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

Abstract

The invention discloses a steel wire rod for an intrinsic stress corrosion resistant prestressed steel strand, the steel strand and a preparation method. The steel wire rod comprises the following chemical components in percentage by mass: 0.74-0.82% of C, 0.20-0.60% of Si, 0.20-0.80% of Mn, 0.15-0.40% of Cr, 0.01-0.05% of V, less than or equal to 0.008% of S, less than or equal to 0.010% of P, less than or equal to 0.004% of N, less than or equal to 0.0020% of O and the balance of Fe and other inevitable impurities. 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] This application belongs to the technical field of iron and steel metallurgy and metal products, and particularly relates to a wire rod, a steel strand for essentially stress corrosion-resistant prestressed steel strands, and a preparation method thereof. Background Art

[0002] Stress corrosion cracking (SCC) is a brittle fracture phenomenon of materials under the combined action of a corrosive environment and a tensile stress. The national standard GB / T5224 requires that the stress corrosion performance of steel strands be at least 2 hours and the median value be 5 hours. However, the anti-stress corrosion performance required by this standard far cannot meet the use requirements of steel strands in a corrosive environment. To improve the corrosion resistance of steel strands, generally, a layer of zinc or zinc-aluminum alloy can be plated on the surface of the steel wire by hot-dip galvanizing, but the cost is high, reaching 1500 yuan / ton; the method of wrapping the entire surface of the steel strand with PE plastic can also be used, but it is easily damaged and has poor reliability. Especially during tension construction, the surface plastic layer is damaged because it cannot deform together with the steel strand, losing the anti-corrosion function. Summary of the Invention

[0003] The purpose of this application is to provide a wire rod, a steel strand for essentially stress corrosion-resistant prestressed steel strands, and a preparation method thereof, so as to solve the technical problem that the anti-stress corrosion performance of existing steel strands far cannot meet the use requirements of steel strands in a corrosive environment.

[0004] To achieve the above purpose, in the first aspect of this application, a wire rod for essentially stress corrosion-resistant prestressed steel strands is provided. The chemical composition of the wire rod includes, by mass percentage:

[0005] C 0.74 - 0.82%, Si 0.20 - 0.60%, Mn 0.20 - 0.80%, Cr 0.15 - 0.40%, V 0.01 - 0.05%, 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 diameter of the wire rod is 8 - 14 mm, the tensile strength is 1180 - 1300 Mpa, and the reduction of area is 38 - 48%.

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

[0008] To achieve the above purpose, in the second aspect of this application, a preparation method of a wire rod for essentially stress corrosion-resistant prestressed steel strands is provided, including:

[0009] Smelt molten steel to obtain target molten steel. The chemical composition of the target molten steel, by mass percentage, includes: C 0.74 - 0.82%, Si 0.20 - 0.60%, Mn 0.20 - 0.80%, Cr 0.15 - 0.40%, V 0.01 - 0.05%, 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;

[0010] Adopt small billet continuous casting to cast the target molten steel into shape to obtain an intermediate billet;

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

[0012] Immediately immerse the coil into a salt bath tank for on-line salt bath isothermal treatment. After the treatment is completed, immediately put the coil into a heat preservation corridor for on-line aging for temperature control treatment. After the treatment is completed, cool it to room temperature to obtain the wire rod.

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

[0014] The converter smelting is specifically to send molten iron into the converter to be mixed with scrap steel to form molten steel, and carry out desiliconization, dephosphorization, and oxygen blowing decarburization. When tapping, add alloys to the ladle for deoxidation alloying;

[0015] The LF furnace refining is specifically to send the molten steel after converter smelting into the LF refining furnace for chemical composition adjustment, temperature control, and regulate the inclusions in the molten steel through soft stirring until the temperature of the molten steel reaches the continuous casting requirement and the chemical composition of the molten steel meets the standard, then tap to obtain the target molten steel.

