High-strength steel for transformer and method for manufacturing the same

Abstract

The present application relates to a kind of high-strength steel for transformer and its preparation method, belong to microalloying high-strength steel technical field, solve the problem of one of the insufficient strength of transformer steel in prior art, poor weldability, large deadweight, high cost.The present application discloses a kind of high-strength steel for transformer, the composition of the high-strength steel is as follows by mass: C 0.06~0.10%, Si 0.30~0.40%, Mn 0.8~1.0%, Ti 0.06~0.10%, Cr 0.02~0.05%, P 0.005~0.010%, S 0.001~0.003%, N≤0.002%, the rest is Fe and inevitable impurities;And [C] is solid solution carbon content, [Ti] is solid solution titanium content.The high-strength steel has excellent weldability, high strength, preparation cost can be controlled, and under the condition of guaranteeing the strength of transformer "thin shell" structure, the shell deadweight can be significantly reduced, and can be widely applied in the preparation of transformer shell and supporting components.

Description

Technical Field

[0001] This invention relates to the field of microalloyed high-strength steel technology, and in particular to a high-strength steel for transformers and its preparation method. Background Technology

[0002] With the rapid development of China's industry, the demand for power transmission and transformation equipment is gradually increasing in fields such as general machinery, automobiles, chemicals, and metallurgy. Furthermore, the construction of renewable energy and smart grids has also led to a surge in demand for power transmission and transformation equipment. Transformers, as an extremely important piece of equipment in the power system, are a crucial component of the entire power transmission process.

[0003] The transformer's oil tank serves as both the outer casing protecting the transformer body and the container holding the oil, as well as the framework for assembling the transformer's external structural components. As a container for oil (not static cold oil, but hot oil in motion), the oil tank must not deform beyond permissible limits, nor crack or leak oil. This requires the oil tank to possess a certain level of mechanical strength.

[0004] The transformer tank / outer shell mainly performs the following five functions:

[0005] 1) Bear the weight of the transformer body and oil, as well as the overall lifting weight.

[0006] 2) Supports all accessories of the transformer (such as bushings, oil conservators, radiators or coolers, etc.).

[0007] 3) It is subjected to impact acceleration during transportation and seismic or wind loads under operating conditions.

[0008] 4) For large transformers, the transformer body needs to be vacuum-filled in the oil tank, or the oil tank needs to be used to dry the transformer body during on-site repairs. This requires the oil tank to be able to withstand the atmospheric pressure when vacuuming.

[0009] 5) In addition to withstanding the internal oil pressure, the tank must also be able to prevent it from bursting in the event of an internal transformer accident. The mechanical properties of the tank, besides considering its mechanical strength under various stress conditions, must also fully consider the stability of the tank as a "thin-shell" structure under vacuum pressure.

[0010] Transformer tanks are typically assembled by welding, resulting in hundreds of alternating horizontal and vertical welds during manufacturing. The numerous and complex distribution of these welds leads to residual stress and deformation after welding, which can affect the stable operation of the transformer and create safety hazards. Furthermore, the casings of large transformers currently weigh tens to hundreds of tons, making hoisting and transportation difficult and costly.

[0011] At present, Q355 steel is generally used as the transformer oil tank shell steel, but the tensile strength, yield strength and elongation of the alloy steel are insufficient, and the welding performance is poor, in order to ensure the structural strength of the shell, the amount of steel is large, the weight of the shell is increased, and the preparation and transportation costs are increased. SUMMARY

[0012] In view of the above analysis, the embodiment of the present application aims to provide a high-strength steel for transformer and a preparation method thereof, to solve one of the problems of insufficient strength of the steel for transformer, poor welding performance, large weight and high cost in the prior art.

[0013] The present application discloses a high-strength steel for transformer, the composition of the high-strength steel is as follows in terms of mass: C 0.06-0.10%, Si 0.30-0.40%, Mn 0.8-1.0%, Ti 0.06-0.10%, Cr 0.02-0.05%, P 0.005-0.010%, S 0.001-0.003%, N≤0.002%, and the rest is Fe and inevitable impurities; and [C] is the solid solution carbon content, and [Ti] is the solid solution titanium content.

