Wire rod for 2200-2260 MPa-grade high-stress-corrosion-resistance prestressed steel strand, steel strand and production method of steel strand

Abstract

The invention discloses a steel wire rod for a 2200-2260 MPa grade high stress corrosion resistance prestressed steel strand, the steel strand and a production method of the steel strand, and an alloy comprises the following components in percentage by mass: 0.83-0.89% of C, 0.35-0.80% of Si, 0.20-0.80% of Mn, 0.15-0.40% of Cr, less than 0.30% of Cu, less than 0.30% of Ni, 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 0.0040% of N, less than or equal to 0.0020% of O and the balance of Fe and other inevitable impurities. Through component design and a reasonable after-rolling controlled cooling process, a microscopic structure is refined, the sorbite rate is greatly increased, and high strength plasticity is obtained with low carbon content.

Description

Technical Field

[0001] The present invention belongs to the technical fields of iron and steel metallurgy and metal products, and particularly relates to an alloy, a wire rod, a steel strand and a method for a prestressed steel strand with high stress corrosion resistance. Background Art

[0002] The national standard GB / T5224 requires the stress corrosion performance of the steel strand to be at least 2 hours and the median value to be 5 hours, which far from meets the use requirements in a corrosive environment. To improve the corrosion resistance of the steel strand, 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 per ton. The way of wrapping the whole surface of the steel strand with PE plastic can also be adopted, but it is easy to be damaged and has poor reliability. Especially during the tensioning construction, the surface plastic layer cannot deform with the steel strand and is damaged, losing the anti-corrosion function. In addition, there is also a slow-bonding prestressed steel strand that reduces the corrosion rate by coating the outer layer with an epoxy adhesive and a sheath. Not only the production process is long, but also there are problems such as environmental pollution during the production process and aggravated corrosion at the damaged sheath during the use process. Starting from the steel strand material itself, it is an urgent need for the industry development to obtain a super-high stress corrosion resistant steel strand with stable reliability, simple process and controllable cost through composition and process optimization.

[0003] Starting from the steel strand material itself, it is an urgent need for the industry to obtain ultra-high stress corrosion resistant steel strands that are stable and reliable, have simple processes, and controllable costs through composition and process optimization. CN 118814088 A provides a 2300 MPa grade stress corrosion resistant steel strand that meets the requirement of stress corrosion for 2 hours. However, its production method requires off-line salt bath treatment of the wire rod, resulting in low output, high cost, and the secondary heat treatment not conforming to the current development trend of green and low-carbon. In addition, off-line salt bath heat treatment requires uncoiling the coil, heat treatment, and then recoiling, which is likely to damage the surface and make the stress corrosion index of the steel strand unstable. CN111321352 A discloses a production method of a 2400 MPa grade prestressed steel strand, and off-line salt bath heat treatment is also required in the wire rod production method, and the processed steel strand does not have good stress corrosion resistance. CN 114369760 A provides an anti-stress corrosion ultra-high strength steel strand. Through V and B alloying composition design, improving the wire rod water bath production process, and improving the wire drawing process during the production of the steel strand, reducing the wire temperature, increasing the stabilization treatment temperature, shot peening the surface of the steel strand and other measures, the anti-stress corrosion performance of the ultra-high strength steel strand is improved to more than 2.5 hours. It is necessary to perform shot peening treatment on the steel strand, and the production process is complex and costly. CN 119287269 A provides a green and environment-friendly wire rod for 2300 MPa grade steel strands and its production method, using an on-line heat treatment method to produce the wire rod for 2300 MPa grade steel strands. After heat treatment, the wire rod still needs artificial aging, and the supply cycle is long; and this document does not involve the manufacturing method of the steel strand and its stress corrosion performance.

[0004] Therefore, in view of the above technical problems, it is necessary to provide an alloy, wire rod, steel strand and method for high stress corrosion resistant prestressed steel strands.

