2360MPa-grade ultrahigh-strength prestressed steel strand and preparation process thereof

Abstract

The invention discloses a 2360MPa-grade ultrahigh-strength prestressed steel strand and a preparation process thereof. A raw material wire rod of the 2360MPa-grade ultrahigh-strength prestressed steel strand comprises the following chemical components in percentage by mass: 0.90-1.00% of C, 0.90-0.95% of Si, 0.40-0.60% of Mn, 0.20-0.40% of Cr, less than or equal to 0.05% of P, less than or equal to 0.005% of S, 0.01-0.05% of V, 0.0002-0.0004% of B and the balance of Fe and inevitable impurities. According to the raw material wire rod for the steel strand, on the basis of a wire rod for the 1860 MPa grade steel strand, the conventional alloy element design is improved and optimized, the content of C and Si elements is increased, metal elements Cr, V and B are reasonably added, and it is guaranteed that the internal organizational structure of the wire rod is uniform, and the strength and plasticity are reasonable. The tensile strength and plasticity are effectively improved through component design and alloy element selection, the strength of the steel strand reaches 2360 MPa or above, the elongation reaches 5.3-5.4%, the 1000-hour stress relaxation rate is smaller than or equal to 2%, and the stress corrosion failure time is smaller than or equal to 1.9 h.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to a 2360MPa-grade ultra-high-strength prestressed steel strand and a preparation process thereof. Background Art

[0002] Prestressed steel strands have the characteristics of high strength, high toughness, good fatigue resistance, low relaxation performance, etc. They are widely used in engineering construction projects such as high-rise buildings, highway bridges, and urban elevated roads.

[0003] With the rapid development of the national economy and massive investment in infrastructure, public facilities such as highways and railways are gradually expanding to remote mountainous areas. Some areas are in urgent need of building larger span bridges due to complex geological conditions. Therefore, higher requirements are placed on the high strength and lightweight of bridges. The mechanical properties (tensile strength, elongation, etc.) of steel strands used for bridge cables are also constantly increasing.

[0004] At present, the strength level of prestressed steel strand products commonly used in my country is limited to 1860MPa. Their strength and comprehensive performance are gradually unable to meet the requirements of use. It is urgent to develop ultra-high-strength prestressed steel strand products with higher strength and plasticity.

[0005] In recent years, many domestic steel mills are trying to develop ultra-high strength prestressed steel strands above 2360MPa. However, due to the high strength of ultra-high strength steel wire rods, it is difficult to draw them, and a large amount of work hardening will occur during drawing, and drawing damage is easy to occur inside, making it easy for micro cracks to appear on the surface during service, causing stress concentration and crack expansion, leading to wire breakage; in addition, the increase in strength usually also leads to a decrease in plasticity and comprehensive performance, which increases the difficulty of research and development of ultra-high strength steel strands above 2360MPa. It is impossible to take into account the strength, plasticity and comprehensive performance (such as stress relaxation and stress corrosion performance) of steel strands through process adjustment, and mass production and application have not yet been achieved. Therefore, it is imperative to invent a 2360MPa ultra-high strength steel strand and its preparation process. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a 2360MPa-grade ultra-high-strength prestressed steel strand with good comprehensive performance; the present invention also provides a preparation process of the 2360MPa-grade ultra-high-strength prestressed steel strand.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is that the chemical composition of the raw material wire rod is as follows by mass percentage: C 0.90-1.00%, Si 0.90-0.95%, Mn 0.40-0.60%, Cr 0.20-0.40%, P≤0.05%, S≤0.005%, V 0.01-0.05%, B 0.0002-0.0004%, and the rest is Fe and unavoidable impurities.

[0008] Furthermore, the troostitization rate of the wire rod is 88-95%, the pearlite lamellar spacing is 120-150nm, the oxide layer thickness is 5.0-10.0μm, and the inclusion size is ≤5μm.

[0009] The chemical composition and organizational structure of the steel grade of the present invention are designed for the following reasons: C is a chemical element that ensures the strength and organization of the wire rod. In the present invention, in order to ensure the strength of the product, the carbon content is not less than 0.90% and the cementite ratio is increased. At the same time, in order to control the segregation of the continuous casting billet, control the organization and improve the plasticity of the wire rod and prevent the grain boundary network cementite, the carbon content is not higher than 1.00%.

