Steel wire rod for 2200-2260 MPa grade ultrahigh stress corrosion resistant prestressed steel strand, steel strand and production method of steel wire rod for 2200-2260 MPa grade ultrahigh stress corrosion resistant prestressed steel strand

Abstract

The invention discloses a steel wire rod for a 2200-2260 MPa grade ultrahigh stress corrosion resistance prestressed steel strand, the steel strand and a production method of the steel strand, and the steel wire rod comprises the following alloy components in percentage by mass: 0.83-0.89% of C, 0.60-1.40% of Si, 0.20-0.80% of Mn, 0.15-0.50% of Cr, less than 0.30% of Cu, less than 0.30% of Ni, less than 0.30% of Mo, 0.01-0.05% of V, 0.001-0.05% of Nb, 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, the microstructure is refined, the sorbite rate is improved, high strength and plasticity are obtained with low carbon content, the drawing deformation can be reduced, material damage can be reduced, and the corrosion resistance of the steel strand is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron and steel metallurgy and metal products, and particularly relates to an alloy, wire rod, steel strand and method for 2200 - 2260 MPa grade prestressed steel strands. Background Art

[0002] The national standard GB / T5224 requires the stress corrosion performance of steel strands to be at least 2 hours and the median value to be 5 hours, which far fails to meet the use requirements in a corrosive environment. The new national standard GB / T5224 has increased the strength level of prestressed steel strands from 1860 MPa to 2360 MPa. With the increase in strength level, the stress corrosion performance of steel strands has significantly decreased to within 2 hours. To improve the corrosion resistance of steel strands, generally, a layer of zinc or zinc-aluminum alloy can be plated on the surface of steel wires by hot-dip galvanizing, but the cost is high, reaching 1500 yuan per ton. It is also possible to use the method of wrapping the entire surface of the steel strand with PE plastic, but it is easily damaged and has poor reliability. Especially during tensioning construction, the surface plastic layer cannot deform with the steel strand and is damaged, losing its anti-corrosion function. In addition, there are also slow-bonding prestressed steel strands that reduce the corrosion rate by coating the outer layer with epoxy adhesive and sheath. Not only is the production process long, but also there are problems such as environmental pollution during the production process and increased corrosion at the damaged sheath during use.

[0003] Starting from the steel strand material itself, it is an urgent need for the industry to obtain a super high stress corrosion resistant steel strand with stable reliability, 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 costs, and 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 performance. CN 114369760 A provides a stress corrosion resistant ultra-high strength steel strand. By means of V and B alloying composition design, improving the water bath production process of the wire rod, 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, etc., the stress corrosion resistance 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 strand and its production method. The wire rod for 2300 MPa grade steel strand is produced by an on-line heat treatment method. After heat treatment, the wire rod still needs artificial aging, and the supply cycle is long; moreover, 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 2200 - 2260 MPa grade prestressed steel strand.

[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 2200 - 2260 MPa grade prestressed steel strand.

[0007] 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 ultra-high stress corrosion resistance at 2200 - 2260 MPa level, characterized in that its composition includes, by mass percentage: C 0.83 - 0.89%, Si 0.60 - 1.40%, Mn 0.20 - 0.80%, Cr 0.15 - 0.50%, Cu < 0.30%, Ni < 0.30%, Mo < 0.30%, V 0.01 - 0.05%, Nb 0.001 - 0.05%, S ≤ 0.008%, P ≤ 0.010%, N ≤ 0.0040%, O ≤ 0.0020%, where 0.30% ≤ Cr + Cu + Ni + Mo ≤ 1.0%, 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 ultra-high stress corrosion resistance at 2200 - 2260 MPa level is prepared from the aforementioned alloy for prestressed steel strand with ultra-high stress corrosion resistance at 2200 - 2260 MPa level.

[0010] In one or more embodiments of the present invention, the metallographic structure of the wire rod is mainly sorbite, the rate of sorbitization is ≥ 93%, and the lamellar spacing of sorbite is 50 - 70 nm. Preferably, the diameter of the wire rod is 7 - 13 mm, the tensile strength is 1340 - 1440 MPa, and the reduction of area is 38 - 48%.

[0011] In one or more embodiments of the present invention, the preparation method of the wire rod for prestressed steel strand with ultra-high stress corrosion resistance at 2200 - 2260 MPa level obtains the wire rod through the processes of molten steel smelting, continuous casting, high-speed wire rolling, and controlled cooling after rolling according to the aforementioned alloy formula for prestressed steel strand with ultra-high stress corrosion resistance at 2200 - 2260 MPa level.