[0016] In one or more embodiments, in the step of adopting small 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 mold is 270 ± 25A, the stirring frequency of the mold is 3 ± 0.5Hz, the drawing speed during continuous casting is 1.2 ± 0.05m / min, the specific water flow rate during continuous casting is 0.22 ± 0.01L / kg, the terminal stirring current is 450 ± 25A, the terminal stirring frequency is 8 ± 0.5Hz, and the total reduction amount of soft reduction is 15.0 ± 0.2mm.

[0017] In one or more embodiments, the step of performing high-speed wire rolling process on the intermediate billet to obtain a coil is specifically: heat the intermediate billet and then sequentially carry out rough rolling, finish rolling and spinning to obtain the coil;

[0018] Among them, the heating temperature is 1080 - 1150 °C, the starting rolling temperature of rough rolling is 950 - 1000 °C, the entry temperature of finish rolling is 850 - 920 °C, and the laying temperature is 850 - 910 °C.

[0019] In one or more embodiments, in the step of immediately immersing the coiled bar into a salt bath tank for on-line salt bath isothermal treatment, immediately entering the coiled bar into a heat preservation corridor for on-line aging for temperature control treatment after the treatment is completed, and cooling to room temperature after the treatment is completed,

[0020] The salt bath temperature of the on-line salt bath isothermal treatment is 500 - 540 °C, the salt bath time is 80 - 200 s, 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 min.

[0021] To achieve the above object, the third aspect of the present application provides a steel strand, including the wire rod described in any one of the above embodiments or the wire rod prepared by the preparation method described in any one of the above embodiments, and the steel strand is prepared by successively subjecting a plurality of the wire rods to pickling, phosphating, drawing, stranding and stabilizing processes.

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

[0023] The phosphating is carried out after the pickled coiled bar is placed for 20 - 28 h;

[0024] The drawing is specifically to draw the coiled bar for 9 - 11 passes, the area reduction rate per pass is 23 - 25%, the drawing speed is not higher than 2 m / s, and the temperature rise per pass is not higher than 100 °C;

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

[0026] The stabilizing temperature of the stabilizing process is 400 - 430 °C.

[0027] Different from the prior art, the beneficial effects of the present application are:

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

[0029] By optimizing the chemical composition ratio of the wire rod, as well as reasonable preparation process parameters and post-rolling controlled cooling process, the present application significantly improves the strength and plasticity of the wire rod and the homogeneity of the steel, enabling it to obtain the target strength with a smaller area reduction rate during the subsequent production process of steel strands, reducing the area reduction rate during drawing and significantly improving 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;

[0030] The sorbitization rate of the wire rod of the present application reaches over 92%, the sorbitic lamellar spacing is 50 - 70 nm, and the tensile strength reaches over 1180 Mpa; the tensile strength of the steel strand of the present application reaches the 1860 Mpa level, and at the same time has excellent stress corrosion resistance. Taking the prepared 1×7 steel strand as an example, the minimum value of stress corrosion is 4 hours and the median value is 6 hours, which is significantly better than the existing 1860 Mpa level steel strands and far exceeds the national standard requirements, meeting the usage requirements of steel strands in corrosive environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings described below are only some embodiments recorded in the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0032] Figure 1 is a schematic flow chart of the preparation method of the wire rod for essentially stress corrosion resistant prestressed steel strands of the present application;

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

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

[0035] Figure 4 is a metallographic structure picture of the wire rod prepared in Example 3 of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] In order to enable those skilled in the art to better understand the technical solutions in the present application, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present application.

[0037] In order to solve the problem in the prior art that the steel strand cannot take into account both high strength and stress corrosion resistance, the applicant has developed a wire rod for essentially stress corrosion resistant prestressed steel strands, which can be used to prepare steel strands with a strength level of 1860 Mpa and has excellent stress corrosion resistance.

[0038] Specifically, the chemical composition of the wire rod for essentially stress corrosion resistant prestressed steel strands of the present application includes, by mass percentage:

[0039] C 0.74 - 0.82%, Si 0.20 - 0.60%, Mn 0.20 - 0.80%, Cr 0.15 - 0.40%, V 0.01 - 0.05%, 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 fractions of the chemical components of the wire rod.