[0010] Si exists in the form of solid solution in steel, which can improve the hardenability of steel, refine the pearlite lamellar spacing, and has a strong strengthening effect. At the same time, Si has the effect of inhibiting the formation of network cementite to better ensure the strength of the wire rod and control the organization. In addition, increasing the Si content will reduce the speed of cementite spheroidization during the stabilization treatment of steel strands and reduce strength loss. Mn, Cr, and V can improve the hardenability of steel, refine the wire rod organization and lamellar structure, and improve strength and plasticity. Therefore, the Si content is controlled at 0.90-0.95%.

[0011] Mn can improve the hardenability of steel, refine the wire rod structure and lamellar structure, and improve strength and plasticity. However, too high Mn content will produce low-temperature structure and reduce the drawing performance of wire rod. Therefore, the Mn content is controlled at 0.40% to 0.60%.

[0012] P and S are harmful elements that can reduce the plasticity and toughness of steel, so the less their content, the better.

[0013] Cr can improve the hardenability of steel, refine the pearlite lamellar spacing, increase the strength of wire rods, and improve the stress corrosion resistance of steel strands. However, too high a Cr content will produce low-temperature structures and reduce the drawing performance of wire rods, so it is controlled at 0.20% to 0.40%.

[0014] V refines the grains, reduces the segregation of grain boundary elements, and forms submicron V compounds with C and N, which precipitate during phase change, effectively improving the strength of the wire rod. Secondly, the V element can inhibit the precipitation of high-carbon steel grain boundary network cementite. At the same time, the V element combines with the N and C elements in the steel to reduce the strain aging during wire drawing and improve the stress corrosion resistance of the steel strand. Therefore, adding 0.01% to 0.05% of the V element can improve the strength and stress corrosion performance of the steel strand, and improve the stress corrosion resistance of the steel strand.

[0015] B exists in steel mainly in the form of solid solution, which can improve the hardenability of steel, refine the pearlite lamellar spacing, and improve the strength of wire rod. At the same time, B combines with N in steel to reduce the strain aging during wire drawing and improve the stress corrosion resistance of steel strands. Therefore, adding 0.0002% to 0.0004% of B can improve the strength and stress corrosion performance of steel strands and improve the stress corrosion resistance of steel strands.

[0016] In order to solve the above technical problems, the technical solution adopted by the method of the present invention is: comprising the steps of pickling, phosphating, drawing and stabilizing heat treatment; The drawing step comprises: a total compression rate of 80-90%, an average pass compression rate of 15-20%, a working cone angle of a drawing die for drawing treatment of 8-10°, and a drawing speed of 4.0-6.0 m / s; The stabilization heat treatment step: the treatment temperature is 370-390°C.

[0017] Furthermore, in the phosphating step, the phosphating treatment time is 5 to 8 minutes, and the temperature of the phosphating solution is 70 to 85°C.

[0018] Furthermore, the phosphating step: the total acidity in the phosphating solution is 60-90 points, the free acidity is 6-12 points, the total zinc content is ≥29g / L, the nitric acid is ≥21g / L, the phosphoric acid is ≥12g / L, and the ferrous metal is ≤5g / L; the upper modulus of the wire rod after the phosphating step is completed is ≥15g / m 2 .

[0019] Furthermore, the pickling step includes a primary pickling and a secondary pickling; the time for the two picklings is 10 to 15 minutes respectively.

[0020] Furthermore, the concentration of the pickling solution of the first pickling is 8-15%, the temperature is 30-40° C., and the ferrous content is ≤250 g / L.

[0021] Furthermore, the concentration of the pickling solution for the secondary pickling is 15-20%, the temperature is ≥50°C, and the ferrous content is ≤150g / L.

[0022] The beneficial effect of adopting the above technical solution is that: the wire rod raw material used in the present invention improves and optimizes the conventional alloy element design, increases the content of C and Si elements, and reasonably adds metal elements Cr, V, and B on the basis of the wire rod for 1860MPa grade steel strand, ensuring that the internal structure of the wire rod is uniform and the strength and plasticity are reasonable. The present invention effectively improves the tensile strength and plasticity through component design and alloy element selection, the strength of the steel strand reaches 2360MPa and above, the elongation reaches 5.3-5.4%, the 1000h stress relaxation rate is ≤2%, and the stress corrosion failure time is ≤1.9h.