[0014] Specifically, the yield strength of the high-strength steel is 460-500 MPa.

[0015] Specifically, the elongation of the high-strength steel is 24%-28%.

[0016] Specifically, the metallographic structure of the high-strength steel is composed of 85%-90% blocky ferrite, 10%-12% pearlite and a small amount of bainite.

[0017] Specifically, the carbon equivalent of the high-strength steel is not higher than 0.27, and the carbon equivalent calculation formula is

[0018] The present application also discloses a preparation method of the high-strength steel, comprising the following steps:

[0019] S1: adopting the blast furnace molten iron raw material for converter smelting, so that the elements C, Si and Cr meet the composition requirements, and obtaining the molten steel A;

[0020] S2: LF refining the molten steel A, adding titanium iron for alloying, so that the content of each element meets the preset value, and degassing by RH vacuum, obtaining the molten steel B;

[0021] S3: injecting the molten steel B into the continuous casting machine for continuous casting, obtaining the continuous casting blank;

[0022] S4: the continuous casting blank is rolled and cooled and coiled to obtain high-strength steel.

[0023] Specifically, the O content in the steel is controlled to be below 700 ppm in the converter smelting process of step S1, and the slag amount at tapping is below 0.01% of the molten steel amount.

[0024] Specifically, the refining time is controlled to be above 35 min in the LF refining process of step S2, and titanium ferroalloy is added for micro-alloying 10-15 min before the end of refining.

[0025] Specifically, the molten steel superheating temperature is controlled to be within 10-35 ℃ in the continuous casting process of step S3, and the casting speed is controlled to be 0.8-1.0 m / min throughout the process; and the cast blank is subjected to stack and slow cooling treatment after being discharged.

[0026] Specifically, the specific operation of step S4 is that the continuous casting blank is soaked at 1100-1150 ℃ for 4-6 hours, the initial rolling temperature is 1020-1050 ℃, the final rolling temperature is 920-950 ℃, and the steel plate is cooled to 600±15 ℃ at a cooling rate of 80-100 ℃ / s after rolling and then coiled.

[0027] Compared with the prior art, the present application can achieve at least one of the following beneficial effects:

[0028] 1. The high-strength steel disclosed in the present application has good weldability. By reducing the C and Mn contents, the present application reduces the carbon equivalent CE and the weld crack sensitivity index Pcm, and improves the weldability of the test material; and by optimizing the process, increasing the coiling temperature and reducing the internal stress of the material, the present application reduces the occurrence of welding deformation and also helps to improve the weldability of the material.

[0029] 2. The high-strength steel disclosed in the present application has good mechanical properties, and the tensile strength, yield strength and elongation are significantly improved. By adding trace amounts of Ti, the present application utilizes the fine-grain strengthening and precipitation strengthening of Ti to improve the mechanical properties of the high-strength steel, makes up for the loss of solid solution strengthening due to the reduction of C and Mn contents, and improves the tensile strength, yield strength and elongation of the material. According to the experimental results, the tensile strength of the high-strength steel is above 550 MPa, the yield strength is above 460 MPa, and the elongation is 24%-28%.

[0030] 3、The high-strength steel structure disclosed by the application has high strength and good welding performance, thereby realizing the weight reduction of the transformer shell. In combination with beneficial effect 1, it can be known that the welding performance of the material is improved, the welding deformation is small, and the steel amount used during welding is reduced after reducing the C and Mn contents and optimizing the process. In combination with beneficial effect 2, it can be known that the strength of the material of the application is obviously improved compared with the Q355 steel, and the steel amount used is small at the same bearing load. In summary, the shell weight is reduced by more than 15% under the premise of ensuring the structural strength and welding quality.

