Wire rod for 2400-2460 MPa grade stress corrosion resistant prestressed steel strand, steel strand and production method

Abstract

The invention discloses a steel wire rod for a 2400-2460 MPa grade stress corrosion resistant prestressed steel strand, the steel strand and a production method. The steel wire rod comprises the following chemical components in percentage by weight: 0.90-0.97% of C, 0.6-1.2% of Si, 0.2-0.8% of Mn, 0.15-0.45% of Cr, 0.02-0.05% of V, 0.01-0.05% of Nb, less than 0.30% of Ni, less than 0.30% of Cu, less than 0.30% of Mo, less than or equal to 0.008% of S, less than or equal to 0.010% of P, less than or equal to 0.004% of N, less than or equal to 0.0020% of O and the balance of Fe and other inevitable impurities. By optimizing the chemical components and the production process of the wire rod, the strength of the prepared steel strand meets 2400-2460 MPa, the minimum stress corrosion value is 2.5 hours, the median value is 5 hours, and the stress corrosion resistance is obviously superior to that of an existing steel strand.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron and steel metallurgy, and particularly relates to a wire rod, a steel strand and a production method for a 2400-2460 MPa grade stress corrosion resistant prestressed steel strand. Background Art

[0002] 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, restricting their application in corrosive environments. 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 / ton. It is also possible to use the method of wrapping the entire surface of the steel strand with PE (polyethylene) plastic, but it is easily damaged and has poor reliability. Especially during tension construction, the surface plastic layer cannot deform with the steel strand and is damaged, losing its anti-corrosion function.

[0003] CN118814088A 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, with low output, high cost, 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 re-coiling, which is likely to damage the surface and make the stress corrosion index of the steel strand unstable. CN111321352A discloses a production method for a 2400 MPa grade prestressed steel strand. The wire rod production method also requires off-line salt bath heat treatment, and the processed steel strand does not have good stress corrosion performance.

[0004] CN114369760A provides a stress corrosion resistant ultra-high strength steel strand. Through the design of alloying components such as V and B, improvement of the water bath production process of the wire rod, and improvement of the wire drawing process during the production process of the steel strand, measures such as reducing the temperature of the steel wire, increasing the stabilization treatment temperature, and shot peening the surface of the steel strand are taken to improve the stress corrosion resistance of the ultra-high strength steel strand to more than 2.5 hours. It requires shot peening treatment of the steel strand, with a complex production process and high cost. CN119287269A provides a green and environment-friendly wire rod for a 2300 MPa grade steel strand and its production method, using an on-line heat treatment method to produce a wire rod for a 2300 MPa grade steel strand. The wire rod still requires artificial aging after heat treatment, with a long supply cycle; and this document does not involve the manufacturing method of the steel strand and its stress corrosion performance.

[0005] In summary, the 2400 MPa grade steel strand based on the technology of improving the inherent corrosion resistance of the steel strand has not been solved.

[0006] The information disclosed in this background section is only intended to enhance the overall understanding of the background of the present invention and should not be regarded as an admission or any form of suggestion that this information constitutes prior art already known to those of ordinary skill in the art. Summary of the Invention

[0007] The object of the present invention is to provide wire rods, steel strands and production methods for prestressed steel strands with stress corrosion resistance at the level of 2400 - 2460 MPa. The minimum stress corrosion time of the steel strands is 2.5 hours and the median is 5 hours, with excellent stress corrosion resistance.

[0008] To achieve the above object, the technical solutions provided by a specific embodiment of the present invention are as follows:

[0009] A wire rod for prestressed steel strands with stress corrosion resistance at the level of 2400 - 2460 MPa, the chemical composition by weight percentage includes: C 0.90 - 0.97%, Si 0.6 - 1.2%, Mn 0.2 - 0.8%, Cr 0.15 - 0.45%, V 0.02 - 0.05%, Nb 0.01 - 0.05%, Ni < 0.30, Cu < 0.30, Mo < 0.30, S ≤ 0.008%, P ≤ 0.010%, N ≤ 0.004%, O ≤ 0.0020%, and the rest is Fe and other inevitable impurities.

[0010] In one or more embodiments of the present invention, the metallographic structure of the wire rod includes sorbite, the sorbitization rate ≥ 95%, and the sorbite lamellar spacing is 50 nm - 70 nm.