[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 drawing 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 870 - 920 °C, and the laying temperature is 860 - 910 °C.

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

[0015] In one or more embodiments of the present invention, in the wire salt bath isothermal treatment process, in order to directly immerse the wire rod after wire drawing into a constant temperature salt bath for isothermal treatment: the salt bath temperature is 520 - 550 °C, and the salt bath time is 108 - 250 s.

[0016] In one or more embodiments of the present invention, the post-rolling controlled cooling process further includes an on-line aging process. The on-line aging is carried out in a heat preservation corridor. The average cooling rate of the wire rod in the heat preservation corridor is not higher than 0.2 °C / s.

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

[0018] In one or more embodiments of the present invention, for the preparation method of the 2200 - 2260 MPa grade ultra-high stress corrosion resistant prestressed steel strand, the wire rod for the 2200 - 2260 MPa grade ultra-high stress corrosion resistant prestressed steel strand as described above is pickled, phosphated, drawn, stranded and stabilized to obtain the steel strand. Among them, phosphating is a conventional technology in the art, which makes no contribution to the innovation of the present invention and does not affect the realization of the purpose of the present invention, so no additional limitation is made.

[0019] In one or more embodiments of the present invention, the 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 23% - 25%, 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 duration is 5 - 15 s.

[0023] Compared with the prior art, the beneficial effects of the alloy, wire rod, steel strand and method for the 2200 - 2260 MPa grade prestressed steel strand of the present invention are as follows:

[0024] (1) Through composition design and a reasonable post-rolling controlled cooling process, the microstructure is refined, the rate of sorbitization is increased, high strength and plasticity are obtained with a relatively low carbon content, the drawing deformation amount can be reduced, material damage can be reduced, and the corrosion resistance of the steel strand can be improved.

[0025] (2) Based on the chemical composition design of the present invention and the control of production processes such as continuous casting, rolling, and after-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 - 1440 MPa, and the reduction of area is 38 - 48%.

[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, the 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 - 2200 steel strand as an example, the minimum value of stress corrosion is 8 hours, and the median value is 12 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 the description of the embodiments or the prior art. Obviously, the drawings in the following description 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 Scanning electron microscope picture of the microstructure of the wire rod in Embodiment 1 of the present invention;

[0029] Figure 2 Scanning electron microscope picture of the microstructure of the wire rod in Embodiment 2 of the present invention;

[0030] Figure 3 Scanning electron microscope picture of the microstructure of the wire rod in 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 of 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 chemical composition of the alloy for 2200 - 2260 MPa grade prestressed steel strand 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 in 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 relaxation resistance of steel. In the present invention, the Si content is limited to 0.60 - 1.40%.

[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 - 0.50%.

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

[0038] Cu, Ni, and Mo can all improve the stress corrosion index of steel. To control production costs, the total content of Cr + Cu + Ni + Mo is controlled within the range of 0.30 - 1.0%.

[0039] S is prone to segregate at grain boundaries, causing grain boundary embrittlement, thus 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 prone to segregate at grain boundaries, causing grain boundary embrittlement, and further reducing the strength and plasticity of steel. In the present invention, the P content is limited to ≤0.010%.

[0041] N can cause the plasticity of steel to deteriorate, increasing the risk of delayed fracture of the wire rod. Moreover, a high N content will coarsen 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 and corrosion resistance of the steel wire. It is necessary to limit O ≤0.0020%.

[0043] Group 1

[0044] Example 1

[0045] In the alloy technical solution for 2200 - 2260 MPa grade prestressed steel strands of this example:

[0046] (1) Molten steel smelting process

[0047] The molten steel is smelted through the BOF smelting and LF furnace refining steps 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 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, all 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 $20^{\circ}C$, 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 stirring current at the end is $425A$, the stirring frequency at the end is $7.5Hz$, and the total reduction of soft reduction is $14.8mm$.

[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 $15mm$. The heating temperature is $1150^{\circ}C$, the starting rolling temperature of rough rolling is $1000^{\circ}C$, the entry temperature of finish rolling is $900^{\circ}C$, and the spinning temperature is $910^{\circ}C$.

[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 isothermal treatment. The temperature of the constant-temperature salt bath is $550^{\circ}C$, and the isothermal treatment time is $120s$. The wire rod after salt bath isothermal treatment immediately enters the heat preservation corridor for on-line aging treatment. The average cooling rate during the on-line aging process of the wire rod is $0.1^{\circ}C / s$.

