A 2300MPa grade ultra-high strength steel strand steel and its production method and a 2300MPa grade ultra-high strength steel strand

Abstract

The present invention discloses a 2300MPa grade ultra-high strength steel strand steel, a production method thereof, and a 2300MPa grade ultra-high strength steel strand. The main chemical components and weight percentages of the steel strand steel are: C 0.89%-1.10%, Mn 0.68%-0.80%, Cr 0.20%-0.35%, V 0.055%-0.080%, Ti 0.010%-0.030%, Si 0.95% to 1.15%; among which, 0.65≤Mn / C≤0.88, 0.6≤1.5*Cr+5.0*V+2.8*Ti≤1.0, it has high strength and high toughness. The steel strand produced by it has a tensile strength ≥2330MPa, an elastic modulus of 190-210GPa, a yield strength ratio of 0.90 to 0.95, a segregation tensile loss ≤20%, a 120h stress relaxation loss rate ≤1.5%, and good delayed fracture resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel strands, and in particular relates to a 2300 MPa grade ultra-high strength steel strand and a production method thereof, as well as a 2300 MPa grade ultra-high strength steel strand. Background Art

[0002] High-strength prestressed steel strand is a type of product widely used in the metal products industry. It has the characteristics of high tensile strength, good elongation, low relaxation value, small stress loss and excellent fatigue resistance. Due to its unique properties, so far no more ideal product has been found to completely or in one field to replace high-strength prestressed steel strand. It has become an indispensable component or material and is widely used in railways, highways, cross-sea bridges, large buildings, water conservancy and other fields.

[0003] Demand for high-strength prestressed steel strand is growing rapidly in my country. This is particularly true as domestic transportation infrastructure development continues to drive increasing demand for public facilities such as highways and railways, which are gradually expanding into remote mountainous areas. Complex geological conditions in some areas are leading to an urgent need for larger-span railways and bridges, with higher demands placed on their high strength and lightweight construction. As a key raw material used in these large-scale construction projects, the cost and quality of steel strand are directly impacting both the construction cost and safety of the buildings.

[0004] Currently, the prestressed concrete steel strand commonly used in domestic railway and bridge construction is 1860MPa grade steel strand. The highest strength grade specified in this standard is only 1960MPa. Improving the strength of steel strands can significantly reduce costs. For example, replacing 1860MPa grade steel strands with 1960MPa grade high-strength steel strands can save approximately 20% of strand usage. Therefore, larger spans, lighter weight, higher strength, and safer bridges will become an inevitable trend in future industry development. Existing steel strands all use a C-Si-Mn composition system. Increasing the C, Si, and Mn content can improve strength, but this can easily lead to the formation of network cementite and core martensite, which severely degrades the material's performance. In particular, the plasticity and toughness decrease dramatically, making it unable to withstand repeated bending and torsion during processing. Furthermore, the fatigue strength also fails to meet user requirements.

[0005] Chinese patent CN110819899A discloses a 2100MPa grade marine steel wire rope steel and a production method. The 2100MPa grade marine steel wire rope steel includes the following chemical components in weight percentage: C 0.95% to 1.10%, Si 0.10% to 0.50%, Mn 0.60% to 1.20%, Cr 0.10% to 0.50%, Nb 0.02% to 0.10%, Ni 0.01% to 0.50%, Al≤0.005%, P≤0.015%, S≤0.015%, O≤0.0015%, N≤0.006%, and the rest are Fe and unavoidable impurity elements. The invention utilizes a specific chemical composition and wire rod production process to produce hot-rolled wire rod with excellent mechanical properties and a high sorbitization rate. The resulting steel wire rope achieves strength exceeding 2100 MPa, along with excellent torsional and bending properties, making it suitable for producing 2100 MPa-grade high-strength marine steel wire rope. However, this invented material can only be used to produce 2100 MPa-grade high-strength steel wire rope products and cannot meet higher-strength requirements.