[0011] In one or more embodiments of the present invention, the thickness of the scale on the surface of the wire rod ≤ 10 μm.

[0012] In one or more embodiments of the present invention, the diameter of the wire rod is 6 mm - 14 mm.

[0013] The technical solutions provided by another specific embodiment of the present invention are as follows:

[0014] A production method for a wire rod for prestressed steel strands with stress corrosion resistance at the level of 2400 - 2460 MPa, including:

[0015] Steel melting: According to the ratio, melt the raw materials to obtain molten steel;

[0016] Continuous casting: Pour the molten steel into a billet;

[0017] High-speed wire rolling: Heat the billet at 1080°C - 1150°C, then perform rough rolling and finish rolling. The rough rolling starting temperature is 950°C - 1000°C, the finish rolling inlet temperature is 860°C - 950°C, and the spinning temperature is 860°C - 920°C;

[0018] Post-rolling controlled cooling process: An on-line salt bath isothermal treatment process is adopted. The wire laying temperature is 860°C - 910°C, the salt bath temperature is 540°C - 570°C, and the salt bath time is 100s - 300s; 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.

[0019] In one or more embodiments of the present invention, in the continuous casting process, the superheat of the molten steel is controlled at 20°C - 25°C, the stirring current of the mold is 270 ± 25A, the stirring rate 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 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.

[0020] The technical solution provided by another specific embodiment of the present invention is as follows:

[0021] A steel strand is prepared by using the wire rod for 2400 - 2460MPa grade stress corrosion resistant prestressed steel strand as the base material.

[0022] The technical solution provided by another specific embodiment of the present invention is as follows:

[0023] A production method of a steel strand includes:

[0024] Pickling: Pickle the wire rod with a hydrochloric acid aqueous solution with a mass concentration of 15% - 20% for 7min - 10min, and the temperature is 35°C - 42°C;

[0025] Phosphating;

[0026] Drawing;

[0027] Stranding;

[0028] Stabilization treatment: The treatment temperature is 400°C - 430°C.

[0029] In one or more embodiments of the present invention, the drawing is carried out in 9 - 11 passes, the area reduction per pass is 23% - 25%, and the drawing speed is not higher than 2m / s.

[0030] In one or more embodiments of the present invention, the stranding tension is not lower than 80kN, and the speed is not higher than 36m / min.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] (1) Through the design of the chemical composition and production process of the wire rod, the microstructure is refined and the rate of sorbitization is significantly increased to improve the strength and plasticity of the wire rod, reduce the scale thickness of the wire rod, and shorten the pickling time. As a result, ultra-high strength above 2400 MPa can be obtained with a smaller reduction ratio during wire drawing. The reduction of the wire drawing reduction ratio and the significant improvement of the plasticity index of the wire rod can reduce surface damage and internal defects during wire drawing, thereby improving the stress corrosion index of the steel strand.

[0033] (2) Based on the chemical composition design scheme 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 sorbitic, with a sorbitization rate ≥ 95%, and the sorbitic lamellar spacing is 50 - 70 nm; the tensile strength is 1570 - 1670 MPa, and the reduction of area is 32 - 48%. Taking the 1×7 - 15.2 - 2400 / 2460 steel strand processed as an example, the minimum value of stress corrosion is 2.5 hours, and the median value is 5 hours.

[0034] (3) The present invention uses the online salt bath and online aging methods to produce wire rods, which is both green and low-carbon and improves production efficiency compared with the prior art. After the wire rods are taken off the production line, they are immediately put into the processing and use of steel strands. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] 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, other drawings can be obtained based on these drawings without creative efforts.

[0036] Figure 1 It is the metallographic structure diagram of the wire rod in Embodiment 1 of the present invention;

[0037] Figure 2 It is the metallographic structure diagram of the wire rod in Embodiment 2 of the present invention;

[0038] Figure 3 It is the metallographic structure diagram of the wire rod in Embodiment 3 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] 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 with reference to 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 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.

[0040] A specific embodiment of the present invention provides a wire rod for prestressed steel strands with a yield strength of 2400 - 2460 MPa and resistance to stress corrosion. The chemical composition by weight percentage includes: C 0.90 - 0.97%, Si 0.6 - 1.2%, Mn 0.2 - 0.8%, Cr 0.15 - 0.45%, V 0.02 - 0.05%, Nb 0.01 - 0.05%, Ni < 0.30, Cu < 0.30, Mo < 0.30, S ≤ 0.008%, P ≤ 0.010%, N ≤ 0.004%, O ≤ 0.0020%, and the balance is Fe and other inevitable impurities.

