Wire rod for 2500-2560MPa-grade stress corrosion resistant prestressed steel strand, steel strand and production method

Abstract

The invention discloses a steel wire rod for a 2500-2560 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 mass: 0.95-1.02% of C, 0.8-1.5% of Si, 0.5-1.0% of Mn, 0.25-0.45% of Cr, 0.02-0.08% 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 and refining the microscopic structure, the steel strand prepared from the steel wire rod has high tensile strength, the minimum stress corrosion value is 2.5 hours, the median value is more than 5 hours, and the steel strand shows excellent stress corrosion resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron and steel metallurgy and metal products, and particularly relates to a wire rod, a steel strand and a production method for a 2500-2560 MPa grade stress corrosion resistant prestressed steel strand. Background Art

[0002] The new national standard GB / T5224 has increased the strength grade of prestressed steel strands from 1860 MPa to 2360 MPa. With the increase in strength grade, 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 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 the secondary heat treatment not conforming to the current development trend of green and low-carbon. CN 114369760 A provides a stress corrosion resistant ultra-high strength steel strand. Through the design of alloying components such as 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 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 stress corrosion resistance of the ultra-high strength steel strand is improved to more than 2.5 hours. It requires shot peening treatment of the steel strand, with a complex production process and high cost. 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 the secondary heat treatment not conforming to the current development trend of green and low-carbon. In addition, off-line salt bath heat treatment requires uncoiling the coil for heat treatment and then recoiling, which is likely to damage the surface, resulting in unstable stress corrosion indicators of the steel strand.

[0004] CN111321352A discloses a production method of 2400 MPa - grade prestressed steel strands. In the production method of wire rods, off - line salt bath heat treatment is also required, and the processed steel strands do not have good stress corrosion resistance. CN114369760A provides a stress - corrosion - resistant ultra - high - strength steel strand. Through the design of alloying components such as V and B, the improvement of the water - bath production process of wire rods, and the improvement of the wire - drawing process during the production of steel strands, reducing the wire temperature, increasing the stabilization treatment temperature, shot - peening the surface of the steel strands, etc., the stress corrosion resistance of the ultra - high - strength steel strand is improved to more than 2.5 hours. It is necessary to perform shot - peening treatment on the steel strands, and the production process is complex and costly. CN119287269A provides a wire rod for 2300 MPa - grade steel strands with green environmental protection and its production method. The wire rod for 2300 MPa - grade steel strands is produced by an on - line heat treatment method. After the heat treatment of the wire rod, artificial aging is still required, and the supply cycle is long; and this document does not involve the manufacturing method of steel strands and their stress corrosion resistance.

[0005] In summary, there is no relevant report on prestressed steel strands with a strength level of 2500 MPa - grade and good stress corrosion index.

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

[0007] The purpose of the present invention is to provide a wire rod, a steel strand and a production method for 2500 - 2560 MPa - grade stress - corrosion - resistant prestressed steel strands, and the steel strand has excellent strength and stress corrosion resistance.

[0008] In order to achieve the above purpose, the technical solutions provided by a specific embodiment of the present invention are as follows:

[0009] A wire rod for 2500 - 2560 MPa - grade stress - corrosion - resistant prestressed steel strands, the chemical composition by mass percentage includes: C 0.95 - 1.02%, Si 0.8 - 1.5%, Mn 0.5 - 1.0%, Cr 0.25 - 0.45%, V 0.02 - 0.08%, 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 ≥ 96%, and the sorbite lamellar spacing is 45 nm - 65 nm.

[0011] In one or more embodiments of the present invention, the diameter of the wire rod is 6 mm - 14 mm.

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

[0013] A production method of wire rod for 2500 - 2560 MPa grade stress corrosion resistant prestressed steel strand, comprising the following processes:

[0014] Steel melting: According to the ratio, the raw materials are melted to obtain molten steel;

[0015] Continuous casting: The molten steel is cast into a billet;

[0016] High-speed wire rolling: After heating the billet, rough rolling and finish rolling are carried out successively. The heating temperature is 1080 °C - 1150 °C, the rough rolling starting temperature is 950 °C - 1000 °C, the finish rolling inlet temperature is 880 °C - 920 °C, and the laying head temperature is 880 °C - 920 °C;

[0017] Controlled cooling after rolling: Online salt bath isothermal treatment is adopted. The laying head temperature is 890 °C - 910 °C, the salt bath temperature is 530 °C - 550 °C, and the salt bath time is 200 s - 300 s; After online salt bath isothermal treatment, online annealing is carried out, the temperature is ≥350 °C, and the time is ≥30 min.

