Wire rod for ultrahigh stress corrosion resistant prestressed steel strand, steel strand and production method

Abstract

The invention discloses a wire rod for an ultrahigh stress corrosion resistant prestressed steel strand, the steel strand and a production method. The wire rod comprises the following chemical components in percentage by mass: 0.65-0.75% 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, 0.02-0.05% of V, 0.01-0.05% 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. By designing the chemical components of the wire rod and combining process improvement, the steel strand made of the wire rod has excellent stress corrosion resistance, the minimum stress corrosion value is 8 hours, and the median value is 12 hours.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy and metal products, and particularly relates to a wire rod, a steel strand for an ultra-high stress corrosion resistant prestressed steel strand, and a production method thereof. Background Art

[0002] The national standard GB / T5224 requires that the stress corrosion performance of the steel strand is at least 2 hours and the median value is 5 hours, which far fails to meet 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 / ton. The method 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 together with the steel strand and is damaged, losing the anti-corrosion function.

[0003] In addition, for the slow-bonding prestressed steel strand, the corrosion rate is reduced by coating the outer layer with an epoxy adhesive and a sheath. Not only is the production process long, but also problems such as environmental pollution during the production process and accelerated corrosion at the damaged sheath during use exist.

[0004] Therefore, starting from the steel strand material itself, it is an urgent need for the industry development to obtain an ultra-high stress corrosion resistant steel strand with stable reliability, simple process and controllable cost through composition and process optimization. However, there is no relevant research on steel strands with a minimum stress corrosion performance higher than 2 hours and a median value higher than 5 hours reported at present.

[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 suggestion that this information constitutes the 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 a wire rod, a steel strand for an ultra-high stress corrosion resistant prestressed steel strand, and a production method thereof, and the steel strand has excellent tensile strength and stress corrosion resistance.

[0007] To achieve the above purpose, the technical solution provided by a specific embodiment of the present invention is as follows:

[0008] A wire rod for ultra-high stress corrosion resistant prestressed steel strands, the chemical composition of which, by mass percentage, includes: C 0.65 - 0.75%, 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 0.02 - 0.05%, Nb 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, in the chemical composition, the total mass percentage of Cr, Cu, Ni, and Mo satisfies 0.30% < Cr + Cu + Ni + Mo < 1.0%.

[0010] In one or more embodiments of the present invention, the metallographic structure of the wire rod includes sorbite, the sorbitization rate ≥ 90%, and the sorbite lamellar spacing is 60 nm - 80 nm.

[0011] In one or more embodiments of the present invention, the diameter of the wire rod is 6 mm - 12 mm.

[0012] The technical solution provided by another specific embodiment of the present invention is as follows:

[0013] A production method of a wire rod for ultra-high stress corrosion resistant prestressed steel strands, comprising the following processes:

[0014] Steel melting: Melting the raw materials according to the ratio to obtain molten steel;

[0015] Continuous casting: Pouring the molten steel into a billet;

[0016] High-speed wire rolling: Heating the billet at 1080°C - 1150°C, then performing rough rolling and finish rolling. The rough rolling starting temperature is 950°C - 1000°C, the finish rolling inlet temperature is 840°C - 880°C, and the laying head temperature is 800°C - 900°C;

[0017] Post-rolling controlled cooling: Adopting an on-line salt bath isothermal treatment process, the laying head temperature is 830°C - 860°C, the salt bath temperature is 495°C - 530°C, and the salt bath time is 90 s - 200 s; after the on-line salt bath isothermal treatment, slow cooling is carried out, and the average cooling rate is not higher than 0.2°C / s.

[0018] 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 flow rate 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.

[0019] The technical solution provided by another specific embodiment of the present invention is as follows:

[0020] A steel strand is prepared by using the above-mentioned wire rod for ultra-high stress corrosion resistant prestressed steel strand as the base material.

[0021] The technical solution provided by another specific embodiment of the present invention is as follows:

[0022] A production method of a steel strand includes the following processes:

[0023] Pickling: Pickle the wire rod with a hydrochloric acid aqueous solution having a mass concentration of 15% - 20% for 7 - 10 minutes at a temperature of 35°C - 42°C;

[0024] Phosphating;

[0025] Drawing;

[0026] Stranding;

[0027] Stabilization treatment: The treatment temperature is 400°C - 420°C.