[0031] 4、The high-strength steel disclosed by the application has controllable cost and good economy. The components of the high-strength steel disclosed by the application are common metal elements or inorganic elements, the improvement of the process flow is mainly parameter optimization, no special equipment or raw materials are needed, and the preparation cost is controllable. And in view of the fact that the steel amount of the shell can be significantly reduced, the preparation and transportation costs of the transformer can be further reduced.

[0032] In the application, the above technical solutions can be combined with each other to realize more preferred combination solutions. Other features and advantages of the application will be described in the subsequent specification, and some advantages will become apparent from the specification or be understood by implementing the application. The purpose and other advantages of the application can be realized and obtained from the contents specifically pointed out in the specification and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0033] The accompanying drawings are included to provide a further understanding of the application and are incorporated herein and constitute a part of the application. The drawings illustrate embodiments of the application and, together with the description, serve to explain the principles of the application.

[0034] Figure 1 It is a metallographic structure photo of Example 1;

[0035] Figure 2 It is a metallographic structure photo of Example 2;

[0036] Figure 3 It is a metallographic structure photo of Example 3;

[0037] Figure 4 It is a preparation method flowchart;

[0038] Figure 5 It is a rolling stage (step S5) process flowchart. DETAILED DESCRIPTION

[0039] The preferred embodiments of the application will be specifically described below in combination with the drawings, wherein the drawings constitute a part of the application and serve to explain the principles of the embodiments of the application, but are not used to limit the scope of the application.

[0040] The application discloses a high-strength steel for a transformer, and the high-strength steel comprises the following components in mass percentage: C 0.06-0.10%, Si 0.30-0.40%, Mn 0.8-1.0%, Ti 0.06-0.10%, Cr 0.02-0.05%, P 0.005-0.010%, S 0.001-0.003%, N less than or equal to 0.002%, and the rest is Fe and inevitable impurities. [C] is the solid solution carbon content, and [Ti] is the solid solution titanium content.

[0041] The selection basis and synergistic effect of the content of each component are as follows:

[0042] C: C is an effective steel strengthening element, and can also significantly deteriorate the welding performance of the steel, but at the same time, in order to ensure that Ti can be completely precipitated to form TiC, the lower limit of the C content is set to 0.06%, on the other hand, in order to reduce the carbon equivalent CE and the welding crack sensitivity index Pcm of the steel, the upper limit of the C content is set to 0.1%, and the suitable range of C in the application is selected to be 0.06-0.10%.

[0043] Si: Si mainly exists as a reducing agent and a deoxidizer in steelmaking, and can also improve the strength of the steel, therefore the lower limit of the Si content is set to 0.3%; on the other hand, considering that when the content is greater than 0.4%, the toughness will be deteriorated, therefore the upper limit is set to 0.4%, and therefore the suitable range of Si in the application is selected to be 0.3%-0.4%.

[0044] Mn: Mn can be infinitely solid-solved with Fe, and mainly exists in the form of substitutional solid solution in the steel. The addition of Mn can improve the strength of the steel, but at the same time, the weldability of the steel will be reduced. The solid solution strengthening effect of Mn is calculated by using a solid solution strengthening formula, and the content range of Mn is finally selected to be 0.8-1.0% by comprehensively considering.

[0045] Ti: Ti has good deoxidation effect and nitrogen fixation effect, is a strong ferrite forming element, and is a strong carbide element, and can play the roles of fine-grain strengthening and precipitation strengthening. The selection of the Ti content is considered from the aspects of fine-grain strengthening and precipitation strengthening of Ti, and the strengthening increment change values of ordinary Q355 steel under the conditions of 0.1% C and 0.1% Ti and 0.1% C and 0.06% Ti (when the other element compositions are unchanged) are exemplarily calculated, and the specific values are shown in Table 1. The calculation results show that the overall strength can be improved by 100-166 MPa by adjusting the C and Ti contents in the steel. In addition, too high Ti content will lead to the decrease of the plasticity of the alloy, and therefore the selection of the Ti content in the application is selected to be 0.06%-0.10%.