[0056] (5) Steel strand processing process

[0057] The wire rod is processed into steel strands through the pickling, phosphating, drawing, stranding, and stabilization processes. Among them, in the pickling process, an aqueous solution with a hydrochloric acid concentration of 5% (mass fraction) is used for pickling for 8 minutes at a temperature of 42°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 1 m / s, and a temperature rise of 100°C per pass. The stranding tension is 90 kN, the speed is 36 m / min, the stabilization temperature is 420°C, and the duration is 5 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 alloy technical solution for 2200 - 2260 MPa grade prestressed steel strands of 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 as shown in Table 1 in mass percentage. In addition, the chemical composition of the continuous casting billet obtained in the continuous casting process, as well as 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 as 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 blowing oxygen for 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] Small billet continuous casting is adopted, and the molten steel obtained in the molten steel smelting process is cast into small billets with a cross-sectional size of 180 mm × 240 mm.

[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 processed into a wire rod with a diameter of 6 mm by high-speed wire rolling. The heating temperature is 1080 °C, the starting rolling temperature for rough rolling is 960 °C, the entry temperature for finish rolling is 870 °C, and the laying head temperature is 860 °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 isothermal treatment. The temperature of the constant temperature salt bath is 520 °C, and the salt bath time is 250 s. The wire rod after salt bath isothermal treatment immediately enters the heat preservation corridor for on-line aging. The average cooling rate during the on-line aging process is 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 processes. Among them, pickling uses an aqueous solution with a hydrochloric acid concentration of 20% (mass fraction), pickling for 7 minutes at a temperature of 40 °C. After pickling, the wire rod is placed for 24 hours before entering the next process. Drawing uses 11 passes, with a reduction ratio of 24% per pass, a drawing speed of 1.5 m / s, and a temperature rise of 80 °C per pass. The stranding tension is 80 kN, the speed is 30 m / min, the stabilization temperature is 410 °C, and the duration is 15 s.

[0072] Example 3 [[ID=1,7]]<o

[0073] In the alloy technical solution for the 2200 - 2260 MPa grade prestressed strand of 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 in terms of 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 inclusion in the molten steel is 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 molten steel smelting process is cast into small billets with a cross-sectional size of 180 mm × 240 mm. Among them, the superheat of the molten steel is controlled at 25 °C, the stirring current of the mold is 295 A, the stirring frequency of the mold is 3.5 Hz, the drawing speed during continuous casting is 1.25 m / min, the specific water consumption for continuous casting is 0.23 L / kg, the stirring current at the end is 475 A, the stirring frequency at the end is 8.5 Hz, and the total reduction of soft reduction is 15.2 mm.

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

[0080] The intermediate billet obtained from the continuous casting process is prepared into wire rods with a diameter of 10 mm through 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 880 °C, and the spinning temperature is 870 °C.

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

[0082] The wire rods after spinning are directly immersed in a molten nitrate constant-temperature salt bath for on-line salt bath isothermal treatment. The temperature is 536 °C and the salt bath time is 108 s. The wire rods after on-line salt bath isothermal treatment immediately enter the heat preservation corridor for on-line aging, and the average cooling rate is 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 19% (mass fraction), pickling for 10 minutes at a temperature of 35 °C, and the wire rods after pickling are placed for 24 hours before entering the next process. Drawing uses 10 passes, the area reduction rate per pass is 25%, the drawing speed is 2 m / s, and the temperature rise per pass is 90 °C. The stranding tension is 100 kN, the speed is 33 m / min, the stabilization temperature is 400 °C, and the duration is 10 s.

[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 10 cm are taken from the head of the wire rods respectively, made into metallographic samples, after mechanical grinding and polishing, etching with nitric acid alcohol, and then placed under a metallographic microscope for tissue observation, or after electrolytic polishing, observed by scanning electron microscope. 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 Diameter / mm Sorbite rate Grain boundary cementite Martensite Tensile strength Elongation after fracture 1 13 94 0 0 1380 38 2 7 93 0 0 1440 48 3 10 93.5 0 0 1400 43

[0092] The performance indexes of the steel stranded wires in Examples 1-3 (the detection 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: the wire rods after spinning are directly immersed in a constant-temperature salt bath for isothermal treatment: the salt bath temperature is 536 °C and the salt bath time is 200 s.

[0100] Example 5

[0101] The difference between this example and Example 3 is only that: the wire rods after spinning are directly immersed in a constant-temperature salt bath for isothermal treatment: the salt bath temperature is 530 °C and the salt bath time is 108 s.