[0028] 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.

[0029] 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.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] (1) Through the 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 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.

[0032] (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 ≥90%, and the sorbite lamellar spacing is 50 - 70 nm; the tensile strength is 1180 - 1300 MPa, and the reduction of area is 42 - 52%.

[0033] (3) By reducing the carbon content, improving the purity, and increasing corrosion-resistant chemical elements, and at the same time 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 - 1860 steel strand as an example, the minimum value of stress corrosion is 8 hours, and the median value is 12 hours. Description of the Drawings

[0034] 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 drawings described below 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.

[0035] Figure 1 It is the scanning electron microscope image of the wire rod microstructure in Example 1 of the present invention;

[0036] Figure 2 It is the scanning electron microscope image of the wire rod microstructure in Example 2 of the present invention;

[0037] Figure 3 It is the scanning electron microscope image of the wire rod microstructure in Example 3 of the present invention. Detailed Embodiments

[0038] 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 in the embodiments of the present invention in conjunction with the drawings in 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.

[0039] A specific embodiment of the present invention provides a wire rod for ultra-high stress corrosion resistant prestressed steel strands. The chemical composition in mass percentage includes: C 0.65 - 0.75%, 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 0.02 - 0.05%, Nb 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.

[0040] Further, in the chemical composition, the total mass percentage of Cr, Cu, Ni, and Mo satisfies 0.30% < Cr + Cu + Ni + Mo < 1.0%.

[0041] 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 0.65 - 0.75% to improve its stress corrosion resistance.

[0042] Si is a strengthening element and a deoxidizing element in steel, and it also helps to improve the corrosion resistance and stress relaxation resistance of steel. In the present invention, the Si content is limited to 0.60 - 1.40%.

[0043] Mn is a strengthening element in steel, which can improve the strength and hardenability of steel and ensure good work hardening rate of the wire rod. In the present invention, the Mn content is limited to 0.20 - 0.80%.

[0044] Cr is a commonly used corrosion-resistant alloying element, which forms a dense oxide film on the steel surface. However, too much content increases the difficulty of controlling segregation. In the present invention, the Cr content is limited to 0.15 - 0.50%.

[0045] The carbonitrides formed by V and Nb are effective hydrogen traps in steel, thereby improving the stress corrosion index of steel.

[0046] 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%.

[0047] 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 solid solution strengthening effect of Mn. In the present invention, the S content is limited to ≤ 0.008%.

[0048] 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%.

[0049] N can lead to poor plasticity of steel, increasing the risk of delayed fracture of wire rods. 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%.

[0050] O combines with alloying elements in steel to form non-metallic inclusions, affecting the strength and plasticity of wire rods and the fatigue, corrosion resistance and other properties of steel wires. It is necessary to limit O≤0.0020%.

[0051] Furthermore, the metallographic structure of the wire rod includes sorbite, the rate of sorbitization is ≥90%, the lamellar spacing of sorbite is 60nm - 80nm, the diameter of the wire rod is 6mm - 12mm, the tensile strength is 1180 - 1300MPa, and the reduction of area is 42 - 52%.

[0052] Specifically, the wire rod in the present invention has a high rate of sorbitization and an appropriate lamellar spacing, making the prepared wire rod have a high strength. Moreover, when used to prepare steel strands, the steel strands not only maintain a high strength but also have excellent stress corrosion resistance.

[0053] Another specific embodiment of the present invention provides a production method of a wire rod for ultra-high stress corrosion resistant prestressed steel strands, including steps 1 - 4.

[0054] Step 1, the molten steel smelting process.

[0055] Specifically, raw materials are taken according to the chemical composition by weight, and the molten steel is smelted through the converter smelting and LF furnace refining steps. 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 inclusion in the molten steel is regulated by soft stirring. After the temperature and chemical composition meet the standards, tapping is carried out.

[0056] Step 2, the continuous casting process.