[0041] Specifically, in the present application, the C content is limited to 0.74 - 0.82%, which helps to improve the stress corrosion resistance while ensuring the tensile strength of the wire rod by reducing the carbon content; by limiting the Si content to 0.20 - 0.60%, it helps to improve the corrosion resistance and stress 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, ensuring a good work hardening rate of the wire rod; by limiting the Cr content to 0.15 - 0.40%, on the one hand, it is beneficial to obtain retained austenite, on the other hand, it forms a dense oxide film on the steel surface, and at the same time avoids the difficulty of controlling segregation caused by too much Cr content; by limiting the V content to 0.01 - 0.05%, the carbon oxides formed by V act as effective hydrogen traps in the steel, improving the stress corrosion index of the steel.

[0042] In addition, in order not to affect the strength and plasticity of the steel, the S content is limited to less than or equal to 0.008%, the P content is limited to less than or equal to 0.010%, the N content is limited to less than or equal to 0.004%, and the O content is limited to less than or equal to 0.0020% in the present application.

[0043] Based on the above content ratio, by reducing the carbon content, improving the purity and increasing the corrosion-resistant chemical elements, the stress corrosion resistance of the wire rod can be significantly improved while ensuring the strength of the wire rod. In one embodiment, the diameter of the wire rod can reach 8 - 14 mm, the tensile strength can reach 1180 - 1300 Mpa, and the reduction of area can be 38 - 48%.

[0044] The present application also provides a preparation method for the above-mentioned wire rod. Please refer to Figure 1 , Figure 1 which is a schematic flow chart of the preparation method for the wire rod used in the essentially stress corrosion resistant prestressed steel strand of the present application.

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

[0046] S100. Smelt molten steel to obtain target molten steel.

[0047] Among them, the chemical composition of the target molten steel is consistent with that of the wire rod, which will not be elaborated 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 can specifically be carried out by converter smelting and LF furnace refining in sequence.

[0049] Among them, converter smelting is specifically to send molten iron into the converter to be mixed with scrap steel to form molten steel, and carry out desiliconization, dephosphorization, and oxygen blowing for decarburization. When tapping, alloys are added to the ladle for deoxidation alloying;

[0050] LF furnace refining is specifically to send the molten steel after converter smelting into the LF refining furnace for chemical composition adjustment, temperature control, and regulate the inclusions in the molten steel through soft stirring until the temperature of the molten steel reaches the continuous casting requirement and the chemical composition of the molten steel meets the standard, and then tap to obtain the target molten steel.

[0051] S200. Adopt small billet continuous casting to cast the target molten steel into shape to obtain an intermediate billet.

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

[0053] In one embodiment, the size of the continuously cast small billet can be 180mm×240mm; in other embodiments, the size of the small billet can also be adjusted based on actual needs, and the effects of this embodiment can be achieved.

[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 superheat of the target molten steel can be 20 - 25°C, the stirring current of the mold can be 270±25A, the stirring frequency of the mold can be 3±0.5Hz, the casting speed during continuous casting can be 1.2±0.05m / min, the specific water consumption during continuous casting can be 0.22±0.01L / kg, the stirring current at the end can be 450±25A, the stirring frequency at the end can be 8±0.5Hz, and the total reduction amount of soft reduction can be 15.0±0.2mm. [[ID= 38]]

[0055] S300. Perform the high-speed wire rolling process on the intermediate billet to obtain coiled bars.

[0056] Among them, the high-speed wire rolling process specifically involves heating the intermediate billet and then sequentially performing rough rolling, finish rolling, and wire laying to obtain coiled bars.

[0057] In one embodiment, the heating temperature can be 1080 - 1150 °C, the starting rolling temperature of rough rolling can be 950 - 1000 °C, and the inlet temperature of finish rolling can be 850 - 920 °C.

[0058] To facilitate the effect of subsequent post-rolling controlled cooling process, the wire laying temperature can be 850 - 910 °C.

[0059] S400. Immediately immerse the coiled bars into a salt bath tank for on-line salt bath isothermal treatment. After the treatment is completed, immediately put the coiled bars into a heat preservation corridor for on-line aging for temperature control treatment. After the treatment is completed, cool to room temperature to obtain wire rods.