[0023] The method of the present invention effectively improves and optimizes the conventional alloy element design on the basis of 1860MPa grade prestressed steel strand, increases the content of C and Si elements, reasonably adds metal elements Cr, V and B, controls the internal microstructure of the wire rod, adjusts the steel strand production process, improves the steel wire drawing process and the steel strand stabilization production process; the troostitization rate of the adopted wire rod is 88-95%, and the pearlite lamellar spacing is 120-150nm, which can ensure that the internal structure of the wire rod is uniform and the strength and plasticity are reasonable; the oxide layer thickness on the surface of the wire rod is 5.0-10.0μm, and the inclusion size is ≤5μm, which can ensure that the internal structure damage during the drawing process is reduced; the strength of the obtained steel strand reaches 2360MPa or above, the elongation reaches 5.3-5.4%, the 1000h stress relaxation rate is ≤2%, and the stress corrosion failure time is ≤1.9h. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0025] Figure 1 is the internal microstructure diagram of the wire rod before drawing in Example 1 of the present invention; Figure 2 This is the internal microstructure diagram of the ultra-high-strength prestressed steel strand described in Example 1 of the present invention. DETAILED DESCRIPTION

[0026] The 2360MPa grade ultra-high strength prestressed steel strand uses heat-treated wire rods with a strength of not less than 1500MPa as raw materials. The chemical composition of the wire rods is as follows by mass percentage: C 0.90-1.00%, Si 0.90-0.95%, Mn 0.40-0.60%, Cr 0.20-0.40%, P≤0.05%, S≤0.005%, V 0.01-0.05%, B 0.0002-0.0004%, and the rest is Fe and unavoidable impurities. The troostitization rate of the wire rod is 88-95%, the pearlite interlamellar spacing is 120-150nm, the oxide layer thickness is 5.0-10.0μm, and the inclusion size is ≤5μm. The tensile strength of the wire rod is 1500MPa or above, the area reduction rate is 10-15%, and the diameter is 13.0-14.0mm. Depend on Figure 1 It can be seen that the internal structure of the wire rod is uniform, and the internal structure is a large amount of troostite plus a small amount of pearlite structure.

[0027] The preparation process of the 2360MPa grade ultra-high strength prestressed steel strand adopts heat-treated wire rods with a tensile strength of not less than 1500MPa as raw materials, and adopts pickling, phosphating, drying, drawing and stabilization heat treatment steps; the process of each step is as follows: (1) Pickling step: The wire rod is pickled, including primary pickling and secondary pickling; the concentration of the pickling solution for the primary pickling is 8-15wt%, the temperature is 30-40°C, the ferrous content is ≤250g / L, and the pickling time is 10-15min. The concentration of the pickling solution for the secondary pickling is 15-20wt%, the temperature is ≥50°C, the ferrous content is ≤150g / L, and the pickling time is 10-15min. The pickling solution is mainly composed of dilute sulfuric acid, and 5wt‰ of an anti-hydrogen embrittlement slow-release inhibitor is added. The pickling step is used to clean the surface oxide layer to prevent severe oxide scale from causing the surface of the wire rod to be rough, causing difficulties in subsequent drawing, and the oxide layer from scratching the surface of the steel wire or pressing into the steel wire during the drawing process, so as to avoid the surface quality and mechanical properties of the produced steel wire not meeting the requirements.

[0028] (2) Phosphating step: the wire rod is phosphated in a phosphating solution; the phosphating time is 5 to 8 minutes, the temperature of the phosphating solution is 70 to 85°C; the phosphating solution has a total acidity of 60 to 90 points, a free acidity of 6 to 12 points, a total zinc content of ≥29 g / L, nitric acid ≥21 g / L, phosphoric acid ≥12 g / L, and ferrous iron ≤5 g / L; the upper modulus of the wire rod after phosphating is ≥15 g / m 2 The phosphating step ensures that a sufficiently dense phosphating film is formed on the surface of the wire rod by relatively extending the phosphating time, thereby establishing good drawing lubrication conditions, reducing damage to the wire drawing die and avoiding the impact of deterioration of lubrication conditions after multiple drawing passes on the finished wire drawing product.

[0029] (3) Drying step: The wire rod is dried for 3 to 5 minutes.