[0041] Specifically, C is the most important strengthening element in steel. To obtain a higher tensile strength, the C content in the present invention is limited to 0.90 - 0.97%. 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. The Si content in the present invention is limited to 0.6 - 1.2%. By controlling the contents of C and Si, the strength of the wire rod can be effectively improved.

[0042] 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. The Mn content in the present invention is limited to 0.2 - 0.8%.

[0043] Cr is an austenite stabilizing element, which is beneficial to obtaining retained austenite; at the same time, it 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. The Cr content in the present invention is limited to 0.15 - 0.45%.

[0044] The carbonitrides formed by V and Nb are effective hydrogen traps in steel, thus improving the stress corrosion index of steel. Using V and Nb in combination and controlling their respective contents can effectively increase the hydrogen traps in steel. By capturing hydrogen atoms, the diffusion of hydrogen in steel can be significantly inhibited, thereby greatly improving the stress corrosion resistance of steel.

[0045] Cu, Ni, and Mo can all improve the stress corrosion index of steel. To control production costs, their contents are all controlled within 0.30%.

[0046] S is likely to segregate at grain boundaries, causing grain boundary embrittlement, thereby reducing the strength and plasticity of steel. In addition, S reacts with Mn to form MnS, thereby reducing the solution strengthening effect of Mn. The S content in the present invention is limited to ≤ 0.008%.

[0047] P is an impurity element in steel, which is likely to segregate at grain boundaries, causing grain boundary embrittlement, and further reducing the strength and plasticity of steel. The P content in the present invention is limited to ≤ 0.010%.

[0048] N can cause the plasticity of steel to deteriorate, increase the risk of delayed fracture of wire rods, 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%.

[0049] O combines with alloying elements in the 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%.

[0050] Furthermore, the metallographic structure of the wire rod includes sorbite, the rate of sorbitization is ≥95%, the sorbite lamellar spacing is 50 nm - 70 nm, the surface scale thickness is ≤10 μm, and the diameter is 6 mm - 14 mm.

[0051] Specifically, a high rate of sorbitization and a fine lamellar spacing can effectively improve the strength of steel and reduce the stress corrosion sensitivity of steel; the scale thickness within the above range can increase the corrosion resistance of steel while ensuring that the steel has a high strength.

[0052] Furthermore, the tensile strength of the wire rod is 1570 MPa - 1670 MPa, and the reduction of area is 32% - 48%.

[0053] Another specific embodiment of the present invention provides a production method for wire rods for 2400 - 2460 MPa grade 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 weight percentage of chemical components, and the molten steel is smelted through the converter smelting and LF furnace refining steps in sequence. 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.

[0056] Step 2, the continuous casting process.

[0057] Specifically, in this step, the molten steel is cast into a rectangular billet. During continuous casting, the superheat of the molten steel is controlled at 20°C - 25°C, the stirring current of the mold is 270 ± 25 A, the stirring rate of the mold is 3 ± 0.5 Hz, the drawing speed during continuous casting is 1.2 ± 0.05 m / min, the specific water ratio during continuous casting is 0.22 ± 0.01 L / kg, the stirring current at the end is 450 ± 25 A, the stirring frequency at the end is 8 ± 0.5 Hz, and the total reduction of soft reduction is 15.0 ± 0.2 mm. By controlling parameters such as superheat, drawing speed, and stirring rate, internal composition segregation is reduced, and the composition uniformity of the steel is improved.

[0058] Step 3, 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. Specifically, it is heated at 1080°C - 1150°C, the rough rolling starting temperature is 950°C - 1000°C, the finish rolling inlet temperature is 860°C - 950°C, and the wire laying temperature is 860°C - 920°C. The heating temperature, rough rolling temperature, finish rolling temperature, and wire laying temperature within the above ranges can optimize the microstructure of the wire rod and improve the strength of the wire rod.