[0005] The information disclosed in this background art section is only intended to enhance the understanding of the overall background of the present invention and should not be regarded as an admission or any form of implication that this information constitutes prior art already known to those of ordinary skill in the art. Summary of the Invention

[0006] The purpose of the present invention is to provide an alloy, wire rod, steel strand and method for high stress corrosion resistant prestressed steel strands.

[0007] In order to achieve the above purpose, the technical solutions provided by a specific embodiment of the present invention are as follows:

[0008] Alloy for prestressed steel strand with high stress corrosion resistance at 2200 - 2260 MPa level, characterized in that its composition includes, by mass percentage: C 0.83 - 0.89%, Si 0.35 - 0.80%, Mn 0.20 - 0.80%, Cr 0.15 - 0.40%, Cu < 0.30%, Ni < 0.30%, V 0.01 - 0.05%, S ≤ 0.008%, P ≤ 0.010%, N ≤ 0.0040%, O ≤ 0.0020%, and the rest is Fe and other inevitable impurities.

[0009] In one or more embodiments of the present invention, the wire rod for prestressed steel strand with high stress corrosion resistance at 2200 - 2260 MPa level is prepared from the alloy for prestressed steel strand with high stress corrosion resistance at 2200 - 2260 MPa level described above.

[0010] In one or more embodiments of the present invention, the metallographic structure of the wire rod is mainly sorbite, the rate of sorbitization ≥ 93%, and the lamellar spacing of sorbite is 50 - 70 nm. The diameter of the wire rod is 8 - 14 mm, the tensile strength is 1340 - 1440 MPa, and the reduction of area is 35 - 45%.

[0011] In one or more embodiments of the present invention, the preparation method of the wire rod for prestressed steel strand with high stress corrosion resistance at 2200 - 2260 MPa level is obtained by the steelmaking, continuous casting, high - speed wire rolling, and controlled cooling after rolling processes in sequence with the raw materials in the ratio of the alloy for prestressed steel strand with high stress corrosion resistance at 2200 - 2260 MPa level described above.

[0012] In one or more embodiments of the present invention, in the continuous casting process, the superheat of the molten steel is controlled at 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 consumption for 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 of soft reduction is 15.0 ± 0.2 mm.

[0013] In one or more embodiments of the present invention, in the high - speed wire rolling process, the rectangular billet obtained from the continuous casting process is heated and then subjected to rough rolling and finish rolling successively. The heating temperature is 1080 - 1150°C, the starting rolling temperature for rough rolling is 950 - 1000°C, the entry temperature for finish rolling is 860 - 920°C, and the spinning temperature is 850 - 900°C.

[0014] In one or more embodiments of the present invention, the controlled cooling process after rolling includes an on - line salt bath isothermal treatment process.

[0015] In one or more embodiments of the present invention, in the online salt bath isothermal process, the wire rod after wire drawing is directly immersed in a constant temperature salt bath for isothermal treatment. The salt bath temperature is 530 - 565 °C, and the salt bath time is 120 - 250 s.

[0016] In one or more embodiments of the present invention, the post-rolling controlled cooling process further includes online aging. Preferably, the wire rod after salt bath isothermal treatment immediately enters the heat preservation corridor for online aging, and the average cooling rate during aging is not higher than 0.2 °C / s.

[0017] In one or more embodiments of the present invention, the 2200 - 2260 MPa high stress corrosion resistant prestressed steel strand is prepared from the wire rod for the 2200 - 2260 MPa high stress corrosion resistant prestressed steel strand described above.

[0018] In one or more embodiments of the present invention, the preparation method of the 2200 - 2260 MPa high stress corrosion resistant prestressed steel strand is obtained by pickling, phosphating, drawing, stranding and stabilization of the wire rod for the 2200 - 2260 MPa high stress corrosion resistant prestressed steel strand described above. The phosphating here can be any existing technology related in the art and has no significant impact on the innovation points of the present invention.