[0060] After the high-speed wire rolling process, at this time, the coiled bars still maintain the wire laying temperature of the rolling process. Without uncoiling, directly immerse the coiled bars into the salt bath tank immediately to realize on-line salt bath isothermal treatment and accurately control the material structure and properties.

[0061] Compared with the traditional off-line salt bath heat treatment, the solution of the present application does not need to uncoil the coiled bars, perform heat treatment and then rewind, avoiding surface damage of 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 on-line salt bath isothermal treatment can be 500 - 540 °C, and the salt bath time can be 80 - 200 s.

[0063] After the on-line salt bath isothermal treatment, the coiled bars can be immediately put into the heat preservation corridor for on-line aging, and the temperature is slowly decreased to accurately control the temperature of the coiled bars, thereby refining the microscopic structure of the steel.

[0064] In one embodiment, 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 min.

[0065] Based on the post-rolling controlled cooling process of on-line salt bath isothermal treatment and heat preservation corridor on-line aging, it can refine the microscopic structure of the wire rods and significantly increase the sorbitization rate to improve the strength and plasticity of the wire rods.

[0066] Based on the wire rod and its preparation method of the above embodiments, by optimizing the chemical composition ratio of the wire rod, reasonable preparation process parameters and post-rolling controlled cooling process, the strength and plasticity of the wire rod are significantly improved, and the homogeneity of the steel is enhanced, enabling the target strength to be obtained with a smaller reduction ratio during the subsequent preparation process of the steel strand, reducing the reduction ratio and significantly improving the plasticity index of the wire rod, reducing 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 multiple wire rods of any one of the above embodiments.

[0068] Specifically, the steel strand is prepared by successively passing multiple wire rods through pickling, phosphating, drawing, stranding and stabilizing processes.

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

[0070] In one embodiment, phosphating is specifically carried out 20-28 h after the pickled coil is placed.

[0071] In one embodiment, drawing is specifically carried out by drawing the coil for 9-11 passes, with a pass reduction ratio of 23-25%, a drawing speed not higher than 2 m / s, and a temperature rise per pass not higher than 100 °C.

[0072] Based on the post-rolling controlled cooling process of the above S400, the wire rod has high strength and plasticity, so the target strength can be achieved with a lower drawing reduction ratio, effectively reducing the surface damage and internal defects of the wire rod, thereby contributing to improving the stress corrosion resistance.

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

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

[0075] The effects of the technical solution of the present application will be further elaborated in detail below in conjunction with specific embodiments.

[0076] Example 1:

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

[0078] (1) Molten steel smelting process

[0079] The molten steel is smelted through the BOF smelting and LF furnace refining steps in sequence to obtain the target molten steel. The chemical composition of the target molten steel is shown in Table 1 below by mass percentage;

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

[0081] In the refining step, the molten steel after BOF smelting is fed into the LF refining furnace for chemical composition adjustment, temperature control, and the inclusions in the molten steel are controlled by soft stirring. After the temperature and chemical composition meet the standards, tapping is carried out. Among them, the superheat of the target molten steel is 20°C.

[0082] (2) Continuous casting process

[0083] Small billet continuous casting is adopted to cast the target molten steel into small billets with a cross-sectional size of 180mm×240mm.

[0084] Among them, the superheat of the target molten steel is controlled at 20°C, the stirring current of the mold is 245A, the stirring frequency of the mold is 2.5Hz, the casting speed during continuous casting is 1.15m / min, the specific water volume for continuous casting is 0.21L / kg, the stirring current at the end is 425A, the stirring frequency at the end is 7.5Hz, and the total reduction of soft reduction is 14.8mm.

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

[0086] The intermediate billet obtained from the continuous casting process is processed into wire rods with a diameter of 14mm by high-speed wire rolling. The heating temperature is 1150°C, the starting rolling temperature of rough rolling is 1000°C, the entry temperature of finish rolling is 850°C, and the spinning temperature is 850°C.

