Alloy for 2230 MPa-grade high-corrosion-resistance steel strand, wire rod, steel strand and method

Abstract

The invention discloses an alloy for a 2230 MPa-grade high-corrosion-resistance steel strand, a wire rod, the steel strand and a method, and the alloy comprises the following components in percentage by mass: 0.89-0.93% of C, 1.20-1.40% of Si, 0.50-0.70% of Mn, 0.30-0.40% of Cr, 0.01-0.04% 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. By optimizing the chemical component design and controlling the production process, the homogeneity of the steel is improved, the homogeneity of the wire rod is improved, the purity is improved, meanwhile, surface damage and internal defects during steel wire drawing machining are reduced, and therefore the stress corrosion index 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, a wire rod, a steel strand and a method for a 2230 MPa high corrosion-resistant steel strand. 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 raises the strength level of prestressed steel strands from 1860 MPa to 2360 MPa. With the increase in the strength level, the stress corrosion performance of steel strands significantly decreases 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 the steel wire by hot-dip galvanizing, but the cost is high, reaching 1500 yuan / ton. The method of wrapping the whole surface of the steel strand with PE plastic can also be adopted, 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. 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 is the production process long, but also there are problems such as environmental pollution during the production process and increased corrosion at the damaged parts of the 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 stress corrosion-resistant steel strand that meets the requirement of 5 hours of stress corrosion. CN 111321352A discloses a production method for a 2400 MPa prestressed steel strand. In the production method of the wire rod, off-line salt bath heat treatment is also required, and the processed steel strand does not have good stress corrosion performance. CN 114369760A provides an anti-stress corrosion ultra-high strength steel strand. Through the alloying composition design of V and B, the improvement of the water bath production process of the wire rod, and the improvement of the wire drawing process during the production process of the steel strand, reducing the temperature of the steel wire, increasing the stabilization treatment temperature, and 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. CN 119287269 A provides a green and environment-friendly wire rod for a 2300 MPa steel strand and its production method, and uses an on-line heat treatment method to produce a wire rod for a 2300 MPa steel strand, without involving the manufacturing method of the steel strand and its stress corrosion performance. In addition, the steel strand specifications reported in the foregoing literatures are all 15.2 mm. There has been no report on a wire rod, a steel strand and a manufacturing method for a 17.8 mm steel strand with a strength level of 2230 MPa and a stress corrosion index greater than 5 hours.

[0004] Therefore, in view of the above technical problems, it is necessary to provide an alloy, wire rod, steel strand and method for a 2230 MPa high corrosion-resistant steel strand.

[0005] The information disclosed in this background art section is only intended to enhance the overall understanding 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 a 2230 MPa high corrosion-resistant steel strand.

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

[0008] The alloy for a 2230 MPa high stress corrosion-resistant prestressed steel strand, its composition includes, by mass percentage: C 0.89 - 0.93%, Si 1.20 - 1.40%, Mn 0.50 - 0.70%, Cr 0.30 - 0.40%, V 0.01 - 0.04%, 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 a 2230 MPa high stress corrosion-resistant prestressed steel strand is prepared from the aforementioned alloy for a 2230 MPa high stress corrosion-resistant prestressed steel strand.

[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 sorbite lamellar spacing is 50 - 70 nm. Preferably, the diameter of the wire rod is 14 mm, the tensile strength is 1440 - 1500 MPa, and the reduction of area is 28 - 35%.

[0011] In one or more embodiments of the present invention, the preparation method of the wire rod for a 2230 MPa high stress corrosion-resistant prestressed steel strand is obtained by subjecting the raw materials of the aforementioned alloy formula for a 2230 MPa high stress corrosion-resistant prestressed steel strand to hot metal pre-desulfurization, converter smelting, secondary refining, bloom continuous casting, blooming and grinding, high-speed wire rolling, Stelmor air cooling, and off-line salt bath heat treatment.