[0006] Chinese patent CN 113897544 A discloses a rare earth high-strength and high-toughness prestressed steel strand wire rod and its smelting and rolling production method. The chemical composition by mass percentage is: C: 0.70% to 0.90%, Si: 0.10% to 0.30%, Mn: 0.60% to 0.90%, P≤0.025%, S≤0.025%, V: 0.01% to 0.07%, Cr: 0.15% to 0.35%, Re: 0.0020% to 0.0040%, and the rest is Fe and unavoidable impurities. The wire rod of this invention boasts a strength level exceeding 1570 MPa. The addition of rare earth elements La and Ce, combined with a high-carbon drawing process, optimizes and improves the centerline segregation of the ingot. The hot-rolled wire rod exhibits excellent initial performance, with improved plasticity indicators such as elongation and reduction of area. This eliminates a distinct ductile-brittle transition temperature range for high-carbon steel, enhancing the overall performance of steel strands. However, this invention requires the addition of rare earth elements to enhance strength and toughness, which is costly and challenging. Summary of the Invention

[0007] In order to solve the above technical problems, the present invention provides a 2300MPa grade ultra-high strength steel strand steel and a production method thereof. The steel strand is mainly micro-alloyed by Cr, V, Ti, etc., without the need to add precious alloying elements, with low cost, high strength and high toughness. The steel strand produced by the present invention has a tensile strength of ≥2330MPa, an elastic modulus of 190-210GPa, a yield ratio of 0.90 to 0.95, a segregation tensile loss of ≤20%, a 120h stress relaxation loss rate of ≤1.5%, and good delayed fracture resistance.

[0008] The present invention also provides a 2300MPa grade ultra-high strength steel strand, which is obtained by drawing and stranding the steel for the 2300MPa grade ultra-high strength steel strand described in the present invention.

[0009] The technical solution adopted by the present invention is as follows:

[0010] The present invention provides a 2300MPa grade ultra-high strength steel strand steel, wherein the chemical composition and weight percentage of the 2300MPa grade ultra-high strength steel strand steel are as follows: C 0.89%-1.10%, Mn 0.68%-0.80%, Cr 0.20%-0.35%, V 0.055%-0.080%, Ti 0.010%-0.030%, Si 0.95%~1.15%, Alt≤0.005%, P≤0.010%, S≤0.010%, O≤0.0020%, N≤0.0065%, and the rest are Fe and unavoidable impurity elements; among which, 0.65≤Mn / C≤0.88, 0.6≤1.5*Cr+5.0*V+2.8*Ti≤1.0, in the formula, the numerical value of each chemical component is calculated according to the content of each chemical component in the steel × 100.

[0011] The hot-rolled wire rod for the 2300MPa grade ultra-high strength steel strand has a sorbite ratio of ≥95%, a grain size of ≥9, a sorbite interlamellar spacing of ≤130um, a tensile strength Rm of ≥1430MPa, a cross-sectional shrinkage Z of ≥37%, and a delayed fracture strength ratio R=R BN / R BN0 ≥0.6, where R BN is the notched tensile strength of the hydrogen sample, R BN0 is the notched tensile strength of the non-hydrogen-filled sample.

[0012] The finished steel strand made of the 2300MPa grade ultra-high strength steel strand has a tensile strength of ≥2330MPa, a yield strength ratio of 0.90-0.95, an elastic modulus of 190-210GPa, a segregation tensile loss of ≤20%, and a 120h stress relaxation loss rate of ≤1.5%.

[0013] The present invention also provides a production method for the 2300MPa grade ultra-high strength steel strand steel, which comprises the following steps: smelting → refining → continuous casting → diffusion annealing → rolling → grinding and peeling → high-wire rolling → controlled cooling → wire rod production.

[0014] The refining step includes LF furnace refining and RH vacuum degassing;

[0015] During RH vacuum degassing, [H] is set to ≤ 1.5ppm before breaking the vacuum, so that good delayed fracture resistance can be obtained.

[0016] During the continuous casting step, the casting is protected throughout, electromagnetic stirring of the crystallizer and the end is adopted, and light pressure is performed, with a pressure reduction of 8 to 12 mm, superheat controlled at 20 to 40° C., and a casting speed of 0.40 to 0.55 mm / min; thus, low-segregation defect-free ingots can be obtained.

[0017] In the diffusion annealing step, the annealing temperature is 1200-1300° C. and the holding time is ≥10 hours. High-temperature diffusion annealing can further improve the segregation of the slab, making the carbon segregation index of the slab ≤1.10.

[0018] Continuously cast into 380mm*450mm large square blooms; after diffusion annealing, rolled into 160mm*160mm or 150mm*150mm square blooms.

[0019] In the high-speed wire rolling step, first, soaking is carried out at 1100-1200°C for 40-60 minutes, and then rolling is carried out, with the starting rolling temperature being 950-1000°C, the finishing rolling temperature being 870-900°C, and the spinning temperature being 850-890°C.