[0046] Table 1: Strengthening component calculation

[0047]

[0048] Cr: Cr has good comprehensive performance, which can improve the hardenability and strength of the steel. In order to prevent the abnormality of the structure caused by the increase of the hardenability of the steel due to the excessive Cr content, the upper limit of the Cr content is selected as 0.05%, and in order to ensure the hardenability of the steel, the lower limit of the Cr content is selected as 0.02%.

[0049] P: P element is generally a harmful element in steel, which endangers the plasticity and toughness of the steel, so it should be reduced as much as possible, and the de-P cost is considered comprehensively, so the P content is selected as 0.005-0.010% in the application.

[0050] S: S is generally a harmful element in steel, and when pressure processing is carried out at high temperature, hot brittleness is easily generated, the higher the content is, the more serious the hot brittleness phenomenon is, so the sulfur content must be controlled. Therefore, the S content is controlled in the range of 0.001-0.003% in the application.

[0051] N: N has a solid solution strengthening effect, which can improve the strength of the steel and improve the hardenability. In addition, in the application, N can form TiN with Ti, and the fine TiN can play the role of pinning grain boundaries, refining grains and improving toughness, but when the N content is too high, large unsolved TiN particles are easily generated in the smelting process, which endangers the overall performance of the steel. It is found by theoretical derivation using the following formula that the N content controlled in the range of 20 ppm or less will not form large size TiN, and ensure that Ti is precipitated in the form of nano-sized TiC, which provides sufficient strengthening increment. Therefore, the N content is designed to be ≤0.002% in the application.

[0052] lg[Ti][N] L = 5.922-16066 / T

[0053] lg[Ti][N] γ = 0.32-8000 / T

[0054] The synergistic effect of each component in the alloy formula of the application:

[0055] The application can realize fine control of the strength of the alloy steel. For low alloy steel plate, the strengthening methods mainly include solid solution strengthening, fine grain strengthening, precipitation strengthening and dislocation strengthening. Through theoretical calculation of the change of the strengthening amount, the change of the strengthening increment caused by the addition of Ti and the Ti content required to meet the strength range requirements are determined.

[0056] The specific formula of the strengthening method is as follows:

[0057] Solid solution strengthening formula:

[0058] σ s= 4570w[C] + 37w[Mn] + 80w[Ti] + 3w[V] + 11w[Mo]

[0059] w[X] is the mass fraction of solid solution elements in the matrix (X = C, Mn, Ti, V, Mo), %

[0060] Precipitation strengthening formula:

[0061]

[0062] In the formula, d is the size of precipitated phase particles, nm; f is the volume fraction.

[0063] Fine-grain strengthening formula:

[0064]

[0065] In the formula, k is the proportionality coefficient, and d is the effective grain size

[0066] The solubility product formula of Ti in austenite and ferrite is as follows:

[0067] lg[Ti][C] γ = 2.75-7000 / T

[0068] lg[Ti][C] α = 4.4-9575 / T

[0069] The present application adds Ti by reducing the content of C and Mn, to ensure that the weldability is improved while the strength is improved. Compared with Q355 steel, the theoretical strength can be increased by 100-166 MPa.

[0070] The carbon equivalent can be used to evaluate the welding performance of the plate in theory, and the carbon equivalent formula is as follows:

[0071]

[0072] By reducing the main alloying elements that increase the carbon equivalent, the carbon equivalent of the inventive steel can be reduced to 0.27 based on Q355 steel (carbon equivalent value of 0.50), and the welding performance is obviously improved.

[0073] Specifically, according to theoretical calculation and experimental verification, when the alloy composition satisfies , the mechanical properties and plasticity of the alloy reach a good balance state, [C] is the solid solution carbon content, and [Ti] is the solid solution titanium content.

[0074] Specifically, the yield strength of the high-strength steel is 460-500 MPa, the higher yield strength can ensure that the shell has sufficient deformation resistance when welded, and can help to reduce the amount of shell steel; but too high yield strength increases the production and processing cost.