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

[0088] The coiled wire after spinning is directly immersed in a salt bath tank for salt bath. The temperature of the salt bath tank is 500°C, and the salt bath time is 200s; the coiled wire after salt bath isothermal treatment immediately enters the heat preservation corridor for slow cooling, the treatment time is 30min, and the average cooling rate is 0.15°C / s.

[0089] (5) Steel strand processing process

[0090] The coiled wire is prepared into wire rods through pickling, phosphating, and drawing, and then 1860MPa grade steel strands are prepared through stranding and stabilization processes;

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

[0092] Examples 2 to 4:

[0093] An 1860 MPa grade 1*7 steel strand, the preparation method 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 content of the wire rods in Examples 1 to 4 can be seen in Table 1 below, and the process parameters in Examples 1 to 3 can be seen 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 detected. The detection method includes:

[0103] A wire rod with a length of 10 cm was taken from the head of the wire rod, made into a metallographic sample, mechanically polished and etched with nitric acid alcohol, and then placed under a metallographic microscope for tissue observation to obtain Figures 2 to 4 , Figure 2 is the metallographic structure picture of the wire rod prepared in Example 1 of this application, Figure 3 is the metallographic structure picture of the wire rod prepared in Example 2 of this application, Figure 4 is the metallographic structure picture of the wire rod prepared in Example 3 of this application.

[0104] It was found from the above detection that the structures of the wire rods in Examples 1 - 3 are all sorbite structures. Their metallographic data are as shown in Table 3 below. The sorbitization rates of Examples 1 to 3 all reach 92% and above, and the sorbite lamellar spacing is 50 - 70 nm, indicating that the wire rods have excellent strength and toughness.

[0105] Table 3

[0106] Example Diameter / mm Sorbite rate Grain boundary cementite Martensite 1 14 92 0 0 2 13 93 0 0 3 8 93 0 0

[0107] Effect Example 2:

[0108] The mechanical properties of the wire rods prepared in Examples 1 to 3 were tested using a tensile testing machine. The testing method referred to the standard test method and definition of GB / T228, and the following data in Table 4 were obtained.

[0109] Table 4

[0110]

[0111] As can be seen from the above data, the tensile strength of the wire rods prepared in Examples 1 to 3 reached 1250 Mpa and above, and the cross-sectional elongation rate reached 43% and above, showing significantly excellent mechanical properties.

[0112] Effect Example 3:

[0113] The strength of the steel strands prepared in Examples 1 to 3 was tested. The testing method referred to the standard GB / T 5224-2020, and the following data in Table 5 were obtained.

[0114] Table 5

[0115]

[0116] As can be seen from the data in the above table, the tensile strength of the steel strands in Examples 1 to 3 all reached 1890 Mpa and above, having excellent mechanical properties.

[0117] Effect Example 4:

[0118] The stress corrosion resistance of the steel strands prepared in Examples 1 to 3 was tested. The testing method referred to the standard GB / T15970.6-2007, and the following data in Table 6 were obtained.

[0119] Table 6

[0120]

[0121] As can be seen from the above data, the steel strands prepared in Examples 1 to 3 all had excellent stress corrosion resistance. The minimum value of stress corrosion was 4 h, and the median was 6 h, far exceeding the national standard requirements and meeting the use requirements of steel strands in corrosive environments.

[0122] For those skilled in the art, it is obvious that the present application is not limited to the details of the above-described exemplary embodiments, and the present application can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, in any aspect, the embodiments should be regarded as exemplary and non-limiting. The scope of the present application is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present application. Any reference signs in the claims should not be construed as limiting the claims involved.

[0123] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A wire rod for prestressed steel strands with inherent stress corrosion resistance, characterized in that, The chemical composition of the wire rod, by mass percentage, includes: C 0.74 - 0.82%, Si 0.20 - 0.60%, Mn 0.20 - 0.80%, Cr 0.15 - 0.40%, V 0.01 - 0.05%, 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 inherent 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 reduction of area is 38 - 48%.