[0030] (4) Drawing step: The wire rod is drawn to obtain a steel wire; the obtained steel wire includes an edge wire and a core wire; the diameter of the obtained edge wire is in the range of 5.025±0.03mm, and the diameter of the core wire is in the range of 5.25±0.03mm. The total compression rate of the drawing step is 80-90%, the number of drawing passes is not less than 9, and the average compression rate per pass is 15-20%. The working cone angle of the wire drawing die used is 8-10°; different working cone angles of the wire drawing die are used to significantly reduce the heat generation of the hard wire rod during deformation and friction and the accumulation of micro-damage to the internal structure. By reducing the compression rate of each wire drawing pass to ensure that the bending performance of the finished steel wire meets the specification requirements, reducing the compression angle of the wire drawing die can reduce the friction coefficient and the internal structure damage of the steel wire, thereby avoiding the stress distribution and uneven deformation on the cross section of the steel wire. The drawing speed of the drawing step is 4.0-6.0m / s. The drawing speed is reduced to ensure that the steel wire has sufficient cooling and lubrication conditions during drawing and reduce the damage during the internal drawing process.

[0031] Drawing is carried out in stages, wherein the average compression rate of the second stage is greater than that of other stages; from the third stage to the end of drawing, the average compression rate of each stage decreases successively; the drawing process complies with the deformation law of ultra-high strength wire rod, the compression rate of the first stage is small, and as a protective lubrication carrier, the phosphating coating and the lubricating powder are tightly combined to form a highly ductile lubricating body; the average compression rate of the second stage is the largest, and then decreases successively, so that the equiaxed grains of the wire rod increase with the increase of compression stages, the degree of fiberization gradually increases, and the spacing between pearlite lamellae becomes smaller and smaller, so that the semi-finished products produced in this way not only have ideal high strength, but also have high toughness.

[0032] (5) Stabilization heat treatment step: The drawn steel wire is first twisted to obtain a steel strand, and then subjected to stabilization heat treatment to obtain a finished steel strand. In the twisting process, a combination of 6 side wires and 1 middle wire is used for twisting, the twisting pitch is in the range of 12 to 16 times the nominal diameter, and the tension is 38 to 42% of the nominal breaking force. The treatment temperature of the stabilization heat treatment is 370 to 390°C to ensure that the steel strand has a tight structure after twisting and stabilization treatment, and the performance meets the corresponding requirements of the national standard; if the temperature is too high, the strength will be reduced, and if it is too low, the stress relaxation and stress corrosion performance will be poor; for chemical compositions with high carbon, high silicon and high alloy elements, twisting treatment is performed before stabilization treatment.

[0033] (6) The diameter of the steel strand obtained by this method is 15.2±0.03mm, and the structure is uniform. Figure 2As shown, the internal structure is a quenching structure such as a network carbide and martensite, with a high sorbitization rate, good surface quality, and small internal inclusions; the tensile strength of the obtained steel strand reaches 2360MPa and above, the elongation reaches 5.3-5.4%, the 1000h stress relaxation rate is ≤2%, and the stress corrosion failure time is ≤1.9h, with good comprehensive performance. Example 1

[0034] A salt bath heat-treated wire rod having the following chemical composition by mass percentage is used as a raw material: C 0.95%, Si 0.90%, Mn 0.45%, Cr 0.27%, P ≤ 0.05%, S ≤ 0.005%, V 0.03%, B 0.0002%, and the rest is Fe and unavoidable impurities; Figure 1 It can be seen that the internal structure is a large amount of troostite plus a small amount of pearlite structure, the troostitization rate is 89%, the pearlite lamellar spacing is 135nm, the oxide layer thickness is 5.0μm, and the inclusion size is ≤5μm; the diameter of the wire rod is 14.0mm, the tensile strength is 1509MPa, and the surface reduction rate is 13.5%.

[0035] (1) Pickling step: The concentration of the pickling solution of the first pickling is 10wt%, the temperature is 35°C, the ferrous content is 200g / L, and the pickling time is 12min. The concentration of the pickling solution of the second pickling is 17wt%, the temperature is 60°C, the ferrous content is 120g / L, and the pickling time is 12min.

[0036] (2) Phosphating step: the phosphating time is 7 minutes, the temperature of the phosphating solution is 80°C; the phosphating solution has a total acidity of 70 points, a free acidity of 9 points, a total zinc content of 30 g / L, nitric acid 25 g / L, phosphoric acid 20 g / L, and ferrous iron 4 g / L; the upper modulus of the wire rod after phosphating is 17 g / m 2 .