[0057] Specifically, the superheat of the molten steel is controlled at 20 - 25°C, the stirring current of the mold is 270±25A, the stirring frequency of the mold is 3±0.5Hz, the casting speed during continuous casting is 1.2±0.05m / min, the specific water volume during continuous casting is 0.22±0.01L / kg, the stirring current at the end is 450±25A, the stirring frequency at the end is 8±0.5Hz, and the total reduction of soft reduction is 15.0±0.2mm. Through the continuous casting process, the molten steel is cast into a rectangular billet, while improving the composition uniformity and the internal quality of the rectangular billet.

[0058] Step 3, the high-speed wire rolling process.

[0059] Specifically, 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°C - 1150°C, the starting rolling temperature for rough rolling is 950°C - 1000°C, the entry temperature for finish rolling is 840°C - 880°C, and the wire laying temperature is 800°C - 900°C. Within the above temperature ranges, the metallographic structure is optimized and the tensile strength of the wire rod is improved.

[0060] Step 4, post-rolling controlled cooling process.

[0061] Specifically, an on-line salt bath isothermal treatment and on-line aging process are adopted. In the on-line salt bath isothermal treatment step, the wire laying temperature is 830°C - 860°C. The wire rod after wire laying is directly immersed in a constant temperature salt bath for isothermal treatment. The salt bath temperature is 495°C - 530°C, the salt bath time is 90s - 200s, and the salt bath uses molten nitrate. The wire rod after salt bath isothermal treatment immediately enters the heat preservation corridor for on-line aging, and the average cooling rate of the wire rod in the heat preservation corridor is not higher than 0.2°C / s. Under the above conditions, the salt bath isothermal treatment and on-line aging process can optimize the microstructure, improve the strength and plasticity, and enhance the stress corrosion resistance.

[0062] Another specific embodiment of the present invention provides a steel strand, which is prepared by using the above-mentioned wire rod for ultra-high stress corrosion resistant prestressed steel strand as the base material.

[0063] Specifically, the wire rod in the present invention has a high rate of sorbitization and tensile strength. After being made into a steel strand, the stress corrosion resistance of the steel strand is greatly improved. Taking the 1×7 - 15.2 - 1860 steel strand processed as an example, its minimum stress corrosion time is 8 hours and the median is 12 hours.

[0064] Another specific embodiment of the present invention provides a production method of a steel strand, including steps (1) - (5).

[0065] Step (1), pickling process.

[0066] Specifically, the wire rod is pickled with an aqueous solution of hydrochloric acid with a concentration of 15 - 20% (mass fraction) for 7min - 10min at a temperature of 35 - 42°C. This pickling condition can ensure the removal of hot-rolled scale and avoid excessive absorption of H by the wire rod. The wire rod after pickling is placed for 24 hours before entering the next process.

[0067] Step (2), phosphating process.

[0068] Specifically, this step is carried out by a conventional process to form a phosphating film on the surface of the wire rod to improve the lubrication effect during subsequent drawing and ensure smooth drawing.

[0069] Step (3), drawing process.

[0070] Specifically, the drawing process is carried out in 9 - 11 passes, with the area reduction rate per pass being 23% - 25%, the drawing speed not exceeding 2 m / s, and the temperature rise per pass not exceeding 100°C. The wire rod diameter is refined through drawing to form steel wire.

[0071] Step (4), the strand twisting process.

[0072] Specifically, the strand twisting tension is not less than 80 kN, and the speed is not higher than 36 m / min. Strand twisting under these conditions can ensure that the steel wires are closely bonded, improving the strength and stability of the steel strand.

[0073] Step (5), the stabilization treatment.

[0074] Specifically, the treatment temperature is 400°C - 420°C, and the time is 3 - 5 s. Residual stress in the steel strand is eliminated at this temperature, improving the strength and stability of the steel strand.

[0075] The following further elaborates on the present invention in conjunction with specific embodiments.

[0076] Embodiment 1

[0077] A production method of steel strand, including:

[0078] (1) The molten steel smelting process

[0079] 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 in the continuous casting process and the chemical composition of the wire rod 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.

[0080] 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 through soft stirring. After the temperature and chemical composition meet the standards, tapping is carried out.

[0081] (2) The continuous casting process

[0082] 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 180 mm × 240 mm.