[0020] In the controlled cooling step, the steel is first cooled to 650-680°C at a cooling rate of 7-11°C / s to prevent the appearance of network cementite and obtain a large degree of undercooling to prepare for obtaining sorbite with fine interlamellar spacing; then cooled to 580-620°C at a cooling rate of 7-9°C / s, and held for 10-15 seconds to allow the steel to fully undergo phase transformation and obtain sorbite structure; finally, cooled to room temperature at a cooling rate of ≤3°C / s to avoid the appearance of martensite, that is, after the phase transformation, the fan is turned off and the cover is opened to cool to room temperature at a cooling rate of ≤3°C / s.

[0021] The present invention also provides a 2300 MPa grade ultra-high strength steel strand, which is obtained by drawing and stranding the steel for the 2300 MPa grade ultra-high strength steel strand described in the present invention.

[0022] The central steel wire diameter of the steel strand is Φ5.10-5.25 mm, the side wire diameter is Φ5.04-5.06 mm, and the finished steel strand is 15.40-15.15 mm thick.

[0023] The functions and controls of the various chemical components in the 2300 MPa grade ultra-high strength steel strand steel provided by the present invention are as follows:

[0024] C: C is essential for achieving high strength and hardness. To achieve the high strength required for high-strength steel strand, the C content must be above 0.89%. However, excessive C content increases carbon segregation, which can lead to the formation of abnormal structures such as central martensite and network cementite, impairing drawing performance. Therefore, the C content should be controlled between 0.89% and 1.10%.

[0025] Mn: Mn is an effective element for deoxidation and desulfurization, and can also improve the hardenability and strength of steel. However, excessive Mn content can easily cause segregation, resulting in the formation of harmful structures such as central martensite and network cementite, which deteriorates the toughness of the steel. Therefore, the Mn content is controlled between 0.68% and 0.80%.

[0026] Cr: It is a strong carbide-forming element and exists in the cementite lamellae to form alloy cementite, thereby improving the strength. At the same time, the addition of Cr shifts the continuous cooling transformation curve of steel to the right, thereby refining the interlamellar spacing. At the same time, Cr can also reduce the activity of C and reduce the decarburization tendency of the steel surface during heating, rolling and heat treatment. It is useful for obtaining high fatigue resistance and can also improve corrosion resistance and wear resistance. Therefore, the Cr content is controlled at 0.20% to 0.35%.

[0027] V: The V element can significantly refine the grain size, which not only increases the strength and toughness of steel but also improves its low-temperature performance. V is also a strong carbide-forming element. Its precipitation at the austenite grain boundaries during the initial phase transformation can reduce the grain boundary carbon content, effectively inhibiting the formation of network cementite. Furthermore, V (C, N) precipitated in ferrite can act as precipitation strengthening. Furthermore, due to the finer grains, corrosion resistance can also be improved. Excessively high V content results in higher costs. The V content can be controlled within the range of 0.055% to 0.080%.

[0028] Ti: Titanium carbide formed by Ti can pin austenite grain boundaries and refine grains. Titanium carbide has a strong hydrogen trapping effect, which can improve the delayed fracture resistance of steel. In addition, Ti is a strong carbide-forming element. Its precipitation on the austenite grain boundaries in the early stage of phase transformation can reduce the carbon content of the grain boundaries, thereby effectively inhibiting the formation of network cementite. At the same time, due to the finer grains, it can also improve corrosion resistance. The Ti content is controlled at 0.010-0.030%.

[0029] Si: As a solid solution hardening element, Si can significantly increase the strength of high carbon steel. Increasing the Si content in high carbon steel wire rods helps reduce the segregation of carbon atoms in the ferrite lamellae, reducing the formation of central martensite and network cementite. Si can also significantly delay the exothermic peak of the steel wire to a higher temperature range, thereby improving the thermal stability of the steel wire. Therefore, the Si content should be controlled between 0.95% and 1.15%.

[0030] Alt: As a strong deoxidizing element, Alt easily forms immutable Al2O3-type brittle inclusions with oxygen. Higher Alt content leads to larger and more brittle inclusions. Larger brittle inclusions, in particular, can cause drawing fractures, impacting serviceability, and significantly reducing fatigue life. Therefore, to control inclusion morphology and size, the Alt content is strictly controlled to ≤0.005%.