[0012] In one or more embodiments of the present invention, in the bloom continuous casting process, the superheat of the molten steel is controlled at 15 - 35 °C, the stirring current of the mold is 600 ± 25 A, the stirring frequency of the mold is 7 ± 0.5 Hz, the casting speed during continuous casting is 0.6 ± 0.05 m / min, the water supply in the secondary cooling section of continuous casting is 500 - 700 NL / min, the total reduction of soft reduction is 15 - 28 mm, and the cross-sectional size of the bloom is 300 mm × 390 mm.

[0013] In one or more embodiments of the present invention, for bloom reheating and grinding, the aforementioned bloom is heated (temperature 1250 °C) and soaked for heat preservation (not less than 5 hours) in a bloom heating furnace. After bloom rolling, a rolled billet with a size of 140 mm × 140 mm is obtained. The rolled billet is subjected to magnetic particle flaw detection, and then the entire surface is ground. For the positions with obvious flaw detection defects on the surface, spot grinding is carried out again, and the average grinding depth is ≥ 0.5 mm.

[0014] In one or more embodiments of the present invention, in the high-speed wire rolling process, the small billet obtained from the bloom reheating and grinding process is heated and then successively subjected to rough rolling and finish rolling. The heating temperature is 1080 - 1180 °C, the rough rolling starting temperature is 980 - 1040 °C, the finish rolling inlet temperature is 900 - 930 °C, and the laying head temperature is 900 - 930 °C.

[0015] In one or more embodiments of the present invention, 100% of the first 16 fans are turned on before the Stelmor air cooling process.

[0016] In one or more embodiments of the present invention, the offline salt bath heat treatment is as follows: After the coiling of the wire rod after Stelmor air cooling treatment, it successively passes through a direct-fired heating furnace for austenitization, an isothermal salt bath tank for cooling, cleaning, and coiling and collecting.

[0017] In one or more embodiments of the present invention, in the offline salt bath heat treatment, the temperature of the direct-fired heating furnace is 900 - 980 °C, the time is 5 - 10 min, the temperature of the isothermal salt bath tank is 535 - 555 °C, and the salt bath time is 150 - 300 s.

[0018] In one or more embodiments of the present invention, the 2230 MPa high stress corrosion resistant prestressed steel strand is prepared from the wire rod of the aforementioned 2230 MPa high stress corrosion resistant prestressed steel strand.

[0019] In one or more embodiments of the present invention, the preparation method of the 2230 MPa high stress corrosion resistant prestressed steel strand is obtained by pickling, phosphating, drawing, stranding, and stabilization of the wire rod of the aforementioned 2230 MPa high stress corrosion resistant prestressed steel strand.

[0020] 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.

[0021] In one or more embodiments of the present invention, drawing is carried out in 9 passes, with a reduction ratio per pass of 23% - 25%, a drawing speed not higher than 3 m / s, and a temperature rise per pass not higher than 100 °C.

[0022] In one or more embodiments of the present invention, the stranding tension is 180 kN and the stranding pitch is 255 - 260 mm.

[0023] In one or more embodiments of the present invention, the stabilization temperature is 360 - 385 °C and the time is 35 - 60 s.

[0024] Compared with the prior art, the beneficial effects of the alloy, wire rod, steel strand and method for 2230 MPa grade high corrosion-resistant steel strand of the present invention are as follows:

[0025] (1) Based on the chemical composition design scheme of the present invention and the control of production processes such as continuous casting, blooming, rolling, and off-line salt bath heat treatment, 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, with a sorbitization rate ≥ 93%, a sorbite lamellar spacing of 50 - 70 nm; the tensile strength is 1440 - 1500 MPa, and the reduction of area is 28 - 35%.

[0026] (2) By improving the homogeneity of the wire rod and the purity, and at the same time reducing the surface damage and internal defects during wire drawing processing, the stress corrosion index of the steel strand is improved. The minimum stress corrosion time of the 1×7 - 17.8 - 2230 steel strand processed is 5 hours, and the median 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 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 It is a scanning electron microscope picture of the microstructural of the wire rod in Embodiment 1 of the present invention;

[0029] Figure 2 It is a scanning electron microscope picture of the microstructural of the wire rod in Embodiment 2 of the present invention;

[0030] Figure 3 It is a scanning electron microscope picture of the microstructural of the wire rod in Embodiment 3 of the present invention. Detailed implementation manners

[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 conjunction 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 scope of protection of the present invention.