[0037] (3) Drying step: The drying time is 5 minutes.

[0038] (4) Drawing step: The total compression rate is 87%, the number of drawing passes is 9, and the average compression rate per pass is 17%. The working cone angle of the wire drawing die used is 8°. The drawing speed of the drawing step is 4.0 m / s. The diameter range of the obtained edge wire is 5.025±0.03 mm, and the diameter range of the core wire is 5.25±0.03 mm.

[0039] (5) Stabilization heat treatment step: In the stranding process, 6 side wires and 1 middle wire are twisted, the twisting pitch is 14 times the nominal diameter, and the tension is 40% of the nominal breaking force. The treatment temperature of the stabilization heat treatment is 380°C.

[0040] (6) The diameter of the steel strand obtained in this embodiment is 15.2 mm. Figure 2 It can be seen that the internal structure is a quenching structure such as a network carbide and martensite; after testing, its tensile strength is 2400MPa, elongation is 5.4%, 1000h stress relaxation rate is 2%, stress corrosion failure time is 1.9h, and the comprehensive performance is good. Example 2

[0041] The salt bath heat-treated wire rod with the following chemical composition in percentage by mass is used as the raw material: C 0.90%, Si 0.95%, Mn 0.45%, Cr 0.20%, P≤0.05%, S≤0.005%, V 0.03%, B 0.0002%, and the rest are Fe and unavoidable impurities; the troostitization rate is 90%, the pearlite interlamellar spacing is 130nm, the oxide layer thickness is 5.0μm, and the inclusion size is ≤5μm; the diameter of the wire rod is 14.0mm, the tensile strength is 1509MPa, and the area reduction rate is 13.5%.

[0042] (1) Pickling step: The concentration of the pickling solution of the first pickling is 10wt%, the temperature is 35°C, the ferrous content is 200g / L, and the pickling time is 12min. The concentration of the pickling solution of the second pickling is 17wt%, the temperature is 60°C, the ferrous content is 120g / L, and the pickling time is 12min.

[0043] (2) Phosphating step: the phosphating time is 7 minutes, the temperature of the phosphating solution is 80°C; the phosphating solution has a total acidity of 70 points, a free acidity of 9 points, a total zinc content of 30 g / L, nitric acid 25 g / L, phosphoric acid 20 g / L, and ferrous iron 4 g / L; the upper modulus of the wire rod after phosphating is 17 g / m 2 .

[0044] (3) Drying step: The drying time is 4 minutes.

[0045] (4) Drawing step: The total compression rate is 87%, the number of drawing passes is 9, and the average compression rate per pass is 17%. The working cone angle of the wire drawing die used is 8°. The drawing speed of the drawing step is 6.0 m / s. The diameter range of the obtained edge wire is 5.025±0.03 mm, and the diameter range of the core wire is 5.25±0.03 mm.

[0046] (5) Stabilization heat treatment step: In the stranding process, 6 side wires and 1 middle wire are twisted, the twisting pitch is 14 times the nominal diameter, and the tension is 40% of the nominal breaking force. The treatment temperature of the stabilization heat treatment is 380°C.

[0047] (6) The diameter of the steel strand obtained in this embodiment is 15.2 mm. After testing, its tensile strength is 2420 MPa, elongation is 5.2%, 1000h stress relaxation rate is 2%, and stress corrosion failure time is 1.9h, with good comprehensive performance. Example 3

[0048] The salt bath heat-treated wire rod with the following chemical composition in percentage by mass is used as the raw material: C 1.00%, Si 0.95%, Mn 0.60%, Cr 0.20%, P≤0.05%, S≤0.005%, V 0.02%, B 0.0002%, and the rest are Fe and unavoidable impurities; the troostitization rate is 92%, the pearlite interlamellar spacing is 120nm, the oxide layer thickness is 5.0μm, and the inclusion size is ≤5μm; the diameter of the wire rod is 14.0mm, the tensile strength is 1509MPa, and the area reduction rate is 13.5%.

[0049] (1) Pickling step: The concentration of the pickling solution of the first pickling is 10wt%, the temperature is 35°C, the ferrous content is 200g / L, and the pickling time is 12min. The concentration of the pickling solution of the second pickling is 17wt%, the temperature is 60°C, the ferrous content is 120g / L, and the pickling time is 12min.