[0031] S and P: Impurity elements such as S and P segregate at grain boundaries, significantly reducing delayed fracture resistance. P can form microsegregations during solidification and subsequently segregate at grain boundaries during austenitization, significantly increasing the steel's brittleness and delayed fracture sensitivity. S forms MnS inclusions and segregates at grain boundaries, further increasing the steel's delayed fracture sensitivity. Therefore, the P and S contents should be controlled within the range of P ≤ 0.010% and S ≤ 0.010%.

[0032] Oxygen and nitrogen: Oxygen forms various oxide inclusions in steel. Under stress, these inclusions easily cause stress concentration, leading to the initiation of microcracks and deteriorating the steel's mechanical properties, especially toughness and fatigue resistance. Therefore, measures must be taken in metallurgical production to minimize its content, controlling it to 0.0020% or less. Nitrogen precipitates as Fe₄N in steel, which diffuses slowly, causing aging. Nitrogen also reduces the steel's cold working properties, so the nitrogen content should be controlled to 0.0065% or less.

[0033] In order to improve the strength and plasticity and toughness of steel strands, the present invention adopts a high C-high Si-low Mn composition design system and re-optimizes the chemical composition. 1) Considering that the Mn content has little effect on strength, the Mn content is appropriately reduced to improve toughness. At the same time, in order to ensure that it does not have too much impact on the plasticity and toughness of the material, the composition must meet 0.65≤Mn / C≤0.88. 2) Adding appropriate amounts of Cr and V elements can improve the tensile strength of the wire rod on the one hand and improve the microstructure and performance of the wire rod on the other hand. Cr and V are both strong carbide-forming elements that can replace iron atoms in cementite to form alloy cementite, which can prevent the growth of austenite grains and refine the original austenite grain size. It can increase the cooling rate before phase transformation and increase the sorbitization rate. At the same time, the addition of Cr shifts the continuous cooling transformation curve of steel to the right, thereby refining the sorbitite interlamellar spacing and improving strength and plasticity and toughness. 3) Adding a small amount of V element can inhibit the formation of network carbides and change the morphology of grain boundary carbides to a discontinuous and dispersed distribution. 4) To avoid the risk of delayed fracture due to high strength, V and Ti microalloying is used. On the one hand, this refines the original austenite grain size, increases the grain boundary area, avoids localized hydrogen concentration, and improves the delayed fracture resistance of the steel. On the other hand, it forms carbides that act as hydrogen traps, preventing hydrogen from accumulating in potentially dangerous areas prone to crack initiation, thereby reducing the material's hydrogen embrittlement susceptibility and improving its delayed fracture resistance. The chemical composition must meet the following requirements: 0.6 ≤ 1.5 * Cr + 5.0 * V + 2.8 * Ti ≤ 1.0.

[0034] In order to achieve high strength, plasticity and toughness, obtain good delayed fracture resistance and strictly control the H content, the present invention adopts the "two-fire material forming" process, that is, after continuous casting, the billet is first subjected to high-temperature diffusion annealing to improve the segregation of the billet, and the carbon segregation index of the billet is controlled to ≤1.10, and then the billet is heated and high-speed wire rolling is carried out to achieve The hot-rolled wire rod is rolled to produce 2300MPa grade ultra-high strength steel strand. The hot-rolled wire rod has a sorbite ratio of ≥95%, a grain size of ≥9, and a spacing between sorbite layers of ≤130um. The hot-rolled wire rod has a tensile strength of Rm ≥1430MPa and a reduction in area of ​​Z ≥37%. After drawing and stranding, such hot-rolled wire rod can be used to produce 2300MPa grade ultra-high strength steel strand. No salt bath treatment is required. The resulting steel strand is free of network cementite and central martensite. The mechanical properties of the finished steel strand meet the following requirements: tensile strength R m ≥2310MPa, elastic modulus 190-210GPa, yield strength ratio 0.90~0.95, with good delayed fracture resistance.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention adopts a high C-high Si-low Mn composition design system and performs microalloying with Cr, V, Ti, etc. to achieve the preparation of hot-rolled wire rods with high strength and plasticity and toughness without adding precious alloy elements and at low cost.

[0037] The present invention controls refining and continuous casting, and adopts high-temperature diffusion annealing after continuous casting to improve the segregation of the cast slab, thereby controlling the carbon segregation index of the cast slab to be ≤1.10.