[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 casting speed during continuous casting is 1.2 ± 0.05 m / min, the specific water consumption during continuous casting is 0.22 ± 0.01 L / kg, the terminal stirring current is 450 ± 25 A, the terminal stirring frequency 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 2500 - 2560 MPa grade 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 steel strand, comprising the following processes:

[0023] Pickling: Pickle the wire rod in a hydrochloric acid aqueous solution with a mass concentration of 15 - 20% for 7 - 10 min, and the temperature is 35 °C - 42 °C;

[0024] Phosphating;

[0025] Drawing;

[0026] Stranding

[0027] Stabilization treatment: The treatment temperature is 400°C - 430°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 as follows:

[0031] (1) Through the design of the chemical composition and production process of the wire rod, the microstructure is refined and the sorbitization rate is significantly increased to improve the strength and plasticity of the wire rod, reduce the scale of the wire rod, and shorten the pickling time. Thus, ultra-high strength above 2500 MPa can be obtained with a relatively small area reduction rate during drawing. The reduction of the drawing area reduction rate and the significant improvement of the plasticity index of the wire rod can reduce surface damage and internal defects during wire drawing processing, thereby improving the stress corrosion index of the steel strand.

[0032] (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 sorbite, the sorbitization rate ≥ 96%, the sorbite lamellar spacing is 45 - 65 nm; the tensile strength is 1600 - 1700 MPa, the reduction of area is 25 - 40%. Taking the 1×7 - 15.2 - 2500 / 2560 steel strand processed as an example, the minimum value of stress corrosion is 2 hours, and the median value is more than 5 hours.

[0033] (3) The present invention uses on-line salt bath isothermal treatment and on-line annealing 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 offline, they are immediately put into use for steel strand processing. BRIEF 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 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.

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

[0036] Figure 2 SEM micrograph of the microstructure of the wire rod in Embodiment 2 of the present invention;

[0037] Figure 3 SEM micrograph of the microstructure of the wire rod in Embodiment 3 of the present invention. Specific 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 with reference to the accompanying 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 making 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 2500 - 2560 MPa grade stress corrosion resistant prestressed steel strand. The chemical composition by mass percentage includes: C 0.95 - 1.02%, Si 0.8 - 1.5%, Mn 0.5 - 1.0%, Cr 0.25 - 0.45%, V 0.02 - 0.08%, 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.

[0040] Specifically, C is the most important strengthening element in steel. In order to obtain a relatively high tensile strength, the C content in the present invention is limited to 0.95 - 1.02%.

[0041] 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 0.8 - 1.5%.

[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. In the present invention, the Mn content is limited to 0.5 - 1.0%.

[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 can form a dense oxide film on the surface of the steel; however, too high a content increases the difficulty of controlling segregation. The present invention limits the Cr content to 0.25 - 0.45%.

[0044] The carbonitrides formed by V and Nb are effective hydrogen traps in steel, thereby improving the stress corrosion index 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 prone to segregation at grain boundaries, causing grain boundary embrittlement, thereby reducing the strength and plasticity of steel. In addition, S reacts with Mn to form MnS, reducing the solid solution strengthening effect of Mn. In the present invention, the S content is limited to ≤0.020%.

[0047] P is an impurity element in steel, which is prone to segregation at grain boundaries, causing grain boundary embrittlement, and further reducing the strength and plasticity of steel. In the present invention, the P content is limited to ≤0.020%.

[0048] N can cause 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 steel wires, reducing the plasticity of steel wires. In the present invention, the nitrogen content is limited to ≤0.0040%.

[0049] O combines with alloying elements in steel to form non-metallic inclusions, affecting the strength and plasticity of wire rods and the fatigue and corrosion resistance of steel wires. It is necessary to limit O ≤0.0020%.

[0050] Furthermore, the metallographic structure of the wire rod includes sorbite, the sorbitization rate is ≥96%, the sorbite lamellar spacing is 45 nm - 65 nm, the wire rod diameter is 6 mm - 14 mm, the tensile strength is 1600 - 1700 MPa, and the reduction of area is 25 - 40%.

[0051] Specifically, a high sorbitization rate and a small sorbite lamellar spacing can improve the strength of the wire rod, and at the same time are beneficial to the subsequent processing of the wire rod, preparing a steel strand with high strength and good stress corrosion resistance.

[0052] Another specific embodiment of the present invention provides a production method for a wire rod for a 2500 - 2560 MPa grade stress corrosion resistant prestressed steel strand, including steps 1 - 4.

[0053] Step 1, the molten steel smelting process.

[0054] Specifically, raw materials are prepared according to the mass 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.

[0055] Step 2, the continuous casting process.