[0019] In one or more embodiments of the present invention, the wire rod pickling process is carried out by pickling in an aqueous solution with a hydrochloric acid concentration of 15 - 20% (mass fraction) for 7 - 10 minutes at a temperature of 35 - 42 °C, which not only ensures the removal of hot rolled scale but also avoids excessive hydrogen absorption by the wire rod. After pickling, the wire rod is placed for 24 hours before entering the next process.

[0020] In one or more embodiments of the present invention, the drawing is carried out in 9 - 11 passes, the area reduction rate per pass is 16% - 23%, the drawing speed is not higher than 2 m / s, and the temperature rise per pass is not higher than 100 °C.

[0021] In one or more embodiments of the present invention, the stranding tension is not lower than 80 kN, and the speed is not higher than 36 m / min.

[0022] In one or more embodiments of the present invention, the stabilization temperature is 400 - 430 °C, and the time is 10 - 15 s.

[0023] Compared with the prior art, the beneficial effects of the alloy, wire rod, steel strand and method for the high stress corrosion resistant prestressed steel strand of the present invention are:

[0024] (1) Through composition design and a reasonable post-rolling controlled cooling process, the microstructure is refined, the sorbitization rate is greatly improved, and high strength and plasticity are obtained with a relatively low carbon content.

[0025] (2) Based on the chemical composition design of the present invention and the control of production processes such as continuous casting, rolling, and post-rolling, the homogeneity of the steel is improved. The metallographic structure of the wire rod prepared by the production method of the present invention is mainly sorbite, the sorbitization rate is ≥93%, and the sorbite lamellar spacing is 50 - 70 nm; the tensile strength is 1340 - 1445 MPa, and the reduction of area is 35 - 45%.

[0026] (3) By reducing the carbon content, improving the purity, and increasing corrosion-resistant chemical elements, while improving the uniformity of the wire rod during the production process, reducing the drawing area reduction rate, and significantly improving the plasticity index of the wire rod, surface damage and internal defects during wire drawing can be reduced, thereby improving the stress corrosion index of the steel strand. Taking the processed 1×7 - 15.2 - 2260 steel strand as an example, the minimum value of stress corrosion is 5 hours, and the median value is 8 hours. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention 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 following drawings are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0028] Figure 1 It is an optical microscope picture of the microstructural of the wire rod of Embodiment 1 of the present invention;

[0029] Figure 2 It is an optical microscope picture of the microstructural of the wire rod of Embodiment 2 of the present invention;

[0030] Figure 3 It is an optical microscope picture of the microstructural of the wire rod of Embodiment 3 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the following will clearly and completely describe the technical solutions of the present invention in combination with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0032] In the alloy for high stress corrosion resistant prestressed steel strand and its related technical solutions of the present invention:

[0033] C is the most important strengthening element in steel. The present invention also uses phase transformation strengthening to improve strength. Therefore, the C content of the present invention is limited to 0.83 - 0.89% to improve its stress corrosion resistance.

[0034] Si is a strengthening element and a deoxidizing element in steel, and it also helps to improve the corrosion resistance and anti-relaxation performance of steel. In the present invention, the Si content is limited to 0.40 - 0.80%.

[0035] Mn is a strengthening element in steel, which can improve the strength and hardenability of steel, and ensure a good work hardening rate of the wire rod. In the present invention, the Mn content is limited to 0.20 - 0.80%.

[0036] Cr is a commonly used corrosion-resistant alloying element, which forms a dense oxide film on the steel surface; however, too high a content increases the difficulty of controlling segregation. In the present invention, the Cr content is limited to 0.15 - 0.40%.

[0037] The carbonitrides formed by V are effective hydrogen traps in steel, thereby improving the stress corrosion index of steel.

[0038] Both Cu and Ni can improve the stress corrosion index of steel. To control production costs, the content is controlled within 0.30.

[0039] S is likely to segregate at grain boundaries, embrittling the grain boundaries, thereby reducing the strength and plasticity of steel. In addition, S reacts with Mn to form MnS, thereby reducing the solution strengthening effect of Mn. In the present invention, the S content is limited to ≤0.008%.