[0050] (2) Phosphating step: the phosphating time is 7 minutes, the temperature of the phosphating solution is 80°C; the phosphating solution has a total acidity of 70 points, a free acidity of 9 points, a total zinc content of 30 g / L, nitric acid 25 g / L, phosphoric acid 20 g / L, and ferrous iron 4 g / L; the upper modulus of the wire rod after phosphating is 17 g / m 2 .

[0051] (3) Drying step: The drying time is 6 minutes.

[0052] (4) Drawing step: The total compression rate is 87%, the number of drawing passes is not less than 9, and the average compression rate per pass is 17%. The working cone angle of the wire drawing die used is 10°. The drawing speed of the drawing step is 6.0 m / s. The diameter range of the obtained edge wire is 5.025±0.03 mm, and the diameter range of the core wire is 5.25±0.03 mm.

[0053] (5) Stabilization heat treatment step: In the stranding process, 6 side wires and 1 middle wire are twisted, the twisting pitch is 14 times the nominal diameter, and the tension is 40% of the nominal breaking force. The treatment temperature of the stabilization heat treatment is 380°C.

[0054] (6) The diameter of the steel strand obtained in this embodiment is 15.2 mm. After testing, its tensile strength is 2380 MPa, elongation is 5.5%, 1000h stress relaxation rate is 2%, and stress corrosion failure time is 1.9h, with good comprehensive performance. Example 4

[0055] The salt bath heat-treated wire rod with the following chemical composition in percentage by mass is used as the raw material: C 1.00%, Si 0.95%, Mn 0.60%, Cr 0.20%, P≤0.05%, S≤0.005%, V 0.02%, B 0.0002%, and the rest are Fe and unavoidable impurities; the troostitization rate is 92%, the pearlite interlamellar spacing is 120nm, the oxide layer thickness is 5.0μm, and the inclusion size is ≤5μm; the diameter of the wire rod is 14.0mm, the tensile strength is 1509MPa, and the area reduction rate is 13.5%.

[0056] (1) Pickling step: The concentration of the pickling solution of the first pickling is 10wt%, the temperature is 35°C, the ferrous content is 200g / L, and the pickling time is 12min. The concentration of the pickling solution of the second pickling is 17wt%, the temperature is 60°C, the ferrous content is 120g / L, and the pickling time is 12min.

[0057] (2) Phosphating step: the phosphating time is 7 minutes, the temperature of the phosphating solution is 80°C; the phosphating solution has a total acidity of 70 points, a free acidity of 9 points, a total zinc content of 30 g / L, nitric acid 25 g / L, phosphoric acid 20 g / L, and ferrous iron 4 g / L; the upper modulus of the wire rod after phosphating is 17 g / m 2 .

[0058] (3) Drying step: The drying time is 6 minutes.

[0059] (4) Drawing step: the total compression rate is 87%, the number of drawing passes is not less than 9, and the average compression rate per pass is 17%. The working cone angle of the wire drawing die used is 10°. The drawing speed of the drawing step is 5.0 m / s. The diameter range of the obtained edge wire is 5.025±0.03 mm, and the diameter range of the core wire is 5.25±0.03 mm.

[0060] (5) Stabilization heat treatment step: In the stranding process, 6 side wires and 1 middle wire are twisted, the twisting pitch is 14 times the nominal diameter, and the tension is 40% of the nominal breaking force. The treatment temperature of the stabilization heat treatment is 380°C.

[0061] (6) The diameter of the steel strand obtained in this embodiment is 15.2 mm. After testing, its tensile strength is 2390 MPa, elongation is 5.3%, 1000h stress relaxation rate is 2%, and stress corrosion failure time is 1.9h, with good comprehensive performance. Example 5

[0062] The salt bath heat-treated wire rod with the following chemical composition in percentage by mass is used as the raw material: C 1.00%, Si 0.95%, Mn 0.60%, Cr 0.20%, P≤0.05%, S≤0.005%, V 0.02%, B 0.0002%, and the rest are Fe and unavoidable impurities; the troostitization rate is 92%, the pearlite interlamellar spacing is 120nm, the oxide layer thickness is 5.0μm, and the inclusion size is ≤5μm; the diameter of the wire rod is 14.0mm, the tensile strength is 1509MPa, and the area reduction rate is 13.5%.