[0056] Specifically, 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. Casting the molten steel into a rectangular billet under the above conditions can optimize the organizational structure and improve the quality of the rectangular billet.

[0057] Step 3, high-speed wire rolling process.

[0058] Specifically, in the high-speed wire rolling process, the rectangular billet obtained from the continuous casting process is heated and then subjected to rough rolling and finish rolling successively. The heating temperature is 1080 - 1150°C, the starting rolling temperature for rough rolling is 950 - 1000°C, the entry temperature for finish rolling is 880 - 920°C, and the wire laying temperature is 880 - 920°C. High-speed wire rolling using the above temperatures can further optimize the microstructure, improve the tissue uniformity, and enhance the strength and stress corrosion resistance of the wire rod.

[0059] Step 4, post-rolling controlled cooling process.

[0060] Specifically, the post-rolling controlled cooling process adopts an on-line salt bath isothermal treatment and an on-line annealing process. In the on-line salt bath isothermal treatment process, the wire laying temperature is 890 - 910°C, and the wire rod after wire laying is directly immersed in a constant temperature salt bath tank for isothermal treatment. The salt bath is molten nitrate, the salt bath temperature is 530 - 550°C, and the salt bath time is 200 - 300 s. The wire rod after salt bath isothermal treatment immediately enters the annealing furnace for on-line annealing, the temperature is ≥350°C, the annealing time is ≥30 min, preferably the annealing temperature is 300 - 500°C, and the time is 30 - 60 min. Through the above conditions, the homogeneity of the steel can be improved, and when using the obtained wire rod to prepare steel strands, it can ensure that the steel strands have high strength and stress corrosion resistance.

[0061] Another specific embodiment of the present invention provides a steel strand, which is prepared by using the above-mentioned wire rod for 2500 - 2560 MPa grade stress corrosion resistant prestressed steel strand as the base material.

[0062] Another specific embodiment of the present invention provides a production method of a steel strand, including steps (1) - (5).

[0063] Step (1), pickling process.

[0064] Specifically, the pickling process of the wire rod is pickled in an aqueous solution with a hydrochloric acid concentration of 15 - 20% (mass fraction) for 7 - 10 minutes at a temperature of 35 - 42°C, which not only ensures the removal of hot-rolled scale but also avoids the wire rod from absorbing excessive H. The wire rod after pickling is placed for 24 hours before entering the next process.

[0065] Step (2), phosphating process.

[0066] Specifically, phosphating is carried out by a conventional process to form a phosphating film on the surface of the wire rod, providing lubrication conditions for subsequent drawing and enabling smooth drawing.

[0067] Step (3), drawing process.

[0068] Specifically, the drawing is carried out in 9 - 11 passes, with a reduction ratio per pass of 23% - 25%, a drawing speed not higher than 2 m / s, and a temperature rise per pass not higher than 100 °C. Under these conditions, the diameter of the wire rod is refined to form steel wire.

[0069] Step (4), strand twisting process.

[0070] Specifically, the strand twisting tension is not lower than 80 kN and the speed is not higher than 36 m / min. Under these conditions, the steel wires can be closely bonded, improving the strength and stress corrosion resistance of the steel strand.

[0071] Step (5), stabilization treatment.

[0072] Specifically, the stabilization temperature is 400 - 430 °C and the time is 3 - 5 s. Conducting the stabilization treatment under these conditions helps to eliminate residual stress and further improve the strength and stress corrosion resistance of the steel strand.

[0073] The present invention will be further described in detail below with reference to specific embodiments.

[0074] Example 1

[0075] A production method of a steel strand, comprising:

[0076] (1) Molten steel smelting process

[0077] 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 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.

[0078] 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 soft stirring to control the inclusions in the molten steel. After the temperature and chemical composition meet the standards, tapping is carried out.

[0079] (2) Continuous casting process

[0080] Using billet continuous casting, the molten steel obtained from the molten steel smelting process is cast into a rectangular billet with a cross-sectional size of 180 mm × 240 mm.

[0081] 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 consumption for 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 of soft reduction is 14.8 mm.

[0082] (3) High-speed wire rolling process

[0083] 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 for rough rolling is 1000 °C, the entry temperature for finish rolling is 880 °C, and the spinning temperature is 900 °C.

[0084] (4) Post-rolling controlled cooling process

[0085] The wire rods after spinning are directly immersed in an on-line salt bath tank for salt bath. The temperature of the salt bath tank is 530 °C, and the salt bath time is 200 s. The wire rods after salt bath isothermal treatment immediately enter an annealing furnace for pre-annealing. The annealing temperature is 300 °C, and the time is 40 min.