[0083] Among them, the superheat of the molten steel is controlled at 20°C, the stirring current of the mold is 245 A, the stirring frequency of the mold is 2.5 Hz, the casting speed during continuous casting is 1.15 m / min, the specific water volume during continuous casting is 0.21 L / kg, the stirring current at the end is 425 A, the stirring frequency at the end is 7.5 Hz, and the total reduction amount of soft reduction is 14.8 mm.

[0084] (3) High-speed wire rolling process

[0085] The billets obtained from the continuous casting process are heated and then subjected to rough rolling and finish rolling successively to produce wire rods with a diameter of 15 mm. The heating temperature is 1150 °C, the starting rolling temperature for rough rolling is 1000 °C, the inlet temperature for finish rolling is 850 °C, and the wire laying temperature is 830 °C.

[0086] (4) Post-rolling controlled cooling process

[0087] The wire rods after wire laying are directly immersed in a constant-temperature salt bath for isothermal treatment. The temperature of the constant-temperature salt bath is 495 °C, and the isothermal treatment time is 200 s. The wire rods after salt bath isothermal treatment immediately enter the heat preservation corridor for on-line aging treatment. The average cooling rate during the on-line aging process of the wire rods is 0.15 °C / s.

[0088] (5) Strand processing process

[0089] The wire rods are processed into 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 8 minutes, at a temperature of 35 - 42 °C. After pickling, the wire rods are placed for 24 hours before entering the next process. Drawing uses 11 passes, with a reduction ratio per pass of 23%, a drawing speed of 2 m / s, and a temperature rise of 100 °C per pass. The stranding tension is 80 kN, the speed is 36 m / min, and the stabilization temperature is 400 °C.

[0090] Example 2

[0091] (1) Molten steel smelting process

[0092] 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 compositions of the continuous casting billets obtained from the continuous casting process and the wire rods 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.

[0093] 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.

[0094] (2) Continuous casting process

[0095] Small billet continuous casting is adopted to cast the molten steel obtained from the molten steel smelting process into small billets with a cross-sectional size of 180 mm × 240 mm.

[0096] 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 volume 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 of soft reduction is 15.0 mm.

[0097] (3) High-speed wire rolling process

[0098] The billet obtained from the continuous casting process is processed into a wire rod with a diameter of 6 mm through 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 880°C, and the spinning temperature is 860°C.

[0099] (4) Post-rolling controlled cooling process

[0100] The wire rod after spinning is directly immersed in a constant-temperature salt bath for isothermal treatment. The temperature of the constant-temperature salt bath is 530°C, and the salt bath time is 90 s. The wire rod after salt bath isothermal treatment immediately enters the heat preservation corridor for on-line aging, and the average cooling rate during the on-line aging process is 0.15°C / s.

[0101] (5) Steel strand processing process

[0102] The wire rod is processed into a steel strand 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 8 minutes, at a temperature of 35 - 42°C. After pickling, the wire rod is placed for 24 hours before entering the next process. Drawing uses 11 passes, with a reduction ratio per pass of 23%, a drawing speed of 2 m / s, and a temperature rise of 100°C per pass. The stranding tension is 80 kN, the speed is 36 m / min, and the stabilization temperature is 410°C.

[0103] Example 3

[0104] (1) Molten steel smelting process

[0105] 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 wire rod 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.

[0106] 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 inclusion in the molten steel is regulated through soft stirring. After the temperature and chemical composition meet the standards, tapping is carried out.

[0107] (2) Continuous casting process

[0108] Small billet continuous casting is adopted to cast the molten steel obtained from the molten steel smelting process 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.

[0109] (3) High-speed wire rolling process

[0110] The intermediate billet obtained from the continuous casting process is processed into wire rods with a diameter of 10 mm by high-speed wire rolling. The heating temperature is 1120 °C, the starting rolling temperature of rough rolling is 950 °C, the entry temperature of finish rolling is 870 °C, and the laying head temperature is 840 °C.

[0111] (4) Post-rolling controlled cooling process

[0112] The wire rods after laying head are directly immersed in a constant-temperature salt bath for on-line salt bath isothermal treatment at a temperature of 510 °C for 120 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.