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

[0061] Specifically, an on-line salt bath isothermal treatment process is adopted. The wire laying temperature is controlled at 860°C - 910°C. After the wire rod is laid, it is immersed in a constant-temperature salt bath. The salt bath is molten nitrate, the salt bath temperature is 540°C - 570°C, and the salt bath time is 120 s - 300 s. The wire rod after on-line salt bath isothermal treatment immediately enters the heat preservation corridor for on-line aging, and the average cooling rate is not higher than 0.2°C / s. On-line salt bath isothermal treatment can refine the microstructure, obtain a uniform sorbite structure, improve the rate of sorbitization, and thus improve the strength and plasticity of the wire rod. Slow cooling through the heat preservation corridor to achieve on-line aging can further improve the plasticity of the wire rod and increase the strength.

[0062] Another specific embodiment of the present invention provides a steel strand prepared using the above-mentioned wire rod as the base material.

[0063] Specifically, using the above-mentioned wire rod to prepare a steel strand, taking the steel strand of specification 1×7 - 15.2 - 2400 / 2460 as an example, the minimum stress corrosion time of the steel strand is 2.5 hours, the median is 5 hours, and the stress corrosion resistance performance is excellent.

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

[0065] Step (1), pickling process.

[0066] Specifically, pickling 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. Such pickling conditions can ensure the removal of hot-rolled scale while avoiding excessive hydrogen absorption by the wire rod. After pickling, the wire rod is left standing for 24 hours before entering the next process step.

[0067] Step (2), phosphating process.

[0068] Specifically, this process uses a conventional process to form a phosphating film on the surface of the wire rod, providing lubrication conditions for subsequent drawing and ensuring smooth drawing.

[0069] Step (3), drawing process.

[0070] Specifically, the drawing is carried out in 9-11 passes, with a reduction ratio per pass of 23%-25%, a drawing speed not exceeding 2 m / s, and a temperature rise per pass not exceeding 100°C. Through drawing, the diameter of the wire rod is refined to obtain steel wire.

[0071] Step (4), 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. By controlling the strand twisting tension and speed, it can be ensured that the steel wires are closely fitted together, improving the production quality of the steel strand.

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

[0074] Specifically, the stabilization treatment temperature is 400°C-430°C and the time is 3-5 s. The stabilization treatment is carried out within the above temperature range to eliminate residual stress and improve the stability and strength of the steel strand.

[0075] The following further elaborates on the present invention with reference to specific embodiments.

[0076] Example 1

[0077] A method for producing a steel strand, comprising:

[0078] (1) Molten steel smelting process

[0079] The molten steel is smelted through the sequentially carried out converter smelting and LF furnace refining steps. 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 subsequent 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, and are all 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 then desiliconization, dephosphorization, and oxygen blowing 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 inclusions in the molten steel are controlled by soft stirring. After the temperature and chemical composition meet the standards, tapping is carried out.

[0081] (2) Continuous casting process

[0082] Small billet continuous casting is adopted, and 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.

[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 drawing speed during continuous casting is 1.15 m / min, the specific water flow during continuous casting is 0.21 L / kg, the terminal stirring current is 425 A, the terminal stirring frequency is 7.5 Hz, and the total reduction of soft reduction is 14.8 mm.

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

[0085] The small billets obtained from the continuous casting process are heated and then subjected to rough rolling and finish rolling successively to prepare wire rods with a diameter of 15 mm. The heating temperature is 1150 °C, the starting rolling temperature of rough rolling is 1000 °C, the entry temperature of finish rolling is 880 °C, and the spinning temperature is 880 °C.

[0086] (4) Online salt bath isothermal treatment process

[0087] The wire rods after spinning are directly immersed in the salt bath tank for salt bath. The temperature of the salt bath tank is 540 °C, and the salt bath time is 300 s. The wire rods after salt bath isothermal treatment immediately enter the heat preservation corridor for slow cooling, and the average cooling rate is 0.15 °C / s. The metallographic structure of the obtained wire rods is as Figure 1 shown.

[0088] (5) Steel strand processing process

[0089] The wire rods are processed into 2400 - 2460 MPa grade steel 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, 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, the area reduction rate per pass is 23%, 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 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, and 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.

[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 and 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 in the molten steel smelting process into a rectangular billet with a cross-sectional size of 180mm×240mm.

[0096] Among them, the superheat of the molten steel is controlled at 21°C, the stirring current of the mold is 270A, the stirring frequency of the mold is 3Hz, the drawing speed during continuous casting is 1.2m / min, the specific water volume for continuous casting is 0.22L / kg, the terminal stirring current is 450A, the terminal stirring frequency is 8Hz, and the total reduction of soft reduction is 15.0mm.