[0086] (5) Steel strand processing process

[0087] 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 °C. The wire rods after pickling 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.

[0088] Example 2

[0089] A production method of steel strands, including:

[0090] (1) Molten steel smelting process

[0091] 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 billets obtained from the continuous casting process and the chemical composition of the wire rods 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.

[0092] 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 the inclusions in the molten steel are controlled by soft stirring. After the temperature and chemical composition meet the standards, tapping is carried out.

[0093] (2) Continuous casting process

[0094] Small billet continuous casting is adopted, and the molten steel obtained from the molten steel smelting process is cast into a rectangular billet with a cross-sectional size of 180 mm × 240 mm.

[0095] 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 3.0 Hz, the drawing speed during continuous casting is 1.20 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 8.0 Hz, and the total reduction of soft reduction is 15.0 mm.

[0096] (3) High-speed wire rolling process

[0097] The small 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 1080°C, the starting rolling temperature for rough rolling is 980°C, the entry temperature for finish rolling is 900°C, and the spinning temperature is 900°C.

[0098] (4) Post-rolling controlled cooling process

[0099] The wire rods after spinning are directly immersed in an on-line salt bath tank for salt bath. The temperature of the salt bath tank is 550°C, and the salt bath time is 250 s. The wire rods after salt bath isothermal treatment immediately enter the annealing furnace for pre-annealing. The annealing temperature is 400°C, and the time is 50 min.

[0100] (5) Steel strand processing process

[0101] 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 42°C. After pickling, the wire rods are placed for 24 hours before entering the next process. Drawing uses 9 passes, the area reduction rate per pass is 25%, 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.

[0102] Example 3

[0103] A production method of steel strands, including:

[0104] (1) Molten steel smelting process

[0105] The molten steel is smelted through the BOF smelting and LF 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, and are all shown in Table 1.

[0106] 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 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.

[0107] (2) Continuous casting process

[0108] Small billet continuous casting is adopted, and the molten steel obtained in the molten steel smelting process is cast into a rectangular billet with a cross-sectional size of 180mm×240mm.

[0109] Among them, the superheat of the molten steel is controlled at 20°C, the stirring current of the mold is 270A, the stirring frequency of the mold is 3.5Hz, the drawing speed during continuous casting is 1.25m / min, the specific water volume for continuous casting is 0.23L / kg, the terminal stirring current is 475A, the terminal stirring frequency is 8.5Hz, and the total reduction of soft reduction is 15.2mm.

[0110] (3) High-speed wire rolling process

[0111] The small billet obtained in the continuous casting process is heated and then subjected to rough rolling and finish rolling successively to prepare a wire rod with a diameter of 15mm. The heating temperature is 1000°C, the starting rolling temperature of rough rolling is 950°C, the entry temperature of finish rolling is 920°C, and the spinning temperature is 920°C.

[0112] (4) Post-rolling controlled cooling process

[0113] The wire rod after spinning is directly immersed in an on-line salt bath tank for salt bath. The temperature of the salt bath tank is 530°C, and the salt bath time is 300s. The wire rod after salt bath isothermal treatment immediately enters the annealing furnace for pre-annealing. The annealing temperature is 500°C, and the time is 60min.

[0114] (5) Steel strand processing process

[0115] The wire rod is processed into 2400 - 2460 MPa grade steel strand 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. The pickling time is 8 minutes, and the temperature is 35°C. After pickling, the wire rod is left for 24 hours before entering the next process. The drawing process uses 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 400°C.

[0116] Example 4

[0117] The production method of the steel strand in this example is the same as that in Example 1, except for the different chemical composition, as shown in Table 1 specifically.

[0118] Comparative Examples 1 - 2

[0119] The production methods of the steel strands in Comparative Example 1 and Comparative Example 2 are the same as that in Example 1, except for the different chemical composition, as shown in Table 1 specifically.

[0120] Comparative Example 3

[0121] The production method of the steel strand in this comparative example is the same as that in Example 1, except that: in the high - speed wire rolling process, the entry temperature of the finishing mill is 850°C, and the spinning temperature is 850°C;

[0122] In the post - rolling controlled cooling process, the salt bath temperature is 500°C.

[0123] Comparative Example 4

[0124] The production method of the steel strand in this comparative example 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 treatment temperature is 380°C.

[0125] Table 1 Chemical Composition Table

[0126]

[0127] 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 methods and detection results are as follows:

[0128] (1) In terms of metallographic structure, wire rods with a length of 10 cm are 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 are placed under a metallographic microscope for tissue observation, or after electrolytic polishing, observed under a 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.