[0113] (5) Steel strand processing process

[0114] The wire rods are processed into steel strands through pickling, phosphating, drawing, stranding, and stabilization process pickling process. Among them, pickling is carried out with an aqueous solution of hydrochloric acid with a concentration of 19% (mass fraction) for 8 minutes at a temperature of 35 - 42 °C. The wire rods after pickling are placed for 24 hours before entering the next process. Drawing is carried out in 10 passes, the area reduction rate per pass is 18%, the drawing speed is 2 m / s, and the temperature rise per pass is 100 °C. The stranding tension is 80 kN, the speed is 36 m / min, and the stabilization temperature is 420 °C.

[0115] Examples 4 - 5

[0116] The production methods of steel strands in Examples 4 and 5 are the same as those in Example 1, except that the chemical composition is different, as shown in Table 1 specifically.

[0117] Example 6

[0118] The production method of steel strands in Example 6 is the same as that in Example 1, except that: in the high-speed wire rolling process, the entry temperature of finish rolling is 840 °C and the laying head temperature is 800 °C;

[0119] In the pickling process, an aqueous solution of hydrochloric acid with a concentration of 15% (mass fraction) is used for pickling for 7 minutes.

[0120] Example 7

[0121] The production method of the steel strand in Example 7 is the same as that in Example 1, except that: in the high-speed wire rolling process, the wire laying temperature is 900 °C;

[0122] In the pickling process, an aqueous solution with a hydrochloric acid concentration of 20% (mass fraction) is used for pickling for 10 minutes.

[0123] Comparative Examples 1-2

[0124] The production method of the steel strand in Comparative Example 1 and Comparative Example 2 is the same as that in Example 1, except that the chemical composition is different, as shown in Table 1 specifically.

[0125] Comparative Example 3

[0126] The production method of the steel strand in Comparative Example 3 and Example 1 is the same as that in Example 1, except that: in the high-speed wire rolling process, the wire laying temperature is 920 °C; in the post-rolling controlled cooling process, the salt bath temperature is 560 °C and the salt bath time is 250 s.

[0127] Comparative Example 4

[0128] The production method of the steel strand in Comparative Example 4 and Example 1 is the same as that in Example 1, except that: in the steel strand processing process, the pickling time is 17 min and the stabilization temperature is 395 °C.

[0129] Table 1 Chemical composition table

[0130]

[0131] For the wire rods of Examples 1-3, samples were taken according to the same test method and subjected to metallographic structure detection and mechanical property detection. The specific test methods and detection results are as follows:

[0132] (1) In terms of metallographic structure, wire rods with a length of 10 cm were taken from the head of the wire rod respectively, made into metallographic samples, and after mechanical grinding and polishing and nitric acid alcohol etching, they were placed under a metallographic microscope for tissue observation, or after electrolytic polishing, scanning electron microscopy observation was carried out. It was found that the structures of the wire rods of Examples 1-3 were 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.

[0133] (2) In terms of mechanical properties, referring to the test method and definition of GB / T228 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 of Examples 1-3 are shown in Table 2 respectively.

[0134] Table 2 Wire rod test results

[0135]

[0136]

[0137] In addition, through detection, the sorbitization rate of the wire rods in Examples 4-7 reaches 90%, the tensile strength ranges from 1180 to 1300 MPa, and the reduction of area ranges from 42% to 52%. In the microstructure of the wire rod in Comparative Example 1, there is more martensite, the sorbitization rate is less than 90%, and the tensile strength is 1350 MPa; in the microstructure of the wire rod in Comparative Example 2, there is more ferrite, the sorbitization rate is less than 90%, and the tensile strength is 1080 MPa; in Comparative Example 3, the sorbitized part of the wire rod is spheroidized, and the tensile strength is 1130 MPa.

[0138] The performance indexes of the steel stranded wires produced according to this embodiment (the inspection method refers to the provisions of GB / T 5224) are shown in Tables 3 and 4.