[0075] Specifically, the high-strength steel has an elongation of 24% to 28%, which is more conducive to cold bending or cold working than Q355 steel. However, the elongation should not be too large (e.g., more than 30%) to avoid excessive deformation or stretching during processing, which may result in insufficient structural strength at the deformation position.

[0076] Specifically, the high-strength steel has a metallographic structure composed of 85% to 90% blocky ferrite, 10% to 12% pearlite, and a small amount of bainite. The average size of the blocky ferrite, which is the main component of the metallographic structure, is 6.4 to 7 μm, which helps to improve the strength of the alloy steel. The pearlite and a small amount of bainite are dispersedly distributed around the ferrite, which helps to improve the plasticity and toughness of the alloy steel. Too high a content of blocky ferrite may result in hard and brittle alloy steel, and too high a content of pearlite and bainite may result in insufficient strength of the alloy steel.

[0077] Specifically, the high-strength steel has a carbon equivalent of not more than 0.27. Compared with Q355 steel (carbon equivalent value of 0.50), the carbon equivalent of the inventive steel can be reduced to 0.27, and the welding performance is significantly improved.

[0078] The application also discloses a preparation method of the high-strength steel, which comprises the following steps:

[0079] S1: adopting blast furnace molten iron raw material for converter smelting to make elements C, Si and Cr reach the composition requirement, and obtaining molten steel A;

[0080] S2: performing LF refining on the molten steel A, adding titanium iron for alloying to make the content of each element reach a preset value, and performing RH vacuum degassing to obtain molten steel B;

[0081] S3: injecting the molten steel B into a continuous casting machine for continuous casting to obtain continuous casting blank;

[0082] S4: performing rolling, cooling and coiling on the continuous casting blank to obtain the high-strength steel.

[0083] Specifically, the blast furnace molten iron raw material (which already contains excessive elements except Ti element in common industrial blast furnace molten iron raw material, and does not need additional raw material) is added in the converter, oxygen blowing is started after the slag is formed, the oxygen blowing intensity is controlled according to the amount of molten iron added in the furnace to prevent excessive oxidation of the molten steel when tapping; C, Si and Cr reach the composition range, the temperature is greater than or equal to 1620 DEG C, and the basicity is controlled to be greater than 3.0, and then the molten steel can be tapped.

[0084] Specifically, the O content in the steel is controlled to be less than 700 ppm in the converter smelting process of step S1, and the slag amount when tapping is less than 0.01% of the amount of molten steel to ensure the cleanliness of the molten steel.

[0085] Specifically, in the LF refining process described in step S2, FeSi powder is added in batches at a dosage of 2-4 kg / t, and the refining time is controlled to be above 35 min. Titanium iron is added for microalloying 10-15 min before the end of refining. When the slag is white and the temperature is ≥1580℃, a sample is taken, and the composition is adjusted to the required range according to the analysis results. When the composition meets the standard and the temperature reaches 1660-1680℃, the steel can be tapped.

[0086] Preferably, 150-250 kg of ferrotitanium is added to each ton of steel for microalloying.

[0087] Specifically, the RH vacuum degassing operation involves using argon gas to drive the circulation of molten steel, with an argon gas flow rate of 80–100 N*m. 3 / h, pressure 1.5MPa, light treatment is adopted during vacuum treatment, and the vacuum degree is controlled at 10±2kPa. After RH refining, the O content in the molten steel is reduced to 200ppm. The purpose is to reduce the O content in the molten steel and control the oxide inclusion content.

[0088] Specifically, in the continuous casting process described in step S3, the superheating temperature of the molten steel is controlled within the range of 10 to 35°C to obtain a billet structure with good uniformity; the casting speed is controlled at 0.8 to 1.0 m / min throughout the process to ensure full solidification; and the billets are stacked and slowly cooled after being removed from the casting line to prevent cracking.