[0040] P is an impurity element in steel, which is likely to segregate at grain boundaries, embrittling the grain boundaries, and further reducing the strength and plasticity of steel. In the present invention, the P content is limited to ≤0.010%.

[0041] N causes the plasticity of steel to deteriorate, increasing the risk of delayed fracture of the wire rod. Moreover, a high N content causes the coarsening of AlN and TiN, which is not conducive to fine grain strengthening. In addition, free nitrogen atoms undergo dynamic aging in the steel wire, reducing the plasticity of the steel wire. In the present invention, the nitrogen content is limited to ≤0.0040%.

[0042] O combines with alloying elements in steel to form non-metallic inclusions, affecting the strength and plasticity of the wire rod and the fatigue, corrosion resistance and other properties of the steel wire. It is necessary to limit O ≤0.0020%.

[0043] Group 1

[0044] Example 1

[0045] In the technical solutions of the alloy, wire rod, steel strand and method for high stress corrosion resistant prestressed steel strand in this example:

[0046] (1) Molten steel smelting process

[0047] The molten steel is smelted through the BOF smelting and LF refining steps in sequence. The chemical composition of the molten steel at the end of smelting is shown in Table 1 in terms of mass percentage. In addition, the chemical composition of the continuous casting billet obtained in the continuous casting process and the chemical composition of the high-carbon steel wire rod for ultra-high-strength prestressed steel strands finally prepared are consistent with the chemical composition of the molten steel at the end of the molten steel smelting process, both as shown in Table 1.

[0048] Among them, in the BOF smelting step, hot metal is fed into the BOF and mixed with scrap steel 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; 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.

[0049] (2) Continuous casting process

[0050] Small billet continuous casting is adopted to cast the molten steel obtained in the molten steel smelting process into a rectangular billet with a cross-sectional size of 180mm×240mm.

[0051] Among them, the superheat of the molten steel is controlled at 20℃, the stirring current of the mold is 245A, the stirring frequency of the mold is 2.5Hz, the drawing speed during continuous casting is 1.15m / min, the specific water consumption for continuous casting is 0.21L / kg, the terminal stirring current is 425A, the terminal stirring frequency is 7.5Hz, and the total reduction of soft reduction is 14.8mm.

[0052] (3) High-speed wire rolling process

[0053] The small billet obtained in the continuous casting process is heated and then subjected to rough rolling and finish rolling successively to prepare a wire rod with a diameter of 14mm. The heating temperature is 1150℃, the starting rolling temperature of rough rolling is 1000℃, the inlet temperature of finish rolling is 920℃, and the spinning temperature is 880℃.

[0054] (4) Post-rolling controlled cooling process

[0055] The wire rod after spinning is directly immersed in a molten nitrate constant-temperature salt bath for on-line salt bath isothermal treatment. The temperature of the salt bath is 545℃ and the salt bath time is 180s. The wire rod after on-line salt bath isothermal treatment immediately enters the heat preservation corridor for slow cooling, and the average cooling rate is 0.1℃ / s.

[0056] (5) Steel strand processing process

[0057] The wire rod is processed into steel strands through pickling, phosphating, drawing, stranding, and stabilization processes. Among them, in the pickling process, an aqueous solution with a hydrochloric acid concentration of 19% (mass fraction) is used for pickling for 10 minutes at a temperature of 35°C. After pickling, the wire rod is placed for 24 hours before entering the next process. The 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 90°C per pass. The stranding tension is 80 kN, the speed is 30 m / min, and the stabilization temperature is 400°C for 15 s. Regarding phosphating, any conventional technology applicable to related products in this field can be used without affecting the improvement and optimization of the performance for the purpose of innovation. The same applies hereinafter.