[0102] Example 6

[0103] The difference between this example and Example 3 is only that: the wire rods after spinning are directly immersed in a constant-temperature salt bath for isothermal treatment: the salt bath temperature is 545 °C and the salt bath time is 108 s.

[0104] Group Three

[0105] Example 7

[0106] The difference between this example and Example 3 is only that: the average cooling rate of the wire rods in the heat preservation corridor is 0.15 °C / s.

[0107] Example 8

[0108] The difference between this example and Example 4 is only that: the average cooling rate of the wire rods in the heat preservation corridor is 0.15 °C / s.

[0109] Example 9

[0110] The difference between this embodiment and Embodiment 5 is only that: the average cooling rate of the wire rod in the heat preservation aisle is 0.15 °C / s.

[0111] Embodiment 10

[0112] The difference between this embodiment and Embodiment 6 is only that: the average cooling rate of the wire rod in the heat preservation aisle is 0.15 °C / s.

[0113] The tensile strength and percentage reduction of area of the wire rods in Embodiments 4-10 are shown in Table 5 respectively.

[0114] Table 5

[0115] Example Diameter / mm Sorbite rate Grain boundary cementite Martensite Tensile strength Elongation after fracture 4 10 93.4 0 0 1420 44 5 10 93.1 0 0 1430 47 6 10 93.3 0 0 1330 41 7 10 94 0.1 0 1400 39 8 10 93.2 0 0 1410 46 9 10 93.3 0 0 1350 44 10 10 93.1 0 0 1340 45

[0116] The performance indexes of the steel strands in Embodiments 4-10 (the detection method is carried out in accordance with the requirements of GB / T 5224) are shown in Tables 6 and 7.

[0117] Table 6

[0118]

[0119] Table 7

[0120]

[0121]

[0122] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-mentioned exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. 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 included in the present invention.

[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. An alloy for ultra-high stress corrosion resistant prestressed steel strands with a strength level of 2200 - 2260 MPa, characterized in that, Its composition includes, by mass percentage: C 0.83 - 0.89%, Si 0.60 - 1.40%, Mn 0.20 - 0.80%, Cr 0.15 - 0.50%, Cu < 0.30%, Ni < 0.30%, Mo < 0.30%, V 0.01 - 0.05%, Nb 0.001 - 0.05%, S ≤ 0.008%, P ≤ 0.010%, N ≤ 0.0040%, O ≤ 0.0020%, where 0.30% ≤ Cr + Cu + Ni + Mo ≤ 1.0%, and the rest is Fe and other inevitable impurities.

2. Wire rod for prestressed steel strand with ultra-high stress corrosion resistance at 2200 - 2260 MPa level, characterized in that, It is prepared from the alloy for 2200 - 2260 MPa grade ultra - high stress corrosion resistant prestressed steel strands according to claim 1.

3. The preparation method of the wire rod for 2200 - 2260 MPa ultra-high stress corrosion resistant prestressed steel strand according to claim 2, characterized in that, The wire rods are obtained through the processes of molten steel smelting, continuous casting, high - speed wire rolling, and controlled cooling after rolling according to the alloy formula for 2200 - 2260 MPa grade ultra - high stress corrosion resistant prestressed steel strands in claim 1.

4. The preparation method of the wire rod for 2200-2260 MPa grade ultra-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 ultra-high stress corrosion resistant prestressed steel strand according to claim 3, characterized in that, 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 870 - 920°C, and the wire - laying temperature is 860 - 910°C.

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

7. The preparation method of the wire rod for 2200-2260 MPa grade ultra-high stress corrosion resistant prestressed steel strand according to claim 6, characterized in that, In the online salt - bath isothermal treatment process, the wire rods after wire - laying are directly immersed in a constant - temperature salt bath for isothermal treatment: the salt - bath temperature is 520 - 550°C, and the salt - bath time is 108 - 250 s.

8. The preparation method of the wire rod for 2200-2260 MPa grade ultra-high stress corrosion resistant prestressed steel strand according to claim 6, characterized in that, The controlled cooling process after rolling also includes an online aging process. 9.2200 - 2260 MPa ultra-high stress corrosion resistant prestressed steel strand, characterized in that, It is prepared from the wire rods for 2200 - 2260 MPa grade ultra - high stress corrosion resistant prestressed steel strands according to claim 2.

10. The preparation method of the 2200-2260 MPa grade ultra-high stress corrosion resistant prestressed steel strand according to claim 9, characterized in that, The wire rods for 2200 - 2260 MPa grade ultra - high stress corrosion resistant prestressed steel strands according to claim 2 are pickled, phosphated, drawn, stranded, and stabilized to obtain steel strands.

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