3. The wire rod for essentially stress corrosion resistant prestressed steel strands according to claim 1, characterized in that, The sorbitization rate of the wire rod is greater than or equal to 92%, and the spacing of the sorbitic lamellae is 50 - 70 nm.

4. A preparation method of wire rod for prestressed steel strand with inherent stress corrosion resistance, characterized in that, Including: Smelting molten steel to obtain target molten steel, the chemical composition of the target molten steel, by mass percentage, includes: C 0.74 - 0.82%, Si 0.20 - 0.60%, Mn 0.20 - 0.80%, Cr 0.15 - 0.40%, V 0.01 - 0.05%, 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; Adopting small billet continuous casting to cast the target molten steel into shape to obtain an intermediate billet; Performing high-speed wire rolling on the intermediate billet to obtain a coiled bar; Immediately immersing the coiled bar into a salt bath tank for on-line salt bath isothermal treatment, and immediately after the treatment is completed, putting the coiled bar into a heat preservation corridor for on-line aging for temperature control treatment, and after the treatment is completed, cooling to room temperature to obtain the wire rod.

5. The preparation method according to claim 4, wherein The step of smelting molten steel is specifically: sequentially carrying out converter smelting and LF furnace refining; The converter smelting is specifically feeding molten iron into a converter to mix with scrap steel to form molten steel, and carrying out desiliconization, dephosphorization, and oxygen blowing decarburization, and adding alloys to the ladle for deoxidation alloying during tapping; The LF furnace refining is specifically feeding the molten steel after converter smelting into an LF refining furnace for chemical composition adjustment, temperature control, and regulating inclusions in the molten steel through soft stirring until the temperature of the molten steel meets the continuous casting requirements and the chemical composition of the molten steel meets the standards, and then tapping to obtain the target molten steel.

6. The preparation method according to claim 4, wherein In the step of adopting small 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 mold is 270 ± 25 A, the stirring frequency of the mold is 3 ± 0.5 Hz, the casting speed during continuous casting is 1.2 ± 0.05 m / min, the specific water flow rate during continuous casting is 0.22 ± 0.01 L / kg, the stirring current at the end is 450 ± 25 A, the stirring frequency at the end is 8 ± 0.5 Hz, and the total reduction amount of soft reduction is 15.0 ± 0.2 mm.

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 a coiled bar is specifically: heating the intermediate billet and then sequentially carrying out rough rolling, finish rolling, and spinning to obtain the coiled bar; Among them, the heating temperature is 1080 - 1150 °C, the starting rolling temperature of rough rolling is 950 - 1000 °C, the entry temperature of finish rolling is 850 - 920 °C, and the laying temperature is 850 - 910 °C.

8. The preparation method according to claim 4, characterized in that, In the step of immediately immersing the coiled bar into a salt bath tank for on-line salt bath isothermal treatment, and immediately after the treatment is completed, putting the coiled bar into a heat preservation corridor for on-line aging for temperature control treatment, and then cooling to room temperature after the treatment is completed, the salt bath temperature of the on-line salt bath isothermal treatment is 500 - 540 °C, the salt bath time is 80 - 200 s, 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 min.

9. A steel strand, characterized in that, It includes the wire rod according to any one of claims 1 to 3 or the wire rod prepared by the preparation method according to any one of claims 4 to 8. The steel strand is prepared by successively subjecting a plurality of the wire rods to pickling, phosphating, drawing, stranding and stabilizing processes.

10. The steel strand according to claim 9, wherein, The pickling is specifically carried out by pickling the coiled bar in a hydrochloric acid solution with a concentration of 15 - 20 wt% for 7 - 10 min, and the pickling temperature is 35 - 42 °C; The phosphating is carried out 20 - 28 h after the pickled coiled bar is placed; The drawing is specifically carried out by drawing the coiled bar for 9 - 11 passes, the area reduction rate per pass is 23 - 25%, the drawing speed is not higher than 2 m / s, and the temperature rise per pass is not higher than 100 °C; The tension of the stranding is greater than or equal to 80 KN, and the speed is less than or equal to 36 m / min; The stabilizing temperature of the stabilizing process is 400 - 430 °C.

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