[0038] The present invention adopts a three-stage cooling method after high-speed wire rolling, which effectively controls the transformation speed of the wire rod from the austenite region to the phase transformation point and the entire phase transformation range, making the phase transformation process smooth and the phase transformation time increased, which is beneficial to increasing the sorbite content of the wire rod and reducing the generation of abnormal tissues, and is beneficial to controlling the final cooling temperature and final cooling speed, reducing or eliminating the generation of abnormal tissues. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The metallographic structure of the hot-rolled wire rod of the steel strand in Example 1;

[0040] Figure 2 Schematic diagram of the slow strain rate tensile test apparatus. DETAILED DESCRIPTION

[0041] The present invention provides a 2300MPa grade ultra-high strength steel strand steel, wherein the chemical composition and weight percentage of the 2300MPa grade ultra-high strength steel strand steel are as follows: C 0.89%-1.10%, Mn 0.68%-0.80%, Cr 0.20%-0.35%, V 0.055%-0.080%, Ti 0.010%-0.030%, Si 0.95%~1.15%, Alt≤0.005%, P≤0.010%, S≤0.010%, O≤0.0020%, N≤0.0065%, and the rest are Fe and unavoidable impurity elements; among which, 0.65≤Mn / C≤0.88, 0.6≤1.5*Cr+5.0*V+2.8*Ti≤1.0, in the formula, the numerical value of each chemical component is calculated according to the content of each chemical component in the steel × 100.

[0042] The production method of the 2300MPa grade ultra-high strength steel strand steel comprises the following steps: smelting → refining → continuous casting → diffusion annealing → rolling → grinding and peeling → high-strength wire rolling → controlled cooling → wire rod production.

[0043] The smelting adopts electric furnace smelting: the end point C is controlled at ≤0.10%, P≤0.010%; slag is blocked for tapping, and refined slag and lime are added when about 1 / 5 of the molten steel is tapped. When about 1 / 3 of the molten steel is tapped, deoxidizer and alloy are added in the following order: silicon balls → manganese silicon alloy → high carbon ferromanganese → high carbon ferrochrome → ferrovanadium → recarburizer → slag.

[0044] The refining step includes LF furnace refining and RH vacuum degassing;

[0045] During the LF furnace refining process, argon is blown from the ladle bottom throughout the entire process, with the argon flow rate being sufficient to prevent molten steel from splashing out of the ladle. To control inclusions, Si deoxidation is employed, using an acidic slag system. Silica balls are used as a deoxidizer. Wollastonite and lime are added to form the slag, with a basicity R ≤ 1.5 and a white slag time of ≥ 20 minutes. Based on the composition analysis results before entering the LF furnace, alloys are added before and during refining to adjust the Si, Mn, Cr, V, and Ti contents.

[0046] During RH vacuum degassing, in the early stages of vacuum degassing, if the vacuum degree is ≤100Pa, the vacuum holding time must be ≥10 minutes; if the vacuum degree is ≤200Pa, the vacuum holding time must be ≥15 minutes; and in the later stages of vacuum degassing, the vacuum holding time must be ≥10 minutes. Based on the composition analysis results of the early stages of vacuum degassing, if composition adjustment is required in the mid-term, the vacuum holding time must be maintained for at least 5 minutes after the adjustment. To achieve good delayed fracture resistance, [H] is set to ≤1.5ppm before vacuum degassing. This ensures good delayed fracture resistance. After vacuum degassing, calcium line treatment is performed. Soft argon blowing is performed before leaving the station, with a soft blowing time of ≥15 minutes. Alloying is added to adjust the V, Ti, B, and Ni contents based on the composition analysis results at the RH endpoint.

[0047] During the continuous casting step, the casting is protected throughout, electromagnetic stirring of the crystallizer and the end is adopted, and light pressure is performed, with a pressure reduction of 8 to 12 mm, superheat controlled at 20 to 40° C., and a casting speed of 0.40 to 0.55 mm / min; thus, low-segregation defect-free ingots can be obtained.

[0048] The crystallizer electromagnetic stirring frequency is 3.0 Hz, the current is 400 A; the end electromagnetic stirring frequency is 4.0 Hz, the current is 800 A.

[0049] In the diffusion annealing step, the annealing temperature is 1200-1300° C. and the holding time is ≥10 hours. High-temperature diffusion annealing can further improve the segregation of the slab, making the carbon segregation index of the slab ≤1.10.