[0032] In the chemical compositions of the alloy, wire rod, steel strand and method technical solutions for 2230MPa grade high corrosion-resistant steel strands of the present invention:

[0033] C is the most important strengthening element in steel. In order to obtain large-sized high-strength steel strands, the present invention limits the C content to 0.92 - 0.96%.

[0034] Si is a strengthening element and a deoxidizing element in steel, and at the same time helps to improve the corrosion resistance and stress relaxation resistance of steel. In the present invention, the Si content is limited to 1.20 - 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 0.50 - 0.70%.

[0036] Cr is a commonly used corrosion-resistant alloy element, which forms a dense oxide film on the steel surface; however, too high a content increases the difficulty of controlling segregation. The present invention limits the Cr content to 0.30 - 0.40%.

[0037] The carbonitrides formed by V are effective hydrogen traps in steel, thereby improving the stress corrosion index of steel. The present invention limits the V content to 0.01 - 0.04%.

[0038] S is prone to segregation at grain boundaries, which embrittles the grain boundaries, thereby reducing the strength and plasticity of steel. In addition, S reacts with Mn to form MnS, thereby reducing the solid solution strengthening effect of Mn. In the present invention, the S content is limited to ≤0.008%.

[0039] P is an impurity element in steel, which is prone to segregation at grain boundaries, embrittles the grain boundaries, and further reduces the strength and plasticity of steel. In the present invention, the P content is limited to ≤0.010%.

[0040] N will cause the plasticity of steel to deteriorate, increase the risk of delayed fracture of the wire rod, and 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%.

[0041] O combines with alloying elements in steel to form non-metallic inclusions, which affect the strength and plasticity of the wire rod and the fatigue and corrosion resistance of the steel wire. Therefore, it is necessary to limit O≤0.0020%.

[0042] Example 1

[0043] The technical solutions of the wire rod, steel strand and their production methods for 2230MPa grade ultra-high stress corrosion resistant prestressed steel strands in this example include:

[0044] (1) Molten steel smelting process

[0045] 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 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.

[0046] Among them, in the converter smelting step, 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.

[0047] (2) Continuous casting process

[0048] Large bloom 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 300mm×390mm.

[0049] Among them, the superheat of the molten steel is controlled at 20°C, the stirring current of the mold is 575A, the stirring frequency of the mold is 7.5Hz, the casting speed during continuous casting is 0.55m / min, the water supply in the secondary cooling section of continuous casting is 500NL / min, and the total reduction of soft reduction is 15mm.

[0050] (3) Blooming and grinding

[0051] The large bloom is heated and soaked in the blooming heating furnace at a temperature of 1250°C for 5 hours. After blooming rolling, a small bloom with a size of 140mm×140mm is obtained. The rolled billet is subjected to magnetic particle flaw detection, and then the surface is completely ground. The positions with obvious flaw detection defects on the surface are spot-ground again, and the average grinding depth is 0.6mm.

[0052] (4) High-speed wire rolling and Stelmor air cooling process

[0053] The billets are heated and then rough rolled and finish rolled successively to produce wire rods with a diameter of 14 mm. The heating temperature is 1150 °C, the starting rolling temperature for rough rolling is 1000 °C, the inlet temperature for finish rolling is 920 °C, and the laying head temperature is 920 °C. The wire rods after laying head are cooled by Stelmor air cooling, and the first 16 fans are turned on at 100%.

[0054] (5) Offline salt bath process

[0055] In the said offline salt bath heat treatment, the temperature of the open flame heating furnace is 930 °C and the time is 6 min, the temperature of the isothermal salt bath tank is 545 °C, and the salt bath time is 250 s.