[0129] (2) In terms of mechanical properties, referring to the test methods and definitions of GB / T 228 standard, a tensile testing machine was used to test the mechanical properties of the wire rods. The tensile strength and reduction of area of the wire rods in Examples 1-3 are shown in Table 2 respectively.

[0130] Table 2 Test Results of Wire Rod Properties

[0131]

[0132] In addition, through detection, the sorbitization rate of the wire rods in Example 4 reached more than 96%, the tensile strength was in the range of 1600-1700 MPa, and the reduction of area was in the range of 25-40%. The sorbitization rate of the wire rods in Comparative Example 1 was 93%, and the tensile strength was 1530 MPa; there was a large amount of martensite in the microstructure of the wire rods in Comparative Example 3, with a tensile strength of 1520 MPa and a reduction of area of 15%; the properties of the wire rods in Comparative Examples 2 and 4 met those of the present invention.

[0133] The performance indexes of the steel strands processed from the wire rods in Examples 1-3 produced according to this embodiment are shown in Tables 3 and 4.

[0134] Table 3 Performance Indexes of Steel Strands

[0135]

[0136] Table 4 Performance Indexes of Steel Strands

[0137]

[0138] It can be seen from Tables 3 and 4 that for the 1×7-15.2-2500 / 2560 steel strands prepared by the present invention, the strength meets 2500-2560 MPa, the minimum value of stress corrosion is 2.5 hours, and the median value is above 5 hours. In addition, the performance of the steel strands in Example 4 also meets the tensile strength of 2500-2560 MPa, the minimum value of stress corrosion is greater than 2 hours, and the median value is greater than 5 hours. However, through testing, the tensile strength of the steel strands in Comparative Examples 1 and 3 is less than 2400 MPa and the stress corrosion is less than 1.5 hours; the minimum value of stress corrosion of the steel strands in Comparative Examples 2 and 4 is less than 1.5 hours, the median value is less than 2.5 hours, and the stress corrosion resistance is significantly weaker than that of the present invention.

[0139] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, in any aspect, 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 claims involved.

[0140] In addition, it should be understood that although this specification is described in terms of embodiments, not every embodiment only contains an independent technical solution. This narrative manner of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A wire rod for prestressed steel strand with 2500-2560 MPa level of stress corrosion resistance, characterized in that, The chemical components by mass percentage include: C 0.95 - 1.02%, Si 0.8 - 1.5%, Mn 0.5 - 1.0%, Cr 0.25 - 0.45%, V 0.02 - 0.08%, 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 2500-2560 MPa grade prestressed steel strand resistant to stress corrosion according to claim 1, wherein The metallographic structure of the wire rod includes sorbite, the sorbitization rate ≥ 96%, and the sorbite lamellar spacing is 45nm - 65nm.

3. The wire rod for 2500-2560 MPa class stress corrosion resistant prestressed steel strands according to claim 1, characterized in that, The diameter of the wire rod is 6mm - 14mm.

4. A production method of wire rod for prestressed steel strand with 2500-2560 MPa level of stress corrosion resistance, characterized in that, It includes the following processes: Steel melting: According to the ratio, the 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 and then subjected to rough rolling and finish rolling successively. The heating temperature is 1080°C - 1150°C, the rough rolling starting temperature is 950°C - 1000°C, the finish rolling inlet temperature is 880°C - 920°C, and the laying head temperature is 880°C - 920°C. Post-rolling controlled cooling: Online salt bath isothermal treatment is adopted. The laying head temperature is 890°C - 910°C, the salt bath temperature is 530°C - 550°C, and the salt bath time is 200s - 300s. After the online salt bath isothermal treatment, online annealing is carried out at a temperature ≥ 350°C for a time ≥ 30min.

5. The production method of the wire rod for 2500-2560 MPa grade stress corrosion resistant prestressed steel strand according to claim 4, 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 casting speed during continuous casting is 1.2 ± 0.05m / min, the specific water consumption 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.

6. A steel strand, characterized in that, It is prepared by using the wire rod for 2500 - 2560MPa grade stress corrosion resistant prestressed steel strand described in any one of claims 1 - 3 or the wire rod for 2500 - 2560MPa grade stress corrosion resistant prestressed steel strand prepared by the production method described in any one of claims 4 - 5 as the base material.

7. The production method of the steel strand according to claim 6, characterized in that, It includes the following processes: Pickling: The wire rod is pickled with a hydrochloric acid aqueous solution with a mass concentration of 15 - 20% for 7 - 10min at a temperature of 35°C - 42°C. Phosphating; Drawing; Stranding; Stabilization treatment: The treatment temperature is 400°C - 430°C.

8. 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 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.

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

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