[0063] (1) Pickling step: The concentration of the pickling solution of the first pickling is 10wt%, the temperature is 35°C, the ferrous content is 200g / L, and the pickling time is 12min. The concentration of the pickling solution of the second pickling is 17wt%, the temperature is 60°C, the ferrous content is 120g / L, and the pickling time is 12min.

[0064] (2) Phosphating step: the phosphating time is 7 minutes, the temperature of the phosphating solution is 80°C; the phosphating solution has a total acidity of 70 points, a free acidity of 9 points, a total zinc content of 30 g / L, nitric acid 25 g / L, phosphoric acid 20 g / L, and ferrous iron 4 g / L; the upper modulus of the wire rod after phosphating is 17 g / m 2 .

[0065] (3) Drying step: The drying time is 6 minutes.

[0066] (4) Drawing step: the total compression rate is 87%, the number of drawing passes is not less than 9, and the average compression rate per pass is 17%. The working cone angle of the wire drawing die used is 9°. The drawing speed of the drawing step is 6.0 m / s. The diameter range of the obtained edge wire is 5.025±0.03 mm, and the diameter range of the core wire is 5.25±0.03 mm.

[0067] (5) Stabilization heat treatment step: In the stranding process, 6 side wires and 1 middle wire are twisted, the twisting pitch is 14 times the nominal diameter, and the tension is 40% of the nominal breaking force. The treatment temperature of the stabilization heat treatment is 380°C.

[0068] (6) The diameter of the steel strand obtained in this embodiment is 15.2 mm. After testing, its tensile strength is 2400 MPa, elongation is 5.5%, 1000h stress relaxation rate is 2%, and stress corrosion failure time is 1.9h, with good comprehensive performance.

Claims

1. A 2360MPa grade ultra-high strength prestressed steel strand, characterized in that: The chemical composition of the raw material wire rod is as follows by mass percentage: C 0.90-1.00%, Si 0.90-0.95%, Mn 0.40-0.60%, Cr 0.20-0.40%, P≤0.05%, S≤0.005%, V 0.01-0.05%, B 0.0002-0.0004%, and the rest is Fe and unavoidable impurities.

2. The 2360MPa grade ultra-high strength prestressed steel strand according to claim 1, characterized in that: The wire rod has a troostitization rate of 88-95%, a pearlite lamellar spacing of 120-150nm, an oxide layer thickness of 5.0-10.0μm, and an inclusion size of ≤5μm.

3. The preparation process of a 2360MPa grade ultra-high strength prestressed steel strand according to claim 1, characterized in that: Includes pickling, phosphating, drawing and stabilization heat treatment steps; The drawing step comprises: a total compression rate of 80-90%, an average pass compression rate of 15-20%, a working cone angle of a drawing die for drawing treatment of 8-10°, and a drawing speed of 4.0-6.0 m / s; The stabilization heat treatment step: the treatment temperature is 370-390°C.

4. The preparation process of a 2360MPa grade ultra-high strength prestressed steel strand according to claim 3, characterized in that: The phosphating step: the phosphating treatment time is 5 to 8 minutes, and the temperature of the phosphating solution is 70 to 85°C.

5. The preparation process of a 2360MPa grade ultra-high strength prestressed steel strand according to claim 4, characterized in that: The phosphating step: the total acidity in the phosphating solution is 60-90 points, the free acidity is 6-12 points, the total zinc content is ≥29g / L, the nitric acid is ≥21g / L, the phosphoric acid is ≥12g / L, and the ferrous metal is ≤5g / L; the upper modulus of the wire rod after the phosphating step is completed is ≥15g / m 2 .

6. The process for preparing a 2360MPa grade ultra-high strength prestressed steel strand according to claim 3, 4 or 5, characterized in that: The pickling step includes a primary pickling and a secondary pickling; the time of the two picklings is 10 to 15 minutes respectively.

7. The process for preparing a 2360MPa grade ultra-high strength prestressed steel strand according to claim 6, characterized in that: The concentration of the pickling solution for the primary pickling is 8-15%, the temperature is 30-40° C., and the ferrous content is ≤250 g / L.

8. The process for preparing a 2360MPa grade ultra-high strength prestressed steel strand according to claim 6, characterized in that: The concentration of the pickling solution for the secondary pickling is 15-20%, the temperature is ≥50°C, and the ferrous content is ≤150g / L.

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