[0058] Example 2

[0059] In the technical solutions of the alloy, wire rod, steel strand, and method for high stress corrosion resistant prestressed steel strands in this example:

[0060] (1) Molten steel smelting process

[0061] The molten steel is smelted through the converter smelting and LF furnace refining steps carried out in sequence, so that the chemical composition of the molten steel at the end of smelting is shown in Table 1 in terms of mass percentage. In addition, the chemical composition of the continuous casting billet obtained in the continuous casting process, and the chemical composition of the high carbon steel wire rod for ultra-high strength prestressed steel strands finally prepared are consistent with the chemical composition of the molten steel at the end of the molten steel smelting process, and are all shown in Table 1.

[0062] Among them, in the converter smelting step, the pretreated hot metal is fed into the converter and mixed with scrap steel 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; in the refining step, the molten steel after converter 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.

[0063] (2) Continuous casting process

[0064] Rectangular billet continuous casting is adopted, and the molten steel obtained in the molten steel smelting process is cast into a rectangular billet with a cross-sectional size of 180 mm × 240 mm.

[0065] Among them, the superheat of the molten steel is controlled at 21°C, the stirring current of the mold is 270 A, the stirring frequency of the mold is 3 Hz, the casting speed during continuous casting is 1.2 m / min, the specific water consumption for continuous casting is 0.22 L / kg, the stirring current at the end is 450 A, the stirring frequency at the end is 8 Hz, and the total reduction amount of soft reduction is 15.0 mm.

[0066] (3) High-speed wire rolling process

[0067] The intermediate billet obtained from the continuous casting process is rolled into a wire rod with a diameter of 8 mm by high-speed wire rolling. The heating temperature is 1080 °C, the starting rolling temperature of rough rolling is 960 °C, the entry temperature of finish rolling is 860 °C, and the laying head temperature is 850 °C.

[0068] (4) Post-rolling controlled cooling process

[0069] The wire rod after laying head is directly immersed in a molten nitrate constant temperature salt bath for on-line salt bath isothermal treatment. The temperature of the salt bath is 530 °C and the salt bath time is 250 s. The wire rod after on-line salt bath isothermal treatment immediately enters the heat preservation corridor for slow cooling, with an average cooling rate of 0.15 °C / s.

[0070] (5) Strand processing process

[0071] The wire rod is processed into a strand through pickling, phosphating, drawing, stranding, and stabilization process pickling process. Among them, pickling uses an aqueous solution with a hydrochloric acid concentration of 15% (mass fraction), pickling for 7 minutes at a temperature of 40 °C, and the wire rod after pickling is placed for 24 hours before entering the next process. Drawing is carried out in 9 passes, with a reduction rate per pass of 16%, a drawing speed of 1.5 m / s, and a temperature rise of 100 °C per pass. The stranding tension is 90 kN, the speed is 33 m / min, and the stabilization temperature is 410 °C for 12 s.

[0072] Example 3

[0073] In the technical solutions of the alloy, wire rod, strand, and method for high stress corrosion resistant prestressed strand in this example:

[0074] (1) Molten steel smelting process

[0075] The molten steel is smelted through the converter smelting and LF furnace refining steps carried out in sequence. The chemical composition of the molten steel at the end of smelting is shown in Table 1 by mass percentage. In addition, the chemical composition of the continuous casting billet obtained from the continuous casting process and the chemical composition of the high carbon steel wire rod for ultra-high strength prestressed strand finally prepared are consistent with the chemical composition of the molten steel at the end of the molten steel smelting process, and are all shown in Table 1.

[0076] Among them, in the converter smelting step, the pretreated hot metal is fed into the converter and mixed with scrap steel to form a molten steel, and desiliconization, dephosphorization, and oxygen blowing decarburization are carried out. When tapping, alloys are added to the ladle for deoxidation alloying; in the refining step, the molten steel after converter 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.