[0056] (5) Strand processing process

[0057] The wire rods are processed into strands through pickling, phosphating, drawing, stranding, and stabilization process pickling process. Among them, pickling uses an aqueous solution with a hydrochloric acid concentration of 19% (mass fraction), pickling for 8 minutes, and the temperature is 40 °C. Drawing uses 9 passes, the area reduction rate per pass is 23%, the drawing speed is 1.5 m / s, and the temperature rise per pass is 100 °C; the stranding tension is 180 kN, and the stranding pitch is 260 mm; the stabilization temperature is 385 °C and the time is 60 s. Regarding phosphating, any conventional technology applicable to related products in the art 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] The technical solutions of the wire rod for 2230 MPa grade ultra-high stress corrosion resistant prestressed strands, the strands and their production methods in this example include:

[0060] (1) Molten steel smelting process

[0061] The molten steel is smelted through the converter 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 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 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, 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] Using bloom continuous casting, the molten steel obtained from the molten steel smelting process is cast into a rectangular billet with a cross-sectional size of 300 mm × 390 mm.

[0065] Among them, the superheat of the molten steel is controlled at 15 °C, the stirring current of the mold is 600 A, the stirring frequency of the mold is 7 Hz, the drawing speed during continuous casting is 0.6 m / min, the water supply amount in the secondary cooling section of continuous casting is 600 NL / min, and the total reduction amount of soft reduction is 20 mm.

[0066] (3) Bloom breakdown and grinding

[0067] The bloom is heated and soaked in a bloom heating furnace at a temperature of 1250 °C for 6 hours. After bloom rolling, a small square billet with a size of 140 mm × 140 mm is obtained. The rolled billet is subjected to magnetic particle flaw detection, and then the surface is completely ground. For the positions with obvious flaw detection defects on the surface, point grinding is carried out again, and the average grinding depth is 0.55 mm.

[0068] (4) High-speed wire rolling and Stelmor air cooling process

[0069] The small square billet is heated and then subjected to rough rolling and finish rolling successively to prepare a wire rod with a diameter of 14 mm. The heating temperature is 1080 °C, the starting rolling temperature of rough rolling is 980 °C, the entry temperature of finish rolling is 900 °C, and the laying temperature is 930 °C. The wire rod after laying is subjected to Stelmor air cooling, and the first 16 fans are turned on 100%.

[0070] (5) Offline salt bath process

[0071] In the said offline salt bath heat treatment, the temperature of the open-flame heating furnace is 900 °C and the time is 5 min, the temperature of the isothermal salt bath tank is 535 °C, and the salt bath time is 150 s.

[0072] (5) Strand processing process

[0073] The wire rod is processed into a strand through pickling, phosphating, drawing, stranding, and stabilization process pickling process. Among them, the pickling uses an aqueous solution with a hydrochloric acid concentration of 20% (mass fraction), pickling for 7 minutes at a temperature of 42 °C. The drawing adopts 9 passes, the area reduction rate per pass is 24%, the drawing speed is 2 m / s, and the temperature rise per pass is 90 °C; the stranding tension is 180 kN, and the stranding pitch is 258 mm; the stabilization temperature is 375 °C and the time is 45 s.

[0074] Example 3

[0075] The technical solutions of the wire rod, strand and their production methods for the 2230 MPa grade ultra-high stress corrosion resistant prestressed strand of this example include:

[0076] (1) Molten steel smelting process

[0077] 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 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.

[0078] 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.

[0079] (2) Continuous casting process

[0080] Slab 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 300 mm × 390 mm.

[0081] Among them, the superheat of the molten steel is controlled at 35 °C, the stirring current of the mold is 625 A, the stirring frequency of the mold is 6.5 Hz, the casting speed during continuous casting is 0.65 m / min, the water supply amount in the secondary cooling section of continuous casting is 700 NL / min, and the total reduction amount of soft reduction is 28 mm.

[0082] (3) Blooming and grinding

[0083] The slab is heated and soaked in the blooming heating furnace at a temperature of 1250 °C for 7 hours, and a small square billet of 140 mm × 140 mm is obtained after blooming rolling. The rolled billet is subjected to magnetic particle flaw detection, and then the surface is fully ground. For the positions with obvious flaw detection defects on the surface, spot grinding is carried out again, and the average grinding depth is 0.5 mm.