[0050] Continuously cast into 380mm*450mm large square blooms; after diffusion annealing, rolled into 160mm*160mm square billets.

[0051] In the high-speed wire rolling step, first, soaking is carried out at 1100-1200°C for 40-60 minutes, and then rolling is carried out, with the starting rolling temperature being 950-1000°C, the finishing rolling temperature being 870-900°C, and the spinning temperature being 850-890°C.

[0052] In the controlled cooling step, the temperature is first cooled to 650-680° C. at a cooling rate of 7-11° C. / s, then cooled to 580-620° C. at a cooling rate of 7-9° C. / s, and held for 10-15 seconds; and finally cooled to room temperature at a cooling rate of ≤3° C. / s.

[0053] The present invention also provides a 2300 MPa grade ultra-high strength steel strand, which is obtained by drawing and stranding the steel for the 2300 MPa grade ultra-high strength steel strand described in the present invention.

[0054] The central wire diameter of the steel strand is Φ5.10 mm, the side wire diameter is Φ5.06 mm, and the finished steel strand is 15.2 mm thick.

[0055] The present invention is described in detail below with reference to the embodiments.

[0056] The chemical composition and weight percentage of the steel used for the steel strands in the embodiments and comparative examples are shown in Table 1.

[0057] Table 1

[0058]

[0059] The steel strand steel in each embodiment and comparative example adopts the following production route: electric furnace smelting → LF refining + RH vacuum degassing → 380*450mm bloom continuous casting → high temperature diffusion annealing → 160*160mm rolled billet → grinding and peeling → high-speed wire rolling → controlled cooling → finished wire rod. Specifications of wire.

[0060] The production process parameters of the steel strand steel in each embodiment and comparative example are shown in Table 2.

[0061] Table 2

[0062]

[0063]

[0064] The microstructure and grain size of the hot-rolled wire rods for steel strands in the embodiments and comparative examples are shown in Table 3.

[0065] Table 3

[0066]

[0067] The mechanical properties of the hot-rolled steel wire rods for steel strands in the embodiments and comparative examples are shown in Table 4.

[0068] Table 4

[0069]

[0070]

[0071] In Table 4, the tensile strength Rm and the post-fracture shrinkage Z were tested for mechanical properties according to the method of GB / T 228.1-2010 “Tensile tests on metallic materials - Part 1: Room temperature test methods”.

[0072] The delayed fracture resistance is evaluated and analyzed by slow strain rate tensile test (SSRT) at room temperature. The schematic diagram of the slow strain rate tensile test device is as follows: Figure 2 As shown, the delayed fracture strength ratio R=R BN / RB N0 , R BN is the notch tensile strength of the hydrogen-filled sample; R BN0 is the notched tensile strength of the non-hydrogen-filled sample.

[0073] The steel strands in the embodiments and comparative examples were prepared by drawing and stranding the hot-rolled steel wire rods into steel strands with a center wire diameter of Φ5.10 mm, a side wire diameter of Φ5.06 mm, and a finished steel strand thickness of 15.2 mm. The properties of the steel strands are shown in Table 5.

[0074] Table 5

[0075]

[0076] The test methods for each property in Table 5 are as follows: All properties of the steel strand were tested in accordance with GB / T 21839-2019. Mechanical properties (including Rm, elastic modulus, and yield strength ratio) were tested using a tensile test, deflection tensile loss was tested using a deflection tensile test, and 120h stress relaxation loss rate was tested using an isothermal relaxation test.

[0077] From the above, it can be seen that in Comparative Example 1, no Cr, V, or Ti was added, and the strength of the finished steel strand could not reach 2330 MPa. Although Cr, V, and Ti were added in Comparative Example 2, the chemical composition of 1.5*Cr+5.0*V+2.8*Ti did not meet the requirement of 0.6≤1.5*Cr+5.0*V+2.8*Ti≤1.0, resulting in coarse grains of the hot-rolled wire rod, coarse spacing between sorbite lamellae, and insufficient strength and toughness. Although the chemical composition of Comparative Example 3 was the same as that of Example 1, the three-stage controlled cooling method required by the present invention was not followed, resulting in the presence of central martensite and network cementite in the structure, and a low sorbitization rate.

[0078] From the above content, it can be seen that according to the scheme provided by the present invention, a 2300MPa grade ultra-high strength steel strand hot-rolled wire rod with a sorbite rate ≥95%, a grain size ≥9 levels, a sorbite lamellar spacing ≤130um, a tensile strength Rm ≥1430MPa, and a cross-sectional shrinkage rate Z ≥37% can be obtained.