[0077] (2) Continuous casting process

[0078] Using billet continuous casting, the molten steel obtained from the steelmaking process is cast into small billets with a cross-sectional size of 180mm×240mm. Among them, the superheat of the molten steel is controlled at 25°C, the stirring current of the mold is 295A, the stirring frequency of the mold is 3.5Hz, the drawing speed during continuous casting is 1.25m / min, the specific water consumption for continuous casting is 0.23L / kg, the stirring current at the end is 475A, the stirring frequency at the end is 8.5Hz, and the total reduction of soft reduction is 15.2mm.

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

[0080] The intermediate billet obtained from the continuous casting process is processed into wire rods with a diameter of 12.5mm by high-speed wire rolling. The heating temperature is 1120°C, the starting rolling temperature for rough rolling is 950°C, the entry temperature for finish rolling is 900°C, and the laying head temperature is 900°C.

[0081] (4) Post-rolling controlled cooling process

[0082] The wire rods after laying head are directly immersed in a molten nitrate constant-temperature salt bath for on-line salt bath isothermal treatment. The temperature of the salt bath is 565°C and the salt bath time is 120s. The wire rods after salt bath isothermal treatment immediately enter the heat preservation corridor for on-line aging, with an average cooling rate of 0.20°C / s.

[0083] (5) Steel strand processing process

[0084] The wire rods are processed into steel strands through pickling, phosphating, drawing, stranding, and stabilization process pickling processes. Among them, pickling uses an aqueous solution with a hydrochloric acid concentration of 20% (mass fraction), pickling for 8 minutes at a temperature of 42°C. After pickling, the wire rods are placed for 24 hours before entering the next process. Drawing uses 10 passes, with a reduction ratio of 18% per pass, a drawing speed of 1m / s, and a temperature rise of 80°C per pass. The stranding tension is 100kN, the speed is 36m / min, and the stabilization temperature is 430°C for 10S.

[0085] Table 1

[0086]

[0087] For the wire rods of Examples 1-3, samples are taken according to the same test method and metallographic structure detection and mechanical property detection are carried out. The specific test method and detection results are as follows:

[0088] (1) In terms of metallographic structure, wire rods with a length of 10cm are taken from the head of the wire rods respectively to make metallographic samples. After mechanical grinding and polishing, and etching with nitric acid alcohol, they are placed under a metallographic microscope for tissue observation, or observed by scanning electron microscope after electrolytic polishing. It is found that the structures of the wire rods of Examples 1-3 are all sorbite structures. As shown in Table 2, the metallographic structure pictures of the wire rods of Examples 1-3 are respectively as Figures 1 to 3 shown.

[0089] (2) In terms of mechanical properties, referring to the test methods and definitions of GB / T 228 standard, a tensile testing machine was used to test the mechanical properties of the wire rods. The tensile strength and reduction of area of the wire rods in Examples 1 - 3 are shown in Table 2 respectively.

[0090] Table 2

[0091] Example Sorbite rate Grain boundary cementite Martensite Tensile strength Reduction of area 1 94 0 0 1385 39 2 93 0 0 1445 45 3 93.5 0 0 1403 43

[0092] The performance indexes of the steel strands produced according to this embodiment (the testing method is carried out in accordance with the requirements of GB / T 5224) are shown in Tables 3 and 4.

[0093] Table 3

[0094]

[0095] Table 4

[0096]

[0097] Group Two

[0098] Example 4

[0099] The difference between this example and Example 3 is only that: in the on-line salt bath isothermal process, the wire rods after spinning are directly immersed in a constant temperature salt bath for isothermal treatment, and the salt bath temperature is 530 °C.

[0100] Example 5

[0101] The difference between this example and Example 3 is only that: in the on-line salt bath isothermal process, the wire rods after spinning are directly immersed in a constant temperature salt bath for isothermal treatment, the salt bath temperature is 565 °C, and the salt bath time is 250 s.

[0102] Example 6

[0103] The difference between this example and Example 3 is only that: the wire rods after salt bath isothermal treatment immediately enter the heat preservation corridor for on-line aging, and the average cooling rate is 0.15 °C / s.

[0104] The tensile strength and reduction of area of the wire rods in Examples 4 - 6 are shown in Table 5 respectively.