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

[0098] The intermediate billet obtained in the continuous casting process is prepared into a wire rod with a diameter of 14mm by high-speed wire rolling. The heating temperature is 1080°C, the starting rolling temperature of rough rolling is 960°C, the entry temperature of finish rolling is 900°C, and the spinning temperature is 910°C.

[0099] (4) Salt bath isothermal treatment process

[0100] The wire rod after spinning is directly immersed in the salt bath tank for salt bath. The temperature of the salt bath tank is 550°C, and the salt bath time is 190s. The wire rod after salt bath isothermal treatment immediately enters the heat preservation corridor for on-line aging, and the average cooling rate is 0.15°C / s. The metallographic structure of the obtained wire rod is as Figure 2 shown.

[0101] (5) Steel strand processing process

[0102] The wire rod is processed into a steel strand with a strength level of 2400 - 2460 MPa through pickling, phosphating, drawing, stranding, and stabilization processes. In the pickling process, an aqueous solution with a hydrochloric acid concentration of 19% (mass fraction) is used for pickling for 8 minutes at a temperature of 35 - 42°C. After pickling, the wire rod is left for 24 hours before entering the next process. The drawing process consists of 11 passes with a reduction ratio of 23% per pass, a drawing speed of 2 m / s, and a temperature rise of 100°C per pass. The stranding tension is 80 kN, the speed is 36 m / min, and the stabilization temperature is 420°C.

[0103] Example 3

[0104] (1) Molten steel smelting process

[0105] The molten steel is smelted through a converter smelting and LF furnace refining process carried out in sequence. The chemical composition of the molten steel at the end of smelting is shown in Table 1 in 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.

[0106] Among them, in the converter smelting process, the pre-treated 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 process, 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 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 in 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 amount of soft reduction is 15.2 mm.

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

[0110] The intermediate billet obtained in the continuous casting process is processed into a wire rod with a diameter of 8 mm through 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 880°C, and the spinning temperature is 880°C.

[0111] (4) Online salt bath isothermal treatment process

[0112] The wire rod after spinning is directly immersed in a salt bath tank for salt bath. The temperature of the salt bath tank is 570 °C and the salt bath time is 100 s. The wire rod after salt bath isothermal treatment immediately enters the heat preservation corridor for slow cooling, with an average cooling rate of 0.10 °C / s. The metallographic structure of the obtained wire rod is as Figure 3 shown.

[0113] (5) Steel strand processing procedures

[0114] The wire rod is processed into a steel strand with a grade of 2400 - 2460 MPa through pickling, phosphating, drawing, stranding, and stabilization 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 rate 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 430 °C.

[0115] Examples 4 - 5

[0116] The production methods of the wire rod and steel strand 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 difference between this example and Example 1 is that in the high - speed wire rolling process, the finishing mill inlet temperature is 860 °C and the spinning temperature is 860 °C;

[0119] In the pickling process, the pickling time is 7 min.

[0120] Example 7

[0121] The difference between this example and Example 1 is that in the high - speed wire rolling process, the finishing mill inlet temperature is 950 °C and the spinning temperature is 920 °C;

[0122] In the pickling process, the pickling time is 10 min.

[0123] Comparative Examples 1 - 2

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

[0125] Comparative Example 3

[0126] The difference between this comparative example and Example 1 is that in the high - speed wire rolling process, the heating temperature is 1020 °C, the starting rolling temperature of rough rolling is 920 °C, the finishing mill inlet temperature is 850 °C, and the spinning temperature is 850 °C;

[0127] In the online salt bath isothermal treatment process, the salt bath temperature is 500 °C.

[0128] Comparative Example 4

[0129] The difference between this comparative example and Example 1 is that in the pickling process, the pickling time is 17 min; in the stabilization treatment process, the stabilization temperature is 390 °C.

[0130] Table 1 Chemical composition table

[0131]

[0132] 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:

[0133] (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, polishing and etching with nitric acid alcohol, they were placed under a metallographic microscope for tissue observation, or observed by scanning electron microscope after electrolytic polishing. 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.

[0134] (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.

[0135] Table 2 Performance data

[0136]

[0137] In addition, through detection, the metallographic structures of the wire rods in Examples 4-7 were all sorbite structures, the rate of sorbitization reached 95%, the tensile strength met 1570 MPa - 1670 MPa, and the reduction of area was in the range of 32% - 48%.