[0089] Specifically, the specific operation described in step S4 is to heat the continuously cast billet at 1100-1150℃ for 4-6 hours, with an initial rolling temperature of 1020-1050℃ and a final rolling temperature of 920-950℃. After rolling, the steel plate is cooled to 600±15℃ at a cooling rate of 80℃-100℃ / s and then rolled.

[0090] A soaking temperature above 1100℃ ensures that most Ti elements are dissolved in the matrix (experimental data shows that over 80% of Ti elements can be dissolved in this step), while some TiN can be pinned to the grain boundaries to prevent grain growth. A soaking time of 4–6 hours allows the above process to proceed fully. The initial rolling temperature is 1020–1050℃, within which the TiN pinning effect is optimal and the grains are less prone to coarsening. The final rolling temperature is 920–950℃, ensuring that the deformation of the steel plate is within the austenite recrystallization region, and refining the grains through recrystallization during rolling. A cooling rate of 80℃–100℃ / s ensures that over 80% of the bulk ferrite metallographic structure is obtained during slow cooling of the coil. Coiling at 600±15℃ helps reduce internal stress and promotes TiC precipitation.

[0091] Examples and comparative examples:

[0092] Preparation of alloy steel:

[0093] S1: Add blast furnace iron as raw material to the converter, start oxygen blowing when slag is formed, control the O content in the steel to be below 700ppm, and tap the steel when the C, Si and Cr reach the preset content, the temperature is ≥1620℃, the basicity is controlled to be greater than 3.0, and the amount of slag discharged after tapping is controlled to be below 0.01% of the steel content.

[0094] S2: FeSi powder is added in batches during converter refining, at a dosage of 2-4 kg / t. The refining time is controlled to be above 35 min. 10-15 min before the end of refining, ferrotitanium is added. According to the Ti content set by this invention, 150-250 kg of ferrotitanium is used for microalloying at a rate of 150-250 kg per ton of steel. When the temperature is above 1580℃, samples are taken to adjust the composition range. After reaching the standard, the steel can be tapped when the temperature reaches 1660℃-1680℃. The specific chemical composition of each embodiment / comparative example is detailed in Table 2. In addition, argon gas is used to drive the circulation of molten steel in RH vacuum degassing, and the flow rate is controlled at 80-100 N*m. 3 / h.

[0095] S3: The refined molten steel B is guaranteed to be tapped at a temperature of 1660-1680℃, and then continuously cast at a casting speed of 0.8-1.0m / min; after the billets are removed from the line, they are stacked and slowly cooled to room temperature.

[0096] S4: As Figure 5 As shown, the billet is rolled at the selected process temperature according to the process curve. The continuously cast billet is homogenized at 1100℃~1150℃, the initial rolling temperature is guaranteed to be 1020℃~1050℃, and the final rolling temperature is controlled between 920℃~950℃. After the final rolling, cooling and coiling are performed. The specific cooling rate and coiling temperature (and mechanical property parameters) of each embodiment / comparative example are shown in Table 3.

[0097] Table 2 Chemical composition of the examples and comparative examples

[0098]

[0099] Table 3 Mechanical properties of specific embodiments

[0100]

[0101]

[0102] Based on Tables 2 and 3 of the embodiments, it can be seen that when the Ti content exceeds the limit specified in this invention, although the performance can still meet the requirements, the plasticity is significantly lower than that required by this invention, and even lower than that of Q355 steel, which is detrimental to the cold working performance during the shell manufacturing process. When the Ti content is lower than the limit specified in this invention, the mechanical properties are difficult to meet the requirements of this invention.