[0105] Table 5

[0106] Example Sorbite rate Grain boundary cementite Martensite Tensile strength Reduction of area 4 94.1 0 0 1435 42 5 93.2 0 0 1385 40 6 93.4 0 0 1405 43

[0107] The performance indexes of the steel strands produced according to this embodiment (the testing method is carried out in accordance with the requirements of GB / T 5224) are shown in Tables 6 and 7.

[0108] Table 6

[0109]

[0110]

[0111] Table 7

[0112]

[0113] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention 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 invention.

[0114] In addition, it should be understood that although this specification is described in terms of embodiments, not every embodiment only contains an independent technical solution. This narrative manner 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. An alloy for prestressed steel strands with high stress corrosion resistance at the 2200 - 2260 MPa level, characterized in that, Its composition includes, by mass percentage: C 0.83 - 0.89%, Si 0.35 - 0.80%, Mn 0.20 - 0.80%, Cr 0.15 - 0.40%, Cu < 0.30%, Ni < 0.30%, V 0.01 - 0.05%, S ≤ 0.008%, P ≤ 0.010%, N ≤ 0.0040%, O ≤ 0.0020%, and the balance is Fe and other inevitable impurities.

2. Wire rod for prestressed steel strand with high stress corrosion resistance in the range of 2200 - 2260 MPa, characterized in that, It is prepared from the alloy for 2200 - 2260 MPa high stress corrosion resistant prestressed steel strand according to Claim 1.

3. Preparation method of wire rod for prestressed steel strand with high stress corrosion resistance at 2200 - 2260 MPa level, characterized in that, It is obtained from the alloy raw materials for 2200 - 2260 MPa high stress corrosion resistant prestressed steel strand according to Claim 1 through the sequential processes of molten steel smelting, continuous casting, high wire rolling, and controlled cooling after rolling.

4. The preparation method of the wire rod for 2200 - 2260 MPa high stress corrosion resistant prestressed steel strand according to claim 3, characterized in that, In the continuous casting process, the superheat of the molten steel is controlled at 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 consumption for 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 of soft reduction is 15.0 ± 0.2 mm.

5. The preparation method of the wire rod for 2200-2260 MPa high stress corrosion resistant prestressed steel strand according to claim 3, characterized in that, In the high wire rolling process, the rectangular billet obtained from the continuous casting process is heated and then subjected to rough rolling and finish rolling successively. The heating temperature is 1080 - 1150°C, the starting rolling temperature for rough rolling is 950 - 1000°C, the entry temperature for finish rolling is 860 - 920°C, and the laying temperature is 850 - 900°C.

6. The preparation method of the wire rod for 2200-2260 MPa high stress corrosion resistant prestressed steel strand according to claim 3, characterized in that, The controlled cooling process after rolling includes an on - line salt bath isothermal treatment process.

7. The preparation method of the wire rod for 2200 - 2260 MPa high stress corrosion resistant prestressed steel strand according to claim 6, characterized in that, In the on - line salt bath isothermal process, the wire rod after laying is directly immersed in a constant - temperature salt bath for isothermal treatment. The salt bath temperature is 530 - 565°C, and the salt bath time is 120 - 250 s.

8. The preparation method of the wire rod for 2200-2260 MPa high stress corrosion resistant prestressed steel strand according to claim 6, characterized in that, The controlled cooling process after rolling also includes on - line aging. 9.2200 - 2260 MPa high stress corrosion resistant prestressed steel strand, characterized in that, It is prepared from the wire rod for 2200 - 2260 MPa high stress corrosion resistant prestressed steel strand according to Claim 2. A method for preparing a prestressed steel strand for a 10.2200 - 2260 MPa high stress corrosion resistant prestressed steel strand, characterized in that, It is obtained from the wire rod for 2200 - 2260 MPa high stress corrosion resistant prestressed steel strand according to Claim 2 through pickling, phosphating, drawing, stranding, and stabilization.

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