by twisting other numbers of wire rods 201. For example, the specification of the steel strand 200 may be 1*19, i.e., it is obtained by twisting 19 wire rods 201. The nominal diameter of the steel strand 200 may be 21.8 to 28.6 mm, and the nominal area of the steel strand 200 may be 313 to 532 mm. 2, can also achieve the effect of this embodiment.

[0055] In this embodiment, the tensile strength of the steel strand reaches 1860 MPa or more, and the minimum stress corrosion test time of the steel strand 200 in solution A reaches 5 hours or more, and the median time reaches 8 hours or more.

[0056] The stress corrosion test time refers to the test time in solution A when conducting stress corrosion test in accordance with standard GB / T 15970.6-2007.

[0057] In order to further improve the stress corrosion resistance of prestressed tendons and increase the strength of prestressed tendons, the material and preparation method of the steel strand in this application are further improved.

[0058] Specifically, the chemical composition of the wire rod for high stress corrosion resistance prestressed steel strand of the present application includes, by mass percentage:

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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%.

[0063] 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%.

[0064] This application also provides a method for preparing the above-mentioned wire rod, please refer to Figure 2 , Figure 2 It is a schematic flow chart of the method for preparing wire rod for high stress corrosion resistant prestressed steel strand of the present application.

[0065] like Figure 2 As shown, the preparation method comprises:

[0066] S100, smelting molten steel to obtain target molten steel.

[0067] 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 a wire rod with a target chemical composition can be prepared based on the target molten steel.

[0068] In one embodiment, the step of smelting molten steel may specifically include sequentially performing converter smelting and LF furnace refining.

[0069] 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.

[0070] 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.

[0071] S200, adopt small billet continuous casting to cast the target molten steel into shape and obtain intermediate billet.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] S300: Perform high-speed wire rolling on the intermediate billet to obtain a coil.

[0076] 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.

[0077] 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.

[0078] In order to facilitate the effect of the subsequent post-rolling controlled cooling process, the spinning temperature can be 820-880°C.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] The present application also provides a steel strand, which is prepared from a plurality of wire rods according to any of the above embodiments.

[0088] Specifically, the steel strand is prepared from a plurality of wire rods through the processes of pickling, phosphating, drawing, stranding and stabilization in sequence.

[0089] 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.

[0090] In one embodiment, phosphating is performed after the pickled coil is left for 20 to 28 hours;

[0091] 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.

[0092] 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.

[0093] 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.

[0094] In one embodiment, the steel strand may be a 1860 MPa grade 1*7 steel strand.

[0095] The effects of the technical solution of this application are further elaborated in detail below with reference to specific embodiments.

[0096] Example 1:

[0097] A 1860MPa grade 1*7 steel strand is prepared by the following process:

[0098] (1) Molten steel smelting process

[0099] 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.

[0100] 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;

[0101] 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.

[0102] (2) Continuous casting process

[0103] The target molten steel was cast into billets with a cross-sectional size of 180 mm × 240 mm by billet continuous casting.

[0104] 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.

[0105] (3) High-speed wire rolling process

[0106] 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℃.

[0107] (4) Post-rolling controlled cooling process

[0108] 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.

[0109] (5) Steel strand processing procedures

[0110] The coil is pickled, phosphated and drawn to produce wire rod, which is then twisted and stabilized to produce 1860MPa grade steel strand.

[0111] 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.

[0112] Examples 2 to 4:

[0113] 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.

[0114] 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.

[0115] Table 1

[0116]

[0117]

[0118] Table 2

[0119]

[0120]

[0121] Effect example 1:

[0122] The metallographic structure of the wire rods prepared in Examples 1 to 3 was tested, and the testing method included:

[0123] 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 3 to 5 , Figure 3 This is a metallographic image of the wire rod prepared in Example 1 of the present application. Figure 4This is a metallographic image of the wire rod prepared in Example 2 of the present application. Figure 5 This is a metallographic image of the wire rod prepared in Example 3 of the present application.

[0124] 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.

[0125] Table 3

[0126] Example Diameter / mm Sorbentation rate Grain boundary cementite Martensite 1 14 92 0 0 2 8 93 0 0 3 12.5 93 0 0

[0127] Effect example 2:

[0128] 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.

[0129] Table 4

[0130]

[0131] 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.

[0132] Effect example 3:

[0133] 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.

[0134] Table 5

[0135]

[0136]

[0137] 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.

[0138] Effect example 4:

[0139] 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.

[0140] Table 6

[0141]

[0142] 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.

[0143] 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.

[0144] 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. An ultra-high corrosion-resistant slow-bonding prestressed tendon, characterized in that: The prestressed tendons include: casing; A steel strand arranged inside the casing, the steel strand extending axially along the casing, with a gap formed between the steel strand and the inner wall of the casing, the tensile strength of the steel strand reaching 1860 MPa or greater, and the minimum stress corrosion test time of the steel strand in solution A reaching 5 hours or greater, and the median time reaching 8 hours or greater; The slow-bonding layer is arranged in the gap between the casing and the steel strand.

2. The ultra-high corrosion-resistant slow-bonding prestressed tendon according to claim 1, characterized in that: The slow-bonding layer is an epoxy resin layer, and the slow-bonding layer evenly fills the gap between the steel strand and the sleeve. The thickness of the controllable bonding layer in the radial direction of the steel strand is 1.15 to 1.25 mm.

3. The ultra-high corrosion-resistant slow-bonding prestressed tendon according to claim 1, characterized in that: The nominal diameter of the steel strand is 21.8 to 28.6 mm, and the nominal area of the steel strand is 313 to 532 mm. 2 ;or, The steel strand is obtained by twisting 7 wire rods, the nominal diameter of the steel strand is 15.2 to 21.6 mm, and the nominal area of the steel strand is 140 to 285 mm. 2 .

4. The ultra-high corrosion-resistant slow-bonding prestressed tendon according to claim 1, characterized in that: The steel strand is obtained by twisting a plurality of wire rods, and the chemical composition of the wire rods comprises, 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.

5. The ultra-high corrosion-resistant slow-bonding prestressed tendon according to claim 4, 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 is 38-48%. The sorbitization rate of the wire rod is greater than or equal to 92%, and the spacing between sorbitan lamellae is 50-70 nm.

6. The ultra-high corrosion-resistant slow-bonding prestressed tendon according to claim 1, characterized in that: The steel strand is prepared by the following steps: 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 shape by continuous casting of small square billets to obtain intermediate billets; 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, 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 to obtain a wire rod; The steel strand is prepared by sequentially subjecting a plurality of the wire rods to the processes of pickling, phosphating, drawing, stranding and stabilization.

7. The ultra-high corrosion-resistant slow-bonding prestressed tendon according to claim 6, 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.

8. The ultra-high corrosion-resistant slow-bonding prestressed tendon according to claim 6, 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.

9. The ultra-high corrosion-resistant slow-bonding prestressed tendon according to claim 6, 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.

10. The ultra-high corrosion-resistant slow-bonding prestressed tendon according to claim 6, characterized in that: In the step of preparing the steel strand by sequentially subjecting the plurality of wire rods to pickling, phosphating, drawing, stranding and stabilizing processes, 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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