[0138] The performance indexes of the steel strands processed from the wire rods of Examples 1-3 produced according to this embodiment are shown in Tables 3 and 4.

[0139] Table 3 Steel strand performance indexes

[0140]

[0141]

[0142] Table 4 Steel strand performance indexes

[0143]

[0144] In addition, for the stress corrosion of the steel strands in Comparative Examples 1-4, the minimum value is 1.5-2 hours and the median value is 2.5-3.5 hours. For the 1×7-15.2-2400 / 2460 steel strands prepared in the examples of the present invention, the minimum value of stress corrosion is 2.5 hours and the median value is more than 5 hours. The stress corrosion resistance is significantly better than that of the comparative examples.

[0145] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and 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 embraced within the present invention. Any reference signs in the claims should not be construed as limiting the claimed invention.

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

Claims

1. A wire rod for prestressed steel strand with a yield strength of 2400 - 2460 MPa and resistance to stress corrosion, characterized in that, The chemical components by weight percentage include: C 0.90 - 0.97%, Si 0.6 - 1.2%, Mn 0.2 - 0.8%, Cr 0.15 - 0.45%, V 0.02 - 0.05%, Nb 0.01 - 0.05%, Ni < 0.30, Cu < 0.30, Mo < 0.30, S ≤ 0.008%, P ≤ 0.010%, N ≤ 0.004%, O ≤ 0.0020%, and the balance is Fe and other inevitable impurities.

2. The wire rod for prestressed steel strand with 2400-2460 MPa stress corrosion resistance according to claim 1, characterized in that, The metallographic structure of the wire rod includes sorbite, the sorbitization rate ≥ 95%, and the sorbite lamellar spacing is 50nm - 70nm.

3. The wire rod for prestressed steel strand with 2400-2460 MPa level of stress corrosion resistance according to claim 1, characterized in that, The thickness of the scale on the surface of the wire rod ≤ 10μm.

4. The wire rod for prestressed steel strand with 2400-2460 MPa level of stress corrosion resistance according to claim 1, characterized in that, The diameter of the wire rod is 6mm - 14mm.

5. A production method of wire rod for prestressed steel strand with 2400 - 2460 MPa level of stress corrosion resistance, characterized in that, Including: Steel melting: According to the ratio, raw materials are melted to obtain molten steel. Continuous casting: The molten steel is cast into a billet. High-speed wire rolling: The billet is heated at 1080°C - 1150°C, and then rough rolling and finish rolling are carried out. The rough rolling starting temperature is 950°C - 1000°C, the finish rolling entry temperature is 860°C - 950°C, and the laying temperature is 860°C - 920°C. Post-rolling controlled cooling process: The online salt bath isothermal treatment process is adopted. The laying temperature is 860°C - 910°C, the salt bath temperature is 540°C - 570°C, and the salt bath time is 100s - 300s. 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 2400 - 2460 MPa grade prestressed steel strand resistant to stress corrosion according to claim 1, characterized in that, In the continuous casting process, the superheat of the molten steel is controlled at 20°C - 25°C, the stirring current of the mold is 270 ± 25A, the stirring rate of the mold is 3 ± 0.5Hz, the drawing speed during continuous casting is 1.2 ± 0.05m / min, the specific water volume during continuous casting is 0.22 ± 0.01L / kg, the terminal stirring current is 450 ± 25A, the terminal stirring frequency is 8 ± 0.5Hz, and the total reduction of soft reduction is 15.0 ± 0.2mm.

7. A steel strand, characterized in that, It is prepared by using the wire rod for 2400 - 2460MPa grade stress corrosion resistant prestressed steel strand described in any one of claims 1 - 4 or the wire rod for 2400 - 2460MPa grade 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, Including: Pickling: The wire rod is pickled with a hydrochloric acid aqueous solution with a mass concentration of 15% - 20% for 7min - 10min, and the temperature is 35°C - 42°C. Phosphating; Drawing; Stranding; Stabilization treatment: The treatment temperature is 400°C - 430°C.

9. The production method of the steel strand according to claim 8, characterized in that, The drawing is carried out in 9 - 11 passes, the area reduction rate per pass is 23% - 25%, and the drawing speed is not higher than 2m / s.

10. The production method of the steel strand according to claim 8, characterized in that, The stranding tension is not less than 80kN, and the speed is not higher than 36m / min.

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