[0084] (4) High-speed wire rolling and Stelmor air cooling process

[0085] The small square billet is heated and then subjected to rough rolling and finish rolling successively to prepare a wire rod with a diameter of 14 mm. The heating temperature is 1180 °C, the starting rolling temperature of rough rolling is 1040 °C, the entry temperature of finish rolling is 930 °C, and the spinning temperature is 900 °C. The wire rod after spinning is subjected to Stelmor air cooling, and the first 16 fans are turned on 100%.

[0086] (5) Offline salt bath process

[0087] In the offline salt bath heat treatment, the temperature of the open-flame heating furnace is 980 °C and the time is 10 min, the temperature of the isothermal salt bath tank is 555 °C, and the salt bath time is 300 s.

[0088] (5) Steel strand processing process

[0089] The wire rod is processed into steel strand through pickling, phosphating, drawing, stranding and stabilizing processes. Among them, in the pickling process, an aqueous solution with a hydrochloric acid concentration of 15% (mass fraction) is used for pickling for 10 minutes at a temperature of 35°C. The drawing process is carried out in 9 passes, with a reduction ratio of 25% per pass, a drawing speed of 3 m / s, and a temperature rise of 95°C per pass; the stranding tension is 180 kN and the stranding pitch is 255 mm; the stabilizing temperature is 360°C and the time is 35 s.

[0090] Table 1

[0091]

[0092] 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:

[0093] (1) In terms of metallographic structure, wire rods with a length of 10 cm are taken from the head of the wire rod respectively to make metallographic samples. After mechanical grinding, polishing and etching with nitric acid alcohol, they are placed under a metallographic microscope for tissue observation, or after electrolytic polishing, they are 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.

[0094] (2) In terms of mechanical properties, referring to the test method and definition of GB / T228 standard, a tensile testing machine is used to test the mechanical properties of the wire rod. The tensile strength and reduction of area of the wire rods of Examples 1 - 3 are shown in Table 2 respectively.

[0095] Table 2

[0096] Example Sorbite rate Grain boundary cementite Martensite Tensile strength Reduction of area 1 93 0 0 1440 38 2 93.4 0 0 1470 33 3 94 0 0 1500 30

[0097] The performance indexes of the steel strand produced according to this embodiment (the detection method is carried out according to the requirements of GB / T 5224) are shown in Tables 3 and 4.

[0098] Table 3

[0099] Example Tensile strength / MPa Yield strength / MPa Total elongation at maximum force / % 70% stress relaxation rate / % 1 2260 1985 7.2 1.4 2 2263 1991 6.6 1.3 3 2258 1981 6.9 1.3

[0100] Table 4

[0101]

[0102]

[0103] Comparative Example 1

[0104] The difference between this comparative example and Example 2 is only that: in the off-line salt bath heat treatment, the temperature of the open flame heating furnace is 880 °C, the time is 5 min, the temperature of the isothermal salt bath tank is 535 °C, and the salt bath time is 150 s.

[0105] Comparative Example 2

[0106] The difference between this comparative example and Example 2 is only that: in the off-line salt bath heat treatment, the temperature of the open flame heating furnace is 900 °C, the time is 5 min, the temperature of the isothermal salt bath tank is 530 °C, and the salt bath time is 150 s.

[0107] The tensile strength and percentage reduction of area of the wire rods of Comparative Examples 1-2 are shown in Table 5 respectively.

[0108] Table 5

[0109] Comparative example Sorbite rate Grain boundary cementite Martensite Tensile strength Reduction of area 1 93.1 0 0 1420 30 2 93.2 0 0 1450 36

[0110] The performance indexes of the steel strands produced according to Comparative Examples 1-2 (the detection method is carried out in accordance with the requirements of GB / T 5224) are shown in Tables 6 and 7.

[0111] Table 6

[0112] Comparative example Tensile strength / MPa Yield strength / MPa Total elongation at maximum force / % 70% stress relaxation rate / % 1 2231 1963 5.9 1.4 2 2259 1984 6.8 1.4

[0113] Table 7

[0114]

[0115]

[0116] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above 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.