[0079] After drawing and stranding, the hot-rolled wire rod can be prepared to have a tensile strength of ≥2330MPa, a yield strength ratio of 0.90-0.95, an elastic modulus of 190-210GPa, a segregation tensile loss of ≤20%, a 120h stress relaxation loss rate of ≤1.5%, and a delayed fracture strength ratio R=R BN / R BN0 Finished steel strand with a diameter of ≥0.6.

[0080] The above-mentioned detailed description of a 2300MPa grade ultra-high strength steel strand steel and its production method and a 2300MPa grade ultra-high strength steel strand with reference to the embodiments is illustrative rather than restrictive. Several embodiments can be listed according to the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A 2300MPa grade ultra-high strength steel strand steel, characterized in that: The chemical composition and weight percentage of the 2300MPa grade ultra-high strength steel strand steel are as follows: C 0.89%-1.10%, Mn 0.68%-0.80%, Cr 0.20%-0.35%, V 0.055%-0.080%, Ti 0.010%-0.030%, Si 0.95%-1.15%, Alt≤0.005%, P≤0.010%, S≤0.010%, O≤0.0020%, N≤0.0065%, and the remainder is Fe and unavoidable impurity elements; wherein, 0.65≤Mn / C≤0.88, 0.6≤1.5*Cr+5.0*V+2.8*Ti≤1.0; The hot-rolled wire rod for the 2300MPa grade ultra-high strength steel strand has a sorbite ratio of ≥95%, a grain size of ≥9, and a sorbite lamellar spacing of ≤130um.

2. The 2300 MPa grade ultra-high strength steel strand steel according to claim 1, characterized in that: The 2300MPa grade ultra-high strength steel strand hot-rolled wire rod has a tensile strength Rm≥1430MPa, a cross-sectional shrinkage Z≥37%, and a delayed fracture strength ratio R=R BN / R BN0 ≥0.6, where R BN is the notched tensile strength of the hydrogen sample, R BN0 is the notched tensile strength of the non-hydrogen-filled sample.

3. The 2300 MPa grade ultra-high strength steel strand steel according to claim 1, characterized in that: The finished steel strand made of the 2300MPa grade ultra-high strength steel strand has a tensile strength of ≥2330MPa, a yield strength ratio of 0.90-0.95, an elastic modulus of 190-210GPa, and a segregation tensile loss of ≤20%. The 120h stress relaxation loss rate is ≤1.5%.

4. A method for producing 2300 MPa grade ultra-high strength steel strand steel according to any one of claims 1 to 3, characterized in that: The production method comprises the following steps: smelting→refining→continuous casting→diffusion annealing→rolling→grinding and peeling→high-speed wire rolling→controlled cooling→wire rod production.

5. The production method according to claim 4, characterized in that The refining step includes LF furnace refining and RH vacuum degassing; during the RH vacuum degassing, [H] is set to be ≤1.5ppm before breaking the vacuum.

6. The production method according to claim 4, characterized in that In the continuous casting step, electromagnetic stirring of the crystallizer and electromagnetic stirring of the end are adopted, and soft reduction is performed, with a reduction of 8 to 12 mm, superheating is controlled at 20 to 40° C., and a casting speed of 0.40 to 0.55 mm / min.

7. The production method according to claim 4, characterized in that In the diffusion annealing step, the annealing temperature is 1200-1300° C., and the holding time is ≥10 h.

8. The production method according to any one of claims 4 to 7, characterized in that: In the high-speed wire rolling step, first, soaking is carried out at 1100-1200°C for 40-60 minutes, and then rolling is carried out, with the starting rolling temperature being 950-1000°C, the finishing rolling temperature being 870-900°C, and the spinning temperature being 850-890°C.

9. The production method according to any one of claims 4 to 7, characterized in that: In the controlled cooling step, the temperature is first cooled to 650-680° C. at a cooling rate of 7-11° C. / s, then cooled to 580-620° C. at a cooling rate of 7-9° C. / s, held for 10-15 seconds, and finally cooled to room temperature at a cooling rate of ≤3° C. / s.

10. A 2300MPa grade ultra-high strength steel strand, characterized in that: The 2300MPa grade ultra-high strength steel strand is obtained by drawing and stranding the steel for the steel strand as described in any one of claims 1 to 3.

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