[0103] Table 4 Welding performance

[0104] No. Carbon equivalent CE wt.% Shell welding deformation amount / mm Example 1 0.27 3.6 Example 2 0.26 3.2 Example 3 0.24 2.6 Example 4 0.28 2.8 Example 5 0.24 3.0 Comparative Example 1 0.21 4.8 Comparative Example 2 0.24 4.9 Comparative Example 3 0.28 5.2 Q355 0.48 6.4

[0105] Table 5 Residual stress after curling

[0106] No. Coiling temperature / °C Residual stress / MPa Example 1 586 -88 Comparative Example 1 500 -165

[0107] The yield strength of each embodiment is ≥460 MPa, the tensile strength is ≥550 MPa, and the elongation is ≥25.5%. When the Ti content in the comparative example is ≤0.05%, the yield strength is difficult to meet the index requirements. The main reason is that Ti first combines with N and S in the steel to form TiN and Ti4C2S2, resulting in too little effective Ti that can combine with C to form TiC in the steel. When the Ti content is too high, although the strength does not change much compared to the embodiments, the plasticity decreases. The main reason is that when the Ti content is too high, the number of non-coherent precipitates increases, reducing the precipitation strengthening effect. In addition, too high Ti content leads to an increase in large-size TiN in the molten steel, reducing the plasticity. In addition, further increasing the curling temperature can release the internal stress in the steel, reducing the degree of welding deformation.

[0108] The above description is merely preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any changes or replacements within the technical scope disclosed by the present application can be easily thought of by those skilled in the art, and should be encompassed within the protection scope of the present application.

Claims

1. A high-strength steel for transformers, characterized in that: The composition of the high-strength steel, by mass, is: C 0.06–0.10%, Si 0.30–0.40%, Mn 0.8–1.0%, Ti 0.06–0.10%, Cr 0.02–0.05%, P 0.005–0.010%, S 0.001–0.003%, N ≤0.002%, with the remainder being Fe and unavoidable impurities; and -4570[C]+254 ≥450, [C] represents the solid solution carbon content, and [Ti] represents the solid solution titanium content; The metallographic structure of the high-strength steel is: 85%–90% blocky ferrite, 10%–12% pearlite, and a small amount of bainite; The carbon equivalent of the high-strength steel is no higher than 0.27, and the carbon equivalent is calculated using the following formula: .

2. The high-strength steel according to claim 1, characterized in that: The yield strength of the high-strength steel is 460–500 MPa.

3. The high-strength steel according to claim 1, characterized in that: The elongation of the high-strength steel is 24% to 28%.

4. The high-strength steel according to claim 1, characterized in that: The average size of the bulk ferrite is 6.4~7μm.

5. The high-strength steel according to claim 1, characterized in that: The carbon equivalent of the high-strength steel is not higher than 0.

26.

6. A method for preparing the high-strength steel according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1: Using blast furnace molten iron as raw material for converter smelting, the elements C, Si, and Cr meet the composition requirements to obtain molten steel A; S2: LF refining of molten steel A, alloying with ferrotitanium to achieve the preset values ​​of each element content, and RH vacuum degassing to obtain molten steel B; S3: Inject molten steel B into the continuous casting machine for continuous casting to obtain continuously cast billets; S4: Rolling, cooling, and coiling the continuously cast billet to obtain high-strength steel.

7. The preparation method according to claim 6, characterized in that: In step S1, the oxygen content in the steel is controlled to be below 700 ppm, and the amount of slag discharged during tapping is below 0.01% of the molten steel.

8. The preparation method according to claim 6, characterized in that: In step S2, the refining time in the LF refining process is controlled to be above 35 minutes, and titanium-iron is added for micro-alloying 10 to 15 minutes before the end of refining.

9. The preparation method according to claim 6, characterized in that: In step S3 of the continuous casting process, the superheated temperature of the molten steel is controlled within 10 to 35°C, and the casting speed is controlled within 0.8 to 1.0 m / min throughout the process; after the billet is removed from the line, it is stacked for slow cooling.

10. The preparation method according to claim 6, characterized in that: Step S4 involves homogenizing the continuously cast billet at 1100–1150°C for 4–6 hours, initial rolling at 1020–1050°C, final rolling at 920–950°C, and then cooling the rolled steel plate to 600±15°C at a cooling rate of 80–100°C / s before curling it.

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