[0117] 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 2230 Mpa high stress corrosion resistant prestressed steel strands, characterized in that, Its composition includes, by mass percentage: C 0.89 - 0.93%, Si 1.20 - 1.40%, Mn 0.50 - 0.70%, Cr 0.30 - 0.40%, V 0.01 - 0.04%, S ≤ 0.008%, P ≤ 0.010%, N ≤ 0.0040%, O ≤ 0.0020%, and the balance is Fe and other inevitable impurities. 2.2230 Mpa high stress corrosion resistant wire rod for prestressed steel strand, characterized in that, It is prepared from the alloy for 2230 Mpa high stress corrosion resistant prestressed steel strand according to Claim 1. Preparation method of wire rod for prestressed steel strand with high stress corrosion resistance of 3.2230 Mpa, characterized in that, It is obtained by subjecting the raw materials of the alloy formula for 2230 Mpa high stress corrosion resistant prestressed steel strand according to Claim 1 to hot metal desulfurization, converter smelting, secondary refining, bloom continuous casting, blooming and grinding, high-speed wire rolling, Stelmor air cooling, and off-line salt bath heat treatment.

4. The preparation method of the wire rod for 2230 Mpa high stress corrosion resistant prestressed steel strand according to claim 3, characterized in that, In the bloom continuous casting process, the superheat of the molten steel is controlled at 15 - 35°C, the stirring current of the mold is 600 ± 25 A, the stirring frequency of the mold is 7 ± 0.5 Hz, the casting speed during continuous casting is 0.6 ± 0.05 m / min, the water supply in the secondary cooling section of continuous casting is 500 - 700 NL / min, the total reduction of soft reduction is 15 - 28 mm, and the cross-sectional size of the bloom is 300 mm × 390 mm.

5. The preparation method of the wire rod for 2230 Mpa high stress corrosion resistant prestressed steel strand according to claim 3, characterized in that, For the blooming and grinding, the aforementioned bloom is heated and soaked in the blooming heating furnace, and a rolled billet of 140 mm × 140 mm is obtained after blooming rolling. The rolled billet is subjected to magnetic particle flaw detection, and then the surface is fully ground. For the positions with obvious flaw detection defects on the surface, point grinding is carried out again, and the average grinding depth is ≥ 0.5 mm.

6. The preparation method of the wire rod for 2230 Mpa high stress corrosion resistant prestressed steel strand according to claim 3, characterized in that, In the high-speed wire rolling process, the small billet obtained from the blooming and grinding process is heated and then subjected to rough rolling and finish rolling successively. The heating temperature is 1080 - 1180°C, the rough rolling starting temperature is 980 - 1040°C, the finish rolling inlet temperature is 900 - 930°C, and the laying head temperature is 900 - 930°C.

7. The preparation method of the wire rod for 2230 Mpa high stress corrosion resistant prestressed steel strand according to claim 3, characterized in that, The off-line salt bath heat treatment is as follows: After the coiled bar after Stelmor air cooling is uncoiled, it successively passes through an open-flame heating furnace for austenitization, an isothermal salt bath tank for cooling, cleaning, and coiling and collecting.

8. The preparation method of the wire rod for 2230 Mpa high stress corrosion resistant prestressed steel strand according to claim 7, characterized in that, In the off-line salt bath heat treatment, the temperature of the open-flame heating furnace is 900 - 980°C and the time is 5 - 10 min, the temperature of the isothermal salt bath tank is 535 - 555°C, and the salt bath time is 150 - 300 s. 9.2230 Mpa high stress corrosion resistant prestressed steel strand, characterized in that, It is prepared from the wire rod for 2230 Mpa high stress corrosion resistant prestressed steel strand according to Claim 2. Preparation method of prestressed steel strand with high stress corrosion resistance of 10.2230 Mpa, characterized in that, It is obtained by subjecting the wire rod for 2230 Mpa high stress corrosion resistant prestressed steel strand according to Claim 2 to pickling, phosphating, drawing, stranding, and stabilization.

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