[0139] Table 3 Performance Indexes of Steel Stranded Wires

[0140] Embodiment Tensile strength / MPa Yield strength / MPa Total elongation at maximum force / % 70% stress relaxation rate / % 1 1890 1685 7.0 1.3 2 1895 1670 6.5 1.3 3 1898 1680 6.5 1.3

[0141] Table 4 Performance Indexes of Steel Stranded Wires

[0142]

[0143]

[0144] As can be seen from Table 4, the minimum value of stress corrosion of the steel stranded wires in Examples 1-3 reaches 4-4.5 times that of the standard 2 hours, and the median reaches 2.4-2.5 times that of the standard value of 5 hours. Through detection, the minimum value of stress corrosion of the steel stranded wires in Examples 4-7 is within the range of 4-4.5 times that of the standard 2 hours, and the median is within the range of 2.4-2.5 times that of the standard value of 5 hours. In Comparative Examples 1-4, the minimum value of stress corrosion of the steel stranded wires is 2 hours, and the median is 5 hours. The stress corrosion resistance is significantly weaker than that of the 1×7-15.2-1860 steel stranded wires prepared in the examples of the present invention.

[0145] 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 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-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 embraced within the present invention. Any reference signs in the claims should not be regarded as limiting the claimed rights.

[0146] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A wire rod for prestressed steel strand with ultra-high stress corrosion resistance, characterized in that, The chemical components by mass percentage include: C 0.65 - 0.75%, 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 0.02 - 0.05%, Nb 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. The wire rod for super high stress corrosion resistant prestressed steel strand according to claim 1, characterized in that, In the above chemical components, the total mass percentage of Cr, Cu, Ni and Mo satisfies 0.30% < Cr + Cu + Ni + Mo < 1.0%.

3. The wire rod for ultra-high stress corrosion resistant prestressed steel strand according to claim 1, characterized in that, The metallographic structure of the wire rod includes sorbite, the rate of sorbitization is ≥ 90%, and the sorbite lamellar spacing is 60nm - 80nm.

4. The wire rod for super high stress corrosion resistant prestressed steel strand according to claim 1, characterized in that, The diameter of the wire rod is 6mm - 12mm.

5. A production method of wire rod for prestressed steel strand with ultra-high stress corrosion resistance, characterized in that, It includes the following processes: Steel melting: According to the ratio, melt the raw materials to obtain molten steel. Continuous casting: Pour the molten steel into a billet. High-speed wire rolling: Heat the billet at 1080°C - 1150°C, then carry out rough rolling and finish rolling. The rough rolling starting temperature is 950°C - 1000°C, the finish rolling inlet temperature is 840°C - 880°C, and the laying temperature is 800°C - 900°C. Post-rolling controlled cooling: Adopt the online salt bath isothermal treatment process. The laying temperature is 830°C - 860°C, the salt bath temperature is 495°C - 530°C, and the salt bath time is 90s - 200s. After the online salt bath isothermal treatment, slow cooling is carried out, and the average cooling rate is not higher than 0.2°C / s.

6. The production method of the wire rod for the ultra-high stress corrosion resistant prestressed steel strand according to claim 5, 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 ± 25A, the stirring frequency of the mold is 3 ± 0.5Hz, the drawing speed during continuous casting is 1.2 ± 0.05m / min, the specific water volume for continuous casting is 0.22 ± 0.01L / kg, the terminal stirring current is 450 ± 25A, the terminal stirring frequency is 8 ± 0.5Hz, and the total reduction of soft reduction is 15.0 ± 0.2mm.

7. A steel strand, characterized in that, It is prepared by using the wire rod for ultra-high stress corrosion resistant prestressed steel strand described in any one of claims 1 - 4 or the wire rod for ultra-high stress corrosion resistant prestressed steel strand prepared by the production method described in any one of claims 5 - 6 as the base material.

8. The production method of the steel strand according to claim 7, characterized in that, It includes the following processes: Pickling: Pickle the wire rod with a hydrochloric acid aqueous solution with a mass concentration of 15% - 20% for 7min - 10min at a temperature of 35°C - 42°C. Phosphating; Drawing; Stranding; Stabilization treatment: The treatment temperature is 400°C - 420°C.

9. The production method of the steel strand according to claim 7, characterized in that, 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 2m / s, and the temperature rise per pass is not higher than 100°C.

10. The production method of the steel strand according to claim 7, characterized in that, The stranding tension is not less than 80kN, and the speed is not higher than 36m / min.

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